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Accumulation of triacylglycerols (TAGs) and acylcarnitines in skeletal muscle upon high-fat (HF) feeding is the resultant of fatty acid uptake and oxidation and is associated with insulin resistance. As medium-chain fatty acids (MCFAs) are preferentially β-oxidized over long-chain fatty acids, we examined the effects of medium-chain TAGs (MCTs) and long-chain TAGs (LCTs) on muscle lipid storage and whole-body glucose tolerance. Rats fed a low-fat (LF), HFLCT, or an isocaloric HFMCT diet displayed a similar body weight gain over 8 weeks of treatment. Only HFLCT increased myocellular TAG (42.3 ± 4.9, 71.9 ± 6.7, and 48.5 ± 6.5 µmol/g for LF, HFLCT, and HFMCT, respectively, P < 0.05) and long-chain acylcarnitine content (P < 0.05). Neither HF diet increased myocellular diacylglycerol (DAG) content. Intraperitoneal (IP) glucose tolerance tests (1.5 g/kg) revealed a significantly decreased glucose tolerance in the HFMCT compared to the HFLCT-fed rats (802 ± 40, 772 ± 18, and 886 ± 18 area under the curve for LF, HFLCT, and HFMCT, respectively, P < 0.05). Finally, no differences in myocellular insulin signaling after bolus insulin injection (10 U/kg) were observed between LF, HFLCT, or HFMCT-fed rats. These results show that accumulation of TAGs and acylcarnitines in skeletal muscle in the absence of body weight gain do not impede myocellular insulin signaling or whole-body glucose intolerance. [ABSTRACT FROM AUTHOR]

Objective: It is believed that an organism remains normoglycemic despite an increase in the beta-cell mass because of decreased insulin production by beta-cells on a per-cell basis. However, some transgenic mouse models with beta-cell hyperplasia suggest that insulin production remains excessive and that normoglycemia is maintained by insulin resistance.Methods: Here, we investigated the effect of an increased beta-cell mass on glycemia and insulin resistance by grafting excess normal islets in normoglycemic mice, as well as using targeted PLAG1 expression in beta-cells, which leads to beta-cell expansion.Results: In both models, fasting plasma insulin levels were increased, even though animals were normoglycemic. After an intraperitoneal glucose tolerance test, plasma insulin levels increased, which was associated with improved glucose clearing. Under these conditions, normoglycemia is maintained by hepatic insulin resistance as demonstrated by hyperinsulinemic euglycemic clamp experiments.Conclusions: In conclusion, we demonstrate that when excess beta-cells are grafted, insulin production on a per beta-cell basis is not sufficiently decreased, leading to hyperinsulinemia and hepatic insulin resistance. This observation might be important for the design of stem cell-based islet replacement therapies. [ABSTRACT FROM AUTHOR]

There is substantial evidence in the literature that elevated plasma free fatty acids (FFA) play a role in the pathogenesis of type 2 diabetes. CVT-3619 is a selective partial A1 adenosine receptor agonist that inhibits lipolysis and lowers circulating FFA. The present study was undertaken to determine the effect of CVT-3619 on insulin resistance induced by high-fat (HF) diet in rodents. HF diet feeding to rats for 2 wk caused a significant increase in insulin, FFA, and triglyceride (TG) concentrations compared with rats fed chow. CVT-3619 (1 mg/kg) caused a time-dependent decrease in fasting insulin, FFA, and TG concentrations. Acute administration of CVT-3619 significantly lowered the insulin response, whereas glucose response was not different with an oral glucose tolerance test. Treatment with CVT-3619 for 2 wk resulted in significant lowering of FFA, TG, and insulin concentrations in rats on HF diet. To determine the effect of CVT-3619 on insulin sensitivity, hyperinsulinemic euglycemic clamp studies were performed in C57BL/J6 mice fed HF diet for 12 wk. Glucose infusion rate was decreased significantly in HF mice compared with chow-fed mice. CVT-3619 treatment 15 mm prior to the clamp study significantly (P < 0.01) increased glucose infusion rate to values similar to that for chow-fed mice. In conclusion, CVT-3619 treatment lowers FFA and TG concentrations and improves insulin sensitivity in rodent models of insulin resistance. [ABSTRACT FROM AUTHOR]

