Diet-induced Metabolic Dysfunction Research Articles

Maternal obesity during lactation may protect offspring from high fat diet-induced metabolic dysfunction

Background/ObjectivesThe current obesity epidemic has spurred exploration of the developmental origin of adult heath and disease. A mother’s dietary choices and health can affect both the early wellbeing and lifelong disease-risk of the offspring.Subjects/MethodsTo determine if changes in the mother’s diet and adiposity have long-term effects on the baby’s metabolism, independently from a prenatal insult, we utilized a mouse model of diet-induced-obesity and cross-fostering. All pups were born to lean dams fed a low fat diet but were fostered onto lean or obese dams fed a high fat diet. This study design allowed us to discern the effects of a poor diet from those of mother’s adiposity and metabolism. The weaned offspring were placed on a high fat diet to test their metabolic function.ResultsIn this feeding challenge, all male (but not female) offspring developed metabolic dysfunction. We saw increased weight gain in the pups nursed on an obesity-resistant dam fed a high fat diet, and increased pathogenesis including liver steatosis and adipose tissue inflammation, when compared to pups nursed on either obesity-prone dams on a high fat diet or lean dams on a low fat diet.ConclusionExposure to maternal over-nutrition, through the milk, is sufficient to shape offspring health outcomes in a sex- and organ-specific manner, and milk from a mother who is obesity-prone may partially protect the offspring from the insult of a poor diet.

An Extract of Russian Tarragon Prevents Obesity‐Related Ectopic Lipid Accumulation

The primary disorder underlying metabolic syndrome is insulin resistance due to excess body weight and abdominal visceral fat accumulation. In this study, it is asked if dietary intake of an ethanolic extract from Russian tarragon (Artemisia dracunculus L., termed PMI5011), shown to improve glucose utilization by enhancing insulin signaling in skeletal muscle, could prevent obesity-induced insulin resistance, skeletal muscle metabolic inflexibility, and ectopic lipid accumulation in the skeletal muscle and liver. Male wild-type mice are fed a high-fat diet alone or supplemented with PMI5011 (1% w/w) over 3 months. Dietary intake of PMI5011 improved fatty acid oxidation and metabolic flexibility in the skeletal muscle, reduced insulin levels, and enhanced insulin signaling in the skeletal muscle and liver independent of robust changes in expression of factors that control fatty acid oxidation. This corresponds with significantly reduced lipid accumulation in the skeletal muscle and liver, although body weight gain is comparable to a high-fat diet alone. Previous studies showed that PMI5011 enhances insulin sensitivity in the setting of established obesity-induced insulin resistance. The current study demonstrates that dietary intake of PMI5011 prevents high-fat diet-induced insulin resistance, metabolic dysfunction, and ectopic lipid accumulation in the skeletal muscle and liver without reducing body weight.

Frontline Science: High fat diet and leptin promote tumor progression by inducing myeloid-derived suppressor cells.

Obesity is a risk factor for cancer incidence and cancer mortality. The association of obesity and cancer is attributed to multiple factors, but the tightest linkage is with the chronic, low-grade inflammation that accompanies obesity. Myeloid-derived suppressor cells (MDSC) are known facilitators of cancer progression that act by suppressing the activation and function of tumor-reactive T cells. Because MDSC quantity and function are driven by chronic inflammation, we hypothesized that MDSC may accumulate in obese individuals and facilitate tumor growth by suppressing antitumor immunity. To test this hypothesis, tumor-bearing mice on a high fat or low fat diet (HFD or LFD) were assessed for tumor progression and the metabolic dysfunction associated with obesity. HFD enhanced the accumulation of MDSC, and the resulting MDSC had both beneficial and detrimental effects. HFD-induced MDSC protected mice against diet-induced metabolic dysfunction and reduced HFD-associated inflammation, but also increased the accumulation of fat, enhanced tumor progression, and spontaneous metastasis and reduced survival time. HFD-induced MDSC facilitated tumor growth by limiting the activation of tumor-reactive CD8+ T cells. Leptin, an adipokine that regulates appetite satiety and is overexpressed in obesity, undergoes crosstalk with MDSC in which leptin drives the accumulation of MDSC while MDSC down-regulate the production of leptin. Collectively, these studies demonstrate that although MDSC protect against some metabolic dysfunction associated with HFD they enhance tumor growth in HFD mice and that leptin is a key regulator linking HFD, chronic inflammation, immune suppression, and tumor progression.

