Objective/Rationale:
The most widely prescribed therapy for Parkinson’s disease is levodopa (L-DOPA), which allows patients to regain motor control. However, many patients develop adverse reactions to L-DOPA, including abnormal involuntary movements termed dyskinesias. We seek to understand the basis of these abnormal movements by studying genes that we discovered in animal models of dyskinesias. We will test whether manipulation of these genes can alleviate L-DOPA-induced abnormal movements in animals, thereby laying the groundwork for novel therapeutic targets.
Project Description:
Two of the genes that we discovered to be abnormally regulated in animal models of dyskinesia, called CalDAG-GEF1 and CalDAG-GEF2, are well situated to play a central role in driving L-DOPA-induced movements. These genes are expressed in the striatum, which is the main dopamine-modulated, motor-control center of the brain that suffers loss of dopamine in Parkinson’s disease. These genes can activate ERK proteins, which mediate abnormal motor responses to L-DOPA. We will test whether manipulation of the CalDAG-GEFs can alleviate L-DOPA-induced dyskinesias by using two strategies: First, we will test whether mice that we have engineered to lack CalDAG-GEF1 or 2 are resistant to developing L-DOPA-induced motor complications. Second, we will use viruses to either repress or activate the CalDAG-GEFs in parkinsonian rodents, to test for mitigation of motoric side-effects at various stages of L-DOPA therapy.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
The CalDAG-GEF genes have never been tested for therapeutic relevance in motor disorders and were only recently discovered to be altered in parkinsonian animal models of L-DOPA-induced dyskinesias. Thus, our proposed study is the very first step to testing CalDAG-GEFs as targets for the treatment of Parkinson’s disease. Our initial data suggest that enhancing CalDAG-GEF1 function and repressing CalDAG-GEF2 function may alleviate dyskinesias that result from L-DOPA therapy.
Anticipated Outcome:
We think, based on our work so far, that activation of CalDAG-GEF1 and repression of CalDAG-GEF2 will alleviate L-DOPA-induced dyskinesias in parkinsonian models. If so, agents altering CalDAG-GEF function could be used for pre-clinical testing. In addition, we will test whether CalDAG-GEF deletion alters neurotoxin susceptibility in the substantia nigra, a region that degenerates in Parkinson’s disease. From this, we will determine whether CalDAG-GEF gene-types might be a contributing risk-factor for Parkinson’s disease.
Final Outcome
We found that the protein, CalDAG-GEF2, is present at abnormally high levels in two pre-clinical models of L-DOPA-induced dyskinesia, a severe and disabling complication of the standard therapy for Parkinson’s disease. We previously published that CalDAG-GEF2 and a related protein, CalDAG-GEF1, are both dysregulated in another type of parkinsonian pre-clinical model of dyskinesia. In the first types of models, however, it appeared that the changes are more specific to CalDAG-GEF2. The CalDAG-GEF proteins are of special interest because they regulate the activity of extracellular signal regulated kinase (ERK), an enzyme that is essential for the development of L-DOPA-induced dyskinesia in a pre-clinical model of the disorder.
To test whether disrupting CalDAG-GEF2 might be therapeutically relevant to treating L-DOPA-induced dyskinesia, we studied a pre-clinical model lacking the gene for CalDAG-GEF2. We induced dopamine depletions (mimicking the parkinsonian state) by two different methods: injections of 6-OHDA, a neurotoxin that kills dopamine-producing neurons, and pitx3 mutations, which disrupt the development of dopamine-producing neurons. We found that model lacking the gene for CalDAG-GEF2 could still develop dyskinesia following 6-OHDA dopamine depletion and L-DOPA treatment. However, there was a significant degree of inter-model variability, which confounded definitive conclusions regarding the viability of CalDAG-GEF2 manipulation as a means of dyskinesia therapy. We are in the process of analyzing data from experiments that measured how deletions of the CalDAG-GEF2 gene in the pitx3 pre-clinical model modify their dyskinetic response to L-DOPA.