Gut-associated cGMP mediates colitis and dysbiosis in a mouse model of an activating mutation in GUCY2C

Abstract

Activating mutations in receptor guanylyl cyclase C (GC-C), the target of gastrointestinal peptide hormones guanylin and uroguanylin, and bacterial heat-stable enterotoxins cause early-onset diarrhea and chronic inflammatory bowel disease (IBD). GC-C regulates ion and fluid secretion in the gut via cGMP production and activation of cGMP-dependent protein kinase II. We characterize a novel mouse model harboring an activating mutation in Gucy2c equivalent to that seen in an affected Norwegian family. Mutant mice demonstrated elevated intestinal cGMP levels and enhanced fecal water and sodium content. Basal and linaclotide-mediated small intestinal transit was higher in mutant mice, and they were more susceptible to DSS-induced colitis. Fecal microbiome and gene expression analyses of colonic tissue revealed dysbiosis, up-regulation of IFN-stimulated genes, and misregulation of genes associated with human IBD and animal models of colitis. This novel mouse model thus provides molecular insights into the multiple roles of intestinal epithelial cell cGMP, which culminate in dysbiosis and the induction of inflammation in the gut.

Receptor Guanylyl Cyclase C and Cyclic GMP in Health and Disease: Perspectives and Therapeutic Opportunities

“…As anticipated, these mice showed elevated cGMP levels in the small intestine and diarrhea-like features, including increased fecal sodium and water content (13). Significantly, our findings in this mutant mouse model demonstrating dysbiosis and increased susceptibility to dextran sulfate sodium (DSS)-induced colitis delineated an essential rheostatic role of GC-C signaling in intestinal homeostasis (13).…”

“…As previously discussed, activating mutations in GC-C are associated with IBD, supporting the observation that higher levels of mucosal cGMP are maintained in inflammatory states (10,16,250). An animal model of a gain-of-function mutation in GC-C confirmed these clinical observations (13). In contrast to expectations, IBD patients and an experimental colitis model showed downregulation of GC-C and its ligands in response to antecedent or concomitant inflammatory stimuli, implying that direct treatment with uroguanylin mimetic drugs can reduce inflammatory cytokines and play a protective role in inflammation (251).…”

“…Given the links between activating GC-C mutations and IBD in humans, as well as the supporting evidence from transgenic mice of GC-C activation, we cannot rule out that downregulation of GC-C and its ligands in IBD patients and in a mouse model of experimental colitis could be an adaptive mechanism of epithelial preservation (10,13,16). In this context, it is worth considering studies demonstrating that barrier loss in IBD is associated with a decrease in levels of occludin, a tight junction-associated protein, in patient biopsy specimens from IBD patients (254).…”

“…This transmembrane receptor is encoded by GUCY2C . Its predominant expression on the intestinal brush border epithelium ( 20 ) strategically positions it to critically regulate fluid ion homeostasis in the gut ( 13 ). GC-C is a multidomain protein that includes an extracellular domain (ECD), transmembrane domain, juxta-membrane domain, kinase homology domain (KHD), a linker region, guanylyl cyclase domain (GCD), and C-terminal domain ( Figure 2 ).…”

“…These studies, along with the discovery of disease-causing mutations, helped elucidate how GC-C activation and deficiency contribute to human disease (6,(10)(11)(12). In the last five years, new and unexplored interactions between GC-C, mucosal homeostasis, the gut microbiome, and host immunity have emerged, along with a better mechanistic understanding of its role in colorectal cancer (13)(14)(15).…”