PYY3-36 is a gut-derived hormone acting on hypothalamic nuclei to inhibit food intake. We recently showed that PYY3-36 acutely reinforces insulin action on glucose disposal in mice. We aimed to evaluate effects of PYY3-36 on energy metabolism and the impact of chronic PYY3-36 treatment on insulin sensitivity. Mice received a single injection of PYY3-36 or were injected once daily for 7 days, and energy metabolism was subsequently measured in a metabolic cage. Furthermore, the effects of chronic PYY3-36 administration (continuous and intermittent) on glucose turnover were determined during a hyperinsulinemic-euglycemic clamp. PYY3-36 inhibited cumulative food intake for 30 min of refeeding after an overnight fast (0.29 ± 0.04 vs. 0.56 ± 0.12 g, P = 0.036) in an acute setting, but not after 7 days of daily dosing. Body weight, total energy expenditure, and physical activity were not affected by PYY3-36. However, it significantly decreased the respiratory quotient. Both continuous and intermittent PYY3-36 treatment significantly enhanced insulin-mediated whole body glucose disposal compared with vehicle treatment (81.2 ± 6.2 vs. 77.1 ± 5.2 vs. 63.4 ± 5.5 µmol·min-1·kg-1, respectively). In particular, PYY3-36 treatment increased glucose uptake in adipose tissue, whereas its impact on glucose disposal in muscle did not attain statistical significance. PYY3-36 treatment shifts the balance of fuel use in favor of fatty acids and enhances insulin sensitivity in mice, where it particularly promotes insulin-mediated glucose disposal. Notably, these metabolic effects of PYY3-36 remain unabated after chronic administration, in contrast to its anorexic effects. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptor (PPAR)gamma is a key transcription factor facilitating fat deposition in adipose tissue through its proadipogenic and lipogenic actions. Human patients with dominant-negative mutations in PPARgamma display lipodystrophy and extreme insulin resistance. For this reason it was completely unexpected that mice harboring an equivalent mutation (P465L) in PPARgamma developed normal amounts of adipose tissue and were insulin sensitive. This finding raised important doubts about the interspecies translatability of PPARgamma-related findings, bringing into question the relevance of other PPARgamma murine models. Here, we demonstrate that when expressed on a hyperphagic ob/ob background, the P465L PPARgamma mutant grossly exacerbates the insulin resistance and metabolic disturbances associated with leptin deficiency, yet reduces whole-body adiposity and adipocyte size. In mouse, coexistence of the P465L PPARgamma mutation and the leptin-deficient state creates a mismatch between insufficient adipose tissue expandability and excessive energy availability, unmasking the deleterious effects of PPARgamma mutations on carbohydrate metabolism and replicating the characteristic clinical symptoms observed in human patients with dominant-negative PPARgamma mutations. Thus, adipose tissue expandability is identified as an important factor for the development of insulin resistance in the context of positive energy balance. [ABSTRACT FROM AUTHOR]

Physical activity increases energy metabolism in exercising muscle. Whether acute exercise elicits metabolic changes in nonexercising muscles remains unclear. We show that one of the few genes that is more highly induced in nonexercising muscle than in exercising human muscle during acute exercise encodes angiopoietin-like 4 (ANGPTL4), an inhibitor of lipoprotein lipase-mediated plasma triglyceride clearance. Using a combination of human, animal, and in vitro data, we show that induction of ANGPTL4 in nonexercising muscle is mediated by elevated plasma free fatty acids via peroxisome proliferator-activated receptor-δ, presumably leading to reduced local uptake of plasma triglyceride-derived fatty acids and their sparing for use by exercising muscle. In contrast, the induction of ANGPTL4 in exercising muscle likely is counteracted via AMP-activated protein kinase (AMPK)-mediated down-regulation, promoting the use of plasma triglycerides as fuel for active muscles. Our data suggest that nonexercising muscle and the local regulation of ANGPTL4 via AMPK and free fatty acids have key roles in governing lipid homeostasis during exercise.

Objective: The scavenger receptor CD36 facilitates the cellular uptake of long-chain fatty acids. As CD36-deficiency attenuates the development of high fat diet (HFD)-induced obesity, the role of CD36-deficiency in preadipocyte recruitment and adipocyte function was set out to characterize., Design and Methods: Fat cell size and number were determined in gonadal, visceral, and subcutaneous adipose tissue of CD36(-/-) and WT mice after 6 weeks on HFD. Basal lipolysis and insulin-inhibited lipolysis were investigated in gonadal adipose tissue., Results: CD36(-/-) mice showed a reduction in adipocyte size in all fat pads. Gonadal adipose tissue also showed a lower total number of adipocytes because of a lower number of very small adipocytes (diameter <50 μm). This was accompanied by an increased pool of preadipocytes, which suggests that CD36-deficiency reduces the capacity of preadipocytes to become adipocytes. Regarding lipolysis, in adipose tissue from CD36(-/-) mice, cAMP levels were increased and both basal and 8-bromo-cAMP stimulated lipolysis were higher. However, insulin-mediated inhibition of lipolysis was more potent in CD36(-/-) mice., Conclusions: These results indicate that during fat depot expansion, CD36-deficiency negatively affects preadipocyte recruitment and that in mature adipocytes, CD36-deficiency is associated with increased basal lipolysis and insulin responsiveness., (Copyright © 2013 The Obesity Society.)

