Gene Expression Of Sterol Regulatory Element Binding Protein 1c Research Articles

DNAJA1 positively regulates amino acid-stimulated milk protein and fat synthesis in bovine mammary epithelial cells.

Several cellular processes, including the recovery of misfolded proteins, the folding of polypeptide chains, transit of polypeptides across the membrane, construction and disassembly of protein complexes, and modulation of protein control, are carried out by DnaJ homologsubfamily A member 1(DNAJA1), which belongs to the DnaJ heat-shock protein family. It is unknown if DNAJA1 regulates the production of milk in bovine mammary epithelium cells (BMECs). Methionine and leucine increased DNAJA1 expression and nuclear location, as seen by us. In contrast to DNAJA1 knockdown, overexpression of DNAJA1 boosted the production of milk proteins and fats as well as mammalian target of rapamycin (mTOR) and sterol regulatory element binding protein-1c(SREBP-1c). As a result of amino acids, mTOR and SREBP-1c gene expression are stimulated, and DNAJA1 is a positive regulator of BMECs'amino acid-induced controlled milk protein and fat production.

Isoleucine stimulates mTOR and SREBP-1c gene expression for milk synthesis in mammary epithelial cells through BRG1-mediated chromatin remodelling.

Several amino acids can stimulate milk synthesis in mammary epithelial cells (MEC); however, the regulatory role of isoleucine (Ile) and underlying molecular mechanism remain poorly understood. In this study, we aimed to evaluate the regulatory effects of Ile on milk protein and fat synthesis in MEC and reveal the mediation mechanism of Brahma-related gene 1 (BRG1) on this regulation. Ile dose dependently affected milk protein and fat synthesis, mechanistic target of rapamycin (mTOR) phosphorylation, sterol regulatory element binding protein 1c (SREBP-1c) expression and maturation, and BRG1 protein expression in bovine MEC. Phosphatidylinositol 3 kinase (PI3K) inhibition by LY294002 treatment blocked the stimulation of Ile on BRG1 expression. BRG1 knockdown and gene activation experiments showed that it mediated the stimulation of Ile on milk protein and fat synthesis, mTOR phosphorylation, and SREBP-1c expression and maturation in MEC. ChIP-PCR analysis detected that BRG1 bound to the promoters of mTOR and SREBP-1c, and ChIP-qPCR further detected that these bindings were increased by Ile stimulation. In addition, BRG1 positively regulated the binding of H3K27ac to these two promoters, while it negatively affected the binding of H3K27me3 to these promoters. BRG1 knockdown blocked the stimulation of Ile on these two gene expressions. The expression of BRG1 was higher in mouse mammary gland in the lactating period, compared with that in the puberty or dry period. Taken together, these experimental data reveal that Ile stimulates milk protein and fat synthesis in MEC via the PI3K-BRG1-mTOR/SREBP-1c pathway.

Qingluotongbi formula regulates the LXRα-ERS-SREBP-1c pathway in hepatocytes to alleviate the liver injury caused by Tripterygium wilfordii Hook. f.

Ethnopharmacological relevanceTripterygium wilfordii Hook. f. (TW) is widely used to treat autoimmune and inflammatory diseases; however, its development and application is limited by its significant association with liver injury. The compound formula Qingluotongbi (QLT) employs TW as its main component and is used to treat rheumatoid arthritis with no adverse reactions, suggesting that QLT may reduce the liver toxicity of TW. Aim of the studyWe examined whether TW interferes with lipid metabolism to induce liver injury, and evaluated the protective effect of QLT in in vivo and in vitro experiments. Materials and methodsAfter administration of QLT and its ingredients, HepaRG cells and SD rats were tested for biochemical indicators, hepatocytes lipid changes, and rat liver pathological changes, and then we analyzed for the gene expression of liver X receptor α (LXRα), endoplasmic reticulum stress (ERS) key proteins, sterol regulatory element binding protein-1c (SREBP-1c), and lipid-synthesizing enzymes. In HepaRG cells, the protein expression of glucose-regulated protein 78 kDa (GRP78) and LXRα was detected after addition of an LXRα inhibitor, LXRα agonist, and ERS inhibitor. ResultsTW caused significant elevation of biochemical indicators and lipid droplet deposition in hepatocytes, as well as upregulated the gene expression of LXRα, ERS key proteins, SREBP-1c, and lipid-synthesizing enzymes in both in vitro and in vivo settings, and caused liver injury in rats. QLT can alleviate the lipotoxic liver injury caused by TW. LXRα agonist further activated ERS induced by TW, whereas LXRα inhibitor significantly reduced ERS and lipotoxic injury induced by TW in HepaRG cells. ConclusionsTW upregulated LXRα to activate ERS and increased the gene expression of SREBP-1c and lipid-synthesizing enzymes, leading to increased lipid synthesis in hepatocytes to result in liver injury. QLT inhibited the LXRα-ERS-SREBP-1c pathway and reduced abnormal lipid synthesis in hepatocytes and the hepatotoxicity of TW.

