Aging-dependent regulatory cells emerge in subcutaneous fat to inhibit adipogenesis

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.

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.

Intermittent fasting promotes rejuvenation of immunosenescent phenotypes in aged adipose tissue

The aging of white adipose tissue (WAT) involves senescence of adipose stem and progenitor cells (ASPCs) and dysregulation of immune cell populations, serving as a major driver of age-associated adipose dysfunction and metabolic diseases. Conversely, the elimination of senescent ASPCs is associated with improvements in overall health. Intermittent fasting (IF), a dietary intervention that incorporates periodic cycles of fasting and refeeding, has been reported to promote weight loss and fat mass reduction and improve glucose and insulin homeostasis in both murine and human studies. While previous studies have assessed the effects of IF on obesity-associated metabolic dysfunction, few studies have examined the aging-specific changes to ASPCs and immune cell populations in WAT. Here, we show that IF in 18-20-month-old mice reduced senescent phenotypes of ASPCs and restored their adipogenic potential. Intriguingly, IF-treated mice exhibited an increase in adipose eosinophils, which has been reported to be associated with improved WAT homeostasis and immunological fitness in aged mice. The observed cellular and metabolic changes suggest that IF may be a feasible lifestyle regimen to reduce cellular senescence which could result in attenuation of downstream aging-induced WAT dysfunction and metabolic diseases.

M2 macrophage-derived TGF-β induces age-associated loss of adipogenesis through progenitor cell senescence

OBJECTIVES

Adipose tissue is an endocrine and energy storage organ composed of several different cell types, including mature adipocytes, stromal cells, endothelial cells, and a variety of immune cells. Adipose tissue aging contributes to the pathogenesis of metabolic dysfunction and is likely induced by crosstalk between adipose progenitor cells (APCs) and immune cells, but the underlying molecular mechanisms remain largely unknown. In this study, we revealed the biological role of p16high senescent APCs, and investigated the crosstalk between each cell type in the aged white adipose tissue.

METHODS

We performed the single-cell RNA sequencing (scRNA-seq) analysis on the p16high adipose cells sorted from aged p16-CreERT2/Rosa26-LSL-tdTomato mice. We also performed the time serial analysis on the age-dependent bulk RNA-seq datasets of human and mouse white adipose tissues to infer the transcriptome alteration of adipogenic potential within aging.

RESULTS

We show that M2 macrophage-derived TGF-β induces APCs senescence which impairs adipogenesis in vivo. p16high senescent APCs increase with age and show loss of adipogenic potential. The ligand-receptor interaction analysis reveals that M2 macrophages are the donors for TGF-β and the senescent APCs are the recipients. Indeed, treatment of APCs with TGF-β1 induces senescent phenotypes through mitochondrial ROS-mediated DNA damage in vitro. TGF-β1 injection into gonadal white adipose tissue (gWAT) suppresses adipogenic potential and induces fibrotic genes as well as p16 in APCs. A gWAT atrophy is observed in cancer cachexia by APCs senescence, whose induction appeared to be independent of TGF-β induction.

CONCLUSIONS

Our results suggest that M2 macrophage-derived TGF-β induces age-related lipodystrophy by APCs senescence. The TGF-β treatment induced DNA damage, mitochondrial ROS, and finally cellular senescence in APCs.

Estrogen counteracts age-related decline in beige adipogenesis through the NAMPT-regulated ER stress response

Thermogenic beige adipocytes are recognized as potential therapeutic targets for combating metabolic diseases. However, the metabolic advantages that they offer are compromised with aging. Here we show that treating mice with estrogen (E2), a hormone that decreases with age, can counteract the age-related decline in beige adipogenesis when exposed to cold temperature while concurrently enhancing energy expenditure and improving glucose tolerance in mice. Mechanistically, we found that nicotinamide phosphoribosyl transferase (NAMPT) plays a pivotal role in facilitating the formation of E2-induced beige adipocytes, which subsequently suppresses the onset of age-related endoplasmic reticulum (ER) stress. Furthermore, we found that targeting NAMPT signaling, either genetically or pharmacologically, can restore the formation of beige adipocytes by increasing the number of perivascular adipocyte progenitor cells. Conversely, the absence of NAMPT signaling prevents this process. Together, our findings shed light on the mechanisms regulating the age-dependent impairment of beige adipocyte formation and underscore the E2-NAMPT-controlled ER stress pathway as a key regulator of this process.

Aging impairs cold-induced beige adipogenesis and adipocyte metabolic reprogramming

The energy-burning capability of beige adipose tissue is a potential therapeutic tool for reducing obesity and metabolic disease, but this capacity is decreased by aging. Here, we evaluate the impact of aging on the profile and activity of adipocyte stem and progenitor cells (ASPCs) and adipocytes during the beiging process in mice. We found that aging increases the expression of Cd9 and other fibro-inflammatory genes in fibroblastic ASPCs and blocks their differentiation into beige adipocytes. Fibroblastic ASPC populations from young and aged mice were equally competent for beige differentiation in vitro, suggesting that environmental factors suppress adipogenesis in vivo. Examination of adipocytes by single nucleus RNA-sequencing identified compositional and transcriptional differences in adipocyte populations with aging and cold exposure. Notably, cold exposure induced an adipocyte population expressing high levels of de novo lipogenesis (DNL) genes, and this response was severely blunted in aged animals. We further identified Npr3, which encodes the natriuretic peptide clearance receptor, as a marker gene for a subset of white adipocytes and an aging-upregulated gene in adipocytes. In summary, this study indicates that aging blocks beige adipogenesis and dysregulates adipocyte responses to cold exposure and provides a resource for identifying cold and aging-regulated pathways in adipose tissue.

Adipose tissue as a linchpin of organismal ageing

Ageing is a conserved biological process, modulated by intrinsic and extrinsic factors, that leads to changes in life expectancy. In humans, ageing is characterized by greatly increased prevalence of cardiometabolic disease, type 2 diabetes and disorders associated with impaired immune surveillance. Adipose tissue displays species-conserved, temporal changes with ageing, including redistribution from peripheral to central depots, loss of thermogenic capacity and expansion within the bone marrow. Adipose tissue is localized to discrete depots, and also diffusely distributed within multiple organs and tissues in direct proximity to specialized cells. Thus, through their potent endocrine properties, adipocytes are capable of modulating tissue and organ function throughout the body. In addition to adipocytes, multipotent progenitor/stem cells in adipose tissue play a crucial role in maintenance and repair of tissues throughout the lifetime. Adipose tissue may therefore be a central driver for organismal ageing and age-associated diseases. Here we review the features of adipose tissue during ageing, and discuss potential mechanisms by which these changes affect whole-body metabolism, immunity and longevity. We also explore the potential of adipose tissue-targeted therapies to ameliorate age-associated disease burdens.

