SIRT6 protects against pathological damage caused by diet‐induced obesity

The NAD+‐dependent SIRT6 deacetylase is a therapeutic candidate against the emerging metabolic syndrome epidemic. SIRT6, whose deficiency in mice results in premature aging phenotypes and metabolic defects, was implicated in a calorie restriction response that showed an opposite set of phenotypes from the metabolic syndrome. To explore the role of SIRT6 in metabolic stress, wild type and transgenic (TG) mice overexpressing SIRT6 were fed a high fat diet. In comparison to their wild‐type littermates, SIRT6 TG mice accumulated significantly less visceral fat, LDL‐cholesterol, and triglycerides. TG mice displayed enhanced glucose tolerance along with increased glucose‐stimulated insulin secretion. Gene expression analysis of adipose tissue revealed that the positive effect of SIRT6 overexpression is associated with down regulation of a selective set of peroxisome proliferator‐activated receptor‐responsive genes, and genes associated with lipid storage, such as angiopoietin‐like protein 4, adipocyte fatty acid‐binding protein, and diacylglycerol acyltransferase 1, which were suggested as potential targets for drugs to control metabolic syndrome. These results demonstrate a protective role for SIRT6 against the metabolic consequences of diet‐induced obesity and suggest a potentially beneficial effect of SIRT6 activation on age‐related metabolic diseases.     

Intake compensates for resting metabolic rate variation in female C57BL/6J mice fed high-fat diets

Objective: The literature is divided over whether variation in resting metabolic rate (RMR) is related to subsequent obesity. We set out to see whether the effect of RMR on weight gain in mice could be revealed with high‐fat feeding. Research Methods and Procedures: Female C57BL/6J mice received a low‐ (10 kcal%fat n = 47), medium‐ (45 kcal%fat n = 50), or high‐fat diet (60 kcal%fat n = 50) for 12 weeks. Pre‐treatment RMR was measured by indirect calorimetry. Body composition was estimated using DXA before and after treatment. Results: Mice on the high‐fat diet gained 39% of body mass, whereas control animals gained 3.5%. There was no interaction between RMR and dietary type on weight gain, and there was no association between weight gain and RMR for any of the treatments. RMR accounted for 2.4% of the variation in pre‐treatment food intake corrected for initial body mass; however, the gradient of this relationship indicated that variations in RMR were, on average, compensated for by adjustments in food intake. Discussion: Individual variations in RMR did not predispose mice to weight gain independent of the dietary treatment. Deviations from the relationship between RMR and food intake were not associated with weight gain. This suggests that variations in energy expenditure, caused by RMR and physical activity, are closely linked to dietary intake, and, therefore, well compensated. Individual variations in the strength of this association may underpin individual variability in the responses to diet.     

pRb is an obesity suppressor in hypothalamus and high‐fat diet inhibits pRb in this location

pRb is frequently inactivated in tumours by mutations or phosphorylation. Here, we investigated whether pRb plays a role in obesity. The Arcuate nucleus (ARC) in hypothalamus contains antagonizing POMC and AGRP/NPY neurons for negative and positive energy balance, respectively. Various aspects of ARC neurons are affected in high‐fat diet (HFD)‐induced obesity mouse model. Using this model, we show that HFD, as well as pharmacological activation of AMPK, induces pRb phosphorylation and E2F target gene de‐repression in ARC neurons. Some affected neurons express POMC; and deleting Rb1 in POMC neurons induces E2F target gene de‐repression, cell‐cycle re‐entry, apoptosis, and a hyperphagia‐obesity‐diabetes syndrome. These defects can be corrected by combined deletion of E2f1. In contrast, deleting Rb1 in the antagonizing AGRP/NPY neurons shows no effects. Thus, pRb‐E2F1 is an obesity suppression mechanism in ARC POMC neurons and HFD‐AMPK inhibits this mechanism by phosphorylating pRb in this location.     

