High-fat Diet-induced Insulin Resistance Research Articles

The microbiota-dependent tryptophan metabolite alleviates high-fat diet–induced insulin resistance through the hepatic AhR/TSC2/mTORC1 axis

Type 2 diabetes (T2D) is potentially linked to disordered tryptophan metabolism that attributes to the intricate interplay among diet, gut microbiota, and host physiology. However, underlying mechanisms are substantially unknown. Comparing the gut microbiome and metabolome differences in mice fed a normal diet (ND) and high-fat diet (HFD), we uncover that the gut microbiota-dependent tryptophan metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) is present at lower concentrations in mice with versus without insulin resistance. We further demonstrate that the microbial transformation of tryptophan into 5-HIAA is mediated by Burkholderia spp. Additionally, we show that the administration of 5-HIAA improves glucose intolerance and obesity in HFD-fed mice, while preserving hepatic insulin sensitivity. Mechanistically, 5-HIAA promotes hepatic insulin signaling by directly activating AhR, which stimulates TSC2 transcription and thus inhibits mTORC1 signaling. Moreover, T2D patients exhibit decreased fecal levels of 5-HIAA. Our findings identify a noncanonical pathway of microbially producing 5-HIAA from tryptophan and indicate that 5-HIAA might alleviate the pathogenesis of T2D.

Gut microbiota metabolite tyramine ameliorates high-fat diet-induced insulin resistance via increased Ca2+ signaling

The gut microbiota and their metabolites are closely linked to obesity-related diseases, such as type 2 diabetes, but their causal relationship and underlying mechanisms remain largely elusive. Here, we found that dysbiosis-induced tyramine (TA) suppresses high-fat diet (HFD)-mediated insulin resistance in both Drosophila and mice. In Drosophila, HFD increases cytosolic Ca2+ signaling in enterocytes, which, in turn, suppresses intestinal lipid levels. 16 S rRNA sequencing and metabolomics revealed that HFD leads to increased prevalence of tyrosine decarboxylase (Tdc)-expressing bacteria and resulting tyramine production. Tyramine acts on the tyramine receptor, TyrR1, to promote cytosolic Ca2+ signaling and activation of the CRTC-CREB complex to transcriptionally suppress dietary lipid digestion and lipogenesis in enterocytes, while promoting mitochondrial biogenesis. Furthermore, the tyramine-induced cytosolic Ca2+ signaling is sufficient to suppress HFD-induced obesity and insulin resistance in Drosophila. In mice, tyramine intake also improves glucose tolerance and insulin sensitivity under HFD. These results indicate that dysbiosis-induced tyramine suppresses insulin resistance in both flies and mice under HFD, suggesting a potential therapeutic strategy for related metabolic disorders, such as diabetes.

Therapeutic effects of Lingguizhugan decoction in a rat model of high-fat diet-induced insulin resistance

BACKGROUND Lingguizhugan (LGZG) decoction is a widely used classic Chinese medicine formula that was recently shown to improve high-fat diet (HFD)-induced insulin resistance (IR) in animal studies. AIM To assess the therapeutic effect of LGZG decoction on HFD-induced IR and explore the potential underlying mechanism. METHODS To establish an IR rat model, a 12-wk HFD was administered, followed by a 4-wk treatment with LGZG. The determination of IR status was achieved through the use of biochemical tests and oral glucose tolerance tests. Using a targeted meta-bolomics platform to analyze changes in serum metabolites, quantitative real-time PCR (qRT-PCR) was used to assess the gene expression of the ribosomal protein S6 kinase beta 1 (S6K1). RESULTS In IR rats, LGZG decreased body weight and indices of hepatic steatosis. It effectively controlled blood glucose and food intake while protecting islet cells. Metabolite analysis revealed significant differences between the HFD and HFD-LGZG groups. LGZG intervention reduced branched-chain amino acid levels. Levels of IR-related metabolites such as tryptophan, alanine, taurine, and asparagine decreased significantly. IR may be linked to amino acids due to the contemporaneous increase in S6K1 expression, as shown by qRT-PCR. CONCLUSIONS Our study strongly suggests that LGZG decoction reduces HFD-induced IR. LGZG may activate S6K1 via metabolic pathways. These findings lay the groundwork for the potential of LGZG as an IR treatment.

