CREB-Regulated Transcriptional Coactivator 2 Proteome Landscape is Modulated by SREBF1

cAMP response element-binding protein (CREB) regulated transcriptional coactivator 2 (CRTC2) is a critical transcription factor that maintains glucose homeostasis by activating CREB. Energy homeostasis is maintained through multiple pathways; therefore, CRTC2 may interact with other transcription factors, particularly under metabolic stress. CRTC2 liver-specific KO mice were created, and the global proteome, phosphoproteome, and acetylome from liver tissue under high-fat diet conditions were analyzed using liquid chromatography-tandem mass spectrometry and bioinformatics analysis. Differentially regulated proteins (DRPs) were enriched in metabolic pathways, which were subsequently corroborated through animal experiments. The consensus DRPs from these datasets were used as seed proteins to generate a protein-protein interaction network using STRING, and GeneMANIA identified fatty acid synthase as a mutually relevant protein. In an additional local-protein-protein interaction analysis of CRTC2 and fatty acid synthase with DRPs, sterol regulatory element binding transcription factor 1 (SREBF1) was the common mediator. CRTC2-CREB and SREBF1 are transcription factors, and DNA-binding motif analysis showed that multiple CRTC2-CREB-regulated genes possess SREBF1-binding motifs. This indicates the possible induction by the CRTC2-SREBF1 complex, which is validated through luciferase assay. Therefore, the CRTC2-SREBF1 complex potentially modulates the transcription of multiple proteins that fine-tune cellular metabolism under metabolic stress.

Impaired BCAA catabolism in adipose tissues promotes age-associated metabolic derangement

Adipose tissues are central in controlling metabolic homeostasis and failure in their preservation is associated with age-related metabolic disorders. The exact role of mature adipocytes in this phenomenon remains elusive. Here we describe the role of adipose branched-chain amino acid (BCAA) catabolism in this process. We found that adipocyte-specific Crtc2 knockout protected mice from age-associated metabolic decline. Multiomics analysis revealed that BCAA catabolism was impaired in aged visceral adipose tissues, leading to the activation of mechanistic target of rapamycin complex (mTORC1) signaling and the resultant cellular senescence, which was restored by Crtc2 knockout in adipocytes. Using single-cell RNA sequencing analysis, we found that age-associated decline in adipogenic potential of visceral adipose tissues was reinstated by Crtc2 knockout, via the reduction of BCAA-mTORC1 senescence-associated secretory phenotype axis. Collectively, we propose that perturbation of BCAA catabolism by CRTC2 is critical in instigating age-associated remodeling of adipose tissue and the resultant metabolic decline in vivo.

Peli3 ablation ameliorates acetaminophen-induced liver injury through inhibition of GSK3β phosphorylation and mitochondrial translocation

The signaling pathways governing acetaminophen (APAP)-induced liver injury have been extensively studied. However, little is known about the ubiquitin-modifying enzymes needed for the regulation of APAP-induced liver injury. Here, we examined whether the Pellino3 protein, which has E3 ligase activity, is needed for APAP-induced liver injury and subsequently explored its molecular mechanism. Whole-body Peli3-/- knockout (KO) and adenovirus-mediated Peli3 knockdown (KD) mice showed reduced levels of centrilobular cell death, infiltration of immune cells, and biomarkers of liver injury, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), upon APAP treatment compared to wild-type (WT) mice. Peli3 deficiency in primary hepatocytes decreased mitochondrial and lysosomal damage and reduced the mitochondrial reactive oxygen species (ROS) levels. In addition, the levels of phosphorylation at serine 9 in the cytoplasm and mitochondrial translocation of GSK3β were decreased in primary hepatocytes obtained from Peli3-/- KO mice, and these reductions were accompanied by decreases in JNK phosphorylation and mitochondrial translocation. Pellino3 bound more strongly to GSK3β compared with JNK1 and JNK2 and induced the lysine 63 (K63)-mediated polyubiquitination of GSK3β. In rescue experiments, the ectopic expression of wild-type Pellino3 in Peli3-/- KO hepatocytes restored the mitochondrial translocation of GSK3β, but this restoration was not obtained with expression of a catalytically inactive mutant of Pellino3. These findings are the first to suggest a mechanistic link between Pellino3 and APAP-induced liver injury through the modulation of GSK3β polyubiquitination.

Tcf7l2 in hepatocytes regulates de novo lipogenesis in diet-induced non-alcoholic fatty liver disease in mice

AIMS/HYPOTHESIS

Non-alcoholic fatty liver disease (NAFLD) associated with type 2 diabetes may more easily progress towards severe forms of non-alcoholic steatohepatitis (NASH) and cirrhosis. Although the Wnt effector transcription factor 7-like 2 (TCF7L2) is closely associated with type 2 diabetes risk, the role of TCF7L2 in NAFLD development remains unclear. Here, we investigated how changes in TCF7L2 expression in the liver affects hepatic lipid metabolism based on the major risk factors of NAFLD development.

METHODS

Tcf7l2 was selectively ablated in the liver of C57BL/6N mice by inducing the albumin (Alb) promoter to recombine Tcf7l2 alleles floxed at exon 5 (liver-specific Tcf7l2-knockout [KO] mice: Alb-Cre;Tcf7l2f/f). Alb-Cre;Tcf7l2f/f and their wild-type (Tcf7l2f/f) littermates were fed a high-fat diet (HFD) or a high-carbohydrate diet (HCD) for 22 weeks to reproduce NAFLD/NASH. Mice were refed a standard chow diet or an HCD to stimulate de novo lipogenesis (DNL) or fed an HFD to provide exogenous fatty acids. We analysed glucose and insulin sensitivity, metabolic respiration, mRNA expression profiles, hepatic triglyceride (TG), hepatic DNL, selected hepatic metabolites, selected plasma metabolites and liver histology.

RESULTS

Alb-Cre;Tcf7l2f/f essentially exhibited increased lipogenic genes, but there were no changes in hepatic lipid content in mice fed a normal chow diet. However, following 22 weeks of diet-induced NAFLD/NASH conditions, liver steatosis was exacerbated owing to preferential metabolism of carbohydrate over fat. Indeed, hepatic Tcf7l2 deficiency enhanced liver lipid content in a manner that was dependent on the duration and amount of exposure to carbohydrates, owing to cell-autonomous increases in hepatic DNL. Mechanistically, TCF7L2 regulated the transcriptional activity of Mlxipl (also known as ChREBP) by modulating O-GlcNAcylation and protein content of carbohydrate response element binding protein (ChREBP), and targeted Srebf1 (also called SREBP1) via miRNA (miR)-33-5p in hepatocytes. Eventually, restoring TCF7L2 expression at the physiological level in the liver of Alb-Cre;Tcf7l2f/f mice alleviated liver steatosis without altering body composition under both acute and chronic HCD conditions.

CONCLUSIONS/INTERPRETATION

In mice, loss of hepatic Tcf7l2 contributes to liver steatosis by inducing preferential metabolism of carbohydrates via DNL activation. Therefore, TCF7L2 could be a promising regulator of the NAFLD associated with high-carbohydrate diets and diabetes since TCF7L2 deficiency may lead to development of NAFLD by promoting utilisation of excess glucose pools through activating DNL.

DATA AVAILABILITY

RNA-sequencing data have been deposited into the NCBI GEO under the accession number GSE162449 ( www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE162449 ).

Involvement of a novel cAMP signaling mediator for beige adipogenesis

BACKGROUND

Exposure to cold temperature stimulates the sympathetic nervous system that activates β-adrenergic receptor signals in brown and beige adipocytes, leading to the induction of adaptive thermogenesis in mammals. Prominin-1 (PROM1) is a pentaspan transmembrane protein that is widely identified as a marker for stem cells, although the role of this protein as a regulator of many intracellular signaling cascades has been recently delineated. The main focus of the current study is to identify the previously unknown role of PROM1 in beige adipogenesis and adaptive thermogenesis.

METHODS

Prom1 whole body knockout (Prom1 KO) mice, Prom1 adipogenic progenitor (AP) cell-specific knockout (Prom1 APKO) mice and Prom1 adipocyte-specific knockout (Prom1 AKO) mice were constructed and were subject for the induction of adaptive thermogenesis. The effect of systemic Prom1 depletion was evaluated by hematoxylin and eosin staining, immunostaining, and biochemical analysis in vivo. Flow cytometric analysis was performed to determine the identity of PROM1-expressing cell types, and the resultant cells were subject to beige adipogenesis in vitro. The potential role of PROM1 and ERM in cAMP signaling was also assessed in undifferentiated AP cells in vitro. Finally, the specific effect of Prom1 depletion on AP cell or mature adipocytes on adaptive thermogenesis was evaluated by hematoxylin and eosin staining, immunostaining, and biochemical analysis in vivo.

RESULTS

Prom1 KO mice displayed an impairment in cold- or β3-adrenergic agonist-induced adaptive thermogenesis in subcutaneous adipose tissues (SAT) but not in brown adipose tissues (BAT). By fluorescence-activated cell sorting (FACS) analysis, we identified that PROM1 positive cells are enriched in PDGFRα⁺Sca1⁺ AP cells from SAT. Interestingly, Prom1 knockout stromal vascular fractions showed reduced PDGFRα expression, suggesting a role of PROM1 in beige adipogenic potential. Indeed, we found that Prom1-deficient AP cells from SAT showed reduced potential for beige adipogenesis. Furthermore, AP cell-specific depletion of Prom1, but not adipocyte-specific depletion of Prom1, displayed defects in adaptive thermogenesis as evidenced by resistance to cold-induced browning of SAT and dampened energy expenditure in mice.

