Dissociation of hepatic steatosis and insulin resistance in mice overexpressing DGAT in the liver

Hepatic steatosis, the accumulation of lipids in the liver, is widely believed to result in insulin resistance. To test the causal relationship between hepatic steatosis and insulin resistance, we generated mice that overexpress acyl-CoA:diacylglycerol acyltransferase 2 (DGAT2), which catalyzes the final step of triacylglycerol (TG) biosynthesis, in the liver (Liv-DGAT2 mice). Liv-DGAT2 mice developed hepatic steatosis, with increased amounts of TG, diacylglycerol, ceramides, and unsaturated long-chain fatty acyl-CoAs in the liver. However, they had no abnormalities in plasma glucose and insulin levels, glucose and insulin tolerance, rates of glucose infusion and hepatic glucose production during hyperinsulinemic-euglycemic clamp studies, or activities of insulin-stimulated signaling proteins in the liver. DGAT1 overexpression in the liver also failed to induce glucose or insulin intolerance. Our results indicate that DGAT-mediated lipid accumulation in the liver is insufficient to cause insulin resistance and show that hepatic steatosis can occur independently of insulin resistance.     

Hepatic deficiency of selenoprotein S exacerbates hepatic steatosis and insulin resistance

Nonalcoholic fatty liver disease (NAFLD) is closely associated with insulin resistance (IR) and type 2 diabetes mellitus (T2DM), which are all complex metabolic disorders. Selenoprotein S (SelS) is an endoplasmic reticulum (ER) resident selenoprotein involved in regulating ER stress and has been found to participate in the occurrence and development of IR and T2DM. However, the potential role and mechanism of SelS in NAFLD remains unclear. Here, we analyzed SelS expression in the liver of high-fat diet (HFD)-fed mice and obese T2DM model (db/db) mice and generated hepatocyte-specific SelS knockout (SelS^H-KO) mice using the Cre-loxP system. We showed that hepatic SelS expression levels were significantly downregulated in HFD-fed mice and db/db mice. Hepatic SelS deficiency markedly increased ER stress markers in the liver and caused hepatic steatosis via increased fatty acid uptake and reduced fatty acid oxidation. Impaired insulin signaling was detected in the liver of SelS^H-KO mice with decreased phosphorylation levels of insulin receptor substrate 1 (IRS1) and protein kinase B (PKB/Akt), which ultimately led to disturbed glucose homeostasis. Meanwhile, our results showed hepatic protein kinase Cɛ (PKCɛ) activation participated in the negative regulation of insulin signaling in SelS^H-KO mice. Moreover, the inhibitory effect of SelS on hepatic steatosis and IR was confirmed by SelS overexpression in primary hepatocytes in vitro. Thus, we conclude that hepatic SelS plays a key role in regulating hepatic lipid accumulation and insulin action, suggesting that SelS may be a potential intervention target for the prevention and treatment of NAFLD and T2DM.Subject terms: Metabolic syndrome, Obesity     

Targeted proteomics reveals strain‐specific changes in the mouse insulin and central metabolic pathways after a sustained high‐fat diet

The metabolic syndrome is a collection of risk factors including obesity, insulin resistance and hepatic steatosis, which occur together and increase the risk of diseases such as diabetes, cardiovascular disease and cancer. In spite of intense research, the complex etiology of insulin resistance and its association with the accumulation of triacylglycerides in the liver and with hepatic steatosis remains not completely understood. Here, we performed quantitative measurements of 144 proteins involved in the insulin‐signaling pathway and central metabolism in liver homogenates of two genetically well‐defined mouse strains C57BL/6J and 129Sv that were subjected to a sustained high‐fat diet. We used targeted mass spectrometry by selected reaction monitoring (SRM) to generate accurate and reproducible quantitation of the targeted proteins across 36 different samples (12 conditions and 3 biological replicates), generating one of the largest quantitative targeted proteomics data sets in mammalian tissues. Our results revealed rapid response to high‐fat diet that diverged early in the feeding regimen, and evidenced a response to high‐fat diet dominated by the activation of peroxisomal β‐oxidation in C57BL/6J and by lipogenesis in 129Sv mice.     

