Actomyosin-mediated tension orchestrates uncoupled respiration in adipose tissues
Ontology highlight
ABSTRACT: The activation of brown/beige adipose tissue (BAT) metabolism and the induction of uncoupling protein-1 (UCP1) expression are essential for BAT-based strategies to improve metabolic homeostasis. Adrenergic signaling is viewed as a key regulator of thermogenesis and UCP1-expression in BAT, while also operating as a potent contractile stimulator in muscle. The muscle-like gene expression patterns of UCP1+ adipocytes have previously been utilized as tissue specific markers, but have not been attributed with any functional role. Here, we demonstrate that BAT utilizes actomyosin machinery to generate tensional responses following adrenergic stimulation, similar to muscle tissues. We show that activation of actomyosin mechanics are critical for the acute induction of oxidative metabolism and uncoupled respiration in UCP1+ adipocytes. Additionally, actomyosin-mediated elasticity regulates mechanosensitive transcriptional co-activators, YAP/TAZ, that facilitate the thermogenic capacity of adipocytes. These unappreciated signaling and mechanical mechanisms may inform future strategies to promote the expansion and activation of brown/beige adipocytes.
Project description:Since brown adipose tissue (BAT) dissipates energy through UCP1, BAT has garnered attention as a therapeutic intervention for obesity and metabolic diseases including type 2 diabetes. As we better understand the roles of classical brown and beige adipocytes, increased beige fat mass in response to a variety of external/internal cues is associated with significant improvements in glucose and lipid homeostasis that may not be entirely mediated by UCP1. We aim to analyze transcriptome of wild type and UCP1-null beige adipocyte to identify the UCP1-independent function.
Project description:In acute cold stress in mammals, JMJD1A, an H3K9 demethylase, up-regulates thermogenic gene expressions through β-adrenergic signaling in brown adipose tissue (BAT). Aside BAT-driven thermogenesis, mammals also have another mechanism to cope with long-term cold stress by inducing the browning of subcutaneous white adipose tissue (scWAT). Here, we show that this occurs through a two-step process that requires both β-adrenergic dependent phosphorylation of S265 and demethylation of H3K9me2 by JMJD1A. The histone demethylation independent acute Ucp1 induction in BAT and demethylation dependent chronic Ucp1 expression in beige-scWAT provide complementary molecular mechanisms to ensure an ordered transition between acute and chronic adaptation to cold stress. JMJD1A mediates two major signaling pathways, namlely β-adrenergic receptor and PPARγ activation, via PRDM16-PPARγ-P-JMJD1A complex for beige adipogenesis.
Project description:In acute cold stress in mammals, JMJD1A, an H3K9 demethylase, up-regulates thermogenic gene expressions through β-adrenergic signaling in brown adipose tissue (BAT). Aside BAT-driven thermogenesis, mammals also have another mechanism to cope with long-term cold stress by inducing the browning of subcutaneous white adipose tissue (scWAT). Here, we show that this occurs through a two-step process that requires both β-adrenergic dependent phosphorylation of S265 and demethylation of H3K9me2 by JMJD1A. The histone demethylation independent acute Ucp1 induction in BAT and demethylation dependent chronic Ucp1 expression in beige-scWAT provide complementary molecular mechanisms to ensure an ordered transition between acute and chronic adaptation to cold stress. JMJD1A mediates two major signaling pathways, namlely β-adrenergic receptor and PPARγ activation, via PRDM16-PPARγ-P-JMJD1A complex for beige adipogenesis.
Project description:Various physiological stimuli, such as cold environment, diet, and hormones, trigger brown adipose tissue (BAT) to produce heat through sympathetic nervous system (SNS)- and -adrenergic receptors (ARs). The AR stimulation increases intracellular cAMP levels through heterotrimeric G proteins and adenylate cyclases, but the processes by which cAMP modulates brown adipocyte function are not fully understood. Here we described that specific ablation of cAMP production in brown adipocytes led to reduced lipolysis, mitochondrial biogenesis, uncoupling protein 1 (Ucp1) expression, and consequently defective adaptive thermogenesis. Elevated cAMP signaling by sympathetic activation inhibited Salt-inducible kinase 2 (Sik2) through protein kinase A (PKA)-mediated phosphorylation in brown adipose tissue. Inhibition of SIKs enhanced Ucp1 expression in differentiated brown adipocytes and Sik2 knockout mice exhibited enhanced adaptive thermogenesis at thermoneutrality in an Ucp1-dependent manner. Taken together, our data indicate that suppressing Sik2 by PKA-mediated phosphorylation is a requisite for SNS-induced Ucp1 expression and adaptive thermogenesis in BAT, and targeting Sik2 may present a novel therapeutic strategy to ramp up BAT thermogenic activity in humans.
