While it is well established that the cellular composition of white adipose tissue (WAT) varies between depots, the functional relevance of this heterogeneity remains unclear. By combining spatial and single-nucleus RNA sequencing, we provide a comprehensive map of subcutaneous and visceral (omental, mesenteric, mesocolic, and epiploic) WAT in both men and women. Our analyses reveal shared features, such as the spatial organization of adipogenesis, alongside depot-specific characteristics, including distinct cell-type enrichments and unique cell-cell communication routes. Epiploic WAT stands out by harboring high proportions of serum amyloid A expressing fat cells (encoded by SAA1/SAA2) and several leukocyte populations. Through mechanistic studies, we demonstrate that adipocyte SAA1/SAA2 expression is induced by inflammatory signals, including lipopolysaccharide, and that SAA1 activates immune responses in adipose-resident myeloid cells. Collectively, our findings suggest that visceral WAT exhibits distinct cytoarchitectural properties, with those located near the colon adapting by developing specialized adipocytes and immune cell populations.

White adipose tissue (WAT) is a remarkably plastic organ integrating metabolic, endocrine and immune functions. In humans, perturbations in adipocyte turnover, size regulation and cellular heterogeneity underpin the transition from metabolic health to obesity-related disease. This review, based on the 2025 Camillo Golgi Prize Lecture, highlights selected mechanistic and translational insights, primarily from our work and that of close collaborators, that have contributed to reshaping our understanding of human adipose biology. 14C-dating and clinical studies demonstrate that adipocytes are continuously renewed, and that impaired lipid turnover predisposes to weight gain, insulin resistance and type 2 diabetes. Obesity induces persistent transcriptional and structural alterations, an ‘adipose memory’, that provides a biological basis for understanding the difficulty of maintaining weight loss. Spatial transcriptomics has revealed at least three major adipocyte states in human WAT that differ in insulin responsiveness and lipid-handling capacity, suggesting that adipocyte composition influences depot function and responsiveness to interventions such as weight loss or pharmacological therapies. In addition, depot-specific enrichment of immunomodulatory adipocytes, particularly in epiploic WAT, highlights local adipocyte–immune crosstalk as a contributor to systemic inflammation. Collectively, these advances redefine human WAT as an active driver of cardiometabolic disease and highlight therapeutic strategies targeting adipocyte plasticity and immune–metabolic interactions.

Adipose tissue homeostasis depends on an intact vascular network that ensures adequate nutrient delivery and immune regulation. In obesity, vascular dysfunction, particularly within endothelial cells (ECs), contributes to inflammation and metabolic disease progression, yet the cellular organization of the human adipose vasculature remains poorly defined. Here we show, using single-cell RNA sequencing of nearly 70,000 vascular cells from human subcutaneous adipose tissue of 65 individuals, that the adipose vasculature is highly heterogeneous and consists of seven canonical EC subtypes. In addition, we identify a distinct population of ECs that display mixed endothelial, mesenchymal, adipocytic and immune transcriptional features. Computational analyses and whole-mount imaging support their presence and suggest that they emerge through endothelial-to-mesenchymal transition. Comparative analyses further reveal inflammatory and fibrotic vascular signatures in obesity and type 2 diabetes. Together, this atlas delineates the cellular complexity of the human adipose vasculature and highlights its contribution to metabolic disease.

Insulin-driven gene regulation is central to adipocyte function, but the roles of many of these genes in lipid metabolism remain unclear. Here, we integrate three transcriptomic datasets to identify insulin-responsive genes and define their functions in human adipocytes using a multiparametric lipid turnover screen. Our results reveal four major clusters involved in metabolic regulation, transcription, stress responses, and lipid metabolism. Among lipid-related hits, phospholipase C X domain-containing protein-1 (PLCXD1) emerges as a regulator of insulin-stimulated lipogenesis, without affecting lipolysis or adipogenesis. PLCXD1 is induced by insulin via sterol regulatory element-binding proteins, a response attenuated in insulin-resistant states. This atypical phospholipase is genetically associated with fat mass-related traits, localizes to early endosomes and catalyzes phosphatidylinositol conversion into diacylglycerol. Through structure-function analyses, we show that PLCXD1 catalytic activity is required for insulin-stimulated lipogenesis. Altogether, our results uncover PLCXD1 as an insulin-regulated enzyme linking endosomal phosphoinositide metabolism to lipid storage in adipocytes.

