Dysfonctions mitochondriales et neurodégénérescence dopaminergique sélective dans la maladie de Parkinson : Quelles relations ? – MITOPARK

Parkinson¿s disease (PD) is a common, severe neurodegenerative disorder due to the preferential degeneration of the dopaminergic neurons of the substantia nigra, which may be intrinsically vulnerable to oxidative stress. There is growing evidence that mitochondrial dysfunction plays a key role in PD pathogenesis. The neurotoxin MPP+ has long been known to promote PD by blocking mitochondrial complex I of the respiratory chain. Several of the genes recently found to be mutated in familial forms of PD, including parkin and PINK1, have putative functions in mitochondrial homeostasis. However, these genes are ubiquitously expressed and the mitochondrial dysfunction that they may trigger cannot account alone for the selective dopaminergic degeneration in PD. We propose that the dopaminergic phenotype renders some brain neurons particularly sensitive to oxidative stress, which combined to the mitochondrial alterations induced by gene mutations, accounts for neurodegeneration in PD. Our preliminary results suggest that Parkin regulates the mitochondrial abundance of its newly identified substrate SCHAD (Team 1, unpublished observations), and possibly of PINK1. In a first set of experiments, we will define the mechanisms underlying this interaction by evaluating whether Parkin promotes the ubiquitin-dependent import of SCHAD and PINK1 at the outer mitochondrial membrane. Since there is evidence that Parkin and PINK1 may regulate mitochondrial dynamics, we will determine how Parkin, PINK1 and SCHAD, alone or in combination, affect mitochondrial morphology, fusion and fission, for comparison with other key components of the mitochondrial fusion/fission machinery with already characterized effects. To this end, conventional immunofluorescent techniques, immuno-electron microscopy and imaging in live cells will be applied to analyze mitochondrial shape and morphology and define the epistatic relationships between Parkin, PINK1 and SCHAD, in a set of complementary models: transfected cell lines, primary cells from Parkin- and PINK1-deficient mice or from PD patients with mutations in these genes, and genetically modified zebrafish. Tissue from Parkin- and PINK1-deficient zebrafish, mice, and patients will also be used search for more general, potentially cell-sepcific alterations of mitochondrial functions: reduced OXPHOS activities; altered supramolecular organization of OXPHOS complexes; altered mitochondrial DNA abundance; oxidative modification of mitochondrial DNA, proteins and lipids. Finally, zebrafish will serve as a unique model to explore the possibility that alterations in the levels of Parkin and/or its substrates render dopaminergic neurons particularly vulnerable to dopamine-mediated oxidative stress.
This highly integrated approach is expected to several important advances in our understanding of mitochondrial dysfucntions linked to familial and sporadic forms of PD. It will provide a new view of mitochondrial dynamics and function, and how it can be altered in a major neurodegenerative disease. Most importantly, data gathered from this project will link these general mitochondrial dysfunction with specific alteration in dopamine induced oxidative stress. This will represent a major breakthrough for the physiopathology of the disease, leading to new concepts on the pathological mechanisms and an effective rationale for the development of new tharapeutic approaches of PD.