Control of adipocyte differentiation

A multifunctional 3D co-culture system for studies of mammary tissue morphogenesis and stem cell biology

Studies on the stem cell niche and the efficacy of cancer therapeutics require complex multicellular structures and interactions between different cell types and extracellular matrix (ECM) in three dimensional (3D) space. We have engineered a 3D in vitro model of mammary gland that encompasses a defined, porous collagen/hyaluronic acid (HA) scaffold forming a physiologically relevant foundation for epithelial and adipocyte co-culture. Polarized ductal and acinar structures form within this scaffold recapitulating normal tissue morphology in the absence of reconstituted basement membrane (rBM) hydrogel. Furthermore, organoid developmental outcome can be controlled by the ratio of collagen to HA, with a higher HA concentration favouring acinar morphological development. Importantly, this culture system recapitulates the stem cell niche as primary mammary stem cells form complex organoids, emphasising the utility of this approach for developmental and tumorigenic studies using genetically altered animals or human biopsy material, and for screening cancer therapeutics for personalised medicine.

Mechanisms behind early life nutrition and adult disease outcome

Obesity is increasing around the globe. While adult lifestyle factors undoubtedly contribute to the incidence of obesity and its attendant disorders, mounting evidence suggests that programming of obesity may occur following under- and over-nutrition during development. As hypothalamic control of appetite and energy expenditure is set early in life and can be perturbed by certain exposures such as undernutrition and altered metabolic and hormonal signals, in utero exposure to altered maternal nutrition and inadequate nutrition during early postnatal life may contribute to programming of obesity in offspring. Data from animal studies indicate both intrauterine and postnatal environments are critical determinants of the development of pathways regulating energy homeostasis. This review summarizes recent evidence of the impact of maternal nutrition as well as postnatal nutrition of the offspring on subsequent obesity and disease risk of the offspring. While much of the experimental work reviewed here was conducted in the rodent, these observations provide useful insights into avenues for future research into developing preventive measures to curb the obesity epidemic.

Diet-induced obesity in stem cell antigen-1 KO mice

Stem Cell Antigen-1 (Sca-1) is a member of the lymphocyte-activated protein 6 family and has served as a marker for the identification of stem cells in various tissues, including fat depots. In vitro and in vivo studies suggest the possible involvement of Sca-1 in adipogenic differentiation and link Sca-1 antigenicity with adipocyte progenitors. Previously, we showed that Sca-1-enriched populations of ear mesenchymal stem cells possess enhanced capacity to differentiate into adipocytes. Additionally, we determined the natural frequency and localization of Sca-1-positive progenitor/stem cells in brown and white fat in situ. The present study addressed the question whether Sca-1 deficiency alters the white adipose tissue response to a high-saturated-fat diet. Our results show that Sca-1 null mice (Sca-1(-/-)) fed high-fat diet developed obesity equally well as wild-type mice, suggesting either an indirect in vivo effect of Sca-1 or a compensatory response to Sca-1 deficiency. However, contrary to wild-type mice, high fat diet-fed Sca-1(-/-) mice showed no alterations in serum adipocytokines. The data lead to the conclusion that Sca-1 is either redundant or a nonessential marker of adipose progenitor/stem cells. Nevertheless, since Sca-1-deficient mice displayed elevated blood glucose at fasting and exhibited glucose intolerance and insulin resistance, Sca-1 has subtle effects on adipose function. Thus, the Sca-1-deficient mice may provide a useful model for metabolic studies.

Microarray evidences the role of pathologic adipose tissue in insulin resistance and their clinical implications

Clustering of insulin resistance and dysmetabolism with obesity is attributed to pathologic adipose tissue. The morphologic hallmarks of this pathology are adipocye hypertrophy and heightened inflammation. However, it's underlying molecular mechanisms remains unknown. Study of gene function in metabolically active tissues like adipose tissue, skeletal muscle and liver is a promising strategy. Microarray is a powerful technique of assessment of gene function by measuring transcription of large number of genes in an array. This technique has several potential applications in understanding pathologic adipose tissue. They are: (1) transcriptomic differences between various depots of adipose tissue, adipose tissue from obese versus lean individuals, high insulin resistant versus low insulin resistance, brown versus white adipose tissue, (2) transcriptomic profiles of various stages of adipogenesis, (3) effect of diet, cytokines, adipokines, hormones, environmental toxins and drugs on transcriptomic profiles, (4) influence of adipokines on transcriptomic profiles in skeletal muscle, hepatocyte, adipose tissue etc., and (5) genetics of gene expression. The microarray evidences of molecular basis of obesity and insulin resistance are presented here. Despite the limitations, microarray has potential clinical applications in finding new molecular targets for treatment of insulin resistance and classification of adipose tissue based on future risk of insulin resistance syndrome.

Association of thyroglobulin gene variants with carcass and meat quality traits in beef cattle

Thyroid hormones play an important role in regulating metabolism and can affect homeostasis of fat deposition. The gene encoding thyroglobulin (TG), producing the precursor for thyroid hormones, has been proposed as a positional and functional candidate gene for a QTL with an effect on fat deposition. In the present study, we identified 6 novel SNPs at the 3' flanking region of the TG gene. The SNP marker association analysis indicated that the T354C, G392A, A430G and T433G SNP markers were significantly associated with marbling score (P < 0.05). Animals with the new homozygote genotype had higher marbling score than those with the other genotypes. Otherwise, the linkage disequilibrium analysis indicated that these four SNPs were completely linked (r (2) = 1). Results from this study suggest that TG gene-specific SNP may be a useful marker for meat quality traits in future marker assisted selection programs in beef cattle.