CONCLUSION

We found that PROM1 positive AP cells are essential for the adaptive thermogenesis by ensuing stress-induced beige adipogenesis. Identification of PROM1 ligand might be useful in the activation of thermogenesis that could be potentially beneficial in combating obesity.

Hepatocyte-specific Prominin-1 protects against liver injury-induced fibrosis by stabilizing SMAD7

Prominin-1 (PROM1), also known as CD133, is expressed in hepatic progenitor cells (HPCs) and cholangiocytes of the fibrotic liver. In this study, we show that PROM1 is upregulated in the plasma membrane of fibrotic hepatocytes. Hepatocellular expression of PROM1 was also demonstrated in mice (Prom1^CreER; R26^TdTom) in which cells expressed TdTom under control of the Prom1 promoter. To understand the role of hepatocellular PROM1 in liver fibrosis, global and liver-specific Prom1-deficient mice were analyzed after bile duct ligation (BDL). BDL-induced liver fibrosis was aggravated with increased phosphorylation of SMAD2/3 and decreased levels of SMAD7 by global or liver-specific Prom1 deficiency but not by cholangiocyte-specific Prom1 deficiency. Indeed, PROM1 prevented SMURF2-induced SMAD7 ubiquitination and degradation by interfering with the molecular association of SMAD7 with SMURF2. We also demonstrated that hepatocyte-specific overexpression of SMAD7 ameliorated BDL-induced liver fibrosis in liver-specific Prom1-deficient mice. Thus, we conclude that PROM1 is necessary for the negative regulation of TGFβ signaling during liver fibrosis.

A novel role of CRTC2 in promoting nonalcoholic fatty liver disease

OBJECTIVE

Diet-induced obesity is often associated with nonalcoholic fatty liver disease (NAFLD), which instigates severe metabolic disorders, including cirrhosis, hepatocellular carcinoma, and type 2 diabetes. We have shown that hepatic depletion of CREB regulated transcription co-activator (CRTC) 2 protects mice from the progression of diet-induced fatty liver phenotype, although the exact mechanism by which CRTC2 modulates this process is elusive to date. Here, we investigated the role of hepatic CRTC2 in the instigation of NAFLD in mammals.

METHODS

Crtc2 liver-specific knockout (Crtc2 LKO) mice and Crtc2 flox/flox (Crtc2 f/f) mice were fed a high fat diet (HFD) for 7-8 weeks. Body weight, liver weight, hepatic lipid contents, and plasma triacylglycerol (TG) levels were determined. Western blot analysis was performed to determine Sirtuin (SIRT) 1, tuberous sclerosis complex (TSC) 2, and mammalian target of rapamycin complex (mTORC) 1 activity in the liver. Effects of Crtc2 depletion on lipogenesis was determined by measuring lipogenic gene expression (western blot analysis and qRT-PCR) in the liver as well as Oil red O staining in hepatocytes. Effects of miR-34a on mTORC1 activity and hepatic lipid accumulation was assessed by AAV-miR-34a virus in mice and Ad-miR-34a virus and Ad-anti-miR-34a virus in hepatocytes. Autophagic flux was assessed by western blot analysis after leupeptin injection in mice and bafilomycin treatment in hepatocytes. Lipophagy was assessed by transmission electron microscopy and confocal microscopy. Expression of CRTC2 and p-S6K1 in livers of human NAFLD patients was assessed by immunohistochemistry.

RESULTS

We found that expression of CRTC2 in the liver is highly induced upon HFD-feeding in mice. Hepatic depletion of Crtc2 ameliorated HFD-induced fatty liver disease phenotypes, with a pronounced inhibition of the mTORC1 pathway in the liver. Mechanistically, we found that expression of TSC2, a potent mTORC1 inhibitor, was enhanced in Crtc2 LKO mice due to the decreased expression of miR-34a and the subsequent increase in SIRT1-mediated deacetylation processes. We showed that ectopic expression of miR-34a led to the induction of mTORC1 pathway, leading to the hepatic lipid accumulation in part by limiting lipophagy and enhanced lipogenesis. Finally, we found a strong association of CRTC2, miR-34a and mTORC1 activity in the NAFLD patients in humans, demonstrating a conservation of signaling pathways among species.

CONCLUSIONS

These data collectively suggest that diet-induced activation of CRTC2 instigates the progression of NAFLD by activating miR-34a-mediated lipid accumulation in the liver via the simultaneous induction of lipogenesis and inhibition of lipid catabolism. Therapeutic approach to specifically inhibit CRTC2 activity in the liver could be beneficial in combating NAFLD in the future.

Liver-Specific Deletion of Mouse CTCF Leads to Hepatic Steatosis via Augmented PPARγ Signaling

BACKGROUND & AIMS

The liver is the major organ for metabolizing lipids, and malfunction of the liver leads to various diseases. Nonalcoholic fatty liver disease is rapidly becoming a major health concern worldwide and is characterized by abnormal retention of excess lipids in the liver. CCCTC-binding factor (CTCF) is a highly conserved zinc finger protein that regulates higher-order chromatin organization and is involved in various gene regulation processes. Here, we sought to determine the physiological role of CTCF in hepatic lipid metabolism.

METHODS

We generated liver-specific, CTCF-ablated and/or CD36 whole-body knockout mice. Overexpression or knockdown of peroxisome proliferator-activated receptor (PPAR)γ in the liver was achieved using adenovirus. Mice were examined for development of hepatic steatosis and inflammation. RNA sequencing was performed to identify genes affected by CTCF depletion. Genome-wide occupancy of H3K27 acetylation, PPARγ, and CTCF were analyzed by chromatin immunoprecipitation sequencing. Genome-wide chromatin interactions were analyzed by in situ Hi-C.

RESULTS

Liver-specific, CTCF-deficient mice developed hepatic steatosis and inflammation when fed a standard chow diet. Global analysis of the transcriptome and enhancer landscape revealed that CTCF-depleted liver showed enhanced accumulation of PPARγ in the nucleus, which leads to increased expression of its downstream target genes, including fat storage-related gene CD36, which is involved in the lipid metabolic process. Hepatic steatosis developed in liver-specific, CTCF-deficient mice was ameliorated by repression of PPARγ via pharmacologic blockade or adenovirus-mediated knockdown, but hardly rescued by additional knockout of CD36.

CONCLUSIONS

Our data indicate that liver-specific deletion of CTCF leads to hepatosteatosis through augmented PPARγ DNA-binding activity, which up-regulates its downstream target genes associated with the lipid metabolic process.

Depletion of Prmt1 in Adipocytes Impairs Glucose Homeostasis in Diet-Induced Obesity

Protein arginine methyltransferase (PRMT) 1 is involved in the regulation of various metabolic pathways such as glucose metabolism in liver and atrophy in the skeletal muscle. However, the role of PRMT1 in the fat tissues under the disease state has not been elucidated to date. In this study, we delineate the function of this protein in adipocytes in vivo. PRMT1 expression was abundant in the white adipose tissues (WAT), which was induced upon a high-fat diet in mice and by obesity in humans. We found that adipocyte-specific depletion of Prmt1 resulted in decreased fat mass without overall changes in body weight in mice. Mechanistically, the depletion of Prmt1 in WAT led to the activation of the AMPK pathway, which was causal to the increased lipophagy, mitochondrial lipid catabolism, and the resultant reduction in lipid droplet size in WAT in vivo. Interestingly, despite the increased energy expenditure, we observed a promotion of adipose tissue inflammation and an ectopic accumulation of triglycerides in the peripheral tissues in Prmt1 adipocyte-specific knockout mice, which promoted the impaired insulin tolerance that is reminiscent of mouse models of lipodystrophy. These data collectively suggest that PRMT1 prevents WAT from excessive degradation of triglycerides by limiting AMPK-mediated lipid catabolism to control whole-body metabolic homeostasis in diet-induced obesity conditions.

Results from the Survey of Antibiotic Resistance (SOAR) 2016-18 in Vietnam, Cambodia, Singapore and the Philippines: data based on CLSI, EUCAST (dose-specific) and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints

OBJECTIVES

To determine antibiotic susceptibility of Streptococcus pneumoniae and Haemophilus influenzae isolates collected from community-acquired respiratory tract infections (CA-RTIs) in 2016-18 in four Asian countries.

METHODS

MICs were determined by CLSI broth microdilution and susceptibility was assessed using CLSI, EUCAST (dose-specific) and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints.

RESULTS

In total, 260 S. pneumoniae and 258 H. influenzae isolates were tested. Pneumococci from Vietnam (n = 161) were the least susceptible, with rates of susceptibility >90% for fluoroquinolones by CLSI breakpoints, ∼60% for amoxicillin, amoxicillin/clavulanic acid and ceftriaxone but <14% for most other agents. Pneumococcal isolates from Cambodia (n = 48) and Singapore (n = 34) showed susceptibilities ranging from ∼30% for trimethoprim/sulfamethoxazole and oral penicillin to 100% for fluoroquinolones. Among isolates of H. influenzae from Cambodia (n = 30), the Philippines (n = 59) and Singapore (n = 80), rates of susceptibility using CLSI breakpoints were >90% for amoxicillin/clavulanic acid, cephalosporins [except cefaclor in Singapore (77.5%)], macrolides and fluoroquinolones; for isolates from Vietnam (n = 89) the rates of susceptibility were >85% only for amoxicillin/clavulanic acid (95.5%), ceftriaxone (100%) and macrolides (87.6%-89.9%). Susceptibility to other antibiotics ranged from 7.9% (trimethoprim/sulfamethoxazole) to 57.3%-59.6% (fluoroquinolones) and 70.8% (cefixime). The application of different EUCAST breakpoints for low and higher doses for some of the antibiotics (amoxicillin, amoxicillin/clavulanic acid, ampicillin, penicillin, ceftriaxone, clarithromycin, erythromycin, levofloxacin and trimethoprim/sulfamethoxazole) allowed, for the first time in a SOAR study, the effect of raising the dosage on susceptibility to be quantified. A limitation of the study was the small sample sizes and only one or two sites participating per country; however, since susceptibility data are scarce in some of the participating countries any information concerning antibiotic susceptibility is of value.

