Rab27b promotes lysosomal function and alpha-synuclein clearance in neurons
Alpha-synuclein (syn) is the key pathogenic protein implicated in synucleinopathies including Parkinsons Disease (PD) and Dementia with Lewy Bodies (DLB). In these diseases, syn is thought to spread between cells where it accumulates and induces pathology; however, mechanisms that drive its propagation or aggregation are poorly understood. We have previously reported that the small GTPase Rab27b is elevated in human PD and DLB and that it can mediate the autophagic clearance and toxicity of syn in a paracrine syn cell culture neuronal model. Here, we expanded our previous work and further characterized a role for Rab27b in neuronal lysosomal processing and syn clearance. We found that Rab27b KD in this syn inducible neuronal model resulted in lysosomal dysfunction and increased syn levels in lysosomes. Similar lysosomal proteolytic defects and enzymatic dysfunction were observed in both primary neuronal cultures and brain lysates from Rab27b knockout (KO) mice. Syn aggregation was exacerbated in Rab27b KO neurons upon treatment with syn preformed fibrils. We found no changes in lysosomal counts or lysosomal pH in either model, but we did identify defects in acidic vesicle trafficking in Rab27b KO primary neurons which may drive lysosomal dysfunction and promote syn aggregation. Rab27b OE enhanced lysosomal activity and reduced insoluble syn accumulation. Finally we found elevated Rab27b levels in human postmortem incidental Lewy Body Disease (iLBD) subjects relative to healthy controls. These data suggest a role for Rab27b in neuronal lysosomal activity and identify it as a potential therapeutic target in synucleinopathies.