Regulation Of Lipogenesis Research Articles

The hyperglycemia stimulated myocardial endoplasmic reticulum (ER) stress contributes to diabetic cardiomyopathy in the transgenic non-obese type 2 diabetic rats: A differential role of unfolded protein response (UPR) signaling proteins

It has been well demonstrated that excessive blood glucose level could be detrimental to the myocardial function through the variety of mechanisms, of which endoplasmic reticulum stress (ERS) could play an unprecedented role through the activation of unfolded protein response (UPR). Recently, reports are coming out with the evidences that UPR signaling proteins are regulated differentially depend on the experimental conditions and cell types. In addition, ERS has been proposed to be closely associated with the regulation of lipogenesis. Therefore, in this study we tried to find out the expressions of myocardial UPR signaling proteins as well as proteins involved in lipid and glucose metabolism in non-obese type 2 diabetic mellitus (DM) condition using Spontaneous Diabetic Torii (SDT) rat. We have found the significant up-regulation of oxidative, nitrosative and ERS marker proteins in the myocardium of the SDT rats, in comparison to its normal (Sprague-Dawley – SD) rats. In addition, the sub-arm of UPR signaling proteins, such as p-PERK, p-eIF2α, ATF6, CHOP/GADD153, TRAF2, apoptotic signaling proteins, such as BAD, cytochrome C, cleaved caspase-7 and -12, were significantly up-regulated in the SDT rats, in comparison to the SD rats. Interestingly, there were no significant changes in the phosphorylation of IRE-1α, and XBP-1 protein expression. In addition, the proteins involved in lipid and glucose metabolisms, such as PPARα, PPARγ, CPT1, PGC-1α except GLUT4, and the proteins involved in insulin signaling, such as p-Akt and p-PI3K were shown significant attenuation in its expressions in the SDT rats, when compared with the SD rats. Taken together, it is suggested that the activation of PERK and ATF6 pathway are the major determinant rather than the IRE-1α-XBP1 pathway for the ERS-mediated metabolic dysfunction, which might eventually leads to diabetic cardiomyopathy in non-obese type 2 DM.

Knockout of SOD1 alters murine hepatic glycolysis, gluconeogenesis, and lipogenesis

We previously observed a stronger effect of knockout of Cu,Zn-superoxide dismutase (SOD1) than that of Se-dependent glutathione peroxidase 1 (GPX1) on murine body weight and glucose homeostasis. Two experiments were conducted to determine how hepatic lipid profiles and key metabolic regulators were correlated with this difference. SOD1−/− and GPX1−/− mice and their respective wild-type (WT) littermates (n=6 or 7/group, male) were fed a Se-adequate Torula yeast–sucrose diet and killed at 6 months of age to collect liver samples. In Experiment 1, fasted SOD1−/− mice displayed pyruvate intolerance and a 61% decrease (P<0.05) in liver glycogen compared with their WT littermates. The former had lower (P<0.05) activities of phosphoenolpyruvate carboxykinase, total protein phosphatase, and protein phosphatase 2A, but a higher (P<0.05) activity of glucokinase in the liver than the latter. In contrast, hepatic concentrations of total cholesterol, triglycerides, and nonesterified fatty acids were increased by 11 to 100% (P<0.05) in the SOD1−/− mice. Meanwhile, these mice had elevated (P<0.05) hepatic protein levels of sterol-regulatory element binding proteins 1 and 2, p53 MAPK, total and phosphorylated AMP-activated protein kinase α1 protein, protein tyrosine phosphatase 1B, and protein phosphatase 2B. In Experiment 2, GPX1−/− mice and their WT littermates were compared, but showed no difference in any of the measures. In conclusion, knockout of SOD1, but not GPX1, led to a decreased liver glycogen storage synchronized with pyruvate intolerance and elevated hepatic lipid profiles in adult mice. This striking comparison was possibly due to unique impacts of these two knockouts on intracellular tone of H2O2 and key regulators of liver gluconeogenesis, glycolysis, and lipogenesis.

