High-fat Diet-induced Hepatic Insulin Resistance Research Articles

Sesamol Alleviates High-Fat Diet-Induced Hepatic Insulin Resistance in C57BL/6J Mice Through AMPK Activation Mediated by Adipose Adiponectin.

Sesamol is the major bioactive constituent isolated from sesame seeds and has a variety of bioactivities. However, its role and mechanism in liver insulin resistance remain unknown. The current study was designed to investigate the underlying adipose-liver crosstalk mechanism of sesamol ameliorating hepatic insulin sensitivity. The therapeutic effect of sesamol was evaluated in high-fat diet (HFD)-fed C57BL/6J mice (100mg/kg for 8weeks, XYGW-2021-75) and the mechanism was further explored in HepG2 cells with/without adiponectin and adenosine 5 '-monophosphate-activated protein kinase (AMPK) inhibitor administration. Our in vivo data showed that sesamol reduced hepatic insulin resistance in HFD-induced mice with obesity by modulating protein expression levels of glycogen synthase (GS), phosphoenolpyruvate carboxykinase (PEPCK) and protein kinase B (AKT). Moreover, sesamol not only increased the serum and adipose tissue adiponectin concentrations but also activated the phosphorylation of AMPK in the liver. Furthermore, in vitro studies using recombinant human adiponectin and an AMPK inhibitor revealed that adiponectin and sesamol have a synergic impact on increasing glycogenesis and reducing gluconeogenesis, of which the effects could be attenuated by the AMPK inhibitor. Taken together, our results suggested that sesamol stimulated adiponectin secretion from adipocytes, whereby exhibited a co-effect on activating the downstream signal of hepatic AMPK, resulting in the alleviation of hepatic insulin resistance. The novel findings of sesamol on hepatic effects provides prospective therapeutic approaches to treat insulin resistance.

Ethno-pharmacological insulin signaling induction of aqueous extract of Syzygium paniculatum fruits in a high-fat diet induced hepatic insulin resistance

Ethnopharmacological relevanceThe ethnopharmacological significance of the fruits of Syzygium paniculatum Gaertn (Magenta Cherry) is widely recognized in the Indian traditional medicine system to treat various disorders, such as diabetes, hyperlipidaemia, hypertension, and cardiovascular problems. Aim of the studyThis research work investigated the supplementation of the aqueous extract of S. paniculatum fruit (AESPF) on liver function; the molecular effects on the expression of the protein of insulin receptor (IR) and insulin receptor substrate 1 (IRS-1) in high-fat diet-induced hepatic insulin resistance in the rat model. Materials and methodsHigh-fat diet was used to induce obesity in albino Wistar for 120 days. Biochemical, enzymatic, and histopathological analysis, as well as analysis of hepatic insulin resistance proteins and expression of IRS-1, were performed. ResultsThe supplementation of AESPF with a dose of 100 mg/kg bw significantly reduced bodyweight, blood sugar, insulin, lipid profiles, and liver enzymes. Hepatic insulin resistance was improved with a reduced level of IR and IRS-1 to protein levels. HFD alters the sensitivity of hepatocytes to insulin due to the down-regulation of insulin receptor proteins. ConclusionsThe fruits of S. paniculatum possess biological activities to alleviate all risky effects by regulating hepatic lipogenesis activity that can be used in the progress of medication for HFD-induced hepatic insulin resistance and metabolic disorders.

Integrated analysis of differentially expressed long noncoding RNAs and mRNAs associated with high-fat diet-induced hepatic insulin resistance in mice

BackgroundHepatic insulin resistance (IR) is an early pathological characteristic of many metabolic diseases, such as type 2 diabetes. Long noncoding RNAs (lncRNAs) have been identified as mediators of IR and related diseases. However, the roles of lncRNAs in hepatic IR remain largely unknown.MethodHigh-throughput sequencing was performed on ten liver tissue samples from five normal diet (ND)-fed mice and five high-fat diet (HFD)-induced hepatic IR mice, respectively. lncRNAs and mRNAs that were differentially expressed (DE) between the two groups were identified by bioinformatic analyses. Seven DE lncRNAs were validated by quantitative real-time PCR (q-PCR). The potential functions of the DE lncRNAs were predicted by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses of target genes. In addition, integrated analysis was performed for the DE lncRNAs and mRNAs to predict their interaction relationships.ResultsA total of 232 DE lncRNAs were identified in the HFD-induced hepatic IR mice compared with the ND-fed mice. These DE lncRNAs included 108 upregulated and 124 downregulated lncRNAs, and 7 of the DE lncRNAs were validated by q-PCR. In addition, 291 DE mRNAs including 166 upregulated and 125 downregulated mRNAs were identified in the HFD group. Furthermore, target genes of the DE lncRNAs were predicted, and functional enrichment results showed that the enriched genes were involved in IR- and glycolipid metabolism-related processes. Additionally, the coexpression network was also constructed to further reflect the potential functions of the DE lncRNAs.ConclusionThe study describes the expression profiles of lncRNAs and mRNAs and the functional networks involved in HFD-induced hepatic IR. These findings may provide a new perspective for the study of lncRNAs in hepatic IR- and glycolipid metabolism-related diseases.

