Mutations in the glucosylceramidase beta (GBA) gene cause the lysosomal lipid storage disorder Gaucher?s disease and are the most frequent genetic association with Parkinson?s disease and Lewy body dementia. GBA encodes glucocerebrosidase, a lysosomal enzyme that catalyzes the breakdown of the sphingolipid glucosylceramide to ceramide and glucose. To explore the mechanism by which mutations in GBA predispose to these diseases, we created a Drosophila model of glucocerebrosidase deficiency by inactivating the Drosophila GBA ortholog, Gba1b. Gba1b mutants recapitulate many of the features of these diseases, including shortened lifespan, locomotor impairment, accumulation of glucosylceramide, protein aggregation in brain and other tissues, and neurodegeneration. In recently published work, we reported the results of a proteomic study of Drosophila Gba1b mutants that revealed dramatic alterations in the abundance and turnover of extracellular vesicle (EV) proteins. Our experiments also demonstrated that these proteomic findings reflected actual changes in the composition of EVs, and that genetic perturbations targeting factors involved in the production of EVs suppressed a Gba1b mutant phenotype. In more recent unpublished work, we used RNA-Seq to compare transcript abundance in Gba1b mutants and controls. This study revealed a profound induction of the innate immune response pathway in Gba1b mutants. This induction was specific to Gba1b mutants and was further corroborated in our proteomic data, and RNAi-mediated knockdown of an innate immune pathway component partially suppressed the brain protein aggregation phenotype of Gba1b mutants. From these and other findings, we hypothesize that the production of glucosylceramide-enriched EVs by Gba1b mutants triggers an innate immune response because these EVs resemble the glucosylceramide-enriched EVs released by pathogens during infection. We further hypothesize that this innate immune response accounts for the phenotypes of Gba1b mutants. We propose two aims to address these hypotheses; the first will investigate the mechanism of immune activation, and the second will investigate the importance of immune activation to Gba1b mutant pathogenesis. Thus, the primary goal of our research proposal is to provide a foundation for further mechanistic work by asking the two most fundamental questions raised by our preliminary findings: how does innate immune activation occur in Gba1b mutants, and is it important to their phenotypes? Given the increasing evidence for neuroinflammation in neurodegenerative disorders, including those caused by GBA mutations, we anticipate that our work will have broad medical significance.
Mutations in the glucosylceramidase beta (GBA) gene, which encodes glucocerebrosidase, cause Gaucher?s disease and are the most frequent genetic association with Parkinson?s disease and Lewy body dementia. Using a Drosophila model of glucocerebrosidase deficiency, we have obtained evidence that innate immune activation is a component of the pathogenic mechanism by which mutations in GBA predispose to these diseases. The goal of our current proposal is to further test this model, and to explore the mechanism of immune activation.