Inflammation causes insulin resistance in mice via interferon regulatory factor 3 (IRF3)-mediated reduction in FAHFA levels

Obesity-induced inflammation causes metabolic dysfunction, but the mechanisms remain elusive. Here we show that the innate immune transcription factor interferon regulatory factor (IRF3) adversely affects glucose homeostasis through induction of the endogenous FAHFA hydrolase androgen induced gene 1 (AIG1) in adipocytes. Adipocyte-specific knockout of IRF3 protects male mice against high-fat diet-induced insulin resistance, whereas overexpression of IRF3 or AIG1 in adipocytes promotes insulin resistance on a high-fat diet. Furthermore, pharmacological inhibition of AIG1 reversed obesity-induced insulin resistance and restored glucose homeostasis in the setting of adipocyte IRF3 overexpression. We, therefore, identify the adipocyte IRF3/AIG1 axis as a crucial link between obesity-induced inflammation and insulin resistance and suggest an approach for limiting the metabolic dysfunction accompanying obesity.

Dietary Oat β-Glucan Alleviates High-Fat Induced Insulin Resistance through Regulating Circadian Clock and Gut Microbiome.

High-fat diet induced circadian rhythm disorders (CRD) are associated with metabolic diseases. As the main functional bioactive component in oat, β-glucan (GLU) can improve metabolic disorders, however its regulatory effect on CRD remains unclear. In this research, the effects of GLU on high-fat diet induced insulin resistance and its mechanisms are investigated, especially focusing on circadian rhythm-related process. Male C57BL/6 mice are fed a low fat diet, a high-fat diet (HFD), and HFD supplemented 3% GLU for 13 weeks. The results show that GLU treatment alleviates HFD-induced insulin resistance and intestinal barrier dysfunction in obese mice. The rhythmic expressions of circadian clock genes (Bmal1, Clock, and Cry1) in the colon impaired by HFD diet are also restored by GLU. Further analysis shows that GLU treatment restores the oscillatory nature of gut microbiome, which can enhance glucagon-like peptide (GLP-1) secretion via short-chain fatty acids (SCFAs) mediated activation of G protein-coupled receptors (GPCRs). Meanwhile, GLU consumption significantly relieves colonic inflammation and insulin resistance through modulating HDAC3/NF-κB signaling pathway. GLU can ameliorate insulin resistance due to its regulation of colonic circadian clock and gut microbiome.

Relationship between Serum Concentrations and Muscular Expressions of Selenoproteins on Selenium-Supplemented Insulin Resistance Mouse Model.

Previously, insulin resistance and hepatic oxidative stress with increased expressions of glutathione peroxidase (GPx) 1 and selenoprotein P (SelP) were induced in NSY mice, a diabetic mouse model, by administrating a high fat diet (HFD) and seleno-L-methionine (SeMet) for 12 weeks. In this study we developed an analysis method for serum selenoproteins using LC-tandem mass spectrometry (LC-MS/MS) and investigated the effects of supplementary selenium on serum concentrations of selenoproteins as well as protein expression in skeletal muscle as a major insulin target tissue under the same experimental condition. The glucose area under the curves for oral glucose tolerance and insulin tolerance tests indicated that the HFD induced insulin resistance, whereas the treatment of SeMet + HFD showed insignificant promotion compared with the HFD-induced insulin resistance. Although the expressions of GPx1 in gastrocnemius and soleus were not significantly induced by supplementary SeMet nor HFD administration, the expressions of SelP in both skeletal muscles were significantly induced by the treatment of SeMet + HFD. There were also significant increases in serum concentrations of SelP by supplementary SeMet + HFD administration, whereas GPx3 was augmented by supplementary SeMet only. These results indicated that the HFD intake under the sufficient selenium status augmented the blood secretion of SelP, which may participate in the reduction of insulin sensitivity in skeletal muscles as well as liver or adipose tissues, and it is a better indicator of deterioration than GPx3 as it is a major selenoprotein in serum.

