Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by act... more Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by activating the nuclear bile acid receptor farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor-1 (aka takeda G protein couple receptor 5, TGR5) signaling. Paradoxical roles of FXR in the regulation of glucose and lipid metabolism and metabolic disorder have been reported recently. The activation or inhibition of intestinal FXR signaling has been shown to improve insulin and glucose sensitivity and energy metabolism to prevent diabetes, obesity and non-alcoholic fatty liver disease (NAFLD). TGR5 has an anti-inflammatory function in the intestine and stimulates glucagon-like peptide-1 (GLP-1) secretion in the intestine to stimulate insulin secretion from the pancreas. The role of TGR5 in metabolism and metabolic regulation is not clear and warrants further study. FXR and TGR5 are co-expressed in the ileum and colon. These 2 bile acid–activated receptors may cooperate t...
ObjectivesTRPV1 channels have been linked to the development and progression of diabetes at multi... more ObjectivesTRPV1 channels have been linked to the development and progression of diabetes at multiple levels, including control of appetite and weight, regulation of pancreatic function, thermogenesis, metabolism and energy homeostasis. Despite this, little information is known regarding its role in liver homeostasis and nonalcoholic fatty liver disease (NAFLD).Methods and ResultsTo better understand the role of TRPV1 in liver metabolism, we explored the effects of a high fat/sugar diet (Western, 24-week regimen) in male and female wild type (WT) and TRPV1-null (V1KO) mice. Our data reveal that loss of the TRPV1 gene makes mice susceptible to diet-induced obesity and induces NAFLD. V1KO mice displayed gross phenotypic and gross morphological changes including insulin resistance, glucose intolerance, increased body mass and central adiposity on a western diet compared to WT counterparts. Western fed V1KO mice exhibited gross changes in liver morphology and size compared to western fed...
Sterol 12α-hydroxylase (CYP8B1) is required for the synthesis of cholic acid in the classic bile ... more Sterol 12α-hydroxylase (CYP8B1) is required for the synthesis of cholic acid in the classic bile acid synthesis pathway and plays a role in dyslipidemia and insulin resistance. However, the mechanism of the involvement of Cyp8b1 in dyslipidemia and insulin resistance is not known. CYP8B1 mRNA and protein expression are elevated in diabetic and obese (db/db) mouse liver. In this study adenovirus-mediated transduction of CYP8B1 was used to study the effect of Cyp8b1 on lipid metabolism in mice. Results show that Ad-Cyp8b1 increased 12α-hydroxylated bile acids and induced sterol regulatory element-binding protein 1c (Srebp-1c)-mediated lipogenic gene expression. Interestingly, Ad-Cyp8b1 increased ceramide synthesis and activated hepatic mechanistic target of rapamycin complex 1 (mTORC1)-p70S6K signaling cascade and inhibited AKT/insulin signaling in mice. Ad-Cyp8b1 increased free fatty acid uptake into mouse primary hepatocytes. Ceramides stimulated S6K phosphorylation in both mouse an...
Bile acids activate farnesoid X receptor (FXR) and G protein-coupled bile acid receptor-1 (Gpbar-... more Bile acids activate farnesoid X receptor (FXR) and G protein-coupled bile acid receptor-1 (Gpbar-1, aka TGR5) to regulate bile acid metabolism and glucose and insulin sensitivity. FXR and TGR5 are co-expressed in the enteroendocrine L cells but their roles in integrated regulation of metabolism are not completely understood. We reported recently that activation of FXR induces TGR5 to stimulate glucagon-like peptide-1 (GLP-1) secretion to improve insulin sensitivity and hepatic metabolism. In this study, we used the intestine-restricted FXR agonist fexaramine (FEX) to study the effect of activation of intestinal FXR on the gut microbiome, bile acid metabolism, and FXR and TGR5 signaling. The current study revealed that FEX markedly increased taurolithocholic acid (TLCA), increased fibroblast growth factor 15 (FGF15) and FGF21 and GLP-1 secretion, improved insulin and glucose tolerance, and promoted white adipose tissue browning in mice. Analysis of 16S ribosomal RNA sequences of the ...
Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by act... more Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by activating the nuclear bile acid receptor farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor-1 (aka takeda G protein couple receptor 5, TGR5) signaling. Paradoxical roles of FXR in the regulation of glucose and lipid metabolism and metabolic disorder have been reported recently. The activation or inhibition of intestinal FXR signaling has been shown to improve insulin and glucose sensitivity and energy metabolism to prevent diabetes, obesity and non-alcoholic fatty liver disease (NAFLD). TGR5 has an anti-inflammatory function in the intestine and stimulates glucagon-like peptide-1 (GLP-1) secretion in the intestine to stimulate insulin secretion from the pancreas. The role of TGR5 in metabolism and metabolic regulation is not clear and warrants further study. FXR and TGR5 are co-expressed in the ileum and colon. These 2 bile acid-activated receptors may cooperate t...
The bile acid-activated receptors, nuclear farnesoid X receptor (FXR) and the membrane Takeda G-p... more The bile acid-activated receptors, nuclear farnesoid X receptor (FXR) and the membrane Takeda G-protein receptor 5 (TGR5), are known to improve glucose and insulin sensitivity in obese and diabetic mice. However, the metabolic roles of these two receptors and the underlying mechanisms are incompletely understood. Here we studied the effects of the dual FXR and TGR5 agonist INT-767 on hepatic bile acid synthesis and intestinal secretion of glucagon-like peptide-1 (GLP-1) in wild type, Fxr(-/-), and Tgr5(-/-) mice. INT-767 efficaciously stimulated intracellular Ca(2+) levels, cAMP activity, and GLP-1 secretion and improved glucose and lipid metabolism more than did the FXR-selective obeticholic acid and TGR5-selective INT-777 agonists. Interestingly, INT-767 reduced expression of the genes in the classic bile acid synthesis pathway but induced those in the alternative pathway, which is consistent with decreased tauro-cholic acid and increased tauro-muricholic acids in bile. Furthermor...
Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by act... more Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by activating the nuclear bile acid receptor farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor-1 (aka takeda G protein couple receptor 5, TGR5) signaling. Paradoxical roles of FXR in the regulation of glucose and lipid metabolism and metabolic disorder have been reported recently. The activation or inhibition of intestinal FXR signaling has been shown to improve insulin and glucose sensitivity and energy metabolism to prevent diabetes, obesity and non-alcoholic fatty liver disease (NAFLD). TGR5 has an anti-inflammatory function in the intestine and stimulates glucagon-like peptide-1 (GLP-1) secretion in the intestine to stimulate insulin secretion from the pancreas. The role of TGR5 in metabolism and metabolic regulation is not clear and warrants further study. FXR and TGR5 are co-expressed in the ileum and colon. These 2 bile acid–activated receptors may cooperate t...
ObjectivesTRPV1 channels have been linked to the development and progression of diabetes at multi... more ObjectivesTRPV1 channels have been linked to the development and progression of diabetes at multiple levels, including control of appetite and weight, regulation of pancreatic function, thermogenesis, metabolism and energy homeostasis. Despite this, little information is known regarding its role in liver homeostasis and nonalcoholic fatty liver disease (NAFLD).Methods and ResultsTo better understand the role of TRPV1 in liver metabolism, we explored the effects of a high fat/sugar diet (Western, 24-week regimen) in male and female wild type (WT) and TRPV1-null (V1KO) mice. Our data reveal that loss of the TRPV1 gene makes mice susceptible to diet-induced obesity and induces NAFLD. V1KO mice displayed gross phenotypic and gross morphological changes including insulin resistance, glucose intolerance, increased body mass and central adiposity on a western diet compared to WT counterparts. Western fed V1KO mice exhibited gross changes in liver morphology and size compared to western fed...
