Gelatinases impart susceptibility to high-fat diet-induced obesity in mice

Gelatinases play a role in adipose and muscle hypertrophy and could be involved in tissue remodeling in response to high-fat diet (HFD) intake. This study tested potential roles of gelatinases (matrix metalloproteinses-2 and ?9 [MMP-2 and -9]) in relationship to an antigrowth factor [myostatin (MSTN)] known to be dysregulated in relation to HFD-induced obesity (HFDIO) propensity. In vitro and ex vivo analyses demonstrated that MMP-9 increased mature MSTN levels, indicating a potential role of gelatinases in MSTN activation in vivo. HFD intake resulted in increased body weight and circulating blood glucose values in C57BL/6J and MMP-9 null mice, with no changes observed in SWR/J mice. HFD intake attenuated MMP-9 and MMP-2 mRNA levels in SWR/J mice while elevating MMP-2 levels in skeletal muscle in C57BL/6J mice. In MMP-9 null mice, the effects of HFD intake were muted. Consistent with changes in mRNA levels, HFD intake increased MMP-9 activity in muscle tissue of C57BL/6J mice, demonstrating a strong relationship between HFDIO susceptibility and local MMP regulation. Overall, resistance to HFDIO appears to correspond to low MMP-9 and MSTN levels, suggesting a role of MMP-9 in MSTN activation in local tissue responses to HFD intake.     

Enhanced susceptibility to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity in high-fat diet-induced obesity

Currently, obesity is considered a systemic inflammation; however, the effects of obesity on the vulnerability of dopaminergic neurons to oxidative stress are not fully defined. We evaluated the effects of high-fat diet-induced obesity (HF DIO) on neurotoxicity in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Eight weeks after a HF or matched normal diet, a severe decrease in the levels of striatal dopamine and of nigral microtubule-associated protein 2, manganese superoxide dismutase, and tyrosine hydroxylase was observed in obese mice treated with subtoxic doses of MPTP (20 mg/kg) compared with the matched lean group. In addition, the levels of nitrate/nitrite and thiobarbituric acid-malondialdehyde adducts in the substantia nigra of obese mice were reciprocally elevated or suppressed by MPTP. Interestingly, striatal nNOS phosphorylation and dopamine turnover were elevated in obese mice after MPTP treatment, but were not observed in lean mice. The nitrotyrosine immunoreactivity for evaluation of nigral nitrogenous stress in obese mice with MPTP was higher than that in matched lean mice. At higher doses of MPTP (60 mg/kg), the mortality was higher in obese mice than in lean mice. These results suggest that DIO may increase the vulnerability of dopaminergic neurons to MPTP via increased levels of reactive oxygen and nitrogen species, and the role of nNOS phosphorylation in the MPTP toxicities and dopamine homeostasis should be further evaluated.     

Gut microbiota-mediated xanthine metabolism is associated with resistance to high-fat diet-induced obesity

Resistance to high-fat diet-induced obesity (DIR) has been observed in mice fed a high-fat diet and may provide a potential approach for anti-obesity drug discovery. However, the metabolic status, gut microbiota composition, and its associations with DIR are still unclear. Here, ultraperformance liquid chromatography-tandem mass spectrometry-based urinary metabolomic and 16S rRNA gene sequencing-based fecal microbiome analyses were conducted to investigate the relationship between metabolic profile, gut microbiota composition, and body weight of C57BL/6J mice on chow or a high-fat diet for 8 weeks. PICRUSt analysis of 16S rRNA gene sequences predicted the functional metagenomes of gut bacteria. The results demonstrated that feeding a high-fat diet increased body weight and fasting blood glucose of high-fat diet-induced obesity (DIO) mice and altered the host-microbial co-metabolism and gut microbiota composition. In DIR mice, high-fat diet did not increase body weight while fasting blood glucose was increased significantly compared to chow fed mice. In DIR mice, the urinary metabolic pattern was shifted to a distinct direction compared to DIO mice, which was mainly contributed by xanthine. Moreover, high-fat diet caused gut microbiota dysbiosis in both DIO and DIR mice, but in DIR mice, the abundance of Bifidobacteriaceae, Roseburia, and Escherichia was not affected compared to mice fed a chow diet, which played an important role in the pathway coverage of FormylTHF biosynthesis I. Meanwhile, xanthine and pathway coverage of FormylTHF biosynthesis I showed significant positive correlations with mouse body weight. These findings suggest that gut microbiota-mediated xanthine metabolism correlates with resistance to high-fat DIO.     