Chronic administration of hydrolysed pine nut oil to mice improves insulin sensitivity and glucose tolerance and increases energy expenditure via a free fatty acid receptor 4-dependent mechanism.

A healthy diet is at the forefront of measures to prevent type 2 diabetes. Certain vegetable and fish oils, such as pine nut oil (PNO), have been demonstrated to ameliorate the adverse metabolic effects of a high-fat diet. The present study investigates the involvement of the free fatty acid receptors 1 (FFAR1) and 4 (FFAR4) in the chronic activity of hydrolysed PNO (hPNO) on high-fat diet-induced obesity and insulin resistance. Male C57BL/6J wild-type, FFAR1 knockout (-/-) and FFAR4-/- mice were placed on 60 % high-fat diet for 3 months. Mice were then dosed hPNO for 24 d, during which time body composition, energy intake and expenditure, glucose tolerance and fasting plasma insulin, leptin and adiponectin were measured. hPNO improved glucose tolerance and decreased plasma insulin in the wild-type and FFAR1-/- mice, but not the FFAR4-/- mice. hPNO also decreased high-fat diet-induced body weight gain and fat mass, whilst increasing energy expenditure and plasma adiponectin. None of these effects on energy balance were statistically significant in FFAR4-/- mice, but it was not shown that they were significantly less than in wild-type mice. In conclusion, chronic hPNO supplementation reduces the metabolically detrimental effects of high-fat diet on obesity and insulin resistance in a manner that is dependent on the presence of FFAR4.

Hairless (Hr) Deficiency Mitigates High-Fat Diet-Induced Obesity and Insulin Resistance in Mice.

Obesity is a significant global health concern linked to excessive dietary energy intake. This research focuses on the mammalian hairless protein (HR), known for its role in skin and hair function, and its impact on metabolism. Examining male wild-type (Hr+/+) and Hr null (Hr-/-) mice over a 14-week normal chow diet (NCD) or high-fat diet (HFD) intervention. This study reveals that HR deficiency exhibited a protective effect against HFD-induced obesity and insulin resistance. This protective effect is attributed to increased energy expenditure in Hr-/- mice. Moreover, the brown adipose tissue (BAT) of Hr-/- mice displays elevated levels of the thermogenic protein, uncoupling protein 1 (Ucp1), and its key transcriptional regulators (PPARγ and PGC1α), compared to Hr+/+ mice. In summary, the findings underscore the protective role of HR deficiency in countering HFD-induced adiposity by enhancing insulin sensitivity, raising energy expenditure, and augmenting thermogenic factors in BAT. Further exploration of HR metabolic regulation holds promise for potential therapeutic targets in addressing obesity-related metabolic disorders.

Glycogen synthesis is required for adaptive thermogenesis in beige adipose tissue and affects diet-induced obesity.

Glycogen is a form of energy storage for glucose in different tissues such as liver and skeletal muscle. It remains incompletely understood how glycogen impacts on adipose tissue functionality. Cold exposure elevated the expression of Gys1 that encodes glycogen synthase 1 in brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT). The in vivo function of Gys1 was analyzed using a mouse model in which Gys1 was deleted specifically in adipose tissues. Under normal chow conditions, Gys1 deletion caused little changes to body weight and glucose metabolism. Deletion of Gys1 abrogated upregulation of UCP1 and other thermogenesis-related genes in iWAT upon prolonged cold exposure or treatment with β3-adrenergic receptor agonist CL-316,243. Stimulation of UCP1 by CL-316,243 in adipose-derived stromal cells (stromal vascular fractions, SVFs) was also reduced by Gys1 deletion. Both the basal glycogen content and CL-316,243-stimulated glycogen accumulation in adipose tissues were reduced by Gys1 deletion. High-fat diet-induced obesity and insulin resistance were aggravated in Gys1-deleted mice. The loss of body weight upon CL-316,243 treatment was also abrogated by the loss of Gys1. In conclusion, our results underscore the pivotal role of glycogen synthesis in adaptive thermogenesis in beige adipose tissue and its impact on diet-induced obesity in mice.NEW & NOTEWORTHY Glycogen is one of major types of fuel reserve in the body and its classical function is to maintain blood glucose level. This study uncovers that glycogen synthesis is required for beige fat tissue to generate heat upon cold exposure. Such a function of glycogen is linked to development of high-fat diet-induced obesity, thus extending our understanding about the physiological functions of glycogen.

