Induced Glucose Intolerance Research Articles

Linagliptin Ameliorates Hepatic Steatosis via Non-Canonical Mechanisms in Mice Treated with a Dual Inhibitor of Insulin Receptor and IGF-1 Receptor.

Abnormal hepatic insulin signaling is a cause or consequence of hepatic steatosis. DPP-4 inhibitors might be protective against fatty liver. We previously reported that the systemic inhibition of insulin receptor (IR) and IGF-1 receptor (IGF1R) by the administration of OSI-906 (linsitinib), a dual IR/IGF1R inhibitor, induced glucose intolerance, hepatic steatosis, and lipoatrophy in mice. In the present study, we investigated the effects of a DPP-4 inhibitor, linagliptin, on hepatic steatosis in OSI-906-treated mice. Unlike high-fat diet-induced hepatic steatosis, OSI-906-induced hepatic steatosis is not characterized by elevations in inflammatory responses or oxidative stress levels. Linagliptin improved OSI-906-induced hepatic steatosis via an insulin-signaling-independent pathway, without altering glucose levels, free fatty acid levels, gluconeogenic gene expressions in the liver, or visceral fat atrophy. Hepatic quantitative proteomic and phosphoproteomic analyses revealed that perilipin-2 (PLIN2), major urinary protein 20 (MUP20), cytochrome P450 2b10 (CYP2B10), and nicotinamide N-methyltransferase (NNMT) are possibly involved in the process of the amelioration of hepatic steatosis by linagliptin. Thus, linagliptin improved hepatic steatosis induced by IR and IGF1R inhibition via a previously unknown mechanism that did not involve gluconeogenesis, lipogenesis, or inflammation, suggesting the non-canonical actions of DPP-4 inhibitors in the treatment of hepatic steatosis under insulin-resistant conditions.

Improved Glucose Intolerance through a Distinct Mouse Olfactory Receptor 23-Induced Signaling Pathway Mediating Glucose Uptake in Myotubes and Adipocytes.

It is aimed to determine the role of mouse olfactory receptor 23 (MOR23) in regulation of glucose uptake in myotubes and adipocytes and investigate whether administration of a possible MOR23 ligand, α-cedrene, attenuates the high fat diet (HFD)-induced glucose intolerance by enhancing the OR-mediated signaling pathway in mice. MOR23 is genetically inactivated by specific small interfering RNA in C2C12 myotubes and 3T3-L1 adipocytes and stimulated with α-cedrene under both basal and insulin-stimulated conditions. In addition, Male C57BL/6N mice are fed a normal diet, HFD, or HFD supplemented with 0.2% α-cedrene. In C2C12 myotubes and 3T3-L1 adipocytes, genetic inactivation of MOR23 significantly decrease glucose uptake and MOR23 downstream signaling under both basal and insulin-stimulated conditions. On the other hand, α-cedrene-mediated MOR23 stimulation results in increased glucose uptake and upregulation of MOR23 signaling molecules, absent in MOR23-depleted myotubes and adipocytes. Moreover, in mice, α-cedrene administration ameliorates HFD-induced glucose intolerance. Activation of MOR23 signaling cascade is also confirmed in basal and insulin stimulated skeletal muscles and adipose tissues of α-cedrene-treated mice. These findings suggest that MOR23 is a novel factor for the regulation of glucose uptake and whole-body glucose homeostasis and has therapeutic potential for diabetes treatment.

Maternal low-protein diet on the last week of pregnancy contributes to insulin resistance and β-cell dysfunction in the mouse offspring.

Maternal low-protein diet (LP) throughout gestation affects pancreatic β-cell fraction of the offspring at birth, thus increasing their susceptibility to metabolic dysfunction and type 2 diabetes in adulthood. The present study sought to strictly examine the effects of LP during the last week of gestation (LP12.5) alone as a developmental window for β-cell programming and metabolic dysfunction in adulthood. Islet morphology analysis revealed normal β-cell fraction in LP12.5 newborns. Normal glucose tolerance was observed in 6- to 8-wk-old male and female LP12.5 offspring. However, male LP12.5 offspring displayed glucose intolerance and reduced insulin sensitivity associated with β-cell dysfunction with aging. High-fat diet exposure of metabolically normal 12-wk-old male LP12.5 induced glucose intolerance due to increased body weight, insulin resistance, and insufficient β-cell mass adaptation despite higher insulin secretion. Assessment of epigenetic mechanisms through microRNAs (miRs) by a real-time PCR-based microarray in islets revealed elevation in miRs that regulate insulin secretion (miRs 342, 143), insulin resistance (miR143), and obesity (miR219). In the islets, overexpression of miR143 reduced insulin secretion in response to glucose. In contrast to the model of LP exposure throughout pregnancy, islet protein levels of mTOR and pancreatic and duodenal homeobox 1 were normal in LP12.5 islets. Collectively, these data suggest that LP diet during the last week of pregnancy is critical and sufficient to induce specific and distinct developmental programming effects of tissues that control glucose homeostasis, thus causing permanent changes in specific set of microRNAs that may contribute to the overall vulnerability of the offspring to obesity, insulin resistance, and type 2 diabetes.

