Developmental origins of the adipocyte lineage: new insights from genetics and genomics studies

Early Life Programming of Adipose Tissue Remodeling and Browning Capacity by Micronutrients and Bioactive Compounds as a Potential Anti-Obesity Strategy

The early stages of life, especially the period from conception to two years, are crucial for shaping metabolic health and the risk of obesity in adulthood. Adipose tissue (AT) plays a crucial role in regulating energy homeostasis and metabolism, and brown AT (BAT) and the browning of white AT (WAT) are promising targets for combating weight gain. Nutritional factors during prenatal and early postnatal stages can influence the development of AT, affecting the likelihood of obesity later on. This narrative review focuses on the nutritional programming of AT features. Research conducted across various animal models with diverse interventions has provided insights into the effects of specific compounds on AT development and function, influencing the development of crucial structures and neuroendocrine circuits responsible for energy balance. The hormone leptin has been identified as an essential nutrient during lactation for healthy metabolic programming against obesity development in adults. Studies have also highlighted that maternal supplementation with polyunsaturated fatty acids (PUFAs), vitamin A, nicotinamide riboside, and polyphenols during pregnancy and lactation, as well as offspring supplementation with myo-inositol, vitamin A, nicotinamide riboside, and resveratrol during the suckling period, can impact AT features and long-term health outcomes and help understand predisposition to obesity later in life.

The Impact of Excessive Fructose Intake on Adipose Tissue and the Development of Childhood Obesity

Worldwide, childhood obesity cases continue to rise, and its prevalence is known to increase the risk of non-communicable diseases typically found in adults, such as cardiovascular disease and type 2 diabetes mellitus. Thus, comprehending its multiple causes to build healthier approaches and revert this scenario is urgent. Obesity development is strongly associated with high fructose intake since the excessive consumption of this highly lipogenic sugar leads to white fat accumulation and causes white adipose tissue (WAT) inflammation, oxidative stress, and dysregulated adipokine release. Unfortunately, the global consumption of fructose has increased dramatically in recent years, which is associated with the fact that fructose is not always evident to consumers, as it is commonly added as a sweetener in food and sugar-sweetened beverages (SSB). Therefore, here, we discuss the impact of excessive fructose intake on adipose tissue biology, its contribution to childhood obesity, and current strategies for reducing high fructose and/or free sugar intake. To achieve such reductions, we conclude that it is important that the population has access to reliable information about food ingredients via food labels. Consumers also need scientific education to understand potential health risks to themselves and their children.

Injectable hyperbranched PEG crosslinked hyaluronan hydrogel microparticles containing mir-99a-3p modified subcutaneous ADSCs-derived exosomes was beneficial for long-term treatment of osteoarthritis

Exosomes (Exos) secreted by adipose-derived stem cells (ADSCs) have shown potential in alleviating osteoarthritis (OA). Previous studies indicated that infrapatellar fat pad (IPFP) derived stem cells (IPFSCs) may be more suitable for the treatment of OA than subcutaneous adipose tissue (ScAT) derived stem cells (ScASCs). However, it remains unclear which type of Exos offers superior therapeutic benefit for OA. This study first compared the differences between Exos derived from IPFP stem cells (ExosIPFP) and ScAT stem cells (ExosScAT) in OA treatment. Results suggested that ExosIPFP significantly inhibit the degradation of cartilage extracellular matrix (ECM) than ExosScAT, following this, the differences in microRNA (miRNA) expression between the two types of Exos using small RNA sequencing were performed. Subsequently, miR-99 b-3p was chosen and over-expressed in ExosScAT (ExosScAT-99b-3p), both in vivo and in vitro experiments demonstrated its efficacy in inhibiting the expression of ADAMTS4, promoting the repair of the ECM in OA. Finally, microfluidic technology was performed to fabricate a hyaluronan-based hydrogel microparticles (HMPs) for encapsulating Exos (HMPs@exos), the injectability, sustained release of Exos and long-term therapeutic effect on OA were validated. In summary, these results suggest miR-99 b-3p regulates the degradation of cartilage ECM by targeting ADAMTS4, the upregulation of miR-99 b-3p in ExosScAT would enable them to exhibit comparable or even superior effectiveness to ExosIPFP for OA treatment, making it a promising approach for OA treatment. Considering the abundant resources of ScAT and the limited availability of IPFP, ScAT harvested through liposuction could be genetically engineered to yield Exos for OA treatment. Furthermore, the encapsulation of Exos in HMPs provides an injectable sustained local drug release system, which could potentially enhance the efficacy of Exos and hold potential as future therapeutic strategies.

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.

Fat Graft Retention: Adipose Tissue, Adipose-Derived Stem Cells, and Aging

SUMMARY

Over the past 30 years, there has been a dramatic increase in the use of autologous fat grafting for soft-tissue augmentation and to improve facial skin quality. Several studies have highlighted the impact of aging on adipose tissue, leading to a decrease of adipose tissue volume and preadipocyte proliferation and increase of fibrosis. Recently, there has been a rising interest in adipose tissue components, including adipose-derived stem/stromal cells (ASCs) because of their regenerative potential, including inflammation, fibrosis, and vascularization modulation. Because of their differentiation potential and paracrine function, ASCs have been largely used for fat grafting procedures, as they are described to be a key component in fat graft survival. However, many parameters as surgical procedures or adipose tissue biology could change clinical outcomes. Variation on fat grafting methods have led to numerous inconsistent clinical outcomes. Donor-to-donor variation could also be imputed to ASCs, tissue inflammatory state, or tissue origin. In this review, the authors aim to analyze (1) the parameters involved in graft survival, and (2) the effect of aging on adipose tissue components, especially ASCs, that could lead to a decrease of skin regeneration and fat graft retention.

CLINICAL RELEVANCE STATEMENT

This review aims to enlighten surgeons about known parameters that could play a role in fat graft survival. ASCs and their potential mechanism of action in regenerative medicine are more specifically described.

A Review of Structural Features, Biological Functions and Biotransformation Studies in Adipose Tissues and an Assessment of Progress and Implications

Roles for adipose tissues in energy metabolism, health maintenance and disease onset have been established. Evidence indicates that white, brown and beige fats are quite different in terms of their cellular origin and biological characteristics. These differences are significant in targeting adipocytes to study the pathogenesis and prevention strategies of related diseases. The biotransformations of white, brown and beige fat cells constitute an intriguing topic worthy of further study, and the molecular mechanisms underlying the biotransformations of white, brown and beige fat cells remain to be elucidated. Hence, we herein collected evidence from studies on adipose tissue or adipocytes, and we extracted the structural features, biologic functions, and biotransformations of adipose tissue/adipocytes. The present review aimed to summarize the latest research progress and propose novel research directions with respect to adipose tissue and adipocytes. We posit that this work will provide new insights and opportunities in the effective treatment strategies for obesity, diabetes and other lipid-related diseases. It will also contribute to our knowledge of the basic biologic underpinnings of adipocyte biology.

A review of TSHR- and IGF-1R-related pathogenesis and treatment of Graves' orbitopathy

Graves' orbitopathy (GO) is an organ-specific autoimmune disease, but its pathogenesis remains unclear. There are few review articles on GO research from the perspective of target cells and target antigens. A systematic search of PubMed was performed, focusing mainly on studies published after 2015 that involve the role of target cells, orbital fibroblasts (OFs) and orbital adipocytes (OAs), target antigens, thyrotropin receptor (TSHR) and insulin-like growth factor-1 receptor (IGF-1R), and their corresponding antibodies, TSHR antibodies (TRAbs) and IGF-1R antibodies (IGF-1R Abs), in GO pathogenesis and the potentially effective therapies that target TSHR and IGF-1R. Based on the results, OFs may be derived from bone marrow-derived CD34+ fibrocytes. In addition to CD34+ OFs, CD34- OFs are important in the pathogenesis of GO and may be involved in hyaluronan formation. CD34- OFs expressing Slit2 suppress the phenotype of CD34+ OFs. β-arrestin 1 can be involved in TSHR/IGF-1R crosstalk as a scaffold. Research on TRAbs has gradually shifted to TSAbs, TBAbs and the titre of TRAbs. However, the existence and role of IGF-1R Abs are still unknown and deserve further study. Basic and clinical trials of TSHR-inhibiting therapies are increasing, and TSHR is an expected therapeutic target. Teprotumumab has become the latest second-line treatment for GO. This review aims to effectively describe the pathogenesis of GO from the perspective of target cells and target antigens and provide ideas for its fundamental treatment.

