Epigenetically active chromatin in neonatal iWAT reveals GABPα as a potential regulator of beige adipogenesis.

Background: Thermogenic beige adipocytes, which dissipate energy as heat, are found in neonates and adults. Recent studies show that neonatal beige adipocytes are highly plastic and contribute to >50% of beige adipocytes in adults. Neonatal beige adipocytes are distinct from recruited beige adipocytes in that they develop independently of temperature and sympathetic innervation through poorly defined mechanisms. Methods: We characterized the neonatal beige adipocytes in the inguinal white adipose tissue (iWAT) of C57BL6 postnatal day 3 and 20 mice (P3 and P20) by imaging, genome-wide RNA-seq analysis, ChIP-seq analysis, qRT-PCR validation, and biochemical assays. Results: We found an increase in acetylated histone 3 lysine 27 (H3K27ac) on the promoter and enhancer regions of beige-specific gene UCP1 in iWAT of P20 mice. Furthermore, H3K27ac ChIP-seq analysis in the iWAT of P3 and P20 mice revealed strong H3K27ac signals at beige adipocyte-associated genes in the iWAT of P20 mice. The integration of H3K27ac ChIP-seq and RNA-seq analysis in the iWAT of P20 mice reveal epigenetically active signatures of beige adipocytes, including oxidative phosphorylation and mitochondrial metabolism. We identify the enrichment of GA-binding protein alpha (GABPα) binding regions in the epigenetically active chromatin regions of the P20 iWAT, particularly on beige genes, and demonstrate that GABPα is required for beige adipocyte differentiation. Moreover, transcriptomic analysis and glucose oxidation assays revealed increased glycolytic activity in the neonatal iWAT from P20. Conclusions: Our findings demonstrate that epigenetic mechanisms regulate the development of peri-weaning beige adipocytes via GABPα. Further studies to better understand the upstream mechanisms that regulate epigenetic activation of GABPα and characterization of the metabolic identity of neonatal beige adipocytes will help us harness their therapeutic potential in metabolic diseases.

Uncoupling protein 1-driven Cre (Ucp1-Cre) is expressed in the epithelial cells of mammary glands and various non-adipose tissues.

OBJECTIVE: Uncoupling protein 1 (UCP1), a mitochondrial protein responsible for nonshivering thermogenesis in adipose tissue, serves as a distinct marker for thermogenic brown and beige adipocytes. Ucp1-Cre mice are thus widely used to genetically manipulate these thermogenic adipocytes. However, evidence suggests that UCP1 may also be expressed in non-adipocyte cell types. In this study, we investigated the presence of UCP1 expression in different mouse tissues that have not been previously reported. METHODS: We employed Ucp1-Cre mice crossed with Cre-inducible transgenic reporter Nuclear tagging and Translating Ribosome Affinity Purification (NuTRAP) mice to investigate Ucp1-Cre expression in various tissues of adult female mice and developing embryos. Tamoxifen-inducible Ucp1-CreERT2 mice crossed with NuTRAP mice were used to assess active Ucp1 expression in adult mice. Immunostaining, RNA analysis, and single-cell/nucleus RNA-seq (sc/snRNA-seq) data analysis were performed to determine the expression of endogenous UCP1 and Ucp1-Cre-driven reporter expression. We also investigated the impact of UCP1 deficiency on mammary gland development and function using Ucp1-knockout (KO) mice. RESULTS: Ucp1-Cre expression was observed in the mammary glands within the inguinal white adipose tissue of female Ucp1-Cre; NuTRAP mice. Ucp1-Cre was activated during embryonic development in various tissues, including mammary glands, as well as in the brain, kidneys, eyes, and ears, specifically in epithelial cells in these organs. However, Ucp1-CreERT2 showed no or only partial activation in these tissues of adult mice, indicating the potential for low or transient expression of endogenous Ucp1. While sc/snRNA-seq data suggest potential expression of UCP1 in mammary epithelial cells in adult mice and humans, Ucp1-KO female mice displayed normal mammary gland development and function. CONCLUSIONS: Our findings reveal widespread Ucp1-Cre expression in various non-adipose tissue types, starting during early development. These results highlight the importance of exercising caution when interpreting data and devising experiments involving Ucp1-Cre mice.

Terrestrial Birth and Body Size Tune UCP1 Functionality in Seals.

