Improved glucose control and reduced body fat mass in free fatty acid receptor 2-deficient mice fed a high-fat diet

Free fatty acid receptor 2 (Ffar2), also known as GPR43, is activated by short-chain fatty acids (SCFA) and expressed in intestine, adipocytes, and immune cells, suggesting involvement in lipid and immune regulation. In the present study, Ffar2-deficient mice (Ffar2-KO) were given a high-fat diet (HFD) or chow diet and studied with respect to lipid and energy metabolism. On a HFD, Ffar2-KO mice had lower body fat mass and increased lean body mass. The changed body composition was accompanied by improved glucose control and lower HOMA index, indicating improved insulin sensitivity in Ffar2-KO mice. Moreover, the Ffar2-KO mice had higher energy expenditure accompanied by higher core body temperature and increased food intake. The liver weight and content of triglycerides as well as plasma levels of cholesterol were lower in the Ffar2-KO mice fed a HFD. A histological examination unveiled decreased lipid interspersed in brown adipose tissue of the Ffar2-KO mice. Interestingly, no significant differences in white adipose tissue (WAT) cell size were observed, but significantly lower macrophage content was detected in WAT from HFD-fed Ffar2-KO compared with wild-type mice. In conclusion, Ffar2 deficiency protects from HFD-induced obesity and dyslipidemia at least partly via increased energy expenditure.     

Long-term high-fat diet links the regulation of the insulin-sensitizing fibroblast growth factor-21 and visfatin

High-fat diet (HFD) is associated with insulin resistance, hyperinsulinemia, elevated plasma free fatty acid (FFA), and increased risk for atherosclerotic vascular disease. However, the mechanisms underlying the HFD-induced insulin resistance have not been fully clarified. The aim of present study is to evaluate the effects of long-term HFD on the regulation of the insulin-sensitizing fibroblast growth factor-21 (FGF-21) and visfatin in ApoE(-/-) mice. A total of twenty male ApoE(-/-) mice were randomly divided into normal chow diet (NC) or HFD (HF) group for 16 weeks. Euglycemic-hyperinsulinemic clamp was performed to evaluate insulin sensitivity in this animal model. Both mRNA and protein contents of FGF-21 and visfatin were assayed by Quantitative real-time PCR and Western blot. Long-term HFD resulted in the marked abnormality of glucose and lipid metabolism as well as a large decrease in whole-body insulin sensitivity. Accompanied by abnormal glucose-lipid metabolism and aggravated insulin resistance, FGF-21, β-klotho, FGFR1, FGFR3 and FGFR4 mRNA expressions were markedly up-regulated, whereas visfatin mRNA expression was markedly down-regulated in liver and/or adipose tissue of HFD-fed mice. In addition, Western blotting also revealed both up-regulation of the FGF-21 protein and down-regulation of visfatin protein in liver, adipose tissue and plasma of HFD-fed mice. Both FGF-21 and visfatin expression and secretion are regulated by a potent regulator, long-term HFD. And these adipokines are associated with glucose-lipid metabolism and insulin resistance.     

On the role of liver X receptors in lipid accumulation in adipocytes

The pivotal role of liver X receptors (LXRs) in the metabolic conversion of cholesterol to bile acids in mice is well established. More recently, the LXRalpha promoter has been shown to be under tight regulation by peroxisome proliferator-activated receptors (PPARs), implying a role for LXRalpha in mediating the interplay between cholesterol and fatty acid metabolism. We have studied the role of LXR in fat cells and demonstrate that LXR is regulated during adipogenesis and augments fat accumulation in mature adipocytes. LXRalpha expression in murine 3T3-L1 adipocytes as well as in human adipocytes was up-regulated in response to PPARgamma agonists. Administration of a PPARgamma agonist to obese Zucker rats also led to increased LXRalpha mRNA expression in adipose tissue in vivo. LXR agonist treatment of differentiating adipocytes led to increased lipid accumulation. An increase of the expression of the LXR target genes, sterol regulatory binding protein-1 and fatty acid synthase, was observed both in vivo and in vitro after treatment with LXR agonists for 24 h. Finally, we demonstrate that fat depots in LXRalpha/beta-deficient mice are smaller than in age-matched wild-type littermates. These findings imply a role for LXR in controlling lipid storage capacity in mature adipocytes and point to an intriguing physiological interplay between LXR and PPARgamma in controlling pathways in lipid handling.     

