Regulation Of Brown Adipocyte Differentiation Research Articles

Mitochondrial respiratory complex I deficiency inhibits brown adipogenesis by limiting heme regulation of histone demethylation

Mitochondrial functions play a crucial role in determining the metabolic and thermogenic status of brown adipocytes. Increasing evidence reveals that the mitochondrial oxidative phosphorylation (OXPHOS) system plays an important role in brown adipogenesis, but the mechanistic insights are limited. Herein, we explored the potential metabolic mechanisms leading to OXPHOS regulation of brown adipogenesis in pharmacological and genetic models of mitochondrial respiratory complex I deficiency. OXPHOS deficiency inhibits brown adipogenesis through disruption of the brown adipogenic transcription circuit without affecting ATP levels. Neither blockage of calcium signaling nor antioxidant treatment can rescue the suppressed brown adipogenesis. Metabolomics analysis revealed a decrease in levels of tricarboxylic acid cycle intermediates and heme. Heme supplementation specifically enhances respiratory complex I activity without affecting complex II and partially reverses the inhibited brown adipogenesis by OXPHOS deficiency. Moreover, the regulation of brown adipogenesis by the OXPHOS-heme axis may be due to the suppressed histone methylation status by increasing histone demethylation. In summary, our findings identified a heme-sensing retrograde signaling pathway that connects mitochondrial OXPHOS to the regulation of brown adipocyte differentiation and metabolic functions.

311-OR: Regulation of Brown Adipocyte Differentiation and Thermogenesis by Prostaglandin F2a

Brown adipocytes hold the potential to mitigate body fat accumulation and type 2 diabetes (T2D) via their specialized function in dissipating energy as heat, a process known as thermogenesis. To fuel their function, brown adipocytes release the bond energy of fat through lipolysis and β-oxidation; then, uncoupling cellular respiration releases this energy as physical heat. In addition to their energy-dissipating function, brown adipocytes can release factors, such as lipids, metabolites, peptides, or microRNA, to regulate metabolism. Signaling lipids have demonstrated roles in regulating thermogenesis in brown adipocytes by regulating lipid uptake and utilization. To further explore these pathways, we performed signaling lipidomics analysis in in vitro differentiated human brown adipocytes and found 15-keto-PGF2α was increased when treated with forskolin, an adenylyl cyclase activator that mimics adrenergic stimulation. Previous studies have shown PGF2α, the parent molecule of 15-keto-PGF2α, inhibits maturation, or adipogenesis, in white adipocyte cell lines by preventing the expression of key adipogenesis genes, such as PPARγ and C/EBPα. Similarly, PGF2α inhibits thermogenic gene expression in brown adipocyte cells. To explore and compare the functional activities of PGF2α and 15-keto-PGF2α, we characterized the dose-response relationship of these lipids on thermogenic gene and protein expression. We found that 15-keto-PGF2α is not as potent as PGF2α at inhibiting both thermogenic gene and protein expression. This suggests the conversion of PGF2α to 15-keto-PGF2α represents a significant signaling event to promote thermogenesis in brown adipocytes. Interestingly, carbonyl reductase 1, an enzyme that catalyzes this conversion, is regulated by treatment with the adrenergic agonist, norepinephrine, in vitro and by cold exposure in vivo. Targeting this conversion may be an attractive approach towards activating thermogenesis to mitigate obesity and T2D. Disclosure E.Fadumiye: None. S.Kodani: None. M.Kiebish: None. V.Bussberg: None. Y.Tseng: Consultant; Cellarity. Funding National Institutes of Health (R01DK122808)

NFIA differentially controls adipogenic and myogenic gene program through distinct pathways to ensure brown and beige adipocyte differentiation.