Impaired Remodeling of White Adipose Tissue in Obesity and Aging: From Defective Adipogenesis to Adipose Organ Dysfunction

The adipose organ adapts and responds to internal and environmental stimuli by remodeling both its cellular and extracellular components. Under conditions of energy surplus, the subcutaneous white adipose tissue (WAT) is capable of expanding through the enlargement of existing adipocytes (hypertrophy), followed by de novo adipogenesis (hyperplasia), which is impaired in hypertrophic obesity. However, an impaired hyperplastic response may result from various defects in adipogenesis, leading to different WAT features and metabolic consequences, as discussed here by reviewing the results of the studies in animal models with either overexpression or knockdown of the main molecular regulators of the two steps of the adipogenesis process. Moreover, impaired WAT remodeling with aging has been associated with various age-related conditions and reduced lifespan expectancy. Here, we delve into the latest advancements in comprehending the molecular and cellular processes underlying age-related changes in WAT function, their involvement in common aging pathologies, and their potential as therapeutic targets to influence both the health of elderly people and longevity. Overall, this review aims to encourage research on the mechanisms of WAT maladaptation common to conditions of both excessive and insufficient fat tissue. The goal is to devise adipocyte-targeted therapies that are effective against both obesity- and age-related disorders.

Tissue fibrosis associated depletion of lipid-filled cells

Fibrosis is primarily described as the deposition of excessive extracellular matrix, but in many tissues it also involves a loss of lipid or lipid-filled cells. Lipid-filled cells are critical to tissue function and integrity in many tissues including the skin and lungs. Thus, loss or depletion of lipid-filled cells during fibrogenesis, has implications for tissue function. In some contexts, lipid-filled cells can impact ECM composition and stability, highlighting their importance in fibrotic transformation. Recent papers in fibrosis address this newly recognized fibrotic lipodystrophy phenomenon. Even in disparate tissues, common mechanisms are emerging to explain fibrotic lipodystrophy. These findings have implications for fibrosis in tissues composed of fibroblast and lipid-filled cell populations such as skin, lung, and liver. In this review, we will discuss the roles of lipid-containing cells, their reduction/loss during fibrotic transformation, and the mechanisms of that loss in the skin and lungs.

Aging impairs cold-induced beige adipogenesis and adipocyte metabolic reprogramming

The energy-burning capability of beige adipose tissue is a potential therapeutic tool for reducing obesity and metabolic disease, but this capacity is decreased by aging. Here, we evaluate the impact of aging on the profile and activity of adipocyte stem and progenitor cells (ASPCs) and adipocytes during the beiging process. We found that aging increases the expression of Cd9 and other fibro-inflammatory genes in fibroblastic ASPCs and blocks their differentiation into beige adipocytes. Fibroblastic ASPC populations from young and aged mice were equally competent for beige differentiation in vitro, suggesting that environmental factors suppress adipogenesis in vivo. Examination of adipocytes by single nucleus RNA-sequencing identified compositional and transcriptional differences in adipocyte populations with age and cold exposure. Notably, cold exposure induced an adipocyte population expressing high levels of de novo lipogenesis (DNL) genes, and this response was severely blunted in aged animals. We further identified natriuretic peptide clearance receptor Npr3, a beige fat repressor, as a marker gene for a subset of white adipocytes and an aging-upregulated gene in adipocytes. In summary, this study indicates that aging blocks beige adipogenesis and dysregulates adipocyte responses to cold exposure and provides a unique resource for identifying cold and aging-regulated pathways in adipose tissue.

Lipodystrophy as a target to delay premature aging

Lipodystrophy syndromes are rare diseases characterized by low levels and an abnormal distribution of adipose tissue, caused by diverse genetic or acquired causes. These conditions commonly exhibit metabolic complications, including insulin resistance, diabetes, hypertriglyceridemia, nonalcoholic fatty liver disease, and adipose tissue dysfunction. Moreover, genetic lipodystrophic laminopathies exhibit a premature aging phenotype, emphasizing the importance of restoring adipose tissue distribution and function. In this opinion, we discuss the relevance of adipose tissue reestablishment as a potential approach to alleviate premature aging and age-related complications in genetic lipodystrophy syndromes.

Aging adipose tissue, insulin resistance, and type 2 diabetes

With the increase of population aging, the prevalence of type 2 diabetes (T2D) is also rising. Aging affects the tissues and organs of the whole body, which is the result of various physiological and pathological processes. Adipose tissue has a high degree of plasticity and changes with aging. Aging changes the distribution of adipose tissue, affects adipogenesis, browning characteristics, inflammatory status and adipokine secretion, and increases lipotoxicity. These age-dependent changes in adipose tissue are an important cause of insulin resistance and T2D. Understanding adipose tissue changes can help promote healthy aging process. This review summarizes changes in adipose tissue ascribable to aging, with a focus on the role of aging adipose tissue in insulin resistance and T2D.

Protocol for quantitative proteomic analysis of heterogeneous adipose tissue-residing progenitor subpopulations in mice

Recent studies have revealed cellular heterogeneity of mesenchymal stromal cells and immune cells in adipose tissue and emphasized the need for quantitative analysis of small numbers of functionally distinct cells using state-of-the-art "omics" technologies. Here, we present an optimized protocol for precise protein quantification from minute amounts of samples. We describe steps for isolation of mouse adipose progenitor cells, proteomics sample preparation, mass spectrometry measurement, and computational analysis. This protocol can be adapted to other samples with limited amounts. For complete details on the use and execution of this protocol, please refer to Shan et al. (2022).1.

The evolving functions of the vasculature in regulating adipose tissue biology in health and obesity

Adipose tissue is an endocrine organ and a crucial regulator of energy storage and systemic metabolic homeostasis. Additionally, adipose tissue is a pivotal regulator of cardiovascular health and disease, mediated in part by the endocrine and paracrine secretion of several bioactive products, such as adipokines. Adipose vasculature has an instrumental role in the modulation of adipose tissue expansion, homeostasis and metabolism. The role of the adipose vasculature has been extensively explored in the context of obesity, which is recognized as a global health problem. Obesity-induced accumulation of fat, in combination with vascular rarefaction, promotes adipocyte dysfunction and induces oxidative stress, hypoxia and inflammation. It is now recognized that obesity-associated endothelial dysfunction often precedes the development of cardiovascular diseases. Investigations have revealed heterogeneity within the vascular niche and dynamic reciprocity between vascular and adipose cells, which can become dysregulated in obesity. Here we provide a comprehensive overview of the evolving functions of the vasculature in regulating adipose tissue biology in health and obesity.

