HFD-induced Glucose Intolerance Research Articles

N-acetyl-L-cysteine reduces testis ROS in obese fathers but fails in protecting offspring from acquisition of epigenetic traits at cyp19a1 and IGF11/H19 ICR loci.

Paternal nutrition before conception has a marked impact on offspring's risk of developing metabolic disorders during adulthood. Research on human cohorts and animal models has shown that paternal obesity alters sperm epigenetics (DNA methylation, protamine-to-histone replacement, and non-coding RNA content), leading to adverse health outcomes in the offspring. So far, the mechanistic events that translate paternal nutrition into sperm epigenetic changes remain unclear. High-fat diet (HFD)-driven paternal obesity increases gonadic Reactive Oxygen Species (ROS), which modulate enzymes involved in epigenetic modifications of DNA during spermatogenesis. Thus, the gonadic pool of ROS might be responsible for transducing paternal health status to the zygote through germ cells. The involvement of ROS in paternal intergenerational transmission was assessed by modulating the gonadic ROS content in male mice. Testicular oxidative stress induced by HFD was counterbalanced by N-acetylcysteine (NAC), an antioxidant precursor of GSH. The sires were divided into four feeding groups: i) control diet; ii) HFD; iii) control diet in the presence of NAC; and iv) HFD in the presence of NAC. After 8weeks, males were mated with females that were fed a control diet. Antioxidant treatment was then evaluated in terms of preventing the HFD-induced transmission of dysmetabolic traits from obese fathers to their offspring. The offspring were weaned onto a regular control diet until week 16 and then underwent metabolic evaluation. The methylation status of the genomic region IGFII/H19 and cyp19a1 in the offspring gDNA was also assessed using Sanger sequencing and methylation-dependent qPCR. Supplementation with NAC protected sires from HFD-induced weight gain, hyperinsulinemia, and glucose intolerance. NAC reduced oxidative stress in the gonads of obese fathers and improved sperm viability. However, NAC did not prevent the transmission of epigenetic modifications from father to offspring. Male offspring of HFD-fed fathers, regardless of NAC treatment, exhibited hyperinsulinemia, glucose intolerance, and hypoandrogenism. Additionally, they showed altered methylation at the epigenetically controlled loci IGFII/H19 and cy19a1. Although NAC supplementation improved the health status and sperm quality of HFD-fed male mice, it did not prevent the epigenetic transmission of metabolic disorders to their offspring. Different NAC dosages and antioxidants other than NAC might represent alternatives to stop the intergenerational transmission of paternal dysmetabolic traits.

Atractylodes Lancea and Its Constituent, Atractylodin, Ameliorates Metabolic Dysfunction-Associated Steatotic Liver Disease via AMPK Activation.

Metabolic dysfunction-associated steatotic liver disease (MASLD), which encompasses a spectrum of conditions ranging from simple steatosis to hepatocellular carcinoma, is a growing global health concern associated with insulin resistance. Since there are limited treatment options for MASLD, this study investigated the therapeutic potential of Atractylodes lancea, a traditional herbal remedy for digestive disorders in East Asia, and its principal component, atractylodin, in treating MASLD. Following 8 weeks of high-fat diet (HFD) feeding, mice received oral doses of 30, 60, or 120 mg/kg of Atractylodes lancea. In HFD-fed mice, Atractylodes lancea treatment reduced the body weight; serum triglyceride, total cholesterol, and alanine aminotransferase levels; and hepatic lipid content. Furthermore, Atractylodes lancea significantly ameliorated fasting serum glucose, fasting serum insulin, and homeostatic model assessment of insulin resistance levels in response to HFD. Additionally, a glucose tolerance test demonstrated improved glucose homeostasis. Treatment with 5 or 10 mg/kg atractylodin also resulted in anti-obesity, anti-steatosis, and glucose-lowering effects. Atractylodin treatment resulted in the downregulation of key lipogenic genes (Srebf1, Fasn, Scd2, and Dgat2) and the upregulation of genes regulated by peroxisome proliferator-activated receptor-α. Notably, the molecular docking model suggested a robust binding affinity between atractylodin and AMP-activated protein kinase (AMPK). Atractylodin activated AMPK, which contributed to SREBP1c regulation. In conclusion, our results revealed that Atractylodes lancea and atractylodin activated the AMPK signaling pathway, leading to improvements in HFD-induced obesity, fatty liver, and glucose intolerance. This study suggests that the phytochemical, atractylodin, can be a treatment option for MASLD.

