Distinct populations of adipogenic and myogenic Myf5-lineage progenitors in white adipose tissues

Brown adipose tissues (BAT) are derived from a myogenic factor 5 (Myf5)-expressing cell lineage and white adipose tissues (WAT) predominantly arise from non-Myf5 lineages, although a subpopulation of adipocytes in some WAT depots can be derived from the Myf5 lineage. However, the functional implication of the Myf5- and non-Myf5-lineage cells in WAT is unclear. We found that the Myf5-lineage constitution in subcutaneous WAT depots is negatively correlated to the expression of classical BAT and newly defined beige/brite adipocyte-specific genes. Consistently, fluorescent-activated cell sorting (FACS)-purified Myf5-lineage adipo-progenitors give rise to adipocytes expressing lower levels of BAT-specific Ucp1, Prdm16, Cidea, and Ppargc1a genes and beige adipocyte-specific CD137, Tmem26, and Tbx1 genes compared with the non-Myf5-lineage adipocytes from the same depots. Ablation of the Myf5-lineage progenitors in WAT stromal vascular cell (SVC) cultures leads to increased expression of BAT and beige cell signature genes. Strikingly, the Myf5-lineage cells in WAT are heterogeneous and contain distinct adipogenic [stem cell antigen 1(Sca1)-positive] and myogenic (Sca1-negative) progenitors. The latter differentiate robustly into myofibers in vitro and in vivo, and they restore dystrophin expression after transplantation into mdx mouse, a model for Duchenne muscular dystrophy. These results demonstrate the heterogeneity and functional differences of the Myf5- and non-Myf5-lineage cells in the white adipose tissue.     

Adipose tissue: a subtle and complex cell system

White adipose tissue (WAT) represents a large amount of all adult tissues. For a long time, it was considered as a poorly active, overgrown and undesirable tissue. It was mainly studied for its involvement in energy metabolism and disorders, as well as for its endocrine functions. WAT is composed of two main populations, matures adipocytes and stroma vascular fraction (SVF) that can be separated easily. The SVF contains two compartments, stromal and hematopoietic that have been recently characterized. The stromal population (or ADAS for Adipose Derived Stromal Cells) presents functional features of, as well as lineage relationship with, macrophages. These stromal cells, that are able to differentiate into adipocytes, also display endothelial potential, and could be considered as vascular progenitors. Differentiation of various adipose-derived cell subsets towards functional cardiomyocytes, osteoblasts, chondrocytes, muscle, hematopoietic and neural cells was also obtained in vitro or in vivo. Adipose tissue thus appears as a complex tissue composed of different cell subsets that could vary according to the nature and the location of fat pads, or to the physiological or pathological status. WAT appears as a very plastic and heterogeneous tissue that is very easy to sample. This represents a great advantage when considering adipose tissue as a potential and suitable source of stem cell for cell therapy. Further investigations in this way have to lead to the emergence of new insights fundamental to progress in our knowledge of adipose tissue biology.     

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.     

Adipose stromal/stem cells in regenerative medicine:Potentials and limitations

This article presents the stem and progenitor cells from subcutaneous adipose tissue,briefly comparing them with their bone marrow counterparts,and discussing their potential for use in regenerative medicine.Subcutaneous adipose tissue differs from other mesenchymal stromal/stem cells(MSCs) sources in that it contains a pre-adipocyte population that dwells in the adventitia of robust blood vessels.Pre-adipocytes are present both in the stromal-vascular fraction(SVF;freshly isolated cells) and in the adherent fraction of adipose stromal/stem cells(ASCs;in vitro expanded cells),and have an active role on the chronic inflammation environment established in obesity,likely due their monocyticmacrophage lineage identity.The SVF and ASCs have been explored in cell therapy protocols with relative success,given their paracrine and immunomodulatory effects.Importantly,the widely explored multipotentiality of ASCs has direct application in bone,cartilage and adipose tissue engineering.The aim of this editorial is to reinforce the peculiarities of the stem and progenitor cells from subcutaneous adipose tissue,revealing the spheroids as a recently described biotechnological tool for cell therapy and tissue engineering.Innovative cell culture techniques,in particular 3 D scaffold-free cultures such as spheroids,are now available to increase the potential for regeneration and differentiation of mesenchymal lineages.Spheroids are being explored not only as a model for cell differentiation,but also as powerful 3 D cell culture tools to maintain the stemness and expand the regenerative and differentiation capacities of mesenchymal cell lineages.     

