Hepatocyte-specific deletion of BAP31 promotes SREBP1C activation,promotes hepatic lipid accumulation,and worsens IR in mice

Conditional knockout mice with targeted disruption of B-cell associated protein (BAP)31 in adult mouse liver were generated and challenged with a high-fat diet (HFD) for 36 or 96 days and markers of obesity, diabetes, and hepatic steatosis were determined. Mutant mice were indistinguishable from WT littermates, but exhibited increased HFD-induced obesity. BAP31-deletion in hepatocytes increased the expression of SREBP1C and the target genes, including acetyl-CoA carboxylase 1 and stearoyl-CoA desaturase-1, and increased hepatic lipid accumulation and HFD-induced liver steatosis. Immunoprecipitation assay showed that BAP31 interacts with SREBP1C and insulin-induced gene 1 (INSIG1), and BAP31-deletion reduces INSIG1 expression, suggesting that BAP31 may regulate SREBP1C activity by modulating INSIG1 protein levels. Additionally, BAP31-deletion induced glucose and insulin intolerance, decreased Akt and glycogen synthase kinase 3β phosphorylation, and enhanced hepatic glucose production in mice. Expression of endoplasmic reticulum (ER) stress markers was significantly induced in BAP31-mutant mice. HFD-induced inflammation was aggravated in mutant mice, along with increased c-Jun N-terminal kinase and nuclear factor-κB activation. These findings demonstrate that BAP31-deletion induces SREBP activation and promotes hepatic lipid accumulation, reduces insulin signaling, impairs glucose/insulin tolerance, and increases ER stress and hepatic inflammation, explaining the protective roles of BAP31 in the development of liver steatosis and insulin resistance in HFD-induced obesity in animal models.     

Niemann-Pick C1-Like 1 deletion in mice prevents high-fat diet-induced fatty liver by reducing lipogenesis

Niemann-Pick C1-Like 1 (NPC1L1) mediates intestinal absorption of dietary and biliary cholesterol. Ezetimibe, by inhibiting NPC1L1 function, is widely used to treat hypercholesterolemia in humans. Interestingly, ezetimibe treatment appears to attenuate hepatic steatosis in rodents and humans without a defined mechanism. Overconsumption of a high-fat diet (HFD) represents a major cause of metabolic disorders including fatty liver. To determine whether and how NPC1L1 deficiency prevents HFD-induced hepatic steatosis, in this study, we fed NPC1L1 knockout (L1-KO) mice and their wild-type (WT) controls an HFD, and found that 24 weeks of HFD feeding causes no fatty liver in L1-KO mice. Hepatic fatty acid synthesis and levels of mRNAs for lipogenic genes are substantially reduced but hepatic lipoprotein-triglyceride production, fatty acid oxidation, and triglyceride hydrolysis remain unaltered in L1-KO versus WT mice. Strikingly, L1-KO mice are completely protected against HFD-induced hyperinsulinemia under both fed and fasted states and during glucose challenge. Despite similar glucose tolerance, L1-KO relative WT mice are more insulin sensitive and in the overnight-fasted state display significantly lower plasma glucose concentrations. In conclusion, NPC1L1 deficiency in mice prevents HFD-induced fatty liver by reducing hepatic lipogenesis, at least in part, through attenuating HFD-induced insulin resistance, a state known to drive hepatic lipogenesis through elevated circulating insulin levels.     

