The effects of Parkinson's disease mimetics on the proteasomal and neurofilament systems in SH-SY5Y cells

Mitochondrial impairment, glutathione depletion and oxidative stress have been implicated in the pathogenesis of Parkinson's disease, linked recently to proteasomal dysfunction. This study analyses how these factors influence the various activities of the proteasome in SH-SY5Y human neuroblastoma cells treated with the PD mimetics MPP+ (a complex I inhibitor) or dopamine. Treatment with these toxins led to dose and time dependent reductions in ATP and glutathione levels and also chymotrypsin-like and postacidic-like activities; however, trypsin-like activity was unaffected. Antioxidants blocked the effects of dopamine but not MPP+, suggesting that oxidative stress was more important in the dopamine-mediated effects. With MPP+, ATP depletion was a pre-requisite for loss of proteasomal function. This study also shows that addition of MPP+ or dopamine to purified samples of the human 20S proteasome also reduced proteasomal activities; with dopamine being most damaging. As was the case with toxin-treated cells chymotrypsin-like activity was the most sensitive and trypsin-like activity, the least sensitive. The direct effect of both compounds on proteasomal activity was, at least, partly due to oxidative damage to the proteasome, since the antioxidant vitamin C could partially alleviate the proteasomal impairment

Assessment of the direct and indirect effects of MPP+ and dopamine on the human proteasome: implications for Parkinson's disease aetiology

Mitochondrial impairment, glutathione depletion and oxidative stress have been implicated in the pathogenesis of Parkinson’s disease (PD), linked recently to proteasomal dysfunction. Our study analysed how these factors influence the various activities of the proteasome in human SH-SY5Y neuroblastoma cells treated with the PD mimetics MPP+ (a complex 1 inhibitor) or dopamine. Treatment with these toxins led to dose- and time-dependent reductions in ATP and glutathione and also chymotrypsin-like and post-acidic like activities; trypsin-like activity was unaffected. Antioxidants blocked the effects of dopamine, but not MPP+, suggesting that oxidative stress was more important in the dopamine-mediated effects. With MPP+, ATP depletion was a prerequisite for loss of proteasomal activity. Thus in a dopaminergic neuron with complex 1 dysfunction both oxidative stress and ATP depletion will contribute independently to loss of proteasomal function. We show for the first time that addition of MPP+ or dopamine to purified samples of the human 20S proteasome also reduced proteasomal activities; with dopamine being most damaging. As with toxin-treated cells, chymotrypsin-like activity was most sensitive and trypsin-like activity the least sensitive. The observed differential sensitivity of the various proteasomal activities to PD mimetics is novel and its significance needs further study in human cells