Dopamine D2 Receptor Stimulation Potentiates PolyQ- Huntingtin-Induced Mouse Striatal Neuron Dysfunctions via Rho/ROCK-II Activation Carole Deyts1,2,3, Beatriz Galan-Rodriguez1,2, Elodie Martin1,2, Nicolas Bouveyron1,2, Emmanuel Roze1,2,4, Delphine Charvin1,2, Jocelyne Caboche1,2., Sandrine Be´ tuing1,2,5.* 1 CNRS UMR 7102, Universite´ Pierre et Marie Curie-Paris 6, Paris, France, 2 INSERM UMRS 952, CNRS UMR 7224, Universite´ Pierre et Marie Curie-Paris 6, Paris, France, 3 Biological Sciences Division, University of Chicago, Chicago, Illinois, United States of America, 4 Service de Neurologie, H oˆpital Salpeˆtrie`re, Assitance Publique-Hoˆ pitaux de Paris, Paris, France, 5 Universite´ Evry Val d’Essonne, Evry, France Abstract Background: Huntington’s disease (HD) is a polyglutamine-expanded related neurodegenerative disease. Despite the ubiquitous expression of expanded, polyQ-Huntingtin (ExpHtt) in the brain, striatal neurons present a higher susceptibility to the mutation. A commonly admitted hypothesis is that Dopaminergic inputs participate to this vulnerability. We previously showed that D2 receptor stimulation increased aggregate formation and neuronal death induced by ExpHtt in primary striatal neurons in culture, and chronic D2 antagonist treatment protects striatal dysfunctions induced by ExpHtt in a lentiviral-induced model system in vivo. The present work was designed to elucidate the signalling pathways involved, downstream D2 receptor (D2R) stimulation, in striatal vulnerability to ExpHtt. Methodology/Principal Findings: Using primary striatal neurons in culture, transfected with a tagged-GFP version of human exon 1 ExpHtt, and siRNAs against D2R or D1R, we confirm that DA potentiates neuronal dysfunctions via D2R but not D1R stimulation. We demonstrate that D2 agonist treatment induces neuritic retraction and growth cone collapse in Htt- and ExpHtt expressing neurons. We then tested a possible involvement of the Rho/ROCK signalling pathway, which plays a key role in the dynamic of the cytoskeleton, in these processes. The pharmacological inhibitors of ROCK (Y27632 and Hydroxyfasudil), as well as siRNAs against ROCK-II, reversed D2-related effects on neuritic retraction and growth cone collapse. We show a coupling between D2 receptor stimulation and Rho activation, as well as hyperphosphorylation of Cofilin, a downstream effector of ROCK-II pathway. Importantly, D2 agonist-mediated potentiation of aggregate formation and neuronal death induced by ExpHtt, was totally reversed by Y27632 and Hydroxyfasudil and ROCK-II siRNAs. Conclusions/Significance: Our data provide the first demonstration that D2R-induced vulnerability in HD is critically linked to the activation of the Rho/ROCK signalling pathway. The inclusion of Rho/ROCK inhibitors could be an interesting therapeutic option aimed at forestalling the onset of the disease. Citation: Deyts C, Galan-Rodriguez B, Martin E, Bouveyron N, Roze E, et al. (2009) Dopamine D2 Receptor Stimulation Potentiates PolyQ-Huntingtin-Induced Mouse Striatal Neuron Dysfunctions via Rho/ROCK-II Activation. PLoS ONE 4(12): e8287. doi:10.1371/journal.pone.0008287 Editor: Howard E. Gendelman, University of Nebraska, United States of America Received May 12, 2009; Accepted November 18, 2009; Published December 15, 2009 Copyright: 2009 Deyts et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by Centre National de la Recherche Scientifique (CNRS), Universite´ Pierre et Marie Curie-Paris 6 and High Q Foundation for Jocelyne Caboche and Sandrine Be´tuing. Carole Deyts and Beatriz Galan-Rodriguez were grant recipients from the High Q foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: sandrine.betuing@snv.jussieu.fr . These authors contributed equally to this work. Introduction Huntington’s disease (HD), a neurodegenerative disorder char- acterized by motor, cognitive, and psychiatric disorders (1) is caused by abnormal expansion of a CAG tract in exon 1 of the IT15 gene. This mutation leads to an abnormal polyglutamine expansion in the N-terminal part of the huntingtin (Htt) protein. Cleavage of polyQ expanded huntingtin (ExpHtt) by caspases, leads to the release of N- terminal fragments containing the polyglutamine repeats, which can aggregate in neurites, cytoplasm, and nuclei. Despite ubiquitous expression of Htt throughout the brain and other tissues, medium spiny GABAergic neurons in the striatum predominantly degenerate in the brain of HD patients [1]. Among various mechanisms [2] dopamine (DA) may be important in this preferential vulnerability. HD neuropathology progresses in the striatum according to the same dorsoventral gradient as local DA concentration [1,3,4]. Variations of DA concentration can modulate striatal death in various models [5,6,7]. Dopamine transporter knock-out (DAT-/-) mice display both spontaneous striatal death and behavioral alterations that resemble HD [8]. When mated to knock-in HD mice these mice showed exacerbation of HD pathophysiology and acceleration of aggregate formation [9]. We recently extended these observations and demonstrated, in vitro, that DA accelerates two neuropathological hallmarks induced by PLoS ONE | www.plosone.org 1 December 2009 | Volume 4 | Issue 12 | e8287