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

Studies on the Effect of Piperine on Hepatocyte Nuclear Factor 1 Alpha (HNF-1α) and Sterol Regulatory Element-Binding Protein 1c (SREBP-1c) Levels in High-Fat-Diet and Sucrose-Induced Type 2 Diabetes Mellitus Rats.

Piperine, a naturally occurring compound in black pepper (Piper nigrum), is known for its potential health benefits, including its reported enhancement of insulin sensitivity. However, the precise impact of piperine on hepatocyte nuclear factor 1 alpha (HNF-1α) and sterol regulatory element-binding protein 1c (SREBP-1c), transcription factors for insulin signaling and glucose metabolism in hepatocytes, remains unclear. This study aims to investigate the effect of piperine, compared to metformin, on blood glucose and insulin levels by modifying the expression of hepatic HNF-1α and SREBP-1c in high-fat-diet (HFD) and sucrose-induced type 2 diabetes mellitus (T2DM) rats and in human Chang liver cells. Adult male albino rats were categorized into four groups: group 1 as the control, group 2 as T2DM, group 3 as T2DM rats treated with piperine (40 mg), and group 4 as T2DM rats treated with metformin (50 mg). Fasting blood glucose (FBG) and serum insulin levels were measured using enzyme-linked immunosorbent assay (ELISA), while real-time polymerase chain reaction (RT-PCR) analysis was conducted to assess the mRNA expression of HNF-1α and SREBP-1c. Further, piperine was treated with normal and high glucose-induced Chang liver cells, and gene expression was analysed.Data analysis was performed using one-way analysis of variance (ANOVA), with a significance set at p<0.05. Treatment with piperine led to a notable decrease in blood glucose levels and circulating insulin when compared with T2DM rats (group 2). Additionally, piperine administration resulted in the upregulation of HNF-1α mRNA expression and downregulation of SREBP-1c mRNA levels whose effects were found to be near that of the control and standard drug metformin's effects. In vitro study also confirmed that piperine improved the HNF-1αexpression and reduced the expression of SREBP-1c in Chang liver cells. Our findings suggest that piperine treatment effectively regulates hyperglycemic and hyperinsulinemic insulin resistance in the liver by modulating the expression of HNF-1α and SREBP-1c. Consequently, piperine emerges as a promising candidate for therapeutic intervention in managing T2DM.

Hepatic retinaldehyde dehydrogenases are modulated by tocopherol supplementation in mice with hepatic steatosis

ObjectivesAn altered retinol metabolism might play a role in the development of nonalcoholic fatty liver disease (NAFLD). Tocopherols (TF) modulate metabolic pathways and have been proposed as a complementary treatment of obesity-induced metabolic alterations. Moreover, there is evidence suggesting that TF may modulate retinol metabolism. The aim of this study was to evaluate whether the dietary supplementation of α- and γ-TF modulates the expression of hepatic retinaldehyde dehydrogenases, RALDH1, RALDH2, and RALDH3 (involved in retinol metabolism) and, lipogenic factors sterol regulatory element binding protein-1c (SREBP-1c) and cluster differentiation 36 (CD36) in an animal model of diet-induced NAFLD. MethodsMale C57BL/6J mice were divided into four groups: a control diet (CD) group (10% fat, 20% protein, 70% carbohydrates); a CD + TF group (α-tocopherol: 0.7 mg·kg·d–1, γ-tocopherol: 3.5 mg·kg·d–1); a high-fat diet (HFD) group (60% fat, 20% protein, 20% carbohydrates); and a HFD + TF group (0.01 mL·g body weight·d–1), for 12 wk. General parameters (body-adipose tissue weight, glucose-triacylglyceride serum levels), liver steatosis (histology, liver triacylglycerides content), and hepatic RALDH1, RALDH2, RALDH3, SREBP-1c and CD36 (qPCR, quantitative polymerase chain reaction; IHQ, immunohistochemistry) were measured. ResultsTF supplementation in HFD-fed mice decreased the presence of lipid vesicles (90%) and total lipid content (75%) and downregulated the expression of RALDH1, RALDH3, SREBP-1c, and CD36. ConclusionsThe present study demonstrated that α- and γ-TF (1:5 ratio) might play a role in modulating retinol metabolism in the prevention of NAFLD induced by a HFD.

