Sterol Regulatory Element-binding Protein-1c Protein Research Articles

Dimethyloxalylglycine Suppresses SREBP1c and Lipogenic Gene Expressions in Hepatocytes Independently of HIF1A.

Dimethyloxalylglycine (DMOG) is a representative inhibitor of the prolyl hydroxylase domain (PHD), which mediates the degradation of hypoxia-inducible factor-1-alpha (HIF1A). DMOG exerts its pharmacological effects via the canonical pathway that involves PHD inhibition; however, it remains unclear whether DMOG affects lipogenic gene expression in hepatocytes. We aimed to elucidate the effects of DMOG on sterol regulatory element-binding protein-1c (SREBP1c), a master regulator of fatty acid synthesis in hepatocytes. DMOG treatment inhibited SREBP1c mRNA and protein expression in HepG2 and AML12 hepatocytes and reduced the transcript levels of SREBP1c-regulated lipogenic genes. A luciferase reporter assay revealed that DMOG inhibited the transcriptional activity of SREBP1c. Moreover, DMOG suppressed SREBP1c expression in mice liver. Mechanistically, treatment with DMOG enhanced the expression of HIF1A and insulin-induced gene 2 (INSIG2), which inhibits the activation of SREBP1c. However, HIF1A or INSIG2 knockdown failed to reverse the inhibitory effect of DMOG on SREBP1c expression, suggesting a redundant role of HIF1A and INSIG2 in terms of repressing SREBP1c. DMOG did not function through the canonical pathway involving inhibition of SREBP1c by PHD, highlighting the presence of non-canonical pathways that mediate its anti-lipogenic effect.

Exploring effects of natural hyperoxic environment on liver lipid metabolism based on the bile acid-farnesoid X receptor pathway in sub-healthy rats

Objective: To investigate the effect of natural hyperoxic environment on liver lipid metabolism and liver function based on the bile acid-farnesoid X receptor pathway in sub-healthy rats. Methods: Forty adult male Wistar rats were randomly divided into control group (n = 10) and sub-healthy model group (n = 30). The control group was fed a normal diet, and the model group was fed a high-fat-sugar diet with limited daily activities for 5 weeks. The sub-healthy model was successfully established and the feeding conditions were restored. The hyperoxic intervention group (healthy group) were placed in a natural hyperoxic environment for 7 days. The rats feeding status in the spontaneous recovery group were unchanged. The appearance and exhaustive swimming time were compared before and after in healthy rats. Peripheral blood was collected for biochemical measurement. The fluorescence intensity of FXR and peroxisome proliferator activated receptor α (PPAR α) in liver tissue was detected by fluorescence double staining. Real-time fluorescent semi-quantitative PCR and Western blot were used to detect the RNA and protein expression condition of bile acid-FXR signaling pathway related indicators (FXR, PPARα, and SREBP-1c) in liver tissues. Results: Compared with the control group, the model group had gained body weight, and the vitality was decreased, while triglycerides [TG, (1.18 ± 0.20) mmol/L vs. (0.65 ± 0.12) mmol/L] and total cholesterol [TC, (1.23 ± 0.29) mmol/L vs. (1.00 ± 0.25) mmol/L] level was increased, (P < 0.05), which suggests the presence of hepatic steatosis. TG and TC level in the healthy group and spontaneous recovery group were lower than the model group, and the differences between the healthy group and the model group were statistically significant (P < 0.05). Compared with the model group, the expression of FXR and PPARα in the liver of the healthy and the spontaneous recovery group was enhanced, while the expression of the sterol regulatory element binding protein 1c (SREBP-1c) was decreased. FXR and PPARα mRNA levels in the healthy group and the model group were (9.27 ± 0.26 vs. 6.77 ± 0.20), and (9.71 ± 0.21 vs. 7.09 ± 0.24), P < 0.01, respectively. Compared with the model group, spontaneous recovery group mRNA levels were 7.99 ± 0.30 and 8.44 ± 0.28, P < 0.05, respectively. FXR and SREBP-1c protein levels between the healthy group and the model group were (1.30 ± 0.19 vs.0.43 ± 0.28), and (1.56 ± 0.22 vs. 2.43 ± 0.19), P < 0.01, respectively. Compared with the model group, the FXR and SREBP-1c protein levels of the spontaneous recovery group were 0.81 ± 0.33 vs. 2.10 ± 0.38, P < 0.05, respectively. In addition, natural hyperoxic environment had enhanced liver lipid metabolism and improved lipid disorders. Conclusion: The natural hyperoxic environment have the ability to regulate liver lipid metabolism and can improve mild hyperlipidemia to a certain extent.