Expression of the key metabolic regulators in the white adipose tissue of rats; the role of high-fat diet and aerobic training

Lipid metabolism, especially in the white adipose tissue as an active metabolic organ, is tightly regulated by the key transcription factors, such as the sterol regulatory element binding protein 1c (SREBP-1c) and the Farnesoid X Receptor (FXR). We have studied the expression of these genes in the white adipose tissue to see how a high fat diet (HFD) and two intensities of aerobic training change the lipogenic and lipolytic pathways. 44 male Wistar rats randomly divided into the normal (12% calories from fat) and HFD (56% calories from fat) groups. Each group included control (n=6), moderate trained (n=8, ~65% Vo2max) and high intensity trained (n=8, ~75% Vo2max) rats. After 8 weeks of training, the weight changes, plasma insulin and lipid profile levels and the relative gene expression of SREBP-1c and FXR in the adipose tissue was measured. Data were analysed by 2-way ANOVA (P<0.05). HFD fed rats showed higher levels of insulin and dyslipidemia that was correlated with the higher weight gain. Also, the adipose expression of SREBP-1c was higher in the HFD fed rats that it was strongly correlated with the lower FXR expression. Trained rats independent of the intensity of the training showed lower SREBP-1c and higher FXR expression, but no change was observed in the lipid profile levels. HFD-induced dyslipidemia could occur via SREBP-1c activation in the adipose tissue while the aerobic training activates FXR and inhibits the lipogenic pathways. Despite the activation of lipolytic pathways in the trained rats, it seems that diet has more effect on the lipid profile than the aerobic training.

Scutellaria baicalensis regulates FFA metabolism to ameliorate NAFLD through the AMPK-mediated SREBP signaling pathway.

Scutellaria baicalensis has been reported to improve the lipid metabolism of high-fat diet-induced liver dysfunction, but direct evidence is rare. This study aimed to explore the effects and mechanisms of S. baicalensis and its major constituent baicalin on hepatic lipotoxicity. KK-Ay mice and orotic acid (OA)-induced nonalcoholic fatty liver disease (NAFLD) rats were used to evaluate lipid metabolism regulatory effects. Sodium oleate-induced triglyceride-accumulated HepG2 cells were used for the mechanism study, pretreated with or without compound C or STO-609 or transfected with liver kinase B1 (LKB1) siRNA. In KK-Ay mice, S. baicalensis extract showed a decreased effect on serum and hepatic triglycerides, total cholesterols, and free fatty acid (FFA) levels after 8weeks of treatment. In OA-induced NAFLD rats, 18days of treatment with baicalin significantly inhibited hepatic lipid accumulation, attenuating hepatocyte hypertrophy, vacuolization and necrosis. S. baicalensis and baicalin treatment significantly suppressed the sterol regulatory element binding protein-1c (SREBP-1c) transcriptional program with downregulation of gene and protein expression of SREBP-1c (both precursor and mature fraction) and acetyl-CoA carboxylase, fatty acid synthase and stearoyl-CoA desaturase, and upregulation of AMP-activated protein kinase (AMPK), carnitine palmitoyl transferase 1 and nuclear respiratory factor 2 in the liver. Furthermore, activation of AMPK by baicalin was observed to be relative to the increase in phosphorylation of calmodulin-dependent protein kinase kinase. Taken together, S. baicalensis conferred preventive effects against FFA-induced lipotoxicity through the AMPK-mediated SREBP signaling pathway.

Nimbolide attenuate the lipid accumulation, oxidative stress and antioxidant in primary hepatocytes.

