Myogenic gene expression signature establishes that brown and white adipocytes originate from distinct cell lineages

Strongylocentrotus intermedius Extract Suppresses Adiposity by Inhibiting Adipogenesis and Promoting Adipocyte Browning via AMPK Activation in 3T3-L1 Cells

The current study aimed to determine whether Strongylocentrotus intermedius (S. intermedius) extract (SIE) exerts anti-obesity potentials employing 3T3-L1 cells as in vitro model. Herein we reported that treatment of SIE for 6 days reduced lipid accretion and triglyceride content whereas it increased the release of free glycerol. The inhibited lipid accumulation and induced lipolysis were evidenced by the downregulation of lipogenesis proteins, such as fatty acid synthase and lipoprotein lipase, and the upregulation of hormone-sensitive lipase expression. Furthermore, the downregulation of adipogenic transcription factors, including peroxisome proliferator-activated receptor gamma, CCAAT/enhancer-binding protein α, and sterol regulatory element-binding protein 1, highlights that reduced lipid accumulation is supported by lowering adipocyte differentiation. Additionally, treatment activates brown adipocyte phenotype in 3T3-L1 cells by inducing expression of brown adipose tissue-specific proteins, such as uncoupling protein 1 and peroxisome proliferator-activated receptor-γ coactivator 1α. Moreover, SIE induced the phosphorylation of AMP-activated protein kinase (AMPK). The pharmacological approach using AMPK inhibitor revealed that the restraining effect of SIE on adipogenesis and promotion of adipocyte browning were blocked. In GC-MS analysis, SIE was mainly composed of cholest-5-en-3-ol (36.71%) along with saturated and unsaturated fatty acids which have favorable anti-obesity potentials. These results reveal that SIE has the possibility as a lipid-lowering agent for the intervention of obesity.

Developmental overlap between skeletal muscle maturation and perirenal fat brown-to-white transition in goats: Exploring the role of Myf-5

In mammals, skeletal muscles (SkMs) and adipose tissues regulate energy homeostasis and share developmental origins. Notably, the perirenal adipose tissue (PRAT) depot has been reported to display adipocyte heterogeneity: while some originated from Myogenic factor 5 (Myf-5) expressing progenitors, others did not. Our study examines the expression and distribution of Myf-5 using immunohistochemical staining and western blotting of PRAT, gastrocnemius, and trapezius from goat at various developmental stages. Contrary to earlier beliefs, functionally divergent SkM gastrocnemius and trapezius showed similar Myf-5 expressional pattern. SkM abundantly expresses Myf-5 in developing myocytes which gradually becomes limited to the nucleus of myogenic stem cells and is retained only in a few differentiated postnatal fibers. During the same period, PRAT displays a unique brown-to-white transition. PRAT exhibited an elevated expression of Myf-5 during prenatal periods, which declines thereafter and becomes negligible during adulthood where it gets fully enriched white adipocytes. The reduction of Myf-5 during the neonatal period was common to all three tissues. However, Myf-5 expression was retained in some of the differentiated myofibers while it was undetectable in adult PRAT. These observations suggest a possible developmental interplay between adipose tissue and SkM where Myf-5 might be a major regulator.

Vestigial like 4 regulates the adipogenesis of classical brown adipose tissue

Brown adipose tissue (BAT) is mammals' primary non-shivering thermogenesis organ, and the molecular mechanisms regulating BAT growth and adipogenesis are largely unknown. The Hippo-YAP pathway has been well-known for controlling organ size, and Vestigial like 4 (VGLL4) is a transcriptional regulator that modulates the Hippo-YAP pathway by competing against YAP for binding to TEAD proteins. In this study, we dissected the function of VGLL4 in regulating BAT development. We generated a conventional Vgll4 mutant mouse line, in which the two Tondu (TDU) domains of VGLL4 were disrupted. We found that deletion of the TDU domains of VGLL4 resulted in perinatal lethality and paucity of the interscapular BAT. Histological and magnetic resonance imaging studies confirmed that the adipogenesis of BAT was impaired in Vgll4 mutants. Adeno-associated virus (AAV) mediated, brown adipocyte-specific overexpression of VGLL4 increased BAT volume and protected the adult male mice from acute cold stress. Genomic studies suggest that VGLL4/TEAD1 complex directly regulates the myogenic and adipogenic gene expression programs of BAT. In conclusion, our data identify VGLL4 as a previously unrecognized adipogenesis factor that regulates classical BAT development.

Role of Brown Adipose Tissue in Metabolic Health and Efficacy of Drug Treatment for Obesity

(1) Background: Brown adipose tissue (BAT) is responsible for non-shivering thermogenesis, and its activation has become a new object as both a determinant of metabolic health and a target for therapy. This study aimed to identify the relationships between the presence of BAT, parameters that characterize metabolic health (glucose, lipids, blood pressure (BP)), and the dynamics of body mass index (BMI) during weight-reducing therapy. (2) Methods: The study included 72 patients with obesity. We investigated metabolic parameters, anthropometric parameters, and BP. Dual-energy X-ray absorptiometry (DXA) and positron emission tomography and computed tomography (PET/CT) imaging with 18F-fluorodeoxyglucose (18F-FDG) were performed. (3) Results: Before weight-reducing therapy, BAT was revealed only in 19% patients with obesity. The presence of BAT was associated with a lower risk of metabolic deviations that characterize metabolic syndrome: shorter waist circumference (WC) (p = 0.02) and lower levels of glucose (p = 0.03) and triglycerides (p = 0.03). Thereafter, patients were divided into four groups according to the type of therapy (only lifestyle modification or with Liraglutide or Reduxin or Reduxin Forte). We did not find a relationship between the presence of BAT and response to therapy: percent weight reduction was 10.4% in patients with BAT and 8.5% in patients without BAT (p = 0.78) during six months of therapy. But we noted a significant positive correlation between the volume of BAT and the effectiveness of weight loss at 3 months (r = 0.52, p = 0.016). The dynamic analysis of BAT after 6 months of therapy showed a significant increase in the volume of cold-induced metabolically active BAT, as determined by PET/CT with 18F-FDG in the Liraglutide group (p = 0.04) and an increase in the activity of BAT standardized uptake value (SUV mean and SUV max) in the Reduxin (p = 0.02; p = 0.01, respectively) and Liraglutide groups (p = 0.02 in both settings). (4) Conclusions: The presence of brown adipose tissue is associated with a lower risk of metabolic abnormalities. In general, our study demonstrated that well-established drugs in the treatment of obesity (Liraglutide and Reduxin) have one more mechanism for implementing their effects. These drugs have the ability to increase the activity of BAT. A significant positive relationship between the total volume of BAT and the percentage of weight loss may further determine the priority mechanism of the weight-reducing effect of these medicaments.

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 β3 adrenergic receptor (β3-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.

The evolution of thermogenesis in mammals

Comparative genomics elucidates the steps enabling heat production in fat tissue.

Genetic or pharmacological GHSR blockade has sexually dimorphic effects in rodents on a high-fat diet

The stomach-derived hormone ghrelin regulates essential physiological functions. The ghrelin receptor (GHSR) has ligand-independent actions; therefore, GHSR gene deletion may be a reasonable approach to investigate the role of this system in feeding behaviors and diet-induced obesity (DIO). Here, we investigate the effects of a long-term (12-month) high-fat (HFD) versus regular diet on obesity-related measures in global GHSR-KO and wild-type (WT) Wistar male and female rats. Our main findings are that the GHSR gene deletion protects against DIO and decreases food intake during HFD in male but not in female rats. GHSR gene deletion increases thermogenesis and brain glucose uptake in male rats and modifies the effects of HFD on brain glucose metabolism in a sex-specific manner, as assessed with small animal positron emission tomography. We use RNA-sequencing to show that GHSR-KO rats have upregulated expression of genes responsible for fat oxidation in brown adipose tissue. Central administration of a novel GHSR inverse agonist, PF-5190457, attenuates ghrelin-induced food intake, but only in male, not in female mice. HFD-induced binge-like eating is reduced by inverse agonism in both sexes. Our results support GHSR as a promising target for new pharmacotherapies for obesity.