Effects of lysophosphatidic acid on the in vitro proliferation and differentiation of a novel porcine preadipocyte cell line

We examined the effects of lysophosphatidic acid (LPA) on in vitro proliferation and differentiation of a porcine preadipocyte cell line, DFAT-P, and a mouse preadipocyte cell line, 3T3-L1. During the proliferation and differentiation phases, DFAT-P and 3T3-L1 cells expressed only the endothelial differentiation gene (EDG)-2 receptor and not EDG-4 and EDG-7 receptors. LPA promoted the proliferation of DFAT-P cells more extensively than that of 3T3-L1 cells. After adipogenic induction, LPA inhibited glycerol-3-phosphate dehydrogenase activity and lipid droplet accumulation, and suppressed peroxisome proliferator-activated receptor γ (PPARγ) protein expression, this inhibitory effect in DFAT-P cells was twice as high as that in 3T3-L1 cells. Furthermore, treatments with low LPA concentrations significantly inhibited adipocyte differentiation in DFAT-P cells but not in 3T3-L1 cells. We conclude that LPA promotes the proliferation of porcine preadipocytes through the EDG-2 receptor but inhibits their differentiation, and these effects depend on the down-regulation of PPARγ expression via the EDG-2 receptor. Furthermore, DFAT-P cells are more sensitive to LPA than 3T3-L1 cells. These findings in a porcine model will contribute to the understanding of LPA action mechanisms on in vitro proliferation and differentiation of preadipocytes in domestic animals and/or humans.

Ectopic fat and cardiovascular disease: what is the link?

AIM

of this paper is to review the recent literature on the relationship between ectopic fat accumulation and cardiovascular disease.

DATA SYNTHESIS

Ectopic fat is an important predictor of metabolic (in particular insulin resistance) and cardiovascular disease, carrying more risk than general fat accumulation. Recent studies have shown a link between ectopic fat accumulation, as cardiac (epicardial or intra-myocardial fat) and/or visceral and/or hepatic fat, and development of atherosclerosis, coronary heart disease and hypertension.

CONCLUSIONS

Ectopic fat accumulation is not only a marker of cardiometabolic disease, since through the release of adipocitokines, lipotoxic and glucotoxic agents, participates in the crosstalk with insulin-sensitive organs leading to metabolic, cardiac and vascular dysfunctions.

Establishment and characteristics of porcine preadipocyte cell lines derived from mature adipocytes

Development of established preadipocyte cell lines, such as 3T3-L1 and 3T3-F442A, greatly facilitated the study of molecular mechanisms of adipocyte differentiation under defined conditions. Most of these cell lines are derived from mouse embryos, and preadipocyte cell lines of other species have not yet been maintained in culture long enough to study differentiation under a variety of conditions. This is the first report on the establishment of porcine preadipocyte cell lines derived from mature adipocytes by a simple method, known as ceiling culture, for culturing mature adipocytes in vitro. This cell line can proliferate extensively until the cells become confluent and fully differentiated into mature adipocytes, depending on adipogenic induction. No changes in their differentiation pattern are observed during their propagation, and they have been successfully carried and differentiated for at least 37 passages. This cell line maintains a normal phenotype without transforming spontaneously, even after long-term maintenance in culture. This achievement may lead to easy establishment of porcine preadipocyte cell lines and novel model systems for studying the mechanisms of adipocyte differentiation and metabolism as a substitute for human preadipocytes.

Visceral Adiposity, Insulin Resistance, and Type 2 Diabetes

The worldwide prevalence of obesity and obesity-related diseases continues to rise. Insulin resistance, the metabolic syndrome, and type 2 diabetes are all associated with obesity. Visceral fat is now recognized to have metabolic, endocrine, and immune functions; increased visceral adiposity enhances the risk of metabolic and cardiovascular disorders. Potential mechanisms of this increased risk may include increased free fatty acid release and alterations in adipokines. Lifestyle interventions resulting in weight loss and loss of visceral fat can have a significant impact on cardiometabolic risk. Bariatric surgery has also been shown to improve insulin resistance, type 2 diabetes, and other comorbidities of obesity. Several medical therapies for type 2 diabetes or obesity also show promise for an impact on visceral adiposity-related comorbidities.

The use of decellularized adipose tissue to provide an inductive microenvironment for the adipogenic differentiation of human adipose-derived stem cells

The development of an engineered adipose tissue substitute, capable of supporting reliable, predictable, and complete fat tissue formation, would be of significant value in the fields of plastic and reconstructive surgery. Towards the goal of engineering an optimized microenvironment for adipogenesis, a decellularization strategy was developed for adipose tissue, which yielded 3-D scaffolds with preserved extracellular matrix architecture. A significant volume of scaffolding material could be obtained from a human tissue source that is commonly discarded. Histology, immunohistochemistry, and scanning electron microscopy confirmed the efficacy and reproducibility of the approach, and also indicated that the basement membrane was conserved in the processed matrix, including laminin and collagen type IV. Seeding experiments with human adipose-derived stem cells indicated that the decellularized adipose tissue (DAT) provided an inductive microenvironment for adipogenesis, supporting the expression of the master regulators PPARgamma and CEBPalpha, without the need for exogenous differentiation factors. High levels of adipogenic gene expression and glycerol-3-phosphate dehydrogenase activity were observed in the induced DAT scaffolds, as compared to cells grown in monolayer or cell aggregate culture. The protein data emphasized the importance of the cell donor source in the development of tissue-engineering strategies for large-volume soft tissue regeneration.

