Diet-induced Insulin Resistance Research Articles

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.

The Role of Interferon Receptors α/β/γ Ablation During Western Diet-Induced Obesity and Insulin Resistance in the Inflectional Model AG129 Mice Strain.

Diet-induced obesity triggers elevation of circulating pro-inflammatory cytokines and acute-phase proteins, including interferons (IFNs). IFNs strongly contribute to low-grade inflammation associated with obesity-related complications, such as nonalcoholic fat liver disease and diabetes. In this study, AG129 mice model (double-knockout strain for IFN α/β/γ receptors) was fed with a high-fat high-sucrose (HFHS) diet (Western diet) for 20 weeks aiming to understand the impact of IFN receptor ablation on diet-induced obesity, insulin resistance, and nonalcoholic fat liver disease. Mice were responsive to the diet, becoming obese after 20 weeks of HFHS diet which was accompanied by 2-fold increase of white adipose tissues. Moreover, animals developed glucose and insulin intolerance, as well as dysregulation of insulin signaling mediators such as Insulin Receptor Substrate 1 (IRS1), protein kinase B (AKT), and S6 ribosomal protein. Liver increased interstitial cells, and lipid accumulation was also found, presenting augmented fibrotic markers (transforming growth factor beta 1 [Tgfb1], Keratin 18 [Krt18], Vimentin [Vim]), yet lower expression on IFN receptor downstream proteins (Toll-like receptor [TLR] 4, nuclear factor kappa-light-chain-enhancer of activated B cells [NFκB], and cAMP response element-binding protein [CREB]). Thus, IFN receptor ablation promoted effects on NFκB and CREB pathways, with no positive effects on systemic homeostasis in diet-induced obese mice. Therefore, we conclude that IFN receptor signaling is not essential for promoting the complications of diet-induced obesity and thus cannot be correlated with metabolic diseases in a noninfectious condition.

1563-P: Hepatic PHD3 Stimulates Gluconeogenesis and Aggravates Hyperglycemia and Type 2 Diabetes by Hydroxylating CRTC2 at Pro129 and Pro615

Hepatic gluconeogenesis is critical for metabolic adaption in response to fasting, and its abnormal elevation contributes to the pathogenesis of hyperglycemia and type 2 diabetes. However, whether and how protein hydroxylation regulates hepatic gluconeogenesis and glucose metabolism remains largely unknown. Here we report that PHD3 is identified as a fasting-induced factor and regulates hepatic gluconeogenesis through interaction and hydroxylation of CRTC2. Pro129 and Pro615 hydroxylation of CRTC2 following PHD3 activation is necessary for its nuclear translocation and association with CREB, and enhanced binding to promoters of gluconeogenic target genes in response to fasting or the cAMP activator forskolin. CRTC2 hydroxylation-stimulated gluconeogenic gene expression is independent of SIK-mediated phosphorylation of CRTC2. Liver-specific knockout of PHD3 (PHD3 LKO) mice or prolyl hydroxylase-deficient knockin mice with alanine mutation in PHD3 at Pro196 (PHD3 KI) show significant attenuated gluconeogenic genes, glycaemia and hepatic capacity to produce glucose during fasting or fed with high-fat, high-sucrose diet. The efficacies of glucagon or adenylyl cyclase activator forskolin on stimulating the expression of gluconeogenic enzymes, such as PEPCK and G6Pase, and on glucose output are abolished in PHD3-/- mouse primary hepatocytes. Importantly, Pro615 hydroxylation of CRTC2 by PHD3 is increased in livers of fasted mice, diet-induced insulin resistance or genetically obese ob/ob mice and humans with diabetes. Together, these findings increase our understanding of the molecular mechanisms linking protein hydroxylation to gluconeogenesis under physiological and insulin resistant conditions, and may offer therapeutic potential for treating sustained gluconeogenesis, hyperglycemia and type 2 diabetes. Disclosure Y.Xue: None. W.Su: None. J.Zhao: None. C.Gao: None. J.Wen: None. Y.Xu: None. W.Fu: None. J.C.Fang: None. Y.Li: None. A.Cui: None. S.Wei: None. F.Ma: None. Z.Liu: None. X.Fang: None. W.Li: None. Y.Liu: None. G.Cai: None. Funding National Key R&D Program of China (2019YFA0802502); National Natural Science Foundation of China (81925008, 82073061, 82170587, 32100943); Ministry of Science and Technology of China (2020YFA0803301); Open Project Program of Metabolic Vascular Diseases Key Laboratory of Sichuan Province (2022MVDKL-K2); Shandong Natural Science Foundation (ZR2020MH206); China Postdoctoral Science Foundation (2021M693273)