Liver X receptor α-mediated regulation of lipogenesis by core and NS5A proteins contributes to HCV-induced liver steatosis and HCV replication

Molecular mechanisms contributing to hepatitis C virus (HCV)-associated steatosis are not well established, although HCV gene expression has been shown to alter host cell cholesterol/lipid metabolism. As liver X receptors (LXRs) play a role as key modulators of metabolism signaling in the development of steatosis, we aimed to investigate in an HCV in vitro model the effect of HCV NS5A protein, core protein, and viral replication on the intracellular lipid accumulation and the LXRα-regulated expression of lipogenic genes. The effects of LXRα siRNA or agonist GW3965 treatment on lipogenesis and HCV replication capacity in our HCV replicon system were also examined. NS5A- and core-expressing cells and replicon-containing cells exhibited an increase of lipid accumulation by inducing the gene expression and the transcriptional activity of LXRα, and leading to an increased expression of its lipogenic target genes sterol regulatory element binding protein-1c, peroxisome proliferator-activated receptor-γ, and fatty acid synthase. Transcriptional induction by NS5A protein, core protein, and viral replication occurred via LXR response element activation in the lipogenic gene promoter. No physical association between HCV proteins and LXRα was observed, whereas NS5A and core proteins indirectly upregulated LXRα through the phosphatidylinositol 3-kinase pathway. Finally, it was found that LXRα knockdown or agonist-mediated LXRα induction directly regulated HCV-induced lipogenesis and HCV replication efficiency in replicon-containing cells. Combined, our data suggest that LXRα-mediated regulation of lipogenesis by core and NS5A proteins may contribute to HCV-induced liver steatosis and to the efficient replication of HCV.

Identification of Akt-independent Regulation of Hepatic Lipogenesis by Mammalian Target of Rapamycin (mTOR) Complex 2

Mammalian target of rapamycin complex 2 (mTORC2) is a key activator of protein kinases that act downstream of insulin and growth factor signaling. Here we report that mice lacking the essential mTORC2 component rictor in liver (Lrictor(KO)) are unable to respond normally to insulin. In response to insulin, Lrictor(KO) mice failed to inhibit hepatic glucose output. Lrictor(KO) mice also fail to develop hepatic steatosis on a high fat diet and manifest half-normal serum cholesterol levels. This is accompanied by lower levels of expression of SREBP-1c and SREBP-2 and genes of fatty acid and cholesterol biosynthesis. Lrictor(KO) mice had defects in insulin-stimulated Akt Ser-473 and Thr-308 phosphorylation, leading to decreased phosphorylation of Akt substrates FoxO, GSK-3β, PRAS40, AS160, and Tsc2. Lrictor(KO) mice also manifest defects in insulin-activated mTORC1 activity, evidenced by decreased S6 kinase and Lipin1 phosphorylation. Glucose intolerance and insulin resistance of Lrictor(KO) mice could be fully rescued by hepatic expression of activated Akt2 or dominant negative FoxO1. However, in the absence of mTORC2, forced Akt2 activation was unable to drive hepatic lipogenesis. Thus, we have identified an Akt-independent relay from mTORC2 to hepatic lipogenesis that separates the effects of insulin on glucose and lipid metabolism.

Supplemental palmitoleic (C16:1 cis-9) acid reduces lipogenesis and desaturation in bovine adipocyte cultures1

Our objective was to determine if palmitoleic (C16:1 cis-9) acid supplementation to primary bovine adipocytes regulates lipogenic gene expression and rates of lipogenesis. Stromal vascular cells were isolated from subcutaneous and intermuscular fat, propagated, and frozen for use in this study. Cells were passaged 4 times, allowed to reach confluence, held for 2 d, and then differentiated with a standard hormone cocktail (d 0). At d 2, secondary differentiation media containing 1 of 4 concentrations of palmitoleic acid (0, 50, 150, or 300 μM) were added for 10 d. Cells were harvested on d 6 and 12 to assess fatty acid concentrations and gene expression. In addition, (13)C2 and (13)C18:0 stable isotopes were added on d 6 to measure lipogenesis and desaturase activity, respectively. Concentrations of C16:1 and total fatty acids increased (P < 0.05) linearly in response to palmitoleic acid supplement. Concentrations of C18:1 cis-11 and C20:1 cis-13 also increased (P < 0.01) in response to supplementation, suggesting elongation of palmitoleic acid in vitro. Concentrations of C16:1, C18:1 cis-11, and total fatty acids were also greater (P < 0.05) at d 12 compared with d 6. In contrast, C16:0, C18:0, and C18:1 cis-9 concentrations decreased (P < 0.05) in response to palmitoleic acid supplementation and were not affected (P > 0.05) by harvest day. The ratio of C18:1 cis-9/C18:0 and fractional synthetic rate (FSR) of desaturation decreased (P < 0.05) in response to increasing palmitoleic acid supplementation. In addition, FSR of lipogenesis was reduced (P < 0.05) in palmitoleic acid-treated cells. Messenger RNA abundance as determined by real-time quantitative PCR for stearoyl-CoA desaturase 1 (SCD1), fatty acid synthase (FASN), and elongase protein 6 (ELOVL6) genes were reduced (P < 0.05) by palmitoleic acid supplementation. Expression of a β-oxidation gene, carnitine palmitoyltransferase 1A (CPT1A), was upregulated (P < 0.05) with palmitoleic acid supplementation in a dose-responsive manner. Supplementation of palmitoleic acid to bovine adipocytes results in increased incorporation of this fatty acid and its elongation products into the adipocyte, which downregulates SCD1, FASN, and ELOVL6 to decrease lipogenesis and upregulates CPT1A, potentially increasing β-oxidation. These results suggest that palmitoleic acid, an end product of desaturation, can act as a regulator of lipogenesis, desaturation, and β-oxidation in bovine adipocytes.

