Impaired Glucose Clearance Research Articles

Dietary nitrate attenuates high-fat diet-induced obesity via mechanisms involving higher adipocyte respiration and alterations in inflammatory status

Emerging evidence indicates that dietary nitrate can reverse several features of the metabolic syndrome, but the underlying molecular mechanisms still remain elusive. The aim of the present study was to explore mechanisms involved in the effects of dietary nitrate on the metabolic dysfunctions induced by high-fat diet (HFD) in mice. Four weeks old C57BL/6 male mice, exposed to HFD for ten weeks, were characterised by increased body weight, fat content, increased fasting glucose and impaired glucose clearance. All these metabolic abnormalities were significantly attenuated by dietary nitrate. Mechanistically, subcutaneous primary mouse adipocytes exposed to palmitate (PA) and treated with nitrite exhibited higher mitochondrial respiration, increased protein expression of total mitochondrial complexes and elevated gene expression of the thermogenesis gene UCP-1, as well as of the creatine transporter SLC6A8. Finally, dietary nitrate increased the expression of anti-inflammatory markers in visceral fat, plasma and bone marrow-derived macrophages (Arginase-1, Egr-2, IL-10), which was associated with reduction of NADPH oxidase-derived superoxide production in macrophages. In conclusion, dietary nitrate may have therapeutic utility against obesity and associated metabolic complications possibly by increasing adipocyte mitochondrial respiration and by dampening inflammation and oxidative stress.

Prenatal alcohol exposure programmes offspring disease: insulin resistance in adult males in a rat model of acute exposure.

Prenatal alcohol exposure has the potential to affect fetal development and programme chronic disease in offspring. Previous preclinical models typically use high, chronic doses of alcohol throughout pregnancy to examine effects on offspring, particularly on the brain and behaviour. In this study we use a rat model of moderate, acute, prenatal alcohol exposure to determine if this can be detrimental to maintenance of glucose homeostasis in adolescent and adult offspring. Although female offspring were relatively unaffected, there was evidence of insulin resistance in 6-month-old male offspring exposed to prenatal alcohol, suggestive of a pre-diabetic state. This result suggests that even a relatively low-dose, acute exposure to alcohol during pregnancy can still programme metabolic dysfunction in a sex-specific manner. Alcohol consumption is highly prevalent amongst women of reproductive age. Given that approximately 50% of pregnancies are unplanned, alcohol has the potential to affect fetal development and programme chronic disease in offspring. We examined the effect of an acute but moderate prenatal alcohol exposure (PAE) on glucose metabolism, lipid levels and dietary preference in adolescent and/or adult rat offspring. Pregnant Sprague-Dawley rats received an oral gavage of ethanol (1gkg-1 maternal body weight, n=9 dams) or an equivalent volume of saline (control, n=8 dams) at embryonic days 13.5 and 14.5. PAE resulted in a blood alcohol concentration of 0.05-0.06% 1h post-gavage in dams. Fasting blood glucose concentration was not affected by PAE in offspring at any age, nor were blood glucose levels during a glucose tolerance test (GTT) in 6-month-old offspring (P>0.5). However, there was evidence of insulin resistance in PAE male offspring at 6months of age, with significantly elevated fasting plasma insulin (P=0.001), a tendency for increased first phase insulin secretion during the GTT and impaired glucose clearance following an insulin challenge (P=0.007). This was accompanied by modest alterations in protein kinase B (AKT) signalling in adipose tissue. PAE also resulted in reduced calorie consumption by offspring compared to controls (P=0.04). These data suggest that a relatively low-level, acute PAE programmes metabolic dysfunction in offspring in a sex-specific manner. These results highlight that alcohol consumption during pregnancy has the potential to affect the long-term health of offspring.