The transcription factor nuclear factor I-A (NFIA) is a regulator of brown adipocyte differentiation. Here we show that the C-terminal 17 amino acid residues of NFIA (which we call pro#3 domain) are required for the transcriptional activity of NFIA. Full-length NFIA—but not deletion mutant lacking pro#3 domain—rescued impaired expression of PPARγ, the master transcriptional regulator of adipogenesis and impaired adipocyte differentiation in NFIA-knockout cells. Mechanistically, the ability of NFIA to penetrate chromatin and bind to the crucial Pparg enhancer is mediated through pro#3 domain. However, the deletion mutant still binds to Myod1 enhancer to repress expression of MyoD, the master transcriptional regulator of myogenesis as well as proximally transcribed non-coding RNA called DRReRNA, via competition with KLF5 in terms of enhancer binding, leading to suppression of myogenic gene program. Therefore, the negative effect of NFIA on the myogenic gene program is, at least partly, independent of the positive effect on PPARγ expression and its downstream adipogenic gene program. These results uncover multiple ways of action of NFIA to ensure optimal regulation of brown and beige adipocyte differentiation.

1697-P: NFIA Differentially Regulates Adipogenesis and Myogenesis through Distinct Molecular Pathways to Ensure Adipocyte Differentiation

Brown and beige fat dissipate chemical energy in the form of heat through uncoupling protein-1 (Ucp1) on the mitochondrial inner membrane as well as through the other pathways, while white fat generally stores energy in the form of lipid. Stimulating development and/or function of brown fat is highly anticipated as a novel strategy for the treatment of obesity and its complications including type 2 diabetes. Previously, we identified a transcription factor nuclear factor I-A (NFIA) as a crucial regulator of brown fat. NFIA binds to and activates the brown-fat-specific enhancers even before differentiation and later facilitates the binding of PPARgamma (peroxisome proliferator-activated receptor gamma—a master transcription factor of adipogenesis), to control the brown fat gene program. Here we show that the C-terminal 17 amino acid residues of NFIA (which we call pro#3 domain) are required for the transcriptional activity of NFIA. Full-length NFIA—but not deletion mutant lacking pro#3 domain—rescued impaired Pparg expression and adipogenesis in NFIA-knockout cells. However, the deletion mutant still binds to Myod1 enhancer to represses Myod1 expression via competition with KLF5 in terms of enhancer binding, leading to suppression of myogenic gene program. Therefore, the negative effect of NFIA on the myogenic gene program is, at least partly, independent of the positive effect on Pparg expression and its downstream adipogenic gene program. Overall, our results uncover multiple ways of action of NFIA to ensure optimal regulation of brown adipocyte differentiation. Disclosure Y. Hiraike: Research Support; Self; Daiichi Sankyo, Daiichi Sankyo, Novo Nordisk Inc., Novo Nordisk Inc. H. Waki: Research Support; Self; Astellas Pharma Inc., Novartis Pharma K.K., Ono Pharmaceutical Co., Ltd., Takeda Science Foundation, The Cell Science Research Foundation. Speaker’s Bureau; Self; AstraZeneca K.K., AstraZeneca K.K., Chugai Pharmaceutical Co., Ltd., Daiichi Sankyo, Kyowa Hakko Kirin Co., Ltd., Nippon Boehringer Ingelheim Co. Ltd., Novo Nordisk Inc., Ono Pharmaceutical Co., Ltd., Sanofi K.K. K. Miyake: Research Support; Self; NTT DOCOMO, INC. M. Oguchi: None. T. Yamauchi: Research Support; Self; AeroSwitch, Asahi Mutual Life Insurance Company, Astellas Pharma Inc., AstraZeneca K.K., Boehringer Ingelheim International GmbH, Daiichi Sankyo Company, Limited, Kowa Pharmaceutical company,limited., Kyowa Hakko Kirin Co., Ltd., Merck Sharp & Dohme Corp., Mitsubishi Corporation Life Sciences Limited, Mitsubishi Tanabe Pharma Corporation, Novartis Pharma K.K., Novo Nordisk Inc., NTT Docomo Inc., Ono Pharmaceutical Co., Ltd., Sanofi K.K., Sanwa Kagaku Kenkyusho, Shionogi & Co., Ltd., Sumitomo Dainippon Pharma Co., Ltd., Taisho Pharmaceutical Co., Ltd., Takeda Pharmaceutical Company Limited, TOSOH CORPORATION. Other Relationship; Self; Covidien Japan Inc. (Medtronic Japan Co., Ltd.), Eli Lilly Japan K.K., Johnson & Johnson, Kissei Pharmaceutical Co., Ltd. T. Kadowaki: Research Support; Self; Astellas Pharma Inc., Daiichi Sankyo, Mitsubishi Tanabe Pharma Corporation, MSD Corporation, Novartis Pharma K.K., Novo Nordisk Pharma Ltd., Ono Pharmaceutical Co., Ltd., Sanofi, Sumitomo Dainippon Pharma Co., Ltd., Takeda Pharmaceutical Company Limited. Speaker’s Bureau; Self; Abbott, Astellas Pharma Inc., AstraZeneca K.K., Boehringer Ingelheim Pharmaceuticals, Inc., Cosmic Corporation, Daiichi Sankyo, Eli Lilly Japan K.K., FUJIFILM, Kowa Company, Ltd., Kyowa Hakko Kirin Co., Ltd., Medscape Education, Medtronic, Mitsubishi Tanabe Pharma Corporation, MSD Corporation, NIPRO Medical Corporation, Novartis Pharma K.K., Novo Nordisk Pharma Ltd., Ono Pharmaceutical Co., Ltd., Sanofi, Sanwa Kagaku Kenkyusho, Sumitomo Dainippon Pharma Co., Ltd., Taisho Pharmaceutical Co., Ltd., Takeda Pharmaceutical Company Limited, Terumo Medical Corporation. Other Relationship; Self; Asahi Mutual Life Insurance.

