title: Interaction of postsynaptic density protein-95 with NMDA receptors influences excitotoxicity in the yeast artificial chromosome mouse model of Huntington's disease.
abstract: Evidence suggests that NMDA-type glutamate receptors contribute to degeneration of striatal medium-sized spiny neurons (MSNs) in Huntington's disease (HD). Previously, we demonstrated that NMDA receptor (NMDAR)-mediated current and/or toxicity is increased in MSNs from the yeast artificial chromosome (YAC) transgenic mouse model expressing polyglutamine (polyQ)-expanded (mutant) full-length human huntingtin (htt). Others have shown that membrane-associated guanylate kinases (MAGUKs), such as PSD-95 and SAP102, modulate NMDAR surface expression and excitotoxicity in hippocampal and cortical neurons and that htt interacts with PSD-95. Here, we tested the hypothesis that an altered association between MAGUKs and NMDARs in mutant huntingtin-expressing cells contributes to increased susceptibility to excitotoxicity. We show that htt coimmunoprecipitated with SAP102 in HEK293T cells and striatal tissue from wild-type and YAC transgenic mice; however, the association of SAP102 with htt or the NMDAR NR2B subunit was unaffected by htt polyQ length, whereas association of PSD-95 with NR2B in striatal tissue was enhanced by increased htt polyQ length. Treatment of cultured MSNs with Tat-NR2B9c peptide blocked binding of NR2B with SAP102 and PSD-95 and reduced NMDAR surface expression by 20% in both YAC transgenic and wild-type MSNs, and also restored susceptibility to NMDAR excitoxicity in YAC HD MSNs to levels observed in wild-type MSNs; a similar effect on excitotoxicity was observed after knockdown of PSD-95 by small interfering RNA. Unlike previous findings in cortical and hippocampal neurons, rescue of NMDA toxicity by Tat-NR2B9c occurred independently of any effect on neuronal nitric oxide synthase activity. Our results elucidate further the mechanisms underlying enhanced excitotoxicity in HD.
authors.affiliation: Graduate Program in Neuroscience, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Jing
authors.initials: J
authors.lastname: Fan
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Cowan
authors.forename: Lily Y J
authors.initials: LY
authors.lastname: Zhang
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hayden
authors.forename: Lynn A
authors.initials: LA
authors.lastname: Raymond
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D018244:Chromosomes, Artificial, Yeast / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D000076122:Disks Large Homolog 4 Protein; D018683:Excitatory Amino Acid Agents / Q000378:metabolism*; D020022:Genetic Predisposition to Disease; D051528:Guanylate Kinases; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000378:metabolism*
chemical_list: D000076122:Disks Large Homolog 4 Protein; C501447:Dlg4 protein, mouse; D018683:Excitatory Amino Acid Agents; C086055:HTT protein, human; D000071058:Huntingtin Protein; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D016194:Receptors, N-Methyl-D-Aspartate; D051528:Guanylate Kinases