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

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

Gut microbiota in overweight and obesity: crosstalk with adipose tissue

Overweight and obesity are characterized by excessive fat mass accumulation produced when energy intake exceeds energy expenditure. One plausible way to control energy expenditure is to modulate thermogenic pathways in white adipose tissue (WAT) and/or brown adipose tissue (BAT). Among the different environmental factors capable of influencing host metabolism and energy balance, the gut microbiota is now considered a key player. Following pioneering studies showing that mice lacking gut microbes (that is, germ-free mice) or depleted of their gut microbiota (that is, using antibiotics) developed less adipose tissue, numerous studies have investigated the complex interactions existing between gut bacteria, some of their membrane components (that is, lipopolysaccharides), and their metabolites (that is, short-chain fatty acids, endocannabinoids, bile acids, aryl hydrocarbon receptor ligands and tryptophan derivatives) as well as their contribution to the browning and/or beiging of WAT and changes in BAT activity. In this Review, we discuss the general physiology of both WAT and BAT. Subsequently, we introduce how gut bacteria and different microbiota-derived metabolites, their receptors and signalling pathways can regulate the development of adipose tissue and its metabolic capacities. Finally, we describe the key challenges in moving from bench to bedside by presenting specific key examples.

Engrailed: Pathological and physiological effects of a multifunctional developmental gene

Engrailed-1 (EN1) is a developmental gene that encodes En1, a highly conserved transcription factor involved in regionalization during early embryogenesis and in the later maintenance of normal neurons. After birth, EN1 still plays a role in the development and physiology of the body; for example, it exerts a protective effect on midbrain dopaminergic (mDA) neurons, and loss of EN1 causes mDA neurons in the ventral midbrain to gradually die approximately 6 weeks after birth, resulting in motor and nonmotor symptoms similar to those observed in Parkinson's disease. Notably, EN1 has been identified as a possible susceptibility gene for idiopathic Parkinson's disease in humans. EN1 is involved in the processes of wound-healing scar production and tissue and organ fibrosis. Additionally, EN1 can lead to tumorigenesis and thus provides a target for the treatment of some tumors. In this review, we summarize the effects of EN1 on embryonic organ development, describe the consequences of the deletion or overexpression of the EN1 gene, and discuss the pathways in which EN1 is involved. We hope to clarify the role of EN1 as a developmental gene and present potential therapeutic targets for diseases involving the EN1 gene.

Anti-Obesity Effects of GABA in C57BL/6J Mice with High-Fat Diet-Induced Obesity and 3T3-L1 Adipocytes

Obesity is the excessive accumulation of body fat resulting from impairment in energy balance mechanisms. In this study, we aimed to investigate the mechanism whereby GABA (γ-aminobutyric acid) prevents high-fat diet-induced obesity, and whether it induces lipolysis and browning in white adipose tissue (WAT), using high-fat diet (HFD)-fed obese mice and 3T3-L1 adipocytes. We demonstrated that GABA substantially inhibits the body mass gain of mice by suppressing adipogenesis and lipogenesis. Consistent with this result, histological analysis of WAT demonstrated that GABA decreases adipocyte size. Moreover, we show that GABA administration decreases fasting blood glucose and improves serum lipid profiles and hepatic lipogenesis in HFD-fed obese mice. Furthermore, Western blot and immunofluorescence analyses showed that GABA activates protein kinase A (PKA) signaling pathways that increase lipolysis and promote uncoupling protein 1 (UCP1)-mediated WAT browning. Overall, these results suggest that GABA exerts an anti-obesity effect via the regulation of lipid metabolism.

Acetylation and deacetylation of histone in adipocyte differentiation and the potential significance in cancer

Adipocytes are derived from pluripotent mesenchymal stem cells and can develop into several cell types including adipocytes, myocytes, chondrocytes, and osteocytes. Adipocyte differentiation is regulated by a variety of transcription factors and signaling pathways. Various epigenetic factors, particularly histone modifications, play key roles in adipocyte differentiation and have indispensable functions in altering chromatin conformation. Histone acetylases and deacetylases participate in the regulation of protein acetylation, mediate transcriptional and post-translational modifications, and directly acetylate or deacetylate various transcription factors and regulatory proteins. The adipocyte differentiation of stem cells plays a key role in various metabolic diseases. Cancer stem cells(CSCs) play an important function in cancer metastasis, recurrence, and drug resistance, and have the characteristics of stem cells. They are expressed in various cell lineages, including adipocytes. Recent studies have shown that cancer stem cells that undergo epithelial-mesenchymal transformation can undergo adipocytic differentiation, thereby reducing the degree of malignancy. This opens up new possibilities for cancer treatment. This review summarizes the regulation of acetylation during adipocyte differentiation, involving the functions of histone acetylating and deacetylating enzymes as well as non-histone acetylation modifications. Mechanistic studies on adipogenesis and acetylation during the differentiation of cancer cells into a benign cell phenotype may help identify new targets for cancer treatment.

Adipose Tissue Dysfunction Determines Lipotoxicity and Triggers the Metabolic Syndrome: Current Challenges and Clinical Perspectives

The adipose tissue organ is organised as distinct anatomical depots located all along the body axis, and it is constituted of three different types of adipocytes: white, beige and brown, which are integrated with vascular, immune, neural, and extracellular stroma cells. These distinct adipocytes serve different specialised functions. The main function of white adipocytes is to ensure healthy storage of excess nutrients/energy and its rapid mobilisation to supply the demand of energy imposed by physiological cues in other organs, whereas brown and beige adipocytes are designed for heat production through uncoupling lipid oxidation from energy production. The concerted action of the three types of adipocytes/tissues ensures an optimal metabolic status. However, when one or several of these adipose depots become dysfunctional because of sustained lipid/nutrient overload, then insulin resistance and associated metabolic complications ensue. These metabolic alterations close a vicious cycle that negatively affects the adipose tissue functionality and compromises global metabolic homeostasis. Optimising white adipose tissue expandability and ensuring its functional metabolic flexibility and/or promoting brown/beige mediated thermogenic activity are complementary strategies that counteract obesity and its associated lipotoxic metabolic effects. However, the development of these therapeutic approaches requires a deep understanding of adipose tissue in all broad aspects. In this chapter, we will discuss the characteristics of the different adipose tissue depots with respect to origins and precursors recruitment, plasticity, cellular composition, and expandability capacity potential as well as molecular and metabolic characteristic signatures in both physiological and pathophysiological conditions. Current antilipotoxic strategies for future clinical application are also discussed in this chapter.

The Effects of Intermittent Cold Exposure on Adipose Tissue

Intermittent cold exposure (ICE) has garnered increased attention in popular culture, largely for its proposed effects on mood and immune function, but there are also suggestions that the energy-wasting mechanisms associated with thermogenesis may decrease body weight and fat mass. Considering the continued and worsening prevalence of obesity and type II diabetes, any protocol that can reduce body weight and/or improve metabolic health would be a substantial boon. Here, we present a narrative review exploring the research related to ICE and adipose tissue. Any publicly available original research examining the effects of repeated bouts of ICE on adipose-related outcomes was included. While ICE does not consistently lower body weight or fat mass, there does seem to be evidence for ICE as a positive modulator of the metabolic consequences of obesity, such as glucose tolerance and insulin signaling. Further, ICE consistently increases the activity of brown adipose tissue (BAT) and transitions white adipose tissue to a phenotype more in line with BAT. Lastly, the combined effects of ICE and exercise do not seem to provide any additional benefit, at least when exercising during ICE bouts. The majority of the current literature on ICE is based on rodent models where animals are housed in cold rooms, which does not reflect protocols likely to be implemented in humans such as cold water immersion. Future research could specifically characterize ICE via cold water immersion in combination with controlled calorie intake to clearly determine the effects of ICE as it would be implemented in humans looking to lower their body weight via reductions in fat mass.

