Brown Adipose Tissue Function Research Articles

The function of brown adipose tissue at different sites of the body in Brandt's voles during cold acclimation

Ambient temperatures have great impacts on thermoregulation of small mammals. Brown adipose tissue (BAT), an obligative thermogenic tissue for small mammals, is localized not only in the interscapular depot (iBAT), but also in supraclavicular, infra/subscapular, cervical, paravertebral, and periaortic depots. The iBAT is known for its cold-induced thermogenesis, however, less has been paid attention to the function of BAT at other sites. Here, we investigated the function of BAT at different sites of the body during cold acclimation in a small rodent species. As expected, Brandt's voles (Lasiopodomys brandtii) consumed more food and reduced the body mass gain when they were exposed to cold. The voles increased resting metabolic rate and maintained a relatively lower body temperature in the cold (36.5 ± 0.27 °C) compared to those in the warm condition (37.1 ± 0.36 °C). During cold acclimation, the uncoupling protein 1 (UCP1) increased in aBAT (axillary), cBAT (anterior cervical), iBAT (interscapular), nBAT (supraclavicular), and sBAT (suprascapular). The levels of proliferating cell nuclear antigen (PCNA), a marker for cell proliferation, were higher in cBAT and iBAT in the cold than in the warm group. The pAMPK/AMPK and pCREB/CREB were increased in cBAT and iBAT during cold acclimation, respectively. These data indicate that these different sites of BAT play the cold-induced thermogenic function for small mammals.

Cold-induced expression of a truncated adenylyl cyclase 3 acts as rheostat to brown fat function.

Promoting brown adipose tissue (BAT) activity innovatively targets obesity and metabolic disease. While thermogenic activation of BAT is well understood, the rheostatic regulation of BAT to avoid excessive energy dissipation remains ill-defined. Here, we demonstrate that adenylyl cyclase 3 (AC3) is key for BAT function. We identified a cold-inducible promoter that generates a 5' truncated AC3 mRNA isoform (Adcy3-at), whose expression is driven by a cold-induced, truncated isoform of PPARGC1A (PPARGC1A-AT). Male mice lacking Adcy3-at display increased energy expenditure and are resistant to obesity and ensuing metabolic imbalances. Mouse and human AC3-AT are retained in the endoplasmic reticulum, unable to translocate to the plasma membrane and lack enzymatic activity. AC3-AT interacts with AC3 and sequesters it in the endoplasmic reticulum, reducing the pool of adenylyl cyclases available for G-protein-mediated cAMP synthesis. Thus, AC3-AT acts as a cold-induced rheostat in BAT, limiting adverse consequences of cAMP activity during chronic BAT activation.

Histone proteoform analysis reveals epigenetic changes in adult mouse brown adipose tissue in response to cold stress

BackgroundRegulation of the thermogenic response by brown adipose tissue (BAT) is an important component of energy homeostasis with implications for the treatment of obesity and diabetes. Our preliminary analyses of RNA-Seq data uncovered many nodes representing epigenetic modifiers that are altered in BAT in response to chronic thermogenic activation. Thus, we hypothesized that chronic thermogenic activation broadly alters epigenetic modifications of DNA and histones in BAT.ResultsMotivated to understand how BAT function is regulated epigenetically, we developed a novel method for the first-ever unbiased top-down proteomic quantitation of histone modifications in BAT and validated our results with a multi-omic approach. To test our hypothesis, wildtype male C57BL/6J mice were housed under chronic conditions of thermoneutral temperature (TN, 28°C), mild cold/room temperature (RT, 22°C), or severe cold (SC, 8°C) and BAT was analyzed for DNA methylation and histone modifications. Methylation of promoters and intragenic regions in genomic DNA decrease in response to chronic cold exposure. Integration of DNA methylation and RNA expression datasets suggest a role for epigenetic modification of DNA in regulation of gene expression in response to cold. In response to cold housing, we observe increased bulk acetylation of histones H3.2 and H4, increased histone H3.2 proteoforms with di- and trimethylation of lysine 9 (K9me2 and K9me3), and increased histone H4 proteoforms with acetylation of lysine 16 (K16ac) in BAT.ConclusionsOur results reveal global epigenetically-regulated transcriptional “on” and “off” signals in murine BAT in response to varying degrees of chronic cold stimuli and establish a novel methodology to quantitatively study histones in BAT, allowing for direct comparisons to decipher mechanistic changes during the thermogenic response. Additionally, we make histone PTM and proteoform quantitation, RNA splicing, RRBS, and transcriptional footprint datasets available as a resource for future research.

