High-fat Diet-induced Insulin Resistance Research Articles

Anthocyanins from the fruits of Lycium ruthenicum Murray improve high-fat diet-induced insulin resistance by ameliorating inflammation and oxidative stress in mice.

A high-fat diet (HFD) promotes tissue inflammation, oxidative stress and insulin resistance (IR), thereby contributing to the development of obesity and diabetes. Anthocyanins from Lycium ruthenicum (AC) have demonstrated anti-obesity effects and modulated IR. To investigate the mechanism by which AC attenuates the adverse effects of consuming a HFD, C57BL/6J mice were fed a HFD supplemented with AC or a control diet without AC for 12 weeks. AC supplementation decreased the amount of weight gain, hepatic lipid, and sequentially improved dyslipidemia, inflammation, oxidative stress, and IR in HFD-fed mice. Molecular data revealed that AC inhibited hepatic inflammation by reducing TLR4/NF-κB/JNK in the liver tissues and ameliorated oxidative stress by activating the Nrf2/HO-1/NQO1 pathway. Thus, AC might activate IRS-1/AKT and prevent HFD-induced gluconeogenesis and IR by ameliorating inflammation and oxidative stress. Modulation of inflammation and oxidative stress with AC may represent a promising target for the treatment of IR and provide insight into the mechanism by which AC protects against obesity.

TIR-Domain-Containing Adaptor-Inducing Interferon-β (TRIF) Is Involved in Glucose Metabolism in Adipose Tissue through the Insulin/AKT Signaling Pathway.

Obesity significantly increases the risk of developing type 2 diabetes mellitus and other metabolic diseases. Obesity is associated with chronic low-grade inflammation in white adipose tissues, which is thought to play an essential role in developing insulin resistance. Many lines of evidence indicate that toll-like receptors (TLRs) and their downstream signaling pathways are involved in development of chronic low-grade inflammation and insulin resistance, which are associated with obesity. Mice lacking molecules positively involved in the TLR signaling pathways are generally protected from high-fat diet-induced inflammation and insulin resistance. In this study, we have determined the effects of genetic deficiency of toll/interleukin-1 receptor-domain-containing adaptor-inducing interferon-β (TRIF) on food intake, bodyweight, glucose metabolism, adipose tissue macrophage polarization, and insulin signaling in normal chow diet-fed mice to investigate the role of the TRIF-dependent TLR signaling in adipose tissue metabolism and inflammation. TRIF deficiency (TRIF−/−) increased food intake and bodyweight. The significant increase in bodyweight in TRIF−/− mice was discernible as early as 24 weeks of age and sustained thereafter. TRIF−/− mice showed impaired glucose tolerance in glucose tolerance tests, but their insulin tolerance tests were similar to those in TRIF+/+ mice. Although no difference was found in the epididymal adipose mass between the two groups, the percentage of CD206+ M2 macrophages in epididymal adipose tissue decreased in TRIF−/− mice compared with those in TRIF+/+ mice. Furthermore, activation of epididymal adipose AKT in response to insulin stimulation was remarkably diminished in TRIF−/− mice compared with TRIF+/+ mice. Our results indicate that the TRIF-dependent TLR signaling contributes to maintaining insulin/AKT signaling and M2 macrophages in epididymal adipose tissue under a normal chow diet and provide new evidence that TLR4-targeted therapies for type 2 diabetes require caution.

Mechanisms by which adiponectin reverses high fat diet-induced insulin resistance in mice

