Characterization and time course of MPP+-induced apoptosis in human SH-SY5Y neuroblastoma cells

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Abstract
A genetic defect in complex I of the mitochondrial electron transport chain (ETC) is implicated in the etiology of Parkinson's disease (PD), and has been studied in cybrid mitochondrial transgene cells based on the SH‐SY5Y neuroblastoma. We sought to characterize further the mechanisms and time course of cell death in cultures of human SH‐SY5Y neuroblastoma cells exposed to the ETC complex I inhibitor methylpyridinium ion (MPP+). We verify previous reports that apoptosis occurs after MPP+ exposure in SH‐SY5Y cells. Nuclear pyknosis, the end stage of apoptosis, is evident after 18‐hr exposure to 5 mM MPP+ and reversible until 10 hr, providing a temporal window within which to look for molecular and physiological correlates of MPP+‐induced apoptosis. We then looked for mitochondrial correlates of MPP+‐induced apoptosis in SH‐SY5Y cells. Using flow cytometry, we found that MPP+‐induced increased reactive oxygen species (ROS) and lactate production consistent with inhibition of the ETC. ρ° cells, lacking a functional ETC, showed no ROS production, compensatory lactate production or apoptosis after exposure to MPP+. Finally, we show a collapse in ROS production and mitochondrial potential that is temporally correlated with irreversibility of MPP+‐induced apoptosis. J. Neurosci. Res. 55:620–628, 1999.