A Renewable Source of Human Beige Adipocytes for Development of Therapies to Treat Metabolic Syndrome

Loss of RREB1 reduces adipogenesis and improves insulin sensitivity in mouse and human adipocytes

There are multiple independent genetic signals at the Ras-responsive element binding protein 1 (RREB1) locus associated with type 2 diabetes risk, fasting glucose, ectopic fat, height, and bone mineral density. We have previously shown that loss of RREB1 in pancreatic beta cells reduces insulin content and impairs islet cell development and function. However, RREB1 is a widely expressed transcription factor and the metabolic impact of RREB1 loss in vivo remains unknown. Here, we show that male and female global heterozygous knockout (Rreb1 +/-) mice have reduced body length, weight, and fat mass on high-fat diet. Rreb1+/- mice have sex- and diet-specific decreases in adipose tissue and adipocyte size; male mice on high-fat diet had larger gonadal adipocytes, while males on standard chow and females on high-fat diet had smaller, more insulin sensitive subcutaneous adipocytes. Mouse and human precursor cells lacking RREB1 have decreased adipogenic gene expression and activated transcription of genes associated with osteoblast differentiation, which was associated with Rreb1 +/- mice having increased bone mineral density in vivo. Finally, human carriers of RREB1 T2D protective alleles have smaller adipocytes, consistent with RREB1 loss-of-function reducing diabetes risk.

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.

Use of brown adipose tissue transplantation and engineering as a thermogenic therapy in obesity and metabolic disease

The induction of thermogenesis in brown adipose tissue is emerging as an attractive therapy for obesity and metabolic syndrome. However, the long-term efficacy and safety of clinical pharmaceutical agents have yet to be fully characterized. The transplantation of brown adipose tissue represents an alternative approach that might have a therapeutic effect by inducing a long-term increase in energy expenditure. However, limited tissue resources hinder the development of transplantation. Stem cell-based therapy and brown adipose tissue engineering, in addition to transplantation, represent alternative approaches that might resolve this problem. In this article, we discuss recent advances in understanding the mechanisms and applications of brown adipose tissue transplantation in the treatment of obesity and related metabolic disorders. Specifically, the induction of brown adipocytes and the fabrication of engineered brown adipose tissue as novel transplantation resources have long-term effects on ameliorating metabolic defects in rodent models. Additionally, we explore future prospects regarding the development of three-dimensional engineered brown adipose tissue and the associated challenges.

Unleashing the potential of adipose organoids: A revolutionary approach to combat obesity-related metabolic diseases

Obesity-related metabolic diseases, including obesity, diabetes, hyperlipidemia, and non-alcoholic fatty liver diseases pose a significant threat to health. However, comprehensive pathogenesis exploration and effective therapy development are impeded by the limited availability of human models. Notably, advances in organoid technology enable the generation of adipose organoids that recapitulate structures and functions of native human adipose tissues to investigate mechanisms and develop corresponding treatments for obesity-related metabolic diseases. Here, we review the general principles, sources, and three-dimensional techniques for engineering adipose organoids, along with strategies to promote maturation. We also outline the application of white adipose organoids, primarily for disease modeling and drug screening, and highlight the therapeutic potential of thermogenic beige and brown adipose organoids in promoting weight loss and glucose and lipid metabolic homeostasis. We also discuss the challenges and prospects in the establishment and bench-to-bedside of adipose organoids, as well as their potential applications.

Navigating the Adipocyte Precursor Niche: Cell-Cell Interactions, Regulatory Mechanisms and Implications for Adipose Tissue Homeostasis

Support for stem cell self-renewal and differentiation hinges upon the intricate microenvironment termed the stem cell 'niche'. Within the adipose tissue stem cell niche, diverse cell types, such as endothelial cells, immune cells, mural cells, and adipocytes, intricately regulate the function of adipocyte precursors. These interactions, whether direct or indirect, play a pivotal role in governing the balance between self-renewal and differentiation of adipocyte precursors into adipocytes. The mechanisms orchestrating the maintenance and coordination of this niche are still in the early stages of comprehension, despite their crucial role in regulating adipose tissue homeostasis. The complexity of understanding adipocyte precursor renewal and differentiation is amplified due to the challenges posed by the absence of suitable surface receptors for identification, limitations in creating optimal ex vivo culture conditions for expansion and constraints in conducting in vivo studies. This review delves into the current landscape of knowledge surrounding adipocyte precursors within the adipose stem cell niche. We will review the identification of adipocyte precursors, the cell-cell interactions they engage in, the factors influencing their renewal and commitment toward adipocytes and the transformations they undergo during instances of obesity.

Adipose tissue‑derived extracellular vesicles: Systemic messengers in health and disease (Review)

Adipose tissue (AT) is a complicated metabolic organ consisting of a heterogeneous population of cells that exert wide‑ranging effects on the regulation of systemic metabolism and in maintaining metabolic homeostasis. Various obesity‑related complications are associated with the development of dysfunctional AT. As an essential transmitter of intercellular information, extracellular vesicles (EVs) have recently been recognized as crucial in regulating multiple physiological functions. AT‑derived extracellular vesicles (ADEVs) have been shown to facilitate cellular communication both inside and between ATs and other peripheral organs. Here, the role of EVs released from ATs in the homeostasis of metabolic and cardiovascular diseases, cancer, and neurological disorders by delivering lipids, proteins, and nucleic acids between different cells is summarized. Furthermore, the differences in the sources of ADEVs, such as adipocytes, AT macrophages, AT‑derived stem cells, and AT‑derived mesenchymal stem cells, are also discussed. This review may provide valuable information for the potential application of ADEVs in metabolic syndrome, cardiovascular diseases, cancer, and neurological disorders.