The molecular evolution of the mammalian heater protein UCP1 is a powerful biomarker to understand thermoregulatory strategies during species radiation into extreme climates, such as aquatic life with high thermal conductivity. While fully aquatic mammals lost UCP1, most semiaquatic seals display intact UCP1 genes, apart from large elephant seals. Here, we show that UCP1 thermogenic activity of the small-bodied harbor seal is equally potent compared to terrestrial orthologs, emphasizing its importance for neonatal survival on land. In contrast, elephant seal UCP1 does not display thermogenic activity, not even when translating a repaired or a recently highlighted truncated version. Thus, the thermogenic benefits for neonatal survival during terrestrial birth in semiaquatic pinnipeds maintained evolutionary selection pressure on UCP1 function and were only outweighed by extreme body sizes among elephant seals, fully eliminating UCP1-dependent thermogenesis.

The Role of ß3-Adrenergic Receptors in Cold-Induced Beige Adipocyte Production in Pigs.

After exposure to cold stress, animals enhance the production of beige adipocytes and expedite thermogenesis, leading to improved metabolic health. Although brown adipose tissue in rodents is primarily induced by ß3-adrenergic receptor (ADRB3) stimulation, the activation of major ß-adrenergic receptors (ADRBs) in pigs has been a topic of debate. To address this, we developed overexpression vectors for ADRB1, ADRB2, and ADRB3 and silenced the expression of these receptors to observe their effects on the adipogenic differentiation stages of porcine preadipocytes. Our investigation revealed that cold stress triggers the transformation of subcutaneous white adipose tissue to beige adipose tissue in pigs by modulating adrenergic receptor levels. Meanwhile, we found that ADRB3 promotes the transformation of white adipocytes into beige adipocytes. Notably, ADRB3 enhances the expression of beige adipose tissue marker genes, consequently influencing cellular respiration and metabolism by regulating lipolysis and mitochondrial expression. Therefore, ADRB3 may serve as a pivotal gene in animal husbandry and contribute to the improvement of cold intolerance in piglets.

Glycogen synthesis is required for adaptive thermogenesis in beige adipose tissue and affects diet-induced obesity.

Glycogen is a form of energy storage for glucose in different tissues such as liver and skeletal muscle. It remains incompletely understood how glycogen impacts on adipose tissue functionality. Cold exposure elevated the expression of Gys1 that encodes glycogen synthase 1 in brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT). The in vivo function of Gys1 was analyzed using a mouse model in which Gys1 was deleted specifically in adipose tissues. Under normal chow conditions, Gys1 deletion caused little changes to body weight and glucose metabolism. Deletion of Gys1 abrogated upregulation of UCP1 and other thermogenesis-related genes in iWAT upon prolonged cold exposure or treatment with ß3-adrenergic receptor agonist CL-316,243. Stimulation of UCP1 by CL-316,243 in adipose-derived stromal cells (stromal vascular fractions, SVFs) was also reduced by Gys1 deletion. Both the basal glycogen content and CL-316,243-stimulated glycogen accumulation in adipose tissues were reduced by Gys1 deletion. High-fat diet-induced obesity and insulin resistance were aggravated in Gys1-deleted mice. The loss of body weight upon CL-316,243 treatment was also abrogated by the loss of Gys1. In conclusion, our results underscore the pivotal role of glycogen synthesis in adaptive thermogenesis in beige adipose tissue and its impact on diet-induced obesity in mice.NEW & NOTEWORTHY Glycogen is one of major types of fuel reserve in the body and its classical function is to maintain blood glucose level. This study uncovers that glycogen synthesis is required for beige fat tissue to generate heat upon cold exposure. Such a function of glycogen is linked to development of high-fat diet-induced obesity, thus extending our understanding about the physiological functions of glycogen.

Molecular targets for management of diabetes: Remodelling of white adipose to brown adipose tissue.

Diabetes mellitus is a disorder characterised metabolic dysfunction that results in elevated glucose level in the bloodstream. Diabetes is of two types, type1 and type 2 diabetes. Obesity is considered as one of the major reasons intended for incidence of diabetes hence it turns out to be essential to study about the adipose tissue which is responsible for fat storage in body. Adipose tissues play significant role in maintaining the balance between energy stabilization and homeostasis. The three forms of adipose tissue are - White adipose tissue (WAT), Brown adipose tissue (BAT) and Beige adipose tissue (intermediate form). The amount of BAT gets reduced, and WAT starts to increase with the age. WAT when exposed to certain stimuli gets converted to BAT by the help of certain transcriptional regulators. The browning of WAT has been a matter of study to treat the metabolic disorders and to initiate the expenditure of energy. The three main regulators responsible for the browning of WAT are PRDM16, PPARγ and PGC-1α via various cellular and molecular mechanism. Presented review article includes the detailed elaborative aspect of genes and proteins involved in conversion of WAT to BAT.

