Adipose tissue plasticity mediated by the counterregulatory axis of the renin-angiotensin system: Role of Mas and MrgD receptors.

The renin-angiotensin system (RAS) is an endocrine system composed of two main axes: the classical and the counterregulatory, very often displaying opposing effects. The classical axis, primarily mediated by angiotensin receptors type 1 (AT1R), is linked to obesity-associated metabolic effects. On the other hand, the counterregulatory axis appears to exert antiobesity effects through the activation of two receptors, the G protein-coupled receptor (MasR) and Mas-related receptor type D (MrgD). The local RAS in adipose organ has prompted extensive research into white adipose tissue and brown adipose tissue (BAT), with a key role in regulating the cellular and metabolic plasticity of these tissues. The MasR activation favors the brown plasticity signature in the adipose organ by improve the thermogenesis, adipogenesis, and lipolysis, decrease the inflammatory state, and overall energy homeostasis. The MrgD metabolic effects are related to the maintenance of BAT functionality, but the signaling remains unexplored. This review provides a summary of RAS counterregulatory actions triggered by Mas and MrgD receptors on adipose tissue plasticity. Focus on the effects related to the morphology and function of adipose tissue, especially from animal studies, will be given targeting new avenues for treatment of obesity-associated metabolic effects.

Effects of short-term high-intensity interval and continuous exercise training on body composition and cardiac function in obese sarcopenic rats.

AIM: We investigated the effects of high-intensity interval and continuous short-term exercise on body composition and cardiac function after myocardial ischemia-reperfusion injury (IRI) in obese rats. METHODS: Rats fed with a standard chow diet (SC) or high-fat diet (HFD) for 20 weeks underwent systolic blood pressure (SBP), glycemia and dual-energy X-ray absorptiometry analyses. Then, animals fed with HFD were subdivided into three groups: sedentary (HFD-SED); moderate-intensity continuous training (HFD-MICT); and high-intensity interval training (HFD-HIIT). Exercised groups underwent four isocaloric aerobic exercise sessions, in which HFD-MICT maintained the intensity continuously and HFD-HIIT alternated it. After exercise sessions, all groups underwent global IRI and myocardial infarct size (IS) was determined histologically. Fat and muscle mass were weighted, and protein levels involved in muscle metabolism were assessed in skeletal muscle. RESULTS: HFD-fed versus SC-fed rats reduced lean body mass by 31% (P < 0.001), while SBP, glycemia and body fat percentage were increased by 10% (P = 0.04), 30% (P = 0.006) and 54% (P < 0.001); respectively. HFD-induced muscle atrophy was restored in exercised groups, as only HFD-SED presented lower gastrocnemius (32%; P = 0.001) and quadriceps mass (62%; P < 0.001) than SC. PGC1-α expression was 2.7-fold higher in HFD-HIIT versus HFD-SED (P = 0.04), whereas HFD-HIIT and HFD-MICT exhibited 1.7-fold increase in p-mTORSer2481 levels compared to HFD-SED (P = 0.04). Although no difference was detected among groups for IS (P = 0.30), only HFD-HIIT preserved left-ventricle developed pressure after IRI (+0.7 mmHg; P = 0.9). SIGNIFICANCE: Short-term exercise, continuous or HIIT, restored HFD-induced muscle atrophy and increased mTOR expression, but only HIIT maintained myocardial contractility following IRI in obese animals.

Medium-chain triglyceride reinforce the hepatic damage caused by fructose intake in mice.