Knockdown of CDC20 promotes adipogenesis of bone marrow-derived stem cells by modulating β-catenin

Background

Bone is a rigid organ that provides physical protection and support to vital organs of the body. Bone loss disorders are commonly associated with increased bone marrow adipose tissue. Bone marrow mesenchymal stromal/stem cells (BMSCs) are multipotent progenitors that can differentiate into osteoblasts, adipocytes, and chondrocytes. Cell division cycle 20 (CDC20) is a co-activator of anaphase promoting complex/cyclosome (APC/C), and is required for ubiquitin ligase activity. Our previous study showed that CDC20 promoted the osteogenic commitment of BMSCs and Cdc20 conditional knockout mice suggested a decline in bone mass. In this study, we found that knockdown of CDC20 promoted adipogenic differentiation of BMSCs by modulating β-catenin, which suggested a link between adipogenesis and osteogenesis.

Methods

Lentivirus containing a CDC20 shRNA was used for CDC20 knockdown in human BMSCs (hBMSCs). Primary mouse BMSCs (mBMSCs) were isolated from Cdc20^f/f and Sp7-Cre;Cdc20^f/f mice. Adipogenesis was examined using quantitative real-time reverse transcription PCR (qRT-PCR) and western blotting analysis of adipogenic regulators, Oil Red O staining, and transplantation into nude mice. CDC20 knockout efficiency was determined through immunochemistry, qRT-PCR, and western blotting of bone marrow. Accumulation of adiposity was measured through histology and staining of bone sections. Exploration of the molecular mechanism was determined through western blotting, Oil Red O staining, and qRT-PCR.

Results

CDC20 expression in hBMSCs was significantly decreased during adipogenic differentiation. CDC20 knockdown enhanced hBMSC adipogenic differentiation in vitro. CDC20-knockdown hBMSCs showed more adipose tissue-like constructs upon hematoxylin and eosin (H&E) and Oil Red O staining. Sp7-Cre;Cdc20^f/f mice presented increased adipocytes in their bone marrow compared with the control mice. mBMSCs from Sp7-Cre;Cdc20^f/f mice showed upregulated adipogenic differentiation. Knockdown of CDC20 led to decreased β-catenin levels, and a β-catenin pathway activator (lithium chloride) abolished the role of CDC20 in BMSC adipogenic differentiation.

Conclusions

Our findings showed that CDC20 knockdown enhanced adipogenesis of hBMSC and mBMSCs adipogenesis in vitro and in vivo. CDC20 regulates both adipogenesis and osteogenesis of BMSCs, and might lead to the development of new therapeutic targets for “fatty bone” and osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03062-0.

Role of adipose tissue macrophages in obesity-related disorders

The obesity epidemic has led researchers and clinicians to reconsider the etiology of this disease and precisely decipher its molecular mechanisms. The excessive accumulation of fat by cells, most notably adipocytes, which play a key role in this process, has many repercussions in tissue physiology. Herein, we focus on how macrophages, immune cells well known for their tissue gatekeeping functions, assume fundamental, yet ill-defined, roles in the genesis and development of obesity-related metabolic disorders. We first discuss the determinants of the biology of these cells before introducing the specifics of the adipose tissue environment, while highlighting its heterogeneity. Finally, we detail how obesity transforms both adipose tissue and local macrophage populations. Understanding macrophage diversity and their cross talk with the diverse cell types constituting the adipose tissue environment will allow us to frame the therapeutic potential of adipose tissue macrophages in obesity.

Role of Distinct Fat Depots in Metabolic Regulation and Pathological Implications

People suffering from obesity and associated metabolic disorders including diabetes are increasing exponentially around the world. Adipose tissue (AT) distribution and alteration in their biochemical properties play a major role in the pathogenesis of these diseases. Emerging evidence suggests that AT heterogeneity and depot-specific physiological changes are vital in the development of insulin resistance in peripheral tissues like muscle and liver. Classically, AT depots are classified into white adipose tissue (WAT) and brown adipose tissue (BAT); WAT is the site of fatty acid storage, while BAT is a dedicated organ of metabolic heat production. The discovery of beige adipocyte clusters in WAT depots indicates AT heterogeneity has a more central role than hither to ascribed. Therefore, we have discussed in detail the current state of understanding on cellular and molecular origin of different AT depots and their relevance toward physiological metabolic homeostasis. A major focus is to highlight the correlation between altered WAT distribution in the body and metabolic pathogenesis in animal models and humans. We have also underscored the disparity in the molecular (including signaling) changes in various WAT tissues during diabetic pathogenesis. Exercise-mediated beneficial alteration in WAT physiology/distribution that protects against metabolic disorders is evolving. Here we have discussed the depot-specific biochemical adjustments induced by different forms of exercise. A detailed understanding of the molecular details of inter-organ crosstalk via substrate utilization/storage and signaling through chemokines provide strategies to target selected WAT depots to pharmacologically mimic the benefits of exercise countering metabolic diseases including diabetes.

Mast cell and heparin promote adipogenesis in superficial fascia of rats

Fascial adipocytes are recently identified as a unique population of adipose cells, which have different developmental origins, anatomical locations, cytological and functional characteristics compared with subcutaneous or visceral adipocytes. Superficial fascia in rats (also in pigs but not obviously in mice) contains numbers of lineage committed preadipocytes which possess adipogenic potential in vivo. The present study aimed to investigate the physiological factors that contribute to fascial adipogenesis in rats. We detected that mast cells, adipose progenitor cells, and mature adipocytes distributed in certain fascia areas were closely associated with each other, and numerous heparin-loaded granules released from mast cells were distributed around fascial preadipocytes. The culture supernatants of rat peritoneal mast cells and RBL-2H3 mast cells contained 20-30 μg/ml of heparin, effectively activated PPAR-responsive luciferase activity, promoted mRNA and protein expressions of key adipogenic genes, and hence increased adipogenic differentiation of fascia- or epididymal adipose-derived stromal cells. Adipogenic effects of mast cell supernatants were mimicked by heparin but not by histamine or 5-hydroxytryptamine, and were antagonized by protamine sulfate. Adipogenic effects of heparin may relate to its chain length of glucosamine units, because heparin stimulated stronger adipogenesis than dalteparin and enoxaparin with relatively short chains. In rats, local administration of heparin-loaded microspheres for 30 days induced adipogenesis in local areas of superficial fascia. Our findings suggested that mast cell and its granule heparin could serve as the endogenous physiological factors to initiate and accelerate local adipogenesis in superficial fascia, or in adipose tissue with the fascia naturally embedded inside.

Surgical Observations of the Levator Aponeurosis Fibrotic Changes in Simple Congenital Ptosis Suggest Complex Pathogenesis

PURPOSE

To shed light upon the possible role of the levator aponeurosis (LA) developmental fibrotic changes as an added etiology for simple congenital ptosis, which causes limitation of the levator function (LF).

METHODS

This retrospective cohort study included patients with simple congenital ptosis who underwent skin approach LA resection as a primary intervention with an intraoperative photographic documentation of LA fibrotic changes. Preoperative demographics and clinical data were reviewed. The effect of LA fibrotic changes on the LF was assessed in different LA fibrotic changes with or without levator palpebrae superioris (LPS) muscle fatty infiltration.

RESULTS

A total of 56 eyelids of 49 patients with a mean age (±SD) 6.7 (±3.2) years were enrolled in this study. The fibrotic changes of LA were observed as a sheet of fibrosis (19 eyelids) or fibrous bands (23 eyelids). Fatty infiltration of LPS was noticed in 28 eyelids, either with or without fibrotic changes of LA. Preoperative LF was diminished in LPS fatty infiltration compared with LA fibrotic sheets (P = 0.026). Postoperative LF improved significantly in both LA fibrotic sheets and LA fibrotic bands (9.4 ± 2.5 mm and 9.6 ± 2.8 mm, respectively) compared with LPS with fatty infiltration (6.4 ± 1.8 mm) (P = 0.004).