Adipose Overexpression of Heme Oxygenase-1 Does Not Protect against High Fat Diet-Induced Insulin Resistance in Mice

Heme oxygenase-1 (HO-1) is a stress-responsive enzyme with potent anti-oxidant and anti-inflammatory activities. Previous studies have shown that systemic induction of HO-1 by chemical inducers reduces adiposity and improves insulin sensitivity. To dissect the specific function of HO-1 in adipose tissue, we generated transgenic mice with adipose HO-1 overexpression using the adipocyte-specific aP2 promoter. The transgenic (Tg) mice exhibit similar metabolic phenotype as wild type (WT) control under chow-fed condition. High fat diet (HFD) challenge significantly increased the body weights of WT and Tg mice to a similar extent. Likewise, HFD-induced glucose intolerance and insulin resistance were not much different between WT and Tg mice. Analysis of the adipose tissue gene expression revealed that the mRNA levels of adiponectin and interleukin-10 were significantly higher in chow diet-fed Tg mice as compared to WT counterparts, whereas HFD induced downregulation of adiponectin gene expression in both Tg and WT mice to a similar level. HFD-induced proinflammatory cytokine expression in adipose tissues were comparable between WT and transgenic mice. Nevertheless, immunohistochemistry and gene expression analysis showed that the number of infiltrating macrophages with preferential expression of M2 markers was significantly higher in the adipose tissue of obese Tg mice than WT mice. Further experiment demonstrated that myeloid cells from Tg mice expressed higher level of HO-1 and exhibited greater migration response toward chemoattractant in vitro. Collectively, these data indicate that HO-1 overexpression in adipocytes does not protect against HFD-induced obesity and the development of insulin resistance in mice.     

A high-fat diet catalyzes progression to hyperglycemia in mice with selective impairment of insulin action in Glut4-expressing tissues

Insulin resistance impairs postprandial glucose uptake through glucose transporter type 4 (GLUT4) and is the primary defect preceding type 2 diabetes. We previously generated an insulin-resistant mouse model with human GLUT4 promoter-driven insulin receptor knockout (GIRKO) in the muscle, adipose, and neuronal subpopulations. However, the rate of diabetes in GIRKO mice remained low prior to 6 months of age on normal chow diet (NCD), suggesting that additional factors/mechanisms are responsible for adverse metabolic effects driving the ultimate progression of overt diabetes. In this study, we characterized the metabolic phenotypes of the adult GIRKO mice acutely switched to high-fat diet (HFD) feeding in order to identify additional metabolic challenges required for disease progression. Distinct from other diet-induced obesity (DIO) and genetic models (e.g., db/db mice), GIRKO mice remained leaner on HFD feeding, but developed other cardinal features of insulin resistance syndrome. GIRKO mice rapidly developed hyperglycemia despite compensatory increases in β-cell mass and hyperinsulinemia. Furthermore, GIRKO mice also had impaired oral glucose tolerance and a limited glucose-lowering benefit from exendin-4, suggesting that the blunted incretin effect contributed to hyperglycemia. Secondly, GIRKO mice manifested severe dyslipidemia while on HFD due to elevated hepatic lipid secretion, serum triglyceride concentration, and lipid droplet accumulation in hepatocytes. Thirdly, GIRKO mice on HFD had increased inflammatory cues in the gut, which were associated with the HFD-induced microbiome alterations and increased serum lipopolysaccharide (LPS). In conclusion, our studies identified important gene/diet interactions contributing to diabetes progression, which might be leveraged to develop more efficacious therapies.     

SIRT3 deficiency and mitochondrial protein hyperacetylation accelerate the development of the metabolic syndrome

Acetylation is increasingly recognized as an important metabolic regulatory posttranslational protein modification, yet the metabolic consequence of mitochondrial protein hyperacetylation is unknown. We find that high-fat diet (HFD) feeding induces hepatic mitochondrial protein hyperacetylation in mice and downregulation of the major mitochondrial protein deacetylase SIRT3. Mice lacking SIRT3 (SIRT3KO) placed on a HFD show accelerated obesity, insulin resistance, hyperlipidemia, and steatohepatitis compared to wild-type (WT) mice. The lipogenic enzyme stearoyl-CoA desaturase 1 is highly induced in SIRT3KO mice, and its deletion rescues both WT and SIRT3KO mice from HFD-induced hepatic steatosis and insulin resistance. We further identify a single nucleotide polymorphism in the human SIRT3 gene that is suggestive of a genetic association with the metabolic syndrome. This polymorphism encodes a point mutation in the SIRT3 protein, which reduces its overall enzymatic efficiency. Our findings show that loss of SIRT3 and dysregulation of mitochondrial protein acetylation contribute to the metabolic syndrome.     