Placenta-Derived Osteoprotegerin Is Required for Glucose Homeostasis in Gestational Diabetes Mellitus.

Osteoprotegerin (OPG) is involved in various biological processes, including bone remodeling, vascular calcification and pancreatic β-cell function. Although some clinical studies have shown an increase in serum OPG level during pregnancy, the role of OPG in gestational diabetes mellitus (GDM) is largely unknown. Therefore, we explored the effect of OPG in metabolic homeostasis during pregnancy. We initially evaluated serum OPG levels using ELISA and western blotting techniques on samples from GDM patients. We also assessed OPG expression levels in maternal mice. We then used blastocysts transduced with lentiviruses capable of trophoblast-specific transgene expression to establish placenta-specific OPG knockdown or overexpression mouse models for functional and mechanistic investigation after embryo transplantation. We found that OPG expression was positively associated with GDM in clinical samples, and OPG levels were significantly increased in GDM patient sera and term placenta. Serum OPG was significantly increased in maternal compared to non-pregnant mice, and expression levels of OPG were the highest in placenta compared with other organs, including bone, liver and pancreas. OPG was also significantly increased in pregnant mice fed a high-fat diet (HFD). Placenta-specific OPG knockdown induced glucose intolerance, decreased β-cell proliferation and decreased serum insulin levels, whereas placenta-specific OPG overexpression promoted glucose tolerance and enhanced β-cell proliferation, which increased serum insulin production and decreased fetal weight in HFD-feeding pregnant mice. Placenta-derived OPG (pl-OPG) regulated glucose homeostasis during pregnancy via enhancement of β-cell proliferation, which suggests a potential therapeutic application of OPG for GDM.

Increased Glucose Availability Attenuates Myocardial Ketone Body Utilization.

BackgroundPerturbations in myocardial substrate utilization have been proposed to contribute to the pathogenesis of cardiac dysfunction in diabetic subjects. The failing heart in nondiabetics tends to decrease reliance on fatty acid and glucose oxidation, and increases reliance on ketone body oxidation. In contrast, little is known regarding the mechanisms mediating this shift among all 3 substrates in diabetes mellitus. Therefore, we tested the hypothesis that changes in myocardial glucose utilization directly influence ketone body catabolism.Methods and ResultsWe examined ventricular‐cardiac tissue from the following murine models: (1) streptozotocin‐induced type 1 diabetes mellitus; (2) high‐fat‐diet–induced glucose intolerance; and transgenic inducible cardiac‐restricted expression of (3) glucose transporter 4 (transgenic inducible cardiac restricted expression of glucose transporter 4); or (4) dominant negative O‐GlcNAcase. Elevated blood glucose (type 1 diabetes mellitus and high‐fat diet mice) was associated with reduced cardiac expression of β‐hydroxybutyrate‐dehydrogenase and succinyl‐CoA:3‐oxoacid CoA transferase. Increased myocardial β‐hydroxybutyrate levels were also observed in type 1 diabetes mellitus mice, suggesting a mismatch between ketone body availability and utilization. Increased cellular glucose delivery in transgenic inducible cardiac restricted expression of glucose transporter 4 mice attenuated cardiac expression of both Bdh1 and Oxct1 and reduced rates of myocardial BDH1 activity and β‐hydroxybutyrate oxidation. Moreover, elevated cardiac protein O‐GlcNAcylation (a glucose‐derived posttranslational modification) by dominant negative O‐GlcNAcase suppressed β‐hydroxybutyrate dehydrogenase expression. Consistent with the mouse models, transcriptomic analysis confirmed suppression of BDH1 and OXCT1 in patients with type 2 diabetes mellitus and heart failure compared with nondiabetic patients.ConclusionsOur results provide evidence that increased glucose leads to suppression of cardiac ketolytic capacity through multiple mechanisms and identifies a potential crosstalk between glucose and ketone body metabolism in the diabetic myocardium.

