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TGR5 potentiates GLP-1 secretion in response to anionic exchange resins.

Harach T, Pols TW, Nomura M, Maida A, Watanabe M, Auwerx J, Schoonjans K - Sci Rep (2012)

Bottom Line: Potentiation of intestinal GLP-1 secretion has been proposed to contribute to the glycemia lowering effect of these non-systemic drugs.Furthermore, we demonstrate that the boost in GLP-1 release by resins is due to both enhanced TGR5-dependent production of the precursor transcript of GLP-1 as well as to the local enrichment of TGR5 agonists in the colon.Thus, TGR5 represents an essential component in the pathway mediating the enhanced GLP-1 release in response to anionic exchange resins.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Integrative and Systems Physiology-LISP, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.

ABSTRACT
Anionic exchange resins are bona fide cholesterol-lowering agents with glycemia lowering actions in diabetic patients. Potentiation of intestinal GLP-1 secretion has been proposed to contribute to the glycemia lowering effect of these non-systemic drugs. Here, we show that resin exposure enhances GLP-1 secretion and improves glycemic control in diet-induced animal models of "diabesity", effects which are critically dependent on TGR5, a G protein-coupled receptor that is activated by bile acids. We identified the colon as a major source of GLP-1 secretion after resin treatment. Furthermore, we demonstrate that the boost in GLP-1 release by resins is due to both enhanced TGR5-dependent production of the precursor transcript of GLP-1 as well as to the local enrichment of TGR5 agonists in the colon. Thus, TGR5 represents an essential component in the pathway mediating the enhanced GLP-1 release in response to anionic exchange resins.

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Enhanced proglucagon transcription in enteroendocrine cells in response to INT-777 requires TGR5.(a–b) TGR5 (a) and proglucagon (b) mRNA levels in the different intestinal sections of diet-induced obese TGR5+/+ and TGR5−/− mice after two weeks of treatment with Colestilan (COL; n = 7 per group). (c–d) Proglucagon mRNA levels in STC-1 (c) and GLUTag (d) mouse enteroendocrine cells transfected with shControl or shTGR5 vectors in the presence of 30 µM INT-777 (black bars) or vehicle (white bars; n = 3 per group). (e–f) INT-777 induces proglucagon promoter activity via TGR5 in enteroendocrine cells. STC-1 (e) and GLUTag (f) mouse enteroendocrine cells were transfected with shControl or shTGR5 constructs in combination with the proglucagon luciferase reporter. Cells were then incubated with vehicle (white bars) or 30 µΜ INT-777 (black bars; n = 3 per group) for 3 hours and assayed for luciferase activity. Data represent mean ± SE. *Statistically significant, p<0.05.
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f2: Enhanced proglucagon transcription in enteroendocrine cells in response to INT-777 requires TGR5.(a–b) TGR5 (a) and proglucagon (b) mRNA levels in the different intestinal sections of diet-induced obese TGR5+/+ and TGR5−/− mice after two weeks of treatment with Colestilan (COL; n = 7 per group). (c–d) Proglucagon mRNA levels in STC-1 (c) and GLUTag (d) mouse enteroendocrine cells transfected with shControl or shTGR5 vectors in the presence of 30 µM INT-777 (black bars) or vehicle (white bars; n = 3 per group). (e–f) INT-777 induces proglucagon promoter activity via TGR5 in enteroendocrine cells. STC-1 (e) and GLUTag (f) mouse enteroendocrine cells were transfected with shControl or shTGR5 constructs in combination with the proglucagon luciferase reporter. Cells were then incubated with vehicle (white bars) or 30 µΜ INT-777 (black bars; n = 3 per group) for 3 hours and assayed for luciferase activity. Data represent mean ± SE. *Statistically significant, p<0.05.

