US 20060234912 A1
The invention provides, in part, methods and reagents for modulating neuronal apoptosis and for modulating synaptic plasticity.
49. A method of modulating NMDA-mediated neuronal apoptosis, the method comprising contacting a neuronal cell with an inhibitor of AMPA receptor endocytosis.
50. The method of
51. The method of
52. The method of
53. The method of
54. The method of
55. A method of modulating AMPA receptor endocytosis, the method comprising contacting a cell expressing an AMPA receptor with a modulatory compound comprising the amino acid sequence set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor or a fragment or variant thereof, or comprising an antibody that specifically binds the amino acid sequence set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor.
56. The method of
57. The method of
58. The method of
59. The method of
60. A method of treating or preventing neurological damage or dysfunction in a subject, the method comprising administering an effective amount of an inhibitor of AMPA receptor endocytosis to the subject.
61. The method of
62. The method of
63. The method of
64. The method of
65. The method of any one of claims 12 through 16, wherein the inhibitor further comprises the amino acid sequence YGRKKRRQRRR or a carrier peptide sequence that facilitates translocation of the inhibitor across cell membranes.
66. The method of
67. The method of
68. The method of
69. The method of
70. A method of modulating synaptic plasticity in a subject, the method comprising administering an effective amount of an inhibitor of AMPA receptor endocytosis to the subject.
71. The method of
72. The method of
73. The method of
74. The method of
75. The method of
76. The method of
77. A method of screening for a modulator of AMPA receptor endocytosis, the method comprising:
(a) providing a system comprising
(i) an AMPA receptor polypeptide or a biologically-active fragment thereof;
(ii) an inhibitor of AMPA receptor endocytosis;
(b) providing a test compound;
(c) contacting the system with the test compound; and
(d) determining whether the test compound modulates AMPA receptor endocytosis.
78. A method of screening for a modulator of AMPA receptor endocytosis, the method comprising:
(a) providing an AMPA receptor polypeptide or a biologically-active fragment thereof;
(b) providing a test compound;
(c) contacting the AMPA receptor polypeptide or a biologically-active fragment thereof with the test compound; and
(d) determining whether the test compound modulates AMPA receptor endocytosis.
79. The method of
80. The method of
81. The method of
82. The method of
83. The method of
84. The method of
85. A polypeptide comprising an amino acid sequence substantially identical to at least one of the sequences selected from the group consisting of YREGYNVYGIE, YKEGYNVYGIE, YREGYNVYG, and YKEGYNVYG.
86. A polypeptide comprising an amino acid sequence substantially identical to at least one of the sequences set forth in Table I.
87. The polypeptide of
88. A nucleic acid molecule encoding the amino acid sequence of
89. An antibody that specifically binds the amino acid sequence of
90. A substantially pure compound comprising of Formula I:
X1 is Y, D, E, S, or T;
X2 is K or R;
X3 is Y, D, E, S, or T;
X4 is Y, D, E, S, or T;
Z, is H2N—, RHN— or, RRN—;
Z2 is —C(O)OH, —C(O)R, —C(O)OR, —C(O)NHR, —C(O)NRR;
R at each occurrence is independently selected from (C1-C6) alkyl, (C1-C6) alkenyl, (C1-C6) alkynyl, substituted (C1-C6) alkyl, substituted (C1-C6) alkenyl, or substituted (C1-C6) alkynyl;
wherein “—” is a covalent linkage, and wherein the compound is an inhibitor of AMPA receptor endocytosis.
91. The compound of
92. The compound of
93. The compound of
94. A method of modulating NMDA-mediated neuronal apoptosis, the method comprising contacting a neuronal cell with an inhibitor of clathrin-mediated endocytosis.
The invention is, in general, in the field of neurology. More specifically, the invention provides, in part, methods and reagents for modulating neuronal apoptosis or synaptic plasticity.
Synaptic transmission is the process by which neurons communicate by excitatory (generation of an action potential) or inhibitory (inhibition of an action potential following excitation) mechanisms. Excitatory synaptic transmission often occurs by means of the neurotransmitter L-glutamate and its cognate glutamate receptors, which include the N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) subtype glutamate receptors. Synaptic plasticity refers to the use-dependent ability of post-synaptic neurons to modulate their response to the release of neurotransmitters during synaptic transmission, and is thought to be important in learning and memory processes.
The excessive stimulation of post-synaptic neurons (a phenomenon known as “excitotoxicity”), which can lead to neuronal death or apoptosis, has been implicated in a variety of central nervous system (CNS) disorders. Activation of the NMDA receptor may induce programmed cell death (apoptosis) in cultured hippocampal neurons, and may underlie the loss of neurons and neuronal function in central nervous system disorders ranging from acute brain trauma and stroke to neurogenerative diseases such as Huntington's, Alzheimer's, and Parkinson's Diseases.1-5
NMDA receptor activation may also lead to facilitation of clathrin-mediated endocytosis of AMPA receptors, which mediate fast synaptic transmission at excitatory synapses in the mammalian CNS.6,7 AMPA receptor function can be modified at the level of open channel probability34, channel conductance27;33, and the kinetics of desensitization.52 Rapid redistribution of AMPA receptors to and from the postsynaptic domain is also thought to be a means of regulating the strength of AMPA receptor-mediated synaptic transmission.43;45;6 AMPA receptors undergo functionally distinct constitutive and regulated clathrin-dependent cycling between intracellular compartments and the plasma membrane via vesicle-mediated plasma membrane insertion (exocytosis) and internalization (endocytosis).22;30;20;24;41;14 Regulating these processes can lead to rapid changes in the number of AMPA receptors expressed in the postsynaptic membrane, thereby contributing to the expression of certain forms of synaptic plasticity, including hippocampal long term potentiation (LTP) 35;42;50 and long term depression (LTD) in the cerebellum and hippocampus.14;24;25;44 AMPA receptors may be subjected to stimulated endocytosis by diverse stimuli including growth factors, such as insulin/IGF-1 14;25, agonist binding22;21;20, and LTD-producing protocols.24;14;25
The invention provides, in part, methods and reagents for modulating neuronal apoptosis. The invention also provides, in part, methods and reagents for modulating synaptic plasticity.
In some aspects, the invention provides a method of modulating NMDA-mediated neuronal apoptosis by contacting a neuronal cell with an inhibitor of AMPA receptor endocytosis. In alternative aspects, the invention provides a method of modulating NMDA-mediated neuronal apoptosis by contacting a neuronal cell with an inhibitor of clathrin-mediated endocytosis. In alternative aspects, the invention provides a method of treating or preventing neurological damage or dysfunction in a subject by administering an effective amount of an inhibitor of AMPA receptor endocytosis to the subject.
In alternative embodiments, the neurological damage may include NMDA-induced neuronal apoptosis, or may occur as a result of excessive activation of NMDA receptors or due to changes in AMPA receptor endocytosis, or may occur as a result of at least one of a disorder selected from the group consisting of stress, anxiety, depression, hypoglycemia, cardiac arrest, epilepsy, cerebral ischemia, brain trauma, Alzheimer's disease, Parkinson's disease, Huntington's disease; neuropathic pain; amyotrophic lateral sclerosis (ALS); Hutchinson Gilford syndrome; diabetes; ataxia; mental retardation; dementias, disorders associated with smoking or obesity, high blood pressure, disorders associated with defects or dysfunction in learning or memory, psychiatric disorders, autism, schizophrenia, fragile X syndrome, or disorders associated with substance abuse or addiction to a drug (e.g., nicotine, alcohol, opiates, heroin, codeine, morphine pethidine, methadone, marijuana, phenyclidene, psychostimulants, amphetamines, cocaine, barbiturates, pentobarbitone, quinalbarbitone, benzodiazepines, temazepam, diazepam or flunitrazepam).
In alternative aspects, the invention provides a method of modulating synaptic plasticity in a subject by administering an effective amount of an inhibitor of AMPA receptor endocytosis to the subject (e.g., a normal subject i.e. one not having or not diagnosed with neurological damage or dysfunction). In alternative embodiments, the method may further include enhancing synaptic plasticity. In alternative acts, the invention provides a method of treating or preventing substance abuse in a subject by administering an effective amount of an inhibitor of AMPA receptor endocytosis to the subject.
In some aspects, the invention provides a method of modulating AMPA receptor endocytosis by contacting a cell or system (for example, a lipid vehicle) expressing an AMPA receptor with a peptide comprising an amino acid sequence selected from the group consisting of YREGYNVYGIE, YKEGYNVYGIE, YREGYNVYG, or YKEGYNVYG, or with an antibody that specifically binds an amino acid sequence selected from the group consisting of YREGYNVYGIE, YKEGYNVYGIE, YREGYNVYG, and YKEGYNVYG.
In some aspects, the invention provides a method of modulating AMPA receptor endocytosis, by contacting a cell expressing an AMPA receptor with a modulatory compound comprising the amino acid sequence set forth in Table I or conservative substitutions thereof. Formula I, or Formula A, or homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor or a fragment or variant thereof, or comprising an antibody that specifically binds the amino acid sequence set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor.
In alternative aspects, the invention provides a method of screening for a modulator of AMPA receptor endocytosis, by providing a system including an AMPA receptor polypeptide or a biologically-active fragment thereof; an inhibitor of AMPA receptor endocytosis; providing a test compound; contacting the system with the test compound; and deter whether the test compound modulates AMPA receptor endocytosis.
In alternative aspects, the invention provides a method of screening for a modulator of AMPA receptor endocytosis, the method including providing an AMPA receptor polypeptide or a biologically-active fragment thereof; providing an inhibitor of AMPA receptor endocytosis; providing a test compound; contacting the AMPA receptor polypeptide or a biologically-active fragment thereof with the test compound or the inhibitor; and determining whether the test compound modulates AMPA receptor endocytosis
In alternative aspects, the invention provides a method of screening for a modulator of AMPA receptor endocytosis, by providing an AMPA receptor polypeptide or a biologically-active fragment thereof; providing a test compound; contacting the AMPA receptor polypeptide or a biologically-active fragment thereof with the test compound; and determining whether the test compound modulates AMPA receptor endocytosis. In alternative embodiments, the method may further include providing an inhibitor of AMPA receptor endocytosis, contacting the AMPA receptor polypeptide or a biologically-active fragment thereof with the inhibitor, and determining whether the test compound modulates AMPA receptor endocytosis when compared to the inhibitor.
In alternative aspects, the invention provides a polypeptide including an amino acid sequence substantially identical to the sequence of YREGYNVYGIE, YKEGYNVYGIE, YREGYNVYG, or YKEGYNVYG, or a nucleic acid molecule encoding any of these amino acid sequences, or an antibody that specifically binds any of these amino acid sequences.
In alternative aspects, the invention provides a substantially pure compound including Formula I: Z1-X1-X2-E-G-X3-N-V-X4-G-Z2; where X1 may be Y, D, E, S, or T; X2 may be K or R; X3 is Y, D, E, S, or T; X4 may be Y, D, E, S, or T; Z1 may be H2N—, RHN— or, RRN—; Z2 may be —C(O)OH, —C(O)R, —C(O)OR, —C(O)NHR, —C(O)NRR; R at each occurrence may be independently selected from (C1-C6) alkyl, (C1-C6) alkenyl, (C1-C6) alkynyl, substituted (C1-C6) alkyl, substituted (C1-C6) alkenyl, or substituted (C1-C6) alkynyl; wherein “—” may be a covalent linkage, and wherein the compound may be an inhibitor of AMPA a endocytosis. In alternative embodiments, any one or more of X1, X3, or X maybe a Y.
In alternative aspects, the invention provides a substantially pure compound including Formula A: Z1-X1-X2-X3-X4-X5-X6-X7-X8-X9-Z2, where X1 may be an amino acid having a hydropathic index of −0.3 to 4.3 or of −1.3 to −3.3 or may be a neutral or an acidic amino acid, or may Gly, Ser, Thr, Cys, Asn, Gln, Tyr, Asp, Glu; X2 may be an amino acid having a hydropathic index of +1.0 to +5.0 or of +2.0 to +4.0 or may be a basic amino acid or may be Lys, Arg, His; X3 may be an amino acid having a hydropathic index of +1.0 to +5.0 or of +2.0 to +4.0 or may be an acidic amino acid or may be Asp, Glu; X4 may be an amino acid having a hydropathic index of −2.0 to +2.0 or of −1.0 to +1.0 to or may be a neutral amino acid or may be Gly, Ser, Thr, Cys, Asn, Gln, Tyr, X5 may be an amino acid having a hydropathic index of 0.3 to 4.3 or of −1.3 to −3.3 or may be a neutral or an acidic amino acid or may be Gly, Ser, Thr, Cys, Asn, Gln, Tyr, Asp, Glu; X6 may be an amino acid having a hydropathic index of-1.8 to +2.2 or of −0.8 to +1.2 or may be a neutral amino acid or may be Gly, Ser, Thy, Cys, Asn, Gln, Tyr; X7 may be an amino acid having a hydropathic index of −3.5 to 0.5 or of −2.5 to −0.5 or nay be a non-polar amino acid or may be Ala, Val, Leu, Ile, Phe, Trp, Pro, Met; X8 may be an amino acid having a hydropathic index of −0.3 to −4.3 or of −1.3 to −3.3 or may be a neutral or an acidic amino acid or may be Gly, Ser, 1 hr, Cys, Asn, Gin, Tyr, Asp, Glu; X9 may be an amino acid having a hydropathic index of −2.0 to +2.0 or of −1.0 to +1.0 to may be a neutral amino acid or may be Gly, Ser, Thr, Cys, Asn, Gln, Tyr, Z, is H2N—, RHN— or, RRN—; Z2 may be C(O)OH, C(O)R, —C(O)OR, —C(O)NHR, —C(O)NRR; R at each occurrence may be independently selected from (C1-C6) alkyl, (C1-C6) alkenyl, (C1-C6) alkynyl, substituted (C1-C6) alkyl, substituted (C1-C6) alkenyl, or substituted (C1-C6) alkynyl; wherein “—” is a covalent linkage, and wherein the compound may be an inhibitor of AMPA receptor endocytosis. In alternative embodiments, any one or more of X1, X5, or X8 may be a Y.
