Release of cytochrome c, Bax migration, Bid cleavage, and activation of caspases 2, 3, 6, 7, 8, and 9 during endothelial cell apoptosis

Although the executioner phase of apoptosis has been well defined in many c ell types, the subcellular events leading to apoptosis in endothelial cells remain undefined. In the current study, apoptosis was induced in primary h uman umbilical venous endothelial cells by the photosensitizer verteporfin and light. Release of mitochondrial cytochrome c into the cytosol was detec table immediately and accumulated over 2 hours after treatment while cytoso lic levels of the proapoptotic Bcl-2 family member, Bax, decreased reciproc ally over the same time period. Cleavage of another proapoptotic Bcl-2 fami ly member, Bid, was observed by 2 hours after treatment. Although Bid cleav age has been shown to occur as an upstream event responsible for inducing c ytochrome c release, we demonstrate that Bid cleavage can also occur after cytochrome c release. Activation of caspases 2, 3, 6, 7, 8, and 9 occurred following the release of cytochrome c, and cleavage of downstream substrate s was observed. In summary, endothelial cell death involves the cellular re distribution of Bar and cytochrome c, followed by the activation of multipl e caspases which manifest the apoptotic phenotype.