Sulforaphane attenuates obesity by inhibiting adipogenesis and activating the AMPK pathway in obese mice

Obesity is associated with metabolic disorders. Sulforaphane, an isothiocyanate, inhibits adipogenesis and the occurrence of cardiovascular disease. In this study, we investigated whether sulforaphane could prevent high-fat diet (HFD)-induced obesity in C57BL/6N mice. Mice were fed a normal diet (ND), HFD or HFD plus 0.1% sulforaphane (SFN) for 6 weeks. Food efficiency ratios and body weight were lower in HFD-SFN-fed mice than in HFD-fed mice. SFN attenuated HFD-induced visceral adiposity, adipocyte hypertrophy and fat accumulation in the liver. Serum total cholesterol and leptin, and liver triglyceride levels were lower in HFD-SFN-fed mice than in HFD-fed mice. SFN decreased the expression of peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα) and leptin in the adipose tissue of HFD-SFN mice and increased adiponectin expression. Phosphorylation of AMP-activated protein kinase α (AMPKα) and acetyl-CoA carboxylase in the adipose tissue of HFD-SFN-fed mice was elevated, and HMG-CoA reductase expression was decreased compared with HFD-fed mice. Thus, these results suggest that SFN may induce antiobesity activity by inhibiting adipogenesis through down-regulation of PPARγ and C/EBPα and by suppressing lipogenesis through activation of the AMPK pathway.     

Targeting the gut microbiota with resveratrol: a demonstration of novel evidence for the management of hepatic steatosis

Resveratrol is a natural polyphenol that has been reported to reduce the risk of obesity and nonalcoholic fatty liver disease (NAFLD). Recent evidence has demonstrated that the gut microbiota plays an important role in the protection against NAFLD and other metabolic diseases. The present study aimed to investigate the relationship between the gut microbiota and the beneficial effects of resveratrol on the amelioration of NAFLD in mice. We observed marked decreases in body weight and liver steatosis and improved insulin resistance in high-fat diet (HFD)-fed mice treated with resveratrol. Furthermore, we found that resveratrol treatment alleviated NAFLD in HFD-fed mice by improving the intestinal microenvironment, including gut barrier function and gut microbiota composition. On the one hand, resveratrol improved gut intestinal barrier integrity through the repair of intestinal mucosal morphology and increased the expression of physical barrier- and physiochemical barrier-related factors in HFD-fed mice. On the other hand, in HFD-fed mice, resveratrol supplementation modulated the gut bacterial composition. The resveratrol-induced gut microbiota was characterized by a decreased abundance of harmful bacteria, including Desulfovibrio, Lachnospiraceae_NK4A316_group and Alistipes, as well as an increased abundance of short-chain fatty acid (SCFA)-producing bacteria, such as Allobaculum, Bacteroides and Blautia. Moreover, transplantation of the HFDR-microbiota into HFD-fed mice sufficiently decreased body weight, liver steatosis and low-grade inflammation and improved hepatic lipid metabolism. Collectively, resveratrol would provide a potentially dietary intervention strategy against NAFLD through modulating the intestinal microenvironment.     

