Brown Fat Activity Research Articles

Thermogenic Phenotyping in Mice.

Thermogenesis mediated by brown adipose tissue (BAT) and brown-like fat plays an important role in regulating metabolic homeostasis in mammals. Accurate measurement of metabolic responses to brown fat activation, including heat generation and increased energy expenditure is essential for characterizing thermogenic phenotypes in preclinical studies. Here, we describe two methods for assessing thermogenic phenotypes in mice under non-basal states. First, we describe a protocol for measuring body temperature in cold-treated mice using implantable temperature transponders, which allow for continuous monitoring of body temperature. Second, we describe a method for using indirect calorimetry to measure β3-adrenergic agonist-stimulated changes in oxygen consumption, a proxy for thermogenic fat activation.

Developmental thyroid hormone action on pro-opiomelanocortin-expressing cells programs hypothalamic BMPR1A depletion and brown fat activation.

Thyroid hormone excess secondary to global type 3 deiodinase (DIO3) deficiency leads to increased locomotor activity and reduced adiposity, but also to concurrent alterations in parameters of the leptin-melanocortin system that would predict obesity. To distinguish the underlying contributions to the energy balance phenotype of DIO3 deficiency, we generated mice with thyroid hormone excess targeted to pro-opiomelanocortin (POMC)-expressing cells via cell-specific DIO3 inactivation. These mice exhibit a male-specific phenotype of reduced hypothalamic Pomc expression, hyperphagia, and increased activity in brown adipose tissue, with adiposity and serum levels of leptin and thyroid hormones remained normal. These male mice also manifest a marked and widespread hypothalamic reduction in the expression of bone morphogenetic receptor 1a (BMPR1A), which has been shown to cause similar phenotypes when inactivated in POMC-expressing cells. Our results indicate that developmental overexposure to thyroid hormone in POMC-expressing cells programs energy balance mechanisms in a sexually dimorphic manner by suppressing adult hypothalamic BMPR1A expression.

Mirabegron-induced brown fat activation does not exacerbate atherosclerosis in mice with a functional hepatic ApoE-LDLR pathway

Activation of brown adipose tissue (BAT) with the β3-adrenergic receptor agonist CL316,243 protects mice from atherosclerosis development, and the presence of metabolically active BAT is associated with cardiometabolic health in humans. In contrast, exposure to cold or treatment with the clinically used β3-adrenergic receptor agonist mirabegron to activate BAT exacerbates atherosclerosis in apolipoprotein E (ApoE)- and low-density lipoprotein receptor (LDLR)-deficient mice, both lacking a functional ApoE-LDLR pathway crucial for lipoprotein remnant clearance. We, therefore, investigated the effects of mirabegron treatment on dyslipidemia and atherosclerosis development in APOE*3-Leiden.CETP mice, a humanized lipoprotein metabolism model with a functional ApoE-LDLR clearance pathway. Mirabegron activated BAT and induced white adipose tissue (WAT) browning, accompanied by selectively increased fat oxidation and attenuated fat mass gain. Mirabegron increased the uptake of fatty acids derived from triglyceride (TG)-rich lipoproteins by BAT and WAT, which was coupled to increased hepatic uptake of the generated cholesterol-enriched core remnants. Mirabegron also promoted hepatic very low-density lipoprotein (VLDL) production, likely due to an increased flux of fatty acids from WAT to the liver, and resulted in transient elevation in plasma TG levels followed by a substantial decrease in plasma TGs. These effects led to a trend toward lower plasma cholesterol levels and reduced atherosclerosis. We conclude that BAT activation by mirabegron leads to substantial metabolic benefits in APOE*3-Leiden.CETP mice, and mirabegron treatment is certainly not atherogenic. These data underscore the importance of the choice of experimental models when investigating the effect of BAT activation on lipoprotein metabolism and atherosclerosis.

Brown fat activation demonstrated on FDG PET/CT predicts survival outcome.