Adiponectin has emerged as a potential therapy for type 2 diabetes mellitus, but the molecular mechanism by which adiponectin reverses insulin resistance remains unclear. Two weeks of globular adiponectin (gAcrp30) treatment reduced fasting plasma glucose, triglyceride (TAG), and insulin concentrations and reversed whole-body insulin resistance, which could be attributed to both improved insulin-mediated suppression of endogenous glucose production and increased insulin-stimulated glucose uptake in muscle and adipose tissues. These improvements in liver and muscle sensitivity were associated with ∼50% reductions in liver and muscle TAG and plasma membrane (PM)-associated diacylglycerol (DAG) content and occurred independent of reductions in total ceramide content. Reductions of PM DAG content in liver and skeletal muscle were associated with reduced PKCε translocation in liver and reduced PKCθ and PKCε translocation in skeletal muscle resulting in increased insulin-stimulated insulin receptor tyrosine1162 phosphorylation, IRS-1/IRS-2-associated PI3-kinase activity, and Akt-serine phosphorylation. Both gAcrp30 and full-length adiponectin (Acrp30) treatment increased eNOS/AMPK activation in muscle and muscle fatty acid oxidation. gAcrp30 and Acrp30 infusions also increased TAG uptake in epididymal white adipose tissue (eWAT), which could be attributed to increased lipoprotein lipase (LPL) activity. These data suggest that adiponectin and adiponectin-related molecules reverse lipid-induced liver and muscle insulin resistance by reducing ectopic lipid storage in these organs, resulting in decreased plasma membrane sn-1,2-DAG-induced nPKC activity and increased insulin signaling. Adiponectin mediates these effects by both promoting the storage of TAG in eWAT likely through stimulation of LPL as well as by stimulation of AMPK in muscle resulting in increased muscle fat oxidation.

MiR-125b-2 knockout increases high-fat diet-induced fat accumulation and insulin resistance

Obese individuals are more susceptible to comorbidities than individuals of healthy weight, including cardiovascular disease and metabolic disorders. MicroRNAs are a class of small and noncoding RNAs that are implicated in the regulation of chronic human diseases. We previously reported that miR-125b plays a critical role in adipogenesis in vitro. However, the involvement of miR-125b-2 in fat metabolism in vivo remains unknown. In the present study, miR-125b-2 knockout mice were generated using CRISPR/CAS9 technology, resulting in mice with a 7 bp deletion in the seed sequence of miR-125b-2. MiR-125b-2 knockout increased the weight of liver tissue, epididymal white fat and inguinal white fat. MiR-125b-2 knockout also increased adipocyte volume in HFD-induced obese mice, while there were no significant differences in body weight and feed intake versus mice fed a normal diet. Additionally, qRT-PCR and western blot analysis revealed that the expression of the miR-125b-2 target gene SCD-1 and fat synthesis-associated genes, such as PPARγ and C/EBPα, were significantly up-regulated in miR-125b-2KO mice (P < 0.05). Moreover, miR-125b-2KO altered HFD-induced changes in glucose tolerance and insulin resistance. In conclusion, we show that miR-125b-2 is a novel potential target for regulating fat accumulation, and also a candidate target to develop novel treatment strategies for obesity and diabetes.

ADAR1 deficiency protects against high-fat diet-induced obesity and insulin resistance in mice.

Obesity is an important independent risk factor for type 2 diabetes, cardiovascular diseases, and many other chronic diseases. The objective of this study was to determine the role of adenosine deaminase acting on RNA 1 (ADAR1) in the development of obesity and insulin resistance. Wild-type (WT) and heterozygous ADAR1-deficient (Adar1+/-) mice were fed normal chow or a high-fat diet (HFD) for 12 wk. Adar1+/- mice fed with HFD exhibited a lean phenotype with reduced fat mass compared with WT controls, although no difference was found under chow diet conditions. Blood biochemical analysis and insulin tolerance test showed that Adar1+/- improved HFD-induced dyslipidemia and insulin resistance. Metabolic studies showed that food intake was decreased in Adar1+/- mice compared with the WT mice under HFD conditions. Paired feeding studies further demonstrated that Adar1+/- protected mice from HFD-induced obesity through decreased food intake. Furthermore, Adar1+/- restored the increased ghrelin expression in the stomach and the decreased serum peptide YY levels under HFD conditions. These data indicate that ADAR1 may contribute to diet-induced obesity, at least partially, through modulating the ghrelin and peptide YY expression and secretion.NEW & NOTEWORTHY This study identifies adenosine deaminase acting on RNA 1 as a novel factor promoting high-fat diet-induced obesity, at least partially, through modulating appetite-related genes ghrelin and PYY.