The developmental Wnt signaling pathway effector β-catenin/TCF mediates hepatic functions of the sex hormone estradiol in regulating lipid metabolism.

The bipartite transcription factor β-catenin (β-cat)/T cell factor (TCF), formed by free β-cat and a given TCF family member, serves as the effector of the developmental Wnt signaling cascade. β-cat/TCFs also serve as effectors of certain peptide hormones or growth factors during adulthood. We reported that liver-specific expression of dominant-negative Transcription factor 7 like 2 (TCF7L2DN) led to impaired glucose disposal. Here we show that, in this LTCFDN transgenic mouse model, serum and hepatic lipid contents were elevated in male but not in female mice. In hepatocytes, TCF7L2DN adenovirus infection led to stimulated expression of genes that encode lipogenic transcription factors and lipogenic enzymes, while estradiol (E2) treatment attenuated the stimulation, associated with Wnt-target gene activation. Mechanistically, this E2-mediated activation can be attributed to elevated β-cat Ser675 phosphorylation and TCF expression. In wild-type female mice, ovariectomy (OVX) plus high-fat diet (HFD) challenge impaired glucose disposal and insulin tolerance, associated with increased hepatic lipogenic transcription factor sterol regulatory element-binding protein 1-c (SREBP-1c) expression. In wild-type mice with OVX, E2 reconstitution attenuated HFD-induced metabolic defects. Some of the attenuation effects, including insulin intolerance, elevated liver-weight gain, and hepatic SREBP-1c expression, were not affected by E2 reconstitution in HFD-fed LTCFDN mice with OVX. Finally, the effects of E2 in hepatocytes on β-cat/TCF activation can be attenuated by the G-protein-coupled estrogen receptor (GPER) antagonist G15. Our study thus expanded the scope of functions of the Wnt pathway effector β-cat/TCF, as it can also mediate hepatic functions of E2 during adulthood. This study also enriches our mechanistic understanding of gender differences in the risk and pathophysiology of metabolic diseases.

Attenuation of high-fat diet-induced fatty liver through PPARα activation by stevioside

Abstract This study aimed to investigate the effect of stevioside on fatty liver. Rats with hyperlipidemic fatty liver were treated with 75–150 mg/kg stevioside for 6 weeks. After oral administration of stevioside, the levels of serum and hepatic lipids and degree of hepatic steatosis were decreased. Stevioside treatment increased the expressions of hepatic peroxisome proliferator-activated receptor (PPAR)α and carnitine palmitoyltransferase-1A proteins and decreased the expressions of hepatic sterol regulatory element-binding protein-1c, fatty acid synthase and diacylglycerol acyltransferase proteins. Following treatment of oleic acid-stimulated hepatocytes with 100–400 μM stevioside, the intracellular lipids were also decreased. In the hepatocytes of PPARα gene silence, the lipid-lowering effect of stevioside was abolished, and its regulatory effects on PPARα-mediated target proteins were reversed. These findings demonstrated that stevioside was effective in treating fatty liver, and its mechanisms were associated with the increment of hepatic PPARα expression and subsequent modulation of its target gene expressions.

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.

