Caspase 9

Caspase 9 plays a central role in the mitochondrial, or intrinsic, apoptotic pathway, where cytochrome c release promotes apoptosome formation with Apaf-1 and procaspase-9[1]. Mechanistically, activated caspase 9 cleaves and activates effector caspases 3 and 7, linking mitochondrial dysfunction to proteolytic cell death execution[1][2]. In disease models, diminished Apaf-1 activity reduced cytochrome c-dependent caspase activation in ovarian cancer cell lines, while ischemic hippocampal neurons showed caspase 9 activation before neuronal death[2][3]. Compared with caspase 8 in the extrinsic pathway, caspase 9 primarily mediates the intrinsic route to caspase 3 activation in ischemic neurons and TNFR-mediated hepatocyte apoptosis[3][4]. For experimental applications, Apaf-1 ligands inhibited apoptosome-mediated procaspase-9 activation and reduced apoptotic phenotypes in mitochondrial apoptosis models[5].