Myeloid P2Y2 receptor promotes acute inflammation but is dispensable for chronic high-fat diet-induced metabolic dysfunction.

The purinergic receptor P2Y2 binds ATP to control chemotaxis of myeloid cells, and global P2Y2 receptor knockout mice are protected in models of acute inflammation. Chronic inflammation mediated by macrophages and other immune cells in adipose tissue contributes to the development of insulin resistance. Here, we investigate whether mice lacking P2Y2 receptors on myeloid cells are protected against acute and chronic inflammation. Wild-type mice were transplanted with either wild-type or P2Y2 receptor null bone marrow and treated with a sublethal dose of endotoxin as a model of acute inflammation, or fed a high-fat diet to induce obesity and insulin resistance as a model of chronic inflammation. P2Y2-/- chimeric mice were protected against acute inflammation. However, high-fat diet feeding induced comparable inflammation and insulin resistance in both WT and P2Y2-/- chimeric mice. Of note, confocal microscopy revealed significantly fewer crown-like structures, assemblies of macrophages around adipocytes, in P2Y2-/- chimeric mice compared to WT chimeric mice. We conclude that P2Y2 receptors on myeloid cells are important in mediating acute inflammation but are dispensable for the development of whole body insulin resistance in diet-induced obese mice.

Variable cartilage degradation in mice with diet-induced metabolic dysfunction: food for thought.

Human cohort studies have demonstrated a role for systemic metabolic dysfunction in osteoarthritis (OA) pathogenesis in obese patients. To explore the mechanisms underlying this metabolic phenotype of OA, we examined cartilage degradation in the knees of mice from different genetic backgrounds in which a metabolic phenotype was established by various dietary approaches. Wild-type C57BL/6J mice and genetically modified mice (hCRP, LDLr-/-. Leiden and ApoE*3Leiden.CETP mice) based on C57BL/6J background were used to investigate the contribution of inflammation and altered lipoprotein handling on diet-induced cartilage degradation. High-caloric diets of different macronutrient composition (i.e., high-carbohydrate or high-fat) were given in regimens of varying duration to induce a metabolic phenotype with aggravated cartilage degradation relative to controls. Metabolic phenotypes were confirmed in all studies as mice developed obesity, hypercholesteremia, glucose intolerance and/or insulin resistance. Aggravated cartilage degradation was only observed in two out of the twelve experimental setups, specifically in long-term studies in male hCRP and female ApoE*3Leiden.CETP mice. C57BL/6J and LDLr-/-. Leiden mice did not develop HFD-induced OA under the conditions studied. Osteophyte formation and synovitis scores showed variable results between studies, but also between strains and gender. Long-term feeding of high-caloric diets consistently induced a metabolic phenotype in various C57BL/6J (-based) mouse strains. In contrast, the induction of articular cartilage degradation proved variable, which suggests that an additional trigger might be necessary to accelerate diet-induced OA progression. Gender and genetic modifications that result in a humanized pro-inflammatory state (human CRP) or lipoprotein metabolism (human-E3L.CETP) were identified as important contributing factors.

Intermittent fasting promotes adipose thermogenesis and metabolic homeostasis via VEGF-mediated alternative activation of macrophage

Intermittent fasting (IF), a periodic energy restriction, has been shown to provide health benefits equivalent to prolonged fasting or caloric restriction. However, our understanding of the underlying mechanisms of IF-mediated metabolic benefits is limited. Here we show that isocaloric IF improves metabolic homeostasis against diet-induced obesity and metabolic dysfunction primarily through adipose thermogenesis in mice. IF-induced metabolic benefits require fasting-mediated increases of vascular endothelial growth factor (VEGF) expression in white adipose tissue (WAT). Furthermore, periodic adipose-VEGF overexpression could recapitulate the metabolic improvement of IF in non-fasted animals. Importantly, fasting and adipose-VEGF induce alternative activation of adipose macrophage, which is critical for thermogenesis. Human adipose gene analysis further revealed a positive correlation of adipose VEGF-M2 macrophage-WAT browning axis. The present study uncovers the molecular mechanism of IF-mediated metabolic benefit and suggests that isocaloric IF can be a preventive and therapeutic approach against obesity and metabolic disorders.

