Funded Studies
Objective/Rationale:
Levodopa, the most effective therapy for Parkinson’s disease, induces severe involuntary movements termed dyskinesias. The development of these motor dysfunctions has been associated to alterations of dopamine D1 receptor signalling. It has been demonstrated that the phosphatase SHP-2 plays a crucial role in signalling transduction of various receptors including the D1. In this project we will investigate whether down-regulation of SHP-2 expression alleviates levodopa-induced dyskinesias in an experimental model of Parkinson’s disease.
Project Description:
The pre-clinical model of Parkinson’s disease obtained by injecting the neurotoxin 6-hydroxy-dopamine into dopaminergic neurons will be used. SHP-2 expression will be inhibited by injecting into the striatum, a key area for movement control, small RNA sequences interfering with SHP-2 biosynthesis. We will evaluate whether SHP-2 down-regulation prevents the development of levodopa-induced dyskinesias. Hemi-parkinsonian rats with low levels of striatal SHP-2 will be chronically treated with levodopa and dyskinesias will be evaluated by behavioural testing. Abnormal involuntary movements will be classified into axial, limb, orolingual or locomotor. Each symptom will be scored on a validated severity scale from 0 to 4. SHP-2 expression and ERK phosphorylation in the striatum will be measured. The efficiency of SHP-2 silencing will be related to behavioural data.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
The development of dyskinesias hampers the efficacy of levodopa, the most used antiparkinsonian drug. Despite the clinical relevance of levodopa-induced dyskinesias, drugs that can efficiently prevent these complications are still lacking. Investigating whether inhibition of SHP2 expression in a rodent model of Parkinson’s disease reduces the severity of levodopa-induced dyskinesias will open the way for the development of drugs to treat these complications and improve the quality of life of parkinsonian patients.
Anticipated Outcome:
Normalizing D1 receptor signalling could be a strategy to treat levodopa-induced dyskinesias. The results of this study will elucidate: 1) whether D1 receptor signalling via SHP-2 phosphatase is correlated to the development of dyskinesias; 2) whether inhibition of SHP-2 expression in the striatum normalizes D1 receptor-dependent signalling and attenuates levodopa-induced dyskinesias; 3) whether SHP-2 or the D1 receptor/SHP-2 interface may be a new target for the development of drugs to alleviate dyskinesias.
Final Outcome
Treatment of cultured neurons from pre-clinical striatum -- a key area for movement control -- with a small RNA sequence interfering with Shp-2 biosynthesis (Shp-2 shRNA) decreased Shp-2 levels and impaired dopamine D1 receptor (D1R) coupling to one of its major signalling effectors, the Extracellular Signal Regulated Kinases (Erk). Similar effects were observed when the Shp-2 shRNA was injected in vivo into pre-clinical striatum.
Since dysfunctions of D1R signalling are involved in levodopa-induced dyskinesia (LID), we evaluated whether Shp-2 down-regulation may prevent the development of these side effects of levodopa. We used the pre-clinical model of PD obtained by injecting the neurotoxin 6-hydoxy-dopamine into dopaminergic neurons innervating the striatum. Chronic administration of levodopa to parkinsonian pre-clinical models induced the development of dyskinesia and the exaggerated and persistent activation of both Shp-2 and Erk. Inhibition of Shp-2 expression in the striatum of parkinsonian pre-clinical models prevented development of dyskinesia and overactivation of Shp-2 and Erk, both induced by levodopa. These results indicate that malfunctioning of the D1R/Shp-2/Erk pathway is causally linked to the development of LID and suggest that Shp-2 or the D1R/Shp-2 interface may be a promising target for the development of new drugs to prevent or treat motor dysfunctions induced by levodopa therapy.