G protein-coupled receptor 119 (GPR119) is expressed in pancreatic islets and intestine, and is involved in insulin and incretin hormone release. GPR119-knockout (Gpr119−/−) mice were reported to have normal islet morphology and normal size, body weight (BW), and fed/fasted glucose levels. However, the physiological function of GPR119 and its role in maintaining glucose homeostasis under metabolic stress remain unknown. Here, we report the phenotypes of an independently generated line of Gpr119−/− mice under basal and high-fat diet (HFD)-induced obesity. Under low-fat diet feeding, Gpr119−/− mice show normal plasma glucose and lipids, but have lower BWs and lower post-prandial levels of active glucagon-like peptide 1 (GLP-1). Nutrient-stimulated GLP-1 release is attenuated in Gpr119−/− mice, suggesting that GPR119 plays a role in physiological regulation of GLP-1 secretion. Under HFD-feeding, both Gpr119+/+ and Gpr119−/− mice gain weight similarly, develop hyperinsulinemia and hyperleptinemia, but not hyperglycemia or dyslipidemia. Glucose and insulin tolerance tests did not reveal a genotypic difference. These data show that GPR119 is not essential for the maintenance of glucose homeostasis. Moreover, we found that oleoylethanolamide (OEA), reported as a ligand for GPR119, was able to suppress food intake in both Gpr119+/+ and Gpr119−/− mice, indicating that GPR119 is not required for the hypophagic effect of OEA. Our results demonstrate that GPR119 is important for incretin and insulin secretion, but not for appetite suppression.

OBJECTIVE-FFAR1/GPR40 is a G-protein-coupled receptor expressed predominantly in pancreatic islets mediating free fatty acid-induced insulin secretion. However, the physiological role of FFAR1 remains controversial. It was previously reported that FFAR1 knockout (Ffar1 Ϫ/Ϫ ) mice were resistant to high-fat diet-induced hyperinuslinemia, hyperglycemia, hypertriglyceridemia, and hepatic steatosis. A more recent report suggested that although FFAR1 was necessary for fatty acid-induced insulin secretion in vivo, deletion of FFAR1 did not protect pancreatic islets against fatty acid-induced islet dysfunction. This study is designed to investigate FFAR1 function in vivo using a third line of independently generated Ffar1 Ϫ/Ϫ mice in the C57BL/6 background.RESEARCH DESIGN AND METHODS-We used CL-316,243, a ␤3 adrenergic receptor agonist, to acutely elevate blood free fatty acids and to study its effect on insulin secretion in vivo. Ffar1ϩ/ϩ (wild-type) and Ffar1 Ϫ/Ϫ (knockout) mice were placed on two distinct high-fat diets to study their response to dietinduced obesity. RESULTS-Insulin secretion was reduced by ϳ50% in Ffar1Ϫ/Ϫ mice, confirming that FFAR1 contributes significantly to fatty acid stimulation of insulin secretion in vivo. However, Ffar1 ϩ/ϩ and Ffar1 Ϫ/Ϫ mice had similar weight, adiposity, and hyperinsulinemia on high-fat diets, and Ffar1 Ϫ/Ϫ mice showed no improvement in glucose or insulin tolerance tests. In addition, high-fat diet induced comparable levels of lipid accumulation in livers of Ffar1 ϩ/ϩ and Ffar1 Ϫ/Ϫ mice. CONCLUSIONS-FFAR1is required for normal insulin secretion in response to fatty acids; however, Ffar1 Ϫ/Ϫ mice are not protected from high-fat diet-induced insulin resistance or hepatic steatosis.

G-protein-coupled bile acid receptor 1 (GPBAR1/TGR5/ M-Bar/GPR131) is a cell surface receptor involved in the regulation of bile acid metabolism. We have previously shown that Gpbar1-null mice are resistant to cholesterol gallstone disease when fed a lithogenic diet. Other published studies have suggested that Gpbar1 is involved in both energy homeostasis and glucose homeostasis. Here, we examine the functional role of Gpbar1 in diet-induced obese mice. We found that body weight, food intake, and fasted blood glucose levels were similar between Gpbar1-null mice and their wild-type (WT) littermates when fed a chow or high-fat diet (HFD) for 2 months. However, insulin tolerance tests revealed improved insulin sensitivity in male Gpbar1 K/K mice fed chow, but impaired insulin sensitivity when fed a HFD. In contrast, female Gpbar1 K/K mice exhibited improved insulin sensitivity when fed a HFD compared with their WT littermates. Female Gpbar1 K/K mice had significantly lower plasma cholesterol and triglyceride levels than their WT littermates on both diets. Male Gpbar1 K/K mice on HFD displayed increased hepatic steatosis when compared with Gpbar1 C/C males and Gpbar1 K/K females on HFD. These results suggest a gender-dependent regulation of Gpbar1 function in metabolic disease.

FGF21 is a novel secreted protein with robust anti-diabetic, anti-obesity, and anti-atherogenic activities in preclinical species. In the current study, we investigated the signal transduction pathways downstream of FGF21 following acute administration of the growth factor to mice. Focusing on adipose tissues, we identified FGF21-mediated downstream signaling events and target engagement biomarkers. Specifically, RNA profiling of adipose tissues and phosphoproteomic profiling of adipocytes, following FGF21 treatment revealed several specific changes in gene expression and post-translational modifications, specifically phosphorylation, in several relevant proteins. Affymetrix microarray analysis of white adipose tissues isolated from both C57BL/6 (fed either regular chow or HFD) and db/db mice identified over 150 robust potential RNA transcripts and over 50 potential secreted proteins that were changed greater than 1.5 fold by FGF21 acutely. Phosphoprofiling analysis identified over 130 phosphoproteins that were modulated greater than 1.5 fold by FGF21 in 3T3-L1 adipocytes. Bioinformatic analysis of the combined gene and phosphoprotein profiling data identified a number of known metabolic pathways such as glucose uptake, insulin receptor signaling, Erk/Mapk signaling cascades, and lipid metabolism. Moreover, a number of novel events with hitherto unknown links to FGF21 signaling were observed at both the transcription and protein phosphorylation levels following treatment. We conclude that such a combined "omics" approach can be used not only to identify robust biomarkers for novel therapeutics but can also enhance our understanding of downstream signaling pathways; in the example presented here, novel FGF21-mediated signaling events in adipose tissue have been revealed that warrant further investigation.

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