Nimbolide is a bioactive compound found in Azadirachta indica. This work was devised to investigate the potential effects of nimbolide on intracellular lipid deposition and its associated redox modulation in primary hepatocytes (Heps). Lipid accumulation was induced in Heps by supplementing 1mM oleic acid for 24h which was marked by significant accumulation of lipids. The results demonstrated that nimbolide can decrease intracellular cholesterol, free fatty acids and triglycerides. Nimbolide may also improve hepatocytes function through its antioxidant effects by inhibiting oxidative DNA damage and lipid peroxidation by curtailing the reactive oxygen species levels. Further it also restore the mitochondrial potential, improving the endogenous antioxidant levels such as GSH and antioxidant enzyme activities. Nimbolide increased (P < 0.05) liver X receptor-α (LXRα), peroxisome proliferator-activated receptor-γ (PPARγ) and sterol regulatory element-binding protein-1c (SREBP1c) gene expression in Heps. The biological significance of nimbolide may involve hypolipidemic effect, lipid peroxidation inhibition, DNA damage inhibition, ROS inhibition, restoring mitochondrial function, increases in GSH and SOD & CAT activities, and direct regulation of LXRα, PPARγ and SREBP1c gene expression. Nimbolide may be used as effective lipid lowering compound and lipid deposition-induced Heps changes.

Lithospermum erythrorhizon Root and its Naphthoquinones Repress SREBP1c and Activate PGC1α Through AMPKα.

To examine specific molecular mechanisms involved in modulating hepatic lipogenesis and mitochondria biogenesis signals by Lithospermum erythrorhizon (gromwell) root extract. Stable cell lines with luciferase reporter constructs were generated to examine sterol regulatory element binding protein 1c (SREBP1c) and peroxisome proliferator-activated receptor gamma, coactivator 1 (PGC1) α promoter activity and estrogen-related receptor (ERR) α response element activity. Gene expression of SREBP1c, stearoyl coenzyme A desaturase 1, and PGC1α was measured by using reverse transcription polymerase chain reaction. Lipogenesis was measured in human hepatoma cells with Nile red staining and flow cytometry. Phosphorylation of AMP-activated protein kinase (AMPK) α was determined by using ELISA and Western blot. Gromwell root extract and its naphthoquinones dose-dependently repressed high glucose and liver X receptor α induction of SREBP1c promoter activity and gene expression. Hepatic lipogenesis was repressed, and PGC1α promoter and gene expression and ERRα response element activity were increased by gromwell root extract. Gromwell root extract, shikonin, and α-methyl-n-butyrylshikonin increased AMPKα phosphorylation, and inhibition of AMPK blunted the repression in SREBP1c promoter activity by gromwell root extract and its naphthoquinones. Data suggest that gromwell root extract and its naphthoquinones repress lipogenesis by increasing the phosphorylated state of AMPKα and stimulating mitochondrial biogenesis signals.

How high-fat diet and high-intensity interval training affect lipid metabolism in the liver and visceral adipose tissue of rats

Lipogenic and lipolytic pathways are tightly regulated by nuclear receptors and binding proteins, such as farnesoid x receptor (FXR) and sterol regulatory element binding protein 1c (SREBP-1c). We designed this research to study the effects of high-intensity interval training (HIIT) and high-fat diet (HFD) on hepatic and adipose FXR and SREBP-1c gene expression beside the plasma levels of lipid profile and insulin. 24 male Wistar rats were randomly divided into normal (~12% fat) and HFD (~56% fat) groups with or without participating in the 8 weeks HIIT protocol. Results from two-way ANOVA and Pearson tests (P&lt;0.05) showed that the HFD rats experienced a larger weight gain correlated with dyslipidemia and hyperinsulinemia, higher hepatic and adipose SREBP-1c expression and lower hepatic FXR expression compared with normal diet fed rats. Although HIIT rats showed higher hepatic FXR and lower hepatic and adipose SREBP-1c expression and lower weight gain compared with untrained rats, plasma lipid profile levels had not any significant difference between trained and untrained rats. Interestingly, hepatic FXR expression was negatively correlated with weight gain and SREBP-1c expression in both tissues while only the hepatic SREBP-1c was positively correlated to insulin levels. In conclusion, HFD-induced dyslipidemia could occur via the activation of the hepatic SREBP-1c pathway under the insulin effect. Although HIIT rats showed lower SREBP-1c correlated to hepatic FXR activation it seems diet is more effective on lipid profile than HIIT. Also, in presence of HFD, HIIT only affects adipose lipolysis.

