Background: Guanylate Cyclase C (GC-C; Gucy2c) is a transmembrane receptor expressed in intestinal epithelial cells. Activation of GC-C by its secreted ligand guanylin stimulates intestinal fluid secretion. Familial mutations in GC-C cause chronic diarrheal disease or constipation and are associated with intestinal inflammation and infection. Here, we investigated the impact of GC-C activity on mucosal immune responses.
Methods: We utilized intraperitoneal injection of lipopolysaccharide to elicit a systemic cytokine challenge and then measured pro-inflammatory gene expression in colonic mucosa. GC-C(+/+) and GC-C(-/-) mice were bred with interleukin (IL)-10 deficient animals and colonic inflammation were assessed. Immune cell influx and cytokine/chemokine expression was measured in the colon of wildtype, IL-10(-/-), GC-C(+/+)IL-10(-/-) and GC-C(-/-)IL-10(-/-) mice. GC-C and guanylin production were examined in the colon of these animals and in a cytokine-treated colon epithelial cell line.
Results: Relative to GC-C(+/+) animals, intraperitoneal lipopolysaccharide injection into GC-C(-/-) mice increased proinflammatory gene expression in both whole colon tissue and in partially purified colonocyte isolations. Spontaneous colitis in GC-C(-/-)IL-10(-/-) animals was significantly more severe relative to GC-C(+/+)IL-10(-/-) mice. Unlike GC-C(+/+)IL-10(-/-) controls, colon pathology in GC-C(-/-)IL-10(-/-) animals was apparent at an early age and was characterized by severely altered mucosal architecture, crypt abscesses, and hyperplastic subepithelial lesions. F4/80 and myeloperoxidase positive cells as well as proinflammatory gene expression were elevated in GC-C(-/-)IL-10(-/-) mucosa relative to control animals. Guanylin was diminished early in colitis in vivo and tumor necrosis factor α suppressed guanylin mRNA and protein in intestinal goblet cell-like HT29-18-N2 cells.
Conclusions: The GC-C signaling pathway blunts colonic mucosal inflammation that is initiated by systemic cytokine burst or loss of mucosal immune cell immunosuppression. These data as well as the apparent intestinal inflammation in human GC-C mutant kindred underscore the importance of GC-C in regulating the response to injury and inflammation within the gut.