Type 2 diabetes susceptibility genes on mouse chromosome 11 under high sucrose environment

BackgroundBoth genetic and environmental factors contribute to type 2 diabetes development. We used consomic mice established from an animal type 2 diabetes model to identify susceptibility genes that contribute to type 2 diabetes development under specific environments. We previously established consomic strains (C3H-Chr 11NSY and C3H-Chr 14NSY) that possess diabetogenic Chr 11 or 14 of the Nagoya-Shibata-Yasuda (NSY) mouse, an animal model of spontaneous type 2 diabetes, in the genetic background of C3H mice. To search genes contribute to type 2 diabetes under specific environment, we first investigated whether sucrose administration deteriorates type 2 diabetes-related traits in the consomic strains. We dissected loci on Chr 11 by establishing congenic strains possessing different segments of NSY-derived Chr 11 under sucrose administration.ResultsIn C3H-Chr 11NSY mice, sucrose administration for 10 weeks deteriorated hyperglycemia, insulin resistance, and impaired insulin secretion, which is comparable to NSY mice with sucrose. In C3H-Chr 14NSY mice, sucrose administration induced glucose intolerance, but not insulin resistance and impaired insulin secretion. To dissect the gene(s) existing on Chr 11 for sucrose-induced type 2 diabetes, we constructed four novel congenic strains (R1, R2, R3, and R4) with different segments of NSY-derived Chr 11 in C3H mice. R2 mice showed marked glucose intolerance and impaired insulin secretion comparable to C3H-Chr 11NSY mice. R3 and R4 mice also showed impaired insulin secretion. R4 mice showed significant decreases in white adipose tissue, which is in the opposite direction from parental C3H-Chr 11NSY and NSY mice. None of the four congenic strains showed insulin resistance.ConclusionsGenes on mouse Chr 11 could explain glucose intolerance, impaired insulin secretion, insulin resistance in NSY mice under sucrose administration. Congenic mapping with high sucrose environment localized susceptibility genes for type 2 diabetes associated with impaired insulin secretion in the middle segment (26.0–63.4 Mb) of Chr 11. Gene(s) that decrease white adipose tissue were mapped to the distal segment of Chr 11. The identification of diabetogenic gene on Chr 11 in the future study will facilitate precision medicine in type 2 diabetes by controlling specific environments in targeted subjects with susceptible genotypes.

Effects of high-intensity infrasound on liver lipid content of rats

Previous experimental studies show that exposure to noise with high and audible frequencies causes multiple metabolic alterations, such as increased liver glycogen and triglycerides. However, the effect of exposure to sound with lower frequencies, such as high-intensity infrasound (frequency <20 Hz and sound pressure level >90 dB), on the liver lipid content is still unclear. As such, we aimed to study the effect of exposure to high-intensity infrasound of both normal and glucose intolerant rats on the liver lipid content. For this study, 79 wild-type male Wistar rats were randomly divided into two groups: G1, no treatment, and G2, induced glucose intolerance. Each of these two groups was randomly divided in two subgroups: s (animals kept in silence) and i (animals continuously exposed to high-intensity infrasound noise). At three noise-exposure time-points (1, 6 and 12 weeks) the rats were sacrificed, the liver was excised and hepatic lipids extracted. Data analysis was performed using a two-way ANOVA (p = 0.05). No significant effects due to interactions between the several factors exist on the liver lipid content (p=0.077). Moreover, no significant effects due to infrasound exposure (p=0.407) or glucose tolerance status (p=0.938) were observed. Our study shows that continuous exposure to high-intensity infrasound has no influence on the lipid content of the liver of both normal and glucose intolerant animals. This finding reinforces the need for further experimental studies on the physiological effects of infrasound due to its possible hazardous effects on human health.

Activation of the renin-angiotensin system in high fructose-induced metabolic syndrome.

High fructose intake induces hyperglycemia and hypertension. However, the mechanism by which fructose induces metabolic syndrome is largely unknown. We hypothesized that high fructose intake induces activation of the renin-angiotensin system (RAS), resulting in hypertension and metabolic syndrome. We provided 11-week-old Sprague–Dawley rats with drinking water, with or without 20% fructose, for two weeks. We measured serum renin, angiotensin II (Ang II), and aldosterone (Aldo) using ELISA kits. The expression of RAS genes was determined by quantitative reverse transcription polymerase chain reaction. High fructose intake increased body weight and water retention, regardless of food intake or urine volume. After two weeks, fructose intake induced glucose intolerance and hypertension. High fructose intake increased serum renin, Ang II, triglyceride, and cholesterol levels, but not Aldo levels. High fructose intake increased the expression of angiotensinogen in the liver; angiotensin-converting enzyme in the lungs; and renin, angiotensin II type 1a receptor (AT1aR), and angiotensin II type 1b receptor (AT1bR) in the kidneys. However, expression of AT1aR and AT1bR in the adrenal glands did not increase in rats given fructose. Taken together, these results indicate that high fructose intake induces activation of RAS, resulting in hypertension and metabolic syndrome.