Luteolin alleviates muscle atrophy, mitochondrial dysfunction and abnormal FNDC5 expression in high fat diet-induced obese rats and palmitic acid-treated C2C12 myotubes

Obesity is associated with a series of skeletal muscle impairments and dysfunctions, which are characterized by metabolic disturbances and muscle atrophy. Luteolin is a phenolic phytochemical with broad pharmacological activities. The present study aimed to evaluate the protective effects of Luteolin on muscle function and explore the potential mechanisms in high-fat diet (HFD)-induced obese rats and palmitic acid (PA)-treated C2C12 myotubes. Male Sprague-Dawley (SD) rats were fed with a control diet or HFD and orally administrated 0.5% sodium carboxymethyl cellulose (vehicle) or Luteolin (25, 50 and 100 mg/kg, respectively) for 12 weeks. The results showed that Luteolin ameliorated HFD-induced body weight gain, glucose intolerance and hyperlipidemia. Luteolin also alleviated muscle atrophy, decreased ectopic lipid deposition and prompted muscle-fiber-type conversion in the skeletal muscle. Meanwhile, we observed an evident improvement in mitochondrial quality control and respiratory capacity, accompanied by reduced oxidative stress. Mechanistic studies indicated that AMPK/SIRT1/PGC-1α signaling pathway plays a key role in the protective effects of Luteolin on skeletal muscle in the obese states, which was further verified by using specific inhibitors of AMPK and SIRT1. Moreover, the mRNA expression levels of markers in brown adipocyte formation were significantly up-regulated post Luteolin supplementation in different adipose depots. Taken together, these results revealed that Luteolin supplementation might be a promising strategy to prevent obesity-induced loss of mass and biological dysfunctions of skeletal muscle.

Human milk oligosaccharide 2’-fucosyllactose protects against high-fat diet-induced obesity by changing intestinal mucus production, composition and degradation linked to changes in gut microbiota and faecal proteome profiles in mice

ObjectiveTo decipher the mechanisms by which the major human milk oligosaccharide (HMO), 2’-fucosyllactose (2’FL), can affect body weight and fat mass gain on high-fat diet (HFD) feeding in mice. We...

GPR55 Antagonist CID16020046 Attenuates Obesity-Induced Airway Inflammation by Suppressing Chronic Low-Grade Inflammation in the Lungs.

GPR55 is a receptor for lysophosphatidylinositols (LPIs) in digestive metabolites. Overnutrition leads to obesity, insulin resistance, and increased LPI levels in the plasma. The involvement of LPIs and GPR55 in adiposity, hepatic steatosis, and atherosclerosis has been previously elucidated. However, the therapeutic efficacy of GPR55 antagonists against obesity-induced airway inflammation has not been studied. The present study investigated whether CID16020046, a selective antagonist of GPR55, could modulate obesity-induced airway inflammation caused by a high-fat diet (HFD) in C57BL/6 mice. Administration of CID16020046 (1 mg/kg) inhibits HFD-induced adiposity and glucose intolerance. Analysis of immune cells in BALF showed that CID16020046 inhibited HFD-induced increase in immune cell infiltration. Histological analysis revealed the HFD induced hypersecretion of mucus and extensive fibrosis in the lungs. CID16020046 inhibited these HFD-induced pathological features. qRT-PCR revealed the HFD-induced increase in the expression of Ifn-γ, Tnf-α, Il-6, Il-13, Il-17A, Il-1β, Nlrp3, and Mpo mRNAs in the lungs. CID16020046 inhibited the HFD-induced increases in these genes. The expression levels of adipokines were regulated by the HFD and CID16020046. AdipoQ in the lungs and gonadal white adipose tissue was decreased by the HFD and reversed by CID16020046. In contrast, Lep was increased by the HFD and suppressed by CID16020046. The findings suggest the potential application of the GPR55 antagonist CID16020046 in obesity-induced airway inflammation.

