Glutathione depletion in PC12 results in selective inhibition of mitochondrial complex I activity - Implications for Parkinson's disease

Oxidative stress appears to play an important role in degeneration of dopam inergic neurons of the substantia nigra (SN) associated with Parkinson's di sease (PD), The SN of early PD patients have dramatically decreased levels of the thiol tripeptide glutathione (GSH), GSH plays multiple roles in the nervous system both as an antioxidant and a redox modulator. We have genera ted dopaminergic PC12 cell lines in which levels of GSH can be inducibly do wn-regulated via doxycycline induction of antisense messages against both t he heavy and light subunits of gamma-glutamyl-cysteine synthetase, the rate -limiting enzyme in glutathione synthesis. Down-regulation of glutamyl-cyst eine synthetase results in reduction in mitochondrial GSH levels, increased oxidative stress, and decreased mitochondrial function. Interestingly, dec reases in mitochondrial activities in GSH-depleted PC12 cells appears to be because of a selective inhibition of complex I activity as a result of thi ol oxidation. These results suggest that the early observed GSH losses in t he SN may be directly responsible for the noted decreases in complex I acti vity and the subsequent mitochondrial dysfunction, which ultimately leads t o dopaminergic cell death associated with PD.