Amino acids contribute to adaptive thermogenesis. New insights into the mechanisms of action of recent drugs for metabolic disorders are emerging

Adaptive thermogenesis is the heat production by muscle contractions (shivering thermogenesis) or brown adipose tissue (BAT) and beige fat (non-shivering thermogenesis) in response to external stimuli, including cold exposure. BAT and beige fat communicate with peripheral organs and the brain through a variegate secretory and absorption processes - controlling adipokines, microRNAs, extracellular vesicles, and metabolites - and have received much attention as potential therapeutic targets for managing obesity-related disorders. The sympathetic nervous system and norepinephrine-releasing adipose tissue macrophages (ATM) activate uncoupling protein 1 (UCP1), expressed explicitly in brown and beige adipocytes, dissolving the electrochemical gradient and uncoupling tricarboxylic acid cycle and the electron transport chain from ATP production. Mounting evidence has attracted attention to the multiple effects of dietary and endogenously synthesised amino acids in BAT thermogenesis and metabolic phenotype in animals and humans. However, the mechanisms implicated in these processes have yet to be conclusively characterized. In the present review article, we aim to define the principal investigation areas in this context, including intestinal microbiota constitution, adipose autophagy modulation, and secretome and metabolic fluxes control, which lead to increased brown/beige thermogenesis. Finally, also based on our recent epicardial adipose tissue results, we summarise the evidence supporting the notion that the new dual and triple agonists of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon (GCG) receptor - with never before seen weight loss and insulin-sensitizing efficacy - promote thermogenic-like amino acid profiles in BAT with robust heat production and likely trigger sympathetic activation and adaptive thermogenesis by controlling amino acid metabolism and ATM expansion in BAT and beige fat.

Optogenetic activation of UCP1-dependent thermogenesis in brown adipocytes

Brown adipocytes are unique in that they expend energy and produce heat to maintain euthermia through expression of uncoupling protein-1 (UCP1). Given their propensity to stimulate weight loss and promote resistance to obesity, they are a compelling interventional target for obesity-related disorders. Here, we tested whether an optogenetic approach could be used to activate UCP1-dependent thermogenesis in brown adipocytes. We generated brown adipocytes expressing a bacterial-derived photoactivatable adenylyl cyclase (bPAC) that, upon blue light stimulation, increases UCP1 expression, fuel uptake and thermogenesis. This unique system allows for precise, chemical free, temporal control of UCP1-dependent thermogenesis, which can aid in our understanding of brown adipocyte biology and development of therapies that target obesity-related disorders.

Knocking Down CDKN2A in 3D hiPSC-Derived Brown Adipose Progenitors Potentiates Differentiation, Oxidative Metabolism and Browning Process

Human induced pluripotent stem cells (hiPSCs) have the potential to be differentiated into any cell type, making them a relevant tool for therapeutic purposes such as cell-based therapies. In particular, they show great promise for obesity treatment as they represent an unlimited source of brown/beige adipose progenitors (hiPSC-BAPs). However, the low brown/beige adipocyte differentiation potential in 2D cultures represents a strong limitation for clinical use. In adipose tissue, besides its cell cycle regulator functions, the cyclin-dependent kinase inhibitor 2A (CDKN2A) locus modulates the commitment of stem cells to the brown-like type fate, mature adipocyte energy metabolism and the browning of adipose tissue. Here, using a new method of hiPSC-BAPs 3D culture, via the formation of an organoid-like structure, we silenced CDKN2A expression during hiPSC-BAP adipogenic differentiation and observed that knocking down CDKN2A potentiates adipogenesis, oxidative metabolism and the browning process, resulting in brown-like adipocytes by promoting UCP1 expression and beiging markers. Our results suggest that modulating CDKN2A levels could be relevant for hiPSC-BAPs cell-based therapies.

Blockage of PPARγ T166 phosphorylation enhances the inducibility of beige adipocytes and improves metabolic dysfunctions

Beige adipocytes in mammalian white adipose tissue (WAT) can reinforce fat catabolism and energy expenditure. Promoting beige adipocyte biogenesis is a tantalizing tactic for combating obesity and its associated metabolic disorders. Here, we report that a previously unidentified phosphorylation pattern (Thr166) in the DNA-binding domain of PPARγ regulates the inducibility of beige adipocytes. This unique posttranslational modification (PTM) pattern influences allosteric communication between PPARγ and DNA or coactivators, which impedes the PPARγ-mediated transactivation of beige cell-related gene expression in WAT. The genetic mutation mimicking T166 phosphorylation (p-T166) hinders the inducibility of beige adipocytes. In contrast, genetic or chemical intervention in this PTM pattern favors beige cell formation. Moreover, inhibition of p-T166 attenuates metabolic dysfunction in obese mice. Our results uncover a mechanism involved in beige cell fate determination. Moreover, our discoveries provide a promising strategy for guiding the development of novel PPARγ agonists for the treatment of obesity and related metabolic disorders.

Optogenetics Sheds Light on Brown and Beige Adipocytes

Excessive food intake leads to lipid accumulation in white adipose tissue, triggering inflammation, cellular stress, insulin resistance, and metabolic syndrome. In contrast, the dynamic energy expenditure and heat generation of brown and beige adipose tissue, driven by specialized mitochondria, render it an appealing candidate for therapeutic strategies aimed at addressing metabolic disorders. This review examines the therapeutic potential of brown and beige adipocytes for obesity and metabolic disorders, focusing on recent studies that employ optogenetics for thermogenesis control in these cells. The findings delve into the mechanisms underlying UCP1-dependent and UCP1-independent thermogenesis and how optogenetic approaches can be used to precisely modulate energy expenditure and induce thermogenesis. The convergence of adipocyte biology and optogenetics presents an exciting frontier in combating metabolic disorders and advancing our understanding of cellular regulation and energy balance.