77-OR: Targeting JunB Induces a Shift from Low- to High-Thermogenic Adipocytes and Ameliorates Diet-Induced Insulin Resistance

The coexistence of brown adipocytes with low and high thermogenic activity is a fundamental feature of brown adipose tissue (BAT) heterogeneity and plasticity. However, the mechanisms that govern thermogenic adipocyte heterogeneity and its significance in obesity and metabolic disease remain poorly understood. In the current study, we identified a population of JunB-enriched adipocytes (JunB+ adipocytes) within the brown fat depot that exhibits lower thermogenic capacity and fewer and smaller lipid droplets compared to high-thermogenic adipocytes. This population of JunB+ adipocytes exhibited marked expansion during obesity, in part through induction of pro-inflammatory cytokines TNFα and IL-6. Depletion of JunB in adipocytes or UCP1+ adipocytes increased the fraction of adipocytes exhibiting high mitochondrial content and thermogenic capacity, leading to enhanced basal and cold-induced energy expenditure and protection against diet-induced obesity and insulin resistance. Mechanistically, JunB directly binds to the promoter of estrogen-related receptor α (Errα), a downstream effector of PGC1α, and suppresses its transcriptional function. JunB antagonizes the stimulatory effects of PGC1α-ERRα on mitochondrial biogenesis and high-thermogenic adipocyte development. Taken together, our studies uncover a novel mechanism involving JunB that shapes thermogenic adipocyte heterogeneity and serves a critical role in maintaining systemic metabolic health. Disclosure X.Zhang: None. C.Wang: None. M.Liu: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK110439); American Heart Association (20POST35120020)

1489-P: iPLA2gamma as a Mediator of Lipid-Induced Metabolic Inflammation and Insulin Resistance

We have reported that bromenol lactone (BEL) improves metabolic profile. Here, we studied effect of BEL and its target iPLA2 in inflammasome which is a crucial in insulin resistance and metabolic inflammation. BEL inhibited inflammasome by LPS+palmitic acid (PA). BEL also ameliorated mitochondrial ROS and mitochondrial potential loss by LPS+PA, explaining reduced inflammasome. BEL administration in vivo also reduced metabolic inflammation and inflammasome. iPLA2gamma-KO but not iPLA2beta-KO macrophages showed reduced inflammasome by LPS+PA. Mitochondrial ROS and mitochondrial potential loss by LPS+PA were markedly reduced by iPLA2gamma KO. Cardiolipin content in macrophages was reduced by LPS+PA, which was recovered by BEL or myxothiazol, an inhibitor of mitochondrial complex bc1. Cardiolipin loss by LPS+PA was also ameliorated by iPLA2gamma KO. Cardiolipin liposome or expression of CRLS1, a gene for rate-limiting step of cardiolipin biosynthesis, reduced inflammasome by LPS+PA, while CRLS1 siRNA aggravated, suggesting that reduced cardiolipin content is critical in inflammasome by LPS+PA. iPLA2gamma-KO mice were protected from diet-induced insulin resistance, associated with reduced inflammasome and metabolic inflammation. These results suggest that initial reduction of cardiolipin content by PA-induced ROS probably due to removal of oxidized cardiolipin by iPLA2gamma might induce further mitochondrial ROS accumulation likely due to compromised mitochondrial complex activity, which would eventually lead to massive mitochondrial ROS production, marked loss of mitochondrial cardiolipin, profound mitochondrial dysfunction, and finally metabolic inflammation with lipid-induced insulin resistance, through a feed-forward mechanism. Replenishment of cardiolipin could a novel modality for treatment of diet-induced insulin resistance through recovery of mitochondrial function and amelioration of lipid-mediated inflammasome or metabolic inflammation. Disclosure M.Lee: None. H.Kang: None. Funding National Research Foundation of Korea (2019R1A2C3002924)