Refeeding-associated AMPKγ1 complex activity is a hallmark of health and longevity

Late-life-initiated dietary interventions show limited efficacy in extending longevity or mitigating frailty, yet the underlying causes remain unclear. Here we studied the age-related fasting response of the short-lived killifish Nothobranchius furzeri. Transcriptomic analysis uncovered the existence of a fasting-like transcriptional program in the adipose tissue of old fish that overrides the feeding response, setting the tissue in persistent metabolic quiescence. The fasting-refeeding cycle triggers an inverse oscillatory expression of genes encoding the AMP-activated protein kinase (AMPK) regulatory subunits Prkag1 (γ1) and Prkag2 (γ2) in young individuals. Aging blunts such regulation, resulting in reduced Prkag1 expression. Transgenic fish with sustained AMPKγ1 countered the fasting-like transcriptional program, exhibiting a more youthful feeding and fasting response in older age, improved metabolic health and longevity. Accordingly, Prkag1 expression declines with age in human tissues and is associated with multimorbidity and multidimensional frailty risk. Thus, selective activation of AMPKγ1 prevents metabolic quiescence and preserves healthy aging in vertebrates, offering potential avenues for intervention.

Profiling of Skeletal Muscle and Adipose Tissue Depots in Men with Advanced Prostate Cancer Receiving Different Forms of Androgen Deprivation Therapy

Background

Androgen deprivation therapy (ADT) is a common treatment modality for men with prostate cancer. Increases in adipose tissue mass and decreases in skeletal muscle mass are known on-target adverse effects of standard ADT. The effects of newer agents such as abiraterone acetate (ABI) and enzalutamide (ENZA) on body composition and how these compare with standard luteinizing hormone-releasing hormone agonists (aLHRHs) are unclear.

Objective

To assess the effects of different forms of androgen deprivation therapy on body composition in men with prostate cancer.

Design setting and participants

Using a retrospective design, 229 patients receiving aLHRHs alone (n = 120) or in combination with ABI (n = 53) or ENZA (n = 56) were studied.

Outcome measurements and statistical analysis

Muscle, visceral adipose tissue (VAT), and subcutaneous adipose tissue (SAT) were assessed at baseline, 6 mo, and 18 mo after initiating therapy using a cross-sectional densitometry analysis performed on standard of care computed tomography images. Response trajectories for all treatment groups were calculated via a two-way analysis of variance post hoc test, for both within-group and between-group differences.

Results and limitations

Treatment with aLHRHs, ABI, and ENZA was associated with a median muscle volume loss of -1.4%, -4.8%, and -5.5% at 6 mo, and -7.1%, -8.1%, and -8.3% at 18 mo, respectively. Therapy with aLHRHs was associated with minimal changes in VAT (0.3% at 6 mo and -0.1% at 18 mo). ABI therapy was associated with significant increases in VAT at 6 mo (4.9%) but not at 18 mo (0.5%), and ENZA therapy was associated with significant decreases in VAT (-4.6% at 6 mo and -5.4% at 18 mo). With respect to SAT, treatment with aLHRHs was associated with increases over time (8.6% at 6 mo and 4.7% at 18 mo), ABI was associated with decreases over time (-3.6% at 6 mo and -6.8% at 18 mo), and ENZA had no clear effects (1.7% at 6 mo and 3.3% at 18 mo).

Conclusions

ADT regimens cause significant short-term losses in muscle mass, with the most rapid effects occurring with ABI and ENZA. The three regimens have disparate effects on SAT and VAT, suggesting distinct roles of androgens in these tissues.

Patient summary

Androgen deprivation therapy alters body composition in men with prostate cancer. Abiraterone and enzalutamide are associated with losses in muscle mass compared with luteinizing hormone-releasing hormone agonists. These treatments impact subcutaneous and visceral fat mass, suggesting distinct roles of androgens in these tissues.

Association between adiposity and facial aging: results from a Mendelian randomization study

BACKGROUND

Skin, as a sociologically meaningful interface, has psychological implications different from other organs, particularly in the context of the global population aging. Growing evidence suggests that facial aging is associated with an increased risk of adiposity. Existing research, however, were observational, and while they may find some correlations, it is difficult to simply disentangle non-causal or reverse-causal links because these associations may be confounded or fail to accurately reflect true causative linkages.

OBJECTIVES

We conducted a 2-sample Mendelian randomization (MR) study to examine the potential effect of facial aging on the risk of broad obesity and its three major adiposity indicators, including body mass index (BMI), body fat percentage (BF%) and waist circumference (WC).

METHODS

Genetic instruments from IEU OpenGWAS project, one of the largest available genome-wide association studies (GWAS) for facial aging (423,999 samples) were used to investigate the relation to broad obesity (32,858 cases, 65,839 controls). Using the inverse-variance weighted (IVW) technique, single nucleotide polymorphisms (SNPs) associated with adiposity indicators (BMI (461,460 samples), BF% (454,633 samples), and WC (462,166 samples)) were investigated in relationship to facial aging. Further sensitivity analyses were performed, including Mendelian randomization-Egger (MR-Egger), weighted median estimates, and leave-one-out analysis, to evaluate the consistency of the results and related potential issues in MR studies.

RESULTS

We identified strong and significant correlations between adiposity and facial aging in the 17 broad obesity-associated SNPs (IVW estimate of odds ratio OR = 1.020, 95% CI 1.010-1.029, P = 7.303e - 05), 458 BMI-associated SNPs (IVW estimate of odds ratio OR = 1.047, 95% CI 1.0357-1.058, P = 1.154e - 16),for the 395 BF%-associated SNPs (OR = 1.056, 95%CI 1.040-1.072,P = 7.617e - 12), or for the 374 WC-associated SNPs (OR = 1.072, 95% CI 1057-1.087,P = 1.229e - 23). A range of complementary methodologies have been employed to evaluate horizontal pleiotropy and related potential caveats occurring in MR research.

CONCLUSIONS

Using Mendelian randomization as an alternative approach to investigate causality, we found a causal relationship between adiposity and facial aging, which was statistically strong and significant.

Mesenchymal stromal cells as conductors of adipose tissue remodeling

Adipose tissue exhibits a remarkable capacity to expand, contract, and remodel in response to changes in physiological and environmental conditions. Here, we describe recent advances in our understanding of how functionally distinct tissue-resident mesenchymal stromal cell subpopulations orchestrate several aspects of physiological and pathophysiological adipose tissue remodeling, with a particular focus on the adaptations that occur in response to changes in energy surplus and environmental temperature. The study of adipose tissue remodeling provides a vehicle to understand the functional diversity of stromal cells and offers a lens through which several generalizable aspects of tissue reorganization can be readily observed.