Consumption of the Artificial Sweetener Acesulfame Potassium throughout Pregnancy Induces Glucose Intolerance and Adipose Tissue Dysfunction in Mice

Sugar-sweetened beverage consumption is associated with metabolic dysfunction. Artificially sweetened beverages (ASBs) are often promoted as an alternative. However, evidence for the safety of ASB consumption during pregnancy is lacking. The effects of sugar-sweetened beverage and ASB consumption during pregnancy in mice were examined, and we hypothesized that both sugar-sweetened beverages and ASBs would impair maternal metabolic function. Pregnant female C57BL/6J mice received control drinking water (CD), high-fructose corn syrup (Fr; 20% kcal intake; 335 mM), or the artificial sweetener acesulfame potassium (AS; 12.5 mM) in their drinking water, from gestational day (GD) 0.5 (n=8/group). Body weights and food and water intakes were assessed every second day, an oral-glucose-tolerance test (OGTT) was performed at GD 16.5, and mice were culled at GD 18.5. RT-PCR was carried out on adipose tissue, liver, and gut. Adipose tissue morphology was assessed using histological methods. In a separate cohort of animals, pregnancy length was assessed. Repeated-measures ANOVA was performed for the OGTT and weight gain data. All other data were analyzed by 1-way ANOVA. Fr and AS significantly impaired glucose tolerance, as demonstrated by OGTT (21% and 24% increase in AUC, respectively; P=0.0006). Fr and AS reduced expression of insulin receptor (39.5% and 33% reduction, respectively; P=0.02) and peroxisome proliferator-activated receptor γ (45.2% and 47%, respectively; P=0.039), whereas Fr alone reduced expression of protein kinase B (36.9% reduction; P=0.048) and resulted in an increase in adipocyte size and leptin concentrations (40% increase; P=0.03). AS, but not Fr, reduced male fetal weight (16.5% reduction; P=0.04) and female fetal fasting blood glucose concentration at cull (20% reduction; P=0.02) compared with CD. AS significantly reduced the length of pregnancy compared with the CD and Fr groups (1.25 d shorter; P=0.02). Fr and AS consumption were associated with maternal metabolic dysfunction in mice. AS was also associated with reduced fetal growth and fetal hypoglycemia. Therefore, ASBs may not be a beneficial alternative to sugar-sweetened beverages during pregnancy.

1805-P: Dietary Nitrate Prevents High-Fat Diet-Induced Glucose Intolerance and Liver-Specific Reactive Oxygen Species Emission

Introduction: The liver is particularly susceptible to the detrimental effects of a high fat diet (HFD), and rapidly develops insulin resistance. While the underlying mechanisms associated with hepatic insulin resistance are not fully understood, mitochondria play a crucial role in regulating lipid metabolism and redox balance. Recently, dietary nitrate was shown to attenuate HFD-induced glucose intolerance, however the mechanism(s) remains unknown. Therefore, in the present study we examined the possibility that dietary nitrate increased mitochondrial lipid-supported respiration and/or attenuated reactive oxygen species (ROS) emission. Methods: Male C57Bl/6J mice (n = 22) were randomly assigned to consume a control diet (10% fat), HFD (60% fat), or HFD with 4mM sodium nitrate in drinking water for 8 weeks. Whole body glucose tolerance and energy expenditure (indirect calorimetry) were determined, and mitochondrial respiration and reactive oxygen species (ROS) emission were assessed in liver samples. Results: Compared to control animals, the consumption of HFD increased whole body fat oxidation and body mass, and induced glucose intolerance. The consumption of dietary nitrate did not affect HFD-mediated changes in energy expenditure, rates of fat oxidation or body mass, but nevertheless attenuated the induction of glucose intolerance. Within the liver, HFD-feeding in the presence or absence of dietary nitrate, did not alter pyruvate or lipid (palmitoyl-CoA) supported respiration, or the sensitivity to malonyl-CoA-mediated inhibition of lipid-supported respiration. In contrast, while HFD increased the endogenous ROS production, nitrate prevented this response. Conclusion: These data demonstrate that nitrate supplementation attenuated the HFD-mediated induction of whole-body glucose intolerance in association with a reduction in ROS emission within the liver. Future research needs to determine causality between these observations. Disclosure G. DesOrmeaux: None. H.L. Petrick: None. H. Brunetta: None. G. Holloway: None. Funding Natural Sciences and Engineering Research Council of Canada (400362)