Alogliptin improves survival and health of mice on a high‐fat diet

Alogliptin is a commonly prescribed drug treating patients with type 2 diabetes. Here, we show that long‐term intervention with alogliptin (0.03% w/w in diet) improves survival and health of mice on a high‐fat diet. Alogliptin intervention takes beneficial effects associated with longevity, including increased insulin sensitivity, attenuated functionality decline, decreased organ pathology, preserved mitochondrial function, and reduced oxidative stress. Autophagy activation is proposed as an underlying mechanism of these beneficial effects. We conclude that alogliptin intervention could be considered as a potential strategy for extending lifespan and healthspan in obesity and overweight.     

A high‐fat diet reverses metabolic disorders and premature aging by modulating insulin and IGF1 signaling in SIRT6 knockout mice

Mammalian sirtuin 6 (SIRT6) is involved in the regulation of many essential processes, especially metabolic homeostasis. SIRT6 knockout mice undergo premature aging and die at age ~4 weeks. Severe glycometabolic disorders have been found in SIRT6 knockout mice, and whether a dietary intervention can rescue SIRT6 knockout mice remains unknown. In our study, we found that at the same calorie intake, a high‐fat diet dramatically increased the lifespan of SIRT6 knockout mice to 26 weeks (males) and 37 weeks (females), reversed multi‐organ atrophy, and reduced body weight, hypoglycemia, and premature aging. Furthermore, the high‐fat diet partially but significantly normalized the global gene expression profile in SIRT6 knockout mice. Regarding the mechanism, excessive glucose uptake and glycolysis induced by the SIRT6 deficiency were attenuated in skeletal muscle through inhibition of insulin and IGF1 signaling by the high‐fat diet. Similarly, fatty acids but not ketone bodies inhibited glucose uptake, glycolysis, and senescence in SIRT6 knockout fibroblasts, whereas PI3K inhibition antagonized the effects of a high‐fatty‐acid medium in vitro. Overall, the high‐fat diet dramatically reverses numerous consequences of SIRT6 deficiency through modulation of insulin and IGF1 signaling, providing a new basis for elucidation of SIRT6 and fatty‐acid functions and supporting novel therapeutic approaches against metabolic disorders and aging‐related diseases.     

Time sequence of the intensification of the liver glucose production induced by high‐fat diet in mice

It is well established that the development of insulin resistance shows a temporal sequence in different organs and tissues. Moreover, considering that the main aspect of insulin resistance in liver is a process of glucose overproduction from gluconeogenesis, we investigated if this metabolic change also shows temporal sequence. For this purpose, a well‐established experimental model of insulin resistance induced by high‐fat diet (HFD) was used. The mice received HFD (HFD group) or standard diet (COG group) for 1, 7, 14 or 56 days. The HFD group showed increased (P < 0.05 versus COG) epididymal, retroperitoneal and inguinal fat weight from days 1 to 56. In agreement with these results, the HFD group also showed higher body weight (P < 0.05 versus COG) from days 7 to 56. Moreover, the changes induced by HFD on liver gluconeogenesis were progressive because the increment (P < 0.05 versus COG) in glucose production from l ‐lactate, glycerol, l ‐alanine and l ‐glutamine occurred 7, 14, 56 and 56 days after the introduction of the HFD schedule, respectively. Furthermore, glycaemia and cholesterolemia increased (P < 0.05 versus COG) 14 days after starting the HFD schedule. Taken together, the results suggest that the intensification of liver gluconeogenesis induced by an HFD is not a synchronous ‘all‐or‐nothing process’ but is specific for each gluconeogenic substrate and is integrated in a temporal manner with the progressive augmentation of fasting glycaemia. Copyright © 2012 John Wiley & Sons, Ltd.     