Resveratrol and fenofibrate ameliorate fructose-induced nonalcoholic steatohepatitis by modulation of genes expression.

To evaluate the effect of resveratrol, alone and in combination with fenofibrate, on fructose-induced metabolic genes abnormalities in rats. Giving a fructose-enriched diet (FED) to rats for 12 wk was used as a model for inducing hepatic dyslipidemia and insulin resistance. Adult male albino rats (150-200 g) were divided into a control group and a FED group which was subdivided into 4 groups, a control FED, fenofibrate (FENO) (100 mg/kg), resveratrol (RES) (70 mg/kg) and combined treatment (FENO + RES) (half the doses). All treatments were given orally from the 9(th) week till the end of experimental period. Body weight, oral glucose tolerance test (OGTT), liver index, glucose, insulin, insulin resistance (HOMA), serum and liver triglycerides (TGs), oxidative stress (liver MDA, GSH and SOD), serum AST, ALT, AST/ALT ratio and tumor necrosis factor-α (TNF-α) were measured. Additionally, hepatic gene expression of suppressor of cytokine signaling-3 (SOCS-3), sterol regulatory element binding protein-1c (SREBP-1c), fatty acid synthase (FAS), malonyl CoA decarboxylase (MCD), transforming growth factor-β1 (TGF-β1) and adipose tissue genes expression of leptin and adiponectin were investigated. Liver sections were taken for histopathological examination and steatosis area were determined. Rats fed FED showed damaged liver, impairment of glucose tolerance, insulin resistance, oxidative stress and dyslipidemia. As for gene expression, there was a change in favor of dyslipidemia and nonalcoholic steatohepatitis (NASH) development. All treatment regimens showed some benefit in reversing the described deviations. Fructose caused deterioration in hepatic gene expression of SOCS-3, SREBP-1c, FAS, MDA and TGF-β1 and in adipose tissue gene expression of leptin and adiponectin. Fructose showed also an increase in body weight, insulin resistance (OGTT, HOMA), serum and liver TGs, hepatic MDA, serum AST, AST/ALT ratio and TNF-α compared to control. All treatments improved SOCS-3, FAS, MCD, TGF-β1 and leptin genes expression while only RES and FENO + RES groups showed an improvement in SREBP-1c expression. Adiponectin gene expression was improved only by RES. A decrease in body weight, HOMA, liver TGs, AST/ALT ratio and TNF-α were observed in all treatment groups. Liver index was increased in FENO and FENO + RES groups. Serum TGs was improved only by FENO treatment. Liver MDA was improved by RES and FENO + RES treatments. FENO + RES group showed an increase in liver GSH content. When resveratrol was given with half the dose of fenofibrate it improved NASH-related fructose-induced disturbances in gene expression similar to a full dose of fenofibrate.

Preventive effect of total glycosides from Ligustri Lucidi Fructus against nonalcoholic fatty liver in mice.

The protective effects of the total glycosides from Ligustri Lucidi Fructus against nonalcoholic fatty liver (NAFL) in mice were investigated. Liver injury was induced by the administration of high fat diet for 60 days. During this period, the model group received high fat diet only; the treatment groups received various drugs plus high fat diet. Compared with the model group, the total glycosides significantly decreased the contents of triglyceride (TG) and cholesterol (TC), as well as the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the serum. Moreover, the contents of TG and TC in liver tissue and the liver index were reduced. Histological findings also confirmed antisteatosis. Compared with the model group, total glycosides significantly reduced the levels of the sterol regulatory element binding protein-1c (SREBP-1c) and liver X receptor-a (LXR-α) protein, and down-regulated the expression of SREBP-1c, LXR-α and interleukin-6 (IL-6) mRNA in the liver. These results suggest that the total glycosides are effective in the treatment of NAFL of mice. Their mode of action is associated with inhibiting SREBP-1c, LXR-α and IL-6 mRNA, reducing lipid synthesis factor SREBP-1c and LXR-α protein and gene expression, suppressing inflammatory responses, then decreasing serum lipid and hepatic lipid.