Insulin resistance drives cardiometabolic disease, yet its molecular signatures and tissue origins remain incompletely characterized, and scalable assessment methods are lacking. Here, we apply Multi-Workflow Proteomics on plasma from 161 individuals spanning the metabolic spectrum defined by hyperinsulinemic–euglycemic clamp–derived insulin sensitivity. We identify 488 proteins associated with insulin sensitivity, revealing contributions from liver, adipose tissue, and immune cells alongside underappreciated roles for brain and heart. An exercise intervention demonstrated these signatures are modifiable. We developed a model combining 13 proteins, including IGFBP1, LEP, GDF15, PON3, and LDLR, with clinical variables (sex, HbA1c, TG/HDL ratio) that estimates hyperinsulinemic–euglycemic clamp-derived insulin sensitivity (R² = 0.73). Applied to ~20,000 UK Biobank participants, estimated insulin sensitivity outperformed TG/HDL in predicting type 2 diabetes (c-index 0.86 vs. 0.71) and other cardiometabolic outcomes, including obesity, cardiovascular disease, and chronic kidney disease. This proteomic atlas enables scalable insulin resistance assessment and precision risk stratification.

BACKGROUND:Mature adipocytes are difficult to study ex vivo, prompting the use of human adipose progenitor cells (hAPCs). However, hAPCs undergo replicative senescence, limiting their utility in long-term studies. METHODS:We inserted human telomerase reverse transcriptase (TERT) into the AAVS1 locus of CD55+ hAPCs derived from abdominal subcutaneous adipose tissue, and characterized the cells before and after adipogenic differentiation. RESULTS:TERT-hAPCs retained proliferative and adipogenic capacities for over 80 passages, comparable to early-passage wild type hAPCs. Transcriptomic and proteomic analyses confirmed strong adipocyte gene expression. Functionally, TERT-hAPCs responded to insulin and lipolytic stimuli (isoprenaline, dibutyryl cAMP, TNF-α). They adapted well to both 2D and 3D cultures, with improved adipogenesis under spheroid conditions. CONCLUSION:Immortalization of CD55+ hAPCs yields cells with stable proliferative and adipogenic capacity across passages. Being cryopreservable and suitable for both 2D and 3D cultures, TERT-hAPCs offer a reliable, reusable model system for adipocyte studies using cells with a consistent genetic background.

We developed the Adipose Tissue Knowledge Portal by centralizing previously dispersed datasets, integrating clinical and experimental results with transcriptomic and proteomic data from >6,000 women and men. The platform includes multiple adipose depots, resident cell types, and adipocyte perturbation studies. By providing streamlined data access, the portal enables integrative analyses and serves as a powerful tool to interrogate various dimensions of adipose biology down to the single-cell level.

Adipose tissue (AT) is a complex connective tissue with a high relative proportion of adipocytes, which are specialized cells with the ability to store lipids in large droplets. AT is found in multiple discrete depots throughout the body, where it serves as the primary repository for excess calories. In addition, AT has an important role in functions as diverse as insulation, immunity and regulation of metabolic homeostasis. The Human Cell Atlas Adipose Bionetwork was established to support the generation of single-cell atlases of human AT as well as the development of unified approaches and consensus for cell annotation. Here, we provide a first roadmap from this bionetwork, including our suggested cell annotations for humans and mice, with the aim of describing the state of the field and providing guidelines for the production, analysis, interpretation and presentation of AT single-cell data. In this Review, the authors present a roadmap towards achieving consensus on development, analysis and interpretation of single-cell transcriptomics data in adipose tissue, including discussion of roadblocks, best practices and ideal cell-type markers for annotation of adipose tissue cell types in mice and humans.