High‐fat diet‐induced dysbiosis mediates MCP‐1/CCR2 axis‐dependent M2 macrophage polarization and promotes intestinal adenoma‐adenocarcinoma sequence

High‐fat diet (HFD) is a well‐known risk factor for gut microbiota dysbiosis and colorectal cancer (CRC). However, evidence relating HFD, gut microbiota and carcinogenesis is limited. Our study aimed to demonstrate that HFD‐induced gut dysbiosis promoted intestinal adenoma‐adenocarcinoma sequence. In clinical study, we found that HFD increased the incidence of advanced colorectal neoplasia (AN). The expression of monocyte chemoattractant protein 1 (MCP‐1), CC chemokine receptor 2 (CCR2) and CD163 in CRC patients with HFD was significantly higher than that in CRC patients with normal diet. When it comes to the Apc^min/+ mice, HFD consumption could induce gut dysbiosis and promote intestinal carcinogenesis, accompanying with activation of MCP‐1/CCR2 axis that recruited and polarized M2 tumour‐associated macrophages. Interestingly, transfer of faecal microbiota from HFD‐fed mice to another batch of Apc^min/+ mice in the absence of HFD could also enhance carcinogenesis without significant body weight gain and induced MCP‐1/CCR2 axis activation. HFD‐induced dysbiosis could also be transmitted. Meanwhile, antibiotics cocktail treatment was sufficient to inhibit HFD‐induced carcinogenesis, indicating the vital role of dysbiosis in cancer development. Conclusively, these data indicated that HFD‐induced dysbiosis accelerated intestinal adenoma‐adenocarcinoma sequence through activation of MCP‐1/CCR2 axis, which would provide new insight into better understanding of the mechanisms and prevention for HFD‐related CRC.     

Chronic voluntary ethanol intake hypersensitizes 5‐HT1A autoreceptors in C57BL/6J mice

Alcoholism is a complex disorder involving, among others, the serotoninergic (5‐HT) system, mainly regulated by 5‐HT_1A autoreceptors in the dorsal raphe nucleus. 5‐HT_1A autoreceptor desensitization induced by chronic 5‐HT reuptake inactivation has been associated with a decrease in ethanol intake in mice. We investigated here whether, conversely, chronic ethanol intake could induce 5‐HT_1A autoreceptor supersensitivity, thereby contributing to the maintenance of high ethanol consumption. C57BL/6J mice were subjected to a progressive ethanol intake procedure in a free‐choice paradigm (3–10% ethanol versus tap water; 21 days) and 5‐HT_1A autoreceptor functional state was assessed using different approaches. Acute administration of the 5‐HT_1A receptor agonist ipsapirone decreased the rate of tryptophan hydroxylation in striatum, and this effect was significantly larger (+75%) in mice that drank ethanol than in those drinking water. Furthermore, ethanol intake produced both an increased potency (+45%) of ipsapirone to inhibit the firing of 5‐HT neurons, and a raise (+35%) in 5‐HT_1A autoreceptor‐mediated stimulation of [³⁵S]GTP‐γ‐S binding in the dorsal raphe nucleus. These data showed that chronic voluntary ethanol intake in C57BL/6J mice induced 5‐HT_1A autoreceptor supersensitivity, at the origin of a 5‐HT neurotransmission deficit, which might be causally related to the addictive effects of ethanol intake.     

Diet‐induced obesity accelerates the onset of terminal phenotypes in α‐synuclein transgenic mice

Parkinson's disease (PD) and diabetes belong to the most common neurodegenerative and metabolic syndromes, respectively. Epidemiological links between these two frequent disorders are controversial. The neuropathological hallmarks of PD are protein aggregates composed of amyloid‐like fibrillar and serine‐129 phosphorylated (pS129) α‐synuclein (AS). To study if diet‐induced obesity could be an environmental risk factor for PD‐related α‐synucleinopathy, transgenic (TG) mice, expressing the human mutant A30P AS in brain neurons, were subjected after weaning to a lifelong high fat diet (HFD). The TG mice became obese and glucose‐intolerant, as did the wild‐type controls. Upon aging, HFD significantly accelerated the onset of the lethal locomotor phenotype. Coinciding with the premature movement phenotype and death, HFD accelerated the age of onset of brainstem α‐synucleinopathy as detected by immunostaining with antibodies against pathology‐associated pS129. Amyloid‐like neuropathology was confirmed by thioflavin S staining. Accelerated onset of neurodegeneration was indicated by Gallyas silver‐positive neuronal dystrophy as well as astrogliosis. Phosphorylation of the activation sites of the pro‐survival signaling intermediate Akt was reduced in younger TG mice after HFD. Thus, diet‐induced obesity may be an environmental risk factor for the development of α‐synucleinopathies. The molecular and cellular mechanisms remain to be further elucidated.

