Enhancement of cyanide-induced mitochondrial dysfunction and cortical cell necrosis by uncoupling protein-2

Uncoupling protein 2 (UCP-2) is expressed in the inner mitochondrial membrane and modulates mitochondrial function by partially uncoupling oxidative phosphorylation, and it has been reported to modulate cell death. Cyanide is a potent neurotoxin that inhibits complex IV to alter mitochondrial function to induce neuronal death. In primary rat cortical cells KCN produced an apoptotic death at 200-400 microM. Higher concentrations of potassium cyanide (KCN) (500-600 microM) switched the mode of death from apoptosis to necrosis. In necrotic cells, ATP levels were severely depleted as compared to cortical cells undergoing apoptosis. To determine if UCP-2 expression could alter KCN-induced cell death, cells were transiently transfected with full-length human UCP-2 cDNA (UCP-2+). Overexpression switched the mode of death produced by KCN (400 microM) from apoptosis to necrosis. The change in cell death was mediated by impaired mitochondrial function as reflected by a marked decrease of ATP levels and reduction in mitochondrial membrane potential. RNA interference or transfection with a dominant interfering mutant blocked the necrotic response observed in UCP-2+ cells. Additionally, treatment of UCP-2+ cells with cyclosporin A blocked necrosis, indicating the involvement of mitochondrial permeability pore transition in the necrotic death. These results show that increased expression of UCP-2 alters the response to a potent mitochondrial toxin by switching the mode of cell death from apoptosis to necrosis. It is concluded that UCP-2 levels influence cellular responses to cyanide-induced mitochondrial dysfunction.