53-OR: Deletion of YTHDF2 in Beta Cells Results in Glucose Intolerance

N6-methyladenosine (m6A) is the most common and abundant mRNA modification. However, the role of m6A in regulating β-cell function is unclear. YTHDF2 is a ’reader’ protein that recognizes m6A-containing mRNAs and targets them for degradation. To address the functional role of YTHDF2 in β-cells, we generated an Ythdf2 β-cell knockout mouse using RIP-Cre transgenic mice. At the 3-month old age, the feeding and fasting glucose of βKO mice were similar to that in control mice (RIP-Cre mice). However, both male and female βKO mice are glucose intolerant after glucose challenge. The AUC was increased by 44.6% in male βKO mice and 71.1% in female mice, respectively (both P&amp;lt;0.01). The response to insulin was similar between βKO and control mice. Interestingly, although the fasting insulin levels were comparable between βKO and control mice, the feeding insulin levels in both male and female βKO mice were increased. The serum insulin levels from βKO mice were significantly lower at 15 min after glucose challenge. In addition, the insulin secretion from βKO islets was less due to decreased insulin protein. Surprisingly, β-cell mass in βKO mice was significantly higher than that in control mice (P&amp;lt;0.05). Both islets number and size were increased in βKO mice. To understand the molecular mechanism, we performed RNA-seq to detect the gene expression in βKO and control islets isolated from male mice. Among 626 altered genes in βKO islets, 421 genes were upregulated and 205 genes were downregulated. The genes response to ER stress were among the top up-regulated genes. The genes related to insulin secretion were downregulated. We applied m6A-seq in MIN6 cells and confirmed that Ire1α was indeed modified by m6A in its last exon and 3’ UTR region. We further confirmed that both mRNA and protein levels of Ire1α and spliced XBP-1 were significantly increased in βKO islets. In conclusion, YTHDF2 plays an important role in regulating insulin secretion, and YTHDF2 deficiency in β-cells induces glucose intolerance by regulating insulin secretion and ER stress. Disclosure D. Ren: None. J. Sun: None. Funding The University of Chicago (P30-DK020595)

OR04-02 The Role of the Sympathetic Nervous System in Metabolic Disorder and Adipose Dysfunction in Obesity and Aging

Both obesity and aging increase susceptibility to metabolic disease and type 2 diabetes where adipose tissue dysfunction is a hallmark. In both conditions, impaired autonomic control is believed to play a key role in disrupted CNS control of metabolism. However, the role of the sympathetic nervous system (SNS) and catecholaminergic signaling in metabolic disease has not been well defined in large part due to a lack of suitable animal models(1). Surgical denervation is not specific to the SNS and chemical sympathectomy through 6-hydroxydopamine causes inflammation due to toxic effects. Abrogation of catecholamine (CA) synthesis in the whole body due to genetic deletion of the gene for tyrosine hydroxylase (th), a key enzyme in CA synthesis, results in embryonic lethality likely due to the lack of dopamine and norepinephrine in the CNS where they serve as key neurotransmitters.Here we studied the role of the SNS and catecholaminergic signaling in metabolic control in both aging as well as high fat diet (HFD) induced obesity. We created a mouse model of inducible th gene deletion that is restricted to the periphery, including sympathetic fibers of the peripheral NS but spares the brain as a pharmaco-genetic model of sympathectomy(2). TH is deleted and CA levels were reduced more than 90% in peripheral tissues of TH KO mice, while intact in the CNS. TH KO mice are cold intolerant consistent with functional sympathectomy. Interestingly, TH KO mice are protected from HFD feeding induced glucose intolerance (AUC during GTT: WT1018.8±42.0 mg/dl/hr vs. TH KO 485.0±85.8 mg/dl/hr; p < 0.0001; n = 6) even though food intake increased in TH KO mice. In 20 months old TH KO mice glucose tolerance was improved and fasting blood glucose levels were reduced (AUC during GTT: WT 357.3±16.2 mg/dl/hr vs. TH KO 254.5±15.6 mg/dl/hr; p < 0.01; n = 12) with higher insulin levels (WT 0.35±0.07 μg/l vs. TH KO 1.28±0.28 μg/l; p < 0.001; n = 9). Of note, insulin tolerance tests did not show marked differences. Both obesity and aging are characterized by impaired adipose tissue function with reduced lipogenic capacity. TH KO mice fed a HFD exhibit increased WAT de novo lipogenesis, lower lipolysis, and trend to exhibit decreased adipose tissue inflammation, suggesting that the SNS is a major culprit for the impaired lipogenic capacity in adipose tissue. Our data provides support for the paradigm that impaired SNS function plays an important role in the dysmetabolic states of obesity and aging.Reference1. Ryu V, Buettner C. Fat cells gobbling up norepinephrine? PLoS Biol. 2019;17(2):e3000138.2. Fischer K, Ruiz HH, Jhun K, Finan B, Oberlin DJ, van der Heide V, et al. Alternatively activated macrophages do not synthesize catecholamines or contribute to adipose tissue adaptive thermogenesis. Nature medicine. 2017;23(5):623-30.

Effect of stevia on the gut microbiota and glucose tolerance in a murine model of diet-induced obesity.

