Single-cell analysis of human adipose tissue identifies depot and disease specific cell types

Identifying Immunomodulatory Subpopulations of Adipose Stromal Vascular Fraction and Stem/Stromal Cells Through Single-Cell Transcriptomics and Bulk Proteomics

A primary therapeutic characteristic of mesenchymal stem/stromal cells (MSCs) is their immunomodulatory activity. Adipose-derived stem/stromal cells (ASCs) are an abundant and easily isolated source of MSCs shown to have high immunosuppressive activity, making them attractive for therapy. Understanding the heterogeneous immunomodulatory potential of ASCs within the stromal vascular fraction (SVF) of adipose tissue could better inform treatment strategies. In this study, we integrate single-cell RNA sequencing (scRNA seq) with bulk proteomics to characterize subpopulations of SVF-derived ASCs that are phenotypically similar to cytokine-licensed, cultured ASCs. To better define the licensing process, we present scRNA seq and bulk proteomics data of cultured (P2) ASCs exposed to inflammatory cytokines, showing enrichment of pathways related to inflammation and apoptosis that positively correlate to the cytokine-mediated, trajectory-derived pseudotime. Using the Scissor algorithm, we integrate the proteomics data with uncultured (P0) SVF scRNA seq data, identifying an ASC subpopulation that is phenotypically like the cytokine-stimulated ASCs (Scissor-positive). Interactome analysis identifies Scissor-positive ASCs as stress adaptive immune regulators that function through IL6 and broad SEMA4 interactions and higher Visfatin signaling, while Scissor-negative ASCs show strong signatures of ECM remodeling through FN1 and immunosuppression through THY1 and MIF signaling. Our multimodal, integrative approach enabled identification of previously unidentified, distinct ASC subpopulations with differing immunomodulatory phenotypes that are present in, and can potentially be selected from, P0 SVF ASCs.

Variant-to-function approaches for adipose tissue: Insights into cardiometabolic disorders

Genome-wide association studies (GWASs) have identified thousands of genetic loci associated with cardiometabolic disorders. However, the functional interpretation of these loci remains a daunting challenge. This is particularly true for adipose tissue, a critical organ in systemic metabolism and the pathogenesis of various cardiometabolic diseases. We discuss how variant-to-function (V2F) approaches are used to elucidate the mechanisms by which GWAS loci increase the risk of cardiometabolic disorders by directly influencing adipose tissue. We outline GWAS traits most likely to harbor adipose-related variants and summarize tools to pinpoint the putative causal variants, genes, and cell types for the associated loci. We explain how large-scale perturbation experiments, coupled with imaging and multi-omics, can be used to screen variants' effects on cellular phenotypes and how these phenotypes can be tied to physiological mechanisms. Lastly, we discuss the challenges and opportunities that lie ahead for V2F research and propose a roadmap for future studies.

Towards a consensus atlas of human and mouse adipose tissue at single-cell resolution

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.

Multitissue single-cell analysis reveals differential cellular and molecular sensitivity between fructose and high-fat high-sucrose diets

Metabolic syndrome (MetS), a conglomerate of dysregulated metabolic traits that vary between individuals, is partially driven by modern diets high in fat, sucrose, or fructose and their interactions with host genes in metabolic tissues. To elucidate the roles of individual tissues and cell types in diet-induced MetS, we performed single-cell RNA sequencing on the hypothalamus, liver, adipose tissue, and small intestine of mice fed high-fat high-sucrose (HFHS) or fructose diets. We found that hypothalamic neurons were sensitive to fructose, while adipose progenitor cells and macrophages were responsive to HFHS. Ligand-receptor analysis revealed lipid metabolism and inflammation networks among peripheral tissues driven by HFHS, while both diets stimulated synaptic remodeling within the hypothalamus. mt-Rnr2, a top responder to both diets, mitigated diet-induced MetS by stimulating thermogenesis. Our study demonstrates that HFHS and fructose diets have differential cell type and network targets but also share regulators such as mt-Rnr2 to affect MetS risk.

Single-Cell and Single-Nuclei transcriptomics profiling reveals dynamic cellular features in tumor-related adipose microenvironment of breast cancer patients with high BMI

OBJECTIVES

High body mass index (BMI), encompassing overweight and obesity, is a well-established risk factor for developing breast cancer (BC). The underlying mechanisms linking elevated BMI to increased BC risk involve metabolic reprogramming and chronic inflammatory microenvironments regulated by cellular networks within breast white adipose tissue (WAT). However, the complicated landscape and specific cell chat leading to BC-related adipose microenvironment remained unclear.

MATERIALS AND METHODS

We unveiled a comprehensive cell atlas by employing single-cell (N = 27) and single-nuclei (N = 6) transcriptomics to address dynamic changes of immune and stromal cell components within WAT in high BMI population. Bulk RNA-seq data sets were used for validation.

RESULTS

Characteristics of adipose-infiltrating tissue-resident macrophages (PVMs), APOD+γδ T cells, and mature FKBP5+ adipocytes in breast cancer women with high BMI were revealed, in terms of transcriptional genes, metabolism features, developmental trajectories and gene set enrichment analysis (GSEA). PVMs upregulated c-Maf combined with its co-activator CREB1 to increase TCA cycles. APOD+γδ T cells were found to elevate intracellular lipid metabolism, leading to poor clinical prognosis. Mature FKBP5+adipocytes served as an advanced adipogenesis mediator to promote tumor aggressiveness. In-depth analysis of cell-cell interactions uncovered a remodeling trend towards metabolic dysfunction and chronic inflammation in WAT with weight gain via EGF, CXCL, and CCL signalings.

CONCLUSION

These results provided a novel understanding of detailed and unbiased cellular landscape of WAT in breast cancer with high BMI from single-cell atlas perspective, uncovering interplays between breast adipose-infiltrating immune cells and stromal cells that promote progression of BC under high BMI conditions.

Enhancing adipose tissue plasticity: progenitor cell roles in metabolic health

Adipose tissue demonstrates considerable plasticity and heterogeneity, enabling metabolic, cellular and structural adaptations to environmental signals. This adaptability is key for maintaining metabolic homeostasis. Impaired adipose tissue plasticity can lead to abnormal adipose tissue responses to metabolic cues, which contributes to the development of cardiometabolic diseases. In chronic obesity, white adipose tissue undergoes pathological remodelling marked by adipocyte hypertrophy, chronic inflammation and fibrosis, which are linked to local and systemic insulin resistance. Research data suggest that the capacity for healthy or unhealthy white adipose tissue remodelling might depend on the intrinsic diversity of adipose progenitor cells (APCs), which sense and respond to metabolic cues. This Review highlights studies on APCs as key determinants of adipose tissue plasticity, discussing differences between subcutaneous and visceral adipose tissue depots during development, growth and obesity. Modulating APC functions could improve strategies for treating adipose tissue dysfunction and metabolic diseases in obesity.

Obesity, white adipose tissue and cancer

White adipose tissue (WAT) is crucial for whole-body energy homeostasis and plays an important role in metabolic and hormonal regulation. While healthy WAT undergoes controlled expansion and contraction to meet the body's requirements, dysfunctional WAT in conditions like obesity is characterized by excessive tissue expansion, alterations in lipid homeostasis, inflammation, hypoxia, and fibrosis. Obesity is strongly associated with an increased risk of numerous cancers, with obesity-induced WAT dysfunction influencing cancer development through various mechanisms involving both systemic and local interactions between adipose tissue and tumors. Unhealthy obese WAT affects circulating levels of free fatty acids and factors like leptin, adiponectin, and insulin, altering systemic lipid metabolism and inducing inflammation that supports tumor growth. Similar mechanisms are observed locally in an adipose-rich tumor microenvironment (TME), where WAT cells can also trigger extracellular matrix remodeling, thereby enhancing the TME's ability to promote tumor growth. Moreover, tumors reciprocally interact with WAT, creating a bidirectional communication that further enhances tumorigenesis. This review focuses on the complex interplay between obesity, WAT dysfunction, and primary tumor growth, highlighting potential targets for therapeutic intervention.

