Hepatic Sterol Regulatory Element-binding Protein Research Articles

Protective Effects of Melatonin in High-Fat Diet-Induced Hepatic Steatosis via Decreased Intestinal Lipid Absorption and Hepatic Cholesterol Synthesis.

The preventative effect of melatonin on the development of obesity and the progression of fatty liver under a high-fat diet (HFD) has been well elucidated through previous studies. We investigated the mechanism behind this effect regarding cholesterol biosynthesis and regulation of cholesterol levels. Mice were divided into three groups: normal chow diet (NCD); HFD; and HFD and melatonin administration group (HFD+M). We assessed the serum lipid profile, mRNA expression levels of proteins involved in cholesterol synthesis and reabsorption in the liver and nutrient transporters in the intestines, and cytokine levels. Additionally, an in vitro experiment using HepG2 cells was performed. Expression of hepatic sterol regulatory element-binding protein 2 (SREBP-2), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), and low-density lipoprotein receptor (LDLR) demonstrated that melatonin administration significantly reduces hepatic cholesterol synthesis in mice fed an HFD. Expression of intestinal sodium-glucose transporter 1 (SGLT1), glucose transporter 2 (GLUT2), GLUT5, and Niemann-pick C1-like 1 (NPC1L1) demonstrated that melatonin administration significantly reduces intestinal carbohydrate and lipid absorption in mice fed an HFD. There were no differences in local and circulatory inflammatory cytokine levels among the NCD, HFD, and HFD+M group. HepG2 cells stimulated with palmitate showed reduced levels of SREBP, LDLR, and HMGCR indicating these results are due to the direct mechanistic effect of melatonin on hepatocytes. Collectively, these data indicate the mechanism behind the protective effects of melatonin from weight gain and liver steatosis under HFD is through a reduction in intestinal caloric absorption and hepatic cholesterol synthesis highlighting its potential in the treatment of obesity and fatty liver disease.

Oleanolic Acid Inhibits SCD1 Gene Expression to Ameliorate Fructose-Induced Hepatosteatosis through SREBP1c-Dependent and -Independent Mechanisms.

The mechanisms of oleanolic acid (OA) regulating hepatic sterol regulatory element-binding protein (SREBP) 1c/stearoyl-CoA desaturase (SCD) 1 pathway to ameliorate fructose-induced hepatosteatosis are investigated. Rats treated with 10% w/v fructose solution are co-administered by OA for 5 weeks, and then sacrifice after fasting for 14 h. OA reverses the fructose-induced increase in hepatic triglyceride (TG) content and downregulates Scd1 mRNA expression. However, two upstream transcription factors, ChREBP and SREBP1c, remain at normal levels with or without fructose and/or OA. In vivo and in vitro studies using SREBP1c-/- mice and HepG2 cell models show that OA also inhibits SCD1 gene overexpression and high hepatic TG levels induced by fructose. On the other hand, in SCD1-/- mice, when the fructose diet is supplemented with high levels of oleic acid (OLA) to compensate for the deficiency of SCD1, OA inhibits hepatic SREBP1c and lipogenic gene expression and reduces hepatic OLA (C18:1) production to improve fructose and/or OLA induced liver lipid deposition. Furthermore, OA promotes PPARα and AMPK to enhance fatty acid oxidation in fructose + OLA-fed SCD1-/- mice. OA may inhibit SCD1 gene expression to ameliorate fructose-induced hepatosteatosis through SREBP1c-dependent and -independent mechanisms.

Phytogenic feed additives improve broiler feed efficiency via modulation of intermediary lipid and protein metabolism–related signaling pathways