Autophagy is not involved in lipid accumulation and the development of insulin resistance in skeletal muscle

ObjectiveTo investigate the effect of high fat diet-induced insulin resistance on autophagy markers in the liver and skeletal muscle of mice in the fasted state and following an oral glucose bolus. MethodsForty C57BL/6J male mice were fed either a high fat, high sucrose (HFSD, n = 20) or standard chow control (CON, n = 20) diet for 16 weeks. Upon trial completion, mice were gavaged with water or glucose and skeletal muscle and liver were collected 15 min post gavage. Protein abundance and gene expression of autophagy markers and activation of related signalling pathways were assessed. ResultsCompared to CON, the HFSD intervention increased LC3B-II and p62/SQSTM1 protein abundance in the liver which is indicative of elevated autophagosome content via reduced clearance. These changes coincided with inhibitory autophagy signalling through elevated p-mTOR S2448 and p-ULK1S758. HFSD did not alter autophagy markers in skeletal muscle. Administration of an oral glucose bolus had no effect on autophagy markers or upstream signalling responses in either tissue regardless of diet. ConclusionHFSD induces tissue-specific autophagy impairments, with autophagosome accumulation indicating reduced lysosomal clearance in the liver. In contrast, autophagy markers were unchanged in skeletal muscle, indicating that autophagy is not involved in the development of skeletal muscle 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.

Cardiolipin Synthase 1 Ameliorates NASH Through Activating Transcription Factor 3 Transcriptional Inactivation

NASH is an increasingly prevalent disease that is the major cause of liver dysfunction. Previous research has indicated that adipose cardiolipin synthase 1 (CRLS1) levels are associated with insulin sensitivity; however, the precise roles of CRLS1 and underlying mechanisms involving CRLS1 in the pathological process of NASH have not been elucidated. Here, we discovered that CRLS1 was significantly down-regulated in genetically obese and diet-induced mice models. In vitro studies demonstrated that overexpression of CRLS1 markedly attenuated hepatic steatosis and inflammation in hepatocytes, whereas short hairpin RNA-mediated CRLS1 knockdown aggravated these abnormalities. Moreover, high-fat diet-induced insulin resistance and hepatic steatosis were significantly exacerbated in hepatocyte-specific Crls1-knockout (Crls1-HKO) mice. It is worth noting that Crls1 depletion significantly aggravated high-fat and high-cholesterol diet-induced inflammatory response and fibrosis during NASH development. RNA-sequencing analysis systematically demonstrated a prominently aggravated lipid metabolism disorder in which inflammation and fibrosis resulted from Crls1 deficiency. Mechanically, activating transcription factor 3 (ATF3) was identified as the key differentially expressed gene in Crls1-HKO mice through transcriptomic analysis, and our investigation further showed that CRLS1 suppresses ATF3 expression and inhibits its activity in palmitic acid-stimulated hepatocytes, whereas ATF3 partially reverses lipid accumulation and inflammation inhibited by CRLS1 overexpression under metabolic stress. In conclusion, CRLS1 ameliorates insulin resistance, hepatic steatosis, inflammation, and fibrosis during the pathological process of NASH by inhibiting the expression and activity of ATF3.

Menthol to Induce Non-shivering Thermogenesis via TRPM8/PKA Signaling for Treatment of Obesity.

Increasing basal energy expenditure via uncoupling protein 1 (UCP1)-dependent non-shivering thermogenesis is an attractive therapeutic strategy for treatment of obesity. Transient receptor potential melastatin 8 (TRPM8) channel activation by cold and cold mimetics induces UCP1 transcription and prevents obesity in animals, but the clinical relevance of this relationship remains incompletely understood. A review of TRPM8 channel agonism for treatment of obesity focusing on menthol was undertaken. Adipocyte TRPM8 activation results in Ca2+ influx and protein kinase A (PKA) activation, which induces mitochondrial elongation, mitochondrial localization to lipid droplets, lipolysis, β-oxidation, and UCP1 expression. Ca2+-induced mitochondrial reactive oxygen species activate UCP1. In animals, TRPM8 agonism increases basal metabolic rate, non-shivering thermogenesis, oxygen consumption, exercise endurance, and fatty acid oxidation and decreases abdominal fat percentage. Menthol prevents high-fat diet-induced obesity, glucose intolerance, insulin resistance, and liver triacylglycerol accumulation. Hypothalamic TRPM8 activation releases glucagon, which activates PKA and promotes catabolism. TRPM8 polymorphisms are associated with obesity. In humans, oral menthol and other TRPM8 agonists have little effect. However, topical menthol appears to increase core body temperature and metabolic rate. A randomized clinical control trial of topical menthol in obese patients is warranted.