205-OR: Hepatic Protein Kinase C-e Is Necessary and Sufficient in Mediating Lipid-Induced Hepatic Insulin Resistance

Nonalcoholic fatty liver disease (NAFLD) is strongly associated with hepatic insulin resistance (HIR), however the key lipid species and molecular mechanisms linking these conditions are widely debated. In order to address these questions, we examined the metabolic impact of a liver-specific antisense oligonucleotide against PKCε and found that liver-specific PKCε knockdown ameliorated high-fat diet-induced HIR in rats, reflected by ∼2x increase in insulin-stimulated hepatic glycogen synthesis rate and improved insulin-mediated suppression of endogenous glucose production during a hyperinsulinemic-hyperglycemic (HH) clamp. This was associated with increased IRK Y1162 and Akt S473 phosphorylation and could be attributed to decreased PKCε-mediated IRK T1160 phosphorylation. Overexpressing a constitutively active PKCε (A159E) in the liver induced HIR in regular chow-fed rats, reflected by reduced insulin-stimulated glycogen synthesis rate during an HH clamp. This was associated with impaired IRK Y1162 and Akt S473 phosphorylation and could be attributed to increased PKCε-mediated IRK T1160 phosphorylation. We also developed a subcellular fractionation method to quantify diacylglycerol (DAG) stereoisomers and ceramides in the endoplasmic reticulum, mitochondria, plasma membrane (PM), lipid droplet and cytosol and applied this method to a cohort of obese human subjects with and without NAFLD and HIR. Liver PM sn-1,2 DAG content was ∼5x higher in HIR individuals with NAFLD compared to insulin-sensitive individuals without NAFLD, associated with ∼3x higher IRK T1160 phosphorylation, supporting the importance of PM sn-1,2 DAG-PKCε-IRK pT1160 pathway to mediate HIR in humans with NAFLD. In contrast there were no significant differences in ceramide content in any of the subcellular compartments. Conclusion: These data identify PM sn-1,2 DAGs as the key lipids that activate PKCε, and that hepatic PKCε is both necessary and sufficient in mediating HIR. Disclosure K. Lyu: None. D. Zhang: None. M. Kahn: None. M.R.S. Rodrigues: None. S. Hirabara: None. P. Luukkonen: None. S. Lee: None. S. Bhanot: None. J. Rinehart: None. N. Blume: Employee; Self; Novo Nordisk A/S. Stock/Shareholder; Self; Novo Nordisk A/S. M. Rasch: Employee; Self; Novo Nordisk A/S. Stock/Shareholder; Self; Novo Nordisk A/S. M.J. Serlie: None. J. Bogan: None. G. Cline: None. V. Samuel: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research & Development, LLC, Merck & Co., Inc. Advisory Panel; Spouse/Partner; Merck & Co., Inc. Consultant; Self; Novo Nordisk A/S. Consultant; Spouse/Partner; Novo Nordisk A/S. Other Relationship; Self; Gilead Sciences, Inc., iMetabolic Biopharma Corporation. Other Relationship; Spouse/Partner; iMetabolic Biopharma Corporation. Other Relationship; Self; Maze Therapeutics. Funding U.S. Public Health Service (R01DK116774, R01DK119968, R01DK113984, P30DK045735, R01 DK092661); U.S. Department of Veternas Affairs (I01BX000901)

High-throughput sequencing of small RNAs and analysis of differentially expressed microRNAs associated with high-fat diet-induced hepatic insulin resistance in mice