Diets enriched with phytogenic feed additives (PFA) such as AV/HGP/16 premix (AVHGP), Superliv concentrate premix (SCP), and bacteriostatic herbal growth promotor (BHGP) with essential oils have been shown to improve feed efficiency (FE) in broilers. This FE improvement was achieved via modulation of hypothalamic neuropeptides, which results despite feed intake reduction, in increased breast yield without changes in body weight compared to the control group. To gain further insights into the mode of action of these PFA, the present study aimed to determine the potential involvement of signaling pathways associated with lipid and protein metabolism. One day-old male Cobb 500 chicks were randomly assigned into 1 of 4 treatments, comprising 8 replicates per treatment in a completely randomized design. The dietary treatments included a basal diet (control) or 0.55 g/kg diet of AVHGP, SCP, or BHGP. The birds had ad libitum access to water and feed. On day 35, after blood sampling, the liver, abdominal adipose tissue (AT), and breast muscle samples were collected. The levels of phosphorylated mechanistic target of rapamycin (mTOR)Ser2481 as well as its levels of mRNA and those of its downstream mediator RPS6B1 were significantly upregulated in the muscle of the PFA-fed groups compared with the control group. In the liver, the phosphorylated levels of acetyl-CoA carboxylase alpha at Ser79, the rate-limiting enzyme in fat synthesis, was significantly induced in the PFA-fed groups compared with the control group, indicating a lower hepatic lipogenesis. The hepatic expression of hepatic triglyceride lipase (LIPC) and adipose triglyceride lipase (ATGL) was significantly upregulated in the AVHGP-fed group compared with the control group. These hepatic changes were accompanied by a significant downregulation of hepatic sterol regulatory element-binding protein cleavage-activating protein in all the PFA groups and an upregulation of peroxisome proliferator–activated receptor alpha and gamma in the SCP-fed compared with the control group. In the AT, the mRNA abundances of ATGL and LIPC were significantly increased in both SCP- and BHGP-fed birds compared with the control group. Together these data indicate that PFA improve FE via modulation of muscle mTOR pathway and hepatic lipolytic/lipogenic programs, thus, favoring muscle protein synthesis and lowering hepatic lipogenesis.

Enterohepatic Transcription Factor CREB3L3 Protects Atherosclerosis via SREBP Competitive Inhibition.

Background & AimscAMP responsive element-binding protein 3 like 3 (CREB3L3) is a membrane-bound transcription factor involved in the maintenance of lipid metabolism in the liver and small intestine. CREB3L3 controls hepatic triglyceride and glucose metabolism by activating plasma fibroblast growth factor 21 (FGF21) and lipoprotein lipase. In this study, we intended to clarify its effect on atherosclerosis.MethodsCREB3L3-deficifient, liver-specific CREB3L3 knockout, intestine-specific CREB3L3 knockout, both liver- and intestine-specific CREB3L3 knockout, and liver CREB3L3 transgenic mice were crossed with LDLR−/− mice. These mice were fed with a Western diet to develop atherosclerosis.ResultsCREB3L3 ablation in LDLR−/− mice exacerbated hyperlipidemia with accumulation of remnant APOB-containing lipoprotein. This led to the development of enhanced aortic atheroma formation, the extent of which was additive between liver- and intestine-specific deletion. Conversely, hepatic nuclear CREB3L3 overexpression markedly suppressed atherosclerosis with amelioration of hyperlipidemia. CREB3L3 directly up-regulates anti-atherogenic FGF21 and APOA4. In contrast, it antagonizes hepatic sterol regulatory element-binding protein (SREBP)–mediated lipogenic and cholesterogenic genes and regulates intestinal liver X receptor–regulated genes involved in the transport of cholesterol. CREB3L3 deficiency results in the accumulation of nuclear SREBP proteins. Because both transcriptional factors share the cleavage system for nuclear transactivation, full-length CREB3L3 and SREBPs in the endoplasmic reticulum (ER) functionally inhibit each other. CREB3L3 promotes the formation of the SREBP-insulin induced gene 1 complex to suppress SREBPs for ER-Golgi transport, resulting in ER retention and inhibition of proteolytic activation at the Golgi and vice versa.ConclusionsCREB3L3 has multi-potent protective effects against atherosclerosis owing to new mechanistic interaction between CREB3L3 and SREBPs under atherogenic conditions.