Obesity and altered glucose metabolism impact HDL composition in CETP transgenic mice: a role for ovarian hormones

Mechanisms underlying changes in HDL composition caused by obesity are poorly defined, partly because mice lack expression of cholesteryl ester transfer protein (CETP), which shuttles triglyceride and cholesteryl ester between lipoproteins. Because menopause is associated with weight gain, altered glucose metabolism, and changes in HDL, we tested the effect of feeding a high-fat diet (HFD) and ovariectomy (OVX) on glucose metabolism and HDL composition in CETP transgenic mice. After OVX, female CETP-expressing mice had accelerated weight gain with HFD-feeding and impaired glucose tolerance by hyperglycemic clamp techniques, compared with OVX mice fed a low-fat diet (LFD). Sham-operated mice (SHAM) did not show HFD-induced weight gain and had less glucose intolerance than OVX mice. Using shotgun HDL proteomics, HFD-feeding in OVX mice had a large effect on HDL composition, including increased levels of apoA2, apoA4, apoC2, and apoC3, proteins involved in TG metabolism. These changes were associated with decreased hepatic expression of SR-B1, ABCA1, and LDL receptor, proteins involved in modulating the lipid content of HDL. In SHAM mice, there were minimal changes in HDL composition with HFD feeding. These studies suggest that the absence of ovarian hormones negatively influences the response to high-fat feeding in terms of glucose tolerance and HDL composition. CETP-expressing mice may represent a useful model to define how metabolic changes affect HDL composition and function.     

Inhibition of high-fat diet–induced obesity via reduction of ER-resident protein Nogo occurs through multiple mechanisms

Obesity is a risk factor for insulin resistance, type 2 diabetes, and cardiovascular diseases. Reticulon-4 (Nogo) is an endoplasmic reticulum–resident protein with unclear functions in obesity. Herein, we investigated the effect of Nogo on obesity and associated metabolic disorders. Human serum samples were collected to explore the relationship between circulating Nogo-B and body mass index value. Nogo-deficient and WT littermate control mice were fed normal chow or high-fat diet (HFD) for 14 weeks, and HFD-induced obese C57BL/6J mice were injected scrambled or Nogo siRNA for 2 weeks. We found that in human and mouse serum, Nogo-B was positively correlated to body mass index/bodyweight and lipid profiles. Reduced Nogo (by genetic deletion or siRNA transfection) protected mice against HFD-induced obesity and related metabolic disorders. We demonstrate that Nogo deficiency reversed HFD-induced whitening of brown adipose tissue, thereby increasing thermogenesis. It also ameliorated lipid accumulation in tissues by activating the adiponectin–adiponectin receptor 1–AMP-activated kinase α signaling axis. Finally, Nogo deficiency potently reduced HFD-induced serum proinflammatory cytokines and infiltration of macrophages into metabolic organs, which is related to enhanced NF-κB p65 degradation via the lysosome pathway. Collectively, our study suggests that reduced levels of Nogo protect mice against HFD-induced obesity by increasing thermogenesis and energy metabolism while inhibiting NF-κB-mediated inflammation. Our results indicate that inhibition of Nogo may be a potential strategy for obesity treatment.     