Artificial sweeteners have been shown to induce glucose intolerance by altering the gut microbiota; however, little is known about the effect of stevia. Here, we investigate whether stevia supplementation induces glucose intolerance by altering the gut microbiota in mice, hypothesizing that stevia would correct high fat diet-induced glucose intolerance and alter the gut microbiota. Mice were split into four treatment groups: low fat, high fat, high fat + saccharin and high fat + stevia. After 10 weeks of treatment, mice consuming a high fat diet (60%kcal from fat) developed glucose intolerance and gained more weight than mice consuming a low fat diet. Stevia supplementation did not impact body weight or glucose intolerance. Differences in species richness and relative abundances of several phyla were observed in low fat groups compared to high fat, stevia and saccharin. We identified two operational taxonomic groups that contributed to differences in beta-diversity between the stevia and saccharin groups: Lactococcus and Akkermansia in females and Lactococcus in males. Our results demonstrate that stevia does not rescue high fat diet-induced changes in glucose tolerance or the microbiota, and that stevia results in similar alterations to the gut microbiota as saccharin when administered in concordance with a high fat diet.

Dietary Fat and Sugar Differentially Affect β-Adrenergic Stimulation of Cardiac ERK and AKT Pathways in C57BL/6 Male Mice Subjected to High-Calorie Feeding

High dietary fat and sugar promote cardiac hypertrophy independently from an increase in blood pressure. The respective contribution that each macronutrient exerts on cardiac growth signaling pathways remains unclear. The goal of this study was to investigate the mechanisms by which high amounts of dietary fat and sugar affect cardiac growth regulatory pathways. Male C57BL/6 mice (9 wk old; n=20/group) were fed a standard rodent diet (STD; kcal% protein-fat-carbohydrate, 29-17-54), a high-fat diet (HFD; 20-60-20), a high-fat and high-sugar Western diet (WD; 20-45-35), a high-sugar diet with mixed carbohydrates (HCD; 20-10-70), or a high-sucrose diet (HSD; 20-10-70). Body composition was assessed weekly by EchoMRI. Whole-body glucose utilization was assessed with an intraperitoneal glucose tolerance test. After 6 wk on diets, mice were treated with saline or 20 mg/kg isoproterenol (ISO), and the activity of cardiac growth regulatory pathways was analyzed by immunoblotting. Data were analyzed by ANOVA with data from the STD group included for references only. Compared with HCD and HSD, WD and HFD increased body fat mass 2.7- to 3.8-fold (P<0.001), induced glucose intolerance (P<0.001), and increased insulin concentrations >1.5-fold (P<0.05), thereby enhancing basal and ISO-stimulated AKT phosphorylation at both threonine 308 and serine 473 residues (+25-63%; P<0.05). Compared with HFD, the high-sugar diets potentiated ISO-mediated stimulation of the glucose-sensitive kinases PYK2 (>47%; P<0.05 for HCD and HSD) and ERK (>34%; P<0.05 for WD, HCD, and HSD), thereby leading to increased phosphorylation of protein synthesis regulator S6K1 at threonine 389 residue (>64%; P<0.05 for WD, HCD, and HSD). Dietary fat and sugar affect cardiac growth signaling pathways in C57BL/6 mice through distinct and additive mechanisms. The findings may provide new insights into the role of overnutrition in pathological cardiac remodeling.

Deregulation of hepatic lipid metabolism associated with insulin resistance in rats subjected to chronic monocrotophos exposure.

In our previous study, we demonstrated the potential of monocrotophos (MCP), an organophosphorus insecticide (OPI), to induce glucose intolerance, insulin resistance (IR), and dyslipidemia with hyperinsulinemia in rats after chronic exposure. As hyperinsulinemia is likely to exert an impact on hepatic lipid metabolism, we carried out this study to establish the effect of chronic MCP exposure (0.9 and 1.8 mg/kg/day for 180 days) on hepatic lipid metabolism in rats. The state of IR induced by MCP in rats was associated with an increase in the liver lipid content (triglyceride and cholesterol) and expression levels of sterol regulatory element-binding proteins, PPARγ, acetyl-CoA carboxylase, and fatty acid synthase in the liver. Similarly, activities of key enzymes (acetyl-COA carboxylase, fatty acid synthase, lipin 1, malic enzyme, glucose-6-phosphate dehydrogenase, and glycerol-3-phosphate dehydrogenase), which regulate lipogenesis, were enhanced in livers of pesticide-treated rats. A strong correlation was observed between insulin levels, hepatic lipid content, and plasma lipid profile in treated rats. Our study suggests that long-term exposure to OPIs not only has a propensity to induce a state of hyperinsulinemic IR, but it is also associated with augmented hepatic lipogenesis, which may explain dyslipidemia induced by chronic exposure to MCP.

