Liver Steatosis In Mice Research Articles

Resveratrol Ameliorates Lipid Droplet Accumulation in Liver Through a SIRT1/ ATF6-Dependent Mechanism

Background/Aims: Lipid droplets (LDs) are dynamic organelles that store neutral lipids during times of energy excess, and an increased accumulation of LDs in the liver is closely linked to hepatic steatosis. Our previous studies suggested that resveratrol (RSV) supplement could improve hepatic steatosis, but the underlying mechanism, particularly which related to LD accumulation, has not yet been elucidated. Methods: A high-fat diet (HFD) and palmitic acid were used to induce hepatic steatosis in mouse liver and hepatocytes, respectively. The effects of RSV on LD accumulation were analyzed in vivo and in vitro. The effects of RSV on the expression levels of LD-associated genes (ATF6, Fsp27β/CIDEC, CREBH, and PLIN1) were measured by qRT-PCR and western blot assays, followed by KD or overexpression of SIRT1 and ATF6 with small interfering RNAs or overexpressed plasmids, respectively. The dual luciferase reporter assay, chromatin immunoprecipitation assay, coimmunoprecipitation, and proximity ligation assay were utilized to clarify the mechanism of transcriptional regulation and possible interaction between SIRT1 and ATF6. Results: There was a significant increase in the accumulation of LDs in liver and hepatocytes during the process of HFD-induced steatosis, respectively, which was significantly inhibited by RSV supplementation. RSV notably activated SIRT1 expression and decreased the expression levels of ATF6, Fsp27β/CIDEC, CREBH, and PLIN1, which are associated with LD accumulation. Interestingly, the inhibitory effects of RSV on LD accumulation and the associated expression of genes in hepatocytes were abrogated or strengthened with SIRT1 silencing or overexpression, respectively. On the contrary, the benefits of RSV in hepatocytes were eliminated or aggravated when transfected with the overexpressed ATF6 or ATF6 siRNA, respectively. Furthermore, we found that RSV stimulated SIRT1 expression significantly, which was followed by increased deacetylation and inactivation of ATF6, resulting in a positive feedback loop for SIRT1 transcription associated with ATF6 binding to the SIRT1 promoter region. Conclusion: Taken together, these findings indicate that RSV supplementation improves hepatic steatosis by ameliorating the accumulation of LDs, and this might be partially mediated by a SIRT1/ATF6-dependent mechanism.

Short-term treatment with hepatoselective NO donor V-PYRRO/NO improves blood flow in hepatic microcirculation in liver steatosis in mice.

The impairment of liver sinusoidal endothelial cells (LSECs) function and diminished nitric oxide (NO) production has been regarded as an important pathogenic factor in liver steatosis. Restoring NO-dependent function was shown to counteract liver steatosis, obesity, and insulin resistance. However, it is not known whether restored liver perfusion and improvement in hepatic blood flow contributes to the anti-steatotic effects of NO. Taking advantage of in vivo MRI, we have examined the effects of short-term treatment with the hepatoselective NO donor V-PYRRO/NO on hepatic microcirculation in advanced liver steatosis. Male C57BL/6 mice fed for six months a high fat diet (HFD; 60 kcal% of fat) were treated for 3 weeks with V-PYRRO/NO (twice a day 5mg/kg b.w. ip). An MRI assessment of liver perfusion using the FAIR-EPI method and a portal vein blood flow using the FLASH method were performed. Blood biochemistry, glucose tolerance tests, a histological evaluation of the liver, and liver NO concentrations were also examined. Short-term treatment with V-PYRRO/NO releasing NO selectively in the liver improved liver perfusion and portal vein blood flow. This effect was associated with a slight improvement in glucose tolerance but there was no effect on liver steatosis, body weight, white adipose tissue mass, plasma lipid profile, or aminotransferase activity. Short-term treatment with V-PYRRO/NO-derived NO improves perfusion in hepatic microcirculation and this effect may also contribute to the anti-steatotic effects of hepatoselective NO donors linked previously to the modulation of glucose and lipid metabolism in the liver.

