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Fundamentals of apoptosis

Apoptosis is evolutionary conserved, programmed pattern of cell death with an essential role in various physiological processes, such as normal cell turnover and embryonic development, hormone-regulated cell demise, aging, immune system functioning and development and removal of defective and harmful cells. There are two general pathways for activation of apoptosis: the intrinsic and extrinsic pathways. While the intrinsic apoptotic pathway can be triggered by a cytotoxic accumulation of intracellular Ca 2+ , followed permeabilization of mitochondrial membrane and release of pro-apoptotic proteins into the cytosol from mitochondria, the extrinsic mechanisms of apoptosis include the participation of death receptors of tumor necrosis factor-a (TNF-a), receptor superfamily such as TNFR-1, Fas, and TNF-related apoptosis-inducing ligand receptors (TRAIL-R) located on the plasma membrane. There is also the perforin-granzyme pathway that involves T-cell mediated cytotoxicity. All three pathways converge on the same execution pathway, resulting in DNA fragmentation, degradation of cytoskeletal and nuclear proteins, cross-linking of proteins, formation of apoptotic bodies, expression of ligands for phagocytic cell receptors and finally uptake by phagocytic cells. In this review we summarize data from recent studies focusing on apoptotic proteins that have been identified and molecular mechanisms of apoptosis. Understanding apoptotic mechanism might provide useful information and a new approach to prevention and development of new therapies for variety of diseases.