Loss of Uncoupling Protein 1 Expression in the Subcutaneous Adipose Tissue Predicts Childhood Obesity

Stimulation of thermogenesis by inducing uncoupling protein 1 (UCP1) expression in adipocytes is thought to promote weight loss by increasing energy expenditure, and it is postulated that the human newborn has thermogenic subcutaneous fat depots. However, it remains unclear whether a relevant number of UCP1-expressing (UCP1+) adipocytes exist in the early postnatal life. Here we studied the distribution of UCP1 and the expression of thermogenic genes in the subcutaneous adipose tissues of the human fetus, infant and child. We show that the deep layer of human fetal and neonatal subcutaneous fat, particularly the abdominal wall, is rich in UCP1+ adipocytes. These adipocytes develop in the late third trimester and persist throughout childhood, expressing a panel of genes linked to mitochondrial biogenesis and thermogenesis. During the early childhood adiposity rebound-a critical phase that determines obesity risk later in life-the absence of adipose tissue UCP1 expression in children with normal body mass index (BMI) correlates with an obesity-associated gene expression signature. Finally, UCP1 expression is negatively correlated with BMI z-score and adipocyte size in infants and children. Overall, our results show that the absence of UCP1 expression in adipose tissue is an early indicator of adipose tissue expansion in children.

GCN2 is required to maintain core body temperature in mice during acute cold

Nonshivering thermogenesis in rodents requires macronutrients to fuel the generation of heat during hypothermic conditions. In this study, we examined the role of the nutrient sensing kinase, general control nonderepressible 2 (GCN2) in directing adaptive thermogenesis during acute cold exposure in mice. We hypothesized that GCN2 is required for adaptation to acute cold stress via activation of the integrated stress response (ISR) resulting in liver production of FGF21 and increased amino acid transport to support nonshivering thermogenesis. In alignment with our hypothesis, female and male mice lacking GCN2 failed to adequately increase energy expenditure and veered into torpor. Mice administered a small molecule inhibitor of GCN2 were also profoundly intolerant to acute cold stress. Gcn2 deletion also impeded liver-derived FGF21 but in males only. Within the brown adipose tissue (BAT), acute cold exposure increased ISR activation and its transcriptional execution in males and females. RNA sequencing in BAT identified transcripts that encode actomyosin mechanics and transmembrane transport as requiring GCN2 during cold exposure. These transcripts included class II myosin heavy chain and amino acid transporters, critical for maximal thermogenesis during cold stress. Importantly, Gcn2 deletion corresponded with higher circulating amino acids and lower intracellular amino acids in the BAT during cold stress. In conclusion, we identify a sex-independent role for GCN2 activation to support adaptive thermogenesis via uptake of amino acids into brown adipose.NEW & NOTEWORTHY This paper details the discovery that GCN2 activation is required in both male and female mice to maintain core body temperature during acute cold exposure. The results point to a novel role for GCN2 in supporting adaptive thermogenesis via amino acid transport and actomyosin mechanics in brown adipose tissue.

Genetic or pharmacological GHSR blockade has sexually dimorphic effects in rodents on a high-fat diet

The stomach-derived hormone ghrelin regulates essential physiological functions. The ghrelin receptor (GHSR) has ligand-independent actions, therefore, GHSR gene deletion may be a reasonable approach to investigate the role of this system in feeding behaviors and diet-induced obesity (DIO). Here we investigated the effects of a long-term (12 month) high-fat (HFD) versus regular diet on obesity-related measures in global GHSR-KO and wild type (WT) Wistar male and female rats. Our main findings were that the GHSR gene deletion protects against DIO and decreases food intake during HFD in male but not in female rats. GHSR gene deletion increased thermogenesis and brain glucose uptake in male rats and modified the effects of HFD on brain glucose metabolism in a sex-specific manner, as assessed with small animal positron emission tomography. RNA-sequencing was also used to show that GHSR-KO rats had upregulated expression of genes responsible for fat oxidation in brown adipose tissue. Central administration of a novel GHSR inverse agonist, PF-5190457, attenuated ghrelin-induced food intake, but only in male, not in female mice. HFD-induced binge-like eating was reduced by inverse agonism in both sexes. Our results support GHSR as a promising target for new pharmacotherapies for obesity.

Myoglobin in Brown Adipose Tissue: A Multifaceted Player in Thermogenesis

Brown adipose tissue (BAT) plays an important role in energy homeostasis by generating heat from chemical energy via uncoupled oxidative phosphorylation. Besides its high mitochondrial content and its exclusive expression of the uncoupling protein 1, another key feature of BAT is the high expression of myoglobin (MB), a heme-containing protein that typically binds oxygen, thereby facilitating the diffusion of the gas from cell membranes to mitochondria of muscle cells. In addition, MB also modulates nitric oxide (NO•) pools and can bind C16 and C18 fatty acids, which indicates a role in lipid metabolism. Recent studies in humans and mice implicated MB present in BAT in the regulation of lipid droplet morphology and fatty acid shuttling and composition, as well as mitochondrial oxidative metabolism. These functions suggest that MB plays an essential role in BAT energy metabolism and thermogenesis. In this review, we will discuss in detail the possible physiological roles played by MB in BAT thermogenesis along with the potential underlying molecular mechanisms and focus on the question of how BAT-MB expression is regulated and, in turn, how this globin regulates mitochondrial, lipid, and NO• metabolism. Finally, we present potential MB-mediated approaches to augment energy metabolism, which ultimately could help tackle different metabolic disorders.

A single-cell CRISPRi platform for characterizing candidate genes relevant to metabolic disorders in human adipocytes

CROP-Seq combines gene silencing using CRISPR interference with single-cell RNA sequencing. Here, we applied CROP-Seq to study adipogenesis and adipocyte biology. Human preadipocyte SGBS cell line expressing KRAB-dCas9 was transduced with a sgRNA library. Following selection, individual cells were captured using microfluidics at different timepoints during adipogenesis. Bioinformatic analysis of transcriptomic data was used to determine the knockdown effects, the dysregulated pathways, and to predict cellular phenotypes. Single-cell transcriptomes recapitulated adipogenesis states. For all targets, over 400 differentially expressed genes were identified at least at one timepoint. As a validation of our approach, the knockdown of PPARG and CEBPB (which encode key proadipogenic transcription factors) resulted in the inhibition of adipogenesis. Gene set enrichment analysis generated hypotheses regarding the molecular function of novel genes. MAFF knockdown led to downregulation of transcriptional response to proinflammatory cytokine TNF-α in preadipocytes and to decreased CXCL-16 and IL-6 secretion. TIPARP knockdown resulted in increased expression of adipogenesis markers. In summary, this powerful, hypothesis-free tool can identify novel regulators of adipogenesis, preadipocyte, and adipocyte function associated with metabolic disease.NEW & NOTEWORTHY Genomics efforts led to the identification of many genomic loci that are associated with metabolic traits, many of which are tied to adipose tissue function. However, determination of the causal genes, and their mechanism of action in metabolism, is a time-consuming process. Here, we use an approach to determine the transcriptional outcome of candidate gene knockdown for multiple genes at the same time in a human cell model of adipogenesis.