Modelling metabolic diseases and drug response using stem cells and organoids

Metabolic diseases, including obesity, diabetes mellitus and cardiovascular disease, are a major threat to health in the modern world, but efforts to understand the underlying mechanisms and develop rational treatments are limited by the lack of appropriate human model systems. Notably, advances in stem cell and organoid technology allow the generation of cellular models that replicate the histological, molecular and physiological properties of human organs. Combined with marked improvements in gene editing tools, human stem cells and organoids provide unprecedented systems for studying mechanisms of metabolic diseases. Here, we review progress made over the past decade in the generation and use of stem cell-derived metabolic cell types and organoids in metabolic disease research, especially obesity and liver diseases. In particular, we discuss the limitations of animal models and the advantages of stem cells and organoids, including their application to metabolic diseases. We also discuss mechanisms of drug action, understanding the efficacy and toxicity of existing therapies, screening for new treatments and pursuing personalized therapies. We highlight the potential of combining stem cell-derived organoids with gene editing and functional genomics to revolutionize the approach to finding treatments for metabolic diseases.

FTO m6A Demethylase in Obesity and Cancer: Implications and Underlying Molecular Mechanisms

Fat mass and obesity-associated protein (FTO) is the first reported RNA N6-methyladenosine (m6A) demethylase in eukaryotic cells. m6A is considered as the most abundant mRNA internal modification, which modulates several cellular processes including alternative splicing, stability, and expression. Genome-wide association studies (GWAS) identified single-nucleotide polymorphisms (SNPs) within FTO to be associated with obesity, as well as cancer including endometrial cancer, breast cancer, pancreatic cancer, and melanoma. Since the initial classification of FTO as an m6A demethylase, various studies started to unravel a connection between FTO’s demethylase activity and the susceptibility to obesity on the molecular level. FTO was found to facilitate adipogenesis, by regulating adipogenic pathways and inducing pre-adipocyte differentiation. FTO has also been investigated in tumorigenesis, where emerging studies suggest m6A and FTO levels are dysregulated in various cancers, including acute myeloid leukemia (AML), glioblastoma, cervical squamous cell carcinoma (CSCC), breast cancer, and melanoma. Here we review the molecular bases of m6A in tumorigenesis and adipogenesis while highlighting the controversial role of FTO in obesity. We provide recent findings confirming FTO’s causative link to obesity and discuss novel approaches using RNA demethylase inhibitors as targeted oncotherapies. Our review aims to confirm m6A demethylation as a risk factor in obesity and provoke new research in FTO and human disorders.

Melatonin induces fat browning by transdifferentiation of white adipocytes and de novo differentiation of mesenchymal stem cells

The role of melatonin in obesity control is extensively accepted, but its mechanism of action is still unclear. Previously we demonstrated that chronic oral melatonin acts as a brown-fat inducer, driving subcutaneous white adipose tissue (sWAT) into a brown-fat-like function (beige) in obese diabetic rats. However, immunofluorescence characterization of beige depots in sWAT and whether melatonin is a beige-fat inducer by de novo differentiation and/or transdifferentiation of white adipocytes are still undefined. Lean (ZL) and diabetic fatty (ZDF) Zücker rats were subdivided into two groups, control (C) and oral melatonin-supplemented (M, 10 mg kg^-1 day^-1) for 6 weeks. Mesenchymal stem cells (MSCs) were isolated from both rat inguinal fat and human lipoaspirates followed by adipogenesis assays with or without melatonin (50 nM for 12 h in a 24 h period, 12 h+/12 h-) mimicking the light/dark cycle. Immunofluorescence and western-blot assays showed the partial transdifferentiation of white adipocytes in both ZL and ZDF rats, with increasing thermogenic and beige markers, UCP1 and CITED1 and decreasing white adipocyte marker ASC-1 expression. In addition, melatonin increased UCP1, CITED1, and PGC1-α expression in differentiated adipocytes in both rats and humans. These results demonstrate that melatonin increases brown fat in obese diabetic rats by both adipocyte transdifferentiation and de novo differentiation. Furthermore, it promotes beige MSC adipogenesis in humans. This may contribute to the control of body weight attributed to melatonin and its metabolic benefits in human diabesity.

Adipose-Derived Extracellular Vesicles: Systemic Messengers and Metabolic Regulators in Health and Disease

Adipose tissue is comprised of a heterogeneous population of cells that co-operate to perform diverse physiological roles including endocrine-related functions. The endocrine role of adipose tissue enables it to communicate nutritional and health cues to other organs, such as the liver, muscle, and brain, in order to regulate appetite and whole body metabolism. Adipose tissue dysfunction, which is often observed in obesity, is associated with changes in the adipose secretome, which can subsequently contribute to disease pathology. Indeed, secreted bioactive factors released from adipose tissue contribute to metabolic homeostasis and likely play a causal role in disease; however, what constitutes the entirety of the adipose tissue secretome is still poorly understood. Recent advances in nanotechnology have advanced this field substantially and have led to the identification of small, secreted particles known as extracellular vesicles (EVs). These small nano-sized lipid envelopes are released by most cell types and are capable of systemically delivering bioactive molecules, such as nucleic acids, proteins, and lipids. EVs interact with target cells to deliver specific cargo that can then elicit effects in various tissues throughout the body. Adipose tissue has recently been shown to secrete EVs that can communicate with the periphery to maintain metabolic homeostasis, or under certain pathological conditions, drive disease. In this review, we discuss the current landscape of adipose tissue-derived EVs, with a focus on their role in the regulation of metabolic homeostasis and disease pathology.

Functional and Genetic Characterization of Porcine Beige Adipocytes

Beige adipocytes are a distinct type of fat cells with a thermogenic activity that have gained substantial attention as an alternative cellular anti-obesity target in humans. These cells may provide an alternative strategy for the genetic selection of pigs with reduced fat deposition. Despite the presence of beige adipocytes in piglets, the molecular signatures of porcine beige adipocytes remain unclear. Here, white and beige adipocytes from Tibetan piglets were primarily cultured and differentiated. Compared to the white adipocytes, the beige adipocytes exhibited a stronger thermogenic capacity. RNA-sequencing-based genome-wide comparative analyses revealed distinct gene expression profiles for white and beige adipocytes. In addition, two genes, integrin alpha-2 (ITGA2) and calponin 1 (CNN1), which were specifically differentially expressed in porcine beige adipocytes, were further functionally characterized using a loss-of-function approach. Our data showed that both genes were involved in differentiation and thermogenesis of porcine beige adipocytes. Collectively, these data furthered our understanding of gene expression in porcine white and beige adipocytes. Elucidating the genetic basis of beige adipogenesis in pigs will pave the way for molecular design breeding in both pigs and large animal models of human diseases.

