Apoptosis: overview and signal transduction pathways.

Apoptosis is a form of cell death that is driven by an intrinsic cellular suicide program. The roles of apoptosis and other forms of programmed cell death in neural development, maintenance, and disease states are increasingly being recognized and defined. Therapies directed at the apoptotic program have seen at least some degree of success in animal models of neurodegenerative disease, vascular disease, and traumatic CNS injury. This article describes the signal transduction pathways that mediate apoptosis. Broadly speaking, intrinsic and extrinsic pathways for apoptosis activation may be distinguished, as can be cross-talk between these two. These pathways converge on a system of proteases referred to as "capases" (cysteinyl aspartic proteinases), and modulators exist that multimerize, activate, amplify, or inhibit caspases. Activated caspases are the executioners of the apoptotic program, and carry out this function by cleaving specific cellular substrates. Modulation of this process holds promise as a therapeutic approach in neurotrauma.