Loss of Parkin contributes to mitochondrial turnover and dopaminergic neuronal loss in aged mice

Parkinson's disease (PD), the second most common neurodegenerative disorder, is characterized by the loss of nigrostriatal dopamine neurons. PARK2 mutations cause early-onset Parkinson's disease (EO-PD). PARK2 encodes an E3 ubiquitin ligase, Parkin. Extensive in vitro studies and cell line characterization have shown that Parkin is required for mitophagy, but the physiological pathology and context of the pathway remain unknown. In general, monogenic Parkin knockout mice do not accurately reflect human PD symptoms and exhibit no signs of dopaminergic (DA) neurodegeneration. To assess the critical role of Parkin-mediated mitophagy in DA neurons, we characterized Parkin knockout mice over a long period of time. At the age of 110 weeks, Parkin knockout mice exhibited locomotor impairments, including hindlimb defects and neuronal loss. In their DA neurons, fragmented mitochondria with abnormal internal structures accumulated. The age-related motor dysfunction and damaged mitochondria pathology in Parkin-deficient mice suggest that impairment of mitochondria! clearance may underlie the pathology of PD.