Estrogen prevents age-dependent beige adipogenesis failure through NAMPT-controlled ER stress pathway

Thermogenic beige adipocytes are recognized as potential therapeutic targets for combating metabolic diseases. However, the metabolic advantages they offer are compromised with aging. Here, we show that treating mice with estrogen (E2), a hormone that decreases with age, to mice can counteract the aging- related decline in beige adipocyte formation when subjected to cold, while concurrently enhancing energy expenditure and improving glucose tolerance. Mechanistically, we find that nicotinamide phosphoribosyltranferase (NAMPT) plays a pivotal role in facilitating the formation of E2-induced beige adipocytes, which subsequently suppresses the onset of age-related ER stress. Furthermore, we found that targeting NAMPT signaling, either genetically or pharmacologically, can restore the formation of beige adipocytes by increasing the number of perivascular adipocyte progenitor cells. Conversely, the absence of NAMPT signaling prevents this process. In conclusion, our findings shed light on the mechanisms governing the age-dependent impairment of beige adipocyte formation and underscore the E2-NAMPT controlled ER stress as a key regulator of this process.

Highlights

Estrogen restores beige adipocyte failure along with improved energy metabolism in old mice.Estrogen enhances the thermogenic gene program by mitigating age-induced ER stress.Estrogen enhances the beige adipogenesis derived from SMA+ APCs.Inhibiting the NAMPT signaling pathway abolishes estrogen-promoted beige adipogenesis.

Pegylated Liposomal Alendronate Biodistribution, Immune Modulation, and Tumor Growth Inhibition in a Murine Melanoma Model

While tumor-associated macrophages (TAM) have pro-tumoral activity, the ablation of macrophages in cancer may be undesirable since they also have anti-tumoral functions, including T cell priming and activation against tumor antigens. Alendronate is a potent amino-bisphosphonate that modulates the function of macrophages in vitro, with potential as an immunotherapy if its low systemic bioavailability can be addressed. We repurposed alendronate in a non-leaky and long-circulating liposomal carrier similar to that of the clinically approved pegylated liposomal doxorubicin to facilitate rapid clinical translation. Here, we tested liposomal alendronate (PLA) as an immunotherapeutic agent for cancer in comparison with a standard of care immunotherapy, a PD-1 immune checkpoint inhibitor. We showed that the PLA induced bone marrow-derived murine non-activated macrophages and M2-macrophages to polarize towards an M1-functionality, as evidenced by gene expression, cytokine secretion, and lipidomic profiles. Free alendronate had negligible effects, indicating that liposome encapsulation is necessary for the modulation of macrophage activity. In vivo, the PLA showed significant accumulation in tumor and tumor-draining lymph nodes, sites of tumor immunosuppression that are targets of immunotherapy. The PLA remodeled the tumor microenvironment towards a less immunosuppressive milieu, as indicated by a decrease in TAM and helper T cells, and inhibited the growth of established tumors in the B16-OVA melanoma model. The improved bioavailability and the beneficial effects of PLA on macrophages suggest its potential application as immunotherapy that could synergize with T-cell-targeted therapies and chemotherapies to induce immunogenic cell death. PLA warrants further clinical development, and these clinical trials should incorporate tumor and blood biomarkers or immunophenotyping studies to verify the anti-immunosuppressive effect of PLA in humans.

Convergent alteration of the mesenchymal stem cell heterogeneity in adipose tissue during aging

Adipose-derived stem cells (ASCs) from distinct age groups possess different characteristics; however, the age-associated changes in ASCs heterogenicity remain largely unknown. In this study, several publicly available single-cell RNA sequencing (RNA-seq) data cohorts of inguinal adipose tissues, including young (2 weeks), adult (8 weeks), and old (18 months) C57BL/6 mice, were analyzed. Transcriptomic clustering of integrated single-cell RNA-seq data from different age groups revealed the existence of five ASCs subtypes. Interestingly, ASCs showed a loss of heterogeneity with aging, and ASCs subtype 4 (ASC-4) was the dominant subpopulation accounting for more than 98% of aged ASCs converging to the terminal differentiation state. The multidirectional differentiation potentials of different ASCs subtypes were largely distinct while the adipogenic ability of ASC-4 increased with age persistently. Regulon analysis of ASC subtypes further identified Cebpb as the ASC-4-specific transcription factor, which was known as one of the major adipogenic regulators. Analysis of ligand-receptor pairs between ASCs and other cell types in adipose tissue identified age-associated upregulation of inflammatory responses-associated factors including CCL2 and CCL7. Treatment with 100 ng/mL CCL2 in vitro could significantly promote the adipogenesis of ASCs through enhanced phosphorylation of AKT and decreased expression of β-catenin. In addition, supplementation of 100 ng/mL CCL7 could significantly increase the expression of inflammatory genes and ASC-4-specific transcriptional factors in 2-week-old ASCs, potentially acting as a driver of ASCs convergence. Our findings help to delineate the complex biological processes of ASCs aging and shed light on better regenerative and therapeutic applications of ASCs.

Single-cell analysis of white adipose tissue reveals the tumor-promoting adipocyte subtypes

BACKGROUND

The tumor-adipose microenvironment (TAME) is characterized by the enrichment of adipocytes, and is considered a special ecosystem that supports cancer progression. However, the heterogeneity and diversity of adipocytes in TAME remains poorly understood.

METHODS

We conducted a single-cell RNA sequencing analysis of adipocytes in mouse and human white adipose tissue (WAT). We analyzed several adipocyte subtypes to evaluate their relationship and potential as prognostic factors for overall survival (OS). The potential drugs are screened by using bioinformatics methods. The tumor-promoting effects of a typical adipocyte subtype in breast cancer are validated by performing in vitro functional assays and immunohistochemistry (IHC) in clinical samples.

RESULTS

We profiled a comprehensive single-cell atlas of adipocyte in mouse and human WAT and described their characteristics, origins, development, functions and interactions with immune cells. Several cancer-associated adipocyte subtypes, namely DPP4+ adipocytes in visceral adipose and ADIPOQ+ adipocytes in subcutaneous adipose, are identified. We found that high levels of these subtypes are associated with unfavorable outcomes in four typical adipose-associated cancers. Some potential drugs including Trametinib, Selumetinib and Ulixertinib are discovered. Emphatically, knockdown of adiponectin receptor 1 (AdipoR1) and AdipoR2 impaired the proliferation and invasion of breast cancer cells. Patients with AdipoR2-high breast cancer display significantly shorter relapse-free survival (RFS) than those with AdipoR2-low breast cancer.

CONCLUSION

Our results provide a novel understanding of TAME at the single-cell level. Based on our findings, several adipocyte subtypes have negative impact on prognosis. These cancer-associated adipocytes may serve as key prognostic predictor and potential targets for treatment in the future.