Human leucine zipper protein promotes hepatic steatosisviainduction of apolipoprotein A‐IV

The molecular mechanism of stress-induced hepatic steatosis is not well known. Human leucine zipper protein (LZIP) regulates the expression of genes involved in inflammation, cell migration, and stress response. The aim of this study was to determine the regulatory role of LZIP in stress-induced hepatic steatosis. We used a microarray analysis to identify LZIP-induced genes involved in hepatic lipid metabolism. LZIP increased the expression of apolipoprotein A-IV (APOA4) mRNA. In the presence of stress inducer, APOA4 promoter analysis was performed, and LZIP-induced lipid accumulation was monitored in mouse primary cells and human tissues. Under Golgi stress conditions, LZIP underwent proteolytic cleavage and was phosphorylated by AKT to protect against proteasome degradation. The stabilized N-terminal LZIP was translocated to the nucleus, where it directly bound to the APOA4 promoter, leading to APOA4 induction. LZIP-induced APOA4 expression resulted in increased absorption of surrounding free fatty acids. LZIP also promoted hepatic steatosis in mouse liver. Both LZIP and APOA4 were highly expressed in human steatosis samples. Our findings indicate that LZIP is a novel modulator of APOA4 expression and hepatic lipid metabolism. LZIP might be a therapeutic target for developing treatment strategies for hepatic steatosis and related metabolic diseases.-Kang, M., Kim, J., An, H.-T., Ko, J. Human leucine zipper protein promotes hepatic steatosis via induction of apolipoprotein A-IV.

Ubiquitin Ligase COP1 Controls Hepatic Fat Metabolism by Targeting ATGL for Degradation

Optimal control of hepatic lipid metabolism is critical for organismal metabolic fitness. In liver, adipose triglyceride lipase (ATGL) serves as a major triacylglycerol (TAG) lipase and controls the bulk of intracellular lipid turnover. However, regulation of ATGL expression and its functional implications in hepatic lipid metabolism, particularly in the context of fatty liver disease, is unclear. We show that E3 ubiquitin ligase COP1 (also known as RFWD2) binds to the consensus VP motif of ATGL and targets it for proteasomal degradation by K-48 linked polyubiquitination, predominantly at the lysine 100 residue. COP1 thus serves as a critical regulator of hepatocyte TAG content, fatty acid mobilization, and oxidation. Moreover, COP1-mediated regulation of hepatic lipid metabolism requires optimum ATGL expression for its metabolic outcome. In vivo, adenovirus-mediated depletion of COP1 ameliorates high-fat diet-induced steatosis in mouse liver and improves liver function. Our study thus provides new insights into the regulation of hepatic lipid metabolism by the ubiquitin-proteasome system and suggests COP1 as a potential therapeutic target for nonalcoholic fatty liver disease.

Liver-specific Gene Inactivation of the Transcription Factor ATF4 Alleviates Alcoholic Liver Steatosis in Mice

Although numerous biological functions of the activating transcription factor 4 (ATF4) have been identified, a direct effect of ATF4 on alcoholic liver steatosis has not been described previously. The aim of our current study is to investigate the role of ATF4 in alcoholic liver steatosis and elucidate the underlying mechanisms. Here, we showed that the expression of ATF4 is induced by ethanol in hepatocytes in vitro and in vivo, and liver-specific ATF4 knock-out mice are resistant to ethanol-induced liver steatosis, associated with stimulated hepatic AMP-activated protein kinase (AMPK) activity. Furthermore, adenovirus-mediated AMPK knockdown significantly reversed the suppressive effects of ATF4 deficiency on ethanol-induced liver steatosis in mice. In addition, ethanol-fed ATF4 knock-out mice exhibit AMPK-dependent inhibition of fatty acid synthase and stimulation of carnitine palmitoyltransferase 1 (CPT1) in the liver. Moreover, hepatic Tribbles homolog 3 (TRB3) expression was stimulated by ethanol in an ATF4-dependent manner, and adenovirus-mediated TRB3 knockdown blocked ATF4-dependent ethanol-induced AMPK inhibition and triglyceride accumulation in AML-12 cells. Finally, TRB3 directly interacted with AMPK to suppress its phosphorylation. Taken together, these results identify the ATF4-TRB3-AMPK axis as a novel pathway responsible for ethanol-induced liver steatosis.

