Caspase 8 is a protein found in humans, numerous other mammals and some birds. It is part of the caspase family of inactive proenzymes that play a crucial role in cell apoptosis. Caspases are composed of a prodomain, a large protease subunit and a small protease subunit.
When related to apoptosis, caspase 8 is specifically known as a death receptor. Cell apoptosis is the process by which programmed cellular death occurs at a controlled and expected rate, as opposed to necrosis, which is when cellular death occurs traumatically because of an injury. The programmed cell death of apoptosis is responsible for the development of individual digits in embryos as the cellular matter between them is broken down, and caspase 8 is a crucial aspect of this process. As the death receptor, it is responsible for receiving the signal to begin the cellular breakdown, essentially beginning the caspase cascade that leads to the cleaving of the cellular proteins.
Upon receiving the signal, caspase 8 activates, causing a cascade of caspase protein activations, eventually leading to the activation of caspase 3 and caspase 6. These proteins are directly responsible for the cellular breakdown that marks apoptosis. There are, however, instances of caspase 8 activation without receiving the precursor signal. Even without the precursor signal, this still causes the caspase cascade to occur, resulting in an unprogrammed apoptosis. These instances and the unprogrammed cellular death that necessarily follows have connected the protein with certain degenerative brain disorders and other ailments.
Research into degenerative brain disorders has uncovered a link between caspase 8 and several mental illnesses. There have been studies that link the activation of the protein to illnesses such as Alzheimer’s disease and Huntington's disease. Caspase 8 was found in the brain matter of sufferers of Huntington's disease, but not in people without the disease, implicating the protein as a possible cause of mental illness. There has been speculation that a greater understanding of the chemical process behind apoptosis and, specifically, caspase 8 could lead to the development of treatments for these disorders.