Objective/Rationale:
Levodopa-induced dyskinesias are caused by an increased and aberrant response of dopamine receptors to dopamine in the striatum. Among other intracellular pathways, the MAP kinase signaling cascade has been shown to be dramatically enhanced suggesting that inhibitors of this pathway could dampen the pathological activity of the dopamine-sensitive neurons in the striatum. RasGRF1 is, luckily, an upstream striatum-specific member of this ubiquitous signaling pathway, suggesting that diminishing its expression should decrease the activity of the cascade in the striatum, and hopefully decrease the severity of dyskinesias.
Project Description:
We aim at downregulating RasGRF1 levels in parkinsonian non-human primates either never exposed to L-dopa (de novo-like) or previously exposed and rendered dyskinetic (late stage-like). We will first use a gene therapy approach and deliver the genes with lentivirus to the striatum for functionally invalidating RasGRF1. This step should validate the concept. As gene therapy is unlikely to be an easily accessible option for patients, we will then build a TAT-RasGRF1 dominant negative fusion protein. This technology allows designing a competitor of the native RasGRF1 that we will infuse into the brain of dyskinetic primates. It should mimic the effects of the gene therapy, constituting therefore a further step towards clinical use of the concept.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
L-dopa-induced dyskinesia severely limits the usability of L-dopa, the most powerful antiparkinsonian drug. The treatment of dyskinesia would greatly improve the quality of life of parkinsonian patients. If we find that inhibiting RasGRF1 using a dominant negative approach prevents priming in naïve MPTP animals and/or reduces dyskinesia in primed ones, it would open new venues for therapy of L-dopa-induced motor complications.
Anticipated Outcome:
The project is original because it would (i) validate an original hypothesis about dyskinesia manifestation and (ii) provide a method for controlling their severity. Finally, we believe we can then set-up an in vitro screening protocol for identifying chemical inhibitors of RasGrf1 designed by classical combinatorial chemistry that could then be refined for high-throughput screening, paving the way for industrial search of existing / new chemical entities able to inhibit RasGRF1 activity.