We aimed to investigate the effects of medium-chain triglyceride oil on the high fructose diet-provoked hepatic abnormalities in mice. We used C57bl/6 mice of 3-months-old divided into four groups for 12 weeks: control (C), control with MCT (C-MCT), fructose (F), and fructose with MCT (F-MCT). We investigated food and water intake, body mass, blood pressure, glucose tolerance, plasma and liver biochemistry, hepatic protein and gene expression. There were no changes in body mass, food intake and glucose tolerance among the groups. The F group presented increased water intake and blood pressure associated with hepatic steatosis and elevated de novo lipogenesis, beta-oxidation, mitochondrial biogenesis and inflammation in the liver. Surprisingly, the C-MCT group also showed hepatic steatosis and inflammation in the liver, and the F-MCT group had no exacerbations of fructose-induced abnormalities, showing marked hepatic steatosis, lipogenesis de novo and hepatic inflammation. The MCT oil groups also presented increased beta-oxidation and mitochondrial biogenesis. In conclusion, MCT oil showed detrimental hepatic effects and should be used with caution, especially in the presence of hepatic alterations.

Administration of eicosapentaenoic and docosahexaenoic acids may improve the remodeling and browning in subcutaneous white adipose tissue and thermogenic markers in brown adipose tissue in mice.

The role of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in browning and thermogenesis has not been fully elucidated. Thus, we meant to evaluate the effect of EPA and DHA, administered alone or combined, with the activation of browning markers in subcutaneous white adipose tissue (sWAT), and thermogenic markers in brown adipose tissue (BAT). C57BL/6 adult male mice received a control diet or a high-fructose diet (HFru) for eight weeks, but after the first three weeks, HFru was divided into new groups: HFru, HFru + EPA, HFru + DHA, and HFru-EPA + DHA. EPA and DHA diminished adipocyte hypertrophy, recovered markers of browning in sWAT and thermogenic factors in the BAT, and improved gene expressions linked with mitochondrial biogenesis and lipid metabolism. Importantly, EPA and DHA administrated alone showed stronger results than the combination of EPA + DHA. The results suggest that EPA and DHA might be useful as adjuvant strategies to treat metabolic-associated disorders.

Modulation of the renin-angiotensin system in white adipose tissue and skeletal muscle: focus on exercise training.

Overactivation of the renin-angiotensin (Ang) system (RAS) increases the classical arm (Ang-converting enzyme (ACE)/Ang II/Ang type 1 receptor (AT1R)) to the detriment of the protective arm (ACE2/Ang 1-7/Mas receptor (MasR)). The components of the RAS are present locally in white adipose tissue (WAT) and skeletal muscle, which act co-operatively, through specific mediators, in response to pathophysiological changes. In WAT, up-regulation of the classical arm promotes lipogenesis and reduces lipolysis and adipogenesis, leading to adipocyte hypertrophy and lipid storage, which are related to insulin resistance and increased inflammation. In skeletal muscle, the classical arm promotes protein degradation and increases the inflammatory status and oxidative stress, leading to muscle wasting. Conversely, the protective arm plays a counter-regulatory role by opposing the effect of Ang II. The accumulation of adipose tissue and muscle mass loss is associated with a higher risk of morbidity and mortality, which could be related, in part, to overactivation of the RAS. On the other hand, exercise training (ExT) shifts the balance of the RAS towards the protective arm, promoting the inhibition of the classical arm in parallel with the stimulation of the protective arm. Thus, fat mobilization and maintenance of muscle mass and function are facilitated. However, the mechanisms underlying exercise-induced changes in the RAS remain unclear. In this review, we present the RAS as a key mechanism of WAT and skeletal muscle metabolic dysfunction. Furthermore, we discuss the interaction between the RAS and exercise and the possible underlying mechanisms of the health-related aspects of ExT.

Eicosapentaenoic acid (EPA) vs. Docosahexaenoic acid (DHA): Effects in epididymal white adipose tissue of mice fed a high-fructose diet.

