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Adipocyte dysfunction plays a critical role in the pathogenesis of metabolic diseases, including type 2 diabetes (T2D). Human induced pluripotent stem cells (hiPSCs) offer a powerful platform for generating white, beige, and brown adipocytes, supporting both disease modeling and therapeutic research. This review provides a comprehensive summary of current differentiation methods to produce three functionally mature adipocyte types from pluripotent stem cells (PSCs), including forced gene expression techniques, developmental biology-inspired approaches, and advanced three-dimensional (3D) culture systems that enhance cellular maturity and functional relevance. PSC-derived white adipocytes contribute to modeling adipocyte dysfunction not only in conditions such as insulin resistance, lipodystrophy, and premature aging but also in more complex metabolic diseases, including T2D, facilitating the investigation of disease mechanisms and the identification of novel therapeutic targets. In addition, iPSC-based models provide a robust platform for exploring genetic regulation by genome-wide association studies (GWAS)–identified variants through population genetics. This review also evaluates the therapeutic potential of iPSC-derived white, beige, and brown adipocytes in cell transplantation therapy for metabolic diseases, with a focus on engraftment potential and metabolic improvement. Enhancing the maturity and subtype specificity of PSC-derived adipocytes is expected to accelerate the development of personalized medicine and innovative therapeutic strategies for metabolic diseases. Graphical Abstract

Key Points Brown and beige adipocytes dissipate energy in the form of heat. This thermogenic function is coordinately regulated by adipose-selective chromatin architectures and by a set of unique transcriptional and epigenetic regulators. Histone modification, DNA methylation and chromatin conformational changes have crucial roles in the determination and maintenance of brown and beige adipocyte fate. Currently, more than 50 transcriptional regulators are known to control brown or beige adipocyte differentiation. A large proportion of the regulators, if not all of them, function through master regulators such as peroxisome proliferator-activated receptor-γ (PPARγ) and their partners CCAAT/enhancer-binding protein-ß (C/EBPβ), PR domain zinc-finger protein 16 (PRDM16) and PPARγ co-activator-1α (PGC1α). Various external stimuli, such as chronic cold exposure and synthetic PPARγ ligands, promote beige adipocyte biogenesis in adipocyte precursors. These cues are sensed by cell surface receptors (such as the β-adrenergic receptor) and nuclear receptors (such as PPARγ), leading to dynamic changes in chromatin structures, as well as changes in expression and activity of the key transcriptional regulators. Embryonic, brown adipocytes, together with beige, brown-like adipocytes induced in white fat depots in response to various stimuli, constitute specialized heat-producing fat cells that contribute to organismal energy expenditure. Important insights have now been gained into the transcriptional and epigenetic regulation of biogenesis and thermogenesis of these cells, opening up new possibilities for the treatment of metabolic disorders. White adipocytes store excess energy in the form of triglycerides, whereas brown and beige adipocytes dissipate energy in the form of heat. This thermogenic function relies on the activation of brown and beige adipocyte-specific gene programmes that are coordinately regulated by adipose-selective chromatin architectures and by a set of unique transcriptional and epigenetic regulators. A number of transcriptional and epigenetic regulators are also required for promoting beige adipocyte biogenesis in response to various environmental stimuli. A better understanding of the molecular mechanisms governing the generation and function of brown and beige adipocytes is necessary to allow us to control adipose cell fate and stimulate thermogenesis. This may provide a therapeutic approach for the treatment of obesity and obesity-associated diseases, such as type 2 diabetes.