Pyruvate dehydrogenase kinase 4 mediates lipogenesis and contributes to the pathogenesis of nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a progressive disease and poses a high risk of severe liver damage. However, the pathogenesis of NASH is still unclear. Accumulation of lipid droplets and insulin resistance is the hallmark of NASH. Pyruvate dehydrogenase kinase isoenzyme 4 (PDK4) plays key role in glucose metabolism via regulating the activity of pyruvate dehydrogenase complex (PDC). Here, we demonstrated a novel of PDK4 in NASH by regulating hepatic steatosis and insulin signaling pathway in methionine and choline deficient (MCD) diet induced NASH model. Hepatic PDK4 levels were highly induced in human patients with NASH and MCD diet fed mice, as well as in hepatocytes treated with oleic acid. The glucose and lipid metabolism were impaired in Pdk4^?/? mice. Pdk4 deficiency ameliorated the hepatic steatosis significantly in NASH mice. Pdk4^?/?-MCD mice had reduced liver weights and triglyceride (TG) levels. And Pdk4 deficiency dramatically reduced the expression of genes related to fatty acid uptake, synthesis and gluconeogenesis. In addition, elevated phosphorylated AMPK (p-AMPK), p-SAPK/JNK and diminished p-ERK, p-P38, p-Akt and p-mTOR/p-4EBP1 proteins were observed. In conclusion, our data indicated that PDK4 potentially contributes to the hepatic steatosis in NASH via regulating several signaling pathway and PDK4 may be a new therapeutic strategy against NAFLD.     

Hepatocyte-specific deletion of BAP31 promotes SREBP1C activation,promotes hepatic lipid accumulation,and worsens IR in mice

Conditional knockout mice with targeted disruption of B-cell associated protein (BAP)31 in adult mouse liver were generated and challenged with a high-fat diet (HFD) for 36 or 96 days and markers of obesity, diabetes, and hepatic steatosis were determined. Mutant mice were indistinguishable from WT littermates, but exhibited increased HFD-induced obesity. BAP31-deletion in hepatocytes increased the expression of SREBP1C and the target genes, including acetyl-CoA carboxylase 1 and stearoyl-CoA desaturase-1, and increased hepatic lipid accumulation and HFD-induced liver steatosis. Immunoprecipitation assay showed that BAP31 interacts with SREBP1C and insulin-induced gene 1 (INSIG1), and BAP31-deletion reduces INSIG1 expression, suggesting that BAP31 may regulate SREBP1C activity by modulating INSIG1 protein levels. Additionally, BAP31-deletion induced glucose and insulin intolerance, decreased Akt and glycogen synthase kinase 3β phosphorylation, and enhanced hepatic glucose production in mice. Expression of endoplasmic reticulum (ER) stress markers was significantly induced in BAP31-mutant mice. HFD-induced inflammation was aggravated in mutant mice, along with increased c-Jun N-terminal kinase and nuclear factor-κB activation. These findings demonstrate that BAP31-deletion induces SREBP activation and promotes hepatic lipid accumulation, reduces insulin signaling, impairs glucose/insulin tolerance, and increases ER stress and hepatic inflammation, explaining the protective roles of BAP31 in the development of liver steatosis and insulin resistance in HFD-induced obesity in animal models.     

2 型糖尿病合并非酒精性脂肪肝病患者IGF-1 与胰岛素抵抗关系研究

研究胰岛素样生长因子-1(IGF-1)与2型糖尿病(T2DM)胰岛素抵抗关系。有研究证实给予IGF-1后,可改善胰岛素抵抗、肝脏脂质代谢,IGF-1基因缺失的动物会产生胰岛素抵抗和高胰岛素血症,低水平的IGF-1还可能与非酒精性脂肪肝病(NAFLD)肝纤维化有关,而T2DM和NAFLD与胰岛素抵抗共存,T2DM合并NAFLD患者IGF-1水平更低。IGF-1与胰岛素抵抗关系密切,IGF-1水平能反映胰岛素抵抗的严重程度,为IGF-l在今后治疗T2DM和NAFLD的提供了潜在的临床应用前景。     

Ipragliflozin Improves Hepatic Steatosis in Obese Mice and Liver Dysfunction in Type 2 Diabetic Patients Irrespective of Body Weight Reduction