Molecular Study on the Potential Protective Effects of Bee Venom against Fructose-Induced Nonalcoholic Steatohepatitis in Rats

Background: There is a causative relation between the increased hepatic steatohepatitis prevalence and sweeteners intake, fructose in particular. Despite an increasing understanding of the mechanisms of nonalcoholic steatohepatitis (NASH) pathogenesis, there are no drugs approved for it. Objectives: Evaluate the effect of bee venom (BV) treatment on the fructose-induced NASH in rats and demonstrate its possible molecular mechanisms. Methods: NASH was induced in rats by 10% fructose in drinking water for 8 weeks. BV was administered (0.1 mg/kg, i.p.) 3 times per week during the last 2 weeks of the experiment. Sera were used for the determination of lipids, cholesterol, glucose, insulin, and liver enzymes. Hepatic gene expressions of farnesoid X receptor (FXR)α and the liver X receptor (LXR) were determined. Hepatic sterol regulatory element-binding protein (SREBP)1/2, oxidative stress, and inflammation parameters were measured. Liver parts were used for histopathological examination. Small intestine was removed for the determination of tight junction proteins. Results: Fructose caused overt histological damage in the liver, and this was associated with parallel changes in all parameters measured. BV effectively prevented these changes, presumably through amelioration of hepatic SREBP1/2, LXR, and FXRα expression as well as intestinal tight junction proteins. Conclusion: These findings support the therapeutic usefulness of BV, a remedy with a favorable safety profile, in the prevention of fructose-induced NASH.

Mulberry Fruit Extract Promotes Serum HDL-Cholesterol Levels and Suppresses Hepatic microRNA-33 Expression in Rats Fed High Cholesterol/Cholic Acid Diet.

Serum high-density lipoprotein cholesterol (HDL-C) levels and cholesterol excretion are closely associated with the risk of cardiovascular complications. The specific aim of the present study was to investigate the cholesterol lowering effect of mulberry fruit in rats fed a high cholesterol/cholic acid diet. Four-week supplementation with mulberry fruit extract significantly decreased serum and hepatic cholesterol (TC), serum low-density lipoprotein cholesterol (LDL-C), and fecal bile acid levels without changes in body weight and food intake (p < 0.05). Mulberry fruit extract significantly inhibited hepatic sterol-regulatory element binding protein (Srebp) 2 gene expression and upregulated hepatic mRNA levels of liver X receptor alpha (Lxr-α), ATP-binding cassette transporter 5 (Abcg5), and cholesterol 7 alpha-hydroxylase (Cyp7a1), which are involved in hepatic bile acid synthesis and cholesterol metabolism (p < 0.05). In addition, hepatic microRNA-33 expression was significantly inhibited by supplementation of mulberry fruit extract (p < 0.05). These results suggest the involvement of miR-33, its associated hepatic bile acid synthesis, HDL formation, and cholesterol metabolism in mulberry fruit-mediated beneficial effects on serum and hepatic lipid abnormalities.

Epigenetic Regulation of Key Enzymes CYP7a1 and HMGCR Affect Hepatic Cholesterol Metabolism in Different Breeds of Piglets.

Liver is the place where cholesterol is synthesized, transported, secreted, and transformed, thus liver takes an irreplaceable role in cholesterol homeostasis. Hepatic cholesterol metabolism differs between breeds, yet the molecular mechanism is unclear. In this study Large White (LW) and Erhualian (EHL) piglets (at birth and 25-day-old) were used, 6 each time point per breed. Erhualian piglets had significantly lower body and liver weight compared with Large White at birth and weaning, but the liver/ body weight ratio was higher at weaning, associated with increased serum and liver cholesterol and triglyceride content. The mRNA expression of Cholesterol-7alpha-hydroxylase (CYP7a1) and Recombinant Acetyl Coenzyme Acetyltransferase 2 (ACAT2) were down-regulated in Erhualian piglets at birth, while hepatic Sterol-regulatory element binding protein 2 (SREBP2) mRNA expression was up-regulated in Erhualian piglets at weaning, as well as SREBP2 protein content, compared with Large White piglets. At birth, the depressed CYP7a1 transcription in Erhualian piglets was associated with decreased Histone H3 (H3) and increased Histone H3 lysine 27 trimethylation (H3K27me3). While the results revealed significant promoter hypermethylation of 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGCR) promoter in Erhualian piglets at weaning, together with increased Histone H3 lysine 9 monomethylation (H3K9me1) and Histone H3 lysine 4 trimethylation (H3K4me3). These results suggest that epigenetic modification may be an important mechanism in hepatic cholesterol metabolism among different species, which is vital for maintaining cholesterol homeostasis and decreasing risk of cardiovascular disease.