94-OR: Myeloid-Specific ERa Deletion Disrupts Mitochondrial Function Driving Iron Accumulation and Cardiometabolic Disease

Sex differences in metabolism and cardiometabolic disease risk are well described. Because estrogen action is thought to underlie female-biased protection of immunometabolism and cardiometabolic health, we selectively deleted the estrogen receptor alpha (ERa, encoded by Esr1) from myeloid cells of mice to understand the impact of estrogen action on macrophage function. Our previous findings in other glucoregulatory cell types point to an important role of ERa in the control of mitochondrial form and function. Mitochondria play a critical role in innate immunity, and disruption of mitochondrial function is linked to the pathogenesis of cardiometabolic disease. In addition to a primary role in energy production, mitochondria are central in the regulation of iron homeostasis, a critical process governing immune cell function. Myeloid-specific Esr1 knockout mice (MACER) showed increased diet-induced glucose intolerance, insulin resistance, adiposity, and atherosclerotic lesion area compared with f/f controls. A key phenotype of MACER mice was marked accumulation of iron in liver, spleen, gonadal white adipose tissue, and bone marrow-derived macrophages compared with f/f controls. Specifically, iron accumulated in mitochondria from macrophages within tissues of MACER mice. Iron accumulation was linked with alteration of mitochondrial inner and outer membrane morphology and mtDNA replication machinery, and associated with increased transferrin receptor (Tfrc) expression and cellular inflammation driven by interleukin-1-β. We utilized chromatin immunoprecipitation approaches to identify novel ERa-regulated chromatin structures and target genes that modulate immunometabolism of macrophages. Our findings indicate that Esr1 is critical in the regulation of mitochondrial metabolism and iron homeostasis in macrophages, and the action of ERa is critical for the protection against inflammation and cardiometabolic-related disease. Disclosure H.Iwasaki: None. B.K.Leyva: None. A.Ma: None. N.L.Yang: None. P.H.Tran: None. Z.Zhou: None. A.L.Hevener: None. Funding National Institutes of Health (DK128957)

1561-P: Dietary Proteins Impact Glucose Tolerance and Hepatic Insulin Resistance in Mice through Modulation of the Urea Cycle

We recently reported that dietary proteins (DP) modulate diet-induced obesity and insulin resistance in mice (Nat Commun 12: 3377, 2021). We posit that these metabolic alterations are caused by differential activation of the hepatic urea cycle in response to different amino acid (AA) compositions and total nitrogen load. Objective: To test whether DP sources alter hepatic metabolism and insulin resistance through the urea cycle. Methods: Metabolic phenotypes, hepatic urea cycle and insulin resistance were measured in mice fed low-fat, low-sucrose (LFLS) or high-fat, high-sucrose (HFHS) diets containing either pork (PP), soy (SP) or casein (CP) protein for 12 weeks. Based on their AA composition, PP had the highest nitrogen load, followed by SP and CP. Results: When compared to SP and CP, feeding PP to HFHS mice induced more glucose intolerance which was correlated with higher post-prandial AA-derived nitrogen load in the portal vein. PP feeding in HFHS mice induced hepatic insulin resistance, revealed by impaired insulin-induced Akt phosphorylation on Ser473. Mice fed the LFLS diet were, however, protected from PP-induced glucose intolerance and insulin resistance, and this was associated with robust increase in the protein levels of urea cycle enzymes (CPS1, OTC) in the liver. In starked contrast, induction of urea cycle enzymes was blunted in the liver of PP-fed HFHS mice. PP feeding also increased the expression of inducible nitric oxide synthase (iNOS) and reactive oxygen species (ROS) as showed by DHE staining of liver sections. Conclusion: Dietary PP increases total nitrogen load activating the urea cycle, which may protect against metabolic dysfunction and hepatic insulin resistance in LFLS mice. This protective mechanism is lost in PP-fed HFHS mice, likely by downregulation of urea cycle activity, when the liver is overloaded with dietary fat. iNOS induction could be acting as an alternative nitrogen handling pathway, causing a build-up of mitochondrial ROS. Disclosure F.Bégin: None. A.Caron: None. A.Marette: Advisory Panel; Valbiotis, Amancia, Plexus, Acasti.