Project description:Beyond its thermogenic potential, brown adipose tissue (BAT) performs important endocrine functions that regulate metabolism. However, the BAT microenvironment and the factors involved in BAT homeostasis and adaptation to cold remain poorly characterized. We therefore aimed to study secreted factors from active brown adipocytes that may be involved in adipocyte function and/or may orchestrate inter-cellular communications. For this, mRNA levels in mature adipocytes of brown, beige and white adipose depots from mice exposed to 21 days of cold were evaluated using RNA sequencing, and bioinformatic analysis was used to predict for potentially secreted factors. Cxcl12 was found to be the most cold-induced C-X-C chemokine in BAT, and Cxcl12 mRNA expression analysis by qPCR and fluorescence in-situ hybridization revealed its enrichment in brown adipocytes upon cold. Cold increased CXCL12 secretion from BAT, yet its level in plasma remained unchanged indicating a potential local action. Cxcl12 knockdown in mature brown adipocytes impaired thermogenesis, estimated by norepinephrine (NE)-induced Ucp1 gene expression, glycerol release and mitochondrial respiration despite unaltered β-adrenergic signaling, suggesting Cxcl12 regulates adipocyte function independently from the β-adrenergic pathway. Importantly, unaltered adipocyte characteristics upon Cxcl12 loss may indicate CXCL12 primarily regulates the NE-induced adipocyte activation. Furthermore, CXCL12 might exert inter-cellular crosstalk via its capacity to promote macrophage chemotaxis and neurite outgrowth. Here we present CXCL12 as a novel brown adipocyte, cold-induced secreted factor involved in adipocyte function and inter-cellular crosstalk within BAT.
Project description:Classical brown adipocytes in interscapular BAT (Myf-5 derived) and inducible beige cells in WAT (non-Myf-5 derived) have distinct developmental origins, although both cell types have morphological and biochemical characteristics of brown fat such as the expression of UCP1. This raises an important question as to how similar the two types of brown adipocytes are at molecular and functional levels. To this end, we employed RNA-seq to systematically determine the transcriptional signatures unique to each cell type.
Project description:Activation of brown adipose tissue (BAT) thermogenesis increases energy expenditure and alleviates obesity. Epigenetic regulation has emerged as a key mechanism underlying BAT development and function. To study the epigenetic regulation of BAT thermogenesis, we surveyed the expression of epigenetic enzymes that catalyze histone modifications in developmental beige adipocytes and found a unique expression pattern of suppressor of variegation 4-20 homolog 2 (Drosophila) (Suv420h2), a histone methyltransferase that preferentially catalyzes the tri-methylation at histone H4 lysine 20 (H4K20me3), a hallmark of gene silencing. Here we discovered that Suv420h2 expression parallels that of UCP1 expression in brown and beige adipocytes and that SUV420H2 knockdown significantly reduces, whereas SUV420H2 overexpression significantly increases UCP1 levels in brown adipocytes. Suv420h2 knockout (H2KO mice exhibit impaired cold-induced thermogenesis and are prone to diet-induced obesity. In contrast, mice with specific overexpression of Suv420h2 in adipocytes display enhanced cold-induced thermogenesis and are resistant to diet-induced obesity. Further study showed that Suv420h2 catalyzes H4K20 trimethylation at eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) promoter, leading to down-regulated expression of 4E-BP1, a negative regulator of the translation initiation complex. This in turn up-regulates PGC1α protein levels, which is associated with increased expression of thermogenic program. We conclude that Suv420h2 is a key regulator of brown/beige adipocyte development and thermogenesis.