BACKGROUND: Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been demonstrated to be beneficial for many diseases, including those associated with the metabolic syndrome (e.g. insulin resistance and hypertension). Nevertheless, not only their actions are not entirely understood, but also their only effects were not yet elucidated. Therefore, we aimed to compare the effects of EPA and DHA, alone or in combination, on the epididymal white adipose tissue (WAT) metabolism in mice fed a high-fructose diet. METHODS: 3-mo-old C57Bl/6 mice were fed a control diet (C) or a high-fructose diet (HFru). After three weeks on the diets, the HFru group was subdivided into four new groups for another five weeks: HFru, HFru+EPA, HFru+DHA, and HFru-EPA+DHA (n=10/group). Besides evaluating biometric and metabolic parameters of the animals, we measured the adipocyte area and performed molecular analyses (inflammation and lipolysis) in the epididymal WAT. RESULTS: The HFru group showed adipocyte hypertrophy, inflammation, and uncontrolled lipolysis. The treated animals showed a reversion of adipocyte hypertrophy, inhibition of inflammation with activation of anti-inflammatory mediators, and regularization of lipolysis. Overall, the beneficial effects were more marked with DHA than EPA. CONCLUSION: Although the whole-body metabolic effects were similar between EPA and DHA, DHA appeared to be the central actor in WAT metabolism, modulating pro and anti-inflammatory pathways and alleviating adipocytes abnormalities. Therefore, when considering fructose-induced adverse effects in WAT, the most prominent actions were observed with DHA.

Browning of white adipose tissue: lessons from experimental models.

Beige or brite (brown-in-white) adipocytes are present in white adipose tissue (WAT) and have a white fat-like phenotype that when stimulated acquires a brown fat-like phenotype, leading to increased thermogenesis. This phenomenon is known as browning and is more likely to occur in subcutaneous fat depots. Browning involves the expression of many transcription factors, such as PR domain containing 16 (PRDM16) and peroxisome proliferator-activated receptor (PPAR)-γ, and of uncoupling protein (UCP)-1, which is the hallmark of thermogenesis. Recent papers pointed that browning can occur in the WAT of humans, with beneficial metabolic effects. This fact indicates that these cells can be targeted to treat a range of diseases, with both pharmacological and nutritional activators. Pharmacological approaches to induce browning include the use of PPAR-α agonist, adrenergic receptor stimulation, thyroid hormone administration, irisin and FGF21 induction. Most of them act through the induction of PPAR-γ coactivator (PGC) 1-α and the consequent mitochondrial biogenesis and UCP1 induction. About the nutritional inducers, several compounds have been described with multiple mechanisms of action. Some of these activators include specific amino acids restriction, capsaicin, bile acids, Resveratrol, and retinoic acid. Besides that, some classes of lipids, as well as many plant extracts, have also been implicated in the browning of WAT. In conclusion, the discovery of browning in human WAT opens the possibility to target the adipose tissue to fight a range of diseases. Studies have arisen showing promising results and bringing new opportunities in thermogenesis and obesity control.

A rich medium-chain triacylglycerol diet benefits adiposity but has adverse effects on the markers of hepatic lipogenesis and beta-oxidation.

We investigated the increasing amounts of medium-chain triacylglycerol (MCT) in the diet on hepatic lipid metabolism. Mature C57BL/6 male mice were randomly divided into five groups (n = 10/group). The animals received their diet for 12 weeks, as a control (C group, 10% of energy from lipids); high-fat lard (HF group, isoenergetic diet, 50% of energy from lipids with lard); a mixture of lard and MCT oil (with a gradual replacement of lard by MCT: HF-MCT25%, HF-MCT75%, and HF-MCT100% groups). At euthanasia, we collected blood and dissected the liver for analyses (glucose, insulin, HOMA-IR, QUICK index, and triacylglycerol, light microscopy, western blotting, and RT-qPCR). The HF diet groups showed a greater body mass gain compared to the C group, but the HF-MCT100% group showed diminished adiposity and amelioration of insulin resistance. All the HF groups also showed a clear increase in hepatic lipid accumulation, increased lipogenesis and decreased PPAR-alpha expression, although HF-MCT groups showed improved local insulin signaling. Lastly, the HF-MCT100% group had raised markers of beta-oxidation (UCP3 and MCAD) and mitochondrial biogenesis (PGC1-alpha and NRF1). In conclusion, the findings demonstrated that a high amount of MCT (HF-MCT100% group) added to an HF diet reduces the body fat accumulation and insulin resistance. However, the lipid accumulation as well as the lipid metabolism is altered in the liver of animals fed with a very high MCT diet, indicating that higher doses of MCT may be harmful in a long-term.