The purpose of this study was to compare the survival of patients with and without BAT activity on FDG PET/CT. PET/CT exams from 3937 breast cancer patients were retrospectively reviewed for bilateral symmetric elongated FDG activity in the neck and chest, typical of BAT activation. A control group of age-matched (± 1year) breast cancer patients who underwent PET/CT the same week was also enrolled for comparison. Kaplan-Meier curves of progression-free survival (PFS) and overall survival (OS) for BAT positive patients and the control group were calculated. Further sub-analysis was performed to account for the hormonal changes associated with menopause. 2.0% (80/3937) of the breast cancer patients who underwent PET/CT demonstrated BAT activation, and 80 additional patients were analyzed for comparison as the group without BAT activity. Mean follow-up was 76months (range 1-225months). There were 4 recurrences in the BAT group, compared to 12 in the control. The mean PFS for the BAT group was 127months, which was significantly lower than the mean PFS of 180months in the control (p = 0.047). Sub-analysis of premenopausal women again showed longer PFS for the BAT group (129 vs. 196months, p = 0.095) while no difference was found in postmenopausal women (mean 102 vs. 135months, p = 0.360). Presence of BAT activity was also a significant predictor variable for PFS on Cox regression. Patients with BAT activity showed longer progression-free survival than those without, emphasizing the need for further evaluation of its role in metabolism, treatment response, tumor microenvironment and long-term prognosis.

HCBP6-induced activation of brown adipose tissue and upregulated of BAT cytokines genes

Brown adipose tissue is a thermogenic organ, which consumes chemical energy as heat to protect animals from low temperature and metabolic diseases. However, the role and mechanism of the new factor that up-regulates the heat-generating capacity of brown adipose tissue is still unclear. Here, we found that hepatitis C virus core binding protein 6 (HCBP6), as a key regulator gene in the homeostasis of liver lipid metabolism, is an important enhancer for activating brown fat to ensure thermogenesis. HCBP6 upregulates the expression of UCP1 and increases the number of mitochondria in brown adipocytes. In the BAT of HCBP6-knockout mice induced by a high-fat diet, UCP1 and BAT activity-related genes Pgc1α, Cidea and oxidation phosphorylation-related genes (OXPHOS) were significantly reduced. In addition, the transcriptomics results show that the loss of HCBP6 caused disorder of the metabolic pathway, the expression of brown adipocyte development genes was significantly reduced, and the expression of most BAT cytokine genes was reduced. In conclusion, HCBP6 increased ucp1-dependent thermogenesis in BAT and improved liver lipid metabolism, possibly by enhancing the activity of brown fat and changing the expression of BAT cytokine genes.

Autophagy-mediated NCOR1 degradation is required for brown fat maturation and thermogenesis

Brown adipose tissue (BAT) thermogenesis affects energy balance, and thereby it has the potential to induce weight loss and to prevent obesity. Here we document a macroautophagic/autophagic-dependent mechanism of PPARG activity regulation that induces brown adipose differentiation and thermogenesis, and that is mediated by TP53INP2. Disruption of TP53INP2-dependent autophagy reduced brown adipogenesis in cultured cells. In vivo specific-tp53inp2 ablation in brown precursor cells or in adult mice decreased the expression of thermogenic and mature adipocytes genes in BAT. As a result, TP53INP2-deficient mice had reduced UCP1 content in BAT and impaired maximal thermogenic capacity, leading to lipid accumulation and to positive energy balance. Mechanistically, TP53INP2 stimulates PPARG activity and adipogenesis in brown adipose cells by promoting the autophagic degradation of NCOR1, a PPARG co-repressor. Moreover, the modulation of TP53INP2 expression in BAT and in human brown adipocytes suggest that this protein increases PPARG activity during metabolic activation of brown fat. In all, we have identified a novel molecular explanation to the contribution of autophagy to BAT energy metabolism that could facilitate the design of therapeutic strategies against obesity and its metabolic complications.

QS34. Prostaglandin F2a Analog Focally Depletes Adipose Volume Without Concurrent Cytolysis