Mentions: In order to gain insight into the mechanisms underlying the TGR5-dependent secretion of GLP-1 upon AERs, we first assessed expression of TGR5 in different sections of the intestine. We observed that AERs did not modulate TGR5 expression in the intestine, as TGR5 mRNA levels in Colestilan-treated TGR5+/+ intestinal sections were indistinguishable from those of untreated TGR5+/+ mice (Fig. 2a). Interestingly, in addition to enhanced GLP-1 secretion, mRNA levels of proglucagon, encoding the precursor of GLP-1, were also significantly increased in the colons of AER-treated TGR5+/+ mice relative to untreated TGR5+/+ mice. This increase in proglucagon mRNA was not observed in TGR5−/− mice (Fig. 2b). Although not statistically significant, a similar trend for proglucagon expression was found in the ileum (Fig. 2b). To investigate the mechanism by which TGR5 regulates proglucagon gene expression, TGR5 was silenced in cultured STC-1 and GLUTag mouse enteroendocrine cells using shRNA constructs. Proglucagon mRNA levels were then assessed in the absence or presence of the semi-synthetic cholic acid derivative and TGR5-specific agonist, 6α-ethyl-23(S)-methyl-cholic acid, referred to as INT-7771133. Interestingly, INT-777 robustly induced proglucagon mRNA levels in both cell lines, whereas no induction was observed in cells in which endogenous TGR5 expression was repressed (Fig. 2c and 2d). TGR5 activation is known to induce cAMP signaling and the proglucagon gene is an established target of cAMP signaling34353637. To obtain more mechanistic insight into the TGR5-mediated induction of proglucagon mRNA, we measured the activity of the proglucagon promoter by transfecting STC-1 and GLUTag cells with a luciferase reporter driven by the 2.3 kb upstream regulatory region of the proglucagon gene, which contains several cAMP responsive elements34353637. In line with the TGR5-dependent increase of colonic proglucagon gene expression after AERs (Fig. 2b), INT-777 significantly induced proglucagon promoter activity in STC-1 and GLUTag cells. This effect was significantly blunted upon shTGR5 transfection, indicating that TGR5 is critical in mediating the increase of proglucagon promoter activity in response to INT-777 (Fig. 2e and 2f).


TGR5 potentiates GLP-1 secretion in response to anionic exchange resins.

Harach T, Pols TW, Nomura M, Maida A, Watanabe M, Auwerx J, Schoonjans K - Sci Rep (2012)