In alternative embodiments, the compound of Formula I or A may inhibit AMPA receptor endocytosis with an affinity that is at least as great as the affinity when the compound is a polypeptide including a sequence of YREGYNVYGIE, YKEGYNVYGIE, YREGYNVYG, or YKEGYNVYG. In alternative embodiments, the compound of Formula I or A may include a similarity score of over zero based on either of the PAM or Blosum similarity matrices. In alternative embodiments, the compound of Formula I or A may further include the amino acid sequence YGRKKRRQRRR.
In alternative aspects, the invention provides the use of any of the polypeptides, nucleic acid molecules, antibodies, or compounds according to the invention for treating or preventing neurological damage or substance abuse in a subject, or for modulating NMDA-mediated-neuronal apoptosis, or for modulating AMPA receptor endocytosis, or for modulating sync plasticity in a subject.
In various embodiments of the aspects of the invention, the inhibitor may include an inhibitor of regulated AMPA receptor endocytosis. In various embodiments of the aspects of the invention, the inhibitor may include a GluR2, GluR3, or GluR4 polypeptide. In various embodiments of the aspects of the invention, the inhibitor of AMPA receptor endocytosis may include a peptide including any of the amino acid sequences of YREGYNVYGIE, YKEGYNVYGIE, YREGYNVYG, or YKEGYNVYG or a fragment or variant thereof, or may be a GluR2, GluR3, or GluR4 polypeptide, or may include an antibody that specifically binds any of the amino acid sequences of YREGYNVYGIE, YKEGYNVYGIE, YREGYNVYG, and YKEGYNVYG. In various embodiments of the aspects of the invention, the inhibitor may include the amino acid sequence set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor or a fragment or variant thereof or include an antibody that specifically binds the amino acid sequence set forth in Table I or conservative substitutions thereof, Formula L or Formula A, or homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor. In various embodiments of the aspects of the invention, may further include the amino acid sequence YGRKKRRQRRR.
α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid or “AMPA” receptors are glutamate-gated ion channel receptors that are involved in transduction of the post-synaptic signal. Native AMPA receptors may be heteromeric, e.g, heteropentameric, protein complexes assembled from combinations of GluR subunits 1-4. When transiently expressed in non-neuronal mammalian cells, individual GluR subunits can form functional homomeric AMPA receptor channels, and AMPA receptors in these heterologous expression systems can undergo both constitutive and regulated clathrin-dependent endocytosis. In some embodiments, an AMPA receptor includes a GluR2 subunit. GluR subunits may include without limitation the sequences described in Accession numbers NP—113796; NPL032191; NP—000818 for GluR1; NP_058957; NP—038568; NP—000817; P23819 for GluR2; NP—116785 for GluR3; or NP—058959 or NP—000820 for GluR4, and related nucleotide sequences, for example, NM—000826. Other GluR polypeptide or nucleotide sequences may be found in public databases, such as GenBank.
A “phosphorylated” AMPA receptor includes polypeptide subunits that are post-translationally modified on any amino acid residue, for example, serine, threonine, or tyrosine, that is capable of being phosphorylated in vivo. For example, a phosphorylated AMPA receptor may include a GluR2 subunit that is phosphorylated, for example, on any one or more of tyrosines 869, 873, and 876 of the sequence described in Accession number NP—000817, or phosphorylated on any one or more of tyrosine residues present in corresponding sequences in GluR subunits.
An “unphosphorylated” AMPA receptor may be incapable of being phosphorylated on an amino acid residue capable of being phosphorylated in vivo, for example, by mutation of that residue to an amino acid that is not capable of being phosphorylated. A mutation of a tyrosine to an alamine in a polypeptide sequence, for example, results in a protein that is not capable of being phosphorylated at that particular position in the polypeptide sequence. A GluR2 polypeptide that possesses an alanine or other unphosphorylatable amino acid at positions 869, 873, and/or 876 of the sequence described in Accession number NP—000817, instead of a tyrosine, is an example of such an “unphosphorylated” AMPA receptor. An unphosphorylated AMPA receptor may also be a protein that is capable of being phosphorylated in vivo, but is not phosphorylated due to, for example, the presence of an inhibitor, for example, a kinase inhibitor, due to an antibody that interferes with the phosphorylation site; due to the activity of a phosphatase; or prevented from being phosphorylated by some other means. A “constitutively phosphorylated” AMPA receptor is a protein that possesses a mutation at an amino acid residue that is capable of being phosphorylated in vivo, where the mutation mimics phosphorylation at that residue, and the resultant polypeptide possesses the biological activity of a phosphorylated polypeptide. Generally, mutation of a phosphorylatable residue to a glutamic acid or aspartic acid residue results in constitutive phosphorylation.
A GluR CT polypeptide includes a peptide derived form, or substantially identical to, the C-terminus of a GluR polypeptide and that is capable of inhibiting AMPA receptor endocytosis, or modulating neuronal apoptosis or synaptic plasticity. GluR CT peptides include, without limitation, peptides including the sequences set forth in Table I or conservative substitutions thereof, Formula 1, or Formula A, or homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor. In some embodiments, a GluR CT peptide may include other sequences (e.g, TAT PTD) in the form of for example a fusion protein.
A “biologically-active fragment” of an AMPA receptor includes an amino acid sequence found in a naturally ring AMPA receptor that is capable of modulating apoptosis or cell death or synaptic plasticity, or undergoing endocytosis, as described herein or known to those of ordinary skill in the art. A “variant” of an AMPA receptor includes a modification, for example, by deletion, addition, or substitution, of an amino acid sequence found in a naturally-occurring AMPA receptor that is capable of modulating apoptosis or cell death, or synaptic plasticity, undergoing endocytosis, as described herein or known to those of ordinary skill in the art.
A “protein,” “peptide” or “polypeptide” is any chain of two or more amino acids, including naturally occurring or non-naturally occurring amino acids or amino acid analogues, regardless of post-translational modification (e.g., glycosylation or phosphorylation). An “amino acid sequence”, ““polypeptide”, “peptide” or protein” of the invention may include peptides or proteins that have abnormal linkages, cross links and end caps, non-peptidyl bonds or alternative modifying groups. Such modified peptides are also within the scope of the invention. The term “modifying group” is intended to include structures that are directly attached to the peptidic structure (e.g., by covalent coupling), as well as those that are indirectly attached to the peptidic structure (e.g., by a stable non-covalent association or by covalent coupling to additional amino acid residues, or mimetics, analogues or derivatives thereof; which may flank the core peptidic structure). For example, the modifying group can be coupled to the amino-terminus or carboxy-terminus of a peptidic structure, or to a peptidic or peptidomimetic region flanking the core domain. Alternatively, the modifying group can be coupled to a side chain of at least one amino acid residue of a peptidic structure, or to a peptidic or peptido-mimetic region flanking the core domain (e.g., through the epsilon amino group of a lysyl residue(s), though the carboxyl group of an aspartic acid residue(s) or a glutamic acid residue(s), through a hydroxy group of a tyrosyl residue(s), a serine residue(s) or a threonine residue(s) or other suitable reactive group on an amino acid side chain). Modifying groups covalently coupled to the peptidic structure can be attached by means and using methods well known in the art for linking chemical structures, including, for example, amide, alkylamino, carbamate or urea bonds. Peptides according to the invention may include the sequences set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or homologous sequences thereto, found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor. In some embodiments, the peptides may include other sequences (e.g, TAT PTD) in the form of for example a fusion protein.
A “nucleic acid molecule” is any chain of two or more nucleotides including naturally occurring or non-naturally occurring nucleotides or nucleotide analogues. A nucleic acid molecule is “complementary”to another nucleic acid molecule if it hybridizes, under conditions of high stringency, with the second nucleic acid molecule. Nucleic acid molecules according to the invention include those molecules that encode the sequences set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or homologous sequences thereto, found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor. In some embodiments, a nucleic acid molecule may include other sequences (e.g., sequence coding for TAT PTD) to generate for example a fusion protein.
A “substantially identical” sequence is an amino acid or nucleotide sequence that differs from a reference sequence only by one or more conservative substitutions, as discussed herein, or by one or more non-conservative substitutions, deletion, or insertions located at positions of the sequence that do not destroy biological function as described herein. Such a sequence can be any integer from 60% to 99%, or more generally at least 75%, 80%, 85%, 90%, or 95%, or as much as 96%, 97%, 98%, or 99% identical at the amino acid or nucleotide level to the sequence used for comparison. Sequence identity can be readily measured using publicly available sequence analysis software (e.g., Sequence Analysis Software Package of the Genetics Computer Group, University of Wisconsin Biotechnology Center, 1710 University Avenue, Madison, Wis. 53705, or BLAST software available from the National Library of Medicine, USA). Examples of useful software include the programs, Pile-up and PrettyBox. Such software matches similar sequences by assigning degrees of homology to various substitutions, deletions, substitutions, and other modifications. Substantially identical sequences may for example be sequences that are substantially identical to the amino acid sequences set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or to homologous sequences thereto found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor. In some embodiments, a substantially identical sequence may further include sequences substantially identical to other sequences (e.g, TAT PTD).
An antibody “specifically binds” an antigen when it recognises and binds the antigen, for example, a GluR CT peptide, but does not substantially recognise and bind other molecules in a sample, for example, a GluR CT peptide that does not include such sequences. Such an antibody has, for example, an affinity for the antigen which is 10, 100, 1000 or 10000 times greater than the affinity of the antibody for another reference molecule in a sample.
“cell death” or “apoptosis,” defines a specific execution of programmed cell death that can be triggered by several factors.55 NMDA-mediated neuronal apoptosis is the neuronal cell death observed upon activation of NMDA receptors.
“Endocytosis” is the process by which the plasma membrane of a cell folds inward, to internalize components of the membrane as well as other materials. Receptor endocytosis is typically mediated by clathrin coated pits and vesicles.
An “inhibitor of chin mediated endocytosis” includes an compound that is capable of specifically inhibiting clathrin mediated endocytosis, without substantially inhibiting endocytosis in general. An inhibitor of clathrin mediated endocytosis may include, for example, myr -dyn, or inhibitors as described in Jarousse and Kelly.62 In some embodiments, an inhibitor of AMA receptor endocytosis may also be an inhibitor of clathrin mediated endocytosis.
An “inhibitor of AMPA receptor endocytosis” includes a compound that may be in general capable of specifically inhibiting endocytosis of the AMPA receptor, without substantially inhibiting clathrin-mediated endocytosis in general, when compared with an inhibitor of clathrin mediated endocytosis. In some embodiments, an inhibitor of AMPA receptor endocytosis may include compounds that do not affect basal levels of AMPA receptor endocytosis e.g., compounds that are inhibitors of “regulated” AMPA receptor endocytosis. In some embodiments, an inhibitor of AMPA receptor endocytosis may include compounds that are substantially identical to the amino acid sequences set forth in Table I or conservative substitutions thereof, Formula L or Formula A, or to homologous sequences found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor. In some embodiments, an inhibitor of AMPA receptor endocytosis may include an antibody that mimics the sequences set forth in Table I or conservative substitutions thereof, Formula L or Formula A, or to homologous sequences found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor, e.g., an anti-idiotypic antibody to an antibody that specifically binds a GluR CT peptide.
“Synaptic plasticity” refer to the use-dependent changes (long-term or short-term) in the efficiency of synaptic transmission between neuronal cells. Synaptic plasticity is thought to underlie the processes behind leaning and memory.
A “test compound” is any naturally-occurring or artificially-derived chemical compound. Test compounds may include, without limitation, peptides, polypeptides, synthesised organic molecules, naturally occurring organic molecules, and nucleic acid molecules. A test compound may “compete” with a known compound, for example, an inhibitor of clathrin mediated endocytosis or an inhibitor of AMPA receptor endocytosis, such as a GluR-CT peptide or fragment thereof by, for example, interfering with modulation of neuronal apoptosis or cell death or synaptic plasticity, endocytosis, or protein phosphorylation, or other biological response. Generally, a test compound can exhibit any value between 10% and 200%, or over 500%, modulation when compared to a GluR-CT peptide or peptide analogue, or other reference compound. For example, a test compound may exhibit at least any positive or negative integer from 10% to 200% modulation, or at least any positive or negative integer from 30% to 150% modulation, or at least any positive or negative integer from 60% to 100% modulation, or any positive or negative integer over 100% modulation. A compound that is a negative modulator will in general decrease modulation relative to a known compound, while a compound that is a positive modulator will in general increase modulation relative to a known compound.