Purpose: Adipose is one of the most mutable and commonly treated tissues in plastic surgery. Adipose tissue is often the thickest and most variable of the cutaneous layers and is a key contributor to smooth contour, feature, and expression. Unwanted focal adiposity is a common complaint and can arise physiologically, pathologically as lipomas, or iatrogenically after fat grafting. While some indications are amenable to liposuction or resection, not all patients want invasive procedures. Non-invasive ablative procedures have arisen to fill this need including cryolipolysis and the injectable cytolytic deoxycholic acid (Kybella). This agent, however, caries significant comorbid risk. In this study, we investigated repurposing a potent FDA approved prostaglandin F2α (PGF2a) analogue, Latanoprost, currently used as first-line treatment for glaucoma, as an alternative adipolytic agent for small volume focal adipose reduction. Methods: Human adipose obtained under IRB exemption was incubated for 14-days and treated with Kybella and either low- or high-dose soluble Latanoprost every 48-hours. Mature adipocytes and the stromal vascular fractions were collected via enzymatic dissolution and size, count, morphology, and viability were assessed using Calcein-AM/PI imaging. Additionally, single administration of Kybella (500µl) or Latanoprost (1.5 or 150mcg) was performed in vitro to murine fat pads and maintained 2-weeks. These samples were harvested and evaluated via H&E, Pentachrome to assess inguinal fat volume, and fibrotic tissue architecture. Samples were further interrogated via immunofluorescence against Perilipin, Hypoxia Inducible Factor 1-alpha (Hif1a), Uncoupling Protein 1 (UCP1), and hexokinase 2 to assess the variable contributions of Latanoprost therapy to white/brown adipose ratio, focal hypoxia, and metabolic flux. Results: Incubation of lipoaspirate with Kybella resulted in total tissue dissolution and loss of viability. In contrast, Latanoprost did not negatively affect viability of stromal cells or adipocytes. In vivo, both 150 mcg Latanoprost and Kybella significantly decreased inguinal fat pad volume at 2-weeks. Kybella treatment resulted in consistent dermal lesions and histologic evidence of inflammation that were not present in Latanoprost treatment. Furthermore, Latanoprost and vehicle-control treated samples did not significantly vary in presence of fibrotic collagen, Hif1a activation, or presence of UCP1-positive brown fat. Conclusion: Single administration of soluble Latanoprost safely reduced fat pad volume at two weeks post injection in vivo with no ex vivo loss of viability in human tissues. This supports a potential application for reduction in focal adiposity without undesirable cytolysis and future studies will be conducted to optimize dose and determine duration of the effect.

Fish Oil Intake During Gestation and Lactation Attenuated STZ-Induced Diabetes in Male Offspring via Activation of Brown Fat and Modulating Oxylipin Profile

ObjectivesFish oil (FO) has been demonstrated to activate brown thermogenesis and attenuate inflammation in the brown adipose tissue (BAT). Previously, we have reported that maternal FO supplementation promotes BAT activity of the weaned mice pups. However, whether maternal FO intake could confer sustainable metabolic benefits to offspring remains uncovered. Therefore, this study aimed to determine the differential impact of maternal FO during pregnancy versus lactation on BAT transcriptome and evaluate the role of bioactive lipid metabolites derived from maternal FO supplementation on the extended metabolic benefits of older pups in the context of type 1 diabetes (T1D).MethodsBAT samples were collected for RNA sequencing at birth and weaning in the pups with or without maternal FO supplementation. Transcriptomic data were analyzed for profiling of differential expression genes (DEGs) and pathway enrichment analysis. The separate set of 8-week-old male pups with or without maternal FO were injected with streptozotocin (STZ) to induce type 1 diabetes (T1D). In these animals, glucose tolerance, insulin secretion, and plasma levels of oxylipins were assessed. The expression levels of thermogenesis-related genes, inflammatory markers, and mitochondrial respiratory chain complexes were measured in the BATs.ResultsThe RNA-seq analysis revealed that FO intake throughout pregnancy and lactation, but not gestation only, significantly altered BAT transcriptome by upregulating glucose and lipid metabolism pathways and downregulating apoptosis-related pathways. The n-6/n-3 ratio maintained lowered in the 8-week-old pups with maternal fish oil. Consequently, the pups with maternal FO 1) provided the resistance to STZ-induced T1D, 2) promoted thermogenesis-related gene expression and mitochondrial respiratory protein complex in the BAT, 3) reduced proinflammatory oxylipin production compared with the control mice.ConclusionsOur results suggested that maternal FO intake in pregnancy and lactation, at least partly, protects against the risk of T1D of the offspring through augmented BAT function and anti-inflammatory oxylipin production.Funding SourcesNational Institute of Health (NIH), Project #7R21HD094273-02.