Fucoxanthin from edible seaweed, Undaria pinnatifida, shows antiobesity effect through UCP1 expression in white adipose tissues

Mitochondrial uncoupling protein 1 (UCP1) is usually expressed only in brown adipose tissue (BAT) and a key molecule for metabolic thermogenesis to avoid an excess of fat accumulation. However, there is little BAT in adult humans. Therefore, UCP1 expression in tissues other than BAT is expected to reduce abdominal fat. Here, we show reduction of abdominal white adipose tissue (WAT) weights in rats and mice by feeding lipids from edible seaweed, Undaria pinnatifida. Clear signals of UCP1 protein and mRNA were detected in WAT of mice fed the Undaria lipids, although there is little expression of UCP1 in WAT of mice fed control diet. The Undaria lipids mainly consisted of glycolipids and seaweed carotenoid, fucoxanthin. In the fucoxanthin-fed mice, WAT weight significantly decreased and UCP1 was clearly expressed in the WAT, while there was no difference in WAT weight and little expression of UCP1 in the glycolipids-fed mice. This result indicates that fucoxanthin upregulates the expression of UCP1 in WAT, which may contribute to reducing WAT weight.     

Plasticity of human adipose stem cells to perform adipogenic and endothelial differentiation

Recent research findings postulate that adipocytes and endothelial cells (EC) may share a common progenitor. However, the interlinking pathways between adipose tissue and endothelium, and the differentiation potential of cells to convert from one tissue into the other via progenitor cells have not been elucidated and are therefore the focus of this study. Stromal vascular fraction (SVF) cells were isolated from liposuction aspirates or excised adipose tissue and separated into CD31+ and CD31- populations by magnet-assisted cell sorting. Differentiation to fat tissue was induced in both CD31 fractions after expansion by insulin, dexamethasone, isobutylmethylxanthine, triiodothyronine, pioglitazone, and transferrin. Differentiation was assayed enzymatically and by cell counting. Maturation to endothelium was performed with vascular endothelial growth factor (VEGF), insulin-like growth factor-1 plus 2% fetal calf serum, and confirmed by flow cytometry and tube formation assays on Matrigel. Our results show that the SVF contains a CD31-, S100+ cell type that can differentiate into adipocytes and EC. The SVF also comprises CD31+ cells that, although they have an endothelial phenotype, can be converted into mature adipocytes. These findings demonstrate the potency of SVF cells to perform both adipogenic and endothelial differentiation. Further, they reveal the plasticity of mature cells of mesenchymal origin to undergo conversion from endothelium to adipose tissue and vice versa.     

Characterization and comparison of adipose tissue‐derived cells from human subcutaneous and omental adipose tissues

Different fat depots contribute differently to disease and function. These differences may be due to the regional variation in cell types and inherent properties of fat cell progenitors. To address the differences of cell types in the adipose tissue from different depots, the phenotypes of freshly isolated adipose tissue‐derived cells (ATDCs) from subcutaneous (SC) and omental (OM) adipose tissues were compared using flow cytometry. Our results showed that CD31^?CD34⁺CD45^?CD90^‐CD105^?CD146⁺ population, containing vascular smooth muscle cells and pericytes, was specifically defined in the SC adipose tissue while no such population was observed in OM adipose tissue. On the other hand, CD31^?CD34⁺CD45^?CD90^?CD105^?CD146^? population, which is an undefined cell population, were found solely in OM adipose tissue. Overall, the SC adipose tissue contained more ATDCs than OM adipose tissue, while OM adipose tissue contained more blood‐derived cells. Regarding to the inherent properties of fat cell progenitors from the two depots, adipose‐derived stem cells (ADSCs) from SC had higher capacity to differentiate into both adipogenic and osteogenic lineages than those from OM, regardless of that the proliferation rates of ADSCs from both depots were similar. The higher differentiation capacity of ADSCs from SC adipose tissue suggests that SC tissue is more suitable cell source for regenerative medicine than OM adipose tissue. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitative trait Loci for regional adiposity in mouse lines divergently selected for food intake