     

Oral intake of Lactobacillus plantarum L‐14 extract alleviates TLR2‐ and AMPK‐mediated obesity‐associated disorders in high‐fat‐diet‐induced obese C57BL/6J mice

ObjectivesWhether periodic oral intake of postbiotics positively affects weight regulation and prevents obesity‐associated diseases in vivo is unclear. This study evaluated the action mechanism of Lactobacillus plantarum L‐14 (KTCT13497BP) extract and the effects of its periodic oral intake in a high‐fat‐diet (HFD) mouse model.Materials and methodsMouse pre‐adipocyte 3T3‐L1 cells and human bone marrow mesenchymal stem cells (hBM‐MSC) were treated with L‐14 extract every 2 days during adipogenic differentiation, and the mechanism underlying anti‐adipogenic effects was analysed at cellular and molecular levels. L‐14 extract was orally administrated to HFD‐feeding C57BL/6J mice every 2 days for 7 weeks. White adipose tissue was collected and weighed, and liver and blood serum were analysed. The anti‐adipogenic mechanism of exopolysaccharide (EPS) isolated from L‐14 extract was also analysed using Toll‐like receptor 2 (TLR2) inhibitor C29.ResultsL‐14 extract inhibited 3T3‐L1 and hBM‐MSC differentiation into mature adipocytes by upregulating AMPK signalling pathway in the early stage of adipogenic differentiation. The weight of the HFD + L‐14 group (31.51 ± 1.96 g) was significantly different from that of the HFD group (35.14 ± 3.18 g). L‐14 extract also significantly decreased the serum triacylglycerol/high‐density lipoprotein cholesterol ratio (an insulin resistance marker) and steatohepatitis. In addition, EPS activated the AMPK signalling pathway by interacting with TLR2, consequently inhibiting adipogenesis.ConclusionsEPS from L‐14 extract inhibits adipogenesis via TLR2 and AMPK signalling pathways, and oral intake of L‐14 extract improves obesity and obesity‐associated diseases in vivo. Therefore, EPS can be used to prevent and treat obesity and metabolic disorders.     

Myeloid differentiation protein 1 protected myocardial function against high‐fat stimulation induced pathological remodelling

Myeloid differentiation 1 (MD‐1) is a secreted protein that regulates the immune response of B cell through interacting with radioprotective 105 (RP105). Disrupted immune response may contribute to the development of cardiac diseases, while the roles of MD‐1 remain elusive. Our studies aimed to explore the functions and molecular mechanisms of MD‐1 in obesity‐induced cardiomyopathy. H9C2 myocardial cells were treated with free fatty acid (FFA) containing palmitic acid and oleic acid to challenge high‐fat stimulation and adenoviruses harbouring human MD‐1 coding sequences or shRNA for MD‐1 overexpression or knockdown in vitro. MD‐1 overexpression or knockdown transgenic mice were generated to assess the effects of MD‐1 on high‐fat diet (HD) induced cardiomyopathy in vivo. Our results showed that MD‐1 was down‐regulated in H9C2 cells exposed to FFA stimulation for 48 hours and in obesity mice induced by HD for 20 weeks. Both in vivo and in vitro, silencing of MD‐1 accelerated myocardial function injury induced by HD stimulation through increased cardiac hypertrophy and fibrosis, while overexpression of MD‐1 alleviated the effects of HD by inhibiting the process of cardiac remodelling. Moreover, the MAPK and NF‐κB pathways were overactivated in MD‐1 deficient mice and H9C2 cells after high‐fat treatment. Inhibition of MAPK and NF‐κB pathways played a cardioprotective role against the adverse effects of MD‐1 silencing on high‐fat stimulation induced pathological remodelling. In conclusion, MD‐1 protected myocardial function against high‐fat stimulation induced cardiac pathological remodelling through negative regulation for MAPK/NF‐κB signalling pathways, providing feasible strategies for obesity cardiomyopathy.     