Loss of β‐cell Gαz protects against high‐fat diet induced glucose intolerance by preserving incretin responsiveness and enhancing insulin secretion

Cyclic‐adenosine monophosphate (cAMP) is an important secondary messenger in the insulin‐secreting pancreatic β‐cells. Intracellular production of cAMP is augmented by stimulatory heterotrimeric G proteins (Gs) and blocked by inhibitory heterotrimeric G proteins (Gi). Pancreatic expression of the unique Gi family member, Gαz, is restricted to the islet, which contains β‐cells and other endocrine cell types, including glucagon/GLP‐1‐secreting alpha cells and somatostatin‐secreting delta cells. We have previously shown that full body Gαz‐null mice are protected from hyperglycemia in several diabetes model systems. Here, we use a high fat diet (HFD) model of obesity and insulin resistance to explore the impact of loss of beta‐cell Gαz on the type 2 diabetes (T2D) phenotype of male C57BL/6J mice. We hypothesized that loss of beta‐cell Gαz in the context of HFD feeding would enhance insulin secretion, protecting mice from HFD‐induced glucose intolerance. To generate beta‐cell specific Gαz‐null and control mice, we bred Gαz flox/flox mice with rat insulin promoter RIP‐Creherr mice. At 12 weeks of age, transgenic Gαz‐null mice were fed a diet containing 45 kcal% fat or a 10 kcal% fat control diet for 26 weeks. At study end, mice were metabolically phenotyped and sacrificed for whole pancreas and islet phenotyping. Beta‐cell‐specific Gαz loss protected mice from HFD induced glucose intolerance due to a selective effect on islet insulin secretion, particularly in concert with a stable agonist of the Gs‐coupled GLP‐1 receptor. This protective effect was independent of changes in Gαz‐coupled EP3 receptor signaling, as neither EP3 expression nor production of its endogenous ligand, PGE2, were enhanced in islets from HFD‐fed mice. This protective effect was also beta‐cell autonomous, as both full‐body and beta‐cell‐specific Gαz‐null mice had enhanced GLP‐1‐positive alpha‐cells, albeit with no changes in active GLP‐1 secretion. Finally, gene microarray results confirm that Gαz loss and HFD feeding synergize to differentially regulate islet gene expression, specifically up‐regulating secretion‐centric genes, many of which are related to cAMP signaling. This study presents a novel inhibitory mechanism of receptor‐independent G‐protein signaling that may hold promise for developing beta‐cell targeted diabetes therapeutics.

Dietary Fat and Sugar Differentially Affect Beta‐Adrenergic Stimulation of Cardiac ERK and AKT Pathways in Mice Subjected to High‐Calorie Feeding

Introduction. High dietary fat and sugar promote cardiac hypertrophy independently from an increase in blood pressure. The respective contribution that each macronutrient exerts on cardiac growth signaling pathways remains unclear. The goal of this study was to investigate the mechanisms by which high dietary fat and sugar levels affect cardiac growth regulatory pathways in the mouse heart.Methods. Nine‐week‐old male C57BL/6 mice (n = 20/group) were fed a standard rodent diet (STD; 3.0 kcal/g), a high‐fat diet (HFD; 5.24 kcal/g), a high‐fat and high‐sugar Western diet (WD; 4.73 kcal/g), a high‐sugar diet with mixed carbohydrates (HCD; 3.85 kcal/g), or a high‐sucrose diet (HSD; 3.85 kcal/g). Body composition was assessed weekly by EchoMRI. Whole‐body glucose utilization was assessed with an intraperitoneal glucose tolerance test. After six weeks on diets, mice were treated with saline or 20 mg/kg isoproterenol (ISO) and the activity of cardiac growth regulatory pathways was analyzed by immunoblotting. One‐ or two‐way ANOVA was used for statistical comparisons.Results. Compared with STD, HFD increased body fat mass 4.5‐fold (P &lt; 0.0001), induced glucose intolerance (P &lt; 0.0001), and increased insulin levels 3.6‐fold (P &lt; 0.0001), thereby enhancing basal and ISO‐stimulated AKT phosphorylation at both threonine 308 and serine 473 residues (+37–100%; P &lt; 0.05). Both HCD and HSD potentiated ISO‐mediated stimulation of the glucose‐sensitive kinases PYK2 (&gt;50%; P &lt; 0.05) and ERK (&gt;30%; P &lt; 0.05), thereby leading to increased phosphorylation of protein synthesis regulator S6K1 at threonine 389 residue (≥70%; P &lt; 0.05). All these anthropometric, metabolic and cardiac growth signaling alterations occurred simultaneously in WD‐fed mice.Conclusions. The results indicate that dietary fat and sugar affect cardiac cell growth signaling pathways in C57BL/6 mice through distinct and additive mechanisms. The findings may provide new insights into the role of overnutrition in pathological remodeling of the heart.Support or Funding InformationThis work was supported by grants R01HL136438, P20GM104357 and P01HL051971 from the National Institutes of Health.