Synthetic small molecule analogues of the immunomodulatory Acanthocheilonema viteae product ES-62 promote metabolic homeostasis during obesity in a mouse model

One of the most rapidly increasing human public health problems is obesity, whose sequelae like type-2 diabetes, represent continuously worsening, life-long conditions. Over the last 15 years, data have begun to emerge from human and more frequently, mouse studies, that support the idea that parasitic worm infection can protect against this condition. We have therefore investigated the potential of two synthetic small molecule analogues (SMAs) of the anti-inflammatory Acanthocheilonema viteae product ES-62, to protect against metabolic dysfunction in a C57BL/6 J mouse model of high calorie diet-induced obesity. We found weekly subcutaneous administration of the SMAs in combination (1 μg of each), starting one week before continuous exposure to high calorie diet (HCD), decreased fasting glucose levels and reversed the impaired glucose clearance observed in male mice, when measured at approximately 7 and 13 weeks after exposure to HCD. Fasting glucose levels were also-reduced in male mice fed a HCD for some 38 weeks when given SMA-treatment 13 weeks after the start of HCD, indicating an SMA-therapeutic potential. For the most part, protective effects were not observed in female mice. SMA treatment also conferred protection against each of reduced ileum villus length and liver fibrosis, but more prominently in female mice. Previous studies in mice indicate that protection against metabolic dysfunction is usually associated with polarisation of the immune system towards a type-2/anti-inflammatory direction but our attempts to correlate improved metabolic parameters with such changes were unsuccessful. Further analysis will therefore be required to define mechanism of action. Nevertheless, overall our data clearly show the potential of the drug-like SMAs as a preventative or treatment for metabolic dysregulation associated with obesity.

Maternal exercise before and during pregnancy alleviates metabolic dysfunction associated with high-fat diet in pregnant mice, without significant changes in gut microbiota

Although maternal exercise before and during pregnancy is beneficial, the effects of exercise on microbiota changes during pregnancy are unknown. Here we tested the hypothesis that maternal exercise before and during pregnancy would positively affect glucose homeostasis, pancreatic cell function, and gut microbiota dysbiosis in high-fat diet (HFD) fed dams. Female C57BL/6 mice were fed either a HFD or a low-fat diet (LFD) for 12 weeks. The HFD mice were split into two groups for 4 weeks prior to pregnancy initiation and throughout the pregnancy: sedentary (HFD) or exercised (HFD + Ex). Food intake, body weight, body composition, and glucose and insulin tolerance were measured. At gestation day 19, blood, pancreas, gonadal visceral and subcutaneous fat, plantaris muscle, and cecum were collected for analysis. Both HFD and HFD + Ex mice had impaired glucose clearance compared to LFD mice at 15 days of gestation. No changes were found in pancreatic α- or β-cell health. HFD + Ex mice had significantly reduced visceral fat mass, serum insulin, and leptin levels and increased high-density lipoprotein levels, compared to HFD-fed mice. In contrast to our hypothesis, microbiota diversity and composition were not different among groups. The relative abundance of five bacterial phyla, such as Firmicutes, Bacteroidetes, Verrucomicrobia, Deferribacteres, and Actinobacteria, were not significantly altered with diet or exercise during pregnancy. Our findings suggest that maternal exercise prevents excess visceral fat accumulation, hyperinsulinemia, and hyperleptinemia associated with a HFD, but not through the alterations of gut microbiota composition or diversity during pregnancy.

1940-P: Disruption of the Exocyst Trafficking Complex Results in Impaired Glucose Uptake in Skeletal Muscle