LRG ameliorates steatohepatitis by activating the AMPK/mTOR/SREBP1 signaling pathway in C57BL/6J mice fed a high‑fat diet.

The pathogenesis of nonalcoholic fatty liver disease non‑alcoholic steatohepatitis (NASH) has not been fully elucidated, and there are currently no effective treatments for NASH. The aim of the present study was to explore the therapeutic effects of the glucagon‑like peptide‑1 (GLP‑1) receptor agonist liraglutide (LRG) on NASH and the underlying mechanisms. C57BL6J mice were fed a high‑fat diet (HFD) for 8weeks to induce hepatic steatosis, and then LRG was injected subcutaneously for 4weeks. The expression of sterol regulatory element‑binding protein 1 (SREBP1) and adenosine monophosphate‑activated protein kinase (AMPK) as well as the phosphorylation of mechanistic target of rapamycin (mTOR) and p70 ribosomal S6 kinase (p70S6K) were determined by western blot analysis. The intracellular distribution of SREBP1 was assessed by immunofluorescence staining. The results revealed that LRG treatment ameliorated HFD‑induced hepatic lipid accumulation and inhibited body weight gain. In addition, LRG treatment significantly suppressed the expression of hepatic SREBP1 as well as the phosphorylation of mTOR and p70S6K; it also increased the phosphorylation of AMPK and acetyl coenzyme A carboxylase. Furthermore, LRG treatment inhibited the hepatic nuclear translocation of SREBP1. It was suggested that the GLP‑1 receptor agonist LRG may have ameliorated hepatic steatosis by activating the AMPK/mTOR/SREBP1 signaling pathway as opposed to inhibiting body weight gain.

Gpnmb secreted from liver promotes lipogenesis in white adipose tissue and aggravates obesity and insulin resistance.

Metabolism in mammals is regulated by complex interplay among different organs. Fatty acid synthesis is increased in white adipose tissue (WAT) when it is inhibited in the liver. Here we identify glycoprotein non-metastatic melanoma protein B (Gpnmb) as one liver-WAT cross-talk factor involved in lipogenesis. Inhibition of the hepatic sterol regulatory element-binding protein pathway leads to increased transcription of Gpnmb and promotes processing of the membrane protein to a secreted form. Gpnmb stimulates lipogenesis in WAT and exacerbates diet-induced obesity and insulin resistance. In humans, Gpnmb is tightly associated with body mass index and is a strong risk factor for obesity. Gpnmb inhibition by a neutralizing antibody or liver-specific knockdown improves metabolic parameters, including weight gain reduction and increased insulin sensitivity, probably by promoting the beiging of WAT. These results suggest that Gpnmb is a liver-secreted factor regulating lipogenesis in WAT, and that Gpnmb inhibition may provide a therapeutic strategy in obesity and diabetes.

Impact of silencing hepatic SREBP-1 on insulin signaling.

Sterol Regulatory Element Binding Protein-1 (SREBP-1) is a conserved transcription factor of the basic helix-loop-helix leucine zipper family (bHLH-Zip) that plays a central role in regulating expression of genes of carbohydrate and fatty acid metabolism in the liver. SREBP-1 activity is essential for the control of insulin-induced anabolic processes during the fed state. In addition, SREBP-1 regulates expression of key molecules in the insulin signaling pathway, including insulin receptor substrate 2 (IRS2) and a subunit of the phosphatidylinositol 3-kinase (PI3K) complex, PIK3R3, suggesting that feedback mechanisms exist between SREBP-1 and this pathway. Nevertheless, the overall contribution of SREBP-1 activity to maintain insulin signal transduction is unknown. Furthermore, Akt is a known activator of mTORC1, a sensor of energy availability that plays a fundamental role in metabolism, cellular growth and survival. We have silenced SREBP-1 and explored the impact on insulin signaling and mTOR in mice under fed, fasted and refed conditions. No alterations in circulating levels of insulin were observed. The studies revealed that depletion of SREBP-1 had no impact on IRS1Y612, AktS473, and downstream effectors GSK3αS21 and FoxO1S256 during the fed state. Nevertheless, reduced levels of these molecules were observed under fasting conditions. These effects were not associated with changes in phosphorylation of mTOR. Overall, our data indicate that the contribution of SREBP-1 to maintain insulin signal transduction in liver is modest.