Glucose regulation of adipose tissue browning by CBP/p300- and HDAC3-mediated reversible acetylation of CREBZF.

Glucose is required for generating heat during cold-induced nonshivering thermogenesis in adipose tissue, but the regulatory mechanism is largely unknown. CREBZF has emerged as a critical mechanism for metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease (NAFLD). We investigated the roles of CREBZF in the control of thermogenesis and energy metabolism. Glucose induces CREBZF in human white adipose tissue (WAT) and inguinal WAT (iWAT) in mice. Lys208 acetylation modulated by transacetylase CREB-binding protein/p300 and deacetylase HDAC3 is required for glucose-induced reduction of proteasomal degradation and augmentation of protein stability of CREBZF. Glucose induces rectal temperature and thermogenesis in white adipose of control mice, which is further potentiated in adipose-specific CREBZF knockout (CREBZF FKO) mice. During cold exposure, CREBZF FKO mice display enhanced thermogenic gene expression, browning of iWAT, and adaptive thermogenesis. CREBZF associates with PGC-1α to repress thermogenic gene expression. Expression levels of CREBZF are negatively correlated with UCP1 in human adipose tissues and increased in WAT of obese ob/ob mice, which may underscore the potential role of CREBZF in the development of compromised thermogenic capability under hyperglycemic conditions. Our results reveal an important mechanism of glucose sensing and thermogenic inactivation through reversible acetylation.

Perirenal adipose tissue contains a subpopulation of cold-inducible adipocytes derived from brown-to-white conversion.

Perirenal adipose tissue (PRAT) is a unique visceral depot that contains a mixture of brown and white adipocytes. The origin and plasticity of such cellular heterogeneity remains unknown. Here, we combine single-nucleus RNA sequencing with genetic lineage tracing to reveal the existence of a distinct subpopulation of Ucp1-&Cidea+ adipocytes that arises from brown-to-white conversion during postnatal life in the periureter region of mouse PRAT. Cold exposure restores Ucp1 expression and a thermogenic phenotype in this subpopulation. These cells have a transcriptome that is distinct from subcutaneous beige adipocytes and may represent a unique type of cold-recruitable adipocytes. These results pave the way for studies of PRAT physiology and mechanisms controlling the plasticity of brown/white adipocyte phenotypes.

The histone methyltransferase SMYD1 is induced by thermogenic stimuli in adipose tissue.

Aim: To study the expression of histone methyltransferase SMYD1 in white adipose tissue (WAT) and brown adipose tissue and during differentiation of preadipocytes to white and beige phenotypes. Methods: C57BL/6J mice fed a high-fat diet (and exposed to cold) and 3T3-L1 cells stimulated to differentiate into white and beige adipocytes were used. Results: SMYD1 expression increased in WAT of high-fat diet fed mice and in WAT and brown adipose tissue of cold-exposed mice, suggesting its role in thermogenesis. SMYD1 expression was higher in beige adipocytes than in white adipocytes, and its silencing leads to a decrease in mitochondrial content and in Pgc-1α expression. Conclusion: These data suggest a novel role for SMYD1 as a positive regulator of energy control in adipose tissue.

In this study, a protein called SMYD1 was examined in the adipose tissue of mice to understand its role in the development of different types of fat cells. The authors used mice fed a high-fat diet or mice exposed to a cold environment. The experiments were also performed on cultured cells that were stimulated to form specific types of fat cells (white adipocytes, which store energy; or beige adipocytes, which are responsible for releasing energy in the form of heat). The study found that SMYD1 increased in white adipose tissue particularly in response to cold exposure and high-fat diet, suggesting involvement in body temperature regulation. SMYD1 was higher in beige adipocytes than in white fat cells, and when SMYD1 was reduced, there was a decrease in certain factors related to energy control. Overall, these results suggest that SMYD1 plays a novel role in energy regulation in adipose tissues.

A comparative assessment of reference genes in mouse brown adipocyte differentiation and thermogenesis in vitro.