Objective: We investigated whether a reduced iso-α acid derived from an extract of Humulus lupulus L., META060, had an effect on weight gain, body composition, and metabolism in a high-fat-diet (HFD) fed mouse model., Methods: Weight gain was monitored for up to 20 wk in mice receiving a low-fat diet, an HFD, or an HFD supplemented with META060 or rosiglitazone. Body composition was determined using dual-energy x-ray absorptiometric analysis. Indirect calorimetric measurements were performed to investigate the energy balance in the mice, and oral glucose tolerance tests were administered to examine the effect of META060 on the glycemic response., Results: The HFD-fed mice administered META060 for 14 wk had a significantly lower mean weight than HFD-fed mice (30.58 ± 0.5 versus 37.88 ± 0.7 g, P < 0.05). Indirect calorimetric measurements showed an increased metabolic flexibility in mice supplemented with META060. In addition, glucose tolerance was improved, comparable to the effects of rosiglitazone treatment., Conclusions: META060 has potential therapeutic value for managing obesity and insulin resistance, and further research into the mechanism of action is warranted., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Synucleins are a family of homologous proteins principally known for their involvement in neurodegeneration. γ-Synuclein is highly expressed in human white adipose tissue and increased in obesity. Here we show that γ-synuclein is nutritionally regulated in white adipose tissue whereas its loss partially protects mice from high-fat diet (HFD)-induced obesity and ameliorates some of the associated metabolic complications. Compared with HFD-fed WT mice, HFD-fed γ-synuclein-null mutant mice display increased lipolysis, lipid oxidation, and energy expenditure, and reduced adipocyte hypertrophy. Knockdown of γ-synuclein in adipocytes causes redistribution of the key lipolytic enzyme ATGL to lipid droplets and increases lipolysis. γ-Synuclein-deficient adipocytes also contain fewer SNARE complexes of a type involved in lipid droplet fusion. We hypothesize that γ-synuclein may deliver SNAP-23 to the SNARE complexes under lipogenic conditions. Via these independent but complementary roles, γ-synuclein may coordinately modulate lipid storage by influencing lipolysis and lipid droplet formation. Our data reveal γ-synuclein as a regulator of lipid handling in adipocytes, the function of which is particularly important in conditions of nutrient excess.