A “sample” can be any organ, tissue, cell, or cell extract isolated from a subject, such as a sample isolated form an animal having neurological damage or neuronal dysfunction or a neurological disorder. For example, a sample can include, without limitation, hippocampal tissue or cells, cerebellar tissue or cells, etc., or other neuronal or other tissue (e.g., from a biopsy or autopsy), isolated from an animal with neurological damage, dysfunction, or disorder, or from a normal animal i.e., not having neurological damage, dysfunction, or disorder. A sample can also include, without limitation, tissue such as neuronal cells, peripheral blood, whole blood, red cell concentrates, platelet concentrates, leukocyte concentrates, blood cell proteins, blood plasma, platelet-rich plasma, a plasma concentrate, a precipitate from any fractionation of the plasma, a supernatant from any fractionation of the plasma, blood plasma protein fractions, purified or partially purified blood proteins or other components, serum, semen, mammalian colostrum, milk, urine, stool, saliva, placental extracts, amniotic fluid, a cryoprecipitate, a cryosupernatant, a cell lysate, mammalian cell culture or culture medium, products of fermentation, ascitic fluid, proteins present in blood cells, solid tumours isolated from a mammal with a neuronal carcinoma, or any other specimen, or any extract thereof, obtained from a patient (human or animal), test subject, or experimental animal. A sample may also include, without limitation, products produced in cell culture by normal cells or cells isolated from a subject with neurological damage or neuronal dysfunction (e.g., via recombinant DNA technology). A “sample” may also be a cell or cell line created under experimental conditions, that are not directly isolated from a subject. A sample can also be cell-free, artificially derived or synthesised. In some embodiments, samples refer to neuronal tissue or cells. In some embodiments, the sample may be from a subject having neurological damage or neuronal dysfunction; or from a normal subject i.e., not diagnosed with or at risk for or suspected of having neurological damage or neuronal dysfunction.
As used herein, a subject may be a human, non-human primate, rat, mouse, cow, horse, pig, sheep, goat, dog, cat, Aplysia, etc. The subject may be a clinical patient, a clinical trial volunteer, an experimental animal, etc. The subject may be suspected of having or at risk for having neurological damage or neuronal dysfunction, be diagnosed with neurological damage or neuronal dysfunction, or be a control subject that is confirmed to not have neurological damage or neuronal dysfunction. Diagnostic methods for neurological damage or neuronal dysfunction and the clinical delineation of neurological damage or neuronal dysfunction diagnoses are known to those of ordinary skill in the art.
By “contacting”is meant to submit an animal, cell, lysate, extract, molecule derived from a cell or synthetic molecule to a test compound.
By “determining”is meant analysing the effect of a test compound on the test system. The means for analysing may include, without limitation, antibody labelling, apoptosis assays, immunoprecipitation, in vivo and in vitro phosphorylation assays, cell death assays, immunofluorescence assays, ELISA, ultrastructural analysis, histological analysis, animal models, or any other methods described herein or known to those skilled in the art.
“modulating” or “modulates” means changing, by either increase or decrease. The increase or decrease may be a change of any value between 10% and 90%, or of any value between 30% and 60%, or may be over 100%, over 200%, over 300% or over 500% when compared with a control or reference sample or compound.
Other features and advantages of the invention will be apparent from the following description of the drawings and the invention, and from the claims.
FIGS. 1A-F. NMDA induces apoptosis in primary cultures of rat hippocampal neurons. Mature hippocampal neurons were treated with NMDA (100 μM plus 10 μM glycine; 1 h) and then returned to normal media for 24 h. In this and the following Figs., all data are expressed as mean±SEM and analyzed using a non-paired Student's t-test. A, B, NMDA treatment induces a time-dependent increase in caspase-3 activity. A: western blot of cell lysates using anti-cleaved caspase-3; B: ELISA assay detecting DEVD-pNA cleavage. C, Agarose gel electrophoresis shows significant DNA laddering after NMDA treatment. D, Cell Death ELISA assay for apoptosis measuring histone-biotinylation shows that NMDA-induced apoptosis is blocked by the competitive NMDA receptor antagonist, APV. E, F, Cell Death ELISA assays for apoptosis show that endocytosis inhibitors specifically block NMDA—but not STS—induced apoptosis in cultured hippocampal neurons.
FIGS. 2A-D. Inhibitors of endocytosis disrupt NMDA receptor-mediated activation of the cell death signaling pathway without altering NMDA receptor function. A, B, Inhibition of endocytosis has little effect on Ca2+ influx through activated NMDA receptor channels. The upper trace (A) shows a record of NMDA receptor activation-induced [Ca2+]fluctuations as measured by ratiometric changes in Fura-2 fluorescence in a single hippocampal neuron. Repetitive NMDA application (100 μM) in the region of the neuron under observation was accomplished using a pressure ejection pipette at the time points indicated by the lower black squares (500 ms each). Sucrose (400 mM) was applied to the bath as indicated by the upper black bar. The histogram at the bottom (B) summarizes [Ca2+]responses at indicated time points from three individual neurons (mean±SEM). C, A myristoylated dynamin-derived peptide inhibits NMDA induced activation of caspase-3. D, Endocytosis inhibition specifically disrupts the NMDA-, but not the STS-induced reduction in Akt phosphorylation. Cell lysates from neurons treated as indicated were first probed with an antibody specific to Akt phosphorylated on serine 473, the active form of the enzyme. Membranes were then stripped and re-probed with an anti-Akt antibody. Blots from four individual experiments were scanned and quantified. The histogram represents Akt phosphorylation relative to total Akt. **, p<0.01 when compared with the respective control group.
FIGS. 3A-B. NMDA induces AMPA receptor but not NMDA receptor endocytosis, which is blocked by the membrane permeable myristoylated dynamin peptide (Myr-Dyn) as well as a peptide derived from GluR c-tail (R2-CT). A, ELISA-based cell-surface receptor assay for NMDA receptor and AMPA receptor. NMDA treatment induced a significant reduction in cell surface AMPA receptor but not NMDA receptor, and AMPA receptor internalization was prevented by pretreatment of neurons with the myristoylated, membrane permeable dynamin inhibitor peptide (Myr-Dyn; 10 μM), but not the membrane impermeable control Dyn (** denotes p<0.01, compared with control; n=36-72 wells from three separate experiments for each group). B, NMDA-induced AMPA receptor internalization is blocked by R2-CT , a peptide that specifically blocked regulated AMPA receptor endocytosis.
FIGS. 4A-B. Blocking AMPA receptor endocytosis with R2-CT prevents NMDA—but not STS-induced apoptosis in cultured hippocampal neurons. A, Cell Death ELISA assay for apoptosis showing that R2-CT blocks NMDA—but not STS-induced apoptosis. B, Cell counting for apoptosis of PI stained cells after fixation, showing that R2-CT blocked NMDA-induced apoptosis.
FIGS. 5A-B. Construction of GluR2 internal deletion or carboxyl terminal truncation mutants and identification of a tyrosine-based signal (GluR2-3Y). A. CT sequences of internal deletion or truncation mutants of the full-length HA-tagged or non-tagged GluR2 subunit. B. Quantification of cell-surface expressed AMPARs containing the GluR2, or its various mutant constructs, which were transiently transfected into HEK293 cells and assayed by colorimetric cell-ELISA (n=6). Expression levels of the constructs following transient transfection into HEK293 cells were determined by cell-ELISA assays using an anti-HA antibody for HA tagged constructs, or an anti-GluR2 subunit antibody for the non-HA tagged construct, under permeabilized conditions. The level of expression was normalized to the expression level of the corresponding wild type construct (i.e. HA-GluR2 or GluR2). All mutants were expressed at a level similar to the wild type counterparts. Removing the tyrosine based signal prevents insulin-induced depletion of cell surface AMPARs (filled bars) without affecting the basal receptor level. Removing NSF-binding domains affects basal, but not insulin-reduced receptor expression, and that unlike neurons, both AP2 and PICK1-based endocytosis signals are non-functional in HEK cells. *p<0.05, **p<0.01.
FIGS. 6A-B. Effects of GluR2 CT mutations on endocytosis and cell-surface expression of AMPA receptors. A. Quantitation of the changes in constitutive (Basal) and regulated (insulin) endocytosis of GluR2 and its various mutants using a colorimetric ELISA assay with pre-labeled cells following the internalization of the receptors over 30 min (% AMPAR endocytosis=100%−remaining cell-surface receptors/total number of receptors; n=6). Control: internalization measured in cells at 4 E C without any 37 E C exposure (under these conditions, both constitutive and regulated endocytosis is blocked). B. Cell-surface AMPA receptors in HEK293 cells transiently expressing GluR2 and its various mutants were quantitated using colorimetric cell-ELISA based cell-surface receptor assays (n=6). Statistical comparisons were made between basal and insulin-treated conditions, except where indicated by lines. *p<0.05, **p<0.01
FIGS. 7A-D. Insulin increases phosphorylation of tyrosine residues within the GluR2 carboxyl terminal (CT) region. A. In vitro tyrosine phosphorylation of the GluR2 CT. GST fusion proteins of the GluR1 CT (GST-GluR1CT), the GluR2 CT (GST-GluR2CT), residues 869-876 (YKEGYNVYG) of the GluR2 CT (GST-GluR23Y), which contains a cluster of three tyrosine residues (Y869, Y873, and Y876) and the same amino acid stretch of the GluR2 CT with its tyrosine residues replaced by alanines (GST-GluR23A), along with the GST back bone (GST) as control were incubated in the absence (−) or presence (+) of active recombinant pp60 c-Src. Phosphorylation products were immunoblotted using an anti-phosphotyrosine antibody (top panel). Ponceau S staining of the same blot showed that a similar amount of GST fusion protein was used in each of the reactions (lower panel). B. Expression levels of HA-GluR2 and HA-GluR23Y-3A (where tyrosines 869, 873 and 876 were mutated to alanines) 48 h after transient transfection into HEK293 cells were determined by a cell ELISA assay using permeabilized cells. C. HEK293 cells transiently transfected with HA-GluR1, HA-GluR2 or HA-GluR23Y-3A, along with empty vector (mock transfection) as control. Forty-eight hours later, the cells were treated with or without 0.5 μM insulin for 10 min. The lysates were then subjected to immunoprecipitation with an anti-HA antibody under denaturing conditions and immunoblotting with an anti-phosphotyrosine antibody (Top blot; IB: PY). The same blot was stripped and re-immunoblotted with the anti-HA antibody to ensure similar immunoprecipitation efficiency in all individual experiments (lower blot; IB: HA). D. Mutation of individual tyrosines of the Glu23Y CT peptide to alanines.
FIGS. 8A-B. The tyrosine cluster in the GluR2 CT is required for regulated, but not constitutive, AMPA receptor endocytosis in HEK293 cells. A. Colorimetric cell-ELISA receptor endocytosis assays were performed with (Insulin) or without (Control) stimulation (see
FIGS. 9A-D. Insulin stimulates tyrosine phosphorylation of GluR2 and long-lasting depression of AMPA receptor-mediated synaptic transmission. A. Tissue homogenates from hippocampal slices treated with (Basal) or without insulin (INS; 0.5 μM, 10 min) were immunoprecipitated with anti-GluR1 or GluR2 antibodies under denaturing conditions (IP: GluR1 or GluR2). Immunoprecipitates were the immunoblotted using an anti-phosphotyrosine antibody (IB: PY). The blot was sequentially stripped and re-probed with anti-GluR2 (IB: GluR2) and anti-GluR1 (IB: GluR1) antibodies. B. Densitometric quantitation expressed as the ratio of phosphorylated GluR2 to total GluR2 from three separate experiments is summarized in the histogram on the right. ** p<0.01 C. EPSCs were recorded in CA1 neurons from hippocampal slices using whole-cell recordings under the voltage-clamp mode at a holding potential of −60 mV. Normalized EPSCs (EPSC/EPSC0) are plotted from neurons recorded with pipettes containing standard intracellular solution (Control, n=7) or intracellular solution supplemented with GST-Y869KEGY873NVY876G (GluR23Y; n=5) or GST-A869KEGA873NVA876G (GluR3A; n=6). Time zero is defined as the time point at which the amplitudes of EPSCs were stabilize (typically 5-10 min after the start of whole-cell recording), and at t=10 min, insulin (0.5 μM was applied in the bath as indicated by the horizontal black bar-D. Representative EPSCs averaged from four individual recordings before (Basal) or 10 min following application of insulin (INS) are shown on the left.
FIGS. 10A-E. Tyrosine phosphorylation of the GluR2 subunit is required for LFS-induced hippocampal CA1 long-term depression (LTD). A. Homogenates of control or LFS-treated hippocampal slices were immunoprecipitated with anti-GluR1 or GluR2 antibodies and sequentially probed with anti-phosphotyrosine (PY), anti-GluR1 (GluR1) and anti-GluR2 antibodies (GluR2) as described herein. The lane marked M contains molecular weight standards. B. The results of three individual experiments are summarized in the bar graph. ** p<0.01 C. Representative responses are shown on the left D. The graphs on the right, and in E, depict normalized EPSCs (EPSCt/EPSC0) from neurons recorded as described with pipettes containing standard intracellular solution (Control, n=7) or intracellular solution supplemented with GluR23Y (B; n=6), GluR23A (B; n=7) or GluR2834-843 (C; n=5). The LFS was delivered during the time period indicated by the black horizontal bar.
FIGS. 11A-B. GluR2-CT peptide prevents ishemia-induced AMA receptor endocytosis and neuronal apoptosis in a neuronal culture model of stroke. A. Colorimetric (Cell-ELISA) assay shows that OGD facilitates AMPA receptor endocytosis, thereby decreasing their expression on the plasma membrane surface and pre-incubation of the GluR2-CT peptide reduced the OGD-induced decrease in cell-surface AMPA receptor expression. (n=6; *: P<0.05, Student's test, compared with Control). B. Quantitative apoptosis assay 24 hr after OGD using the Cell Death Detection ELISAplus kit (Roche, Cat# 1 774 425) demonstrates that OGD produces neuronal death that is largely prevented by pretreatment of neurons with GluR2-CT. (n=6; **: P<0.01, Student's t test, compared with OGD.
