title: Enhanced Store-Operated Calcium Entry Leads to Striatal Synaptic Loss in a Huntington's Disease Mouse Model.
abstract: In Huntington's disease (HD), mutant Huntingtin (mHtt) protein causes striatal neuron dysfunction, synaptic loss, and eventual neurodegeneration. To understand the mechanisms responsible for synaptic loss in HD, we developed a corticostriatal coculture model that features age-dependent dendritic spine loss in striatal medium spiny neurons (MSNs) from YAC128 transgenic HD mice. Age-dependent spine loss was also observed in vivo in YAC128 MSNs. To understand the causes of spine loss in YAC128 MSNs, we performed a series of mechanistic studies. We previously discovered that mHtt protein binds to type 1 inositol (1,4,5)-trisphosphate receptor (InsP3R1) and increases its sensitivity to activation by InsP3. We now report that the resulting increase in steady-state InsP3R1 activity reduces endoplasmic reticulum (ER) Ca(2+) levels. Depletion of ER Ca(2+) leads to overactivation of the neuronal store-operated Ca(2+) entry (nSOC) pathway in YAC128 MSN spines. The synaptic nSOC pathway is controlled by the ER resident protein STIM2. We discovered that STIM2 expression is elevated in aged YAC128 striatal cultures and in YAC128 mouse striatum. Knock-down of InsP3R1 expression by antisense oligonucleotides or knock-down or knock-out of STIM2 resulted in normalization of nSOC and rescue of spine loss in YAC128 MSNs. The selective nSOC inhibitor EVP4593 was identified in our previous studies. We now demonstrate that EVP4593 reduces synaptic nSOC and rescues spine loss in YAC128 MSNs. Intraventricular delivery of EVP4593 in YAC128 mice rescued age-dependent striatal spine loss in vivo. Our results suggest EVP4593 and other inhibitors of the STIM2-dependent nSOC pathway as promising leads for HD therapeutic development.
  
  
  CONCLUSIONS
  In Huntington's disease (HD) mutant Huntingtin (mHtt) causes early corticostriatal synaptic dysfunction and eventual neurodegeneration of medium spine neurons (MSNs) through poorly understood mechanisms. We report here that corticostriatal cocultures prepared from YAC128 HD mice feature age-dependent MSN spine loss, mirroring YAC128 MSN spine loss in vivo. This finding establishes a system for mechanistic studies of synaptic instability in HD. We use it to demonstrate that sensitization of type 1 inositol (1,4,5)-trisphosphate receptors by mHtt, which depletes endoplasmic reticulum calcium, contributes to synaptotoxic enhancement of STIM2-dependent store-operated calcium (SOC) entry. Treatment with EVP4593, a neuroprotective inhibitor of neuronal SOC channels, rescues YAC128 MSN spine loss both in vitro and in vivo. These results suggest that enhanced neuronal SOC causes synaptic loss in HD-afflicted MSNs.
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
authors.forename: Jun
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
authors.forename: Daniel A
authors.identifier: http://orcid.org/0000-0002-2197-0730
authors.initials: DA
authors.lastname: Ryskamp
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
authors.forename: Xia
authors.initials: X
authors.lastname: Liang
authors.affiliation: Laboratory of Molecular Neurodegeneration, St. Petersburg State Polytechnical University, St. Petersburg 195251, Russia, and.
authors.forename: Polina
authors.initials: P
authors.lastname: Egorova
authors.affiliation: Laboratory of Molecular Neurodegeneration, St. Petersburg State Polytechnical University, St. Petersburg 195251, Russia, and.
authors.forename: Olga
authors.identifier: http://orcid.org/0000-0002-2384-0681
authors.initials: O
authors.lastname: Zakharova
authors.affiliation: Isis Pharmaceuticals, Inc., Carlsbad, California 92010.
authors.forename: Gene
authors.initials: G
authors.lastname: Hung
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, Laboratory of Molecular Neurodegeneration, St. Petersburg State Polytechnical University, St. Petersburg 195251, Russia, and Ilya.Bezprozvanny@UTSouthwestern.edu.
authors.forename: Ilya
authors.initials: I
authors.lastname: Bezprozvanny
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002478:Cells, Cultured; D003342:Corpus Striatum / Q000378:metabolism* / Q000473:pathology; D006816:Huntington Disease / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D013569:Synapses / Q000378:metabolism* / Q000473:pathology*
chemical_list: D002118:Calcium
keywords: Huntingtin; calcium; imaging; synapse; transgenic