From heterogeneity to plasticity in adipose tissues: site-specific differences

In mammals, two types of adipose tissues are present, brown (BAT) and white (WAT). WAT itself can be divided into subcutaneous and internal fat deposits. All these tissues have been shown to present a great tissue plasticity, and recent data emphasized on the multiple differentiation potentials obtained from subcutaneous WAT. However, no study has compared the heterogeneity of stroma-vascular fraction (SVF) cells and their differentiation potentials according to the localization of the fat pad. This study clearly demonstrates that WAT and BAT present different antigenic features and differentiation potentials. WAT by contrast to BAT contains a large population of hematopoietic cells composed essentially of macrophages and hematopoietic progenitor cells. In WAT, the non-hematopoietic population is mainly composed of mesenchymal stem cell (MSC)-like but contains also a significant proportion of immature cells, whereas in BAT, the stromal cells do not present the same phenotype. Internal and subcutaneous WAT present some discrete differences in the phenotype of their cell populations. WAT derived SVF cells give rise to osteoblasts, endothelial cells, adipocytes, hematopoietic cells, and cardiomyoblasts only from inguinal cells. By contrast, BAT derived SVF cells display a reduced plasticity. Adipose tissues thus appear as complex tissues composed of different cell subsets according to the location of fat pads. Inguinal WAT appears as the most plastic adipose tissue and represents a potential and suitable source of stem cell, considering its easy sampling as a major advantage for cell therapy.     

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.     

The stromal‐vascular fraction of adipose tissue contributes to major differences between subcutaneous and visceral fat depots

Adipose tissue represents a complex tissue both in terms of its cellular composition, as it includes mature adipocytes and the various cell types comprising the stromal‐vascular fraction (SVF), and in relation to the distinct biochemical, morphological and functional characteristics according to its anatomical location. Herein, we have characterized the proteomic profile of both mature adipocyte and SVF from human visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) fat depots in order to unveil differences in the expression of proteins which may underlie the distinct association of VAT and SAT to several pathologies. Specifically, 24 proteins were observed to be differentially expressed between SAT SVF versus VAT SVF from lean individuals. Immunoblotting and RT‐PCR analysis confirmed the differential regulation of the nuclear envelope proteins lamin A/C, the membrane‐cytoskeletal linker ezrin and the enzyme involved in retinoic acid production, aldehyde dehydrogenase 1A2, in the two fat depots. In sum, the observation that proteins with important cell functions are differentially distributed between VAT and SAT and their characterization as components of SVF or mature adipocytes pave the way for future research on the molecular basis underlying diverse adipose tissue‐related pathologies such as metabolic syndrome or lipodystrophy.     

Proteome of human subcutaneous adipose tissue stromal vascular fraction cells versus mature adipocytes based on DIGE

Adipose tissue contains a heterogeneous population of mature adipocytes, endothelial cells, immune cells, pericytes, and preadipocytic stromal/stem cells. To date, a majority of proteomic analyses have focused on intact adipose tissue or isolated adipose stromal/stem cells in vitro. In this study, human subcutaneous adipose tissue from multiple depots (arm and abdomen) obtained from female donors was separated into populations of stromal vascular fraction cells and mature adipocytes. Out of 960 features detected by 2-D gel electrophoresis, a total of 200 features displayed a 2-fold up- or down-regulation relative to each cell population. The protein identity of 136 features was determined. Immunoblot analyses comparing SVF relative to adipocytes confirmed that carbonic anhydrase II was up-regulated in both adipose depots while catalase was up-regulated in the arm only. Bioinformatic analyses of the data set determined that cytoskeletal, glycogenic, glycolytic, lipid metabolic, and oxidative stress related pathways were highly represented as differentially regulated between the mature adipocytes and stromal vascular fraction cells. These findings extend previous reports in the literature with respect to the adipose tissue proteome and the consequences of adipogenesis. The proteins identified may have value as biomarkers for monitoring the physiology and pathology of cell populations within subcutaneous adipose depots.     