Type 2 diabetes mellitus (T2DM) is associated with a high incidence of non-alcoholic fatty liver disease (NAFLD) related to obesity and insulin resistance. Currently, medical interventions for NAFLD have focused on diet control and exercise to reduce body weight, and there is a requirement for effective pharmacological therapies. Sodium-glucose cotransporter 2 (SGLT2) inhibitors are oral antidiabetic drugs that promote the urinary excretion of glucose by blocking its reabsorption in renal proximal tubules. SGLT2 inhibitors lower blood glucose independent of insulin action and are expected to reduce body weight because of urinary calorie loss. Here we show that an SGLT2 inhibitor ipragliflozin improves hepatic steatosis in high-fat diet-induced and leptin-deficient (ob/ob) obese mice irrespective of body weight reduction. In the obese mice, ipragliflozin-induced hyperphagia occurred to increase energy intake, attenuating body weight reduction with increased epididymal fat mass. There is an inverse correlation between weights of liver and epididymal fat in ipragliflozin-treated obese mice, suggesting that ipragliflozin treatment promotes normotopic fat accumulation in the epididymal fat and prevents ectopic fat accumulation in the liver. Despite increased adiposity, ipragliflozin ameliorates obesity-associated inflammation and insulin resistance in epididymal fat. Clinically, ipragliflozin improves liver dysfunction in patients with T2DM irrespective of body weight reduction. These findings provide new insight into the effects of SGLT2 inhibitors on energy homeostasis and fat accumulation and indicate their potential therapeutic efficacy in T2DM-associated hepatic steatosis.     

Hepatic Hdac3 promotes gluconeogenesis by repressing lipid synthesis and sequestration

Fatty liver disease is associated with obesity and type 2 diabetes, and hepatic lipid accumulation may contribute to insulin resistance. Histone deacetylase 3 (Hdac3) controls the circadian rhythm of hepatic lipogenesis. Here we show that, despite severe hepatosteatosis, mice with liver-specific depletion of Hdac3 have higher insulin sensitivity without any changes in insulin signaling or body weight compared to wild-type mice. Hdac3 depletion reroutes metabolic precursors towards lipid synthesis and storage within lipid droplets and away from hepatic glucose production. Perilipin 2, which coats lipid droplets, is markedly induced upon Hdac3 depletion and contributes to the development of both steatosis and improved tolerance to glucose. These findings suggest that the sequestration of hepatic lipids in perilipin 2–coated droplets ameliorates insulin resistance and establish Hdac3 as a pivotal epigenomic modifier that integrates signals from the circadian clock in the regulation of hepatic intermediary metabolism.     

Hepatocyte-specific deletion of Janus kinase 2 (JAK2) protects against diet-induced steatohepatitis and glucose intolerance

Non-alcoholic fatty liver disease (NAFLD) is becoming the leading cause of chronic liver disease and is now considered to be the hepatic manifestation of the metabolic syndrome. However, the role of steatosis per se and the precise factors required in the progression to steatohepatitis or insulin resistance remain elusive. The JAK-STAT pathway is critical in mediating signaling of a wide variety of cytokines and growth factors. Mice with hepatocyte-specific deletion of Janus kinase 2 (L-JAK2 KO mice) develop spontaneous steatosis as early as 2 weeks of age. In this study, we investigated the metabolic consequences of jak2 deletion in response to diet-induced metabolic stress. To our surprise, despite the profound hepatosteatosis, deletion of hepatic jak2 did not sensitize the liver to accelerated inflammatory injury on a prolonged high fat diet (HFD). This was accompanied by complete protection against HFD-induced whole-body insulin resistance and glucose intolerance. Improved glucose-stimulated insulin secretion and an increase in β-cell mass were also present in these mice. Moreover, L-JAK2 KO mice had progressively reduced adiposity in association with blunted hepatic growth hormone signaling. These mice also exhibited increased resting energy expenditure on both chow and high fat diet. In conclusion, our findings indicate a key role of hepatic JAK2 in metabolism such that its absence completely arrests steatohepatitis development and confers protection against diet-induced systemic insulin resistance and glucose intolerance.     

Blocking Nuclear Factor-Kappa B Protects against Diet-Induced Hepatic Steatosis and Insulin Resistance in Mice

Inflammation critically contributes to the development of various metabolic diseases. However, the effects of inhibiting inflammatory signaling on hepatic steatosis and insulin resistance, as well as the underlying mechanisms remain obscure. In the current study, male C57BL/6J mice were fed a chow diet or high-fat diet (HFD) for 8 weeks. HFD-fed mice were respectively treated with p65 siRNA, non-silence control siRNA or vehicle every 4^th day for the last 4 weeks. Vehicle-treated (HF) and non-silence siRNA-treated (HFNS) mice displayed overt inflammation, hepatic steatosis and insulin resistance compared with chow-diet-fed (NC) mice. Upon treatment with NF-κB p65 siRNA, HFD-fed (HFPS) mice were protected from hepatic steatosis and insulin resistance. Furthermore, Atg7 and Beclin1 expressions and p-AMPK were increased while p-mTOR was decreased in livers of HFPS mice in relative to HF and HFNS mice. These results suggest a crosslink between NF-κB signaling pathway and liver AMPK/mTOR/autophagy axis in the context of hepatic steatosis and insulin resistance.     