Neddylation of sterol regulatory element-binding protein 1c is a potential therapeutic target for nonalcoholic fatty liver treatment

Nonalcoholic fatty liver disease (NAFLD) is a risk factor for progression of steatohepatitis, liver cirrhosis, and liver cancer. Although pathological condition of NAFLD, which arises from an excessive accumulation of triglyceride in the liver, is accompanied by elevated sterol regulatory element-binding protein 1c (SREBP1c) level, it is largely unknown which factors are involved in the modification of SREBP1c. In this study, we discovered that neddylation of SREBP1c competes with its ubiquitination and stabilizes SREBP1c protein level, and eventually promotes hepatic steatosis. We also demonstrated that human homolog of mouse double minute 2 (HDM2) acts as an E3 neddylation ligase of SREBP1c. Further, treatment with the neddylation inhibitor, MLN4924, attenuates high-fat diet-induced hepatic steatosis by reducing the levels of SREBP1c protein and hepatic triglyceride. Our results indicate that the blockade of SREBP1c neddylation could be a novel approach in the defense against NAFLD.

Role of Jumonji‐C Histone Demethylase in the Development of Hepatocellular Carcinoma

Reprogramming in lipid metabolism has received increasing recognition as a hallmark of cancer cells. In cancer cells, large demands of lipids were required to meet excessive synthesis of membranes, energy production and activation of intracellular signaling pathways during cell proliferation. To meet these demands, cancer cells express increased levels of lipogenic enzymes responsible for FAs synthesis, which is a target of crucial transcriptional regulator, sterol regulatory element binding protein 1c (SREBP1c). SREBP1c is a well‐known master transcription factor for de novo lipogenesis and is found frequently increased in many human cancers. However, the molecular mechanisms involved in the regulation of SREBP1c remain incompletely understood. In this study, we uncover the role of jumonji‐C histone demethylase (JHDM) as a repressor of SREBP1c, thereby preventing lipogenesis and proliferation of hepatocellular carcinoma (HCC) cells. JHDM directly interacts with SREBP1c at basic helix‐loop‐helix domain of SREBP1c and plant homeodomain of JHDM, promoting proteasomal degradation of SREBP1c protein. In addition, knockdown of JHDM stimulates mRNA levels of lipogenic enzymes and induces lipogenesis in HCC cells. However, JHDM‐loss‐induced lipogenesis is recovered by SREBP1c knockdown, implying that SREBP1c is crucial for the effects of JHDM toward lipogenesis. In contrast, ectopic expression of JHDM shows protective effects on oleic acid‐induced lipid accumulation in HCC cells. We also found that JHDM knockdown using si‐RNAs promotes mRNA expressions of cell cycle regulators, accompanied with enhanced cell growth, colony formation and spheroid formation. However, the effects of JHDM knockdown which promote HCC proliferation are reversed by knockdown of SREBP1c. In accordance with these data, JHDM overexpression represses cell growth in HCC cells, indicating that JHDM acts as a tumor suppressor by inhibiting SREBP1c‐mediated lipogenesis and cell cycle regulation. Overall, our findings suggest that JHDM serves as a molecular bridge between lipid metabolism and cancer development through regulation of SREBP1c and thus JHDM could be a therapeutic target in defense against HCC.Support or Funding InformationThis work was supported by grants from the National Research Foundation of Korea (2016R1A2B4013377, 2018R1A2B6007241, 2019R1A2C2083886).