UCP1 deficiency increases susceptibility to diet-induced obesity with age

Loss of nonshivering thermogenesis in mice by inactivation of the mitochondrial uncoupling protein gene (Ucp1-/- mice) causes increased sensitivity to cold and unexpected resistance to diet-induced obesity at a young age. To clarify the role of UCP1 in body weight regulation throughout life and influence of UCP1 deficiency on longevity, we longitudinally analyzed the phenotypes of Ucp1-/- mice maintained in a room at 23 degrees C. There was no difference in body weight and lifespan between genotypes under the standard chow diet condition, whereas the mutant mice developed obesity with age under the high-fat (HF) diet condition. Compared with Ucp1+/+ mice, Ucp1-/- mice showed increased expression of genes related to thermogenesis and fatty acid metabolism, such as beta3-adrenergic receptor, in adipose tissues of the 3-month-old mutants; however, the augmented expression was reduced in Ucp1+/+ mice in 11-month-old Ucp1-/- mice fed the HF diet. Likewise, the increased levels of UCP3 and cAMP-dependent protein kinase in the brown adipose tissue of Ucp1-/- mice given the standard diet were decreased significantly in that of Ucp1-/- mice fed the HF diet, which animals showed impaired norepinephrine-induced lipolysis in their adipose tissues. These results suggest profound attenuation of beta-adrenergic responsiveness and fatty acid utilization in Ucp1-/- mice fed the HF diet, bringing them to late-onset obesity. Our findings provide evidence that UCP1 is neither essential for body weight regulation nor for longevity under conditions of standard diet and normal housing temperature, but deficiency increases susceptibility to obesity with age in combination with HF diet.     

Nobiletin improves obesity and insulin resistance in high-fat diet-induced obese mice

Nobiletin (NOB) is a polymethoxylated flavone present in citrus fruits and has been reported to have antitumor and anti-inflammatory effects. However, little is known about the effects of NOB on obesity and insulin resistance. In this study, we examined the effects of NOB on obesity and insulin resistance, and the underlying mechanisms, in high-fat diet (HFD)-induced obese mice. Obese mice were fed a HFD for 8 weeks and then treated without (HFD control group) or with NOB at 10 or 100 mg/kg. NOB decreased body weight gain, white adipose tissue (WAT) weight and plasma triglyceride. Plasma glucose levels tended to decrease compared with the HFD group and improved plasma adiponectin levels and glucose tolerance. Furthermore, NOB altered the expression levels of several lipid metabolism-related and adipokine genes. NOB increased the mRNA expression of peroxisome proliferator-activated receptor (PPAR)-γ, sterol regulatory element-binding protein-1c, fatty acid synthase, stearoyl-CoA desaturase-1, PPAR-α, carnitine palmitoyltransferase-1, uncoupling protein-2 and adiponectin, and decreased the mRNA expression of tumor necrosis factor-α and monocyte chemoattractant protein-1 in WAT. NOB also up-regulated glucose transporter-4 protein expression and Akt phosphorylation and suppressed IκBα degradation in WAT. Taken together, these results suggest that NOB improves adiposity, dyslipidemia, hyperglycemia and insulin resistance. These effects may be elicited by regulating the expression of lipid metabolism-related and adipokine genes, and by regulating the expression of inflammatory makers and activity of the insulin signaling pathway.     

Peripheral-specific y2 receptor knockdown protects mice from high-fat diet-induced obesity