Distinct adipose progenitor cells emerging with age drive active adipogenesis

Starting at middle age, adults often suffer from visceral adiposity and associated adverse metabolic disorders. Lineage tracing in mice revealed that adipose progenitor cells (APCs) in visceral fat undergo extensive adipogenesis during middle age. Thus, despite the low turnover rate of adipocytes in young adults, adipogenesis is unlocked during middle age. Transplantations quantitatively showed that APCs in middle-aged mice exhibited high adipogenic capacity cell-autonomously. Single-cell RNA sequencing identified a distinct APC population, the committed preadipocyte, age-enriched (CP-A), emerging at this age. CP-As demonstrated elevated proliferation and adipogenesis activity. Pharmacological and genetic manipulations indicated that leukemia inhibitory factor receptor signaling was indispensable for CP-A adipogenesis and visceral fat expansion. These findings uncover a fundamental mechanism of age-dependent adipose remodeling, offering critical insights into age-related metabolic diseases.

Exploration of Conserved Human Adipose Subpopulations Using Targeted Single-Nuclei RNA Sequencing Data Sets

BACKGROUND

Smooth-muscle cells and pericytes are mural cells. Pericytes can differentiate into myofibroblasts, chondrocytes, vascular smooth-muscle cells, and adipocytes, marking them as a distinct progenitor population. Our goal was to molecularly define the progenitor cell populations in human adipose tissues and test the adipogenic potential of human mural cells.

METHODS

We used informatic analysis of single-cell RNA sequencing data from human tissues to identify and define pericytes and adipose progenitor cells found in human adipose tissues, including perivascular, brown, and white adipose tissues.

RESULTS

We established tissue-specific patterns of gene expression in pericytes and other putative human adipocyte progenitor cells. PPARG-expressing pericytes were present in multiple human adipose depots with consistent expression of COL25A1, MYO1B, and POSTN. We also found evidence of tissue-specific pericyte markers. Although there is some conservation between human and mouse adipose tissues, human pericyte populations have unique, depot-specific gene expression signatures. Immunofluorescence staining of human adipose tissue revealed the presence of pericytes both distant from and adjacent to vasculature in human adipose tissue. Additionally, we demonstrated the potential of human brain pericytes and aortic vascular smooth-muscle cells to differentiate into adipocytes in vitro on the basis of intracellular lipid accumulation and expression of adipocyte markers.

CONCLUSIONS

Human adipose cell populations are distinct from mice, and the pericyte subpopulation in human adipose tissues are present across adipose depots. Given that vascular mural cells, including pericytes and smooth-muscle cells, can undergo adipogenesis, we postulate that they are a novel source of adipocytes in the vascular microenvironment.

Single-cell transcriptomics of clinical grade adipose-derived regenerative cells reveals consistency between donors independent of gender and BMI

Adipose-derived regenerative cells (ADRCs) also referred to as the stromal vascular fraction, provide an ample source of stem cells with widespread regenerative therapeutic use. Being heterogenous in nature, possibly affecting the clinical outcome after stem cell treatment, the ADRC- donor, -BMI, and -gender may have a large impact on ADRC composition and quality but this remains largely unexplored. Herein, we provide a comprehensive single-cell RNA sequencing ADRC mapping across two cell trial intervention studies but found no gender- or BMI-related variations, except for a minor female increase in PI16/CD55-expressing stem cells. Indeed, ADRC heterogeneity was surprisingly minimal between donors. This provides important decision-making support on adipose stem cell donor selection for stem cell treatments, and suggest that donor, gender and BMI should be regarded as less influential.

Chirality Regulates Bone Regeneration through Mechanoresponse and Immunoregulation

As an omnipresent occurrence in the natural world, chirality plays a crucial role in numerous biological and physiological processes. Therefore, incorporation of chirality into biointerface materials has been emerging as a research hotspot in the development of regenerative biomaterials. Nevertheless, how chiral biointerface materials interact with biological organisms remains poorly understood. In the current study, a bioinspired chiral self-assembled nanohydroxyapatite material is developed for bone regeneration using a distraction osteogenesis model. We found that the left-handed chirality, rather than the right-handed chirality, possessed the greatest heightened ability for bone regeneration. Molecular mechanism research reveals that the left-handed chirality can activate mechanosensitive pathways to promote Ca2+ influx, subsequently enhancing macrophage type-2 polarization through phosphorylation of signal transducer and activator of transcription (STAT6), which eventually stimulates bone regeneration by harnessing the synergistic effects of angiogenesis and osteogenesis. These findings provide additional insights into the underlying mechanism of chiral recognition between biological systems and biointerface materials, offering alternative pathways for the development of biomaterials.

Identifying differentiation markers between dermal fibroblasts and adipose-derived mesenchymal stromal cells (AD-MSCs) in human visceral and subcutaneous tissues using single-cell transcriptomics

BACKGROUND

Adipose-derived mesenchymal stromal cells (AD-MSCs) and fibroblasts are both widely used in regenerative medicine, demonstrating significant potential for personalized cell therapy. A major challenge in their use lies in their high biological similarity, encompassing morphology, differentiation capabilities, and flow cytometric markers, making their distinction difficult.

METHODS

In our study, we aimed to compare AD-MSCs obtained from two types of adipose tissue, subcutaneous and visceral, alongside skin fibroblasts. Notably, all tissue samples were sourced from the same donors. We analyzed the cells for surface antigens via flow cytometry and conducted single-cell RNA sequencing, followed by verification with quantitative PCR (qPCR).

RESULTS

Our results revealed phenotypic similarities between the isolated AD-MSCs and dermal fibroblasts, particularly in the expression of markers characteristic of AD-MSCs. However, through in-depth analyses, we identified distinct differences between these cell types. Specifically, we pinpointed 30 genes exhibiting the most significant variations in expression between AD-MSCs and fibroblasts. These genes are associated with biological processes such as tissue remodeling, cell movement, and activation in response to external stimuli. Among them, MMP1, MMP3, S100A4, CXCL1, PI16, IGFBP5, COMP were further validated using qPCR, clearly demonstrating their potential to differentiate between AD-MSCs and fibroblasts.

CONCLUSIONS

Our scRNA-seq analysis elucidates the transcriptional landscape of AD-MSCs and fibroblasts with unprecedented resolution, highlighting both the population-specific markers and the intrapopulation heterogeneity. Our findings underscore the importance of employing high-resolution techniques for cell identification.

Combining transcriptomic and metabolomic insights to guide the clinical application of adipose- and bone marrow-derived mesenchymal stem cells

Adipose-derived mesenchymal stem cells (ADSCs) and bone marrow-derived mesenchymal stem cells (BMSCs) have shown great potential in clinical applications. However, the similarities and differences between these two cell types have not been fully elucidated. Recent advances in transcriptomic and metabolomic research have provided valuable insight into the characteristics and functions of ADSCs and BMSCs. In this perspective article, we review the key findings from these studies, including cellular heterogeneity as well as differences in metabolic and secretory properties. We discuss how these insights can help guide the selection of the most suitable cell source for the clinic, and the optimization of preconditioning strategies prior to clinical deployment. Furthermore, we analyze the current landscape of products and clinical trials involving ADSCs and BMSCs, highlighting their therapeutic potential. We propose that the integration of multi-omics datasets will be crucial for establishing a comprehensive understanding of ADSC and BMSC identity and potency, and the provision of quality-assured stem cell-derived products for the clinic.

Human subcutaneous and visceral adipocyte atlases uncover classical and nonclassical adipocytes and depot-specific patterns

Human adipose depots are functionally distinct. Yet, recent single-nucleus RNA sequencing (snRNA-seq) analyses largely uncovered overlapping or similar cell-type landscapes. We hypothesized that adipocyte subtypes, differentiation trajectories and/or intercellular communication patterns could illuminate this depot similarity-difference gap. For this, we performed snRNA-seq of human subcutaneous or visceral adipose tissues (five or ten samples, respectively). Of 27,665 adipocyte nuclei in both depots, most were 'classical', namely enriched in lipid metabolism pathways. However, we also observed 'nonclassical' adipocyte subtypes, enriched in immune-related, extracellular matrix deposition (fibrosis), vascularization or angiogenesis or ribosomal and mitochondrial processes. Pseudo-temporal analysis showed a developmental trajectory from adipose progenitor cells to classical adipocytes via nonclassical adipocytes, suggesting that the classical state stems from loss, rather than gain, of specialized functions. Last, intercellular communication routes were consistent with the different inflammatory tone of the two depots. Jointly, these findings provide a high-resolution view into the contribution of cellular composition, differentiation and intercellular communication patterns to human fat depot differences.