CONCLUSIONS

Although our data are inconclusive due to lack of embryologic studies, the observed LA fibrotic changes may suggest a complex pathogenesis of simple congenital ptosis. The meticulous observation of the LA and the releasing of any adhesion or band to the surrounding structures could improve postoperative LF.

Difference in developmental dynamics between subcutaneous and abdominal adipose tissues in goose (Anser Cygnoides)

Goose (Anas cygnoides), as a typical species domesticated from a migratory bird, has maintained the capability of depositing excess lipid and preferentially accumulating fat within the abdomen and subcutaneous, which not only leads to decrease in yield of meat product, but also affects the feed conversion rate. Here, an experiment was conducted to examine the difference in developmental dynamics between subcutaneous (SAT) and abdominal adipose tissues (AAT) in goose. The results showed that SAT could be clearly observed at embryonic days (E) 15, whereas AAT were clearer until E20. Although the weights of SAT and AAT showed a significant rising with advancing age (P < 0.05), their gains were not completely uniform, and more adipose deposited preferentially toward AAT after birth (P < 0.05). Additionally, a clear expansion in adipocyte size was observed in AAT and SAT during embryonic stages (P < 0.05). The average adipocyte area in AAT continued to increase after birth (P < 0.05), while the cell areas in SAT were relatively invariable (P > 0.05). Furthermore, the expression levels of FABP4/aP2, ACSL1 and PPARγ were much higher in SAT than in AAT, whereas relative higher expression level of IL-6 was observed in the AAT during embryonic stages. After birth, the more expression of LPL and PPARα were detected in AAT than did in SAT (P < 0.05), whereas greater ATGL expression was in SAT (P < 0.05). Taken together, these findings suggest that AAT may display greater fat storage capacity than SAT accompanied by changes in cell area and lipogenic capacity. Considering that there is disparity in the individual adipose tissues, we suggested that careful consideration for the precise interventions used to control SAT or AAT deposition in meat-producing animals to improve feed efficiency.

Molecular and Cellular Bases of Lipodystrophy Syndromes

Lipodystrophy syndromes are rare diseases originating from a generalized or partial loss of adipose tissue. Adipose tissue dysfunction results from heterogeneous genetic or acquired causes, but leads to similar metabolic complications with insulin resistance, diabetes, hypertriglyceridemia, nonalcoholic fatty liver disease, dysfunctions of the gonadotropic axis and endocrine defects of adipose tissue with leptin and adiponectin deficiency. Diagnosis, based on clinical and metabolic investigations, and on genetic analyses, is of major importance to adapt medical care and genetic counseling. Molecular and cellular bases of these syndromes involve, among others, altered adipocyte differentiation, structure and/or regulation of the adipocyte lipid droplet, and/or premature cellular senescence. Lipodystrophy syndromes frequently present as systemic diseases with multi-tissue involvement. After an update on the main molecular bases and clinical forms of lipodystrophy, we will focus on topics that have recently emerged in the field. We will discuss the links between lipodystrophy and premature ageing and/or immuno-inflammatory aggressions of adipose tissue, as well as the relationships between lipomatosis and lipodystrophy. Finally, the indications of substitutive therapy with metreleptin, an analog of leptin, which is approved in Europe and USA, will be discussed.

Distinctive Features of Orbital Adipose Tissue (OAT) in Graves' Orbitopathy

Depot specific expansion of orbital-adipose-tissue (OAT) in Graves' Orbitopathy (GO) is associated with lipid metabolism signaling defects. We hypothesize that the unique adipocyte biology of OAT facilitates its expansion in GO. A comprehensive comparison of OAT and white-adipose-tissue (WAT) was performed by light/electron-microscopy, lipidomic and transcriptional analysis using ex vivo WAT, healthy OAT (OAT-H) and OAT from GO (OAT-GO). OAT-H/OAT-GO have a single lipid-vacuole and low mitochondrial number. Lower lipolytic activity and smaller adipocytes of OAT-H/OAT-GO, accompanied by similar essential linoleic fatty acid (FA) and (low) FA synthesis to WAT, revealed a hyperplastic OAT expansion through external FA-uptake via abundant SLC27A6 (FA-transporter) expression. Mitochondrial dysfunction of OAT in GO was apparent, as evidenced by the increased mRNA expression of uncoupling protein 1 (UCP1) and mitofusin-2 (MFN2) in OAT-GO compared to OAT-H. Transcriptional profiles of OAT-H revealed high expression of Iroquois homeobox-family (IRX-3&5), and low expression in HOX-family/TBX5 (essential for WAT/BAT (brown-adipose-tissue)/BRITE (BRown-in-whITE) development). We demonstrated unique features of OAT not presented in either WAT or BAT/BRITE. This study reveals that the pathologically enhanced FA-uptake driven hyperplastic expansion of OAT in GO is associated with a depot specific mechanism (the SLC27A6 FA-transporter) and mitochondrial dysfunction. We uncovered that OAT functions as a distinctive fat depot, providing novel insights into adipocyte biology and the pathological development of OAT expansion in GO.

A hyaluronic acid-based filler reduces lipolysis in human mature adipocytes and maintains adherence and lipid accumulation of long-term differentiated human preadipocytes

The beneficial role of subcutaneous adipose tissue in skin rejuvenation derived from its capacity to fill the under‐layer volumes but also from its ability to regulate the extracellular matrix production by dermis fibroblasts. Hyaluronic acid (HA), a major component of the extracellular matrix, is a commonly used injectable dermal filler showing excellent efficiencies to maintain tissue augmentation even after its biodegradation. To improve their stability, the HA molecules can also be “cross‐linked” to each other. The effects of cross‐linked HA‐based fillers on the dermal structure are well known. For safety reasons, most of the physicians prefer to use the blunt cannula for injections. However, evidences showed that the cannula could not be located in the dermis, but it passes through immediate hypodermis and the long‐lasting effect of cross‐linked HA‐based fillers may be related to its effects on adipose tissue. To test whether cross‐linked HA has a direct effect on human adipocytes, we treated isolated adipocytes and precursors cells from human skin donors with cross‐linked HA. Biochemical and cellular analysis demonstrated that treatment by cross‐linked HA showed beneficial effects on differentiated cell adherence and survival as well as reduced basal and induced lipolysis in fully mature adipocytes. Taken together, these data showed that cross‐linked HA promoted cell adherence and preserved the adipogenic capacity of preadipocytes during prolonged cell culture, bringing additional evidences of the beneficial role of cross‐linked HA‐based fillers in maintenance of the subcutaneous fat mass. This first study could defend a preventive approach to facial volume loss during natural aging.

Adipose Tissue from Lean and Obese Mice Induces a Mesenchymal to Epithelial Transition-Like Effect in Triple Negative Breast Cancers Cells Grown in 3-Dimensional Culture

Breast cancer is the second leading cause of cancer-related mortality among women globally with obesity being one risk factor. Obese breast cancer patients have at least a 30% increased risk of death from breast cancer compared to non-obese breast cancer patients because they present with larger tumors and generally have increased rates of metastasis. Moreover, obese breast cancer patients respond more poorly to treatment compared to non-obese patients, particularly pre-menopausal women diagnosed with triple negative breast cancer (TNBC). To help understand the molecular mechanisms underlying the increased metastasis associated with obesity, we previously established a three-dimensional culture system that permits the co-culture of adipocytes and TNBC cells in a manner that mimics an in vivo milieu. Using this system, we demonstrate that white adipose tissue from both lean and obese mice can induce a partial mesenchymal-to-epithelial transition (MET). Triple negative breast cancer cells adopt an epithelial morphology and have an increased expression of some epithelial markers, but they maintain the expression of mesenchymal markers, furnishing the breast cancer cells with hybrid properties that are associated with more aggressive tumors. Thus, these data suggest that adipose tissue has the potential to promote secondary tumor formation in lean and obese women. Further work is needed to determine if targeting the partial MET induced by adipose tissue could reduce metastasis.