Roles of fibroblast growth factors in the treatment of diabetes.

Diabetes affects about 422 million people worldwide, causing 1.5 million deaths each year. However, the incidence of diabetes is increasing, including several types of diabetes. Type 1 diabetes (5%-10% of diabetic cases) and type 2 diabetes (90%-95% of diabetic cases) are the main types of diabetes in the clinic. Accumulating evidence shows that the fibroblast growth factor (FGF) family plays important roles in many metabolic disorders, including type 1 and type 2 diabetes. FGF consists of 23 family members (FGF-1-23) in humans. Here, we review current findings of FGFs in the treatment of diabetes and management of diabetic complications. Some FGFs (e.g., FGF-15, FGF-19, and FGF-21) have been broadly investigated in preclinical studies for the diagnosis and treatment of diabetes, and their therapeutic roles in diabetes are currently under investigation in clinical trials. Overall, the roles of FGFs in diabetes and diabetic complications are involved in numerous processes. First, FGF intervention can prevent high-fat diet-induced obesity and insulin resistance and reduce the levels of fasting blood glucose and triglycerides by regulating lipolysis in adipose tissues and hepatic glucose production. Second, modulation of FGF expression can inhibit renal and cardiac fibrosis by regulating the expression of extracellular matrix components, promote diabetic wound healing process and bone repair, and inhibit cancer cell proliferation and migration. Finally, FGFs can regulate the activation of glucose-excited neurons and the expression of thermogenic genes.

Ketogenic diet ameliorates high-fat diet-induced insulin resistance in mouse skeletal muscle by alleviating endoplasmic reticulum stress

ObjectiveKetogenic diets (KD) have been shown to alleviate insulin resistance (IR) by exerting anti-lipogenic and insulin sensitizing effects in the liver through a variety of pathways. The present study sought to investigate whether a ketogenic diet also improves insulin sensitization in skeletal muscle cells through alleviating endoplasmic reticulum stress. MethodsHigh-fat diet-induced IR mice were allowed to a 2-week ketogenic diet. Insulin resistance and glucose tolerance were evaluated through GTT, ITT, and HOMA-IR. The C2C12 myoblasts exposed to palmitic acid were used to evaluate the insulin sensitization effects of β-hydroxybutyric acid (β-OHB). Molecular mechanisms concerning ER stress signaling activation and glucose uptake were assessed. ResultsThe AKT/GSK3β pathway was inhibited, ER stress signaling associated with IRE1, PERK, and BIP was activated, and the number of Glut4 proteins translocated to membrane decreased in the muscle of HFD mice. However, all these changes were reversed after 2 weeks of feeding on a ketogenic diet. Consistently in C2C12 myoblasts, the AKT/GSK3β pathway was inhibited by palmitic acid (PA) treatment. The endoplasmic reticulum stress-related proteins, IRE1, and BIP were increased, and the number of Glut4 proteins on the cell membrane decreased. However, β-OHB treatment alleviated ER stress and improved the glucose uptake of C2C12 cells. ConclusionOur data reveal that KD ameliorated HFD-induced insulin resistance in skeletal muscle, which was partially mediated by inhibiting endoplasmic reticulum stress. The insulin sensitization effect of β-OHB is associated with up regulation of AKT/GSK3β pathway and the increase in the number of Glut4 proteins on the cell membrane.