Objectives: Skeletal muscle cells are responsible for 80-90% of the insulin-induced glucose uptake in the body. Insulin signaling in skeletal muscle results in the targeted trafficking of glucose transporter type 4 (GLUT4) onto the cell membrane, enabling glucose uptake. Insulin resistant cells show defects in insulin-induced GLUT4 exocytosis. The eight-protein exocyst complex has an essential role in the insulin-induced exocytosis of GLUT4 vesicles in cultured adipocytes but it is not known if the exocyst-mediated molecular mechanism is conserved in other, insulin-responsive tissues, such as the skeletal muscle. We hypothesized that the exocyst complex is essential for the insulin-induced exocytosis of GLUT4-containing vesicles in skeletal muscle as well and that the exocyst is a master regulator of glucose homeostasis in insulin-responsive tissues. Methods/Results: We have generated a tamoxifen-inducible skeletal muscle-specific knockout mouse strain of exocyst central subunit Exoc5 (Exoc5-SMKO) to assess the exocyst’s role in glucose homeostasis in vivo. Exoc5 knockout does not affect grip strength, motor coordination or locomotor activity levels in these animals. Both male and female Exoc5-SMKO mice present with elevated fasting glucose levels, as compared to control littermates. Glucose tolerance testing revealed an impaired glucose clearance in Exoc5-SMKO mice, while insulin tolerance, fasting insulin levels, and A1C levels were similar between knockouts and controls. Conclusion: Our findings suggest that Exoc5 and the exocyst are necessary for insulin-stimulated glucose uptake in skeletal muscle. Ongoing work will further investigate the molecular mechanism of exocyst-mediated GLUT4 trafficking in skeletal muscle. Disclosure B. Fujimoto: None. L.T. Carter: None. A.M. Wong: None. M.W. Pitts: None. R.K. Villiger: None. M. Young: None. B. Fogelgren: None. N. Polgar: None. Funding National Institute of General Medical Sciences (5P20GM113134)

Effect of Age on Diabetogenicity of Alloxan in Ossabaw Miniature Swine.

According to a single study in dogs that was conducted in 1949, the diabetic effects of the β-cell toxin alloxan are dependent on age. The current study examined whether this age-dependence of alloxan is present in the clinically relevant Ossabaw miniature swine (Sus scrofa domestica) model of metabolic syndrome. Juvenile swine (n = 8; age, 4.3 ± 0.2 mo) and adult swine (n = 8; age, 7.4 ± 0.2 mo) received alloxan (average dosage, 140 mg/kg IV) and were placed on a hypercaloric, atherogenic diet for 6 mo. The metabolic syndrome profile was confirmed by measuring body weight, cholesterol, and triglycerides. Intravenous glucose tolerance testing was used to assess glucose clearance and peripheral plasma insulin levels. The β-cell mass was calculated by immunohistochemical staining of pancreatic tissue. Although juvenile and adult swine exhibited comparable severity of metabolic syndrome, adult swine developed impaired glucose clearance and elevated fasting blood glucose levels at 6 mo after alloxan administration on the atherogenic diet. Peripheral plasma insulin levels in juvenile and adult swine were comparable at all time points and lower than in nonalloxan-treated age-matched controls, which is reflected in the lower pancreatic β-cell mass of the 2 treated groups. However, compared with adult pigs, juvenile swine exhibited greater insulin response recovery (complete or partial restoration of peripheral insulin levels to reference values) at 6 mo after alloxan administration. Overall, these results indicate that youth can confer some protection against the diabetogenic effects of alloxan in swine, potentially due in part to the greater insulin response recovery of young pigs. This study supports previous research that the effects of alloxan are dependent on the developmental maturity of the animal.

Tissue-dependent effects of cis-9,trans-11- and trans-10,cis-12-CLA isomers on glucose and lipid metabolism in adult male mice

Mixtures of the two major conjugated linoleic acid (CLA) isomers trans-10,cis-12-CLA and cis-9,trans-11-CLA are used as over the counter supplements for weight loss. Because of the reported adverse effects of CLA on insulin sensitivity in some mouse studies, we sought to compare the impact of dietary t10c12-CLA and c9t11-CLA on liver, adipose tissue, and systemic metabolism of adult lean mice. We fed 8 week-old C57Bl/6J male mice with low fat diets (10.5% Kcal from fat) containing 0.8% t10c12-CLA or c9t11-CLA for 9 or 38 days. Diets containing c9t11-CLA had minimal impact on the endpoints studied. However, 7 days after starting the t10c12-CLA diet, we observed a dramatic reduction in fat mass measured by NMR spectroscopy, which interestingly rebounded by 38 days. This rebound was apparently due to a massive accumulation of lipids in the liver, because adipose tissue depots were visually undetectable. Hepatic steatosis and the disappearance of adipose tissue after t10c12-CLA feeding was associated with elevated plasma insulin levels and insulin resistance, compared to mice fed a control diet or c9t11-CLA diet. Unexpectedly, despite being insulin resistant, mice fed t10c12-CLA had normal levels of blood glucose, without signs of impaired glucose clearance. Hepatic gene expression and fatty acid composition suggested enhanced hepatic de novo lipogenesis without an increase in expression of gluconeogenic genes. These data indicate that dietary t10c12-CLA may alter hepatic glucose and lipid metabolism indirectly, in response to the loss of adipose tissue in mice fed a low fat diet.