Y2 receptors, particularly those in the brain, have been implicated in neuropeptide Y (NPY)-mediated effects on energy homeostasis and bone mass. Recent evidence also indicates a role for Y2 receptors in peripheral tissues in this process by promoting adipose tissue accretion; however their effects on energy balance remain unclear. Here, we show that adult-onset conditional knockdown of Y2 receptors predominantly in peripheral tissues results in protection against diet-induced obesity accompanied by significantly reduced weight gain, marked reduction in adiposity and improvements in glucose tolerance without any adverse effect on lean mass or bone. These changes occur in association with significant increases in energy expenditure, respiratory exchange ratio, and physical activity and despite concurrent hyperphagia. On a chow diet, knockdown of peripheral Y2 receptors results in increased respiratory exchange ratio and physical activity with no effect on lean or bone mass, but decreases energy expenditure without effecting body weight or food intake. These results suggest that peripheral Y2 receptor signaling is critical in the regulation of oxidative fuel selection and physical activity and protects against the diet-induced obesity. The lack of effects on bone mass seen in this model further indicates that bone mass is primarily controlled by non-peripheral Y2 receptors. This study provides evidence that novel drugs that target peripheral rather than central Y2 receptors could provide benefits for the treatment of obesity and glucose intolerance without adverse effects on lean and bone mass, with the additional benefit of avoiding side effects often associated with pharmaceuticals that act on the central nervous system.     

Toll-like receptor 3 ablation prevented high-fat diet-induced obesity and metabolic disorder

Inflammation in insulin-sensitive tissues (e.g., liver, visceral adipose tissue [VAT]) plays a major role in obesity and insulin resistance. Recruitment of innate immune cells drives the dysregulation of glucose and lipid metabolism. We aimed to seek the role of Toll like receptor 3 (TLR3), a pattern recognition receptor involved in innate immunity, obesity and the metabolic disorder. TLR3 expression in liver and VAT from diet induced obese mice and in VAT from overweight women was examined. Body weight, glucose homeostasis and insulin sensitivity were evaluated in TLR3 wild-type and knockout (KO) mice on a chow diet (CD) or high-fat diet for 15 weeks. At euthanasia, blood was collected, and plasma biochemical parameters and adipokines were determined with commercial kits. Flow cytometry was used to measure macrophage infiltration and activation in VAT. Standard western blot, immunohistochemistry and quantative PCR were used to assess molecules in pathways about lipid and glucose metabolism, insulin and inflammation in tissues of liver and VAT. Utilizing human and animal samples, we found that expression of TLR3 was upregulated in the liver and VAT in obese mice as well as VAT in overweight women. TLR3-deficiency protected against high-fat diet induced obesity, glucose intolerance, insulin resistance and lipid accumulation. Lipolysis was enhanced in VAT and hepatic lipogenesis was inhibited in TLR3 KO animals. Macrophages infiltration into adipose tissue was attenuated in TLR3 KO mice, accompanied with inhibition of NF-κB-dependent AMPK/Akt signaling pathway. These findings demonstrated that TLR3 ablation prevented obesity and metabolic disorders, thereby providing new mechanistic links between inflammation and obesity and associated metabolic abnormalities in lipid/glucose metabolism.     

Profiling of gender-specific rat plasma proteins associated with susceptibility or resistance to diet-induced obesity

Obesity-prone (OP) and obesity-resistant (OR) rats with different responses to development of obesity in spite of the same genetic background are useful animal models for searching for markers during the development of obesity. Here, we investigated whether plasma proteins of OP and OR rats may behave in a different way in males and females. We performed a comparative proteomic analysis using 2-DE combined with MALDI-TOF/MS on proteins from OP and OR male and female rats to discover gender-specific rat plasma proteins associated with susceptibility or resistance to diet-induced obesity. A total of 29 proteins showing differential expression between the groups were identified by MALDI-TOF/MS and database searches. These proteins were classified into 4 groups according to their regulation patterns in response to diet and gender. 22 proteins showed significant differences between OP and OR rats in males and/or females (Group I, II, and III) and 7 proteins exhibited only a high fat diet (HFD)-responsive difference in male or female rats (Group IV). In conclusion, the proteins negatively (ITIH3, FGG, TUBB5, and ZAG) or positively (Hp, ITIH4, and RBP) correlated with obesity found in this study could be used for selection of new targets for gender specific-medical treatment of obesity.     