Project description:Activation of brown adipose tissue (BAT) thermogenesis increases energy expenditure and alleviates obesity. Epigenetic regulation has emerged as a key mechanism underlying BAT development and function. To study the epigenetic regulation of BAT thermogenesis, we surveyed the expression of epigenetic enzymes that catalyze histone modifications in developmental beige adipocytes and found a unique expression pattern of suppressor of variegation 4-20 homolog 2 (Drosophila) (Suv420h2), a histone methyltransferase that preferentially catalyzes the tri-methylation at histone H4 lysine 20 (H4K20me3), a hallmark of gene silencing. Here we discovered that Suv420h2 expression parallels that of UCP1 expression in brown and beige adipocytes and that SUV420H2 knockdown significantly reduces, whereas SUV420H2 overexpression significantly increases UCP1 levels in brown adipocytes. Suv420h2 knockout (H2KO mice exhibit impaired cold-induced thermogenesis and are prone to diet-induced obesity. In contrast, mice with specific overexpression of Suv420h2 in adipocytes display enhanced cold-induced thermogenesis and are resistant to diet-induced obesity. Further study showed that Suv420h2 catalyzes H4K20 trimethylation at eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) promoter, leading to down-regulated expression of 4E-BP1, a negative regulator of the translation initiation complex. This in turn up-regulates PGC1α protein levels, which is associated with increased expression of thermogenic program. We conclude that Suv420h2 is a key regulator of brown/beige adipocyte development and thermogenesis.
Project description:Low-protein/high carbohydrate (LP/HC) diet promotes metabolic health and longevity in adult human and animal models. However, the complex molecular underpinnings of how LP/HC diet leads to metabolic benefits remain elusive. Through a multi-layered approach, here we observed that LP/HC diet promotes an energy-dissipating response consisting in the parallel recruitment of canonical and non-canonical (muscular) thermogenic systems in subcutaneous adipose tissue (sWAT). In particular, we measured Ucp1 induction in association with up-regulation of actomyosin components and several Serca (Serca1, Serca2a, Serca2b) ATPases. In beige adipocytes, we observed that AMPK activation is responsible for transducing the amino acid lowering in an enhanced fat catabolism, which sustains both Ucp1- and Serca-dependent energy dissipation. Limiting AMPK activation counteracts the expression of brown fat and muscular genes, including Ucp1 and Serca, as well as mitochondrial oxidative genes. We observed that mitochondrial reactive oxygen species are the upstream molecules controlling AMPK-mediated metabolic rewiring in amino acid-restricted beige adipocytes. Our findings delineate a novel metabolic phenotype of responses to amino acid shortage, which recapitulates some of the benefits of cool temperature in sWAT. In conclusion, this study highlights LP/HC diet as a valuable and practicable strategy to prevent metabolic diseases through the enhancement of mitochondrial oxidative metabolism and the recruitment of different energy dissipating routes in beige adipocytes.
Project description:Protein kinase A phosphorylates proteins including histone H3 lysine 9 (H3K9) demethylase JMJD1A to facilitate beige adipogenesis upon β-adrenergic receptor (β-AR) activation, however, phosphatase(s) that antagonizes phosphorylation to inhibit beige adipogenesis is incompletely understood. Here we show that MYPT1-PP1β is a phosphatase that negatively regulates beige adipogenesis via dephosphorylation of pS265-JMJD1A and myosin regulatory light chain. Upon β-AR activation, MYPT1-PP1β is inhibited via T694 phosphorylation of MYPT1, facilitating phosphorylation of JMJD1A and beige adipogenesis under cold stress. Depletion of MYPT1-PP1β induces Ucp1 by orchestrating JMJD1A-mediated H3K9 demethylation and actomyosin-tension mediated YAP/TAZ activation. This induction of Ucp1 is abrogated in adipocytes expressing catalytically dead JMJD1A mutant, indicating that the coordinated epigenetic and transcriptional mechanisms are essential for beige adipogenesis. We also show that preadipocytes specific Mypt1 deficient mice exhibit higher cold tolerance with higher Ucp1 levels in subcutaneous white adipose tissues compared to control mice confirming its role at animal levels.