Tissue-Level Effects of Autologous Fat Grafting in Hypertrophic Scars-A Case Series Study

INTRODUCTION

Fat grafting has antifibrotic effects and it improves scar quality. However, the biological mechanisms of fat grafts on scar healing are poorly understood.

METHODS

This was a prospective study to identify differences in the epidermal and dermal structure, macrophage infiltration, or inflammatory and fibrotic markers in hypertrophic scars before and after fat grafting surgery compared to normal skin. Seven patients with hypertrophic scar completed the study. Biopsies from hypertrophic scars and normal skin were taken at the time of fat grafting surgery and follow-up biopsies 6 mo postoperatively. A clinical Patient and Observer Scar Assessment Scale was used to monitor the clinical aspects of the scars. Immunohistochemical stainings were performed to analyze the changes occurring in the hypertrophic scar tissue after fat grafting.

RESULTS

Hypertrophic scars demonstrated decreased presence of rete ridges and increased levels of the profibrotic transforming growth factor beta-1 (TGF-β1) (P < 0.05) compared to normal skin. Fat grafting significantly increased the presence of rete ridges to the level of normal skin and reduced TGF-β1 expression (hypertrophic scars + fat) (P < 0.05). Fat grafting also increased the total macrophage count (CD68 pan-macrophage marker) (P < 0.05) and M1 macrophage count (inducible nitric oxide synthase M1 macrophage marker) (P < 0.05). The clinical evaluation of the scars (Patient and Observer Scar Assessment Scale) by the observer and patients improved after fat grafting (P < 0.05).

CONCLUSIONS

Our findings indicate that fat grafting promotes normalization of skin by improving epidermal structure and reducing TGF-β1 levels and favors less fibrotic healing by regulating macrophages levels.

Understanding Adipose Tissue Dysfunction

Diseases affecting adipose tissue (AT) function include obesity, lipodystrophy, and lipedema, among others. Both a lack of and excess AT are associated with increased risk for developing diseases including type 2 diabetes mellitus, hypertension, obstructive sleep apnea, and some types of cancer. However, individual risk of developing cardiometabolic and other 'obesity-related' diseases is not entirely determined by fat mass. Rather than excess fat accumulation, AT dysfunction may represent the mechanistic link between obesity and comorbid diseases. There are people who remain metabolically healthy despite obesity, whereas people with normal weight or very low subcutaneous AT mass may develop typically obesity-related diseases. AT dysfunction is characterized by adipocyte hypertrophy, impaired subcutaneous AT expandability (ectopic fat deposition), hypoxia, a variety of stress, inflammatory processes, and the release of proinflammatory, diabetogenic, and atherogenic signals. Genetic and environmental factors might contribute to AT heterogeneity either alone or via interaction with intrinsic biological factors. However, many questions remain regarding the mechanisms of AT dysfunction initiation and whether and how it could be reversed. Do AT signatures define clinically relevant subtypes of obesity? Is the cellular composition of AT associated with variation in obesity phenotypes? What roles do environmental compounds play in the manifestation of AT dysfunction? Answers to these and other questions may explain AT disease mechanisms and help to define strategies for improving AT health. This review focuses on recent advances in our understanding of AT biology.

Exploring the molecular mechanism of estrogen therapy effectiveness after TCRA in IUA patients at single-cell level

BACKGROUND

Intrauterine adhesion (IUA) is a common cause of clinically refractory infertility, and there exists significant heterogeneity in the treatment outcomes among IUA patients with the similar severity after transcervical resection of adhesion(TCRA). The underlying mechanism of different treatment outcomes occur remains elusive, and the precise contribution of various cell subtypes in this process remains uncertain.

RESULTS

Here, we performed single-cell transcriptome sequencing on 10 human endometrial samples to establish a single-cell atlas differences between patients who responded to estrogen therapy and those who did not. The results showed increased infiltration of immune cells such as monocyte macrophages, T cells, and natural killer (NK) cells in patients who did not respond to estrogen therapy. Our findings indicate that distinct fibroblast subsets are implicated in the modulation of the Wnt, Hippo, and Hedgehog signaling pathways, as evidenced by functional enrichment analyses. This may have implications for the therapeutic efficacy in patients with IUA. Furthermore, we delineated the markers and transcriptional status of different macrophage subsets and identified two cell clusters, CXCL10high and CCL4L2high macrophage subsets, which are intimately associated with inflammation and fibrosis. The state of fibrosis and inflammatory response in human endometrial tissues with disparate treatment outcomes is revealed, and providing evidence to clarify the underlying determinants of sensitivity to estrogen therapy.

CONCLUSIONS

We described the transcriptional status of different cell subtypes in the two groups of patients, providing new ideas for exploring the molecular mechanism of the difference in the effectiveness of estrogen therapy in patients, and providing theoretical basis for providing precise and individualized treatment plans for IUA patients.

PPARγ-dependent remodeling of translational machinery in adipose progenitors is impaired in obesity

Adipose tissue regulates energy homeostasis and metabolic function, but its adaptability is impaired in obesity. In this study, we investigate the impact of acute PPARγ agonist treatment in obese mice and find significant transcriptional remodeling of cells in the stromal vascular fraction (SVF). Using single-cell RNA sequencing, we profile the SVF of inguinal and epididymal adipose tissue of obese mice following rosiglitazone treatment and find an induction of ribosomal factors in both progenitor and preadipocyte populations, while expression of ribosomal factors is reduced with obesity. Notably, the expression of a subset of ribosomal factors is directly regulated by PPARγ. Polysome profiling of the epididymal SVF shows that rosiglitazone promotes translational selectivity of mRNAs that encode pathways involved in adipogenesis and lipid metabolism. Inhibition of translation using a eukaryotic translation initiation factor 4A (eIF4A) inhibitor is sufficient in blocking adipogenesis. Our findings shed light on how PPARγ agonists promote adipose tissue plasticity in obesity.

C5aR1-positive adipocytes mediate non-shivering thermogenesis in neonatal mice

Brown adipose tissue (BAT) plays an important role in maintaining body temperature in newborn mammals; however, its mechanisms remain poorly understood. Here, we report the identification of a special population of brown adipose tissue-derived stromal cells (ASCs) in neonatal mice that highly express CD45 and can be differentiated into adipocytes with lower thermogenic ability. These CD45+ adipocytes also characteristically contained complement C5a receptor 1(C5aR1) on the cell membrane. C5ar1 deficiency in BAT resulted in an apparent immaturity of adipocytes and cold intolerance in neonatal mice. Mechanistically, loss of C5aR1 in these CD45+ brown adipocytes caused an increase in the secretion of plate factor four (PF4) from these cells, suppressing the maturity of neighboring brown adipocytes. Overall, our results indicated that the accumulation of C5aR1 positive brown adipocyte in neonatal BAT is essential for thermoregulation in newborn mice, which unveiled the regulatory mechanism of BAT-mediated thermogenesis in newborns.

Immunological roles for resistin and related adipokines in obesity-associated tumors

Rationale Obesity is an independent risk factor for the occurrence and development of tumors. Obesity is influenced by signaling of adipokines, which are secreted factors from adipocytes and resident immune cells within adipose tissues that mediate lipid metabolism. More recently, adipokines have been implicated in chronic inflammation as well as in tumor formation and growth. Among them, resistin has received increasing attention in research related to the growth and expansion of solid tumors and hematological cancers through various signaling pathways. Objective and findings We reviewed the physiological, biochemical, and immune functions of adipose tissue, with a focus on the structure and expression of resistin and adipokines within multiple adipose cell types, their signaling pathways and putative effects on tumor cells, as well as their in vivo regulation. Current evidence indicates that adipokines such as resistin act as pro-inflammatory factors to stimulate immune cells which, in turn, promotes tumor angiogenesis, connective tissue proliferation, and matrix fibrosis. Concurrently, in states of metabolic dysfunction and lipotoxicity in obese individuals, the numbers and functions of immune cells are compromised, leading to an immunosuppressive environment that fosters tumor cell survival and weak cancer immune monitoring. Conclusion Adipokines such as resistin are important to the development of obesity-related tumors. Clarifying the roles for obesity-related factors in immune regulation and tumor progression may lead to the discovery of novel anti-tumor strategies for targeting obesity factors such as resistin to limit tumor growth and manage obesity, or both.