Diacylglycerol kinase delta overexpression improves glucose clearance and protects against the development of obesity

Background and aimDiacylglycerol kinase (DGK) isoforms catalyze an enzymatic reaction that removes diacylglycerol (DAG) and thereby terminates protein kinase C signaling by converting DAG to phosphatidic acid. DGKδ (type II isozyme) downregulation causes insulin resistance, metabolic inflexibility, and obesity. Here we determined whether DGKδ overexpression prevents these metabolic impairments. MethodsWe generated a transgenic mouse model overexpressing human DGKδ2 under the myosin light chain promoter (DGKδ TG). We performed deep metabolic phenotyping of DGKδ TG mice and wild-type littermates fed chow or high-fat diet (HFD). Mice were also provided free access to running wheels to examine the effects of DGKδ overexpression on exercise-induced metabolic outcomes. ResultsDGKδ TG mice were leaner than wild-type littermates, with improved glucose tolerance and increased skeletal muscle glycogen content. DGKδ TG mice were protected against HFD-induced glucose intolerance and obesity. DGKδ TG mice had reduced epididymal fat and enhanced lipolysis. Strikingly, DGKδ overexpression recapitulated the beneficial effects of exercise on metabolic outcomes. DGKδ overexpression and exercise had a synergistic effect on body weight reduction. Microarray analysis of skeletal muscle revealed common gene ontology signatures of exercise and DGKδ overexpression that were related to lipid storage, extracellular matrix, and glycerophospholipids biosynthesis pathways. ConclusionOverexpression of DGKδ induces adaptive changes in both skeletal muscle and adipose tissue, resulting in protection against HFD-induced obesity. DGKδ overexpression recapitulates exercise-induced adaptations on energy homeostasis and skeletal muscle gene expression profiles.

ADAR2 deficiency ameliorates non-alcoholic fatty liver disease and muscle atrophy through modulating serum amyloid A1.

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide. Sarcopenia is a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength, which is commonly associated with NAFLD. Adenosine-to-inosine editing, catalysed by adenosine deaminase acting on RNA (ADAR), is an important post-transcriptional modification of genome-encoded RNA transcripts. Three ADAR gene family members, including ADAR1, ADAR2 and ADAR3, have been identified. However, the functional role of ADAR2 in obesity-associated NAFLD and sarcopenia remains unclear. ADAR2+/+/GluR-BR/R mice (wild type [WT]) and ADAR2-/-/GluR-BR/R mice (ADAR2 knockout [KO]) were subjected to feeding with standard chow or high-fat diet (HFD) for 20weeks at the age of 5weeks. The metabolic parameters, hepatic lipid droplet, grip strength test, rotarod test, muscle weight, fibre cross-sectional area (CSA), fibre types and protein associated with protein degradation were examined. Systemic and local tissues serum amyloid A1 (SAA1) were measured. The effects of SAA1 on C2C12 myotube atrophy were investigated. ADAR2 KO mice fed with HFD exhibited lower body weight (-7.7%, P<0.05), lower liver tissue weight (-20%, P<0.05), reduced liver lipid droplets in concert with a decrease in hepatic triglyceride content (-24%, P<0.001) and liver injury (P<0.01). ADAR2 KO mice displayed protection against HFD-induced glucose intolerance, insulin resistance and dyslipidaemia. Skeletal muscle mass (P<0.01), muscle strength (P<0.05), muscle endurance (P<0.001) and fibre size (CSA; P<0.0001) were improved in ADAR2 KO mice fed with HFD compared with WT mice fed with HFD. Muscle atrophy-associated transcripts, such as forkhead box protein O1, muscle atrophy F-box/atrogin-1 and muscle RING finger 1/tripartite motif-containing 63, were decreased in ADAR2 KO mice fed with HFD compared with WT mice fed with HFD. ADAR2 deficiency attenuates HFD-induced local liver and skeletal muscle tissue inflammation. ADAR2 deficiency abolished HFD-induced systemic (P<0.01), hepatic (P<0.0001) and muscular (P<0.001) SAA1 levels. C2C12 myotubes treated with recombinant SAA1 displayed a decrease in myotube length (-37%, P<0.001), diameter (-20%, P<0.01), number (-39%, P<0.001) and fusion index (-46%, P<0.01). Myogenic markers (myosin heavy chain and myogenin) were decreased in SAA1-treated myoblast C2C12 cells. These results provide novel evidence that ADAR2 deficiency may be important in obesity-associated sarcopenia and NAFLD. Increased SAA1 might be involved as a regulatory factor in developing sarcopenia in NAFLD.