Adipogenic differentiation and thermogenesis in brown adipose tissue (BAT) undergo dynamic processes, altering phenotypes and gene expressions. Proper reference genes in gene expression analysis are crucial to mitigate experimental variances and ensure PCR efficacy. Unreliable reference genes can lead to erroneous gene expression quantification, resulting in data misinterpretation. This study focused on identifying suitable reference genes for mouse brown adipocyte research, utilizing brown adipocytes from the Ucp1-luciferase ThermoMouse model. Comparative analysis of gene expression data under adipogenesis and thermogenesis conditions was conducted, validating 13 housekeeping genes through various algorithms, including DeltaCq, BestKeeper, geNorm, Normfinder, and RefFinder. Tbp and Rer1 emerged as optimal references for Ucp1 and Pparg expression in brown adipogenesis, while Tbp and Ubc were ideal for the expression analysis of these target genes in thermogenesis. Conversely, certain conventional references, including Actb, Tubb5, and Gapdh, proved unstable as reference genes under both conditions. These findings stress the critical consideration of reference gene selection in gene expression analysis within specific biological systems to ensure accurate conclusions.

Olodaterol promotes thermogenesis in brown adipocytes via regulation of the ß2-AR/cAMP/PKA signaling pathway.

The escalating incidence of metabolic pathologies such as obesity and diabetes mellitus underscores the imperative for innovative therapeutics targeting lipid metabolism modulation. Within this context, augmenting thermogenic processes in adipose cells emerges as a viable therapeutic approach. Given the limitations of previous ß3-adrenergic receptor (ß3-AR) agonist treatments in human diseases, there is an increasing focus on therapies targeting the ß2-adrenergic receptor (ß2-AR). Olodaterol (OLO) is a potent ß2-AR agonist that is a potential novel pharmacological candidate in this area. Our study explores the role and underlying mechanisms of OLO in enhancing brown adipose thermogenesis, providing robust evidence from in vitro and in vivo studies. OLO demonstrated a dose-dependent enhancement of lipolysis, notably increasing the expression of Uncoupling Protein 1 (UCP1) and raising the rate of oxygen consumption in primary brown adipocytes. This suggests a significant increase in thermogenic potential and energy expenditure. The administration of OLO to murine models noticeably enhanced cold-induced nonshivering thermogenesis. OLO elevated UCP1 expression in the brown adipose tissue of mice. Furthermore, it promoted brown adipocyte thermogenesis by activating the ß2-AR/cAMP/PKA signaling cascades according to RNA sequencing, western blotting, and molecular docking analysis. This investigation underscores the therapeutic potential of OLO for metabolic ailments and sheds light on the intricate molecular dynamics of adipocyte thermogenesis, laying the groundwork for future targeted therapeutic interventions in human metabolic disorders.

M2 macrophages independently promote beige adipogenesis via blocking adipocyte Ets1.

Adipose tissue macrophages can promote beige adipose thermogenesis by altering local sympathetic activity. Here, we perform sympathectomy in mice and further eradicate subcutaneous adipose macrophages and discover that these macrophages have a direct beige-promoting function that is independent of sympathetic system. We further identify adipocyte Ets1 as a vital mediator in this process. The anti-inflammatory M2 macrophages suppress Ets1 expression in adipocytes, transcriptionally activate mitochondrial biogenesis, as well as suppress mitochondrial clearance, thereby increasing the mitochondrial numbers and promoting the beiging process. Male adipocyte Ets1 knock-in mice are completely cold intolerant, whereas male mice lacking Ets1 in adipocytes show enhanced energy expenditure and are resistant to metabolic disorders caused by high-fat-diet. Our findings elucidate a direct communication between M2 macrophages and adipocytes, and uncover a function for Ets1 in responding to macrophages and negatively governing mitochondrial content and beige adipocyte formation.

Differential responses to UCP1 ablation in classical brown versus beige fat, despite a parallel increase in sympathetic innervation.