NF-κB/HDAC1/SREBP1c pathway mediates the inflammation signal in progression of hepatic steatosis

The transcription factor nuclear factor kappa B (NF-κB) is activated in hepatocytes in the pathogenesis of hepatic steatosis. However, the action mechanism of NF-κB remains to be established in the hepatic steatosis. In this study, the P50 subunit of NF-κB was found to promote the hepatic steatosis through regulation of histone deacetylase 1 (HDAC1) in hepatocytes. The activity was supported by the phenotypes of P50 knockout (P50-KO) mice and P65 knockout (P65-KO) mice. Hepatic steatosis was reduced in the P50-KO mice, but not in the P65-KO mice. The reduction was a result of inhibition of HDAC1 activity in the P50-KO cells. Knockdown of Hdac1 gene led to suppression of hepatocyte steatosis in HepG2 cells. A decrease in sterol-regulatory element binding protein 1c (SREBP1c) protein was observed in the liver of P50-KO mice and in cell with Hdac1 knockdown. The decrease was associated with an increase in succinylation of SREBP1c protein. The study suggests that P50 stabilizes HDAC1 to support the SREBP1c activity in hepatic steatosis in the pathophysiological condition. Interruption of this novel pathway in the P50-KO, but not the P65-KO mice, may account for the difference in hepatic phenotypes in the two lines of transgenic mice.

Involvement of glucocorticoid prereceptor metabolism and signaling in rat visceral adipose tissue lipid metabolism after chronic stress combined with high-fructose diet.

Both fructose overconsumption and increased glucocorticoids secondary to chronic stress may contribute to overall dyslipidemia. In this study we specifically assessed the effects and interactions of dietary fructose and chronic stress on lipid metabolism in the visceral adipose tissue (VAT) of male Wistar rats. We analyzed the effects of 9-week 20% high fructose diet and 4-week chronic unpredictable stress, separately and in combination, on VAT histology, glucocorticoid prereceptor metabolism, glucocorticoid receptor subcellular redistribution and expression of major metabolic genes. Blood triglycerides and fatty acid composition were also measured to assess hepatic Δ9 desaturase activity. The results showed that fructose diet increased blood triglycerides and Δ9 desaturase activity. On the other hand, stress led to corticosterone elevation, glucocorticoid receptor activation and decrease in adipocyte size, while phosphoenolpyruvate carboxykinase, adipose tissue triglyceride lipase, FAT/CD36 and sterol regulatory element binding protein-1c (SREBP-1c) were increased, pointing to VAT lipolysis and glyceroneogenesis. The combination of stress and fructose diet was associated with marked stimulation of fatty acid synthase and acetyl-CoA carboxylase mRNA level and with increased 11β-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase protein levels, suggesting a coordinated increase in hexose monophosphate shunt and de novo lipogenesis. It however did not influence the level of peroxisome proliferator-activated receptor-gamma, SREBP-1c and carbohydrate responsive element-binding protein. In conclusion, our results showed that only combination of dietary fructose and stress increase glucocorticoid prereceptor metabolism and stimulates lipogenic enzyme expression suggesting that interaction between stress and fructose may be instrumental in promoting VAT expansion and dysfunction.

Astragaloside IV Inhibits Triglyceride Accumulation in Insulin-Resistant HepG2 Cells via AMPK-Induced SREBP-1c Phosphorylation.

Objective: Insulin resistance (IR) is a risk factor for non-alcoholic fatty liver disease (NAFLD), which is characterized by lipid accumulation in hepatocytes. AMP-activated protein kinase (AMPK)-induced sterol regulatory element binding protein-1c (SREBP-1c) phosphorylation is crucial for proper regulation of lipid metabolism in the liver. Astragaloside IV (AST-IV) was found to decrease lipid accumulation in hepatocytes by activating AMPK, which is required to regulate lipid metabolism in liver tissue by inducing SREBP-1c phosphorylation.Method: To evaluate the direct effect of AST on lipid accumulation in hepatocytes with IR and elucidate the underlying mechanisms, we induced IR in HepG2 cells, and used compound C and 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) (an AMPK inhibitor and agonist, respectively) as control substances. We evaluated glucose, triglyceride (TG), and non-esterified fatty acid (NEFA) production, as well as SREBP-1c transcription, SREBP-1c protein expression, and downstream gene expression with or without the presence of AST. We also investigated whether phosphorylation of SREBP-1c at Ser372 was required for AST function.Results: We found that AST attenuated IR and lipid accumulation in HepG2 cells. As an AMPK activator, AST promoted gene expression and activation of AMPK by increasing phosphorylation of AMPKa. AST also inhibited translocation of SREBP-1c into the nucleus of insulin-resistant HepG2 cells by inducing phosphorylation of SREBP-1c at Ser372.Conclusion: This study demonstrated that AST attenuates IR and lipid accumulation in HepG2 cells by regulating AMPK-dependent phosphorylation of SREBP-1c at Ser372, suggesting AST as a promising drug for treating hepatic steatosis.