Repurposing lansoprazole to alleviate metabolic syndrome via PHOSPHO1 inhibition

Drug repurposing offers an efficient approach to therapeutic development. In this study, our bioinformatic analysis first predicted an association between obesity and lansoprazole (LPZ), a commonly prescribed drug for gastrointestinal ulcers. We went on to show that LPZ treatment increased energy expenditure and alleviated the high-fat diet-induced obesity, insulin resistance, and hepatic steatosis in mice. Treatment with LPZ elicited thermogenic gene expression and mitochondrial respiration in primary adipocytes, and induced cold tolerance in cold-exposed mice, suggesting the activity of LPZ in promoting adipose thermogenesis and energy metabolism. Mechanistically, LPZ is an efficient inhibitor of adipose phosphocholine phosphatase 1 (PHOSPHO1) and produces metabolic benefits in a PHOSPHO1-dependent manner. Our results suggested that LPZ may stimulate adipose thermogenesis by inhibiting the conversion of 2-arachidonoylglycerol-lysophosphatidic acid (2-AG-LPA) to 2-arachidonoylglycerol (2-AG) and reduce the activity of the thermogenic-suppressive cannabinoid receptor signaling. In summary, we have uncovered a novel therapeutic indication and mechanism of LPZ in managing obesity and its related metabolic syndrome, and identified a potential metabolic basis by which LPZ improves energy metabolism.

Lachnospiraceae-derived butyrate mediates protection of high fermentable fiber against placental inflammation in gestational diabetes mellitus.

Inflammation-associated insulin resistance is a key trigger of gestational diabetes mellitus (GDM), but the underlying mechanisms and effective interventions remain unclear. Here, we report the association of placental inflammation (tumor necrosis factor-α) and abnormal maternal glucose metabolism in patients with GDM, and a high fermentable dietary fiber (HFDF; konjac) could reduce GDM development through gut flora-short-chain fatty acid-placental inflammation axis in GDM mouse model. Mechanistically, HFDF increases abundances of Lachnospiraceae and butyrate, reduces placental-derived inflammation by enhancing gut barrier and inhibiting the transfer of bacterial-derived lipopolysaccharide, and ultimately resists high-fat diet-induced insulin resistance. Lachnospiraceae and butyrate have similar anti-GDM and anti-placental inflammation effects, and they can ameliorate placental function and pregnancy outcome effects probably by dampening placental immune dysfunction. These findings demonstrate the involvement of important placental inflammation-related mechanisms in the progression of GDM and the great potential of HFDFs to reduce susceptibility to GDM through gut-flora-placenta axis.

Effect of herbal extracts and Saroglitazar on high-fat diet-induced obesity, insulin resistance, dyslipidemia, and hepatic lipidome in C57BL/6J mice

We evaluated the effects of select herbal extracts (Tinospora cordifolia [TC], Tinospora cordifolia with Piper longum [TC + PL], Withania somnifera [WS], Glycyrrhiza glabra [GG], AYUSH–64 [AY-64], and Saroglitazar [S]) on various parameters in a diet-induced obesity mouse model. After 12 weeks of oral administration of the herbal extracts in high-fat diet (HFD)-fed C57BL/6J mice, we analyzed plasma biochemical parameters, insulin resistance (IR), liver histology, and the expression of inflammatory and fibrosis markers, along with hepatic lipidome. We also used a 3D hepatic spheroid model to assess their impact on profibrotic gene expression. Among the extracts, TC + PL showed a significant reduction in IR, liver weight, TNF-α, IL4, IL10 expression, and hepatic lipid levels (saturated triglycerides, ceramides, lysophosphocholines, acylcarnitines, diglycerides, and phosphatidylinositol levels). Saroglitazar reversed changes in body weight, IR, plasma triglycerides, glucose, insulin, and various hepatic lipid species (fatty acids, phospholipids, glycerophospholipids, sphingolipids, and triglycerides). With the exception of GG, Saroglitazar, and other extracts protected against palmitic acid-induced fibrosis marker gene expression in the 3D spheroids. TC + PL and Saroglitazar also effectively prevented HFD-induced insulin resistance, inflammation, and specific harmful lipid species in the liver.

4EBP2-regulated protein translation has a critical role in high-fat diet–induced insulin resistance in hepatocytes