Abstract 545: Cinnamon Extract Inhibit Lipids and Inflammation by Modulation of Transcription Factors: in vivo Model

Objectives: CNM (CNM) polyphenol has antioxidant and anti-inflammatory properties. Therefore, we hypothesized CNM decrease heart disease risk factors and may enhance anti- inflammatory properties in rats fed a diet containing CNM. In this study, we evaluated the effects of CNM polyphenol on insulin resistance (IR), hyperlipidemia, hepatic transcription factors expressions [sterol regulatory element-binding protein1c (SREBP-1c), liver X receptor-α (LXR-α), nuclear factor kappa B p65 (NF-κB p65), nuclear factor-E2-related factor-2 (Nrf2)] in rats fed high fat diet (HFD). Method: Twenty-eight Wistar rats were allocated into four groups; (i) normal control; animals fed with normal chow (C ) (ii) CNM (C+CNM 100 mg/kg b.wt.), (iii) HFD (42% of calories as fat, high fat diet [HFD]), and (iv) HFD + CNM for 12 weeks. Blood analysis for triglycerides (TG) and cholesterol (CHOL), glucose, insulin, malonaldehyde (MDA a marker of oxidative stress [OS]) were estimated. Body weight, visceral fat and liver weight recorded and liver MDA assessed. SREBP-1c, LXR-α, ATP-citrate lyase (ACLY), fatty acid synthase (FAS), NF-κB p65 expressions and decreased the PPAR-α, p-IRS-1, Nrf2, HO-1 proteins were evaluated by Western blotting. Results: HFD rats of the liver had increased SREBP-1c, LXR-α, ATP-citrate lyase (ACLY), fatty acid synthase (FAS), NF-κB p65 expressions and decreased the PPAR-α, p-IRS-1, Nrf2, HO-1 expressions compared to control group. CNM supplementation decreased body weight (8.4%), visceral fat (36.6%), liver weight (17.7%), serum glucose and insulin concentrations, lipid profile ( P &lt; 0.05), and serum and liver MDA (23.3% and 25.4 %) concentration compared to HFD rats ( P &lt; 0.05). CNM decreased hepatic SREBP-1c (18.1 %), LXRα (27.9%), ATP-citrate lyase (ACLY, 22.7 %), fatty acid synthase (FAS, 15.8 %), NF-κB p65 (23.3%) and enhanced the PPAR-α, IRS-1 (72.7 %), Nrf2 (111.7 %) and HO-1 (72.1 %) proteins in HFD rat livers ( P &lt; 0.05). Discussion: These results suggest CNM supplementation reduces hyperlipidemia, inflammation, and oxidative stress through activating transcription factors (SREBP-1c, LXR-α, NF-κB, and Nrf2) and anti-oxidative defense signaling pathway.

Glucagon-like peptide-1 analogue prevents nonalcoholic steatohepatitis in non-obese mice.

To investigate whether a glucagon-like peptide-1 (GLP-1) analogue inhibits nonalcoholic steatohepatitis (NASH), which is being increasingly recognized in Asia, in non-obese mice. A methionine-choline-deficient diet (MCD) along with exendin-4 (20 μg/kg per day, ip), a GLP-1 analogue, or saline was administered to male db/db mice (non-obese NASH model). Four or eight weeks after commencement of the diet, the mice were sacrificed and their livers were excised. The excised livers were examined by histochemistry for evidence of hepatic steatosis and inflammation. Hepatic triglyceride (TG) and free fatty acid (FFA) content was measured, and the expression of hepatic fat metabolism- and inflammation-related genes was evaluated. Oxidative stress-related parameters and macrophage recruitment were also examined using immunohistochemistry. Four weeks of MCD feeding induced hepatic steatosis and inflammation and increased the hepatic TG and FFA content. The expression of fatty acid transport protein 4 (FATP4), a hepatic FFA influx-related gene; macrophage recruitment; and the level of malondialdehyde (MDA), an oxidative stress marker, were significantly augmented by a 4-wk MCD. The levels of hepatic sterol regulatory element-binding protein-1c (SREBP-1c) mRNA (lipogenesis-related gene) and acyl-coenzyme A oxidase 1 (ACOX1) mRNA (β-oxidation-related gene) had decreased at 4 wk and further decreased at 8 wk. However, the level of microsomal triglyceride transfer protein mRNA (a lipid excretion-related gene) remained unchanged. The administration of exendin-4 significantly attenuated the MCD-induced increase in hepatic steatosis, hepatic TG and FFA content, and FATP4 expression as well as the MCD-induced augmentation of hepatic inflammation, macrophage recruitment, and MDA levels. Additionally, it further decreased the hepatic SREBP-1c level and alleviated the MCD-mediated inhibition of the ACOX1 mRNA level. These results suggest that GLP-1 inhibits hepatic steatosis and inflammation through the inhibition of hepatic FFA influx and oxidative stress in a non-obese NASH model.