2044-P: Histone Methyltransferase DOT1L Regulates Brown Adipocyte Differentiation and Thermogenesis

Brown fat has been extensively studied due to its potential in therapies against obesity. Various epigenetic regulators have been shown to modulate brown fat development and function. Here we show that histone methyltransferase DOT1L is a key regulator of brown adipocyte differentiation and thermogenesis. In vitro, we demonstrate that inhibition by DOT1L inhibitor or knockdown of DOT1L markedly promotes brown adipocyte differentiation of C3H10T1/2 cells. Moreover, depletion of DOT1L enhances differentiation and thermogenesis of primary brown adipocytes which separated from DOT1LFlox/Flox mice by transfection with Cre-expressing lentiviruses ex vivo. Mechanistically, knockdown of DOT1L results in increased expression of brown-selective genes, and the expression of brown preadipocyte maker EBF2 is significantly increased due to knockdown of DOT1L at early stage. Furthermore, ChIP assays suggest that DOT1L-mediated H3K79 methylations are negatively associated with transcription of UCP1 and PRDM16. Finally, we observe that the skin surface temperature in interscapular area of DOT1LMyf5 knockout mice is significantly higher. Notably, energy expenditure and the oxygen consumption rate are also increased in knockout mice. These in vivo data suggest that DOT1L depletion leads to enhanced thermogenic function of brown fat. Collectively, our work indicates that DOT1L plays an important role in regulating brown fat differentiation and thermogenesis, and provides another linkage between epigenetics and brown fat development and function. Disclosure L. Shuai: None. J. Li: None. J. Li: None. Funding China Postdoctoral Science Foundation

1786-P: ACSL1 Contributes to Thermogenesis and Differentiation of Brown Adipose Tissue