Diet-Induced Obesity in Cannabinoid-2 Receptor Knockout Mice and Cannabinoid Receptor 1/2 Double-Knockout Mice.

Evidence suggests that cannabinoid-1 receptor (CB1R) activation is associated with increased food intake and body weight gain. Human epidemiological studies, however, show decreased prevalence of obesity in cannabis users. Given the overlapping and complementary functions of the cannabinoid receptors (CB1R and CB2R), mice lacking CB2R and mice lacking both CB1R and CB2R were studied. A high-fat diet was used to study metabolic changes in male mice lacking CB2R (CB2-/- ) or lacking both CB1R and CB2R (double-knockout [CB-DKO]) compared with wild-type mice. When CB2-/- mice were maintained on a high-fat diet, their weight gain was not different from wild-type mice (gaining 19 and 21g, respectively), whereas CB-DKO mice gained only 5g. There were no significant differences in food intake or locomotor activity between the three groups. Respiratory exchange rate and heat production were elevated in CB-DKO mice, with upregulation of adipose tissue thermogenic genes. Glucose tolerance test and insulin levels indicated increased insulin sensitivity in CB-DKO mice, whereas CB2-/- displayed signs of impaired glucose clearance. These results indicate that lacking both CB1R and CB2R protected mice from diet-induced obesity, possibly through the prominent role of CB1R in obesity or through an interactive effect of both receptors.

WASH Regulates Glucose Homeostasis by Facilitating Glut2 Receptor Recycling in Pancreatic β-Cells.

WASH is an endosomal protein belonging to the Wiskott-Aldrich syndrome protein superfamily that participates in endosomal receptor trafficking by facilitating tubule fission via activation of the ubiquitously expressed Arp2/3 complex. While several studies have begun to elucidate an understanding of the functions of WASH in cells lines, the in vivo function of WASH has not been fully elucidated, since total body deletion in mice leads to early embryonic lethality. To circumvent this problem, we have used a WASH conditional knockout mouse model to investigate the role of WASH in the pancreas. We find that pancreas-specific deletion of WASH leads to impaired blood glucose clearance and reduced insulin release upon glucose stimulation. Furthermore, WASH depletion results in impaired trafficking of Glut2 in pancreatic β-cells as a consequence of an intracellular accumulation of Glut2 and overall decreased levels of Glut2 protein. Taken together, these results indicate that WASH participates in pancreatic β-cell glucose sensing and whole-body glucose homeostasis. Thus, patients harboring mutations in components of the WASH complex could be at risk for developing type 2 diabetes.

Sexually dimorphic metabolic responses mediated by CRF2 receptor during nutritional stress in mice

BackgroundChronic stress is a major contributor in the development of metabolic syndrome and associated diseases, such as diabetes. High-fat diet (HFD) and sex are known modifiers of metabolic parameters. Peptide hormones corticotropin-releasing factor (CRF) and urocortins (UCN) mediate stress responses via activation and feedback to the hypothalamic-pituitary-adrenal (HPA) axis. UCN3 is a marker of pancreatic β-cell differentiation, and UCN2 is known to ameliorate glucose levels in mice rendered diabetic with HFD. CRF receptor 2 (CRF2) is the only known cognate receptor for UCN2/3. Here, we ascertained the role of CRF2 in glucose clearance, insulin sensitivity, and other parameters associated with metabolic syndrome in a mouse model of nutritional stress.MethodsWild-type (WT) and Crhr2−/− (null) mice of both sexes were fed either normal chow diet or HFD. After 8 weeks, blood glucose levels in response to glucose and insulin challenge were determined. Change in body and fat mass, plasma insulin, and lipid profile were assessed. Histological evaluation of liver sections was performed.ResultsHere, we show that genotype (Crhr2), sex, and diet were all independent variables in the regulation of blood glucose levels, body and fat mass gain/redistribution, and insulin resistance. Surprisingly, CRF2-deficient mice (Crhr2−/−) male mice showed similarly impaired glucose clearance on HFD and chow. HFD-fed female Crhr2−/− mice redistributed their fat depots that were distinct from wild-type females and male mice on either diet. Blood cholesterol and low-density lipoprotein (LDL) levels were elevated significantly in male Crhr2−/− mice; female Crhr2−/− mice were protected. Male, but not female Crhr2−/− mice developed peripheral insulin resistance. HFD, but not chow-fed wild-type male mice developed hepatic macrovesicular steatosis. In contrast, livers of Crhr2−/− male mice showed microvesicular steatosis on either diet, whereas livers of female mice on this 8-week HFD regimen did not develop steatosis.ConclusionsCRF2 receptor dysregulation is a sexually dimorphic risk factor in development of pre-diabetic and metabolic symptoms.