12α-Hydroxylated bile acid induces hepatic steatosis with dysbiosis in rats

There is an increasing need to explore the mechanism of the progression of non-alcoholic fatty liver disease. Steroid metabolism is closely linked to hepatic steatosis and steroids are excreted as bile acids (BAs). Here, we demonstrated that feeding WKAH/HkmSlc inbred rats a diet supplemented with cholic acid (CA) at 0.5 g/kg for 13 weeks induced simple steatosis without obesity. Liver triglyceride and cholesterol levels were increased accompanied by mild elevation of aminotransferase activities. There were no signs of inflammation, insulin resistance, oxidative stress, or fibrosis. CA supplementation increased levels of CA and taurocholic acid (TCA) in enterohepatic circulation and deoxycholic acid (DCA) levels in cecum with an increased ratio of 12α-hydroxylated BAs to non-12α-hydroxylated BAs. Analyses of hepatic gene expression revealed no apparent feedback control of BA and cholesterol biosynthesis. CA feeding induced dysbiosis in cecal microbiota with enrichment of DCA producers, which underlines the increased cecal DCA levels. The mechanism of steatosis was increased expression of Srebp1 (positive regulator of liver lipogenesis) through activation of the liver X receptor by increased oxysterols in the CA-fed rats, especially 4β-hydroxycholesterol (4βOH) formed by upregulated expression of hepatic Cyp3a2, responsible for 4βOH formation. Multiple regression analyses identified portal TCA and cecal DCA as positive predictors for liver 4βOH levels. The possible mechanisms linking these predictors and upregulated expression of Cyp3a2 are discussed. Overall, our observations highlight the role of 12α-hydroxylated BAs in triggering liver lipogenesis and allow us to explore the mechanisms of hepatic steatosis onset, focusing on cholesterol and BA metabolism.     

Dietary fatty acids modulate antigen presentation to hepatic NKT cells in nonalcoholic fatty liver disease

Dietary fatty acids are major contributors to the development and progression of insulin resistance and nonalcoholic fatty liver disease (NAFLD). Dietary fatty acids also alter hepatic NKT cells that are activated by antigens presented by CD1d. In the current study, we examine the mechanism of dietary fatty acid induced hepatic NKT cell deficiency and its causal relationship to insulin resistance and NAFLD. We discover that dietary saturated fatty acids (SFA) or monounsaturated fatty acids (MUFA), but not polyunsaturated fatty acids (PUFA), cause hepatic NKT cell depletion with increased apoptosis. Dietary SFA or MUFA also impair hepatocyte presentation of endogenous, but not exogenous, antigen to NKT cells, indicating alterations of the endogenous antigen processing or presenting pathway. In vitro treatment of normal hepatocytes with fatty acids also demonstrates impaired ability of CD1d to present endogenous antigen by dietary fatty acids. Furthermore, dietary SFA and MUFA activate the NFκB signaling pathway and lead to insulin resistance and hepatic steatosis. In conclusion, both dietary SFA and MUFA alter endogenous antigen presentation to hepatic NKT cells and contribute to NKT cell depletion, leading to further activation of inflammatory signaling, insulin resistance, and hepatic steatosis.     

Suppression of Grb2 expression improved hepatic steatosis, oxidative stress, and apoptosis induced by palmitic acid in vitro partly through insulin signaling alteration