Enhanced proglucagon transcription in enteroendocrine cells in response to INT-777 requires TGR5.(a–b) TGR5 (a) and proglucagon (b) mRNA levels in the different intestinal sections of diet-induced obese TGR5+/+ and TGR5−/− mice after two weeks of treatment with Colestilan (COL; n = 7 per group). (c–d) Proglucagon mRNA levels in STC-1 (c) and GLUTag (d) mouse enteroendocrine cells transfected with shControl or shTGR5 vectors in the presence of 30 µM INT-777 (black bars) or vehicle (white bars; n = 3 per group). (e–f) INT-777 induces proglucagon promoter activity via TGR5 in enteroendocrine cells. STC-1 (e) and GLUTag (f) mouse enteroendocrine cells were transfected with shControl or shTGR5 constructs in combination with the proglucagon luciferase reporter. Cells were then incubated with vehicle (white bars) or 30 µΜ INT-777 (black bars; n = 3 per group) for 3 hours and assayed for luciferase activity. Data represent mean ± SE. *Statistically significant, p<0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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f2: Enhanced proglucagon transcription in enteroendocrine cells in response to INT-777 requires TGR5.(a–b) TGR5 (a) and proglucagon (b) mRNA levels in the different intestinal sections of diet-induced obese TGR5+/+ and TGR5−/− mice after two weeks of treatment with Colestilan (COL; n = 7 per group). (c–d) Proglucagon mRNA levels in STC-1 (c) and GLUTag (d) mouse enteroendocrine cells transfected with shControl or shTGR5 vectors in the presence of 30 µM INT-777 (black bars) or vehicle (white bars; n = 3 per group). (e–f) INT-777 induces proglucagon promoter activity via TGR5 in enteroendocrine cells. STC-1 (e) and GLUTag (f) mouse enteroendocrine cells were transfected with shControl or shTGR5 constructs in combination with the proglucagon luciferase reporter. Cells were then incubated with vehicle (white bars) or 30 µΜ INT-777 (black bars; n = 3 per group) for 3 hours and assayed for luciferase activity. Data represent mean ± SE. *Statistically significant, p<0.05.
Mentions: In order to gain insight into the mechanisms underlying the TGR5-dependent secretion of GLP-1 upon AERs, we first assessed expression of TGR5 in different sections of the intestine. We observed that AERs did not modulate TGR5 expression in the intestine, as TGR5 mRNA levels in Colestilan-treated TGR5+/+ intestinal sections were indistinguishable from those of untreated TGR5+/+ mice (Fig. 2a). Interestingly, in addition to enhanced GLP-1 secretion, mRNA levels of proglucagon, encoding the precursor of GLP-1, were also significantly increased in the colons of AER-treated TGR5+/+ mice relative to untreated TGR5+/+ mice. This increase in proglucagon mRNA was not observed in TGR5−/− mice (Fig. 2b). Although not statistically significant, a similar trend for proglucagon expression was found in the ileum (Fig. 2b). To investigate the mechanism by which TGR5 regulates proglucagon gene expression, TGR5 was silenced in cultured STC-1 and GLUTag mouse enteroendocrine cells using shRNA constructs. Proglucagon mRNA levels were then assessed in the absence or presence of the semi-synthetic cholic acid derivative and TGR5-specific agonist, 6α-ethyl-23(S)-methyl-cholic acid, referred to as INT-7771133. Interestingly, INT-777 robustly induced proglucagon mRNA levels in both cell lines, whereas no induction was observed in cells in which endogenous TGR5 expression was repressed (Fig. 2c and 2d). TGR5 activation is known to induce cAMP signaling and the proglucagon gene is an established target of cAMP signaling34353637. To obtain more mechanistic insight into the TGR5-mediated induction of proglucagon mRNA, we measured the activity of the proglucagon promoter by transfecting STC-1 and GLUTag cells with a luciferase reporter driven by the 2.3 kb upstream regulatory region of the proglucagon gene, which contains several cAMP responsive elements34353637. In line with the TGR5-dependent increase of colonic proglucagon gene expression after AERs (Fig. 2b), INT-777 significantly induced proglucagon promoter activity in STC-1 and GLUTag cells. This effect was significantly blunted upon shTGR5 transfection, indicating that TGR5 is critical in mediating the increase of proglucagon promoter activity in response to INT-777 (Fig. 2e and 2f).

Bottom Line: Potentiation of intestinal GLP-1 secretion has been proposed to contribute to the glycemia lowering effect of these non-systemic drugs.Furthermore, we demonstrate that the boost in GLP-1 release by resins is due to both enhanced TGR5-dependent production of the precursor transcript of GLP-1 as well as to the local enrichment of TGR5 agonists in the colon.Thus, TGR5 represents an essential component in the pathway mediating the enhanced GLP-1 release in response to anionic exchange resins.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Integrative and Systems Physiology-LISP, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.

ABSTRACT
Anionic exchange resins are bona fide cholesterol-lowering agents with glycemia lowering actions in diabetic patients. Potentiation of intestinal GLP-1 secretion has been proposed to contribute to the glycemia lowering effect of these non-systemic drugs. Here, we show that resin exposure enhances GLP-1 secretion and improves glycemic control in diet-induced animal models of "diabesity", effects which are critically dependent on TGR5, a G protein-coupled receptor that is activated by bile acids. We identified the colon as a major source of GLP-1 secretion after resin treatment. Furthermore, we demonstrate that the boost in GLP-1 release by resins is due to both enhanced TGR5-dependent production of the precursor transcript of GLP-1 as well as to the local enrichment of TGR5 agonists in the colon. Thus, TGR5 represents an essential component in the pathway mediating the enhanced GLP-1 release in response to anionic exchange resins.

Show MeSH
Related in: MedlinePlus