PARK19 truncation mutant Dnajc6 causes lysosomal deficiency-induced upregulation of pathologic α-synuclein and neurodegeneration of substantia nigra dopaminergic cells in PARK19 knockin mice

Homozygous (Q789X) DNAJC6 mutation causes PARK19. Q787 of Dnajc6 corresponds to Q789 of DNAJC6. Dnajc6^Q787X/Q787X mouse was utilized to elucidate pathomechanisms underlying (Q789X) DNAJC6-induced PARK19. Dnajc6^Q787X/Q787X mice displayed PARK19 motor deficits and degeneration of substantia nigra (SN) dopaminergic neurons. (Q787X) Dnajc6 decreased clathrin heavy chain and lysosomal number, leading to downregulation of lysosomal cathepsin D and upregulation of α-synuclein or α-synuclein oligomers in SN dopaminergic neurons. Lysosomal biogenesis activator rapamycin precluded (Q787X) Dnajc6-induced downregulation of cathepsin D, upregulation of α-synuclein, and PARK19 phenotypes. (Q787X) Dnajc6-induced elevation of ER and mitochondrial α-synuclein excited ER stress and mitochondrial pro-apoptotic cascades. (Q787X) Dnajc6-evoked α-synuclein oligomer overexpression activated SN microglia and NLRP3 inflammasome and upregulated IL-1β, IL-18, and TNF-α, which stimulated MKK4-JNK -c-Jun/ATF-2 and RIPK1-RIPK3-MLKL death cascades. Our results suggest that PARK19 (Q789X) DNAJC6 mutation causes lysosomal deficiency and impairs cathepsin D-mediated degradation of α-synuclein, resulting in upregulated α-synuclein-induced neurodegeneration of SN dopaminergic cells.