Distinct abdominal and gluteal adipose tissue transcriptome signatures are altered by exercise training in African women with obesity

The differential associations of adipose depots with metabolic risk during obesity have been proposed to be controlled by environmental and genetic factors. We evaluated the regional differences in transcriptome signatures between abdominal (aSAT) and gluteal subcutaneous adipose tissue (gSAT) in obese black South African women and tested the hypothesis that 12-week exercise training alters gene expression patterns in a depot-specific manner. Twelve young women performed 12-weeks of supervised aerobic and resistance training. Pre- and post-intervention measurements included peak oxygen consumption (VO_2peak), whole-body composition and unbiased gene expression analysis of SAT depots. VO_2peak increased, body weight decreased, and body fat distribution improved with exercise training (p < 0.05). The expression of 15 genes, mainly associated with embryonic development, differed between SAT depots at baseline, whereas 318 genes were differentially expressed post-training (p < 0.05). Four developmental genes were differentially expressed between these depots at both time points (HOXA5, DMRT2, DMRT3 and CSN1S1). Exercise training induced changes in the expression of genes associated with immune and inflammatory responses, and lipid metabolism in gSAT, and muscle-associated processes in aSAT. This study showed differences in developmental processes regulating SAT distribution and expandability of distinct depots, and depot-specific adaptation to exercise training in black South African women with obesity.

Epigenetic Programming of Adipose Tissue in the Progeny of Obese Dams

According to the Developmental Origin of Health and Disease (DOHaD) concept, maternal obesity and the resulting accelerated growth in neonates predispose offspring to obesity and associated metabolic diseases that may persist across generations. In this context, the adipose tissue has emerged as an important player due to its involvement in metabolic health, and its high potential for plasticity and adaptation to environmental cues. Recent years have seen a growing interest in how maternal obesity induces long-lasting adipose tissue remodeling in offspring and how these modifications could be transmitted to subsequent generations in an inter- or transgenerational manner. In particular, epigenetic mechanisms are thought to be key players in the developmental programming of adipose tissue, which may partially mediate parts of the transgenerational inheritance of obesity. This review presents data supporting the role of maternal obesity in the developmental programming of adipose tissue through epigenetic mechanisms. Inter- and transgenerational effects on adipose tissue expansion are also discussed in this review.

Flavonoids from Acer okamotoanum Inhibit Adipocyte Differentiation and Promote Lipolysis in the 3T3-L1 Cells

Flavonoids, quercitrin, isoquercitrin (IQ), and afzelin, were isolated from ethyl acetate fraction of Acer okamotoanum. We investigated anti-obesity effects and mechanisms of three flavonoids from A. okamotoanum in the differentiated 3T3-L1 cells. The differentiated 3T3-L1 cells increased triglyceride (TG) contents, compared with non-differentiated normal group. However, treatments of three flavonoids from A. okamotoanum decreased TG contents without cytotoxicity. In addition, they showed significant down-regulation of several adipogenic transcription factors, such as γ-cytidine-cytidine-adenosine-adenosine-thymidine/enhancer binding protein -α, -β, and peroxisome proliferator-activated receptor-γ, compared with non-treated control group. Furthermore, treatment of the flavonoids inhibited expressions of lipogenesis-related proteins including fatty acid synthase, adipocyte protein 2, and glucose transporter 4. Moreover, IQ-treated group showed significant up-regulation of lipolysis-related proteins such as adipose triglyceride lipase and hormone-sensitive lipase. In addition, flavonoids significantly activated 5′-adenosine monophosphate-activated protein kinase (AMPK) compared to control group. In particular, IQ showed higher inhibition of TG accumulation by regulation of pathways related with both adipogenesis and lipolysis, than other flavonoids. The present results indicated that three flavonoids of A. okamotoanum showed anti-obesity activity by regulation of adipocyte differentiation, lipolysis, and AMPK signaling, suggesting as an anti-obesity functional agents.

Emergent Properties of the HNF4α-PPARγ Network May Drive Consequent Phenotypic Plasticity in NAFLD

Non-alcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease in adults and children. It is characterized by excessive accumulation of lipids in the hepatocytes of patients without any excess alcohol intake. With a global presence of 24% and limited therapeutic options, the disease burden of NAFLD is increasing. Thus, it becomes imperative to attempt to understand the dynamics of disease progression at a systems-level. Here, we decoded the emergent dynamics of underlying gene regulatory networks that were identified to drive the initiation and the progression of NAFLD. We developed a mathematical model to elucidate the dynamics of the HNF4α-PPARγ gene regulatory network. Our simulations reveal that this network can enable multiple co-existing phenotypes under certain biological conditions: an adipocyte, a hepatocyte, and a "hybrid" adipocyte-like state of the hepatocyte. These phenotypes may also switch among each other, thus enabling phenotypic plasticity and consequently leading to simultaneous deregulation of the levels of molecules that maintain a hepatic identity and/or facilitate a partial or complete acquisition of adipocytic traits. These predicted trends are supported by the analysis of clinical data, further substantiating the putative role of phenotypic plasticity in driving NAFLD. Our results unravel how the emergent dynamics of underlying regulatory networks can promote phenotypic plasticity, thereby propelling the clinically observed changes in gene expression often associated with NAFLD.

Carotenoids and carotenoid conversion products in adipose tissue biology and obesity: Pre-clinical and human studies

Antiobesity activities of carotenoids and carotenoid conversion products (CCPs) have been demonstrated in pre-clinical studies, and mechanisms behind have begun to be unveiled, thus suggesting these compounds may help obesity prevention and management. The antiobesity action of carotenoids and CCPs can be traced to effects in multiple tissues, notably the adipose tissues. Key aspects of the biology of adipose tissues appear to be affected by carotenoid and CCPs, including adipogenesis, metabolic capacities for energy storage, release and inefficient oxidation, secretory function, and modulation of oxidative stress and inflammatory pathways. Here, we review the connections of carotenoids and CCPs with adipose tissue biology and obesity as revealed by cell and animal intervention studies, studies addressing the role of endogenous retinoid metabolism, and human epidemiological and intervention studies. We also consider human genetic variability influencing carotenoid and vitamin A metabolism, particularly in adipose tissues, as a potentially relevant aspect towards personalization of dietary recommendations to prevent or manage obesity and optimize metabolic health. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

New insights into the pathogenesis and nonsurgical management of Graves orbitopathy

Graves orbitopathy, also known as thyroid eye disease or thyroid-associated orbitopathy, is visually disabling, cosmetically disfiguring and has a substantial negative impact on a patient's quality of life. There is increasing awareness of the need for early diagnosis and rapid specialist input from endocrinologists and ophthalmologists. Glucocorticoids are the mainstay of treatment; however, recurrence occurs frequently once these are withdrawn. Furthermore, in >60% of cases, normal orbital anatomy is not restored, and skilled rehabilitative surgery is required. Clinical trials have shown that considerable benefit can be derived from the addition of antiproliferative agents (such as mycophenolate or azathioprine) in preventing deterioration after steroid cessation. In addition, targeted biologic therapies have shown promise, including teprotumumab, which reduces proptosis, rituximab (anti-CD20), which reduces inflammation, and tocilizumab, which potentially benefits both of these parameters. Other strategies such as orbital radiotherapy have had their widespread role in combination therapy called into question. The pathophysiology of Graves orbitopathy has also been revised with identification of new potential therapeutic targets. In this Review we provide an up-to-date overview of the field, outline the optimal management of Graves orbitopathy and summarize the research developments in this area to highlight future research questions and direct future clinical trials.