CONCLUSIONS

Antibiotic susceptibility varied across countries and species, with isolates from Vietnam demonstrating the lowest susceptibility. Knowledge of resistance patterns can be helpful for clinicians when choosing empirical therapy options for CA-RTIs.

PRMT1 Is Required for the Maintenance of Mature β-Cell Identity

Loss of functional β-cell mass is an essential feature of type 2 diabetes, and maintaining mature β-cell identity is important for preserving a functional β-cell mass. However, it is unclear how β-cells achieve and maintain their mature identity. Here we demonstrate a novel function of protein arginine methyltransferase 1 (PRMT1) in maintaining mature β-cell identity. Prmt1 knockout in fetal and adult β-cells induced diabetes, which was aggravated by high-fat diet-induced metabolic stress. Deletion of Prmt1 in adult β-cells resulted in the immediate loss of histone H4 arginine 3 asymmetric dimethylation (H4R3me2a) and the subsequent loss of β-cell identity. The expression levels of genes involved in mature β-cell function and identity were robustly downregulated as soon as Prmt1 deletion was induced in adult β-cells. Chromatin immunoprecipitation sequencing and assay for transposase-accessible chromatin sequencing analyses revealed that PRMT1-dependent H4R3me2a increases chromatin accessibility at the binding sites for CCCTC-binding factor (CTCF) and β-cell transcription factors. In addition, PRMT1-dependent open chromatin regions may show an association with the risk of diabetes in humans. Together, our results indicate that PRMT1 plays an essential role in maintaining β-cell identity by regulating chromatin accessibility.

Skeletal muscle-specific Prmt1 deletion causes muscle atrophy via deregulation of the PRMT6-FOXO3 axis

Protein arginine methyltransferases (PRMTs) have emerged as important regulators of skeletal muscle metabolism and regeneration. However, the direct roles of the various PRMTs during skeletal muscle remodeling remain unclear. Using skeletal muscle-specific prmt1 knockout mice, we examined the function and downstream targets of PRMT1 in muscle homeostasis. We found that muscle-specific PRMT1 deficiency led to muscle atrophy. PRMT1-deficient muscles exhibited enhanced expression of a macroautophagic/autophagic marker LC3-II, FOXO3 and muscle-specific ubiquitin ligases, TRIM63/MURF-1 and FBXO32, likely contributing to muscle atrophy. The mechanistic study reveals that PRMT1 regulates FOXO3 through PRMT6 modulation. In the absence of PRMT1, increased PRMT6 specifically methylates FOXO3 at arginine 188 and 249, leading to its activation. Finally, we demonstrate that PRMT1 deficiency triggers FOXO3 hyperactivation, which is abrogated by PRMT6 depletion. Taken together, PRMT1 is a key regulator for the PRMT6-FOXO3 axis in the control of autophagy and protein degradation underlying muscle maintenance. Abbreviations: Ad-RNAi: adenovirus-delivered small interfering RNA; AKT: thymoma viral proto-oncogene; AMPK: AMP-activated protein kinase; Baf A1: bafilomycin A₁; CSA: cross-sectional area; EDL: extensor digitorum longus; FBXO32: F-box protein 32; FOXO: forkhead box O; GAS: gatrocnemieus; HDAC: histone deacetylase; IGF: insulin-like growth factor; LAMP: lysosomal-associated membrane protein; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mKO: Mice with skeletal muscle-specific deletion of Prmt1; MTOR: mechanistic target of rapamycin kinase; MYH: myosin heavy chain; MYL1/MLC1f: myosin, light polypeptide 1; PRMT: protein arginine N-methyltransferase; sgRNA: single guide RNA; SQSTM1: sequestosome 1; SOL: soleus; TA: tibialis anterior; TRIM63/MURF-1: tripartite motif-containing 63; YY1: YY1 transcription factor.

PDK4 Deficiency Suppresses Hepatic Glucagon Signaling by Decreasing cAMP Levels

In fasting or diabetes, gluconeogenic genes are transcriptionally activated by glucagon stimulation of the cAMP-protein kinase A (PKA)-CREB signaling pathway. Previous work showed pyruvate dehydrogenase kinase (PDK) inhibition in skeletal muscle increases pyruvate oxidation, which limits the availability of gluconeogenic substrates in the liver. However, this study found upregulation of hepatic PDK4 promoted glucagon-mediated expression of gluconeogenic genes, whereas knockdown or inhibition of hepatic PDK4 caused the opposite effect on gluconeogenic gene expression and decreased hepatic glucose production. Mechanistically, PDK4 deficiency decreased ATP levels, thus increasing phosphorylated AMPK (p-AMPK), which increased p-AMPK-sensitive phosphorylation of cyclic nucleotide phosphodiesterase 4B (p-PDE4B). This reduced cAMP levels and consequently p-CREB. Metabolic flux analysis showed that the reduction in ATP was a consequence of a diminished rate of fatty acid oxidation (FAO). However, overexpression of PDK4 increased FAO and increased ATP levels, which decreased p-AMPK and p-PDE4B and allowed greater accumulation of cAMP and p-CREB. The latter were abrogated by the FAO inhibitor etomoxir, suggesting a critical role for PDK4 in FAO stimulation and the regulation of cAMP levels. This finding strengthens the possibility of PDK4 as a target against diabetes.

Loss of the E3 ubiquitin ligase MKRN1 represses diet-induced metabolic syndrome through AMPK activation

AMP-activated protein kinase (AMPK) plays a key role in controlling energy metabolism in response to physiological and nutritional status. Although AMPK activation has been proposed as a promising molecular target for treating obesity and its related comorbidities, the use of pharmacological AMPK activators has been met with contradictory therapeutic challenges. Here we show a regulatory mechanism for AMPK through its ubiquitination and degradation by the E3 ubiquitin ligase makorin ring finger protein 1 (MKRN1). MKRN1 depletion promotes glucose consumption and suppresses lipid accumulation due to AMPK stabilisation and activation. Accordingly, MKRN1-null mice show chronic AMPK activation in both liver and adipose tissue, resulting in significant suppression of diet-induced metabolic syndrome. We demonstrate also its therapeutic effect by administering shRNA targeting MKRN1 into obese mice that reverses non-alcoholic fatty liver disease. We suggest that ubiquitin-dependent AMPK degradation represents a target therapeutic strategy for metabolic disorders.

AMPK activation has been suggested as treatment for obesity and its complications. Here the authors show that the ubiquitin ligase MKRN1 binds to AMPK and mediates its ubiquitination and degradation. Loss of MKRN1 leads to AMPK activation, increased glucose consumption and decreased lipid accumulation.

The SMILE transcriptional corepressor inhibits cAMP response element-binding protein (CREB)-mediated transactivation of gluconeogenic genes

Under fasting conditions, activation of several hepatic genes sets the stage for gluconeogenesis in the liver. cAMP response element-binding protein (CREB), CREB-regulated transcription coactivator 2 (CRTC2), and peroxisome proliferator-activated receptor γ coactivator 1-alpha (PGC-1α) are essential for this transcriptional induction of gluconeogenic genes. PGC-1α induction is mediated by activation of a CREB/CRTC2 signaling complex, and recent findings have revealed that small heterodimer partner-interacting leucine zipper protein (SMILE), a member of the CREB/ATF family of basic region-leucine zipper (bZIP) transcription factors, is an insulin-inducible corepressor that decreases PGC-1α expression and abrogates its stimulatory effect on hepatic gluconeogenesis. However, the molecular mechanism whereby SMILE suppresses PGC-1α expression is unknown. Here, we investigated SMILE's effects on the CREB/CRTC2 signaling pathway and glucose metabolism. We found that SMILE significantly inhibits CREB/CRTC2-induced PGC-1α expression by interacting with and disrupting the CREB/CRTC2 complex. Consequently, SMILE decreased PGC-1α-induced hepatic gluconeogenic gene expression. Furthermore, SMILE inhibited CREB/CRTC2-induced phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) gene expression by directly repressing the expression of these genes and by indirectly inhibiting the expression of PGC-1α via CREB/CRTC2 repression. Indeed, enhanced gluconeogenesis and circulating blood glucose levels in mice injected with an adenovirus construct containing a constitutively active CRTC2 variant (CRTC2-S171A) were significantly reduced by WT SMILE, but not by leucine zipper-mutated SMILE. These results reveal that SMILE represses CREB/CRTC2-induced PGC-1α expression, an insight that may help inform potential therapeutic approaches targeting PGC-1α-mediated regulation of hepatic glucose metabolism.

RORα Induces KLF4-Mediated M2 Polarization in the Liver Macrophages that Protect against Nonalcoholic Steatohepatitis

The regulation of M1/M2 polarization in liver macrophages is closely associated with the progression of nonalcoholic steatohepatitis (NASH); however, the mechanism involved in this process remains unclear. Here, we describe the orphan nuclear receptor retinoic-acid-related orphan receptor α (RORα) as a key regulator of M1/M2 polarization in hepatic residential Kupffer cells (KCs) and infiltrated monocyte-derived macrophages. RORα enhanced M2 polarization in KCs by inducing the kruppel-like factor 4. M2 polarization was defective in KCs and bone-marrow-derived macrophages of the myeloid-specific RORα null mice, and these mice were susceptible to HFD-induced NASH. We found that IL-10 played an important role in connecting the function of M2 KCs to lipid accumulation and apoptosis in hepatocytes. Importantly, M2 polarization was controlled by a RORα activator, JC1-40, which improved symptoms of NASH. Our results suggest that the M2-promoting effects of RORα in liver macrophages may provide better therapeutic strategies against NASH.

