Role of gut microbial-derived metabolites and other select agents on adipocyte browning.

AIMS: Metabolic disease is a multifaceted condition characterized by the disruption of numerous metabolic parameters within the host. Its prevalence has surged significantly in recent years and it has become a prominent non-communicable disease worldwide. The effect of gut microbiota on various beige fat induction is well studied, while the mechanisms behind the link remain unclear. Given that gut microbiota-derived metabolites (meta-metabolites) secreted in the gut serve as a key mode of communication with their host through direct circulation or indirect host physiology modification, understanding the effect of meta-metabolites on adipose tissue is essential. METHODOLOGY: In our previous in-vivo studies, we observed a correlation between gut microbiota and the formation of beige fat. In this study, we further aimed to validate this correlation by treating the adipocyte cell line (3T3-L1) with meta-metabolites collected from the cecum of mice exhibiting beige adipose tissue formation. Additionally, we treated the adipocyte cell line with known beige fat inducers (L-Rhamnose and Ginsenoside) to assess meta-metabolites' efficacy on beige fat formation. KEY FINDINGS: Upon treatment with the meta-metabolites from the antibiotic-treated mice, we observed a significant increase in lipid metabolism and beige-specific gene expression. Analyzing the metabolites in these cells revealed that a set of metabolites potentially govern adipocytes, contributing to a metabolically active state. These effects were at par or even better than those of cells treated with L-Rhamnose or Ginsenoside. SIGNIFICANCE: This research sheds light on the intricate interplay between microbial metabolites and adipose tissue, offering valuable clues for understanding and potentially manipulating these processes for therapeutic purposes.

Decoding temporal thermogenesis: coregulator selectivity and transcriptional control in brown and beige adipocytes.

In mammals, brown adipose tissue (BAT) and beige adipocytes in white adipose tissue (WAT) play pivotal roles in maintaining body temperature and energy metabolism. In mice, BAT quickly stimulates thermogenesis by activating brown adipocytes upon cold exposure. In the presence of chronic cold stimuli, beige adipocytes are recruited in inguinal WAT to support heat generation. Accumulated evidence has shown that thermogenic execution of brown and beige adipocytes is regulated in a fat depot-specific manner. Recently, we have demonstrated that ubiquitin ligase ring finger protein 20 (RNF20) regulates brown and beige adipocyte thermogenesis through fat-depot-specific modulation. In BAT, RNF20 regulates transcription factor GA-binding protein alpha (GABPα), whereas in inguinal WAT, RNF20 potentiates transcriptional activity of peroxisome proliferator-activated receptor-gamma (PPARγ) through the degradation of nuclear corepressor 1 (NCoR1). This study proposes the molecular mechanisms by which co-regulator(s) selectively and temporally control transcription factors to coordinate adipose thermogenesis in a fat-depot-specific manner. In this Commentary, we provide molecular features of brown and beige adipocyte thermogenesis and discuss the underlying mechanisms of distinct thermogenic processes in two fat depots.

Cocoa extract induces browning of white adipocytes and improves glucose intolerance in mice fed a high-fat diet.

Cocoa extract (CE) offers several health benefits, such as anti-obesity and improved glucose intolerance. However, the mechanisms remain unclear. Adipose tissue includes white adipose tissue (WAT) and brown adipose tissue. Brown adipose tissue leads to body fat reduction by metabolizing lipids to heat via uncoupling protein 1 (UCP1). The conversion of white adipocytes into brown-like adipocytes (beige adipocytes) is called browning, and it contributes to the anti-obesity effect and improved glucose tolerance. This study aimed to evaluate the effect of CE on glucose tolerance in terms of browning. We found that dietary supplementation with CE improved glucose intolerance in mice fed a high-fat diet, and it increased the expression levels of Ucp1 and browning-associated gene in inguinal WAT. Furthermore, in primary adipocytes of mice, CE induced Ucp1 expression through ß3-adrenergic receptor stimulation. These results suggest that dietary CE improves glucose intolerance by inducing browning in WAT.