New concepts in the roles of AMPK in adipocyte stem cell biology

Obesity is a major risk factor for many life-threatening diseases. Adipose tissue dysfunction is emerging as a driving factor in the transition from excess adiposity to comorbidities such as metabolic-associated fatty liver disease, cardiovascular disease, Type 2 diabetes and cancer. However, the transition from healthy adipose expansion to the development of these conditions is poorly understood. Adipose stem cells, residing in the vasculature and stromal regions of subcutaneous and visceral depots, are responsible for the expansion and maintenance of organ function, and are now recognised as key mediators of pathological transformation. Impaired tissue expansion drives inflammation, dysregulation of endocrine function and the deposition of lipids in the liver, muscle and around vital organs, where it is toxic. Contrary to previous hypotheses, it is the promotion of healthy adipose tissue expansion and function, not inhibition of adipogenesis, that presents the most attractive therapeutic strategy in the treatment of metabolic disease. AMP-activated protein kinase, a master regulator of energy homeostasis, has been regarded as one such target, due to its central role in adipose tissue lipid metabolism, and its apparent inhibition of adipogenesis. However, recent studies utilising AMP-activated protein kinase (AMPK)-specific compounds highlight a more subtle, time-dependent role for AMPK in the process of adipogenesis, and in a previously unexplored repression of leptin, independent of adipocyte maturity. In this article, I discuss historic evidence for AMPK-mediated adipogenesis inhibition and the multi-faceted roles for AMPK in adipose tissue.

Regional primary preadipocyte characteristics in humans with obesity and type 2 diabetes mellitus

The excessive accumulation of adipose tissue in obesity appears to result in adipose tissue dysfunction perpetuating the onset of obesity-related diseases, including type 2 diabetes (T2DM). In humans, adipose tissue is stored in several depots including subcutaneous and visceral. These depots contribute to the pathology of obesity differently owing to differences in the tissue microenvironment, a main one being preadipocyte function. In examining adipocyte and preadipocyte characteristics, many have used the 3T3-L1 murine cell lines. Though these cell lines provide valuable mechanistic data, the results remain to be translated to humans. Experiments using primary human preadipocytes has shown that obesity and T2DM impact preadipocyte phenotypes. The objective of this review is to describe the differences in regional characteristics of primary preadipocytes collected from humans with obesity and to discuss how these characteristics might be affected in type 2 diabetes mellitus. In doing so, we will show that the characteristics of regional primary preadipocytes in humans are differentially affected by obesity and the development of T2DM.

Adipocyte associated glucocorticoid signaling regulates normal fibroblast function which is lost in inflammatory arthritis

Fibroblasts play critical roles in tissue homeostasis, but in pathologic states they can drive fibrosis, inflammation, and tissue destruction. Little is known about what regulates the homeostatic functions of fibroblasts. Here, we perform RNA sequencing and identify a gene expression program in healthy synovial fibroblasts characterized by enhanced fatty acid metabolism and lipid transport. We identify cortisol as the key driver of the healthy fibroblast phenotype and that depletion of adipocytes, which express high levels of Hsd11b1, results in loss of the healthy fibroblast phenotype in mouse synovium. Additionally, fibroblast-specific glucocorticoid receptor Nr3c1 deletion in vivo leads to worsened arthritis. Cortisol signaling in fibroblasts mitigates matrix remodeling induced by TNF and TGF-β1 in vitro, while stimulation with these cytokines represses cortisol signaling and adipogenesis. Together, these findings demonstrate the importance of adipocytes and cortisol signaling in driving the healthy synovial fibroblast state that is lost in disease.

Mechanisms by which obesity regulates inflammation and anti-tumor immunity in cancer

Obesity is associated with an increased risk for 13 different cancers. The increased risk for cancer in obesity is mediated by obesity-associated changes in the immune system. Obesity has distinct effects on different types of inflammation that are tied to tumorigenesis. For example, obesity promotes chronic inflammation in adipose tissue that is tumor-promoting in peripheral tissues. Conversely, obesity inhibits acute inflammation that rejects tumors. Obesity therefore promotes cancer by differentially regulating chronic versus acute inflammation. Given that obesity is chronic, the initial inflammation in adipose tissue will lead to systemic inflammation that could induce compensatory anti-inflammatory reactions in peripheral tissues to suppress chronic inflammation. The overall effect of obesity in peripheral tissues is therefore dependent on the duration and severity of obesity. Adipose tissue is a complex tissue that is composed of many cell types in addition to adipocytes. Further, adipose tissue cellularity is different at different anatomical sites throughout the body. Consequently, the sensitivity of adipose tissue to obesity is dependent on the anatomical location of the adipose depot. For example, obesity induces more inflammation in visceral than subcutaneous adipose tissue. Based on these studies, the mechanisms by which obesity promotes tumorigenesis are multifactorial and immune cell type-specific. The objective of our paper is to discuss the cellular mechanisms by which obesity promotes tumorigenesis by regulating distinct types of inflammation in adipose tissue and the tumor microenvironment.

Lipid-associated macrophages between aggravation and alleviation of metabolic diseases

Lipid-associated macrophages (LAMs) are phagocytic cells with lipid-handling capacity identified in various metabolic derangements. During disease development, they locate to atherosclerotic plaques, adipose tissue (AT) of individuals with obesity, liver lesions in steatosis and steatohepatitis, and the intestinal lamina propria. LAMs can also emerge in the metabolically demanding microenvironment of certain tumors. In this review, we discuss major questions regarding LAM recruitment, differentiation, and self-renewal, and, ultimately, their acute and chronic functional impact on the development of metabolic diseases. Further studies need to clarify whether and under which circumstances LAMs drive disease progression or resolution and how their phenotype can be modulated to ameliorate metabolic disorders.

cAMP driven UCP1 induction in human adipocytes requires ATGL-catalyzed lipolysis

OBJECTIVE

The uncoupling protein 1 (UCP1) is induced in brown or "beige" adipocytes through catecholamine-induced cAMP signaling, which activates diverse transcription factors. UCP1 expression can also be enhanced by PPARγ agonists such as rosiglitazone (Rsg). However, it is unclear whether this upregulation results from de-novo differentiation of beige adipocytes from progenitor cells, or from the induction of UCP1 in pre-existing adipocytes. To explore this, we employed human adipocytes differentiated from progenitor cells and examined their acute response to Rsg, to the adenylate-cyclase activator forskolin (Fsk), or to both simultaneously.

METHODS

Adipocytes generated from primary human progenitor cells were differentiated without exposure to PPARγ agonists, and treated for 3, 6 or 78 h to Fsk, to Rsg, or to both simultaneously. Bulk RNASeq, RNAScope, RT-PCR, CRISPR-Cas9 mediated knockout, oxygen consumption and western blotting were used to assess cellular responses.

RESULTS

UCP1 mRNA expression was induced within 3 h of exposure to either Rsg or Fsk, indicating that Rsg's effect is independent on additional adipocyte differentiation. Although Rsg and Fsk induced distinct overall transcriptional responses, both induced genes associated with calcium metabolism, lipid droplet assembly, and mitochondrial remodeling, denoting core features of human adipocyte beiging. Unexpectedly, we found that Fsk-induced UCP1 expression was reduced by approximately 80% following CRISPR-Cas9-mediated knockout of PNPLA2, the gene encoding the triglyceride lipase ATGL. As anticipated, ATGL knockout suppressed lipolysis; however, the associated suppression of UCP1 induction indicates that maximal cAMP-mediated UCP1 induction requires products of ATGL-catalyzed lipolysis. Supporting this, we observed that the reduction in Fsk-stimulated UCP1 induction caused by ATGL knockout was reversed by Rsg, implying that the role of lipolysis in this process is to generate natural PPARγ agonists.

CONCLUSIONS

UCP1 transcription is known to be stimulated by transcription factors activated downstream of cAMP-dependent protein kinases. Here we demonstrate that UCP1 transcription can also be acutely induced through PPARγ-activation. Moreover, both pathways are activated in human adipocytes in response to cAMP, synergistically inducing UCP1 expression. The stimulation of PPARγ in response to cAMP may result from the production of natural PPARγ activating ligands through ATGL-mediated lipolysis.