Peroxisome proliferator-activated receptors as targets to treat metabolic diseases: Focus on the adipose tissue, liver, and pancreas

The world is experiencing reflections of the intersection of two pandemics: Obesity and coronavirus disease 2019. The prevalence of obesity has tripled since 1975 worldwide, representing substantial public health costs due to its comorbidities. The adipose tissue is the initial site of obesity impairments. During excessive energy intake, it undergoes hyperplasia and hypertrophy until overt inflammation and insulin resistance turn adipocytes into dysfunctional cells that send lipotoxic signals to other organs. The pancreas is one of the organs most affected by obesity. Once lipotoxicity becomes chronic, there is an increase in insulin secretion by pancreatic beta cells, a surrogate for type 2 diabetes mellitus (T2DM). These alterations threaten the survival of the pancreatic islets, which tend to become dysfunctional, reaching exhaustion in the long term. As for the liver, lipotoxicity favors lipogenesis and impairs beta-oxidation, resulting in hepatic steatosis. This silent disease affects around 30% of the worldwide population and can evolve into end-stage liver disease. Although therapy for hepatic steatosis remains to be defined, peroxisome proliferator-activated receptors (PPARs) activation copes with T2DM management. Peroxisome PPARs are transcription factors found at the intersection of several metabolic pathways, leading to insulin resistance relief, improved thermogenesis, and expressive hepatic steatosis mitigation by increasing mitochondrial beta-oxidation. This review aimed to update the potential of PPAR agonists as targets to treat metabolic diseases, focusing on adipose tissue plasticity and hepatic and pancreatic remodeling.

The role of long non-coding RNAs in the development of adipose cells

In recent times, the rising prevalence of obesity and its associated comorbidities have had a severe impact on human health and social progress. Therefore, scientists are delving deeper into the pathogenesis of obesity, exploring the role of non-coding RNAs. Long non-coding RNAs (lncRNAs), once regarded as mere "noise" during genome transcription, have now been confirmed through numerous studies to regulate gene expression and contribute to the occurrence and progression of several human diseases. LncRNAs can interact with protein, DNA, and RNA, respectively, and participate in regulating gene expression by modulating the levels of visible modification, transcription, post-transcription, and biological environment. Increasingly, researchers have established the involvement of lncRNAs in regulating adipogenesis, development, and energy metabolism of adipose tissue (white and brown fat). In this article, we present a literature review of the role of lncRNAs in the development of adipose cells.

Transcriptome analysis of perirenal fat from Spanish Assaf suckling lamb carcasses showing different levels of kidney knob and channel fat

Introduction

Suckling lamb meat is highly appreciated in European Mediterranean countries because of its mild flavor and soft texture. In suckling lamb carcasses, perirenal and pelvic fat depots account for a large fraction of carcass fat accumulation, and their proportions are used as an indicator of carcass quality.

Material and Methods

This study aimed to characterize the genetic mechanisms that regulate fat deposition in suckling lambs by evaluating the transcriptomic differences between Spanish Assaf lambs with significantly different proportions of kidney knob and channel fat (KKCF) depots in their carcasses (4 High-KKCF lambs vs. 4 Low-KKCF lambs).

Results

The analyzed fat tissue showed overall dominant expression of white adipose tissue gene markers, although due to the young age of the animals (17-36 days), the expression of some brown adipose tissue gene markers (e.g., UCP1, CIDEA) was still identified. The transcriptomic comparison between the High-KKCF and Low-KKCF groups revealed a total of 80 differentially expressed genes (DEGs). The enrichment analysis of the 49 DEGs with increased expression levels in the Low-KKCF lambs identified significant terms linked to the biosynthesis of lipids and thermogenesis, which may be related to the higher expression of the UCP1 gene in this group. In contrast, the enrichment analysis of the 31 DEGs with increased expression in the High-KKCF lambs highlighted angiogenesis as a key biological process supported by the higher expression of some genes, such as VEGF-A and THBS1, which encode a major angiogenic factor and a large adhesive extracellular matrix glycoprotein, respectively.

Discussion

The increased expression of sestrins, which are negative regulators of the mTOR complex, suggests that the preadipocyte differentiation stage is being inhibited in the High-KKCF group in favor of adipose tissue expansion, in which vasculogenesis is an essential process. All of these results suggest that the fat depots of the High-KKCF animals are in a later stage of development than those of the Low-KKCF lambs. Further genomic studies based on larger sample sizes and complementary analyses, such as the identification of polymorphisms in the DEGs, should be designed to confirm these results and achieve a deeper understanding of the genetic mechanisms underlying fat deposition in suckling lambs.

Characteristic and fate determination of adipose precursors during adipose tissue remodeling

Adipose tissues are essential for actively regulating systemic energy balance, glucose homeostasis, immune responses, reproduction, and longevity. Adipocytes maintain dynamic metabolic needs and possess heterogeneity in energy storage and supply. Overexpansion of adipose tissue, especially the visceral type, is a high risk for diabetes and other metabolic diseases. Changes in adipocytes, hypertrophy or hyperplasia, contribute to the remodeling of obese adipose tissues, accompanied by abundant immune cell accumulation, decreased angiogenesis, and aberrant extracellular matrix deposition. The process and mechanism of adipogenesis are well known, however, adipose precursors and their fate decision are only being defined with recent information available to decipher how adipose tissues generate, maintain, and remodel. Here, we discuss the key findings that identify adipose precursors phenotypically, with special emphasis on the intrinsic and extrinsic signals in instructing and regulating the fate of adipose precursors under pathophysiological conditions. We hope that the information in this review lead to novel therapeutic strategies to combat obesity and related metabolic diseases.

Brown adipose tissue transcriptome unveils an important role of the Beta-alanine/alamandine receptor, MrgD, in metabolism

Alamandine is a recently described heptapeptide component of the renin-angiotensin system (RAS), and its effects are mediated by the receptor Mas-related G protein-coupled receptor D (MrgD) RAS represents an important link between obesity and its consequences by directly modulating the thermogenesis and brown adipose tissue (BAT) function. The alamandine/MrgD metabolic effects and signaling remain unexplored. In this context, the main goal of the present study was to assess the metabolic consequences of MrgD genetic ablation in C57BL6/J mice by evaluating brown adipose tissue RNA sequencing. The main results showed that MrgD-KO mice have diminished brown adipose tissue and that a high-glucose diet (HG) decreased both circulating alamandine levels and MrgD expression in BAT from wild-type mice (WT). BAT transcriptome reveals that MrgD-KO HG mice regulated 45 genes, while WT HG mice regulated 1,148 genes. MrgD-KO mice fed a standard diet (ST) compared with WT ST mice regulated 476 genes, of which 445 genes were downregulated. BAT uses the MrgD receptor to display a normal pattern of gene expression and to respond, like WT mice, to an HG diet. In conclusion, the MrgD signaling is important for the metabolic regulation and manutention of BAT functionality.

Thermogenic adipose tissue in energy regulation and metabolic health

The ability to generate thermogenic fat could be a targeted therapy to thwart obesity and improve metabolic health. Brown and beige adipocytes are two types of thermogenic fat cells that regulate energy balance. Both adipocytes share common morphological, biochemical, and thermogenic properties. Yet, recent evidence suggests unique features exist between brown and beige adipocytes, such as their cellular origin and thermogenic regulatory processes. Beige adipocytes also appear highly plastic, responding to environmental stimuli and interconverting between beige and white adipocyte states. Additionally, beige adipocytes appear to be metabolically heterogenic and have substrate specificity. Nevertheless, obese and aged individuals cannot develop beige adipocytes in response to thermogenic fat-inducers, creating a key clinical hurdle to their therapeutic promise. Thus, elucidating the underlying developmental, molecular, and functional mechanisms that govern thermogenic fat cells will improve our understanding of systemic energy regulation and strive for new targeted therapies to generate thermogenic fat. This review will examine the recent advances in thermogenic fat biogenesis, molecular regulation, and the potential mechanisms for their failure.