Genetic evidence for involvement of β2-adrenergic receptor in brown adipose tissue thermogenesis in humans.

Sympathetic activation of brown adipose tissue (BAT) thermogenesis can ameliorate obesity and related metabolic abnormalities. However, crucial subtypes of the β-adrenergic receptor (AR), as well as effects of its genetic variants on functions of BAT, remains unclear in humans. We conducted association analyses of genes encoding β-ARs and BAT activity in human adults. Single nucleotide polymorphisms (SNPs) in β1-, β2-, and β3-AR genes (ADRB1, ADRB2, and ADRB3) were tested for the association with BAT activity under mild cold exposure (19 °C, 2 h) in 399 healthy Japanese adults. BAT activity was measured using fluorodeoxyglucose-positron emission tomography and computed tomography (FDG-PET/CT). To validate the results, we assessed the effects of SNPs in the two independent populations comprising 277 healthy East Asian adults using near-infrared time-resolved spectroscopy (NIRTRS) or infrared thermography (IRT). Effects of SNPs on physiological responses to intensive cold exposure were tested in 42 healthy Japanese adult males using an artificial climate chamber. We found a significant association between a functional SNP (rs1042718) in ADRB2 and BAT activity assessed with FDG-PET/CT (p < 0.001). This SNP also showed an association with cold-induced thermogenesis in the population subset. Furthermore, the association was replicated in the two other independent populations; BAT activity was evaluated by NIRTRS or IRT (p < 0.05). This SNP did not show associations with oxygen consumption and cold-induced thermogenesis under intensive cold exposure, suggesting the irrelevance of shivering thermogenesis. The SNPs of ADRB1 and ADRB3 were not associated with these BAT-related traits. The present study supports the importance of β2-AR in the sympathetic regulation of BAT thermogenesis in humans. The present collection of DNA samples is the largest to which information on the donor's BAT activity has been assigned and can serve as a reference for further in-depth understanding of human BAT function.

Adipose Tissue Dynamics, Thermogenesis, and Interorgan Connections for Preventing Obesity and Metabolic Disorders.

Adipose tissues, such as white, brown, and beige tissues, play pivotal roles in maintaining energy balance and metabolic health. Whereas white adipocytes store energy, brown and beige adipocytes exhibit high energy expenditure owing to their distinct mitochondrial density and UCP1 expression. Dysfunction in these tissues contributes to metabolic disorders such as type 2 diabetes and cardiovascular diseases. Adipose tissue expansion through cell enlargement or increased cell numbers caused by excess energy storage in white adipocytes substantially influences metabolic health. In obesity, hypertrophic adipocytes trigger inflammation, fibrosis, and hypoxia, whereas smaller adipocytes exert favorable metabolic effects, contributing to insulin sensitivity. Brown and beige adipocytes consume energy for thermogenesis to maintain body temperature, contributing to metabolic homeostasis. The intricate interactions between brown adipose tissues and various organs, such as the liver and heart, highlight the systemic implications of adipose tissue functions. Understanding the complex underlying mechanisms may lead to the development of innovative therapies targeting metabolic disorders by modulating the functions of brown adipose tissue and its interactions with other physiological systems. In this review, we discuss insights into the mechanisms underlying the dysregulation of metabolism owing to abnormalities in adipose tissue remodeling. We focus on the endocrine functions of thermogenic brown and beige adipocytes and explore the interorgan interactions that influence whole-body metabolism.