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

Decreased YB-1 expression denervates brown adipose tissue and contributes to age-related metabolic dysfunction.

Thermogenesis in brown adipose tissue (BAT) declines with aging, however, the underlying mechanism remains unclear. Here, we show that the expression of Y-box binding protein 1 (YB-1), a critical DNA/RNA binding protein, decreased in the BAT of aged mice due to the reduction of microbial metabolite butyrate. Genetic ablation of YB-1 in the BAT accelerated diet-induced obesity and BAT thermogenic dysfunction. In contrast, overexpression of YB-1 in the BAT of aged mice was sufficient to promote BAT thermogenesis, thus alleviating diet-induced obesity and insulin resistance. Interestingly, YB-1 had no direct effect on adipose UCP1 expression. Instead, YB-1 promoted axon guidance of BAT via regulating the expression of Slit2, thus potentiating sympathetic innervation and thermogenesis. Moreover, we have identified that a natural compound Sciadopitysin, which promotes YB-1 protein stability and nuclear translocation, alleviated BAT aging and metabolic disorders. Together, we reveal a novel fat-sympathetic nerve unit in regulating BAT senescence and provide a promising strategy against age-related metabolic disorders.

Salidroside alleviates diet-induced obesity and insulin resistance by activating Nrf2/ARE pathway and enhancing the thermogenesis of adipose tissues.

Recent reports suggest that salidroside protects cardiomyocytes from oxidative injury and stimulates glucose uptake by skeletal muscle cells. Despite these findings, the therapeutic potential of salidroside in the treatment of obesity and insulin resistance remains uncertain and requires further investigation. In the present study, the treatment effect of salidroside on the onset and development of the obese phenotype and insulin resistance as well as the underlying mechanisms was investigated using long-term high-fat diet-induced obese mice supplemented with salidroside. We used biochemical kits to determine serum biochemical parameters (including triacylglycerol, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, fasting glucose, and insulin). The results show that salidroside-supplemented animals showed better glucose tolerance and insulin sensitivity, decreased blood lipids, and weight gain (p < .05). Protein expression of p-Nrf2 and Nrf2 was analyzed by western blotting, and the mRNA levels of thermogenic-related genes (Ucp1, Pgc1a, Prdm16, and Cidea) were detected by quantitative RT-PCR. The results show an improvement in lipid peroxidation and Nrf2/ARE signaling, as well as an increased expression of the Ucp1, Pgc1a, Prdm16, and Cidea (p < .05). Our evidence suggests that salidroside alleviates diet-induced obesity and insulin resistance potentially by activating Nrf2/ARE pathway and enhancing the thermogenesis of adipose tissues. This induction represents a potential technique for the management of comorbidities related to obesity and its prevention.

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.

Brown Adipose Tissue PPARγ Is Required for the Insulin-Sensitizing Action of Thiazolidinediones.

