Defects in the
proton-translocating NADH-quinone oxidoreductase (complex I) of mammalian mitochondria are linked to
neurodegenerative disorders. The mechanism leading to cell death elicited by complex I deficiency remains elusive. We have shown that expression of a
rotenone-insensitive yeast
NADH-quinone oxidoreductase (Ndi1) can rescue mammalian cells from complex I dysfunction. By using the Ndi1
enzyme, we have investigated the key events in the process of cell death using a rat dopaminergic cell line, PC12. We found that complex I inhibition provokes the following events: 1) activation of specific
kinase pathways; 2) release of mitochondrial proapoptotic factors,
apoptosis inducing factor, and
endonuclease G.
AS601245, a
kinase inhibitor, exhibited significant protection against these apoptotic events. The traditional
caspase pathway does not seems to be involved because
caspase 3 activation was not observed. Our data suggest that overproduction of
reactive oxygen species (ROS) caused by complex I inhibition is responsible for triggering the
kinase activation, for the release of the proapoptotic factors, and then for cell death. Nearly perfect prevention of apoptotic cell death by Ndi1 agrees with our earlier observation that the presence of Ndi1 diminishes
rotenone-induced ROS generation from complex I. In fact, this study demonstrated that Ndi1 keeps the redox potential high even in the presence of
rotenone. Under these conditions, ROS formation by complex I is known to be minimal. Possible use of our cellular model is discussed with regard to development of therapeutic strategies for
neurodegenerative diseases caused by complex I defects.