Sterol Regulatory Element Binding Protein 1: A Mediator for High-Fat Diet–Induced Hepatic Gluconeogenesis and Glucose Intolerance in Fish

BackgroundSterol regulatory element binding protein (SREBP) 1 is considered to be a crucial regulator for lipid synthesis in vertebrates. However, whether SREBP1 could regulate hepatic gluconeogenesis under high-fat diet (HFD) condition is still unknown, and the underlying mechanism is also unclear. ObjectivesThis study aimed to determine gluconeogenesis-related gene and protein expressions in response to HFD in large yellow croaker and explore the role and mechanism of SREBP1 in regulating the related transcription and signaling. MethodsCroakers (mean weight, 15.61 ± 0.10 g) were fed with diets containing 12% crude lipid [control diet (ND)] or 18% crude lipid (HFD) for 10 weeks. The glucose tolerance, insulin tolerance, hepatic gluconeogenesis–related genes, and proteins expressions were determined. To explore the role of SREBP1 in HFD-induced gluconeogenesis, SREBP1 was inhibited by pharmacologic inhibitor (fatostatin) or genetic knockdown in croaker hepatocytes under palmitic acid (PA) condition. To explore the underlying mechanism, luciferase reporter and chromatin immunoprecipitation assays were conducted in HEK293T cells. Data were analyzed using analysis of variance or Student t test. ResultsCompared with ND, HFD increased the mRNA expressions of gluconeogenesis genes (2.40-fold to 2.60-fold) (P < 0.05) and reduced protein kinase B (AKT) phosphorylation levels (0.28-fold to 0.34-fold) (P < 0.05) in croakers. However, inhibition of SREBP1 by fatostatin addition or SREBP1 knockdown reduced the mRNA expressions of gluconeogenesis genes (P < 0.05) and increased AKT phosphorylation levels (P < 0.05) in hepatocytes, compared with that by PA treatment. Moreover, fatostatin addition or SREBP1 knockdown also increased the mRNA expressions of irs1 (P < 0.05) and reduced serine phosphorylation of IRS1 (P < 0.05). Furthermore, SREBP1 inhibited IRS1 transcriptions by binding to its promoter and induced IRS1 serine phosphorylation by activating diacylglycerol–protein kinase Cε signaling. ConclusionsThis study reveals the role of SREBP1 in hepatic gluconeogenesis under HFD condition in croakers, which may provide a potential strategy for improving HFD-induced glucose intolerance.

Genetic deletion of hormone-sensitive lipase in mice reduces cerebral blood flow but does not aggravate the impact of diet-induced obesity on memory.

Hormone-sensitive lipase (HSL) is active throughout the brain and its genetic ablation impacts brain function. Its activity in the brain was proposed to regulate bioactive lipid availability, namely eicosanoids that are inflammatory mediators and regulate cerebral blood flow (CBF). We aimed at testing whether HSL deletion increases susceptibility to neuroinflammation and impaired brain perfusion upon diet-induced obesity. HSL-/-, HSL+/-, and HSL+/+ mice of either sex were fed high-fat diet (HFD) or control diet for 8 weeks, and then assessed in behavior tests (object recognition, open field, and elevated plus maze), metabolic tests (insulin and glucose tolerance tests and indirect calorimetry in metabolic cages), and CBF determination by arterial spin labeling (ASL) magnetic resonance imaging (MRI). Immunofluorescence microscopy was used to determine coverage of blood vessels, and morphology of astrocytes and microglia in brain slices. HSL deletion reduced CBF, most prominently in cortex and hippocampus, while HFD feeding only lowered CBF in the hippocampus of wild-type mice. CBF was positively correlated with lectin-stained vessel density. HSL deletion did not exacerbate HFD-induced microgliosis in the hippocampus and hypothalamus. HSL-/- mice showed preserved memory performance when compared to wild-type mice, and HSL deletion did not significantly aggravate HFD-induced memory impairment in object recognition tests. In contrast, HSL deletion conferred protection against HFD-induced obesity, glucose intolerance, and insulin resistance. Altogether, this study points to distinct roles of HSL in periphery and brain during diet-induced obesity. While HSL-/- mice were protected against metabolic syndrome development, HSL deletion reduced brain perfusion without leading to aggravated HFD-induced neuroinflammation and memory dysfunction.