Thermogenesis, fatty acid synthesis with oxidation, and inflammation in the brown adipose tissue of ob/ob (-/-) mice.

Brown adipose tissue (BAT) is specialized in heat production, but its metabolism in ob/ob mice is still a matter of debate. We aimed to verify ob/ob mice BAT using C57Bl/6 male mice (as the wild-type, WT) and leptin-deficient ob/ob mice (on the C57Bl/6 background strain), at three months of age (n=10/group). At euthanasia, animals had their interscapular BAT weighed, and prepared for analysis (Western blot, and RT-qPCR). In comparison with the WT group, the ob/ob group showed reduced thermogenic signaling markers (gene expression of beta 3-adrenergic receptor, beta3-AR; PPARgamma coactivator 1 alpha, PGC1alpha, and uncoupling protein 1, UCP1). The ob/ob group also showed impaired gene expression for lipid utilization (perilipin was increased, while other markers were diminished: carnitine palmitoyltransferase-1b, CPT-1b; cluster of differentiation 36, CD36; fatty acid binding protein 4, FABP4; fatty acid synthase, FAS, and sterol regulatory element-binding protein 1c, SREBP1c), and altered protein expression of insulin signaling (diminished pAKT, TC10, and GLUT-4). Lastly, the ob/ob group showed increased gene expression of markers of inflammation (interleukin 1 beta, IL-1beta; IL-6, tumor necrosis factor alpha, TNFalpha; and monocyte chemotactic protein-1, MCP-1). In conclusion, the ob/ob mice have decreased thermogenic markers associated with reduced gene expression related to fatty acid synthesis, mobilization, and oxidation. There were also alterations in insulin signaling and protein and gene expressions of inflammation. The findings suggest that the lack of substrate for thermogenesis and the local inflammation negatively regulated thermogenic signaling in the ob/ob mice.

Brown adipose tissue: Updates in cellular and molecular biology.

Brown adipose tissue (BAT) is mainly composed of adipocytes, it is highly vascularized and innervated, and can be activated in adult humans. Brown adipocytes are responsible for performing non-shivering thermogenesis, which is exclusively mediated by uncoupling protein (UCP) -1 (a protein found in the inner mitochondrial membrane), the hallmark of BAT, responsible for the uncoupling of the proton leakage from the ATP production, therefore, generating heat (i.e. thermogenesis). Besides UCP1, other compounds are essential not only to thermogenesis, but also to the proliferation and differentiation of BAT, including peroxisome proliferator-activated receptor (PPAR) family, PPARgamma coactivator 1 (PGC1)-alpha, and PRD1-BF-1-RIZ1 homologous domain protein containing protein (PRDM) -16. The sympathetic nervous system centrally regulates thermogenesis through norepinephrine, which acts on the adrenergic receptors of BAT. This bound leads to the initialization of the many pathways that may activate thermogenesis in acute and/or chronic ways. In summary, this mini-review aims to demonstrate the latest advances in the knowledge of BAT.

Fish oil diet modulates epididymal and inguinal adipocyte metabolism in mice.

We aimed to investigate the impact of different high-fat diets containing fish oil on adiposity and white adipose tissue (WAT) function in mice, comparing the effects on epididymal (eWAT) and subcutaneous (sWAT) depots. For this, we used C57BL/6 male mice fed four types of diets for eight weeks: standard chow (SC), high-fat lard (HF-L), high-fat lard plus fish oil (HF-L + FO), and high-fat fish oil (HF-FO). The HF-L group had a greater body mass (BM) gain, insulin resistance, increased gene expression related to lipogenesis (CD36, aP2, SREBP1c, and FAS), decreased gene expression of perilipin in both eWAT and sWAT, and reduced expression of genes related to beta-oxidation (CPT-1a) and to mitochondrial biogenesis (PGC1alpha, NRF1, and TFAM) in eWAT and sWAT. On the other hand, the HF-L + FO and HF-FO groups showed a smaller BM gain and adiposity, and normalization of insulin resistance and lipogenic genes in both eWAT and sWAT. These animals also showed decreased perilipin gene expression and elevated expression of beta-oxidation and mitochondrial biogenesis genes in eWAT and sWAT. 'Beige' adipocytes were identified in sWAT of the HF-FO animals. In conclusion, fish oil intake has anti-obesity effects through modulation of both eWAT and sWAT metabolism in mice and is relevant in diminishing the BM gain, adiposity, and insulin resistance even in combination with a high-fat lard diet in mice.