Transcriptional evidence for transient regulation of muscle regeneration by brown adipose transplant in the rotator cuff.

Chronic rotator cuff (RC) injuries can lead to a degenerative microenvironment that favors chronic inflammation, fibrosis, and fatty infiltration. Recovery of muscle structure and function will ultimately require a complex network of muscle resident cells, including satellite cells, fibro-adipogenic progenitors (FAPs), and immune cells. Recent work suggests that signaling from adipose tissue and progenitors could modulate regeneration and recovery of function, particularly promyogenic signaling from brown or beige adipose (BAT). In this study, we sought to identify cellular targets of BAT signaling during muscle regeneration using a RC BAT transplantation mouse model. Cardiotoxin injured supraspinatus muscle had improved mass at 7 days postsurgery (dps) when transplanted with exogeneous BAT. Transcriptional analysis revealed transplanted BAT modulates FAP signaling early in regeneration likely via crosstalk with immune cells. However, this conferred no long-term benefit as muscle mass and function were not improved at 28 dps. To eliminate the confounding effects of endogenous BAT, we transplanted BAT in the "BAT-free" uncoupling protein-1 diphtheria toxin fragment A (UCP1-DTA) mouse and here found improved muscle contractile function, but not mass at 28 dps. Interestingly, the transplanted BAT increased fatty infiltration in all experimental groups, implying modulation of FAP adipogenesis during regeneration. Thus, we conclude that transplanted BAT modulates FAP signaling early in regeneration, but does not grant long-term benefits.

Overexpression of PRDM16 Improves Muscle Function after Rotator Cuff Tears.

INTRODUCTION: Muscle atrophy, fibrosis and fatty infiltration (FI) are commonly seen in rotator cuff tears (RCT), which are critical factors that directly determine the clinical outcomes for patients with this injury. Therefore, improving muscle quality after RCT is crucial in improving the clinical outcome of tendon repair. In recent years, it has been discovered that adults have functional beige/brown adipose tissue (BAT) which can secrete batokines to promote muscle growth. PRDM16, a PR-domain containing protein, was discovered with the ability to determine the brown fat cell fate and stimulate its development. Thus, the goal of this study is to discover the role of PRDM16 in improving muscle function after massive tendon tears using a transgenic mouse model with an elevated level of PRDM16 expression. METHODS: Transgenic aP2 driven PRDM16 overexpression mice and C57BL/6J mice underwent unilateral supraspinatus (SS) tendon transection and suprascapular nerve transection (TTDN) as described previously (N=8 in each group). DigiGait was performed to evaluate forelimb function at 6 weeks post the TTDN injury. Bilateral SS muscles, interscapular brown fat, epididymal white fat, and inguinal beige fat were harvested for analysis. The expression of PRDM16 in adipose tissue was detected by Western Blot. Masson's trichome staining was conducted to evaluate the muscle fibrosis and Oil Red O staining was used to determine the fat infiltration. Muscle fiber type was determined by MHC expression via immunostaining. All data was presented in the form of mean±SD. T-test and two-way ANOVA analysis was performed to determine a statistically significant difference between groups. Significance was considered when P<0.05. RESULTS: Western blot data showed an increased expression of PRDM16 protein in both white and brown fat in PRDM16-overexpression mice compared to wild-type (WT) mice. Even though PRDM16 overexpression had no effect on increasing muscle weight, it significantly improved the forelimbs function with longer brake, stance and stride time, larger stride length and paw area in mice after RCT. Additionally, PRDM16 overexpression mice showed no difference in amount of fibrosis when compared to WT mice, however, they had significantly reduced area of fatty infiltration. These mice also exhibited abundant MHC-IIx fiber percentage in supraspinatus muscle after TTDN. CONCLUSION: Overexpression of PRDM16 significantly improved muscle function and reduced fatty infiltration after rotator cuff tears. Promoting BAT activity is beneficial in improving rotator cuff muscle quality and shoulder function after RCT.