CREB/CRTC2 controls GLP-1-dependent regulation of glucose homeostasis

Glucagon-like peptide 1 (GLP-1) is a major incretin that controls glucose homeostasis. The secretion of mature GLP-1 is regulated via GPCRs, including bile acid receptor G protein-coupled bile acid receptor 1, which uses cAMP signaling to enhance the exocytosis of GLP-1-containing vesicles. However, the role of cAMP-mediated transcription has not been clearly demonstrated to date. In this study, we explored the role of cAMP response element-binding protein/CREB-regulated transcription coactivator 2 (CREB/CRTC2)-dependent transcription on GLP-1 secretion in the L cells. We found that the reduced CREB/CRTC2 activity impaired the cAMP-dependent increase in GLP-1 secretion, whereas expression of constitutively active CRTC2 increased GLP-1 exocytosis from the L cells. Close investigation revealed that expression of not only proglucagon but also PC1/3, an endopeptidase for GLP-1 maturation, is transcriptionally regulated by CREB/CRTC2. Furthermore, expression of peroxisome proliferator-activating receptor coactivator 1 α is also reduced upon depletion of CRTC2, leading to the decreased expression of oxidative phosphorylation (OxPhos) genes, reduced ATP levels, and calcium concentrations in the L cells. Finally, we observed that intestine-specific CRTC2 knockout mice displayed reduced GLP-1 expression, leading to the lower plasma GLP-1 levels, impaired glucose tolerance, and decreased insulin-containing β cells in pancreatic islets. Our data show that the CREB/CRTC2-dependent transcriptional pathway is critical for regulating glucose homeostasis by controlling production of GLP-1 from the L cells at the level of transcription, maturation, and exocytosis.-Lee, J.-H., Wen, X., Cho, H., Koo, S.-H. CREB/CRTC2 controls GLP-1-dependent regulation of glucose homeostasis.

NFIL3 is a negative regulator of hepatic gluconeogenesis

OBJECTIVE

Nuclear factor interleukin-3 regulated (NFIL3) has been known as an important transcriptional regulator of the development and the differentiation of immune cells. Although expression of NFIL3 is regulated by nutritional cues in the liver, the role of NFIL3 in the glucose metabolism has not been extensively studied. Thus, we wanted to explore the potential role of NFIL3 in the control of hepatic glucose metabolism.

MATERIALS/METHODS

Mouse primary hepatocytes were cultured to perform western blot analysis, Q-PCR and chromatin immunoprecipitation assay. 293T cells were cultured to perform luciferase assay. Male C57BL/6 mice (fed a normal chow diet or high fat diet for 27weeks) as well as ob/ob mice were used for experiments with adenoviral delivery.

RESULTS

We observed that NFIL3 reduced glucose production in hepatocytes by reducing expression of gluconeogenic gene transcription. The repression by NFIL3 required its basic leucine zipper DNA binding domain, and it competed with CREB onto the binding of cAMP response element in the gluconeogenic promoters. The protein levels of hepatic NFIL3 were decreased in the mouse models of genetic- and diet-induced obesity and insulin resistance, and ectopic expression of NFIL3 in the livers of insulin resistant mice ameliorated hyperglycemia and glucose intolerance, with concomitant reduction in expression of hepatic gluconeogenic genes. Finally, we witnessed that knockdown of NFIL3 in the livers of normal chow-fed mice promoted elevations in the glucose levels and expression of hepatic gluconeogenic genes.

CONCLUSIONS

In this study, we showed that NFIL3 functions as an important regulator of glucose homeostasis in the liver by limiting CREB-mediated hepatic gluconeogenesis. Thus, enhancement of hepatic NFIL3 activity in insulin resistant state could be potentially beneficial in relieving glycemic symptoms in the metabolic diseases.

Hepatic Crtc2 controls whole body energy metabolism via a miR-34a-Fgf21 axis

Liver plays a crucial role in controlling energy homeostasis in mammals, although the exact mechanism by which it influences other peripheral tissues has yet to be addressed. Here we show that Creb regulates transcriptional co-activator (Crtc) 2 is a major regulator of whole-body energy metabolism. Crtc2 liver-specific knockout lowers blood glucose levels with improved glucose and insulin tolerance. Liver-specific knockout mice display increased energy expenditure with smaller lipid droplets in adipose depots. Both plasma and hepatic Fgf21 levels are increased in Crtc2 liver-specific knockout mice, as a result of the reduced miR-34a expression regulated by Creb/Crtc2 and the induction of Sirt1 and Pparα. Ectopic expression of miR-34a reverses the metabolic changes in knockout liver. We suggest that Creb/Crtc2 negatively regulates the Sirt1/Pparα/Fgf21 axis via the induction of miR-34a under diet-induced obesity and insulin-resistant conditions.

CREB-regulated transcription coactivator 2, CRTC2, has been associated with regulation of glucose and lipid homeostasis. Here Han et al. show that Creb/Crtc2 modulates lipid and glucose metabolism by inhibiting the expression of mi-R34 that, in turn, represses the expression of Sirt1 and PPARα and consequently Fgf21 levels.

Fast food diet-induced non-alcoholic fatty liver disease exerts early protective effect against acetaminophen intoxication in mice

BACKGROUND

Acetaminophen (APAP) is a readily available and safe painkiller. However, its overdose is the most common cause of acute liver injury (ALI). Many predisposing factors contribute to susceptibility to APAP-induced ALI. Non-alcoholic fatty liver disease (NAFLD), the major cause of chronic liver disease, is considered an important predictor of APAP-induced ALI, although the exact mechanism controversial. In this study, we aimed to elucidate the effects of NAFLD on APAP-induced ALI.

METHODS

Two groups of mice, normal chow (NC) diet-fed and fast food (FF) diet-fed mice for 14 weeks, were further divided into two subgroups: intraperitoneally injected with either saline (NC-S and FF-S groups) or APAP (NC-A and FF-A groups). Biochemical tests, histological analysis, quantitative PCR, and western blotting were conducted.

RESULTS

Alanine aminotransferase (ALT) level (199.0 ± 39.0 vs. 63.8 ± 7.4 IU/L, p < 0.05) and NAFLD activity score (0 vs. 4.5 ± 0.22) were significantly higher in mice in FF-S group than those in NC-S group. ALI features such as ALT level (8447.8 ± 1185.3 vs. 836.6 ± 185.1 IU/L, p < 0.001) and centrizonal necrosis were prominent and mRNA levels of Trib3 (RR, 1.81) was high in mice in the NC-A group. Levels of CYP2E1 and anti-inflammatory molecules such as PPAR-γ, p62, and NRF2 were high in mice in the FF-A group.

CONCLUSIONS

Our results showed that while the FF diet clearly induced non-alcoholic steatohepatitis and metabolic syndrome, NAFLD also attenuates APAP-induced ALI by inducing anti-inflammatory molecules such as PPAR-γ.

Olfactory receptor 544 reduces adiposity by steering fuel preference toward fats

Olfactory receptors (ORs) are present in tissues outside the olfactory system; however, the function of these receptors remains relatively unknown. Here, we determined that olfactory receptor 544 (Olfr544) is highly expressed in the liver and adipose tissue of mice and regulates cellular energy metabolism and obesity. Azelaic acid (AzA), an Olfr544 ligand, specifically induced PKA-dependent lipolysis in adipocytes and promoted fatty acid oxidation (FAO) and ketogenesis in liver, thus shifting the fuel preference to fats. After 6 weeks of administration, mice fed a high-fat diet (HFD) exhibited a marked reduction in adiposity. AzA treatment induced expression of PPAR-α and genes required for FAO in the liver and induced the expression of PPAR-γ coactivator 1-α (Ppargc1a) and uncoupling protein-1 (Ucp1) genes in brown adipose tissue (BAT). Moreover, treatment with AzA increased insulin sensitivity and ketone body levels. This led to a reduction in the respiratory quotient and an increase in the FAO rate, as indicated by indirect calorimetry. AzA treatment had similar antiobesogenic effects in HFD-fed ob/ob mice. Importantly, AzA-associated metabolic changes were completely abrogated in HFD-fed Olfr544-/- mice. To our knowledge, this is the first report to show that Olfr544 orchestrates the metabolic interplay between the liver and adipose tissue, mobilizing stored fats from adipose tissue and shifting the fuel preference to fats in the liver and BAT.

Complex chromosomal rearrangements by single catastrophic pathogenesis in NUT midline carcinoma

Background

Nuclear protein in testis (NUT) midline carcinoma (NMC) is a rare aggressive malignancy often occurring in the tissues of midline anatomical structures. Except for the pathognomonic BRD3/4–NUT rearrangement, the comprehensive landscape of genomic alterations in NMCs has been unexplored.

Patients and methods

We investigated three NMC cases, including two newly diagnosed NMC patients in Seoul National University Hospital, and a previously reported cell line (Ty-82). Whole-genome and transcriptome sequencing were carried out for these cases, and findings were validated by multiplex fluorescence in situ hybridization and using individual fluorescence probes.