Objective: Obesity is thought to result from an interaction between genotype and environment. Excessive adiposity is associated with a number of important comorbidities; however, the risk of obesity‐related disease varies with the distribution of fat throughout the body. The aim of this study was to map quantitative trait loci (QTLs) associated with regional fat depots in mouse lines divergently selected for food intake corrected for body mass. Research Methods and Procedures: Using an F₂ intercross design (n = 457), the dry mass of regional white (subcutaneous, gonadal, retroperitoneal, and mesenteric) adipose tissue (WAT) and brown adipose tissue (BAT) depots were analyzed to map QTLs. Results: The total variance explained by the mapped QTL varied between 12% and 39% for BAT and gonadal fat depots, respectively. Using the genome‐wide significance threshold, nine QTLs were associated with multiple fat depots. Chromosomes 4 and 19 were associated with WAT and BAT and chromosome 9 with WAT depots. Significant sex × QTL interactions were identified for gonadal fat on chromosomes 9, 16, and 19. The pattern of QTLs identified for the regional deposits showed the most similarity between retroperitoneal and gonadal fat, whereas BAT showed the least similarity to the WAT depots. Analysis of total fat mass explained in excess of 40% of total variance. Discussion: There was limited concordance between the QTLs mapped in our study and those reported previously. This is likely to reflect the unique nature of the mouse lines used. Results provide an insight into the genetic basis of regional fat distribution.     

The influence of starvation and natural refeeding on the rate of triacylglycerol/fatty acid substrate cycling in brown adipose tissue and different white adipose sites of the ratin vivo. The role of insulin and the sympathetic nervous system

Triacylglycerol/fatty acid substrate cycling was measuredin vivo in brown adipose tissue (BAT) and white adipose tissue (WAT) of fed, starved and refed rats. Starvation (24 h) significantly decreased the rate of cycling in BAT, and refeeding chow diet led to a rapid, 6-fold increase in cycling. Cycling rate in WAT was much lower than in BAT, and was not influenced by fasting or refeeding. Similar rates of cycling were found in epididymal, mesenteric, subcutaneous, and scapular WAT depots. Sympathetic denervation of interscapular BAT abolished the response of the tissue to refeeding, as did acute suppression of insulin secretion. Similarly, rats fasted for 3 days showed no acute increase in the activity of the cycle following refeeding.     

Cold-induced activation of brown adipose tissue and adipose angiogenesis in mice

Exposure of humans and rodents to cold activates thermogenic activity in brown adipose tissue (BAT). This protocol describes a mouse model to study the activation of BAT and angiogenesis in adipose tissues by cold acclimation. After a 1-week exposure to 4 °C, adult C57BL/6 mice show an obvious transition from subcutaneous white adipose tissue (WAT) into brown-like adipose tissue (BRITE). The BRITE phenotype persists after continuous cold exposure, and by the end of week 5 BRITE contains a high number of uncoupling protein-1-positive mitochondria, a characteristic feature of BAT. During the transition from WAT into BRITE, the vascular density is markedly increased owing to the activation of angiogenesis. In BAT, cold exposure stimulates thermogenesis by increasing the mitochondrial content and metabolic rate. BAT and the increased metabolic rate result in a lean phenotype. This protocol provides an outstanding opportunity to study the molecular mechanisms that control adipose mass.     

