Overexpression of ATP-activated P2X7 Receptors in the Intestinal Mucosa Is Implicated in the Pathogenesis of Crohn's Disease

Background: Extracellular nucleotides released in conditions of cell stress alert the immune system from tissue injury or inflammation. We hypothesized that the P2X7 receptor (P2X7-R) could regulate key elements in inflammatory bowel disease pathogenesis. Methods: Colonoscopy samples obtained from patients with Crohn's disease (CD), ulcerative colitis, and controls were used to analyze P2X7-R expression by RT and real-time PCR, immunohistochemistry, and confocal microscopy. Inflammatory response was determined by the levels of cytokines by enzyme-linked immunosorbent assay in cultures of intestinal explants. Apoptosis was determined by the TUNEL assay. P2X7-R-/- C57BL/6 mice were treated with trinitrobenzene sulfonic acid or dextran sulfate sodium (DSS) for inducing colitis. Results: P2X7-R was expressed in higher levels in inflamed CD epithelium and lamina propria, where it colocalizes more with dendritic cells and macrophages. Basal levels of P2X7-R mRNA were higher in CD inflamed mucosa compared with noninflamed CD and controls and were upregulated after interferon-gamma in controls. Apoptotic rates were higher in CD epithelium and lamina propria compared with ulcerative colitis and controls. Levels of tumor necrosis factor-alpha, interleukin (IL)-1 beta, and IL-17 were higher, whereas IL-10 was lower in CD compared with controls. Levels of tumor necrosis factor-alpha-alpha and interleukin-1 beta increased after adenosine-triphosphate and decreased after KN62 treatment in CD. P2X7-R-/- animals did not develop trinitrobenzene sulfonic acid or DSS colitis. Conclusions: The upregulation of P2X7-R in CD inflamed mucosa is consistent with the involvement of purinoceptors in inflammation and apoptosis. These observations may implicate purinergic signaling in the pathogenesis of intestinal inflammation, and the P2X7-R may represent a novel therapeutic target in CD.