Autophagy-mediated NCOR1 degradation is required for brown fat maturation and thermogenesis

Brown adipose tissue (BAT) thermogenesis affects energy balance, and thereby it has the potential to induce weight loss and to prevent obesity. Here, we document a macroautophagic/autophagic-dependent mechanism of peroxisome proliferator-activated receptor gamma (PPARG) activity regulation that induces brown adipose differentiation and thermogenesis and that is mediated by TP53INP2. Disruption of TP53INP2-dependent autophagy reduced brown adipogenesis in cultured cells. In vivo specific-tp53inp2 ablation in brown precursor cells or in adult mice decreased the expression of thermogenic and mature adipocyte genes in BAT. As a result, TP53INP2-deficient mice had reduced UCP1 content in BAT and impaired maximal thermogenic capacity, leading to lipid accumulation and to positive energy balance. Mechanistically, TP53INP2 stimulates PPARG activity and adipogenesis in brown adipose cells by promoting the autophagic degradation of NCOR1, a PPARG co-repressor. Moreover, the modulation of TP53INP2 expression in BAT and in human brown adipocytes suggests that this protein increases PPARG activity during metabolic activation of brown fat. In all, we have identified a novel molecular explanation for the contribution of autophagy to BAT energy metabolism that could facilitate the design of therapeutic strategies against obesity and its metabolic complications.

Transcriptomics Dissection of Calorie Restriction and Exercise Training in Brown Adipose Tissue and Skeletal Muscle

Calorie restriction (CR) and exercise training (EX) are two critical lifestyle interventions for the prevention and treatment of metabolic diseases, such as obesity and diabetes. Brown adipose tissue (BAT) and skeletal muscle are two important organs for the generation of heat. Here, we undertook detailed transcriptional profiling of these two thermogenic tissues from mice treated subjected to CR and/or EX. We found transcriptional reprogramming of BAT and skeletal muscle as a result of CR but little from EX. Consistent with this, CR induced alterations in the expression of genes encoding adipokines and myokines in BAT and skeletal muscle, respectively. Deconvolution analysis showed differences in the subpopulations of myogenic cells, mesothelial cells and endogenic cells in BAT and in the subpopulations of satellite cells, immune cells and endothelial cells in skeletal muscle as a result of CR or EX. NicheNet analysis, exploring potential inter-organ communication, indicated that BAT and skeletal muscle could mutually regulate their fatty acid metabolism and thermogenesis through ligands and receptors. These data comprise an extensive resource for the study of thermogenic tissue molecular responses to CR and/or EX in a healthy state.

circINSR Inhibits Adipogenic Differentiation of Adipose-Derived Stromal Vascular Fractions through the miR-152/MEOX2 Axis in Sheep

Adipose tissue plays a crucial role in energy metabolism. Several studies have shown that circular RNA (circRNA) is involved in the regulation of fat development and lipid metabolism. However, little is known about their involvement in the adipogenic differentiation of ovine stromal vascular fractions (SVFs). Here, based on previous sequencing data and bioinformatics analysis, a novel circINSR was identified in sheep, which acts as a sponge to promote miR-152 in inhibiting the adipogenic differentiation of ovine SVFs. The interactions between circINSR and miR-152 were examined using bioinformatics, luciferase assays, and RNA immunoprecipitation. Of note, we found that circINSR was involved in adipogenic differentiation via the miR-152/mesenchyme homeobox 2 (MEOX2) pathway. MEOX2 inhibited adipogenic differentiation of ovine SVFs and miR-152 inhibited the expression of MEOX2. In other words, circINSR directly isolates miR-152 in the cytoplasm and inhibits its ability to promote adipogenic differentiation of ovine SVFs. In summary, this study revealed the role of circINSR in the adipogenic differentiation of ovine SVFs and its regulatory mechanisms, providing a reference for further interpretation of the development of ovine fat and its regulatory mechanisms.

Protein kinase D1 (Prkd1) deletion in brown adipose tissue leads to altered myogenic gene expression after cold exposure, while thermogenesis remains intact

Brown adipose tissue (BAT) has in recent times been rediscovered in adult humans, and together with work from preclinical models, has shown to have the potential of providing a variety of positive metabolic benefits. These include lower plasma glucose, improved insulin sensitivity, and reduced susceptibility to obesity and its comorbidities. As such, its continued study could offer insights to therapeutically modulate this tissue to improve metabolic health. It has been reported that adipose-specific deletion of the gene for protein kinase D1 (Prkd1) in mice enhances mitochondrial respiration and improves whole-body glucose homeostasis. We sought to determine whether these effects were mediated specifically through brown adipocytes using a Prkd1 brown adipose tissue (BAT) Ucp1-Cre-specific knockout mouse model, Prkd1BKO . We unexpectedly observed that upon both cold exposure and β3 -AR agonist administration, Prkd1 loss in BAT did not alter canonical thermogenic gene expression or adipocyte morphology. We took an unbiased approach to assess whether other signaling pathways were affected. RNA from cold-exposed mice was subjected to RNA-Seq analysis. These studies revealed that myogenic gene expression is altered in Prkd1BKO BAT after both acute and extended cold exposure. Given that brown adipocytes and skeletal myocytes share a common precursor cell lineage expressing myogenic factor 5 (Myf5), these data suggest that loss of Prkd1 in BAT may alter the biology of mature brown adipocytes and preadipocytes in this depot. The data presented herein clarify the role of Prkd1 in BAT thermogenesis and present new avenues for the further study of Prkd1 function in BAT.

CREG1 stimulates AMPK phosphorylation and glucose uptake in skeletal muscle cells

The cellular repressor of adenovirus early region 1A-stimulated gene 1 (CREG1) is a secreted glycoprotein involved in cell differentiation and energy metabolism. It also binds to insulin-like growth factor 2 receptor (IGF2R), a protein implicated in muscle regeneration. However, whether CREG1 regulates the regeneration and metabolism of skeletal muscles via IGF2R remains unclear. This study investigates the role of CREG1 in skeletal muscle regeneration and glucose uptake in C2C12 myotubes and a cardiotoxin (CTX)-induced mouse skeletal muscle regeneration model. CTX-treated skeletal muscle showed significantly higher levels of IGF2R, CREG1, phospho-AMPKα Thr¹⁷², and GLUT4 proteins. Similarly, treatment of myotubes with CREG1 also stimulated AMPKα phosphorylation and GLUT4 expression. CREG1-induced AMPKα phosphorylation and 2DG uptake in myotubes were suppressed by IGF2R knockdown and Compound C, an AMPK inhibitor. These results suggest that CREG1 stimulates glucose uptake in skeletal muscles partially through AMPK activation. Hence, CREG1 plays an essential role in muscle regeneration by affecting glucose metabolism in skeletal muscles.

Dichotomous Role of Humic Substances in Modulating Transformation of Antibiotic Resistance Genes in Mineral Systems

Widespread antibiotic resistance genes (ARGs) have emerged as a focus of attention for public health. Transformation is essential for ARGs dissemination in soils and associated environments; however, the mechanisms of how soil components contribute to the transformation of ARGs remain elusive. Here we demonstrate that three representative mineral-humic acid (HA) composites exert contrasting influence on the transformation of plasmid-borne ARGs in Bacillus subtilis. Mineral surface-bound HA facilitated transformation in kaolinite and montmorillonite systems, while an inhibitory effect of HA was observed for goethite. The elevated transformation by HA-coated kaolinite was mainly attributed to the enhanced activity of competence-stimulating factor (CSF), while increased transformation by montmorillonite-HA composites was assigned to the weakened adsorption affinity of DNA and enhanced gene expression induced by flagella-driven cell motility. In goethite system, HA played an overriding role in suppressing transformation via alleviation of cell membrane damage. The results obtained offer insights into the divergent mechanisms of humic substances in modulating bacterial transformation by soil minerals. Our findings would help for a better understanding on the fate of ARGs in soil systems and provide potentials for the utilization of soil components, particularly organic matter, to mitigate the spread of ARGs in a range of settings.

