Dopamine D2 receptor stimulation potentiates PolyQ-Huntingtin-induced mouse striatal neuron dysfunctions via Rho/ROCK-II activation

PLoS One. 2009 Dec 15;4(12):e8287. doi: 10.1371/journal.pone.0008287.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Death / drug effects
  • Dopamine / pharmacology
  • Enzyme Activation / drug effects
  • Growth Cones / drug effects
  • Growth Cones / pathology
  • Humans
  • Mice
  • Neostriatum / drug effects
  • Neostriatum / enzymology
  • Neostriatum / physiopathology*
  • Neurites / drug effects
  • Neurites / metabolism
  • Neurons / drug effects
  • Neurons / enzymology*
  • Peptides / toxicity*
  • Protein Structure, Quaternary
  • Quinpirole / pharmacology
  • RNA, Small Interfering
  • Receptors, Dopamine D1 / metabolism
  • Receptors, Dopamine D2 / metabolism*
  • Serotonin Plasma Membrane Transport Proteins / chemistry
  • Serotonin Plasma Membrane Transport Proteins / toxicity*
  • Trinucleotide Repeat Expansion / genetics
  • rho GTP-Binding Proteins / metabolism*
  • rho-Associated Kinases / metabolism*

Substances

  • Peptides
  • RNA, Small Interfering
  • Receptors, Dopamine D1
  • Receptors, Dopamine D2
  • SLC6A4 protein, human
  • Serotonin Plasma Membrane Transport Proteins
  • Quinpirole
  • polyglutamine
  • Rock2 protein, mouse
  • rho-Associated Kinases
  • rho GTP-Binding Proteins
  • Dopamine