Objective: The liver is the key organ involved in systemic inflammation, but the relation between hepatic inflammation and atherogenesis is poorly understood. Since nuclear factor-κB (NF-κB) is a central regulator of inflammatory processes, we hypothesized that chronically enhanced hepatic NF-κB activation, through hepatocyte-specific expression of IκB kinase-β (IKKβ) (LIKK), will aggravate atherosclerosis development in APOE*3-Leiden (E3L) mice., Methods and Results: E3L.LIKK and E3L control littermates were fed a Western-type diet for 24 weeks. E3L.LIKK mice showed a 2.3-fold increased atherosclerotic lesion area and more advanced atherosclerosis in the aortic root with less segments without atherosclerotic lesions (11% vs. 42%), and more segments with mild (63% vs. 44%) and severe (26% vs. 14%) lesions. Expression of LIKK did not affect basal levels of inflammatory parameters, but plasma cytokine levels tended to be higher in E3L.LIKK mice after lipopolysaccharide (LPS) administration. E3L.LIKK mice showed transiently increased plasma cholesterol levels, confined to (V)LDL. This transient character resulted in a mild (+17%) increased cumulative plasma cholesterol exposure., Conclusion: We conclude that selective activation of NF-κB in hepatocytes considerably promotes atherosclerosis development which is (at least partly) explained by an increased sensitivity to proinflammatory triggers and transiently increased plasma cholesterol levels., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Obesity and its associated conditions such as type 2 diabetes mellitus are major causes of morbidity and mortality. The iminosugar N-(5-adamantane-1-yl-methoxy-pentyl)-deoxynojirimycin (AMP-DNM) improves insulin sensitivity in rodent models of insulin resistance and type 2 diabetes mellitus. In the current study, we characterized the impact of AMP-DNM on substrate oxidation patterns, food intake, and body weight gain in obese mice. Eight ob/ob mice treated with 100 mg/(kg d) AMP-DNM mixed in the food and 8 control ob/ob mice were placed in metabolic cages during the first, third, and fifth week of the experiment for measurement of substrate oxidation rates, energy expenditure, activity, and food intake. Mice were killed after 6 weeks of treatment. Initiation of treatment with AMP-DNM resulted in a rapid increase in fat oxidation by 129% (P = .05), a decrease in carbohydrate oxidation by 35% (P = .01), and a reduction in food intake by approximately 26% (P < .01) compared with control mice. Treatment with AMP-DNM decreased hepatic triglyceride content by 66% (P < .01) and, in line with the elevated fat oxidation rates, increased hepatic carnitine palmitoyl transferase 1a expression. Treatment with AMP-DNM increased plasma levels of the appetite-regulating peptide YY compared with control mice. Treatment with AMP-DNM rapidly reduces food intake and increases fat oxidation, resulting in improvement of the obese phenotype. These features of AMP-DNM, together with its insulin-sensitizing capacity, make it an attractive candidate drug for the treatment of obesity and its associated metabolic derangements., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Systemic inflammation is strongly involved in the pathophysiology of the metabolic syndrome, a cluster of metabolic risk factors that includes hypertriglyceridemia. Aspirin treatment lowers inflammation via inhibition of NF-κB activity but also reduces hypertriglyceridemia in humans. The aim of this study was to investigate the mechanism by which aspirin improves hypertriglyceridemia. Human apolipoprotein CI (apoCI)-expressing mice (APOC1 mice), an animal model with elevated plasma triglyceride (TG) levels, as well as normolipidemic wild-type (WT) mice were fed a high-fat diet (HFD) and treated with aspirin. Aspirin treatment reduced hepatic NF-κB activity in HFD-fed APOC1 and WT mice, and in addition, aspirin decreased plasma TG levels (-32%, P < 0.05) in hypertriglyceridemic APOC1 mice. This TG-lowering effect could not be explained by enhanced VLDL-TG clearance, but aspirin selectively reduced hepatic production of VLDL-TG in both APOC1 (-28%, P < 0.05) and WT mice (-33%, P < 0.05) without affecting VLDL-apoB production. Aspirin did not alter hepatic expression of genes involved in FA oxidation, lipogenesis, and VLDL production but decreased the incorporation of plasma-derived FA by the liver into VLDL-TG (-24%, P < 0.05), which was independent of hepatic expression of genes involved in FA uptake and transport. We conclude that aspirin improves hypertriglyceridemia by decreasing VLDL-TG production without affecting VLDL particle production. Therefore, the inhibition of inflammatory pathways by aspirin could be an interesting target for the treatment of hypertriglyceridemia.

Cardiac patients often are obese and have hypertension, but in most studies these conditions are investigated separately. Here, we aimed at 1) elucidating the interaction of metabolic and mechanophysical stress in the development of cardiac dysfunction in mice and 2) preventing this interaction by ablation of the fatty acid transporter CD36. Male wild-type (WT) C57Bl/6 mice and CD36(-/-) mice received chow or Western-type diet (WTD) for 10 wk and then underwent a sham surgery or transverse aortic constriction (TAC) under anesthesia. After a 6-wk continuation of the diet, cardiac function, morphology, lipid profiles, and molecular parameters were assessed. WTD administration affected body and organ weights of WT and CD36(-/-) mice, but it affected only plasma glucose and insulin concentrations in WT mice. Cardiac lipid concentrations increased in WT mice receiving WTD, decreased in CD36(-/-) on chow, and remained unchanged in CD36(-/-) receiving WTD. TAC induced cardiac hypertrophy in WT mice on chow but did not affect cardiac function and cardiac lipid concentrations. WTD or CD36 ablation worsened the outcome of TAC. Ablation of CD36 protected against the WTD-related aggravation of cardiac functional and structural changes induced by TAC. In conclusion, cardiac dysfunction and remodeling worsen when the heart is exposed to two stresses, metabolic and mechanophysical, at the same time. CD36 ablation prevents the metabolic stress resulting from a WTD. Thus, metabolic conditions are a critical factor for the compromised heart and provide new targets for metabolic manipulation in cardioprotection.

