Gender and age-related cell compositional differences in C57BL/6 murine adipose tissue stromal vascular fraction

Lesson on obesity and anatomy of adipose tissue: new models of study in the era of clinical and translational research

Obesity is a serious global illness that is frequently associated with metabolic syndrome. Adipocytes are the typical cells of adipose organ, which is composed of at least two different tissues, white and brown adipose tissue. They functionally cooperate, interconverting each other under physiological conditions, but differ in their anatomy, physiology, and endocrine functions. Different cellular models have been proposed to study adipose tissue in vitro. They are also useful for elucidating the mechanisms that are responsible for a pathological condition, such as obesity, and for testing therapeutic strategies. Each cell model has its own characteristics, culture conditions, advantages and disadvantages. The choice of one model rather than another depends on the specific study the researcher is conducting. In recent decades, three-dimensional cultures, such as adipose spheroids, have become very attractive because they more closely resemble the phenotype of freshly isolated cells. The use of such models has developed in parallel with the evolution of translational research, an interdisciplinary branch of the biomedical field, which aims to learn a scientific translational approach to improve human health and longevity. The focus of the present review is on the growing body of data linking the use of new cell models and the spread of translational research. Also, we discuss the possibility, for the future, to employ new three-dimensional adipose tissue cell models to promote the transition from benchside to bedsite and vice versa, allowing translational research to become routine, with the final goal of obtaining clinical benefits in the prevention and treatment of obesity and related disorders.

Gender-specific abdominal fat distribution and insulin resistance associated with organophosphate esters and phthalate metabolites exposure

The worldwide prevalence of obesity highlights the potential contribution of endocrine-disrupting chemicals (EDCs). However, common epidemiological measures such as body mass index and waist circumference may misrepresent the intricate obesity risks these chemicals pose across genders. This study delves deeper into abdominal fat by differentiating between subcutaneous and visceral regions by analyzing data from National Health and Nutrition Examination Surveys (NHANES). We particularly investigated the gender-specific associations between organophosphorus flame-retardant metabolites (mOPFRs), phthalates (mPAEs) and accumulated fat indexes from 2536 people. Aiding by Bayesian Kernel Machine Regression (BKMR), we found while co-exposure to mOPFRs and mPAEs was linked to general and abdominal obesity across the entire and gender-specific populations, a gender-specific fat distribution emerged. For women, urinary BDCPP and MBzP were linked to an increased subcutaneous fat index (SFI) [BDCPP OR: 1.12 (95% CI: 1.03-1.21), MBzP OR: 1.09 (95% CI: 1.01-1.18)], but not to visceral fat index (VFI). These metabolites had a combined linkage with SFI, with BDCPP (weighting 22.0%) and DPHP (weighting 31.0%) being the most influential in Quantile g-computation model (qgcomp) model. In men, BCEP exposure exclusively associated with the elevated VFI [OR: 1.14 (95% CI: 1.03-1.26)], a trend further highlighted in mixture models with BCEP as the predominant association. Intriguingly, only males displayed a marked correlation between these metabolites and insulin resistance in subpopulation. An attempted mediation analysis revealed that elevated C-reactive protein mediated 12.1% of the association between urinary BCEP and insulin resistance, suggesting a potential role of inflammation. In conclusion, the gender-specific fat distribution and insulin resistance that associated with mOPFRs represented the potential risk of these chemicals to man.

The potency of mesenchymal stem/stromal cells: does donor sex matter?

Mesenchymal stem/stromal cells (MSCs) are a promising therapeutic tool in cell therapy and tissue engineering because of their multi-lineage differentiation capacity, immunomodulatory effects, and tissue protective potential. To achieve optimal results as a therapeutic tool, factors affecting MSC potency, including but not limited to cell source, donor age, and cell batch, have been investigated. Although the sex of the donor has been attributed as a potential factor that can influence MSC potency and efficacy, the impact of donor sex on MSC characteristics has not been carefully investigated. In this review, we summarize published studies demonstrating donor-sex-related MSC heterogeneity and emphasize the importance of disclosing donor sex as a key factor affecting MSC potency in cell therapy.

Age-dependent genes in adipose stem and precursor cells affect regulation of fat cell differentiation and link aging to obesity via cellular and genetic interactions

BACKGROUND

Age and obesity are dominant risk factors for several common cardiometabolic disorders, and both are known to impair adipose tissue function. However, the underlying cellular and genetic factors linking aging and obesity on adipose tissue function have remained elusive. Adipose stem and precursor cells (ASPCs) are an understudied, yet crucial adipose cell type due to their deterministic adipocyte differentiation potential, which impacts the capacity to store fat in a metabolically healthy manner.

