Backgound: Mutations in PARK9 (ATP13A2, a lysosomal type 5 P-type ATPase) have been reported to cause autosomal recessive early-onset parkinsonism, a condition known as Kufor-Rakeb Syndrome (KRS). We have reported a family with two siblings who had KRS and found two novel mutations, c.3176T>G (p.L1059R) and c.3253del (p.L1085WfsX1088) in the PARK9 gene.
Aim: We aimed to study the pathogenic mechanisms of PARK9 mutations by creating in vitro cell models.
Methods: We investigated the cellular effects of both mutations in the PARK9 by over-expression of wild-type and mutant PARK9 with tags in vitro. We performed confocal microscopy to determine the localization of wild-type and mutant protein. We used proteasomal and lysosomal inhibitors to determine the degradation pathway of the mutant protein. Real-time PCR was performed to detect expression of endoplasmic reticulum (ER) stress-related genes in the KRS patient cell line.
Results: Wild-type PARK9 localised to the lysosomal membrane whereas both mutant proteins were found to be retained in the ER. Mutant PARK9 was degraded by the proteasomal but not the lysosomal pathway. Real-time PCR revealed up-regulation of unfolded protein response related gene expression indicating ER stress in the KRS patient cell line.
Conclusions: These findings indicate that these PARK9 mutations are indeed pathogenic and further support the notion that alterations in the proteasomal pathways and ER stress contribute to the aetiology of Parkinson’s disease.