Brown adipose tissue (BAT) plays a critical role in metabolic homeostasis. BAT dysfunction is associated with the development of obesity through an imbalance between energy expenditure and energy intake. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is the master regulator of adipogenesis. However, the roles of PPARγ and thiazolidinediones (TZDs) in the regulation of BAT metabolism remain unclear. TZDs, which are selective PPARγ activators, improve systemic insulin resistance in animals and humans. In the present study, we generated brown adipocyte-specific PPARγ-deficient mice (BATγKO) to examine the in vivo roles of PPARγ and TZDs in BAT metabolism. In electron microscopic examinations, brown adipocyte-specific PPARγ deletion promoted severe whitening of brown fat and morphological alteration of mitochondria. Brown adipocyte-specific PPARγ deletion also reduced mRNA expression of BATselective genes. Although there was no difference in energy expenditure between control and BATγKO mice in calorimetry, norepinephrine-induced thermogenesis was impaired in BATγKO mice. Moreover, pioglitazone treatment improved diet-induced insulin resistance in the control mice but not in the BATγKO mice. These findings suggest that BAT PPARγ is necessary for the maintenance of brown adipocyte function and for the insulin-sensitizing action of TZDs.

Proline hydroxylation of CREB-regulated transcriptional coactivator 2 controls hepatic glucose metabolism

Prolyl hydroxylase domain (PHD) enzymes change HIF activity according to oxygen signal; whether it is regulated by other physiological conditions remains largely unknown. Here, we report that PHD3 is induced by fasting and regulates hepatic gluconeogenesis through interaction and hydroxylation of CRTC2. Pro129 and Pro615 hydroxylation of CRTC2 following PHD3 activation is necessary for its association with cAMP-response element binding protein (CREB) and nuclear translocation, and enhanced binding to promoters of gluconeogenic genes by fasting or forskolin. CRTC2 hydroxylation-stimulated gluconeogenic gene expression is independent of SIK-mediated phosphorylation of CRTC2. Liver-specific knockout of PHD3 (PHD3 LKO) or prolyl hydroxylase-deficient knockin mice (PHD3KI) show attenuated fasting gluconeogenic genes, glycemia, and hepatic capacity to produce glucose during fasting or fed with high-fat, high-sucrose diet. Importantly, Pro615 hydroxylation of CRTC2 by PHD3 is increased in livers of fasted mice, diet-induced insulin resistance or genetically obese ob/ob mice, and humans with diabetes. These findings increase our understanding of molecular mechanisms linking protein hydroxylation to gluconeogenesis and may offer therapeutic potential for treating excessive gluconeogenesis, hyperglycemia, and type 2 diabetes.

The IP6K Inhibitor LI-2242 Ameliorates Diet-Induced Obesity, Hyperglycemia, and Hepatic Steatosis in Mice by Improving Cell Metabolism and Insulin Signaling.

Obesity and nonalcoholic fatty liver disease (NAFLD) are global health concerns, and thus, drugs for the long-term treatment of these diseases are urgently needed. We previously discovered that the inositol pyrophosphate biosynthetic enzyme IP6K1 is a target in diet-induced obesity (DIO), insulin resistance, and NAFLD. Moreover, high-throughput screening (HTS) assays and structure-activity relationship (SAR) studies identified LI-2242 as a potent IP6K inhibitor compound. Here, we tested the efficacy of LI-2242 in DIO WT C57/BL6J mice. LI-2242 (20 mg/kg/BW daily, i.p.) reduced body weight in DIO mice by specifically reducing the accumulation of body fat. It also improved glycemic parameters and reduced hyperinsulinemia. LI-2242-treated mice displayed reduced the weight of various adipose tissue depots and an increased expression of metabolism- and mitochondrial-energy-oxidation-inducing genes in these tissues. LI-2242 also ameliorated hepatic steatosis by reducing the expression of genes that enhance lipid uptake, lipid stabilization, and lipogenesis. Furthermore, LI-2242 enhances the mitochondrial oxygen consumption rate (OCR) and insulin signaling in adipocytes and hepatocytes in vitro. In conclusion, the pharmacologic inhibition of the inositol pyrophosphate pathway by LI-2242 has therapeutic potential in obesity and NAFLD.

Hachimijiogan, a traditional herbal medicine, modulates adipose cell function and ameliorates diet-induced obesity and insulin resistance in mice.