Transplantation of fat tissues and iPSC-derived energy expenditure adipocytes to counteract obesity-driven metabolic disorders: Current strategies and future perspectives

Several therapeutic options have been developed to address the obesity epidemic and treat associated metabolic diseases. Despite the beneficial effects of surgery and drugs, effective therapeutic solutions have been held back by the poor long-term efficiency and detrimental side effects. The development of alternative approaches is thus urgently required. Fat transplantation is common practice in many surgical procedures, including aesthetic and reconstructive surgery, and is a budding future direction for treating obesity-related metabolic defects. This review focuses on adipose tissue transplantation and the recent development of cell-based therapies to boost the mass of energy-expenditure cells. Brown adipocyte transplantation is a promising novel therapy to manage obesity and associated metabolic disorders, but the need to have an abundant and relevant source of brown fat tissue or brown adipocytes for transplantation is a major hurdle to overcome. Current studies have focused on the rodent model to obtain a proof of concept of a tissue-transplantation strategy able to achieve effective long-term effects to reverse metabolic defects in obese patients. Future perspectives and opportunities to develop innovative human fat tissue models and 3D engineered hiPSC-adipocytes are discussed.

Mitochondrial regulation and white adipose tissue homeostasis

The important role of mitochondria in the regulation of white adipose tissue (WAT) remodeling and energy balance is increasingly appreciated. The remarkable heterogeneity of the adipose tissue stroma provides a cellular basis to enable adipose tissue plasticity in response to various metabolic stimuli. Regulating mitochondrial function at the cellular level in adipocytes, in adipose progenitor cells (APCs), and in adipose tissue macrophages (ATMs) has a profound impact on adipose homeostasis. Moreover, mitochondria facilitate the cell-to-cell communication within WAT, as well as the crosstalk with other organs, such as the liver, the heart, and the pancreas. A better understanding of mitochondrial regulation in the diverse adipose tissue cell types allows us to develop more specific and efficient approaches to improve adipose function and achieve improvements in overall metabolic health.

Histone H3 methyltransferase Ezh2 promotes white adipocytes but inhibits brown and beige adipocyte differentiation in mice

Obesity is a disease characterized by imbalance between energy intake and expenditure, excessive energy store in white adipocytes, but brown and beige adipocytes consume energy to relieve obesity. In this study, we want to explore the role of the histone H3 methyltransferase Ezh2 in the differentiation of white, brown and beige adipocytes with Ezh2 conditional knockout mice (Ezh2flox/floxPrx1-cre) and mouse embryonic fibroblasts (MEFs). The results showed that Ezh2-deficient mice have a leaner phenotype and less white adipose tissues. The morphological changes in the adipose tissue included smaller white adipose tissue depots, white adipocytes with smaller diameter, smaller lipid droplets inside the brown adipocytes and more beige adipocytes in the Ezh2-deficient mice compared with the control. The differentiation markers of white adipocytes in Ezh2 knockout mice decreased; Ucp1 and other browning markers increased in brown and beige adipocytes. The Ezh2 knockout mice could better tolerate cold stimulation, and they can also resist obesity and insulin resistance induced by a high-fat diet. The Ezh2 inhibitor GSK126 could inhibit the differentiation of MEFs into white adipocytes but promote their differentiation into brown/beige adipocytes. The H3K27me3 demethylase Jmjd3/UTX inhibitor GSKJ4 inhibited MEFs' differentiation into brown/beige adipocytes. These results showed that Ezh2 promotes the differentiation of white adipocytes and inhibits the differentiation of brown and beige adipocytes in vivo and in vitro through its methylase activity and this may represent new knowledge for obesity therapeutic strategy.

Mitochondrial dynamics keep balance of nutrient combustion in thermogenic adipocytes

Non-shivering thermogenesis takes place in brown and beige adipocytes and facilitates cold tolerance and acclimation. However, thermogenesis in adipose tissue also was found to be activated in metabolic overload states for fast utilization of nutrients excess. This observation spurred research interest in mechanisms of thermogenesis regulation for metabolic overload and obesity prevention. One of proposed regulators of thermogenic efficiency in adipocytes is the dynamics of mitochondria, where thermogenesis takes place. Indeed, brown and beige adipocytes exhibit fragmented round-shaped mitochondria, while white adipocytes have elongated organelles with high ATP synthesis. Mitochondrial morphology can determine uncoupling protein 1 (UCP1) content, efficiency of catabolic pathways and electron transport chain, supplying thermogenesis. This review will highlight the co-regulation of mitochondrial dynamics and thermogenesis and formulate hypothetical ways for excessive nutrients burning in response to mitochondrial morphology manipulation.

Pathogenic LMNA variants disrupt cardiac lamina-chromatin interactions and de-repress alternative fate genes

Pathogenic mutations in LAMIN A/C (LMNA) cause abnormal nuclear structure and laminopathies. These diseases have myriad tissue-specific phenotypes, including dilated cardiomyopathy (DCM), but how LMNA mutations result in tissue-restricted disease phenotypes remains unclear. We introduced LMNA mutations from individuals with DCM into human induced pluripotent stem cells (hiPSCs) and found that hiPSC-derived cardiomyocytes, in contrast to hepatocytes or adipocytes, exhibit aberrant nuclear morphology and specific disruptions in peripheral chromatin. Disrupted regions were enriched for transcriptionally active genes and regions with lower LAMIN B1 contact frequency. The lamina-chromatin interactions disrupted in mutant cardiomyocytes were enriched for genes associated with non-myocyte lineages and correlated with higher expression of those genes. Myocardium from individuals with LMNA variants similarly showed aberrant expression of non-myocyte pathways. We propose that the lamina network safeguards cellular identity and that pathogenic LMNA variants disrupt peripheral chromatin with specific epigenetic and molecular characteristics, causing misexpression of genes normally expressed in other cell types.