Increased expression of mu opioid receptors in animals susceptible to diet-induced obesity

Stimulation of mu opioid receptors preferentially increases the intake of a high fat diet. In this paper we investigated whether there was a difference in the expression of mu opioid receptors between animals susceptible (Osborne–Mendel) or resistant (S5B/Pl) to obesity induced by eating a high fat diet. Immunohistochemical studies demonstrated that Osborne–Mendel rats eating a chow diet had an increased number of mu opioid receptors in the arcuate nucleus when compared to S5B/Pl rats. These immunohistochemical findings were supported by Real Time-PCR which demonstrated that the mRNA level of mu opioid receptors was also increased in the hypothalamus of Osborne–Mendel rats compared to S5B/Pl rats. Low doses of the mu opioid receptor agonist DAMGO [d-Ala²-N-Me-Phe⁴-Glycol⁵]-enkephalin administered to Osborne–Mendel rats caused a significant increase in the preference for a diet high in fat. The same doses of DAMGO switched the diet preference of S5B/Pl rats to high fat but did not significantly increase food intake. The combination of these findings suggests that the increased levels of hypothalamic mu opioid receptors in Osborne–Mendel rats may contribute to their preference for a diet high in fat and increase their susceptibility to becoming obese.     

Long-term high-fat diet-induced obesity decreases the cardiac leptin receptor without apparent lipotoxicity

AimsLeptin resistance has been associated with cardiac lipotoxicity; however, whether leptin resistance is a risk factor associated with cardiac lipotoxicity at different time points in diet-induced obesity is unclear. The objective of this study was to evaluate this relationship.Main methodsMale Wistar rats were fed a normal chow diet (12% from fat) or a high-fat diet (49% from fat) for 15 and 45 weeks, respectively. The adiposity index, body weight and co-morbidities were evaluated. Heart lipotoxicity was assessed by analyzing cardiac function and morphological changes as well as cardiac triglyceride, ceramide and lipid hydroperoxide accumulations. Cardiac apoptosis was examined using the TUNEL method. Leptin function was determined by examining plasma leptin levels, cardiac leptin receptors (OB-R) and related phosphorylations of AMP-activated kinase protein (AMPK) and Acetyl CoA carboxylase (ACC).Key findingsThe diet-induced obesity was characterized by an elevated adiposity index, body weight and leptin levels at both 15 and 45 weeks. There was no difference between groups in the cardiac triglyceride or lipid hydroperoxide levels. Interestingly, ceramide levels decreased in obese animals in both experimental periods. The cardiac morphological and functional parameters were not altered. Although down-regulation of OB-R has occurred in chronic obesity, it did not adversely affect AMPK or ACC phosphorylation.SignificanceThe development of obesity via long-term feeding of a high-fat diet to rats does not result in cardiac lipotoxicity but promotes the down-regulation of OB-R. However, this does not result in altered levels of AMPK or ACC phosphorylations in this animal model.     

CXCL14 enhances insulin-dependent glucose uptake in adipocytes and is related to high-fat diet-induced obesity

Accumulating evidence suggests an association between obesity and adipose tissue inflammation. Chemokines are involved in the regulation of inflammation status. Chemokine (C-X-C motif) ligand 14 (CXCL14) is known to be a chemoattractant for monocyte and dendritic cells. Recently, it was reported that CXCL14-deficient mice show resistance to high-fat diet-induced obesity. In this study, we identified CXCL14 as a growth hormone (GH)-induced gene in HepG2 hepatoma cells. Substantial in vivo expression of CXCL14 was detected in the adipose tissue and liver. Its expression and secretion were strikingly increased by insulin administration and high-fat diet. Intriguingly, incubation of 3T3-L1 adipocytes with CXCL14 stimulated insulin-dependent glucose uptake. Further, this effect was associated with enhanced insulin signaling. CXCL14 enhanced the insulin-induced tyrosine phosphorylation of insulin receptors and insulin receptor substrate-1. These results suggest that CXCL14 plays a causal role in high-fat diet-induced obesity.     

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.     

Effects of Korean white ginseng extracts on obesity in high-fat diet-induced obese mice

