HFD-induced Fatty Liver Disease Research Articles

8-OR: Plasminogen Deficiency Protects against Nonalcoholic Fatty Liver Disease and Insulin Resistance, but Not Diet-Induced Obesity

Obesity affects over 40% of the US population and predisposes individuals to metabolic syndrome, which is associated with a 50% increase in the risk of cardiovascular events. A documented clinical manifestation of obesity is a procoagulant and anti-fibrinolytic state. Elevated levels of circulating plasminogen activator inhibitor (PAI) -1 are correlated with metabolic syndrome, and PAI-1-deficient mice are protected from diet-induced obesity (DIO) . However, an unresolved question is whether plasminogen itself influences the development of obesity and associated disease sequelae? Here, we analyzed the impact of genetically-imposed plasminogen deficiency on the development of DIO and associated pathologies. Over the course of 20 weeks, plasminogen-deficient (Plg-) mice gained as much weight as the control mice (Plg+) on HFD, although HFD-fed Plg- mice had larger epididymal white adipose tissues than those of HFD-fed Plg+ mice. In contrast, while HFD-fed Plg+ animals displayed a fatty liver disease phenotype characterized by histological evidence of steatosis, elevated triglyceride content, and hepatocellular injury, HFD-fed Plg- mice were protected from developing each of these pathologies. HFD-fed Plg+ mice also developed hypercholesterolemia, whereas circulating cholesterol levels in Plg- mice were comparable to LFD-fed mice. Intriguingly, while the brown adipose tissue mass was comparable between diet and genotype, there was an upregulation of uncoupling protein-1 (Ucp1) expression in BAT of HFD-fed Plg- mice. Notably, whereas HFD-fed Plg+ mice showed evidence of insulin resistance as revealed by compromised glucose clearance, HFD-fed Plg- mice were partially protected. Collectively, our data suggest that plasmin (ogen) contributes to HFD-induced fatty liver disease and insulin resistance, and that plasminogen deficiency imposes a state of metabolically healthy obesity. Disclosure W.S.Hur: None. Y.Nguyen: None. Y.Patel: None. K.C.King: None. M.J.Flick: None. Funding National Institutes of Health (RDK112778)

A novel role of CRTC2 in promoting nonalcoholic fatty liver disease

ObjectiveDiet-induced obesity is often associated with nonalcoholic fatty liver disease (NAFLD), which instigates severe metabolic disorders, including cirrhosis, hepatocellular carcinoma, and type 2 diabetes. We have shown that hepatic depletion of CREB regulated transcription co-activator (CRTC) 2 protects mice from the progression of diet-induced fatty liver phenotype, although the exact mechanism by which CRTC2 modulates this process is elusive to date. Here, we investigated the role of hepatic CRTC2 in the instigation of NAFLD in mammals. MethodsCrtc2 liver-specific knockout (Crtc2 LKO) mice and Crtc2 flox/flox (Crtc2 f/f) mice were fed a high fat diet (HFD) for 7–8 weeks. Body weight, liver weight, hepatic lipid contents, and plasma triacylglycerol (TG) levels were determined. Western blot analysis was performed to determine Sirtuin (SIRT) 1, tuberous sclerosis complex (TSC) 2, and mammalian target of rapamycin complex (mTORC) 1 activity in the liver. Effects of Crtc2 depletion on lipogenesis was determined by measuring lipogenic gene expression (western blot analysis and qRT-PCR) in the liver as well as Oil red O staining in hepatocytes. Effects of miR-34a on mTORC1 activity and hepatic lipid accumulation was assessed by AAV-miR-34a virus in mice and Ad-miR-34a virus and Ad-anti-miR-34a virus in hepatocytes. Autophagic flux was assessed by western blot analysis after leupeptin injection in mice and bafilomycin treatment in hepatocytes. Lipophagy was assessed by transmission electron microscopy and confocal microscopy. Expression of CRTC2 and p-S6K1 in livers of human NAFLD patients was assessed by immunohistochemistry. ResultsWe found that expression of CRTC2 in the liver is highly induced upon HFD-feeding in mice. Hepatic depletion of Crtc2 ameliorated HFD-induced fatty liver disease phenotypes, with a pronounced inhibition of the mTORC1 pathway in the liver. Mechanistically, we found that expression of TSC2, a potent mTORC1 inhibitor, was enhanced in Crtc2 LKO mice due to the decreased expression of miR-34a and the subsequent increase in SIRT1-mediated deacetylation processes. We showed that ectopic expression of miR-34a led to the induction of mTORC1 pathway, leading to the hepatic lipid accumulation in part by limiting lipophagy and enhanced lipogenesis. Finally, we found a strong association of CRTC2, miR-34a and mTORC1 activity in the NAFLD patients in humans, demonstrating a conservation of signaling pathways among species. ConclusionsThese data collectively suggest that diet-induced activation of CRTC2 instigates the progression of NAFLD by activating miR-34a-mediated lipid accumulation in the liver via the simultaneous induction of lipogenesis and inhibition of lipid catabolism. Therapeutic approach to specifically inhibit CRTC2 activity in the liver could be beneficial in combating NAFLD in the future.