Deficiency of T-type voltage-gated calcium channels results in attenuated weight gain and improved endothelium-dependent dilatation of resistance vessels induced by a high-fat diet in mice

The deletion of T-type Cav3.1 channels may reduce high-fat diet (HFD)-induced weight gain, which correlates positively with obesity and endothelial dysfunction. Therefore, experiments were designed to study the involvement of T-type Cav3.1 channels in HFD-induced endothelial dysfunction in mice. Wildtype (WT) and Cav3.1−/− mice were fed either a normal diet (ND) or an HFD for 8 weeks. Body composition was assessed, and thoracic aortae and mesenteric arteries were harvested for myography to assess endothelium-dependent responses. Changes in intracellular calcium were measured by fluorescence imaging, and behavior was assessed with the open-field test. Cav3.1−/− mice had attenuated HFD-induced weight gain and lower total fat mass compared with WT mice. Cav3.1−/− mice on an HFD had reduced plasma cholesterol levels compared with WT mice on the same diet. Increased feeding efficiency, independent of food intake, was observed in WT mice on an HFD compared with an ND, but no difference in feeding efficiency between diets was observed for Cav3.1−/− mice. Nitric oxide-dependent dilatation was increased in mesenteric arteries of Cav3.1−/− mice compared with WT mice on an HFD, with no difference observed in aortae. No differences in mouse locomotor activity were observed between the experimental groups. Mice on an HFD lacking T-type channels have reduced weight gain, lower total cholesterol levels, and increased dilatation of resistance vessels compared with WT mice on an HFD, suggesting that Cav3.1 deletion protects against endothelial dysfunction in resistance vessels but not in large conduit vessels.     

High-fat diet–induced obesity and insulin resistance were ameliorated via enhanced fecal bile acid excretion in tumor necrosis factor-alpha receptor knockout mice

Tumor necrosis factor-α (TNF-α) is one of the main mediators of inflammatory response activated by fatty acids in obesity, and this signaling through TNF-α receptor (TNFR) is responsible for obesity-associated insulin resistance. Recently, TNF-α has shown to affect lipid metabolism including the regulation of lipase activity and bile acid synthesis. However, there is scanty in vivo evidence for the involvement of TNF-α in this process, and the mechanistic role of TNFR remains unclear. In this study, TNFR2 knockout mice (R2KO) and wild-type (WT) mice were fed commercial normal diet (ND) or high-fat diet (HFD) for 8 weeks. In R2KO/HFD mice, the increase in body weight and the accumulation of fat were significantly ameliorated compared with WT/HFD mice in association with the decrease in plasma total cholesterol (137.7±3.1 vs. 98.6±3.1 mg/dL, P<0.005), glucose (221.9±14.7 vs. 167.3±8.1 mg/dL, P<0.01), and insulin (5.1±0.3 vs. 3.4±0.3 ng/mL, P<0.05). Fecal excretion of lipid contents was significantly increased in R2KO mice. In R2KO/HFD mice, the decrease in hepatic cholesterol-7a-hydroxylase activity, the rate-limiting enzyme in bile acid synthesis, was inhibited (1.7±0.2 vs. 8.1±1.0 pmol/min/mg protein, P<0.01). These results suggested that HFD-induced obesity with metabolic derangements could be ameliorated in mice lacking TNF-α receptor 2 via increasing fecal bile acid and lipid content excretion. Therefore, TNF-α signaling through TNFR2 is essentially involved in the bile acid synthesis and excretion of lipids, resulting in its beneficial effects.     

GPR105 Ablation Prevents Inflammation and Improves Insulin Sensitivity in Mice with Diet-Induced Obesity

