Depletion of glutathione up-regulates mitochondrial complex I expression in glial cells

Glutathione deficiency is commonly associated with mitochondrial complex I dysfunction and loss of viability in neurones, but not in glia. In order to address the possible mechanism responsible for this cellular difference, t he regulation of mitochondrial complex I expression by glutathione depletio n was investigated in glial cells. Incubation of rat-cultured astrocytes an d C6 glioma cells with the specific gamma -glutamyl-cysteine synthetase inh ibitor L-buthionine-(S, R)-sulfoximine ((L)-BSO; 0.1-1 mM) decreased the to tal specific content of glutathione in a dose- and time-dependent fashion. Northern blot analyses revealed that glutathione deficiency caused by L-BSO (0.1 mM) was associated with a twofold enhancement in complex I regulatory subunit ND6 (mitochondrially encoded) mRNA expression after 24-72 h. This effect was accompanied by a twofold increase in complex-I activity at 72 h in (L)-BSO-treated cells, as compared with control cells, but complex II-II I, complex IV and citrate synthase activities were unaltered. It is suggest ed that the oxidative stress caused by glutathione depletion in glial cells would up-regulate complex-I activity by enhancing the expression of the mi tochondrially encoded regulatory subunit. These results could offer further insight into the different degree of cellular susceptibility observed in g lial vs. neuronal cells against oxidative stress.