Metabolic syndrome

The metabolic syndrome (MetS) is a multiplex modifiable risk factor for cardiovascular disease, type 2 diabetes mellitus and other health outcomes, and is a major challenge to clinical practice and public health. The rising global prevalence of MetS, driven by urbanization, sedentary lifestyles and dietary changes, underlines the urgency of addressing this syndrome. We explore the complex underlying mechanisms, including genetic predisposition, insulin resistance, accumulation of dysfunctional adipose tissue and ectopic lipids in abdominal obesity, systemic inflammation and dyslipidaemia, and how they contribute to the clinical manifestations of MetS. Diagnostic approaches vary but commonly focus on abdominal obesity (assessed using waist circumference), hyperglycaemia, dyslipidaemia and hypertension, highlighting the need for population-specific and phenotype-specific diagnostic strategies. Management of MetS prioritizes lifestyle modifications, such as healthy dietary patterns, physical activity and management of excess visceral and ectopic adiposity, as foundational interventions. We also discuss emerging therapies, including new pharmacological treatments and surgical options, providing a forward-looking perspective on MetS research and care. This Primer aims to inform clinicians, researchers and policymakers about MetS complexities, advocating for a cohesive, patient-centred management and prevention strategy. Emphasizing the multifactorial nature of MetS, this Primer calls for integrated public health efforts, personalized care and innovative research to address this escalating health issue.

Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications

For a long time, white adipocytes were thought to function as lipid storages due to the sizeable unilocular lipid droplet that occupies most of their space. However, recent discoveries have highlighted the critical role of white adipocytes in maintaining energy homeostasis and contributing to obesity and related metabolic diseases. These physiological and pathological functions depend heavily on the mitochondria that reside in white adipocytes. This article aims to provide an up-to-date overview of the recent research on the function and dysfunction of white adipocyte mitochondria. After briefly summarizing the fundamental aspects of mitochondrial biology, the article describes the protective role of functional mitochondria in white adipocyte and white adipose tissue health and various roles of dysfunctional mitochondria in unhealthy white adipocytes and obesity. Finally, the article emphasizes the importance of enhancing mitochondrial quantity and quality as a therapeutic avenue to correct mitochondrial dysfunction, promote white adipocyte browning, and ultimately improve obesity and its associated metabolic diseases. © 2024 American Physiological Society. Compr Physiol 14:5581-5640, 2024.

A novel long non-coding RNA connects obesity to impaired adipocyte function

BACKGROUND

Long non-coding RNAs (lncRNAs) can perform tasks of key relevance in fat cells, contributing, when defective, to the burden of obesity and its sequelae. Here, scrutiny of adipose tissue transcriptomes before and after bariatric surgery (GSE53378) granted identification of 496 lncRNAs linked to the obese phenotype. Only expression of linc-GALNTL6-4 displayed an average recovery over 2-fold and FDR-adjusted p-value <0.0001 after weight loss. The aim of the present study was to investigate the impact on adipocyte function and potential clinical value of impaired adipose linc-GALNTL6-4 in obese subjects.

METHODS

We employed transcriptomic analysis of public dataset GSE199063, and cross validations in two large transversal cohorts to report evidence of a previously unknown association of adipose linc-GALNTL6-4 with obesity. We then performed functional analyses in human adipocyte cultures, genome-wide transcriptomics, and untargeted lipidomics in cell models of loss and gain of function to explore the molecular implications of its associations with obesity and weight loss.

RESULTS

The expression of linc-GALNTL6-4 in human adipose tissue is adipocyte-specific and co-segregates with obesity, being normalized upon weight loss. This co-segregation is demonstrated in two longitudinal weight loss studies and two cross-sectional samples. While compromised expression of linc-GALNTL6-4 in obese subjects is primarily due to the inflammatory component in the context of obesity, adipogenesis requires the transcriptional upregulation of linc-GALNTL6-4, the expression of which reaches an apex in terminally differentiated adipocytes. Functionally, we demonstrated that the knockdown of linc-GALNTL6-4 impairs adipogenesis, induces alterations in the lipidome, and leads to the downregulation of genes related to cell cycle, while propelling in adipocytes inflammation, impaired fatty acid metabolism, and altered gene expression patterns, including that of apolipoprotein C1 (APOC1). Conversely, the genetic gain of linc-GALNTL6-4 ameliorated differentiation and adipocyte phenotype, putatively by constraining APOC1, also contributing to the metabolism of triglycerides in adipose.

CONCLUSIONS

Current data unveil the unforeseen connection of adipocyte-specific linc-GALNTL6-4 as a modulator of lipid homeostasis challenged by excessive body weight and meta-inflammation.

Key questions and gaps in understanding adipose tissue macrophages and early-life metabolic programming

The global obesity epidemic, with its associated comorbidities and increased risk of early mortality, underscores the urgent need for enhancing our understanding of the origins of this complex disease. It is increasingly clear that metabolism is programmed early in life and that metabolic programming can have life-long health consequences. As a critical metabolic organ sensitive to early-life stimuli, proper development of adipose tissue (AT) is crucial for life-long energy homeostasis. Early-life nutrients, especially fatty acids (FAs), significantly influence the programming of AT and shape its function and metabolism. Of growing interest are the dynamic responses during pre- and postnatal development to proinflammatory omega-6 (n6) and anti-inflammatory omega-3 (n3) FA exposures in AT. In the US maternal diet, the ratio of "pro-inflammatory" n6- to "anti-inflammatory" n3-FAs has grown dramatically due to the greater prevalence of n6-FAs. Notably, AT macrophages (ATMs) form a significant population within adipose stromal cells, playing not only an instrumental role in AT formation and maintenance but also acting as key mediators of cell-to-cell lipid and cytokine signaling. Despite rapid advances in ATM and immunometabolism fields, research has focused on responses to obesogenic diets and during adulthood. Consequently, there is a significant gap in identifying the mechanisms contributing metabolic health, especially regarding lipid exposures during the establishment of ATM physiology. Our review highlights the current understanding of ATM diversity, their critical role in AT, their potential role in early-life metabolic programming, and the broader implications for metabolism and health.

Heterogeneity in extracellular matrix and immune microenvironment of anterior vaginal wall revealed by single-cell sequencing in women with stress urinary incontinence

Stress urinary incontinence (SUI), characterized by involuntary urine leakage during increased abdominal pressure, remains poorly understood regarding its pathophysiology and treatment. In this study, we utilized single-cell sequencing to analyze the transcriptomic profiles of different cell types in anterior vaginal wall of SUI patients, aiming to explore the heterogeneity of the extracellular matrix (ECM) and immune microenvironment in SUI pathogenesis. Our results identified eleven cell types, including connective tissue cells, immune cells, and glial cells. Specifically, fibroblasts, smooth muscle cells, epithelial cells and T cells displayed transcriptional characteristics highly relevant to SUI pathogenesis. We observed that most cell types participate in ECM metabolism and immune-inflammatory responses, indicating a synergistic role of multiple vaginal cell types in SUI. Furthermore, altered intercellular communication, particularly between fibroblasts and T cells, was noted in SUI. This study provides novel single-cell insights into SUI and identifies potential biomarkers and therapeutic targets for future research.

Dynamic Roles and Expanding Diversity of Adipose Tissue Macrophages in Obesity

Adipose tissue macrophages (ATMs) are key regulators of adipose tissue (AT) inflammation and insulin resistance in obesity, and the traditional M1/M2 characterization of ATMs is inadequate for capturing their diversity in obese conditions. Single-cell transcriptomic profiling has revealed heterogeneity among ATMs that goes beyond the old paradigm and identified new subsets with unique functions. Furthermore, explorations of their developmental origins suggest that multiple differentiation pathways contribute to ATM variety. These advances raise concerns about how to define ATM functions, how they are regulated, and how they orchestrate changes in AT. This review provides an overview of the current understanding of ATMs and their updated categorization in both mice and humans during obesity. Additionally, diverse ATM functions and contributions in the context of obesity are discussed. Finally, potential strategies for targeting ATM functions as therapeutic interventions for obesity-induced metabolic diseases are addressed.