GPR105, a G protein-coupled receptor for UDP-glucose, is highly expressed in several human tissues and participates in the innate immune response. Because inflammation has been implicated as a key initial trigger for type 2 diabetes, we hypothesized that GPR105 (official gene name: P2RY14) might play a role in the initiation of inflammation and insulin resistance in obesity. To this end, we investigated glucose metabolism in GPR105 knockout (KO) and wild-type (WT) mice fed a high-fat diet (HFD). We also examined whether GPR105 regulates macrophage recruitment to liver or adipose tissues by in vivo monocyte tracking and in vitro chemotaxis experiments, followed by transplantation of bone marrow from either KO or WT donors to WT recipients. Our data show that genetic deletion of GPR105 confers protection against HFD-induced insulin resistance, with reduced macrophage infiltration and inflammation in liver, and increased insulin-stimulated Akt phosphorylation in liver, muscle, and adipose tissue. By tracking monocytes from either KO or WT donors, we found that fewer KO monocytes were recruited to the liver of WT recipients. Furthermore, we observed that uridine 5-diphosphoglucose enhanced the in vitro migration of bone marrow-derived macrophages from WT but not KO mice, and that plasma uridine 5-diphosphoglucose levels were significantly higher in obese versus lean mice. Finally, we confirmed that insulin sensitivity improved in HFD mice with a myeloid cell-specific deletion of GPR105. These studies indicate that GPR105 ablation mitigates HFD-induced insulin resistance by inhibiting macrophage recruitment and tissue inflammation. Hence GPR105 provides a novel link between innate immunity and metabolism.     

Lectin-like oxidized low-density lipoprotein receptor-1 is required for the adipose tissue expression of proinflammatory cytokines in high-fat diet-induced obese mice

Lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (LOX-1) is a receptor for oxidized LDL, and is strongly expressed in endothelial cells at an early stage of atherosclerosis. LOX-1 expression in adipocytes is induced by PPARγ (ligands and appears to be involved in adipocyte cholesterol metabolism. However, the role of adipose tissue LOX-1 in high-fat diet-induced obesity is unknown. We found that mRNA levels of adipose tissue LOX-1 were markedly increased in obese mice fed a high-fat diet (HFD) compared with those fed normal chow. The levels were closely correlated with those of a proinflammatory cytokine, monocyte chemoattractant protein-1 (MCP-1). Then, LOX-1 knockout (LOX-1-KO) and wild-type (WT) mice were fed HFD for 16 weeks. HFD feeding increased the body and mesenteric fat weights similarly in WT and LOX-1-KO mice. HFD-induced expressions of proinflammatory cytokines such as MCP-1, MIP-1α, and IL-6 were significantly less in LOX-1-KO than WT mice. Thus, LOX-1 is required for the HFD-induced expression of proinflammatory cytokines in the adipose tissue of obese mice.     

Transgenic MSH overexpression attenuates the metabolic effects of a high-fat diet

To determine whether long-term melanocortinergic activation can attenuate the metabolic effects of a high fat diet, mice overexpressing an NH(2)-terminal POMC transgene that includes alpha- and gamma(3)-MSH were studied on either a 10% low-fat diet (LFD) or 45% high-fat diet (HFD). Weight gain was modestly reduced in transgenic (Tg-MSH) male and female mice vs. wild type (WT) on HFD (P < 0.05) but not LFD. Substantial reductions in body fat percentage were found in both male and female Tg-MSH mice on LFD (P < 0.05) and were more pronounced on HFD (P < 0.001). These changes occurred in the absence of significant feeding differences in most groups, consistent with effects of Tg-MSH on energy expenditure and partitioning. This is supported by indirect calorimetry studies demonstrating higher resting oxygen consumption and lower RQ in Tg-MSH mice on the HFD. Tg-MSH mice had lower fasting insulin levels and improved glucose tolerance on both diets. Histological and biochemical analyses revealed that hepatic fat accumulation was markedly reduced in Tg-MSH mice on the HFD. Tg-MSH also attenuated the increase in corticosterone induced by the HFD. Higher levels of Agrp mRNA, which might counteract effects of the transgene, were measured in Tg-MSH mice on LFD (P = 0.02) but not HFD. These data show that long-term melanocortin activation reduces body weight, adiposity, and hepatic fat accumulation and improves glucose metabolism, particularly in the setting of diet-induced obesity. Our results suggest that long-term melanocortinergic activation could serve as a potential strategy for the treatment of obesity and its deleterious metabolic consequences.     