Effect of chronic corticosterone application on depression‐like behavior in C57BL/6N and C57BL/6J mice

Many studies using genetic mouse models are performed with animals on either one of the two closely related genetic backgrounds, C57BL/6J or C57BL/6N. These strains differ only in a few genetic loci, but have some phenotypic differences that also affect behavior. In order to determine the effects of chronic stress hormone exposure, which is relevant for the pathogenesis of psychiatric disorders, we investigated here the behavioral manifestations of long‐term increase in corticosterone levels. Thus, male mice from both sub‐strains were subcutaneously implanted with corticosterone (20 mg) or placebo pellets that released the hormone for a period of 21 days and resulted in significantly elevated plasma corticosterone levels. Corticosterone significantly increased food intake in B6N, but not in B6J mice. At various time points after pellet implantation, we performed tests relevant to activity and emotional behaviors. B6J mice displayed a generally higher activity in the home cage and the open field. Corticosterone decreased the activity. In B6N mice, corticosterone also decreased sucrose preference, worsened the coat state and increased forced swim immobility, while it had no effect in the B6J strain. Altogether, these results indicate that B6N mice are more sensitive to some of the effects of chronic corticosterone treatment than B6J mice.     

Alisol A attenuates high‐fat‐diet‐induced obesity and metabolic disorders via the AMPK/ACC/SREBP‐1c pathway

Obesity and its associated metabolic disorders such as diabetes, hepatic steatosis and chronic heart diseases are affecting billions of individuals. However there is no satisfactory drug to treat such diseases. In this study, we found that alisol A, a major active triterpene isolated from the Chinese traditional medicine Rhizoma Alismatis, could significantly attenuate high‐fat‐diet‐induced obesity. Our biochemical detection demonstrated that alisol A remarkably decreased lipid levels, alleviated glucose metabolism disorders and insulin resistance in high‐fat‐diet‐induced obese mice. We also found that alisol A reduced hepatic steatosis and improved liver function in the obese mice model.In addition, protein expression investigation revealed that alisol A had an active effect on AMPK/ACC/SREBP‐1c pathway. As suggested by the molecular docking study, such bioactivity of alisol A may result from its selective binding to the catalytic region of AMPK.Therefore, we believe that Alisol A could serve as a promising agent for treatment of obesity and its related metabolic diseases.     

Effect of linseed oil and macadamia oil on metabolic changes induced by high‐fat diet in mice

The effects of linseed oil (LO) and macadamia oil (MO) on the metabolic changes induced by a high‐fat diet (HFD) rich in saturated fatty acid were investigated. For the purpose of this study, the vegetable oil present in the HFD, i.e. soybean oil (SO) was replaced with LO (HFD‐LO) or MO (HFD‐MO). For comparative purposes, a group was included, which received a normal fat diet (NFD). Male Swiss mice (6‐week old) were used. After 14 days under the dietary conditions, the mice were fasted for 18 h, and experiments were then performed. The HFD‐SO, HFD‐LO and HFD‐MO groups showed higher glycaemia (p < 0.05 versus NFD). However, no significant effect was observed on glycaemia, liver gluconeogenesis and liver ketogenesis when SO was replaced by either LO or MO. The body weight and the sum of epididymal, mesenteric, retroperitoneal and inguinal fat weights were higher (p < 0.05) in the HFD‐SO and HFD‐MO groups as compared with the NFD group. However, there was no significant difference in these parameters between the NFD and HFD‐LO groups. Thus, the protective role of LO on lipid accumulation induced by an HFD rich in saturated fatty acid is potentially mediated by the high content of ?‐3 polyunsaturated fatty acid in LO. Copyright © 2013 John Wiley & Sons, Ltd.     