Brown adipose tissue and alzheimer's disease

Alzheimer's disease (AD), the most common type of senile dementia, is a chronic neurodegenerative disease characterized by cognitive dysfunction and behavioral disability. The two histopathological hallmarks in this disease are the extraneuronal accumulation of amyloid-β (Aβ) and the intraneuronal deposition of neurofibrillary tangles (NFTs). Despite this, central and peripheral metabolic dysfunction, such as abnormal brain signaling, insulin resistance, inflammation, and impaired glucose utilization, have been indicated to be correlated with AD. There is solid evidence that the age-associated thermoregulatory deficit induces diverse metabolic changes associated with AD development. Brown adipose tissue (BAT) has been known as a thermoregulatory organ particularly vital during infancy. However, in recent years, BAT has been accepted as an endocrine organ, being involved in various functions that prevent AD, such as regulating energy metabolism, secreting hormones, improving insulin sensitivity, and increasing glucose utilization in adult humans. This review focuses on the mechanisms of BAT activation and the effect of aging on BAT production and signaling. Specifically, the evidence demonstrating the effect of BAT on pathological mechanisms influencing the development of AD, including insulin pathway, thermoregulation, and other hormonal pathways, are reviewed in this article.

Ketogenic Diet Increases Serum and White Adipose Tissue SIRT1 Expression in Mice

Overnutrition and its sequelae have become a global concern due to the increasing incidence of obesity and insulin resistance. A ketogenic diet (KD) is widely used as a dietary treatment for metabolic disorders. Sirtuin1 (SIRT1), a metabolic sensor which regulates fat homeostasis, is modulated by dietary interventions. However, the influence of nutritional ketosis on SIRT1 is still debated. We examined the effect of KD on adipose tissue, liver, and serum levels of SIRT1 in mice. Adult C57BL/6J male mice were randomly assigned to two isocaloric dietary groups and fed with either high-fat KD or normal chow (NC) for 4 weeks. Serum SIRT1, beta-hydroxybutyrate (βHB), glucose, and triglyceride levels, as well as SIRT1 expression in visceral (VAT), subcutaneous (SAT), and brown (BAT) adipose tissues, and in the liver, were measured. KD-fed mice showed an increase in serum βHB in parallel with serum SIRT1 (r = 0.732, p = 0.0156), and increased SIRT1 protein expression in SAT and VAT. SIRT1 levels remained unchanged in BAT and in the liver, which developed steatosis. Normal glycemia and triglycerides were observed. Under a KD, serum and white fat phenotypes show higher SIRT1, suggesting that one of the molecular mechanisms underlying a KD's potential benefits on metabolic health involves a synergistic interaction with SIRT1.

Glucose supplementation improves intestinal amino acid transport and muscle amino acid pool in pigs during chronic cold exposure

Mammals in northern regions chronically suffer from low temperatures during autumn-winter seasons. The aim of this study was to investigate the response of intestinal amino acid transport and the amino acid pool in muscle to chronic cold exposure via Min pig models (cold adaptation) and Yorkshire pig models (non-cold adaptation). Furthermore, this study explored the beneficial effects of glucose supplementation on small intestinal amino acid transport and amino acid pool in muscle of cold-exposed Yorkshire pigs. Min pigs (Exp. 1) and Yorkshire pigs (Exp. 2) were divided into a control group (17 °C, n = 6) and chronic cold exposure group (7 °C, n = 6), respectively. Twelve Yorkshire pigs (Exp. 3) were divided into a cold control group and cold glucose supplementation group (8 °C). The results showed that chronic cold exposure inhibited peptide transporter protein 1 (PepT1) and excitatory amino acid transporter 3 (EAAT3) expression in ileal mucosa and cationic amino acid transporter-1 (CAT-1) in the jejunal mucosa of Yorkshire pigs (P < 0.05). In contrast, CAT-1, PepT1 and EAAT3 expression was enhanced in the duodenal mucosa of Min pigs (P < 0.05). Branched amino acids (BCAA) in the muscle of Yorkshire pigs were consumed by chronic cold exposure, accompanied by increased muscle RING-finger protein-1 (MuRF1) and muscle atrophy F-box (atrogin-1) expression (P < 0.05). More importantly, reduced concentrations of dystrophin were detected in the muscle of Yorkshire pigs (P < 0.05). However, glycine concentration in the muscle of Min pigs was raised (P < 0.05). In the absence of interaction between chronic cold exposure and glucose supplementation, glucose supplementation improved CAT-1 expression in the jejunal mucosa and PepT1 expression in the ileal mucosa of cold-exposed Yorkshire pigs (P < 0.05). It also improved BCAA and inhibited MuRF1 and atrogin-1 expression in muscle (P < 0.05). Moreover, dystrophin concentration was improved by glucose supplementation (P < 0.05). In summary, chronic cold exposure inhibits amino acid absorption in the small intestine, depletes BCAA and promotes protein degradation in muscle. Glucose supplementation ameliorates the negative effects of chronic cold exposure on amino acid transport and the amino acid pool in muscle.

Chronic Intermittent Hypoxia during Sleep Causes Browning of Interscapular Adipose Tissue Accompanied by Local Insulin Resistance in Mice

Obstructive sleep apnea (OSA) is a highly prevalent condition, characterized by intermittent hypoxia (IH), sleep disruption, and altered autonomic nervous system function. OSA has been independently associated with dyslipidemia, insulin resistance, and metabolic syndrome. Brown adipose tissue (BAT) has been suggested as a modulator of systemic glucose tolerance through adaptive thermogenesis. Reductions in BAT mass have been associated with obesity and metabolic syndrome. No studies have systematically characterized the effects of chronic IH on BAT. Thus, we aimed to delineate IH effects on BAT and concomitant metabolic changes. C57BL/6J 8-week-old male mice were randomly assigned to IH during sleep (alternating 90 s cycles of 6.5% F_IO₂ followed by 21% F_IO₂) or normoxia (room air, RA) for 10 weeks. Mice were subjected to glucose tolerance testing and ¹⁸F-FDG PET-MRI towards the end of the exposures followed by BAT tissues analyses for morphological and global transcriptomic changes. Animals exposed to IH were glucose intolerant despite lower total body weight and adiposity. BAT tissues in IH-exposed mice demonstrated characteristic changes associated with "browning"-smaller lipids, increased vascularity, and a trend towards higher protein levels of UCP1. Conversely, mitochondrial DNA content and protein levels of respiratory chain complex III were reduced. Pro-inflammatory macrophages were more abundant in IH-exposed BAT. Transcriptomic analysis revealed increases in fatty acid oxidation and oxidative stress pathways in IH-exposed BAT, along with a reduction in pathways related to myogenesis, hypoxia, and IL-4 anti-inflammatory response. Functionally, IH-exposed BAT demonstrated reduced absorption of glucose on PET scans and reduced phosphorylation of AKT in response to insulin. Current studies provide initial evidence for the presence of a maladaptive response of interscapular BAT in response to chronic IH mimicking OSA, resulting in a paradoxical divergence, namely, BAT browning but tissue-specific and systemic insulin resistance. We postulate that oxidative stress, mitochondrial dysfunction, and inflammation may underlie these dichotomous outcomes in BAT.

Ciliary control of adipocyte progenitor cell fate regulates energy storage

The primary cilium is a cellular sensory organelle found in most cells in our body. This includes adipocyte progenitor cells in our adipose tissue, a complex organ involved in energy storage, endocrine signaling, and thermogenesis. Numerous studies have shown that the primary cilium plays a critical role in directing the cell fate of adipocyte progenitor cells in multiple adipose tissue types. Accordingly, diseases with dysfunctional cilia called ciliopathies have a broad range of clinical manifestations, including obesity and diabetes. This review summarizes our current understanding of how the primary cilium regulates adipocyte progenitor cell fate in multiple contexts and illustrates the importance of the primary cilium in regulating energy storage and adipose tissue function.