Protective Role of Plasminogen Deficiency in Non-Alcoholic Fatty Liver Disease and Glucose Dysmetabolism

Obesity is global health problem with 40% of the world population being classified as overweight (BMI > 25) and 13% as obese (BMI > 30). Obesity drives chronic metabolic inflammation leading to metabolic syndrome, cardiovascular disease, fatty liver disease, Type II diabetes, and certain cancers. A documented clinical manifestation of obesity is perturbed and dysregulated hemostatic system leading to a procoagulant and anti-fibrinolytic state that ultimately results in an increased risk of thrombosis.Previous work suggested that clotting system components thrombin and fibrin engage in reciprocal mechanisms and contribute to the development of obesity. Specifically, we have shown that fibrin accumulates within obese adipose tissue and liver of obesity patients and mice challenged with a high fat diet (HFD) and colocalizes with macrophages, a key driver of inflammation in obesity. Despite the fact that obesity is known to be linked to an impaired fibrinolytic system, a potential functional contribution of fibrinolytic proteases to the development of obesity and associated downstream diseases has been understudied.Here, we tested the hypothesis that elimination of the fibrinolytic protease plasminogen would increase HFD-driven fibrin deposition and exacerbate macrophage accumulation and subsequent weight gain and obesity-associated pathologies. Contrary to our hypothesis, plasminogen-deficient (Plg-) mice gained as much weight as the Plg+ mice after 20 weeks on HFD. However, whereas the liver mass of HFD-challenged Plg+ mice was significantly higher than that of low fat diet (LFD)-fed mice, the livers of HFD-fed Plg- mice had a mass comparable to LFD-fed mice. HFD-fed Plg- mice had reduced hepatocellular damage, measured by plasma ALT activity, as well as reduced hepatosteatosis, measured by hepatic triglyceride content and liver histology, compared to HFD-fed Plg+ mice. Circulating cholesterol levels in HFD-fed Plg -/- mice were comparable to LFD-fed Plg- mice, while it was significantly elevated in HFD-fed Plg+ mice. While the epididymal white adipose tissue mass was higher in HFD-fed Plg- mice compared to HFD-fed Plg+ mice, the brown adipose tissue mass was comparable. However, there was an upregulation of uncoupling protein-1 (UCP-1) expression BAT of HFD-fed Plg- mice. Glucose clearance was more efficient in HFD-fed Plg- mice compared to HFD-fed Plg+ mice in a glucose tolerance test. Collectively, our data suggest that plasmin(ogen) contributes to HFD-induced fatty liver disease and glucose dysmetabolism. DisclosuresNo relevant conflicts of interest to declare.

Metabolism and antioxidation regulation of total flavanones from Sedum sarmentosum Bunge against high-fat diet-induced fatty liver disease in Nile tilapia (Oreochromis niloticus).

Diet-induced fatty liver is a considerable threaten to fish aquaculture due to the popularity of the high-fat diet (HFD) feeding. Our study aims to investigate the effects of flavanones from Sedum sarmentosum Bunge (FSSB) on the liver function to identify a potential treatment for HFD-induced fatty liver disease. Physiological and pathological indicators were tested in the liver of Nile tilapia (Oreochromis niloticus) and results showed parameters including lipid metabolites, redox parameters, and inflammatory factors could be adequately restored to normal level by addition of 150 mg/kg FSSB to HFD. Proteomics analysis was performed in liver tissues from tilapia with normal diet (ND), HFD, and HFD+FSSB. Totally, 51 upregulated proteins and 77 downregulated proteins were identified in HFD groups and 67 proteins of them were restored after treated with FSSB. Bioinformatics analysis showed that differentially expressed proteins (DEPs) in HFD+FSSB150 group compared with HFD group are mainly enriched in acety-CoA metabolic process, adenosine-triphosphate (ATP) biosynthetic process, lipid metabolic process, and phospholipid metabolic process. The dysregulated proteins were involved in peroxidosome proliferators-activated receptor (PPAR) signaling pathway, fat digestion and absorption, and immune system. The quantitative real-time PCR (qRT-PCR) assay further revealed that the expression of GST, PPARα, PPARγ, and multiple-inflammatory cytokines could be also reversed in HFD group under the treatment of 150 mg/kg FSSB. Our findings demonstrated FSSB is efficient for the treatment of fatty liver disease through regulation of lipid metabolism and antioxidation in Nile tilapia, providing a new treatment of non-alcoholic fatty liver disease (NAFLD) in fish aquaculture.

