Parkinson's Disease (PD) is the most common neurodegenerative movement disorder, affecting about 1% of the population over 65 years-old. At least a large percentage of PD cases have some genetic component and many genes have been identified that are either causative of familial forms of the disease or enhance disease risk. While PD does not have a monogenic origin in most patients, studies of genes whose mutations are sufficient to cause disease will help reveal pathogenic mechanisms. The vacuolar protein sorting 13C (VPS13C) locus was initially linked to PD through genome-wide association studies (GWAS), and more recently loss-of-function mutations in the gene encoding VPS13C were shown to cause early-onset, autosomal recessive PD. VPS13C, a 422 kDa protein, is one of four mammalian paralogues (VPS13A, B, C and D) whose mutations result in either neurodegenerative or neurodevelopmental diseases. Studies of the single Vps13 protein in yeast have shown that it localizes at membrane contact sites between either the mitochondria and vacuole (the yeast lysosome), or between the vacuole and the ER, and have suggested that it may play a role in lipid transfer. Little is known about the function of VPS13 family members in mammals. Studies of VPS13C have suggested various localizations (lipid droplets (LDs), lysosomes and mitochondria). Additionally, VPS13C knock-down in fibroblastic cells was reported to cause mitochondrial defects and exacerbate PINK1/Parkin- dependent mitophagy. The overall goal of my proposal is to investigate the physiological role of VPS13C and to explore the mechanism by which VPS13C loss-of-function contributes to PD pathogenesis. My preliminary data, based on the expression of tagged VPS13C, suggests its localization at contact sites between the endoplasmic reticulum (ER) and either late-endosomes/lysosomes (LE/LYS) or lipid droplets (LDs), but not at contacts involving mitochondria. They also support a role of VPS13C in lipid transfer at organelle contacts. I plan to corroborate these data by tagging the protein at the endogenous locus in cultured cells (including human iPS-derived neuronal cells) to study its localization/dynamics when expressed at endogenous levels. To test the hypothesis that VPS13C mediates lipid transfer, I will perform lipidomic analysis of cells and tissues harboring loss-of-function mutations in the VPS13C gene, and in subcellular fractions derived from this material (endosomes/lysosomes, ER, and mitochondria) to detect alterations in the lipid composition. Furthermore, I will use microscopy, biochemical, and functional approaches to investigate defects in endosomal sorting and lysosome function, as well as any potential downstream mitochondrial defects that may underlie neurodegeneration. Finally, I will investigate the consequences of VPS13C knockout in mice on structural features of the CNS (the nigrostriatal pathway in particular), as well as on survival and motor function. From these studies I expect new insight into cellular pathways involved with PD pathogenesis and the potential identification of new targets for therapies aimed at preventing, slowing, or reversing the course of the disease.
Loss-of-function mutations in VPS13C cause early-onset, autosomal recessive Parkinson's disease. Preliminary data indicates that VPS13C may function as a lipid transfer protein at membrane contact sites between the endoplasmic reticulum and late endosomes/lysosomes. This project aims to elucidate the molecular mechanisms linking VPS13C loss-of-function to Parkinson's disease pathogenesis, which will have broad implications for our understanding of this devastating illness and may inform future therapeutic strategies.