Abstract P152: Female Mice Are Not Protected From High Fat Diet-induced Metabolic Dysfunction

Female clinical populations are generally protected from obesity-related blood pressure and metabolic complications such as hypertension and type II diabetes, despite increased adiposity compared to males. Similar cardiovascular protection has been observed in obese female mice produced by high fat diet (HFD) feeding, a well-established animal model of obesity. The impact of HFD on glucose homeostasis and insulin action in relation to gender differences, however, remains unclear. In this study, we tested the hypothesis that female mice would be protected from HFD-induced glucose intolerance and insulin resistance. To test this, five-week old male and female C57BL/6J mice were placed on control chow diet or 60% HFD for 12 weeks (n=11 chow male; n=6 chow female; n=15 HFD male; n=5 HFD female). Body composition was measured and glucose tolerance testing (GTT; 2g/kg of 50% dextrose) and insulin tolerance testing (ITT; 0.75 units/kg) were performed during the last week of diet. Females had lower body mass compared with males over the 12-week study period. Both genders increased body mass to a similar extent in response to chow diet (24.6±1.7 male vs. 26.5±2.3% female; p=0.517), and HFD (85.0±2.1 males vs. 79.8±6.7% females; p=0.332). HFD females had similar adiposity compared with males (22.9±0.7 males vs. 22.5±1.6% females; p=0.780). HFD reduced insulin sensitivity in male mice [area under the curve (AUC) for blood glucose levels during ITT: -5903±662 chow vs. -1748±1024 HFD; p=0.005] and female mice (-6599±966 chow vs. -2904±1507 HFD; p=0.041), with no differences between genders (p=0.567). HFD also resulted in glucose intolerance in male (AUC for blood glucose levels during GTT: 40262±1769 chow vs. 52800±2502 HFD; p=0.001) and female (36951±2270 chow vs. 55507±3582 HFD; p=0.001) mice, with no gender differences (p=0.582). These data suggest that in contrast to our hypothesis, HFD female mice develop obesity-related insulin resistance and glucose intolerance to a similar extent as males. These findings have important implications for use of this mouse model to study impact of gender on metabolic function in obesity.

Moderate alcohol intake induces thermogenic brown/beige adipocyte formation via elevating retinoic acid signaling.

Clinically, low and moderate alcohol intake improves human health with protection against metabolic syndromes, including type 2 diabetes; however, mechanisms that are associated with these effects remain to be elucidated. The aims of this study were to investigate the effects of moderate alcohol intake on thermogenic brown/beige adipocyte formation and glucose and lipid homeostasis, as well as the involvement of retinoic acid (RA) signaling in the entire process. C57BL6 male mice were supplemented with 8% (w/v) alcohol in water for 1 or 4 mo. Alcohol intake prevented body weight gain, induced the formation of uncoupling protein 1-positive beige adipocytes in white adipose tissue, and increased thermogenesis in mice, which is associated with decreased serum glucose and triacylglycerol levels. Mechanistically, alcohol intake increased RA levels in serum and adipose tissue, which was associated with increased expression of aldehyde dehydrogenase family 1 subfamily A1 (Aldh1a1). When RA receptor-α signaling was conditionally blocked in platelet-derived growth factor receptor-α-positive adipose progenitors, the effects of alcohol on beige adipogenesis were largely abolished. Finally, moderate alcohol prevented high-fat diet-induced obesity and metabolic dysfunction. In conclusion, moderate alcohol intake induces thermogenic brown/beige adipocyte formation and promotes glucose and lipid oxidation via elevation of RA signaling.-Wang, B., Wang, Z., de Avila, J. M., Zhu, M.-J., Zhang, F., Gomez, N. A., Zhao, L., Tian, Q., Zhao, J., Maricelli, J., Zhang, H., Rodgers, B. D., Du, M. Moderate alcohol intake induces thermogenic brown/beige adipocyte formation via elevating retinoic acid signaling.