Enzymatically degradable poly(ethylene glycol) based hydrogels for adipose tissue engineering

Adipose tissue engineering requires biomaterials that promote the differentiation of seeded adipocytes. Here, we report on the development and characterization of in situ forming, poly(ethylene glycol) (PEG) based hydrogels for soft tissue augmentation. Branched PEG-amines were modified with collagenase-sensitive peptides and cross-linked with branched PEG-succinimidyl propionates without the use of free-radical initiators (enzymatically degradable hydrogels). Alanine-modified PEG-amines were used for the preparation of non-degradable gels. Depending on the used polymer concentration, the strength of degradable gels after swelling ranged from 1708 to 7412 Pa; the strength of non-degradable hydrogels varied between 1496 and 7686 Pa. Enzyme mediated gel degradation occurred within 10, 16, and 19 days (5%, 10%, and 15% initial polymer content). To evaluate their suitability as scaffold materials for adipose tissue engineering, the hydrogels were functionalized with the laminin-derived adhesion peptide YIGSR, and seeded with 3T3-L1 preadipocytes. Compared to a standard two-dimensional cell culture model, the developed hydrogels significantly enhanced the intracellular triglyceride accumulation of encapsulated adipocytes. Functionalization with YIGSR further enhanced lipid synthesis within differentiating adipocytes. Long-term studies suggested that enzymatically degradable hydrogels furthermore promote the formation of coherent adipose tissue-like structures featuring many mature unilocular fat cells.

Effect of conjugated linoleic acid on body fat, tumor necrosis factor alpha and resistin secretion in spontaneously hypertensive rats

Conjugated linoleic acid (CLA) is a naturally occurring group of dienoic derivaties of linoleic acid found mainly in beef and dairy products. CLA has been reported to reduce body fat, as well as to possess anticarcinogenic, antiatherogenic and procatabolic activities in animals. The objective of this study was to evaluate the effect of CLA supplementation to spontaneously hypertensive rats (SHR) on body fat, biochemical parameters of serum related tumor necrosis factor alpha (TNF-alpha) and resistin secretion. Thirty rats were divided in three groups, the first group of spontaneously hypertensive rats received a standard diet (V-SHR group, n=10), a second group of SHR was fed 1.5% of conjugated linoleic acid (CLA-SHR group, n=10) and the third was the control, non-hypertensive group (KW, n=10) also on a standard diet including 7.5% of sunflower oil during eight weeks. After CLA diet administration, spontaneously hypertensive rats showed a significant reduction in blood pressure, serum glucose, cholesterol and triacylglycerols, together with reduction of index of body fat, pericardic, abdominal and epididymal adipose tissue. These effects were accompanied by a decrease in the secretion of TNF-alpha and resistin.

The ZEB1 transcription factor is a novel repressor of adiposity in female mice

Background

Four genome-wide association studies mapped an “obesity” gene to human chromosome 10p11–12. As the zinc finger E-box binding homeobox 1 (ZEB1) transcription factor is encoded by the TCF8 gene located in that region, and as it influences the differentiation of various mesodermal lineages, we hypothesized that ZEB1 might also modulate adiposity. The goal of these studies was to test that hypothesis in mice.

Methodology/Principal Findings

To ascertain whether fat accumulation affects ZEB1 expression, female C57BL/6 mice were fed a regular chow diet (RCD) ad libitum or a 25% calorie-restricted diet from 2.5 to 18.3 months of age. ZEB1 mRNA levels in parametrial fat were six to ten times higher in the obese mice. To determine directly whether ZEB1 affects adiposity, wild type (WT) mice and mice heterozygous for TCF8 (TCF8+/−) were fed an RCD or a high-fat diet (HFD) (60% calories from fat). By two months of age on an HFD and three months on an RCD, TCF8+/− mice were heavier than WT controls, which was attributed by Echo MRI to increased fat mass (at three months on an HFD: 0.517±0.081 total fat/lean mass versus 0.313±0.036; at three months on an RCD: 0.175±0.013 versus 0.124±0.012). No differences were observed in food uptake or physical activity, suggesting that the genotypes differ in some aspect of their metabolic activity. ZEB1 expression also increases during adipogenesis in cell culture.

Conclusion/Significance

These results show for the first time that the ZEB1 transcription factor regulates the accumulation of adipose tissue. Furthermore, they corroborate the genome-wide association studies that mapped an “obesity” gene at chromosome 10p11–12.

Active plasma kallikrein localizes to mast cells and regulates epithelial cell apoptosis, adipocyte differentiation, and stromal remodeling during mammary gland involution

The plasminogen cascade of serine proteases directs both development and tumorigenesis in the mammary gland. Plasminogen can be activated to plasmin by urokinase-type plasminogen activator (uPA), tissue-type plasminogen activator (tPA), and plasma kallikrein (PKal). The dominant plasminogen activator for mammary involution is PKal, a serine protease that participates in the contact activation system of blood coagulation. We observed that the prekallikrein gene (Klkb1) is expressed highly in the mammary gland during stromal remodeling periods including puberty and postlactational involution. We used a variant of ecotin (ecotin-PKal), a macromolecular inhibitor of serine proteases engineered to be highly specific for active PKal, to demonstrate that inhibition of PKal with ecotin-PKal delays alveolar apoptosis, adipocyte replenishment, and stromal remodeling in the involuting mammary gland, producing a phenotype resembling that resulting from plasminogen deficiency. Using biotinylated ecotin-PKal, we localized active PKal to connective tissue-type mast cells in the mammary gland. Taken together, these results implicate PKal as an effector of the plasminogen cascade during mammary development.