Hydroxytyrosol ameliorates insulin resistance by modulating endoplasmic reticulum stress and prevents hepatic steatosis in diet-induced obesity mice

Endoplasmic reticulum (ER) is a principal organelle responsible for energy and nutrient management. Its dysfunction has been viewed in the context of obesity and related glucolipid metabolic disorders. However, therapeutic approaches to improve ER adaptation and systemic energy balance in obesity are limited. Thus, we examined whether hydroxytyrosol (HT), an important polyphenolic compound found in virgin olive oil, could correct the metabolic impairments in diet-induced obesity (DIO) mice. Here, we found that HT gavage for 10 weeks significantly ameliorated glucose homeostasis and chronic inflammation and decreased hepatic steatosis in DIO mice. At the molecular level, ER stress indicators, inflammatory and insulin signaling markers demonstrated that high-fat diet (HFD)-induced ER stress and insulin resistance (IR) in insulin sensitive tissue were corrected by HT. In vitro studies confirmed that HT supplementation (100 μM) attenuated palmitate-evoked ER stress, thus rescuing the downstream JNK/IRS pathway. As a result from suppression of ER stress in the liver, HT further decreased hepatic sterol regulatory element-binding protein-1 expression (SREBP1). Additionally, aberrant expression of genes involved in hepatic lipogenesis (SREBP1, ACC, FAS, SCD1) caused by HFD was restored by HT. These findings suggested that HT ameliorated chronic inflammation and IR and decreased hepatic steatosis in obesity by beneficial modulation of ER stress.

Dietary fibre alleviates hepatic fat deposition via inhibiting lipogenic gene expression in meat ducks

This study investigated the effect of dietary fibre (DF) supplementation on hepatic fat deposition of Cherry Valley meat ducks. A total of 600 1-d-old ducks were randomly allotted to five dietary fibre diets (1.46 (basal diet), 3.09, 4.15, 6.18 and 7.52% (analysed)) for 14days. Growth performance decreased with increasing DF concentrations, when the DF level more than 6.18% the average daily gain (ADG) and feed conversion ratio (F/G) markedly decreased in meat ducks. Meat ducks supplemented over 4.15% DF had lower percentage of liver reported to live weight, liver lipid contents, hepatic triglyceride and total cholesterol concentrations as well as decreased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) concentrations at 14days. The transcription of fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC) and sterol-regulatory element-binding protein-1 (SREBP-1) in liver was significantly reduced by DF, while no any significant difference was found about the effect of DF on hepatic peroxisome proliferator-activated receptor α (PPARα), adipose triglyceride lipase (ATGL), transcription as well as caecal digesta short-chain fatty acids (SCFA). Data suggested that dietary fibre supplementation decreased hepatic lipid deposition and improved characteristics of liver health via inhibiting hepatic FAS, ACC and SREBP-1 expression in meat ducks.

Resveratrol improves high-fat diet induced fatty liver and insulin resistance by concomitantly inhibiting proteolytic cleavage of sterol regulatory element-binding proteins, free fatty acid oxidation, and intestinal triglyceride absorption

Resveratrol (RES) has the ability to ameliorate nonalcoholic fatty liver disease (NAFLD) and the mechanism remains unclear. Hence, using high-fat diet (HFD) obese rat model, we investigated the effect of a low dose of RES (20 mg/kg) on the hepatic sterol regulatory element-binding protein (SREBPs) - lipogenesis pathway, enzymes involved in β-oxidation and activity of pancreatic lipase. Four groups of rats (n = 8) of control (12% of calories as fat) and HFD (40% of calories as fat) were administered orally with either normal saline as a vehicle or RES as a concomitant treatment for 8 weeks on a daily basis. Then, various biochemical, histological, and molecular experiments were carried out. RES prevented the development and progression of NAFLD and significantly improved insulin sensitivity through (1) inhibiting the proteolytic cleavage of SREBPs-1 and SREBPs-2 without affecting their precursor mRNA or protein levels, (2) inhibiting free fatty acid β-oxidation and generation of reactive oxygen species through significant inhibition of CPT-1 and UCP-2, and (3) decreasing activity of pancreatic lipase in vivo and in vitro. In conclusion, our findings are the first in the literature to show new mechanisms of the hepatoprotective effect of RES against HFD induced NAFLD in rats.