FIG. 16. Transient middle cerebral artery occlusion results in increased apoptosis. Two adult male Sprague-Dawley rats were subjected to either 90 min of MCA occlusion or surgery without MCA occlusion (sham). At 24 h, the rats were sacrificed, and 12 μm brain slices were TUNEL stained. The number of TUNEL positive nuclei was counted for 3 visual fields and are presented as mean±SEM (B). * p<0.01, Student's t-test.
FIGS. 17A-B. The effect Tat-GluR2-3Y on apoptosis in a rat model of transient focal ischemia. Adult male Sprague-Dawley rats were pretreated for 1 h with either saline, or 3 nmol/g of Tat-GluR2-3Y or Tat-GluR2-3A and then subjected to 60 min of MCA occlusion. The rats were given a neurological exam before sacrifice at 24 h (A). 12 μm coronal brain slices were TUNEL stained and the number of TUNEL positive cells were counted for each section (B). Data are normalized to a sham surgery control and are expressed as mean values±SEM. The peptide reduced apoptosis by 55% with respect to the control.
FIGS. 18 A-B. Control experiments to confirm that GluR2-3Y does not have non-specific effects on learned behaviours reinforced by food or drug-reward stimuli. These experiments also demonstrate that this interference peptide does not disrupt sensory motor or memory functions related to performance of operant behaviour on two different schedules of reinforcement A. Rats maintained on a restricted feeding schedule were trained to lever-press for food pellets (45 mg) on a fixed-ratio 2 (FR2) schedule during 2-hour test sessions. Rats received IV injections of saline, GluR2-3A, or GluR2-3Y, in a counterbalanced order, 60 min prior to the test session. There were no significant differences in total number of responses for food reward, between the three conditions. B. Rats were first trained to self-administer d-amphetamine (0.2 mg/infusion) via a jugular catheter on an FR2 schedule of reinforcement. Once responding in the 3 hour test sessions had stabilized, the rats were then trained on a Progressive Ratio Schedule in which successively more responses were required to obtain each successive reinforcement. The ratio at which rats failed to perform the appropriate number of responses in a 1 hour period is called the beak point and this test is a sensitive measure of the unconditional reward value of a specific reward stimulus. Once stable Break point values were established, rats received IV injections of saline, GluR2-3A, or GluR2-3Y, in a counterbalanced order, 60 min prior to the test session. There were no significant differences in the Break Point measures for drug-reward, between the three conditions.
FIG. 19 GluR23y peptide blocked stress induced anxiety in a rat model of stress. Rats (n=2) were injected with either 10 nM/g GluR2-3Y or equal volume of vehicle ACSF (IP). They were given 30 minutes in a dark room post injection. After that they were placed on an elevated platform for 30 minutes as a stressor. After that 30 minutes they were placed on the elevated plus maze for 5 minutes. The GluR2-3Y injected rats spent more time on the open arms than the ACSF rats. The ACSF rats spent most of their time in the corners of the closed arms or rearing to look over the walls. Thus, GluR23Y peptide blocked stress induced anxiety. These results strongly suggest that facilitated AMPAR endocytosis and hence the ession of LTD play an indispensable role in the expression of stress-induced behaviors and that LTD blocker such as the GluR23Y may be used therapeutics to treat stress-related brain disorders.
The invention provides, in part, methods and reagents for modulating neuronal apoptosis. The invention also provides, in part, methods and reagents for modulating synaptic plasticity. For example, compounds according to the invention may be used as neuroprotective agents that are capable of modulating AMPA receptor endocytosis. In some embodiments, such compounds can modulate AMPA receptor endocytosis and block neuronal apoptosis without affecting NMDA receptor function, and therefore may bypass the negative effects of blocking NMDA receptor function.
Alternative embodiments and examples of the invention are described herein. These embodiments and examples are illustrative and should not be construed as limiting the scope of the invention.
Various assays, as described herein or known to one of ordinary skill in the art, may be performed to determine the modulatory activity of a compound according to the invention. For example, modulation of synaptic plasticity, AMPA receptor endocytosis, NMDA-induced neuronal apoptosis, or AMPA receptor phosphorylation, may be tested as described herein or as known to one of ordinary skill in the art. In some embodiments, assays may be performed to test compounds for ability to inhibit AMPA receptor endocytosis. Such assays include without limitation nucleic acid, polypeptide, small molecule etc. based assays, such as immunoassays, hybridization assays, small molecule binding assays, peptide binding assays, antibody binding assays, competition assays, endocytosis assays, phosphorylation assays, apoptosis and cell death assays, histochemistry, animal and in vitro model assays, etc.
AMPA receptor polypeptides may be provided in neuronal or non-neuronal cells, or cell lysates. Cells and cell lines may be obtained from commercial sources, for example, ATCC, Manassas, Va., USA. Suitable animal models for neurological disorders may be obtained from, for example, The Jackson Laboratory, Bar Harbor, Me., USA or from other sources. Suitable animal models include models for stroke87-94, drug addiction 101-106, 112, schizophrenia107-111, Huntington's Disease112, Epilepsy115, neurocomplication of AIDS116, mental retardation (e.g., Fragile X retardation, Rett syndrome)117,118, and multiple sclerosis119,120.
The assays may be conducted using detectably labelled molecules, i.e., any means for marking and identifying the presence of a molecule, e.&, an oligonucleotide probe or primer, a gene or fragment thereof, a peptide, or a cDNA molecule. Methods for detectably-labeling a molecule are well known in the art and include, without limitation, radioactive labelling (e.&, with an isotope such as 32P or 35S) and nonradioactive labelling such as, enzymatic labelling (for example, using horseradish peroxidase or alkaline phosphatase), chemiluminescent labeling, fluorescent labeling (for example, using fluorescein), bioluminescent labeling, or antibody detection of a ligand attached to the probe. Also included in this definition is a molecule that is detectably labelled by an indirect means, for example, a molecule that is bound with a first moiety (such as biotin) that is, in turn, bound to a second moiety that may be observed or assayed (such as fluorescein-labeled streptavidin). Labels also include digoxigenin, luciferases, and aequorin.
Disorders and Conditions
Any disorder or condition which includes neural dysfunction, for example due to neurological damage or behavioural sensitization due to the excessive activation of NMDA receptors or due to changes in AMPA receptor endocytosis may be treated, prevented, or studied according to the methods and compounds of the invention. Therefore, disorders associated with other conditions ranging from hypoglycemia, hypoxia, and cardiac arrest to epilepsy are considered neurological damage disorders according to the invention. Disorders according to the invention include without limitation cerebral ischemia, occurring for example after stroke (ischemic stroke due to for example atherothrombotic disease of e.g., extracranial arteries, or to emboli from the heart or lacunar infarcts) or brain trauma (e.g., intracerebral hemorrhage or subarachnoid hemorrhage); head injury, neurodegenerative disorders in which compromised neurons become sensitive to excitotoxic damage; Alzheimer's, Parkinson's, or Huntington's disease; epilepsy, neuropathic pain; amyotrophic lateral sclerosis (ALS); Hutchinson Gilford syndrome; diabetes; ataxia; mental retardation; or dementias. Major risk factors for stroke include smoking, diabetes, obesity, and high blood pressure. Accordingly, subjects having any of these conditions or behaviours may be considered as having a disorder according to the invention.
Disorders according to the invention also include those disorders associated with defects or dysfunction in learning or memory; psychiatric disorders, such as autism, schizophrenia or fragile X syndrome; or disorders associated with substance abuse or addition to drugs, including nicotine, alcohol, opiates such as heroin, codeine and morphine, including derivatives such as pethidine and methadone, nicotine, marijuana, phenyclidene, psychostimulants such as amphetamines and cocaine, barbiturates such as pentobarbitone and quinalbarbitone, and benzodiazepines such as temazepam, diazepam and flunitrazepam.
The compounds of the invention can be used to prepare antibodies to GluR2-CT peptides or analogues thereof, for example, the sequences set forth in Table I or conservative substitutions thereof, Formula I, or Formula A, or to homologous sequences found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor, using standard techniques of preparation as, for example, described in Harlow and Lane56, or known to those skilled in the art. Antibodies can be tailored to minimise adverse host immune response by, for example, using chimeric antibodies contain an antigen binding domain from one species and the Fc portion from another species, or by using antibodies made from hybridomas of the appropriate species. In alternative embodiments of the invention, antibodies may be raised, for exile, against a phosphorylated GluR-CT peptide that is phosphorylated one or more tyrosines or serines or threonines. In alternative embodiments of the invention, antibodies may be raised, for example against a constitutively phosphorylated GluR-CT peptide that replaces existing tyrosines or seines or threonines with glutamates and aspartates. In some embodiments, anti-idiotypic antibodies may be raised, for example, against to an antibody that specifically binds a GluR CT peptide or analogue thereof.
Polypeptides And Test Compounds
In one aspect, compounds according to the invention include GluR2, GluR3, or GluR4 peptides and analogues and variants thereof including, for example, the peptides described herein that are phosphorylated or unphosphorylated at any one of the three tyrosines, including polypeptides that are constitutively phosphorylated, or that are unphosphorylatable, as well as homologs and fragments thereof. For example, compounds according to the invention include peptides including the sequences set forth in Table I or analogues or variants thereof.
In some embodiments, compounds according to the invention do not have, or have to a lesser extent, the negative side effects associated with the use of other neuroprotective agents. For example, compounds according to the invention may exhibit any value from between 10% to 100% reduction in psychotomimesis, respiratory depression, cardiovascular disregulation, or any other adverse side effect when compared to a NMDA receptor antagonist or glutamate release blocker (such as Selfotel, Gavestinel, Aptinagel, memantine. etc.75-78,95-99).
In some embodiments, compounds according to the invention are similarly efficacious or more efficacious than existing neuroprotective agents such as NMDA receptor antagonists (e.g., Gavestinel or Aptinagel) or other neuroprotective agents (e.g., Kappa opiod peptide R antagonist such as Cervene; NOS inhibitors such as Lubeluzole; Na+ channel blockers such as Lubeluzole;cell membrane stabilizers such as Citicoline; Ca2+ channel antagonists; anti-ICAM antibodies such as Enlimornab; GABAA receptor modulators such as Clomethiazole; glutamate release inhibitors such as Riluzole).79-84,100 For example, compounds according to the invention may exhibit any value from between 0% to 100% or greater than 100% efficacy when compared with other neuroprotective agents.
In alternative embodiments, one or more of the compounds described herein may be specifically excluded from one or more aspects of the invention.
Compounds can be prepared by, for example, replacing, deleting, or inserting an amino acid residue at any position of a GluR peptide or peptide analogue, for example, a GluR2-CT peptide sequence as set forth in Table I, Formula I, or Formula A, or to homologous sequences found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor, as described herein, with other conservative amino acid residues, i.e., residues having similar physical, biological, or chemical properties, and screening for the ability of the compound to inhibit endocytosis of the AMPA receptor. In some embodiments of the invention, compounds of the invention include antibodies that specifically bind to a GluR polypeptide, for example, a GluR2-CT peptide, which may be phosphorylated, unphosphorylated, unphosphorylatable, or constitutively phosphorylated. In some embodiments of the invention, compounds of the invention include antibodies that bind to antibodies that specifically bind GluR CT peptides.
It is well known in the art that some modifications and changes can be made in the structure of a polypeptide without substantially altering the biological function of that peptide, to obtain a biologically equivalent polypeptide. For example, in some embodiments, compounds according to the invention may be adapted or modified for oral administration such that they are resistant to digestion by stomach acids. In one aspect of the invention, polypeptides of the present invention also extend to biologically equivalent peptides that differ from a portion of the sequence of the polypeptides of the present invention by conservative amino acid substitutions. As used herein, the term “conserved amino acid substitutions” or “conservative substitution” refers to the substitution of one amino acid for another at a given location in a GluR CT peptide (e.g., as set forth in Table I, Formula I, or Formula A, or to homologous sequences found in the C-terminus of the GluR2, GluR3, or GluR4 subunits of the AMPA receptor), where the substitution can be made without substantial loss of the relevant function. In making such changes, substitutions of like amino acid residues can be made on the basis of relative similarity of side-chain substituents, for example, their size, charge, hydrophobicity, hydrophilicity, and the like, and such substitutions may be assayed for their effect on the function of the peptide by routine testing.
As used herein, the term “ammo acids” means those L-amino acids commonly found in naturally occurring proteins, D-amino acids and such amino acids when they have been modified. Accordingly, amino acids of the invention may include, for example: 2-Aminoadipic acid; 3-Aminoadipic acid; beta-Alanine; beta-Aminopropionic acid; 2-Aminobutyric acid; 4-Aminobutyric acid; piperidinic acid; 6-Aminocaproic acid; 2-Aminoheptanoic acid; 2-Aminoisobutyric acid, 3-Aminoisobutyric acid; 2-Aminopimelic acid; 2,4 Diaminobutyric acid; Desmosine; 2,2′-Diaminopimelic acid; 2,3-Diamiopropionic acid; N-Ethylglycine; N-Ethylasparagine; Hydroxylysine; allo-Hydroxylysine; 3-Hydroxyproline; 4-Hydroxyproline; Isodesmosine; allo-Isoleucine; N-Methylglycine; sarcosine; N-Methylisoleucine; 6-N-methyllysine; N-Methylvaline; Norvaline; Norleucine; and Ornithine,
In some embodiments, conserved amino acid substitutions may be made where an amino acid residue is substituted for another having a similar hydrophilicity value (e.g., within a value of plus or minus 2.0, or plus or minus 1.5, or plus or minus 1.0, or plus or minus 0.5), where the following may be an amino acid having a hydropathic index of about −1.6 such as Tyr (−1.3) or Pro (−1.6) are assigned to amino acid residues (as detailed in U.S. Pat. No. 4,554,101, incorporated herein by reference): Arg (+3.0); Lys (+3.0); Asp (+3.0); Glu (+3.0); Ser (+0.3); Asn (+0.2); Gln (+0.2); Gly (0); Pro (−0.5); Thr (−0.4); Ala (−0.5); His (−0.5); Cys (−1.0); Met (−1.3); Val (−1.5); Leu (−1.8); Ile (−1.8); Tyr (−2.3); Phe (−2.5); and Trp (−3.4).