A high-fat diet (HFD) plays a critical role in hepatocyte insulin resistance. Numerous models and factors have been proposed to elucidate the mechanism of palmitic acid (PA)-induced insulin resistance. However, proteomic studies of insulin resistance by HFD stimulation are usually performed under insulin conditions, leading to an unclear understanding of how a HFD alone affects hepatocytes. Here, we mapped the phosphorylation rewiring events in PA-stimulated HepG2 cells and found PA decreased the phosphorylation level of the eukaryotic translation initiation factor 4E-binding protein 2 (4EBP2) at S65/T70. Further experiments identified 4EBP2 as a key node of insulin resistance in either HFD mice or PA-treated cells. Reduced 4EBP2 levels increased glucose uptake and insulin sensitivity, whereas the 4EBP2_S65A/T70A mutation exacerbated PA-induced insulin resistance. Additionally, the nascent proteome revealed many glycolysis-related proteins translationally regulated by 4EBP2 such as hexokinase-2, pyruvate kinase PKM, TBC1 domain family member 4, and glucose-6-phosphate 1-dehydrogenase. In summary, we report the critical role of 4EBP2 in regulating HFD-stimulated insulin resistance in hepatocytes.

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.

Akebia saponin D from Dipsacus asper wall. Ex C.B. Clarke ameliorates skeletal muscle insulin resistance through activation of IGF1R/AMPK signaling pathway

Ethnopharmacological relevanceDipsacus asper Wall. Ex C.B. Clarke (DA), a perennial herb, is one of the most commonly used herbs in Traditional Chinese Medicine for strengthening muscles and bones and regulating blood vessels. Akebia saponin D (ASD/AVI) is a triterpenoid saponin extracted from the root of DA, which has favorable pharmacological properties such as anti-osteoporosis, anti-apoptosis, liver protection and hypolipidemic. Aim of the studyTo explore the underlying mechanisms and regulatory role of Akebia saponin D (ASD/AVI) on high-fat diet-induced insulin resistance in skeletal muscle. Materials and methodsC2C12 cells were used to explore the best concentration in the skeletal muscle insulin resistance model in an in vitro experiment. The protective effect of AVI on insulin resistance and the corresponding signaling pathway were detected by glucose content measurement, quantitative PCR, and Western blot. A high-fat diet STZ-induced insulin resistance mice model was used to evaluate the protective function of AVI in vivo. After four weeks of treatment, ITT, OGTT, and treadmill tests were applied to examine insulin sensitivity and their serum and skeletal muscle tissues were collected for further analysis. ResultsAVI effectively reduced body weight, blood glucose levels and calorie intake in insulin-resistant mice, and reduced lipid accumulation and in their muscle tissue. AVI also improved glucose uptake and insulin sensitivity in both in vivo and in vitro experiments. Following AVI administration, there was an increase in the expression of the AMPK signaling pathway. Our experiments further confirmed that AVI specifically targets the IGF1R, thereby more effectively regulating the insulin signaling pathway. ConclusionAVI improves type 2 diabetes-induced insulin resistance in skeletal muscle by activating the IGF1R-AMPK signaling pathway, promoting glucose uptake and energy metabolism in IR.

Red ginseng extracts ameliorate high-fat diet-induced obesity and insulin resistance by activating the intestinal TGR5-mediated bile acids signaling pathway

BackgroundObesity has emerged as a worldwide metabolic disease, given its rapid growth in global prevalence. Red ginseng extracts (RGS), one of the traditional processed products of ginseng, show the potential to improve the metabolic phenotype of obesity. However, the RGS mechanism for regulating obesity and late insulin resistance remains to be clarified. PurposeThis study aimed to emphasize the potential use of RGS in treatment of obesity and insulin resistance (IR) and explore the underlying mechanism affecting glucose and lipid metabolism improvements. MethodsThe role of RGS was evaluated in a high-fat diet (HFD) rodent model. Glucose tolerance test (GTT) and insulin tolerance test (ITT) were performed to characterize the glucose metabolism level. The expression of lipolysis proteins and uncoupling protein-1 (UCP-1) were investigated by western blot. Glucagon-like peptide-1 (GLP-1) and apical sodium-dependent bile acid transporter (ASBT) protein expression in the intestine were determined via immunofluorescence. UPLC-Q-TOF-MS were used to detect the alterations in bile acids (BAs) levels in serum, ileum, and inguinal white adipose tissue (iWAT). In addition, intestine-specific Tgr5 knockout mice were employed to verify the efficacy of RGS in improving obesity. ResultsRGS treatment alleviated dietary-induced dyslipidemia and IR in obese mice in a dose-dependent manner and improved glucose and insulin tolerance, and energy expenditure. RGS treatment significantly reduced lipid deposition and induced GLP-1 secretion in the intestine of wild-type mice but not in Tgr5ΔIN obese mice. Furthermore, RGS intervention increased BA levels in serum, ileum, and iWAT. The increase of circulating BAs in mice was related to the activation of ileal TGR5 and the promotion of ASBT translocation to the plasma membrane, thus affecting BA transport. Next, the increased level of circulating BAs entered the periphery, which might facilitate lipolysis and energy consumption by activating TGR5 in iWAT. ConclusionOur results demonstrated that RGS significantly alleviated HFD-induced obesity and insulin resistance in mice. RGS intervention improved glucose metabolism, promoted lipolysis, and energy metabolism by activating TGR5 in the intestine. In addition, we found that activating intestinal TGR5 facilitated the localization of ASBT to the plasma membrane, which ultimately promoted the transport of BAs to regulate metabolic phenotype.