Comparative analysis of cell populations with a phenotype similar to that of mesenchymal stem cells derived from subcutaneous fat

Two cell populations with a phenotype similar to that of mesenchymal stem cells (MSC) with different characteristics for expression of surface antigene CD34 were derived from subcutaneous fat. CD34-positive cells were derived from subcutaneous fat of the inferior eyelid obtained during transconjuctival blepharoplasty. CD34-negative cells were derived from adipose tissue obtained during lipoaspiration from the same patients. These cells displayed common characteristics for morphology and expression of basic markers characterizing them as mesenchymal stem cells. On being induced for differentiation, these two cell populations were able to differentiate to cells of adipose (adipocytes), bone (osteoblastes, osteocytes), cartilage (chondroblasts, chondrocytes), and nervous (neurons, astrocytes and oligodendrocytes) tissues.     

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.     

Comparing lipid remodeling of brown adipose tissue,white adipose tissue,and liver after one-week high fat diet intervention with quantitative Raman microscopy

Brown adipose tissue (BAT) consists of highly metabolically active adipocytes that catabolize nutrients to produce heat. Playing an active role in triacylglycerol (TAG) clearance, research has shown that dietary fatty acids can modulate the TAG chemistry deposition in BAT after weeks-long dietary intervention, similar to what has been shown in white adipose tissue (WAT). Our objective was to compare the influence of sustained, nonchronic dietary intervention (a 1-week interval) on WAT and interscapular BAT lipid metabolism and deposition in situ. We use quantitative, label-free chemical microscopy to show that 1 week of high fat diet (HFD) intervention results in dramatically larger lipid droplet (LD) growth in BAT (and liver) compared to LD growth in inguinal WAT (IWAT). Moreover, BAT showed lipid remodeling as increased unsaturated TAGs in LDs, resembling the dietary lipid composition, while WAT (and liver) did not show lipid remodeling on this time scale. Concurrently, expression of genes involved in lipid metabolism, particularly desaturases, was reduced in BAT and liver from HFD-fed mice after 1 week. Our data show that BAT lipid chemistry remodels exceptionally fast to dietary lipid intervention compared WAT, which further points towards a role in TAG clearance.     

Major involvement of mTOR in the PPARγ-induced stimulation of adipose tissue lipid uptake and fat accretion

Evidence points to a role of the mammalian target of rapamycin (mTOR) signaling pathway as a regulator of adiposity, yet its involvement as a mediator of the positive actions of peroxisome proliferator-activated receptor (PPAR)γ agonism on lipemia, fat accretion, lipid uptake, and its major determinant lipoprotein lipase (LPL) remains to be elucidated. Herein we evaluated the plasma lipid profile, triacylglycerol (TAG) secretion rates, and adipose tissue LPL-dependent lipid uptake, LPL expression/activity, and expression profile of other lipid metabolism genes in rats treated with the PPARγ agonist rosiglitazone (15 mg/kg/day) in combination or not with the mTOR inhibitor rapamycin (2 mg/kg/day) for 15 days. Rosiglitazone stimulated adipose tissue mTOR complex 1 and AMPK and induced TAG-derived lipid uptake (136%), LPL mRNA/activity (2- to 6-fold), and fat accretion in subcutaneous (but not visceral) white adipose tissue (WAT; 50%) and in brown adipose tissue (BAT; 266%). Chronic mTOR inhibition attenuated the upregulation of lipid uptake, LPL expression/activity, and fat accretion induced by PPARγ activation in both subcutaneous WAT and BAT, which resulted in hyperlipidemia. In contrast, rapamycin did not affect most of the other WAT lipogenic genes upregulated by rosiglitazone. Together these findings demonstrate that mTOR is a major regulator of adipose tissue LPL-mediated lipid uptake and a critical mediator of the hypolipidemic and lipogenic actions of PPARγ activation.     

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.     