Sterol 12α-hydroxylase (CYP8B1) is required for the synthesis of cholic acid in the classic bile ... more Sterol 12α-hydroxylase (CYP8B1) is required for the synthesis of cholic acid in the classic bile acid synthesis pathway and plays a role in dyslipidemia and insulin resistance. However, the mechanism of the involvement of Cyp8b1 in dyslipidemia and insulin resistance is not known. CYP8B1 mRNA and protein expression are elevated in diabetic and obese (db/db) mouse liver. In this study adenovirus-mediated transduction of CYP8B1 was used to study the effect of Cyp8b1 on lipid metabolism in mice. Results show that Ad-Cyp8b1 increased 12α-hydroxylated bile acids and induced sterol regulatory element-binding protein 1c (Srebp-1c)-mediated lipogenic gene expression. Interestingly, Ad-Cyp8b1 increased ceramide synthesis and activated hepatic mechanistic target of rapamycin complex 1 (mTORC1)-p70S6K signaling cascade and inhibited AKT/insulin signaling in mice. Ad-Cyp8b1 increased free fatty acid uptake into mouse primary hepatocytes. Ceramides stimulated S6K phosphorylation in both mouse an...
Bile acids activate farnesoid X receptor (FXR) and G protein-coupled bile acid receptor-1 (Gpbar-... more Bile acids activate farnesoid X receptor (FXR) and G protein-coupled bile acid receptor-1 (Gpbar-1, aka TGR5) to regulate bile acid metabolism and glucose and insulin sensitivity. FXR and TGR5 are co-expressed in the enteroendocrine L cells but their roles in integrated regulation of metabolism are not completely understood. We reported recently that activation of FXR induces TGR5 to stimulate glucagon-like peptide-1 (GLP-1) secretion to improve insulin sensitivity and hepatic metabolism. In this study, we used the intestine-restricted FXR agonist fexaramine (FEX) to study the effect of activation of intestinal FXR on the gut microbiome, bile acid metabolism, and FXR and TGR5 signaling. The current study revealed that FEX markedly increased taurolithocholic acid (TLCA), increased fibroblast growth factor 15 (FGF15) and FGF21 and GLP-1 secretion, improved insulin and glucose tolerance, and promoted white adipose tissue browning in mice. Analysis of 16S ribosomal RNA sequences of the ...
Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by act... more Bile acids play a critical role in the regulation of glucose, lipid and energy metabolisms by activating the nuclear bile acid receptor farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor-1 (aka takeda G protein couple receptor 5, TGR5) signaling. Paradoxical roles of FXR in the regulation of glucose and lipid metabolism and metabolic disorder have been reported recently. The activation or inhibition of intestinal FXR signaling has been shown to improve insulin and glucose sensitivity and energy metabolism to prevent diabetes, obesity and non-alcoholic fatty liver disease (NAFLD). TGR5 has an anti-inflammatory function in the intestine and stimulates glucagon-like peptide-1 (GLP-1) secretion in the intestine to stimulate insulin secretion from the pancreas. The role of TGR5 in metabolism and metabolic regulation is not clear and warrants further study. FXR and TGR5 are co-expressed in the ileum and colon. These 2 bile acid-activated receptors may cooperate t...
The bile acid-activated receptors, nuclear farnesoid X receptor (FXR) and the membrane Takeda G-p... more The bile acid-activated receptors, nuclear farnesoid X receptor (FXR) and the membrane Takeda G-protein receptor 5 (TGR5), are known to improve glucose and insulin sensitivity in obese and diabetic mice. However, the metabolic roles of these two receptors and the underlying mechanisms are incompletely understood. Here we studied the effects of the dual FXR and TGR5 agonist INT-767 on hepatic bile acid synthesis and intestinal secretion of glucagon-like peptide-1 (GLP-1) in wild type, Fxr(-/-), and Tgr5(-/-) mice. INT-767 efficaciously stimulated intracellular Ca(2+) levels, cAMP activity, and GLP-1 secretion and improved glucose and lipid metabolism more than did the FXR-selective obeticholic acid and TGR5-selective INT-777 agonists. Interestingly, INT-767 reduced expression of the genes in the classic bile acid synthesis pathway but induced those in the alternative pathway, which is consistent with decreased tauro-cholic acid and increased tauro-muricholic acids in bile. Furthermor...
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