Long chain acyl-CoA synthetases (ACSLs) convert fatty acids (FA) to fatty acyl-CoAs that are utilized for various cellular processes, including triglyceride synthesis, activation of transcription factors, signal transduction, and providing energy sources via oxidation. Among 5 isotypes (ACSL1, 3, 4, 5, and 6), ACSL1 is the predominant isotype in adipocytes, and it is known to play important roles in adipocyte physiology, including FA uptake, triglyceride (TG) synthesis, thermogenesis, and FA oxidation. However, the roles of ACSL1 in brown adipocyte differentiation is incompletely understood. During the in vitro differentiation of brown adipocytes from stromal vascular cells (SVC), mRNA expression of ACSL1 was drastically increased. Pharmacological inhibition of ACSLs by triacsin C suppressed the differentiation of brown adipocytes. Interestingly, triacsin C inhibited the expression of uncoupled protein 1 (UCP1), which plays the major role in thermogenesis in mitochondria. Thus, we hypothesize that ACSL1 regulates thermogenesis and energy utilization by regulation of brown adipocyte differentiation. To examine the role of ACSL1 in brown adipose tissue (BAT), we generated BAT specific ACSL1 knockout mice by breeding UCP1-Cre with ACSL1 flox/flox mice (ACSL1BATKO). ACSL1 deficiency in BAT reduced the weight gain and glucose intolerance in high fat diet (HFD)-fed mice. ACSL1BATKO mice were severely cold intolerant. Furthermore, ACSL1BATKO mice were resistant to beta 3-agonist (CL-316243)-stimulated weight loss. Fat mass in HFD-fed ACSL1BATKO was lower than HFD-fed wild type mice. These data suggest that ACSL1 in BAT contributes to BAT differentiation, which causes the impairment of FA utilization. However, the mechanisms by which deficiency of ACSL1 in BAT reduces HFD-induced weight gain need to be further investigated. Disclosure G. Ren: None. J. Kim: None. Funding National Institutes of Health (R01HL128695R03AG058078)

Protein Tyrosine Phosphatase, Receptor Type B (PTPRB) Inhibits Brown Adipocyte Differentiation through Regulation of VEGFR2 Phosphorylation.

Brown adipocytes have an important role in the regulation of energy balance through uncoupling protein-1 (UCP-1)-mediated nonshivering thermogenesis. Although brown adipocytes have been highlighted as a new therapeutic target for the treatment of metabolic diseases, such as obesity and type II diabetes in adult humans, the molecular mechanism underlying brown adipogenesis is not fully understood. We recently found that protein tyrosine phosphatase receptor type B (PTPRB) expression dramatically decreased during brown adipogenic differentiation. In this study, we investigated the functional roles of PTPRB and its regulatory mechanism during brown adipocyte differentiation. Ectopic expression of PTPRB led to a reduced brown adipocyte differentiation by suppressing the tyrosine phosphorylation of VEGFR2, whereas a catalytic inactive PTPRB mutant showed no effects on differentiation and phosphorylation. Consistently, the expression of brown adipocyte-related genes, such as UCP-1, PGC-1α, PRDM16, PPAR-γ, and CIDEA, were significantly inhibited by PTPRB overexpression. Overall, these results suggest that PTPRB functions as a negative regulator of brown adipocyte differentiation through its phosphatase activity-dependent mechanism and may be used as a target protein for the regulation of obesity and type II diabetes.

Protein tyrosine phosphatase, receptor type B (PTPRB) inhibits brown adipocyte differentiation through regulation of VEGFR2 phosphorylation

Brown adipocytes have an important role in the regulation of energy balance through uncoupling protein‐1 (UCP‐1)‐mediated nonshivering thermogenesis. Although brown adipocytes have been highlighted as a new therapeutic target for the treatment of metabolic diseases, such as obesity and type 2 diabetes in adult humans, the molecular mechanism underlying brown adipogenesis is not fully understood. We recently found that protein tyrosine phosphatase receptor type B (PTPRB) expression dramatically decreased during brown adipogenic differentiation. In this study, we investigated the functional roles of PTPRB and its regulatory mechanism during brown adipocyte differentiation. Ectopic expression of PTPRB led to a reduced brown adipocyte differentiation by suppressing the tyrosine phosphorylation of VEGFR2, whereas a catalytic inactive PTPRB mutant showed no effects on differentiation and phosphorylation. Consistently, the expression of brown adipocyte‐related genes, such as UCP‐1, PGC‐1α, PRDM16, PPAR‐γ and CIDEA, were significantly inhibited by PTPRB overexpression. Overall, these results suggest that PTPRB functions as a negative regulator of brown adipocyte differentiation through its phosphatase activity‐dependent mechanism and may be used as a target protein for the regulation of obesity and diabetes.Support or Funding InformationThis work was supported by grants from the KRIBB and from the Research Program (grants 2016R1C1B2013430, 2015M3A9B5030308, 2015M3A7B6027948, and 2015M3A9D7029882) through the National Research Foundation of Korea.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A truncated PPAR gamma 2 localizes to mitochondria and regulates mitochondrial respiration in brown adipocytes.

Peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of brown adipocyte differentiation and thermogenesis. The PPARγ gene produces two isoforms, PPARγ1 and PPARγ2. PPARγ2 is identical to PPARγ1 except for additional 30 amino acids present in the N-terminus of PPARγ2. Here we report that the C-terminally truncated form of PPARγ2 is predominantly present in the mitochondrial matrix of brown adipocytes and that it binds to the D-loop region of mitochondrial DNA (mtDNA), which contains the promoter for mitochondrial electron transport chain (ETC) genes. Expression of mitochondrially targeted MLS-PPARγ2 in brown adipocytes increases mtDNA-encoded ETC gene expression concomitant with enhanced mitochondrial respiration. These results suggest that direct regulation of mitochondrially encoded ETC gene expression by mitochondrial PPARγ2, in part, underlies the isoform-specific role for PPARγ2 in brown adipocytes.

Histone Demethylase LSD1 Promotes Adipocyte Differentiation through Repressing Wnt Signaling

Adipose tissue plays important roles in animals. White fat stores energy in lipids, while brown fat is responsible for nonshivering thermogenesis through UCP1-mediated energy dissipation. Although epigenetic mechanisms modulate differentiation in multiple lineages, the epigenetic regulation of brown adipocyte differentiation is poorly understood. By screening acollection of epigenetic compounds, we found that Lysine-Specific Demethylase 1 (LSD1) inhibitors repress brown adipocyte differentiation. RNAi-mediated Lsd1 knockdown causes a similar effect, which can be rescued by expression of wild-type but not catalytic-inactive LSD1. Mechanistically, LSD1 promotes brown adipogenesis by demethylating H3K4 on promoter regions of Wnt signaling components and repressing the Wnt pathway. Furthermore, deletion of Lsd1 in mice leads to inhibition of brown adipogenesis, validating the pivotal role of LSD1 in brownfat development invivo. Our work identifies LSD1 as a key epigenetic regulator in brown adipogenesis. The link between LSD1 and the Wnt pathway provides potential opportunities to modulate brown fat differentiation.

Increased Expression of Beige/Brown Adipose Markers from Host and Breast Cancer Cells Influence Xenograft Formation in Mice.

The initiation and progression of breast cancer is a complex process that is influenced by heterogeneous cell populations within the tumor microenvironment. Although adipocytes have been shown to promote breast cancer development, adipocyte characteristics involved in this process remain poorly understood. In this study, we demonstrate enrichment of beige/brown adipose markers, contributed from the host as well as tumor cells, in the xenografts from breast cancer cell lines. In addition to uncoupling protein-1 (UCP1) that is exclusively expressed in beige/brown adipocytes, gene expression for classical brown (MYF5, EVA1, and OPLAH) as well as beige (CD137/TNFRSF9 and TBX1) adipocyte markers was also elevated in the xenografts. Enrichment of beige/brown characteristics in the xenografts was independent of the site of implantation of the breast tumor cells. Early stages of xenografts showed an expansion of a subset of mammary cancer stem cells that expressed PRDM16, a master regulator of brown adipocyte differentiation. Depletion of UCP1(+) or Myf5(+) cells significantly reduced tumor development. There was increased COX2 (MT-CO2) expression, which is known to stimulate formation of beige adipocytes in early xenografts and treatment with a COX2 inhibitor (SC236) reduced tumor growth. In contrast, treatment with factors that induce brown adipocyte differentiation in vitro led to larger tumors in vivo. A panel of xenografts derived from established breast tumor cells as well as patient tumor tissues were generated that expressed key brown adipose tissue-related markers and contained cells that morphologically resembled brown adipocytes. This is the first report demonstrating that beige/brown adipocyte characteristics could play an important role in breast tumor development and suggest a potential target for therapeutic drug design.