Antiresistin RNA Oligonucleotide Ameliorates Diet-Induced Nonalcoholic Fatty Liver Disease in Mice through Attenuating Proinflammatory Cytokines.

The aim of this study was to determine whether inhibition of resistin by a synthetic antiresistin RNA (oligonucleotide) oligo ameliorates metabolic and histological abnormalities in nonalcoholic fatty liver disease (NAFLD) induced by high-fat diet (HFD) in mice. The antiresistin RNA oligo and a scrambled control oligo (25 mg/kg of body weight) were i.p. injected to HFD mice. Serum metabolic parameters and hepatic enzymes were measured after 4-week treatment. The treatment significantly reduced epididymal fat and attenuated the elevated serum resistin, cholesterol, triglycerides, glucose, and insulin with an improved glucose tolerance test. Antiresistin RNA oligo also normalized serum AST and ALT levels with improved pathohistology of NAFLD. Immunoblotting and qRT-PCR revealed that decreased protein and mRNA expression of resistin in fat and liver tissues of the treated mice were associated with reduction of adipose TNF-α and IL-6 expression and secretion into circulation. mRNA and protein expression of hepatic phosphoenolpyruvate carboxykinase (PEPCK) and sterol regulatory element-binding protein-1c (SREBP-1c) were also significantly decreased in the treated mice. Our results suggest that resistin may exacerbate NAFLD in metabolic syndrome through upregulating inflammatory cytokines and hepatic PEPCK and SREBP-1c. Antiresistin RNA oligo ameliorated metabolic abnormalities and histopathology of NAFLD through attenuating proinflammatory cytokines.

Herbal SGR Formula Prevents Acute Ethanol-Induced Liver Steatosis via Inhibition of Lipogenesis and Enhancement Fatty Acid Oxidation in Mice.

Our previous study indicated that herbal SGR formula partially attenuates ethanol-induced fatty liver, but the underlying mechanisms remain unclear. In the present study, mice were pretreated with SGR (100 and 200 mg/kg/d bw) for 30 d before being exposed to ethanol (4.8 g/kg bw). The biochemical indices and histopathological changes were examined to evaluate the protective effects and to explore potential mechanisms by investigating the adiponectin, tumor necrosis factor-α (TNF-α), peroxisome proliferators-activated receptor-α (PPAR-α), sterol regulatory element binding protein-1c (SREBP-1c), adenosine monophosphate-activated protein kinase (AMPK), and so forth. Results showed that SGR pretreatment markedly inhibited acute ethanol-induced liver steatosis, significantly reduced serum and hepatic triglyceride (TG) level, and improved classic histopathological changes. SGR suppressed the protein expression of hepatic SREBP-1c and TNF-α and increased adiponectin, PPAR-α, and AMPK phosphorylation in the liver. Meanwhile, acute toxicity tests showed that no death or toxic side effects within 14 days were observed upon oral administration of the extracts at a dose of 16 g/kg body wt. These results demonstrate that SGR could protect against acute alcohol-induced liver steatosis without any toxic side effects. Therefore, our studies provide novel molecular insights into the hepatoprotective effect of SGR formula, which may be exploited as a therapeutic agent for ethanol-induced hepatosteatosis.