Chemokines and their association with body mass index among healthy Saudis

Obesity is a chronic disorder that is associated with body mass index (BMI) of greater or equal to 30 kg/m2. The prevalence of obesity in the Kingdom of Saudi Arabia (KSA) is increasing at an alarming rate and is expected to reach 41% in men and up to 78% in women by 2022. Since chemokines are associated with involuntary weight loss, the objective of this study was to elucidate their association with BMI among Saudis. A questionnaire was used to collect information about diet, health conditions, and demographics from 15 men and 16 women who participated in the study. BMI was calculated based on clinical measurements and participants were classified according to their BMI category as: normal, underweight, overweight, or obese. Serum samples were collected for a multiplex assay using the Human Chemokine Magnetic 30-plex panel. The serum concentration of either the monokine induced by gamma interferon (MIG) or the CXC-motif chemokine ligand 9 (CXCL-9) was significantly increased in obese men (P = 0.0194) and women (P = 0.043) as compared to underweight men and women, respectively. However, the serum levels of other chemokines were not significantly different among the groups. We found that MIG levels are differentially regulated in serum, based on individuals' BMI.

The Beige Adipocyte as a Therapy for Metabolic Diseases

Adipose tissue is traditionally categorized into white and brown relating to their function and morphology. The classical white adipose tissue builds up energy in the form of triglycerides and is useful for preventing fatigue during periods of low caloric intake and the brown adipose tissue more energetically active, with a greater number of mitochondria and energy production in the form of heat. Since adult humans possess significant amounts of active brown fat depots and its mass inversely correlates with adiposity, brown fat might play an important role in human obesity and energy homeostasis. New evidence suggests two types of thermogenic adipocytes with distinct developmental and anatomical features: classical brown adipocytes and beige adipocytes. Beige adipocyte has recently attracted special interest because of its ability to dissipate energy and the possible ability to differentiate themselves from white adipocytes. The presence of brown and beige adipocyte in human adults has acquired attention as a possible therapeutic intervention for metabolic diseases. Importantly, adult human brown appears to be mainly composed of beige-like adipocytes, making this cell type an attractive therapeutic target for obesity and obesity-related diseases, such as atherosclerosis, arterial hypertension and diabetes mellitus type 2. Because many epigenetics changes can affect beige adipocyte differentiation from adipose progenitor cells, the knowledge of the circumstances that affect the development of beige adipocyte cells may be important to new pathways in the treatment of metabolic diseases. New molecules have emerged as possible therapeutic targets, which through the impulse to develop beige adipocytes can be useful for clinical studies. In this review will discuss some recent observations arising from the unique physiological capacity of these cells and their possible role as ways to treat obesity and diabetes mellitus type 2.

Lipodystrophic syndromes due to LMNA mutations: recent developments on biomolecular aspects, pathophysiological hypotheses and therapeutic perspectives

Mutations in LMNA, encoding A-type lamins, are responsible for laminopathies including muscular dystrophies, lipodystrophies, and premature ageing syndromes. LMNA mutations have been shown to alter nuclear structure and stiffness, binding to partners at the nuclear envelope or within the nucleoplasm, gene expression and/or prelamin A maturation. LMNA-associated lipodystrophic features, combining generalized or partial fat atrophy and metabolic alterations associated with insulin resistance, could result from altered adipocyte differentiation or from altered fat structure.

Recent studies shed some light on how pathogenic A-type lamin variants could trigger lipodystrophy, metabolic complications, and precocious cardiovascular events. Alterations in adipose tissue extracellular matrix and TGF-beta signaling could initiate metabolic inflexibility. Premature senescence of vascular cells could contribute to cardiovascular complications. In affected families, metabolic alterations occur at an earlier age across generations, which could result from epigenetic deregulation induced by LMNA mutations. Novel cellular models recapitulating adipogenic developmental pathways provide scalable tools for disease modeling and therapeutic screening.

Ontogeny and evolution of the sound-generating structures in the infraorder Delphinida (Odontoceti: Delphinida)

The ontogeny of the structures involved in sound generation and modulation in dolphins was investigated through a comparison of the soft nasal structures of foetal, perinatal, neonatal and adult specimens of Pontoporiidae, Phocoenidae and Delphinidae. Foetal samples were sectioned at 10 µm in the saggital and coronal planes, and stained for histological examination. Computed tomography and magentic resonance imaging scan series were combined with new data to represent the ontogenetic stages of the three groups. The images were analysed in 3D-Slicer to characterize the general head topography. The origins of the melon and the vestibular air sac were detected between Carnegie stages C16 and F22. The three groups analysed showed distinct formation of the nasal plug and nasal plug muscles, mainly with regard to the loss of fat pathways (or their maintenance in Pontoporiidae) and the development of the nasal plug muscles on both sides (during perinatal development of Phocoenidae) or just on the left side (during postnatal development in Delphinidae). Broadband vocalizing delphinidans might have evolved under heterochronic events acting on the formation of sound-generating structures such as the rostrum and vestibular air sacs, and on the transformation of the branches of the melon, probably leading to a reduced directionality of the sonar beam.

Elevated bone morphogenic protein 4 expression implicated in site-specific adipogenesis in thyroid associated orbitopathy

Periorbital adipose tissue expansion is a key pathological change in thyroid associated orbitopathy (TAO). Bone morphogenic protein 4 (BMP4) is instrumental in adipogenesis. We compared site-specific BMP4 expression and its effect on adipogenesis using donor-matched adipose tissue-derived stromal cells (ADSC) from TAO patients. In this study, ADSC were generated from periorbital (eyelid, orbital) and subcutaneous (abdominal) adipose tissue. BMP4 expression was characterized by RT-PCR and immunofluorescent staining and compared among ADSC from the three anatomic depots. Effects on adipogenesis after knocking down endogenous BMP4 were quantified by adipogenic markers PPARγ and perilipin. Exogenous BMP4 protein was added after BMP4 knockdown to study the role of BMP4 in adipogenesis. Our results showed that BMP4 staining in periorbital adipose tissue was stronger than those in subcutaneous. BMP4 mRNA expression was higher in eyelid (4.4-2489.4-fold) and orbital (6.9-1811-fold) than that of subcutaneous ADSC, whereas expression fell during induced adipogenesis. After BMP4 knockdown, both adipogenic markers PPARγ (eyelid: 1.7-fold, p = 0.038; orbital: 1.4-fold, p = 0.126) and perilipin (eyelid:1.7-fold, p = 0.001; orbital:2.6-fold, p = 0.066) increased in periorbital ADSC upon induction. These increased expression fell after adding exogenous BMP4 protein. Our findings demonstrated higher BMP4 expression was found in periorbital ADSC and adipose tissue compared to donor-matched subcutaneous counterparts, which fell during adipogenic induction. Knocking down BMP4 expression further enhanced adipogenesis in periorbital ADSC. This effect was reversed by adding exogenous BMP4 protein. We suggested a novel role of BMP4 in modulating site-specific adipogenesis in TAO patients.

Developmental and functional characteristics of the thoracic aorta perivascular adipocyte

Thoracic aorta perivascular adipose tissue (T-PVAT) has critical roles in regulating vascular homeostasis. However, the developmental characteristics and cellular lineage of adipocyte in the T-PVAT remain unclear. We show that T-PVAT contains three long strip-shaped fat depots, anterior T-PVAT (A-T-PVAT), left lateral T-PVAT (LL-T-PVAT), and right lateral T-PVAT (RL-T-PVAT). A-T-PVAT displays a distinct transcriptional profile and developmental origin compared to the two lateral T-PVATs (L-T-PVAT). Lineage tracing studies indicate that A-T-PVAT adipocytes are primarily derived from SM22α+ progenitors, whereas L-T-PVAT contains both SM22α+ and Myf5+ cells. We also show that L-T-PVAT contains more UCP1+ brown adipocytes than A-T-PVAT, and L-T-PVAT exerts a greater relaxing effect on aorta than A-T-PVAT. Angiotensin II-infused hypertensive mice display greater macrophage infiltration into A-T-PVAT than L-T-PVAT. These combined results indicate that L-T-PVAT has a distinct development from A-T-PVAT with different cellular lineage, and suggest that L-T-PVAT and A-T-PVAT have different physiological and pathological functions.