Altered growth in male peroxisome proliferator-activated receptor gamma (PPARgamma) heterozygous mice: involvement of PPARgamma in a negative feedback regulation of growth hormone action

The peroxisome proliferator-activated receptor gamma (PPARgamma) plays a major role in fat tissue development and physiology. Mutations in the gene encoding this receptor have been associated to disorders in lipid metabolism. A thorough investigation of mice in which one PPARgamma allele has been mutated reveals that male PPARgamma heterozygous (PPARgamma +/-) mice exhibit a reduced body size associated with decreased body weight, reflecting lean mass reduction. This phenotype is reproduced when treating the mice with a PPARgamma- specific antagonist. Monosodium glutamate treatment, which induces weight gain and alters body growth in wild-type mice, further aggravates the growth defect of PPARgamma +/- mice. The levels of circulating GH and that of its downstream effector, IGF-I, are not altered in mutant mice. However, the IGF-I mRNA level is decreased in white adipose tissue (WAT) of PPARgamma +/- mice and is not changed by acute administration of recombinant human GH, suggesting an altered GH action in the mutant animals. Importantly, expression of the gene encoding the suppressor of cytokine signaling-2, which is an essential negative regulator of GH signaling, is strongly increased in the WAT of PPARgamma +/- mice. Although the relationship between the altered GH signaling in WAT and reduced body size remains unclear, our results suggest a novel role of PPARgamma in GH signaling, which might contribute to the metabolic disorder affecting insulin signaling in PPARgamma mutant mice.     

Comparing lipid remodeling of brown adipose tissue,white adipose tissue,and liver after one-week high fat diet intervention with quantitative Raman microscopy

Brown adipose tissue (BAT) consists of highly metabolically active adipocytes that catabolize nutrients to produce heat. Playing an active role in triacylglycerol (TAG) clearance, research has shown that dietary fatty acids can modulate the TAG chemistry deposition in BAT after weeks-long dietary intervention, similar to what has been shown in white adipose tissue (WAT). Our objective was to compare the influence of sustained, nonchronic dietary intervention (a 1-week interval) on WAT and interscapular BAT lipid metabolism and deposition in situ. We use quantitative, label-free chemical microscopy to show that 1 week of high fat diet (HFD) intervention results in dramatically larger lipid droplet (LD) growth in BAT (and liver) compared to LD growth in inguinal WAT (IWAT). Moreover, BAT showed lipid remodeling as increased unsaturated TAGs in LDs, resembling the dietary lipid composition, while WAT (and liver) did not show lipid remodeling on this time scale. Concurrently, expression of genes involved in lipid metabolism, particularly desaturases, was reduced in BAT and liver from HFD-fed mice after 1 week. Our data show that BAT lipid chemistry remodels exceptionally fast to dietary lipid intervention compared WAT, which further points towards a role in TAG clearance.     

Continuous intake of a high-fat diet beyond one generation promotes lipid accumulation in liver and white adipose tissue of female mice

Lipid metabolism in a child may be altered when the mother has a high-fat diet (HFD), but it is unclear whether the lipid metabolism of future offspring (grandchildren) is also changed under these circumstances. In this study, we examined the influence of intake of an HFD beyond one generation on offspring in normal mice. Parent mice fed an HFD were bred and the resultant second and third generations were also fed an HFD. The diets used in the study had approximately 20% more energy than a standard chow diet. Changes in lipid metabolism were examined in each generation. Intake of an HFD from generation to generation promoted lipid accumulation in the white adipose tissue of female mice, increased lipid, glucose and insulin levels in the serum, increased the activities of enzymes associated with fatty acid metabolism in the liver, promoted lipid accumulation in hepatocytes and adipocytes and increased the mRNA levels of Cdkn1a in the liver and white adipose tissue. These results suggest that activation of Cdkn1a promoted lipid accumulation in the liver and white adipose tissue of third-generation female mice that were offspring from earlier generations fed HFDs. Moreover, intake of a high-energy diet beyond one generation led to offspring with obesity, fatty liver and hyperinsulinemia.     