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

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

Alleviative effects of deep-seawater drinking water on hepatic lipid accumulation and oxidation induced by a high-fat diet

BackgroundHepatic steatosis is defined as excessive amounts of triglyceride and other fats inside liver cells and has become an emergent liver disease in developed and developing countries. MethodsDeep seawater (DSW)300, DSW900, and DSW1500 drinking waters were formulated via a combination of reverse osmosis and electrodialysis. Hamsters on a high-fat diet were assigned to drink the following solutions: (1) normal distilled water, (2) DSW300, (3) DSW900, or (4) DSW1500. Serum, liver, and fecal biochemical values, expression of hepatic genes related to fatty-acid homeostasis, as well as liver antioxidative levels were measured after a 6-week feeding period. Additionally, hematoxylin and eosin staining was used to investigate the liver histopathology. ResultsSerum/liver lipids, liver sizes, liver malondialdehyde content, and serum aspartate aminotransferase and alanine aminotransferase of high-fat diet hamsters were reduced (p < 0.05) by drinking DSW, while daily fecal lipid and bile acid outputs were increased (p < 0.05). DSW drinking water maintained (p < 0.05) higher liver glutathione and Trolox equivalent antioxidant capacity levels. Although hepatic sterol regulatory element-binding protein-1c, acetyl-CoA carboxylase, fatty acid synthase, and malic enzyme gene expression were not (p > 0.05) altered, DSW drinking water upregulated (p < 0.05) hepatic peroxisome proliferator-activated receptor-alpha, retinoid X receptor alpha, and uncoupling protein-2 gene expression in high-fat diet hamsters. The lipid droplets in livers were also reduced in DSW-drinking-water groups as compared to those only drinking distilled water. ConclusionDSW shows a preventive effect on development of hepatosteatosis induced by a high-fat diet.

CAMP response element binding protein H mediates fenofibrate-induced suppression of hepatic lipogenesis

Fenofibrate is a drug used to treat hyperlipidaemia that works by inhibiting hepatic triacylglycerol synthesis. Sterol regulatory element binding protein-1c (SREBP-1c) is a major regulator of the expression of genes involved in hepatic triacylglycerol synthesis. In addition, endoplasmic reticulum (ER)-bound transcription factor families are involved in the control of various metabolic pathways. Here, we show a novel function for an ER-bound transcription factor, cAMP response element binding protein H (CREBH), in fenofibrate-mediated inhibition of hepatic lipogenesis. The effects of fenofibrate and adenovirus-mediated Crebh (also known as Creb313) overexpression (Ad-Crebh) on hepatic SREBP-1c production and lipogenesis in vitro and in vivo were investigated. We also examined whether downregulation of endogenous hepatic Crebh by small interfering (si)RNA restores the fenofibrate effect on hepatic lipogenesis and SREBP-1c production. Finally, we examined the mechanism by which CREBH inhibits hepatic SREBP-1c production. Fasting and fenofibrate treatment induced CREBH production and decreased SREBP-1c levels. Indeed, Ad-Crebh inhibited insulin- and liver X receptor agonist TO901317-induced Srebp-1c (also known as Srebf1) mRNA expression in cultured hepatocytes. Moreover, increased production of CREBH in the liver of mice following tail-vein injection of Ad-Crebh inhibited high-fat diet-induced hepatic steatosis through inhibition of Srebp-1c expression. The inhibition of endogenous Crebh expression by siRNA restored fenofibrate-induced suppression of Srebp-1c expression and hepatic lipid accumulation both in vitro and in vivo. These results show that fenofibrate decreases hepatic lipid synthesis through induction of CREBH. This study suggests CREBH as a novel negative regulator of SREBP-1c production and hepatic lipogenesis.

Fructose intake during pregnancy up-regulates the expression of maternal and fetal hepatic sterol regulatory element-binding protein-1c in rats