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.

Involution of brown adipose tissue through a Syntaxin 4 dependent pyroptosis pathway

Aging, chronic high-fat diet feeding, or housing at thermoneutrality induces brown adipose tissue (BAT) involution, a process characterized by reduction of BAT mass and function with increased lipid droplet size. Single nuclei RNA sequencing of aged mice identifies a specific brown adipocyte population of Ucp1-low cells that are pyroptotic and display a reduction in the longevity gene syntaxin 4 (Stx4a). Similar to aged brown adipocytes, Ucp1-STX4KO mice display loss of brown adipose tissue mass and thermogenic dysfunction concomitant with increased pyroptosis. Restoration of STX4 expression or suppression of pyroptosis activation protects against the decline in both mass and thermogenic activity in the aged and Ucp1-STX4KO mice. Mechanistically, STX4 deficiency reduces oxidative phosphorylation, glucose uptake, and glycolysis leading to reduced ATP levels, a known triggering signal for pyroptosis. Together, these data demonstrate an understanding of rapid brown adipocyte involution and that physiologic aging and thermogenic dysfunction result from pyroptotic signaling activation.

Dissection, Histological Processing, and Gene Expression Analysis of Murine Supraclavicular Brown Adipose Tissue.

Brown adipose tissue (BAT)-mediated thermogenesis plays an important role in the regulation of metabolism, and its morphology and function can be greatly impacted by environmental stimuli in mice and humans. Currently, murine interscapular BAT (iBAT), which is located between two scapulae in the upper dorsal flank of mice, is the main BAT depot used by research laboratories to study BAT function. Recently, a few previously unknown BAT depots were identified in mice, including one analogous to human supraclavicular brown adipose tissue. Unlike iBAT, murine supraclavicular brown adipose tissue (scBAT) is situated in the intermediate layer of the neck and thus cannot be accessed as readily. To facilitate the study of newly identified mouse scBAT, presented herein is a protocol detailing the steps to dissect intact scBAT from postnatal and adult mice. Due to scBAT's small size relative to other adipose depots, procedures have been modified and optimized specifically for processing scBAT. Among these modifications is the use of a dissecting microscope during tissue collection to increase the precision and homogenization of frozen scBAT samples to raise the efficiency of subsequent qPCR analysis. With these optimizations, the identification of, morphological appearance of, and molecular characterization of the scBAT can be determined in mice.

Beyond the Cold: Activating Brown Adipose Tissue as an Approach to Combat Obesity.

With a dramatic increase in the number of obese and overweight people, there is a great need for new anti-obesity therapies. With the discovery of the functionality of brown adipose tissue in adults and the observation of beige fat cells among white fat cells, scientists are looking for substances and methods to increase the activity of these cells. We aimed to describe how scientists have concluded that brown adipose tissue is also present and active in adults, to describe where in the human body these deposits of brown adipose tissue are, to summarize the origin of both brown fat cells and beige fat cells, and, last but not least, to list some of the substances and methods classified as BAT promotion agents with their benefits and side effects. We summarized these findings based on the original literature and reviews in the field, emphasizing the discovery, function, and origins of brown adipose tissue, BAT promotion agents, and batokines. Only studies written in English and with a satisfying rating were identified from electronic searches of PubMed.

Effect of Electroacupuncture Stimulation on Brown Adipose Tissue Thermogenesis.