An increasing number of studies have characterized the bone as an endocrine organ, and that bone secreted factors may not only regulate local bone remodeling, but also other tissues and whole-body metabolic functions. The precise nature of these regulatory factors and their roles at bridging the bone, bone marrow adipose tissue, extramedullary body fat and whole-body energy homeostasis are being explored. In this study, we report that KIAA1199, a secreted factor produced from bone and bone marrow, previously described as an inhibitor of bone formation, also plays a role at promoting adipogenesis. KIAA1199-deficient mice exhibit reduced bone marrow adipose tissue, subcutaneous and visceral fat tissue mass, blood cholesterol, triglycerides, free fatty acids and glycerol, as well as improved insulin sensitivity in skeletal muscle, liver and fat. Moreover, these mice are protected from the detrimental effects of high-fat diet feeding, with decreased obesity, lower blood glucose and glucose tolerance, as well as decreased adipose tissue inflammation, insulin resistance and hepatic steatosis. In human studies, plasma levels of KIAA1199 or its expression levels in adipose tissue are positively correlated with insulin resistance and blood levels of cholesterol, triglycerides, free fatty acids, glycerol, fasting glucose and HOMA-IR. Mechanistically, KIAA1199 mediates its effects on adipogenesis through modulating osteopontin-integrin and AKT / ERK signaling. These findings provide evidence for the role of bone secreted factors on coupling bone, fat and whole-body energy homeostasis.

Obesity rates have surged since 1990 worldwide. This rise is paralleled by increases in pathological processes affecting organs such as the heart, liver, and kidneys, here termed systemic metabolic disorders (SMDs). For clinical management of SMD, the European Atherosclerosis Society proposes a pathophysiology-based system comprising three stages: Stage 1, where metabolic abnormalities such as dysfunctional adiposity and dyslipidaemia occur without detectable organ damage; Stage 2, which involves early organ damage manifested as Type 2 diabetes, asymptomatic diastolic dysfunction, metabolic-associated steatohepatitis (MASH), and chronic kidney disease (CKD); and Stage 3, characterized by more advanced organ damage affecting multiple organs. Various forms of high-risk obesity, driven by maintained positive energy balance, are the most common cause of SMD, leading to ectopic lipid accumulation and insulin resistance. This progression affects various organs, promoting comorbidities such as hypertension and atherogenic dyslipidaemia. Genetic factors influence SMD susceptibility, and ethnic disparities in SMD are attributable to genetic and socioeconomic factors. Key SMD features include insulin resistance, inflammation, pre-diabetes, Type 2 diabetes, MASH, hypertension, CKD, atherogenic dyslipidaemia, and heart failure. Management strategies involve lifestyle changes, pharmacotherapy, and metabolic surgery in severe cases, with emerging treatments focusing on genetic approaches. The staging system provides a structured approach to understanding and addressing the multi-faceted nature of SMD, which is crucial for improving health outcomes. Categorization of SMD abnormalities by presence and progression is aimed to improve awareness of a multi-system trait and encourage a tailored and global approach to treatment, ultimately aiming to reduce the burden of obesity-related comorbidities.

In adipocytes, hormone-sensitive lipase (HSL) plays a key role in hydrolyzing triacylglycerols that are stored in lipid droplets. Contrary to the expected phenotype, HSL-deficient mice and humans exhibit lipodystrophy. Here, we show that HSL is also present in the adipocyte nucleus. Mouse models with different HSL subcellular localizations reveal that nuclear HSL is essential for the maintenance of adipose tissue. Gene silencing in human adipocytes shows that HSL, independently of its enzymatic activity, exerts opposing effects on mitochondrial oxidative phosphorylation and the extracellular matrix. Mechanistically, we found that HSL accumulates in the nucleus by interacting with the transforming growth factor β (TGF-β) signaling mediator, mothers against decapentaplegic homolog 3 (SMAD3). Conversely, HSL phosphorylation induces nuclear export. In vivo, HSL accumulates in the nucleus of adipocytes during high-fat feeding with the converse effect during fasting. Together, our data show that as both a cytosolic enzyme and a nuclear factor, HSL plays a pivotal role in adipocyte biology and adipose tissue maintenance.