Dietary sweet cherry anthocyanins attenuates diet-induced hepatic steatosis by improving hepatic lipid metabolism in mice

ObjectiveAnthocyanins have been reported to have beneficial effects on obesity and obesity-related metabolic disorders (e.g., insulin resistance and dyslipidemia). The objective of this study was to examine the beneficial effects of sweet cherry anthocyanins (SWCN) on high-fat diet-induced liver steatosis and investigate the underlying molecular mechanism. MethodsC57 BL/6 J mice were fed low-fat diet, high-fat diet, or high-fat diet supplemented with SWCN of 200 mg/kg for 15 wk. The hepatic gene expression profile was analyzed by DNA microarray analysis. ResultsSWCN supplementation alleviated high-fat diet-induced liver steatosis in mice. Microarray analysis of hepatic gene expression profiles indicated that SWCN treatment significantly changed the expression profiles of 1119 genes which were enriched in 16 pathways, such as PPAR signaling pathway, steroid biosynthesis, fatty acid metabolism, and biosynthesis of unsaturated fatty acids. ConclusionThese results confirmed the previous findings regarding the occurrence and development of hepatic steatosis under high-fat-diet conditions, elucidated that SWCN protected from diet-induced hepatic steatosis and the beneficial effects might be involved in multiple molecular pathways, especially the PPARγ pathway.

Exercise training improves liver steatosis in mice.

BackgroundNon-alcoholic fatty liver disease (NAFLD) is rapidly turning into the most common liver disorder worldwide. One of the strategies that has been shown to effectively improve NAFLD is regular exercise, which seems to lower steatosis partly independent of weight loss. However, limited data are available about the mechanisms involved. The aim of the present study was to identify the mechanisms underlying the effect of regular exercise on liver steatosis.MethodsNon-obese male mice were rendered steatotic by feeding a sucrose-enriched choline-deficient diet. They were then subjected to daily treadmill running for three weeks, whereas the control mice remained sedentary.ResultsCompared to the untrained mice, trained mice showed similar adipose tissue mass but had significantly reduced size of lipid droplets in the liver coupled with a reduction in liver triglyceride content (~30 %, P < 0.05). Levels of various plasma lipid parameters and plasma glucose were similar between the trained and untrained mice, whereas levels of hepatic glycogen were significantly higher in the trained mice. Hepatic triglyceride secretion rate and de novo lipogenesis were unchanged between the two sets of mice, as were indicators of lipolysis and autophagy. Finally, whole genome expression profiling indicated a mild stimulatory effect of exercise training on PPARα-mediated regulation of oxidative metabolism, including fatty acid oxidation.ConclusionsTaken together, our study suggests that the lowering of hepatic steatosis by repeated exercise is likely due to activation of fuel oxidation pathways in liver.

Margarine supplemented with conjugated linolenic acid (CLnA) has no effect on atherosclerosis but alleviates the liver steatosis and affects the expression of lipid metabolism genes in apoE/LDLR‐/‐ mice

AbstractThe objective of this study was to evaluate the effect of margarine supplemented with punicic acid (cis‐9,trans‐11,cis‐13 C18:3) (CLnA) compared to CLA and linolenic acid (LnA) in apoE/LDLR‐/‐ mice in two independent experiments: LONG (18 weeks) and SHORT (10 weeks). Liver weight was increased in CLA group in both studies. Hepatic steatosis was found in animals fed CLA and margarine diets but less signs of the steatosis were observed in mice fed LnA and CLnA diets. In LONG, TC was significantly increased in animals fed LnA, whereas LDL + VLDL, HDL and TAG levels were unchanged. In mice fed CLnA the upregulated expression of PPARα and ACO was reported, however, SREBP‐1 was 7‐fold increased. Punicic acid and CLA isomers were determined both in adipose tissue and liver in CLnA fed mice. No effects of treatments on the area of atherosclerotic plaque were recognized. In conclusion margarine supplemented with CLA significantly increased liver weight and induced steatosis in mice in both studies. Our results did not support the notion that CLnA supplementation to the margarine possesses anti‐atheroclerotic effect but it alleviated the liver steatosis and affected the expression of lipid metabolism genes.Practical applications: It has been reported that conjugated linolenic acid isomers (CLnA) have several health‐related effects. Margarine with omega‐3 fatty acids is commonly used as a functional food product. Therefore, the effect of margarine supplemented with CLnA compared to CLA and linolenic acid (LnA) in apoE/LDLR‐/‐ mice was evaluated. CLA supplementation increased liver weight and lead to steatosis, but CLnA alleviated the liver steatosis in mice. No effects of treatments on the area of atherosclerotic plaque were recognized. The up‐regulated expression of PPARα and SREBP‐1 and their target genes ACO and FAS was reported for studied fatty acids. More research is warranted to assess the potential health‐related properties of conjugated linolenic acids as bioactive compounds in the context of production of functional foods.Effect of margarine supplemented with pomegranate seed oil as a source of conjugated linolenic acid (CLnA) on development of atherosclerotic plaque, liver steatosis, lipid profile and expression of lipid metabolism genes in apoE/LDLR‐/‐ mice.