Increasing adipocyte number and reducing adipocyte size: the role of retinoids in adipose tissue development and metabolism

The rising prevalence of obesity is a grave public health threat. In response to excessive energy intake, adipocyte hypertrophy impairs cellular function and leads to metabolic dysfunctions while de novo adipogenesis leads to healthy adipose tissue expansion. Through burning fatty acids and glucose, the thermogenic activity of brown/beige adipocytes can effectively reduce the size of adipocytes. Recent studies show that retinoids, especially retinoic acid (RA), promote adipose vascular development which in turn increases the number of adipose progenitors surrounding the vascular vessels. RA also promotes preadipocyte commitment. In addition, RA promotes white adipocyte browning and stimulates the thermogenic activity of brown/beige adipocytes. Thus, vitamin A is a promising anti-obesity micronutrient.

Circadian mechanisms in adipose tissue bioenergetics and plasticity

The circadian clock plays an essential role in coordinating feeding and metabolic rhythms with the light/dark cycle. Disruption of clocks is associated with increased adiposity and metabolic disorders, whereas aligning feeding time with cell-autonomous rhythms in metabolism improves health. Here, we provide a comprehensive overview of recent literature in adipose tissue biology as well as our understanding of molecular mechanisms underlying the circadian regulation of transcription, metabolism, and inflammation in adipose tissue. We highlight recent efforts to uncover the mechanistic links between clocks and adipocyte metabolism, as well as its application to dietary and behavioral interventions to improve health and mitigate obesity.

Plasticity of adipose tissues in response to fasting and refeeding declines with aging in mice

To explore the plasticity of adipose tissues, C57BL/6J mice at the age of 1 month, 3 months, and 15 months corresponding to adolescence, adulthood, and middle-aged transitional period, respectively, were fasted and refed subsequently at different times. Body adipose tissues ratio (BATR) was calculated, the morphology of adipose tissue and the area of adipocytes were observed by histological analysis, and the mitochondria in adipocytes were observed under the transmission electron microscope. Furthermore, the expression levels of Ucp-1, Cidea, Cox7a1, Cpt-1m, Atgl, and Hsl were detected by qRT-PCR. Our results showed a significant increase in the adipocytes area and body visceral adipose tissue (VAT) ratio in all groups of mice with aging. Moreover, body mesenteric white adipose tissue (mWAT) ratio decreased the most after 72 h fasting. In the middle-aged transitional mice, the white adipocytes did not decrease until 72 h fasting, and most of them still appeared as unaffected unilocular cells. Besides, the number of mitochondria and the expression of Ucp-1, Cidea, Cox7a1, Cpt-1m, Atgl and Hsl were lower in these mice. After 72h refeeding, the body subcutaneous white adipose tissue (sWAT) ratio returned to normal, while the VAT kept decreasing. The above results indicated an impairment in adipose tissue plasticity in mice with aging, suggesting that age modulated the metabolic adaptiveness of adipose tissues in mice.

The Transcriptomic Landscape of Age-Induced Changes in Human Visceral Fat and the Predicted Omentum-Liver Connectome in Males

Aging causes alterations in body composition. Specifically, visceral fat mass increases with age and is associated with age-related diseases. The pathogenic potential of visceral fat accumulation has been associated with its anatomical location and metabolic activity. Visceral fat may control systemic metabolism by secreting molecules that act in distal tissues, mainly the liver, through the portal vein. Currently, little is known about age-related changes in visceral fat in humans. Aiming to identify molecular and cellular changes occurring with aging in the visceral fat of humans, we analyzed publicly available transcriptomic data of 355 omentum samples from the Genotype-Tissue Expression portal (GTEx) of 20-79-year-old males and females. We identified the functional enrichment of genes associated with aging, inferred age-related changes in visceral fat cellularity by deconvolution analysis, profiled the senescence-associated secretory phenotype of visceral adipose tissue, and predicted the connectivity of the age-induced visceral fat secretome with the liver. We demonstrate that age induces alterations in visceral fat cellularity, synchronous to changes in metabolic pathways and a shift toward a pro-inflammatory secretory phenotype. Furthermore, our approach identified candidates such as ADIPOQ-ADIPOR1/ADIPOR2, FCN2-LPR1, and TF-TFR2 to mediate visceral fat-liver crosstalk in the context of aging. These findings cast light on how alterations in visceral fat with aging contribute to liver dysfunction and age-related disease etiology.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Targeting cancer metabolic vulnerabilities for advanced therapeutic efficacy

Cancer metabolism is how cancer cells utilize nutrients and energy to support their growth and proliferation. Unlike normal cells, cancer cells have a unique metabolic profile that allows them to generate energy and the building blocks they need for rapid growth and division. This metabolic profile is marked by an increased reliance on glucose and glutamine as energy sources and changes in how cancer cells use and make key metabolic intermediates like ATP, NADH, and NADPH. This script analyzes a comprehensive overview of the latest advances in tumor metabolism, identifying the key unresolved issues, elaborates on how tumor cells differ from normal cells in their metabolism of nutrients, and explains how tumor cells conflate growth signals and nutrients to proliferate. The metabolic interaction of tumorigenesis and lipid metabolism within the tumor microenvironment and the role of ROS as an anti-tumor agent by mediating various signaling pathways for clinical cancer therapeutic targeting are outlined. Cancer metabolism is highly dynamic and heterogeneous; thus, advanced technologies to better investigate metabolism at the unicellular level without altering tumor tissue are necessary for better research and clinical transformation. The study of cancer metabolism is an area of active research, as scientists seek to understand the underlying metabolic changes that drive cancer growth and to identify potential therapeutic targets.

Thermogenic adipose tissue in energy regulation and metabolic health

The ability to generate thermogenic fat could be a targeted therapy to thwart obesity and improve metabolic health. Brown and beige adipocytes are two types of thermogenic fat cells that regulate energy balance. Both adipocytes share common morphological, biochemical, and thermogenic properties. Yet, recent evidence suggests unique features exist between brown and beige adipocytes, such as their cellular origin and thermogenic regulatory processes. Beige adipocytes also appear highly plastic, responding to environmental stimuli and interconverting between beige and white adipocyte states. Additionally, beige adipocytes appear to be metabolically heterogenic and have substrate specificity. Nevertheless, obese and aged individuals cannot develop beige adipocytes in response to thermogenic fat-inducers, creating a key clinical hurdle to their therapeutic promise. Thus, elucidating the underlying developmental, molecular, and functional mechanisms that govern thermogenic fat cells will improve our understanding of systemic energy regulation and strive for new targeted therapies to generate thermogenic fat. This review will examine the recent advances in thermogenic fat biogenesis, molecular regulation, and the potential mechanisms for their failure.

