Release of GLP-1 and PYY in response to the activation of G protein-coupled bile acid receptor TGR5 is mediated by Epac/PLC-ε pathway and modulated by endogenous H2S

Abstract

Activation of plasma membrane TGR5 receptors in enteroendocrine cells by bile acids is known to regulate gastrointestinal secretion and motility and glucose homeostasis. The endocrine functions of the gut are modulated by microenvironment of the distal gut predominantly by sulfur-reducing bacteria of the microbiota that produce H2S. However, the mechanisms involved in the release of peptide hormones, GLP-1 and PYY in response to TGR5 activation by bile acids and the effect of H2S on bile acid-induced release of GLP-1 and PYY are unclear. In the present study, we have identified the signaling pathways activated by the bile acid receptor TGR5 to mediate GLP-1 and PYY release and the mechanism of inhibition of their release by H2S in enteroendocrine cells. The TGR5 ligand oleanolic acid (OA) stimulated Gαs and cAMP formation, and caused GLP-1 and PYY release. OA-induced cAMP formation and peptide release were blocked by TGR5 siRNA. OA also caused an increase in PI hydrolysis and intracellular Ca2+. Increase in PI hydrolysis was abolished in cells transfected with PLC-ε siRNA. 8-pCPT-2′-O-Me-cAMP, a selective activator of Epac, stimulated PI hydrolysis, and GLP-1 and PYY release. L-Cysteine, which activates endogenous H2S producing enzymes cystathionine-γ-lyase and cystathionine-β-synthase, and NaHS and GYY4137, which generate H2S, inhibited PI hydrolysis and GLP-1 and PYY release in response to OA or 8-pCPT-2′-O-Me-cAMP. Propargylglycine, an inhibitor of CSE, reversed the effect of L-cysteine on PI hydrolysis and GLP-1 and PYY release. We conclude: (i) activation of Gαs-coupled TGR5 receptors causes stimulation of PI hydrolysis, and release of GLP-1 and PYY via a PKA-independent, cAMP-dependent mechanism involving Epac/PLC-ε/Ca2+ pathway, and (ii) H2S has potent inhibitory effects on GLP-1 and PYY release in response to TGR5 activation, and the mechanism involves inhibition of PLC-ε/Ca2+ pathway.

Chenodeoxycholic acid stimulates glucagon‐like peptide‐1 secretion in patients after Roux‐en‐Y gastric bypass

“…Administration of BAs has been demonstrated to stimulate PYY in vitro via activation of TGR5 (Bala et al. ). Stimulation also appears to occur in vivo (Adrian et al.…”

Obesity: Current and potential pharmacotherapeutics and targets

“…In enteroendocrine cells, TGR5 stimulates the release of both GLP-1 and PYY thereby maintaining glucose homeostasis and decreasing food intake (Thomas et al, 2009; Bala et al, 2014). In muscle and brown adipose tissue, TGR5 regulates energy expenditure through activation of thyroid hormone-activating enzyme, type 2 iodothyronine deiodinase (Eggink et al, 2014).…”

Lithocholic acid attenuates cAMP-dependent Cl− secretion in human colonic epithelial T84 cells

“…It is widely distributed in many species and found in a variety of human tissues, including in the intestine, endocrine glands, adipocytes, muscle, spleen, and lymph nodes (30). Activation of TGR5 results in an increase in adenosine 3=,5=-cyclic monophosphate (cAMP) and activation of protein kinase A (PKA) and the exchange protein activated by cAMP (6,44,61). In the intestine, TGR5 is localized to enteroendocrine, neuronal, and smooth muscle cells, activating glucagon-like peptide release (73), serotonin release (2), and causing membrane hyperpolarization (45), respectively.…”