Apoptosis: its origin, history, maintenance and the medical implications for cancer and aging

Programmed cell death is a basic cellular mechanism. Apoptotic-like programmed cell death (called apoptosis in animals) occurs in both unicellular and multicellular eukaryotes, and some apoptotic mechanisms are observed in bacteria. Endosymbiosis between mitochondria and eukaryotic cells took place early in the eukaryotic evolution, and some of the apoptotic-like mechanisms of mitochondria that were retained after this event now serve as parts of the eukaryotic apoptotic machinery. Apoptotic mechanisms have several functions in unicellular organisms: they include kin-selected altruistic suicide that controls population size, sharing common goods, and responding to viral infection. Apoptotic factors also have non-apoptotic functions. Apoptosis is involved in the cellular aging of eukaryotes, including humans. In addition, apoptosis is a key part of the innate tumor-suppression mechanism. Several anticancer drugs induce apoptosis, because apoptotic mechanisms are inactivated during oncogenesis. Because of the ancient history of apoptosis, I hypothesize that there is a deep relationship between mitochondrial metabolism, its role in aerobic versus anaerobic respiration, and the connection between apoptosis and cancer. Whereas normal cells rely primarily on oxidative mitochondrial respiration, most cancer cells use anaerobic metabolism. According to the Warburg hypothesis, the remodeling of the metabolism is one of the processes that leads to cancer. Recent studies indicate that anaerobic, non-mitochondrial respiration is particularly active in embryonic cells, stem cells, and aggressive stem-like cancer cells. Mitochondrial respiration is particularly active during the pathological aging of human cells in neurodegenerative diseases. According to the reversed Warburg hypothesis formulated by Demetrius, pathological aging is induced by mitochondrial respiration. Here, I advance the hypothesis that the stimulation of mitochondrial metabolism leads to pathological aging.