Adipose tissue at single-cell resolution

Adipose tissue exhibits remarkable plasticity with capacity to change in size and cellular composition under physiological and pathophysiological conditions. The emergence of single-cell transcriptomics has rapidly transformed our understanding of the diverse array of cell types and cell states residing in adipose tissues and has provided insight into how transcriptional changes in individual cell types contribute to tissue plasticity. Here, we present a comprehensive overview of the cellular atlas of adipose tissues focusing on the biological insight gained from single-cell and single-nuclei transcriptomics of murine and human adipose tissues. We also offer our perspective on the exciting opportunities for mapping cellular transitions and crosstalk, which have been made possible by single-cell technologies.

Heterogeneity of white adipocytes in metabolic disease

PURPOSE OF REVIEW

This review aims to discuss the most recent evidence identifying the presence of distinct white adipocyte subpopulations in white adipose tissue (WAT) and how these may be altered with increasing adiposity and/or metabolic disease. We conceptualize how changes in adipocyte subpopulations may contribute to alterations in WAT function and the development of metabolic diseases such as type 2 diabetes mellitus (T2DM), nonalcoholic fatty liver disease (NAFLD) and cardiovascular disease (CVD).

RECENT FINDINGS

Studies utilizing novel analytical approaches support the existence of distinct white adipocyte subpopulations in both human and murine WAT. Adipocyte subtypes are potentially functionally distinct and may have different roles in WAT function and obesity-associated metabolic diseases.

SUMMARY

The exploration of white adipocyte heterogeneity using novel analytical technologies, has unveiled a new layer of complexity in the study of WAT biology. Interrogation of potential functional differences between adipocyte subpopulations and their role in the function of different WAT depots is now needed. Through understanding the mechanisms regulating white adipocyte subtype development and potential pathophysiological consequences of changes in the presence of adipocyte subpopulations, studies could provide novel therapeutic targets for the treatment of T2DM, NAFLD, and CVD.

Maternal obesity and programming of metabolic syndrome in the offspring: searching for mechanisms in the adipocyte progenitor pool

BACKGROUND

It is now understood that it is the quality rather than the absolute amount of adipose tissue that confers risk for obesity-associated disease. Adipose-derived stem cells give rise to adipocytes during the developmental establishment of adipose depots. In adult depots, a reservoir of progenitors serves to replace adipocytes that have reached their lifespan and for recruitment to increase lipid buffering capacity under conditions of positive energy balance. MAIN: The adipose tissue expandability hypothesis posits that a failure in de novo differentiation of adipocytes limits lipid storage capacity and leads to spillover of lipids into the circulation, precipitating the onset of obesity-associated disease. Since adipose progenitors are specified to their fate during late fetal life, perturbations in the intrauterine environment may influence the rapid expansion of adipose depots that occurs in childhood or progenitor function in established adult depots. Neonates born to mothers with obesity or diabetes during pregnancy tend to have excessive adiposity at birth and are at increased risk for childhood adiposity and cardiometabolic disease.

CONCLUSION

In this narrative review, we synthesize current knowledge in the fields of obesity and developmental biology together with literature from the field of the developmental origins of health and disease (DOHaD) to put forth the hypothesis that the intrauterine milieu of pregnancies complicated by maternal metabolic disease disturbs adipogenesis in the fetus, thereby accelerating the trajectory of adipose expansion in early postnatal life and predisposing to impaired adipose plasticity.

Adipose Tissue Remodeling in Pathophysiology

Rather than serving as a mere onlooker, adipose tissue is a complex endocrine organ and active participant in disease initiation and progression. Disruptions of biological processes operating within adipose can disturb healthy systemic physiology, the sequelae of which include metabolic disorders such as obesity and type 2 diabetes. A burgeoning interest in the field of adipose research has allowed for the elucidation of regulatory networks underlying both adipose tissue function and dysfunction. Despite this progress, few diseases are treated by targeting maladaptation in the adipose, an oft-overlooked organ. In this review, we elaborate on the distinct subtypes of adipocytes, their developmental origins and secretory roles, and the dynamic interplay at work within the tissue itself. Central to this discussion is the relationship between adipose and disease states, including obesity, cachexia, and infectious diseases, as we aim to leverage our wealth of knowledge for the development of novel and targeted therapeutics.

Mitochondrial Energy Metabolism in the Regulation of Thermogenic Brown Fats and Human Metabolic Diseases

Brown fats specialize in thermogenesis by increasing the utilization of circulating blood glucose and fatty acids. Emerging evidence suggests that brown adipose tissue (BAT) prevents the incidence of obesity-associated metabolic diseases and several types of cancers in humans. Mitochondrial energy metabolism in brown/beige adipocytes regulates both uncoupling protein 1 (UCP1)-dependent and -independent thermogenesis for cold adaptation and the utilization of excess nutrients and energy. Many studies on the quantification of human BAT indicate that mass and activity are inversely correlated with the body mass index (BMI) and visceral adiposity. Repression is caused by obesity-associated positive and negative factors that control adipocyte browning, de novo adipogenesis, mitochondrial energy metabolism, UCP1 expression and activity, and noradrenergic response. Systemic and local factors whose levels vary between lean and obese conditions include growth factors, inflammatory cytokines, neurotransmitters, and metal ions such as selenium and iron. Modulation of obesity-associated repression in human brown fats is a promising strategy to counteract obesity and related metabolic diseases through the activation of thermogenic capacity. In this review, we highlight recent advances in mitochondrial metabolism, thermogenic regulation of brown fats, and human metabolic diseases.

Ageing-associated small RNA cargo of extracellular vesicles

Previous work on murine models and humans demonstrated global as well as tissue-specific molecular ageing trajectories of RNAs. Extracellular vesicles (EVs) are membrane vesicles mediating the horizontal transfer of genetic information between different tissues. We sequenced small regulatory RNAs (sncRNAs) in two mouse plasma fractions at five time points across the lifespan from 2-18 months: (1) sncRNAs that are free-circulating (fc-RNA) and (2) sncRNAs bound outside or inside EVs (EV-RNA). Different sncRNA classes exhibit unique ageing patterns that vary between the fcRNA and EV-RNA fractions. While tRNAs showed the highest correlation with ageing in both fractions, rRNAs exhibited inverse correlation trajectories between the EV- and fc-fractions. For miRNAs, the EV-RNA fraction was exceptionally strongly associated with ageing, especially the miR-29 family in adipose tissues. Sequencing of sncRNAs and coding genes in fat tissue of an independent cohort of aged mice up to 27 months highlighted the pivotal role of miR-29a-3p and miR-29b-3p in ageing-related gene regulation that we validated in a third cohort by RT-qPCR.