Intestinal HuR deficiency exacerbates diet‐induced fatty liver disease

Background Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide. However, no effective treatment is available due to the limited knowledge regarding the complex disease pathology. We and others have previously reported that impaired intestinal barrier function promotes the progression of various liver diseases, including NAFLD. Human antigen R (HuR) is a member of the Hu family of RNA-binding proteins. It is reported that HuR is essential for maintaining gut epithelial integrity, and targeted deletion of HuR in the intestinal epithelium disrupts mucosal regeneration in mice. However, the role of intestinal HuR in NAFLD remains unclear and is the focus of this study. Methods: Intestinal epithelial tissue-specific HuR deletion (IE-HuR–/–) mice were generated by crossing the HuRflox/flox (HuRfl/fl) and villin-Cre mice. Age and gender-matched IE-HuR–/–and control mice were fed ad libitum a high-fat diet (HFD, Harlan TD.88137) for 4 weeks. At the end of the treatment, FITC-Dextran was administered to mice by oral gavage. The serum concentration of FITC-dextran was measured. The serum lipids and liver function enzymes were measured using the Alfa Wassermann Vet ACE Axcel® System. Small intestine and liver tissues were processed for H&E staining and isolation of total RNA. Hepatic lipid was stained by Oil Red O. RNAseq transcriptome analysis was used to profile hepatic gene expression. The mRNA levels of the key genes were confirmed by qRT-PCR. Results Compared to control mice, the serum levels of FITC-Dextran were significantly higher in IE-HuR–/– mice fed an HFD. Consistently, the H&E staining of small intestine tissues revealed that the intestinal barrier was disrupted in IE-HuR–/– mice fed an HFD. Besides, the serum levels of ALP, ALT and AST significantly increased in HFD-fed IE-HuR–/– mice. The H&E and Oil Red O staining of liver tissues showed a significant increase in hepatic lipid accumulation in IE-HuR–/– mice. Bioinformatics analysis of RNAseq data showed that intestinal-specific deficiency of HuR significantly affected hepatic metabolic pathways, activated inflammatory and ER stress response. The qRT-PCR further confirmed that in IE-HuR–/– mice, the key genes involved in bile acid metabolisms (Cyp7a1, Cyp27a1, Cyp7b, and Cyp8b1) were significantly reduced, but the expression of genes involved in inflammation (Mcp-1, Il1α, Cd63, and Cxcl1) and endoplasmic reticulum stress (Chop, Atf4, Xbp-1s, and Grp78) were increased. Furthermore, the key genes involved in sphingosine lipid pathways, such as Smpd3 and Spt1c1, were significantly increased while the expression of Sphk2 was decreased. Conclusions Intestinal HuR deficiency exacerbates HFD-induced fatty liver disease via inducing intestinal barrier dysfunction, activating ER stress, and inflammatory response in the liver.

Hepatoprotective Effects of Insect Extracts in an Animal Model of Nonalcoholic Fatty Liver Disease.

Insects represent the largest and most diverse group of organisms on earth and are potential food and drug resources. Recently, we have demonstrated that a Forsythia viridissima extract prevented free fatty acid-induced lipid accumulation in an in vitro cellular nonalcoholic fatty liver disease (NAFLD) model. In this study, we aimed to evaluate the hepatoprotective effects of extracts of the insects Protaetia brevitarsis seulensis Kolbe, 1886 (PB), Oxya chinensis sinuosa Mishchenko, 1951 (OC), and Gryllus bimaculatus De Geer, 1773 (GB) in a high-fat diet (HFD)-induced NAFLD animal model, as well as to elucidate the underlying mechanisms. The effects of the supplementation with PB, OC, and GB extracts were evaluated histopathologically and histochemically. PB, OC, and GB extract supplementation inhibited the HFD-induced increase in body weight and body fat mass and ameliorated other adverse changes, resulting in decreased liver function parameters, lower serum triglyceride and cholesterol levels, and increased serum adiponectin levels. The expression of hepatic genes involved in lipid droplet accumulation and in fatty acid uptake also decreased upon treatment of HFD-fed mice with the extracts. These results provide evidence of the protective effects of the PB, OC, and GB extracts against HFD-induced fatty liver disease in an animal model.