Bone loss in C57BL/6J‐OlaHsd mice,a substrain of C57BL/6J carrying mutated alpha‐synuclein and multimerin‐1 genes

The inbred mouse strain C57BL/6 is commonly used for the generation of transgenic mouse and is a well established strain in bone research. Different vendors supply different substrains of C57BL/6J as wild‐type animals when genetic drift did not incur any noticeable phenotype. However, we sporadically observed drastic differences in the bone phenotype of “WT” C57BL/6J mice originating from different labs and speculated that these variations are attributable, at least in part, to the variation between C57BL/6J substrains, which is often overlooked. C57BL/6J‐OlaHsd is a commonly used substrain that despite a well defined deletion in the alpha‐synuclein (Snca) and multimerin‐1 (Mmrn1) genes, was reported to display no obvious phenotype and is used as WT control. Here, we compared the bone phenotype of C57BL/6J‐OlaHsd (6J‐OLA) to C57BL/6J‐RccHsd (6J‐RCC) and to the original C57BL/6J (6J‐JAX). Using μCT analysis, we found that 6J‐OLA mice display a significantly lower trabecular bone mass compared to 6J‐RCC and 6J‐JAX. PCR analysis revealed that both the Snca and Mmrn1 genes are expressed in bone tissue of 6J‐RCC animals but not of 6J‐OLA mutants, suggesting either one or both genes play a role in bone metabolism. In vitro analysis demonstrated increase in osteoclasts number and decreased osteoblast mineralization in cells derived from 6J‐OLA compared with 6J‐RCC. Our data may shed light on unexplained differences in basal bone measurements between different research centers and reiterate the importance of specifying the exact substrain type. In addition, our findings describe the physiological role for Mmrn1 and/or Snca in bone remodeling.     

Diet‐Induced Changes in Stearoyl‐CoA Desaturase 1 Expression in Obesity‐Prone and ‐Resistant Mice

Objective: To investigate stearoyl‐coenzyme A desaturase (SCD) 1 expression in obesity‐prone C57BL/6 mice and in obesity‐resistant FVB mice to explore the relationship of SCD1 expression and susceptibility to diet‐induced obesity. Research Methods and Procedures: Nine‐week‐old C57BL/6 and FVB mice were fed either a high‐ or low‐fat diet for 8 weeks. Body weight and body composition were measured before and at weeks 4 and 8 of the study. Energy expenditure was measured at weeks 1 and 5 of the study. Hepatic SCD1 mRNA was measured at 72 hours and at the end of study. Plasma leptin and insulin concentrations were measured at the end of study. Results: When C57BL/6 mice were switched to a calorie‐dense high‐fat diet, animals gained significantly more body weight than those maintained on a low‐calorie density diet primarily due to increased fat mass accretion. Fat mass continued to accrue throughout 8 weeks of study. Increased calorie intake did not account for all weight gain. On the high‐fat diet, C57BL/6 mice decreased their energy expenditure when compared with mice fed a low‐fat diet. In response to 8 weeks of a high‐fat diet, SCD1 gene expression in liver increased >2‐fold. In contrast, feeding a high‐fat diet did not change body weight, energy expenditure, or SCD1 expression in FVB mice. Discussion: Our study showed that a high‐fat hypercaloric diet increased body adiposity first by producing hyperphagia and then by decreasing energy expenditure of mice susceptible to diet‐induced obesity. Consumption of a high‐fat diet in species predisposed to obesity selectively increased SCD1 gene expression in liver.