Arginase Inhibition Ameliorates Hepatic Metabolic Abnormalities in Obese Mice

Objectives

We examined whether arginase inhibition influences hepatic metabolic pathways and whole body adiposity in diet-induced obesity.

Methods and Results

After obesity induction by a high fat diet (HFD), mice were fed either the HFD or the HFD with an arginase inhibitor, N^ω-hydroxy-nor-L-arginine (nor-NOHA). Nor-NOHA significantly prevented HFD-induced increases in body, liver, and visceral fat tissue weight, and ameliorated abnormal lipid profiles. Furthermore, nor-NOHA treatment reduced lipid accumulation in oleic acid-induced hepatic steatosis in vitro. Arginase inhibition increased hepatic nitric oxide (NO) in HFD-fed mice and HepG2 cells, and reversed the elevated mRNA expression of hepatic genes in lipid metabolism. Expression of phosphorylated 5′ AMPK-activated protein kinase α was increased by arginase inhibition in the mouse livers and HepG2 cells.

Conclusions

Arginase inhibition ameliorated obesity-induced hepatic lipid abnormalities and whole body adiposity, possibly as a result of increased hepatic NO production and subsequent activation of metabolic pathways involved in hepatic triglyceride metabolism and mitochondrial function.     

Involvement of G protein-coupled receptor kinase 2 (GRK2) in the development of non-alcoholic steatosis and steatohepatitis in mice and humans

Insulin resistance (IR) and obesity are important risk factors for non-alcoholic fatty liver disease (NAFLD). G protein-coupled receptor kinase 2 (GRK2) is involved in the development of IR and obesity in vivo. However, its possible contribution to NAFLD and/or non-alcoholic steatohepatitis (NASH) independently of its role on IR or fat mass accretion has not been explored. Here, we used wild-type (WT) or GRK2 hemizygous (GRK2±) mice fed a high-fat diet (HFD) or a methionine and choline-deficient diet (MCD) as a model of NASH independent of adiposity and IR. GRK2± mice were protected from HFD-induced NAFLD. Moreover, MCD feeding caused an increased in triglyceride content and liver-to-body weight ratio in WT mice, features that were attenuated in GRK2± mice. According to their NAFLD activity score, MCD-fed GRK2± mice were diagnosed with simple steatosis and not overt NASH. They also showed reduced expression of lipogenic and lipid-uptake markers and less signs of inflammation in the liver. GRK2± mice preserved hepatic protective mechanisms as enhanced autophagy and mitochondrial fusion and biogenesis, together with reduced endoplasmic reticulum stress. GRK2 protein was increased in MCD-fed WT but not in GRK2± mice, and enhanced GRK2 expression potentiated palmitic acid-triggered lipid accumulation in human hepatocytes directly relating GRK2 levels to steatosis. GRK2 protein and mRNA levels were increased in human liver biopsies from simple steatosis or NASH patients in two different human cohorts. Our results describe a functional relationship between GRK2 levels and hepatic lipid accumulation and implicate GRK2 in the establishment and/or development of NASH.     

Sex hormone-binding globulin overexpression protects against high-fat diet-induced obesity in transgenic male mice

Obese subjects of all ages and sex have reduced plasma SHBG levels. Whether these low plasma SHBG levels play a role in obesity development is unknown. In the present work we wanted to explore if SHBG overexpression could prevent obesity development induced by high fat diet (HFD). To do so, we fed humanized SHBG transgenic male mice and their wild-type littermates with control diet (CD) or HFD over the course of 8 weeks. The results showed that SHBG overexpression protected against body weight gain and fat accumulation induced by HFD. In addition, SHBG overexpression also abrogated the increase in insulin, leptin and resistin levels, as well as the reduction in adiponectin, induced by HFD. Mechanistically, the SHBG protection against HFD-induced obesity was achieved by stimulating lipolysis in white adipose tissue. Furthermore, we have demonstrated the SHBG cell-autonomous effect using human primary visceral adipocytes. Taking together, our results demonstrate that SHBG overexpression protects against diet-induced obesity and improves the metabolic profile of male mice fed a HFD diet.     