A familiar stranger:CD34 expression and putative functions in SVF cells of adipose tissue

Human adipose tissue obtained by liposuction is easily accessible and an abundant potential source of autologous cells for regenerative medicine applications. After digestion of the tissue and removal of differentiated adipocytes, the so-called stromal vascular fraction (SVF) of adipose, a mix of various cell types, is obtained. SVF contains mesenchymal fibroblastic cells, able to adhere to culture plastic and to generate large colonies in vitro , that closely resemble bone marrow-derived colony forming units-fibroblastic, and whose expanded progeny, adipose mesenchymal stem/stromal cells (ASC), show strong similarities with bone marrow mesenchymal stem cells. The sialomucin CD34, which is well known as a hematopoietic stem cell marker, is also expressed by ASC in native adipose tissue but its expression is gradually lost upon standard ASC expansion in vitro . Surprisingly little is known about the functional role of CD34 in the biology and tissue forming capacity of SVF cells and ASC. The present editorial provides a short introduction to the CD34 family of sialomucins and reviews the data from the literature concerning ex- pression and function of these proteins in SVF cells and their in vitro expanded progeny.     

Stromal stem cells from adipose tissue and bone marrow of age‐matched female donors display distinct immunophenotypic profiles

Adipose tissue is composed of lipid‐filled mature adipocytes and a heterogeneous stromal vascular fraction (SVF) population of cells. Similarly, the bone marrow (BM) is composed of multiple cell types including adipocytes, hematopoietic, osteoprogenitor, and stromal cells necessary to support hematopoiesis. Both adipose and BM contain a population of mesenchymal stromal/stem cells with the potential to differentiate into multiple lineages, including adipogenic, chondrogenic, and osteogenic cells, depending on the culture conditions. In this study we have shown that human adipose‐derived stem cells (ASCs) and bone marrow mesenchymal stem cells (BMSCs) populations display a common expression profile for many surface antigens, including CD29, CD49c, CD147, CD166, and HLA‐abc. Nevertheless, significant differences were noted in the expression of CD34 and its related protein, PODXL, CD36, CD 49f, CD106, and CD146. Furthermore, ASCs displayed more pronounced adipogenic differentiation capability relative to BMSC based on Oil Red staining (7‐fold vs. 2.85‐fold induction). In contrast, no difference between the stem cell types was detected for osteogenic differentiation based on Alizarin Red staining. Analysis by RT‐PCR demonstrated that both the ASC and BMSC differentiated adipocytes and osteoblast displayed a significant upregulation of lineage‐specific mRNAs relative to the undifferentiated cell populations; no significant differences in fold mRNA induction was noted between ASCs and BMSCs. In conclusion, these results demonstrate human ASCs and BMSCs display distinct immunophenotypes based on surface positivity and expression intensity as well as differences in adipogenic differentiation. The findings support the use of both human ASCs and BMSCs for clinical regenerative medicine. J. Cell. Physiol. 226: 843–851, 2011. © 2010 Wiley‐Liss, Inc.     

Adipocyte lineages: Tracing back the origins of fat

The obesity epidemic has intensified efforts to understand the mechanisms controlling adipose tissue development. Adipose tissue is generally classified as white adipose tissue (WAT), the major energy storing tissue, or brown adipose tissue (BAT), which mediates non-shivering thermogenesis. It is hypothesized that brite adipocytes (brown in white) may represent a third adipocyte class. The recent realization that brown fat exist in adult humans suggests increasing brown fat energy expenditure could be a therapeutic strategy to combat obesity. To understand adipose tissue development, several groups are tracing the origins of mature adipocytes back to their adult precursor and embryonic ancestors. From these studies emerged a model that brown adipocytes originate from a precursor shared with skeletal muscle that expresses Myf5-Cre, while all white adipocytes originate from a Myf5-negative precursors. While this provided a rational explanation to why BAT is more metabolically favorable than WAT, recent work indicates the situation is more complex because subsets of white adipocytes also arise from Myf5-Cre expressing precursors. Lineage tracing studies further suggest that the vasculature may provide a niche supporting both brown and white adipocyte progenitors; however, the identity of the adipocyte progenitor cell is under debate. Differences in origin between adipocytes could explain metabolic heterogeneity between depots and/or influence body fat patterning particularly in lipodystrophy disorders. Here, we discuss recent insights into adipose tissue origins highlighting lineage-tracing studies in mice, how variations in metabolism or signaling between lineages could affect body fat distribution, and the questions that remain unresolved. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.     