Hachimijiogan (HJG) has originally been used to ameliorate a variety of symptoms associated with low ambient temperatures. However, its pharmacological action in metabolic organs remains unclear. We hypothesized that HJG may modulate metabolic function and have a potential therapeutic application to metabolic diseases. To test this hypothesis, we investigated metabolic action of HJG in mice. Male C57BL/6J mice chronically administered with HJG showed a reduction in adipocyte size with increased transcription of beige adipocyte-related genes in subcutaneous white adipose tissue. HJG-mixed high-fat diet (HFD)-fed mice showed alleviation of HFD-induced weight gain, adipocyte hypertrophy, liver steatosis with a significant reduction in circulating leptin and Fibroblast growth factor 21 despite no changes in food intake or oxygen consumption. Feeding an HJG-mixed HFD following 4-weeks of HFD feeding, while a limited effect on body weight, improved insulin sensitivity with a reversal of decreased circulating adiponectin. In addition, HJG improved insulin sensitivity in the leptin-deficient mice without significant effects on body weight. Treatment with n-butanol soluble extracts of HJG potentiated transcription of Uncoupling protein 1 mediated by β3-adrenergic agonism in 3T3L1 adipocytes. These findings provide evidence that HJG modulates adipocyte function and may exert preventive or therapeutic effects against obesity and insulin resistance.

NMP4, an Arbiter of Bone Cell Secretory Capacity and Regulator of Skeletal Response to PTH Therapy.

The skeleton is a secretory organ, and the goal of some osteoporosis therapies is to maximize bone matrix output. Nmp4 encodes a novel transcription factor that regulates bone cell secretion as part of its functional repertoire. Loss of Nmp4 enhances bone response to osteoanabolic therapy, in part, by increasing the production and delivery of bone matrix. Nmp4 shares traits with scaling factors, which are transcription factors that influence the expression of hundreds of genes to govern proteome allocation for establishing secretory cell infrastructure and capacity. Nmp4 is expressed in all tissues and while global loss of this gene leads to no overt baseline phenotype, deletion of Nmp4 has broad tissue effects in mice challenged with certain stressors. In addition to an enhanced response to osteoporosis therapies, Nmp4-deficient mice are less sensitive to high fat diet-induced weight gain and insulin resistance, exhibit a reduced disease severity in response to influenza A virus (IAV) infection, and resist the development of some forms of rheumatoid arthritis. In this review, we present the current understanding of the mechanisms underlying Nmp4 regulation of the skeletal response to osteoanabolics, and we discuss how this unique gene contributes to the diverse phenotypes among different tissues and stresses. An emerging theme is that Nmp4 is important for the infrastructure and capacity of secretory cells that are critical for health and disease.

Abstract 317: Adipose Tissue Phosphatidylcholine Remodeling Modulates Insulin Signaling

Phosphatidylcholines (PCs) are major components of cell membranes. Previous studies indicated that membrane PC composition is regulated by lysophosphatidylcholine acyltransferase (LPCAT) and an alteration in cell membrane saturation has been implicated in a variety of metabolic disorders, including obesity, insulin resistance, and cardiovascular diseases. LPCAT3 is the major isoform of LPCAT in adipose tissues. To study the impact of LPCAT3 on adipose tissue lipid metabolism and its metabolic consequences, we prepared adipocyte-specific Lpcat3 gene knockout (KO) mice. Based on the analysis of bulk RNA sequencing, we gained insights to investigate the role of LPCAT3 in regulating adipose tissue insulin signaling. We revealed that LPCAT3 deficiency significantly reduced polyunsaturated PCs in the plasma membrane of adipocytes, resulting in increased insulin sensitivity. Mechanistically, we demonstrated that inhibiting LPCAT3 in adipose tissue promoted insulin receptor and AKT activation by influencing membrane lipid rafts and attenuated diet-induced insulin resistance. Conversely, adipose tissues from ob/ob, db/db, and high fat diet-fed mice had significantly higher LPCAT3 activity which blunts insulin signaling. Moreover, the treatment of polyunsaturated PCs on human or mouse mature adipocytes significantly worsened cellular insulin signaling. Our findings suggest that targeting LPCAT3 in adipose tissues to manipulate membrane phospholipid saturation would be a new strategy to treat insulin resistance.

