Chronic mitochondrial inhibition induces selective motoneuron death in vitro: A new model for amyotrophic lateral sclerosis

Evidence is increasing that mitochondrial dysfunction is involved in amyotr ophic lateral sclerosis, a neurodegenerative disease characterized by selec tive motoneuron death. To study the role of mitochondrial dysfunction in th e pathways leading to motoneuron death, we developed an in vitro model of c hronic motoneuron toxicity, based on malonate-induced inhibition of complex II in the mitochondrial electron transport chain. Treatment with malonate resulted in a dose-dependent decrease in cellular ATP levels. We observed t hat motoneurons were significantly more vulnerable to mitochondrial inhibit ion than control neurons in the dorsal horn. We could reproduce this dose-d ependent phenomenon with the complex IV inhibitor sodium azide. The free ra dical scavenger alpha-phenyl-N-tert-butylnitrone, the AMPA/kainate receptor blocker 6-cyano-7-nitroquinoxaline-2,3-dione, and riluzole, a drug that is currently used for the treatment of amyotrophic lateral sclerosis, were pr otective against malonate-induced motoneuron death. Furthermore, the caspas e inhibitors N-benzy[oxycarbonyl-Val-Ala-Asp-fluoromethyl ketone and z-Asp- Glu-Val-Asp-fluoromethyl ketone were both protective against malonate toxic ity. Our model shows that chronic mitochondrial inhibition leads to selecti ve motoneuron death, which is most likely apoptotic.