Ceramide Induces Release of Pro-Apoptotic Proteins from Mitochondria by Either a Ca 2+ -Dependent or a Ca 2+ -Independent Mechanism

Several observations have been reported in the last years indicating that ceramide may activate the mitochondrial route of apoptosis. We show here that on addition of either C 2 - or C 16 -ceramide to mitochondria isolated from rat heart and suspended in a saline medium, release of cytochrome c and apoptosis-inducing factor (AIF) from the intermembrane space takes place. The release process is Ca 2+ -independent and is not inhibited by Cyclosporin A (CsA). For the protein release process to occur, the presence of an oxidizable substrate is required. When mitochondria are suspended in sucrose instead of potassium medium, only short chain C 2 -ceramide causes cytochrome c release through a Ca 2+ -dependent and CsA sensitive mitochondrial permeability transition (MPT) mechanism. The latter effect appears to be related to the membrane potential dissipating ability exhibited by short chain C 2 -ceramide.