Gut DYSBIOSIS and altered barrier function precedes the appearance of metabolic syndrome in a rat model of nutrient-induced catch-up growth

Nutritional restriction early in life followed by catch-up growth has been associated with increased risk of metabolic syndrome in adulthood. To elucidate whether altered gut colonization underlies the mechanisms responsible of this predisposition gut microbiome was studied before or afterwards catch-up growth. Offspring of dams fed ad libitum (C) or undernourished during pregnancy and suckling (U), were weaned onto high-fat diet (HFD) for 22 weeks (CHF and UHF, respectively) or continued on their diet. HF-feeding induced glucose intolerance (P<.05), insulin resistance (P<.001), and white adipose tissue inflammation (P<.001) in UHF rats compared to CHF. Analyses of gut microbial composition before catch-up growth revealed reduced F/B ratio and significant expansion of the mucolytic genera Akkermansia (P<.05) and Desulfovibrio (P<.05) in U pups. Although relative abundance of Akkermansia remained elevated to adulthood in U rats, HFD normalized its levels to C and CHF. Food-restriction increased intestinal permeability causing disorganization on the tight-junction proteins of colonic epithelium, Zonula Occludens-1 (ZO-1) and occludin, and reducing the mucus thickness layer in U adult rats. The levels of ZO-1 and occludin were not recovered in U rats after HF-feeding. This event was correlated with increased circulating levels of bacterial lipopolysaccharides in both U and UHF adult rats. Even more, serum lipopolysaccharides were already elevated in U rats compared to C group (P<.001) at weaning. Thus, gut dysbiosis and chronic endotoxemia observed in U rats, even before catch-up growth, might anticipate a pro-inflammatory milieu promoting metabolic diseases when fed hyperlipidic diets.

Swimming Differentially Affects T2DM-Induced Skeletal Muscle ER Stress and Mitochondrial Dysfunction Related to MAM.

PurposeMitochondrial dysfunction and endoplasmic reticulum stress (ERS) are associated with metabolic diseases such as obesity and Type 2 diabetes mellitus (T2DM). Mitochondria and ER are connected via mitochondria-associated membranes (MAM) that are involved in glucose homeostasis and insulin resistance. We postulated that exercise might positively benefit T2DM-induced ER and mitochondrial dysfunction that might be associated with MAM.Materials and MethodsMice were fed a high-fat diet and injected with streptozotocin (STZ) to create T2DM models. Glucose tolerance, mitochondrial quality, MAM quality, and ERS were investigated in diabetic mice after six weeks of swimming.ResultsType 2 DM induced decreased MAM quantity, impaired mitochondrial quality, and deteriorated ERS in skeletal muscle that led to endoplasmic reticulum-associated degradation (ERAD). Swimming alleviated strong ERS caused by T2DM. Importantly, MAM quantity was positively associated with mitochondrial function and tended to negatively correlate with the ERS branch, ATF6. Moreover, both ATF6 branches of ERS and ERAD were positively associated with the pIRE1α branch of ERS.ConclusionType 2 DM induced glucose intolerance, powerful ERS, and mitochondrial dysfunction associated with decreased amounts of MAM. Swimming improved glucose intolerance and selectively mitigated the ERS in skeletal muscle. Therefore, MAM quality and ATF6 might be novel and important targets for T2DM treatment. Endoplasmic reticulum stress might be an effective target of swimming to improve diabetes.

High-sugar diet leads to obesity and metabolic diseases in ad libitum -fed rats irrespective of caloric intake.

Objective Provide a comprehensive view of the events surrounding the sugar consumption, under conditions of energy equivalence; through the analysis of behavioral aspects of intake, and of biochemical, metabolic and physiological parameters, as well as the effect of this nutrient on the plasticity of adipose tissue. Materials and methods Newly weaned male Wistar rats were classified in two groups and subjected to the following normocaloric diets: standard chow diet or to high-sugar diet (HSD) ad libitum for 18 weeks. Results The animals submitted to the HSD were associated with a lower caloric intake during the 18 weeks of experimentation. However, the HSD induced a significant increase in body weight, white adipose tissue weight, adiposity index, Lee index, and the levels of triglycerides and very low-density lipoprotein in the serum. In addition, it induced glucose intolerance, insulin resistance and compensatory increase of insulin secretion by pancreatic β-cells. Also increased heart rate and induced hyperplasia, and hypertrophy of retroperitoneal visceral adipose tissue. In the liver, the HSD was associated with increased hepatic lipid content (i.e., triglycerides and cholesterol) and hepatomegaly. Conclusion The post-weaning consumption of HSD induces an adaptive response in metabolism; however, such an event is not enough to reverse the homeostatic imbalance triggered by the chronic consumption of this macronutrient, leading to the development of metabolic syndrome, irrespective of caloric intake. These findings corroborate recent evidence indicating that sugar is a direct contributor to metabolic diseases independent of a positive energy balance. Arch Endocrinol Metab. 2020;64(1):71-81.