Myoglobin-mediated lipid shuttling increases adrenergic activation of brown and white adipocyte metabolism and is as a marker of thermogenic adipocytes in humans

BACKGROUND

Recruitment and activation of brown adipose tissue (BAT) results in increased energy expenditure (EE) via thermogenesis and represents an intriguing therapeutic approach to combat obesity and treat associated diseases. Thermogenesis requires an increased and efficient supply of energy substrates and oxygen to the BAT. The hemoprotein myoglobin (MB) is primarily expressed in heart and skeletal muscle fibres, where it facilitates oxygen storage and flux to the mitochondria during exercise. In the last years, further contributions of MB have been assigned to the scavenging of reactive oxygen species (ROS), the regulation of cellular nitric oxide (NO) levels and also lipid binding. There is a substantial expression of MB in BAT, which is induced during brown adipocyte differentiation and BAT activation. This suggests MB as a previously unrecognized player in BAT contributing to thermogenesis.

METHODS AND RESULTS

This study analyzed the consequences of MB expression in BAT on mitochondrial function and thermogenesis in vitro and in vivo. Using MB overexpressing, knockdown or knockout adipocytes, we show that expression levels of MB control brown adipocyte mitochondrial respiratory capacity and acute response to adrenergic stimulation, signalling and lipolysis. Overexpression in white adipocytes also increases their metabolic activity. Mutation of lipid interacting residues in MB abolished these beneficial effects of MB. In vivo, whole-body MB knockout resulted in impaired thermoregulation and cold- as well as drug-induced BAT activation in mice. In humans, MB is differentially expressed in subcutaneous (SC) and visceral (VIS) adipose tissue (AT) depots, differentially regulated by the state of obesity and higher expressed in AT samples that exhibit higher thermogenic potential.

CONCLUSIONS

These data demonstrate for the first time a functional relevance of MBs lipid binding properties and establish MB as an important regulatory element of thermogenic capacity in brown and likely beige adipocytes.

Identification and characterization of novel abdominal and pelvic brown adipose depots in mice

Brown adipose tissue (BAT) generates heat through non-shivering thermogenesis, and increasing BAT amounts or activity could facilitate obesity treatment and provide metabolic benefits. In mice, BAT has been reported in perirenal, thoracic and cranial sites. Here, we describe new pelvic and lower abdominal BAT depots located around the urethra, internal reproductive and urinary tract organs and major lower pelvic blood vessels, as well as between adjacent muscles where the upper hind leg meets the abdominal cavity. Immunohistochemical, western blot and PCR analyses revealed that these tissues expressed BAT markers such as uncoupling protein 1 (UCP1) and CIDEA, but not white adipose markers, and β3-adrenergic stimulation increased UCP1 amounts, a classic characteristic of BAT tissue. The newly identified BAT stores contained extensive sympathetic innervation with high mitochondrial density and multilocular lipid droplets similar to interscapular BAT. BAT repositories were present and functional neonatally, and showed developmental changes between the neonatal and adult periods. In summary, several new depots showing classical BAT characteristics are reported and characterized in the lower abdominal/pelvic region of mice. These BAT stores are likely significant metabolic regulators in the mouse and some data suggests that similar BAT depots may also exist in humans.

Brown adipose tissue as an endocrine organ: updates on the emerging role of batokines

Brown adipose tissue (BAT) remains active in adults, oxidizing fatty acids or glucose and releasing energy in the form of heat. Brown adipocytes and enhanced thermogenesis are targets for treating obesity and its comorbidities. BAT shows high synthesis activity and secretes several signaling molecules. The brown adipokines, or batokines, take action in an autocrine, paracrine, and endocrine manner. Batokines have a role in the homeostasis of the cardiovascular system, central nervous system, white adipose tissue, liver, and skeletal muscle and exert beneficial effects on BAT. The systemic function of batokines gives BAT an endocrine organ profile. Besides, the batokines Fibroblast Growth Factor-21, Vascular Endothelial Growth Factor A, Bone Morphogenetic Protein 8, Neuregulin 4, Myostatin, and Interleukin-6 emerge as targets to treat obesity and its comorbidities, deserving attention. This review outlines the role of six emerging batokines on BAT and their cross-talk with other organs, focusing on their physiological significance and diet-induced changes.

Immunoglobulin Superfamily Containing Leucine-Rich Repeat (Islr) Participates in IL-6-Mediated Crosstalk between Muscle and Brown Adipose Tissue to Regulate Energy Homeostasis

Brown adipose tissue (BAT) is functionally linked to skeletal muscle because both tissues originate from a common progenitor cell, but the precise mechanism controlling muscle-to-brown-fat communication is insufficiently understood. This report demonstrates that the immunoglobulin superfamily containing leucine-rich repeat (Islr), a marker of mesenchymal stromal/stem cells, is critical for the control of BAT mitochondrial function and whole-body energy homeostasis. The mice loss of Islr in BAT after cardiotoxin injury resulted in improved mitochondrial function, increased energy expenditure, and enhanced thermogenesis. Importantly, it was found that interleukin-6 (IL-6), as a myokine, participates in this process. Mechanistically, Islr interacts with NADH: Ubiquinone Oxidoreductase Core Subunit S2 (Ndufs2) to regulate IL-6 signaling; consequently, Islr functions as a brake that prevents IL-6 from promoting BAT activity. Together, these findings reveal a previously unrecognized mechanism for muscle-BAT cross talk driven by Islr, Ndufs2, and IL-6 to regulate energy homeostasis, which may be used as a potential therapeutic target in obesity.

Effect of Acute Cold Exposure on Energy Metabolism and Activity of Brown Adipose Tissue in Humans: A Systematic Review and Meta-Analysis

Background: The benefit of cold exposure for humans against obesity has brought the energy metabolism and activity of brown adipose tissue (BAT) induced by cold into focus. But the results are inconsistent. This review is aimed to systematically explore the effect of cold exposure on the activity of BAT and energy metabolism in humans.

Methods: We searched relevant papers that were published from 1990 to 2021 and were cited in PubMed Central, Web of science, Embase and Cochrane Library databases to conduct this systematic review and meta-analysis. Energy metabolism, BAT volume, BAT activity and non-esterified fatty acids (NEFA) data reported in eligible researches were extracted. Meta-analysis was applied to combine the mean difference or standard mean difference with their 95% confidence intervals (95%CI). RevMan 5.3 software was used for meta-analysis and evaluating the risk of bias. Stata 16.0 was used for evaluating the publication bias.

Results: Ten randomized controlled trials were included in meta-analysis. Compared with human exposed in room temperature at 24°C, the energy expenditure (EE) was increased after acute cold exposure at 16∼19°C (Z = 7.58, p < 0.05, mean different = 188.43kal/d, 95% CI = 139.73–237.13); BAT volume (Z = 2.62, p < 0.05; standard mean different = 0.41, 95% CI = 0.10–0.73); BAT activity (Z = 2.05, p = 0.04, standard mean difference = 1.61, 95% CI = 0.07–3.14) and the intake of BAT NEFA (Z = 2.85, p < 0.05; standard mean different = 0.53, 95% CI = 0.17–0.90) also increased.

Conclusion: Acute cold exposure could improve the energy expenditure and BAT activity in adults, which is beneficial for human against obesity.

Influence of adipose tissue immune dysfunction on childhood obesity

In recent decades, a dramatic rise has been observed in the prevalence of obesity in childhood and adolescence, along with an increase in fetal microsomia rates. The increased risk of obesity during this key period in development negatively affects the health of the individual later in life. Immune cells residing and recruited to white adipose tissue have been highlighted as important factors contributing to the pathogenesis of childhood obesity. Immune dysfunction in the context of obesity begins early in childhood, which is different from the pathological characteristics and influencing factors of adipose immunity in adults. Here, we explore the current understanding of the roles of childhood and early life events that result in high risks for obesity by influencing adipose tissue immune dysfunction under the pathological condition of obesity. Such knowledge will help in determining the mechanisms of childhood and early life obesity in efforts to ameliorate chronic inflammation-related metabolic diseases.