In the cold, the absence of the mitochondrial uncoupling protein 1 (UCP1) results in hyper-recruitment of beige fat, but classical brown fat becomes atrophied. Here we examine possible mechanisms underlying this phenomenon. We confirm that in brown fat from UCP1-knockout (UCP1-KO) mice acclimated to the cold, the levels of mitochondrial respiratory chain proteins were diminished; however, in beige fat, the mitochondria seemed to be unaffected. The macrophages that accumulated massively not only in brown fat but also in beige fat of the UCP1-KO mice acclimated to cold did not express tyrosine hydroxylase, the norepinephrine transporter (NET) and monoamine oxidase-A (MAO-A). Consequently, they could not influence the tissues through the synthesis or degradation of norepinephrine. Unexpectedly, in the cold, both brown and beige adipocytes from UCP1-KO mice acquired an ability to express MAO-A. Adipose tissue norepinephrine was exclusively of sympathetic origin, and sympathetic innervation significantly increased in both tissues of UCP1-KO mice. Importantly, the magnitude of sympathetic innervation and the expression levels of genes induced by adrenergic stimulation were much higher in brown fat. Therefore, we conclude that no qualitative differences in innervation or macrophage character could explain the contrasting reactions of brown versus beige adipose tissues to UCP1-ablation. Instead, these contrasting responses may be explained by quantitative differences in sympathetic innervation: the beige adipose depot from the UCP1-KO mice responded to cold acclimation in a canonical manner and displayed enhanced recruitment, while the atrophy of brown fat lacking UCP1 may be seen as a consequence of supraphysiological adrenergic stimulation in this tissue.

The TRPM2 ion channel regulates metabolic and thermogenic adaptations in adipose tissue of cold-exposed mice.

Introduction: During thermogenesis, adipose tissue (AT) becomes more active and enhances oxidative metabolism. The promotion of this process in white AT (WAT) is called "browning" and, together with the brown AT (BAT) activation, is considered as a promising approach to counteract obesity and metabolic diseases. Transient receptor potential cation channel, subfamily M, member 2 (TRPM2), is an ion channel that allows extracellular Ca2+ influx into the cytosol, and is gated by adenosine diphosphate ribose (ADPR), produced from NAD+ degradation. The aim of this study was to investigate the relevance of TRPM2 in the regulation of energy metabolism in BAT, WAT, and liver during thermogenesis. Methods: Wild type (WT) and Trpm2-/- mice were exposed to 6°C and BAT, WAT and liver were collected to evaluate mRNA, protein levels and ADPR content. Furthermore, O2 consumption, CO2 production and energy expenditure were measured in these mice upon thermogenic stimulation. Finally, the effect of the pharmacological inhibition of TRPM2 was assessed in primary adipocytes, evaluating the response upon stimulation with the ß-adrenergic receptor agonist CL316,243. Results: Trpm2-/- mice displayed lower expression of browning markers in AT and lower energy expenditure in response to thermogenic stimulus, compared to WT animals. Trpm2 gene overexpression was observed in WAT, BAT and liver upon cold exposure. In addition, ADPR levels and mono/poly-ADPR hydrolases expression were higher in mice exposed to cold, compared to control mice, likely mediating ADPR generation. Discussion: Our data indicate TRPM2 as a fundamental player in BAT activation and WAT browning. TRPM2 agonists may represent new pharmacological strategies to fight obesity.

ATF4 expression in thermogenic adipocytes is required for cold-induced thermogenesis in mice via FGF21-independent mechanisms.

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially by increasing FGF21 expression. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis under physiological stress by generating mice selectively lacking either Atf4 (ATF4 BKO) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum-fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue. Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum-fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis under fed conditions likely in a FGF21-independent manner, in part via increased amino acid uptake and metabolism.

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.

Perfluorooctanoate (PFOA) cell-autonomously promotes thermogenic and adipogenic differentiation of brown and white adipocytes.

Perfluorooctanoic acid (PFOA) is a synthetic organofluoride surfactant associated with several toxic effects in humans and animals. Particularly, it has been observed that PFOA treatment of mice results in weight loss associated with recruited brown adipose tissue (BAT), including an increased amount of uncoupling protein 1 (UCP1). The molecular mechanism behind this BAT recruitment is presently unknown. To investigate the existence of possible cell-autonomous effects of PFOA, we treated primary cultures of brown and white (inguinal) adipocytes with PFOA, or with the non-fluorinated equivalent octanoate, or with vehicle, for 48 h (from day 5 to day 7 of differentiation). PFOA in itself increased the gene expression (mRNA levels) of UCP1 and carnitine palmitoyltransferase 1A (CPT1α) (thermogenesis-related genes) in both brown and white adipocytes. In addition, PFOA increased the expression of fatty acid binding protein 4 (FABP4) and peroxisome proliferator-activated receptor α (PPARα) (adipogenesis-related genes). Also the protein levels of UCP1 were increased in brown adipocytes exposed to PFOA. This increase was more due to an increase in the fraction of cells that expressed UCP1 than to an increase in UCP1 levels per cell. The PFOA-induced changes were even more pronounced under simultaneous adrenergic stimulation. Octanoate induced less pronounced effects on adipocytes than did PFOA. Thus, PFOA in itself increased the levels of thermogenic markers in brown and white adipocytes. This could enhance the energy metabolism of animals (and humans) exposed to the compound, resulting in a negative energy balance, leading to diminished fitness.

