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Diacylglycerol kinase ? couples farnesoid X receptor-dependent bile acid signalling to Akt activation and glucose homoeostasis in hepatocytes.

ABSTRACT: DGKs (diacylglycerol kinases) catalyse the conversion of diacylglycerol into PA (phosphatidic acid), a positive modulator of mTOR (mammalian target of rapamycin). We have found that chenodeoxycholic acid and the synthetic FXR (farnesoid X receptor) ligand GW4064 induce the mRNA and protein expression of DGK? in the HepG2 cell line and in primary human hepatocytes. Reporter gene studies using 1.5 kB of the DGK? promoter fused to the luciferase gene revealed that bile acids increase DGK? transcriptional activity. Mutation of putative FXR-binding sites attenuated the ability of GW4046 to increase DGK? luciferase activity. Consistent with this finding, ChIP (chromatin immunoprecipitation) assays demonstrated that bile acid signalling increased the recruitment of FXR to the DGK? promoter. Furthermore, GW4064 evoked a time-dependent increase in the cellular concentration of PA. We also found that GW4064 and PA promote the phosphorylation of mTOR, Akt and FoxO1 (forkhead box O1), and that silencing DGK? expression significantly abrogated the ability of GW4046 to promote the phosphorylation of these PA-regulated targets. DGK? was also required for bile-acid-dependent decreased glucose production. Taken together, our results establish DGK? as a key mediator of bile-acid-stimulated modulation of mTORC2 (mTOR complex 2), the Akt pathway and glucose homoeostasis.

SUBMITTER: Cai K

PROVIDER: S-EPMC3976421 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Diacylglycerol kinase θ couples farnesoid X receptor-dependent bile acid signalling to Akt activation and glucose homoeostasis in hepatocytes.

Cai Kai K Sewer Marion B MB

The Biochemical journal 20130901 2

DGKs (diacylglycerol kinases) catalyse the conversion of diacylglycerol into PA (phosphatidic acid), a positive modulator of mTOR (mammalian target of rapamycin). We have found that chenodeoxycholic acid and the synthetic FXR (farnesoid X receptor) ligand GW4064 induce the mRNA and protein expression of DGKθ in the HepG2 cell line and in primary human hepatocytes. Reporter gene studies using 1.5 kB of the DGKθ promoter fused to the luciferase gene revealed that bile acids increase DGKθ transcrip ...[more]

PMID: 23767959

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Project description:Background and aim: Diacylglycerol kinase (DGK) isoforms catalyze an enzymatic reaction that removes diacylglycerol (DAG) and thereby terminates protein kinase C (PKC) signaling by converting DAG to phosphatidic acid (PA). We have reported that downregulation of DGKδ (type II isozyme) causes peripheral insulin resistance, metabolic inflexibility, and obesity. Our aim was to determine whether overexpression of DGKδ protects against the development of metabolic impairments and obesity. Methods: We generated a transgenic mouse model overexpressing the human DGKδ2 isoform under the myosin light change promoter (DGKδ TG). We performed deep metabolic phenotyping of DGKδ TG and wild-type mice fed chow or high-fat diet. Mice were also given free access to running wheels to examine the effects of DGKδ overexpression on exercise-induced metabolic outcomes. Results: DGKδ TG mice were leaner than wild-type littermates, with improved glucose tolerance, increased glycogen storage in skeletal muscle, and enhanced glucose uptake in white adipose tissue. Moreover, DGKδ TG mice were protected against high fat diet (HFD)-induced glucose intolerance and obesity. DGKδ TG mice had reduced epididymal fat pad weight, and enhanced lipolysis. Strikingly, DGKδ overexpression recapitulates the beneficial effects exercise on metabolic outcomes. DGKδ overexpression and exercise have a synergistic effect on body weight reduction. Microarray analysis of skeletal muscle confirmed an overlap between genes associated with exercise and DGKδ overexpression. Gene ontology signatures of exercise and DGKδ overexpression were related to lipid storage, extracellular matrix, and glycogen biosynthesis pathways. Conclusion: We identify a role for DGKδ in glucose and energy homeostasis. Overexpression of DGKδ induces adaptive changes in both skeletal muscle and adipose tissue, resulting in protection against high fat diet-induced obesity. DGKδ overexpression recapitulates exercise-induced adaptations on energy homeostasis and skeletal muscle gene expression profiles.

Project description:INTRODUCTION:Bile acid (BA) biotransformation by gut bacteria impacts BA profile and signaling to nuclear receptors, such as the farnesoid X receptor (FXR) regulating glucose metabolism. Altered BA-FXR signaling was therefore investigated as a potential mechanism linking polyphenol-induced gut bacterial changes and improved glucose metabolism. RESEARCH DESIGN AND METHODS:Diabetic db/db were fed low-fat diet (LFD) or LFD supplemented with a proanthocyanidin-rich extract of grape polyphenols (LFD-GP) for 4 weeks. Metabolic phenotypes, serum BAs, gut microbiota composition, and gene expression markers relevant to gut barrier and glucose metabolism were assessed. Gut organoids were used to investigate effects of individual BAs on ileal FXR activity. RESULTS:Compared with LFD-fed controls, GP supplemented db/db mice showed improved glucose metabolism, decreased relative abundance of gut bacteria associated with production of secondary BAs (SBAs), and depleted serum levels of SBAs taurohyodeoxycholic acid (THDCA), ?-muricholic acid (?MCA), and tauro-?-muricholic acid (T?MCA). Serum levels of primary BAs (PBAs) increased, consistent with higher gene expression of PBA synthesis enzyme Cyp7a1. GP-induced BA changes associated with FXR inhibition as evidenced by reduced expression of FXR-responsive genes Shp, Fgf15, and Fabp6 in ileum tissue as well as hepatic Shp, which negatively regulates PBA synthesis. GP treatment did not affect expression of hepatic Fxr or expression of Abcb11, Slc51b, and Obp2a genes controlling BA transport. Ceramide biosynthesis genes Smpd3, Sptlc2, and Cers4 were decreased in liver and intestine suggesting lower tissue ceramides levels may contribute to improved glucose metabolism. THDCA, ?MCA, and T?MCA behaved as FXR agonists in ileal organoid experiments; therefore, their depletion in serum of GP-supplemented db/db and wild type (WT) mice was consistent with FXR inhibition. CONCLUSION:These data suggest that by altering the gut microbiota, GPs modify BA-FXR signaling pathways to promote glucoregulation.

Dataset Information

Diacylglycerol kinase ? couples farnesoid X receptor-dependent bile acid signalling to Akt activation and glucose homoeostasis in hepatocytes.

Publications

Diacylglycerol kinase θ couples farnesoid X receptor-dependent bile acid signalling to Akt activation and glucose homoeostasis in hepatocytes.

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