Biochanin A, a soy isoflavone, diminishes insulin resistance by modulating insulin-signalling pathway in high-fat diet-induced diabetic mice

Aim The objective of this study was to evaluate the probable mechanism of action of Biochanin A (BCA) on high-fat diet-induced insulin resistance mice. Methods Twenty-four male C57/BL/6J mice were divided into two and fed either control diet or a high fat-high diet (HFD). After 6 weeks, mice were grouped into: Control, Control + BCA, HFD and HFD + BCA (n = 6). Mice were made diabetic by feeding them an HFD. Results Body weight, plasma glucose, insulin, leptin levels and HOMA values were significantly lower in the BCA supplemented HFD group when related to the HFD group. Furthermore, BCA supplementation significantly increased Insulin receptor substrate 1 (IRS 1), PI3K, Akt and Glucose transporter type 4 (GLUT-4) protein abundance in skeletal muscle when equated with HFD. Conclusion This study demonstrates that BCA can improve insulin sensitivity by activating insulin signalling, suggesting that it may possess antidiabetic activities.

Targeting Mitochondria-Located circRNA SCAR Alleviates NASH via Reducing mROS Output

Mitochondria, which play central roles in immunometabolic diseases, have their own genome. However, the functions of mitochondria-located noncoding RNAs are largely unknown due to the absence of a specific delivery system. By circular RNA (circRNA) expression profile analysis of liver fibroblasts from patients with nonalcoholic steatohepatitis (NASH), we observe that mitochondrial circRNAs account for a considerable fraction of downregulated circRNAs in NASH fibroblasts. By constructing mitochondria-targeting nanoparticles, we observe that Steatohepatitis-associated circRNA ATP5B Regulator (SCAR), which is located in mitochondria, inhibits mitochondrial ROS (mROS) output and fibroblast activation. circRNA SCAR, mediated by PGC-1α, binds to ATP5B and shuts down mPTP by blocking CypD-mPTP interaction. Lipid overload inhibits PGC-1α by endoplasmic reticulum (ER) stress-induced CHOP. Invivo, targeting circRNA SCAR alleviates high fat diet-induced cirrhosis and insulin resistance. Clinically, circRNA SCAR is associated with steatosis-to-NASH progression. Collectively, we identify a mitochondrial circRNA that drives metaflammation and serves as a therapeutic target for NASH.

A Combination of Apple Vinegar Drink with Bacillus coagulans Ameliorates High Fat Diet-Induced Body Weight Gain, Insulin Resistance and Hepatic Steatosis.

Obesity is a worldwide epidemic characterized by excessive fat accumulation, associated with multiple comorbidities and complications. Emerging evidence points to gut microbiome as a driving force in the pathogenesis of obesity. Vinegar intake, a traditional remedy source of exogenous acetate, has been shown to improve glycemic control and to have anti-obesity effects. New functional foods may be developed by supplementing traditional food with probiotics. B. coagulans is a suitable choice because of its resistance to high temperatures. To analyze the possible synergic effect of Vinegar and B. coagulans against the metabolic alterations induced by a high fat diet (HFD), we fed twelve-week-old C57BL/6 mice with HFD for 5 weeks after 2 weeks of acclimation on a normal diet. Then, food intake, body weight, blood biochemical parameters, histology and liver inflammatory markers were analyzed. Although vinegar drink, either alone or supplemented with B. coagulans, reduced food intake, attenuated body weight gain and enhanced glucose tolerance, only the supplemented drink improved the lipid serum profile and prevented hepatic HFD-induced overexpression of CD36, IL-1β, IL-6, LXR and SREBP, thus reducing lipid deposition in the liver. The beneficial properties of the B. coagulans-supplemented vinegar appear to be mediated by a reduction in insulin and leptin circulating levels.

A Specific Strain of Lactic Acid Bacteria, Lactobacillus paracasei, Inhibits Inflammasome Activation In Vitro and Prevents Inflammation-Related Disorders.