Possible molecular mechanisms soy-mediated in preventing and treating nonalcoholic fatty liver disease.

The aim of this review is to describe the molecular mechanisms of nonalcoholic fatty liver disease (NAFLD) and to present evidence regarding the mechanisms of soy-mediated therapeutic activity in preventing and treating NAFLD. NAFLD is induced by multiple metabolic pathways, including an increase in the release of fatty acids from the adipose tissue (lipolysis), insulin resistance (IR), and an increase in "de novo" fatty acid synthesis. Furthermore, NAFLD is correlated with a decrease in liver β-oxidation, an increase in oxygen free radical production, and an increase in pro-inflammatory cytokine production, which leads to an increase in liver fat and, subsequently, to tissue damage. The bioactive compounds in soy can prevent and treat NAFLD by modulating lipid metabolism and regulating the expression of related transcription factors. Soy intake decreases the expression of sterol regulatory-element binding protein-lc (SREBP-1) and increases the expression of SREBP-2, which are transcription factors associated with the regulation of hepatic lipogenesis and reduction of cholesterol synthesis and absorption in the liver, respectively. Besides, interactions between soy components, such as standard amino acids, polyunsaturated fat, and the isoflavonoid-enriched fraction, are believed to improve fatty acid oxidation in the liver parenchyma by increasing the expression of peroxisome proliferator-activated receptor α (PPARα)-regulated genes, thus decreasing lipid accumulation in the liver. Therefore, including soy-derived foods in the diet as a therapeutic tool for patients with NAFLD might improve their clinical evolution.

Stress management: How the unfolded protein response impacts fatty liver disease

Induction of the unfolded protein response (UPR) is recognized as central to fatty liver disease (FLD) pathophysiology. This pathway may be a potential therapeutic target for FLD, as well as other diseases. However, fundamental questions as to how UPR contributes to FLD remain unanswered. Conflicting data suggest that this pathway can both protect against and augment this disease. Here, we review the relationship between protein secretion, endoplasmic reticulum function (ER), and UPR activation. The UPR serves to maintain secretory pathway homeostasis by enhancing the protein folding environment in the ER, and we review data investigating the role for individual UPR players in fatty liver (steatosis). We explore a novel concept in the field that all cases of UPR activation do not equal "ER stress". Rather, different types of UPRs that can either protect against or cause FLD are discussed. Refining our current understanding of this complex pathway is particularly important, as drugs that affect the protein folding environment in the ER and affect UPR activation are being successful in clinical trials for FLD.

Homology modelling of CB1 receptor and selection of potential inhibitor against Obesity.