Defective adipose tissue development associated with hepatomegaly in cathepsin E-deficient mice fed a high-fat diet

Cathepsin E is an intracellular aspartic proteinase, which is predominantly distributed in immune-related and epithelial cells. However, the role of the enzyme in adipose tissues remains unknown. In this study, we investigated the characteristics of cathepsin E-deficient (CatE^−/−) mice fed a high-fat diet (HFD), as a mouse model of obesity. HFD-fed CatE^−/− mice displayed reduced body weight gain and defective development of white adipose tissue (WAT) and brown adipose tissue (BAT), compared with HFD-fed wild-type mice. Moreover, fat-induced CatE^−/− mice showed abnormal lipid accumulation in non-adipose tissues characterized by hepatomegaly, which is probably due to defective adipose tissue development. Detailed pathological and biochemical analyses showed that hepatomegaly was accompanied by hepatic steatosis and hypercholesterolemia in HFD-induced CatE^−/− mice. In fat-induced CatE^−/− mice, the number of macrophages infiltrating into WAT was significantly lower than in fat-induced wild-type mice. Thus, the impaired adipose tissue development in HFD-induced CatE^−/− mice was probably due to reduced infiltration of macrophages and may lead to hepatomegaly accompanied by hepatic steatosis and hypercholesterolemia.     

HVEM-deficient mice fed a high-fat diet are protected from adipose tissue inflammation and glucose intolerance

HVEM is a member of the TNF receptor superfamily that plays a role in the development of various inflammatory diseases. In this study, we show that HVEM deficiency attenuates adipose tissue inflammatory responses and glucose intolerance in diet-induced obesity. Feeding a high-fat diet (HFD) to HVEM-deficient mice elicited a reduction in the number of macrophages and T cells infiltrated into adipose tissue. Proinflammatory cytokine levels in the adipose tissue decreased in HFD-fed HVEM-deficient mice, while levels of the anti-inflammatory cytokine IL-10 increased. Moreover, glucose intolerance and insulin sensitivity were markedly improved in the HFD-fed HVEM-deficient mice. These findings indicate that HVEM may be a useful target for combating obesity-induced inflammatory responses and insulin resistance.     

Omija fruit ethanol extract improves adiposity and related metabolic disturbances in mice fed a high-fat diet

This study investigated the biological and molecular mechanisms underlying the antiobesity effect of omija fruit ethanol extract (OFE) in mice fed a high-fat diet (HFD). C57BL/6J mice were fed an HFD (20% fat, w/w) with or without OFE (500 mg/kg body weight) for 16 weeks. Dietary OFE significantly increased brown adipose tissue weight and energy expenditure while concomitantly decreasing white adipose tissue (WAT) weight and adipocyte size by up-regulating the expression of brown fat-selective genes in WAT. OFE also improved hepatic steatosis and dyslipidemia by enhancing hepatic fatty acid oxidation-related enzymes activity and fecal lipid excretion. In addition to steatosis, OFE decreased the expression of pro-inflammatory genes in the liver. Moreover, OFE improved glucose tolerance and lowered plasma glucose, insulin and homeostasis model assessment of insulin resistance, which may be linked to decreases in the activity of hepatic gluconeogenic enzymes and the circulating level of gastric inhibitory polypeptide. These findings suggest that OFE may protect against diet-induced adiposity and related metabolic disturbances by controlling brown-like transformation of WAT, fatty acid oxidation, inflammation in the liver and fecal lipid excretion. Improved insulin resistance may be also associated with its antiobesity effects.     

S100A16, a novel lipogenesis promoting factor in livers of mice and hepatocytes in vitro

To investigate the role of S100 calcium-binding protein A16 (S100A16) in hepatic lipid metabolism, S100a16 transgenic, S100a16 knockdown, and wildtype C57BL/6 mice were fed either a high-fat diet (HFD) or normal-fat diet (NFD) for 16 weeks. The results showed that for HFD-fed mice, S100a16 transgenic mice showed significantly more severe fatty liver than other HFD-fed mice, with a significant increase in serum triglyceride (TG) concentration, with more and larger lipid droplets in the liver, whereas S100a16 knockdown mice were completely opposite, with liver fat lesions and TG serological changes being the mildest; for NFD-fed mice, liver fat accumulation and serum TG concentrations were significantly lower than those fed HFD, and no significant lipid droplets were found in the liver. Further, we found that calmodulin (CaM) interacts with S100A16, a member of the AMP-activated protein kinase (AMPK) pathway. Our research found that S100A16 regulates the AMPK pathway-associated protein by interacting with CaM to regulate liver lipid synthesis. S100A16 regulates liver lipid metabolism through the CaM/CAMKK2/AMPK pathway. Overexpression of S100A16 promotes the deterioration of fatty liver induced by HFD, and low expression of S100A16 can attenuate fatty liver.     

