Apoptosis in the nervous system

Apoptosis (from the Greek apoptosis, i.e., falling of leaves) is the phenomenon of programmed cell death, which plays an important role in the normal embryonic development and maintenance of the homeostasis of the differentiated tissues of adult organisms. Completion of the apoptosis process is accompanied by specific morphological and biochemical changes in the involved cells. Various disturbances in the control of apoptosis underlie various neurodegenerative diseases, the formation of malignant tumors, autoimmune disturbances, and developmental abnormalities. A deficit of neurotrophic factors leads to apoptosis of neurons. The survival of specific cell populations of neurons is controlled by neurotrophic factors and their combinations. Oncogene bcl-2, a repressor of cell death, belongs to the better-studied factors controlling apoptosis. The terminal stages of cell death, including the death of neurons, depend on the activation of caspases, specifically caspase-1 (interleukin-1β-converting enzyme). Ca2+and reactive forms of oxygen play an important role in the initiation of apoptosis by changing the mitochondrial permeability. Neuregulin, a factor of neuronal origin, is the main controlling factor in apoptosis of Schwann cells, and this process determines the size of their definitive population. Fibroblast growth factor b diminishes the apoptosis of Schwann cells in regenerating nerve fibers.