Obesity and patient morbidity has become a health concern worldwide. Obesity is associated with over activity of the endocannabinoid system, which is involved in the regulation of appetite, lipogenesis and insulin resistance. Hypothalamic cannabinoid-1 receptor (CB1R) inverse agonists reduce body weight and improve cardiometabolic abnormalities in experimental and human obesity but displayed neuropsychiatric side effects. Hence, there is a need to develop therapeutics which employs blocking peripheral CB1 receptors and still achieve substantial weight loss. In view of the same, adipose tissue CB1 receptors are employed for this study since it is more specific in reducing visceral fat. Computer aided structure based virtual screening finds application to screen novel inhibitors and develop highly selective and potential drug. The rational drug design requires crystal structure for the CB1 receptor. However, the structure for the CB1 receptor is not available in its native form. Thus, we modelled the crystal structure using a lipid G-Protein coupled receptor (PDB: 3V2W, chain A) as template. Furthermore, we have screened a herbal ligand Quercetin [- 2- (3, 4-dihydroxyphenyl) - 3, 5, 7-trihydroxychromen-4-one] a flavonol present in Mimosa pudica based on its better pharmacokinetics and bioavailability profile. This ligand was selected as an ideal lead molecule. The docking of quercetin with CB1 receptor showed a binding energy of -6.56 Kcal/mol with 4 hydrogen bonds, in comparison to the known drug Rimonabant. This data finds application in proposing antagonism of CB1 receptor with Quercetin, for controlling obesity.

Regulation of lipogenesis by cyclin-dependent kinase 8–mediated control of SREBP-1

Altered lipid metabolism underlies several major human diseases, including obesity and type 2 diabetes. However, lipid metabolism pathophysiology remains poorly understood at the molecular level. Insulin is the primary stimulator of hepatic lipogenesis through activation of the SREBP-1c transcription factor. Here we identified cyclin-dependent kinase 8 (CDK8) and its regulatory partner cyclin C (CycC) as negative regulators of the lipogenic pathway in Drosophila, mammalian hepatocytes, and mouse liver. The inhibitory effect of CDK8 and CycC on de novo lipogenesis was mediated through CDK8 phosphorylation of nuclear SREBP-1c at a conserved threonine residue. Phosphorylation by CDK8 enhanced SREBP-1c ubiquitination and protein degradation. Importantly, consistent with the physiologic regulation of lipid biosynthesis, CDK8 and CycC proteins were rapidly downregulated by feeding and insulin, resulting in decreased SREBP-1c phosphorylation. Moreover, overexpression of CycC efficiently suppressed insulin and feeding-induced lipogenic gene expression. Taken together, these results demonstrate that CDK8 and CycC function as evolutionarily conserved components of the insulin signaling pathway in regulating lipid homeostasis.

Novel mechanisms by which fat cells regulate systemic insulin sensitivity and diabetes risk

The adipose cell functions as an endocrine organ in addition to its role in energy storage. Adipocytes secrete hormones, cytokines and other factors that influence energy balance, glucose homeostasis, insulin sensitivity and vascular biology through effects in peripheral tissues and the central nervous system. In humans with obesity and type 2 diabetes, expression of the Glut4 glucose transporter is down-regulated selectively in adipocytes and this has systemic metabolic effects. Knocking out Glut4 selectively in adipocytes in mice causes insulin-resistant and increases the risk of diabetes while adipose-specific Glut4 overexpression confers enhanced glucose tolerance and insulin sensitivity in spite of increased adiposity. To discover novel pathways that regulate glucose homeostasis and insulin sensitivity, we used DNA microarray analysis of adipose tissue from mice with adipose-specific alterations in Glut4 expression. We found novel adipocyte-secreted proteins that alter systemic insulin sensitivity. In addition, gene set enrichment analysis showed coordinate regulation of lipogenic genes in adipose tissue. This led to the discovery that the glucose-responsive transcription factor, Carbohydrate responsive-element binding protein (ChREBP), is a dominant regulator of lipogenesis in adipose tissue and that its expression in adipose tissue is highly associated with insulin sensitivity in humans even in the presence of obesity. Furthermore, we identified a novel, potent ChREBP isoform and defined a new “feed forward” mode of regulation of ChREBP by which adipose-lipogenesis regulates systemic glucose homeostasis. This could provide new strategies for prevention and treatment of insulin resistance and type 2 diabetes.

