The Parkinson Disease-Associated Mutant DNAJC13(N855S) Leads to Its Accelerated Degradation and Negatively Affects Macroautophagy and Retromer Complex-Mediated Dynamics

While Parkinson's disease has a multifactorial etiology, 5%-10% of cases present with identifiable disease-causing gene mutations. Further investigation into these mutations is a way to identify underlying pathologic mechanism. One of the rare Parkinson-associated genes is DNAJC13, coding for an endosome-associated protein. Several lines of evidence suggest that disturbed endosomal pathways are instrumental in the development of Parkinson pathology. Recently, we have shown that DNAJC13/RME-8 is a positive modulator of autophagy, a lysosome-associated degradative process. Here, we further characterize the role of the disease-linked DNAJC13(N855S) mutant and perform biochemical, cell biological, co-localization, and expression analysis by employing a newly established cell line with reduced DNAJC13 expression and by transiently expressing the DNAJC13(N855S) mutant variant. We observed that the DNAJC13(N855S) variant is less stable than the wild-type protein and might thus impact proteostasis. Furthermore, the protein has functional deficits as it cannot compensate for the impaired autophagic activity in cells with chronically reduced DNAJC13 levels. In addition, the DNAJC13(N855S) showed a dominant negative effect on the distribution of the cation-independent mannose-6-phosphate receptor without affecting overall cathepsin D levels or activity. Lastly, we observed a decreased expression of several genes related to autophagy induction and biogenesis in stable DNAJC13 knockdown cells. Our data point toward a loss-of-function mechanism of the DNAJC13(N855S) variant and that chronically reduced DNAJC13 protein levels result in a reduced expression of genes largely involved in endosomal traffic and autophagosome biogenesis. The DNAJC13(N855S) mutant might thus cause disease in part by its instability and in part by a dominant negative effect on the autophagic pathway. These data support a pivotal role of endosomal pathway impairment in Parkinson's disease pathogenesis.