METHODS

We integrated subcutaneous adipose tissue (SAT) bulk (n=435) and large single-nucleus RNA sequencing (n=105) data with the UK Biobank (UKB) (n=391,701) data to study age-obesity interactions originating from ASPCs by performing cell-type decomposition, differential expression testing, cell-cell communication analyses, and construction of polygenic risk scores for body mass index (BMI).

RESULTS

We found that the SAT ASPC proportions significantly decrease with age in an obesity-dependent way consistently in two independent cohorts, both showing that the age dependency of ASPC proportions is abolished by obesity. We further identified 76 genes (72 SAT ASPC marker genes and 4 transcription factors regulating ASPC marker genes) that are differentially expressed by age in SAT and functionally enriched for developmental processes and adipocyte differentiation (i.e., adipogenesis). The 76 age-perturbed ASPC genes include multiple negative regulators of adipogenesis, such as RORA, SMAD3, TWIST2, and ZNF521, form tight clusters of longitudinally co-expressed genes during human adipogenesis, and show age-based differences in cellular interactions between ASPCs and adipose cell types. Finally, our genetic data demonstrate that cis-regional variants of these genes interact with age as predictors of BMI in an obesity-dependent way in the large UKB, while no such gene-age interaction on BMI is observed with non-age-dependent ASPC marker genes, thus independently confirming our cellular ASPC results at the biobank level.

CONCLUSIONS

Overall, we discover that obesity prematurely induces a decrease in ASPC proportions and identify 76 developmentally important ASPC genes that implicate altered negative regulation of fat cell differentiation as a mechanism for aging and directly link aging to obesity via significant cellular and genetic interactions.

Individual Variabilities in Adipose Stem Cell Proliferation, Gene Expression and Responses to Lipopolysaccharide Stimulation

Adipose stem cells (ASCs) are reported to play a role in normal physiology as well as in inflammation and disease. The objective of this work was to elucidate inter-individual differences in growth, gene expression and response to inflammatory stimuli in ASCs from different donors. Human ASC1 (male donor) and ASC2 (female donor) were purchased from Lonza (Walkersville, MD). Cell proliferation was determined by the sulforhodamine B assay. After time-dependent treatment of ASCs with or without bacterial lipopolysaccharide (LPS), marker gene mRNAs for proliferation, steroid hormones, and xenobiotic and immune pathways were determined using RT-PCR, and secreted cytokine levels in media were measured using the Bio-Plex cytokine assay kit. ASCs from both donors expressed androgen receptors but not estrogen receptors. ASC2 had a 2-fold higher proliferation rate and a 6-fold higher level of proliferation marker Ki67 mRNA than ASC1. ASC2 exhibited significantly greater fold induction of TNF-α and CCL2 by LPS compared to ASC1. TNF-α and GM-CSF protein levels were also significantly higher in the LPS-induced ASC2 media, but IL-6 secretion was higher in the LPS-induced ASC1 media. Our findings suggest that inter-individual variability and/or possible sex differences exist in ASCs, which may serve as a key determinant to inflammatory responses of ASCs.

Adipose-Derived Stromal/Stem Cell Response to Tumors and Wounds: Evaluation of Patient Age

Tumors were characterized as nonhealing wounds by Virchow in 1858 and Dvorak in 1986. Since then, researchers have analyzed tumors from a new perspective. The parallels between tumorigenesis and physiological wound healing can provide a new framework for developing antitumor therapeutics. One commonality between tumors and wounds is the involvement of the stromal environment, particularly adipose stromal/stem cells (ASCs). ASCs exhibit dual functions, in which they stimulate tumor progression and assist in tissue repair and regeneration. Numerous studies have focused on the role of ASCs in cancer and wound healing, but none to date has linked age, cancer, and wound healing. Furthermore, very few studies have focused on the role of donor-specific characteristics of ASCs, such as age and their role in facilitating ASC behavior in cancer and wound healing. This review article is designed to provide important insights into the impact of donor age on ASC tumor and wound response and their role in facilitating ASC behavior in cancer and wound healing.

