DLP1-dependent mitochondrial fragmentation mediates 1-methyl-4-phenylpyridinium toxicity in neurons: Implications for Parkinson's disease

Selective degeneration of nigrostriatal dopaminergic neurons in Parkinson's disease (PD) can be modeled by the administration of the neurotoxin 1-methyl-4-phenylpyridinium (MPP ⁺). Because abnormal mitochondrial dynamics are increasingly implicated in the pathogenesis of PD, in this study, we investigated the effect of MPP ⁺ on mitochondrial dynamics and assessed temporal and causal relationship with other toxic effects induced by MPP ⁺ in neuronal cells. In SH-SY5Y cells, MPP ⁺ causes a rapid increase in mitochondrial fragmentation followed by a second wave of increase in mitochondrial fragmentation, along with increased DLP1 expression and mitochondrial translocation. Genetic inactivation of DLP1 completely blocks MPP ⁺-induced mitochondrial fragmentation. Notably, this approach partially rescues MPP ⁺-induced decline in ATP levels and ATP/ADP ratio and increased [Ca ²⁺] _i and almost completely prevents increased reactive oxygen species production, loss of mitochondrial membrane potential, enhanced autophagy and cell death, suggesting that mitochondria fragmentation is an upstream event that mediates MPP ⁺-induced toxicity. On the other hand, thiol antioxidant N-acetylcysteine or glutamate receptor antagonist D-AP5 also partially alleviates MPP ⁺-induced mitochondrial fragmentation, suggesting a vicious spiral of events contributes to MPP ⁺-induced toxicity. We further validated our findings in primary rat midbrain dopaminergic neurons that 0.5μm MPP ⁺ induced mitochondrial fragmentation only in tyrosine hydroxylase (TH)-positive dopaminergic neurons in a similar pattern to that in SH-SY5Y cells but had no effects on these mitochondrial parameters in TH-negative neurons. Overall, these findings suggest that DLP1-dependent mitochondrial fragmentation plays a crucial role in mediating MPP ⁺-induced mitochondria abnormalities and cellular dysfunction and may represent a novel therapeutic target for PD.