Cannabidiol protects liver from binge alcohol-induced steatosis by mechanisms including inhibition of oxidative stress and increase in autophagy

Acute alcohol drinking induces steatosis, and effective prevention of steatosis can protect liver from progressive damage caused by alcohol. Increased oxidative stress has been reported as one mechanism underlying alcohol-induced steatosis. We evaluated whether cannabidiol, which has been reported to function as an antioxidant, can protect the liver from alcohol-generated oxidative stress-induced steatosis. Cannabidiol can prevent acute alcohol-induced liver steatosis in mice, possibly by preventing the increase in oxidative stress and the activation of the JNK MAPK pathway. Cannabidiol per se can increase autophagy both in CYP2E1-expressing HepG2 cells and in mouse liver. Importantly, cannabidiol can prevent the decrease in autophagy induced by alcohol. In conclusion, these results show that cannabidiol protects mouse liver from acute alcohol-induced steatosis through multiple mechanisms including attenuation of alcohol-mediated oxidative stress, prevention of JNK MAPK activation, and increasing autophagy.

Sex-Specific Differences in the Development of Acute Alcohol-Induced Liver Steatosis in Mice

Results of several animal studies suggest that similar to humans, female rodents are more susceptible to chronic alcohol-induced liver disease (ALD). The aim of the present study was to determine whether female mice are more susceptible to acute alcohol-induced steatosis than male mice and to investigate possible mechanisms involved. Male and female C57BL/6J mice received one single dose of ethanol (6 g/kg bodyweight) or isocaloric maltose-dextrin solution intragastrically. Plasma alcohol concentration, markers of hepatic steatosis, activation of the TLR-4 signaling cascade and triglyceride export as well as lipid peroxidation and of iron metabolism were measured 12 h after acute alcohol intake. In male and female ethanol-treated mice, plasma alcohol concentrations were still markedly increased 12 h after the alcohol challenge, which was associated with a significant accumulation of lipids in the liver and increase of transaminases in plasma; however, lipid accumulation was ∼3-fold higher in females in comparison with male animals. Expression of MyD88 was only found to be significantly induced in livers of female alcohol-exposed mice, whereas protein levels of ApoB were found to be significantly lower only in livers of female mice exposed to ethanol. Levels of 4-HNE protein adducts and ferritin were induced in livers of male and female ethanol-treated mice. Taken together, these data suggest that female mice are also more susceptible to acute alcohol-induced liver steatosis and that this involves an increased activation of TLR-4-dependent signaling pathways in the liver.

Hepatic menin recruits SIRT1 to control liver steatosis through histone deacetylation

The development and progression of non-alcoholic fatty liver disease are associated with aging, obesity, and type 2 diabetes. Understanding the precise regulatory networks of this process will contribute to novel therapeutic strategies. Hepatocyte-specific Men1 knockout mice were generated using Cre/loxP technology. Lipid and glucose metabolic phenotypes and mechanisms were investigated in aging and high-fat diet fed mice. The expression of menin, encoded by multiple endocrine neoplasia 1 (Men1) gene, is reduced in the liver of aging mice. Hepatocyte-specific deletion of Men1 induces liver steatosis in aging mice. Menin deficiency promotes high-fat diet-induced liver steatosis in mice. Menin recruits SIRT1 to control hepatic CD36 expression and triglyceride accumulation through histone deacetylation. Our work reveals that the adaptor protein menin is critical for the progression of hepatic steatosis during aging and metabolic imbalance.

