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Summary Glucagon-like peptide-1 (GLP-1) secreted from enteroendocrine L cells promotes nutrient disposal via the incretin effect. However, the majority of L cells are localized to the distal gut, suggesting additional biological roles for GLP-1. Here, we demonstrate that GLP-1 receptor (GLP-1R) signaling controls mucosal expansion of the small bowel (SB) and colon. These actions did not require the epidermal growth factor (EGF) or intestinal epithelial insulin-like growth factor (IGF1) receptors but were absent in Glp1r −/− mice. Polyp number and size were increased in SB of exendin-4-treated Apc Min/+ mice, whereas polyp number was reduced in SB and colon of Glp1r −/− : Apc Min/+ mice. Exendin-4 increased fibroblast growth factor 7 (Fgf7) expression in colonic polyps of Apc Min/+ mice and failed to increase intestinal growth in mice lacking Fgf7 . Exogenous exendin-4 and Fgf7 regulated an overlapping set of genes important for intestinal growth. Thus, gain and loss of GLP-1R signaling regulates gut growth and intestinal tumorigenesis. [ABSTRACT FROM AUTHOR]

Background & Aims: Glucagon-like peptide-2 (GLP-2) is a 33-amino acid peptide hormone secreted by enteroendocrine cells in response to nutrient ingestion. GLP-2 stimulates crypt cell proliferation leading to expansion of the mucosal epithelium; however, the mechanisms transducing the trophic effects of GLP-2 are incompletely understood. Methods: We examined the gene expression profiles and growth-promoting actions of GLP-2 in normal mice in the presence or absence of an inhibitor of ErbB receptor signaling, in Glp2r −/− mice and in Egfr wa2 mice harboring a hypomorphic point mutation in the epidermal growth factor receptor. Results: Exogenous GLP-2 administration rapidly induced the expression of a subset of ErbB ligands including amphiregulin, epiregulin, and heparin binding (HB)-epidermal growth factor, in association with induction of immediate early gene expression in the small and large bowel. These actions of GLP-2 required a functional GLP-2 receptor because they were eliminated in Glp2r −/− mice. In contrast, insulin-like growth factor-I and keratinocyte growth factor, previously identified mediators of GLP-2 action, had no effect on the expression of these ErbB ligands. The GLP-2-mediated induction of ErbB ligand expression was not metalloproteinase inhibitor sensitive but was significantly diminished in Egfr wa2 mice and completed abrogated in wild-type mice treated with the pan-ErbB inhibitor CI-1033. Furthermore, the stimulatory actions of GLP-2 on crypt cell proliferation and bowel growth were eliminated in the presence of CI-1033. Conclusions: These findings identify the ErbB signaling network as a target for GLP-2 action leading to stimulation of growth factor-dependent signal transduction and bowel growth in vivo. [Copyright &y& Elsevier]

Summary: Perturbation of endoplasmic reticulum (ER) homeostasis impairs insulin biosynthesis, β cell survival, and glucose homeostasis. We show that a murine model of diabetes is associated with the development of ER stress in β cells and that treatment with the GLP-1R agonist exendin-4 significantly reduced biochemical markers of islet ER stress in vivo. Exendin-4 attenuated translational downregulation of insulin and improved cell survival in purified rat β cells and in INS-1 cells following induction of ER stress in vitro. GLP-1R agonists significantly potentiated the induction of ATF-4 by ER stress and accelerated recovery from ER stress-mediated translational repression in INS-1 β cells in a PKA-dependent manner. The effects of exendin-4 on the induction of ATF-4 were mediated via enhancement of ER stress-stimulated ATF-4 translation. Moreover, exendin-4 reduced ER stress-associated β cell death in a PKA-dependent manner. These findings demonstrate that GLP-1R signaling directly modulates the ER stress response leading to promotion of β cell adaptation and survival. [Copyright &y& Elsevier]