Mitochondrial Dysfunction Precedes Other Sub-Cellular Abnormalities in an In Vitro Model Linked with Cell Death in Parkinson’s Disease

Dysfunction of mitochondria, the ubiquitin proteasome system (UPS), and lysosomes are believed to contribute to the pathogenesis of Parkinson’s disease (PD). If it were possible to rescue functionally compromised, but still viable neurons early in the disease process, this would slow the rate of neurodegeneration. Here, we used a catecholaminergic neuroblastoma cell line (SH-SY5Y) as a model of susceptible neurons in PD. To identify a target early in the cell death process that was common to all neurodegenerative processes linked with PD, cells were exposed to toxins that mimic cell death mechanisms associated with PD. The sub-cellular abnormalities that occur shortly after toxin exposure were determined. 3 h of exposure to either naphthazarin, to inhibit lysosomal function, Z-Ile-Glu(OBut)-Ala-Leu-H (PSI), to inhibit the UPS, or rotenone, to inhibit mitochondrial complex I, caused depolarisation of the mitochondrial membrane potential (2.5-fold, twofold, and 4.6-fold change, respectively compared to vehicle), suggesting impaired mitochondrial function. Following 24 h exposure to the same toxins, UPS and lysosomal function were also impaired, and ubiquitin levels were increased. Thus, following exposure to toxins that mimic three important, but disparate cell death mechanisms associated with PD, catecholaminergic cells initially experience mitochondrial dysfunction, which is then followed by abnormalities in UPS and lysosomal function. Thus, mitochondrial dysfunction is an early event in cell stress. We suggest that, in patients with PD, the surviving cells of the substantia nigra pars compacta are most susceptible to mitochondrial impairment. Thus, targeting the mitochondria may be useful for slowing the progression of neurodegeneration in PD.