Serum amyloid A3 does not contribute to circulating SAA levels

Adipose tissue secretes proteins like serum amyloid A (SAA), which plays important roles in local and systemic inflammation. Circulating SAA levels increase in obese humans, but the roles of adipose-derived SAA and hyperlipidemia in this process are unclear. We took advantage of the difference in the inducible isoforms of SAA secreted by adipose tissue (SAA3) and liver (SAA1 and 2) of mice to evaluate whether adipose tissue contributes to the circulating pool of SAA in obesity and hyperlipidemia. Genetically obese (ob/ob) mice, but not hyperlipidemic mice deficient in apolipoprotein E (Apoe(-/-)), had significantly higher circulating levels of SAA than their littermate controls. SAA1/2 mRNA expression in the liver and SAA3 mRNA expression in intra-abdominal fat were significantly higher in obese than thin mice, but they were not affected by hyperlipidemia in Apoe(-/-) mice. However, only SAA1/2 and the constitutive form of SAA (SAA4) could be detected in the circulation by mass spectrometric analysis of HDL, the major carrier of circulating SAA. In contrast, SAA3 could be detected in medium from cultured adipocytes. Our findings indicate that the expression of SAA3 in adipose tissue is upregulated by obesity, but it does not contribute to the circulating pool of SAA in mice.

Association analysis of thyroglobulin gene variants with carcass and meat quality traits in beef cattle

Thyroid hormones play an important role in regulating the metabolism and can affect the homeostasis of fat deposition. The gene encoding thyroglobulin (TG), producing the precursor for thyroid hormones, has been proposed as a positional and functional candidate gene for a QTL with an effect on fat deposition. In the present study, we identified 6 novel SNPs at the 3' flanking region of the TG gene. The SNP marker association analysis indicated that the SNP markers G133C, G156A, C220T and A506C were significantly associated with marbling score (P<0.05, N=271). Animals with the new homozygote genotype had higher marbling scores than those with the other genotypes. Besides, the linkage disequilibrium analysis indicated that these 4 SNPs were completely linked (r2 = 1). Results of this study suggest that the TG-gene-specific SNP may be a useful marker for meat quality traits in future marker-assisted selection programmes in beef cattle.

Small functional groups for controlled differentiation of hydrogel-encapsulated human mesenchymal stem cells

Cell-matrix interactions have critical roles in regeneration, development and disease. The work presented here demonstrates that encapsulated human mesenchymal stem cells (hMSCs) can be induced to differentiate down osteogenic and adipogenic pathways by controlling their three-dimensional environment using tethered small-molecule chemical functional groups. Hydrogels were formed using sufficiently low concentrations of tether molecules to maintain constant physical characteristics, encapsulation of hMSCs in three dimensions prevented changes in cell morphology, and hMSCs were shown to differentiate in normal growth media, indicating that the small-molecule functional groups induced differentiation. To our knowledge, this is the first example where synthetic matrices are shown to control induction of multiple hMSC lineages purely through interactions with small-molecule chemical functional groups tethered to the hydrogel material. Strategies using simple chemistry to control complex biological processes would be particularly powerful as they could make production of therapeutic materials simpler, cheaper and more easily controlled.

Proteomic analysis for inhibitory effect of chitosan oligosaccharides on 3T3-L1 adipocyte differentiation

In the present study, we performed a differential proteomic analysis using 2-DE combined with MS to clarify the molecular mechanism for the suppressive effect of chitosan oligosaccharides (CO) during differentiation of adipocyte 3T3-L1. Cell differentiation was significantly inhibited by CO at the concentration of 4 mg/mL. Protein mapping of adipocyte homogenates by 2-DE revealed that numerous protein spots were differentially altered in response to CO treatment. Out of 50 identified proteins showing significant alterations, six were up-regulated and 44 were down-regulated by CO treatment in comparison to control mature adipocytes. Among them, most of the proteins are associated with lipid metabolism, cytoskeleton, and redox regulation, in which the levels of farnesyl diphosphate synthetase (FDS), dedicator of cytokinesis 9 (DOCK9), and chloride intracellular channel 1 (CLIC1) were significantly reduced (>two-fold) with CO treatment. These results have not previously been examined in the context of adipogenesis, and thus can be used as novel biomarkers. Taken together with immunoblot analysis, it was concluded that the inhibitory effect of CO on adipocyte differentiation was mediated by C/EBPalpha and PPARgamma pathway through significant downregulations of important adipogenic molecules such as fatty acid binding protein and glucose transporter 4.

Preventive effects of puerarin on alcohol-induced osteonecrosis

Alcohol can induce adipogenesis by bone marrow stromal cells and may cause osteonecrosis of the femoral head. Currently, there are no medications available to prevent alcohol-induced osteonecrosis. We hypothesized puerarin, a Chinese herbal medicine with antioxidative and antithrombotic effects, can prevent alcohol-induced adipogenesis and osteonecrosis. Both bone marrow stromal cells (in vitro) and mice (in vivo) were treated either with ethanol or with ethanol and puerarin, with an untreated group serving as a control. In the in vitro study, the number of adipocytes, contents of triglycerides, and levels of PPAR gamma mRNA expression were decreased and alkaline phosphatase activity, contents of osteocalcin, and levels of osteocalcin mRNA expression were increased in cells treated with both alcohol and puerarin, compared with cells treated with alcohol only. In the in vivo study, marrow necrosis, fat cell hypertrophy and proliferation, thinner and sparse trabeculae, diminished hematopoiesis, and increased empty osteocyte lacunae in the subchondral region of the femoral head were observed in mice treated with alcohol. However, no such changes were seen in femoral heads of mice treated with alcohol and puerarin. The data suggest puerarin can inhibit adipogenic differentiation by bone marrow stromal cells both in vitro and in vivo and prevents alcohol-induced osteonecrosis in this model.