Arsenic trioxide suppresses liver X receptor β and enhances cholesteryl ester transfer protein expression without affecting the liver X receptor α in HepG2 cells

Chronic arsenic exposure is associated with cerebrovascular disease and the formation of atherosclerotic lesions. Our previous study demonstrated that arsenic trioxide (ATO) exposure was associated with atherosclerotic lesion formation through alterations in lipid metabolism in the reverse cholesterol transport process. In mouse livers, the expression of the liver X receptor β (LXR-β) and the cholesteryl ester transfer protein (CETP) was suppressed without any changes to the lipid profile. The aim of this study was to elucidate whether ATO contributes to atherosclerotic lesions by suppressing LXR-β and CETP levels in hepatocytes. HepG2 cells, human hepatocytes, were exposed to different ATO concentrations in vitro. Cell viability was determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay. The liver X receptor α (LXR-α), LXR-β, sterol regulatory element-binding protein-1c (SREBP-1c) and CETP protein levels were measured by Western blotting, and their mRNA levels were measured by real-time PCR. Cholesterol efflux was analyzed by flow cytometry.The results showed ATO inhibited LXR-β mRNA and protein levels with a subsequent decrease in SREBP-1c protein levels and reduced cholesterol efflux from HepG2 cells into the extracellular space without influencing LXR-α mRNA and protein levels. CETP protein levels of HepG2 cells were significantly elevated under arsenic exposure. Transfection of LXR-β shRNA did not change CETP protein levels, implying that there is no cross-talk between LXR-β and CETP. In conclusion, arsenic not only inhibits LXR-β and SREBP-1c mRNA and protein levels but also independently increases CETP protein levels in HepG2 cells.

Expression and clinical significance of LXRα and SREBP-1c in placentas of preeclampsia.

ObjectiveTo evaluate the expression and correlations of liver X receptor alpha (LXRa) and its target gene sterol regulatory element-binding protein-1c (SREBP-1c) in placentas of preeclampsia (PE) and their significance in PE.MethodsPregnancies were divided into two groups, 60 cases (29 cases of mild and 31 cases of severe) of PE group and 56 cases of normal group. The level of mRNA and protein of LXRa and SREBP-1c were analyzed by reverse transcription-polymerase chain reaction (RTPCR) and immunohistochemistry (IHC) in the placentas.ResultsRT-PCR and IHC results showed that the mRNA and protein expression of both LXRa and SREBP-1c increased gradually with the extent of PE among normal pregnancy, mild PE and severe PE groups, and the differences were of statistically significance (P<0.01 or P<0.05). There were positive correlations between the expression of LXRa mRNA and SREBP-1c mRNA, also between LXRa mRNA and LXRa protein (r=0.521, P<0.01; r=0.422, P<0.01). The expression of SREBP-1c mRNA positively correlated with its protein level (r=0.598, P<0.01). There were positive correlations between the expression of LXRa protein and SREBP-1c protein (r=0.612, P<0.01).ConclusionThe expression of LXRa is elevated significantly in placentas of PE patients, and might contribute for promoting the transcription and translation of its target gene SREBP1-c, which is related to the occurrence and development of PE.

The effects of PCB126 on intra-hepatic mechanisms associated with non alcoholic fatty liver disease.

BackgroundNon alcoholic fatty liver disease (NAFLD) results from alteration in lipid synthesis and elimination mechanisms such as very-low density lipoprotein (VLDL) production and de novo lipogenesis. Persistent organic pollutants (POPs) are chemicals that were mostly used historically as pesticides, solvents, flame retardant, and other applications. Among POPs, polychlorinated biphenyls (PCB) have been recognized to be of environmental and potential toxicologic concerns. Specifically, PCB126 could act as endocrine disruptors and has recently been associated with hepatic fat accumulation. The purpose of the study was to investigate the effects of PCB126 on the molecular development of NAFLD using hepatocyte and rat models.MethodsHepatocytes were exposed to PCB 126 for 72 h and lipid accumulation in cells was quantified by Oil-Red-O. Rats were injected with a single dose of PCB126 or vehicle. Seven days later, liver triglycerides (TAG) content was measured along with protein quantification of hepatic microsomal triglyceride transfer protein (MTP), sterol regulatory element-binding protein 1c (SREBP1c) and diacylglycerol O-acyltransferase 2 (DGAT-2).ResultsExposure to PCB126 resulted in significant increases of lipid accumulation in hepatocytes (38 %, P <0.05) and hepatic TAG concentrations (64 %, P <0.001) in rats compared to respective control groups. Rats with fatty livers depicted lower MTP (40 %, P <0.02), higher SREBP1c (27 %, P < 0.05) and DGAT-2 (120 %, P < 0.02) protein content levels compared to Placebo group in rats.ConclusionsIt seems that exposure to PCB126 has an important emerging role in the pathophysiology of NAFLD by 1) altering elimination mechanisms such as VLDL synthesis and secretion, through MTP; and 2) increasing hepatic TAG synthesis mechanisms through DGAT 2 and SREBP1c.