Exposure to Vinyl Chloride and Its Influence on Western Diet-Induced Cardiac Remodeling.

Obesity, usually caused by high fat diets (HFD), is a major public health issue worldwide, causing obesity associated cardiomyopathy. Moreover, the environmental toxicant vinyl chloride (VC) can exacerbate HFD-induced fatty liver disease. However, whether VC serves to enhance obesity-associated cardiomyopathy remains unclear. This study aims to investigate the interaction of western diet (WD) containing relatively low fat (42%) with VC on cardiac remodeling and its underling mechanisms. Adult male C57BL/6J mice were exposed to WD coinhalation of low-dose VC (<1 ppm/d) for 12 weeks. Results showed that WD feeding for 12 weeks caused slight cardiac systolic dysfunction without significant hypertrophy or fibrosis, even with VC. Nevertheless, WD upregulated NF-κB function and expression of IL-1β and PAI-1, while VC showed no significant impact on these effects. In contrast, WD together with VC significantly increased the expression of CHOP and TGF-β1, key markers for endoplasmic reticulum stress and profibrotic cytokine, respectively. In summary, exposure to low-dose of environmental toxicant VC while a WD is consumed for a relatively short time does not have significant impact on cardiac remodeling except for a mild systolic dysfunction of the heart.

Dolichos lablab Protects Against Nonalcoholic Fatty Liver Disease in Mice Fed High-Fat Diets

Hyacinth bean, Dolichos lablab or Lablab purpureus, has been used for centuries in India and China as an edible pod and animal forage, as well as to treat diarrhea and other gastrointestinal disease in traditional Korean medicine. Recently, we have demonstrated that D. lablab extract (DLL-Ex) prevented free fatty acid-induced lipid accumulation in an in vitro cellular nonalcoholic fatty liver disease (NAFLD) model. In this study, we, thus, aimed at clarifying the hepatoprotective effects of DLL-Ex in a high-fat diet-induced in vivo animal NAFLD model, as well as at elucidating underlying mechanisms of identified effects. Sixty, 6-week-old, male C57BL/6J mice were randomly divided into six groups: a control group fed a low-fat diet, four high-fat diet (HFD) groups, three receiving daily oral supplementation of DLL-Ex (25, 50, and 100 mg/kg/day), and one HFD group receiving daily oral supplementation of MILK (100 mg/kg/day). Effects of DLL-Ex supplementation were evaluated by histopathological and histochemical assessments. DLL-Ex supplementation inhibited HFD-induced increases in body weight and body fat mass and ameliorated increases in body weight, manifested as decreased liver function tests, lower serum triglycerides and cholesterol levels, and increased serum adiponectin levels. The expression of hepatic genes involved in lipid droplet accumulation and in fatty acid uptake was also decreased. We provide evidence of a protective effect of DLL-Ex against HFD-induced fatty liver disease in an animal model.

Gastric bypass surgery is protective from high-fat diet-induced non-alcoholic fatty liver disease and hepatic endoplasmic reticulum stress.

High-fat diets are known to contribute to the development of obesity and related co-morbidities including non-alcoholic fatty liver disease (NAFLD). The accumulation of hepatic lipid may increase endoplasmic reticulum (ER) stress and contribute to non-alcoholic steatohepatitis and metabolic disease. We hypothesized that bariatric surgery would counter the effects of a high-fat diet (HFD) on obesity-associated NAFLD. Sixteen of 24 male Sprague Dawley rats were randomized to Sham (N=8) or Roux-en-Y gastric bypass (RYGB) surgery (N=8) and compared to Lean controls (N=8). Obese rats were maintained on a HFD throughout the study. Insulin resistance (HOMA-IR), and hepatic steatosis, triglyceride accumulation, ER stress and apoptosis were assessed at 90days post-surgery. Despite eating a HFD for 90days post-surgery, the RYGB group lost weight (-20.7±6%, P<0.01) and improved insulin sensitivity (P<0.05) compared to Sham. These results occurred with no change in food intake between groups. Hepatic steatosis and ER stress, specifically glucose-regulated protein-78 (Grp78, P<0.001), X-box binding protein-1 (XBP-1) and spliced XBP-1 (P<0.01), and fibroblast growth factor 21 (FGF21) gene expression, were normalized in the RYGB group compared to both Sham and Lean controls. Significant TUNEL staining in liver sections from the Obese Sham group, indicative of accelerated cell death, was absent in the RYGB and Lean control groups. Additionally, fasting plasma glucagon like peptide-1 was increased in RYGB compared to Sham (P<0.02). These data suggest that in obese rats, RYGB surgery protects the liver against HFD-induced fatty liver disease by attenuating ER stress and excess apoptosis.