Insulin resistance is a hallmark of type 2 diabetes, which is a highly heterogeneous disease with diverse pathology. Understanding the molecular signatures of insulin resistance and its association with individual phenotypic traits is crucial for advancing precision medicine in type 2 diabetes. Utilizing cutting-edge proteomics technology, we mapped the proteome and phosphoproteome of skeletal muscle from >120 men and women with normal glucose tolerance or type 2 diabetes, with varying degrees of insulin sensitivity. Leveraging deep in vivo phenotyping, we reveal that fasting proteome and phosphoproteome signatures strongly predict insulin sensitivity. Furthermore, the insulin-stimulated phosphoproteome revealed both dysregulated and preserved signaling nodes-even in individuals with severe insulin resistance. While substantial sex-specific differences in the proteome and phosphoproteome were identified, molecular signatures of insulin resistance remained largely similar between men and women. These findings emphasize the necessity of incorporating disease heterogeneity into type 2 diabetes care strategies.

Regular exercise training is associated with systemic and tissue-specific performance and health benefits, yet long-term molecular adaptations in subcutaneous abdominal white adipose tissue (scWAT) remain unclear. We analyzed the resting scWAT transcriptome of 89 adults (35–50 years) who were long-term (>15 years) endurance- or strength-trained, or untrained. Long-term training was linked to enrichment of ribosomal, mitochondrial, and aerobic metabolism-related pathways, while immune-related pathways were enriched in untrained individuals. A distinct sex dimorphic scWAT was identified: untrained females exhibited a more metabolically favorable, ‘trained-like’ transcriptomic profile, and untrained males an ‘untrained-like’ profile. In trained males, the inflammatory gene signature was lower than in untrained males. We also identified 11 genes specific to lipid-associated macrophages with lower expression in trained individuals, particularly in all endurance-trained individuals and strength-trained females. These findings highlight sex-specific, exercise-induced adaptations in scWAT relevant to metabolic health, and underscore the importance of including both sexes in scWAT research. ### Competing Interest Statement The authors have declared no competing interest. Swedish Research Council, 2018-02932 Swedish Center for Sports Research, D2018-0007, P2022-0082 Whitaker International Program

Background Combination of increased physical exercise and hypocaloric diet has long been recognized to improve cardiometabolic health and adipose tissue function, including lipid turnover. How such lifestyle interventions mediate benefits at the cellular level remains unknown. Given the critical role of subcutaneous white adipose tissue (scWAT) to systemic metabolic homeostasis, we set out to interrogate how exercise and diet lifestyle intervention impacted scWAT in individuals living with obesity, with a particular focus on lipolytic capacity and cell-specific gene profiling. Methods Single nuclei RNA sequencing (snRNAseq) was performed on cryopreserved scWAT biopsies originally collected before and after lifestyle intervention, involving regular exercise and hypocaloric diet in obese individuals. Findings on regulation of lipolysis in adipocytes were followed up with meta-analysis of clinical studies and pharmacological experiments in mature human adipocytes. Results snRNAseq analysis revealed intervention-induced changes in all scWAT cell-types. In adipocytes genes linked to protein and organelle turnover, branch chain amino acid catabolism, and lipolytic control were most significantly regulated. We identified a cell autonomous brake on adipocyte lipolysis via the neuropeptide Y receptor 1 (NPY1R). Expression of adipocyte NPY1R was reduced after weight loss and correlated positively with body fat percentage and body mass index. Findings were confirmed in meta-analysis across 23 studies. Finally, we found a negative correlation between NPY1R and beta-adrenergic-induced lipolysis and that NPY dose-dependently attenuated lipolysis and cAMP-signaling in primary human subcutaneous adipocytes. Conclusions Our work suggests that decreases in adipocyte NPY1R during weight loss boost lipolytic capacity and contribute to improved systemic cardiometabolic health.