Intramuscular injection of exogenous leptin induces adiposity, glucose intolerance and fatty liver by repressing the JAK2-STAT3/PI3K pathway in a rat model

Obesity, diabetes and fatty liver disease are extremely common in leptin-resistant patients. Dysfunction of leptin or its receptor is associated with obesity. The present study aimed to assess the effects of intramuscular injection of exogenous leptin or its receptor on fat deposition and leptin-insulin feedback regulation. Forty-five 40-day old female Sprague Dawley (SD) rats were injected thrice with leptin or its receptor intramuscularly. Adiposity and fat deposition were assessed by assessing the Lee’s index, body weight, food intake, and total cholesterol, high density lipoprotein, low density lipoprotein, and triglyceride levels, as well as histological properties (liver and adipose tissue). Serum glucose, leptin, and insulin amounts were evaluated, and glucose tolerance assessed to monitor glucose metabolism in SD rats; pancreas specimens were analyzed immunohistochemically. Hypothalamic phosphorylated Janus kinase 2 (p-JAK2), phosphorylated signal transducer and activator of transcription 3 (p-STAT3), and phosphatidylinositol-3-kinase (PI3K) signaling, and hepatic sterol regulatory element binding protein-1 (SREBP-1) were qualified by Western blotting. Leptin receptor immunogen reduced fat deposition, increased appetite, and lowered serum leptin levels, enhancing STAT3 signaling in hypothalamus and down-regulating hepatic SREBP-1. In contrast, SD rats administered leptin immunogen displayed significantly increased body weight and fat deposition, with up-regulated SREBP-1, indicating adiposity occurrence. SD rats administered leptin immunogen also showed glucose intolerance, β- cell reduction in the pancreas, and deregulation of JAK2-STAT3/PI3K signaling, indicating that Lep rats were at risk of diabetes. In conclusion, intramuscular injection of exogenous leptin or its receptor, a novel rat model approach, can be used in obesity pathogenesis and therapeutic studies.

Tlr4-mutant mice are resistant to acute alcohol-induced sterol-regulatory element binding protein activation and hepatic lipid accumulation.

Previous studies demonstrated that acute alcohol intoxication caused hepatic lipid accumulation. The present study showed that acute alcohol intoxication caused hepatic lipid accumulation in Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic sterol-regulatory element binding protein (SREBP)-1, a transcription factor regulating fatty acid and triglyceride (TG) synthesis, was activated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic Fas, Acc, Scd-1 and Dgat-2, the key genes for fatty acid and TG synthesis, were up-regulated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Additional experiment showed that hepatic MyD88 was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic NF-κB was activated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Moreover, hepatic GSH content was reduced and hepatic MDA level was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic CYP2E1 was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic p67phox and gp91phox, two NADPH oxidase subunits, were up-regulated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Alpha-phenyl-N-t-butylnitrone (PBN), a free radical spin-trapping agent, protected against alcohol-induced hepatic SREBP-1 activation and hepatic lipid accumulation. In conclusion, Tlr4-mutant mice are resistant to acute alcohol-induced hepatic SREBP-1 activation and hepatic lipid accumulation.

TTC39B deficiency stabilizes LXR reducing both atherosclerosis and steatohepatitis.

