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The Journal of Neuroscience, September 2, 2009, 29(35):10928-10938; doi:10.1523/JNEUROSCI.2491-09.2009

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Neurobiology of Disease
Interaction of Postsynaptic Density Protein-95 with NMDA Receptors Influences Excitotoxicity in the Yeast Artificial Chromosome Mouse Model of Huntington's Disease

Jing Fan,¹ Catherine M. Cowan,² Lily Y. J. Zhang,² Michael R. Hayden,⁴ and Lynn A. Raymond^2,3

¹Graduate Program in Neuroscience, ²Department of Psychiatry, and ³Brain Research Centre, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada, and ⁴Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada

Correspondence should be addressed to Dr. Lynn A. Raymond, Department of Psychiatry, University of British Columbia, Room 4834, 2255 Wesbrook Mall, Vancouver, British Columbia V6T 1Z3, Canada. E-mail: Email: lynnr{at}interchange.ubc.ca

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.

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Received May 28, 2009; accepted July 21, 2009.

Correspondence should be addressed to Dr. Lynn A. Raymond, Department of Psychiatry, University of British Columbia, Room 4834, 2255 Wesbrook Mall, Vancouver, British Columbia V6T 1Z3, Canada. E-mail: Email: lynnr{at}interchange.ubc.ca

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