title: Phosphorylation of huntingtin at Ser421 in YAC128 neurons is associated with protection of YAC128 neurons from NMDA-mediated excitotoxicity and is modulated by PP1 and PP2A.
abstract: YAC transgenic mice expressing poly(Q)-expanded full-length huntingtin (mhtt) recapitulate many behavioral and neuropathological features of Huntington disease (HD). We have previously observed a reduction in phosphorylation of mhtt at S421 in the presence of the mutation for HD. In addition, phosphorylation of normal S421-htt is reduced after excitotoxic stimulation of NMDA receptors (NMDARs). To test whether NMDAR stimulation contributes to reduced pS421-htt levels in HD, we determined phosphorylation of htt at Ser421 after NMDA-induced excitotoxicity in neurons from YAC128 mice. Here, we report that the total level of pS421-htt is reduced in YAC128 primary neurons after excitotoxic NMDAR stimulation. Similarly, the total level of pS421-htt is reduced in YAC128 transgenic mice after quinolinic acid injection into the striatum. In contrast, loss of phosphorylation of pS421-htt is prevented in YAC mice that never develop clinical or neuropathological features of HD [the caspase 6-resistant YAC128 transgene (C6R)]. To gain insight into the mechanisms underlying these findings, we determined that the Ser/Thr protein phosphatases PP1 and PP2A dephosphorylate pS421-htt in situ and after excitotoxic stimulation of NMDARs in neurons. Furthermore, increasing the phosphorylation of htt at S421 by blocking PP1 and PP2A activity protects YAC128 striatal neurons from NMDA-induced cell death. These results, together with the observed modulation of pS421-htt levels by dopamine, the reduced expression of PP1 inhibitor Darpp-32 in the striatum of YAC128 mice, and the reduced phosphorylation of PP1 substrate CreB, point to altered regulation of phosphatase activity in HD and highlight enhancing phosphorylation of htt at S421 as a therapeutic target.
authors.affiliation: Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada.
authors.forename: Martina
authors.initials: M
authors.lastname: Metzler
authors.forename: Lu
authors.initials: L
authors.lastname: Gan
authors.forename: Gelareh
authors.initials: G
authors.lastname: Mazarei
authors.forename: Rona K
authors.initials: RK
authors.lastname: Graham
authors.forename: Lili
authors.initials: L
authors.lastname: Liu
authors.forename: Nagat
authors.initials: N
authors.lastname: Bissada
authors.forename: Ge
authors.initials: G
authors.lastname: Lu
authors.forename: Blair R
authors.initials: BR
authors.lastname: Leavitt
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hayden
mesh_terms: D000818:Animals; D016923:Cell Death / Q000502:physiology; D002478:Cells, Cultured; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D016291:Dizocilpine Maleate / Q000494:pharmacology; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000096:biosynthesis / Q000235:genetics; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D000071058:Huntingtin Protein; D008297:Male; D051379:Mice; D009154:Mutation; D016202:N-Methylaspartate / Q000037:antagonists & inhibitors* / Q000633:toxicity*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000502:physiology*; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000502:physiology*; D017378:Quinolinic Acid / Q000494:pharmacology; D017447:Receptors, Dopamine D1 / Q000187:drug effects; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D013238:Stereotaxic Techniques
chemical_list: D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; C497928:PPP1R1B protein, human; D017447:Receptors, Dopamine D1; D016194:Receptors, N-Methyl-D-Aspartate; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; C517189:PPP2CA protein, human; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D017378:Quinolinic Acid