Insulin signaling in the central nervous system (CNS) is required for the inhibitory effect of insulin on glucose production. Our aim was to determine whether the CNS is also involved in the stimulatory effect of circulating insulin on the tissue-specific retention of fatty acid (FA) from plasma. In wild-type mice, hyperinsulinemic-euglycemic clamp conditions stimulated the retention of both plasma triglyceride-derived FA and plasma albumin-bound FA in the various white adipose tissues (WAT) but not in other tissues, including brown adipose tissue (BAT). Intracerebroventricular (ICV) administration of insulin induced a similar pattern of tissue-specific FA partitioning. This effect of ICV insulin administration was not associated with activation of the insulin signaling pathway in adipose tissue. ICV administration of tolbutamide, a K(ATP) channel blocker, considerably reduced (during hyperinsulinemic-euglycemic clamp conditions) and even completely blocked (during ICV administration of insulin) WAT-specific retention of FA from plasma. This central effect of insulin was absent in CD36-deficient mice, indicating that CD36 is the predominant FA transporter in insulin-stimulated FA retention by WAT. In diet-induced insulin-resistant mice, these stimulating effects of insulin (circulating or ICV administered) on FA retention in WAT were lost. In conclusion, in insulin-sensitive mice, circulating insulin stimulates tissue-specific partitioning of plasma-derived FA in WAT in part through activation of K(ATP) channels in the CNS. Apparently, circulating insulin stimulates fatty acid uptake in WAT but not in BAT, directly and indirectly through the CNS.

Background: Pomegranate seed oil has been shown to protect against diet induced obesity and insulin resistance., Objective: To characterize the metabolic effects of punicic acid on high fat diet induced obesity and insulin resistance., Design: High-fat diet or high-fat diet with 1% Pomegranate seed oil (PUA) was fed for 12 weeks to induce obesity and insulin resistance. We assessed body weight and composition (pSABRE DEXA-scan), energy expenditure (Columbus Instruments) and insulin sensitivity at the end of the 12 weeks., Results: PSO intake resulted in a lower body weight, 30.5±2.9 vs 33.8±3.2 g PSO vs HFD respectively, p=0.02, without affecting food intake or energy expenditure. The lower body weight was fully explained by a decreased body fat mass, 3.3±2.3 vs 6.7±2.7 g for PSO and HFD fed mice, respectively, p=0.02. Insulin clamps showed that PSO did not affect liver insulin sensitivity but clearly improved peripheral insulin sensitivity, 164±52% vs 92±24% for PSO and HFD fed mice respectively, p=0.01., Conclusions: We conclude that dietary PSO ameliorates high-fat diet induced obesity and insulin resistance in mice, independent of changes in food intake or energy expenditure., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Low-grade inflammation in different tissues, including activation of the nuclear factor κB pathway in liver, is involved in metabolic disorders such as type 2 diabetes and cardiovascular diseases (CVDs). In this study, we investigated the relation between chronic hepatocyte-specific overexpression of IkB kinase (IKK)-β and hypertriglyceridemia, an important risk factor for CVD, by evaluating whether activation of IKK-β only in the hepatocyte affects VLDL-triglyceride (TG) metabolism directly. Transgenic overexpression of constitutively active human IKK-β specifically in hepatocytes of hyperlipidemic APOE*3-Leiden mice clearly induced hypertriglyceridemia. Mechanistic in vivo studies revealed that the hypertriglyceridemia was caused by increased hepatic VLDL-TG production rather than a change in plasma VLDL-TG clearance. Studies in primary hepatocytes showed that IKK-β overexpression also enhances TG secretion in vitro, indicating a direct relation between IKK-β activation and TG production within the hepatocyte. Hepatic lipid analysis and hepatic gene expression analysis of pathways involved in lipid metabolism suggested that hepatocyte-specific IKK-β overexpression increases VLDL production not by increased steatosis or decreased FA oxidation, but most likely by carbohydrate-responsive element binding protein-mediated upregulation of Fas expression. These findings implicate that specific activation of inflammatory pathways exclusively within hepatocytes induces hypertriglyceridemia. Furthermore, we identify the hepatocytic IKK-β pathway as a possible target to treat hypertriglyceridemia.