: Brown adipose tissue (BAT) is a unique thermogenic tissue in mammals mediated by uncoupling protein 1 (UCP1). The energy generated by glucose and triglyceride metabolism is released and transmitted throughout the body as heat. Understanding the factors influencing BAT function is crucial to determine its metabolic significance and effects on overall health. Although studies have shown that electroacupuncture (EA) at specific acupoints (e.g., ST36) can stimulate BAT, its effects at other acupoints are not well understood. Further research is needed to investigate the potential effects of EA at these acupoints and their association with BAT activation. : This study aimed to investigate the effects of EA at the GV20 and EX-HN3 acupoints. Specifically, the effects of EA on BAT thermogenesis were analyzed by infrared thermography, western blotting, and real-time polymerase chain reaction (PCR). : A total of 12 C57BL/6J mice were randomly divided into the EA and control groups. The EA group received EA at GV20 and EX-HN3 for 20 min once daily for 14 days. The control group underwent the same procedure but without EA. The core body temperature was monitored. Infrared thermal images of the back of each mouse in both groups were captured. BAT samples were collected after euthanasia to analyze UCP1 protein and UCP1 mRNA. : The average skin temperature in the scapular region of the EA group was increased by 1.1℃ compared with that of the C group (p < 0.05). Additionally, the average temperature along the governor vessel in the EA group was increased by 1.6℃ (p = 0.045). EA significantly increased the expression of UCP1 protein (p = 0.001) and UCP1 mRNA (p = 0.002) in BAT, suggesting a potential link between EA and BAT thermogenesis. : EA induced BAT thermogenesis, suggesting GV20 and EX-HN3 as potential acupoints for BAT stimulation. The experimental results also highlighted unique meridian characteristics as demonstrated by elevated skin temperature along the governor vessel in mice.

Citrus aurantium L. and synephrine improve brown adipose tissue function in adolescent mice programmed by early postnatal overfeeding.

Obesity is a multifactorial condition with high health risk, associated with important chronic disorders such as diabetes, dyslipidemia, and cardiovascular dysfunction. Citrus aurantium L. (C. aurantium) is a medicinal plant, and its active component, synephrine, a β-3 adrenergic agonist, can be used for weight loss. We investigated the effects of C. aurantium and synephrine in obese adolescent mice programmed by early postnatal overfeeding. Three days after birth, male Swiss mice were divided into a small litter (SL) group (3 pups) and a normal litter (NL) group (9 pups). At 30 days old, SL and NL mice were treated with C. aurantium standardized to 6% synephrine, C. aurantium with 30% synephrine, isolated synephrine, or vehicle for 19 days. The SL group had a higher body weight than the NL group. Heart rate and blood pressure were not elevated. The SL group had hyperleptinemia and central obesity that were normalized by C. aurantium and synephrine. In brown adipose tissue, the SL group showed a higher lipid droplet sectional area, less nuclei, a reduction in thermogenesis markers related to thermogenesis (UCP-1, PRDM16, PGC-1α and PPARg), and mitochondrial disfunction. C. aurantium and synephrine treatment normalized these parameters. Our data indicates that the treatment with C. aurantium and synephrine could be a promising alternative for the control of some obesity dysfunction, such as improvement of brown adipose tissue dysfunction and leptinemia.

CLCF1 inhibits energy expenditure via suppressing brown fat thermogenesis.

Brown adipose tissue (BAT) is the main site of nonshivering thermogenesis which plays an important role in thermogenesis and energy metabolism. However, the regulatory factors that inhibit BAT activity remain largely unknown. Here, cardiotrophin-like cytokine factor 1 (CLCF1) is identified as a negative regulator of thermogenesis in BAT. Adenovirus-mediated overexpression of CLCF1 in BAT greatly impairs the thermogenic capacity of BAT and reduces the metabolic rate. Consistently, BAT-specific ablation of CLCF1 enhances the BAT function and energy expenditure under both thermoneutral and cold conditions. Mechanistically, adenylate cyclase 3 (ADCY3) is identified as a downstream target of CLCF1 to mediate its role in regulating thermogenesis. Furthermore, CLCF1 is identified to negatively regulate the PERK-ATF4 signaling axis to modulate the transcriptional activity of ADCY3, which activates the PKA substrate phosphorylation. Moreover, CLCF1 deletion in BAT protects the mice against diet-induced obesity by promoting BAT activation and further attenuating impaired glucose and lipid metabolism. Therefore, our results reveal the essential role of CLCF1 in regulating BAT thermogenesis and suggest that inhibiting CLCF1 signaling might be a potential therapeutic strategy for improving obesity-related metabolic disorders.

