Bax and caspases regulate increased production of mitochondria-derived reactive species in neuronal apoptosis: LACK of A role for depletion of cytochrome c from the mitochondrial electron transport chain.

A Bax-dependent increase of reactive oxygen species (ROS) and other reactive species (RS) occurs after withdrawing NGF from mouse sympathetic neurons in cell culture. Possible mechanisms underlying the increased ROS/RS are leakage of electrons from the mitochondrial electron transport chain secondary to caspase cleavage of respiratory complexes or leakage secondary to depletion of cytochrome from the chain. We previously demonstrated that deletion of Bax or caspase 3 from these cells reduces ROS/RS production to near baseline levels indicating a central role for both Bax and caspase 3 in generating the ROS/RS. Here we depleted cytochrome to a similar level in neurons from wild type and hemizygous or knockout mice by NGF withdrawal or treatment with HO. Death was prevented with a caspase inhibitor that caused a partial reduction of ROS/RS levels but did not completely prevent the ROS/RS increase. ROS/RS was highest in wild-type cells, lowest in knockout cells, and at an intermediate level in the hemizygous cells. These and our previous findings indicate that Bax and caspase 3 are necessary for the increased ROS/RS after withdrawing NGF from these cells and that little or none of the increased ROS/RS are secondary to a depletion of cytochrome from the electron transport chain.