In alternative embodiments, conservative amino acid substitutions may be made where an amino acid residue is substituted for another having a similar hydropathic index (e.g., within a value of plus or minus 2.0, or plus or minus 1.5, or plus or minus 1.0, or plus or minus 0.5). In such embodiments, each amino acid residue may be assigned a hydropathic index on the basis of its hydrophobicity and charge characteristics, as follows: Ile (+4.5); Val (+4.2); Leu (+3.8); Phe (+2.8); Cys (+2.5); Met (+1.9); Ala (+1.8); Gly (−0.4); Thr (−0.7); Ser (−0.8); Trp (−0.9); Tyr (−1.3); Pro (−1.6); His (−3.2); Glu (−3.5); Gln (−3.5); Asp (−3.5); Asn (−3.5); Lys (−3.9); and Arg (−4.5).
In alternative embodiments, conservative amino acid substitutions may be made using publicly available families of similarity matrices.63-69 The PAM matrix is based upon counts derived from an evolutionary model, while the Blosum matrix uses counts derived from highly conserved blocks within an alignment. A similarity score of above zero in either of the PAM or Blosum matrices may be used to make conservative amino acid substitutions.
In alternative embodiments, conservative amino acid substitutions may be made where an amino acid residue is substituted for another in the same class, where the amino acids are divided into non-polar, acidic, basic and neutral classes, as follows: non-polar: Ala, Val, Leu, Ile, Phe, Trp, Pro, Met; acidic: Asp, Glu; basic: Lys, Arg, His; neutral: Gly, Ser, Thr, Cys, Asn, Gln, Tyr.
Conservative ammo acid changes can include the substitution of an L-amino acid by the corresponding D-amino acid, by a conservative D-amino acid, or by a naturally-occurring, non-genetically encoded form of amino acid, as well as a conservative substitution of an L-amino acid. Naturally occurring non-genetically encoded amino acids include beta-alanine, 3-amino-propionic acid, 2,3-diamino propionic acid, alpha-aminoisobutyric acid, 4-amino-butyric acid, N-methylglycine (sarcosine), hydroxyproline, ornithine, citrulline, t-butylalanine, t-butylglycine, N-methylisoleucine, phenylglycine, cyclohexylalanine, norleucine, norvaline, 2-napthylalanine, pyridylalanine, 3-benzothienyl alanine, 4-chlorophenylalanine, 2-fluorophenylalanine, 3-fluorophenylalanine, 4-fluorophenylalanine, penicillamine, 1,2,3,4-tetrahydro-isoquinoline-3 carboxylix acid, beta-2-thienylalanine, methionine sulfoxide, homoarginine, N-acetyl lysine, 2-amino butyric acid, 2-amino butyric acid, 2,4-diamino butyric acid, p-aminophenylalanine, N-methylvaline, homocysteine, homoserine, cysteic acid, epsilon-amino hexanoic acid, delta-amino valeric acid, or 2,3-diaminobutyric acid.
In alternative embodiments, conservative amino acid changes include changes based on considerations of hydrophilicity or hydrophobicity, size or volume, or charge. Amino acids can be generally characterized as hydrophobic or hydrophilic, depending primarily on the properties of the amino acid side chain. A hydrophobic amino acid exhibits a hydrophobicity of greater than zero, and a hydrophilic amino acid exhibits a hydrophilicity of less than zero, based on the normalized consensus hydrophobicity scale of Eisenberg et al.57 Genetically encoded hydrophobic amino acids include Gly, Ala, Phe, Val, Leu, Ile, Pro, Met and Trp, and genetically encoded hydrophilic amino acids include Thr, His, Glu, Gin, Asp, Arg, Ser, and Lys. Non-genetically encoded hydrophobic amino acids include t-butylalanine, while non-genetically encoded hydrophilic amino acids include citrulline and homocysteine.
Hydrophobic or hydrophilic amino acids can be further subdivided based on the characteristics of their side chains. For example, an aromatic amino acid is a hydrophobic amino acid with a side chain containing at least one aromatic or heteroaromatic ring, which may contain one or more substituents such as —OH, —SH, —CN, —F, Cl, —Br, —I, —NO2, —NO, —NH2, —NHR -NRR, —C(O)R, —C(O)OH, —C(O)OR, —C(O)NH2, —C(O)NHR C(O)NRR, etc., where R is independently (C1-C6) alkyl, substituted (C1-C6) alkyl, (C1-C6) alkenyl, substituted (C1-C6) alkenyl, (C1-C6) alkynyl, substituted (C1-C6) alknyl, (C5-C20) aryl, substituted (C5-C20) aryl, (C6-C26) alkaryl, substituted (C6-C26) alkaryl, 5-20 membered heteroaryl substituted 5-20 membered heteroaryl, 6-26 membered alkheteroaryl or substituted 6-26 membered alkheteroaryl. Genetically encoded aromatic amino acids include Phe, Tyr, and Trp, while non-genetically encoded aromatic ammo acids include phenylglycine, 2-napthylalanine, beta-2-thienylalanine, 12,3,4 tetrahydro-isoquinoline-3-carboxylic acid, 4-chlorophenylalanine, 2-fluorophenylalanine3-fluorophenylalanine, and 4-fluorophenylalanine.
An apolar amino acid is a hydrophobic amino acid with a side chain that is uncharged at physiological pH and which has bonds in which a pair of electrons shared in common by two atoms is generally held equally by each of the two atoms (i.e., the side chain is not polar). Genetically encoded apolar amino acids include Gly, Leu, Val, Ile, Ala, and Met, while non-genetically encoded apolar amino acids include cyclohexylalanine . Apolar amino acids can be further subdivided to include aliphatic amino acids, which is a hydrophobic amino acid having an aliphatic hydrocarbon side chain. Genetically encoded aliphatic amino acids include Ala, Leu, Val, and Ile, while non-genetically encoded aliphatic amino acids include norleucine.
A polar amino acid is a hydrophilic amino acid with a side chain that is uncharged at physiological pH, but which has one bond in which the pair of electrons shared in common by two atoms is held more closely by one of the atoms. Genetically encoded polar amino acids include Ser, Thr, Asn, and Gln, while non-genetically encoded polar amino acids include citrulline, N-acetyl lysine, and methionine sulfoxide. An acidic amino acid is a hydrophilic amino acid with a side chain pKa value of less than 7. Acidic amino acids typically have negatively charged side chains at physiological pH due to loss of a hydrogen ion. Genetically encoded acidic amino acids include Asp and Glu. A basic amino acid is a hydrophilic amino acid with a side chain pKa value of greater than 7. Basic amino acids typically have positively charged side chains at physiological pH due to association with hydronium ion. Genetically encoded basic amino acids include Arg, Lys, and His, while non-genetically encoded basic amino acids include the non-cyclic amino acids ornithine, 2,3,-diaminopropionic acid, 2,4-diaminobutyric acid, and homoarginine.
It will be appreciated by one skilled in the art that the above classifications are not absolute and that an amino acid may be classified in more than one category. In addition, amino acids can be classified based on known behaviour and or characteristic chemical, physical, or biological properties based on specified assays or as compared with previously identified amino acids. Amino acids can also include bifunctional moieties having amino acid-like side chains.
Conservative changes can also include the substitution of a chemically derivatised moiety for a non-derivatised residue, by for example, reaction of a functional side group of an amino acid. Thus, these substitutions can include compounds whose free amino groups have been derivatised to amine hydrochlorides, p-toluene sulfonyl groups, carbobenzoxy groups, t-butyloxycarbonyl groups, chloroacetyl groups or formyl groups. Similarly, free carboxyl groups can be derivatized to form salts, methyl and ethyl esters or other types of esters or hydrazides, and side chains can be derivatized to from O-acyl or O-alkyl derivatives for free hydroxyl groups or N-im-benzylhistidine for the imidazole nitrogen of histidine, Peptide analogues also include amino acids that have been chemically altered, for example, by methylation, by amidation of the C-terminal amino acid by an alkylamine such as ethylamine, ethanolamine, or ethylene diamine, or acylation or methylation of an amino acid side chain (such as acylation of the epsilon amino group of lysine). Peptide analogues can also include replacement of the amide linkage in the peptide with a substituted amide (for example, groups of the formula —C(O)—NR, where R is (C1-C6) alkyl, (C1-C6) alkenyl, (C1-C6) alkynyl, substituted (C1-C6) alkyl, substituted (C1-C6) alkenyl, or substituted (C1-C6) alkynyl) or isostere of an amide linkage (for example, —CH2NH—, —CH2S, —CH2CH2—, —CH═CH— (cis and trans), —C(O)CH2——CH(OH)CH2—, or —CH2SO—).
The compound can be covalently linked, for example, by polymerisation or conjugation, to form homopolymers or heteropolymers. Spacers and linkers, typically composed of small neutral molecules, such as amino acids that are uncharged under physiological conditions, can be used. Linkages can be achieved in a number of ways. For example, cysteine residues can be added at the peptide termini, and multiple peptides can be covalently bonded by controlled oxidation. Alternatively, heterobifunctional agents, such as disulfide/amide forming agents or thioether/amide forming agents can be used. The compound can also be linked to a another compound that can modulate neuronal apoptosis, AMPA receptor endocytosis, synaptic plasticity, learning or memory, or substance abuse or addiction etc. The compound can also be constrained, for example, by having cyclic portions.
Peptides or peptide analogues can be synthesised by standard chemical techniques, for example, by automated synthesis using solution or solid phase synthesis methodology. Automated peptide synthesisers are commercially available and use techniques well known in the art. Peptides and peptide analogues can also be prepared using recombinant DNA technology using standard methods such as those described in, for example, Sambrook, et al.58 or Ausubel et al.59 In general, candidate compounds are identified from large libraries of both natural products or synthetic (or semi-synthetic) extracts or chemical libraries according to methods known in the art. Those skilled in the field of drug discovery and development will understand that the precise source of test extracts or compounds is not critical to the method(s) of the invention. Accordingly, virtually any number of chemical extracts or compounds can be screened using the exemplary methods described herein. Examples of such extracts or compounds include, but are not limited to, plant-, fungal-, prokaryotic- or animal-based extract, fermentation broths, and synthetic compounds, as well as modification of existing compounds. Numerous methods are also available for generating random or dire synthesis (e.g., semi-synthesis or total synthesis) of any number of chemical compounds, including, but not limited to, saccharide-, lipid-, peptide-, and nucleic acid-based compounds. Synthetic compound libraries are commercially available. Alternatively, libraries of natural compounds in the form of bacterial, fungal plant, and animal ex are commercially available from a number of sources, including Biotics (Sussex, UK), Xenova (Slough, UK), Harbor Branch Oceanographic Institute (FL Pierce, FL, USA), and PharmaMar, MA, USA. In addition, natural and synthetically produced libraries of, for example, neuronal polypeptides, are produced, if desired, according to methods known in the art, e.g., by stand extraction and fractionation methods. Furthermore, if desired, any library or compound is readily modified using standard chemical, physical, or biochemical methods.
When a crude extract is found to modulate neuronal apoptosis, AMPA receptor endocytosis, synaptic plasticity, learning or memory, or substance abuse or addiction etc., further fractionation of the positive lead extract is necessary to isolate chemical constituents responsible for the observed effect. Thus, the goal of the extraction, fractionation, and purification process is the careful characterization and identification of a chemical entity within the crude extract having neuronal apoptosis, AMPA receptor endocytosis, synaptic plasticity, etc., modulatory activities. The same assays described herein for the detection of activities in mixtures of compounds can be used to purify the active component and to test derivatives thereof. Methods of fractionation and purification of such heterogeneous extracts are known in the art. If desired, compounds shown to be useful agents for treatment are chemically modified according to methods known in the art. Compounds identified as being of therapeutic value may be subsequently analyzed using a mammalian model, or any other animal model for neuronal damage, neural dysfunction, synaptic plasticity, learning or memory, or substance abuse or addiction.
Pharmaceutical Compositions, Dosages, And Administration
Compounds of the invention can be provided alone or in combination with other compounds (for example, nucleic acid molecules, small molecules, peptides, or peptide analogs), in the presence of a liposome, an adjuvant, or any pharmaceutically acceptable carrier, in a form suitable for administration to humans. If desired, treatment with a compound according to the invention may be combined with more traditional and existing therapies for neurological damage, synaptic plasticity, learning or memory, or substance abuse. For example, compounds according to the invention may be administered as combination therapy with other treatments such as free-radical inhibitors to maximise neuronal survival; as complementary therapy to anti-coagulant prophylaxis in subjects undergoing atrial fibrillation or are considered to be at risk for stroke.86 In some embodiments, the compounds may be administered at specific therapeutic windows. For example, in some embodiments, the compounds may be administered approximately 3 hours after onset of ischemia.
In some embodiments, compounds according to the invention may be provided in fusion with a heterologous peptide to facilitate translocation of the compounds across cell membranes, as for example, described in U.S. Pat. No. 6,348,185; issued to Piwnica-Worms; U.S. Patent Publication US 2003/0229202 (Guo et al.), or PCT publication WO 00/62067 (Dowdy), Becker-Hapak et al.85, or Kabouridis114. In some embodiments, compounds according to the invention may be provided in combination with a carrier peptide, e.g., PEP 1.
