Necrosis Is an Active and Controlled Form of Programmed Cell Death

In all studies on programmed cell death (PCD) and apoptosis as its most showy form, this process was considered to be a paradigmatic antithesis to necrotic cell death. On one hand, a concept on necrosis as a cellular cataclysm, an uncontrolled and passive phenomenon, had been provoked by an enormous bulk of experimental data on its inducibility by super-physiological exposures. On the other hand, much attention was attracted to a rapidly expanding (from nematodes) field of genetic studies on PCD. However, the findings accumulated which suggested a likeness rather than the opposition of the necrotic and apoptotic forms of elimination of unwanted cells. 1. Very diverse pathophysiological exposures (stimuli, stresses), such as heat, ionizing radiation, pathogens, cytokines cause both forms of cell death in the same cell population. 2. Antiapoptotic mechanisms (e.g., Bcl-2) can protect cells from both necrotic and apoptotic destruction. 3. Biochemical interventions (e.g., with inhibitors of poly-(ADP-riboso)-polymerase) into the signal and executive mechanisms of PCD can change the choice of the cell death form. 4. During both necrosis and epigenetic programs of apoptotic cell death that need no macromolecular synthesis (e.g., the CD95-dependent death), the nucleus plays a passive role. Therefore, necrosis, similarly to apoptosis, is suggested to be a form of the programmed cell death. However, for the whole body the physiological consequences of apoptosis and necrosis are quite different. In the case of apoptosis, all constituents of the nucleus and cytoplasm are isolated by an undamaged membrane and then by phagocytes together with the membrane-bound eat me markers (phosphatidylserine, etc.). In other words, the elimination of the cell which has realized its apoptotic program remains virtually unnoticed by the body. In the case of necrosis, the cytoplasmic content released into the intercellular space provokes an inflammatory response, i.e., an activation of resident phagocytes and attraction of leukocytes into the necrosis zone. It is suggested that under pathophysiological conditions, the necrotic cell destruction should amplify and catalyze pathological processes. The experimental data available now suggest that a disturbance in the body of optimal balance between the necrotic and apoptotic forms of PCD should be a crucial factor in the development of various pathophysiological processes associated with inflammation (diabetes, arthritis) or with aging (atherosclerosis, neurodegenerative diseases).