Excess fructose consumption is associated with the development of type 2 diabetes and obesity. However, the impact of fructose intake on maternal and fetal lipid metabolism during pregnancy is not known. The aim of this study was to examine whether maternal fructose intake during pregnancy would affect fetal and maternal hepatic lipid metabolism. Pregnant Wistar rats were randomly divided into untreated control and fructose-treated groups; the fructose-treated group received fructose via drinking water throughout pregnancy. On gestational day 20, glucose and insulin concentration in the maternal plasma were measured. The mRNA expression of sterol regulatory element-binding protein (SREBP)-1c and its target genes in the liver of dams and fetuses were analyzed by real-time PCR. Significantly higher maternal plasma glucose levels, indicating hyperglycemia, was observed in the fructose-treated group than in the control group. Furthermore, the fructose-treated group showed significantly higher expression levels of both maternal and fetal SREBP-1c mRNA and protein and significantly elevated expression of fatty acid synthase; the group also showed reduced acyl-CoA oxidase levels in the maternal liver. Thus, our results suggest that maternal fructose intake during pregnancy causes maternal hyperglycemia and up-regulates hepatic SREBP-1c expression in both fetuses and dams. This may lead to defects in carbohydrate and lipid metabolism in the adult offspring.

Palmitoleate Induces Hepatic Steatosis but Suppresses Liver Inflammatory Response in Mice

The interaction between fat deposition and inflammation during obesity contributes to the development of non-alcoholic fatty liver disease (NAFLD). The present study examined the effects of palmitoleate, a monounsaturated fatty acid (16∶1n7), on liver metabolic and inflammatory responses, and investigated the mechanisms by which palmitoleate increases hepatocyte fatty acid synthase (FAS) expression. Male wild-type C57BL/6J mice were supplemented with palmitoleate and subjected to the assays to analyze hepatic steatosis and liver inflammatory response. Additionally, mouse primary hepatocytes were treated with palmitoleate and used to analyze fat deposition, the inflammatory response, and sterol regulatory element-binding protein 1c (SREBP1c) activation. Compared with controls, palmitoleate supplementation increased the circulating levels of palmitoleate and improved systemic insulin sensitivity. Locally, hepatic fat deposition and SREBP1c and FAS expression were significantly increased in palmitoleate-supplemented mice. These pro-lipogenic events were accompanied by improvement of liver insulin signaling. In addition, palmitoleate supplementation reduced the numbers of macrophages/Kupffer cells in livers of the treated mice. Consistently, supplementation of palmitoleate decreased the phosphorylation of nuclear factor kappa B (NF-κB, p65) and the expression of proinflammatory cytokines. These results were recapitulated in primary mouse hepatocytes. In terms of regulating FAS expression, treatment of palmitoleate increased the transcription activity of SREBP1c and enhanced the binding of SREBP1c to FAS promoter. Palmitoleate also decreased the phosphorylation of NF-κB p65 and the expression of proinflammatory cytokines in cultured macrophages. Together, these results suggest that palmitoleate acts through dissociating liver inflammatory response from hepatic steatosis to play a unique role in NAFLD.

N−3 Fatty acids ameliorate hepatic steatosis and dysfunction after LXR agonist ingestion in mice

Liver X receptor (LXR) agonists slow atherogenesis, but cause hepatic steatosis and dysfunction in part by increasing expression of sterol regulatory element binding protein 1-c (SREBP1-c), a transcription factor that upregulates fatty acid (FA) synthesis. n−3 FAs decrease hepatic FA synthesis by down-regulating SREBP1-c. To test the hypothesis that n−3 FAs decrease hepatic steatosis in mice given LXR agonist, C57BL/6 mice received daily gavage of an LXR agonist T0901317 (LXR T) or vehicle for 4 weeks with concomitant intakes chow or high-fat diets enriched in saturated fat (SAT) or n−3 fat (n−3). Mice on LXR T and SAT developed hepatomegaly with a large increase in size and number of hepatic lipid droplets; an n−3 diet reduced liver weight/body weight with decreased hepatic steatosis and triglyceride levels. Effects of n−3 diet on hepatic lipogenesis were linked to a blunting of LXR T upregulation of hepatic SREBP1-c and FA synthase mRNA. n−3 diets also normalized LXR T-mediated increases of plasma ALT and AST levels, whereas SAT diet increased these markers. Conclusion: These studies suggest that n−3 FAs when given together with LXR agonists have the potential to improve both hepatic steatosis and hepatotoxicity in humans that might receive LXR agonists to decrease risk of atherosclerosis.