P13 COMPLETE ATRIOVENTRICULAR BLOCK IN A 52–YEAR–OLD MAN ASSOCIATED WITH LYMPHATIC CANCER WITH CARDIAC INVOLVEMENT

Abstract A 52–year–old man arrived at the local emergency room for worsening dyspnea and asthenia, present for about a month, but significantly worsening during the night of the access. The ECG (Figure 1) revealed complete AtrioVentricular Block (ABV) with a narrow–QRS junctional escape rhythm, with a heart rate of about 30 beats per minute (bpm). The other vital parameters were within the normal limits and no anomalies were detected on the physical examination. Medium–dose intravenous isoprenaline infusion was immediately started, with an increase in the junctional escape rate up to 50 bpm. The patient also underwent chest x–ray, which showed interstitial thickening in the pulmonary hilus, which was judged to be nonspecific. The blood chemistry was normal and the echocardiogram (Figure 2) did not show any abnormalities. Since there were no apparent reversible causes of the complete AV block, on the next day, a bicameral pacemaker was implanted via the left cephalic vein. The procedure was uneventful and the patient was discharged home two days later, in good general condition. Eight days after the discharge, surgical wound control and pacemaker control were performed, with completely normal parameters. About 15 days after the discharge the patient went back to the local emergency room for dyspnea and fever. Chest Computed Tomography (CT) without contrast medium was performed, which revealed the presence of widespread pathological mediastinal lymphadenopathy. Therefore, the patient was admitted to the internal medicine ward. An in–depth diagnostic was performed first with thoraco–abdominal angio–CT, then with Positron Emission Tomography (PET)–CT (see Figure 3), which revealed the presence of diffuse areas of fixation of the radio–drug (18F–Fluorodeoxyglucose –FDG–), at the ilo–mediastinal, hepatic, pulmonary, retrocrural, retrocaval, iliac, supra and subclavicular, and also cardiac area (activation of interatrial brown fat and between aortic root and the superior vena cava). The patient was therefore transferred to another hospital for diagnostic investigations and lymphoma therapy. In the light of the picture that emerged, the arrhythmological disease was considered to be referred to the cardiac involvement of the oncological disease; to date there are few similar cases described in the literature. Legend of the figures: Figure 1: ECG at the admission Figura 2: Echocardiogram at the admission Figura 3: PET / CT with myocardial areas of 18F–FDG fixation.

Bile acid‐mediated activation of brown fat protects from alcohol‐induced steatosis and liver injury

Background & AimsAlcohol associated liver disease (AALD) is one of the most common causes of liver injury and failure. Limited knowledge of the mechanisms underlying AALD impedes the development of efficacious therapies. Bile acid (BA) signaling was shown to participate in progression of AALD, the mechanisms of which remain poorly understood.Approach & ResultsMice were exposed to chronic‐plus‐one‐binge ethanol feeding to induce AALD. Interestingly, ethanol feeding increased expression of the thermogenesis genes downstream of TGR5 (Takeda G protein‐coupled BA receptor 5) in brown adipose tissue (BAT) of wild‐type (WT) but not TGR5 knockout (KO) mice. TGR5 deficiency significantly diminished BAT activity and energy expenditure in mice after ethanol feeding. Alcohol increased serum BA levels in mice and humans through altering BA transportation rather than increasing hepatic BA synthesis, which activated TGR5 signaling in BAT. TGR5 deficiency did not alter alcohol‐stimulated adipose lipolysis, de novo hepatic lipogenesis, or alcohol effects on hepatic β‐oxidation of free fatty acids (FFA). However, compared to ethanol‐fed WT mice, ethanol‐fed TGR5 KO mice showed less FFA β‐oxidation in BAT, leading to increased circulation and liver uptake of FFA. Importantly, in ethanol‐fed mice housed under thermoneutral conditions, TGR5‐mediated fat burning in BAT was unchanged. Finally, administration of a specific TGR5 agonist significantly activated TGR5 signaling in BAT to increase thermogenesis, reduce serum FFA level and ameliorate hepatic steatosis and injury in AALD mice.ConclusionsBA signaling plays a protective role in AALD by enhancing BAT thermogenesis and BAT crosstalk with the liver via TGR5 activation. Targeting TGR5 in BAT may be a promising approach for the treatment of AALD.