Abstract 003: Mrap2 Dissociate Mc4r-Mediated Sympathetic Control of Metabolism and Blood Pressure

The brain melanocortin-4 receptor (MC4R) plays an important in the control of food intake and energy expenditure by increasing thermogenic sympathetic nerve activity (SNA). In addition, brain MC4R-mediated activation of SNA subserving cardiovascular organs such as the kidneys increase blood pressure. The melanocortin receptor accessory protein 2 (MRAP2) regulates the activity of the MC4R and other G-protein coupled receptors, but its specific role in MC4R-containing neurons is not clear . We hypothesized that MRAP2 in MC4R neurons is essential for the regulation of SNA, energy homeostasis and blood pressure. We generated mice (MRAP2 MC4R ) that lack MRAP2 in MC4R neurons by crossing MRAP2 fl/fl mice with MC4R Cre mice and confirmed Cre recombinase activity in MC4R neurons using td-Tomato reporter mice. Interestingly, the MRAP2 MC4R mice displayed obesity as indicated by the increased (p<0.05) body weight (males: 40.1±2.2 vs 32.9±0.9g in littermate controls, females: 28.6±2.8 vs 24.2±1.3g in controls at 16 weeks of age) and fat mass, but not lean mass. Weights of fat pads and liver were also significantly elevated in the MRAP2 MC4R relative to littermate controls. Food intake was increased in the MRAP2 MC4R mice relative to littermate controls (males: 4.7±0.3 vs 3.9±0.3g and females: 3.5±0.2 vs 2.8±0.2g). Glucose and insulin tolerance tests revealed impaired glucose tolerance and insulin-induced glucose clearance in MRAP2 MC4R mice compared to littermate controls. Baseline brown adipose tissue (BAT) SNA tended to be lower in MRAP2 MC4R mice relative to controls. Moreover, intracerebroventricular (icv) injection of MTII (MC4R agonist, 1 μg) increased BAT SNA in control mice (107±31%) but not in MRAP2 MC4R mice (18±24%, p=0.02). On the other hand, icv the MTII (1 and 2 μg)-induced increase in renal SNA (p=0.2) and blood pressure (p=0.4) was not different in MRAP2 MC4R (100±32% and 15±8mmHg, respectively) relative to controls (74±24% and 12±6mmHg). These findings support a critical role for MRAP2 in uncoupling neuronal MC4R-mediated control of regional sympathetic traffic impacting energy metabolism versus blood pressure.

Effect of adipocyte-derived IGF-I on adipose tissue mass and glucose metabolism in the Berlin Fat Mouse

Besides liver, IGF-I is expressed in adipose tissue. However, the effects of this local IGF-I on adipose tissue and metabolism are unclear. We generated adipocyte-specific knock-out mice on the background of the Berlin Fat Mouse Inbred (BFMI) line to evaluate the contribution of adipocyte-IGF-I on glucose metabolism and adipose tissue development. BFMI mice are obese, non-diabetic with elevated plasma insulin and IGF-I concentration. The knock-out in adipocytes led to a total white adipose tissue expression of 50–60% due to unaltered Igf-1 expression in stromavascular cells. The lack of IGF-I from adipocytes did not alter plasma IGF-I concentration. BFMIChr3-Igf-I-KOQ-AT mice had reduced adipose tissue mass in most depots. During oral glucose tolerance tests, BFMIChr3-Igf-I-KOQ-AT mice showed an impaired glucose clearance (p = .03). Interestingly, insulin action was enhanced during insulin tolerance tests (p = .05). In conclusion, adipocyte-specific IGF-I ablation in obese BFMI mice results in reduced adipose tissue mass and thereby alters glucose metabolism.