Osthol ameliorates fat milk-induced fatty liver in mice by regulation of hepatic sterol regulatory element-binding protein-1c/2-mediated target gene expression

The objective of this study was to examine the therapeutic effect of osthol, an active constituent of Cnidium monnieri (L.) Cusson (Apiaceae), in hyperlipidemic fatty liver mice and investigate the potential mechanism of the osthol treatment. A mouse model with hyperlipidemic fatty liver was induced by orally feeding the fat milk for 4 weeks. The experimental mice were then treated with osthol 10–40 mg/kg for 6 weeks. After oral administration, the mice in the model and medicine-treated groups were continuously given the fat milk for 2 weeks again. Whereafter, the lipid levels in serum and liver, hepatic weight coefficient and histopathological evaluation were measured. The sterol regulatory element-binding protein (SREBP)-1c, SREBP-2, fatty acid synthase (FAS), low density lipoprotein (LDL) receptor and cholesterol 7α-hydroxylase (CYP7A) mRNA expressions in liver were examined. The results showed that in the osthol-treated groups, the total cholesterol, triglyceride and free fatty acid levels in serum and liver, and the hepatic weight coefficient were gradually decreased with dose. Importantly, the histopathological evaluation of liver specimens demonstrated that osthol might decrease lipid accumulation. Osthol could increase the mRNA expression of CYP7A and decrease the mRNA expressions of SREBP-1c, SREBP-2, FAS and LDL receptor in liver in fat milk-induced fatty liver mice. These results suggested that osthol might exert the therapeutic effect on fat milk-induced fatty liver in mice, by inhibiting hepatic SREBP-1c/2 mRNA expressions and subsequent modulation of SREBP-1c/2-mediated target genes such as FAS, CYP7A and LDL receptor.

Upregulation of Lipogenesis and Protein Tyrosine Phosphatase-1B Expression in the Liver of Wistar Rats with Metabolic Syndrome Chronically Induced by Drinking Sucrose Water

Background: Establishing animal models with metabolic disorders similar to human metabolic syndrome (MS) is important. In terms of eliciting a full array of MS, we have previously shown that Wistar rats are more responsive to sucrose water drinking than are C57BL/6J mice. This study was aimed at investigating the underlying molecular mechanism of sucrose water-induced MS in Wistar rats. Methods: Male Wistar rats were divided into 2 groups (n = 8 for each group) which were given plain water (C group) or 30% sucrose water (SW group) to drink ad libitum. After 20 weeks, the transcriptional levels and protein translocation of hepatic sterol regulatory element-binding protein-1c (SREBP-1c) and carbohydrate response element-binding protein (ChREBP) as well as the protein levels of protein tyrosine phosphatase-1B (PTP-1B) in insulin-responsive tissues (liver, muscle, and adipose tissue) were measured. Results: The sucrose water regimen successfully elicited visceral obesity, hypertriglyceridemia, insulin resistance, and high blood pressure. The upregulation of de novo lipogenesis in the liver of the sucrose water-treated rats was demonstrated by an increased activity of enzymes, mRNA levels of lipogenic proteins, and nuclear levels of SREBP-1c and ChREBP. Moreover, in the sucrose water-treated rats, protein levels of PTP-1B were significantly increased in liver and skeletal muscle but decreased in adipose tissue. Conclusion: The susceptibility of Wistar rats to sucrose water-induced MS is associated with the transactivation of SREBP-1c and ChREBP in the liver, and PTP-1B is involved in the upregulation of de novo lipogenesis in the liver and the pathology of systemic insulin resistance in rats with MS chronically induced by drinking sucrose water.