Some strains of lactic acid bacteria (LAB) have anti-inflammatory effects, but the mechanism underlying the alleviation of inflammation by LAB is not fully understood. In this study, we examined the inhibitory effect of a certain strain of LAB, Lactobacillus paracasei, on inflammasome activation, which is associated with various inflammatory disorders. Using bone marrow-derived macrophages from BALB/c mice, we found that L. paracasei, but not L. rhamnosus, suppressed NLRP3 inflammasome activation and inhibited subsequent caspase-1 activation and IL-1β secretion. L. paracasei also had inhibitory effects on AIM2 and NLRC4 inflammasome activation as well as the NLRP3 inflammasome. These inhibitory effects of L. paracasei on inflammasome activation were dependent on autocrine IL-10 induced by L. paracasei-stimulated macrophages. Furthermore, IL-10 production by L. paracasei-stimulated macrophages was involved with phagocytosis and the NOD2 signaling pathway in macrophages. In addition to in vitro studies, oral administration of L. paracasei in C57BL/6 mice reduced monosodium urate crystal-induced peritoneal inflammation in vivo. Moreover, continuous intake of L. paracasei in C57BL/6 mice alleviated high fat diet-induced insulin resistance and aging-induced expression of biomarkers for T cell senescence. Taken together, we demonstrated that L. paracasei inhibits inflammasome activation in vitro and exhibits an anti-inflammatory function in vivo. These results indicate that LAB that have inhibitory effects on inflammasome activation might contribute to the alleviation of inflammation-related disorders.

Abstract MP121: Deleting the 2-oxoglutarate- and Iron-dependent Prolyl Hydroxylase Ogfod1 Alters Purine Nucleotide Regulation and is Cardioprotective

Prolyl hydroxylation is a post-translational modification that regulates protein stability, turnover, and activity. The proteins that catalyze prolyl hydroxylation belong to the 2-oxoglutarate- and iron-dependent oxygenase family of enzymes. A newly-described member of this family is 2-oxoglutarate- and iron-dependent oxygenase domain containing protein 1 (Ogfod1), which catalyzes prolyl hydroxylation of the ribosomal protein s23 (Rps23). To investigate the cardiovascular function of Ogfod1, we isolated hearts from 5 Ogfod1 -WT and 5 Ogfod1 -KO mice and used Liquid Chromatography and Tandem Mass Spectrometry (LC-MS/MS) to identify proteomic changes. Ingenuity Pathway Analysis (IPA) identified “Purine Nucleotides Degradation II (Aerobic)” ( P = 0.00017) to be one of the most significantly-enriched pathways. We then did metabolomics and found that Inosine 5’-monophosphate (IMP) was 3.5x higher in Ogfod1 -KO hearts ( P = 0.011), further supporting a role for Ogfod1 in regulating purine nucleotide metabolism. Recent evidence has shown that altering purine nucleotide degradation protects against diet-induced obesity and insulin resistance, so we tested this hypothesis in Ogfod1 -KO mice by feeding them high-fat diets. Ogfod1 ablation protects against high-fat diet-induced obesity and insulin resistance. Altering purine nucleotide degradation has also been shown to be protective against cardiac injury, so we tested the hypothesis that Ogfod1 loss protects the heart from ischemia-reperfusion (I/R) injury by subjecting perfused hearts from 6 Ogfod1 -WT and 6 Ogfod1 -KO mice to ischemia and reperfusion and assessed tissue death. We found a 37% decrease in infarct size in Ogfod1 -KO hearts (56% in Ogfod1 -WT and 35% in Ogfod1 -KO, P = 0.0003). In a separate set of experiments, we treated Ogofd1 -KO mice with isoproterenol to induce hypertrophy, and Ogfod1 -KO hearts showed protection against hypertrophic remodeling. Interestingly, OGFOD1 transcripts were up-regulated in human heart failure, indicating a potential role for OGFOD1 in the human failing heart. Altogether, these data show that Ogfod1 deletion alters the myocardial proteome and myocardial metabolism and protects against obesity, insulin sensitivity, I/R injury, and hypertrophy.