Molecular Mechanisms of Estrogen Receptors' Suppression of Lipogenesis in Pancreatic β-Cells

The gonadal steroid, 17β-estradiol (E2), suppresses pancreatic islet fatty acid and glycerolipid synthesis and prevents β-cell failure in rodent models of type 2 diabetes. β-Cell estrogen receptors (ER) mediate these actions by suppressing the expression and enzymatic activity of fatty acid synthase (FAS). Here, we explored the mechanism of FAS suppression. We show that E2, and pharmacological agonists for ERα, ERβ, and the G protein-coupled ER, suppress mRNA and protein expression of the transcriptional regulators of FAS, namely, sterol regulatory element-binding protein 1c (SREBP1c) and carbohydrate response element binding protein (ChREBP) in insulin-secreting INS-1 cells. ER suppress SREBP1c and ChREBP mRNA and protein expression via an extranuclear localization. Using two mouse lines with pancreas-specific null deletion of either ERα or the signal transducer and activator of transcription 3 (STAT3), we show that ERα activation in vivo reduces SREBP1c and ChREBP mRNA expression via a direct islet action involving STAT3 activation. The master regulators of lipogenesis, liver X receptor (LXR) α and β, transcriptionally up-regulate SREBP1c and ChREBP. We find that activation of ERα, ERβ, and G protein-coupled ER suppresses LXR's mRNA expression in INS-1 cells. We also observe that activation of ERα in mouse islets in vivo suppresses LXR mRNA in a STAT3-dependent manner. Finally, we show that E2 also activates and uses AMP-activated protein kinase in INS-1 cells to suppress SREBP1c protein expression. This study identifies extranuclear ER pathways involving STAT3 and AMP-activated protein kinase in the genetic control of lipogenesis with therapeutic implications to protect β-cells in type 2 diabetes.

Abstract 5169: Roles of lipogenesis in cancer stem-like cells at early stage of breast cancer

Abstract Ductal carcinoma in situ (DCIS) is considered an early stage of breast cancer and it is the precursor of invasive breast carcinoma. However, the transition from normal breast epithelial cells to DCIS is still not clearly elucidated. In order to determine the role of lipogenesis in normal to DCIS transition, we investigated the roles of SREBP1, a major transcription regulator of lipogenesis and its downstream lipogenic genes such as ACLY, ACC1 and FAS, by isolating cancer stem-like cells (CSCs) from DCIS.com cell line which forms typical DCIS lesions in animals by using the well-established cell surface markers, CD24−/CD44+/ESA+. We found that lipid synthesis was significantly upregulated in CSCs from DCIS.com in contrast to the corresponding population from normal breast epithelial cells (MCF10A). Furthermore, we found that this elevation of lipogenesis is indeed caused by the overexpression of SREBP1 which co-ordinately induces the overexpression of the downstream lipogenic genes. The CSCs obtained from DCIS.com were also found to be more tumorigenic than the parental cells as shown by the limiting dilution analysis. To determine the role of elevated level of SREBP1 and lipogenesis in the transition of normal breast epithelial cells to DCIS phenotype, we overexpressed SREBP1 in MCF10A and examined the transforming properties. Our in vitro data showed that MCF10A-SREBP1 cells indeed expressed a significantly higher level of SREBP1 and other lipogenic genes and this elevated level of lipogenesis resulted in the increased cell proliferation, increased mammospheres forming ability and enhanced cellular growth in 3D culture. These data suggest that increased lipogenesis in breast CSCs plays critical roles in DCIS formation. We also examined the effects of Resveratrol on CSCs from DCIS.com. Resveratrol significantly reduced the total lipid content by inhibiting SREBP1 and in turn other lipogenic genes and induced a series of pro-apoptotic genes such as DAPK2 and BNIP3 causing the death of CSCs from DCIS. The mammosphere forming ability of CSCs from DCIS was also blocked by Resveratrol. We also observed that Resveratrol indeed significantly suppressed the formation of DCIS by inhibiting lipogenesis and by upregulating DAPK2 and BNIP3 in our animal model of human DCIS. Collectively, our results indicate that lipogenic genes ACLY, ACC-1, FAS and SREBP1 are significantly up regulated in early stage of breast tumorigenesis and they confer proliferative and growth advantages to these cells. Lipogenesis targeting effect of Resveratrol on CSCs from DCIS provides us with a strong rationale to use this agent for chemo-prevention against DCIS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5169. doi:1538-7445.AM2012-5169

Abstract 1332: Cisd2 haploinsufficiency leads to non-alcoholic fatty liver disease (NAFLD) and accelerates hepatocarcinogenesis in mice