Subcutaneous Administration of a Nitric Oxide-Releasing Nanomatrix Gel Ameliorates Obesity and Insulin Resistance in High-Fat Diet-Induced Obese Mice.

Nitric oxide (NO) is a gaseous signaling molecule, which plays crucial roles in various biological processes, including inflammatory responses, metabolism, cardiovascular functions, and cognitive function. NO bioavailability is reduced with aging and cardiometabolic disorders in humans and rodents. NO stimulates the metabolic rate by increasing the mitochondrial biogenesis and brown fat activation. Therefore, we propose a novel technology of providing exogenous NO to improve the metabolic rate and cognitive function by promoting the development of brown adipose tissue. In the present study, we demonstrate the effects of the peptide amphiphiles-NO-releasing nanomatrix gel (PANO gel) on high-fat diet-induced obesity, insulin resistance, and cognitive functions. Eight-week-old male C57BL/6 mice were subcutaneously injected in the brown fat area with the PANO gel or vehicle (PA gel) every 2 weeks for 12 weeks. The PANO gel-injected mice gained less body weight, improved glucose tolerance, and decreased fasting serum insulin and leptin levels compared with the PA gel-injected mice. Insulin signaling in the muscle, liver, and epididymal white adipose tissue was improved by the PANO gel injection. The PANO gel reduced inflammation, increased lipolysis in the epididymal white adipose tissue, and decreased serum lipids and liver triglycerides. Interestingly, the PANO gel stimulated uncoupled protein 1 gene expression in the brown and beige fat tissues. Furthermore, the PANO gel increased the cerebral blood flow and improved learning and memory abilities. Our results suggest that using the PANO gel to supply exogenous NO is a novel technology to treat metabolic disorders and cognitive dysfunctions.

Polysaccharides from Enteromorpha prolifera improves insulin sensitivity and promotes adipose thermogenesis in diet-induced obese mice associated with activation of PGC-1α-FNDC5/irisin pathway

• Enteromorpha prolifera polysaccharides (EPP) ameliorates inflammation and improves insulin sensitivity in high-fat diet (HFD)-induced obese mice. • EPP improves energy expenditure in HFD-fed mice, which accompanied by the enhancement of metabolic activity in brown and white fat. • The beneficial effect of EPP on energy metabolism may be mediated by activation of PGC-1α-FNDC5/irisin. Polysaccharide from Enteromorpha prolifera (EPP) has therapeutic and nutraceutical potential for obesity management due to its high hypolipidaemic activity. However, the metabolic mechanism by which EPP mediates anti-adiposity effects are not fully understood. This study aimed to evaluate the effects of EPP on insulin signaling and adaptive thermogenesis in high-fat diet (HFD)-fed obese mice, and further explore the underlying mechanisms. C57BL/6 male mice were fed a control diet or an HFD diet with or without 5% EPP for 12 weeks. The insulin signaling and thermogenic program in adipose tissue, and energy expenditure, as well as involvement of PPARγ coactivator-1α (PGC-1α)-fibronectin type 3 domain-containing protein 5 (FNDC5)/irisin pathway were assessed. EPP alleviated diet-induced adiposity, and decreased inflammatory response and improved insulin signaling in white adipose tissue (WAT) of HFD mice. Moreover, EPP administration increased oxygen consumption, carbon dioxide production and heat production in HFD mice, as reflected by the increased thermogenesis observed in brown fat and inguinal WAT. Meanwhile, EPP increased serum irisin concentration and activated PGC-1α/FNDC5/adenosine monophosphate-activated protein kinase α (AMPKα) pathway. These results suggested that dietary EPP improved insulin signaling and whole-body energy metabolism in obese mice, likely by activating the PGC-1α-FNDC5/irisin pathways.

Uncoupling Protein 1 Does Not Produce Heat without Activation.