Excess dietary long-chain fatty acid (LCFA) intake results in ectopic lipid accumulation and insulin resistance. Since medium-chain fatty acids (MCFA) are preferentially oxidized over LCFA, we hypothesized that diets rich in MCFA result in a lower ectopic lipid accumulation and insulin resistance compared to diets rich in LCFA. Feeding mice high-fat (HF) (45% kcal fat) diets for 8 weeks rich in triacylglycerols composed of MCFA (HFMCT) or LCFA (HFLCT) revealed a lower body weight gain in the HFMCT-fed mice. Indirect calorimetry revealed higher fat oxidation on HFMCT compared to HFLCT (0.011.0±0.0007 vs. 0.0096±0.0015 kcal/g body weight per hour, P<.05). In line with this, neutral lipid immunohistochemistry revealed significantly lower lipid storage in skeletal muscle (0.05±0.08 vs. 0.30±0.23 area%, P <.05) and in liver (0.9±0.4 vs. 6.4±0.8 area%, P<.05) after HFMCT vs. HFLCT, while ectopic fat storage in low fat (LF) was very low. Hyperinsulinemic euglycemic clamps revealed that the HFMCT and HFLCT resulted in severe whole body insulin resistance (glucose infusion rate: 53.1±6.8, 50.8±15.3 vs. 124.6±25.4 μmol min(-1) kg(-1), P<.001 in HFMCT, HFLCT and LF-fed mice, respectively). However, under hyperinsulinemic conditions, HFMCT revealed a lower endogenous glucose output (22.6±8.0 vs. 34.7±8.5 μmol min(-1) kg(-1), P<.05) and a lower peripheral glucose disappearance (75.7±7.8 vs. 93.4±12.4 μmol min(-1) kg(-1), P<.03) compared to HFLCT-fed mice. In conclusion, both HF diets induced whole body insulin resistance compared to LF. However, the HFMCT gained less weight, had less ectopic lipid accumulation, while peripheral insulin resistance was more pronounced compared to HFLCT. This suggests that HF-diets rich in medium- versus long-chain triacylglycerols induce insulin resistance via distinct mechanisms., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Obesity-induced inflammation originating from expanding adipose tissue interferes with insulin sensitivity. Important metabolic effects have been recently attributed to IL-1β and IL-18, two members of the IL-1 family of cytokines. Processing of IL-1β and IL-18 requires cleavage by caspase-1, a cysteine protease regulated by a protein complex called the inflammasome. We demonstrate that the inflammasome/caspase-1 governs adipocyte differentiation and insulin sensitivity. Caspase-1 is upregulated during adipocyte differentiation and directs adipocytes toward a more insulin-resistant phenotype. Treatment of differentiating adipocytes with recombinant IL-1β and IL-18, or blocking their effects by inhibitors, reveals that the effects of caspase-1 on adipocyte differentiation are largely conveyed by IL-1β. Caspase-1 and IL-1β activity in adipose tissue is increased both in diet-induced and genetically induced obese animal models. Conversely, mice deficient in caspase-1 are more insulin sensitive as compared to wild-type animals. In addition, differentiation of preadipocytes isolated from caspase-1(-/-) or NLRP3(-/-) mice resulted in more metabolically active fat cells. In vivo, treatment of obese mice with a caspase-1 inhibitor significantly increases their insulin sensitivity. Indirect calorimetry analysis revealed higher fat oxidation rates in caspase-1(-/-) animals. In conclusion, the inflammasome is an important regulator of adipocyte function and insulin sensitivity, and caspase-1 inhibition may represent a novel therapeutic target in clinical conditions associated with obesity and insulin resistance., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Glycogen synthase (GS), a key enzyme in glycogen synthesis, is activated by the allosteric stimulator glucose-6-phosphate (G6P) and by dephosphorylation through inactivation of GS kinase-3 with insulin. The relative importance of these two regulatory mechanisms in controlling GS is not established, mainly due to the complex interplay between multiple phosphorylation sites and allosteric effectors. Here we identify a residue that plays an important role in the allosteric activation of GS by G6P. We generated knockin mice in which wild-type muscle GS was replaced by a mutant that could not be activated by G6P but could still be activated normally by dephosphorylation. We demonstrate that knockin mice expressing the G6P-insensitive mutant display an ∼80% reduced muscle glycogen synthesis by insulin and markedly reduced glycogen levels. Our study provides genetic evidence that allosteric activation of GS is the primary mechanism by which insulin promotes muscle glycogen accumulation in vivo., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Considerable variation in energy expenditure is observed in C57Bl/6 mice on a high-fat diet. Because muscle tissue is a major determinant of whole-body energy expenditure, we set out to determine the variation in energy expenditure and its possible association with skeletal muscle mitochondrial function upon high-fat diet intervention. Metabolic cages using indirect calorimetry were used to assess whole-body energy metabolism in C57Bl/6 male mice during the first 3 days of high-fat diet intervention. Mice were grouped in a negative or positive residual nocturnal energy expenditure group after correction of total nocturnal energy expenditure for body mass by residual analysis. The positive residual energy expenditure group was characterized by higher uncorrected total nocturnal energy expenditure and food intake. On day 7, mitochondria were isolated from the skeletal muscle of the hind limb. Mitochondrial density was determined by mitochondrial protein content and did not differ between the positive and negative residual energy expenditure groups. Using high-resolution respirometry, mitochondrial oxidative function was assessed using various substrates. Mitochondria from the positive residual energy expenditure group were characterized by a lower adenosine diphosphate-stimulated respiration and lower respiratory control rates using palmitoyl-coenzyme A as substrate. These results indicate that reduced mitochondrial coupling is associated with positive residual energy expenditure and high rates of total energy expenditure in vivo., (Copyright © 2010 Elsevier Inc. All rights reserved.)