PEX13 is required for thermogenesis of white adipose tissue in cold-exposed mice

Non-shivering thermogenesis (NST) is a heat generating process controlled by the mitochondria of brown adipose tissue (BAT). In the recent decade, ‘functionally’ acting brown adipocytes in white adipose tissue (WAT) has been identified as well: the so-called process of the ‘browning’ of WAT. While the importance of uncoupling protein 1 (UCP1)-oriented mitochondrial activation has been intensely studied, the role of peroxisomes during the browning of white adipocytes is poorly understood. Here, we assess the change in peroxisomal membrane proteins, or peroxins (PEXs), during cold stimulation and importantly, the role of PEX13 in the cold-induced remodeling of white adipocytes. PEX13, a protein that originally functions as a docking factor and is involved in protein import into peroxisome matrix, was highly increased during cold-induced recruitment of beige adipocytes within the inguinal WAT of C57BL/6 mice. Moreover, beige-induced 3 T3-L1 adipocytes and stromal vascular fraction (SVF) cells by exposure to the peroxisome proliferator-activated receptor gamma (PPARγ) agonist rosiglitazone showed a significant increase in mitochondrial thermogenic factors along with peroxisomal proteins including PEX13, and these were confirmed in SVF cells with the beta 3 adrenergic receptor (β3AR)-selective agonist CL316,243. To verify the relevance of PEX13, we used the RNA silencing method targeting the Pex13 gene and evaluated the subsequent beige development in SVF cells. Interestingly, siPex13 treatment suppressed expression of thermogenic proteins such as UCP1 and PPARγ coactivator 1 alpha (PGC1α). Overall, our data provide evidence supporting the role of peroxisomal proteins, in particular PEX13, during beige remodeling of white adipocytes.     

Adipose Tissue Is a Neglected Viral Reservoir and an Inflammatory Site during Chronic HIV and SIV Infection

Two of the crucial aspects of human immunodeficiency virus (HIV) infection are (i) viral persistence in reservoirs (precluding viral eradication) and (ii) chronic inflammation (directly associated with all-cause morbidities in antiretroviral therapy (ART)-controlled HIV-infected patients). The objective of the present study was to assess the potential involvement of adipose tissue in these two aspects. Adipose tissue is composed of adipocytes and the stromal vascular fraction (SVF); the latter comprises immune cells such as CD4⁺ T cells and macrophages (both of which are important target cells for HIV). The inflammatory potential of adipose tissue has been extensively described in the context of obesity. During HIV infection, the inflammatory profile of adipose tissue has been revealed by the occurrence of lipodystrophies (primarily related to ART). Data on the impact of HIV on the SVF (especially in individuals not receiving ART) are scarce. We first analyzed the impact of simian immunodeficiency virus (SIV) infection on abdominal subcutaneous and visceral adipose tissues in SIVmac251 infected macaques and found that both adipocytes and adipose tissue immune cells were affected. The adipocyte density was elevated, and adipose tissue immune cells presented enhanced immune activation and/or inflammatory profiles. We detected cell-associated SIV DNA and RNA in the SVF and in sorted CD4⁺ T cells and macrophages from adipose tissue. We demonstrated that SVF cells (including CD4⁺ T cells) are infected in ART-controlled HIV-infected patients. Importantly, the production of HIV RNA was detected by in situ hybridization, and after the in vitro reactivation of sorted CD4⁺ T cells from adipose tissue. We thus identified adipose tissue as a crucial cofactor in both viral persistence and chronic immune activation/inflammation during HIV infection. These observations open up new therapeutic strategies for limiting the size of the viral reservoir and decreasing low-grade chronic inflammation via the modulation of adipose tissue-related pathways.     

Ethacrynic acid targets GSTM1 to ameliorate obesity by promoting browning of white adipocytes

Dear Editor, Obesity is caused by an imbalance between energy intake and expenditure,and has become a global epidemic with over 650 million adults affected.Adipose tissues in mam-mals are composed of white adipose tissue (WAT) and classical brown adipose tissue (BAT),and their balance is highly related to the occurrence of obesity.The browning of white adipocytes results in "beige" or "brite" adipocytes,which appear functionally similar to classical brown adipo-cytes,and can be detected in WAT deposits of animals that have been exposed to cold or other inducers (Fu et al.,2015).     