Dipeptidyl peptidase-4 marks distinct subtypes of human adipose stromal/stem cells with different hepatocyte differentiation and immunoregulatory properties

BACKGROUND

Human adipose-derived stromal/stem cells (hASCs) play important roles in regenerative medicine and numerous inflammatory diseases. However, their cellular heterogeneity limits the effectiveness of treatment. Understanding the distinct subtypes of hASCs and their phenotypic implications will enable the selection of appropriate subpopulations for targeted approaches in regenerative medicine or inflammatory diseases.

METHODS

hASC subtypes expressing dipeptidyl peptidase-4 (DPP4) were identified via fluorescence-activated cell sorting (FACS) analysis. DPP4 expression was knocked down in DPP4+ hASCs via DPP4 siRNA. The capacity for proliferation, hepatocyte differentiation, inflammatory factor secretion and T-cell functionality regulation of hASCs from DPP4-, DPP4+, and control siRNA-treated DPP4+ hASCs and DPP4 siRNA-treated DPP4+ hASCs were assessed.

RESULTS

DPP4+ hASCs and control siRNA-treated DPP4+ hASCs presented a lower proliferative capacity but greater hepatocyte differentiation capacity than DPP4- hASCs and DPP4 siRNA-treated DPP4+ hASCs. Both DPP4+ hASCs and DPP4- hASCs secreted high levels of vascular endothelial growth factor-A (VEGF-A), monocyte chemoattractant protein-1 (MCP-1), and interleukin 6 (IL-6), whereas the levels of other factors, including matrix metalloproteinase (MMP)-1, eotaxin-3, fractalkine (FKN, CX3CL1), growth-related oncogene-alpha (GRO-alpha, CXCL1), monokine induced by interferon-gamma (MIG), macrophage inflammatory protein (MIP)-1beta, and macrophage colony-stimulating factor (M-CSF), were significantly greater in the supernatants of DPP4+ hASCs than in those of DPP4- hASCs. Exposure to hASC subtypes and their conditioned media triggered changes in the secreted cytokine profiles of T cells from healthy donors. The percentage of functional T cells that secreted factors such as MIP-1beta and IL-8 increased when these cells were cocultured with DPP4+ hASCs. The percentage of polyfunctional CD8+ T cells that secreted multiple factors, such as IL-17A, tumour necrosis factor alpha (TNF-α) and TNF-β, decreased when these cells were cocultured with supernatants derived from DPP4+ hASCs.

CONCLUSIONS

DPP4 may regulate proliferation, hepatocyte differentiation, inflammatory cytokine secretion and T-cell functionality of hASCs. These data provide a key foundation for understanding the important role of hASC subpopulations in the regulation of T cells, which may be helpful for future immune activation studies and allow them to be customized for clinical application.

Dissecting human adipose tissue heterogeneity using single-cell omics technologies

Single-cell omics technologies that profile genes (genomic and epigenomic) and determine the abundance of mRNA (transcriptomic), protein (proteomic and secretomic), lipids (lipidomic), and extracellular matrix (matrisomic) support the dissection of adipose tissue heterogeneity at unprecedented resolution in a temporally and spatially defined manner. In particular, cell omics technologies may provide innovative biomarkers for the identification of rare specific progenitor cell subpopulations, assess transcriptional and proteomic changes affecting cell proliferation and immunomodulatory potential, and accurately define the lineage hierarchy and differentiation status of progenitor cells. Unraveling adipose tissue complexity may also provide for the precise assessment of a dysfunctional state, which has been associated with cancer, as cancer-associated adipocytes play an important role in shaping the tumor microenvironment supporting tumor progression and metastasis, obesity, metabolic syndrome, and type 2 diabetes mellitus. The information collected by single-cell omics has relevant implications for regenerative medicine because adipose tissue is an accessible source of multipotent cells; alternative cell-free approaches, including the use of adipose tissue stromal cell-conditioned medium, extracellular vesicles, or decellularized extracellular matrix, are clinically valid options. Subcutaneous white adipose tissue, which is generally harvested via liposuction, is highly heterogeneous because of intrinsic biological variability and extrinsic inconsistencies in the harvesting and processing procedures. The current limited understanding of adipose tissue heterogeneity impinges on the definition of quality standards appropriate for clinical translation, which requires consistency and uniformity of the administered product. We review the methods used for dissecting adipose tissue heterogeneity and provide an overview of advances in omics technology that may contribute to the exploration of heterogeneity and dynamics of adipose tissue at the single-cell level.

Single-Cell Landscape and a Macrophage Subset Enhancing Brown Adipocyte Function in Diabetes

BACKGRUOUND

Metabolic dysregulation is a hallmark of type 2 diabetes mellitus (T2DM), in which the abnormalities in brown adipose tissue (BAT) play important roles. However, the cellular composition and function of BAT as well as its pathological significance in diabetes remain incompletely understood. Our objective is to delineate the single-cell landscape of BAT-derived stromal vascular fraction (SVF) and their characteristic alterations in T2DM rats.

METHODS

T2DM was induced in rats by intraperitoneal injection of low-dose streptozotocin and high-fat diet feeding. Single-cell mRNA sequencing was then performed on BAT samples and compared to normal rats to characterize changes in T2DM rats. Subsequently, the importance of key cell subsets in T2DM was elucidated using various functional studies.

RESULTS

Almost all cell types in the BAT-derived SVF of T2DM rats exhibited enhanced inflammatory responses, increased angiogenesis, and disordered glucose and lipid metabolism. The multidirectional differentiation potential of adipose tissue-derived stem cells was also reduced. Moreover, macrophages played a pivotal role in intercellular crosstalk of BAT-derived SVF. A novel Rarres2+macrophage subset promoted the differentiation and metabolic function of brown adipocytes via adipose-immune crosstalk.

CONCLUSION

BAT SVF exhibited strong heterogeneity in cellular composition and function and contributed to T2DM as a significant inflammation source, in which a novel macrophage subset was identified that can promote brown adipocyte function.

Contributions of white adipose tissue to energy requirements for female reproduction

Body composition impacts female fertility and there are established relationships between adipose tissue and the reproductive system. Maintaining functional adipose tissue is vital for meeting the energetic demands during the reproductive process, from ovulation to delivery and lactation. White adipose tissue (WAT) shows plastic responses to daily physiology and secretes diverse adipokines that affect the hypothalamic-pituitary-ovarian axis, but many other interorgan interactions remain to be determined. This review summarizes the current state of research on the dialogue between WAT and the female reproductive system, focusing on the impact of this crosstalk on ovarian and endometrial factors essential for fecundity.

The fibro-adipogenic progenitor APOD+DCN+LUM+ cell population in aggressive carcinomas

We identified a progenitor cell population highly enriched in samples from invasive and chemo-resistant carcinomas, characterized by a well-defined multigene signature including APOD, DCN, and LUM. This cell population has previously been labeled as consisting of inflammatory cancer-associated fibroblasts (iCAFs). The same signature characterizes naturally occurring fibro-adipogenic progenitors (FAPs) as well as stromal cells abundant in normal adipose tissue. Our analysis of human gene expression databases provides evidence that adipose stromal cells (ASCs) are recruited by tumors and undergo differentiation into CAFs during cancer progression to invasive and chemotherapy-resistant stages.

The role of adipose tissue dysfunction in hepatic insulin resistance and T2D

The root cause of type 2 diabetes (T2D) is insulin resistance (IR), defined by the failure of cells to respond to circulating insulin to maintain lipid and glucose homeostasis. While the causes of whole-body insulin resistance are multifactorial, a major contributing factor is dysregulation of liver and adipose tissue function. Adipose dysfunction, particularly adipose tissue-IR (adipo-IR), plays a crucial role in the development of hepatic insulin resistance and the progression of metabolic dysfunction-associated steatotic liver disease (MASLD) in the context of T2D. In this review, we will focus on molecular mechanisms of hepatic insulin resistance and its association with adipose tissue function. A deeper understanding of the pathophysiological mechanisms of the transition from a healthy state to insulin resistance, impaired glucose tolerance, and T2D may enable us to prevent and intervene in the progression to T2D.

