Complex roles of caspases in the pathogenesis of inflammatory bowel disease.

Caspases are cysteine proteases that regulate embryonic development, cell differentiation, tissue homoeostasis, and removal of damaged and harmful cells from the intestine and other parts of the body. Caspase activity is mainly regulated at the posttranslational level, which allows their rapid activation and response to cellular stress and pathogenic stimuli. In most cell types, caspases are initially expressed as inactive proenzymes, which undergo proteolytic cleavage to become functional enzymes. Caspase dysfunction has been associated with intestinal diseases, including inflammatory bowel disease (IBD) and colorectal cancer. Although the roles of caspases have been studied extensively in regulation of apoptosis, recent discoveries have highlighted cell death-independent functions of this protein family. In particular, caspase-1, caspase-4, caspase-5, and caspase-12 are activated during innate immune responses and participate in the formation of the inflammasome. Caspase-8 controls necroptosis of Paneth cells and potentially the death of intestinal epithelial cells in patients with Crohn's disease and appears to be involved in mucosal inflammation. Regulators of caspase-8 might therefore be used to prevent cell death in patients with IBD. Improving our understanding of the regulation and function of caspases in the intestine might lead to new therapeutics for chronic intestinal inflammation and inflammation-associated cancer.