FK506 binding protein 51: Its role in the adipose organ and beyond

There is a great body of evidence that the adipose organ plays a central role in the control not only of energy balance, but importantly, in the maintenance of metabolic homeostasis. Interest in the study of different aspects of its physiology grew in the last decades due to the pandemic of obesity and the consequences of metabolic syndrome. It was not until recently that the first evidence for the role of the high molecular weight immunophilin FK506 binding protein (FKBP) 51 in the process of adipocyte differentiation have been described. Since then, many new facets have been discovered of this stress-responsive FKBP51 as a central node for precise coordination of many cell functions, as shown for nuclear steroid receptors, autophagy, signaling pathways as Akt, p38 MAPK, and GSK3, as well as for insulin signaling and the control of glucose homeostasis. Thus, the aim of this review is to integrate and discuss the recent advances in the understanding of the many roles of FKBP51 in the adipose organ.

Dipeptidyl peptidase-4 cell surface expression marks an abundant adipose stem/progenitor cell population with high stemness in human white adipose tissue

The capacity of adipose stem/progenitor cells (ASCs) to undergo self-renewal and differentiation is crucial for adipose tissue homoeostasis, regeneration and expansion. However, the heterogeneous ASC populations of the adipose lineage constituting adipose tissue are not precisely known. In the present study, we demonstrate that cell surface expression of dipeptidyl peptidase-4 (DPP4)/cluster of differentiation 26 (CD26) subdivides the DLK1^-/CD34⁺/CD45^-/CD31^- ASC pool of human white adipose tissues (WATs) into two large populations. Ex vivo, DPP4⁺ ASCs possess higher self-renewal and proliferation capacity and lesser adipocyte differentiation potential than DDP4^- ASCs. The knock-down of DPP4 in ASC leads to significantly reduced proliferation and self-renewal capacity, while adipogenic differentiation is increased. Ectopic overexpression of DPP4 strongly inhibits adipogenesis. Moreover, in whole mount stainings of human subcutaneous (s)WAT, we detect DPP4 in CD34⁺ ASC located in the vascular stroma surrounding small blood vessels and in mature adipocytes. We conclude that DPP4 is a functional marker for an abundant ASC population in human WAT with high proliferation and self-renewal potential and low adipogenic differentiation capacity.

Adipose Tissue Plasticity in Aging

As a dynamic endocrine organ, white adipose tissue (WAT) stores lipids and plays a critical role in maintaining whole-body energy homeostasis and insulin sensitivity. A large group of the population over 65 years old suffer from increased WAT mass, especially in the visceral location. Visceral adiposity accelerates aging through promoting age-associated chronic conditions, significantly shortening life expectancy. Unlike WAT, brown adipose tissue (BAT) functions as an effective energy sink that burns and disposes of excess lipids and glucose upon activation of thermogenesis. Unfortunately, the thermogenic activity of BAT declines during aging. New appreciation of cellular and functional remodeling of WAT and BAT during aging has emerged in recent years. Efforts are underway to explore the potential underlying mechanisms behind these age-associated alterations in WAT and BAT and the impact of these alterations on whole-body metabolism. Lastly, it is intriguing to translate our knowledge obtained from animal models to the clinic to prevent and treat age-associated metabolic disorders. © 2022 American Physiological Society. Compr Physiol 12: 4119-4132, 2022.

Mammalian adipogenesis regulator (Areg) cells use retinoic acid signalling to be non- and anti-adipogenic in age-dependent manner

Adipose stem and precursor cells (ASPCs) give rise to adipocytes and determine the composition and plasticity of adipose tissue. Recently, several studies have demonstrated that ASPCs partition into at least three distinct cell subpopulations, including the enigmatic CD142⁺ cells. An outstanding challenge is to functionally characterise this population, as discrepant properties, from adipogenic to non- and anti-adipogenic, have been reported for these cells. To resolve these phenotypic ambiguities, we characterised mammalian subcutaneous CD142⁺ ASPCs across various experimental conditions, demonstrating that CD142⁺ ASPCs exhibit high molecular and phenotypic robustness. Specifically, we find these cells to be firmly non- and anti-adipogenic both in vitro and in vivo, with their inhibitory signals also impacting adipogenic human cells. However, these CD142⁺ ASPC-specific properties exhibit surprising temporal phenotypic alterations, and emerge only in an age-dependent manner. Finally, using multi-omic and functional assays, we show that the inhibitory nature of these adipogenesis-regulatory CD142⁺ ASPCs (Aregs) is driven by specifically expressed secretory factors that cooperate with the retinoic acid signalling pathway to transform the adipogenic state of CD142^- ASPCs into a non-adipogenic, Areg-like state.

Metabolic changes in aging humans: current evidence and therapeutic strategies

Aging and metabolism are inextricably linked, and many age-related changes in body composition, including increased central adiposity and sarcopenia, have underpinnings in fundamental aging processes. These age-related changes are further exacerbated by a sedentary lifestyle and can be in part prevented by maintenance of activity with aging. Here we explore the age-related changes seen in individual metabolic tissues - adipose, muscle, and liver - as well as globally in older adults. We also discuss the available evidence for therapeutic interventions such as caloric restriction, resistance training, and senolytic and senomorphic drugs to maintain healthy metabolism with aging, focusing on data from human studies.

Distinct functional properties of murine perinatal and adult adipose progenitor subpopulations

Adult white adipose tissue (WAT) harbors distinct mesenchymal stromal cell subpopulations that differentially affect WAT function and plasticity. Here we unveil the cellular landscape of the perinatal epididymal WAT primordium using single-cell transcriptomics in male mice. We reveal that adipocyte precursor cells and fibro-inflammatory progenitors (FIPs) emerge as functionally distinct PDGFRβ⁺ subpopulations within the epididymal WAT anlagen prior to adipocyte accrual. We further identify important molecular and functional differences between perinatal and adult FIPs, including differences in their pro-inflammatory response, adipogenic capacity and anti-adipogenic behavior. Notably, we find that transient overexpression of Pparg in PDGFRβ⁺ cells only during postnatal days 0.5 to 7.5 in male mice leads to hyperplastic WAT development, durable progenitor cell reprogramming, and protection against pathologic WAT remodeling and glucose intolerance in adult-onset obesity. Thus, factors that alter the adipogenic capacity of perinatal adipose progenitors can have long-lasting effects on progenitor plasticity, tissue expandability and metabolic health into adulthood.