In some embodiments, compounds according to the invention may be provided in stem cells, e.g., neuronal stem cells, modified to express the peptide. Suitable cells and vectors for such delivery include viral vectors such as adenovirus, adeno-associated virus, or Herpes Simplex Virus121,122.
Conventional pharmaceutical practice may be employed to provide suitable formulations or compositions to administer the compounds to patients suffering from or presymptomatic for neurological damage or neural dysfunction. Compounds may be administered systemically or may be administered directly to the CNS or other region of neurological damage. In some embodiments, compounds according to the invention may be provided in a form suitable for delivery across the blood brain barrier. Any appropriate route of administration may be employed, for example, parenteral, intravenous, subcutaneous, intramuscular, intracranial, intraorbital, ophthalmic, intraventricular, intracapsular, intraspinal, intracisternal, intraperitoneal, intranasal, aerosol, or oral administration. Therapeutic formulations may be in the form of liquid solutions or suspensions; for oral administration, formulations may be in the form of tablets or capsules; and for intranasal formulations, in the form of powders, nasal drops, or aerosols.
Methods well known in the art for making formulations are found in, for example, “Remington's Pharmaceutical Sciences” (19th edition), ed. A. Gennaro, 1995, Mack Publishing Company, Easton, Pa Formulations for parenteral administration may, for example, contain excipients, sterile water, or saline, polyalkylene glycols such as polyethylene glycol, oils of vegetable origin, or hydrogenated napthalenes. Biocompatible, biodegradable lactide polymer, lactide/glycolide copolymer, or polyoxyethylene-polyoxypropylene copolymers may be used to control the release of the compounds. Other potentially useful parenteral delivery systems for modulatory compounds include ethylene-vinyl acetate copolymer particles, osmotic pumps, implantable infusion systems, and liposomes. Formulations for inhalation may contain excipients, for example, lactose, or may be aqueous solutions containing, for example, polyoxyethylene-9-lauryl ether, glycocholate and deoxycholate, or may be oily solutions for administration in the form of nasal drops, or as a gel.
For therapeutic or prophylactic compositions, the compounds are administered to an individual in an amount sufficient to stop or slow cell degeneration or apoptosis, or to enhance or maintain synaptic plasticity, depending on the disorder. An “effective amount” of a compound according to the invention includes a therapeutically effective amount or a prophylactically effective amount. A “therapeutically effective amount” refers to an amount effective, at dosages and for periods of time necessary, to achieve the desired therapeutic result, such as reduction of cell degeneration or apoptosis, or to enhance synaptic plasticity. A therapeutically effective amount of a compound may vary according to factors such as the disease state, age, sex, and weight of the individual, and the ability of the compound to elicit a desired response in the individual. Dosage regimens may be adjusted to provide the optimum therapeutic response. A therapeutically effective amount is also one in which any toxic or detrimental effects of the compound are outweighed by the therapeutically beneficial effects. A “prophylactically effective amount”refers to an amount effective, at dosages and for periods of time necessary, to achieve the desired prophylactic result, such as inhibition of call degeneration or apoptosis, or to enhance synaptic plasticity. Typically, a prophylactic dose is used in subjects prior to or at an earlier stage of disease, so that a prophylactically effective amount may be less than a therapeutically effective amount. A preferred range for therapeutically or prophylactically effective amounts of a compound maybe 0.1 nM-0.1M, 0.1 nM-0.05M 0.05 nM-15 μM or 0.01 nM-10 μM.
It is to be noted that dosage values may vary with the severity of the condition to be alleviated or with the route of administration selected. For example, for oral administration, dosage values may be higher than for intravenous or intraperitoneal administration. For any particular subject, specific dosage regimens may be adjusted over time according to the individual need and the professional judgement of the person administering or supervising the administration of the compositions. Dosage ranges set forth herein are exemplary only and do not limit the dosage ranges that may be selected by medical practitioners. The amount of active compound in the composition may vary according to factors such as the disease state, age, sex, and weight of the individual. Dosage regimens may be adjusted to provide the optimum therapeutic response. For example, a single bolus may be administered, several divided doses may be administered over time or the dose may be proportionally reduced or increased as indicated by the exigencies of the therapeutic situation. It may be advantageous to formulate parenteral compositions in dosage unit form for ease of administration and uniformity of dosage.
In the case of vaccine formulations, an immunogenically effect amount of a compound of the invention can be provided, alone or in combination with other compounds, with an adjuvant, for example, Freund's incomplete adjuvant or aluminum hydroxide. The compound may also be linked with a carrier molecule, such as bovine serum albumin or keyhole limpet hemocyanin to enhance immunogenicity.
In general compounds of the invention should be used without causing substantial toxicity. Toxicity of the compounds of the invention can be determined using standard techniques, for example, by testing in cell cultures or experimental animals and determining the therapeutic index, i.e., the ratio between the LD50 (the dose lethal to 50% of the population) and the ID100 (the dose lethal to 100% of the population). In some circumstances however, such as in severe disease conditions, it may be necessary to administer substantial excesses of the compositions.
Primary Cultures of Hippocampal Neurons
Hippocampi were rapidly removed from embryonic E18 Sprague Dawley rats and pooled prior to trituration. Hippocampal cell suspensions were plated onto poly-D-lysine coated culture dishes or glass coverslips and grown in Neurobasal™ media (Invitrogen) for 14 days in vitro (DIV). The media from mature 14 DIV neurons was removed and replaced with 100 μM NMDA plus 10 μM glycine for 1 h at 37 μC prior to restoring neurons to the defined growth media. Twenty four hours after NMDA/glycine application, neurons were processed using cell death assays. NMDA-induced [Ca2+]responses were evoked and measured using methods described previously26.
Cell Death Assays
Apoptosis quantification: NMDA-induced apoptosis was quantified either using a Cell Death Detection Elisa Plus Kit (Roche Applied Sciences), which is based on the in vitro determination of cytoplasmic histone-associated DNA fragments, or using TdT mediated addition of biotinylated 11-dUTP to the free 3′-OH ends of DNA. Absorbance readings for both assays were cared out using a microplate reader.
Propidium Iodide (PI) staining of nuclei: After the induction of apoptosis, cells were fixed with 4% paraformaldehyde/4% sucrose for 10 min followed by ice cold acetone for 1 min, and then stained with 20 mg/ml PI in Dulbecco's PBS for 30 min. Stained coverslips were mounted onto glass slides and viewed with a Leica fluorescence microscope to identify condensed nuclei. Cells with condensed nuclei were counted as apoptotic and the percentage of apoptotic cells to the total number of cells was calculated to give a semi-quantitative analysis, expressed as percentage of apoptosis.
Treatment of Cells With Peptides
A short peptide (YKEGYNVYGIE) corresponding to amino acid residues from 869 to 879 of the C-terminus of GluR2 (R2-CT) was synthesised and incubated with a carrier protein (Pep-1)23 at a ratio of 1:20 in Dulbecco's modified Eagle's medium (DMEM, Gibco) at 37° C. in a humidified atmosphere containing 5% CO2 for 30 min to allow the formation of R2-CT/Pep-1 complex. Hippocampal neurons (DIV 12-14) were then overlaid with the preformed complex to reach a final R2-CT concentration of 1 μM a and further incubated for 1 h before experiments commenced.
Receptor Trafficking Assays
Cell ELISA assay: Quantification of cell-surface AMPA or NMDA receptors was performed by a colorimetric cell-ELISA assay essentially as described previously14. Briefly, hippocampal neurons were treated with 100 μM NMDA plus 10 μM glycine for. 1 h and then fixed with 4% paraformaldehyde/4% sucrose in PBS for 10 min. Half of the cells in each treatment condition were then permeabilized with 0.1% Triton-X 100 for 5 min. Receptors on the plasma membrane surface and the total cellular pool were then determined by incubating the cells with monoclonal antibodies against the extracellular domains of GluR2 or NR1 (Chemicon, 1 μg/ml) overnight at 4° C., followed by incubation with HRP-conjugated anti-mouse IgG secondary antibody (1:1000, Amerisham Life Sciences) for 1 h at room temperature. Following extensive washing with PBS, cells were incubated with OPD substrate (Sigma) for approximately 10 min. Reactions were stopped with 0.2 volumes of 3N HCl, and absorbance at 492 nm was read using a spectrophotometric microplate reader.
Transferrin receptor endocytosis assay: To assess the effect of endocytosis inhibitors on transferrin receptor endocytosis, hippocampal neurons were incubated with 2 mg/ml Alexa-A488 conjugated transferrin (Molecular Probes) for 30 min at 37° C. in the presence or absence of endocytosis inhibitors. Internalized receptors were then viewed with a Leica fluorescence microscope.
cDNA Plasmids and Cell Transfection
Rat HA-tagged GluR1 and GluR2 receptor subunit cDNAs have been described previously14. Constructs of HA-GluR2 carboxyl internal deletion or truncation mutants were made by standard PCR methods. The HA-GluR3Y-3A mutant was made using a Quick-Change Site Directed Mutagenesis Kit (Stratagene). HEK293 cells (ATCC) were using the calcium phosphate precipitation method. Thirty six to forty eight hours after transfection, cells were washed with extracellular recording solution (ECS in mM: 140 NaCl, 33 glucose, 25 HEPES, 5.4 KCl, 1.3 CaCl2; pH 7.4, 320 mOsm) and incubated in ECS for at least one hour (serum starvation). For insulin treatment, cells were incubated with ECS supplemented with 0.5 μM human recombinant insulin (Sigma) for 10 min, after which the cells were processed for immunocytochemistry and colorimetric assays or lysed in RIPA buffer (50 mM Tris-HCl, 150 μM NaCl and 0.1% triton X-100) for immunoprecipitation as described below.
Cloning, Expression, and Purification of GST Fusion Proteins
GST-GluR23Y and GST-GluR23A were constructed by subcloning corresponding PCR fragments into pGEX 4T-1 vectors. GST fusion proteins were expressed in DH5α E. coli and purified from bacterial lysates according to the man s protocol (Pharmacia). Products were dialyzed in PBS and concentrated using Microcon-10 columns (Amicon) for intracellular application during whole-cell recordings.
Immunofluorescent Confocal Microscopy
HEK293 cells were plated onto poly-D-lysine coated glass cover slips set in 35 mm culture dishes and transfected with 2 μg of the plasmid of interest. For cell-surface receptor expression assays, cells at 48 h post-transfection were fixed with 4% paraformaldehyde in PBS for 10 min. Surface AMPA receptors were first labeled with monoclonal anti-HA antibody (1:2000, Babco, Berkeley, Calif.) and visualized with an FITC-conjugated anti-mouse IgG antibody (1:500, Sigma). For the surface AMPA receptor internalization assay, HEK293 cells transfected with HA-tagged GluR2 constructs were incubated live at 4° C. with monoclonal anti-HA antibody (10:g/ml) for 1 h to label surface AMPA receptors. Cells were then incubated at 37° C. in ECS supplemented with or without 0.5 μM insulin for 10 min before an additional 20 min incubation in ECS to allow for constitutive or regulated internalization of labeled receptors. Following a 10 min fixation with 4% paraformaldehyde without permeabilization, receptors remaining on the plasma membrane surface were stained with FITC-conjugated anti-mouse IgG antibodies. The internalized cell-surface receptors were subsequently labeled with Cy3-conjugated anti-mouse IgG antibodies following cell permeabilization as described by Man et al.14
Colorimetric assays were performed essentially as previously reported.14
Immunoprecipitation and Western Blotting
Immunoprecipitation and Western blotting were carried out essentially as previously reported.14 Proteins from cerebral cortex, hippocampal slices, cultured hippocampal neurons or transfected HEK 293 cells were solubilzed in RIPA buffer containing either 1% SDS (pha 5 min boiling; denaturing conditions) or 1% DOC (non-denaturing conditions). For immunoprecipitation, 500 μg of protein from these tissue lysates was incubated with their respective antibodies in 500 μl of RIPA buffer for 4 h at 4° C. Protein A-sepharose was added to the mixture and incubated for an additional 2 h. The complex was isolated by centrifugation and washed three times. Proteins eluted from the sepharose beads were subjected to SDS-PAGE and immunoblotting using their respective antibodies. For sequential re-probing of the same blots, the membranes were stripped of the initial primary and secondary antibodies and subjected to immunoblotting with another antibody. Blots were developed using enhanced chemiluminescence detection. (Amersham). Band intensities were quantified using Scion Image PC software.
Hippocampal Neuron Cultures, Transfection, and Fluorescence-Based Internalization Assays
As in Lee et al., 200240 Pa et al., 2001.49
Hippocampal slices (400 μm thickness) were prepared from Sprague-Dawley rats aged 16-26 postnatal days and perfused at room temperature with artificial cerebrospinal fluid containing (mM): 126 NaCl, 26 NaHCO3, 10 glucose, 3 KCl, 1.2 KH2PO4, 1 MgCl2, and 1 CaCl2, saturated with 95% O2/5% CO2 14. The recording pipettes (4-5 MΩ) were filled with solution containing (mM): 135 CsCl, 10 HEPES, 5 QX-314, 4 Mg-ATP, 2 MgCl2, 0.5 EGTA, 0.2 GTP and 0.1 CaCl2, pH 7.4, 310 mOsm. Whole-cell recording of CA1 neurons and the induction of LFS-LTD were performed as previously described.14
Student's t-tests were used whenever intra-experiment samples were compared. For cross comparisons or analysis of data between experiments all values were first subjected to a one-way ANOVA and all groups were compared against control basal values. Values were not statistically significant at F<0.5. Groups that were found to be statistically significant were individually compared using Dunnett's t-test. All analysis was done using normalized values in the Statistica statistics package (Statsoft).