Impact of Different Mineral Reinforcements on HDPE Composites: Effects of Melt Flow Index and Particle Size on Physical and Mechanical Properties.

The use of mineral reinforcements in polymer matrix composites has emerged as an alternative for sustainable production, reducing waste and enhancing the physical and mechanical properties of these materials. This study investigated the impact of the melt flow index (MFI) of HDPE and the particle size of two mineral reinforcements, Bahia Beige (BB) and Rio Grande do Norte Limestone (CRN), on the composites. All composites were processed via extrusion, followed by injection, with the addition of 30 wt.% reinforcement. Chemical analyses revealed similar compositions with high CaO content for both minerals, while X-ray diffraction (XRD) identified predominantly calcite, dolomite, and quartz phases. Variations in the MFI, reinforcement type, and particle size showed a minimal influence on composite properties, supported by robust statistical analyses that found no significant differences between groups. Morphological analysis indicated that composites with lower MFI exhibited less porous structures, whereas larger particles of BB and CRN formed clusters, affecting impact resistance, which was attributed to poor interfacial adhesion.

The Effect of KSK-94, a Dual Histamine H3 and Sigma-2 Receptor Ligand, on Adipose Tissue in a Rat Model of Developing Obesity.

BACKGROUND: Numerous studies highlight the critical role that neural histamine plays in feeding behavior, which is controlled by central histamine H3 and H1 receptors. This is the fundamental motivation for the increased interest in creating histamine H3 receptor antagonists as anti-obesity medications. On the other hand, multiple other neurotransmitter systems have been identified as pharmacotherapeutic targets for obesity, including sigma-2 receptor systems. Interestingly, in our previous studies in the rat excessive eating model, we demonstrated a significant reduction in the development of obesity using dual histamine H3/sigma-2 receptor ligands. Moreover, we showed that compound KSK-94 (structural analog of Abbott's A-331440) reduced the number of calories consumed, and thus acted as an anorectic compound. Therefore, in this study, we extended the previous research and studied the influence of KSK-94 on adipose tissue collected from animals from our previous experiment. METHODS: Visceral adipose tissue was collected from four groups of rats (standard diet + vehicle, palatable diet + vehicle, palatable diet + KSK-94, and palatable diet + bupropion/naltrexone) and subjected to biochemical, histopathological, and immunohistochemical studies. RESULTS: The obtained results clearly indicate that compound KSK-94 prevented the hypertrophy and inflammation of visceral adipose tissue, normalized the levels of leptin, resistin and saved the total reduction capacity of adipose tissue, being more effective than bupropion/naltrexon in these aspects. Moreover, KSK-94 may induce browning of visceral white adipose tissue. CONCLUSION: Our study suggests that dual compounds with a receptor profile like KSK-94, i.e., targeting histamine H3 receptor and, to a lesser extent, sigma-2 receptor, could be attractive therapeutic options for patients at risk of developing obesity or with obesity and some metabolic disorders. However, more studies are required to determine its safety profile and the exact mechanism of action of KSK-94.

Thermogenic Fat as a New Obesity Management Tool: From Pharmaceutical Reagents to Cell Therapies.

Obesity is a complex medical condition caused by a positive imbalance between calorie intake and calorie consumption. Brown adipose tissue (BAT), along with the newly discovered "brown-like" adipocytes (called beige cells), functions as a promising therapeutic tool to ameliorate obesity and metabolic disorders by burning out extra nutrients in the form of heat. Many studies in animal models and humans have proved the feasibility of this concept. In this review, we aim to summarize the endeavors over the last decade to achieve a higher number/activity of these heat-generating adipocytes. In particular, pharmacological compounds, especially agonists to the ß3 adrenergic receptor (ß3-AR), are reviewed in terms of their feasibility and efficacy in elevating BAT function and improving metabolic parameters in human subjects. Alternatively, allograft transplantation of BAT and the transplantation of functional brown or beige adipocytes from mesenchymal stromal cells or human induced pluripotent stem cells (hiPSCs) make it possible to increase the number of these beneficial adipocytes in patients. However, practical and ethical issues still need to be considered before the therapy can eventually be applied in the clinical setting. This review provides insights and guidance on brown- and beige-cell-based strategies for the management of obesity and its associated metabolic comorbidities.

