Janus kinases in inflammatory bowel disease: Four kinases for multiple purposes

Inflammatory bowel disease (IBD) comprises mainly Crohn's disease and ulcerative colitis. These pathologies are characterized by inflammation of the gut and destruction of its epithelium. Many cytokines play key roles in this pathology. They are generally involved in the inflammatory process but also display anti-inflammatory activities and some regulate the gut epithelium homeostasis, constituting therapeutic targets for IBD. Many of these cytokines signal through the JAK/STAT pathway and thus, JAKs represent also very promising therapeutic targets and selective or non-selective inhibitors of these kinases have already been assayed in clinical trials with various success. The existence of four JAKs and six STAT factors that are used in combination make these pathways complex enough to generate various responses. Here we summarize the role of the JAKs in some cytokines involved in IBD. The multifunctional role they play through the various functions of the cytokines they signal for makes difficult the anticipation of the effective beneficial role that JAK inhibitors may have.