Insulin resistance in diabetes: The promise of using induced pluripotent stem cell technology

Insulin resistance (IR) is associated with several metabolic disorders, including type 2 diabetes (T2D). The development of IR in insulin target tissues involves genetic and acquired factors. Persons at genetic risk for T2D tend to develop IR several years before glucose intolerance. Several rodent models for both IR and T2D are being used to study the disease pathogenesis; however, these models cannot recapitulate all the aspects of this complex disorder as seen in each individual. Human pluripotent stem cells (hPSCs) can overcome the hurdles faced with the classical mouse models for studying IR. Human induced pluripotent stem cells (hiPSCs) can be generated from the somatic cells of the patients without the need to destroy a human embryo. Therefore, patient-specific hiPSCs can generate cells genetically identical to IR individuals, which can help in distinguishing between genetic and acquired defects in insulin sensitivity. Combining the technologies of genome editing and hiPSCs may provide important information about the genetic factors underlying the development of different forms of IR. Further studies are required to fill the gaps in understanding the pathogenesis of IR and diabetes. In this review, we summarize the factors involved in the development of IR in the insulin-target tissues leading to diabetes. Also, we highlight the use of hPSCs to understand the mechanisms underlying the development of IR.

Effect of Panax notoginseng Saponins and Major Anti-Obesity Components on Weight Loss

The prevalence of individuals who are overweight or obese is rising rapidly globally. Currently, majority of drugs used to treat obesity are ineffective or are accompanied by obvious side effects; hence, the options are very limited. Therefore, it is necessary to find more effective and safer anti-obesity drugs. It has been proven in vivo and in vitro that the active ingredient notoginsenosides isolated from traditional Chinese medicine Panax notoginseng (Burk.) F. H. Chen exhibits anti-obesity effects. Notoginsenosides can treat obesity by reducing lipid synthesis, inhibiting adipogenesis, promoting white adipose tissue browning, increasing energy consumption, and improving insulin sensitivity. Although notoginsenosides are potential drugs for the treatment of obesity, their effects and mechanisms have not been analyzed in depth. In this review, the anti-obesity potential and mechanism of action of notoginsenosides were analyzed; thus laying emphasis on the timely prevention and treatment of obesity.

Adipose stem cells in obesity: challenges and opportunities

Adipose tissue, the storage of excessive energy in the body, secretes various proteins called adipokines, which connect the body’s nutritional status to the regulation of energy balance. Obesity triggers alterations of quantity and quality of various types of cells that reside in adipose tissue, including adipose stem cells (ASCs; referred to as adipose-derived stem/stromal cells in vitro). These alterations in the functionalities and properties of ASCs impair adipose tissue remodeling and adipose tissue function, which induces low-grade systemic inflammation, progressive insulin resistance, and other metabolic disorders. In contrast, the ability of ASCs to recruit new adipocytes when faced with caloric excess leads to healthy adipose tissue expansion, associated with lower amounts of inflammation, fibrosis, and insulin resistance. This review focuses on recent advances in our understanding of the identity of ASCs and their roles in adipose tissue development, homeostasis, expansion, and thermogenesis, and how these roles go awry in obesity. A better understanding of the biology of ASCs and their adipogenesis may lead to novel therapeutic targets for obesity and metabolic disease.

Temperature and species-dependent regulation of browning in retrobulbar fat

Retrobulbar fat deposits surround the posterior retina and optic nerve head, but their function and origin are obscure. We report that mouse retrobulbar fat is a neural crest-derived tissue histologically and transcriptionally resembles interscapular brown fat. In contrast, human retrobulbar fat closely resembles white adipose tissue. Retrobulbar fat is also brown in other rodents, which are typically housed at temperatures below thermoneutrality, but is white in larger animals. We show that retrobulbar fat in mice housed at thermoneutral temperature show reduced expression of the brown fat marker Ucp1, and histological properties intermediate between white and brown fat. We conclude that retrobulbar fat can potentially serve as a site of active thermogenesis, that this capability is both temperature and species-dependent, and that this may facilitate regulation of intraocular temperature.

Caffeic and Chlorogenic Acids Synergistically Activate Browning Program in Human Adipocytes: Implications of AMPK- and PPAR-Mediated Pathways

Caffeic acid (CA) and chlorogenic acid (CGA) are phenolic compounds claimed to be responsible for the metabolic effects of coffee and tea consumption. Along with their structural similarities, they share common mechanisms such as activation of the AMP-activated protein kinase (AMPK) signaling. The present study aimed to investigate the anti-obesity potential of CA and CGA as co-treatment in human adipocytes. The molecular interactions of CA and CGA with key adipogenic transcription factors were simulated through an in silico molecular docking approach. The expression levels of white and brown adipocyte markers, as well as genes related to lipid metabolism, were analyzed by real-time quantitative PCR and Western blot analyses. Mechanistically, the CA/CGA combination induced lipolysis, upregulated AMPK and browning gene expression and downregulated peroxisome proliferator-activated receptor γ (PPARγ) at both transcriptional and protein levels. The gene expression profiles of the CA/CGA-co-treated adipocytes strongly resembled brown-like signatures. Major pathways identified included the AMPK- and PPAR-related signaling pathways. Collectively, these findings indicated that CA/CGA co-stimulation exerted a browning-inducing potential superior to that of either compound used alone which merits implementation in obesity management. Further, the obtained data provide additional insights on how CA and CGA modify adipocyte function, differentiation and lipid metabolism.