Establishment of a preadipocyte cell line derived from mature adipocytes of GFP transgenic mice and formation of adipose tissue

We established a preadipocyte cell line from mature adipocytes obtained from subcutaneous fat tissue of green fluorescent protein (GFP) transgenic mice. The floating top layer, containing mature adipocytes, was isolated from subcutaneous fat tissue by collagenase digestion and filtration. Fluorescence-activated cell sorting and microscopic analysis revealed that the floating cell fraction comprised a highly homogeneous adipocyte population with no adipose stromal-vascular cells. Isolated mature adipocytes dedifferentiated into fibroblast-like cells and actively proliferated in ceiling culture. In vitro studies showed that the cells could redifferentiate into mature adipocytes in an identical way to 3T3-L1 preadipocytes. No changes in the differentiation pattern were observed during the propagation of our cells. They were successfully maintained and differentiated for at least 22 passages. We named these cells dedifferentiated fat (DFAT-GFP) cells. When DFAT-GFP cells were implanted subcutaneously into C57BL/6N mice, they developed highly vascularized fat pads that morphologically resembled normal subcutaneous adipose tissue and consisted of GFP-positive cells; however, implanted 3T3-L1 cells did not have such an effect on the mice. We conclude that DFAT-GFP cells provide a model that should enable us to study the mechanisms of adipocyte differentiation and adipose tissue formation in vivo and in vitro.

Pathogenic potential of adipose tissue and metabolic consequences of adipocyte hypertrophy and increased visceral adiposity

When caloric intake exceeds caloric expenditure, the positive caloric balance and storage of energy in adipose tissue often causes adipocyte hypertrophy and visceral adipose tissue accumulation. These pathogenic anatomic abnormalities may incite metabolic and immune responses that promote Type 2 diabetes mellitus, hypertension and dyslipidemia. These are the most common metabolic diseases managed by clinicians and are all major cardiovascular disease risk factors. 'Disease' is traditionally characterized as anatomic and physiologic abnormalities of an organ or organ system that contributes to adverse health consequences. Using this definition, pathogenic adipose tissue is no less a disease than diseases of other body organs. This review describes the consequences of pathogenic fat cell hypertrophy and visceral adiposity, emphasizing the mechanistic contributions of genetic and environmental predispositions, adipogenesis, fat storage, free fatty acid metabolism, adipocyte factors and inflammation. Appreciating the full pathogenic potential of adipose tissue requires an integrated perspective, recognizing the importance of 'cross-talk' and interactions between adipose tissue and other body systems. Thus, the adverse metabolic consequences that accompany fat cell hypertrophy and visceral adiposity are best viewed as a pathologic partnership between the pathogenic potential adipose tissue and the inherited or acquired limitations and/or impairments of other body organs. A better understanding of the physiological and pathological interplay of pathogenic adipose tissue with other organs and organ systems may assist in developing better strategies in treating metabolic disease and reducing cardiovascular disease risk.

Assessment of fat-specific protein 27 in the adipocyte lineage suggests a dual role for FSP27 in adipocyte metabolism and cell death

Fat-specific protein 27 (FSP27)/CIDEC was initially identified by its upregulation in TA1 adipogenesis and is one of three cell death-inducing DFF45-like effector (CIDE) family proapoptotic proteins. Ectopic expression of CIDEs promotes apoptosis of mammalian cells. On the other hand, FSP27 has very recently been illustrated to regulate lipid droplet size and promote lipid storage in adipocytes. Regulation of endogenous FSP27 expression is unknown. We assessed the FSP27 transcript level in the well-characterized 3T3-L1 in vitro adipocyte differentiation model and found its emergence parallels the adipocyte-enriched transcript adipocyte fatty acid binding protein and stearoyl Co-A desaturase 1. Furthermore, FSP27 is a differentiation-dependent transcript in adipogenesis of primary rodent and human preadipocytes and in brown adipogenesis. The FSP27 transcript is inversely regulated by TNF-alpha and insulin, consistent with an antilipolytic function. It is nearly abolished with a 4-h exposure of 3T3-L1 adipocytes to 10 ng/ml TNF-alpha, while treatment with 100 nM insulin increased the FSP27 transcript eightfold. In the latter case LY-294002 blocked this response, indicating involvement of phosphatidylinositol 3-kinase signals. Northern blot analysis of murine tissues indicated exclusive expression of FSP27 in white and brown adipose tissue; however, a dramatic upregulation occurred in the liver of ob/ob mice. Ectopic expression of murine FSP27 in 293T cells and in 3T3-L1 preadipocytes led to the appearance of key apoptotic hallmarks and cell death. However, despite the upregulation for FSP27 in adipogenesis, we failed to detect DNA laddering indicative of apoptosis in 3T3-L1 adipocytes. This suggests that adipogenesis is accompanied by decreased susceptibility to the proapoptotic effects of FSP27. Overall, our findings support roles for FSP27 in cell death and in adipocyte function.