Induction of Peroxisomes by Butyrate-Producing Probiotics

We previously found that peroxisomal biogenesis factor 11a (Pex11a) deficiency is associated with a reduction in peroxisome abundance and impaired fatty acid metabolism in hepatocytes, and results in steatosis. In the present study, we investigated whether butyrate induces Pex11a expression and peroxisome proliferation, and studied its effect on lipid metabolism. C57BL/6 mice fed standard chow or a high-fat diet (HFD) were treated with tributyrin, 4-phelybutyrate acid (4-PBA), or the butyrate-producing probiotics (Clostridium butyricum MIYAIRI 588 [CBM]) plus inulin (dietary fiber), and the body weight, white adipose tissue, serum triglycerides, mRNA expression, and peroxisome abundance were evaluated. Tributyrin or 4-PBA treatment significantly decreased body weight and increased hepatic mRNA expression of peroxisome proliferator-activated receptor-α (PPARα) and Pex11a. In addition, 4-PBA treatment increased peroxisome abundance and the expression of genes involved in peroxisomal fatty acid β-oxidation (acyl-coenzyme A oxidase 1 and hydroxysteroid [17-beta] dehydrogenase 4). CBM and inulin administration reduced adipose tissue mass and serum triglycerides, induced Pex11a, acyl-coenzyme A oxidase 1, and hydroxysteroid (17-beta) dehydrogenase 4 genes, and increased peroxisome abundance in mice fed standard chow or an HFD. In conclusion, elevation of butyrate availability (directly through administration of butyrate or indirectly via administration of butyrate-producing probiotics plus fiber) induces PPARα and Pex11a and the genes involved in peroxisomal fatty acid β-oxidation, increases peroxisome abundance, and improves lipid metabolism. These results may provide a new therapeutic strategy against hyperlipidemia and obesity.     

A high-fat diet and high-fat and high-cholesterol diet may affect glucose and lipid metabolism differentially through gut microbiota in mice

This study was conducted to investigate the effects of a high-fat diet (HFD) and high-fat and high-cholesterol diet (HFHCD) on glucose and lipid metabolism and on the intestinal microbiota of the host animal. A total of 30 four-week-old female C57BL/6 mice were randomly divided into three groups (n=10) and fed with a normal diet (ND), HFD, or HFHCD for 12 weeks, respectively. The HFD significantly increased body weight and visceral adipose accumulation and partly lowered oral glucose tolerance compared with the ND and HFHCD. The HFHCD increased liver weight, liver fat infiltration, liver triglycerides, and liver total cholesterol compared with the ND and HFD. Moreover, it increased serum high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and total cholesterol compared with the ND and HFD and upregulated alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase significantly. The HFHCD also significantly decreased the α-diversity of the fecal bacteria of the mice, to a greater extent than the HFD. The composition of fecal bacteria among the three groups was apparently different. Compared with the HFHCD-fed mice, the HFD-fed mice had more Oscillospira, Odoribacter, Bacteroides, and [Prevotella], but less [Ruminococcus] and Akkermansia. Cecal short-chain fatty acids were significantly decreased after the mice were fed the HFD or HFHCD for 12 weeks. Our findings indicate that an HFD and HFHCD can alter the glucose and lipid metabolism of the host animal differentially; modifications of intestinal microbiota and their metabolites may be an important underlying mechanism.