Insulin/Glucose-Responsive Cells Derived from Induced Pluripotent Stem Cells: Disease Modeling and Treatment of Diabetes

Type 2 diabetes, characterized by dysfunction of pancreatic β-cells and insulin resistance in peripheral organs, accounts for more than 90% of all diabetes. Despite current developments of new drugs and strategies to prevent/treat diabetes, there is no ideal therapy targeting all aspects of the disease. Restoration, however, of insulin-producing β-cells, as well as insulin-responsive cells, would be a logical strategy for the treatment of diabetes. In recent years, generation of transplantable cells derived from stem cells in vitro has emerged as an important research area. Pluripotent stem cells, either embryonic or induced, are alternative and feasible sources of insulin-secreting and glucose-responsive cells. This notwithstanding, consistent generation of robust glucose/insulin-responsive cells remains challenging. In this review, we describe basic concepts of the generation of induced pluripotent stem cells and subsequent differentiation of these into pancreatic β-like cells, myotubes, as well as adipocyte- and hepatocyte-like cells. Use of these for modeling of human disease is now feasible, while development of replacement therapies requires continued efforts.

The effects of oxytocin to rectify metabolic dysfunction in obese mice are associated with increased thermogenesis

Oxytocin, a protein hormone mainly produced by hypothalamus, has been shown to repress body weight gain in obese animals, in part, by reducing food intake and increasing energy expenditure. Till now, activation of brown fat tissue (BAT) thermogenesis and white adipose tissue (WAT) browning are considered as two main factors for oxytocin-induced energy expenditure. However, the underlying molecular mechanisms are still not understood well. Here, we observed that oxytocin expression in the hypothalamus and its receptor in adipose tissues were induced by cold exposure in mice. In differentiated adipocytes, oxytocin stimulated brown adipocyte specific gene expression by inducing PRDM16. In high fat diet induced obese mice, oxytocin delivery by osmotic minipumps increased body core temperature and decreased body weight gain. Glucose and insulin tolerance were improved by oxytocin. Hyperinsulinemia and fatty liver were ameliorated in oxytocin-treated animals. Moreover, oxytocin treatment induced thermogenic gene expressions in BAT, inguinal WAT (iWAT), and skeletal muscle. Taken together, our findings revealed a new aspect of oxytocin, i.e. oxytocin induces iWAT browning and stimulates thermogenesis in BAT, iWAT and skeletal muscle, through which oxytocin promotes thermogenesis and thus combats obesity and metabolic dysfunctions.

GATA3 induces the upregulation of UCP-1 by directly binding to PGC-1α during adipose tissue browning

OBJECTIVE

Obesity is recognized as the cause of multiple metabolic diseases and is rapidly increasing worldwide. As obesity is due to an imbalance in energy homeostasis, the promotion of energy consumption through browning of white adipose tissue (WAT) has emerged as a promising therapeutic strategy to counter the obesity epidemic. However, the molecular mechanisms of the browning process are not well understood. In this study, we investigated the effects of the GATA family of transcription factors on the browning process.

METHODS

We used qPCR to analyze the expression of GATA family members during WAT browning. In order to investigate the function of GATA3 in the browning process, we used the lentivirus system for the ectopic expression and knockdown of GATA3. Western blot and real-time qPCR analyses revealed the regulation of thermogenic genes upon ectopic expression and knockdown of GATA3. Luciferase reporter assays, co-immunoprecipitation, and chromatin immunoprecipitation were performed to demonstrate that GATA3 interacts with proliferator-activated receptor-γ co-activator-1α (PGC-1α) to regulate the promoter activity of uncoupling protein-1 (UCP-1). Enhanced energy expenditure by GATA3 was confirmed using oxygen consumption assays, and the mitochondrial content was assessed using MitoTracker. Furthermore, we examined the in vivo effects of lentiviral GATA3 overexpression and knockdown in inguinal adipose tissue of mice.

RESULTS

Gata3 expression levels were significantly elevated in the inguinal adipose tissue of mice exposed to cold conditions. Ectopic expression of GATA3 enhanced the expression of UCP-1 and thermogenic genes upon treatment with norepinephrine whereas GATA3 knockdown had the opposite effect. Luciferase reporter assays using the UCP-1 promoter region showed that UCP-1 expression was increased in a dose-dependent manner by GATA3 regardless of norepinephrine treatment. GATA3 was found to directly bind to the promoter region of UCP-1. Furthermore, our results indicated that GATA3 interacts with the transcriptional coactivator PGC-1α to increase the expression of UCP-1. Taken together, we demonstrate that GATA3 has an important role in enhancing energy expenditure by increasing the expression of thermogenic genes both in vitro and in vivo.

CONCLUSION

GATA3 may represent a promising target for the prevention and treatment of obesity by regulating thermogenic capacity.

EoTHINophils: Eosinophils as key players in adipose tissue homeostasis

Eosinophils are granular cells of the innate immune system that are found in almost all vertebrates and some invertebrates. Knowledge of their wide-ranging roles in health and disease has largely been attained through studies in mice and humans. Although eosinophils are typically associated with helminth infections and allergic diseases such as asthma, there is building evidence that beneficial homeostatic eosinophils residing in specific niches are important for tissue development, remodelling and metabolic control. In recent years, the importance of immune cells in the regulation of adipose tissue homeostasis has been a focal point of research efforts. There is an abundance of anti-inflammatory innate immune cells in lean white adipose tissue, including macrophages, eosinophils and group 2 innate lymphoid cells, which promote energy homeostasis and stimulate the development of thermogenic beige adipocytes. This review will evaluate evidence for the role of adipose-resident eosinophils in local tissue homeostasis, beiging and systemic metabolism, highlighting where more research is needed to establish the specific effector functions that adipose eosinophils perform in response to different internal and external cues.