Functional structure of adipocytes differentiated from human umbilical cord stroma-derived stem cells

It has been previously demonstrated that human umbilical cord stroma-derived stem cells (HUCSCs) are competent to differentiate into adipocytes. However, controversies have arisen as to whether HUCSCs can become mature adipocytes or not, and to what extent these cells can be induced in adipogenic pathway. Here, we extensively analyzed their adipogenic potency with a structural and functional approach by determining lipid formation dynamics in concordance to adipocyte-specific markers. During a 35-day period, HUCSCs respond to adipogenic induction, at which point 88% of cells exhibited multilocular lipid granules (LGs) having a mean diameter of 3 mum in round-shaped, F-actin-poor cells. Although the 1st week of induction did not generally display typical lipidogenic phenotypes, the degree of adipogenesis was dissected and confirmed by mRNA expressions of peroxisome proliferator-activated receptor gamma, C/EBP-beta, sterol regulatory element-binding transcription factor 1, adipophilin, stearoyl-CoA desaturase, glycerol 3-phosphate dehydrogenase 1, LIPE, adiponectin, and leptin. All markers tested were found elevated in various amounts (3-70-fold) around day 7 and reached a plateau after day 14 or 21 (5-335-fold). Perilipin as a surface protein around the LGs was confined exclusively to the enlarging LGs. Conclusively, we propose that after the termination of proliferation, HUCSCs possess the biochemical and cellular machinery to successfully differentiate into maturing adipocytes under adipogenic conditions, and this feature will ultimately allow these fetus-derived stem cells to be used for various therapeutic or esthetic purposes.

Extracellular Matrix Components as Modulators of Adult Stem Cell Differentiation in an Adipose System

The viability of a cell-based device may be controlled post-implantation by managing the level of cellular differentiation. Cellular adhesion to extracellular matrix (ECM) proteins is fundamentally linked to tissue development, maintenance of tissue organization, and many pathological conditions. Cellular interaction with ECM regulates the proliferation and differentiation of cells. This study investigates the efficacy of ECM components (laminin and collagen) in modulating the differentiation of adult mouse bone marrow stem cells (D1) to adipocytes. This study should assist in the development of clinically viable soft-tissue implants.

Subcutaneous fat in normal and diseased states

The quest for effective strategies to treat obesity has propelled fat research into an exploration of the molecular processes that drive adipocyte formation, and hence body fat mass. The development of obesity is dependent on the coordinated interplay of adipocyte hypertrophy (increased fat cell size), adipocyte hyperplasia (increased fat cell number), and angiogenesis. Evidence suggests that adipocyte hyperplasia, or adipogenesis, occurs throughout life, both in response to normal cell turnover as well as in response to the need for additional fat mass stores that arises when caloric intake exceeds nutritional requirements. Adipogenesis involves two major events-the recruitment and proliferation of adipocyte precursor cells, called preadipocytes, followed by the subsequent conversion of preadipocytes, or differentiation, into mature fat cells. In vitro studies using experimental and primary preadipocyte cell lines have uncovered the mechanisms that drive the adipogenic process, a tightly controlled sequence of events guided by the strict temporal regulation of multiple inhibitory and stimulatory signaling events involving regulators of cell-cycle functions and differentiation factors. This article reviews the current understanding of adipogenesis with emphasis on the various stages of adipocyte development; on key hormonal, nutritional, paracrine, and neuronal control signals; as well as on the components involved in cell-cell or cell-matrix interactions that are pivotal in regulating fat cell formation. Special consideration is given to clinical applications derived from adipogenesis research with impact on medical, surgical and cosmetic fields.

Role of adipose tissue as an inflammatory organ in human diseases

Reviews on the inflammatory role of adipose tissue outside the field of metabolism are rare. There is increasing evidence provided by numerous basic research studies from nearly all internal medicine subspecializations that adipocytes and adipocytokines are involved in primary inflammatory processes and diseases. Therefore, it is the aim of the present review to discuss and to summarize the current knowledge on the inflammatory role of adipocytokines and special types of regional adipocytes such as retroorbital, synovial, visceral, subdermal, peritoneal, and bone marrow adipocytes in internal medicine diseases. Future clinical and therapeutic implications are discussed.

Ectodomain shedding of preadipocyte factor 1 (Pref-1) by tumor necrosis factor alpha converting enzyme (TACE) and inhibition of adipocyte differentiation

Preadipocyte factor 1 (Pref-1), an epidermal growth factor repeat containing transmembrane protein found in the preadipocytes, inhibits adipocyte differentiation in vitro and in vivo. Here, we examined the processing of membrane form of Pref-1A to release the 50-kDa soluble form that inhibits adipocyte differentiation. The ectodomain cleavage of Pref-1 is markedly enhanced by phorbol 12-myristate 13-acetate in a dose- and time-dependent manner. The basal and stimulated cleavage is inhibited by the broad metalloproteinase inhibitor GM6001, a fact that suggests that cleavage of membrane Pref-1A is dependent on a metalloproteinase. Next, we showed that release of soluble Pref-1A is inhibited by TAPI-0 and by a tissue inhibitor of metalloproteinase-3, TIMP-3, that can inhibit tumor necrosis factor alpha converting enzyme (TACE), but not by TIMP-1 or TIMP-2. On the other hand, overexpression of TACE increases Pref-1 cleavage to produce the 50-kDa soluble form. Furthermore, this cleavage was not detected in cells with TACE mutation or with TACE small interfering RNA. TACE-mediated shedding of Pref-1 ectodomain inhibits adipocyte differentiation of 3T3-L1 cells and in Pref-1-null mouse embryo fibroblasts transduced with Pref-1A. Identification of TACE as the major protease responsible for conversion of membrane-bound Pref-1 to the biologically active diffusible form provides a new insight into Pref-1 function in adipocyte differentiation.

