Mitochondrial phospholipid hydroperoxide glutathione peroxidase inhibits the release of cytochrome c from mitochondria by suppressing the peroxidation of cardiolipin in hypoglycaemia-induced apoptosis

Cytochrome c (cyt. c) is a proapoptotic factor that binds preferentially to cardiolipin (CL), a mitochondrial lipid, but not to cardiolipin hydroperox ide (CL-OOH). Cyt. c that had bound to CL liposomes was liberated on peroxi dation of the liposomes by a radical. The generation of CL-OOH in mitochond ria occurred before the release of cyt. c in rat basophile leukaemia (RBL)2 H3 cells that had been induced to undergo apoptosis by exposure to hypoglyc aemia with 2-deoxyglucose (2DG). The amount of cyt. c bound to CL prepared from the mitochondria of 2DG-treated cells was lower than that of untreated cells. The release of cyt. c was completely suppressed when the production of CL-OOH in mitochondria was inhibited by the overexpression of mitochond rial phospholipid hydroperoxide glutathione peroxidase (PHGPx). The fluores cence from CL-labelling dye (10-N-nonyl Acridine Orange) decreased on the i nduction of apoptosis by 2DG. However, no decrease in fluorescence was obse rved in PHGPx-overexpressing cells. Cyt. c was released from mitochondria t hat had been isolated from control cells on peroxidation by t-butylhydroper oxide, but no similar liberation of cyt. c from mitochondria isolated from mitochondrial PHGPx-overexpressing cells was observed. These findings sugge st that the generation of CL-OOH in mitochondria might be a primary event t hat triggers the release of cyt. c from mitochondria in the apoptotic proce ss in which mitochondrial PHGPx participates as an anti-apoptotic factor by preventing the formation of CL-OOH.