Gene expression and characterization of clonally derived murine embryonic brown and brite adipocytes.

White adipocytes store energy, while brown and brite adipocytes release heat via nonshivering thermogenesis. In this study, we characterized two murine embryonic clonal preadipocyte lines, EB5 and EB7, each displaying unique gene marker expression profiles. EB5 cells differentiate into brown adipocytes, whereas EB7 cells into brite (also known as beige) adipocytes. To draw a comprehensive comparison, we contrasted the gene expression patterns, adipogenic capacity, as well as carbohydrate and lipid metabolism of these cells to that of F442A, a well-known white preadipocyte and adipocyte model. We found that commitment to differentiation in both EB5 and EB7 cells can be induced by 3-Isobutyl-1-methylxanthine/dexamethasone (Mix/Dex) and staurosporine/dexamethasone (St/Dex) treatments. Additionally, the administration of rosiglitazone significantly enhances the brown and brite adipocyte phenotypes. Our data also reveal the involvement of a series of genes in the transcriptional cascade guiding adipogenesis, pinpointing GSK3ß as a critical regulator for both EB5 and EB7 adipogenesis. In a developmental context, we observe that, akin to brown fat progenitors, brite fat progenitors make their appearance in murine development by 11-12 days of gestation or potentially earlier. This result contributes to our understanding of adipocyte lineage specification during embryonic development. In conclusion, EB5 and EB7 cell lines are valuable for research into adipocyte biology, providing insights into the differentiation and development of brown and beige adipocytes. Furthermore, they could be useful for the characterization of drugs targeting energy balance for the treatment of obesity and metabolic diseases.

Development of a functional beige fat cell line uncovers independent subclasses of cells expressing UCP1 and the futile creatine cycle.

Although uncoupling protein 1 (UCP1) is established as a major contributor to adipose thermogenesis, recent data have illustrated an important role for alternative pathways, particularly the futile creatine cycle (FCC). How these pathways co-exist in cells and tissues has not been explored. Beige cell adipogenesis occurs in vivo but has been difficult to model in vitro; here, we describe the development of a murine beige cell line that executes a robust respiratory response, including uncoupled respiration and the FCC. The key FCC enzyme, tissue-nonspecific alkaline phosphatase (TNAP), is localized almost exclusively to mitochondria in these cells. Surprisingly, single-cell cloning from this cell line shows that cells with the highest levels of UCP1 express little TNAP, and cells with the highest expression of TNAP express little UCP1. Immunofluorescence analysis of subcutaneous fat from cold-exposed mice confirms that the highest levels of these critical thermogenic components are expressed in distinct fat cell populations.

Circulating plasma fibronectin affects tissue insulin sensitivity, adipocyte differentiation, and transcriptional landscape of adipose tissue in mice.