Primary Neuronal Culture
The cortex was dissected from 18 days in utero Wistar embryos and was treated with trypsin-EDTA for 15 min at 37° C. The cells were then washed 3 times and triturated to a single cell suspension. The neurons with glia were then seeded at a density of ˜2.5×105 neurons/well in 12 well tissue culture plates coated with poly-D lysine. The cells were then cultured for 24-48 h in plating media (Gibco Neurobasal™, 1% FBS, 2% B-27 supplement, 0.5 mM L-glutamate, and 25 μM glutamic acid), after which the cells were treated with Neurobasal™ maintenance media (NMM: Gibco Neurobasal™ Media+.SmM L-glutamate, 2% B27 supplement) with 10 μM 5-Fluoro-2′-deoxyuridine (FDU) to enrich the culture for neurons (˜85%). After 24 h-48 h culture in FDU, the cells were maintained on NMM changed every 4 days.
Tat-GluR2-3Y, Tat-GluR2-3A, and dansyl-conjugated Tat-GluR2-3Y were all synthesized on an ABI 433A peptide synthesizer (NAPS).
Neuronal Uptake of Dansyl-Labeled Tat-GluR2-3Y Peptide
Day in vitro (DIV) 13 primary cortical neurons at a density of 2.5×105/well in 12 well plates were washed once with extracellular solution (ECS: 140 mM NaCl, 5.4 mM KCl, 1.3 mM CaCl2, 10 mM HEPES, 33 mM D-glucose, pH 7.4) and then 1 mL containing either no peptide (control) or 1 μM dansyl labeled-Tat-GluR2-3Y was added to the wells. After 5 min, 10 min, 30 min, or 60 min incubation at 37° C. the wells were washed twice with ECS and imaged using fluorescence microscopy using an excitation wavelength of 550 nm.
Quantification of AMPAR Endocytosis in Response to NMDA Treatment
Using cellular ELISA, the amount of intracellular versus extracellular AMPAR expression was measured allowing quantification of AMPAR endocytosis in response to NMDA insult. DIV 12-13 neurons were washed once with room temperature ECS. 1 mL of NMM with or without 1 μM Tat-GluR2-3Y or Tat-GluR2-3A peptide was added to the wells and the cells were incubated for 1 h at 37° C. The media was then aspirated and 1 mL of ECS with different combinations of peptide (1 μM Tat-GluR2-3Y or Tat-GluR2-3A) and NMDA-glycine treatment (50 μM NMDA+10 μM glycine) was added to the wells and the cells were incubated at room temperature for 30 min. The wells were then washed once with ECS and then immediately fixed with 0.5 mLs of cold fixative (4% paraformaldehyde, and 4% sucrose in PBS) for 10 min with shaking. The cells were then washed 3 times with 1 mL of PBS. Half of the wells for each treatment group were left unpermeabilized (representing the extracellular AMPAR expression) and half were permeabilized (representing total intracellular and extracellular AMPAR expression) with 0.5 mLs of 0.2% Triton X 100 in PBS for 10 min with shaking followed by 3 PBS washes. The wells were then blocked with 2% goat serum in PBS for 1 h. After blocking the blocking buffer was aspirated and either 400 μL of 1 ug/mL of mouse anti-rat GluR2 N-terminus antibody in 2% goat serum (clone: 6C4, Chemicon) or 400 μL of blocking buffer (no primary antibody controls) was added to the wells and the plates were incubated overnight with shaking at 4° C. The plates were then washed 3 times with PBS and 400 μL of 1/1000 horseradish peroxidase-conjugated sheep anti-mouse IgG2a antibody in 2% goat serum was added and the plates were incubated for 1 h at room temperature with shaking. The plates were then washed 3 times with PBS, then 1 mL of OPD solution (0.4 mg/mL o-phenylenediamine, 0.4 mg/mL urea hydrogen peroxide, and 50 mM phosphate-citrate buffer, Sigma) was added and the plates were incubated for 5-10 min at room teat with shaking. The peroxidase reaction was terminated by the addition of 200 μL of 3N HCl. The absorbance at 492 nm was read using a μQuant plate reader (Bio-Tek Instruments Inc.). The data were analyzed by first subtracting the absorbance values for the no-primary controls from the other samples. The percentage AMPAR surface expression was then expressed as a ratio of the non-permeabilized samples to the permeabilized samples. The individual repeat experiments were then normalized and treatment groups were compared using ANOVA followed by the Tukey-Kramer test, (p=0.05).
Quantification of Neuronal Apoptosis in Oxygen and Glucose Deprivation (OGD)
Neurons were subjected to 60 min of oxygen and glucose deprivation and the apoptosis was quantified using a mono- and oligonucleosome ELISA. DIV 13 neurons seeded at a density of 2.5×105/well in 12 well plates were washed once with ECS, and the cells were pretreated for 60 min with or without 1 μM Tat-GluR2-3Y in NMM. The cells were then washed twice with either OGD buffer (121 mM NaCl, 5 mM KCl, 1 mM Na-private, 1.8mM CaCl2, 25 mM NaHCO3, 0.01 mM glycine; pH 7.4) for the OGD samples, or with ECS for the non-OGD samples. The non-OGD samples were then incubated for 25 h at 37° C. in NMM and the OGD samples were incubated in OGD buffer with or without Tat-GluR-3Y in an anaerobic chamber at 37° C. for 60 min. The OGD samples were then incubated for 24 h at 37° C. The neuronal apoptosis was then quantified using a Cell Death Detection ELISAPLUS kit (Roche Applied Science) as per the manufacturer's instructions. The absorbance at 405 nm (reference wavelength, 490 nm) was read using a μQuant plate reader (Bio-Tek Instruments Inc.). The individual repeat experiments were then normalized and treatment groups were compared using ANOVA followed by the Tukey-Kramer test, (p=0.05).
Tat-GluR2-3Y Infiltration of Brain Tissue
Two adult male C57-Black/6 mice weighing ˜22 g were given an intraperitoneal injection of either saline or 30 nmol/g of dansyl-labeled Tat-GluR2-3Y. The mice were sacrificed at 2 h and the brains were immediately removed and frozen at −80° C. 40 micron coronal sections were cut with a cryostat and visualized with fluorescence microscopy.
Transient Focal Ischemia Model
The procedure was performed essentially as described previously (70). Briefly, adult male Sprague-Dawley rats between 280 and 320 g (20 h fasted weight) were anesthetized with an inhaled mixture of 4% isofluorane, in 30% oxygen balanced nitrous oxide, and maintained on 1.5% isofluorane. Bronchial secretions were minimized by administering 0.5 mg/kg of atropine intraperitoneally. Either, 3 nmoles/g of Tat-GluR2-3Y in saline, 3 mmoles/g Tat-GluR2-3A in saline, or saline only was administered 1 h before middle cerebral artery (MCA) occlusion, via a femoral vein PE-50 catheter. The experimenter was blinded to the identity of the treatment groups for all surgeries and down-stream experiments. Under a dissection microscope, the common carotid artery (CCA), external carotid artery (ECA), and internal carotid artery (ICA) were exposed and dissected. The terminal lingual and maxillary arteries were then cauterized and the pterygopalitine artery was then ligated with 5-0 silk suture. After this point the ICA was the only remaining extracranial branch of the CCA. The ECA was then partially cut close to the rostral ligature and a 30 mm 3-0 nylon monofilament with a heat rounded tip was inserted into the ECA and advanced past the CCA bifurcation. The ECA was then completely cut, mobilizing the ECA stamp containing the nylon suture. The nylon suture was then flipped so that its tip was facing the ICA and the nylon suture was then gently advanced approximately 20 mm until resistance was felt. At this point the suture reached the origin of the MCA and the anterior cerebral artery completely blocking the blood flow to the MCA territory. The wound was then stitched closed with silk suture and the animal was awoken by turning off the isoflurane. Rectal temperature, and blood pressure measured with a tail cuff were measured before treatment, 15 min post injection, 50 min post injection, and 15 min post MCA occlusion. The plasma pH, O2, and CO2 were measured with a Rapidlab™ 348 blood gas analyzer (Bayer Diagnostics) in some animals to ensure that the gas flow rates used were appropriate and yielded reproducible blood gases. The animal was then given a neurological examination after 45 min of MCA occlusion. This exam was used to exclude any animal that did not experience significant occlusion of the MCA. The examination consisted of 10 tests with a maximum deficit score of 23 (71). The individual tests are summarized in Table II.
The animal was induced again after the neurological examination and the nylon monofilament was withdrawn at 60 min after the onset of occlusion returning blood flow to the MCA territory. The neurological examination was performed again at the time of sacrifice (−24 h). The sham surgery was performed as the MCA occlusion, however, the nylon monofilament was not inserted.
Rats were sacrificed 3 days post MCA occlusion by deep anesthesia followed by decapitation. The brain was removed immediately after sacrifice and placed in an acrylic rat brain matrix (Harvard Apparatus) and incubated at −80C. for 5 min. 1 mm coronal slices were then cut with razor blades and placed in 37C. solution of 2% 2,3,5-triphenyltetrazolium chloride (TTC, Sigma) in PBS. The slices were then incubated for approximately 15 min until sufficient colour developed.
At day 1 post MCAo rats were anesthetized with 1.5 mL of 25% urethane and were perfused with 100 mL of 0.9% saline followed by 120 mLs of 4% paraformaldehyde in PBS. The brains were then removed and stored overnight at 4° C. in 4% paraformaldehyde. The brains were then transferred to a 30% sucrose and 0.1% sodium azide, in PBS solution and stored at 4° C. until the brains completely sunk. The brains were then frozen in dry ice and 12 micron coronal slices were cut with a cryostat at −0.8 mm with respect to the bregma using a free floating method (72). The slices were then mounted on glass slides and stained with TMR-TUNEL (terminal deoxyribonucleotide transferase [TdT]-mediated dUTP nick end labeling) (Roche Applied Science) as per the manufacturer's instructions. The slices were scored for number of cells that stained positive for TMR-TUNEL per field of view at 10× magnification. For each section the same 3 fields along the lateral portion of the cortex on the affected hemisphere were scored (the affected hemisphere was defined as the side with the greatest amount of apoptosis).
In order to induce apoptosis in mature cultures of rat hippocampal neurons (14 DIV+) we treated cells with a mild NMDA insult of 100 μM NMDA with 10 μM glycine for 1 h followed by recovery of the cells in normal media for periods of up to 24 h. As shown in
In order to determine the role of NMDA-induced endocytosis in mediating neuronal apoptosis, we first examined the effect of hypertonic sucrose, a well-characterized clathrin-dependent endocytosis inhibitor that inhibits the assembly of clathrin-coated pits13;14. AS shown in
Activation of certain forms of caspases, such as caspase-3 and -716 (also
The serine/threonine kinase Akt/PKB has been implicated in protecting neurons from apoptotic cell death17 and inhibition of this kinase activity has been suspected to be involved in NMDA receptor-mediated apoptosis18. We investigated whether the endocytosis process plays a critical role in the inhibition of Akt activity by determining the level of Akt phosphorylation at serine 473, a residue whose phosphorylation is required for full activation of Akt19. As shown in
A significant reduction of cell-surface AMPA, but not NMDA, receptors was observed following NMDA treatment and this reduction was a result of facilitated receptor endocytosis as it was blocked by endocytosis inhibitor myr-Dyn, but not the control peptide, Dyn (
In order to be sure that the blockade by this peptide was not due to non-specific effects on the endocytotic process, we examined its effect on transferrin receptor endocytosis, a well-characterized clathrin-mediated receptor endocytosis13. Incubation of hippocampal neurons with fluorescently-labeled transferrin for 30 min resulted in an accumulation of the fluorescently-labeled transferrin in the intracellular compartment. This was a result of clathrin-mediated transferrin receptor endocytosis as it was eliminated when 0.4 M sucrose was also present during the period of transferrin incubation. In contrast, R2-CT+Pep-1, applied to these neurons one hour prior to and during the transferrin incubation, failed to prevent transferrin receptor endocytosis. Thus, the R2-CT peptide is a dominant inhibitor that can specifically block NMDA-induced AMPA receptor endocytosis, but not non-specifically affect clathrin-mediated endocytotic processes.
Furthermore, pre-treatment of the neurons with R2-CT+Pep-1 significantly reduced NMDA-induced apoptosis as quantified by the histone biotinylation assay (
Therefore, a clathrin-dependent AMPA receptor endocytosis is specifically required for NMDA-, but not STS-, induced apoptosis of hippocampal neurons maintained in primary culture. Blocking endocytosis has no effect on NMDA-induced Ca2+ responses, but prevents both NMDA-induced activation of caspase-3 and inhibition of Akt phosphorylation. Thus, AMPA receptor endocytosis may be a critical link between NMDA-induced [Ca2+]i overload and intracellular cascades leading to apoptosis.
Thus, stimulation of NMDA receptor activates intracellular signaling cascades leading to apoptosis, and facilitates dynamin-dependent internalization on of the AMPA subtype glutamate receptors. Blocking the dynamin-dependent internalization specifically ameliorated NMDA (but not staurosporine)-activated apoptotic cascades, without affecting NMDA-induced rises in [Ca2+]i. Specific inhibition of NMDA-induced AMPA receptor endocytosis by a GluR2-derived peptide prevents NMDA induced apoptosis, without affecting that produced by staurosporine. These results demonstrate that AMPA receptor endocytosis may be required in linking NMDA receptor activation to neuronal apoptosis, and thereby suggests that AMPA receptor endocytosis plays an essential role in reducing synaptic strength, and also actively mediates other important intracellular pathways, including apoptotic cell death.