MAP kinase phosphatase 3 inhibits brown adipocyte differentiation via regulation of Erk phosphorylation

Brown fat has been highlight as a new therapeutic target for treatment of obesity and diabetes. However, molecular mechanism underlying brown adipogenesis are not fully understood. Here, we identified that MAP kinase phosphatase 3 (MKP3) has a novel role as regulator of brown adipocyte differentiation. The expression of MKP3 was significantly decreased during the early stage(s) of brown adipocyte differentiation in HIB-1B cells and primary cells. Ectopic expression of MKP3 led to reduced brown adipocyte differentiation, whereas depletion of MKP3 significantly enhanced the differentiation of primary brown preadipocytes. Consistently, we found an increased brown adipocyte differentiation in MKP3-null MEF cells. These inhibitory effects of MKP3 could be resulted via the temporal regulation of Erk activation. In recent, it was reported that MKP3 deficient mice are resistant to diet-induced obesity, and display enhanced energy expenditure. Taken together, we suggest that MKP3 could be an important factor in the regulation of brown adipocyte differentiation.

MicroRNAs in the regulation of brown adipocyte differentiation

MicroRNAs (miRNAs), a class of endogenous non-coding RNA about 22 nucleotide long, regulate gene expression at the post-transcription level by inhibiting the translation or inducing the degradation of their target mRNAs in organisms. There are two types of adipose tissues: brown and white. White adipose tissues store energy in the form of triglycerides (TGs), while brown adipose tissues catabolize TGs to generate energy. Brown adipose tissues are of great importance to the research of obesity and related metabolic diseases due to their function of preventing people from obesity. A lot of studies have revealed that miRNAs play crucial roles in regulating brown adipocyte differentiation and are modulated by lots of transcription factors and environmental factors, which form a complex regulatory network maintaining the homeostasis of adipose tissues. In this review, we summarize the latest studies of miRNAs in brown adipocyte differentiation, which might provide new strategies for the treatment of obesity and other related diseases.

Identification of miR-106b-93 as a negative regulator of brown adipocyte differentiation

microRNAs (miRNAs) have been reported to play an essential role in the regulation of brown adipocyte adipogenesis. In the present study, we investigated the role of the miR-106b-93 cluster in the differentiation of brown adipocytes. We found that knockdown of miR-106b and miR-93 significantly induced the expression of brown fat-specific genes and promoted the accumulation of lipid-droplet in differentiating brown adipocytes. In addition, ectopic expression of miR-106b and miR-93 suppressed the mRNA level of Ucp1, a selective hallmark of brown adipocytes. Furthermore, the expression levels of miR-106b and miR-93 are higher in brown adipose tissues of high fat diet-induced obese mice compared to control mice. Taken together, our results identify miR-106b and miR-93 as negative regulators of brown adipocyte differentiation and the miR-106b-93 cluster may play an important role in regulating energy homeostasis.

Phosphodiesterase 5 is main regulator of brown adipocyte differentiation

Background Obesity, a major threat to global human health, has been shown to be associated with devastating diseases such as stroke, hypertension, cancer and type 2 diabetes. In order to fight the present obesity pandemic it is crucial to better understand regulation of adipocyte differentiation. Phosphodiesterases (PDEs) catalyze hydrolysis of cyclic nucleotides (cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)) to the corresponding 5′ nucleotide monophosphates. To date, eleven different PDEs (PDE1–11) have been characterized, and they differ in their selectivity for cyclic nucleotides, sensitivity to inhibitors and activators, physiological roles, and tissue distribution. The nonselective phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) has been shown to be essential for successful in vitro differentiation of adipocytes.