Plasma fibronectin (pFN) is a hepatocyte-derived circulating extracellular matrix protein that affects cell morphology, adipogenesis, and insulin signaling of adipocytes in vitro. In this study, we show pFN accrual to adipose tissue and its contribution to tissue homeostasis in mice. Hepatocyte-specific conditional Fn1 knockout mice (Fn1-/-ALB) show a decrease in adipose tissue FN levels and enhanced insulin sensitivity of subcutaneous (inguinal), visceral (epididymal) adipose tissue on a normal diet. Diet-induced obesity model of the Fn1-/-ALB mouse showed normal weight gain and whole-body fat mass, and normal adipose tissue depot volumes and unaltered circulating leptin and adiponectin levels. However, Fn1-/-ALB adipose depots showed significant alterations in adipocyte size and gene expression profiles. The inguinal adipose tissue on a normal diet, which had alterations in fatty acid metabolism and thermogenesis suggesting browning. The presence of increased beige adipocyte markers Ucp1 and Prdm16 supported this. In the inguinal fat, the obesogenic diet resulted in downregulation of the browning markers and changes in gene expression reflecting development, morphogenesis, and mesenchymal stem cell maintenance. Epididymal adipose tissue showed alterations in developmental and stem cell gene expression on both diets. The data suggests a role for pFN in adipose tissue insulin sensitivity and cell profiles.

Atomic force microscopy characterization of white and beige adipocyte differentiation.

Adipose tissue plays an essential role in systemic metabolism with white adipose tissue (WAT) making up most of the tissue and being involved in the regulation of energy homeostasis, and brown and beige adipose tissue (BAT) exhibiting thermogenic activity. There is promise in the conversion of white adipocytes into beige ones as a therapeutic potential to control and enhance systemic metabolism, but it is difficult to maintain this transformation in vivo because we do not fully understand the mechanism of conversion. In this study, we applied atomic force microscopy (AFM) to characterize beige or white adipocytes during the process of differentiation for morphology, roughness, adhesion, and elasticity at different time points. As cells differentiated to white and beige adipocytes, they exhibited morphological changes as they lipid loaded, transitioning from flattened elongated cells to a rounded shape indicating adipogenesis. While there was an initial decrease in elasticity for both beige and white adipocytes, white adipocytes exhibited a higher elasticity than beige adipocytes at all time points. Beige and white adipogenesis exhibited a decrease in adhesion energy compared to preadipocytes, yet at day 12, white adipocytes had a significant increase in adhesion energy compared to beige adipocytes. This work shows significant differences in the mechanical properties of white vs. beige adipocytes during differentiation. Results from this study contribute to a better understanding of the differentiation of adipocytes which are vital to the therapeutic induction, engineered models, and maintenance of beige adipocytes as a potential approach for enhancing systemic metabolism.

Alternative isoform expression of key thermogenic genes in human beige adipocytes.

Background: The beneficial effect of thermogenic adipocytes in maintaining body weight and protecting against metabolic disorders has raised interest in understanding the regulatory mechanisms defining white and beige adipocyte identity. Although alternative splicing has been shown to propagate adipose browning signals in mice, this has yet to be thoroughly investigated in human adipocytes. Methods: We performed parallel white and beige adipogenic differentiation using primary adipose stem cells from 6 unrelated healthy subjects and assessed differential gene and isoform expression in mature adipocytes by RNA sequencing. Results: We find 777 exon junctions with robust differential usage between white and beige adipocytes in all 6 subjects, mapping to 562 genes. Importantly, only 10% of these differentially spliced genes are also differentially expressed, indicating that alternative splicing constitutes an additional layer of gene expression regulation during beige adipocyte differentiation. Functional classification of alternative isoforms points to a gain of function for key thermogenic transcription factors such as PPARG and CITED1, and enzymes such as PEMT, or LPIN1. We find that a large majority of the splice variants arise from differential TSS usage, with beige-specific TSSs being enriched for PPARγ and MED1 binding compared to white-specific TSSs. Finally, we validate beige specific isoform expression at the protein level for two thermogenic regulators, PPARγ and PEMT. Discussion: These results suggest that differential isoform expression through alternative TSS usage is an important regulatory mechanism for human adipocyte thermogenic specification.

Molecular Regulation of Thermogenic Mechanisms in Beige Adipocytes.

