Enhanced vulnerability of PARK6 patient skin fibroblasts to apoptosis induced by proteasomal stress

Abstract

Proteasomal dysfunction and apoptosis are major hallmarks in the pathophysiology of Parkinson's disease (PD). PARK6 which is caused by mutations in the mitochondrial protein kinase PINK1 is a rare autosomal-recessively inherited disorder mimicking the clinical picture of PD. To investigate the cytoprotective physiological function of PINK1, we used primary fibroblasts from three patients homozygous for G309D-PINK1 as well as SHEP neuroblastoma cells stably overexpressing GFP-tagged wild type (wt) PINK1. Here we demonstrate that overexpression of wt PINK1 inhibits activation of Bax and release of cytochrome c, thereby diminishing caspase 9 processing and effector caspase activity after induction of proteasomal stress with the proteasome inhibitor (PI) MG132 in SHEP cells. Conversely, effector caspase activation induced by PIs, but not by the unrelated apoptotic stimulus staurosporine was potently enhanced in primary fibroblasts from homozygous PARK6 patients in comparison to those of heterozygous carriers or unaffected siblings. SHEP cells overexpressing wt PINK1 showed an elevated expression of the cytoprotective gene parkin, whereas PARK6 fibroblasts displayed significantly decreased expression of parkin in comparison to wild type control cells. Interestingly, overexpressed GFP-PINK1 was exclusively localized in the mitochondria of SHEP cells, but was redistributed to the cytoplasm under conditions of proteasomal stress. Our data indicate that PINK1 plays an important and specific physiological role in protecting cells from proteasomal stress, and suggest that PINK1 might exert its cytoprotective effects upstream of mitochondria engagement.