The cholesteryl ester transfer protein (CETP) facilitates the bidirectional transfer of cholesteryl esters and triglycerides (TG) between HDL and (V)LDL. By shifting cholesterol in plasma from HDL to (V)LDL in exchange for VLDL-TG, CETP aggravates atherosclerosis in hyperlipidemic APOE*3-Leiden (E3L) mice. The aim of this study was to investigate the role of CETP in TG metabolism and high-fat diet-induced obesity by using E3L mice with and without the expression of the human CETP gene. On chow, plasma lipid levels were comparable between both male and female E3L and E3L.CETP mice. Further mechanistic studies were performed using male mice. CETP expression increased the level of TG in HDL. CETP did not affect the postprandial plasma TG response or the hepatic VLDL-TG and VLDL-apolipoprotein B production rate. Moreover, CETP did not affect the plasma TG clearance rate or organ-specific TG uptake after infusion of VLDL-like emulsion particles. In line with the absence of an effect of CETP on tissue-specific TG uptake, CETP also did not affect weight gain in response to a high-fat diet. In conclusion, the CETP-induced increase of TG in the HDL fraction of E3L mice is not associated with changes in the production of TG or with tissue-specific clearance of TG from the plasma.

The obesity epidemic is associated with an increased incidence of type 2 diabetes, cardiovascular morbidity and various types of cancer. A better insight into the molecular mechanisms that underlie adipogenesis and obesity may result in novel therapeutic handles to fight obesity and these associated diseases. Adipogenesis is determined by the balance between uptake of fatty acids (FA) from plasma into adipocytes, intracellular FA oxidation versus esterification of FA into triglycerides (TG), lipolysis of TG by intracellular lipases, and secretion of FA from adipocytes. Here, we review the mechanisms that are specifically involved in the entry of FA into adipose tissue. In plasma, these originating FA are either present as TG within apoB-containing lipoproteins (i.e. chylomicrons and VLDL) or as free FA bound to albumin. Kinetic studies, however, have revealed that TG are the major source of FA entering adipose tissue, both in the fed and fasted condition. In fact, studies with genetically engineered mice have revealed that the activity of lipoprotein lipase (LPL) is a major determinant for the development of obesity. As a general rule, high fat diet-induced adipogenesis is aggravated by stimulated LPL activity (e.g. by adipose tissue-specific overexpression of LPL or deficiency for apoCIII), and attenuated by inhibited LPL activity (e.g. by adipose-specific deficiency for LPL, overexpression of apoCI or angptl4, or by deficiency for apoE or the VLDL receptor). In addition, we describe that the trans-membrane transport of FA and cytoplasmic binding of FA in adipocytes can also dramatically affect adipogenesis. The relevance of these findings for human pathophysiology is discussed.

Background: Skeletal muscle is responsible for most of the insulin-stimulated glucose uptake and metabolism. Therefore, it plays an important role in the development of insulin resistance, one of the characteristics of the metabolic syndrome (MS). As the prevalence of the MS is increasing, there is an urgent need for more effective intervention strategies., Methods: C57BL/6J mice were fed an 8-week low-fat diet (10 kcal%; LFD) or high-fat diet (45 kcal%; HFD). Microarray analysis was performed by using two comparisons: (1) 8-week HFD transcriptome versus 8-week LFD transcriptome and (2) transcriptome of mice sacrificed at the start of the intervention versus 8-week LFD transcriptome and 8-week HFD transcriptome, respectively., Results: Although an 8-week HFD induced obesity and impaired insulin sensitivity, HFD-responsive changes in the muscle transcriptome were relatively small (<1.3-fold). In fact, 8-weeks of aging induced more pronounced changes than an HFD. One comparison revealed the transcriptional downregulation of the mito- gen-activated protein kinase cascade, whereas both comparisons showed the upregulation of fatty acid oxidation, demonstrating that the two comparison strategies are confirmative as well as complementary., Conclusion: We suggest using complementary analysis strategies in the genome-wide search for gene expression changes induced by mild interventions, such as an HFD., (Copyright © 2010 S. Karger AG, Basel.)