High sugar diet-induced insulin resistance in glia impairs axonal clearance after injury by downregulating Draper signaling

Obesity significantly increases the risk for developing neurodegenerative disorders, yet the precise mechanisms underlying this connection remain unclear. Defects in glial phagocytic function is a key feature of neurodegenerative disorders, as delayed clearance of neuronal debris can result in inflammation, cytotoxicity, secondary neuronal death, and poor nervous system recovery. Whether or how diet-induced obesity disrupts glial phagocytosis is unknown. Here, using a Drosophila diet-induced obesity model, we show that subjecting adult flies to a chronic high sugar diet (HSD) treatment delays the clearance of degenerating axons by causing glial insulin resistance. We find that HSD downregulates the basal and injury-induced expression of the glia-associated phagocytic receptor, Draper. Genetically inducing Insulin release from the Insulin producing cells (IPCs) phenocopies the HSD-induced Draper downregulation and insulin resistance, while attenuating insulin release from the IPCs rescues HSD-induced Draper downregulation and insulin resistance. Significantly, we show that genetically stimulating Phosphoinositide 3-kinase (PI3K), a downstream effector of Insulin receptor signaling rescues HSD-induced glial defects. Together, we provide mechanistic insights into how HSD alters glial phagocytic function in the adult brain. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Heptadecanoic Acid Is Not a Key Mediator in the Prevention of Diet-Induced Hepatic Steatosis and Insulin Resistance in Mice.

Epidemiological studies found that the intake of dairy products is associated with an increased amount of circulating odd-chain fatty acids (OCFA, C15:0 and C17:0) in humans and further indicate that especially C17:0 is associated with a lower incidence of type 2 diabetes. However, causal relationships are not elucidated. To provide a mechanistic link, mice were fed high-fat (HF) diets supplemented with either milk fat or C17:0 for 20 weeks. Cultured primary mouse hepatocytes were used to distinguish differential effects mediated by C15:0 or C17:0. Despite an induction of OCFA after both dietary interventions, neither long-term milk fat intake nor C17:0 supplementation improved diet-induced hepatic lipid accumulation and insulin resistance in mice. HF feeding with milk fat actually deteriorates liver inflammation. Treatment of primary hepatocytes with C15:0 and C17:0 suppressed JAK2/STAT3 signaling, but only C15:0 enhanced insulin-stimulated phosphorylation of AKT. Overall, the data indicate that the intake of milk fat and C17:0 do not mediate health benefits, whereas C15:0 might be promising in further studies.

Fructose-1,6-bisphosphatase is a nonenzymatic safety valve that curtails AKT activation to prevent insulin hyperresponsiveness

Insulin inhibits gluconeogenesis and stimulates glucose conversion to glycogen and lipids. How these activities are coordinated to prevent hypoglycemia and hepatosteatosis is unclear. Fructose-1,6-bisphosphatase (FBP1) is rate controlling for gluconeogenesis. However, inborn human FBP1 deficiency does not cause hypoglycemia unless accompanied by fasting or starvation, which also trigger paradoxical hepatomegaly, hepatosteatosis, and hyperlipidemia. Hepatocyte FBP1-ablated mice exhibit identical fasting-conditional pathologies along with AKT hyperactivation, whose inhibition reversed hepatomegaly, hepatosteatosis, and hyperlipidemia but not hypoglycemia. Surprisingly, fasting-mediated AKT hyperactivation is insulin dependent. Independently of its catalytic activity, FBP1 prevents insulin hyperresponsiveness by forming a stable complex with AKT, PP2A-C, and aldolase B (ALDOB), which specifically accelerates AKT dephosphorylation. Enhanced by fasting and weakened by elevated insulin, FBP1:PP2A-C:ALDOB:AKT complex formation, which is disrupted by human FBP1 deficiency mutations or a C-terminal FBP1 truncation, prevents insulin-triggered liver pathologies and maintains lipid and glucose homeostasis. Conversely, an FBP1-derived complex disrupting peptide reverses diet-induced insulin resistance.