Nod2 and Nod2-regulated microbiota protect BALB/c mice from diet-induced obesity and metabolic dysfunction

Genetics plays a central role in susceptibility to obesity and metabolic diseases. BALB/c mice are known to be resistant to high fat diet (HFD)-induced obesity, however the genetic cause remains unknown. We report that deletion of the innate immunity antibacterial gene Nod2 abolishes this resistance, as Nod2−/− BALB/c mice developed HFD-dependent obesity and hallmark features of metabolic syndrome. Nod2−/− HFD mice developed hyperlipidemia, hyperglycemia, glucose intolerance, increased adiposity, and steatosis, with large lipid droplets in their hepatocytes. These changes were accompanied by increased expression of immune genes in adipose tissue and differential expression of genes for lipid metabolism, signaling, stress, transport, cell cycle, and development in both adipose tissue and liver. Nod2−/− HFD mice exhibited changes in the composition of the gut microbiota and long-term treatment with antibiotics abolished diet-dependent weight gain in Nod2−/− mice, but not in wild type mice. Furthermore, microbiota from Nod2−/− HFD mice transferred sensitivity to weight gain, steatosis, and hyperglycemia to wild type germ free mice. In summary, we have identified a novel role for Nod2 in obesity and demonstrate that Nod2 and Nod2-regulated microbiota protect BALB/c mice from diet-induced obesity and metabolic dysfunction.

High Fat Diet-Induced Metabolic Dysfunction Leads to Aggravation of Osteoarthritis and Inflammation of the Knee Joint in Two Different Murine Models

High Fat Diet-Induced Metabolic Dysfunction Leads to Aggravation of Osteoarthritis and Inflammation of the Knee Joint in Two Different Murine Models

Loss of macrophage fatty acid oxidation does not potentiate systemic metabolic dysfunction.

Fatty acid oxidation in macrophages has been suggested to play a causative role in high-fat diet-induced metabolic dysfunction, particularly in the etiology of adipose-driven insulin resistance. To understand the contribution of macrophage fatty acid oxidation directly to metabolic dysfunction in high-fat diet-induced obesity, we generated mice with a myeloid-specific knockout of carnitine palmitoyltransferase II (CPT2 Mϕ-KO), an obligate step in mitochondrial long-chain fatty acid oxidation. While fatty acid oxidation was clearly induced upon IL-4 stimulation, fatty acid oxidation-deficient CPT2 Mϕ-KO bone marrow-derived macrophages displayed canonical markers of M2 polarization following IL-4 stimulation in vitro. In addition, loss of macrophage fatty acid oxidation in vivo did not alter the progression of high-fat diet-induced obesity, inflammation, macrophage polarization, oxidative stress, or glucose intolerance. These data suggest that although IL-4-stimulated alternatively activated macrophages upregulate fatty acid oxidation, fatty acid oxidation is dispensable for macrophage polarization and high-fat diet-induced metabolic dysfunction. Macrophage fatty acid oxidation likely plays a correlative, rather than causative, role in systemic metabolic dysfunction.

Application of an In Vivo Hepatic Triacylglycerol Production Method in the Setting of a High-Fat Diet in Mice.

High-fat (HF) diets typically promote diet-induced obesity (DIO) and metabolic dysfunction (i.e., insulin resistance, hypertriglyceridemia, and hepatic steatosis). Dysfunction of triacylglycerol (TAG) metabolism may contribute to the development of hepatic steatosis, via increased de novo lipogenesis or repackaging of circulating nonesterified fatty acids (NEFAs). Hepatic TAG production (HTP) rate can be assessed through injecting mice with nonionic detergents that inhibit tissue lipoprotein lipase. Potential confounding effects of detergent-based HTP tests (HTPTs) used in longitudinal studies—including the impact on food intake, energy balance, and weight gain—have not been reported. To examine this, male C57BL/6J mice were fed a 10% or 60% kcal diet. After 4 weeks, the mice underwent an HTPT via poloxamer 407 intraperitoneal injections (1000 mg/kg). Weight gain, energy intake, and postabsorptive TAG levels normalized 7–10 days post-HTPT. The post-HTPT recovery of body weight and energy intake suggest that, in metabolic phenotyping studies, any additional sample collection should occur at least 7–10 days after the HTPT to reduce confounding effects. Diet-specific effects on HTP were also observed: HF-fed mice had reduced HTP, plasma TAG, and NEFA levels compared to controls. In conclusion, the current study highlights the procedural and physiological complexities associated with studying lipid metabolism using a HTPT in the DIO mouse model.