SummaryCellular mechanisms that mediate steato-hepatitis, an increasingly prevalent condition in the Western world for which no therapies are available1, are poorly understood. Despite the fact its synthetic agonists induce fatty liver, the Liver X receptor (LXR) transcription factor remains a target of interest because of its anti-atherogenic, cholesterol removal and anti-inflammatory activities. We discovered that tetratricopeptide repeat (TPR) domain protein 39B (Ttc39b, C9orf52) (T39), a high density lipoprotein (HDL) gene discovered in human genome wide association studies (GWAS)2, promotes the ubiquitination and degradation of LXR. Chow-fed T39-/- mice displayed increased HDL cholesterol levels associated with increased enterocyte ATP binding cassette transporter A1 (Abca1) expression and increased LXR protein without change in LXR mRNA. When challenged with a high fat/high cholesterol/bile salt (HF/HC/BS) diet, T39-/- mice or mice with hepatocyte-specific T39 deficiency showed increased hepatic LXR protein and target gene expression, and unexpectedly protection from steato-hepatitis and death. Western Type Diet (WTD)-fed Low density lipoprotein receptor (Ldlr)-/-T39-/- mice showed decreased fatty liver, increased HDL, decreased LDL and reduced atherosclerosis. In addition to increasing hepatic Abcg5/8 expression and limiting dietary cholesterol absorption, T39 deficiency inhibited hepatic sterol regulatory element binding protein 1 (SREBP-1, ADD1) processing. This was explained by an increase in microsomal phospholipids containing polyunsaturated fatty acids (PUFA), linked to an LXRα-dependent increase in expression of enzymes mediating PC biosynthesis and incorporation of PUFA into phospholipids. The preservation of endogenous LXR protein activates a beneficial profile of gene expression that promotes cholesterol removal and inhibits lipogenesis. T39 inhibition could be an effective strategy for reducing both steato-hepatitis and atherosclerosis.

Obesity-driven prepartal hepatic lipid accumulation in dairy cows is associated with increased CD36 and SREBP-1 expression

We investigated the hypothesis that obesity in dairy cows enhanced expression of proteins involved in hepatic fatty acid uptake and metabolism. Sixteen Holstein-Friesian close-up cows were divided into 2 equal groups based on their body condition score (BCS) as optimal (3.25≤BCS≤3.5) and high (4.0≤BCS≤4.25). Intravenous glucose tolerance test (GTT) and liver biopsies were carried out at day 10 before calving. Blood samples were collected before (basal) and after glucose infusion, and glucose, insulin and non-esterified fatty acid (NEFA) levels were determined at each sample point. In addition, β-hydroxybutyrate and triglycerides levels were measured in the basal samples. The liver biopsies were analyzed for total lipid content and protein expression of insulin receptor beta (IRβ), fatty acid translocase (FAT/CD36) and sterol regulatory element-binding protein-1 (SREBP-1). Basal glucose and insulin were higher in high-BCS cows, which coincided with higher circulating triglycerides and hepatic lipid content. Clearance rate and AUC for NEFA during GTT were higher in optimal-BCS cows. The development of insulin resistance and fatty liver in obese cows was paralleled by increased hepatic expression of the IRβ, CD36 and SREBP-1. These results suggest that increased expression of hepatic CD36 and SREBP-1 is relevant in the obesity-driven lipid accumulation in the liver of dairy cows during late gestation.

Synthesis, characterization, and efficacy evaluation of a new anti-diabetic vanadyl(II) thiamine hydrochloride complex in streptozotocin-induced diabetic rats.

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by hyperglycemia due to abnormalities in either insulin secretion or action. A range of vanadium complexes have been synthesized and demonstrated to be effective in lowering hyperglycemia. Thiamine administration was also reported to prevent deterioration in fasting glucose and insulin levels, and to improve glucose tolerance in hyperglycemic patients. This study has been conducted to evaluate the ionic vanadyl(II) thiamine hydrochloride complex (VC) as a new anti-diabetic candidate. The new complex was characterized by infrared spectroscopy (FT-IR), electronic spectra, magnetic susceptibility, electron spin resonance (ESR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The anti-diabetic effect of VC was investigated in comparison to vanadium sulfate in streptozotocin (STZ)-induced diabetic rats. Treatment of diabetic rats with VC versus vanadyl sulfate showed a more potent effect on reducing serum glucose and cholesterol close to normal levels. VC suppressed the diabetes-induced upregulation of hepatic glucose transporter (GLUT)-2, Phosphoenol pyruvate carboxykinase (PEPCK), and hormone-sensitive lipase (HSL) more significantly than vanadyl sulfate. Either vanadyl sulfate or VC restored hepatic sterol regulatory element-binding protein transcription factor-1c (SREBP-1c) and muscle hexokinase (HK) mRNA expression that was downregulated in diabetic group. Pyruvate kinase (PK) mRNA expression was restored more significantly in VC-treated than vanadyl sulfate-treated diabetic rats. These results indicate that the newly synthesized VC could be an effective anti-diabetic candidate as the anti-diabetic activity of the ionic vanadium was enhanced after being modified with the organic ligand, thiamin. The results also suggest that VC achieves its effect most likely through modulating the transcription of energy metabolizing enzymes.