Mechanisms by which sheep milk consumption ameliorates insulin resistance in high-fat diet-fed mice

Sheep milk is rich in fat, protein, vitamins and minerals and is also one of the most important sources of natural bioactives. Several biopeptides in sheep milk have been reported to possess antibacterial, antiviral and anti-inflammatory properties, and they may prevent type 2 diabetes (T2D), disease and cancer. However, the precise mechanism(s) underlying the protective role of sheep milk against T2D development remains unclear. Therefore, in the current study, we investigated the effect of sheep milk on insulin resistance and glucose intolerance in high-fat diet (HFD)-fed mice, by conducting intraperitoneal glucose tolerance tests, metabolic cage studies, genomic sequencing, polymerase chain reaction, and biochemical assays. Hyperinsulinemic–euglycemic clamp-based experiments revealed that mice consuming sheep milk exhibited lower hepatic glucose production than mice in the control group. These findings further elucidate the mechanism by which dietary supplementation with sheep milk alleviates HFD-induced systemic glucose intolerance.

TALK-1-mediated alterations of β-cell mitochondrial function and insulin secretion impair glucose homeostasis on a diabetogenic diet

Mitochondrial Ca2+ ([Ca2+]m) homeostasis is critical for β-cell function and becomes disrupted during the pathogenesis of diabetes. [Ca2+]m uptake is dependent on elevations in cytoplasmic Ca2+ ([Ca2+]c) and endoplasmic reticulum Ca2+ ([Ca2+]ER) release, both of which are regulated by the two-pore domain K+ channel TALK-1. Here, utilizing a novel β-cell TALK-1-knockout (β-TALK-1-KO) mouse model, we found that TALK-1 limited β-cell [Ca2+]m accumulation and ATP production. However, following exposure to a high-fat diet (HFD), ATP-linked respiration, glucose-stimulated oxygen consumption rate, and glucose-stimulated insulin secretion (GSIS) were increased in control but not TALK1-KO mice. Although β-TALK-1-KO animals showed similar GSIS before and after HFD treatment, these mice were protected from HFD-induced glucose intolerance. Collectively, these data identify that TALK-1 channel control of β-cell function reduces [Ca2+]m and suggest that metabolic remodeling in diabetes drives dysglycemia.

Partial Deletion of Perk Improved High-Fat Diet-Induced Glucose Intolerance in Mice.

Although pancreatic endoplasmic reticulum kinase (PERK) is indispensable to beta cells, low-dose PERK inhibitor improved glucose- stimulated insulin secretion (GSIS) and hyperglycemia in diabetic mice. Current study examined if partial deletion of Perk (Perk+/-) recapitulated the effects of PERK inhibitor, on the contrary to the complete deletion. Perk+/- mice and wild-type controls were fed with a high-fat diet (HFD) for 23 weeks. Glucose tolerance was evaluated along with serum insulin levels and islet morphology. Perk+/- mice on normal chow were comparable to wild-type mice in various metabolic features. HFD-induced obesity was not influenced by Perk reduction; however, HFD-induced glucose intolerance was significantly improved since 15-week HFD. HFD-induced compromises in GSIS were relieved by Perk reduction, accompanied by reductions in phosphorylated PERK and activating transcription factor 4 (ATF4) in the islets. Meanwhile, HFD-induced islet expansion was not significantly affected. In summary, partial deletion of Perk improved glucose tolerance and GSIS impaired by diet-induced obesity, without changes in body weights or islet mass.

Loss of Trim28 in muscle alters mitochondrial signalling but not systemic metabolism.

Type 2 diabetes mellitus (T2DM), a condition characterised by insulin resistance (IR) and skeletal muscle mitochondrial abnormalities, is a leading cause of death in developed societies. Much work has postulated that improving pathways linked to mitochondrial health, including autophagy, may be a potential avenue to prevent or treat T2DM. Given the recent data indicating a role for tripartite motif-containing 28 (TRIM28) in autophagy and mitochondrial pathways, we investigated whether muscle-specific deletion of TRIM28 might impact on obesity, glucose tolerance, and IR in mice. We studied two different muscle-specific (MCK-cre and ACTA1-cre-ERT2) TRIM28 knockout models, which were phenotyped during and after being fed a chow or high-fat diet (HFD). Whilst muscle-specific deletion of TRIM28 in both models demonstrated alterations in markers of mitochondrial activity and autophagy in skeletal muscle, we did not observe major impacts on the majority of metabolic measures in these mice. Specifically, we demonstrate that deletion of TRIM28 in skeletal muscle of mice during (MCK-cre) or post-development (ACTA1-cre-ERT2) does not prevent HFD-induced obesity or glucose intolerance. These findings are consistent with those reported previously in relation to autophagy and mitochondria in other cell types, and thus warrant further study into the biological role TRIM28 has in relation to mitochondrial function.