Chronic High Dose Zinc Supplementation Induces Visceral Adipose Tissue Hypertrophy without Altering Body Weight in Mice.

The trace element zinc plays an important role in human life. Zinc deficiency impairs growth, reproduction, metabolism and immunity in both human and animals. Thus, zinc supplementation is recommended in daily life. However, the effect of long-term chronic zinc supplementation on adipose homeostasis has not been well elucidated. In the current study, mice were supplemented with zinc sulfate in the drinking water for 20 weeks. The results suggested that chronic zinc supplementation impaired systemic glucose clearance after exogenous insulin or glucose challenges, as compared to the control mice. Further study revealed that chronic zinc supplementation made no difference to body weight, but increased visceral adipose tissue weight and adipocyte size. In addition, gene expression of leptin and IL6 in the visceral adipose tissue of zinc-supplemented mice were higher than those of control mice. Moreover, serum level of leptin of the zinc-supplemented mice was twice as high as that of the control mice. Besides, phosphorylation level of AKT T308 was attenuated in the perirenal adipose tissue of zinc-supplemented mice. In comparison, the expression of macrophage marker genes and lipogenic genes were not affected by chronic zinc supplementation, but the protein levels of FAS and SCD1 decreased or tended to decrease in the perirenal adipose tissue of zinc-supplemented mice, as compared to the control mice. Our findings suggest that chronic high dose zinc supplementation induces visceral adipose tissue hypertrophy and impairs AKT signaling in perirenal adipose tissue.

Age-dependent alterations of glucose clearance and homeostasis are temporally separated and modulated by dietary fat

Diet- and age-dependent changes in glucose regulation in mice occur, but the temporal development, mechanisms and influence of dietary fat source remain to be defined.We followed metabolic changes in three groups of mice including a low-fat diet (LFD) reference group and two high-fat, high-sucrose diets based on either fish oil (FOD) or soybean oil (SOD), rich in ω3- and ω6-polyunsaturated fatty acids, respectively, to closely monitor the age-dependent development in glucose regulation in both obese (SOD-fed) and lean (LFD- and FOD-fed) mice. We assessed glucose homeostasis and glucose clearance at week 8, 12, 16, 24, 31, and 39 and performed an insulin tolerance test at week 40. We further analyzed correlations between the gut microbiota and key metabolic parameters.Interestingly, alterations in glucose homeostasis and glucose clearance were temporally separated, while 16S ribosomal gene amplicon sequencing revealed that gut microbial alterations formed correlation clusters with fat mass and either glucose homeostasis or glucose clearance, but rarely both. Importantly, effective glucose clearance was maintained in FOD- and even increased in LFD-fed mice, whereas SOD-fed mice rapidly developed impaired glucose clearance followed by a gradual improvement from week 8 to week 39. All groups had similar responses to insulin 40 weeks post diet initiation despite severe nonalcoholic steatohepatitis in SOD-fed mice.We conclude that age-related alterations in glucose regulation may occur in both lean and obese mice and are modulated by dietary fat as indicated by the sustained metabolic homeostasis observed in mice fed ω3-polyunsaturated fatty acids.