Human Serum from Platelet-Poor Plasma for the Culture of Primary Human Preadipocytes

In adipose tissue engineering, the use of human serum is essential to achieve the goal of an autologous system. Serum from conventional human plasma (SCP) contains platelet-derived growth factor (PDGF), a growth factor known to be both a potent inhibitor of adipose differentiation and also the most important stimulator of proliferation in human serum. Serum from platelet-poor plasma (SPPP) is considered to be PDGF-deprived and should therefore inhibit the differentiation of preadipocytes to adipocytes to a lesser extent. Effective cultivation of preadipocytes with SPPP requires compensating for the missing stimulatory PDGF effect on proliferation. However, the addition of other growth factors to the media needs to provide stimulation of proliferation without significant inhibition of differentiation. Primary human preadipocytes were isolated from adipose tissue samples of 10 healthy human donors and cultured under four different medium conditions (SCP, SPPP, SPPP + 1 nM basic fibroblast growth factor [bFGF], and SPPP + 1 nM epidermal growth factor [EGF]) for five generations. Proliferation activity and differentiation capacity were assessed for each sample, generation, and culture condition by calculating doubling time and measuring glycerol-3-phosphate dehydrogenase (GPDH)-specific activity. The use of SPPP resulted in a marked rise in GPDH activity compared with the cells cultured with SCP. Supplementing SPPP with 1 nM bFGF or EGF increased proliferation activity significantly. SPPP can be considered superior to SCP for the culture of primary human preadipocytes in adipose tissue engineering in terms of proliferation activity and differentiation capacity.

Stromelysin-3 is a potent negative regulator of adipogenesis participating to cancer cell-adipocyte interaction/crosstalk at the tumor invasive front

The initial invasive processes during cancer development remain largely unknown. Stromelysin-3/matrix metalloproteinase 11 (ST3/MMP11) is associated with tumor invasion and poor prognosis. We present novel evidence that adipocytes present at human breast tumor invasive front are induced by cancer cells to express ST3. Using mouse syngeneic model, light and electron microscopy showed that in ST3-deficient mice but not in wild-type mice, forced cancer cell-adipocyte interaction/crosstalk results in adipocyte membrane alteration, allowing cancer cell fat infiltration and death. Thus, adipocytes are involved in initial cancer cell survival into connective tissue, and this effect is ST3 mediated. This suggested that ST3 might play a role in adipocyte metabolism. Accordingly, ST3-deficient mice exhibited fat excess and increased mRNA levels of peroxisome proliferator-activated receptor gamma (PPARgamma) and adipocyte protein 2 (aP2) adipogenic markers, indicating that, in vivo, ST3 negatively regulates fat homeostasis. Moreover, ST3-deficient mouse embryonic fibroblasts exhibited a dramatic enhanced potential to differentiate into adipocytes associated with increased PPARgamma and aP2 expression, and recombinant ST3 treatment reverted their differentiation. Thus, in vitro, ST3 reduces adipocyte differentiation in an autocrine manner. High fibroblasts/adipocytes ratio is a stroma feature, and peritumoral fibroblast origin remains debated. Our results support the concept that invading cancer cells aberrantly restore the negative ST3 function on adipogenesis into proximal adipocytes/preadipocytes, leading to the accumulation/maintenance of a particular peritumoral fibroblast subpopulation. Accordingly, in human breast tumors, we observed that ST3-expressing peritumoral fibroblasts are distinct from alpha-smooth muscle actin-expressing myofibroblasts. This constitutes the first report of implication of a MMP in cancer cell-adipocyte interaction/crosstalk during early steps of connective tissue invasion.

Poly(ethylene glycol) hydrogel system supports preadipocyte viability, adhesion, and proliferation

The ultimate goal of this research is to develop an injectable cell-scaffold system capable of permitting adipogenesis to abrogate soft tissue deficiencies resulting from trauma, tumor resection, and congenital abnormalities. The present work compares the efficacy of photopolymerizable poly(ethylene glycol) and specific derivatives as a scaffold for preadipocyte (adipocyte precursor cell) viability, adhesion, and proliferation. Four variations of a poly(ethylene glycol) scaffold are prepared and examined. The first scaffold consists of poly(ethylene glycol) diacrylate, which is not susceptible to hydrolysis or enzymatic degradation. Preadipocyte death is observed over 1 week in this hydrogel configuration. Adhesion sites, specifically the laminin-binding peptide sequence YIGSR, were incorporated into the second scaffold to promote cellular adhesion as a prerequisite for preadipocyte proliferation. Preadipocytes remain viable in this scaffold system, but do not proliferate in this nondegradable hydrogel. The third scaffold system studied consists of poly(ethylene glycol) modified with the peptide sequence LGPA to permit polymer degradation by cell-secreted collagenase. No adhesion peptide is incorporated into this scaffold system. Cellular proliferation is initially observed, followed by cell death. The previous three scaffold configurations do not permit preadipocyte adhesion and proliferation. In contrast, the fourth system studied, poly(ethylene glycol) modified to incorporate both LGPA and YIGSR, permits preadipocyte adherence and proliferation subsequent to polymer degradation. Our results indicate that a scaffold system containing specific degradation sites and cell adhesion ligands permits cells to adhere and proliferate, thus providing a potential cell-scaffold system for adipogenesis.