Results

Here, we present the first integrative analysis of whole-genome sequencing, transcriptome sequencing and cytogenetic characterization of NUT midline carcinomas. By whole-genome sequencing, we identified a remarkably similar pattern of highly complex genomic rearrangements (previously denominated as chromoplexy) involving the BRD3/4–NUT oncogenic rearrangements in two newly diagnosed NMC cases. Transcriptome sequencing revealed that these complex rearrangements were transcribed as very simple BRD3/4–NUT fusion transcripts. In Ty-82 cells, we also identified a complex genomic rearrangement involving the BRD4–NUT rearrangement underlying the simple t(15;19) karyotype. Careful inspections of rearrangement breakpoints indicated that these rearrangements were likely attributable to single catastrophic events. Although the NMC genomes had >3000 somatic point mutations, canonical oncogenes or tumor suppressor genes were rarely affected, indicating that they were largely passenger events. Mutational signature analysis showed predominant molecular clock-like signatures in all three cases (accounting for 54%−75% of all base substitutions), suggesting that NMCs may arise from actively proliferating normal cells.

Conclusion

Taken together, our findings suggest that a single catastrophic event in proliferating normal cells could be sufficient for neoplastic transformation into NMCs.

Effect of BI-1 on insulin resistance through regulation of CYP2E1

Diet-induced obesity is a major contributing factor to the progression of hepatic insulin resistance. Increased free fatty acids in liver enhances endoplasmic reticulum (ER) stress and production of reactive oxygen species (ROS), both are directly responsible for dysregulation of hepatic insulin signaling. BI-1, a recently studied ER stress regulator, was examined to investigate its association with ER stress and ROS in insulin resistance models. To induce obesity and insulin resistance, BI-1 wild type and BI-1 knock-out mice were fed a high-fat diet for 8 weeks. The BI-1 knock-out mice had hyperglycemia, was associated with impaired glucose and insulin tolerance under high-fat diet conditions. Increased activity of NADPH-dependent CYP reductase-associated cytochrome p450 2E1 (CYP2E1) and exacerbation of ER stress in the livers of BI-1 knock-out mice was also observed. Conversely, stable expression of BI-1 in HepG2 hepatocytes was shown to reduce palmitate-induced ER stress and CYP2E1-dependent ROS production, resulting in the preservation of intact insulin signaling. Stable expression of CYP2E1 led to increased ROS production and dysregulation of insulin signaling in hepatic cells, mimicking palmitate-mediated hepatic insulin resistance. We propose that BI-1 protects against obesity-induced hepatic insulin resistance by regulating CYP2E1 activity and ROS production.

Protein arginine methylation facilitates KCNQ channel-PIP2 interaction leading to seizure suppression

KCNQ channels are critical determinants of neuronal excitability, thus emerging as a novel target of anti-epileptic drugs. To date, the mechanisms of KCNQ channel modulation have been mostly characterized to be inhibitory via Gq-coupled receptors, Ca²⁺/CaM, and protein kinase C. Here we demonstrate that methylation of KCNQ by protein arginine methyltransferase 1 (Prmt1) positively regulates KCNQ channel activity, thereby preventing neuronal hyperexcitability. Prmt1+/- mice exhibit epileptic seizures. Methylation of KCNQ2 channels at 4 arginine residues by Prmt1 enhances PIP₂ binding, and Prmt1 depletion lowers PIP₂ affinity of KCNQ2 channels and thereby the channel activities. Consistently, exogenous PIP₂ addition to Prmt1+/- neurons restores KCNQ currents and neuronal excitability to the WT level. Collectively, we propose that Prmt1-dependent facilitation of KCNQ-PIP₂ interaction underlies the positive regulation of KCNQ activity by arginine methylation, which may serve as a key target for prevention of neuronal hyperexcitability and seizures.

DOI:http://dx.doi.org/10.7554/eLife.17159.001

In the brain, cells called neurons transmit information along their length in the form of electrical signals. To generate electrical signals, ions move into and out of neurons through ion channel proteins – such as the KCNQ channel – in the surface of these cells, which open and close to control the electrical response of the neuron.

Abnormally intense bursts of electrical activity from many neurons at once can cause seizures such as those experienced by people with epilepsy. A significant proportion of patients do not respond to current anti-seizure medications. Openers of KCNQ channels have emerged as a potential new class of anti-epileptic drugs. A better understanding of how KCNQ channels work, and how their opening by PIP₂lipid signals is regulated, could help to develop more effective therapies for epilepsy.

A process called methylation controls many biological tasks by changing the structure of key proteins inside cells. Although methylation occurs throughout the brain, its role in controlling how easily neurons are activated (a property known as “excitability”) remains unclear.

Kim, Jeong, Kim, Jung et al. now show that a protein called Prmt1 methylates the KCNQ channels in mice, and that this methylation is essential for suppressing seizures. Mice born without the Prmt1 protein developed epileptic seizures and the KCNQ channels in their neurons featured a reduced level of methylation. However, increasing the amount of PIP₂ in these neurons restored their excitability back to normal levels. The methylation of KCNQ channel proteins increases their affinity for PIP2, which is critical to open KCNQ channels. Kim et al. propose that these “opening” controllers balance the action of known “closers” of KCNQ channels to maintain neurons in a healthy condition.

In future, Kim et al. plan to investigate whether methylation affects the activity of other ion channels controlled by PIP₂. Such experiments will complement a more widespread investigation into other ways in which the Prtmt1 protein may control the activity of neurons.

DOI:http://dx.doi.org/10.7554/eLife.17159.002

Bax Inhibitor-1 regulates hepatic lipid accumulation via ApoB secretion

In this study, we explored the effects of Bax Inhibitor-1 (BI-1) on ApoB aggregation in high-fat diet (HFD)-induced hepatic lipid accumulation. After 1 week on a HFD, triglycerides and cholesterol accumulated more in the liver and were not effectively secreted into the plasma, whereas after 8 weeks, lipids were highly accumulated in both the liver and plasma, with a greater effect in BI-1 KO mice compared with BI-1 WT mice. ApoB, a lipid transfer protein, was accumulated to a greater extent in the livers of HFD-BI-1 KO mice compared with HFD-BI-1 WT mice. Excessive post-translational oxidation of protein disulfide isomerase (PDI), intra-ER ROS accumulation and folding capacitance alteration were also observed in HFD-BI-1 KO mice. Higher levels of endoplasmic reticulum (ER) stress were consistently observed in KO mice compared with the WT mice. Adenovirus-mediated hepatic expression of BI-1 in the BI-1 KO mice rescued the above phenotypes. Our results suggest that BI-1-mediated enhancement of ApoB secretion regulates hepatic lipid accumulation, likely through regulation of ER stress and ROS accumulation.

Regulation of glucose metabolism from a liver-centric perspective

Glucose homeostasis is tightly regulated to meet the energy requirements of the vital organs and maintain an individual's health. The liver has a major role in the control of glucose homeostasis by controlling various pathways of glucose metabolism, including glycogenesis, glycogenolysis, glycolysis and gluconeogenesis. Both the acute and chronic regulation of the enzymes involved in the pathways are required for the proper functioning of these complex interwoven systems. Allosteric control by various metabolic intermediates, as well as post-translational modifications of these metabolic enzymes constitute the acute control of these pathways, and the controlled expression of the genes encoding these enzymes is critical in mediating the longer-term regulation of these metabolic pathways. Notably, several key transcription factors are shown to be involved in the control of glucose metabolism including glycolysis and gluconeogenesis in the liver. In this review, we would like to illustrate the current understanding of glucose metabolism, with an emphasis on the transcription factors and their regulators that are involved in the chronic control of glucose homeostasis.

Insulin-Inducible SMILE Inhibits Hepatic Gluconeogenesis

The role of a glucagon/cAMP-dependent protein kinase-inducible coactivator PGC-1α signaling pathway is well characterized in hepatic gluconeogenesis. However, an opposing protein kinase B (PKB)/Akt-inducible corepressor signaling pathway is unknown. A previous report has demonstrated that small heterodimer partner-interacting leucine zipper protein (SMILE) regulates the nuclear receptors and transcriptional factors that control hepatic gluconeogenesis. Here, we show that hepatic SMILE expression was induced by feeding in normal mice but not in db/db and high-fat diet (HFD)-fed mice. Interestingly, SMILE expression was induced by insulin in mouse primary hepatocyte and liver. Hepatic SMILE expression was not altered by refeeding in liver-specific insulin receptor knockout (LIRKO) or PKB β-deficient (PKBβ(-/-)) mice. At the molecular level, SMILE inhibited hepatocyte nuclear factor 4-mediated transcriptional activity via direct competition with PGC-1α. Moreover, ablation of SMILE augmented gluconeogenesis and increased blood glucose levels in mice. Conversely, overexpression of SMILE reduced hepatic gluconeogenic gene expression and ameliorated hyperglycemia and glucose intolerance in db/db and HFD-fed mice. Therefore, SMILE is an insulin-inducible corepressor that suppresses hepatic gluconeogenesis. Small molecules that enhance SMILE expression would have potential for treating hyperglycemia in diabetes.

Phylogenetic group distributions, virulence factors and antimicrobial resistance properties of uropathogenic Escherichia coli strains isolated from patients with urinary tract infections in South Korea

Urinary tract infections (UTIs) are one of the most common diseases by which humans seek medical help and are caused mainly by uropathogenic Escherichia coli (UPEC). Studying the virulence and antibiotic resistance of UPEC with respect to various phylogenetic groups is of utmost importance in developing new therapeutic agents. Thus, in this study, we analysed the virulence factors, antibiotic resistance and phylogenetic groups among various UPEC isolates from children with UTIs. The phylogenetic analysis revealed that majority of the strains responsible for UTIs belonged to the phylogenetic groups B2 and D. Of the 58 E. coli isolates, 79·31% belonged to group B2, 15·51% to group D, 3·44% to group A and 1·72% to B1. Simultaneously, the number of virulence factors and antibiotic resistance exhibited were also significantly high in groups B2 and D compared to other groups. Among the isolates, 44·8% were multidrug resistant and of that 73% belonged to the phylogenetic group B2, indicating the compatibility of antibiotic resistance and certain strains carrying virulence factor genes. The antibiotic resistance profiling of UPEC strains elucidates that the antimicrobial agents such as chloramphenicol, cefoxitin, cefepime, ceftazidime might still be used in the therapy for treating UTIs.