In this study, we aimed to study the role of growth factor receptor-bound protein 2 (Grb2) in palmitic acid-induced steatosis and other “fatty liver” symptoms in vitro. HepG2 cells, with or without stably suppressed Grb2 expression, were incubated with palmitic acid for 24 h to induce typical clinical “fatty liver” features, including steatosis, impaired glucose metabolism, oxidative stress, and apoptosis. MTT and Oil Red O assays were applied to test cell viability and fat deposition, respectively. Glucose uptake assay was used to evaluate the glucose utilization of cells. Quantitative polymerase chain reaction and Western blot were used to measure expressional changes of key markers of insulin signaling, lipid/glucose metabolism, oxidative stress, and apoptosis. After 24-h palmitic acid induction, increased fat accumulation, reduced glucose uptake, impaired insulin signaling, enhanced oxidative stress, and increased apoptosis were observed in HepG2 cells. Suppression of Grb2 in HepG2 significantly reduced fat accumulation, improved glucose metabolism, ameliorated oxidative stress, and restored the activity of insulin receptor substrate-1/Akt and MEK/ERK pathways. In addition, Grb2 deficiency attenuated hepatic apoptosis shown by reduced activation of caspase-3 and fluorescent staining. Modulation of Bcl-2 and Bak1 also contributed to reduced apoptosis. In conclusion, suppression of Grb2 expression in HepG2 cells improved hepatic steatosis, glucose metabolism, oxidative stress, and apoptosis induced by palmitic acid incubation partly though modulating the insulin signaling pathway.     

Pathway-selective Insulin Resistance and Metabolic Disease: The Importance of Nutrient Flux

Hepatic glucose and lipid metabolism are altered in metabolic disease (e.g. obesity, metabolic syndrome, and Type 2 diabetes). Insulin-dependent regulation of glucose metabolism is impaired. In contrast, lipogenesis, hypertriglyceridemia, and hepatic steatosis are increased. Because insulin promotes lipogenesis and liver fat accumulation, to explain the elevation in plasma and tissue lipids, investigators have suggested the presence of pathway-selective insulin resistance. In this model, insulin signaling to glucose metabolism is impaired, but insulin signaling to lipid metabolism is intact. We discuss the evidence for the differential regulation of hepatic lipid and glucose metabolism. We suggest that the primary phenotypic driver is altered substrate delivery to the liver, as well as the repartitioning of hepatic nutrient handling. Specific alterations in insulin signaling serve to amplify the alterations in hepatic substrate metabolism. Thus, hyperinsulinemia and its resultant increased signaling may facilitate lipogenesis, but are not the major drivers of the phenotype of pathway-selective insulin resistance.     

Conjugated linoleic acid fails to worsen insulin resistance but induces hepatic steatosis in the presence of leptin in ob/ob mice

Conjugated linoleic acid (CLA) induces insulin resistance preceded by rapid depletion of the adipokines leptin and adiponectin, increased inflammation, and hepatic steatosis in mice. To determine the role of leptin in CLA-mediated insulin resistance and hepatic steatosis, recombinant leptin was coadministered with dietary CLA in ob/ob mice to control leptin levels and to, in effect, negate the leptin depletion effect of CLA. In a 2 x 2 factorial design, 6 week old male ob/ob mice were fed either a control diet or a diet supplemented with CLA and received daily intraperitoneal injections of either leptin or vehicle for 4 weeks. In the absence of leptin, CLA significantly depleted adiponectin and induced insulin resistance, but it did not increase hepatic triglyceride concentrations or adipose inflammation, marked by interleukin-6 and tumor necrosis factor-alpha mRNA expression. Insulin resistance, however, was accompanied by increased macrophage infiltration (F4/80 mRNA) in adipose tissue. In the presence of leptin, CLA depleted adiponectin but did not induce insulin resistance or macrophage infiltration. Despite this, CLA induced hepatic steatosis. In summary, CLA worsened insulin resistance without evidence of inflammation or hepatic steatosis in mice after 4 weeks. In the presence of leptin, CLA failed to worsen insulin resistance but induced hepatic steatosis in ob/ob mice.     

Diabetes of the Liver: The Link Between Nonalcoholic Fatty Liver Disease and HFCS‐55