Central insulin dysregulation and energy dyshomeostasis in two mouse models of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder worldwide. While the causes of AD are not known, several risk factors have been identified. Among these, type two diabetes (T2D), a chronic metabolic disease, is one of the most prevalent risk factors for AD. Insulin resistance, which is associated with T2D, is defined as diminished or absent insulin signaling and is reflected by peripheral blood hyperglycemia and impaired glucose clearance. In this study, we used complementary approaches to probe for peripheral insulin resistance, central nervous system (CNS) insulin sensitivity and energy homeostasis in Tg2576 and 3xTg-AD mice, two widely used animal models of AD. We report that CNS insulin signaling abnormalities are evident months before peripheral insulin resistance. In addition, we find that brain energy metabolism is differentially altered in both mouse models, with 3xTg-AD mice showing more extensive changes. Collectively, our data suggest that early AD may reflect engagement of different signaling networks that influence CNS metabolism, which in turn may alter peripheral insulin signaling.

Acute Hypoglycemia in Healthy Humans Impairs Insulin-Stimulated Glucose Uptake and Glycogen Synthase in Skeletal Muscle: A Randomized Clinical Study.

Hypoglycemia is the leading limiting factor in glycemic management of insulin-treated diabetes. Skeletal muscle is the predominant site of insulin-mediated glucose disposal. Our study used a crossover design to test to what extent insulin-induced hypoglycemia affects glucose uptake in skeletal muscle and whether hypoglycemia counterregulation modulates insulin and catecholamine signaling and glycogen synthase activity in skeletal muscle. Nine healthy volunteers were examined on three randomized study days: 1) hyperinsulinemic hypoglycemia (bolus insulin), 2) hyperinsulinemic euglycemia (bolus insulin and glucose infusion), and 3) saline control with skeletal muscle biopsies taken just before, 30 min after, and 75 min after insulin/saline injection. During hypoglycemia, glucose levels reached a nadir of ∼2.0 mmol/L, and epinephrine rose to ∼900 pg/mL. Hypoglycemia impaired insulin-stimulated glucose disposal and glucose clearance in skeletal muscle, whereas insulin signaling in glucose transport was unaffected by hypoglycemia. Insulin-stimulated glycogen synthase activity was completely ablated during hyperinsulinemic hypoglycemia, and catecholamine signaling via cAMP-dependent protein kinase and phosphorylation of inhibiting sites on glycogen synthase all increased.

Soluble CD93 Is Involved in Metabolic Dysregulation but Does Not Influence Carotid Intima-Media Thickness.

Type 2 diabetes and cardiovascular disease are complex disorders involving metabolic and inflammatory mechanisms. Here we investigated whether sCD93, a group XIV c-type lectin of the endosialin family, plays a role in metabolic dysregulation or carotid intima-media thickness (IMT). Although no association was observed between sCD93 and IMT, sCD93 levels were significantly lower in subjects with type 2 diabetes (n = 901, mean ± SD 156.6 ± 40.0 ng/mL) compared with subjects without diabetes (n = 2,470, 164.1 ± 44.8 ng/mL, P < 0.0001). Genetic variants associated with diabetes risk (DIAGRAM Consortium) did not influence sCD93 levels (individually or combined in a single nucleotide polymorphism score). In a prospective cohort, lower sCD93 levels preceded the development of diabetes. Consistent with this, a cd93-deficient mouse model (in addition to apoe deficiency) demonstrated no difference in atherosclerotic lesion development compared with apoe(-/-) cd93-sufficient littermates. However, cd93-deficient mice showed impaired glucose clearance and insulin sensitivity (compared with littermate controls) after eating a high-fat diet. The expression of cd93 was observed in pancreatic islets, and leaky vessels were apparent in cd93-deficient pancreases. We further demonstrated that stress-induced release of sCD93 is impaired by hyperglycemia. Therefore, we propose CD93 as an important component in glucometabolic regulation.

Diet-induced obesity, energy metabolism and gut microbiota in C57BL/6J mice fed Western diets based on lean seafood or lean meat mixtures