The application of stem cell therapy and brown adipose tissue transplantation in metabolic disorders

The discovery of brown fat in adult humans has led to increased research of the thermogenic function of this tissue in various metabolic diseases. In addition, high levels of brown fat have been correlated with lower body mass index values. Therefore, increasing brown fat mass and/or activity through methods such as the browning of white fat is considered a promising strategy to prevent and treat obesity-associated diseases. Cell-based approaches using mesenchymal stromal cells and brown adipose tissue (BAT) have been utilized to directly increase BAT mass/activity through cell and tissue implantation into animals. In addition, recent studies evaluating the transplantation of human embryonic stem cells and induced pluripotent stem (iPS) cells have shown promising results in terms of positive metabolic function. In this comprehensive review, we provide a summary of the research over the past 10 years with regard to stem cell therapy and brown fat tissue transplantation for the effective treatment of metabolic syndrome. Recent advancements in stem cell methods have allowed for the production of brown adipocytes from human iPS cells, which represent an unlimited source of cellular material with which to study adipocyte development. In addition, this process is expected to be used to further explore drug- and cell-based therapies to treat obesity-related metabolic complications.

Human beige adipocytes for drug discovery and cell therapy in metabolic diseases

Human beige adipocytes (BAs) have potential utility for the development of therapeutics to treat diabetes and obesity-associated diseases. Although several reports have described the generation of beige adipocytes in vitro, their potential utility in cell therapy and drug discovery has not been reported. Here, we describe the generation of BAs from human adipose-derived stem/stromal cells (ADSCs) in serum-free medium with efficiencies >90%. Molecular profiling of beige adipocytes shows them to be similar to primary BAs isolated from human tissue. In vitro, beige adipocytes exhibit uncoupled mitochondrial respiration and cAMP-induced lipolytic activity. Following transplantation, BAs increase whole-body energy expenditure and oxygen consumption, while reducing body-weight in recipient mice. Finally, we show the therapeutic utility of BAs in a platform for high-throughput drug screening (HTS). These findings demonstrate the potential utility of BAs as a cell therapeutic and as a tool for the identification of drugs to treat metabolic diseases.

Methods to generate beige adipocytes from a human cell source are inefficient. Here, the authors present a protocol that efficiently generates beige adipocytes from human adipose-derived stem cells (ADSCs), which have potential utility in therapeutic development relating to metabolic diseases such as type 2 diabetes.

Hepatocyte-like cells derived from induced pluripotent stem cells: A versatile tool to understand lipid disorders

Dyslipidemias are strongly linked to the development of atherosclerotic cardiovascular disease. Most dyslipidemias find their origin in the liver. In recent years, the differentiation of induced pluripotent stem cells (iPSCs) into hepatocyte-like cells has provided a versatile platform for the functional study of various dyslipidemias, both rare genetic dyslipidemia as well as common lipid disorders associated with insulin resistance or non-alcoholic fatty liver disease. In addition, iPSC-derived hepatocytes can serve as a cell model for developing novel lipid lowering therapies and have the potential of regenerative medicine. This review provides an overview of these developments.

A developed serum-free medium and an optimized chemical cocktail for direct conversion of human dermal fibroblasts into brown adipocytes

Brown adipocytes coordinate systemic energy metabolism associated with the pathogenesis of obesity and related metabolic diseases including type 2 diabetes. We have previously reported chemical compound-induced brown adipocytes (ciBAs) converted from human dermal fibroblasts without using transgenes. In this study, to reveal a precise molecular mechanism underlying the direct conversion and human adipocyte browning, we developed serum-free brown adipogenic medium (SFBAM) with an optimized chemical cocktail consisting of Rosiglitazone, Forskolin, and BMP7. During the direct conversion, treatment with BMP7 enhanced Ucp1 expression rather than the conversion efficiency in the absence of BMP signalling inhibitors. Moreover, treatment with a TGF-β signalling pathway inhibitor was no longer required in the serum-free medium, likely because the TGF-β pathway was already suppressed. SFBAM and the chemical cocktail efficiently converted human dermal fibroblasts into ciBAs within four weeks. The ciBAs exhibited increased mitochondrial levels, elevated oxygen consumption rate, and a response to β-adrenergic receptor agonists. Thus the ciBAs converted by the serum-free medium and the chemical cocktail provide a novel model of human brown (beige) adipocytes applicable for basic research, drug screening, and clinical applications.

Engineering Prostate Cancer from Induced Pluripotent Stem Cells-New Opportunities to Develop Preclinical Tools in Prostate and Prostate Cancer Studies

One of the key issues hampering the development of effective treatments for prostate cancer is the lack of suitable, tractable, and patient-specific in vitro models that accurately recapitulate this disease. In this review, we address the challenges of using primary cultures and patient-derived xenografts to study prostate cancer. We describe emerging approaches using primary prostate epithelial cells and prostate organoids and their genetic manipulation for disease modelling. Furthermore, the use of human prostate-derived induced pluripotent stem cells (iPSCs) is highlighted as a promising complimentary approach. Finally, we discuss the manipulation of iPSCs to generate 'avatars' for drug disease testing. Specifically, we describe how a conceptual advance through the creation of living biobanks of "genetically engineered cancers" that contain patient-specific driver mutations hold promise for personalised medicine.

Adipose-Derived Stromal Cells Attenuate Adipose Inflammation in Obesity through Adipocyte Browning and Polarization of M2 Macrophages

Obesity is a metabolic condition associated with multiple health problems such as endocrine and metabolic dysfunction and chronic inflammation in adipose tissues. In this study, the ADSCs could be stimulated to differentiate into brown adipocyte with rosiglitazone treatment based on the Oil-Red-O staining trial. Furthermore, the multilocular lipid droplets located in the center was increased in differentiated brown adipocytes, and brown fat-associated proteins, UCP1, PPAR-γ, and LPL were highly expressed in brown adipocytes differentiated from ADSCs. Additionally, the results of animal experiments showed that both weight and amount of VLDL and LDL were decreased in the serum of obese mice after transplantation of rosiglitazone-induced brown adipocytes, while the level of HDL increased. Moreover, the proteins associated with lipid metabolism, LPA and UCP1, were downregulated, and the inflammatory response was suppressed through inhibition of the ITGAM/NF-κB-mediated proinflammatory responses and polarization of M2 macrophages. Similarly, the amounts of proinflammatory cytokines, TNF-α, IL-6, and IL-1β were decreased after rosiglitazone-induced brown adipocyte transplantation. On the contrary, anti-inflammatory cytokine IL-10 was significantly increased in both groups of obese mice, with or without brown adipocyte transplantation. Therefore, the adipose-derived stromal cells with induced browning could promote lipid consumption and alternative polarization of M2 macrophages to attenuate adipose inflammation in obesity mouse models, which thus provides a potential therapy for obesity.