Two-step regulation by matrix Gla protein in brown adipose cell differentiation

ObjectiveBone morphogenetic protein (BMP) signaling is intricately involved in adipose tissue development. BMP7 together with BMP4 have been implicated in brown adipocyte differentiation but their roles during development remains poorly specified. Matrix Gla protein (MGP) inhibits BMP4 and BMP7 and is expressed in endothelial and progenitor cells. The objective was to determine the role of MGP in brown adipose tissue (BAT) development. MethodsThe approach included global and cell-specific Mgp gene deletion in combination with RNA analysis, immunostaining, thermogenic activity, and in vitro studies. ResultsThe results revealed that MGP directs brown adipogenesis at two essential steps. Endothelial-derived MGP limits triggering of white adipogenic differentiation in the perivascular region, whereas MGP derived from adipose cells supports the transition of CD142-expressing progenitor cells to brown adipogenic maturity. Both steps were important to optimize the thermogenic function of BAT. Furthermore, MGP derived from both sources impacted vascular growth. Reduction of MGP in either endothelial or adipose cells expanded the endothelial cell population, suggesting that MGP is a factor in overall plasticity of adipose tissue. ConclusionMGP displays a dual and cell-specific function in BAT, essentially creating a “cellular shuttle” that coordinates brown adipogenic differentiation with vascular growth during development.

Nuciferine prevents obesity by activating brown adipose tissue.

Increasing evidence suggests that brown adipose tissue (BAT) plays an important role in obesity and related diseases. Increasing the amount or activity of BAT could prevent obesity. Therefore, a safe and effective method of activating BAT is urgently required. Here, we evaluated the potential effects of lotus leaf extract (LLE) on BAT function. We found that LLE substantially increased UCP1 mRNA and protein levels as well as thermogenic protein expression in primary brown adipocytes. Additionally, LLE treatment reduced diet-induced obesity and improved glucose homeostasis owing to BAT activation and increased energy expenditure. We found that nuciferine, an active ingredient of LLE, could dose-dependently activate BAT in vitro and in vivo, alleviate diet-induced obesity, and improve glucose homeostasis by increasing energy expenditure. Mechanistically, we found that nuciferine induced PPARG coactivator 1 alpha (PGC1-α) expression, which is a key gene involved in mitochondrial biogenesis promoter activity, by directly binding to RXRA. Furthermore, RXRA knockdown abolished expression of the nuciferine-induced mitochondrial and thermogenesis-related gene in primary brown adipocytes. In summary, we found that LLE and nuciferine have a notable effect on BAT activation and highlight the potential applications of the main component of LLE in preventing obesity and treating metabolic disorders.

An update on the secretory functions of brown, white, and beige adipose tissue: Towards therapeutic applications.

Adipose tissue, including white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, is vital in modulating whole-body energy metabolism. While WAT primarily stores energy, BAT dissipates energy as heat for thermoregulation. Beige adipose tissue is a hybrid form of adipose tissue that shares characteristics with WAT and BAT. Dysregulation of adipose tissue metabolism is linked to various disorders, including obesity, type 2 diabetes, cardiovascular diseases, cancer, and infertility. Both brown and beige adipocytes secrete multiple molecules, such as batokines, packaged in extracellular vesicles or as soluble signaling molecules that play autocrine, paracrine, and endocrine roles. A greater understanding of the adipocyte secretome is essential for identifying novel molecular targets in treating metabolic disorders. Additionally, microRNAs show crucial roles in regulating adipose tissue differentiation and function, highlighting their potential as biomarkers for metabolic disorders. The browning of WAT has emerged as a promising therapeutic approach in treating obesity and associated metabolic disorders. Many browning agents have been identified, and nanotechnology-based drug delivery systems have been developed to enhance their efficacy. This review scrutinizes the characteristics of and differences between white, brown, and beige adipose tissues, the molecular mechanisms involved in the development of the adipocytes, the significant roles of batokines, and regulatory microRNAs active in different adipose tissues. Finally, the potential of WAT browning in treating obesity and atherosclerosis, the relationship of BAT with cancer and fertility disorders, and the crosstalk between adipose tissue with circadian system and circadian disorders are also investigated.

