title: Ectopic expression of the striatal-enriched GTPase Rhes elicits cerebellar degeneration and an ataxia phenotype in Huntington's disease.
abstract: Huntington's disease (HD) is caused by an expansion of glutamine repeats in the huntingtin protein (mHtt) that invokes early and prominent damage of the striatum, a region that controls motor behaviors. Despite its ubiquitous expression, why certain brain regions, such as the cerebellum, are relatively spared from neuronal loss by mHtt remains unclear. Previously, we implicated the striatal-enriched GTPase, Rhes (Ras homolog enriched in the striatum), which binds and SUMOylates mHtt and increases its solubility and cellular cytotoxicity, as the cause for striatal toxicity in HD. Here, we report that Rhes deletion in HD mice (N171-82Q), which express the N-terminal fragment of human Htt with 82 glutamines (Rhes(-/-)/N171-82Q), display markedly reduced HD-related behavioral deficits, and absence of lateral ventricle dilatation (secondary to striatal atrophy), compared to control HD mice (N171-82Q). To further validate the role of GTPase Rhes in HD, we tested whether ectopic Rhes expression would elicit a pathology in a brain region normally less affected in HD. Remarkably, ectopic expression of Rhes in the cerebellum of N171-82Q mice, during the asymptomatic period led to an exacerbation of motor deficits, including loss of balance and motor incoordination with ataxia-like features, not apparent in control-injected N171-82Q mice or Rhes injected wild-type mice. Pathological and biochemical analysis of Rhes-injected N171-82Q mice revealed a cerebellar lesion with marked loss of Purkinje neuron layer parvalbumin-immunoreactivity, induction of caspase 3 activation, and enhanced soluble forms of mHtt. Similarly reintroducing Rhes into the striatum of Rhes deleted Rhes(-/-)Hdh(150Q/150Q) knock-in mice, elicited a progressive HD-associated rotarod deficit. Overall, these studies establish that Rhes plays a pivotal role in vivo for the selective toxicity of mHtt in HD.
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida 33458, USA.
authors.forename: Supriya
authors.initials: S
authors.lastname: Swarnkar
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida 33458, USA.
authors.forename: Youjun
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida 33458, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Pryor
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida 33458, USA.
authors.forename: Neelam
authors.initials: N
authors.lastname: Shahani
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida 33458, USA.
authors.forename: Damon T
authors.initials: DT
authors.lastname: Page
authors.affiliation: Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida 33458, USA. Electronic address: ssubrama@scripps.edu.
authors.forename: Srinivasa
authors.initials: S
authors.lastname: Subramaniam
mesh_terms: D000818:Animals; D001259:Ataxia / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002531:Cerebellum / Q000378:metabolism* / Q000473:pathology; D003342:Corpus Striatum / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D006816:Huntington Disease / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000378:metabolism; D013132:Spinocerebellar Degenerations / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D019204:GTP-Binding Proteins; C488189:Rasd2 protein, mouse
keywords: Ataxia; Cerebellar pathology; Ectopic expression; Huntington's disease; Knock-in HD mice; Neurodegeneration; Neuronal death; Rhes; Soluble Huntingtin; Stereotaxy; Transgenic HD mice