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.

Metformin attenuates palmitic acid-induced insulin resistance in L6 cells through the AMP-activated protein kinase/sterol regulatory element-binding protein-1c pathway

AMP-activated protein kinase (AMPK) is an important effector of metformin action on glucose uptake in skeletal muscle cells. We recently reported that metformin improved insulin receptor substrate-1 (IRS-1)-associated insulin signaling by downregulating sterol regulatory element-binding protein-1c (SREBP-1c) expression. In this study, we investigated whether AMPK activation and SREBP-1c inhibition contribute to the beneficial effects of metformin on IRS-1-associated insulin signaling in L6 myotubes. L6 muscle cells were incubated with palmitic acid (PA) to induce insulin resistance and then treated with metformin and/or the AMPK inhibitor, compound C. AMPK, SREBP-1c, IRS-1 and Akt protein expression levels were determined by western blot analysis. The effects of metformin on SREBP-1c gene transcription were determined by a luciferase reporter assay. Glucose uptake was evaluated using the 2-NBDG method. In the PA-treated L6 cells, metformin treatment enhanced AMPK phosphorylation, reduced SREBP-1c expression and increased IRS-1 and Akt protein expression, whereas treatment with compound C blocked the effects of metformin on SREBP-1c expression and the IRS-1 and Akt levels. Moreover, metformin suppressed SREBP-1c promoter activity and promoted glucose uptake through AMPK. The results from this study demonstrate that metformin ameliorates PA-induced insulin resistance through the activation of AMPK and the suppression of SREBP-1c in skeletal muscle cells.

Effects of transcription factor sterol regulatory element binding protein-1c in palmitate acid-induced L6 cells insulin resistance and its mechanism

Sterol regulatory element binding protein-1c (SREBP-1c) is a master regulator of fatty acid synthase and controls lipogenesis. And insulin receptor substrate-1 (IRS-1) is a key insulin signaling mediator in skeletal muscle. The present study was conducted to explore the mechanism of SREBP-1c in the regulation of IRS-1 in skeletal muscle cells and elucidate the role of SREBP-1c in high fat-induced skeletal muscle insulin resistance. L6 cells differentiated into myotubes in differentiation medium with 2%FBS. An in vitro insulin resistant model in L6 myotubes was established by 500 µmol/L of palmitate acid (PA). SREBP-1c, p-IRS-1(Tyr608/612), IRS-1, p-AKT (Ser473) and AKT were detected by Western blot after incubating L6 myobutes with 500 µmol/L of PA for 0.5, 1, 3, 6, 12, 18 or 24 h.SREBP-1c, FAS and molecules related to insulin signaling pathway were detected by Western blot when L6 myotubes over-expressed SREBP-1c or after a treatment of liver X receptor (LXR) agonist (TO901317, 5 µmol/L). The regulatory effects of transcription factor SREBP-1c on promoter region of IRS-1 were assessed by dual-luciferase reporter assay. SREBP-1c protein expression increased significantly after 1-hour exposure to PA. The protein levels of p-IRS-1(Tyr608/612),IRS-1 and p-AKt (Ser473) decreased significantly after a 6-hour incubation of PA. However AKT protein levels were unaffected. The protein expressions of SREBP-1c and FAS were up-regulated by LXR agonist treatment versus controls. By contrast, LXR agonist treatment led to decreased expressions of IRS-1, p-IRS-1(Tyr608/612) and p-AKt (Ser473)/AKT proteins versus controls. The expressions of related proteins were similar to the observations made with LXR agonist intervention. The results of dual-luciferase reporter assay indicated that IRS-1 promoter activity was repressed significantly by SREBP-1c over-expression or TO901317 treatment whereas the dominant negative form of SREBP-1c (a mutant of Tyr320Ala lacking the ability of binding DNA) had no effect. SREBP-1c may suppress IRS-1 expression and the subsequent insulin signaling pathway. And it plays a key role in PA-induced insulin resistance of skeletal muscle.