Abstract 059: (Pro)renin Receptor Ablation In Tyrosine Hydroxylase Neurons In The Paraventricular Nucleus Of The Hypothalamus Improves Insulin Sensitivity In Mice Fed A High-fat Diet

We recently reported that neuron-specific (pro)renin receptor (PRR) deletion reduces blood pressure (BP), fasting blood glucose (BG) and improves glucose tolerance in high-fat diet (HFD)-treated mice. To investigate underlying mechanisms, we focused on tyrosine hydroxylase (TH) neurons in the hypothalamic paraventricular nucleus (TH PVN neurons), a largely GABAergic population that expresses PRR and projects to autonomic centers important for BP and BG regulation. The PRR was ablated specifically in the TH-positive neurons in the PVN using Cre-LoxP approach. Radio telemetric BP recording, fasting blood glucose (FBG) and frequently sampled intravenous glucose tolerance test (FSIVGTT) were performed following 6-week HFD (60% calories from fat). HFD induced elevation of BP within the first week ( p &lt; 0.05) and maintained elevated during 6-week protocol; however, there was no difference in BP between TH PVN PRRKO and WT control mice in both sexes following HFD. In male mice, the controls had higher FBG when compared with the TH PVN PRRKO mice (144.1 ± 5.74 vs. 121.9 ± 4.34 mg/dl, p &lt; 0.05) at the end of the 6-week HFD treatment. Interestingly, PRR ablation in the TH PVN neurons did not reduce FBG in female mice. The TH PVN PRRKO mice showed improved glucose handling during FSIVGTT (AUC: 3481 ± 247.5 vs. 4263 ± 153.9, p &lt; 0.05), while there was no difference in insulin secretion (AUC: 1782 ± 339.2 vs. 2324 ± 495.6, p &gt; 0.05) between the two groups suggesting that TH PVN PRR ablation attenuates HFD-induced glucose intolerance through either an increase in insulin sensitivity or an insulin-independent pathway. Detected by western blot, the glucose transporter 4, an insulin-dependent glucose transporter, was higher on the plasma membrane of skeletal muscle in the TH PVN PRRKO mice (1.9 ± 0.2 vs. 1.0 ± 0.1, p &lt; 0.05) compared with the controls. The hepatic mRNA expression of glucose-6-phosphatase, a gluconeogenic gene transcriptional negative-regulated by insulin, was lower in the TH PVN PRRKO (0.60 ± 0.07 vs. 0.95 ± 0.10, p &lt; 0.05) compared with the control mice, suggesting improvement of insulin sensitivity in the TH PVN PRRKO mice. In conclusion, PRR ablation in TH PVN neurons attenuates FBG and glucose tolerance through improvement of insulin sensitivity without impacting BP.

Obesity-associated microglial inflammatory activation paradoxically improves glucose tolerance

Hypothalamic gliosis associated with high-fat diet (HFD) feeding increases susceptibility to hyperphagia and weight gain. However, the body-weight-independent contribution of microglia to glucose regulation has not been determined. Here, we show that reducing microglial nuclear factor κB (NF-κB) signaling via cell-specific IKKβ deletion exacerbates HFD-induced glucose intolerance despite reducing body weight and adiposity. Conversely, two genetic approaches to increase microglial pro-inflammatory signaling (deletion of an NF-κB pathway inhibitor and chemogenetic activation through a modified Gq-coupled muscarinic receptor) improved glucose tolerance independently of diet in both lean and obese rodents. Microglial regulation of glucose homeostasis involves a tumor necrosis factor alpha (TNF-α)-dependent mechanism that increases activation of pro-opiomelanocortin (POMC) and other hypothalamic glucose-sensing neurons, ultimately leading to a marked amplification of first-phase insulin secretion via a parasympathetic pathway. Overall, these data indicate that microglia regulate glucose homeostasis in a body-weight-independent manner, an unexpected mechanism that limits the deterioration of glucose tolerance associated with obesity.