Abstract 19181: MicroRNA Regulation of Adipose Browning and Glucose Uptake Improves Cardiometabolic Disease

The prevalence of obesity is on the rise worldwide. Brown adipose tissue (BAT), a highly vascularized organ, is activated in response to cold temperatures to generate heat and modulate metabolic efficiency. MicroRNAs (miRNAs) are small, noncoding RNAs that are implicated in cardiometabolic disease. However, relevant miRNAs in the endothelium of the microvasculature of BAT, how they crosstalk to the surrounding adipose tissue in cardiometabolic disease is not fully understood. We profiled microRNAs from the endothelial cells (ECs) of brown adipose tissue (BAT) of mice with diet-induced obesity (DIO) using microRNA-Seq and identified microRNA-485-5p ( miR-485 ) as one of the most differentially regulated miRNAs compared to the chow control. MiR-485 expression was rapidly induced in ECs in response to glucose (2.2-fold) and palmitate (1.63-fold). Loss-of-function studies revealed that neutralization of miR-485 increased glucose uptake to 3T3-L1 adipocytes and human adipose organoids co-cultured with conditioned media from ECs deficient in miR-485 ; while also increasing the mRNA and protein expression of brown fat marker, UCP1. Multiplex ELISA analyses of conditioned media from ECs overexpressing miR-485 showed a significant decrease in the release of IL-25 from ECs (22.5%) while the inhibition of miR-485 in ECs increased IL-25 release by 36.3%. Interestingly, IL-25 increased glucose uptake to 3T3-L1 adipocytes. Systemic intravenous delivery of LNA-anti-miR-485 inhibitor increased expression of UCP1 (31.4%) in BAT by confocal immunofluorescence, improved BAT function as measured by multispectral optoacoustic tomography (MSOT), while improving glucose tolerance and insulin resistance by 10.2% and 14.2% respectively. Metabolic profiling revealed increased energy expenditure (25%), decreased respiratory exchange rate (6%), and increased left ventricular ejection fraction (LVEF) (9.5%). The global longitudinal strain was higher by 28% compared to control mice with DIO. Our findings indicate that miR-485 plays a key regulatory role in controlling adipose browning and metabolism in an EC-paracrine mediated crosstalk in DIO, an effect that could be exploited for therapeutic intervention in obesity-induced cardiometabolic disease.

Lipocalin 2 regulates mitochondrial phospholipidome remodeling, dynamics, and function in brown adipose tissue in male mice

Mitochondrial function is vital for energy metabolism in thermogenic adipocytes. Impaired mitochondrial bioenergetics in brown adipocytes are linked to disrupted thermogenesis and energy balance in obesity and aging. Phospholipid cardiolipin (CL) and phosphatidic acid (PA) jointly regulate mitochondrial membrane architecture and dynamics, with mitochondria-associated endoplasmic reticulum membranes (MAMs) serving as the platform for phospholipid biosynthesis and metabolism. However, little is known about the regulators of MAM phospholipid metabolism and their connection to mitochondrial function. We discover that LCN2 is a PA binding protein recruited to the MAM during inflammation and metabolic stimulation. Lcn2 deficiency disrupts mitochondrial fusion-fission balance and alters the acyl-chain composition of mitochondrial phospholipids in brown adipose tissue (BAT) of male mice. Lcn2 KO male mice exhibit an increase in the levels of CLs containing long-chain polyunsaturated fatty acids (LC-PUFA), a decrease in CLs containing monounsaturated fatty acids, resulting in mitochondrial dysfunction. This dysfunction triggers compensatory activation of peroxisomal function and the biosynthesis of LC-PUFA-containing plasmalogens in BAT. Additionally, Lcn2 deficiency alters PA production, correlating with changes in PA-regulated phospholipid-metabolizing enzymes and the mTOR signaling pathway. In conclusion, LCN2 plays a critical role in the acyl-chain remodeling of phospholipids and mitochondrial bioenergetics by regulating PA production and its function in activating signaling pathways.