The present study examined the anti-obesity effect and mechanism of action of Korean white ginseng extracts (KGE) using high-fat diet (HFD)-induced obese mice. Mice were fed a low-fat diet (LFD), HFD or HFD containing 0.8 and 1.6% (w/w) KGE diet (HFD + 0.8KGE and HFD + 1.6KGE) for 8 weeks. We also examined the effects of KGE on plasma triglyceride (TG) elevation in mice administrated with oral lipid emulsion. Body weight gain and white adipose tissue (WAT) weight were significantly decreased in the HFD + 1.6KGE group, compared with the HFD group. The plasma TG levels were also significantly reduced in both HFD + 0.8KGE and HFD + 1.6KGE groups, while leptin levels were significantly decreased in only the HFD + 1.6KGE group, compared with the HFD group. The HFD + 1.6KGE group showed significantly lower mRNA levels of lipogenesis-related genes, including peroxisome proliferator-activated receptorγ2 (PPARγ2), sterol regulatory element binding protein-1c (SREBP-1c), lipoprotein lipase (LPL), fatty acid synthase (FAS) and diacylglycerol acyltransferase 1 (DGAT1), compared with the HFD group. In addition, a dose of 1000 mg/kg KGE inhibited the elevation of plasma TG levels compared with mice given the lipid emulsion alone. These results suggest that the anti-obesity effects of KGE may be elicited by regulating expression of lipogenesis-related genes in WAT and by delaying intestinal fat absorption.     

Intrauterine growth retardation increases the susceptibility of pigs to high-fat diet-induced mitochondrial dysfunction in skeletal muscle

It has been recognized that there is a relationship between prenatal growth restriction and the development of metabolic-related diseases in later life, a process involved in mitochondrial dysfunction. In addition, intrauterine growth retardation (IUGR) increases the susceptibility of offspring to high-fat (HF) diet-induced metabolic syndrome. Recent findings suggested that HF feeding decreased mitochondrial oxidative capacity and impaired mitochondrial function in skeletal muscle. Therefore, we hypothesized that the long-term consequences of IUGR on mitochondrial biogenesis and function make the offspring more susceptible to HF diet-induced mitochondrial dysfunction. Normal birth weight (NBW), and IUGR pigs were allotted to control or HF diet in a completely randomized design, individually. After 4 weeks of feeding, growth performance and molecular pathways related to mitochondrial function were determined. The results showed that IUGR decreased growth performance and plasma insulin concentrations. In offspring fed a HF diet, IUGR was associated with enhanced plasma leptin levels, increased concentrations of triglyceride and malondialdehyde (MDA), and reduced glycogen and ATP contents in skeletal muscle. High fat diet-fed IUGR offspring exhibited decreased activities of lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G6PD). These alterations in metabolic traits of IUGR pigs were accompanied by impaired mitochondrial respiration function, reduced mitochondrial DNA (mtDNA) contents, and down-regulated mRNA expression levels of genes responsible for mitochondrial biogenesis and function. In conclusion, our results suggest that IUGR make the offspring more susceptible to HF diet-induced mitochondrial dysfunction.     

Differential expression of microRNAs in adipose tissue after long-term high-fat diet-induced obesity in mice

Obesity is a major health concern worldwide which is associated with increased risk of chronic diseases such as metabolic syndrome, cardiovascular disease and cancer. The elucidation of the molecular mechanisms involved in adipogenesis and obesogenesis is of essential importance as it could lead to the identification of novel biomarkers and therapeutic targets for the development of anti-obesity drugs. MicroRNAs (miRNAs) have been shown to play regulatory roles in several biological processes. They have become a growing research field and consist of promising pharmaceutical targets in various fields such as cancer, metabolism, etc. The present study investigated the possible implication of miRNAs in adipose tissue during the development of obesity using as a model the C57BLJ6 mice fed a high-fat diet.C57BLJ6 wild type male mice were fed either a standard (SD) or a high-fat diet (HFD) for 5 months. Total RNA was prepared from white adipose tissue and was used for microRNA profiling and qPCR.Twenty-two of the most differentially expressed miRNAs, as identified by the microRNA profiling were validated using qPCR. The results of the present study confirmed previous results. The up-regulation of mmu-miR-222 and the down-regulation of mmu-miR-200b, mmu-miR-200c, mmu-miR-204, mmu-miR-30a*, mmu-miR-193, mmu-miR-378 and mmu-miR-30e* after HFD feeding has also been previously reported. On the other hand, we show for the first time the up-regulation of mmu-miR-342-3p, mmu-miR-142-3p, mmu-miR-142-5p, mmu-miR-21, mmu-miR-146a, mmu-miR-146b, mmu-miR-379 and the down-regulation of mmu-miR-122, mmu-miR-133b, mmu-miR-1, mmu-miR-30a*, mmu-miR-192 and mmu-miR-203 during the development of obesity. However, future studies are warranted in order to understand the exact role that miRNAs play in adipogenesis and obesity.