Single-cell sequencing technologies have revealed an unexpectedly broad repertoire of cells required to mediate complex functions in multicellular organisms. Despite the multiple roles of adipose tissue in maintaining systemic metabolic homeostasis, adipocytes are thought to be largely homogenous with only 2 major subtypes recognized in humans so far. Here we report the existence and characteristics of 4 distinct human adipocyte subtypes, and of their respective mesenchymal progenitors. The phenotypes of these distinct adipocyte subtypes are differentially associated with key adipose tissue functions, including thermogenesis, lipid storage, and adipokine secretion. The transcriptomic signature of “brite/beige” thermogenic adipocytes reveals mechanisms for iron accumulation and protection from oxidative stress, necessary for mitochondrial biogenesis and respiration upon activation. Importantly, this signature is enriched in human supraclavicular adipose tissue, confirming that these cells comprise thermogenic depots in vivo, and explain previous findings of a rate-limiting role of iron in adipose tissue browning. The mesenchymal progenitors that give rise to beige/brite adipocytes express a unique set of cytokines and transcriptional regulators involved in immune cell modulation of adipose tissue browning. Unexpectedly, we also find adipocyte subtypes specialized for high-level expression of the adipokines adiponectin or leptin, associated with distinct transcription factors previously implicated in adipocyte differentiation. The finding of a broad adipocyte repertoire derived from a distinct set of mesenchymal progenitors, and of the transcriptional regulators that can control their development, provides a framework for understanding human adipose tissue function and role in metabolic disease.

Prevalence of obesity among infants and children below 5 years of age is rising dramatically, and early childhood obesity is a forerunner of obesity and obesity-associated diseases in adulthood. Childhood obesity is hence one of the most serious public health challenges today. Here, we have identified a mother-to-child lipid signaling that protects from obesity. We have found that breast milk-specific lipid species, so-called alkylglycerol-type (AKG-type) ether lipids, which are absent from infant formula and adult-type diets, maintain beige adipose tissue (BeAT) in the infant and impede the transformation of BeAT into lipid-storing white adipose tissue (WAT). Breast milk AKGs are metabolized by adipose tissue macrophages (ATMs) to platelet-activating factor (PAF), which ultimately activates IL-6/STAT3 signaling in adipocytes and triggers BeAT development in the infant. Accordingly, lack of AKG intake in infancy leads to a premature loss of BeAT and increases fat accumulation. AKG signaling is specific for infants and is inactivated in adulthood. However, in obese adipose tissue, ATMs regain their ability to metabolize AKGs, which reduces obesity. In summary, AKGs are specific lipid signals of breast milk that are essential for healthy adipose tissue development.

Preadipocytes can give rise to either white adipocytes or beige adipocytes. Owing to their distinct abilities in nutrient storage and energy expenditure, strategies that specifically promote “beiging” of adipocytes hold great promise for counterbalancing obesity and metabolic diseases. Yet, factors dictating the differentiation fate of adipocyte progenitors remain to be elucidated. We found that stearoyl-coenzyme A desaturase 1 (Scd1)-deficient mice, which resist metabolic stress, possess augmentation in beige adipocytes under basal conditions. Deletion of Scd1 in mature adipocytes expressing Fabp4 or Ucp1 did not affect thermogenesis in mice. Rather, Scd1 deficiency shifted the differentiation fate of preadipocytes from white adipogenesis to beige adipogenesis. Such effects are dependent on succinate accumulation in adipocyte progenitors, which fuels mitochondrial complex II activity. Suppression of mitochondrial complex II by Atpenin A5 or oxaloacetic acid reverted the differentiation potential of Scd1-deficient preadipocytes to white adipocytes. Furthermore, supplementation of succinate was found to increase beige adipocyte differentiation both in vitro and in vivo. Our data reveal an unappreciated role of Scd1 in determining the cell fate of adipocyte progenitors through succinate-dependent regulation of mitochondrial complex II.

The induction of beige adipocytes is significantly reduced in aged mice due to the senescence of adipocyte progenitor cells (APCs). Recent studies have revealed the existence of beige adipocyte subtypes, suggesting that APCs comprise a heterogeneous population. Therefore, in this study, we aimed to elucidate the mechanism through which long-term cold exposure induces the production of beige adipocytes even in aged mice. Single-cell RNA sequencing identified carbonic anhydrase 4 (Car4)-positive APCs. The number of Car4-positive APCs increased with age and cold exposure. Car4 knockdown (KD) mitigated intracellular pH reduction and significantly suppressed beige adipocyte differentiation. Furthermore, Car4 KD cells demonstrated reduced expression of genes in the glutathione pathway and increased susceptibility to reactive oxygen species (ROS), which was alleviated by glutathione supplementation. Our findings suggest that ROS resistance is an adaptation to the cellular aging environment. Our study provides insights into the age-related decline in beige adipocyte induction and identifies Car4 as a potential therapeutic target for enhancing energy expenditure in elderly individuals. This may pave the way for the development of new strategies to combat age-related metabolic diseases and offer hope for improved health and longevity in an aging population.