Sex-Dependent Role of Adipose Tissue HDAC9 in Diet-Induced Obesity and Metabolic Dysfunction

Obesity is a major risk factor for both metabolic and cardiovascular disease. We reported that, in obese male mice, histone deacetylase 9 (HDAC9) is upregulated in adipose tissues, and global deletion of HDAC9 protected against high fat diet (HFD)-induced obesity and metabolic disease. Here, we investigated the impact of adipocyte-specific HDAC9 gene deletion on diet-induced obesity in male and female mice. The HDAC9 gene expression was increased in adipose tissues of obese male and female mice and HDAC9 expression correlated positively with body mass index in humans. Interestingly, female, but not male, adipocyte-specific HDAC9 KO mice on HFD exhibited reduced body weight and visceral adipose tissue mass, adipocyte hypertrophy, and improved insulin sensitivity, glucose tolerance and adipogenic differentiation gene expression. Furthermore, adipocyte-specific HDAC9 gene deletion in female mice improved metabolic health as assessed by whole body energy expenditure, oxygen consumption, and adaptive thermogenesis. Mechanistically, compared to female mice, HFD-fed male mice exhibited preferential HDAC9 expression in the stromovascular fraction, which may have offset the impact of adipocyte-specific HDAC9 gene deletion in male mice. These results suggest that HDAC9 expressed in adipocytes is detrimental to obesity in female mice and provides novel evidence of sex-related differences in HDAC9 cellular expression and contribution to obesity-related metabolic disease.

State of the field: cellular and exosomal therapeutic approaches in vascular regeneration

Pathologies of the vasculature including the microvasculature are often complex in nature, leading to loss of physiological homeostatic regulation of patency and adequate perfusion to match tissue metabolic demands. Microvascular dysfunction is a key underlying element in the majority of pathologies of failing organs and tissues. Contributing pathological factors to this dysfunction include oxidative stress, mitochondrial dysfunction, endoplasmic reticular (ER) stress, endothelial dysfunction, loss of angiogenic potential and vascular density, and greater senescence and apoptosis. In many clinical settings, current pharmacologic strategies use a single or narrow targeted approach to address symptoms of pathology rather than a comprehensive and multifaceted approach to address their root cause. To address this, efforts have been heavily focused on cellular therapies and cell-free therapies (e.g., exosomes) that can tackle the multifaceted etiology of vascular and microvascular dysfunction. In this review, we discuss 1) the state of the field in terms of common therapeutic cell population isolation techniques, their unique characteristics, and their advantages and disadvantages, 2) common molecular mechanisms of cell therapies to restore vascularization and/or vascular function, 3) arguments for and against allogeneic versus autologous applications of cell therapies, 4) emerging strategies to optimize and enhance cell therapies through priming and preconditioning, and, finally, 5) emerging strategies to bolster therapeutic effect. Relevant and recent clinical and animal studies using cellular therapies to restore vascular function or pathologic tissue health by way of improved vascularization are highlighted throughout these sections.

RNA-seq analysis of phagocytic cells from murine epididymal white adipose tissue shows immunosenescence and age-related phosphorus metabolism

The underlying state of alterations in adipose tissue is hypothesized to be as a result of age-related changes. Young and aged mice have been documented to show distinct gene expression and distinct macrophage-specific adipose tissue regulation. However, more biological understanding is required to know the processes associated with these conditions in relation to the aging process. Transcriptional profiling with RNA-seq analysis was used to determine differentially expressed genes in young (2 months old) and aged (20 months old) mice macrophage-enriched phagocytic stromal vascular fractions of pooled epididymal white adipose tissue using data obtained from gene expression omnibus. Results showed distinct differentially expressed genes in young and aged mice with a p value cutoff of 0.05 and dissimilarities in the young and aged epididymal white adipose tissue phagocytic cells. Functional enrichment showed activation of cytokine-cytokine receptor interaction pathways, phosphorus metabolic processes and inflammatory pathways such as IL-17, TNF, NF-kappa B, and TGF-β, while AMPK, PPAR and oxidative phosphorylation were suppressed. The analysis showed that aging is linked with phagocytic cell decline, accumulated cellular damages, inflammation, immunosenescence and increased phosphorus metabolism. Interventions that reduce phosphate-containing compound could improve phosphorus metabolism in old age to prolong lifespan and better health.