Lipid-Modulating Effects of Aqueous Extract of Rubus Occidentalis in Hepatocarcinoma HepG2 Cells

Little knowledge exists on the lipid-modulating effect of Rubus occidentalis (RO). The present study investigated the molecular mechanisms of lipid-modulating effects of aqueous extract of RO (ROW) in hepatocarcinoma HepG2 cells. ROW decreased apolipoprotein B100 (ApoB100)/apolipoprotein A-1 (ApoA-1) ratio. ROW increased the expression of LDL-receptor (LDL-R). ROW decreased the gene expression of sterol regulatory element-binding protein 1c (SREBP-1c) as well as fatty acid synthase in a concentration-dependent manner. ROW not only down-regulated gene expression of SREBP-2 and HMG-CoA synthase mRNA expression, but also inhibited HMG-CoA reductase activity in a concentration-dependent manner (IC50 = 240.6 μg/ml). These results indicate that ROW decreases the level of bad cholesterol and increases good cholesterol levels by lowering the gene expression of transcription factors, SREBP-1c and SREBP-2, and by inhibiting the expression and/or activity of their downstream enzymes such as fatty acid synthase and HMG-CoA synthase and reductase.

Role for sterol regulatory element binding protein-1c activation in mediating skeletal muscle insulin resistance via repression of rat insulin receptor substrate-1 transcription

Sterol regulatory element binding protein-1c (SREBP-1c) is a master regulator of fatty acid synthase and controls lipogenesis. IRS-1 is the key insulin signalling mediator in skeletal muscle. In the present study, we investigated the role of SREBP-1c in the regulation of IRS-1 in skeletal muscle cells. L6 muscle cells were treated with palmitic acid (PA) or metformin. Adenovirus vectors expressing Srebp-1c (also known as Srebf1) and small interfering RNA (siRNA) against Srebp-1c were transfected into the L6 cells. Protein-DNA interactions were assessed by luciferase reporter analysis, electrophoretic mobility shift assay and chromatin immunoprecipitation assay. We found that both gene and protein expression of SREBP-1c was increased in contrast to IRS-1 expression in PA-treated L6 cells. SREBP-1c overproduction decreased Irs-1 mRNA and IRS-1 protein expression in a dose-dependent manner, and suppressed the resultant insulin signalling, whereas SERBP-1c knockdown by Serbp-1c siRNA blocked the downregulation of IRS-1 induced by PA. Protein-DNA interaction studies demonstrated that SREBP-1c was able to bind to the rat Irs-1 promoter region, thereby repressing its gene transcription. Of particular importance, we found that metformin treatment downregulated Srebp-1c promoter activity, decreased the specific binding of SREBP-1c to Irs-1 promoter and upregulated Irs-1 promoter activity in PA-cultured L6 cells. Our data indicate for the first time that SREBP-1c activation participates in skeletal muscle insulin resistance through a direct effect of suppressing Irs-1 transcription. These findings imply that SREBP-1c could serve as an attractive therapeutic target for insulin resistance.

FoxO1 Inhibits Sterol Regulatory Element-binding Protein-1c (SREBP-1c) Gene Expression via Transcription Factors Sp1 and SREBP-1c

Induction of lipogenesis in response to insulin is critically dependent on the transcription factor, sterol regulatory element-binding protein-1c (SREBP-1c). FoxO1, a forkhead box class-O transcription factor, is an important mediator of insulin action, but its role in the regulation of lipid metabolism has not been clearly defined. We examined the effects of FoxO1 on srebp1 gene expression in vivo and in vitro. In vivo studies showed that constitutively active (CA) FoxO1 (CA-FoxO1) reduced basal expression of SREBP-1c mRNA in liver by ∼60% and blunted induction of SREBP-1c in response to feeding. In liver-specific FoxO knock-out mice, SREBP-1c expression was increased ∼2-fold. Similarly, in primary hepatocytes, CA-FoxO1 suppressed SREBP1-c expression and inhibited basal and insulin-induced SREBP-1c promoter activity. SREBP-1c gene expression is induced by the liver X receptor (LXR), but CA-FoxO1 did not block the activation of SREBP-1c by the LXR agonist TO9. Insulin stimulates SREBP-1c transcription through Sp1 and via "feed forward" regulation by newly synthesized SREBP-1c. CA-FoxO1 inhibited SREBP-1c by reducing the transactivational capacity of both Sp1 and SREBP-1c. In addition, chromatin immunoprecipitation assays indicate that FoxO1 can associate with the proximal promoter region of the srebp1 gene and disrupt the assembly of key components of the transcriptional complex of the SREBP-1c promoter. We conclude that FoxO1 inhibits SREBP-1c transcription via combined actions on multiple transcription factors and that this effect is exerted at least in part through reduced transcriptional activity of Sp1 and SREBP-1c and disrupted assembly of the transcriptional initiation complex on the SREBP-1c promoter.