Adipose tissue expansion, as seen in obesity, is often metabolically detrimental causing insulin resistance and the metabolic syndrome. However, white adipose tissue expansion at early ages is essential to establish a functional metabolism. To understand the differences between adolescent and adult adipose tissue expansion, we studied the cellular composition of the stromal vascular fraction of subcutaneous adipose tissue of two and eight weeks old mice using single cell RNA sequencing. We identified a subset of adolescent preadipocytes expressing the mature white adipocyte marker Asc-1 that showed a low ability to differentiate into beige adipocytes compared to Asc-1 negative cells in vitro. Loss of Asc-1 in subcutaneous preadipocytes resulted in spontaneous differentiation of beige adipocytes in vitro and in vivo. Mechanistically, this was mediated by a function of the amino acid transporter ASC-1 specifically in proliferating preadipocytes involving the intracellular accumulation of the ASC-1 cargo D-serine. Adipose tissue is composed of a variety of cell types, including adipocyte precursor populations, that contribute to adipose tissue function upon differentiation. Here, using scRNA-sequencing of adolescent and adult mouse subcutaneous adipose tissue, the authors identify an Asc-1 positive preadipocyte population that is enriched in adolescent subcutaneous fat and demonstrate that loss of Asc-1 triggers spontaneous beige adipocyte differentiation.

The transcription factor nuclear factor I-A (NFIA) is a regulator of brown adipocyte differentiation. Here we show that the C-terminal 17 amino acid residues of NFIA (which we call pro#3 domain) are required for the transcriptional activity of NFIA. Full-length NFIA-but not deletion mutant lacking pro#3 domain-rescued impaired expression of PPARγ, the master transcriptional regulator of adipogenesis and impaired adipocyte differentiation in NFIA-knockout cells. Mechanistically, the ability of NFIA to penetrate chromatin and bind to the crucial Pparg enhancer is mediated through pro#3 domain. However, the deletion mutant still binds to Myod1 enhancer to repress expression of MyoD, the master transcriptional regulator of myogenesis as well as proximally transcribed non-coding RNA called DRReRNA, via competition with KLF5 in terms of enhancer binding, leading to suppression of myogenic gene program. Therefore, the negative effect of NFIA on the myogenic gene program is, at least partly, independent of the positive effect on PPARγ expression and its downstream adipogenic gene program. These results uncover multiple ways of action of NFIA to ensure optimal regulation of brown and beige adipocyte differentiation.

Emerging evidence supports the pivotal roles of adipocytes in breast cancer progression. Tumour induced beige/brown adipose tissue differentiation contributes to the hypermetabolic state of the breast cancer. However, the mediators and mechanisms remain unclear. Survival probabilities were estimated using the Kaplan-Meier method based on immunohistochemistry results. Biochemical studies were performed to characterize the novel interrelation between breast cancer cells and adipocytes. We show that tumour-surrounding adipocytes exhibit an altered phenotype in terms of upregulated beige/brown characteristics and increased catabolism associated with an activated state characterized by the release of metabolites, including free fatty acids, pyruvate, lactate and ketone bodies. Likewise, tumour cells cocultivated with mature adipocytes exhibit metabolic adaptation and an aggressive phenotype in vitro and in vivo. Mechanistically, we show that tumour cells induce beige/brown differentiation and remodel metabolism in resident adipocytes by exosomes from the co-culture system that carry high levels of miRNA-144 and miRNA-126. miRNA-144 promotes beige/brown adipocyte characteristics by downregulating the MAP3K8/ERK1/2/PPARγ axis, and exosomal miRNA-126 remodels metabolism by disrupting IRS/Glut-4 signalling, activating the AMPK/autophagy pathway and stabilizing HIF1α expression in imminent adipocytes. In vivo inhibition of miRNA-144 or miRNA-126 decreases adipocyte-induced tumour growth. These results demonstrate that by inducing beige/brown differentiation and enhancing catabolism in recipient adipocytes, exosomal miRNA-144 and miRNA-126 from the tumour-adipocyte interaction reprogram systemic energy metabolism to facilitate tumour progression.

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