Differential expression of adipose tissue proteins between obesity-susceptible and -resistant rats fed a high-fat diet

One of the major questions in the field of obesity is why some humans become obese (obesity prone, OP) and others resist the development of obesity (obesity resistant, OR) when exposed to a high-calorie diet, which has not been completely studied. Therefore, in the present study, in order to gain insight into the molecular mechanisms underlying this propensity, we have performed a comparative analysis of protein expression profiles in white adipose tissue (WAT) and brown adipose tissue (BAT) of rats fed a high-fat diet by 2-DE and MALDI-TOF-MS. Protein mapping of homogenates revealed significant alterations to a number of proteins; 60 and 70 proteins were differentially regulated in BAT and WAT, respectively. For careful interpretation of proteomic results, we categorized the identified proteins into two groups by analysis of both average spot density of pooled six rat adipose tissues and individual spot density of each adipose tissue of six rats as a function of body weight. One of the most striking findings of this study was that significant changes of Ehd1 and laminin receptor in BAT as well as antiquitin, DJ-1 protein, and paraoxonase 2 in WAT were found for the first time in obese rats. In addition, we confirmed the increased expression of some thermogenic enzymes and decreased lipogenic enzymes in adipose tissues of OR rats by immunoblot analysis. To our knowledge, this is the first proteomic study of profiling of protein modulation in OP and OR rats, thereby providing the first global evidence for different propensities to obesity between OP and OR rats.     

Dynamic changes in lipid droplet-associated proteins in the “browning” of white adipose tissues

The morphological and functional differences between lipid droplets (LDs) in brown (BAT) and white (WAT) adipose tissues will largely be determined by their associated proteins. Analysing mRNA expression in mice fat depots we have found that most LD protein genes are expressed at higher levels in BAT, with the greatest differences observed for Cidea and Plin5. Prolonged cold exposure, which induces the appearance of brown-like adipocytes in mice WAT depots, was accompanied with the potentiation of the lipolytic machinery, with changes in ATGL, CGI-58 and G0S2 gene expression. However the major change detected in WAT was the enhancement of Cidea mRNA. Together with the increase in Cidec, it indicates that LD enlargement through LD–LD transference of fat is an important process during WAT browning. To study the dynamics of this phenotypic change, we have applied 4D confocal microscopy in differentiated 3T3-L1 cells under sustained β-adrenergic stimulation. Under these conditions the cells experienced a LD remodelling cycle, with progressive reduction on the LD size by lipolysis, followed by the formation of new LDs, which were subjected to an enlargement process, likely to be CIDE-triggered, until the cell returned to the basal state. This transformation would be triggered by the activation of a thermogenic futile cycle of lipolysis/lipogenesis and could facilitate the molecular mechanism for the unilocular to multilocular transformation during WAT browning. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease.     

Tea catechins enhance the mRNA expression of uncoupling protein 1 in rat brown adipose tissue

The aim of the present study was to determine whether the antiobesity effects of tea catechins (TCs) are associated with the expression of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT). Male Sprague–Dawley rats were fed a high-fat (HF; 35% fat) diet for 5 weeks, then divided into four groups and fed an HF, HF with 0.5% TC (HFTC), normal-fat (NF; 5% fat) or NF with 0.5% TC (NFTC) diet for 8 weeks. At the end of the experimental period, perirenal and epididymal white adipose tissues (WATs) and interscapular BAT were isolated. The NFTC group had significantly lower perirenal WAT weights than the NF group (NF: 12.7±0.53 g; NFTC: 10.2±0.43 g; P<.01), but the HF and HFTC groups did not differ significantly. TC intake had no effects on epididymal WAT weights. The NFTC and HFTC groups had significantly lower BAT weights than the NF and HF groups, respectively. The NFTC group had significantly higher UCP1 mRNA levels in BAT than the NF group (NF: 0.35±0.02; NFTC: 0.60±0.11; P<.05), but the HF and HFTC groups did not differ significantly. Thus, TC intake in the context of the NF diet reduced perirenal WAT weight and up-regulated UCP1 mRNA expression in BAT. These results suggest that the suppressive effect of TC on body fat accumulation is associated with UCP1 expression in BAT.