Mitochondrial uncoupling protein 1 (UCP1) is the crucial mechanistic component of heat production in classical brown fat and the newly identified beige or brite fat. Thermogenesis inevitably comes at a high energetic cost and brown fat, ultimately, is an energy-wasting organ. A constrained strategy that minimizes brown fat activity unless obligate will have been favored during natural selection to safeguard metabolic thriftiness. Accordingly, UCP1 is constitutively inhibited and is inherently not leaky without activation. It follows that increasing brown adipocyte number or UCP1 abundance genetically or pharmacologically does not lead to an automatic increase in thermogenesis or subsequent metabolic consequences in the absence of a plausible route of concomitant activation. Despite its apparent obviousness, this tenet is frequently ignored. Consequently, incorrect conclusions are often drawn from increased BAT or brite/beige depot mass, e.g., predicting or causally linking beneficial metabolic effects. Here, we highlight the inherently inactive nature of UCP1, with a particular emphasis on the molecular brakes and releases of UCP1 activation under physiological conditions. These controls of UCP1 activity represent potential targets of therapeutic interventions to unlock constraints and efficiently harness the energy-expending potential of brown fat to prevent and treat obesity and associated metabolic disorders.

Adipocyte-specific Nos2 deletion improves insulin resistance and dyslipidemia through brown fat activation in diet-induced obese mice

ObjectiveInducible nitric oxide (NO) synthase (NOS2) is a well-documented inflammatory mediator of insulin resistance in obesity. NOS2 expression is induced in both adipocytes and macrophages within adipose tissue during high-fat (HF)-induced obesity. MethodsEight-week-old male mice with adipocyte selective deletion of the Nos2 gene (Nos2AD−KO) and their wildtype littermates (Nos2fl/fl) were subjected to chow or high-fat high-sucrose (HFHS) diet for 10 weeks followed by metabolic phenotyping and determination of brown adipose tissue (BAT) thermogenesis. The direct impact of NO on BAT mitochondrial respiration was also assessed in brown adipocytes. ResultsHFHS-fed Nos2AD−KO mice had improved insulin sensitivity as compared to Nos2fl/fl littermates. Nos2AD−KO mice were also protected from HF-induced dyslipidemia and exhibited increased energy expenditure compared with Nos2fl/fl mice. This was linked to the activation of BAT in HFHS-fed Nos2AD−KO mice as shown by increased Ucp1 and Ucp2 gene expression and augmented respiratory capacity of BAT mitochondria. Furthermore, mitochondrial respiration was inhibited by NO, or upon cytokine-induced NOS2 activation, but improved by NOS2 inhibition in brown adipocytes. ConclusionsThese results demonstrate the key role of adipocyte NOS2 in the development of obesity-linked insulin resistance and dyslipidemia, partly through NO-dependent inhibition of BAT mitochondrial bioenergetics.

Intestinal Microbiome Modified by Bariatric Surgery Improves Insulin Sensitivity and Correlates with Increased Brown Fat Activity and Energy Expenditure

Intestinal Microbiome Modified by Bariatric Surgery Improves Insulin Sensitivity and Correlates with Increased Brown Fat Activity and Energy Expenditure

Discovery of the First in Class 9-N-Berberine Derivative as Hypoglycemic Agent with Extra-Strong Action.

Berberine is well known for its ability to reduce the blood glucose level, but its high effective dose and poor bioavailability limits its use. In this work we synthesized a new derivative of berberine, 9-(hexylamino)-2,3-methylenedioxy-10-methoxyprotoberberine chloride (SHE-196), and analyzed the profile of its hypoglycemic effects. Biological tests have shown that the substance has a very pronounced hypoglycemic activity due to increased insulin sensitivity after single and multiple dosing. In obese type 2 diabetes mellitus (T2DM) mice, it was characterized by improved glucose tolerance, decreased fasting insulin levels and sensitivity, decreased total body weight and interscapular fat mass, and increased interscapular brown fat activity. All these effects were also confirmed histologically, where a decrease in fatty degeneration of the liver, an improvement in the condition of the islets of Langerhans and a decrease in the size of fat droplets in brown adipose tissue were found. Our results indicate that 9-(hexylamino)-2,3-methylenedioxy-10-methoxyprotoberberine chloride could be the first in a new series of therapeutic agents for the treatment of diabetes mellitus.

Bile Acid-Mediated Activation of Brown Fat Protects From Alcohol-Induced Steatosis and Liver Injury in Mice.