BackgroundHepatic insulin resistance (IR) plays a crucial role in the development of many metabolic diseases, such as type 2 diabetes. MicroRNAs (miRNAs) are involved in the pathogenesis of IR and related diseases; however, studies of miRNAs in hepatic IR are limited.MethodIn this study, we adopted a high-throughput sequencing approach to construct small RNA libraries in the livers of normal mice and high-fat diet-induced hepatic IR mice.ResultsThrough analysis of data, 107 known and 56 novel miRNAs were identified as differentially expressed miRNAs between the two groups. Additionally, bioinformatics methods were used to predict targets of the differentially expressed miRNAs and to explore the potential downstream Gene Ontology categories and Kyoto Encyclopedia of Genes and Genomes pathways. Meanwhile, some differentially expressed miRNAs (miR-34a-5p, miR-149-5p, miR-335-3p, miR-10b-5p, miR-1a-3p, miR-411-5p, and miR-592-5p) were validated by quantitative-time PCR, and their potential target genes related to IR or glycolipid metabolism were also predicted and presented in this study.ConclusionTaken together, our results defined miRNA expression signature that may lead to hepatic IR in mice, and the findings provided a foundation for future studies to further explore the effects and underlying mechanisms of the miRNAs and their target genes in the pathogenesis of hepatic IR and related diseases.

PKCε contributes to lipid-induced insulin resistance through cross talk with p70S6K and through previously unknown regulators of insulin signaling

Insulin resistance drives the development of type 2 diabetes (T2D). In liver, diacylglycerol (DAG) is a key mediator of lipid-induced insulin resistance. DAG activates protein kinase C ε (PKCε), which phosphorylates and inhibits the insulin receptor. In rats, a 3-day high-fat diet produces hepatic insulin resistance through this mechanism, and knockdown of hepatic PKCε protects against high-fat diet-induced hepatic insulin resistance. Here, we employed a systems-level approach to uncover additional signaling pathways involved in high-fat diet-induced hepatic insulin resistance. We used quantitative phosphoproteomics to map global in vivo changes in hepatic protein phosphorylation in chow-fed, high-fat-fed, and high-fat-fed with PKCε knockdown rats to distinguish the impact of lipid- and PKCε-induced protein phosphorylation. This was followed by a functional siRNA-based screen to determine which dynamically regulated phosphoproteins may be involved in canonical insulin signaling. Direct PKCε substrates were identified by motif analysis of phosphoproteomics data and validated using a large-scale in vitro kinase assay. These substrates included the p70S6K substrates RPS6 and IRS1, which suggested cross talk between PKCε and p70S6K in high-fat diet-induced hepatic insulin resistance. These results identify an expanded set of proteins through which PKCε may drive high-fat diet-induced hepatic insulin resistance that may direct new therapeutic approaches for T2D.

Low-density lipoprotein receptor–related protein-1 dysfunction synergizes with dietary cholesterol to accelerate steatohepatitis progression

Reduced low-density lipoprotein receptor-related protein-1 (LRP1) expression in the liver is associated with poor prognosis of liver cirrhosis and hepatocellular carcinoma. Previous studies have shown that hepatic LRP1 deficiency exacerbates palmitate-induced steatosis and toxicity in vitro and also promotes high-fat diet-induced hepatic insulin resistance and hepatic steatosis in vivo The current study examined the impact of liver-specific LRP1 deficiency on disease progression to steatohepatitis. hLrp1+/+ mice with normal LRP1 expression and hLrp1-/- mice with hepatocyte-specific LRP1 inactivation were fed a high-fat, high-cholesterol (HFHC) diet for 16 weeks. Plasma lipid levels and body weights were similar between both groups. However, the hLrp1-/- mice displayed significant increases in liver steatosis, inflammation, and fibrosis compared with the hLrp1+/+ mice. Hepatocyte cell size, liver weight, and cell death, as measured by serum alanine aminotransferase levels, were also significantly increased in hLrp1-/- mice. The accelerated liver pathology observed in HFHC-fed hLrp1-/- mice was associated with reduced expression of cholesterol excretion and bile acid synthesis genes, leading to elevated immune cell infiltration and inflammation. Additional in vitro studies revealed that cholesterol loading induced significantly higher expression of genes responsible for hepatic stellate cell activation and fibrosis in hLrp1-/- hepatocytes than in hLrp1+/+ hepatocytes. These results indicate that hepatic LRP1 deficiency accelerates liver disease progression by increasing hepatocyte death, thereby causing inflammation and increasing sensitivity to cholesterol-induced pro-fibrotic gene expression to promote steatohepatitis. Thus, LRP1 may be a genetic variable that dictates individual susceptibility to the effects of dietary cholesterol on liver diseases.

