Programmed Cell Death

Apoptosis is a fundamental process that is required for proper maintenance and survival of multi-cellular organisms. Caspases are cysteinyl-containing active center proteases with specificity for protein cleavage after aspartyl residues. Caspases exist within the cell as inactive zymogens, and their activation is controlled primarily by two distinct mechanisms involving protein–protein interactions within large complexes and proximity-induced processing of the caspases. Since the cell is armed with elaborate mechanisms of self-destruction composed of inactive zymogens that can be rapidly activated by numerous stressors or triggers, these mechanisms must remain under tight control. Apoptosis has been implicated in delayed neuronal death associated with many neurodegenerative disorders such as Parkinson's disease, stroke, Huntington's disease, traumatic head injury, Alzheimer's disease, motor neuron degeneration, spinal cord injury, and multiple sclerosis.