High protein diets may protect against diet-induced obesity, but little is known regarding the effects of different protein sources consumed at standard levels. We investigated how a mixture of lean seafood or lean meat in a Western background diet modulated diet-induced obesity, energy metabolism and gut microbiota. Male C57BL/6J mice fed a Western diet (WD) containing a mixture of lean seafood (seafood WD) for 12weeks accumulated less fat mass than mice fed a WD containing a mixture of lean meat (meat WD). Meat WD-fed mice exhibited increased fasting blood glucose, impaired glucose clearance, elevated fasting plasma insulin and increased plasma and liver lipid levels. We observed no first choice preference for either of the WDs, but over time, mice fed the seafood WD consumed less energy than mice fed the meat WD. Mice fed the seafood WD exhibited higher spontaneous locomotor activity and a lower respiratory exchange ratio (RER) than mice fed the meat WD. Thus, higher activity together with the decreased energy intake contributed to the different phenotypes observed in mice fed the seafood WD compared to mice fed the meat WD. Comparison of the gut microbiomes of mice fed the two WDs revealed significant differences in the relative abundance of operational taxonomic units (OTUs) belonging to the orders Bacteroidales and Clostridiales, with genes involved in metabolism of aromatic amino acids exhibiting higher relative abundance in the microbiomes of mice fed the seafood WD.

The RGD sequence present in IGFBP-2 is required for reduced glucose clearance after oral glucose administration in female transgenic mice.

Recent studies suggest that insulin-like growth factor-binding protein-2 (IGFBP-2) affects both growth and metabolism. Whereas negative growth effects are primarily due to negative interference with IGF-I, the mechanisms for metabolic interference of IGFBP-2 are less clear. As we demonstrate, overexpression of IGFBP-2 in transgenic mice is correlated with a decelerated clearance of blood glucose after oral administration. IGFBP-2 carries an integrin-binding domain (RGD motif), which has been shown to also mediate IGF-independent effects. We thus asked if higher serum levels of IGFBP-2 without an intact RGD motif would also partially block blood glucose clearance after oral glucose application. In fact, transgenic mice overexpressing mutated IGFBP-2 with higher levels of IGFBP-2 carrying an RGE motif instead of an RGD were not characterized by decelerated glucose clearance. Impaired glucose tolerance was correlated with lower levels of GLUT4 present in plasma membranes isolated from muscle tissues after glucose challenge. At the same time, activation of TBC1D1 was depressed in mice overexpressing wild-type but not mutated IGFBP-2. Although we do not have reason to assume altered activation of IGF-I receptor or PDK1/Akt activation in both models, we have identified increased levels of integrin-linked kinase and focal adhesion kinase dependent on the presence of the RGD motif. From our results we conclude that impaired glucose clearance in female IGFBP-2 transgenic mice is dependent on the presence of the RGD motif and that translocation of GLUT4 in the muscle may be regulated by IGFBP-2 via RGD-dependent mechanisms.

Pancreatic Islet APJ Deletion Reduces Islet Density and Glucose Tolerance in Mice.

Protection and replenishment of a functional pancreatic β-cell mass (BCM) are key goals of all diabetes therapies. Apelin, a small regulatory peptide, is the endogenous ligand for the apelin receptor (APJ) receptor. The apelin-APJ signaling system is expressed in rodent and human islet cells. Apelin exposure has been shown to inhibit and to stimulate insulin secretion. Our aim was to assess the influence of a selective APJ deletion in pancreatic islet cells on islet homeostasis and glucose tolerance in mice. Cre-LoxP strategy was utilized to mediate islet APJ deletion. APJ deletion in islet cells (APJ(Δislet)) resulted in a significantly reduced islet size, density and BCM. An ip glucose tolerance test showed significantly impaired glucose clearance in APJ(Δislet) mice. APJ(Δislet) mice were not insulin resistant and in vivo glucose-stimulated insulin secretion was reduced modestly. In vitro glucose-stimulated insulin secretion showed a significantly reduced insulin secretion by islets from APJ(Δislet) mice. Glucose clearance in response to ip glucose tolerance test in obese APJ(Δislet) mice fed a chronic high-fat (HF) diet, but not pregnant APJ(Δislet) mice, was impaired significantly. In addition, the obesity-induced adaptive elevations in mean islet size and fractional islet area were reduced significantly in obese APJ(Δislet) mice when compared with wild-type mice. Together, these findings demonstrate a stimulatory role for the islet cell apelin-APJ signaling axis in regulation of pancreatic islet homeostasis and in metabolic induced β-cell hyperplasia. The results indicate the apelin-APJ system can be exploited for replenishment of BCM.