Age influence on stromal vascular fraction cell yield obtained from human lipoaspirates

Background aimsThe adipose stromal vascular fraction (SVF) is a heterogeneous population of mononuclear cells that includes approximately 1–10% mesenchymal stromal cells. These SVF cells can be freshly obtained from human lipo-aspirates and represent and ideal candidate for regenerative medicine applications. In the present study, we analyzed the SVF yield as a function of the patient's age.MethodsAdipose tissue samples from 52 informed subjects (all women) were processed by means of an innovative point-of-care technology for SVF isolation (GID platform). After enzymatic dissociation of adipose tissue and SVF pellet resuspension, we measured the concentration of mononucleated cells as well as other cell quality analyses on the cell suspension obtained. We then calculated the cell yield as total nucleated cells per milliliter of dry adipose processed.ResultsThe mean SVF yield obtained was 7.19 × 10⁵ ± 2.11 × 10⁵ total nucleated cells per milliliter of adipose tissue. Our results show that there is a clear statistically significant decline in SVF cell yield with increasing age.ConclusionsBecause all samples were obtained from the same donor area and the isolation technique used was the same in all cases, we conclude that the SVF cell yield in women is affected by patient age. Specific age-related factors should be analyzed in the future to explain these results.     

Reconstitution of lethally irradiated mice by cells isolated from adipose tissue

It is suggested that hematopoietic stem cells (HSC) could be found in several tissues of mesodermic origin. Among these, adipose tissue can expand throughout adult life and its expansion is not only due to mature adipocyte hypertrophy but also to the presence of precursor cells in stroma-vascular fraction (SVF). Here we report that transplantation of cells isolated from mice adipose tissue can efficiently rescue lethally irradiated mice and results in a reconstitution of major hematopoietic lineages. Donor cells can be detected in blood and in hematopoietic tissues of recipient mice. Adipose tissue contains a significant percentage of CD34, CD45 positive cells, and SVF cells were able to give rise to hematopoietic colonies in methylcellulose. We demonstrate the presence of hematopoietic progenitors in adipose tissue by phenotypic and functional characteristics. Thus adipose tissue could be considered as an important and convenient source of cells able to support hematopoiesis.     

基质血管组分(SVF)临床分离技术研究

脂肪组织易获取、组织相容性好且对供体影响小,可作为获得成体干细胞的重要来源.基质血管组分(SVF)是从脂肪中分离出来的包括脂源性干细胞(ADSC)和基质细胞的异质性细胞群.SVF促进组织的修复和再生已被大量的临床实验所证实,尤其是在美容整形和组织修复中的应用.早期,SVF通过酶消化法获得,随着近年来在临床中扩大应用,为...     

Expression and distribution of acyl-CoA thioesterases in the white adipose tissue of rats

Acyl-CoA thioesterases (Acots) are enzymes that catalyze the hydrolysis of fatty acyl-CoAs to free fatty acids and coenzyme A, and have the potential to regulate the intracellular levels of these molecules. In this study, we show that a cytosolic isoform, Acot1, is expressed and distributed in immature adipocytes located in the perivascular region of the white adipose tissue (WAT) of rats. Immunoblot analyses detected Acot1 in all of the WATs examined, while immunohistochemistry revealed positively stained layered structures surrounding the adventitia of blood vessels in the subcutaneous WAT. When the subcutaneous WAT was digested with collagenase and centrifuged, Acot1 was recovered in the stromal vascular fraction (SVF), and not in the large mature adipocytes. In the SVF, undigested cells attached to short tubular fragments of blood vessels showed positive immunostaining, as well as a proportion of the dispersed cells. These fibroblast-like cells contained fine particulate lipid droplets, stained by oil-red O dye, in their cytoplasm, or expressed fatty acid-binding protein 4, an adipocyte marker. After induction of adipocyte differentiation following a 15-day preculture without insulin, the dedifferentiated cells showed increased Acot1 expression with a diffuse distribution throughout the cytosol. These findings suggest that Acot1 expression is transiently upregulated at an early stage of adipocyte maturation, possibly to maintain cytosolic acyl-CoAs below a certain level until the cells acquire their full capability for fat storage.     

Distinction of white,beige and brown adipocytes derived from mesenchymal stem cells简

Adipose tissue is a major metabolic organ, and it has been traditionally classified as either white adipose tissue (WAT) or brown adipose tissue (BAT). WAT and BAT are characterized by different anatomical locations, morphological structures, functions, and regulations. WAT and BAT are both involved in energy balance. WAT is mainly involved in the storage and mobilization of energy in the form of triglycerides, whereas BAT specializes in dissipating energy as heat during cold- or diet-induced thermogenesis. Recently, brown-like adipocytes were discovered in WAT. These brown-like adipocytes that appear in WAT are called beige or brite adipocytes. Interestingly, these beige/brite cells resemble white fat cells in the basal state, but they respond to thermogenic stimuli with increased levels of thermogenic genes and increased respiration rates. In addition, beige/brite cells have a gene expression pattern distinct from that of either white or brown fat cells. The current epidemic of obesity has increased the interest in studying adipocyte formation (adipogenesis), especially in beige/brite cells. This review summarizes the developmental process of adipose tissues that originate from the mesenchymal stem cells and the features of these three different types of adipocytes.     