Adipose tissue is conventionally recognized as a metabolic organ responsible for storing energy. However, a proportion of adipose tissue also functions as a thermogenic organ, contributing to the inhibition of weight gain and prevention of metabolic diseases. In recent years, there has been significant progress in the study of thermogenic fats, particularly brown adipose tissue (BAT). Despite this progress, the mechanism underlying thermogenesis in beige adipose tissue remains highly controversial. It is widely acknowledged that beige adipose tissue has three additional thermogenic mechanisms in addition to the conventional UCP1-dependent thermogenesis: Ca2+ cycling thermogenesis, creatine substrate cycling thermogenesis, and triacylglycerol/fatty acid cycling thermogenesis. This paper delves into these three mechanisms and reviews the latest advancements in the molecular regulation of thermogenesis from the molecular genetic perspective. The objective of this review is to provide readers with a foundation of knowledge regarding the beige fats and a foundation for future research into the mechanisms of this process, which may lead to the development of new strategies for maintaining human health.

Adipocyte Mitochondria: Deciphering Energetic Functions across Fat Depots in Obesity and Type 2 Diabetes.

Adipose tissue, a central player in energy balance, exhibits significant metabolic flexibility that is often compromised in obesity and type 2 diabetes (T2D). Mitochondrial dysfunction within adipocytes leads to inefficient lipid handling and increased oxidative stress, which together promote systemic metabolic disruptions central to obesity and its complications. This review explores the pivotal role that mitochondria play in altering the metabolic functions of the primary adipocyte types, white, brown, and beige, within the context of obesity and T2D. Specifically, in white adipocytes, these dysfunctions contribute to impaired lipid processing and an increased burden of oxidative stress, worsening metabolic disturbances. Conversely, compromised mitochondrial function undermines their thermogenic capabilities, reducing the capacity for optimal energy expenditure in brown adipocytes. Beige adipocytes uniquely combine the functional properties of white and brown adipocytes, maintaining morphological similarities to white adipocytes while possessing the capability to transform into mitochondria-rich, energy-burning cells under appropriate stimuli. Each type of adipocyte displays unique metabolic characteristics, governed by the mitochondrial dynamics specific to each cell type. These distinct mitochondrial metabolic phenotypes are regulated by specialized networks comprising transcription factors, co-activators, and enzymes, which together ensure the precise control of cellular energy processes. Strong evidence has shown impaired adipocyte mitochondrial metabolism and faulty upstream regulators in a causal relationship with obesity-induced T2D. Targeted interventions aimed at improving mitochondrial function in adipocytes offer a promising therapeutic avenue for enhancing systemic macronutrient oxidation, thereby potentially mitigating obesity. Advances in understanding mitochondrial function within adipocytes underscore a pivotal shift in approach to combating obesity and associated comorbidities. Reigniting the burning of calories in adipose tissues, and other important metabolic organs such as the muscle and liver, is crucial given the extensive role of adipose tissue in energy storage and release.

Parathyroid hormone promotes induction of beige adipocytes and reversibly ameliorates muscle quality and atrophy following chronic rotator cuff tear in a rat model.