Comparative advantages of infrapatellar fat pad: an emerging stem cell source for regenerative medicine

Growing evidence indicates that infrapatellar fat pad (IPFP)-derived stem cells (IPFSCs) exert robust proliferation capacities and multilineage differentiation potentials. However, few papers summarize the advantages that the IPFP and IPFSCs have in regenerative medicine. In this review we delineate the development and anatomy of the IPFP by comparing it with an adjacent fibrous tissue, synovium, and a more frequently harvested fat depot, subcutaneous adipose tissue. Furthermore, we explore the similarities and differences of stem cells from these three tissues in terms of IPFSCs, synovium-derived stem cells and subcutaneous adipose tissue-derived stem cells in proliferation capacity and tri-lineage differentiation potentials, including chondrogenesis, osteogenesis and adipogenesis. Finally, we highlight the advantages of IPFSCs in regenerative medicine, such as the abundant accessibility and the ability to resist inflammation and senescence, two hurdles for cell-based tissue regeneration. Considering the comparative advantages of IPFSCs, the IPFP can serve as an excellent stem cell source for regenerative medicine, particularly for cartilage regeneration.

Embryologic and Fetal Development of the Human Orbit

PURPOSE

To review the recent data about orbital development and sort out the controversies from the very early stages during embryonic life till final maturation of the orbit late in fetal life, and to appreciate the morphogenesis of all the definitive structures in the orbit in a methodical and timely fashion.

METHODS

The authors extensively review major studies detailing every aspect of human embryologic and fetal orbital morphogenesis including the development of extraocular muscles, orbital fat, vessels, nerves, and the supportive connective tissue framework as well as bone. These interdisciplinary studies span almost a century and a half, and include some significant controversial opposing points of view which the authors hopefully sort out. The authors also highlight a few of the most noteworthy molecular biologic studies regarding the multiple and interacting signaling pathways involved in regulating normal orbital morphogenesis.

RESULTS

Orbital morphogenesis involves a successive series of subtle yet tightly regulated morphogenetic events that could only be explained through the chronological narrative used by the authors. The processes that trigger and contribute to the formation of the orbits are complex and seem to be intricately regulated by multifaceted interactions and bidirectional cross-talk between a multitude of cellular building raw materials including the developing optic vesicles, neuroectoderm, cranial neural crest cells and mesoderm.

CONCLUSIONS

Development of the orbit is a collective enterprise necessitating interactions between, as well as contributions from different cell populations both within and beyond the realm of the orbit. A basic understanding of the processes underlying orbital ontogenesis is a crucial first step toward establishing a genetic basis or an embryologic link with orbital disease.

Homeobox a5 Promotes White Adipose Tissue Browning Through Inhibition of the Tenascin C/Toll-Like Receptor 4/Nuclear Factor Kappa B Inflammatory Signaling in Mice

Lipopolysaccharide (LPS) induces rapid increase in systemic inflammatory factors. As adipose tissue is a key contributor to the inflammatory response to numerous metabolic stimuli, it is important to understand the mechanism behind the LPS-induced inflammation in white adipose tissue (WAT). Homeobox a5 (Hoxa5) is an important transcription factor, which is highly expressed in adipose tissue, and its mRNA expression is increased at cold exposure in mice. So far, the function of Hoxa5 in adipose tissue browning has been poorly understood. So, the objective of this study was conducted to determine the role of Hoxa5 in adipose inflammatory response and white adipose browning in mice. LPS-induced inflammatory and cold-induced browning model were conducted. We compared the coordinated role of Hoxa5 in inflammation and thermogenesis of mice adipose. Transcriptional and methylation regulation was determined by luciferase assay, electrophoretic mobility shift assay, and bisulfite conversion experiment. Hoxa5 and tenascin C (TNC) were involved in WAT inflammation and browning in mice with LPS injection. Furthermore, Hoxa5 inhibited the TNC-involved activation of Toll-like receptor (TLR) 4/nuclear factor kappa B (NF-κB) signal pathway and promoted WAT browning. Moreover, we found that a BMP4/Smad1 signal, closely related to browning, was activated by Hoxa5. Hoxa5 relieved adipocyte inflammation by decreasing TNC-mediated TLR4 transducer and activator of the NF-κB pathway. Interestingly, descended methylation level increased Hoxa5 expression in cold exposure. Our findings demonstrated that Hoxa5 alleviated inflammation and enhanced browning of adipose tissue via negative control of TNC/TLR4/NF-κB inflammatory signaling and activating BMP4/Smad1 pathway. These findings indicated a novel potential means for the regulation of inflammation in adipocytes to prevent obesity and other inflammatory diseases.

Cyp1b1 deletion and retinol deficiency coordinately suppress mouse liver lipogenic genes and hepcidin expression during post-natal development

Cyp1b1 deletion and gestational vitamin A deficiency (GVAD) redirect adult liver gene expression. A matched sufficient pre- and post-natal diet, which has high carbohydrate and normal iron content (LF12), increased inflammatory gene expression markers in adult livers that were suppressed by GVAD and Cyp1b1 deletion. At birth on the LF12 diet, Cyp1b1 deletion and GVAD each suppress liver expression of the iron suppressor, hepcidin (Hepc), while increasing stellate cell activation markers and suppressing post-natal increases in lipogenesis. Hepc was less suppressed in Cyp1b1-/- pups with a standard breeder diet, but was restored by iron supplementation of the LF12 diet.

CONCLUSIONS

The LF12 diet delivered low post-natal iron and attenuated Hepc. Hepc decreases in Cyp1b1-/- and GVAD mice resulted in stellate activation and lipogenesis suppression. Endothelial BMP6, a Hepc stimulant, is a potential coordinator and Cyp1b1 target. These neonatal changes in Cyp1b1-/- mice link to diminished adult obesity and liver inflammation.

Brown adipocytes postnatally arise through both differentiation from progenitors and conversion from white adipocytes in Syrian hamster

To investigate the postnatal development of brown adipose tissue (BAT) in Syrian hamsters, we histologically examined interscapular fat tissue from 5-16-day-old pups, focusing on how brown adipocytes arise. Interscapular fat of 5-day-old hamsters mainly consisted of white adipocytes containing large unilocular lipid droplets, as observed in typical white adipose tissue (WAT). On day 7, clusters of small, proliferative nonadipocytes with a strong immunoreactivity for Ki67 appeared near the edge of the interscapular fat tissue. The area of the Ki67-positive regions expanded to ~50% of the total tissue area by day 10. The interscapular fat showed the typical BAT feature by day 16. A brown adipocyte-specific marker, uncoupling protein-1, was clearly detected on day 10 and thereafter, while not detected on day 7. During conversion of interscapular fat from WAT to BAT, unilocular adipocytes completely and rapidly disappeared without obvious apoptosis. Dual immunofluorescence staining for Ki67 and monocarboxylate transporter 1 (MCT1), another selective marker for brown adipocytes, revealed that most of the proliferating cells were of the brown adipocyte lineage. Electron microscopic examination showed that some of the white adipocytes contained small lipid droplets in addition to the large droplet and expressed MCT1 as do progenitor and mature brown adipocytes, implying a direct conversion from white to brown adipocytes. These results suggest that BAT of Syrian hamsters develops postnatally through two different pathways: the proliferation and differentiation of brown adipocyte progenitors and the conversion of unilocular adipocytes to multilocular brown adipocytes. NEW & NOTEWORTHY Brown and white adipose tissues (BAT and WAT, respectively) are quite different in morphological features and function; however, the boundary between these tissues is obscure. In this study, we histologically evaluated the process of BAT development in Syrian hamsters, which shows postnatal conversion of WAT to BAT. Our results suggest that brown adipocytes arise through two different pathways: the proliferation and differentiation of brown adipocyte progenitors and the conversion from white adipocytes.

Wilms' tumour 1 (WT1) in development, homeostasis and disease

The study of genes mutated in human disease often leads to new insights into biology as well as disease mechanisms. One such gene is Wilms' tumour 1 (WT1), which plays multiple roles in development, tissue homeostasis and disease. In this Primer, I summarise how this multifaceted gene functions in various mammalian tissues and organs, including the kidney, gonads, heart and nervous system. This is followed by a discussion of our current understanding of the molecular mechanisms by which WT1 and its two major isoforms regulate these processes at the transcriptional and post-transcriptional levels.