Brown adipose tissue involution associated with progressive restriction in progenitor competence

Human brown adipose tissue (BAT) undergoes progressive involution. This involution process is not recapitulated in rodents, and the underlying mechanisms are poorly understood. Here we show that the interscapular BAT (iBAT) of rabbits whitens rapidly during early adulthood. The transcriptomic remodeling and identity switch of mature adipocytes are accompanied by loss of brown adipogenic competence of progenitors. Single-cell RNA sequencing reveals that rabbit and human iBAT progenitors highly express the FSTL1 gene. When iBAT involutes in rabbits, adipocyte progenitors reduce FSTL1 expression and are refractory to brown adipogenic recruitment. Conversely, FSTL1 is constitutively expressed in mouse iBAT to sustain WNT signaling and prevent involution. Progenitor incompetence and iBAT paucity can be induced in mice by genetic deletion of the Fstl1 gene or ablation of Fstl1⁺ progenitors. Our results highlight the hierarchy and dynamics of the BAT progenitor compartment and implicate the functional incompetence of FSTL1-expressing progenitors in BAT involution.

Deconstructing Adipose Tissue Heterogeneity One Cell at a Time

As a central coordinator of physiologic metabolism, adipose tissue has long been appreciated as a highly plastic organ that dynamically responds to environmental cues. Once thought of as a homogenous storage depot, recent advances have enabled deep characterizations of the underlying structure and composition of adipose tissue depots. As the obesity and metabolic disease epidemics continue to accelerate due to modern lifestyles and an aging population, elucidation of the underlying mechanisms that control adipose and systemic homeostasis are of critical importance. Within the past decade, the emergence of deep cell profiling at tissue- and, recently, single-cell level has furthered our understanding of the complex dynamics that contribute to tissue function and their implications in disease development. Although many paradigm-shifting findings may lie ahead, profound advances have been made to forward our understanding of the adipose tissue niche in both health and disease. Now widely accepted as a highly heterogenous organ with major roles in metabolic homeostasis, endocrine signaling, and immune function, the study of adipose tissue dynamics has reached a new frontier. In this review, we will provide a synthesis of the latest advances in adipose tissue biology made possible by the use of single-cell technologies, the impact of epigenetic mechanisms on adipose function, and suggest what next steps will further our understanding of the role that adipose tissue plays in systemic physiology.

Versatile role of sirtuins in metabolic disorders: From modulation of mitochondrial function to therapeutic interventions

Sirtuins (SIRT1-7) are distinct histone deacetylases (HDACs) whose activity is determined by cellular metabolic status andnicotinamide adenine dinucleotide (NAD⁺ ) levels. HDACs of class III are the members of the SIRT's protein family. SIRTs are the enzymes that modulate mitochondrial activity and energy metabolism. SIRTs have been linked to a number of clinical and physiological operations, such as energy responses to low-calorie availability, aging, stress resistance, inflammation, and apoptosis. Mammalian SIRT2 orthologs have been identified as SIRT1-7 that are found in several subcellular sections, including the cytoplasm (SIRT1, 2), mitochondrial matrix (SIRT3, 4, 5), and the core (SIRT1, 2, 6, 7). For their deacetylase or ADP-ribosyl transferase action, all SIRTs require NAD⁺ and are linked to cellular energy levels. Evolutionarily, SIRT1 is related to yeast's SIRT2 as well as received primary attention in the circulatory system. An endogenous protein, SIRT1 is involved in the development of heart failure and plays a key role in cell death and survival. SIRT2 downregulation protects against ischemic-reperfusion damage. Increase in human longevity is caused by an increase in SIRT3 expression. Cardiomyocytes are also protected by SIRT3 from oxidative damage and aging, as well as suppressing cardiac hypertrophy. SIRT4 and SIRT5 perform their roles in the heart. SIRT6 has also been linked to a reduction in heart hypertrophy. SIRT7 is known to be involved in the regulation of stress responses and apoptosis in the heart.

Identification of Biochemical Differences in White and Brown Adipocytes Using FTIR Spectroscopy

This study was conducted to investigate the developmental characteristics of adipocytes and to identify selectively white and brown adipocytes through Fourier transform infrared (FTIR) spectroscopy. For the developmental characterization of adipocytes, cells and conditioned media of white and brown adipocytes were respectively collected and analyzed. A higher amide I/amide II ratio was observed in the conditioned medium of brown adipocyte than in that of white adipocyte, indicating differences in secretory protein profiles. In contrast, an amide I/amide II ratio was higher in white adipocytes than in brown adipocytes, and mature adipocytes have higher lipid amounts than pre-adipocytes. Lipid acyl chain length was the longest in white adipocytes. These differences suggested that FTIR spectroscopy can be used to characterize developmental stages and/or types of adipocytes. To identify the possibility of selectively classifying adipose-derived stem cells, FTIR spectroscopy spectra were obtained in cells before/after white/brown adipocyte differentiation using FTIR spectroscopy and then analyzed by the principal component analysis method. All data indicated that the discrimination between adipocytes was possible in the analysis of the infrared spectroscopy spectrum by the principal component analysis technique. This study suggested the possibility of FTIR spectroscopy as a new type of cell sorting system without tagging.

Regulatory mechanisms of the early phase of white adipocyte differentiation: an overview

The adipose organ comprises two main fat depots termed white and brown adipose tissues. Adipogenesis is a process leading to newly differentiated adipocytes starting from precursor cells, which requires the contribution of many cellular activities at the genome, transcriptome, proteome, and metabolome levels. The adipogenic program is accomplished through two sequential phases; the first includes events favoring the commitment of adipose tissue stem cells/precursors to preadipocytes, while the second involves mechanisms that allow the achievement of full adipocyte differentiation. While there is a very large literature about the mechanisms involved in terminal adipogenesis, little is known about the first stage of this process. Growing interest in this field is due to the recent identification of adipose tissue precursors, which include a heterogenous cell population within different types of adipose tissue as well as within the same fat depot. In addition, the alteration of the heterogeneity of adipose tissue stem cells and of the mechanisms involved in their commitment have been linked to adipose tissue development defects and hence to the onset/progression of metabolic diseases, such as obesity. For this reason, the characterization of early adipogenic events is crucial to understand the etiology and the evolution of adipogenesis-related pathologies, and to explore the adipose tissue precursors’ potential as future tools for precision medicine.

Role of lncRNAs into Mesenchymal Stromal Cell Differentiation

Currently, findings support that 75% of the human genome is actively transcribed, but only 2% is translated into a protein, according to databases such as ENCODE (Encyclopedia of DNA Elements) [1]. The development of high-throughput sequencing technologies, computational methods for genome assembly and biological models have led to the realization of the importance of the previously unconsidered non-coding fraction of the genome. Along with this, noncoding RNAs have been shown to be epigenetic, transcriptional and post-transcriptional regulators in a large number of cellular processes [2]. Within the group of non-coding RNAs, lncRNAs represent a fascinating field of study, given the functional versatility in their mode of action on their molecular targets. In recent years, there has been an interest in learning about lncRNAs in MSC differentiation. The aim of this review is to address the signaling mechanisms where lncRNAs are involved, emphasizing their role in either stimulating or inhibiting the transition to differentiated cell. Specifically, the main types of MSC differentiation are discussed: myogenesis, osteogenesis, adipogenesis and chondrogenesis. The description of increasingly new lncRNAs reinforces their role as players in the well-studied field of MSC differentiation, allowing a step towards a better understanding of their biology and their potential application in the clinic.