Amentoflavone protects against high fat-induced metabolic dysfunction: Possible role of the regulation of adipogenic differentiation.

In the present study, we evaluated the protective effects of amentoflavone (AMF) against high-fat (HF) diet-induced metabolic dysfunction and focused on the influence of AMF on adipogenic differentiation during 3T3-L1 adipocyte differentiation. For this purpose, male Wistar rats were fed a HF diet or a HF diet with AMF (10 or 50 mg/kg). We found that AMF protected against HF diet-induced metabolic dysfunction in a dose-dependent manner, as evidenced by a decrease in the fasting blood glucose levels, fasting insulin levels and the homeostatic model assessment-insulin resistance index (HOMA-IR), as well as by a decrease in the glucose level, as shown by the intraperitoneal glucose tolerance test and intraperitoneal insulin tolerance test. Moreover, the results revealed that AMF significantly inhibited the increase in body weight, the weight of perirenal adipose tissues and the serum triglyceride (TG) content of the rats fed the HF diet in a dose-dependent manner. AMF also inhibited the accumulation of oil droplets in differentiated 3T3-L1 adipocytes in a concentration-dependent manner. The incubation of the cells with AMF for 0–8, 0–2, 2–4, or 4–8 days markedly inhibited adipogenesis. During the early phase of the adipocyte differentiation of 3T3-L1 cells, AMF decreased CCAAT/enhancer-binding protein (C/EBP) β expression in a concentration-dependent manner, leading to the inhibition of mitotic clonal expansion (MCE). Moreover, our results demonstrated that AMF significantly increased reactive oxygen species (ROS) generation in the cells and the antioxidant, N-acetylcysteine (NAC), markedly attenuated the inhibitory effects of AMF on adipogenesis. AMF also inhibited the expression of peroxisome proliferator-activated receptor γ (PPARγ) and C/EBPα and the expression of downstream targets in a concentration-dependent manner. The overexpression of PPARγ and C/EBPα (by transfection with respective overexpression plasmids) attentuated the inhibitory effects of AMF on the formation of oil droplets. The inhibitory effects of AMF on adipocyte differentiation may contribute to its protective effects against HF diet-induced metabolic dysfunction. Overall, the data in our study provide novel insight into the mechanisms responsible for the protective effects of AMF against HF diet-induced metabolic dysfunction and those for its inhibitory effect on adipocyte differentiation.

0080 : Involvement of the sympathetic nervous system in the development of carbohydrate metabolism disorders

The causal role of sympathetic nervous system in the development of metabolic disorders has not been clearly defined. The aim of the study was to determine if a chronic increase of the sympathetic nervous activity can induce and/or accelerate the development of glucose metabolism disorders. For that purpose, we used a transgenic mouse model, in which the gene encoding for the reuptake norepinephrine transporter (NET) has been deleted; these animals display increased urinary catecholamine levels. Carbohydrate homeostasis (intraperitoneal glucose tolerance test, IPGTT, insulin tolerance test, ITT, insulin rates) was studied in heterozygous NET knockout mice (±) or wild-type mice (+/+) at 10, 20 and 25 weeks old. Mice were then fed either with normal chow or 30% w/v fructose in drinking water; glucose metabolism was assessed again after 15 weeks of such diet. Heterozygous mice displayed glucose intolerance already at 10 weeks old (area under the curve of the IPGTT (AUC; %) = 24859 vs 18016, p=0.004); similar results were obtained at 25 weeks old, i.e, just before starting the fructose diet: AUC = 24524 vs 20573, p=0.005 for ± and +/+ mice respectively. Moreover sensibility to insulin seemed to be diminished in ± mice compared to +/+ mice (insulin rate = 1.12 vs 0.86 μg/L and HOMAIR= 11.1 vs 8.4). Heterozygous animals were also much more sensitive to high fructose, since a 20% increase in the AUC of the IPGTT was obtained at the end of the high fructose diet, compared to the 2% increase in +/+ mice. This was associated with a decrease of insulin sensibility (HOMA-IR of ± mice = 11.1 vs 18.1, p=0.01, before and after fructose diet respectively). Our data show that constitutive chronic sympathetic hyperactivity can induce the early development of carbohydrate metabolism disorders. Moreover, it seems to represent a major factor of susceptibility to diet-induced metabolic dysfunction. The author hereby declares no conflict of interest