Targeted erasure of DNA methylation by TET3 drives adipogenic reprogramming and differentiation

DNA methylation is a crucial epigenetic modification in the establishment of cell-type-specific characteristics. However, how DNA methylation is selectively reprogrammed at adipocyte-specific loci during adipogenesis remains unclear. Here, we show that the transcription factor, C/EBPδ, and the DNA methylation eraser, TET3, cooperatively control adipocyte differentiation. We perform whole-genome bisulfite sequencing to explore the dynamics and regulatory mechanisms of DNA methylation in adipocyte differentiation. During adipogenesis, DNA methylation selectively decreases at adipocyte-specific loci carrying the C/EBP binding motif, which correlates with the activity of adipogenic promoters and enhancers. Mechanistically, we find that C/EBPδ recruits a DNA methylation eraser, TET3, to catalyse DNA demethylation at the C/EBP binding motif and stimulate the expression of key adipogenic genes. Ectopic expression of TET3 potentiates in vitro and in vivo adipocyte differentiation and recovers downregulated adipogenic potential, which is observed in aged mice and humans. Taken together, our study highlights how targeted reprogramming of DNA methylation through cooperative action of the transcription factor C/EBPδ, and the DNA methylation eraser TET3, controls adipocyte differentiation.

New insight into dyslipidemia‐induced cellular senescence in atherosclerosis

Atherosclerosis, characterized by lipid‐rich plaques in the arterial wall, is an age‐related disorder and a leading cause of mortality worldwide. However, the specific mechanisms remain complex. Recently, emerging evidence has demonstrated that senescence of various types of cells, such as endothelial cells (ECs), vascular smooth muscle cells (VSMCs), macrophages, endothelial progenitor cells (EPCs), and adipose‐derived mesenchymal stem cells (AMSCs) contributes to atherosclerosis. Cellular senescence and atherosclerosis share various causative stimuli, in which dyslipidemia has attracted much attention. Dyslipidemia, mainly referred to elevated plasma levels of atherogenic lipids or lipoproteins, or functional impairment of anti‐atherogenic lipids or lipoproteins, plays a pivotal role both in cellular senescence and atherosclerosis. In this review, we summarize the current evidence for dyslipidemia‐induced cellular senescence during atherosclerosis, with a focus on low‐density lipoprotein (LDL) and its modifications, hydrolysate of triglyceride‐rich lipoproteins (TRLs), and high‐density lipoprotein (HDL), respectively. Furthermore, we describe the underlying mechanisms linking dyslipidemia‐induced cellular senescence and atherosclerosis. Finally, we discuss the senescence‐related therapeutic strategies for atherosclerosis, with special attention given to the anti‐atherosclerotic effects of promising geroprotectors as well as anti‐senescence effects of current lipid‐lowering drugs.

It Is Not Just Fat: Dissecting the Heterogeneity of Adipose Tissue Function

PURPOSE OF REVIEW

The purpose of the current review is to summarize findings from the most recent and impactful studies which investigated human and mouse adipose tissue transcriptomes at a single-cell level. We provide perspective about the potential importance of data derived from these single-cell technologies in improving our understanding of the adipose organ and metabolic disease and likely future directions of this approach.

RECENT FINDINGS

The majority of single-cell or single-nuclei studies of the adipose organ so far have focused on investigating the stromal-vascular fraction (SVF) of mouse subcutaneous and intraabdominal white and interscapular brown fat depots. Few studies have also evaluated the impact of additional factors as drivers of adipose phenotypes, such as high-fat diet-induced obesity, adolescence, aging, and cold exposure. Recent studies have also investigated human cell lines and human fat biopsies across a range of body mass index (BMI) and in response to insulin resistance or T2D. These studies have identified numerous previously unexplored subpopulations of adipocyte progenitors, immune cells, and mature adipocytes in both mice and men. Single-cell and single-nuclei technologies have brought an explosion of data that have advanced our understanding of the adipose organ in health and disease. However, we are still at the dawn of achieving a complete and comprehensive map of the mouse and human adipose organ. Multi-modal single-cell approaches to identify both anatomic localization of specific cellular populations and epigenetic mechanisms responsible for observed transcriptomic patterns are underway and will likely provide an even deeper understanding of the adipose organ in response to health and disease.

The composition, function, and regulation of adipose stem and progenitor cells

White adipose tissue (WAT) is a highly plastic organ that plays a central role in regulating whole-body energy metabolism. Adipose stem and progenitor cells (ASPCs) are essential components of the stromal vascular fraction (SVF) of adipose tissue. They give rise to mature adipocytes and play a critical role in maintaining adipose tissue function. However, the molecular heterogeneity and functional diversity of ASPCs are still poorly understood. Recently, single-cell RNA sequencing (scRNA-seq) analysis has identified distinct subtypes of ASPCs in murine and human adipose tissues, providing new insights into the cellular complexity of ASPCs among multiple fat depots. This review summarizes the current knowledge on ASPC populations, including their markers, functions, and regulatory mechanisms. Targeting one or several of these cell populations may ameliorate metabolic disorders by promoting adaptive hyperplastic adipose growth.

Adipose-tissue plasticity in health and disease

Adipose tissue, colloquially known as "fat," is an extraordinarily flexible and heterogeneous organ. While historically viewed as a passive site for energy storage, we now appreciate that adipose tissue regulates many aspects of whole-body physiology, including food intake, maintenance of energy levels, insulin sensitivity, body temperature, and immune responses. A crucial property of adipose tissue is its high degree of plasticity. Physiologic stimuli induce dramatic alterations in adipose-tissue metabolism, structure, and phenotype to meet the needs of the organism. Limitations to this plasticity cause diminished or aberrant responses to physiologic cues and drive the progression of cardiometabolic disease along with other pathological consequences of obesity.

Adipocyte-Specific Ablation of PU.1 Promotes Energy Expenditure and Ameliorates Metabolic Syndrome in Aging Mice

Objective: Although PU.1/Spi1 is known as a master regulator for macrophage development and function, we have reported previously that it is also expressed in adipocytes and is transcriptionally induced in obesity. Here, we investigated the role of adipocyte PU.1 in the development of the age-associated metabolic syndrome.

Methods: We generated mice with adipocyte-specific PU.1 knockout, assessed metabolic changes in young and older adult PU.1^fl/fl (control) and AdipoqCre PU.1^fl/fl (aPU.1KO) mice, including body weight, body composition, energy expenditure, and glucose homeostasis. We also performed transcriptional analyses using RNA-Sequencing of adipocytes from these mice.

Results: aPU.1KO mice have elevated energy expenditure at a young age and decreased adiposity and increased insulin sensitivity in later life. Corroborating these observations, transcriptional network analysis indicated the existence of validated, adipocyte PU.1-modulated regulatory hubs that direct inflammatory and thermogenic gene expression programs.

Conclusion: Our data provide evidence for a previously uncharacterized role of PU.1 in the development of age-associated obesity and insulin resistance.