Adipose METTL14-Elicited N6 -Methyladenosine Promotes Obesity, Insulin Resistance, and NAFLD Through Suppressing β Adrenergic Signaling and Lipolysis.

White adipose tissue (WAT) lipolysis releases free fatty acids as a key energy substance to support metabolism in fasting, cold exposure, and exercise. Atgl, in concert with Cgi-58, catalyzes the first lipolytic reaction. The sympathetic nervous system (SNS) stimulates lipolysis via neurotransmitter norepinephrine that activates adipocyte β adrenergic receptors (Adrb1-3). In obesity, adipose Adrb signaling and lipolysis are impaired, contributing to pathogenic WAT expansion; however, the underling mechanism remains poorly understood. Recent studies highlight importance of N6 -methyladenosine (m6A)-based RNA modification in health and disease. METTL14 heterodimerizes with METTL3 to form an RNA methyltransferase complex that installs m6A in transcripts. Here, this work shows that adipose Mettl3 and Mettl14 are influenced by fasting, refeeding, and insulin, and are upregulated in high fat diet (HFD) induced obesity. Adipose Adrb2, Adrb3, Atgl, and Cgi-58 transcript m6A contents are elevated in obesity. Mettl14 ablation decreases these transcripts' m6A contents and increases their translations and protein levels in adipocytes, thereby increasing Adrb signaling and lipolysis. Mice with adipocyte-specific deletion of Mettl14 are resistant to HFD-induced obesity, insulin resistance, glucose intolerance, and nonalcoholic fatty liver disease (NAFLD). These results unravel a METTL14/m6A/translation pathway governing Adrb signaling and lipolysis. METTL14/m6A-based epitranscriptomic reprogramming impairs adipose Adrb signaling and lipolysis, promoting obesity, NAFLD, and metabolic disease.

Microbiota-dependent and -independent effects of obesity on transplant rejection and hyperglycemia

Obesity is associated with dysbiosis and a state of chronic inflammation that contributes to the pathogenesis of metabolic diseases, including diabetes. We have previously shown that obese mice develop glucose intolerance, increased alloreactivity, and accelerated transplant rejection. In the present study, we investigated the influence of the microbiota on diet-induced obesity (DIO)–associated transplant rejection and hyperglycemia. Antibiotic treatment prolonged graft survival and reduced fasting glycemia in high-fat diet (HFD)–fed specific-pathogen-free (SPF) mice, supporting a role for the microbiota in promoting accelerated graft rejection and hyperglycemia induced by DIO. Further supporting a microbiota-dependent effect, fecal microbiota transfer from DIO SPF mice into germ-free mice also accelerated graft rejection when compared with lean mice-fecal microbiota transfer. Notably, HFD could be also detrimental to the graft independently from microbiota, obesity, and hyperglycemia. Thus, whereas HFD-associated hyperglycemia was exclusively microbiota-dependent, HFD affected transplant outcomes via both microbiota-dependent and -independent mechanisms. Importantly, hyperglycemia in DIO SPF mice could be reduced by the addition of the gut commensal Alistipes onderdonkii, which alleviated both HFD-induced inflammation and glucose intolerance. Thus, microbial dysbiosis can be manipulated via antibiotics or select probiotics to counter some of the pathogenic effects of obesity in transplantation.

Long-Term Consumption of Sucralose Induces Hepatic Insulin Resistance through an Extracellular Signal-Regulated Kinase 1/2-Dependent Pathway.