Apolipoprotein E2 (apoE2)-associated hyperlipidemia is characterized by a disturbed clearance of apoE2-enriched VLDL remnants. Because excess apoE2 inhibits LPL-mediated triglyceride (TG) hydrolysis in vitro, we investigated whether direct or indirect stimulation of LPL activity in vivo reduces the apoE2-associated hypertriglyceridemia. Here, we studied the role of LPL and two potent modifiers, the LPL inhibitor apoC-III and the LPL activator apoA-V, in APOE2-knockin (APOE2) mice. Injection of heparin in APOE2 mice reduced plasma TG by 53% and plasma total cholesterol (TC) by 18%. Adenovirus-mediated overexpression of LPL reduced plasma TG by 85% and TC by 40%. Both experiments indicate that the TG in apoE2-enriched particles is a suitable substrate for LPL. Indirect activation of LPL activity via deletion of Apoc3 in APOE2 mice did not affect plasma TG levels, whereas overexpression of Apoa5 in APOE2 mice did reduce plasma TG by 81% and plasma TC by 41%. In conclusion, the hypertriglyceridemia in APOE2 mice can be ameliorated by the direct activation of LPL activity. Indirect activation of LPL via overexpression of apoA-V does, whereas deletion of apoC-III does not, affect the plasma TGs in APOE2 mice. These data indicate that changes in apoA-V levels have a dominant effect over changes in apoC-III levels in the improvement of APOE2-associated hypertriglyceridemia.

Sequestration of malaria-parasite-infected erythrocytes in the microvasculature of organs is thought to be a significant cause of pathology. Cerebral malaria (CM) is a major complication of Plasmodium falciparum infections, and PfEMP1-mediated sequestration of infected red blood cells has been considered to be the major feature leading to CM-related pathology. We report a system for the real-time in vivo imaging of sequestration using transgenic luciferase-expressing parasites of the rodent malaria parasite Plasmodium berghei. These studies revealed that: (i) as expected, lung tissue is a major site, but, unexpectedly, adipose tissue contributes significantly to sequestration, and (ii) the class II scavenger-receptor CD36 to which PfEMP1 can bind is also the major receptor for P. berghei sequestration, indicating a role for alternative parasite ligands, because orthologues of PfEMP1 are absent from rodent malaria parasites, and, importantly, (iii) cerebral complications still develop in the absence of CD36-mediated sequestration, dissociating parasite sequestration from CM-associated pathology. Real-time in vivo imaging of parasitic processes may be used to evaluate the molecular basis of pathology and develop strategies to prevent pathology.

Purpose of Review: Apolipoprotein (apo)CIII and apoAV play an important role in triglyceride metabolism as evidenced by the unambiguous and opposing phenotypes of transgenic and knockout mouse models. In this review we discuss studies on the genetics, protein structure, and regulation of apoCIII and apoAV and compare their potential molecular mechanisms of action in triglyceride metabolism. We examine the hypothesis that apoCIII and apoAV synergistically affect triglyceride metabolism., Recent Findings: It has now been firmly established that variation in plasma triglyceride levels in a wide range of human populations is strongly associated with genetic variation at the chromosomal locus encoding both the APOC3 and APOA5 genes, the APOA1/C3/A4/A5 gene cluster. The close physical linkage of these genes and the frequent concurrence of genetic variants, however, complicate the assignment of specific metabolic defects to specific polymorphisms. Recent insight into the regulation of APOC3 and APOA5 gene expression and structural modeling studies on the apoAV protein have provided novel clues for the potential molecular mechanisms responsible for the effects of apoCIII and apoAV on triglyceride metabolism., Summary: Hypertriglyceridemia is a major independent risk factor in the development of cardiovascular disease. Moreover, triglyceride-derived fatty acids are thought to play a key role in the development and progression of the metabolic syndrome. As modulators of triglyceride metabolism, apoCIII and apoAV are key players and potential therapeutic targets. However, little is known of their molecular mechanism and potential cooperativity. Rational therapeutic application will require the filling of this hiatus in our knowledge.

Increasing evidence has implicated the membrane protein CD36 (or fatty acid translocase, FAT) to be involved in high affinity fatty acid uptake. CD36 is expressed in tissues active in fatty acid metabolism, like adipose tissue and skeletal and cardiac muscle, but also in intestine. CD36 is localized in the intestine mainly in the jejunal villi, where it is confined to enterocyte apical membrane. The aim was to determine the role of CD36 in intestinal lipid absorption. Lipid absorption was determined by administering 3H-labeled triolein and 14C-labeled palmitic acid as an olive oil bolus by intragastric gavage and determine appearance of 3H and 14C label in plasma, after blocking lipolysis by i.v. injections of Triton WR 1339. Surprisingly, no differences in plasma appearance of 3H-label or 14C-label were observed in CD36(-/-) mice compared to wild type controls. These results suggest that CD36 does not play a role in intestinal lipid absorption after an acute lipid load.