Directing visceral white adipocyte precursors to a thermogenic adipocyte fate improves insulin sensitivity in obese mice

Visceral adiposity confers significant risk for developing metabolic disease in obesity whereas preferential expansion of subcutaneous white adipose tissue (WAT) appears protective. Unlike subcutaneous WAT, visceral WAT is resistant to adopting a protective thermogenic phenotype characterized by the accumulation of Ucp1⁺ beige/BRITE adipocytes (termed ‘browning’). In this study, we investigated the physiological consequences of browning murine visceral WAT by selective genetic ablation of Zfp423, a transcriptional suppressor of the adipocyte thermogenic program. Zfp423 deletion in fetal visceral adipose precursors (Zfp423^loxP/loxP; Wt1-Cre), or adult visceral white adipose precursors (Pdgfrb^rtTA; TRE-Cre; Zfp423^loxP/loxP), results in the accumulation of beige-like thermogenic adipocytes within multiple visceral adipose depots. Thermogenic visceral WAT improves cold tolerance and prevents and reverses insulin resistance in obesity. These data indicate that beneficial visceral WAT browning can be engineered by directing visceral white adipocyte precursors to a thermogenic adipocyte fate, and suggest a novel strategy to combat insulin resistance in obesity.

DOI:http://dx.doi.org/10.7554/eLife.27669.001

Mammals have different types of fat cells in their bodies. White fat cells store energy for later use, and brown and beige fat cells burn energy to help keep the body warm. Individuals who are obese typically have too many white fat cells in and around their belly. This belly fat, also called visceral fat, accumulates around the organs and is believed to contribute to metabolic diseases, such as diabetes and heart disease. Individuals who are obese also have relatively few brown and beige energy-burning fat cells.

Boosting the amount of brown and beige fat in individuals who are obese has been proposed as a potential way to reduce their risk of metabolic disease. One way to do this would be to encourage white visceral fat cells to become more like energy-burning beige or brown fat cells.

Recent research has shown that white fat cells contain higher amounts of a protein called Zfp423 than brown or beige fat cells. This protein turns off the genes that fat cells use to burn energy and so keeps white fat cells in an energy-storing state. Now, Hepler et al. show that genetically modifying mice to turn off the gene that produces Zfp423 specifically in the precursor cells that become white fat cells causes more energy-burning beige cells to appear in their visceral fat.

The genetically modified mice were better able to tolerate cold than normal mice. When placed on a high-fat diet, the modified mice were also less likely to become resistant to the effects of the hormone insulin – a process that can lead to the development of type 2 diabetes and may be linked to heart disease. This suggests that treatments that prevent Zfp423 from working in fat cells could help to treat or prevent diabetes and heart disease in people who are obese. Before such treatments can be developed, further work is needed to investigate how Zfp423 works in more detail, and to confirm that it has the same effects in human fat cells as it does in mice.

DOI:http://dx.doi.org/10.7554/eLife.27669.002

Fifty shades of white: Understanding heterogeneity in white adipose stem cells

The excessive expansion of white adipose tissue underlies the global obesity epidemic. However, not all fat is equal, and the impact of heterogeneity on the development and expansion of different adipose depots is becoming increasingly apparent. Two mechanisms are responsible for the growth of adipose tissue: hyperplasia (increasing adipocyte number) and hypertrophy (increasing adipocyte size). The former relies on the differentiation of adipocyte stem cells, which reside within the adipose stromal vascular fraction. Many differences in gene expression, adipogenesis, and the response to obesogenic stimuli have been described when comparing adipose stem cells from different depots. Considering that there is disparity in the pathogenicity of the depots, understanding this heterogeneity has clinically relevant implications. Here we review the current knowledge surrounding such differences, in the context of development, expansion and therapeutics. Moreover, given the importance of these differences, we suggest that careful consideration for the precise methodologies used, is essential if we are to truly understand the physiologically relevant consequences of this heterogeneity.

Role of Epicardial Adipose Tissue in Health and Disease: A Matter of Fat?

Epicardial adipose tissue (EAT) is a small but very biologically active ectopic fat depot that surrounds the heart. Given its rapid metabolism, thermogenic capacity, unique transcriptome, secretory profile, and simply measurability, epicardial fat has drawn increasing attention among researchers attempting to elucidate its putative role in health and cardiovascular diseases. The cellular crosstalk between epicardial adipocytes and cells of the vascular wall or myocytes is high and suggests a local role for this tissue. The balance between protective and proinflammatory/profibrotic cytokines, chemokines, and adipokines released by EAT seem to be a key element in atherogenesis and could represent a future therapeutic target. EAT amount has been found to predict clinical coronary outcomes. EAT can also modulate cardiac structure and function. Its amount has been associated with atrial fibrillation, coronary artery disease, and sleep apnea syndrome. Conversely, a beiging fat profile of EAT has been identified. In this review, we describe the current state of knowledge regarding the anatomy, physiology and pathophysiological role of EAT, and the factors more globally leading to ectopic fat development. We will also highlight the most recent findings on the origin of this ectopic tissue, and its association with cardiac diseases. © 2017 American Physiological Society. Compr Physiol 7:1051-1082, 2017.

Homeotic and Embryonic Gene Expression in Breast Adipose Tissue and in Adipose Tissues Used as Donor Sites in Plastic Surgery

BACKGROUND

Autologous fat grafting has become an essential procedure in breast reconstructive surgery. However, molecular knowledge of different adipose donor sites remains inadequate. Tissue regeneration studies have shown that it is essential to match the Hox code of transplanted cells and host tissues to achieve correct repair. This study aims to provide a better molecular understanding of adipose tissue.

METHODS

Over the course of 1 year, the authors prospectively included 15 patients and studied seven adipose areas: chin, breast, arm, abdomen, thigh, hip, and knee. The first step consisted of the surgical harvesting of adipose tissue. RNA was then extracted and converted into cDNA to study gene expression levels of 10 targeted genes by real-time polymerase chain reaction.

RESULTS

Forty samples from Caucasian women with a mean age of 48 years were studied. The expression of PAX3, a marker of neuroectodermal origin, was significantly higher in the breast, with a decreasing gradient from the upper to lower areas of the body. An inverse gradient was found for the expression of HOXC10. This expression profile was statistically significant for the areas of the thigh and knee compared with the breast (p < 0.0083).

CONCLUSIONS

Breast fat may have a specific embryologic origin compared with the knee and thigh. The reinjection of adipocytes from the infraumbilical area leads to the transfer of cells highly expressing HOXC10. This study raises questions about the safety of this procedure, and future studies will be required to examine molecular modifications of adipose cells transferred to a heterotopic location.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

Suboptimal maternal nutrition during early-to-mid gestation in the sheep enhances pericardial adiposity in the near-term fetus

Manipulation of the maternal diet at defined stages of gestation influences long-term health by inducing changes in fetal adipose tissue development, characterised as possessing brown and white adipocytes. We determined whether suboptimal maternal nutrition in early-to-mid gestation, followed by ad libitum feeding until term, increases adiposity in the pericardial depot of the sheep fetus. Pericardial adipose tissue was sampled from near-term (140 days) fetuses delivered to mothers fed either 100% (C) or 60% (i.e. nutrient restricted (NR)) of their total metabolisable requirements from 28 to 80 days gestation and then fed ad libitum. Adipose tissue mass, uncoupling protein (UCP) 1 and gene expression of brown and white adipogenic genes was measured. Total visceral and pericardial adiposity was increased in offspring born to NR mothers. The abundance of UCP1 was increased, together with those genes involved in brown (e.g. BMP7 and C/EBPβ) and white (e.g. BMP4 and C/EBPα) adipogenesis, whereas insulin receptor gene expression was downregulated. In conclusion, suboptimal maternal nutrition between early-to-mid gestation followed by ad libitum feeding enhances pericardial adiposity near to term. A combination of raised UCP1 and adipose tissue mass could improve survival following cold exposure at birth. In the longer term, this enhanced adipogenic potential could predispose to greater pericardial adiposity.