Sugar substitutes have been recommended to be used for weight and glycemic control. However, numerous studies indicate that consumption of artificial sweeteners exerts adverse effects on glycemic homeostasis. Although sucralose is among the most extensively utilized sweeteners in food products, the effects and detailed mechanisms of sucralose on insulin sensitivity remain ambiguous. In this study, we found that bolus administration of sucralose by oral gavage enhanced insulin secretion to decrease plasma glucose levels in mice. In addition, mice were randomly allocated into three groups, chow diet, high-fat diet (HFD), and HFD supplemented with sucralose (HFSUC), to investigate the effects of long-term consumption of sucralose on glucose homeostasis. In contrast to the effects of sucralose with bolus administration, the supplement of sucralose augmented HFD-induced insulin resistance and glucose intolerance, determined by glucose and insulin tolerance tests. In addition, we found that administration of extracellular signal-regulated kinase (ERK)-1/2 inhibitor reversed the effects of sucralose on glucose intolerance and insulin resistance in mice. Moreover, blockade of taste receptor type 1 member 3 (T1R3) by lactisole or pretreatment of endoplasmic reticulum stress inhibitors diminished sucralose-induced insulin resistance in HepG2 cells. Taken together, sucralose augmented HFD-induced insulin resistance in mice, and interrupted insulin signals through a T1R3-ERK1/2-dependent pathway in the liver.

255-LB: Liver Pyruvate Carboxylase Deletion in Mice Prevents Fibrosis from a NASH Diet

Obesity and T2D are closely associated with Nonalcoholic Fatty Liver Disease, which can advance to Nonalcoholic Steatohepatitis (NASH) with fibrosis. We previously found that liver pyruvate carboxylase (PC) is required for hepatic gluconeogenesis and the concentration of metabolites essential to mediating redox state and antioxidant function. Liver PC knockout (LPCKO) mice are protected from HFD-induced hyperinsulinemia and glucose intolerance despite retaining excess liver fat and exhibiting reduced antioxidant capacity. Here, we report that despite impaired antioxidant markers and increased inflammatory markers on a HFD, PC loss protected the liver from fibrosis and other indices of liver damage induced by a long-term NASH diet. LPCKO and control mice were fed a high fat, high cholesterol Western Diet (WD) for 13-14 months. After 10 mos. of WD, markers of insulin resistance were assessed by lactate/pyruvate, glucose, and insulin tolerance tests. After sacrifice, liver damage was assessed by serum markers and histology. Oxidative stress and inflammation were evaluated by gene expression, MDA concentration, GSH/GSSG and NADPH/NADP+ redox states, and H2O2 emission potential in isolated mitochondria. LPCKO-WD mice were more sensitive to an insulin tolerance test and exhibited lower fasting blood glucose and better glycemic control during a lactate/pyruvate or glucose tolerance test than controls. Liver malate/pyruvate indicated substantially lower NADPH/NADP+ in LPCKO-WD mice, but there were no differences in MDA levels, GSH/GSSG, and H2O2 emission potential. Despite similar hepatic steatosis, inflammation, and ballooning between LPCKO-WD and controls, fibrosis and serum markers of liver injury were markedly lower in LPCKO-WD mice. The data suggest that liver PC deletion improves glycemia and insulin resistance during chronic Western Diet exposure by reducing hepatic gluconeogenesis and prevents fibrosis independent of steatosis, inflammation, ballooning, and oxidative stress. Disclosure M. R. Iñigo-Vollmer: None. B. Kucejova: None. M. N. Mizerska: None. S. Khan: None. P. A. Szweda: None. H. Zaki: None. L. I. Szweda: None. X. Fu: None. S. C. Burgess: None.

Cedrol, a Major Component of Cedarwood Oil, Ameliorates High-Fat Diet-Induced Obesity in Mice.

Excellent health-promoting effects of cedrol (CED), including anti-inflammatory, anti-arthritic, and antinociceptive effects, have been reported. The present study aims to investigate the preventive effects of CED on high-fat diet (HFD)-induced obesity and the related metabolic syndrome, and to delineate the underlying mechanism. Ten-week-old C57BL/6J mice are fed chow, HFD, or HFD supplemented with CED (0.2% w/w) for 19 weeks. Results demonstrate that CED effectively reduces HFD-induced body weight gain, decreases visceral fat pad weight, and significantly prevents adipocyte hypertrophy in mice. HFD-induced hepatic steatosis, glucose intolerance, insulin resistance, and gluconeogenesis are ameliorated by CED supplementation. 16S rRNA analysis reveals that CED does not change gut microbiota composition at the phylum and genus levels, indicating that CED may have limited effects on gut microbiota in HFD-fed mice. Further transcriptome analysis of epididymal white adipose tissue reveals reprogrammed RNA profiles by CED. These results demonstrate that incorporating CED in the diet can prevent HFD-induced obesity and related metabolic syndrome, and highlight that CED can be a promising dietary component for obesity therapeutic intervention.