Increased plasma creatine concentrations are associated with the risk of type 2 diabetes, but whether this alteration is associated with or causal for impairments in metabolism remains unexplored. Because skeletal muscle is the main disposal site of both creatine and glucose, we investigated the role of intramuscular creatine metabolism in the pathophysiology of insulin resistance in type 2 diabetes. In men with type 2 diabetes, plasma creatine concentrations were increased, and intramuscular phosphocreatine content was reduced. These alterations were coupled to reduced expression of sarcomeric mitochondrial creatine kinase 2 (CKMT2). In C57BL/6 mice fed a high-fat diet, neither supplementation with creatine for 2 weeks nor treatment with the creatine analog beta-GPA for 1 week induced changes in glucose tolerance, suggesting that increased circulating creatine was associated with insulin resistance rather than causing it. In C2C12 myotubes, silencing Ckmt2 using small interfering RNA reduced mitochondrial respiration, membrane potential, and glucose oxidation. Electroporation-mediated overexpression of Ckmt2 in skeletal muscle of high-fat diet-fed male mice increased mitochondrial respiration, independent of creatine availability. Given that overexpression of Ckmt2 improved mitochondrial function, we explored whether exercise regulates CKMT2 expression. Analysis of public data revealed that CKMT2 content was up-regulated by exercise training in both humans and mice. We reveal a previously underappreciated role of CKMT2 in mitochondrial homeostasis beyond its function for creatine phosphorylation, independent of insulin action. Collectively, our data provide functional evidence for how CKMT2 mediates mitochondrial dysfunction associated with type 2 diabetes.

In white adipose tissue, disturbed creatine metabolism through reduced creatine kinase B (CKB) transcription contributes to obesity-related inflammation. However, the mechanisms regulating CKB expression in human white adipocytes remain unclear. By screening conditions perturbed in obesity, we identified endoplasmic reticulum (ER) stress as a key suppressor of CKB transcription across multiple cell types. Through follow-up studies, we found that ER stress through the IRE1-XBP1s pathway, promotes CKB promoter methylation via the methyltransferase DNMT3A. This epigenetic change represses CKB transcription, shifting metabolism towards glycolysis and increasing the production of the proinflammatory chemokine CCL2. We validated our findings in vivo, demonstrating that individuals living with obesity show an inverse relationship between CKB expression and promoter methylation in white adipocytes, along with elevated CCL2 secretion. Overall, our study uncovers a regulatory axis where ER stress drives inflammation in obesity by reducing CKB abundance, and consequently altering the bioenergetic state of the cell.

STUDY OBJECTIVES:Napping is a common habit in many countries. Nevertheless, studies about the chronic effects of napping on obesity are contradictory, and the molecular link between napping and metabolic alterations has yet to be studied. We aim to identify molecular mechanisms in adipose tissue (AT) that may connect napping and abdominal obesity. METHODS:In this cross-sectional study, we extracted the RNA repeatedly across 24 hours from cultured AT explants and performed RNA sequencing. Circadian rhythms were analyzed using six consecutive time points across 24 hours. We also assessed global gene expression in each group (nappers vs. non-nappers). RESULTS:With napping, there was an 88% decrease in the number of rhythmic genes compared to that in non-nappers, a reduction in rhythm amplitudes of 29%, and significant phase changes from a coherent unimodal acrophase in non-nappers, towards a scattered and bimodal acrophase in nappers. Those genes that lost rhythmicity with napping were mainly involved in pathways of glucose and lipid metabolism, and of the circadian clock. Additionally, we found differential global gene expression between nappers and non-nappers with 34 genes down- and 32 genes upregulated in nappers. The top upregulated gene (IER3) and top down-regulated pseudogene (VDAC2P2) in nappers have been previously shown to be involved in inflammation. CONCLUSIONS:These new findings have implications for our understanding of napping's relationship with obesity and metabolic disorders.