Paraoxonase-1 Deficiency Is Associated with Severe Liver Steatosis in Mice Fed a High-fat High-cholesterol Diet: A Metabolomic Approach

Oxidative stress is a determinant of liver steatosis and the progression to more severe forms of disease. The present study investigated the effect of paraoxonase-1 (PON1) deficiency on histological alterations and hepatic metabolism in mice fed a high-fat high-cholesterol diet. We performed nontargeted metabolomics on liver tissues from 8 male PON1-deficient mice and 8 wild-type animals fed a high-fat, high-cholesterol diet for 22 weeks. We also measured 8-oxo-20-deoxyguanosine, reduced and oxidized glutathione, malondialdehyde, 8-isoprostanes and protein carbonyl concentrations. Results indicated lipid droplets in 14.5% of the hepatocytes of wild-type mice and in 83.3% of the PON1-deficient animals (P < 0.001). The metabolomic assay included 322 biochemical compounds, 169 of which were significantly decreased and 16 increased in PON1-deficient mice. There were significant increases in lipid peroxide concentrations and oxidative stress markers. We also found decreased glycolysis and the Krebs cycle. The urea cycle was decreased, and the pyrimidine cycle had a significant increase in orotate. The pathways of triglyceride and phospholipid synthesis were significantly increased. We conclude that PON1 deficiency is associated with oxidative stress and metabolic alterations leading to steatosis in the livers of mice receiving a high-fat high-cholesterol diet.

Effect of metformin on fatty liver and endoplasmic reticulum stress in high-fat-feeding-induced mice

Objective To observe the effects of high-fat diet on liver steatosis and liver endoplasm reticulum stress in mice and to investigate the interventional effect of metfomin on them.Methods Forth-five male C57BL/J6 mice were divided into healthy control group,high-fat group and metformin group.High fat group and metformin group were fed with high-fat diet.Mice in metformin group were given metformin since the fourth week of high-fat feeding.After feeding for eight weeks,subperitoneal glucose tolerance test was performed in mice.After mice were sacrificed,liver triglyceride (TG) content and the expression of endoplasmic reticulum stress related factors at gene and protein levels were measured.One-way ANOVA was applied for analysis between groups.Results Compared with healthy control group,area under curve (AUC) of glucose tolerance and TG contents in liver tissues significantly increased in high-fat group [998±87 vs 1409±106,(10.05±0.29) μmol/g vs (27.11 ±4.76) μmol/g].Glucose tolerance and liver steatosis were improved in metformin group,AUC and TG of metformin group were significantly lower than those of high-fat group in metformin group [1178±90,(15.12±2.11) μmol/g,F=55.328,89.212,both P ＜0.01].Compared with healthy control group,the expression of glucose-regulated protein 94 (GRP94)at mRNA level significantly increased in high-fat group.Meanwhile,the expression of phosphorylated eukaryotic translation initiation factor 2α at protein level,which indicated endoplasmic reticulum stress,significantly increased.However,the expression of those endoplasmic reticulum stress markers at mRNA and protein level of metformin group were both lower than those of high fat group (F=84.002,137.321,both P＜0.05).Conclusions High fat diet caused liver steatosis in mice and accompanied by endoplasmic reticulum stress.Fatty liver was significantly improved by metformin treatment in high-fat-fed mice.The mechanism may be related with the improvement of endoplasmic reticulum stress by metformin. Key words: Triglycerides; Fatty liver; Metformin; Endoplasmic reticulum stress; Mice,inbred C57BL

N-3 Long-Chain Polyunsaturated Fatty Acid Supplementation Significantly Reduces Liver Oxidative Stress in High Fat Induced Steatosis

Omega-3 (n-3) long-chain polyunsaturated fatty acids (n-3 LCPUFA) are associated with several physiological functions, suggesting that their administration may prevent non transmissible chronic diseases. Therefore, we investigate whether dietary n-3 LCPUFA supplementation triggers an antioxidant response preventing liver steatosis in mice fed a high fat diet (HFD) in relation to n-3 LCPUFA levels. Male C57BL/6J mice received (a) control diet (10% fat, 20% protein, 70% carbohydrate), (b) control diet plus n-3 LCPUFA (108 mg/kg/day eicosapentaenoic acid plus 92 mg/kg/day docosahexaenoic acid), (c) HFD (60% fat, 20% protein, 20% carbohydrate), or (d) HFD plus n-3 LCPUFA for 12 weeks. Parameters of liver steatosis, glutathione status, protein carbonylation, and fatty acid analysis were determined, concomitantly with insulin resistance and serum tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 levels. HFD significantly increased total fat and triacylglyceride contents with macrovesicular steatosis, concomitantly with higher fasting serum glucose and insulin levels, HOMA, and serum TNF-α, IL-1β, and IL-6. Reduced and total liver glutathione contents were diminished by HFD, with higher GSSG/GSH ratio and protein carbonylation, n-3 LCPUFA depletion and elevated n-6/n-3 ratio over control values. These changes were either reduced or normalized to control values in animals subjected to HFD and n-3 LCPUFA, with significant increased hepatic total n-3 LCPUFA content and reduced n-6/n-3 ratio being observed after n-3 LCPUFA supplementation alone. So, repletion of liver n-3 LCPUFA levels by n-3 LCPUFA dietary supplementation in HFD obese mice reduces hepatic lipid content, with concomitant antioxidant and anti-inflammatory responses favouring insulin sensitivity.