291-OR: CREG1 Regulates Hepatic Insulin Sensitivity and Insulin Receptor Trafficking

CREG1 is a small glycoprotein in the endosomal-lysosomal system involved in endocytic trafficking. It contains 3 N-linked glycosylation sites and is highly expressed in the liver. To elucidate its physiological functions, we generated Creg1fl/fl mice using CRISPR technology. Whole-body and hepatocyte-specific deletion of Creg1 was achieved by crossing Creg1fl/fl with UBC-cre-ERT2 and Albumin-cre mice, respectively. Both knockout mice developed elevated glycemia, glucose intolerance, and resistance to the blood glucose-lowering effect of insulin. Loss of hepatic CREG1 also aggravated high-fat diet-induced insulin resistance and hyperinsulinemia. This is likely caused by impaired insulin receptor (IR) trafficking because IR expression on the hepatocyte surface was significant reduced in hepatocyte specific Creg1 knockout mice. In in vitro studies using cultured hepatocytes, CREG1 overexpression increased IR recycling to the cell surface and enhanced insulin signaling, whereas its knockdown had the opposite effect. These findings indicate a cell autonomous role of CREG1 in hepatocyte IR trafficking and insulin signaling. Furthermore, SNP database survey identified 3 missense mutations of CREG1 at the N216 glycosylation site (N216I, N216K, and N216Y). When overexpressed in human hepatocytes, the N216I mutant inhibited insulin signaling in a dominant negative fashion. Taken together, these results suggest CREG1 regulates hepatic insulin sensitivity and signaling likely through its effect on IR trafficking. CREG1 glycosylation at N216 may be required for its function in these processes. Disclosure Y.Qi: None. J.Liu: None. J.C.Chao: None. S.A.Rahimi: None. L.Y.Lee: Speaker's Bureau; Abbott. S.Li: None. Funding Rutgers Biomedical and Health Sciences

Effects of the pesticide deltamethrin on high fat diet-induced obesity and insulin resistance in male mice.

Worldwide, rates of metabolic diseases are rapidly increasing and environmental exposure to pesticides, pollutants and/or other chemicals may play a role. Reductions in Brown Adipose Tissue (BAT) thermogenesis, mediated in part by uncoupling protein 1 (Ucp1), are associated with metabolic diseases. In the current study, we investigated whether the pesticide deltamethrin (0.01-1mg/kg bw/day) incorporated into a high-fat diet and fed to mice housed at either room temperature (21°C) or thermoneutrality (29°C) would suppress BAT activity and accelerate the development of metabolic disease. Importantly, thermoneutrality allows for more accurate modeling of human metabolic disease. We found that, 0.01mg/kg bw/day of deltamethrin induced weight loss, improved insulin sensitivity and increased energy expenditure, effects that were associated with increases in physical activity. In contrast, exposure to 0.1 and 1mg/kg bw/day deltamethrin had no effect on any of the parameters examined. Deltamethrin treatment in mice did not alter molecular markers of BAT thermogenesis, despite observing suppression of UCP1 expression in cultured brown adipocytes. These data indicate that while deltamethrin inhibits UCP1 expression in vitro, 16wks exposure does not alter BAT thermogenesis markers nor exacerbates the development of obesity and insulin resistance in mice.