Loss of Otopetrin 1 affects thermoregulation during fasting in mice.

Otopetrin 1 (OTOP1) is a proton channel that is highly expressed in brown adipose tissue. We examined the physiology of Otop1-/- mice, which lack functional OTOP1. Mice were studied by indirect calorimetry and telemetric ambulatory body temperature monitoring. Mitochondrial function was measured as oxygen consumption and extracellular acidification. Otop1-/- mice had similar body temperatures as control mice at baseline and in response to cold and hot ambient temperatures. However, in response to fasting the Otop1-/- mice exhibited an exaggerated hypothermia and hypometabolism. Similarly, in ex vivo tests of Otop1-/- brown adipose tissue mitochondrial function, there was no change in baseline oxygen consumption, but the oxygen consumption was reduced after maximal uncoupling with FCCP and increased upon stimulation with the β3-adrenergic agonist CL316243. Mast cells also express Otop1, and Otop1-/- mice had intact, possibly greater hypothermia in response to mast cell activation by the adenosine A3 receptor agonist MRS5698. No increase in insulin resistance was observed in the Otop1-/- mice. Loss of OTOP1 does not change basal function of brown adipose tissue but affects stimulated responses.

FRI488 The Effect Of Thyroid Stimulating Hormone On Brown Adipose Tissue In Humans

Abstract Disclosure: L. Salej: None. S.D. Kodani: None. N. Chaves: None. K.N. Youssef: None. R. Monahan-Earley: None. H. Halle: None. H. Shaelah: None. P. Annie: None. J.A. Parker: None. A.M. Cypess: None. G. Kolodny: None. Y. Tseng: None. B.C. James: None. A. Gavrila-Filip: None. Obesity and diabetes are two main public health concerns due to their high impact on global morbidity and mortality. In an effort to find new treatment strategies, highly active metabolic tissues such as brown adipose tissue (BAT) have been studied as potential targets. Animal studies have shown that TSH may have a direct local effect on BAT mass and activity by stimulating local T3 production via increased deiodinase-2 (DIO2) expression and also by increasing the expression of uncoupling protein-1 (UCP-1), the key molecule in BAT thermogenesis. We hypothesized that high circulating TSH levels could increase BAT activity by increasing local T3 production and generating a local tissue "thyrotoxicosis". We studied 7 patients with thyroid cancer who underwent thyroid surgery and required recombinant TSH (rhTSH) administration for standard follow-up procedures. Each patient underwent 2 PET-CT scans for assessment of BAT volume and activity, first one day after the rhTSH administration (high TSH state) and then 1-3 months later on suppressive thyroid hormone (TH) treatment (low TSH state). Indirect calorimetry and serum thyroid function tests, fasting glucose, insulin, HbA1c, and lipid panel were measured. Our results show that there was a statistically significant difference in TSH levels (p = 0.0095), with stable circulating T4 and T3 between the low and high TSH states. There was no statistically significant difference in the BAT volume and activity (SUVmax) between the high TSH and low TSH states. Age was a significant predictor of BAT SUVmax (p = 0.008; coeff = -0.39, CI = -0.65-0.13), while BMI was a significant predictor for resting energy expenditure (REE) (p = 0.04; coeff = -203.95, CI = -396.12 - -10.78). Based on these findings, along with those from our previous study[1] showing that circulating TH levels may not be directly correlated with BAT function, we have extended our study to assess the intracellular thyroid hormone status in BAT. We have collected deep peri-thyroidal adipose tissue and subcutaneous white adipose tissue (WAT) as a control group from patients undergoing thyroid surgery. In these samples, we will measure mRNA expression of TSH receptors, TH receptors, β-adrenergic receptors, DIO2 and UCP-1 and evaluate for correlations with circulating TSH and TH levels as well as different metabolic parameters to get a deeper insight into BAT function in humans. Reference: 1. Gavrila A et al. Variable Cold-Induced Brown Adipose Tissue Response to Thyroid Hormone Status. Thyroid. 2017 Jan 1;27(1):1-10. Presentation: Friday, June 16, 2023