Ellagic acid induces beige remodeling of white adipose tissue by controlling mitochondrial dynamics and SIRT3

To determine whether ellagic acid (EA) induces the "beige remodeling" of white adipose tissue (WAT), we treated cold-exposed mice and mouse stromal vascular fraction (SVF) cells with EA, a phytochemical abundant in fruits and vegetables, in particular berries. We then investigated the mechanism of EA in beige remodeling with a particular focus on DRP1-mediated mitochondrial fission and SIRT3. EA induced the trans-differentiation of white adipocytes to beige adipocytes by promoting the expression of UCP1 and other brown and beige adipocytes/fat factors (PRDM16, UCP1, PGC1α, CD137, and TBX1) and mitochondrial dynamics-related factors (SIRT3, NRF1, CPT1β, DRP1, and FIS1) in 3T3-L1/SVF cells, and these were confirmed in the inguinal WAT of a cold-exposed mouse model. The browning effect of EA was abolished by a potent DRP1 inhibitor Mdivi-1 or SIRT3 knockdown, suggesting that EA induces beige remodeling of WAT by regulating the mitochondrial dynamics and SIRT3.

Human Adipose-Derived Stromal/Stem Cell Culture and Analysis Methods for Adipose Tissue Modeling In Vitro: A Systematic Review

Human adipose-derived stromal/stem cells (hASC) are widely used for in vitro modeling of physiologically relevant human adipose tissue. These models are useful for the development of tissue constructs for soft tissue regeneration and 3-dimensional (3D) microphysiological systems (MPS) for drug discovery. In this systematic review, we report on the current state of hASC culture and assessment methods for adipose tissue engineering using 3D MPS. Our search efforts resulted in the identification of 184 independent records, of which 27 were determined to be most relevant to the goals of the present review. Our results demonstrate a lack of consensus on methods for hASC culture and assessment for the production of physiologically relevant in vitro models of human adipose tissue. Few studies have assessed the impact of different 3D culture conditions on hASC adipogenesis. Additionally, there has been a limited use of assays for characterizing the functionality of adipose tissue in vitro. Results from this study suggest the need for more standardized culture methods and further analysis on in vitro tissue functionality. These will be necessary to validate the utility of 3D MPS as an in vitro model to reduce, refine, and replace in vivo experiments in the drug discovery regulatory process.

Adipose-Derived Mesenchymal Stromal Cells in Regenerative Medicine: State of Play, Current Clinical Trials, and Future Prospects

Significance: Wound healing is a complex process involving pain and inflammation, where innervation plays a central role. Managing wound healing and pain remains an important issue, especially in pathologies such as excessive scarring (often leading to fibrosis) or deficient healing, leading to chronic wounds. Recent Advances: Advances in therapies using mesenchymal stromal cells offer new insights for treating indications that previously lacked options. Adipose-derived mesenchymal stromal cells (AD-MSCs) are now being used to a much greater extent in clinical trials for regenerative medicine. However, to be really valid, these randomized trials must imperatively follow strict guidelines such as consolidated standards of reporting trials (CONSORT) statement. Indeed, AD-MSCs, because of their paracrine activities and multipotency, have potential to cure degenerative and/or inflammatory diseases. Combined with their relatively easy access (from adipose tissue) and proliferation capacity, AD-MSCs represent an excellent candidate for allogeneic treatments. Critical Issues: The success of AD-MSC therapy may depend on the robustness of the biological functions of AD-MSCs, which requires controlling source heterogeneity and production processes, and development of biomarkers that predict desired responses. Several studies have investigated the effect of AD-MSCs on innervation, wound repair, or pain management separately, but systematic evaluation of how those effects could be combined is lacking. Future Directions: Future studies that explore how AD-MSC therapy can be used to treat difficult-to-heal wounds, underlining the need to thoroughly characterize the cells used, and standardization of preparation processes are needed. Finally, how this a priori easy-to-use cell therapy treatment fits into clinical management of pain, improvement of tissue healing, and patient quality of life, all need to be explored.

Age-associated telomere attrition in adipocyte progenitors predisposes to metabolic disease

White and beige adipocytes in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) are maintained by proliferation and differentiation of adipose progenitor cells (APCs). Here we use mice with tissue-specific telomerase reverse transcriptase (TERT) gene knockout (KO), which undergo premature telomere shortening and proliferative senescence in APCs, to investigate the effect of over-nutrition on APC exhaustion and metabolic dysfunction. We find that TERT KO in the Pdgfra⁺ cell lineage results in adipocyte hypertrophy, inflammation and fibrosis in SAT, while TERT KO in the Pdgfrb⁺ lineage leads to adipocyte hypertrophy in both SAT and VAT. Systemic insulin resistance is observed in both KO models and is aggravated by a high-fat diet. Analysis of human biopsies demonstrates that telomere shortening in SAT is associated with metabolic disease progression after bariatric surgery. Our data indicate that over-nutrition can promote APC senescence and provide a mechanistic link between ageing, obesity and diabetes.

