Proteases in intestinal health and disease.

Extracellular proteases, originating from the host or the microbiota, are key signalling molecules involved in cellular communication with the environment. They signal through a wide array of mechanisms, ranging from receptor activation to protein transformation and even degradation. Protease signals are irreversible, as it involves the cleavage of proteins. Therefore, proteases are tightly controlled, and must be understood within the context of the complex networks in which they operate - their activity is tightly regulated by access to specific substrates and the presence of inhibitors. The intestine is particularly exposed to extracellular proteases, which have major roles in gut physiology: digestion, food antigen processing, barrier function, epithelial renewal and microbiome homeostasis. Dysregulated proteolytic balance is associated with intestinal pathologies including inflammatory bowel disease, irritable bowel syndrome, coeliac disease and colorectal cancer. Extracellular proteases are major contributors to a number of gut dysfunctions, including microbiota dysbiosis, barrier dysfunction, matrix remodelling, activation of mucosal immunity and nociceptive or motility abnormalities. Consequently, proteolytic homeostasis at the intestinal mucosa surface has become a goal for intestinal health, and new therapeutic options targeting the interplay among proteases, their inhibitors and their substrates have been explored.