Natriuretic peptide receptor-C perturbs mitochondrial respiration in white adipose tissue

Natriuretic peptide receptor-C (NPR-C) is highly expressed in adipose tissues and regulates obesity-related diseases; however, the detailed mechanism remains unknown. In this research, we aimed to explore the potential role of NPR-C in cold exposure and high-fat/high-sugar (HF/HS) diet-induced metabolic changes, especially in regulating white adipose tissue (WAT) mitochondrial function. Our findings showed that NPR-C expression, especially in epididymal WAT (eWAT), was reduced after cold exposure. Global Npr3 (gene encoding NPR-C protein) deficiency led to reduced body weight, increased WAT browning, thermogenesis, and enhanced expression of genes related to mitochondrial biogenesis. RNA-sequencing of eWAT showed that Npr3 deficiency enhanced the expression of mitochondrial respiratory chain complex genes and promoted mitochondrial oxidative phosphorylation in response to cold exposure. In addition, Npr3 KO mice were able to resist obesity induced by HF/HS diet. Npr3 knockdown in stromal vascular fraction (SVF)-induced white adipocytes promoted the expression of proliferator-activated receptor gamma coactivator 1α (PGC1α), uncoupling protein one (UCP1), and mitochondrial respiratory chain complexes. Mechanistically, NPR-C inhibited cGMP and calcium signaling in an NPR-B-dependent manner but suppressed cAMP signaling in an NPR-B-independent manner. Moreover, Npr3 knockdown induced browning via AKT and p38 pathway activation, which were attenuated by Npr2 knockdown. Importantly, treatment with the NPR-C-specific antagonist, AP-811, decreased WAT mass and increased PGC-1α, UCP1, and mitochondrial complex expression. Our findings reveal that NPR-C deficiency enhances mitochondrial function and energy expenditure in white adipose tissue, contributing to improved metabolic health and resistance to obesity.

Adipose-derived mesenchymal stromal cells in clinical trials: Insights from single-cell studies

Mesenchymal Stromal Cells (MSCs) offer tremendous potential for the treatment of various diseases and their healing properties have been explored in hundreds of clinical trials. These trails primarily focus on immunological and neurological disorders, as well as regenerative medicine. Adipose tissue is a rich source of mesenchymal stromal cells and methods to obtain and culture adipose-derived MSCs (AD-MSCs) have been well established. Promising results from pre-clinical testing of AD-MSCs activity prompted clinical trials that further led to the approval of AD-MSCs for the treatment of complex perianal fistulas in Crohn's disease and subcutaneous tissue defects. However, AD-MSC heterogeneity along with various manufacturing protocols or different strategies to boost their activity create the need for standardized quality control procedures and safety assessment of the intended cell product. High-resolution transcriptomic methods have been recently gaining attention, as they deliver insight into gene expression profiles of individual cells, helping to deconstruct cellular hierarchy and differentiation trajectories, and to understand cell-cell interactions within tissues. This article presents a comprehensive overview of completed clinical trials evaluating the safety and efficacy of AD-MSC treatment, together with current single-cell studies of human AD-MSC. Furthermore, our work emphasizes the increasing significance of single-cell research in elucidating the mechanisms of cellular action and predicting their therapeutic effects.

Identification and Validation of CXCL2 as a Key Gene for Childhood Obesity

This study aims to identify the key genes and their regulatory networks by bioinformatics, increasing understanding of childhood obesity. The data comes from the GEO and Immport database. The immune microenvironment was explored in GSE104815. Key genes were identified by intersection of DEGs with the immune gene set. Enrichment analysis revealed gene-related functions and correlation analysis explored the relationship. Regulatory networks were constructed based on miRcode, TarBase and TargetScan databases. GSE29718 was used to validate our findings. Intercellular communication and cell differentiation trends were further explored using single-cell data from GSE153643. Based on our research, the immune microenvironment in the obese group showed higher immune infiltration. We found 962 DEGs and CXCL2 was identified as the key gene. The co-regulatory network of lncRNA-miRNA-mRNA suggested that obtaining TM4SF19-AS1, GUSBP11, AC105020.1, LINC00189, COL4A2-AS2, VIPR1-AS1 and LINC00242 may regulate CXCL2 (r > 0.9 and P < 0.01). Differential expression of CXCL2 was validated in GSE29718 (P < 0.05) and CXCL2 was identified as a biomarker for childhood obesity (AUC = 0.885). GSVA enrichment analysis revealed many pathways of high group obtaining the TNF-α signaling via NF-κB pathway and interferon γ response pathway. In GSE153643, 11 cell types were identified and CXCL2 was highly expressed in monocyte, macrophage, endothelial cell and pericyte. In CXCL2 high expressing macrophages, there was a tendency for cells to polarize toward M1 macrophages (P < 0.05). In summary, we identified CXCL2 as a potential biomarker of childhood obesity. The development of childhood obesity may be associated with the activation of immune infiltration of macrophage M1 polarization by CXCL2 expression.

Potential Consequences of the Use of Adipose-Derived Stem Cells in the Treatment of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) ranks as the most prevalent of primary liver cancers and stands as the third leading cause of cancer-related deaths. Early-stage HCC can be effectively managed with available treatment modalities ranging from invasive techniques, such as liver resection and thermoablation, to systemic therapies primarily employing tyrosine kinase inhibitors. Unfortunately, these interventions take a significant toll on the body, either through physical trauma or the adverse effects of pharmacotherapy. Consequently, there is an understandable drive to develop novel HCC therapies. Adipose-derived stem cells (ADSCs) are a promising therapeutic tool. Their facile extraction process, coupled with the distinctive immunomodulatory capabilities of their secretome, make them an intriguing subject for investigation in both oncology and regenerative medicine. The factors they produce are both enzymes affecting the extracellular matrix (specifically, metalloproteinases and their inhibitors) as well as cytokines and growth factors affecting cell proliferation and invasiveness. So far, the interactions observed with various cancer cell types have not led to clear conclusions. The evidence shows both inhibitory and stimulatory effects on tumor growth. Notably, these effects appear to be dependent on the tumor type, prompting speculation regarding their potential inhibitory impact on HCC. This review briefly synthesizes findings from preclinical and clinical studies examining the effects of ADSCs on cancers, with a specific focus on HCC, and emphasizes the need for further research.

Comparative single-cell transcriptional and proteomic atlas of clinical-grade injectable mesenchymal source tissues

Bone marrow aspirate concentrate (BMAC) and adipose-derived stromal vascular fraction (ADSVF) are the most marketed stem cell therapies to treat a variety of conditions in the general population and elite athletes. Both tissues have been used interchangeably clinically even though their detailed composition, heterogeneity, and mechanisms of action have neither been rigorously inventoried nor compared. This lack of information has prevented investigations into ideal dosages and has facilitated anecdata and misinformation. Here, we analyzed single-cell transcriptomes, proteomes, and flow cytometry profiles from paired clinical-grade BMAC and ADSVF. This comparative transcriptional atlas challenges the prevalent notion that there is one therapeutic cell type present in both tissues. We also provide data of surface markers that may enable isolation and investigation of cell (sub)populations. Furthermore, the proteome atlas highlights intertissue and interpatient heterogeneity of injected proteins with potentially regenerative or immunomodulatory capacities. An interactive webtool is available online.

A human omentum-specific mesothelial-like stromal population inhibits adipogenesis through IGFBP2 secretion

Adipose tissue plasticity is orchestrated by molecularly and functionally diverse cells within the stromal vascular fraction (SVF). Although several mouse and human adipose SVF cellular subpopulations have by now been identified, we still lack an understanding of the cellular and functional variability of adipose stem and progenitor cell (ASPC) populations across human fat depots. To address this, we performed single-cell and bulk RNA sequencing (RNA-seq) analyses of >30 SVF/Lin- samples across four human adipose depots, revealing two ubiquitous human ASPC (hASPC) subpopulations with distinct proliferative and adipogenic properties but also depot- and BMI-dependent proportions. Furthermore, we identified an omental-specific, high IGFBP2-expressing stromal population that transitions between mesothelial and mesenchymal cell states and inhibits hASPC adipogenesis through IGFBP2 secretion. Our analyses highlight the molecular and cellular uniqueness of different adipose niches, while our discovery of an anti-adipogenic IGFBP2+ omental-specific population provides a new rationale for the biomedically relevant, limited adipogenic capacity of omental hASPCs.