Brown adipose tissue CoQ deficiency activates the integrated stress response and FGF21-dependent mitohormesis.

Coenzyme Q (CoQ) is essential for mitochondrial respiration and required for thermogenic activity in brown adipose tissues (BAT). CoQ deficiency leads to a wide range of pathological manifestations, but mechanistic consequences of CoQ deficiency in specific tissues, such as BAT, remain poorly understood. Here, we show that pharmacological or genetic CoQ deficiency in BAT leads to stress signals causing accumulation of cytosolic mitochondrial RNAs and activation of the eIF2α kinase PKR, resulting in activation of the integrated stress response (ISR) with suppression of UCP1 but induction of FGF21 expression. Strikingly, despite diminished UCP1 levels, BAT CoQ deficiency displays increased whole-body metabolic rates at room temperature and thermoneutrality resulting in decreased weight gain on high-fat diets (HFD). In line with enhanced metabolic rates, BAT and inguinal white adipose tissue (iWAT) interorgan crosstalk caused increased browning of iWAT in BAT-specific CoQ deficient animals. This mitohormesis-like effect depends on the ATF4-FGF21 axis and BAT-secreted FGF21, revealing an unexpected role for CoQ in the modulation of whole-body energy expenditure with wide-ranging implications for primary and secondary CoQ deficiencies.

NG ,NG -Dimethylarginine Dimethylaminohydrolase 1 Expression Is Dispensable for Cold- or Diet-Induced Thermogenesis.

The strategy to activate thermogenic adipocytes has therapeutic potential to overcome obesity as they dissipate surplus energy as heat through various mechanisms. NG,NG-dimethylarginine dimethylaminohydrolases (DDAHs) are enzymes involved in the nitric oxide-protein kinase G signaling axis which increases thermogenic gene expression. However, the role of DDAHs in thermogenic adipocytes has not been elucidated. The adipocyte-specific Ddah1 knockout mice are generated by crossing Ddah1fl/fl mice with adiponectin Cre recombinase mice. Adipocyte-specific DDAH1 overexpressing mice are generated using adeno-associated virus-double-floxed inverse open reading frame (AAV-DIO) system. These mice are analyzed under basal, cold exposure, or high-fat diet (HFD) conditions. Primary inguinal white adipose tissue cells from adipocyte-specific Ddah1 knockout mice expressed comparable amounts of Ucp1 mRNA. Adipocyte-specific DDAH1 overexpressing mice do not exhibit enhanced activation of thermogenic adipocytes. In addition, when these mice are exposed to cold environment or fed an HFD, their body temperature/weight and thermogenesis-related gene and protein expressions are unchanged. These findings indicate that DDAH1 does not play a role in either cold- or diet-induced thermogenesis. Therefore, adipocyte targeting DDAH1 gene therapy for the treatment of obesity is unlikely to be effective.

Trim21 Regulates the Postnatal Development and Thermogenesis of Brown Adipose Tissue.

Brown adipose tissue undergoes rapid postnatal development to mature and plays a crucial role in thermoregulation and energy expenditure, which protects against cold and obesity. Herein, it is shown that the expression of Trim21 mRNA level of interscapular brown adipose tissue elevates after birth, and peaks at P14 (postnatal day 14). Trim21 depletion severely impairs the maturation of interscapular brown adipose tissue, decreases the expression of a series of thermogenic genes, and reduces energy expenditure. Consistently, the loss of Trim21 also leads to a suppression of white adipose tissue "browning", in response to cold exposure and a ß-adrenergic agonist, CL316,243. In addition, Trim21-/- mice are more prone to high-fat diet-induced obesity compared with the control littermates. Taken together, the study for the first time reveals a critical role of Trim21 in regulating iBAT postnatal development and thermogenesis.