Genetic ablation of Fas-activated serine/threonine kinase ameliorates obesity-related hepatic glucose and lipid metabolic disorders via sirtuin-1 signaling

Obesity has become a worldwide pandemic and is associated with various metabolic diseases such as type 2 diabetes mellitus and non-alcoholic fatty liver disease. Fas-activated serine/threonine kinase (Fastk) is a multifunctional protein localized in the mitochondrion; however, the role of Fastk in obesity-related metabolic disorders remains unexplored. Here we found that Fastk expression was specifically induced in livers of high fat (HF) diet-fed mice and in saturated fatty acid (such as palmitate)-loaded hepatocytes. Genetic ablation of Fastk ameliorated HF diet-induced insulin resistance, glucose intolerance, and hepatic steatosis. Further studies confirmed that Fastk knockout suppressed hepatic gluconeogenesis and lipogenesis in HF diet-stressed livers and in palmitate-loaded hepatocytes. Mechanistically, Fastk ablation significantly preserved sirtuin-1 (SIRT1) expression and activity in livers of HF diet-fed mice and in palmitate-loaded hepatocytes. Inhibition of SIRT1 activity by EX-527 (a specific inhibitor of SIRT1) totally abolished the suppressive effects of Fastk knockout on gluconeogenesis and lipogenesis in cultured hepatocytes. In conclusion, these data for the first time demonstrate that Fastk critically controls hepatic gluconeogenesis and lipogenesis mainly through modulating SIRT1 signaling. Intervening Fastk expression or activity might be a promising therapeutic strategy for the treatment of obesity-associated metabolic diseases.

Effect of shengmai san on insulin resistance, tumor necrosis factor-alpha and oxidative stress in rats fed on a high-fat diet

Shengmai San (SMS) is a well-known traditional Chinese medicine formula prescribed for patients with coronary heart disease (CHD). Insulin resistance is the most likely explanation for the development and progression of this disease. To investigate the effect of SMS on high-fat diet-induced insulin resistance, inflammatory cytokine production and oxidative stress, male Wistar rats were fed with low-fat control diet, high-fat diet and high-fat diet supplemented with 4% SMS for eight weeks. An oral glucose tolerance test was conducted in the seventh week. Rats fed the SMS diet had significantly lower plasma fructosamine concentration (p < 0.05) and tended to have lower (p < 0.1) AUC values of plasma glucose and insulin concentrations after glucose challenge, compared to those fed the high-fat diet. Moreover, SMS reduced TNF-α and lipid peroxidation levels in the liver and heart. However, SMS had no effect on fasting plasma concentrations of glucose, insulin, triglyceride, non-esterified fatty acids, total cholesterol, HDL-cholesterol and insulin resistance index (homeostasis model assessment; HOMA) in rats. Our results show that SMS may have little or no significant effect on reducing insulin resistance, but display anti-oxidative and anti-inflammatory properties.

Disrupting phosphatase SHP2 in macrophages protects mice from high-fat diet-induced hepatic steatosis and insulin resistance by elevating IL-18 levels

Chronic low-grade inflammation plays an important role in the pathogenesis of type 2 diabetes. Src homology 2 domain-containing tyrosine phosphatase-2 (SHP2) has been reported to play diverse roles in different tissues during the development of metabolic disorders. We previously reported that SHP2 inhibition in macrophages results in increased cytokine production. Here, we investigated the association between SHP2 inhibition in macrophages and the development of metabolic diseases. Unexpectedly, we found that mice with a conditional SHP2 knockout in macrophages (cSHP2-KO) have ameliorated metabolic disorders. cSHP2-KO mice fed a high-fat diet (HFD) gained less body weight and exhibited decreased hepatic steatosis, as well as improved glucose intolerance and insulin sensitivity, compared with HFD-fed WT littermates. Further experiments revealed that SHP2 deficiency leads to hyperactivation of caspase-1 and subsequent elevation of interleukin 18 (IL-18) levels, both in vivo and in vitro Of note, IL-18 neutralization and caspase-1 knockout reversed the amelioration of hepatic steatosis and insulin resistance observed in the cSHP2-KO mice. Administration of two specific SHP2 inhibitors, SHP099 and Phps1, improved HFD-induced hepatic steatosis and insulin resistance. Our findings provide detailed insights into the role of macrophagic SHP2 in metabolic disorders. We conclude that pharmacological inhibition of SHP2 may represent a therapeutic strategy for the management of type 2 diabetes.