Systems genetics analysis of human body fat distribution genes identifies adipocyte processes

Excess abdominal fat is a sexually dimorphic risk factor for cardio-metabolic disease and is approximated by the waist-to-hip ratio adjusted for body mass index (WHRadjBMI). Whereas this trait is highly heritable, few causal genes are known. We aimed to identify novel drivers of WHRadjBMI using systems genetics. We used two independent cohorts of adipose tissue gene expression and constructed sex- and depot-specific Bayesian networks to model gene-gene interactions from 8,492 genes. Using key driver analysis, we identified genes that, in silico and putatively in vitro, regulate many others. 51-119 key drivers in each network were replicated in both cohorts. In other cell types, 23 of these genes are found in crucial adipocyte pathways: Wnt signaling or mitochondrial function. We overexpressed or down-regulated seven key driver genes in human subcutaneous pre-adipocytes. Key driver genes ANAPC2 and RSPO1 inhibited adipogenesis, whereas PSME3 increased adipogenesis. RSPO1 increased Wnt signaling activity. In differentiated adipocytes, MIGA1 and UBR1 down-regulation led to mitochondrial dysfunction. These five genes regulate adipocyte function, and we hypothesize that they regulate fat distribution.

Single-nucleus RNA transcriptome profiling reveals murine adipose tissue endothelial cell proliferation gene networks involved in obesity development

Endothelial cells play an important role in the metabolism of adipose tissue (AT). This study aimed to analyze the changes that adipose tissue in AT endothelial cells undergo during the development of obesity, using single-nucleus RNA sequence (snRNA-seq). Mouse paraepididymal AT cells were subjected to snRNA-seq with the 10X Genomics platform. The cell types were then clustered using t-distributed stochastic neighbor embedding and unbiased computational informatics analyses. Protein-protein interactions network was established using the STRING database and visualized using Cytoscape. The dataset was subjected to differential gene enrichment analysis. In total, 21,333 cells acquired from 24 mouse paraepididymal AT samples were analyzed using snRNA-seq. This study identified 18 distinct clusters and annotated macrophages, fibroblasts, epithelial cells, T cells, endothelial cells, stem cells, neutrophil cells, and neutrophil cell types based on representative markers. Cluster 12 was defined as endothelial cells. The proportion of endothelial cells decreased with the development of obesity. Inflammatory factors, such as Vegfa and Prdm16 were upregulated in the medium obesity group but downregulated in the obesity group. Genes, such as Prox1, Erg, Flt4, Kdr, Flt1, and Pecam1 promoted the proliferation of AT endothelial cells and maintained the internal environment of AT. This study established a reference model and general framework for studying the mechanisms, biomarkers, and therapeutic targets of endothelial cell dysfunction-related diseases at the single-cell level.

Single-Nucleus Transcriptomic Atlas of Human Pericoronary Epicardial Adipose Tissue in Normal and Pathological Conditions

BACKGROUND

Pericoronary epicardial adipose tissue (EAT) is a unique visceral fat depot that surrounds the adventitia of the coronary arteries without any anatomic barrier. Clinical studies have demonstrated the association between EAT volume and increased risks for coronary artery disease (CAD). However, the cellular and molecular mechanisms underlying the association remain elusive.

METHODS

We performed single-nucleus RNA sequencing on pericoronary EAT samples collected from 3 groups of subjects: patients undergoing coronary bypass surgery for severe CAD (n=8), patients with CAD with concomitant type 2 diabetes (n=8), and patients with valvular diseases but without concomitant CAD and type 2 diabetes as the control group (n=8). Comparative analyses were performed among groups, including cellular compositional analysis, cell type-resolved transcriptomic changes, gene coexpression network analysis, and intercellular communication analysis. Immunofluorescence staining was performed to confirm the presence of CAD-associated subclusters.

RESULTS

Unsupervised clustering of 73 386 nuclei identified 15 clusters, encompassing all known cell types in the adipose tissue. Distinct subpopulations were identified within primary cell types, including adipocytes, adipose stem and progenitor cells, and macrophages. CD83high macrophages and FOSBhigh adipocytes were significantly expanded in CAD. In comparison to normal controls, both disease groups exhibited dysregulated pathways and altered secretome in the primary cell types. Nevertheless, minimal differences were noted between the disease groups in terms of cellular composition and transcriptome. In addition, our data highlight a potential interplay between dysregulated circadian clock and altered physiological functions in adipocytes of pericoronary EAT. ANXA1 (annexin A1) and SEMA3B (semaphorin 3B) were identified as important adipokines potentially involved in functional changes of pericoronary EAT and CAD pathogenesis.

CONCLUSIONS

We built a complete single-nucleus transcriptomic atlas of human pericoronary EAT in normal and diseased conditions of CAD. Our study lays the foundation for developing novel therapeutic strategies for treating CAD by targeting and modifying pericoronary EAT functions.

Aging and homeostasis of the hypodermis in the age-related deterioration of skin function

Adipose tissues in the hypodermis, the crucial stem cell reservoir in the skin and the endocrine organ for the maintenance of skin homeostasis undergo significant changes during skin aging. Dermal white adipose tissue (dWAT) has recently been recognized as an important organ for both non-metabolic and metabolic health in skin regeneration and rejuvenation. Defective differentiation, adipogenesis, improper adipocytokine production, and immunological dissonance dysfunction in dWAT lead to age-associated clinical changes. Here, we review age-related alterations in dWAT across levels, emphasizing the mechanisms underlying the regulation of aging. We also discuss the pathogenic changes involved in age-related fat dysfunction and the unfavorable consequences of accelerated skin aging, such as chronic inflammaging, immunosenescence, delayed wound healing, and fibrosis. Research has shown that adipose aging is an early initiation event and a potential target for extending longevity. We believe that adipose tissues play an essential role in aging and form a potential therapeutic target for the treatment of age-related skin diseases. Further research is needed to improve our understanding of this phenomenon.

Single-cell multiomics profiling reveals heterogeneous transcriptional programs and microenvironment in DSRCTs

Desmoplastic small round cell tumor (DSRCT) is a rare, aggressive sarcoma driven by the EWSR1::WT1 chimeric transcription factor. Despite this unique oncogenic driver, DSRCT displays a polyphenotypic differentiation of unknown causality. Using single-cell multi-omics on 12 samples from five patients, we find that DSRCT tumor cells cluster into consistent subpopulations with partially overlapping lineage- and metabolism-related transcriptional programs. In vitro modeling shows that high EWSR1::WT1 DNA-binding activity associates with most lineage-related states, in contrast to glycolytic and profibrotic states. Single-cell chromatin accessibility analysis suggests that EWSR1::WT1 binding site variability may drive distinct lineage-related transcriptional programs, supporting some level of cell-intrinsic plasticity. Spatial transcriptomics reveals that glycolytic and profibrotic states specifically localize within hypoxic niches at the periphery of tumor cell islets, suggesting an additional role of tumor cell-extrinsic microenvironmental cues. We finally identify a single-cell transcriptomics-derived epithelial signature associated with improved patient survival, highlighting the clinical relevance of our findings.

Adipocyte Progenitor Pools Composition and Cellular Niches Affect Adipogenesis Divergence in Porcine Subcutaneous and Intramuscular Fat

Intramuscular fat (IMF) contributed positively to pork quality, whereas subcutaneous fat (SCF) was often considered to be a detrimental factor impacting growth and carcass traits. Reducing SCF while maintaining optimal IMF levels requires a thorough understanding of the adipogenic differences between these two adipose depots. Our study explored the differences in adipogenesis between porcine IMF and SCF, and the results showed that subcutaneous adipocytes (SCAs) demonstrate a greater potential for adipogenic differentiation, both in vivo and in vitro. Lipidomic and transcriptomic analyses suggested that intramuscular adipocytes (IMAs) are more inclined to biosynthesize unsaturated fatty acids. Furthermore, single-cell RNA sequencing (scRNA-seq) was employed to dissect the intrinsic and microenvironmental discrepancies in adipogenesis between porcine IMF and SCF. Comparative analysis indicated that SCF was enriched with preadipocytes, exhibiting an enhanced adipogenic potential, while IMF was characterized by a higher abundance of stem cells. Furthermore, coculture analyses of porcine intramuscular adipogenic cells and myogenetic cells indicated that the niche of IMAs inhibited its adipogenic differentiation. Cell communication analysis identified 160 ligand-receptor pairs and channels between adipogenic and myogenetic cells in IMF. Collectively, our study elucidated two intrinsic and microenvironmental novel mechanisms underpinning the divergence in adipogenesis between porcine SCF and IMF.