Transcriptional Metabolic Inflexibility in Skeletal Muscle Among Individuals With Increasing Insulin Resistance

Disturbances in skeletal muscle lipid metabolism may play an important role in development of insulin resistance (IR). The aim was to investigate transcriptional control of skeletal muscle fatty acid (FA) metabolism in individuals with the metabolic syndrome (MetS) with varying degrees of insulin sensitivity (S(I)). 122 individuals with MetS (NCEP-ATP III criteria) at age 35-70 years, BMI 27-38 kg/m(2) were studied (subgroup EU-LIPGENE study). Individuals were divided into quartiles of S(I) measured during a frequently sampled insulin modified intravenous glucose tolerance test. Skeletal muscle normalized mRNA expression levels of genes important in skeletal muscle FA handling were analyzed with quantitative real-time PCR. The expression of sterol regulatory element binding protein 1c (SREBP1c), acetyl-CoA carboxylase 2 (ACC2), diacylglycerol acyltransferase (DGAT1), and nuclear respiration factor (NRF) was higher in the lowest two quartiles of S(I) (<50th) compared with the highest two quartiles of S(I) (>50th). Interestingly, peroxisome proliferator-activated receptor coactivator 1α (PGC1α), peroxisome proliferator-activated receptor α (PPARα), and muscle carnitine palmitoyl transferase 1b (mCPT1), important for oxidative metabolism, showed a complex mRNA expression profile; levels were lower in both the most "insulin sensitive" (IS) as well as the most "IR" individuals. Lipoprotein lipase (LPL) mRNA was reduced in the lowest quartile of S(I). Enhanced gene expression of SREBP1c and ACC2 in the IR state suggests a tendency towards FA storage rather than oxidation. From the lower expression of PGC1α, PPARα, and mCPT1 in both the most "IS" as well as the most "IR" individuals, it may be speculated that "IS" subjects do not need to upregulate these genes to have a normal FA oxidation, whereas the most "IR" individuals are inflexible in upregulating these genes.

Role of S6K1 in regulation of SREBP1c expression in the liver

The transcription factor sterol regulatory element-binding protein 1c (SREBP1c) plays an important role in the control of fatty acid metabolism in the liver. Evidence suggests that mammalian target of rapamycin (mTOR) complex 1 (mTORC1) contributes to the regulation of SREBP1c expression, but signaling downstream of mTORC1 remains unclear. We have now shown that medium rich in branched-chain amino acids stimulates expression of the SREBP1c gene in cultured hepatocytes in a manner sensitive both to rapamycin, a pharmacological inhibitor of mTORC1, and to a short hairpin RNA (shRNA) specific for S6 kinase 1 (S6K1), a downstream effector of mTORC1. The phosphorylation of S6K1 was increased in the liver of obese db/db mice. Furthermore, depletion of hepatic S6K1 in db/db mice with the use of an adenovirus vector encoding S6K1 shRNA resulted in down-regulation of SREBP1c gene expression in the liver as well as a reduced hepatic triglyceride content and serum triglyceride concentration. These results thus suggest that S6K1 regulates SREBP1c expression both in cultured hepatocytes and in mouse liver, and that increased hepatic activity of S6K1 contributes at least in part to the pathogenesis of obesity-induced hepatic steatosis and hypertriglyceridemia.