Alcoholic liver steatosis in mice is aggravated by low-protein diet and reversed by FXR agonist

Alcoholic liver steatosis in mice is aggravated by low-protein diet and reversed by FXR agonist

Beneficial effects of rosuvastatin on insulin resistance, adiposity, inflammatory markers and non-alcoholic fatty liver disease in mice fed on a high-fat diet

The aim of the present study was to evaluate the effects of ST (rosuvastatin) and GZ (rosiglitazone) on IR (insulin resistance) and on liver as well as adipose tissue in mice fed on an HF (high-fat) diet. Our data show that treatment with ST resulted in a marked improvement in insulin sensitivity characterized by enhanced glucose clearance during the insulin tolerance test and a 70% decrease in the HOMA-IR (homoeostasis model assessment of insulin resistance) index level (P=0.0008). The ST-treated mice exhibited lower gains in BM (body mass; -8%; P<0.01) and visceral fat pad thickness (-60%; P<0.01) compared with the untreated HF group. In comparison with HF-diet-fed mice, HF+ST-treated mice showed a significant reduction in hepatomegaly and liver steatosis (-6%, P<0.05; and -21%, P<0.01 respectively). In HF+ST-treated mice, the hepatic TAG (triacylglycerol) levels were reduced by 58% compared with the HF group (P<0.01). In addition, the expression of SREBP-1c (sterol-regulatory-element-binding protein-1c) was decreased by 50% in the livers of HF+ST-treated mice (P<0.01) relative to the HF-diet-fed mice. The levels of resistin were lower in the HF+ST-treated group compared with the HF group (44% less, P< 0.01). In conclusion, we demonstrated that ST treatment improved insulin sensitivity and decreased liver steatosis in mice fed on an HF diet. Furthermore, ST reduced BM gains, improved the circulating levels of plasma cholesterol and TAG, and reduced hepatic TAG, which was concomitant with lower resistin levels.

β-catenin is essential for ethanol metabolism and protection against alcohol-mediated liver steatosis in mice.

The liver plays a central role in ethanol metabolism, and oxidative stress is implicated in alcohol-mediated liver injury. β-Catenin regulates hepatic metabolic zonation and adaptive response to oxidative stress. We hypothesized that β-catenin regulates the hepatic response to ethanol ingestion. Female liver-specific β-catenin knockout (KO) mice and wild-type (WT) littermates were fed the Lieber-Decarli liquid diet (5% ethanol) in a pairwise fashion. Liver histology, biochemistry, and gene-expression studies were performed. Plasma alcohol and ammonia levels were measured using standard assays. Ethanol-fed (EtOH) KO mice exhibited systemic toxicity and early mortality. KO mice exhibited severe macrovesicular steatosis and 5 to 6-fold higher serum alanine aminotransferase and aspartate aminotransferase levels. KO mice had a modest increase in hepatic oxidative stress, lower expression of mitochondrial superoxide dismutase (SOD2), and lower citrate synthase activity, the first step in the tricarboxylic acid cycle. N-Acetylcysteine did not prevent ethanol-induced mortality in KO mice. In WT livers, β-catenin was found to coprecipitate with forkhead box O3, the upstream regulator of SOD2. Hepatic alcohol dehydrogenase and aldehyde dehydrogenase activities and expression were lower in KO mice. Hepatic cytochrome P450 2E1 protein levels were up-regulated in EtOH WT mice, but were nearly undetectable in KO mice. These changes in ethanol-metabolizing enzymes were associated with 30-fold higher blood alcohol levels in KO mice. β-Catenin is essential for hepatic ethanol metabolism and plays a protective role in alcohol-mediated liver steatosis. Our results strongly suggest that integration of these functions by β-catenin is critical for adaptation to ethanol ingestion in vivo.