Loss of Toll-Like Receptor 4 Function Partially Protects against Peripheral and Cardiac Glucose Metabolic Derangements During a Long-Term High-Fat Diet

Diabetes is a chronic inflammatory disease that carries a high risk of cardiovascular disease. However, the pathophysiological link between these disorders is not well known. We hypothesize that TLR4 signaling mediates high fat diet (HFD)-induced peripheral and cardiac glucose metabolic derangements. Mice with a loss-of-function mutation in TLR4 (C3H/HeJ) and age-matched control (C57BL/6) mice were fed either a high-fat diet or normal diet for 16 weeks. Glucose tolerance and plasma insulin were measured. Protein expression of glucose transporters (GLUT), AKT (phosphorylated and total), and proinflammatory cytokines (IL-6, TNF-α and SOCS-3) were quantified in the heart using Western Blotting. Both groups fed a long-term HFD had increased body weight, blood glucose and insulin levels, as well as impaired glucose tolerance compared to mice fed a normal diet. TLR4-mutant mice were partially protected against long-term HFD-induced insulin resistance. In control mice, feeding a HFD decreased cardiac crude membrane GLUT4 protein content, which was partially rescued in TLR4-mutant mice. TLR4-mutant mice fed a HFD also had increased expression of GLUT8, a novel isoform, compared to mice fed a normal diet. GLUT8 content was positively correlated with SOCS-3 and IL-6 expression in the heart. No significant differences in cytokine expression were observed between groups, suggesting a lack of inflammation in the heart following a HFD. Loss of TLR4 function partially restored a healthy metabolic phenotype, suggesting that TLR4 signaling is a key mechanism in HFD-induced peripheral and cardiac insulin resistance. Our data further suggest that TLR4 exerts its detrimental metabolic effects in the myocardium through a cytokine-independent pathway.     

Garcinia cambogia extract ameliorates visceral adiposity in C57BL/6J mice fed on a high-fat diet

The aim of present study is to evaluate the effects of Garcinia cambogia on the mRNA levels of the various genes involved in adipogenesis, as well as on body weight gain, visceral fat accumulation, and other biochemical markers of obesity in obesity-prone C57BL/6J mice. Consumption of the Garcinia cambogia extract effectively lowered the body weight gain, visceral fat accumulation, blood and hepatic lipid concentrations, and plasma insulin and leptin levels in a high-fat diet (HFD)-induced obesity mouse model. The Garcinia cambogia extract reversed the HFD-induced changes in the expression pattern of such epididymal adipose tissue genes as adipocyte protein aP2 (aP2), sterol regulatory element-binding factor 1c (SREBP1c), peroxisome proliferator-activated receptor gamma2 (PPARgamma2), and CCAT/enhancer-binding protein alpha (C/EBPalpha). These findings suggest that the Garcinia cambogia extract ameliorated HFD-induced obesity, probably by modulating multiple genes associated with adipogenesis, such as aP2, SREBP1c, PPARgamma2, and C/EBPalpha in the visceral fat tissue of mice.     

The a2b adenosine receptor modulates glucose homeostasis and obesity

Background

High fat diet and its induced changes in glucose homeostasis, inflammation and obesity continue to be an epidemic in developed countries. The A2b adenosine receptor (A2bAR) is known to regulate inflammation. We used a diet-induced obesity murine knockout model to investigate the role of this receptor in mediating metabolic homeostasis, and correlated our findings in obese patient samples.

