Mitochondrial release of apoptosis-inducing factor and cytochrome c duringsmooth muscle cell apoptosis

Photodynamic therapy (PDT) is under investigation for the treatment of inti mal hyperplastia in conditions such as atherosclerosis and restenosis. Alth ough smooth muscle cells (SMCs) may be a key target for treatment, the effe cts of PDT on these cells are poorly characterized, In the present study, a poptosis was induced in primary human aortic SMCs by the combination of the photosensitizer verteporfin and visible light. After PDT, an increase in m itochondrial cytochrome c (cyt c) and apoptosis-inducing factor (AIF) level s were detected In the cytosol immediately and their levels increased stead ily up to 2 hours. Cytosolic levels of the pro-apoptotic Bcl-2 family mem b er Bax decreased reciprocally throughout this period, but this change did n ot occur before cyt c release. Confocal microscopy revealed a diffuse stain ing pattern of cyt c within apoptotic cells as compared to a distinct mitoc hondrial staining in normal cells. AIF translocated from mitochondria to th e nucleus during the progression of apoptosis. After cyt c release, caspase -9 and caspase-3 processing was visible by 1 hour and caspase-6, -7, and -8 processing was apparent by 2 hours after PDT. In summary, these results de monstrate for the first time the cellular redistribution of mitochondrial A IF during SMC apoptosis, as well as the early release of cyt c and the subs equent activation of multiple caspases during PDT-induced SMC apoptosis.