BACKGROUND: Fatty infiltration (FI) and muscle atrophy (MA) in the rotator cuff muscles following rotator cuff tears (RCT) persist postrepair, increasing the risk of re-tears. Brown adipocyte-like "beige adipocytes" are expected to have a therapeutic effect on intramuscular FI and MA due to their lipolytic activity and the muscle regenerative effects of their secreted factors. However, whether parathyroid hormone (PTH) ameliorates the already advanced FI and MA remains unknown. Therefore, this study aimed to clarify whether PTH promotes the expression of beige adipocytes and ameliorates advanced FI and MA following chronic RCT in rats. METHODS: Supraspinatus muscles were harvested from rats with chronic RCT after 4 or 8 weeks of PTH treatment and compared to those in the control group or to those at the start of treatment. FI was assessed by Oil Red O staining, and the staining area was evaluated as a percentage of the muscle cross-sectional area. MA was evaluated by measuring muscle wet weight and cross-sectional area of muscle fiber. Beige adipocyte expression was evaluated by immunostaining for uncoupling protein 1 (UCP1). Fibro-adipogenic progenitors (FAPs) were separated from muscle-injured mice. We assessed whether PTH could diminish fat droplet accumulation by promoting the differentiation of FAPs into beige adipocytes. RESULTS: After 4 weeks, PTH reduced the area fraction of FI in the rat supraspinatus muscle following chronic RCT compared with that at the beginning of treatment (P = .028). In addition, PTH increased wet muscle mass (P < .001), and muscle fiber cross-sectional area (P = .018) compared with measurements at the start of treatment. PTH administration promoted the expression of UCP1, a beige adipocyte marker, in the supraspinatus muscle (P = .019). PTH increased gene expression of beige adipocyte-related markers and suppressed fat droplet accumulation even after adipogenic differentiation of FAPs (P = .004) but did not reduce fat droplets that had already accumulated in in vitro experiments. CONCLUSIONS: PTH facilitated beige adipocyte expression and reversibly ameliorated muscle quality and atrophy following chronic RCT by hindering fat droplet accumulation and facilitating muscle regeneration. Therefore, PTH may be a medical treatment for FI and MA following RCT, leading to expanded rotator cuff repair indications.

Aging impairs cold-induced beige adipogenesis and adipocyte metabolic reprogramming.

The energy-burning capability of beige adipose tissue is a potential therapeutic tool for reducing obesity and metabolic disease, but this capacity is decreased by aging. Here, we evaluate the impact of aging on the profile and activity of adipocyte stem and progenitor cells (ASPCs) and adipocytes during the beiging process in mice. We found that aging increases the expression of Cd9 and other fibro-inflammatory genes in fibroblastic ASPCs and blocks their differentiation into beige adipocytes. Fibroblastic ASPC populations from young and aged mice were equally competent for beige differentiation in vitro, suggesting that environmental factors suppress adipogenesis in vivo. Examination of adipocytes by single nucleus RNA-sequencing identified compositional and transcriptional differences in adipocyte populations with aging and cold exposure. Notably, cold exposure induced an adipocyte population expressing high levels of de novo lipogenesis (DNL) genes, and this response was severely blunted in aged animals. We further identified Npr3, which encodes the natriuretic peptide clearance receptor, as a marker gene for a subset of white adipocytes and an aging-upregulated gene in adipocytes. In summary, this study indicates that aging blocks beige adipogenesis and dysregulates adipocyte responses to cold exposure and provides a resource for identifying cold and aging-regulated pathways in adipose tissue.

The essential role of architectural noncoding RNA Neat1 in cold-induced beige adipocyte differentiation in mice.

Neat1 is an architectural RNA that provides the structural basis for nuclear bodies known as paraspeckles. Although the assembly processes by which Neat1 organizes paraspeckle components are well-documented, the physiological functions of Neat1 are not yet fully understood. This is partly because Neat1 knockout (KO) mice, lacking paraspeckles, do not exhibit overt phenotypes under normal laboratory conditions. During our search for conditions that elicit clear phenotypes in Neat1 KO mice, we discovered that the differentiation of beige adipocytes-inducible thermogenic cells that emerge upon cold exposure-is severely impaired in these mutant mice. Neat1_2, the architectural isoform of Neat1, is transiently upregulated during the early stages of beige adipocyte differentiation, coinciding with increased paraspeckle formation. Genes with altered expression during beige adipocyte differentiation typically cluster at specific chromosomal locations, some of which move closer to paraspeckles upon cold exposure. These observations suggest that paraspeckles might coordinate the regulation of these gene clusters by controlling the activity of certain transcriptional condensates that coregulate multiple genes. We propose that our findings highlight a potential role for Neat1 and paraspeckles in modulating chromosomal organization and gene expression, potentially crucial processes for the differentiation of beige adipocytes.

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.