FRI025 Succinate Receptor Activation Increases Respiration In Human But Not Murine Brown Adipocytes

Abstract Disclosure: B.T. McNeill: None. A. Kelman: None. L.E. Ramage: None. K.J. Suchacki: None. S.J. Wakelin: None. N.M. Morton: None. R.H. Stimson: None. Brown adipose tissue (BAT) is a thermogenic tissue that generates heat to maintain body temperature. BAT activation is a potential therapeutic target for treating obesity-related cardiometabolic disease. We performed RNA sequencing of human primary brown and white adipocytes and identified SUCNR1, which encodes the succinate receptor, as highly differentially expressed (20-fold) in brown versus white adipocytes. Succinate is known to increase BAT thermogenesis, while SUCNR1 activation inhibits lipolysis in white adipose tissue (WAT). We hypothesized that SUCNR1 activation increases BAT thermogenesis in humans and in mice. To test this, we investigated the effect of succinate and the selective SUCNR1 agonist cis-epoxysuccinic acid (C-ESA) in human and murine primary brown/ beige adipocytes. In addition, we determined the metabolic effects of disruption of Sucnr1 in mice either fed control or a high fat (HFD) for 12 weeks and measured energy expenditure when housed at standard room temperature (21°C) and during cold exposure (4°C). In human brown and white adipocytes, succinate increased basal and noradrenaline-stimulated respiration, while C-ESA increased basal respiration only in human brown adipocytes without altering UCP1 mRNA levels. SUCNR1 activation reduced glycerol release only in human white adipocytes. Male (but not female) Sucnr1-/- mice exhibited impaired glucose tolerance versus Sucnr1+/+ littermates after 2 weeks of HFD, and greater fat mass was also observed in the Sucnr1-/- mice following chronic HFD. However, energy expenditure, locomotor activity and tail vein temperature were unchanged in male Sucnr1-/- mice either at 21°C or 4°C. In addition, expression of Ucp1 and Pgc1α in BAT and inguinal WAT were similar between genotypes. Sucnr1 deletion had no effect on fat mass or glucose tolerance in mice fed a control diet. In vitro, differentiated brown adipocytes from Sucnr1-/- mice demonstrated comparable cellular respiration and Ucp1 mRNA levels both basally and during noradrenaline stimulation to Sucnr1+/+ adipocytes. Succinate and C-ESA did not stimulate respiration in murine brown or white adipocytes. These data reveal that SUCNR1 activation enhances brown adipocyte respiration in human but not murine brown adipocytes, highlighting a novel pathway regulating BAT function in addition to differences between species. These data also reveal novel sex-specific differences in the metabolic effects of SUCNR1, although the mechanisms through which female mice are protected from the adverse metabolic effects of Sucnr1 deletion are unclear. SUCNR1 activation may be a novel therapeutic target to treat obesity and associated metabolic disease, but requires further research in humans to determine the specific mechanisms through which SUCNR1 regulates BAT thermogenesis. Presentation: Friday, June 16, 2023