Reduction of lipid accumulation in HepG2 Cells by luteolin is associated with activation of AMPK and Mitigation of oxidative stress

The present study was carried out to investigate the lipid-lowering effect of luteolin by using a cell model of steatosis induced by palmitate. Incubation of HepG2 cells with palmitate markedly increased lipid accumulation (Oil Red O staining), the genes involved in lipogenesis, including fatty acid synthase (FAS) and its upstream regulator sterol regulatory element binding protein 1c (SREBP-1c), and reactive oxygen species (ROS) production. Luteolin enhanced the phosphorylation of AMP-activated protein kinase α (AMPKα) and its primary downstream targeting enzyme, acetyl-CoA carboxylase (ACC), up-regulated gene expression of carnitine palmitoyl transferase 1 (CPT-1), which is the rate-limiting enzyme in mitochondrial fatty acid β-oxidation, and down-regulated SREBP-1c and FAS mRNA levels in the absence and presence of palmitate. In addition, luteolin significantly decreased ROS production and ameliorated lipid accumulation in HepG2 cells caused by palmitate. Furthermore, intracellular triglyceride (TG) measurement indicated that the luteolin-mediated reduction of enhanced TG caused by palmitate was blocked by pretreatment with the AMPK inhibitor, compound C. The results suggested that the lipid-lowering effect of luteolin might be partially mediated by the up-regulation of CPT-1 and down-regulation of SREBP-1c and FAS gene expression, possibly by activation of the AMPK signaling pathway, and partially might be through its antioxidative actions.

Perinatal Exposure to Bisphenol A Alters Early Adipogenesis in the Rat

BackgroundThe causes of the current obesity pandemic have not been fully elucidated. Implication of environmental endocrine disruptors such as bisphenol A (BPA) on adipose tissue development has been poorly investigated.ObjectivesThe aim of the present study was to evaluate the effects of perinatal exposure to BPA on early adipose storage at weaning.MethodsPregnant Sprague-Dawley rats had access to drinking water containing 1 mg/L BPA from day 6 of gestation through the end of lactation. Pups were weaned on postnatal day (PND) 21. At that time, we investigated perigonadal adipose tissue of pups (weight, histology, gene expression). For the remaining animals, we recorded body weight and food intake for animals on either standard chow or a high-fat diet.ResultsGestational exposure to BPA did not alter the sex ratio or litter size at birth. On PND1, the weight of male and female BPA-exposed pups was increased. On PND21, body weight was increased only in females, in which parametrial white adipose tissue (pWAT) weight was increased about 3-fold. This excess of pWAT was associated with adipocyte hypertrophy and overexpression of lipogenic genes such as C/EBP-α (CAAT enhancer binding protein alpha), PPAR-γ (peroxisome proliferator-activated receptor gamma), SREBP-1C (sterol regulatory element binding protein-1C), LPL (lipoprotein lipase), FAS (fatty acid synthase), and SCD-1 (stearoyl-CoA desaturase 1). In addition, gene expression of SREBP-1C, FAS, and ACC (acetyl-CoA carboxylase) was also increased in liver from BPA-exposed females at PND21, without a change in circulating lipids and glucose. After weaning, perinatal BPA exposure predisposed to overweight in a sex- and diet-dependent manner. We observed no change in food intake due to perinatal BPA exposure in rats on either standard chow or a high-fat diet.ConclusionsPerinatal exposure to a low dose of BPA increased adipogenesis in females at weaning. Adult body weight may be programmed during early life, leading to changes dependent on the sex and the nutritional status. Although further studies are required to understand the mechanisms of BPA action in early life, these results are particularly important with regard to the increasing prevalence of childhood obesity and the context-dependent action of endocrine disruptors.

FoxO1negatively regulates sterol regulatory element binding protein‐1c (SREBP‐1c) gene

The induction of genes involved in lipid biosynthesis by insulin is mediated in part by the sterol regulatory element‐binding protein‐1c (SREBP‐1c) and this effect is mediated in part through a mechanism that is dependent on the liver X receptor alpha (LXRα). FoxO1, a forkhead box class‐O transcription factor, is an important target of insulin action. We performed experiments to study the effects of FoxO1 on SREBP‐1c gene expression. Our studies show that over‐expression of constitutively active FoxO1 protein (CA‐FoxO1) inhibits, and small interference RNA against FoxO1 enhances both basal and insulin‐stimulated activity of the rat SREBP‐1c promoter. CA‐FoxO1 suppresses the activities of the SREBP‐1c promoter in a dose‐dependent fashion, and antagonizes the effect of insulin and TO901317 (a synthetic ligand of LXRα) on promoter activity. CA‐FoxO1 significantly reduces the effect of LXRα ?on basal and TO901317‐stimulated activity of a luciferase reporter construct driven by 3 LXR‐response elements, and decreases the transactivational ability of a Gal4‐LXRα fusion protein. These results indicate that FoxO1 plays an important role in regulating basal and insulin‐stimulated SREBP‐1c promoter activity and may exert this effect by antagonizing the function of LXRα.This work was supported by a grant from the Office of Research and Development, Department of Veterans Affairs.