Opposing roles of nitric oxide and rho-kinase in lipid metabolism in mice.

Dyslipidemia is a life-style disorder and is one of the important risk factors of cardiovascular diseases. Nitric oxide (NO) exerts beneficial effects on lipid metabolism through activation of hepatic sterol regulatory element-binding protein (SREBP)-2, a transcriptional factor for cholesterol metabolism and expression of LDL receptor, while Rho-kinase, an effecter protein of small G protein, RhoA, contributes to the pathogenesis of metabolic syndrome through suppressing the whole body energy consumption. However, the crosstalk between NO and Rho-kinase in regulation of lipid metabolism remains to be elucidated. In the present study, we used male wild-type (WT) mice and mice lacking three isoforms of NO synthase (NOSs(-/-)). WT mice were fed either normal diet (ND) or high-fat diet (HFD), while NOSs(-/-) mice were fed ND with or without a selective Rho-kinase inhibitor, fasudil (100 mg/kg/day), for 6 weeks. At 6 weeks, plasma NOx concentration was significantly decreased and Rho-kinase activity and lipid levels were significantly elevated in HFD-fed WT mice and NOSs(-/-) mice compared with ND-fed WT mice. In the liver, SREBP-2 activity was reduced in NOSs(-/-) mice. Fasudil ameliorated lipid levels in HFD-fed WT mice and NOSs(-/-) mice without affecting SREBP-2 activity or LDL receptor expression, whereas it significantly enhanced phosphorylation of AMP-activated kinase (AMPK) in the liver and skeletal muscle. Importantly, the beneficial metabolic effects of fasudil were absent in HFD-fed AMPK(-/-) mice. These results provide the first evidence that NO and Rho-kinase play opposing roles for the lipid metabolism, suggesting that Rho-kinase inhibitors could be novel therapeutic agents of dyslipidemia.

Duodenal-jejunal bypass surgery suppresses hepatic de novo lipogenesis and alleviates liver fat accumulation in a diabetic rat model.

Duodenal-jejunal bypass (DJB) surgery can induce rapid and durable remission of type 2 diabetes mellitus (T2DM), but the intrinsic mechanisms remain to be elucidated. Recent studies indicated that improved hepatic insulin resistance and insulin signaling transduction might contribute to the diabetic control after DJB. Given the important role of liver adiposity in hepatic insulin resistance, this study was aimed at investigating the effects of DJB on glucose homeostasis and liver fat accumulation in a T2DM rat model induced by high-fat diet (HFD) and small dose of streptozotocin (STZ). Forty adult male diabetic rats induced by HFD and small dose of STZ were randomly assigned to sham and DJB groups. Body weight, calorie intake, hormone levels, glucose, and lipid parameters were measured at indicated time points. Subsequently, hepatic triglycerides (TG) content and the protein levels of sterol regulatory element binding protein-1 (SREBP-1), carbohydrate response element binding protein (ChREBP), fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) were evaluated at 2 and 8 weeks postoperatively. Compared with sham group, DJB induced rapid and significant improvements in glucose homeostasis and insulin sensitivity independently of weight loss and calorie restriction. The DJB-operated rats exhibited lower liver TG content and decreased hepatic SREBP-1, ChREBP, ACC, and FAS at 8 weeks postoperatively. DJB alleviated hepatic fat accumulation and downregulated the key transcriptional regulators and enzymes involved in hepatic de novo lipogenesis, which might contribute to improved hepatic insulin sensitivity and glucose homeostasis after DJB.