Mechanism of the antiadipogenic-antiobesity effects of a rice hull smoke extract in 3T3-L1 preadipocyte cells and in mice on a high-fat diet.

The present study investigated the inhibitory effects of a rice hull smoke extract (RHSE) against adipogenesis in 3T3-L1 preadipocyte cells and in mice fed high fat (HFD) and normal (ND) diets. At concentrations of 0.1% and 0.5%, RHSE was shown to reduce the cellular lipid content in MDI-induced 3T3-L1 cells by about 72% and 88%, respectively, compared to that in control cells without RHSE, indicating a strong antiadipogenic effect. This result was supported by the finding that the expression of the adipocyte differentiation marker adiponectin was suppressed. MTT and lactate dehydrogenase (LDH) release assays showed that RHSE doses of up to 0.5% (v/v) were not cytotoxic to the 3T3-L1 cells. RHSE activates AMP-activated protein kinase (AMPK) through raising the phosphorylated ratio during the early phase of cell differentiation, and western blot analysis showed that it dose-dependently inhibited the expression of the peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT-enhancer binding protein (C/EBPα), and sterol regulatory element-binding protein 1c (SREBP-1c) at the late stage of differentiation. The antiadipogenic properties of RHSE were confirmed in vivo using experimental obese mice on a high-fat diet. Dietary supplementations of 0.5% and 1% RHSE resulted in a reduction at the end of the 7-week feeding study of body weight gain of 66.9% and 72.5%, respectively, a reduction of epididymal white adipose tissue weight by up to 87.9%, restoration of elevated total cholesterol and triglyceride levels in plasma and liver to those observed in the ND-fed mice, normalization of distorted serum leptin and adiponectin levels, and restoration of liver weight and glutamate oxaloacetate transaminase/glutamate pyruvate transaminase (GOT/GPT) enzymes, blood urea, and serum creatinine to the normal control levels observed in the ND-fed mice. As was found in the 3T3-L1 cells, RHSE up-regulated AMPK phosphorylation and down-regulated PPARγ, C/EBPα and SREBP-1c protein expression in the epididymal white adipose tissues. These results indicate that RHSE inhibits the AMPK signaling pathway in mice and might serve as an antiobesity multifunctional food additive.

Chronic exposure to low-dose arsenic modulates lipogenic gene expression in mice.

Arsenic, a ubiquitous environmental toxicant, can affect lipid metabolism through mechanisms that are not well understood. We studied the effect of arsenic on serum lipids, lipid-regulating genes, and transcriptional regulator sterol regulatory element binding protein 1c (SREBP-1c). C57BL/6 mice were administered 0 or 100 ppb sodium arsenite in drinking water for 5 weeks. Arsenic exposure was associated with decreased liver weight but no change in body weight. Serum triglycerides level fell in arsenic-exposed animals, but not in fed animals, after short-term fasting. Hepatic expression of SREBP-1c was reduced in arsenic-exposed fed animals, with a 16-fold change in reduction. Similar effects were seen for SREBP-1c in white adipose tissue. However, fasting resulted in dissociation of the expression of SREBP-1c and its targets, and SREBP-1c protein content could not be shown to correlate with its mRNA expression. We conclude that arsenic modulates hepatic expression of genes involved in lipid regulation through mechanisms that are independent of SREBP-1c expression.

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.