IGFBP-2 is a negative predictor of cold-induced brown fat and bone mineral density in young non-obese women

Recent studies have shown a positive correlation between brown adipose tissue (BAT) and bone mineral density (BMD). However, mechanisms underlying this relationship are unknown. Insulin-like growth factor 1 (IGF-1) is an important regulator of stem cell differentiation promoting bone formation. IGF binding protein 2 (IGFBP-2) binds IGF-1 in the circulation and has been reported to inhibit bone formation in humans. IGF-1 is also a crucial regulator of brown adipocyte differentiation. We hypothesized that IGFBP-2 is a negative and IGF-1 a positive regulator of BAT-mediated osteoblastogenesis. We therefore investigated a cohort of 15 women (mean age 27.7±5.7years): 5 with anorexia nervosa (AN) in whom IGF-1 levels were low due to starvation, 5 recovered AN (AN-R), and 5 women of normal weight. All subjects underwent assessment of cold-activated BAT by PET/CT, BMD of the spine, hip, femoral neck, and total body by DXA, thigh muscle area by MRI, IGF-1 and IGFBP-2. There was a positive correlation between BAT and BMD and an inverse association between IGFBP-2 and both BAT and BMD. There was no association between IGF-1 and BAT. We show for the first time that IGFBP-2 is a negative predictor of cold-induced BAT and BMD in young non-obese women, suggesting that IGFBP-2 may serve as a regulator of BAT-mediated osteoblastogenesis.

Blockade of the Activin Receptor IIB Activates Functional Brown Adipogenesis and Thermogenesis by Inducing Mitochondrial Oxidative Metabolism

Brown adipose tissue (BAT) is a key tissue for energy expenditure via fat and glucose oxidation for thermogenesis. In this study, we demonstrate that the myostatin/activin receptor IIB (ActRIIB) pathway, which serves as an important negative regulator of muscle growth, is also a negative regulator of brown adipocyte differentiation. In parallel to the anticipated hypertrophy of skeletal muscle, the pharmacological inhibition of ActRIIB in mice, using a neutralizing antibody, increases the amount of BAT without directly affecting white adipose tissue. Mechanistically, inhibition of ActRIIB inhibits Smad3 signaling and activates the expression of myoglobin and PGC-1 coregulators in brown adipocytes. Consequently, ActRIIB blockade in brown adipose tissue enhances mitochondrial function and uncoupled respiration, translating into beneficial functional consequences, including enhanced cold tolerance and increased energy expenditure. Importantly, ActRIIB inhibition enhanced energy expenditure only at ambient temperature or in the cold and not at thermoneutrality, where nonshivering thermogenesis is minimal, strongly suggesting that brown fat activation plays a prominent role in the metabolic actions of ActRIIB inhibition.

Identification of inducible brown adipocyte progenitors residing in skeletal muscle and white fat

Brown fat is specialized for energy expenditure and has therefore been proposed to function as a defense against obesity. Despite recent advances in delineating the transcriptional regulation of brown adipocyte differentiation, cellular lineage specification and developmental cues specifying brown-fat cell fate remain poorly understood. In this study, we identify and isolate a subpopulation of adipogenic progenitors (Sca-1(+)/CD45(-)/Mac1(-); referred to as Sca-1(+) progenitor cells, ScaPCs) residing in murine brown fat, white fat, and skeletal muscle. ScaPCs derived from different tissues possess unique molecular expression signatures and adipogenic capacities. Importantly, although the ScaPCs from interscapular brown adipose tissue (BAT) are constitutively committed brown-fat progenitors, Sca-1(+) cells from skeletal muscle and subcutaneous white fat are highly inducible to differentiate into brown-like adipocytes upon stimulation with bone morphogenetic protein 7 (BMP7). Consistent with these findings, human preadipocytes isolated from subcutaneous white fat also exhibit the greatest inducible capacity to become brown adipocytes compared with cells isolated from mesenteric or omental white fat. When muscle-resident ScaPCs are re-engrafted into skeletal muscle of syngeneic mice, BMP7-treated ScaPCs efficiently develop into adipose tissue with brown fat-specific characteristics. Importantly, ScaPCs from obesity-resistant mice exhibit markedly higher thermogenic capacity compared with cells isolated from obesity-prone mice. These data establish the molecular characteristics of tissue-resident adipose progenitors and demonstrate a dynamic interplay between these progenitors and inductive signals that act in concert to specify brown adipocyte development.

Adrenergic regulation of brown adipocyte differentiation.

Adrenergic regulation of brown adipocyte differentiation.