The expanding problem of adipose depot remodeling and postnatal adipocyte progenitor recruitment

The rising incidence of obesity and associated metabolic diseases has increased the urgency in understanding all aspects of adipose tissue biology. This includes the function of adipocytes, how adipose tissue expands in obesity, and how expanded adipose tissues in adults can impact physiology. Here, we highlight the growing appreciation for the importance of de novo adipocyte differentiation to adipose tissue expansion in adult humans and animals. We detail recent efforts to identify adipose precursor populations that contribute to the physiological postnatal recruitment of white, brown, and beige adipocytes in mice, and summarize new data that reveal the complexity of adipose tissue development in vivo.

Maternal Retinoids Increase PDGFRα+ Progenitor Population and Beige Adipogenesis in Progeny by Stimulating Vascular Development

Maternal vitamin A intake varies but its impact on offspring metabolic health is unknown. Here we found that maternal vitamin A or retinoic acid (RA) administration expanded PDGFRα⁺ adipose progenitor population in progeny, accompanied by increased blood vessel density and enhanced brown-like (beige) phenotype in adipose tissue, protecting offspring from obesity. Blockage of retinoic acid signaling by either BMS493 or negative RA receptor (RARαDN) over-expression abolished the increase in blood vessel density, adipose progenitor population, and beige adipogenesis stimulated by RA. Furthermore, RA-induced beige adipogenesis was blocked following vascular endothelial growth factor receptor (VEGFR) 2 knock out in PDGFRα⁺ cells, suggesting its mediatory role. Our data reveal an intrinsic link between maternal retinoid level and offspring health via promoting beige adipogenesis. Thus, enhancing maternal retinoids is an amiable therapeutic strategy to prevent obesity in offspring, especially for those born to obese mothers which account for one third of all pregnancies.

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Maternal vitamin A supplementation increases blood vessel density and expands adipose progenitor population in progeny.

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Maternal vitamin A supplementation enhances brown-like phenotype in adipose tissues.

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Maternal vitamin A supplementation protects offspring from diet induced obesity.

Vitamin A and its metabolite, retinoic acid, play key roles in adipogenesis and energy expenditure of adipose tissues. In mice and humans, vitamin A intake is inversely correlated with adiposity. This study has uncovered a role for maternal retinoids in fetal adipose development. Maternal vitamin A supplementation or RA administration increases adipose progenitor population and promotes beige adipogenesis, which protects offspring from diet induced obesity in later life.

Metabolism disrupting chemicals and metabolic disorders

The recent epidemics of metabolic diseases, obesity, type 2 diabetes(T2D), liver lipid disorders and metabolic syndrome have largely been attributed to genetic background and changes in diet, exercise and aging. However, there is now considerable evidence that other environmental factors may contribute to the rapid increase in the incidence of these metabolic diseases. This review will examine changes to the incidence of obesity, T2D and non-alcoholic fatty liver disease (NAFLD), the contribution of genetics to these disorders and describe the role of the endocrine system in these metabolic disorders. It will then specifically focus on the role of endocrine disrupting chemicals (EDCs) in the etiology of obesity, T2D and NAFLD while finally integrating the information on EDCs on multiple metabolic disorders that could lead to metabolic syndrome. We will specifically examine evidence linking EDC exposures during critical periods of development with metabolic diseases that manifest later in life and across generations.

Gene expression regional differences in human subcutaneous adipose tissue

BACKGROUND

Accumulation of visceral adipose tissue (VAT) is clearly associated with an increased risk of obesity-related diseases and all-cause mortality, whereas gluteal subcutaneous fat accumulation (g-SAT) is associated with a lower risk. The relative contribution, in term of cardiovascular risk, of abdominal subcutaneous adipose tissue (a-SAT) is still controversial with studies showing both a detrimental effect and a protective role. Animal and in vitro studies demonstrated that adipocytes from visceral and subcutaneous depots have distinct morphological, metabolic and functional characteristics. These regional differences have a key role in the pathogenesis of obesity-related diseases. There is recent evidence that differentiation between upper-body and lower-body adipose tissues might be under control of site-specific sets of developmental genes, such as Homebox (HOX) genes, a group of related genes that control the body plan of an embryo along the anterior-posterior axis. However, the possible heterogeneity between different subcutaneous regions has not been extensively investigated. Here we studied global mRNA expression in g-SAT and a-SAT with a microarray approach. RNA was isolated from g-SAT and a-SAT biopsy, from eight healthy subjects, and hybridized on RNA microarray chips in order to detect regional differences in gene expression.

RESULTS

A total of 131 genes are significantly and differently (>1.5 fold change, p < 0.05) expressed in a-SAT and g-SAT. Expression profiling reveals significant differences in expression of several HOX genes. Interestingly, two molecular signature of visceral adipocyte lineage, homebox genes HOXA5 and NR2F1, are up-regulated in a-SAT versus g-SAT by a 2.5 fold change.

CONCLUSIONS

Our study shows that g-SAT and a-SAT have distinct expression profiles. The finding of a different expression of HOX genes, fundamental during the embryo development, suggests an early regional differentiation of subcutaneous adipose depots. Moreover, the higher expression of HOXA5 and NR2F1, two molecular signatures of visceral adipocytes, in a-SAT suggests that this subcutaneous adipose depot could be more similar to VAT than g-SAT. Our data suggest that we should look at SAT as composed of distinct depots with possibly different impact in obesity associated metabolic complications.

Nutrition modulates Fto and Irx3 gene transcript levels, but does not alter their DNA methylation profiles in rat white adipose tissues

The fat mass and obesity associated (Fto) and iroquois homeobox 3 (Irx3) genes have been recognised as important obesity-related genes. Studies on the expression of these genes in the fat tissue of human and mouse have produced inconsistent results, while similar data on rat are limited. Environmental factors such as diet, should be considered as potential modulators of gene transcript levels through epigenetic mechanisms including DNA methylation. The aim of this study was to evaluate transcription levels and DNA methylation profiles of rat Fto and Irx3 genes in two white adipose tissue depots in response to high-fat and high-protein diets. The relative transcript levels of Fto and Irx3 were shown to be tissue-specific with higher levels detected in subcutaneous fat tissue than in abdominal fat tissue. Moreover, negative correlations between the transcripts of both genes were observed for subcutaneous fat tissue. The identified interactions (e.g. diet×duration of diet regimen) indicated that the diet had an impact on the transcript level; however, this effect was dependent on the duration of the diet regimen. The high-fat diet led to upregulation of Fto and Irx3 linearly with time across the two tissues. DNA methylation of the regulatory regions of the studied genes was very low and not related with the tissue, diet, or duration of diet regimen. Our study revealed that diet was an important factor modulating transcription of Fto and Irx3, but its effect is time-dependent. In contrast, the DNA methylation profiles of Fto and Irx3 were not altered by nutrition, which may indicate that the feeding type, when applied postnatally, did not affect DNA methylation of these genes.

Sorting out adipocyte precursors and their role in physiology and disease

The ability to maintain and expand the pool of adipocytes in adults is integral to the regulation of energy balance, tissue/stem cell homeostasis, and disease pathogenesis. For decades, our knowledge of adipocyte precursors has relied on cellular models. The identity of native adipocyte precursors has remained unclear. Recent studies have identified distinct adipocyte precursor populations that are physiologically regulated and contribute to the development, maintenance, and expansion of adipocyte pools in mice. With new tools available, the properties of adipocyte precursors can now be defined, and the regulation and function of adipose plasticity in development and physiology can be explored.

Emerging Roles of Adipose Progenitor Cells in Tissue Development, Homeostasis, Expansion and Thermogenesis

Stem or progenitor cells are an essential component for the development, homeostasis, expansion, and regeneration of many tissues. Within white adipose tissue (WAT) reside vascular-resident adipose progenitor cells (APCs) that can proliferate and differentiate into either white or beige/brite adipocytes, which may control adiposity. Recent studies have begun to show that APCs can be manipulated to control adiposity and counteract 'diabesity'. However, much remains unknown about the identity of APCs and how they may control adiposity in response to homeostatic and external cues. Here, we discuss recent advances in our understanding of adipose progenitors and cover a range of topics, including the stem cell/progenitor lineage, their niche, their developmental and adult roles, and their role in cold-induced beige/brite adipocyte formation.