Nonalcoholic fatty liver disease (NAFLD) is associated with obesity and insulin resistance. It is also a predisposing factor for type 2 diabetes. Dietary factors are believed to contribute to all three diseases. NAFLD is characterized by increased intrahepatic fat and mitochondrial dysfunction, and its etiology may be attributed to excessive fructose intake. Consumption of high fructose corn syrup‐55 (HFCS‐55) stands at up to 15% of the average total daily energy intake in the United States, and is linked to weight gain and obesity. The aim of this study was to establish whether HFCS‐55 could contribute to the pathogenesis of NAFLD, by examining the effects of HFCS‐55 on hepatocyte lipogenesis, insulin signaling, and cellular function, in vitro and in vivo. Exposure of hepatocytes to HFCS‐55 caused a significant increase in hepatocellular triglyceride (TG) and lipogenic proteins. Basal production of reactive oxygen metabolite (ROM) was increased, together with a decreased capacity to respond to an oxidative challenge. HFCS‐55 induced a downregulation of the insulin signaling pathway, as indicated by attenuated ^ser473phosphorylation of AKT1. The c‐Jun amino‐terminal kinase (JNK), which is intimately linked to insulin resistance, was also activated; and this was accompanied by an increase in endoplasmic reticulum (ER) stress and intracellular free calcium perturbation. Hepatocytes exposed to HFCS‐55 exhibited mitochondrial dysfunction and released cytochrome C (CytC) into the cytosol. Hepatic steatosis and mitochondrial disruption was induced in vivo by a diet enriched with 20% HFCS 55; accompanied by hypoadiponectinemia and elevated fasting serum insulin and retinol‐binding protein‐4 (RBP4) levels. Taken together our findings indicate a potential mechanism by which HFCS‐55 may contribute to the pathogenesis of NAFLD.     

Kinetic Modeling of Human Hepatic Glucose Metabolism in Type 2 Diabetes Mellitus Predicts Higher Risk of Hypoglycemic Events in Rigorous Insulin Therapy

A major problem in the insulin therapy of patients with diabetes type 2 (T2DM) is the increased occurrence of hypoglycemic events which, if left untreated, may cause confusion or fainting and in severe cases seizures, coma, and even death. To elucidate the potential contribution of the liver to hypoglycemia in T2DM we applied a detailed kinetic model of human hepatic glucose metabolism to simulate changes in glycolysis, gluconeogenesis, and glycogen metabolism induced by deviations of the hormones insulin, glucagon, and epinephrine from their normal plasma profiles. Our simulations reveal in line with experimental and clinical data from a multitude of studies in T2DM, (i) significant changes in the relative contribution of glycolysis, gluconeogenesis, and glycogen metabolism to hepatic glucose production and hepatic glucose utilization; (ii) decreased postprandial glycogen storage as well as increased glycogen depletion in overnight fasting and short term fasting; and (iii) a shift of the set point defining the switch between hepatic glucose production and hepatic glucose utilization to elevated plasma glucose levels, respectively, in T2DM relative to normal, healthy subjects. Intriguingly, our model simulations predict a restricted gluconeogenic response of the liver under impaired hormonal signals observed in T2DM, resulting in an increased risk of hypoglycemia. The inability of hepatic glucose metabolism to effectively counterbalance a decline of the blood glucose level becomes even more pronounced in case of tightly controlled insulin treatment. Given this Janus face mode of action of insulin, our model simulations underline the great potential that normalization of the plasma glucagon profile may have for the treatment of T2DM.     

RGC-32 Deficiency Protects against Hepatic Steatosis by Reducing Lipogenesis

Hepatic steatosis is associated with insulin resistance and metabolic syndrome because of increased hepatic triglyceride content. We have reported previously that deficiency of response gene to complement 32 (RGC-32) prevents high-fat diet (HFD)-induced obesity and insulin resistance in mice. This study was conducted to determine the role of RGC-32 in the regulation of hepatic steatosis. We observed that hepatic RGC-32 was induced dramatically by both HFD challenge and ethanol administration. RGC-32 knockout (RGC32^−/−) mice were resistant to HFD- and ethanol-induced hepatic steatosis. The hepatic triglyceride content of RGC32^−/− mice was decreased significantly compared with WT controls even under normal chow conditions. Moreover, RGC-32 deficiency decreased the expression of lipogenesis-related genes, sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase, and stearoyl-CoA desaturase 1 (SCD1). RGC-32 deficiency also decreased SCD1 activity, as indicated by decreased desaturase indices of the liver and serum. Mechanistically, insulin and ethanol induced RGC-32 expression through the NF-κB signaling pathway, which, in turn, increased SCD1 expression in a SREBP-1c-dependent manner. RGC-32 also promoted SREBP-1c expression through activating liver X receptor. These results demonstrate that RGC-32 contributes to the development of hepatic steatosis by facilitating de novo lipogenesis through activating liver X receptor, leading to the induction of SREBP-1c and its target genes. Therefore, RGC-32 may be a potential novel drug target for the treatment of hepatic steatosis and its related diseases.