In vitro tissue-engineered adipose constructs for modeling disease

BACKGROUND

Adipose tissue is a vital tissue in mammals that functions to insulate our bodies, regulate our internal thermostat, protect our organs, store energy (and burn energy, in the case of beige and brown fat), and provide endocrine signals to other organs in the body. Tissue engineering of adipose and other soft tissues may prove essential for people who have lost this tissue from trauma or disease.

MAIN TEXT

In this review, we discuss the applications of tissue-engineered adipose tissue specifically for disease modeling applications. We provide a basic background to adipose depots and describe three-dimensional (3D) in vitro adipose models for obesity, diabetes, and cancer research applications.

CONCLUSIONS

The approaches to engineering 3D adipose models are diverse in terms of scaffold type (hydrogel-based, silk-based and scaffold-free), species of origin (H. sapiens and M. musculus) and cell types used, which allows researchers to choose a model that best fits their application, whether it is optimization of adipocyte differentiation or studying the interaction of adipocytes and other cell types like endothelial cells. In vitro 3D adipose tissue models support discoveries into the mechanisms of adipose-related diseases and thus support the development of novel anti-cancer or anti-obesity/diabetes therapies.

Brown adipocytes from induced pluripotent stem cells-how far have we come?

A global increase in the number of individuals who are either overweight or obese is leading to a higher incidence of type 2 diabetes (T2D). Behavioral interventions for the treatment of obesity have yet to deliver desired outcomes, thus introducing a pressing need for molecular- and cellular-based therapies. Excess energy from food is stored in the form of triglycerides in white adipose tissue, which expands during weight gain and can lead to insulin resistance and T2D. By contrast, brown adipose tissue (BAT) releases energy from metabolic substrates in the form of heat and secretes factors that can reverse metabolic disease by acting systemically. Therefore, the ability to increase BAT activity is a promising approach to improve energy balance and metabolic homeostasis. Methods are now being developed to generate brown adipocytes from human induced pluripotent stem cells (hiPSCs), which would (1) provide an unlimited source of cellular material to study human brown adipogenesis, and (2) could be used to develop drug- and cell-based therapies for the treatment of metabolic complications associated with obesity. This article reviews basic BAT biology and details the current progress toward developing brown adipocytes from hiPSCs.

Neuregulin 4 Is a Novel Marker of Beige Adipocyte Precursor Cells in Human Adipose Tissue

Background: Nrg4 expression has been linked to brown adipose tissue activity and browning of white adipocytes in mice. Here, we aimed to investigate whether these observations could be translated to humans by investigating NRG4 mRNA and markers of brown/beige adipocytes in human visceral (VAT) and subcutaneous adipose tissue (SAT). We also studied the possible association of NRG4 with insulin action.

Methods: SAT and VAT NRG4 and markers of brown/beige (UCP1, UCP3, and TMEM26)-related gene expression were analyzed in two independent cohorts (n = 331 and n = 59). Insulin resistance/sensitivity was measured using HOMA_IR and glucose infusion rate during euglycemic hyperinsulinemic clamp.

Results: In both cohort 1 and cohort 2, NRG4 and thermogenic/beige-related gene expression were significantly increased in VAT compared to SAT. Adipogenic-related genes followed an opposite pattern. In cohort 1, VAT NRG4 gene expression was positively correlated with BMI and expression of UCP1, UCP3, TMEM26, and negatively with adipogenic (FASN, PPARG, and SLC2A4)- and inflammatory (IL6 and IL8)-related genes. In SAT, NRG4 gene expression was negatively correlated with HOMA_IR and positively with UCP1 and TMEM26 gene expression. Multiple linear regression analysis revealed that expression of TMEM26 gene was the best predictor of NRG4 gene expression in both VAT and SAT. Specifically, NRG4 and TMEM26 gene expression was significantly increased in VAT, but not in SAT stromal vascular fraction cells (p < 0.001). In cohort 2, the significant association between NRG4 and TMEM26 gene expression in both VAT and SAT was confirmed, and SAT NRG4 gene expression also was positively correlated with insulin action and the expression of UCP1.

Conclusion: Current findings suggest NRG4 gene expression as a novel marker of beige adipocytes in human adipose tissue.

Human Pluripotent Stem Cells: A Relevant Model to Identify Pathways Governing Thermogenic Adipocyte Generation

Brown and brown-like adipocytes (BAs) are promising cell targets to counteract obesity thanks to their potential to drain and oxidize circulating glucose and triglycerides. However, the scarcity of BAs in human adults is a major limitation for energy expenditure based therapies. Enhanced characterization of BA progenitor cells (BAPs) and identification of critical pathways regulating their generation and differentiation into mature BAs would be an effective way to increase the BA mass. The identification of molecular mechanisms involved in the generation of thermogenic adipocytes is progressing substantially in mice. Much less is known in humans, thus highlighting the need for an in vitro model of human adipocyte development. Pluripotent stem cells (PSCs), i.e., embryonic stem cells and induced pluripotent stem cells, help gain insight into the different phases in the development of multiple cell types. We will discuss the capacity of human PSCs to differentiate into BAs in this review. Several groups, including ours, have reported low spontaneous adipocyte generation from PSCs. However, factors governing the differentiation of induced pluripotent stem cell-derived BA progenitors cells were recently identified, and the TGFβ signaling pathway has a pivotal role. The development of new relevant methods, such as the differentiation of hPSC-BAPs into 3D adipospheres to better mimick the lobular structure of human adipose tissue, will also be discussed. Differentiation of human PSCs into thermogenic adipocytes at high frequency provides an opportunity to characterize new targets for anti-obesity therapy.