Protein kinase Cbeta mediates hepatic induction of sterol-regulatory element binding protein-1c by insulin

Sterol-regulatory element binding protein-1c (SREBP-1c) is a transcription factor that controls lipogenesis in the liver. Hepatic SREBP-1c is nutritionally regulated, and its sustained activation causes hepatic steatosis and insulin resistance. Although regulation of SREBP-1c is known to occur at the transcriptional level, the precise mechanism by which insulin signaling activates SREBP-1c promoter remains to be elucidated. Here we show that protein kinase C beta (PKCbeta) is a key mediator of insulin-mediated activation of hepatic SREBP-1c and its target lipogenic genes. Activation of SREBP-1c in the liver of refed mice was suppressed by either adenoviral RNAi-mediated knockdown or dietary administration of a specific inhibitor of protein kinase C beta. The effect of PKCbeta inhibition was cancelled in insulin depletion by streptozotocin (STZ) treatment of mice. Promoter analysis indicated that PKCbeta activates SREBP-1c promoter through replacement of Sp3 by Sp1 for binding to the GC box in the sterol regulatory element (SRE) complex, a key cis-element of SREBP-1c promoter. Knockdown of Sp proteins demonstrated that Sp3 and Sp1 play reciprocally negative and positive roles in nutritional regulation of SREBP-1c, respectively. This new understanding of PKCbeta involvement in nutritional regulation of SREBP-1c activation provides a new aspect of PKCbeta inhibition as a potential therapeutic target for diabetic complications.

Maternal undernutrition programmes atherosclerosis in the ApoE*3-Leiden mouse

Poor quality of nutrition during fetal development is associated with adverse health outcomes in adult life. Epidemiological studies suggest that markers of fetal undernutrition are predictive of risk of the metabolic syndrome and CHD. Here we show that feeding a low-protein diet during pregnancy programmed the development of atherosclerosis in ApoE*3-Leiden mice. ApoE*3-Leiden mice carry a mutation of human ApoE*3 rendering them prone to atherosclerosis when fed a diet rich in cholesterol. It was noted that fetal exposure to protein restriction led to a greater degree of dyslipidaemia in mice when fed an atherogenic diet, with low-protein-exposed ApoE*3 mice having elevated total plasma cholesterol (34 % higher; P < 0.001) and TAG (39 % higher; P < 0.001) relative to offspring exposed to a control diet in utero. The low-protein group developed more severe atherosclerotic lesions within the aortic arch (2.61-fold greater lesion area; P < 0.001). Analysis of a targeted gene array suggested a potential role for members of the LDL receptor superfamily, along with similar programmed suppression of the mRNA expression of hepatic sterol regulatory element-binding protein-1c. This indicates that disordered lipid metabolism may play a role in the fetal programming of atherosclerosis in this model. Whereas earlier studies have shown early programming of cardiovascular risk factors, these results demonstrate for the first time that the interaction of prenatal undernutrition with a postnatal atherogenic diet increases the extent of atherosclerotic disease.

Alpha-lipoic acid decreases hepatic lipogenesis through adenosine monophosphate-activated protein kinase (AMPK)-dependent and AMPK-independent pathways

Fatty liver is common in obese subjects with insulin resistance. Hepatic expression of sterol regulatory element binding protein-1c (SREBP-1c), which plays a major role in hepatic steatosis, is regulated by multiple factors, including insulin, adenosine monophosphate-activated protein kinase (AMPK), liver X receptors (LXRs), and specificity protein 1. Alpha-lipoic acid (ALA), a naturally occurring antioxidant, has been shown to decrease lipid accumulation in skeletal muscle by activating AMPK. Here we show that ALA decreases hepatic steatosis and SREBP-1c expression in rats on a high fat diet or given an LXR agonist. ALA increased AMPK phosphorylation in the liver and in cultured liver cells, and dominant-negative AMPK partially prevented ALA-induced suppression of insulin-stimulated SREBP-1c expression. ALA also inhibited DNA-binding activity and transcriptional activity of both specificity protein 1 and LXR. These results show that ALA prevents fatty liver disease through multiple mechanisms, and suggest that ALA can be used to prevent the development and progression of nonalcoholic fatty liver disease in patients with insulin resistance.