Background & AimsAlcohol-associated liver disease (AALD) is one of the most common causes of liver injury and failure. Limited knowledge of the mechanisms underlying AALD impedes the development of efficacious therapies. Bile acid (BA) signaling was shown to participate in the progression of AALD. However, the mechanisms remain poorly understood.MethodsC57BL/6J wild-type (WT), Takeda G-protein–coupled bile acid receptor 5 (TGR5) knockout (KO) and brown adipose tissue (BAT)-specific TGR5 knockdown mice were subjected to ethanol feeding–induced AALD. Liver samples from alcoholic hepatitis patients were used to examine the BA circulation signaling. Human Embryonic Kidney Cells 293 were used for the TGR5 reporter assay. 23(S)-methyl-lithocholic acid was used as a molecular tool to confirm the regulatory functions of BAT in the AALD mouse model.ResultsEthanol feeding increased the expression of the thermogenesis genes downstream of TGR5 in BAT of WT, but not TGR5 KO, mice. TGR5 deficiency significantly blocked BAT activity and energy expenditure in mice after ethanol feeding. Alcohol increased serum BA levels in mice and human beings through altering BA transportation, and the altered BAs activated TGR5 signaling to regulate metabolism. Compared with ethanol-fed WT mice, ethanol-fed TGR5 KO mice showed less free fatty acid (FFA) β-oxidation in BAT, leading to higher levels of FFA in the circulation, increased liver uptake of FFAs, and exacerbated AALD. BAT-specific TGR5 knockdown mice showed similar results with TGR5 KO mice in AALD. Agonist treatment significantly activated TGR5 signaling in BAT, increased thermogenesis, reduced serum FFA level, and ameliorated hepatic steatosis and injury in AALD mice, while these effects were lost in TGR5 KO mice.ConclusionsBA signaling plays a protective role in AALD by enhancing BAT thermogenesis. Targeting TGR5 in BAT may be a promising approach for the treatment of AALD.

Inhibition of phosphodiesterase type 9 reduces obesity and cardiometabolic syndrome in mice.

Central obesity with cardiometabolic syndrome (CMS) is a major global contributor to human disease, and effective therapies are needed. Here, we show that cyclic GMP-selective phosphodiesterase 9A inhibition (PDE9-I) in both male and ovariectomized female mice suppresses preestablished severe diet-induced obesity/CMS with or without superimposed mild cardiac pressure load. PDE9-I reduces total body, inguinal, hepatic, and myocardial fat; stimulates mitochondrial activity in brown and white fat; and improves CMS, without significantly altering activity or food intake. PDE9 localized at mitochondria, and its inhibition in vitro stimulated lipolysis in a PPARα-dependent manner and increased mitochondrial respiration in both adipocytes and myocytes. PPARα upregulation was required to achieve the lipolytic, antiobesity, and metabolic effects of PDE9-I. All these PDE9-I-induced changes were not observed in obese/CMS nonovariectomized females, indicating a strong sexual dimorphism. We found that PPARα chromatin binding was reoriented away from fat metabolism-regulating genes when stimulated in the presence of coactivated estrogen receptor-α, and this may underlie the dimorphism. These findings have translational relevance given that PDE9-I is already being studied in humans for indications including heart failure, and efficacy against obesity/CMS would enhance its therapeutic utility.

Testosterone reduces metabolic brown fat activity in male mice.

Brown adipose tissue (BAT) burns substantial amounts of mainly lipids to produce heat. Some studies indicate that BAT activity and core body temperature are lower in males than females. Here we investigated the role of testosterone and its receptor (the androgen receptor; AR) in metabolic BAT activity in male mice. Castration, which renders mice testosterone deficient, slightly promoted the expression of thermogenic markers in BAT, decreased BAT lipid content, and increased basal lipolysis in isolated brown adipocytes. Further, castration increased the core body temperature. Triglyceride-derived fatty acid uptake, a proxy for metabolic BAT activity in vivo, was strongly increased in BAT from castrated mice (4.5-fold increase vs sham-castrated mice) and testosterone replacement reversed the castration-induced increase in metabolic BAT activity. BAT-specific AR deficiency did not mimic the castration effects in vivo and AR agonist treatment did not diminish the activity of cultured brown adipocytes in vitro, suggesting that androgens do not modulate BAT activity via a direct, AR-mediated pathway. In conclusion, testosterone is a negative regulator of metabolic BAT activity in male mice. Our findings provide new insight into the metabolic actions of testosterone.

Activating thermogenesis to combat obesity: hot topic or cold front?

Activating thermogenesis to combat obesity: hot topic or cold front?