Mice fed fish oil diet and upregulation of brown adipose tissue thermogenic markers.

PURPOSE: Fish oil (FO) elicits diverse beneficial effects. Reduction in or prevention of body mass (BM) gain in animal models may be associated with modulation of brown adipose tissue (BAT). We aimed to evaluate the effects of different high-fat diets with FO on BAT metabolism and thermogenic markers. METHODS: C57BL/6 male mice (3-month-old) were fed different diets during 8 weeks: standard-chow diet (SC 10% fat), high-fat lard diet (HF-L 50% fat), high-fat lard plus FO diet (HF-L+FO 50% fat), and high-fat FO diet (HF-FO 50% fat). We evaluated BM and performed an oral glucose tolerance test. At euthanasia, plasma was collected for leptin, and triacylglycerol measurement and interscapular BAT was dissected and stored for molecular analyses. RESULTS: HF-L group showed elevated BM; glucose intolerance associated with diminished TC10 and GLUT4 expressions; hypertriglyceridemia associated with increased CD36 and diminished CPT1 expression; elevated expression of pro-inflammatory cytokines; and reduced PPAR expression. Furthermore, these animals showed hyperleptinemia with increased expression of thermogenic markers (beta3-AR, PGC1alpha, and UCP1). Conversely, HF-L+FO and HF-FO groups showed reduced BM gain with regularization of glucose tolerance and triglyceridemia, GLUT4, TC10, CD36, CPT1, and cytokines expressions. Both groups exhibited elevated PPAR and thermogenic markers expression in a dose-dependent way. CONCLUSIONS: FO improves metabolic profile and upregulates thermogenic markers, suggesting an elevated thermogenesis that leads to reduced BM gain.

A high-fish-oil diet prevents adiposity and modulates white adipose tissue inflammation pathways in mice.

Fish oil improves obesity and its comorbidities, but its mechanisms of action remain unknown. We evaluate the effects of a diet rich in fish oil in white adipose tissue (WAT) inflammation pathways, renin-angiotensin system (RAS) and mitogen-activated protein kinases (MAPKs). To achieve our aims, four groups of male C57BL/6 mice were fed different diets: standard chow diet (SC; 10% energy from fat), SC+fish oil diet (SC-FO; 10% energy from fat), high-fat lard diet (HF-L; 50% energy from lard) and HF fish oil diet (HF-FO; 50% energy from fish oil). We evaluated body mass, epididymal fat pad mass, food intake and glucose tolerance. In WAT, we assessed adipocyte hypertrophy, monocyte chemotactic protein-1 immunofluorescence, and gene and protein expression of insulin signaling, inflammation, MAPKs, RAS, peroxisome proliferator-activated receptors (PPARs) and AMP-activated protein kinase (AMPK). In relation to the results, the HF-L group, as expected, showed elevated body mass and adiposity, glucose intolerance and hypertrophied adipocytes. In WAT, we found a defect in insulin signaling, infiltration of macrophages and inflammatory markers with the associated activation of MAPKs and local RAS. On the contrary, the HF-FO group did not present increased body mass, adiposity or glucose intolerance. In this group, insulin signaling, macrophage infiltration and inflammation were reduced in WAT in comparison with the HF-L group. We also observed decreases of MAPKs and local RAS and elevation of PPAR and AMPK. In summary, fish oil activates PPAR (the three isoforms) and AMPK, decreases WAT insulin resistance and inflammation, and inhibits MAPK and RAS pathways activation.