Methodology/Principal Findings

Administration of high fat, high cholesterol diet (HFD) for sixteen weeks vastly upregulated the expression of the A2bAR in control mice, while A2bAR knockout (KO) mice under this diet developed greater obesity and hallmarks of type 2 diabetes (T2D), assessed by delayed glucose clearance and augmented insulin levels compared to matching control mice. We identified a novel link between the expression of A2bAR, insulin receptor substrate 2 (IRS-2), and insulin signaling, determined by Western blotting for IRS-2 and tissue Akt phosphorylation. The latter is impaired in tissues of A2bAR KO mice, along with a greater inflammatory state. Additional mechanisms involved include A2bAR regulation of SREBP-1 expression, a repressor of IRS-2. Importantly, pharmacological activation of the A2bAR by injection of the A2bAR ligand BAY 60-6583 for four weeks post HFD restores IRS-2 levels, and ameliorates T2D. Finally, in obese human subjects A2bAR expression correlates strongly with IRS-2 expression.

Conclusions/Significance

Our study identified the A2bAR as a significant regulator of HFD-induced hallmarks of T2D, thereby pointing to its therapeutic potential.     

Deletion of prolyl carboxypeptidase attenuates the metabolic effects of diet-induced obesity

α-Melanocyte-stimulating hormone (α-MSH) is a critical regulator of energy metabolism. Prolyl carboxypeptidase (PRCP) is an enzyme responsible for its degradation and inactivation. PRCP-null mice (PRCP(gt/gt)) showed elevated levels of brain α-MSH, reduced food intake, and a leaner phenotype compared with wild-type controls. In addition, they were protected against diet-induced obesity. Here, we show that PRCP(gt/gt) animals have improved metabolic parameters compared with wild-type controls under a standard chow diet (SD) as well as on a high-fat diet (HFD). Similarly to when they are exposed to SD, PRCP(gt/gt) mice exposed to HFD for 13 wk showed a leaner phenotype due to decreased fat mass, increased energy expenditure, and locomotor activity. They also showed improved insulin sensitivity and glucose tolerance compared with WT controls and a significant reduction in fasting glucose levels. These improvements occured before changes in body weight and composition were evident, suggesting that the beneficial effect of PRCP ablation is independent of the adiposity levels. In support of a reduced gluconeogenesis, liver PEPCK and G-6-Pase mRNA levels were reduced significantly in PRCP(gt/gt) compared with WT mice. A significant decrease in liver weight and hepatic triglycerides were also observed in PRCP(gt/gt) compared with WT mice. Altogether, our data suggest that PRCP is an important regulator of energy and glucose homeostasis since its deletion significantly improves metabolic parameters in mice exposed to both SD and HFD.     

Retinoic acid ameliorates high-fat diet-induced liver steatosis through Sirt1

In this study, treatment of C57 BL/6 J(wild type, WT) mice fed a high-fat diet(HFD) with retinoic acid(RA) decreased body weight and subcutaneous and visceral fat content, reversed the apparent hepatosteatosis, and reduced hepatic intracellular triglyceride and serum alanine transaminase(ALT) and aspartate aminotransferase(AST) concentrations. Moreover, RA treatment improved glucose tolerance and insulin sensitivity in WT mice fed a HFD. However, these RA-induced effects in WT mice fed a HFD were alleviated in liver specific Sirtuin 1(Sirt1) deficient(LKO) mice fed a HFD. Furthermore,RA also could not improve glucose tolerance and insulin sensitivity in LKO mice fed a HFD. The mechanism studies indicated that RA indeed increased the expression of hepatic Sirt1 and superoxide dismutase 2(Sod2), and inhibited the expression of sterol regulatory element binding protein 1 c(Srebp-1 c) in WT mice in vivo and in vitro. RA decreased mitochondrial reactive oxygen species(ROS) production in WT primary hepatocytes and increased mitochondrial DNA(mtDNA) copy number in WT mice liver. However, these RA-mediated molecular effects were also abolished in the liver and primary hepatocytes from LKO mice. In summary, RA protected against HFD-induced hepato steatosis by decreasing Srebp-1 c expression and improving antioxidant capacity through a Sirtl-mediated mechanism.