To identify sequence determinants for constitutive and insulin-stimulated AMPA receptor
endocytosis, we made six GluR2 mutants containing various deletions of the GluR2 CT (
The ability of these mutants to undergo both constructive and regulated endocytosis was assayed as described previously.14 Surface receptors in live cells were pre-labelled with an anti-HA antibody (or an antibody against the extracellular N-terminal domain of GluR2 in the case of GluR2Δ854) at 4° C. (which blocks endocytosis). Surface labelled cells were then incubated at 37° C. for 30 min to allow endocytosis to resume both in the absence and presence of insulin (0.5 μM) to determine changes in constitutive (basal) and regulated (insulin-stimulated) AMPA receptor endocytosis, respectively (
As shown in
The R2-CT sequence contains three tyrosine residues. To determine whether these tyrosine residues are substrates of certain tyrosine kinases, we performed in vitro kinase assays using active recombinant Src and glutathione S-transferase (GST)-fusion proteins of the carboxyl tails of GluR1 (GST-GluR1CT) and GluR2 (GST)-GluR2CT) (
To determine whether these GluR2 CT tyrosine residues are phosphorylated in situ by endogenous tyrosine kinase activity in response to insulin stimulation, we generated a GluR2 subunit mutant in which tyrosine residues Y869, Y873 and Y876 were mutated into alanines (HA-GluR23Y-3A). When transiently expressed in HEK293 cells, the mutant was expressed at the same level as its wild type GluR2 counterpart (
Mutation of tyrosine residues of GluR2-CT prevents insulin-induced reduction of cell-surface AMPA receptors. HEK cells expressing wild type GluR2 or GluR2 Y-A mutants were treated with insulin (0.5 μM) for 10 min and with an additional 20 min incubation period in ECS. Level of cell-surface receptors were assayed using colorimetric assay. Mutation of any one of the tyrosine residues was sufficient to prevent the insulin-induced reduction in cell-surface AMPA receptor expression (
The functional significance of GluR2 CT tyrosine phosphorylation with respect to insulin-stimulated endocytosis was tested by assaying internalization on of HA-GluR2 and HA-GluR23Y-3A in HEK293 cells (
We next examined whether insulin stimulation could change the level of tyrosinephosphorylation of AMPA receptors in intact hippocampus, as it does in HEK293 cells expressing GluR2 subunits (
The effect of postsynaptic application of GST-GluR23Y (GST-YKEGYNVYG), and its mutant counterpart, GST-GluR23A (GST-AKEGANVAG), as a control, during whole-ell recording of CA1 neurons in hippocampal slices was investigated, to determine the correlation, if any, of the insulin-stimulated tyrosine phosphorylation of AMPA receptors to persistent depression of receptor-mediated excitatory postsynaptic currents (EPSCs). As shown in
The level of GluR2 tyrosine phosphorylation was assayed following low-frequency stimulation (LYS) of hippocampal slices (1 Hz for 15 min, which reliably induces LID under our experimental conditions), to determine whether tyrosine phosphorylation of GluR2 CT may be required for LFS-induced long term depression (LTD). Slices were homogenized in denaturing buffer 10 mm after the stimulation and GluR subunits were immunoprecipitated and probed for phosphotyrosine. As shown in
Ischemia-like insult was mimicked by oxygen and glucose deprivation (OGD) for one hour in cultured cortical neurons (DIV 12-14). OGD is a well-characterized cell structure model of ischemia. GluR2CT peptide (1 mM) was delivered into neurons by mixing it with the carrier peptide PEP-1 and incubating neurons with the mixture for one hour before OGD challenge.
Behavioral sensitization is defined as an increase in the psychomotor response to treatment with many classes of addictive drugs (i.e. amphetamine, cocaine, nicotine, heroin) and can be parsed into induction and expression phases. Behavioral sensitization is a well accepted model of neural and behavioural adaptations that are hypothesized to form the bases of addiction, specifically dug-induced changes in the mesocorticolimbic dopamine system that underlie the motivation to engage in drug-seeking behavior60,61.
To induces behaviour sensitization to addictive drugs that lead to substance abuse, four separate groups of adult rats were given repetitive injections of d-amphetamine (2 mg/kg, intraperitoneally (IP)) or saline, every other day for a total of 10 injections. On days 1, 5 and 10 of the injection regimen, the rats were placed in 2-level locomotor boxes for 30 min before the amphetamine injection to habituate to the boxes, and for an additional 2 hours following the injection, and stereotypy scores (drug-induced behaviours) were assessed at 1 minute intervals every 10 minutes for the duration of the 2 hour session. After the 10th injection of d-amphetamine, the rats were given 21 days off, and chronically indwelling catheters were implanted into the jugular vein under anaesthesia.
In order to deliver GluR2-CT peptide into neurons in the brain following intravenous (IV) injection, the wild GluR2-CT peptide containing 3Y residues or the corresponding peptide sequence in which the 3 tyrosines were replaced with alanines was fused to the cell-membrane transduction domain of the human immunodeficiency virus-type 1 (HIV-1) Tat protein (YGRKKRRQRRR), which is capable of crossing the blood brain barrier (BBB)85, to obtain Tat-GluR2-3Y (YGRKKRRQRRR-YKEGYNVYGIE) or Tat-GluR2-3A (YGRKKRRQRRR-AKEGANVAGIE) peptides.
On day 21, the rats were pretreated with 1.5 nM/grTat-GluR2-3Y, or Tat-GluR2-3A or saline by either IV injection, or intracranial microinjection into the nucleus accumbens (Nac), and returned to their home cages for 60 min. The rats were then placed in the locomotor boxes (observation chambers) for 30 min and then treated with a challenge dose of d-amphetamine (2 mg/kg, IP). Stereotypy scores were then assessed as described (
We investigate whether a peptide that can block AMPAR endocytosis can function as a neuroprotective agent by preventing glutamate induced neuronal apoptosis. First, in order to ensue that the peptide was able to permeate neurons, primary Wistar cortical neuron cultures were exposed to a dansyl-labeled Tat-GluR-3Y peptide and the cells were then visualized by fluorescence microscopy. DIV 13 neurons were treated with either saline (control) or 1 μM dansyl-labeled GluR23Y peptide for 10, 20, 30, or 60 min. The peptide was able to permeate the cells in a time dependent manner. The neurons took up the dansylated Tat-GluR2-3Y in a time dependent manner with significant fluorescence visible by 10 min with a maximum at approximately 30 min.
Once it was known that the peptide could enter cortical neurons, the ability of Tat-GluR2-3Y to block NMDA-induced AMPAR endocytosis was examined. Primary Wistar cortical neurons pretreated with or without Tat-GluR2-3Y were ejected to NMDA insult and the surface expression of AMPARs was quantified using a cellar ELISA assay. Baseline levels of AMPAR surface expression were approximately 70%, with a corresponding intracellular pool of 30%. NMDA-glycine treatment resulted in a significant decrease in AMPAR surface expression with reference to the control from 69% to 55% (p<0.05, Tukey-Kramer Test), that was completely blocked by pretreatment with Tat-GluR2-3Y (73% surface expression, p<0.05 compared to NMDA group, Tukey-Kramer Test) (
Since Tat-GluR2-3Y was able to block NMDA induced AMPAR endocytosis, the ability of the peptide to protect cultured neurons against oxygen and glucose deprivation (OGD)-induced apoptosis was investigated. DIV 12-13 neurons were pretreated with either saline or Tat-GluR2-3Y for 60 min, followed by 60 min of OGD at 37° C. or incubation at 37° C. in media (control). The amount of apoptosis was qualified using an ELISA assay targeted to free nucleosomes which are characteristic of apoptosis. OGD induced significant apoptosis compared with the control that was substantially blocked by pretreatment with Tat-GluR2-3Y (p<0.05) (
For study of the peptide in vivo we first investigated whether the peptide could pass the blood brain barrier (BBB) and infiltrate neuronal tissue. Either dansyl-labeled Tat-GluR-3Y or saline was administrated to male C57-Black/6 mice and 40 μm coronal brain slices were cut with a cryostat and visualized with fluorescence microscopy. More specifically, two adult male C57-Black/6 mice were given an intraperitoneal injection of either 30 mmoles/g of dansyl-labeled Tat-GluR2-3Y or saline. The mice were sacrificed 2 h following injection and 40 micron coronal sections were cut with a cryostat and visualized with fluorescence microscopy. The results indicated that the dansyl-labeled peptide brain sections exhibited a greater fluorescence intensity than the control, confirming entry of the peptide into the brain, and that dansyl-labeled Tat-GluR2-3Y crosses the blood brain barrier and enters neural tissue.
In order to qualitatively describe the location and size of the infarct produced by the intraluminal suture method of MCA occlusion, 4 male Sprague Dawley rats were subjected to the procedure, sacrificed at day 3 post MCA occlusion, and 1 mm brain slices were stained with 2,3,5-triphenyltetrazolium chloride (TTC). More specifically, adult male Sprague-Dawley rats of ˜300 g body weight were subjected to 60 min of MCA occlusion using an intraluminal 3-0 nylon monofilament. The rats were then sacrificed at 3 days post MCA occlusion and the brains were sliced into 1 mm sections and stained with TTC. The transient ischemia method resulted in significant infarct volume with the maximum coronal cross-sectional involvement at ˜−1.5 mm with respect to the bregma. The infarct volume was reproducible with significant cortical involvement in each rat. From the TTC staining, 0.8 mm with respect to the bregma was chosen or apoptosis staining using terminal deoxyribonucleotide transferase [TdT]-mediated dUTP nick end labeling (TUNEL).
In order to determine the maximum dose that could be administered without adverse reaction, two male Sprague Dawley rats were injected with serial doses of Tat-GluR2-3Y ranging from 0.5 nmoles/g to 30 nmoles/g and basic vital parameters were monitored. It was found that the drug was tolerated up to a dose of ˜12 nmoles/g after which there was a large decline in blood pressure concurrent with an increase in breathing rate (
As the proposed mechanism of neuroprotection for Tat-GluR2-3Y is the prevention of apoptosis, it was first necessary to demonstrate and quantify apoptosis in the model of transient focal ischemia. Two male Sprague-Dawley rats were subjected to either 90 min of MCA occlusion, or on surgery without occlusion. Using TUNEL staining of brain slices obtained 24 h after surgery, MCA occlusion was shown to cause significant apoptosis (
Given the evidence that Tat GluR-3Y pretreatment was able to block AMPAR receptor endocytosis and reduce OGD-induced apoptosis in vitro, the ability of peptide pretreatment to prevent neurological deficit and penumbral apoptosis in transient focal ischemia was investigated. 15 male Sprague-Dawley rats were pretreated with either 3 nmoles/g of Tat-GluR2-3Y or Tat-GluR2-3A or saline for 60 min, after which, the right MCA was occluded for 60 min. The rats were given a neurological examination 45 min into the MCA occlusion and at sacrifice (˜24 h). No significant difference was noted in the neurological scores at 24 h (
Stress is known to prime the induction of LTD123 and to results in stress-related disorders such as memory impairment124, anxiety and depression125. Thus, the GluR2-3Y peptide, by blocking regulated endocytosis and hence LTD, may have therapeutic effects for these stress-related disorders. As an example, we have therefore tested the effect of the peptide against stress-induced anxiety using a well-established animal anxiety model126. Rats (n=4) were injected with either 10 nM/g GluR2-3Y or equal volume of vehicle ACSF (IP). They were given 30 minutes in a dark room post injection. After that they were placed on an elevated platform for 30 minutes as a stressor and then placed on the elevated plus maze for 5 minutes74. The GluR2-3Y injected rats spent more time on the open arms than the ACSF rats. The ACSF rats spent most of their time in the corners of the closed arms or rearing to look over the walls. Thus, GluR23Y peptide blocked stress induced anxiety (
Relapse induced by presentation of a priming dose of drug or conditional stimuli paired previously with amphetamine or heroin infusions is a critical phase of addictive behaviour. A rat model of intravenous drug self administration is used, coupled with extinction of drug-seeking behaviour prior to tests of relapse73. The Tat-GluR 23Y pride, the mutated control peptide GluR23A, and vehicle is injected intravenously prior to tests of relapse. After demonstration of success in preventing relapse, a battery of behavioural control experiments are conducted to ensure that treatment with the Tat-GluR2 peptides does not produce generalized deficits in learning and memory. This protocol uses tests of recognition and spatial and temporal-order memory used routinely, along with a standard neurological test battery to ensure normal sensory and motor function (
The following publications are incorporated herein by reference.
7. R Malinow and R. C. Malenka, Annu. Rev. Neurosci. 25, 103-126 (2002).
82. Horn J, Limburg M: Calcium antagonists for ischemic stroke: a systematic review. Stroke 32:570-576,2001.
Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Accession numbers, as used herein, refer to Accession numbers from multiple databases, including GenBank, the European Molecular Biology Laboratory (EMBL), the DNA Database of Japan (DDBJ), or the Genome Sequence Data Base (GSDB), for nucleotide sequences, and including the Protein Information Resource (PIR), SWISSPROT, Protein Research Foundation (PRF), and Protein Data Bank (PDB) (sequences from solved structures), as well as from translations from annotated coding regions from nucleotide sequences in GenBank, EMBL, DDBJ, or RefSeq, for polypeptide sequences. Numeric ranges are inclusive of the numbers defining the range. In the specification, the word “comprising” is used as an open-ended term, substantially equivalent to the phrase “including, but not limited to”, and the word “comprises”has a corresponding meaning. Citation of references herein shall not be construed as an admission that such references are prior art to the present invention. All publications are incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.