Quantitation of alpha-linolenic acid elongation to eicosapentaenoic and docosahexaenoic acid as affected by the ratio of n6/n3 fatty acids

BackgroundConversion of linoleic acid (LA) and alpha-linolenic acid (ALA) to their higher chain homologues in humans depends on the ratio of ingested n6 and n3 fatty acids.Design and methodsIn order to determine the most effective ratio with regard to the conversion of ALA to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), human hepatoma cells were incubated with varying ratios of [13C] labeled linoleic acid ([13C]LA)- and alpha-linolenic acid ([13C]ALA)-methylesters. Regulative cellular signal transduction pathways involved were studied by determinations of transcript levels of the genes encoding delta-5 desaturase (D5D) and delta-6 desaturase (D6D), peroxisome proliferator-activated receptor alpha (PPARα) and sterol regulatory element binding protein 1c (SREBP-1c). Mitogen-activated protein kinase kinase 1 (MEK1) and mitogen-activated protein kinase kinase kinase 1 (MEKK1) were also examined.ResultsMaximum conversion was observed in cells incubated with the mixture of [13C]LA/[13C]ALA at a ratio of 1:1, where 0.7% and 17% of the recovered [13C]ALA was converted to DHA and EPA, respectively. Furthermore, differential regulation of enzymes involved in the conversion at the transcript level, dependent on the ratio of administered n6 to n3 fatty acids in human hepatocytes was demonstrated.ConclusionFormation of EPA and DHA was highest at an administered LA/ALA ratio of 1:1, although gene expression of PPARα, SREBP-1c and D5D involved in ALA elongation were higher in the presence of ALA solely. Also, our findings suggest that a diet-induced enhancement of the cell membrane content of highly unsaturated fatty acids is only possible up to a certain level.

Effect of level and duration of dietary n-3 polyunsaturated fatty acid supplementation on the transcriptional regulation of Δ9-desaturase in muscle of beef cattle1

The objective of this study was to examine the effect of level and duration of feeding of an n-3 PUFA-enriched fish oil (FO) supplement in combination with soybean oil (SO) on the transcriptional regulation of Delta(9)-desaturase gene expression in bovine muscle. Beef bulls (n = 40) were assigned to 1 of 4 iso-lipid and isonitrogenous concentrate diets fed for ad libitum intake for a 100-d finishing period. Concentrates were supplemented with one of the following: 1) 6% SO (CON); 2) 6% SO + 1% FO (FO1); 3) 6% SO + 2% FO (FO2); or 4) 8% palmitic acid for the first 50 d and 6% SO + 2% FO for the second 50 d [FO2(50)]. Samples of LM were harvested and concentrations of fatty acids were measured. Total RNA was isolated and the gene expression of Delta(9)-desaturase was determined. The mRNA expression of putative regulators of Delta(9)-desaturase gene expression, sterol regulatory element binding protein-1c (SREBP-1c) and peroxisome proliferator activated receptor-alpha (PPAR-alpha), were also measured in the CON and FO2 groups. Expression of mRNA for Delta(9)-desaturase was decreased (P < 0.05) 2.6-, 4.4-, and 4.9-fold in FO1, FO2(50), and FO2 compared with CON, respectively. Expression of Delta(9)-desaturase mRNA tended to be reduced (P = 0.09) by increasing FO from 1 to 2%, but was not affected by duration of supplementation (P > 0.24). Expression of mRNA for SREBP-1c was decreased 2-fold in FO2 compared with CON (P < 0.05), whereas expression of PPAR-alpha was not affected (P > 0.30). There was a positive relationship between Delta(9)-desaturase and SREBP-1c gene expression (P < 0.01), but the expression of both genes was negatively related to tissue concentrations of n-3 PUFA (P < 0.05) and positively related to concentration of n-6 PUFA (P < 0.01). Simultaneous enhancement of tissue concentrations of CLA and n-3 PUFA concentrations in bovine muscle may be hindered by negative interactions between n-3 PUFA and Delta(9)-desaturase gene expression, possibly mediated through reduced expression of SREBP-1c.