SIGNIFICANCE AND IMPACT OF THE STUDY

As the antibiotic resistance pattern of uropathogenic Escherichia coli varies depending on different geographical regions, the antibiotic resistance pattern from this study will help the physicians to effectively administer antibiotic therapy for urinary tract infections. In addition, the frequency of virulence factors and antibiotic resistance genes among various phylogenic groups could be effectively used to draw new targets for uropathogenic Escherichia coli antibiotic-independent therapies. The study emphasizes need of public awareness on multidrug resistance and for more prudent use of antimicrobials.

Salt-Inducible Kinase 1 Terminates cAMP Signaling by an Evolutionarily Conserved Negative-Feedback Loop in β-Cells

Pancreatic β-cells are critical in the regulation of glucose homeostasis by controlled secretion of insulin in mammals. Activation of protein kinase A by cAMP is shown to be responsible for enhancing this pathway, which is countered by phosphodiesterase (PDE) that converts cAMP to AMP and turns off the signal. Salt-inducible kinases (SIKs) were also known to inhibit cAMP signaling, mostly by promoting inhibitory phosphorylation on CREB-regulated transcription coactivators. Here, we showed that SIK1 regulates insulin secretion in β-cells by modulating PDE4D and cAMP concentrations. Haploinsufficiency of SIK1 led to the improved glucose tolerance due to the increased glucose-stimulated insulin secretion. Depletion of SIK1 promoted higher cAMP concentration and increased insulin secretion from primary islets, suggesting that SIK1 controls insulin secretion through the regulation of cAMP signaling. By using a consensus phosphorylation site of SIK1, we identified PDE4D as a new substrate for this kinase family. In vitro kinase assay as well as mass spectrometry analysis revealed that the predicted Ser(136) and the adjacent Ser(141) of PDE4D are critical in SIK1-mediated phosphorylation. We found that overexpression of either SIK1 or PDE4D in β-cells reduced insulin secretion, while inhibition of PDE4 activity by rolipram or knockdown of PDE4D restored it, showing indeed that SIK1-dependent phosphorylation of PDE4D is critical in reducing cAMP concentration and insulin secretion from β-cells. Taken together, we propose that SIK1 serves as a part of a self-regulatory circuit to modulate insulin secretion from pancreatic β-cells by controlling cAMP concentration through modulation of PDE4D activity.

Vibrio vulnificus Secretes an Insulin-degrading Enzyme That Promotes Bacterial Proliferation in Vivo

We describe a novel insulin-degrading enzyme, SidC, that contributes to the proliferation of the human bacterial pathogen Vibrio vulnificus in a mouse model. SidC is phylogenetically distinct from other known insulin-degrading enzymes and is expressed and secreted specifically during host infection. Purified SidC causes a significant decrease in serum insulin levels and an increase in blood glucose levels in mice. A comparison of mice infected with wild type V. vulnificus or an isogenic sidC-deletion strain showed that wild type bacteria proliferated to higher levels. Additionally, hyperglycemia leads to increased proliferation of V. vulnificus in diabetic mice. Consistent with these observations, the sid operon was up-regulated in response to low glucose levels through binding of the cAMP-receptor protein (CRP) complex to a region upstream of the operon. We conclude that glucose levels are important for the survival of V. vulnificus in the host, and that this pathogen uses SidC to actively manipulate host endocrine signals, making the host environment more favorable for bacterial survival and growth.

Overweight in mice and enhanced adipogenesis in vitro are associated with lack of the hedgehog coreceptor boc

Obesity arises from a combination of genetic, environmental, and behavioral factors. However, the processes that regulate white adipose tissue (WAT) expansion at the level of the adipocyte are not well understood. The Hedgehog (HH) pathway plays a conserved role in adipogenesis, inhibiting fat formation in vivo and in vitro, but it has not been shown that mice with reduced HH pathway activity have enhanced adiposity. We report that mice lacking the HH coreceptor BOC displayed age-related overweight and excess WAT. They also displayed alterations in some metabolic parameters but normal food intake. Furthermore, they had an exacerbated response to a high-fat diet, including enhanced weight gain and adipocyte hypertrophy, livers with greater fat accumulation, and elevated expression of genes related to adipogenesis, lipid metabolism, and adipokine production. Cultured Boc(-/-) mouse embryo fibroblasts showed enhanced adipogenesis relative to Boc(+/+) cells, and they expressed reduced levels of HH pathway target genes. Therefore, a loss-of-function mutation in an HH pathway component is associated with WAT accumulation and overweight in mice. Variant alleles of such HH regulators may contribute to WAT accumulation in human individuals with additional genetic or lifestyle-based predisposition to obesity.

Cyclic AMP Response Element-binding Protein H (CREBH) Mediates the Inhibitory Actions of Tumor Necrosis Factor α in Osteoblast Differentiation by Stimulating Smad1 Degradation

Endoplasmic reticulum (ER) stress transducers, such as old astrocyte specifically induced substance (OASIS) and activating transcription factor 6 (ATF6), which are induced by bone morphogenetic protein 2 (BMP2), regulate bone formation and osteoblast differentiation. Here, we examined the role of cAMP response element-binding protein H (CREBH), a member of the same family of ER membrane-bound basic leucine zipper (bZIP) transcription factors as OASIS and ATF6, in osteoblast differentiation and bone formation. Proinflammatory cytokine TNFα increased CREBH expression by up-regulating the nuclear factor-κB (NF-κB) signaling pathway in osteoblasts, increased the level of N-terminal fragment of CREBH in the nucleus, and inhibited BMP2 induction of osteoblast specific gene expression. Overexpression of CREBH suppressed BMP2-induced up-regulation of the osteogenic markers runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and osteocalcin (OC) in MC3T3-E1 cells and primary osteoblasts, as well as BMP2-induced ALP activity and OC protein production. In contrast, knockdown of CREBH attenuated the inhibitory effect of TNFα on BMP2-induced osteoblast differentiation. Mechanistic studies revealed that CREBH increased the expression of Smad ubiquitination regulatory factor 1 (Smurf1), leading to ubiquitin-dependent degradation of Smad1, whereas knockdown of CREBH inhibited TNFα-mediated degradation of Smad1 by Smurf1. Consistent with these in vitro findings, administration of Ad-CREBH inhibited BMP2-induced ectopic and orthotopic bone formation in vivo. Taken together, these results suggest that CREBH is a novel negative regulator of osteoblast differentiation and bone formation.

Retinoic acid-related orphan receptor alpha reprograms glucose metabolism in glutamine-deficient hepatoma cells

The metabolism of glutamine and glucose is recognized as a promising therapeutic target for the treatment of cancer; however, targeted molecules that mediate glutamine and glucose metabolism in cancer cells have not been addressed. Here, we show that restricting the supply of glutamine in hepatoma cells, including HepG2 and Hep3B cells, markedly increased the expression of retinoic acid-related orphan receptor alpha (RORα). Up-regulation of RORα in glutamine-deficient hepatoma cells resulted from an increase in the level of cellular reactive oxygen species and in the nicotinamide adenine dinucleotide phosphate/nicotinamide adenine dinucleotide phosphate reduced (NADP+ /NADPH) ratio, which was consistent with a reduction in the glutathione/glutathione disulfide (GSH/GSSG) ratio. Adenovirus (Ad)-mediated overexpression of RORα (Ad-RORα) or treatment with the RORα activator, SR1078, reduced aerobic glycolysis and down-regulated biosynthetic pathways in hepatoma cells. Ad-RORα and SR1078 reduced the expression of pyruvate dehydrogenase kinase 2 (PDK2) and inhibited the phosphorylation of pyruvate dehydrogenase and subsequently shifted pyruvate to complete oxidation. The RORα-mediated decrease in PDK2 levels was caused by up-regulation of p21, rather than p53. Furthermore, RORα inhibited hepatoma growth both in vitro and in a xenograft model in vivo. We also found that suppression of PDK2 inhibited hepatoma growth in a xenograft model. These findings mimic the altered glucose utilization and hepatoma growth caused by glutamine deprivation. Finally, tumor tissue from 187 hepatocellular carcinoma patients expressed lower levels of RORα than adjacent nontumor tissue, supporting a potential beneficial effect of RORα activation in the treatment of liver cancer.

CONCLUSION

RORα mediates reprogramming of glucose metabolism in hepatoma cells in response to glutamine deficiency. The relationships established here between glutamine metabolism, RORα expression and signaling, and aerobic glycolysis have implications for therapeutic targeting of liver cancer metabolism.

PKB/Akt phosphorylation of ERRγ contributes to insulin-mediated inhibition of hepatic gluconeogenesis

AIMS/HYPOTHESIS

Insulin resistance, a major contributor to the pathogenesis of type 2 diabetes, leads to increased hepatic glucose production (HGP) owing to an impaired ability of insulin to suppress hepatic gluconeogenesis. Nuclear receptor oestrogen-related receptor γ (ERRγ) is a major transcriptional regulator of hepatic gluconeogenesis. In this study, we investigated insulin-dependent post-translational modifications (PTMs) altering the transcriptional activity of ERRγ for the regulation of hepatic gluconeogenesis.