Human adipose stromal vascular cell delivery in a fibrin spray

Background aimsAdipose tissue represents a practical source of autologous mesenchymal stromal cells (MSCs) and vascular-endothelial progenitor cells, available for regenerative therapy without in vitro expansion. One of the problems confronting the therapeutic application of such cells is how to immobilize them at the wound site. We evaluated in vitro the growth and differentiation of human adipose stromal vascular fraction (SVF) cells after delivery through the use of a fibrin spray system.MethodsSVF cells were harvested from four human adult patients undergoing elective abdominoplasty, through the use of the LipiVage system. After collagenase digestion, mesenchymal and endothelial progenitor cells (pericytes, supra-adventitial stromal cells, endothelial progenitors) were quantified by flow cytometry before culture. SVF cells were applied to culture vessels by means of the Tisseel fibrin spray system. SVF cell growth and differentiation were documented by immunofluorescence staining and photomicrography.ResultsSVF cells remained viable after application and were expanded up to 3 weeks, when they reached confluence and adipogenic differentiation. Under angiogenic conditions, SVF cells formed endothelial (vWF+, CD31+ and CD34+) tubules surrounded by CD146+ and α-smooth muscle actin+ perivascular/stromal cells.ConclusionsHuman adipose tissue is a rich source of autologous stem cells, which are readily available for regenerative applications such as wound healing, without in vitro expansion. Our results indicate that mesenchymal and endothelial progenitor cells, prepared in a closed system from unpassaged lipoaspirate samples, retain their growth and differentiation capacity when applied and immobilized on a substrate using a clinically approved fibrin sealant spray system.     

Distinction of white,beige and brown adipocytes derived from mesenchymal stem cells

Adipose tissue is a major metabolic organ, and it has been traditionally classified as either white adipose tissue(WAT) or brown adipose tissue(BAT). WAT and BAT are characterized by different anatomical locations, morphological structures, functions, and regulations. WAT and BAT are both involved in energy balance. WAT is mainly involved in the storage and mobilization of energy in the form of triglycerides, whereas BAT specializes in dissipating energy as heat during cold- or diet-induced thermogenesis. Recently, brownlike adipocytes were discovered in WAT. These brownlike adipocytes that appear in WAT are called beige or brite adipocytes. Interestingly, these beige/brite cells resemble white fat cells in the basal state, but they respond to thermogenic stimuli with increased levels of thermogenic genes and increased respiration rates. In addition, beige/brite cells have a gene expressionpattern distinct from that of either white or brown fat cells. The current epidemic of obesity has increased the interest in studying adipocyte formation(adipogenesis), especially in beige/brite cells. This review summarizes the developmental process of adipose tissues that originate from the mesenchymal stem cells and the features of these three different types of adipocytes.     

Increased Death of Adipose Cells,a Path to Release Cell‐Free DNA Into Systemic Circulation of Obese Women

Remodeling of adipose tissue is required to support the expansion of adipose mass. In obesity, an increased death of adipocytes contributes to the accelerated cellular turnover. We have shown that obesity in pregnancy is associated with metabolic and immune alterations in the adipose tissue. In this study, we characterized the mechanisms responsible for increased death of adipose cells of pregnant obese women and its functional consequences. We postulated that a higher turnover of dead cells in white adipose tissue of obese women would translate into release of cell‐free DNA (cfDNA) into their systemic circulation. Increase in adipose mass of obese compared to lean women results from a lesser number of hypertrophic adipocytes and an accumulation of macrophages in the stromal vascular fraction (SVF). The adipocytes of obese displayed enhanced necrosis with a loss of perilipin staining at the plasma membrane. Apoptosis was prominent in SVF cells with an increased expression of caspase 9 and caspase 3 and a higher rate of terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate nick end‐labeling (TUNEL) positive CD68 macrophages in obese vs. lean. Whereas circulating fetal cfDNA concentrations were not changed, there was a twofold increase in circulating glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) cfDNA and adipose tissue GAPDH mRNA in obese women. The maternal systemic GAPDH cfDNA was positively correlated with BMI and gestational weight gain. These data suggest that the active remodeling of adipose tissue of obese pregnant women results in an increased release of cfDNA of maternal origin into the circulation.