Abstract Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease. Hepatic steatosis (fatty liver) is a vulnerable factor that could lead to liver damage, inflammation, fibrosis, cirrhosis and hepatocellular carcinoma (HCC). However, despite the high prevalence of NAFLD, the genetic factor determining the disease progression remains poorly understood. CISD2 is a previously uncharacterized novel gene located within the overlapping region of HCC critical region and human longevity region on chromosome 4q. We have recently demonstrated for the first time that Cisd2 is a mitochondrial outer membrane protein which mediates mitochondrial integrity and lifespan in mammals. Surprisingly, we have observed phenotype similar to NAFLD in the liver of Cisd2 heterozygous (+/−) knockout mice. Cisd2 haplo-insufficiency led to abnormal lipid metabolism accompanying with fatty liver, cell death, severe inflammation and fibrosis in the liver. Moreover, there was a low incidence (1/18; 5.6%) of HCC developed at 16-18 months of age in the Cisd2+/− mice. Interestingly, our results revealed a significant increase of the Srebp1c which is the master regulator of lipogenesis; the increase in Srebp1-c seems to further up-regulate the expression of its target gene, fatty acid synthase (Fas), in the Cisd2+/− livers. In addition, we found that liver fibrosis was associated with activation of hepatic stellate cells, as revealed by increased expression of α-ΣMA, in the Cisd2+/− livers. Furthermore, we provide evidence that Cisd2 haplo-insufficiency promoted hepatocarcinogenesis and accelerated HCC development by 4-6 months in the transgenic mice expressing HBV X protein. In summary, our results suggested that Cisd2 is likely to be a haplo-insufficient tumor suppressor gene for HCC. Heterozygous deficiency of Cisd2 led to NAFLD, and accelerated the progression of HBV-associated HCC. Our data suggest that Cisd2 is a molecular target for the development of chemoprevention and therapeutic strategy for NAFLD. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1332. doi:1538-7445.AM2012-1332

Role of Hepatic Monounsaturated Fatty Acid Synthesis in Metabolic Regulation

Stearoyl‐CoA desaturase (SCD) catalyzes the de novo synthesis of monounsaturated fatty acids (MUFA) from saturated fatty acids. Past work demonstrated SCD1 deficiency impairs hepatic lipogenesis and protects against diet‐induced obesity. Our objective was to determine if hepatic MUFA synthesis is sufficient to restore the impaired lipogenic program in SCD1 global knockout mice (GKO). To address this, we produced liver‐specific transgenic mice expressing either human SCD5, which preferentially synthesizes oleate (18:1n‐9), or mouse SCD3, which preferentially synthesizes palmitoleate (16:1n‐7), and introduced these transgenes into GKO mice. Hepatic oleate synthesis largely prevented very‐low‐fat diet‐induced weight loss and increased white adipose tissue weight to a greater extent than hepatic palmitoleate. In females, hepatic SREBP‐1 maturation and lipogenic gene expression increased in hSCD5/GKO while expression of these genes remained low in mSCD3/GKO mice. Hepatic oleate increased plasma glucose levels greater than hepatic palmitoleate. This work suggests that hepatic MUFA are involved in regulation of lipogenesis and gluconeogenesis with oleate being more potent than palmitoleate. Supported by NIH.

SREBP1c is regulated by E3 ligase RNF20/BRE1A upon hormonal changes

Sterol regulatory element binding protein 1c (SREBP1c) is a key transcription factor to regulate de novo lipogenesis. However, molecular mechanisms involved in suppression of SREBP1c are largely unknown. In this study, we reveal that SREBP1c is negatively regulated by ubiquitination upon fasting signals. To better understand which factors are involved in ubiquitination of SREBP1c, we take advantages of affinity purification and mass spectrometry. In this analysis, RNF20/BRE1A is identified as a novel SREBP1c E3 ligase. Here we show that RNF20/BRE1A binds to and ubiquitinates SREBP1c, leading to its degradation. Previously, it has been well established that PKA signaling is activated by fasting signals. Interestingly, we find out that PKA activator such as forskolin enhances expression of RNF20/BRE1A and stimulates ubiquitination of SREBP1c via RNF20/BRE1A. In accordance with these, RNF20/BRE1A negatively regulates the transcriptional activity of SREBP1c and expression of SREBP1c target genes. In contrast, knockdown of RNF20/BRE1A increases expression of SREBP1c and lipogenic genes. Taken together, these data suggest that RNF20/BRE1A would be a negative regulator of lipogenesis through degradation of SREBP1c upon fasting.J. H. Lee was supported by Hi Seoul Science (Humanities) Fellowship funded by Seoul Scholarship Foundation.

