Limits...
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.

Bala V, Rajagopal S, Kumar DP, Nalli AD, Mahavadi S, Sanyal AJ, Grider JR, Murthy KS - Front Physiol (2014)

Bottom Line: 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.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/Ca(2+) 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/Ca(2+) pathway.

View Article: PubMed Central - PubMed

Affiliation: Gastroenterology Division, Department of Internal Medicine, Virginia Commonwealth University Richmond, VA, USA.

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 Ca(2+). 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/Ca(2+) 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/Ca(2+) pathway.

No MeSH data available.


Related in: MedlinePlus

TGR5-mediated release of GLP-1 and PYY by oleanolic acid (OA). Cells transfected with control siRNA or TGR5-specific siRNA for 48 h and then treated with OA (10 μM) for 30 min. Release of GLP-1 (A) and PYY (B) into the medium was measured by ELISA. Inset: Down regulation of TGR5 expression in cells transfected with TGR5 siRNA was determined by western blot. Results are expressed as pg/100 ml. Values are mean ± s.e.m. of 5 experiments. **p < 0.001 vs. basal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4217307&req=5

Figure 2: TGR5-mediated release of GLP-1 and PYY by oleanolic acid (OA). Cells transfected with control siRNA or TGR5-specific siRNA for 48 h and then treated with OA (10 μM) for 30 min. Release of GLP-1 (A) and PYY (B) into the medium was measured by ELISA. Inset: Down regulation of TGR5 expression in cells transfected with TGR5 siRNA was determined by western blot. Results are expressed as pg/100 ml. Values are mean ± s.e.m. of 5 experiments. **p < 0.001 vs. basal.

Mentions: We initially examined whether STC-1 cells are responsive to the TGR5 selective ligand OA to release GLP-1 and PYY. The dose of OA was selected based on our previous work in pancreatic β cells and isolated smooth muscle cells (Kumar et al., 2012; Rajagopal et al., 2013). Treatment of STC-1 cells with OA (10 μM) stimulated GLP-1 and PYY release over a 30 min incubation period (4.1 ± 0.6-fold increase in GLP-1 release above basal levels 0.65 ± 0.09 pg/100 ml; 8.3 ± 1.2-fold increase in PYY release above basal levels 0.42 ± 0.068 pg/100 ml). The specific involvement of TGR5 in GLP-1 and PYY release in response to OA was examined using TGR5 specific siRNA. Neither basal nor OA-induced GLP-1 and PYY secretion was affected in cells transfected with control siRNA (Figure 2); however, the effect of OA on GLP-1 and PYY release was significantly attenuated in cells transfected with TGR5 siRNA compared to cells transfected with control siRNA (78 ± 10% inhibition in GLP-1 release and 88 ± 12% inhibition in PYY release) (Figure 2). Western blot analysis demonstrated suppression of TGR5 expression in cells transfected with TGR5 siRNA (Figure 2; inset). These results suggest that OA-induced GLP-1 and PYY release is mediated by TGR5, but not by other receptors such as nuclear receptor FXR.


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.

Bala V, Rajagopal S, Kumar DP, Nalli AD, Mahavadi S, Sanyal AJ, Grider JR, Murthy KS - Front Physiol (2014)

TGR5-mediated release of GLP-1 and PYY by oleanolic acid (OA). Cells transfected with control siRNA or TGR5-specific siRNA for 48 h and then treated with OA (10 μM) for 30 min. Release of GLP-1 (A) and PYY (B) into the medium was measured by ELISA. Inset: Down regulation of TGR5 expression in cells transfected with TGR5 siRNA was determined by western blot. Results are expressed as pg/100 ml. Values are mean ± s.e.m. of 5 experiments. **p < 0.001 vs. basal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4217307&req=5

Figure 2: TGR5-mediated release of GLP-1 and PYY by oleanolic acid (OA). Cells transfected with control siRNA or TGR5-specific siRNA for 48 h and then treated with OA (10 μM) for 30 min. Release of GLP-1 (A) and PYY (B) into the medium was measured by ELISA. Inset: Down regulation of TGR5 expression in cells transfected with TGR5 siRNA was determined by western blot. Results are expressed as pg/100 ml. Values are mean ± s.e.m. of 5 experiments. **p < 0.001 vs. basal.
Mentions: We initially examined whether STC-1 cells are responsive to the TGR5 selective ligand OA to release GLP-1 and PYY. The dose of OA was selected based on our previous work in pancreatic β cells and isolated smooth muscle cells (Kumar et al., 2012; Rajagopal et al., 2013). Treatment of STC-1 cells with OA (10 μM) stimulated GLP-1 and PYY release over a 30 min incubation period (4.1 ± 0.6-fold increase in GLP-1 release above basal levels 0.65 ± 0.09 pg/100 ml; 8.3 ± 1.2-fold increase in PYY release above basal levels 0.42 ± 0.068 pg/100 ml). The specific involvement of TGR5 in GLP-1 and PYY release in response to OA was examined using TGR5 specific siRNA. Neither basal nor OA-induced GLP-1 and PYY secretion was affected in cells transfected with control siRNA (Figure 2); however, the effect of OA on GLP-1 and PYY release was significantly attenuated in cells transfected with TGR5 siRNA compared to cells transfected with control siRNA (78 ± 10% inhibition in GLP-1 release and 88 ± 12% inhibition in PYY release) (Figure 2). Western blot analysis demonstrated suppression of TGR5 expression in cells transfected with TGR5 siRNA (Figure 2; inset). These results suggest that OA-induced GLP-1 and PYY release is mediated by TGR5, but not by other receptors such as nuclear receptor FXR.

Bottom Line: 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.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/Ca(2+) 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/Ca(2+) pathway.

View Article: PubMed Central - PubMed

Affiliation: Gastroenterology Division, Department of Internal Medicine, Virginia Commonwealth University Richmond, VA, USA.

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 Ca(2+). 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/Ca(2+) 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/Ca(2+) pathway.

No MeSH data available.


Related in: MedlinePlus