PPARβ/δ Activation Induces Enteroendocrine L Cell GLP-1 Production

doi:10.1053/j.gastro.2011.01.045

Gastroenterology

Volume 140, Issue 5, May 2011, Pages 1564-1574

https://doi.org/10.1053/j.gastro.2011.01.045 Get rights and content

Background & Aims

Glucagon-like peptide (GLP)-1, an intestinal incretin produced by L cells through proglucagon processing, is secreted after nutrient ingestion and acts on endocrine pancreas beta cells to enhance insulin secretion. Peroxisome proliferator-activated receptor (PPAR) β/δ is a nuclear receptor that improves glucose homeostasis and pancreas islet function in diabetic animal models. Here, we investigated whether PPARβ/δ activation regulates L cell GLP-1 production.

Methods

Proglucagon regulation and GLP-1 release were evaluated in murine GLUTag and human NCI-H716 L cells and in vivo using wild-type, PPARβ/δ-null, and ob/ob C57Bl/6 mice treated with the PPARβ/δ synthetic agonists GW501516 or GW0742.

Results

PPARβ/δ activation increased proglucagon expression and enhanced glucose- and bile acid–induced GLP-1 release by intestinal L cells in vitro and ex vivo in human jejunum. In vivo treatment with GW0742 increased proglucagon messenger RNA levels in the small intestine in wild-type but not in PPARβ/δ-deficient mice. Treatment of wild-type and ob/ob mice with GW501516 enhanced the increase in plasma GLP-1 level after an oral glucose load and improved glucose tolerance. Concomitantly, proglucagon and GLP-1 receptor messenger RNA levels increased in the small intestine and pancreas, respectively. Finally, PPARβ/δ agonists activate the proglucagon gene transcription by interfering with the β-catenin/TCF-4 pathway.

Conclusions

Our data show that PPARβ/δ activation potentiates GLP-1 production by the small intestine. Pharmacologic targeting of PPARβ/δ is a promising approach in the treatment of patients with type 2 diabetes mellitus, especially in combination with dipeptidyl peptidase IV inhibitors.

Section snippets

Chemicals and Reagents

See the Supplementary Materials and Methods.

Cell culture and treatment

The mouse GLUTag L cell model was kindly provided by D. J. Drucker (University of Toronto, Toronto, Ontario, Canada). The rat INS1-E beta cells were given by K. Ravnskjaer (University of Southern Denmark, Odense M, Denmark). The human NCI-H716 L cell, (Cat. CCL 251) and murine α-TC1/9 alpha cells, (Cat. CRL 2350) were purchased from American Type Culture Collection (ATCC, Manassas, VA). For details, see Supplementary Materials and Methods.

Transient transfection assays

GLUTag L

Glucose Is a Positive Modulator of Proglucagon and PC-1/3 Gene Expression in GLUTag L Cells

Glucose is the primary stimulus for GLP-1 secretion by enteroendocrine L cells. However, the transcriptional impact of glucose on proglucagon expression has not yet been reported. Time course analysis of gene expression in GLUTag L cells shows that proglucagon (Figure 1A) and PC-1/3 (Figure 1B) messenger RNA (mRNA) levels significantly increased on incubation with glucose compared with lactate. By contrast, PC-2 mRNA was not regulated by glucose within 12 hours of incubation, while both glucose

Discussion

Our results show that PPARβ/δ activation positively regulates enteroendocrine L cell GLP-1 production and enhances its response to glucose and bile acids. Proglucagon mRNA levels and GLP-1 production were markedly increased in PPARβ/δ agonist-treated mice, contributing to a significant improvement of glucose homeostasis. Likewise, activation of mouse and human enteroendocrine L cells in vitro or ex vivo with PPARβ/δ agonists significantly increased proglucagon mRNA levels and enhanced glucose-

Acknowledgments

The authors thank D. J. Drucker and F. Gribble for providing the GLUTag L cells, A. Billin and T. Willson for providing GW0742, W. Knepel for the generous gift of −350–base pair proglucagon-Luc plasmid, and D. Bershadsky for the generous gift of pEGFP/β-catenin/S33Y plasmid.

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: Conflicts of interest The authors disclose no conflicts.

: Funding Supported by EU grants AMI-DIAB (Fonds de Compétitivité des Entreprises, convention no. 06 2 90 6169) and Hepadip (LSHM-CT-2005-018734) with the collaboration of Université Lille 2, Région Nord/Pas-de-Calais, the FEDER and French State, and grant support from the Nouvelle Société Française d'Athérosclérose (to M.D.).

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Basic—Alimentary TractPPARβ/δ Activation Induces Enteroendocrine L Cell GLP-1 Production

Background & Aims

Methods

Results

Conclusions

Section snippets

Chemicals and Reagents

Cell culture and treatment

Transient transfection assays

Glucose Is a Positive Modulator of Proglucagon and PC-1/3 Gene Expression in GLUTag L Cells

Discussion

Acknowledgments

J Biol Chem

J Biol Chem

Gastroenterology

Regul Pept

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

Biochem Biophys Res Commun

Best Pract Res Clin Endocrinol Metab

Cell

FEBS Lett

Biochem Biophys Res Commun

Biochem Biophys Res Commun

Cell Metab

J Biol Chem

Eur J Pharmacol

Cell Metab

Biochem Pharmacol

Identical mRNA for preproglucagon in pancreas and gut

Eur J Biochem

Proglucagon processing in a rat islet cell line resembles phenotype of intestine rather than pancreas

Endocrinology

Glucagon and regulation of glucose metabolism

Am J Physiol Endocrinol Metab

Glucagon stimulates expression of the inducible cAMP early repressor and suppresses insulin gene expression in pancreatic beta-cells

Diabetes

Glucagon-like peptide 1 has a physiological role in the control of postprandial glucose in humans: studies with the antagonist exendin 9-39

Diabetes

Enhanced glucose-dependent insulinotropic polypeptide secretion and insulinotropic action in glucagon-like peptide 1 receptor −/− mice

Diabetes

Basic—Alimentary Tract
PPARβ/δ Activation Induces Enteroendocrine L Cell GLP-1 Production