IL-18 Production from the NLRP1 Inflammasome Prevents Obesity and Metabolic Syndrome

Interleukin-18 (IL-18) is activated by Caspase-1 in inflammasome complexes and has anti-obesity effects; however, it is not known which inflammasome regulates this process. We found that mice lacking the NLRP1 inflammasome phenocopy mice lacking IL-18, with spontaneous obesity due to intrinsic lipid accumulation. This is exacerbated when the mice are fed a high-fat diet (HFD) or a high-protein diet, but not when mice are fed a HFD with low energy density (high fiber). Furthermore, mice with an activating mutation in NLRP1, and hence increased IL-18, have decreased adiposity and are resistant to diet-induced metabolic dysfunction. Feeding these mice a HFD further increased plasma IL-18 concentrations and strikingly resulted in loss of adipose tissue mass and fatal cachexia, which could be prevented by genetic deletion of IL-18. Thus, NLRP1 is an innate immune sensor that functions in the context of metabolic stress to produce IL-18, preventing obesity and metabolic syndrome.

Diet-Induced Podocyte Dysfunction in Drosophila and Mammals

Diabetic nephropathy is a major cause of end-stage kidney disease. Characterized by progressive microvascular disease, most efforts have focused on injury to the glomerular endothelium. Recent work has suggested a role for the podocyte, a highly specialized component of the glomerular filtration barrier. Here, we demonstrate that the Drosophila nephrocyte, a cell analogous to the mammalian podocyte, displays defects that phenocopy aspects of diabetic nephropathy in animals fed chronic high dietary sucrose. Through functional studies, we identify an OGT-Polycomb-Knot-Sns pathway that links dietary sucrose to loss of the Nephrin ortholog Sns. Reducing OGT through genetic or drug means is sufficient to rescue loss of Sns, leading to overall extension of lifespan. We demonstrate upregulation of the Knot ortholog EBF2 in glomeruli of human diabetic nephropathy patients and a mouse ob/ob diabetes model. Furthermore, we demonstrate rescue of Nephrin expression and cell viability in ebf2(-/-) primary podocytes cultured in high glucose.

Effects of dietary fat profile on gut permeability and microbiota and their relationships with metabolic changes in mice.

To distinguish the effects of dietary fat profile on gut parameters and their relationships with metabolic changes and to determine the capacity of n-3 fatty acids to modify gut variables in the context of diet-induced metabolic dysfunctions. Mice received control or high-fat diets emphasizing saturated (HFD-sat), n-6 (HFD-n6), or n-3 (HFD-n3) fatty acids for 8 weeks. In another cohort, mice that were maintained on HFD-sat received n-3-rich fish oil or resolvin D1 supplementation. HFD-sat and HFD-n6 induced similar weight gain, but only HFD-sat increased index of insulin resistance (HOMA-IR), colonic permeability, and mesenteric fat inflammation. Hydrogen sulfide-producing bacteria were one of the major groups driving the diet-specific changes in gut microbiome, with the overall microbial profile being associated with changes in body weight, HOMA-IR, and gut permeability. In mice maintained on HFD-sat, fish oil and resolvin D1 restored barrier function and reduced inflammation in the colon but were unable to normalize HOMA-IR. Different dietary fat profiles led to distinct intestinal and metabolic outcomes that are independent of obesity. Interventions targeting inflammation successfully restored gut health but did not reverse systemic aspects of diet-induced metabolic dysfunction, implicating separation between gut dysfunctions and disease-initiating and/or -maintaining processes.