A functional role of Macrophage Migration Inhibitory Factor (MIF) for liver steatosis in mice by activation of AMP kinase

Background: The cytokine macrophage migration inhibitory factor (MIF) is known to be involved in various inflammatory diseases. We have recently discovered an unexpected anti-fibrotic function of MIF in experimental mouse models which is mediated by activation of the stress kinase AMPK (Heinrichs et al. PNAS 2011). AMPK is also known to be involved in lipogenesis. We therefore assessed the specific role of MIF in hepatic steatosis in vivo and in vitro.

ApoB siRNA‐induced Liver Steatosis is Resistant to Clearance by the Loss of Fatty Acid Transport Protein 5 (Fatp5)

The association between hypercholesterolemia and elevated serum apolipoprotein B (APOB) has generated interest in APOB as a therapeutic target for patients at risk of developing cardiovascular disease. In the clinic, mipomersen, an antisense oligonucleotide (ASO) APOB inhibitor, was associated with a trend toward increased hepatic triglycerides, and liver steatosis remains a concern. We found that siRNA-mediated knockdown of ApoB led to elevated hepatic triglycerides and liver steatosis in mice engineered to exhibit a human-like lipid profile. Many genes required for fatty acid synthesis were reduced, suggesting that the observed elevation in hepatic triglycerides is maintained by the cell through fatty acid uptake as opposed to fatty acid synthesis. Fatty acid transport protein 5 (Fatp5/Slc27a5) is required for long chain fatty acid (LCFA) uptake and bile acid reconjugation by the liver. Fatp5 knockout mice exhibited lower levels of hepatic triglycerides due to decreased fatty acid uptake, and shRNA-mediated knockdown of Fatp5 protected mice from diet-induced liver steatosis. Here, we evaluated if siRNA-mediated knockdown of Fatp5 was sufficient to alleviate ApoB knockdown-induced steatosis. We determined that, although Fatp5 siRNA treatment was sufficient to increase the proportion of unconjugated bile acids 100-fold, consistent with FATP5's role in bile acid reconjugation, Fatp5 knockdown failed to influence the degree, zonal distribution, or composition of the hepatic triglycerides that accumulated following ApoB siRNA treatment.Electronic supplementary materialThe online version of this article (doi:10.1007/s11745-011-3596-3) contains supplementary material, which is available to authorized users.

Ablation of PI3K p110-α Prevents High-Fat Diet–Induced Liver Steatosis

OBJECTIVETo determine whether the phosphoinositide 3-kinase (PI3K) catalytic subunits p110-α and p110-β play a role in liver steatosis induced by a high-fat diet (HFD).RESEARCH DESIGN AND METHODSLiver-specific p110-α and p110-β knockout mice and control animals for each group were fed an HFD or normal chow for 8 weeks. Biochemical assays and quantitative real-time PCR were used to measure triglyceride, expression of lipogenic and gluconeogenic genes, and activity of protein kinases downstream of PI3K in liver lysates. Fatty acid uptake and incorporation into triglycerides were assessed in isolated hepatocytes.RESULTSHepatic triglyceride levels in HFD-fed p110-α−/− mice were 84 ± 3% lower than in p110-α+/+ mice, whereas the loss of p110-β did not significantly alter liver lipid accumulation. p110-α−/− livers also showed a reduction in atypical protein kinase C activity and decreased mRNA and protein expression of several lipogenic genes. Hepatocytes isolated from p110-α−/− mice exhibited decreased palmitate uptake and reduced fatty acid incorporation into triglycerides as compared with p110-α+/+ cells, and hepatic expression of liver fatty acid binding protein was lower in p110-α−/− mice fed the HFD as compared with controls. Ablation of neither p110-α nor p110-β ameliorated glucose intolerance induced by the HFD, and genes involved in gluconeogenesis were upregulated in the liver of both knockout animals.CONCLUSIONSPI3K p110-α, and not p110-β, promotes liver steatosis in mice fed an HFD. p110-α might exert this effect in part through activation of atypical protein kinase C, upregulation of lipogenesis, and increased uptake of fatty acids.