METHODS

We examined insulin-dependent phosphorylation and subcellular localisation of ERRγ in cultured cells and in the liver of C57/BL6, leptin receptor-deficient (db/db), liver-specific insulin receptor knockout (LIRKO) and protein kinase B (PKB) β-deficient (Pkbβ (-/-)) mice. To demonstrate the role of ERRγ in the inhibitory action of insulin on hepatic gluconeogenesis, we carried out an insulin tolerance test in C57/BL6 mice expressing wild-type or phosphorylation-deficient mutant ERRγ.

RESULTS

We demonstrated that insulin suppressed the transcriptional activity of ERRγ by promoting PKB/Akt-mediated phosphorylation of ERRγ at S179 and by eliciting translocation of ERRγ from the nucleus to the cytoplasm through interaction with 14-3-3, impairing its ability to promote hepatic gluconeogenesis. In addition, db/db, LIRKO and Pkbβ (-/-) mice displayed enhanced ERRγ transcriptional activity due to a block in PKBβ-mediated ERRγ phosphorylation during refeeding. Finally, the phosphorylation-deficient mutant ERRγ S179A was resistant to the inhibitory action of insulin on HGP.

CONCLUSIONS/INTERPRETATION

These results suggest that ERRγ is a major contributor to insulin action in maintaining hepatic glucose homeostasis.

SIK2 is critical in the regulation of lipid homeostasis and adipogenesis in vivo

Cyclic AMP promotes chronic expression of target genes mainly by protein kinase A-dependent activation of CREB transcription factor machineries in the metabolic tissues. Here, we wanted to elaborate whether CREB-regulated transcription factor (CRTC)2 and its negative regulator salt-inducible kinase (SIK)2 are involved in the transcriptional control of the metabolic pathway in adipocytes. SIK2 knockout (SIK2 KO) mice exhibited higher blood glucose levels that were associated with impaired glucose and insulin tolerance. Hypertriglyceridemia was apparent in SIK2 KO mice, mainly due to the increased lipolysis from white adipocytes and the decreased fatty acid uptake in the peripheral tissues. Investigation of white adipocytes revealed the increases in fat cell size and macrophage infiltration, which could be linked to the metabolic anomaly that is associated in these mice. Interestingly, SIK2 KO promoted the enhancement in the CRTC2-CREB transcriptional pathway in white adipocytes. SIK2 KO mice displayed increased expression of activating transcription factor (ATF)3 and subsequent downregulation of GLUT4 expression and reduction in high-molecular weight adiponectin levels in the plasma, leading to the reduced glucose uptake in the muscle and white adipocytes. The effect of SIK2-dependent regulation of adipocyte metabolism was further confirmed by in vitro cell cultures of 3T3 L1 adipocytes and the differentiated preadipocytes from the SIK2 or CRTC2 KO mice. Collectively, these data suggest that SIK2 is critical in regulating whole-body glucose metabolism primarily by controlling the CRTC2-CREB function of the white adipocytes.

Systemic autophagy insufficiency compromises adaptation to metabolic stress and facilitates progression from obesity to diabetes

Despite growing interest in the relationship between autophagy and systemic metabolism, how global changes in autophagy affect metabolism remains unclear. Here we show that mice with global haploinsufficiency of an essential autophagy gene (Atg7(+/-) mice) do not show metabolic abnormalities but develop diabetes when crossed with ob/ob mice. Atg7(+/-)-ob/ob mice show aggravated insulin resistance with increased lipid content and inflammatory changes, suggesting that autophagy haploinsufficiency impairs the adaptive response to metabolic stress. We further demonstrate that intracellular lipid content and insulin resistance after lipid loading are increased as a result of autophagy insufficiency, and provide evidence for increased inflammasome activation in Atg7(+/-)-ob/ob mice. Imatinib or trehalose improves metabolic parameters of Atg7(+/-)-ob/ob mice and enhances autophagic flux. These results suggest that systemic autophagy insufficiency could be a factor in the progression from obesity to diabetes, and autophagy modulators have therapeutic potential against diabetes associated with obesity and inflammation.

Ring finger protein20 regulates hepatic lipid metabolism through protein kinase A-dependent sterol regulatory element binding protein1c degradation

Sterol regulatory element binding protein1c (SREBP1c) is a key transcription factor for de novo lipogenesis during the postprandial state. During nutritional deprivation, hepatic SREBP1c is rapidly suppressed by fasting signals to prevent lipogenic pathways. However, the molecular mechanisms that control SREBP1c turnover in response to fasting status are not thoroughly understood. To elucidate which factors are involved in the inactivation of SREBP1c, we attempted to identify SREBP1c-interacting proteins by mass spectrometry analysis. Since we observed that ring finger protein20 (RNF20) ubiquitin ligase was identified as one of SREBP1c-interacting proteins, we hypothesized that fasting signaling would promote SREBP1c degradation in an RNF20-dependent manner. In this work, we demonstrate that RNF20 physically interacts with SREBP1c, leading to degradation of SREBP1c via ubiquitination. In accordance with these findings, RNF20 represses the transcriptional activity of SREBP1c and turns off the expression of lipogenic genes that are targets of SREBP1c. In contrast, knockdown of RNF20 stimulates the expression of SREBP1c and lipogenic genes and induces lipogenic activity in primary hepatocytes. Furthermore, activation of protein kinase A (PKA) with glucagon or forskolin enhances the expression of RNF20 and potentiates the ubiquitination of SREBP1c via RNF20. In wild-type and db/db mice, adenoviral overexpression of RNF20 markedly suppresses FASN promoter activity and reduces the level of hepatic triglycerides, accompanied by a decrease in the hepatic lipogenic program. Here, we reveal that RNF20-induced SREBP1c ubiquitination down-regulates hepatic lipogenic activity upon PKA activation.

CONCLUSION

RNF20 acts as a negative regulator of hepatic fatty acid metabolism through degradation of SREBP1c upon PKA activation. Knowledge regarding this process enhances our understanding of how SREBP1c is able to turn off hepatic lipid metabolism during nutritional deprivation.

CREB and FoxO1: two transcription factors for the regulation of hepatic gluconeogenesis

Liver plays a major role in maintaining glucose homeostasis in mammals. Under fasting conditions, hepatic glucose production is critical as a source of fuel to maintain the basic functions in other tissues, including skeletal muscle, red blood cells, and the brain. Fasting hormones glucagon and cortisol play major roles during the process, in part by activating the transcription of key enzyme genes in the gluconeogenesis such as phosphoenol pyruvate carboxykinase (PEPCK) and glucose 6 phosphatase catalytic subunit (G6Pase). Conversely, gluconeogenic transcription is repressed by pancreatic insulin under feeding conditions, which effectively inhibits transcriptional activator complexes by either promoting post-translational modifications or activating transcriptional inhibitors in the liver, resulting in the reduction of hepatic glucose output. The transcriptional regulatory machineries have been highlighted as targets for type 2 diabetes drugs to control glycemia, so understanding of the complex regulatory mechanisms for transcription circuits for hepatic gluconeogenesis is critical in the potential development of therapeutic tools for the treatment of this disease. In this review, the current understanding regarding the roles of two key transcriptional activators, CREB and FoxO1, in the regulation of hepatic gluconeogenic program is discussed.

Arginine methylation of CRTC2 is critical in the transcriptional control of hepatic glucose metabolism

Fasting glucose homeostasis is maintained in part through cAMP (adenosine 3',5'-monophosphate)-dependent transcriptional control of hepatic gluconeogenesis by the transcription factor CREB (cAMP response element-binding protein) and its coactivator CRTC2 (CREB-regulated transcriptional coactivator 2). We showed that PRMT6 (protein arginine methyltransferase 6) promotes fasting-induced transcriptional activation of the gluconeogenic program involving CRTC2. Mass spectrometric analysis indicated that PRMT6 associated with CRTC2. In cells, PRMT6 mediated asymmetric dimethylation of multiple arginine residues of CRTC2, which enhanced the association of CRTC2 with CREB on the promoters of gluconeogenic enzyme-encoding genes. In mice, ectopic expression of PRMT6 promoted higher blood glucose concentrations, which were associated with increased expression of genes encoding gluconeogenic factors, whereas knockdown of hepatic PRMT6 decreased fasting glycemia and improved pyruvate tolerance. The abundance of hepatic PRMT6 was increased in mouse models of obesity and insulin resistance, and adenovirus-mediated depletion of PRMT6 restored euglycemia in these mice. We propose that PRMT6 is involved in the regulation of hepatic glucose metabolism in a CRTC2-dependent manner.

Orphan nuclear receptor Errγ induces C-reactive protein gene expression through induction of ER-bound Bzip transmembrane transcription factor CREBH

The orphan nuclear receptor estrogen-related receptor-γ (ERRγ) is a constitutively active transcription factor regulating genes involved in several important cellular processes, including hepatic glucose metabolism, alcohol metabolism, and the endoplasmic reticulum (ER) stress response. cAMP responsive element-binding protein H (CREBH) is an ER-bound bZIP family transcription factor that is activated upon ER stress and regulates genes encoding acute-phase proteins whose expression is increased in response to inflammation. Here, we report that ERRγ directly regulates CREBH gene expression in response to ER stress. ERRγ bound to the ERRγ response element (ERRE) in the CREBH promoter. Overexpression of ERRγ by adenovirus significantly increased expression of CREBH as well as C-reactive protein (CRP), whereas either knockdown of ERRγ or inhibition of ERRγ by ERRγ specific inverse agonist, GSK5182, substantially inhibited ER stress-mediated induction of CREBH and CRP. The transcriptional coactivator PGC1α was required for ERRγ mediated induction of the CREBH gene as demonstrated by the chromatin immunoprecipitation (ChIP) assay showing binding of both ERRγ and PGC1α on the CREBH promoter. The ChIP assay also revealed that histone H3 and H4 acetylation occurred at the ERRγ and PGC1α binding site. Moreover, chronic alcoholic hepatosteatosis, as well as the diabetic obese condition significantly increased CRP gene expression, and this increase was significantly attenuated by GSK5182 treatment. We suggest that orphan nuclear receptor ERRγ directly regulates the ER-bound transcription factor CREBH in response to ER stress and other metabolic conditions.