0145 : Involvement of the sympathetic nervous system in the development of metabolic disorders

If sympathetic hyperactivity seems to be associated to several components of the metabolic syndrome, its involvement in the development of metabolic syndrome has not been clearly defined. It was to determine if a chronic increase of the sympathetic nervous activity is a sufficient condition for the development of metabolic disorders. For that purpose, we used a transgenic mouse model, in which the gene coding for the reuptake norepinephrine transporter (NET) has been deleted; these animals display increased plasma catecholamine rates, associated to slight increases in blood pressure and heart rate. We focused on the consequences of this sympathetic hyperactivity on glucose and lipid metabolism in this mouse model. Heterozygous NET knockout mice (+/-) or wild-type mice (+/+) were fed either with a normal chow or a 30% w/v fructose in drinking water during a period of 15 weeks to induce metabolic disorders. Metabolic parameters (plasma triglycerides and total cholesterol, intraperitoneal glucose tolerance test, IPGTT) were measured after a 4h fasting period before treatment and then repeated every 5 weeks. No significant difference on triglycerides or cholesterol rates could be detected after the 15 weeks period. Heterozygous mice displayed clear glucose intolerance already before starting the fructose diet (area under the curve (%)=25434 vs 20822, p=0.013 for +/- and +/+ mice respectively). These animals were also much more sensitive to high fructose, since a 50% increase in the area under the curve of the IPGTT was obtained at the end of the high fructose diet, compared to the 11% increase in +/+ mice. Our data suggest that constitutive chronic sympathetic hyperactivity can induce the early development of carbohydrate metabolism disorders. Moreover, it seems to represent a major factor of susceptibility to dietinduced metabolic dysfunction.

Abnormal Regulation of Placental Growth Factor in Skeletal Muscle of Western‐Diet Fed Mice

Diabetics often develop peripheral artery disease (PAD). Arteriogenesis can preserve blood flow distal to occlusion and limit skeletal muscle ischemia in PAD, but is reduced in diabetics by an undefined mechanism. Placental growth factor (PLGF, a VEGF family protein) is a key arteriogenic factor. Therefore, we hypothesized that skeletal muscle PLGF expression and/or regulation could be abnormal in diabetic PAD. We tested this hypothesis in 3 mouse models with varying degrees of metabolic dysfunction: Western diet (WD) fed C57BL/6J (C57‐WD; n=52), control diet (CD) fed ApoE‐/‐ (ApoE‐CD; n=38) and WD fed ApoE‐/‐ (ApoE‐WD; n=32). CD fed C57BL/6J (C57‐CD; n=48) served as controls. Males and females were studied. Metabolic status was characterized by measuring relevant plasma values. After 6 mo on the diets, skeletal muscle PLGF was assessed under baseline conditions (n=58) and 3‐28 d post‐femoral artery occlusion (n=112). VEGF‐A was measured for comparison. Baseline skeletal muscle PLGF protein was decreased in all WD fed groups (p<0.005), with no effect of gender or strain. Regression analysis of PLGF vs metabolic parameters revealed modest correlation with plasma insulin (r2=0.44, p<0.0001). PLGF was sharply elevated in skeletal muscle of C57‐CD mice after femoral occlusion, peaking ~10 d post‐occlusion. This response was decreased and delayed in C57‐WD mice (p<0.05). Even more strikingly, upregulation of PLGF by occlusion was completely abolished in ApoE‐CD and ApoE‐WD mice. We conclude that in skeletal muscle, Western diet‐induced metabolic dysfunction both reduces baseline levels of PLGF and inhibits its upregulation by the physiological stimulus of occlusion. This phenomenon may contribute to the poor arteriogenic response in diabetes. Support: R01 HL084494 (PL).

Systemic VEGF-A Neutralization Ameliorates Diet-Induced Metabolic Dysfunction

The vascular endothelial growth factor (VEGF) family of cytokines are important regulators of angiogenesis that have emerged as important targets for the treatment of obesity. While serum VEGF levels rise during obesity, recent studies using genetic models provide conflicting evidence as to whether VEGF prevents or accelerates metabolic dysfunction during obesity. In the current study, we sought to identify the effects of VEGF-A neutralization on parameters of glucose metabolism and insulin action in a dietary mouse model of obesity. Within only 72 h of administration of the VEGF-A-neutralizing monoclonal antibody B.20-4.1, we observed almost complete reversal of high-fat diet-induced insulin resistance principally due to improved insulin sensitivity in the liver and in adipose tissue. These effects were independent of changes in whole-body adiposity or insulin signaling. These findings show an important and unexpected role for VEGF in liver insulin resistance, opening up a potentially novel therapeutic avenue for obesity-related metabolic disease.