Quercetin Reduces High‐Fat Diet‐Induced Fat Accumulation in the Liver by Regulating Lipid Metabolism Genes

To understand the molecular mechanisms underlying the influence of quercetin on the physiological effects of hyperlipidemia, we investigated its role in the prevention of high-fat diet (HFD)-induced obesity and found that it regulated hepatic gene expression related to lipid metabolism. Quercetin supplementation in mice significantly reduced the HFD-induced gains in body weight, liver weight, and white adipose tissue weight compared with the mice fed only with HFD. It also significantly reduced HFD-induced increases in serum lipids, including cholesterol, triglyceride, and thiobarbituric acid-reactive substance (TBARS). Consistent with the reduced liver weight and white adipose tissue weight, hepatic lipid accumulation and the size of lipid droplets in the epididymal fat pads were also reduced by quercetin supplementation. To further investigate how quercetin may reduce obesity, we analyzed lipid metabolism-related genes in the liver. Quercetin supplementation altered expression profiles of several lipid metabolism-related genes, including Fnta, Pon1, Pparg, Aldh1b1, Apoa4, Abcg5, Gpam, Acaca, Cd36, Fdft1, and Fasn, relative to those in HFD control mice. The expression patterns of these genes observed by quantitative reverse transcriptase-polymerase chain reaction were confirmed by immunoblot assays. Collectively, our results indicate that quercetin prevents HFD-induced obesity in C57B1/6 mice, and its anti-obesity effects may be related to the regulation of lipogenesis at the level of transcription.

Consumo de micronutrientes e excesso de peso: existe relação?

In past decades, the growth in obesity has been associated with changes in the lifestyle of the population, including comprehensive dietary changes, especially in the intake of micronutrients. To describe micronutrient intake and review its consequences on nutritional status. A literature review was performed covering domestic and international articles published over the past 11 years, on the SciELO, LILACS, MEDLINE and governmental databases, using descriptors such as "micronutrients", "food consumption", "excess weight", "health", "nutritional status" in Portuguese and in English. Micronutrient intake deficiency is a global health problem, affecting about 2 billion people and seems to be associated with an increased risk for non-communicable diseases and disorders, including obesity. Insufficient intake of vitamin A favors overweight by altering thyroid metabolism, while vitamin C is related to the synthesis of carnitine and fat oxidation; vitamin D favors the control of satiety and energy expenditure. As for minerals, calcium helps the regulation of thermogenesis and lipogenesis / lipolysis, and zinc is involved in regulating insulin and leptin. The promotion of healthy eating habits through educational practices is necessary for greater public awareness of the implications of micronutrient intake on nutritional status, and should be included in Public Health strategies in order to control obesity and its complications.

Glucose-dependent insulinotropic polypeptide signaling in pancreatic β-cells and adipocytes.

Glucose-dependent insulinotropic polypeptide (GIP) was the first incretin to be identified. In addition to stimulating insulin secretion, GIP plays regulatory roles in the maintenance, growth and survival of pancreatic islets, as well as impacting on adipocyte function. The current review focuses on the intracellular signaling pathways by which GIP contributes to the regulation of β-cell secretion and survival, and adipocyte differentiation and lipogenesis. Studies on signaling underlying the insulinotropic actions of the incretin hormones have largely been carried out with glucagon-like peptide-1. They have provided evidence for contributions by both protein kinase A (PKA) and exchange protein directly activated by cyclic adenosine monophosphate (EPAC2), and their probable role in GIP signaling is discussed. Recent studies have shown that inhibition of the kinase apoptosis signal-regulating kinase 1 (ASK1) by GIP plays a key role in reducing mitochondria-induced apoptosis in β-cells through protein kinase B (PKB)-mediated pathways, and that GIP-induced post-translational modification of voltage- dependent K(+) (Kv) channels also contributes to its prosurvival role. Through regulation of gene expression, GIP tips the balance between pro- and anti-apoptotic members of the B-cell lymphoma-2 (Bcl-2) protein family towards β-cell survival. GIP also plays important roles in the differentiation of pre-adipocytes to adipocytes, and in the regulation of lipoprotein lipase expression and lipogenesis. These events involve interactions between GIP, insulin and resistin signaling pathways. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00196.x, 2012).