Ursodeoxycholic acid inhibits liver X receptor α-mediated hepatic lipogenesis via induction of the nuclear corepressor SMILE

Small heterodimer partner interacting leucine zipper protein (SMILE) has been identified as a nuclear corepressor of the nuclear receptor (NRs) family. Here, we examined the role of SMILE in the regulation of nuclear receptor liver X receptor (LXR)-mediated sterol regulatory element binding protein-1c (SREBP-1c) gene expression. We found that SMILE inhibited T0901317 (T7)-induced transcriptional activity of LXR, which functions as a major regulator of lipid metabolism by inducing SREBP-1c, fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) gene expression. Moreover, we demonstrated that SMILE physically interacts with LXR and represses T7-induced LXR transcriptional activity by competing with coactivator SRC-1. Adenoviral overexpression of SMILE (Ad-SMILE) attenuated fat accumulation and lipogenic gene induction in the liver of T7 administered or of high fat diet (HFD)-fed mice. Furthermore, we investigated the mechanism by which ursodeoxycholic acid (UDCA) inhibits LXR-induced lipogenic gene expression. Interestingly, UDCA treatment significantly increased SMILE promoter activity and gene expression in an adenosine monophosphate-activated kinase-dependent manner. Furthermore, UDCA treatment repressed T7-induced SREBP-1c, FAS, and ACC protein levels, whereas knockdown of endogenous SMILE gene expression by adenovirus SMILE shRNA (Ad-shSMILE) significantly reversed UDCA-mediated repression of SREBP-1c, FAS, and ACC protein levels. Collectively, these results demonstrate that UDCA activates SMILE gene expression through adenosine monophosphate-activated kinase phosphorylation, which leads to repression of LXR-mediated hepatic lipogenic enzyme gene expression.

Nonalcoholic fatty liver disease: molecular mechanisms for the hepatic steatosis

Liver plays a central role in the biogenesis of major metabolites including glucose, fatty acids, and cholesterol. Increased incidence of obesity in the modern society promotes insulin resistance in the peripheral tissues in humans, and could cause severe metabolic disorders by inducing accumulation of lipid in the liver, resulting in the progression of non-alcoholic fatty liver disease (NAFLD). NAFLD, which is characterized by increased fat depots in the liver, could precede more severe diseases such as non-alcoholic steatohepatitis (NASH), cirrhosis, and in some cases hepatocellular carcinoma. Accumulation of lipid in the liver can be traced by increased uptake of free fatty acids into the liver, impaired fatty acid beta oxidation, or the increased incidence of de novo lipogenesis. In this review, I would like to focus on the roles of individual pathways that contribute to the hepatic steatosis as a precursor for the NAFLD.

Inverse agonist of nuclear receptor ERRγ mediates antidiabetic effect through inhibition of hepatic gluconeogenesis

Type 2 diabetes mellitus (T2DM) is a progressive metabolic disorder with diverse pathological manifestations and is often associated with abnormal regulation of hepatic glucose production. Many nuclear receptors known to control the hepatic gluconeogenic program are potential targets for the treatment of T2DM and its complications. Nevertheless, the therapeutic potential of the estrogen-related receptor γ (ERRγ) in T2DM remains unknown. In this study, we show that the nuclear receptor ERRγ is a major contributor to hyperglycemia under diabetic conditions by controlling hepatic glucose production. Hepatic ERRγ expression induced by fasting and diabetic conditions resulted in elevated levels of gluconeogenic gene expression and blood glucose in wild-type mice. Conversely, ablation of hepatic ERRγ gene expression reduced the expression of gluconeogenic genes and normalized blood glucose levels in mouse models of T2DM: db/db and diet-induced obesity (DIO) mice. In addition, a hyperinsulinemic-euglycemic clamp study and long-term studies of the antidiabetic effects of GSK5182, the ERRγ-specific inverse agonist, in db/db and DIO mice demonstrated that GSK5182 normalizes hyperglycemia mainly through inhibition of hepatic glucose production. Our findings suggest that the ability of GSK5182 to control hepatic glucose production can be used as a novel therapeutic approach for the treatment of T2DM.

Hepatic cannabinoid receptor type 1 mediates alcohol-induced regulation of bile acid enzyme genes expression via CREBH

Bile acids concentration in liver is tightly regulated to prevent cell damage. Previous studies have demonstrated that deregulation of bile acid homeostasis can lead to cholestatic liver disease. Recently, we have shown that ER-bound transcription factor Crebh is a downstream effector of hepatic Cb1r signaling pathway. In this study, we have investigated the effect of alcohol exposure on hepatic bile acid homeostasis and elucidated the mediatory roles of Cb1r and Crebh in this process. We found that alcohol exposure or Cb1r-agonist 2-AG treatment increases hepatic bile acid synthesis and serum ALT, AST levels in vivo alongwith significant increase in Crebh gene expression and activation. Alcohol exposure activated Cb1r, Crebh, and perturbed bile acid homeostasis. Overexpression of Crebh increased the expression of key bile acid synthesis enzyme genes via direct binding of Crebh to their promoters, whereas Cb1r knockout and Crebh-knockdown mice were protected against alcohol-induced perturbation of bile acid homeostasis. Interestingly, insulin treatment protected against Cb1r-mediated Crebh-induced disruption of bile acid homeostasis. Furthermore, Crebh expression and activation was found to be markedly increased in insulin resistance conditions and Crebh knockdown in diabetic mice model (db/db) significantly reversed alcohol-induced disruption of bile acid homeostasis. Overall, our study demonstrates a novel regulatory mechanism of hepatic bile acid metabolism by alcohol via Cb1r-mediated activation of Crebh, and suggests that targeting Crebh can be of therapeutic potential in ameliorating alcohol-induced perturbation of bile acid homeostasis.

Estrogen-related receptor γ controls hepatic CB1 receptor-mediated CYP2E1 expression and oxidative liver injury by alcohol

BACKGROUND

The hepatic endocannabinoid system and cytochrome P450 2E1 (CYP2E1), a key enzyme causing alcohol-induced reactive oxygen species (ROS) generation, are major contributors to the pathogenesis of alcoholic liver disease. The nuclear hormone receptor oestrogen-related receptor γ (ERRγ) is a constitutively active transcriptional activator regulating gene expression.

OBJECTIVE

To investigate the role of ERRγ in the alcohol-mediated regulation of CYP2E1 and to examine the possibility to control alcohol-mediated oxidative stress and liver injury through an ERRγ inverse agonist.

DESIGN

For chronic alcoholic hepatosteatosis study, C57BL/6J wild-type and CB1(-/-) mice were administered alcohol for 4 weeks. GSK5182 and chlormethiazole (CMZ) were given by oral gavage for the last 2 weeks of alcohol feeding. Gene expression profiles and biochemical assays were performed using the liver or blood of mice.

RESULTS

Hepatic ERRγ gene expression induced by alcohol-mediated activation of CB1 receptor results in induction of CYP2E1, while liver-specific ablation of ERRγ gene expression blocks alcohol-induced expression of CYP2E1 in mouse liver. An ERRγ inverse agonist significantly ameliorates chronic alcohol-induced liver injury in mice through inhibition of CYP2E1-mediated generation of ROS, while inhibition of CYP2E1 by CMZ abrogates the beneficial effects of the inverse agonist. Finally, chronic alcohol-mediated ERRγ and CYP2E1 gene expression, ROS generation and liver injury in normal mice were nearly abolished in CB1(-/-) mice.

CONCLUSIONS

ERRγ, as a previously unrecognised transcriptional regulator of hepatic CB1 receptor, controls alcohol-induced oxidative stress and liver injury through CYP2E1 induction, and its inverse agonist could ameliorate oxidative liver injury due to chronic alcohol exposure.

Transcriptional cross talk between orphan nuclear receptor ERRγ and transmembrane transcription factor ATF6α coordinates endoplasmic reticulum stress response

Orphan nuclear receptor ERRγ is a member of nuclear receptor superfamily that regulates several important cellular processes including hepatic glucose and alcohol metabolism. However, mechanistic understanding of transcriptional regulation of the ERRγ gene remains to be elucidated. Here, we report that activating transcription factor 6α (ATF6α), an endoplasmic reticulum (ER)-membrane–bound basic leucine zipper (bZip) transcription factor, directly regulates ERRγ gene expression in response to ER stress. ATF6α binds to ATF6α responsive element in the ERRγ promoter. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) is required for this transactivation. Chromatin immunoprecipitation (ChIP) assay confirmed the binding of both ATF6α and PGC1α on the ERRγ promoter. ChIP assay demonstrated histone H3 and H4 acetylation occurs at the ATF6α and PGC1α binding site. Of interest, ERRγ along with PGC1α induce ATF6α gene transcription upon ER stress. ERRγ binds to an ERRγ responsive element in the ATF6α promoter. ChIP assay confirmed that both ERRγ and PGC1α bind to a site in the ATF6α promoter that exhibits histone H3 and H4 acetylation. Overall, for the first time our data show a novel pathway of cross talk between nuclear receptors and ER-membrane–bound transcription factors and suggest a positive feed-forward loop regulates ERRγ and ATF6α gene transcription.