Manganese induces the mitochondrial permeability transition in cultured astrocytes

Manganese is known to cause central nervous system injury leading to parkinsonism and to contribute to the pathogenesis of hepatic encephalopathy. Although mechanisms of manganese neurotoxicity are not completely understood, chronic exposure of various cell types to manganese has shown oxidative stress and mitochondrial energy failure, factors that are often implicated in the induction of the mitochondrial permeability transition (MPT). In this study, we examined whether exposure of cultured neurons and astrocytes to manganese induces the MPT. Cells were treated with manganese acetate (10-100 microM), and the MPT was assessed by changes in the mitochondrial membrane potential and in mitochondrial calcein fluorescence. In astrocytes, manganese caused a dissipation of the mitochondrial membrane potential and decreased the mitochondrial calcein fluorescence in a concentration- and time-dependent manner. These changes were completely blocked by pretreatment with cyclosporin A, consistent with induction of the MPT. On the other hand, similarly treated cultured cortical neurons had a delayed or reduced MPT as compared with astrocytes. The manganese-induced MPT in astrocytes was blocked by pretreatment with antioxidants, suggesting the potential involvement of oxidative stress in this process. Induction of the MPT by manganese and associated mitochondrial dysfunction in astrocytes may represent key mechanisms in manganese neurotoxicity.