Endoplasmic reticulum-tethered transcription factor cAMP responsive element-binding protein, hepatocyte specific, regulates hepatic lipogenesis, fatty acid oxidation, and lipolysis upon metabolic stress in mice

cAMP responsive element-binding protein, hepatocyte specific (CREBH), is a liver-specific transcription factor localized in the endoplasmic reticulum (ER) membrane. Our previous work demonstrated that CREBH is activated by ER stress or inflammatory stimuli to induce an acute-phase hepatic inflammation. Here, we demonstrate that CREBH is a key metabolic regulator of hepatic lipogenesis, fatty acid (FA) oxidation, and lipolysis under metabolic stress. Saturated FA, insulin signals, or an atherogenic high-fat diet can induce CREBH activation in the liver. Under the normal chow diet, CrebH knockout mice display a modest decrease in hepatic lipid contents, but an increase in plasma triglycerides (TGs). After having been fed an atherogenic high-fat (AHF) diet, massive accumulation of hepatic lipid metabolites and significant increase in plasma TG levels were observed in the CrebH knockout mice. Along with the hypertriglyceridemia phenotype, the CrebH null mice displayed significantly reduced body-weight gain, diminished abdominal fat, and increased nonalcoholic steatohepatitis activities under the AHF diet. Gene-expression analysis and chromatin-immunoprecipitation assay indicated that CREBH is required to activate the expression of the genes encoding functions involved in de novo lipogenesis, TG and cholesterol biosynthesis, FA elongation and oxidation, lipolysis, and lipid transport. Supporting the role of CREBH in lipogenesis and lipolysis, forced expression of an activated form of CREBH protein in the liver significantly increases accumulation of hepatic lipids, but reduces plasma TG levels in mice. All together, our study shows that CREBH plays a key role in maintaining lipid homeostasis by regulating the expression of the genes involved in hepatic lipogenesis, FA oxidation, and lipolysis under metabolic stress. The identification of CREBH as a stress-inducible metabolic regulator has important implications in the understanding and treatment of metabolic disease.

EFFECT OF SILYMARIN ON LIPID AND ALCOHOL METABOLISM IN MICE FOLLOWING LONG-TERM ALCOHOL CONSUMPTION

ABSTRACT An alcoholic fatty liver disease was induced by feeding an ethanol diet. Eight mice per group were randomly assigned to each following group: (1) control liquid diet + 0.5 mL ddH2O; (2) control liquid diet + 150 mg silymarin/kg body weight (BW) in 0.5 mL ddH2O; (3) ethanol liquid diet + 0.5 mL ddH2O; and (4) ethanol liquid diet + 150 mg silymarin/kg BW in 0.5 mL ddH2O. The ethanol diet increased (P < 0.05) liver size and total triglyceride levels but a gavage of silymarin reduced (P < 0.05) them. Silymarin also decreased (P < 0.05) aspartate aminotransferase (AST) value, the pathogenic hepatic lipid drop and cytoplasmic vacuolization formation in alcohol-fed mice, with respect to the regulation of lipogenesis and alcohol metabolism, although silymarin did not (P < 0.05) influence 3-hydroxy-3-methylglutaryl-CoA reductase, sterol regulatory element-binding protein-1, acetyl-CoA carboxylase, fatty acid synthase, carnitine palmitoyltransferase 1A (CPT1A), alcohol dehydrogenase 1 and alcohol dehydrogenase 7 gene expressions. However, proliferator-activated receptor-alpha, cytochrome P450, family 1, subfamily e, polypeptide 1, cytochrome P450, family 1, subfamily a, polypeptide 1 and catalase were up-regulated in the livers of alcohol-fed mice with a gavage of silymarin. PRACTICAL APPLICATIONS Hepatoprotection by silymarin has been attributed mainly to its antioxidant properties. Alcoholic fatty liver disease was induced by feeding mice an ethanol diet. Following co-treatment of mice with silymarin and alcohol, serum biochemical values, lipid and alcohol metabolism-related gene expression levels, as well as histopathological analyses of mice were examined. Our results demonstrate the hepatoprotective ability of silymarin against alcohol-induced liver damage in mice. The protective mechanisms of silymarin during alcohol-induced steatosis mainly result from increased energy expenditure as well as accelerated alcohol metabolism, not only from antioxidant properties in the previous literatures. This study offers another aspect of scientific evidence for silymarin on development of hepatoprotective agents.