PROJECT SUMMARY Parkinson’s disease (PD) is the second most common neurodegenerative disease, and ~60,000 veterans currently receive care for PD from the VA Health Care System annually. PD is characterized by progressive motor decline and cognitive impairment. Despite significant medical burden, our understanding of the pathogenesis of PD and therapies remain limited. Mutations in the gene glucosidase, beta acid 1 (GBA1) are the strongest genetic risk factor for developing idiopathic PD, increasing risk by ~5-fold in GBA1 mutation carriers compared to controls. However, most individuals with GBA1 mutations do not develop PD, suggesting that additional genetic modifiers influence PD susceptibility. Identification of these modifiers would provide insight into the pathogenesis of PD, and reveal novel targets for disease-modifying therapies. The proposed work focuses on identifying genetic modifiers of GBA1-mediated neurodegeneration using a Drosophila GBA1 deficient model, using these modifiers to understand the pathogenic mechanisms causing PD, and determining whether modifiers identified in Drosophila translate to clinically relevant modifiers of human disease. Candidate modifiers will be identified through a genetic screen using a GBA1 deficient Drosophila model that I have developed (Aim 1). Two candidate modifiers, brainwashing (bwa) and glucosylceramide transferase 1 (GlcT-1) have already been identified in preliminary work. The function of these modifiers in ceramide metabolism suggests that decreased levels of ceramide may be responsible for GBA1-mediated neurodegeneration. I hypothesize that decreased ceramide levels impair fusion of autophagosomes to lysosomes, causing neurodegeneration. I will test this hypothesis by identifying alterations of lipid abundances in GBA1 mutant and control flies with overexpression or loss of function of bwa and GlcT-1, and examining resulting effects on autophagy flux and autophagosome morphology (Aim 2). I will also test whether increasing levels of ceramide directly through dietary supplementation can ameliorate GBA1 mutant phenotypes, including impaired autophagy. These studies will elucidate the mechanistic link between lipid metabolism and pathologic protein aggregation in GBA1-mediated pathogenesis, which has remained elusive. In Aim 3, I will test whether bwa and GlcT-1 are also modifiers of human disease, by analyzing human homologs of these modifiers for association with rate of progression of symptoms in a longitudinal cohort of GBA1 carriers and noncarriers with PD (Aim 3). The proposed work uses several innovative approaches, including a novel invertebrate model of GBA1 deficiency manifesting phenotypes suggestive of PD, testing the role of lipid metabolism on autophagy through genetic perturbations and dietary supplementation, and attempting to translate findings from a Drosophila model to PD patients. This work will significantly advance our understanding of PD pathogenesis, and could reve...