Impact of Aging on the Characterization of Brown and White Adipose Tissue-Derived Stem Cells in Mice

Adipose tissue enriched with adipose tissue-derived stem cells (ASCs) is often used for stem cell-based therapies. However, the characteristics of ASCs from different types of adipose tissue have varying biochemical and functional properties. We aimed to investigate how age affected the biological and functional characteristics of ASCs from brown (BAT) and white adipose tissue (WAT). ASCs were obtained and cultured from mouse BAT and WAT at different ages: young (2 months of age) and older mice (22 months of age). Mesenchymal markers were characterized by flow cytometry, and cell proliferation, apoptosis, differentiation potential, senescence, and metabolism were then determined. The percentage of WAT was higher in elderly mice, and the percentage of BAT was higher in young mice. All ASC sample phenotypes were characterized as CD29+/CD44+/CD105+/CD45-; the proliferation rate was not statistically different among all age groups. However, the number of senescent cells and the percentage of apoptosis in elderly mouse ASCs were significantly increased, and the ability of osteogenic and lipogenic differentiation was decreased in these same animals. In addition, ASCs from young mice were more inclined to undergo osteogenic differentiation, especially BAT-ASCs, whose gene expression of fat-consuming components was also significantly higher than of WAT-ASCs. The results indicated that ASCs derived from both WAT and BAT possessed different characteristics of fat metabolism and cell differentiation relative to the osteo- and adipolineages. In particular, because BAT-ASCs from young mice contributed to fat consumption, if used for cell grafting, they may potentially be attractive vehicles for treating obesity.

Signature quality attributes of CD146+ mesenchymal stem/stromal cells correlate with high therapeutic and secretory potency

CD146⁺ bone marrow-derived mesenchymal stem/stromal cells (BM-MSCs) play key roles in the perivascular niche, skeletogenesis, and hematopoietic support; however, comprehensive evaluation of therapeutic potency has yet to be determined. In this study, in vitro inflammatory priming to crude human BM-MSCs (n = 8) captured a baseline of signature responses, including enriched CD146⁺ with coexpression of CD107a^High , CXCR4^High , and LepR^High , transcriptional profile, enhanced secretory capacity, and robust immunomodulatory secretome and function, including immunopotency assays (IPAs) with stimulated immune cells. These signatures were significantly more pronounced in CD146⁺ (POS)-sorted subpopulation than in the CD146^- (NEG). Mechanistically, POS BM-MSCs showed a markedly higher secretory capacity with significantly greater immunomodulatory and anti-inflammatory protein production upon inflammatory priming compared with the NEG BM-MSCs. Moreover, IPAs with stimulated peripheral blood mononuclear cells and T lymphocytes demonstrated robust immunosuppression mediated by POS BM-MSC while inducing significant frequencies of regulatory T cells. in vivo evidence showed that POS BM-MSC treatment promoted pronounced M1-to-M2 macrophage polarization, ameliorating inflammation/fibrosis of knee synovium and fat pad, unlike treatment with NEG BM-MSCs. These data correlate the expression of CD146 with innately higher immunomodulatory and secretory capacity, and thus therapeutic potency. This high-content, reproducible evidence suggests that the CD146⁺ (POS) MSC subpopulation are the mediators of the beneficial effects achieved using crude BM-MSCs, leading to translational implications for improving cell therapy and manufacturing.

Bioactive borate glass triggers phenotypic changes in adipose stem cells

A bioactive borate glass, 13-93B3 (B3), has been used successfully in the clinic to treat chronic, nonhealing wounds without scarring. However, the mechanism by which B3 stimulates wound healing is poorly understood. Because adipose stem cells (ASCs) have been shown to have multiple roles in wound repair, we hypothesized that B3 triggers ASCs. In this study, we evaluate the effects of B3 on ASC survival, migration, differentiation, and protein secretion in vitro. In concentrations ≤10 mg/ml, B3 did not affect ASC viability under static conditions. B3 promoted the migration of ASCs but did not increase differentiation into bone or fat. B3 also decreased ASCs secretion of collagen I, PAI-1, MCP-1, DR6, DKK-1, angiogenin, IL-1, IGFBP-6, VEGF, and TIMP-2; increased expression of IL-1R and E-selectin; had a transient decrease in IL-6 secretion; and had a transient increase in bFGF secretion. Together, these results show that B3 alters the protein secretion of ASCs.