GPR119 regulates murine glucose homeostasis through incretin receptor-dependent and independent mechanisms

Abstract

G protein-coupled receptor 119 (GPR119) was originally identified as a β-cell receptor. However, GPR119 activation also promotes incretin secretion and enhances peptide YY action. We examined whether GPR119-dependent control of glucose homeostasis requires preservation of peptidergic pathways in vivo. Insulin secretion was assessed directly in islets, and glucoregulation was examined in wild-type (WT), single incretin receptor (IR) and dual IR knockout (DIRKO) mice. Experimental endpoints included plasma glucose, insulin, glucagon, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and peptide YY. Gastric emptying was assessed in WT, Glp1r-/-, DIRKO, Glp2r-/-, and GPR119-/- mice treated with the GPR119 agonist AR231453. AR231453 stimulated insulin secretion from WT and DIRKO islets in a glucose-dependent manner, improved glucose homeostasis, and augmented plasma levels of GLP-1, GIP, and insulin in WT and Gipr-/- mice. In contrast, although AR231453 increased levels of GLP-1, GIP, and insulin, it failed to lower glucose in Glp1r-/- and DIRKO mice. Furthermore, AR231453 did not improve ip glucose tolerance and had no effect on insulin action in WT and DIRKO mice. Acute GPR119 activation with AR231453 inhibited gastric emptying in Glp1r-/-, DIRKO, Glp2r-/-, and in WT mice independent of the Y2 receptor (Y2R); however, AR231453 did not control gastric emptying in GPR119-/- mice. Our findings demonstrate that GPR119 activation directly stimulates insulin secretion from islets in vitro, yet requires intact IR signaling and enteral glucose exposure for optimal control of glucose tolerance in vivo. In contrast, AR231453 inhibits gastric emptying independent of incretin, Y2R, or Glp2 receptors through GPR119-dependent pathways. Hence, GPR119 engages multiple complementary pathways for control of glucose homeostasis.

FIG. 1

GPR119 activation and control of oral glucose tolerance in WT and IRKO mice. Age-matched male mice were fasted overnight, and AR231453 (20 mg/kg) or vehicle was administered orally 30 min before an oral glucose tolerance test (OGTT) (A–D) or ip glucose tolerance test (IPGTT) (E) (1.5 g/kg). Blood was collected from the tail vein at 5 min (150 μl) and at 15 min (50 μl) after glucose administration. Blood glucose values and AUC analysis during OGTT for (A) WT, (B) Gipr−/−, (C) Glp1r−/−, and (D) DIRKO mice treated with or without AR231453. Blood glucose values during IPGTT for WT mice treated with or without AR231453 (E). Statistical analysis was assessed by ANOVA. *, P < 0.05; **, P < 0.01. For vehicle-treated mice: n = 12 (A), n = 8 (B), n = 10 (C), and n = 12 (D); for AR231453-treated mice: n = 11 (A), n = 8 (B), n = 10 (C), n = 12 (D), and n = 10–12 (E).

FIG. 2

GPR119 activation and plasma levels of GIP, GLP-1, insulin, and glucagon in WT and IRKO mice. Age-matched male mice were fasted overnight, and oral AR231453 (20 mg/kg) or vehicle was administered 30 min before an oral glucose tolerance test (OGTT). Plasma was obtained 5 min after oral glucose administration This sample was used to simultaneously measure the levels of (A) total GIP immunoreactivity, (B) total GLP-1 immunoreactivity, (C) and insulin. A second plasma sample was collected from each mouse at 15 min after glucose for the measurement of glucagon levels (D) in WT, Gipr−/−, Glp1r−/−, and DIRKO mice. Statistical analysis was assessed by ANOVA. *, P < 0.05; **, P < 0.01; ***, P < 0.001.

FIG. 3

GPR119 activation does not modify glucose profiles in an insulin tolerance test (ITT) in WT and DIRKO mice. WT (n = 10) and DIRKO (n = 8) age-matched mice were fasted for 5 h, and oral AR231453 (20 mg/kg) or vehicle was administered 30 min before ip insulin administration (1.2 U/kg). Blood glucose values during ITT for (A) WT and (B) DIRKO mice.

FIG. 4

GPR119 activation increases insulin secretion from WT and DIRKO islets. A, Arg stimulation increases plasma insulin levels in C57BL/6 and DIRKO mice in vivo. Mice were fasted overnight, plasma was collected to assess fasting insulin levels, and a single ip dose of either Arg (1 mg/g) or vehicle was administered at time zero. Blood was collected from the tail vein 5 min later for determination of plasma insulin levels. B, GPR119 and Irs2 gene expression in WT and IRKO islets. GPR119 and Irs2 mRNA levels were measured by real-time PCR in islets isolated from age-matched WT, Gipr−/−, Glp1r−/−, and DIRKO mice and normalized to levels of 18s RNA in the same samples. C, Insulin secretion from WT and DIRKO islets. Islets were isolated from 10-wk-old C57L/6 and DIRKO mice and incubated under conditions of low glucose (LG) (2.5 mM) for 1 h. Islets were then incubated in low glucose or high glucose (HG) (16.6 mM) and treated for 1 h with either vehicle (DMSO), PACAP, exendin-4, or AR231453. Statistical analysis was assessed by ANOVA. *, P < 0.05; **, P < 0.01; ***, P < 0.001.

FIG. 5

Gastric emptying in WT, Glp1r−/−, DIRKO, Gpr119−/−, and Glp2r−/− mice. Age-matched littermate WT and KO male mice were fasted overnight and given a single dose of AR231453 (20 mg/kg) or (A–C) vehicle, or (B) exendin-4 (1ug) before oral administration of a solution of glucose 15% and acetaminophen 1% at a dose of 1.5 g/kg glucose-0.1 g/kg acetaminophen. Gastric emptying rate was determined as described in Research Design and Methods. AUC for plasma acetaminophen levels in (A) WT, Glp1r−/−, and DIRKO mice, (B) Gpr119+/+ and Gpr119−/− mice, and (C) Glp2r+/+ and Glp2r−/− mice. Statistical analysis was assessed by ANOVA and paired t test (as appropriate); *, P < 0.05; **, P < 0.01.

FIG. 6

GPR119 activation increases plasma PYY but inhibits gastric emptying independent of the Y2R. Age-matched male mice were fasted overnight and oral AR231453 (20 mg/kg) or vehicle was administered 30 min before an oral glucose tolerance test (OGTT). Blood samples were collected 5 min after glucose for the measurement PYY plasma levels (A). For gastric emptying (B), 10-wk-old C57Bl6 male mice were fasted overnight. At time zero, a single ip dose of either vehicle (V1 = 1.2% DMSO in water) or BIIE0246 (2 mg/kg) was administered 15 min before a single oral dose of either vehicle (V2 = 80% PEG400, 10% Tween 80, and 10% ethanol) or AR231453 (20 mg/Kg). A solution of glucose (15%)-acetaminophen (1%) was administered orally 30 min later at a dose of 1.5 g/kg glucose-0.1 g/kg acetaminophen, and blood samples were collected at 15 and 45 min for assessment of plasma acetaminophen levels as described in Research Design and Methods. Rate of appearance of acetaminophen in plasma as determined by the AUC (B). Statistical analysis was assessed by t test and ANOVA; *, P < 0.05.