Involvement of gut microbiota in association between GLP-1/GLP-1 receptor expression and gastrointestinal motility

Microbiota in the gut is known to play a pivotal role in host physiology by interacting with the immune and neuroendocrine systems in gastrointestinal (GI) tissues. Glucagon-like peptide 1 (GLP-1), a gut hormone, is involved in metabolism as well as GI motility. We examined how gut microbiota affects the link between GLP-1/GLP-1 receptor (GLP-1R) expression and motility of the GI tract. Germ-free (GF) mice (6 weeks old) were orally administered a fecal bacterial suspension prepared from specific pathogen-free (SPF) mice, and then after fecal transplantation (FT) GI tissues were obtained from the GF mice at various time points. The expression of GLP-1 and its receptor was examined by immunohistochemistry, and gastrointestinal transit time (GITT) was measured by administration of carmine red solution. GLP-1 was expressed in endocrine cells in the colonic mucosa, and GLP-1R was expressed in myenteric neural cells throughout the GI wall. GLP-1R-positive cells throughout the GI wall were significantly fewer in GF mice with FT than in GF mice without gut microbiota reconstitution. The GITT was significantly shorter in GF mice with FT than in control GF mice without FT, and correlated with the number of GLP-1R-positive cells throughout the GI wall. The GITT was significantly longer in GF controls than in SPF mice. When those mice were treated with GLP-1 agonist extendin4, GITT was significantly longer in GF mice group. Gut microbiota may accelerate or at least modify GI motility while suppressing GLP-1R expression in myenteric neural cells throughout the GI tract.