Deficiency of intestinal mucin-2 protects mice from diet-induced fatty liver disease and obesity.

Nonalcoholic fatty liver disease (NAFLD) and obesity are characterized by altered gut microbiota, inflammation, and gut barrier dysfunction. Here, we investigated the role of mucin-2 (Muc2) as the major component of the intestinal mucus layer in the development of fatty liver disease and obesity. We studied experimental fatty liver disease and obesity induced by feeding wild-type and Muc2-knockout mice a high-fat diet (HFD) for 16 wk. Muc2 deficiency protected mice from HFD-induced fatty liver disease and obesity. Compared with wild-type mice, after a 16-wk HFD, Muc2-knockout mice exhibited better glucose homeostasis, reduced inflammation, and upregulated expression of genes involved in lipolysis and fatty acid β-oxidation in white adipose tissue. Compared with wild-type mice that were fed the HFD as well, Muc2-knockout mice also displayed higher intestinal and plasma levels of IL-22 and higher intestinal levels of the IL-22 target genes Reg3b and Reg3g. Our findings indicate that absence of the intestinal mucus layer activates the mucosal immune system. Higher IL-22 levels protect mice from diet-induced features of the metabolic syndrome.

Physiological and molecular changes in large yellow croaker (Pseudosciaena croceaR.) with high-fat diet-induced fatty liver disease

Fatty liver disease is regularly observed in cultured large yellow croaker, and the disease leads to lower growth rates and reduced harvest yields. The goal of this study was to achieve a more detailed understanding of the physiological and molecular changes in response to high-fat diet-induced fatty liver in large yellow croaker. Large yellow croaker fed a high-fat diet (HFD) for 9 weeks developed hepatic steatosis characterized by histological observation and significantly increased plasma triglyceride levels and serum alanine aminotransferase (ALT) activities. However, no significant differences in serum total protein, glucose, cholesterol, non-esterified free fatty acids (NEFA), aspartate aminotransferase, high-density lipoprotein and low-density lipoprotein were observed between the normal diet and the high-fat diet (HFD) group. The fatty acid composition of tissue lipids was not affected significantly by dietary lipid levels. Gene expression analysis demonstrated that the HFD decreased fatty acid synthase expression and increased PPARγ expression, but had no effect on lipoprotein lipase and PPARα expression. These results suggest that the HFD-induced physiological changes and fatty liver may be due to the alteration of related gene expression. As such, further investigations of the metabolic pathways and differentially expressed genes are of particular significance in the mechanistic study and understanding of HFD-induced fatty liver disease.

Chinese Medicine Formula Lingguizhugan Decoction Improves Beta-Oxidation and Metabolism of Fatty Acid in High-Fat-Diet-Induced Rat Model of Fatty Liver Disease

Lingguizhugan decoction (LGZG), a classic traditional Chinese medicine (TCM) formula, has been used to treat obesity and hyperlipidemia in recent years, but the related mechanisms underlying the regulation of lipid metabolism by LGZG are not clear yet. Here, we reported the effectiveness and possible mechanisms of LGZG on rats with fatty liver disease induced by high-fat diet (HFD). Our results demonstrated that LGZG significantly attenuated HFD-induced fatty liver disease, as measured by body weight, liver index, epididymal fat pad-body weight ratio (EFP/BW), liver injury, and hepatic triglycerides (TG) probably through increasing serum thyroid hormone levels, improving beta-oxidation (via modulation of TRβ1 and CPT1A expression), metabolism and transport (through modulation of SREBP-1c, ACSL and ApoB100 expression) of fatty acid. In addition, we discovered the herbal combination with the properties of warming yang to relieve water retention in the formula and proposed the biological basis of LGZG conventional effect via further study on disassembled formula. This study, for the first time, revealed the mechanisms through which LGZG regulates lipid metabolism. Furthermore, our study suggested that it might be feasible to understand the scientific implications of TCM from the perspective of classic formulas' conventional efficacy.