Intestinal GATA4 deficiency protects from diet-induced hepatic steatosis

Background & AimsGATA4, a zinc finger domain transcription factor, is critical for jejunal identity. Mice with an intestine-specific GATA4 deficiency (GATA4iKO) are resistant to diet-induced obesity and insulin resistance. Although they have decreased intestinal lipid absorption, hepatic de novo lipogenesis is inhibited. Here, we investigated dietary lipid-dependent and independent effects on the development of steatosis and fibrosis in GATA4iKO mice.MethodsGATA4iKO and control mice were fed a Western-type diet (WTD) or a methionine and choline-deficient diet (MCDD) for 20 and 3 weeks, respectively. Functional effects of GATA4iKO on diet-induced liver steatosis were investigated.ResultsWTD-but not MCDD-fed GATA4iKO mice showed lower hepatic concentrations of triglycerides, free fatty acids, and thiobarbituric acid reactive species and had reduced expression of lipogenic as well as fibrotic genes compared with controls. Reduced nuclear sterol regulatory element-binding protein-1c protein levels were accompanied by lower lipogenic gene expression. Oil red O and Sirius Red staining of liver sections confirmed the observed reduction in hepatic lipid accumulation and fibrosis. Immunohistochemical staining revealed an increased number of jejunal glucagon-like peptide 1 (GLP-1) positive cells in GATA4iKO mice. Consequently, we found enhanced phosphorylation of hepatic AMP-activated protein kinase and acetyl-CoA carboxylase alpha.ConclusionsOur results provide strong indications for a protective effect of intestinal GATA4 deficiency on the development of hepatic steatosis and fibrosis via GLP-1, thereby blocking hepatic de novo lipogenesis.

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.

Resveratrol inhibits cell differentiation in 3T3-L1 adipocytes via activation of AMPK.

Resveratrol (Res) is a natural polyphenolic compound with anti-inflammatory and antioxidant properties. Also, Res can inhibit lipogenesis and adipocyte differentiation. However, the underlying mechanisms of Res's functions remain largely unknown. AMP-activated protein kinase (AMPK) is a key player in adipocyte differentiation. Therefore, the purpose of our study was to determine the role played by AMPK in the Res-mediated regulation of adipocyte differentiation. Incubation of 3T3-L1 cells with Res confirmed that Res inhibited adipocyte differentiation. The phosphorylation of AMPKα was increased by Res in a dose-dependent manner, while total AMPKα levels were unchanged, and peroxisome proliferator-activated receptor γ (PPARγ), CCAAT-enhancer-binding protein α (C/EBPα), and sterol regulatory element-binding protein 1c (SREBP-1c) levels were decreased. Interestingly, pretreatment with AMPKα siRNA and Res promoted adipocyte differentiation, while the decrease of p-AMPKα increased PPARγ, C/EBPα, and SREBP-1c protein expression. Our study shows that Res is capable of inhibiting lipogenesis and differentiation of 3T3-L1 adipocytes via activation of AMPK, suggesting its potential therapeutic application in the treatment or prevention of obesity.

Overexpression of Insig-1 protects β cell against glucolipotoxicity via SREBP-1c

BackgroundHigh glucose induced lipid synthesis leads to β cell glucolipotoxicity. Sterol regulatory element binding protein-1c (SREBP-1c) is reported to be partially involved in this process. Insulin induced gene-1 (Insig-1) is an important upstream regulator of Insig-1-SREBPs cleavage activating protein (SCAP)-SREBP-1c pathway. Insig-1 effectively blocks the transcription of SREBP-1c, preventing the activation of the genes for lipid biosynthesis. In this study, we aimed to investigate whether Insig-1 protects β cells against glucolipotoxicity.MethodsAn Insig-1 stable cell line was generated by overexpression of Insig-1 in INS-1 cells. The expression of Insig-1 was evaluated by RT-PCR and Western blotting, then, cells were then treated with standard (11.2 mM) or high (25.0 mM) glucose for 0 h, 24 h and 72 h. Cell viability, apoptosis, glucose stimulated insulin secretion (GSIS), lipid metabolism and mRNA expression of insulin secretion relevant genes such as IRS-2, PDX-1, GLUT-2, Insulin and UCP-2 were evaluated.ResultsWe found that Insig-1 suppressed the high glucose induced SREBP-1c mRNA and protein expression. Our results also showed that Insig-1 overexpression protected β cells from ER stress-induced apoptosis by regulating the proteins expressed in the IRE1α pathway, such as p-IRE1α, p-JNK, CHOP and BCL-2. In addition, Insig-1 up-regulated the expression of IRS-2, PDX-1, GLUT-2 and Insulin, down-regulated the expression of UCP-2 and improved glucose stimulated insulin secretion (GSIS). Finally, we found that Insig-1 inhibited the lipid accumulation and free fatty acid (FFA) synthesis in a time-dependent manner.ConclusionsThere results suggest that Insig-1 may play a critical role in protecting β cells against glucolipotoxicity by regulating the expression of SREBP-1c.