Current hypothesis suggests that genetic, immunological, and bacterial factors contribute essentially to the pathogenesis of
inflammatory bowel disease. Variations within the gene loci encoding
protein tyrosine phosphatases (
PTPs) have been associated with the onset of
inflammatory bowel disease.
PTPs modulate the activity of their substrates by dephosphorylation of
tyrosine residues and are critical for the regulation of fundamental cellular signaling processes. Evidence emerges that expression levels of PTPN2, PTPN11, and PTPN22 are altered in actively inflamed intestinal tissue. PTPN2 seems to be critical for protecting intestinal epithelial barrier function, regulating innate and adaptive immune responses and finally for maintaining intestinal homeostasis. These observations have been confirmed in PTPN2 knockout mice in vivo. Those animals are clearly more susceptible to intestinal and systemic
inflammation and feature alterations in innate and adaptive immune responses. PTPN22 controls inflammatory signaling in lymphocytes and mononuclear cells resulting in aberrant
cytokine secretion pattern and autophagosome formation. PTPN22 deficiency in vivo results in more severe
colitis demonstrating the relevance of PTPN22 for intestinal homeostasis in vivo. Of note, loss of PTPN22 promotes
mitogen-activated protein kinase-induced
cytokine secretion but limits secretion of nuclear factor κB-associated
cytokines and autophagy in mononuclear cells. Loss of PTPN11 is also associated with increased
colitis severity in vivo. In summary, dysfunction of those
PTPs results in aberrant and uncontrolled immune responses that result in chronic inflammatory conditions. This way, it becomes more and more evident that dysfunction of
PTPs displays an important factor in the pathogenesis of chronic intestinal
inflammation, in particular
inflammatory bowel disease.