Fish oil has beneficial effects on allergen-induced airway inflammation and hyperreactivity in mice.

BACKGROUND: Fish oil (FO) is rich in n-3 polyunsaturated fatty acids (PUFA), which have been suggested to be anti-inflammatory and are associated with improvement of several inflammatory diseases. In this study, we investigated the influence of FO on allergen-induced lung inflammation and airway hyperreactivity in mice. METHODS: Male A/J mice were fed either a standard-chow (SC) or a FO diet (FO) for 8 weeks. After 4 weeks, each group was further randomized for ovalbumin (SC-OVA and FO-OVA) or saline (SC-SAL and FO-SAL) challenge. Resistance and elastance were measured at baseline and after aerosolized methacholine, 24h after the last challenge. Bronchoalveolar lavage (BAL) was performed for leukocyte counts. Lung tissue mucus deposition, peribronchiolar matrix deposition and eosinophil infiltration were quantified. Serum immunoglobulin E (IgE) and IgG1 (ref 2.2), lung IL-4, IL-5, IL-10, IL-13, IL-17, INFγ and eotaxin-1 and 2 were detected by ELISA and nuclear factor kappa B (NFκB), GATA-3 and peroxisome proliferator-activated receptor gamma (PPARγ) expression was measured by Western blot. RESULTS: Levels of serum IgE and IgG1 were significantly higher in OVA sensitized mice. OVA challenge resulted in increased eosinophil infiltration, increased inflammatory cytokine production, peribronchiolar matrix and mucus deposition and airway hyperreactivity to aerosolized methacholine. Elevated lung NFκB and GATA-3 expression was noted in OVA-challenged mice. These changes were attenuated in mice fed with FO diet. Higher PPARγ expression was also detected in the lungs from the FO-fed groups. CONCLUSION: Our results demonstrate that FO intake attenuated classical asthma features by suppressing the systemic sensitization, thus providing evidence that FO might be a prophylactic alternative for asthma prevention.

Peroxisome proliferator-activated receptors-alpha and gamma are targets to treat offspring from maternal diet-induced obesity in mice.

AIM: The aim of the present study was to evaluate whether activation of peroxisome proliferator-activated receptor (PPAR)alpha and PPARgamma by Bezafibrate (BZ) could attenuate hepatic and white adipose tissue (WAT) abnormalities in male offspring from diet-induced obese dams. MATERIALS AND METHODS: C57BL/6 female mice were fed a standard chow (SC; 10% lipids) diet or a high-fat (HF; 49% lipids) diet for 8 weeks before mating and during gestation and lactation periods. Male offspring received SC diet at weaning and were subdivided into four groups: SC, SC/BZ, HF and HF/BZ. Treatment with BZ (100 mg/Kg diet) started at 12 weeks of age and was maintained for three weeks. RESULTS: The HF diet resulted in an overweight phenotype and an increase in oral glucose intolerance and fasting glucose of dams. The HF offspring showed increased body mass, higher levels of plasmatic and hepatic triglycerides, higher levels of pro-inflammatory and lower levels of anti-inflammatory adipokines, impairment of glucose metabolism, abnormal fat pad mass distribution, higher number of larger adipocytes, hepatic steatosis, higher expression of lipogenic proteins concomitant to decreased expression of PPARalpha and carnitine palmitoyltransferase I (CPT-1) in liver, and diminished expression of PPARgamma and adiponectin in WAT. Treatment with BZ ameliorated the hepatic and WAT abnormalities generated by diet-induced maternal obesity, with improvements observed in the structural, biochemical and molecular characteristics of the animals' livers and epididymal fat. CONCLUSION: Diet-induced maternal obesity lead to alterations in metabolism, hepatic lipotoxicity and adverse liver and WAT remodeling in the offspring. Targeting PPAR with Bezafibrate has beneficial effects reducing the alterations, mainly through reduction of WAT inflammatory state through PPARgamma activation and enhanced hepatic beta-oxidation due to increased PPARalpha/PPARgamma ratio in liver.