Establishment of high-fat diet-induced obesity and insulin resistance model in rats

To investigate the appropriate conditions and duration for establishing a high-fat diet-induced obesity and insulin resistance model in rats. Forty-five 6-week-old male Sprague-Dawley (SD) rats were randomly assigned into 2 groups: (1) control group (CON), (2) high-fat diet group (HFD). HFD was fed with a high-fat diet (45% kcal from fat) while CON with chow diet. After four-weeks of high-fat diet feeding, the rats of obesity resistance (OR) were eliminated according to body weight sorting, whereas obese (OB) rats were continued feeding a high-fat diet until 12 weeks. Body weight and food intake were recorded weekly. Glucose tolerance was evaluated by oral glucose tolerance test (OGTT) in 4 weeks, 8 weeks and 12 weeks. At the end of 12 weeks, insulin releasing test and visceral fat mass were measured and HE staining of the liver, adipose tissue and pancreatic tissue were conducted. After 4 weeks of a high-fat diet, the body weight of HFD was 17.8% higher than that of CON (P=0.001), and the rate of obesity was 67.6%-78.4%. Glucose tolerance of OB rats was impaired with a higher blood glucose concentration at 120 min (P<0.001) and a higher area under the curve (AUC, P=0.037) in OGTT compared with CON. The rate of obesity and insulin-resistance rats was 79.3%. After 8 weeks of feeding, the body weight in OB was 30.4% higher than CON (P<0.001). In OGTT, blood glucose levels at 60 min and 120 min were 35.6% and 36.4% higher than those in CON (both P<0.001), and AUC was 21.7% (P<0.001) higher than that of CON. The rate of obesity and insulin-resistance rats was 100.0%. After 12 weeks of feeding, the body weight in OB was 36.9% higher than that in CON (P<0.001). In OGTT, the blood glucose levels at 60 min and 120 min were 24.8% (P=0.001) and 34.6% (P<0.001) higher than those in CON, and AUC was 16.1% (P=0.019) higher than that of CON. The rate of obesity and insulin-resistance rats was 93.3%. The insulin releasing test showed that serum insulin concentration at each time point (0, 30, 60, 120 min) was higher than that in CON, with a 6.3-times higher than that in CON at 120 min (P=0.008). Pathological changes were observed in islets and liver in the OB rats. After 4 weeks of a high-fat diet (45% kcal from fat) feeding in six-weeks SD rats, the rats of OR were eliminated. Impaired glucose tolerance was found in OB rats after 4 weeks of feeding, and the rate was higher after 8-12 weeks of high-fat diet feeding.

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.

Vimentin Deficiency Prevents High-Fat Diet-Induced Obesity and Insulin Resistance in Mice.

BackgroundObesity and type 2 diabetes mellitus are world-wide health problems, and lack of understanding of their linking mechanism is one reason for limited treatment options. We determined if genetic deletion of vimentin, a type 3 intermediate filament, affects obesity and type 2 diabetes mellitus.MethodsWe fed vimentin-null (Vim−/−) mice and wild-type mice a high-fat diet (HFD) for 10 weeks and measured weight change, adiposity, blood lipids, and glucose. We performed intraperitoneal glucose tolerance tests and measured CD36, a major fatty acid translocase, and glucose transporter type 4 (GLUT4) in adipocytes from both groups of mice.ResultsVim−/− mice fed an HFD showed less weight gain, less adiposity, improved glucose tolerance, and lower serum level of fasting glucose. However, serum triglyceride and non-esterified fatty acid levels were higher in Vim−/− mice than in wild-type mice. Vimentin-null adipocytes showed 41.1% less CD36 on plasma membranes, 27% less uptake of fatty acids, and 50.3% less GLUT4, suggesting defects in intracellular trafficking of these molecules.ConclusionWe concluded that vimentin deficiency prevents obesity and insulin resistance in mice fed an HFD and suggest vimentin as a central mediator linking obesity and type 2 diabetes mellitus.