Adipose tissue inflammation contributes to short-term high-fat diet-induced hepatic insulin resistance

High-fat feeding for 3-4 days impairs glucose tolerance and hepatic insulin sensitivity. However, it remains unclear whether the evolving hepatic insulin resistance is due to acute lipid overload or the result of induced adipose tissue inflammation and consequent dysfunctional adipose tissue-liver cross-talk. In the present study, feeding C57Bl6/J mice a fat-enriched diet [high-fat diet (HFD)] for 4 days induced glucose intolerance, hepatic insulin resistance (as assessed by hyperinsulinemic euglycemic clamp studies), and hepatic steatosis as well as adipose tissue inflammation (i.e., TNFα expression) compared with standard chow-fed mice. Adipocyte-specific depletion of the antiapoptotic/anti-inflammatory factor Fas (CD95) attenuated adipose tissue inflammation and improved glucose tolerance as well as hepatic insulin sensitivity without altering the level of hepatic steatosis induced by HFD. In summary, our results identify adipose tissue inflammation and resulting dysfunctional adipose tissue-liver cross-talk as an early event in the development of HFD-induced hepatic insulin resistance.

Glucagon-Like Peptide-1 Receptor Knockout Mice Are Protected from High-Fat Diet-Induced Insulin Resistance

Glucagon-like peptide-1 augments nutrient-stimulated insulin secretion. Chow-fed mice lacking the glucagon-like peptide-1 receptor (Glp1r) exhibit enhanced insulin-stimulated muscle glucose uptake but impaired suppression of endogenous glucose appearance (endoRa). This proposes a novel role for the Glp1r to regulate the balance of glucose disposal in muscle and liver by modulating insulin action. Whether this is maintained in an insulin-resistant state is unknown. The present studies tested the hypothesis that disruption of Glp1r expression overcomes high-fat (HF) diet-induced muscle insulin resistance and exacerbates HF diet-induced hepatic insulin resistance. Mice with a functional disruption of the Glp1r (Glp1r-/-) were compared with wild-type littermates (Glp1r+/+) after 12 wk on a regular chow diet or a HF diet. Arterial and venous catheters were implanted for sampling and infusions. Hyperinsulinemic-euglycemic clamps were performed on weight-matched male mice. [3-(3)H]glucose was used to determine glucose turnover, and 2[14C]deoxyglucose was used to measure the glucose metabolic index, an indicator of glucose uptake. Glp1r-/- mice exhibited increased glucose disappearance and muscle glucose metabolic index on either diet. This was associated with enhanced activation of muscle Akt and AMP-activated protein kinase and reduced muscle triglycerides in HF-fed Glp1r-/- mice. Chow-fed Glp1r-/- mice exhibited impaired suppression of endoRa and hepatic insulin signaling. In contrast, HF-fed Glp1r-/- mice exhibited improved suppression of endoRa and hepatic Akt activation. This was associated with decreased hepatic triglycerides and impaired activation of sterol regulatory element-binding protein-1. These results show that mice lacking the Glp1r are protected from HF diet-induced muscle and hepatic insulin resistance independent of effects on total fat mass.

Kupffer cell activation is a causal factor for hepatic insulin resistance

Recruited adipose tissue macrophages contribute to chronic and low-grade inflammation causing insulin resistance in obesity. Similarly, we hypothesized here that Kupffer cells, the hepatic resident macrophages, play a pathogenic role in hepatic insulin resistance induced by a high-fat diet. Mice were fed a normal diet or high-fat diet for 3 days. Kupffer cell activation was evaluated by immunohistochemistry and quantitative RT-PCR. Insulin sensitivity was assessed in vivo by hyperinsulinemic-euglycemic clamp and insulin-activated signaling was investigated by Western blot. Liposome-encapsulated clodronate was injected intravenously to deplete macrophages prior to a short-term exposure to high-fat diet. Here, we characterized a short-term high-fat diet model in mice and demonstrated early hepatic insulin resistance and steatosis concurrent with Kupffer cell activation. We demonstrated that selective Kupffer cell depletion obtained by intravenous clodronate, without affecting adipose tissue macrophages, was sufficient to enhance insulin-dependent insulin signaling and significantly improve hepatic insulin sensitivity in vivo in this short-term high-fat diet model. Our study clearly shows that hepatic macrophage response participates to the onset of high-fat diet-induced hepatic insulin resistance and may therefore represent an attractive target for prevention and treatment of diet- and obesity-induced insulin resistance.