Implantation of preadipocyte-loaded hyaluronic acid-based scaffolds into nude mice to evaluate potential for soft tissue engineering

The reconstruction of soft tissue defects following extensive deep burns or tumor resections remains an unresolved problem in plastic and reconstructive surgery since adequate implant materials are still not available. Preadipocytes, immature precursor cells found between mature adipocytes in adipose tissue, are a potential material for soft tissue engineering since they can proliferate and differentiate into adipose tissue after transplantation. In previous studies, we identified hyaluronan benzyl ester (HYAFF 11) sponges to be promising carrier matrices. This study now evaluates, in vitro and in vivo, a new sponge architecture with pores of 400 microm either made of plain HYAFF 11 or HYAFF 11 coated with the extracellular matrix glycosaminoglycan hyaluronic acid. Human preadipocytes were isolated, seeded onto carriers and implanted into nude athymic mice. Explants harvested after 3, 8, and 12 weeks were examined for macroscopical appearance, thickness, weight, pore structure, histology, and immunohistochemistry. Compared to previous studies, we found better penetration of cells into both types of scaffolds, with more extensive formation of new vessels throughout the construct but with only minor adipose tissue. Our encouraging results contribute towards a better seeded and vascularised scaffold but also show that the enhancement of adipogenic conversion of preadipocytes remains a major task for further in vivo experiments.

Changes in integrin expression during adipocyte differentiation

3T3-L1 preadipocytes require cAMP for maximal differentiation. Microarray analysis reveals that the integrins alpha5 and alpha6 are coordinately regulated by cAMP. alpha5 expression is gradually diminished during adipogenesis, whereas alpha6 is increased. Overexpression of alpha5 in preadipocytes results in enhanced proliferation and attenuated differentiation. Conversely, alpha6 overexpression is without effect. The GTPase Rac is normally inhibited during differentiation. However, overexpression of integrin alpha5 increases Rac activity. Constitutively active but not dominant-negative Rac inhibits differentiation when overexpressed in preadipocytes, implying its role downstream of alpha5 integrin in maintaining preadipocytes in an undifferentiated state. Moreover, alpha6 integrin is critically involved in clustering growth-arrested preadipocytes on basement membrane Matrigel. Perturbation of such clustering enhances Rho activity and promotes growth-arrested preadipocytes to reenter the cell cycle. These findings demonstrate a role for integrin alpha6 in connecting morphogenesis with signaling processes leading to terminal differentiation.

Oxygen consumption in undifferentiated versus differentiated adipogenic mesenchymal precursor cells

To date, no adequate implant material for the correction of soft tissue defects such as after extensive deep burns, tumor resections or in congenital defects is available. A biohybrid composed of viable adipose precursor cells and an optimised matrix could help towards a solution. Morphologically, preadipocytes resemble fibroblasts and have not yet built a large cytoplasmic lipid droplet as found in differentiated adipocytes. Additionally, preadipocytes are smaller than mature adipocytes allowing a quicker revascularization after transplantation. Furthermore, transplanted preadipocytes can form adipose tissue in vivo whereas the transplantation of mature adipocytes often gives poor results, i.e. oil cysts or shrinkage of the transplant. Since these observations point to differences in metabolic activity between preadipocytes and adipocytes, we investigated the oxygen consumption of preadipocytes stimulated to undergo differentiation, and fibroblasts, by measuring the respiration with a Clark-type oxygen electrode. Preadipocytes had a significantly lower oxygen consumption than mature adipocytes. This advantage in respiration and the better revascularization of undifferentiated adipose tissue cells allow the development of innovative transplants and point to preadipocytes as promising tool to improve transplantations in adipose tissue reconstruction.

Abundance of two human preadipocyte subtypes with distinct capacities for replication, adipogenesis, and apoptosis varies among fat depots

Fat depots vary in function and size. The preadipocytes that fat cells develop from exhibit distinct regional characteristics that persist in culture. Human abdominal subcutaneous cultured preadipocytes undergo more extensive lipid accumulation, higher adipogenic transcription factor expression, and less TNF-alpha-induced apoptosis than omental preadipocytes. We found higher replicative potential in subcutaneous and mesenteric than in omental preadipocytes. In studies of colonies arising from single preadipocytes, two preadipocyte subtypes were found, one capable of more extensive replication, differentiation, and adipogenic transcription factor expression and less apoptosis in response to TNF-alpha than the other. The former was more abundant in subcutaneous and mesenteric than in omental preadipocyte populations, potentially contributing to regional variation in replication, differentiation, and apoptosis. Both subtypes were found in strains derived from single human preadipocytes stably expressing telomerase, confirming that both subtypes are of preadipocyte lineage. After subcloning of cells of either subtype, both subtypes were found, indicating that switching can occur between subtypes. Thus proportions of preadipocyte subtypes with distinct cell-dynamic properties vary among depots, potentially permitting tissue plasticity through subtype selection during development. Furthermore, mesenteric preadipocyte cell-dynamic characteristics are distinct from omental cells, indicating that visceral fat depots are not functionally uniform.

Mest/Peg1 imprinted gene enlarges adipocytes and is a marker of adipocyte size

Obesity is a common and serious metabolic disorder in the developed world that is occasionally accompanied by type II diabetes, atherosclerosis, hypertension, and hyperlipidemia. We have found that mesoderm-specific transcript (Mest)/paternally expressed gene 1 (Peg1) gene expression was markedly enhanced in white adipose tissue of mice with diet-induced and genetically caused obesity/diabetes but not with streptozotocin-induced diabetes, which does not cause obesity. Administration of pioglitazone, a drug for type II diabetes and activator of peroxisome proliferator-activated receptor (PPAR)gamma, in obese db/db mice reduced the enhanced expression of Mest mRNA in adipose tissue, concomitant with an increase in body weight and a decrease in the size of adipose cells. Ectopic expression of Mest in 3T3-L1 cells caused increased gene expression of adipose markers such as PPARgamma, CCAAT/enhancer binding protein (C/EBP)alpha, and adipocyte fatty acid binding protein (aP)2. In transgenic mice overexpressing Mest in adipose tissue, enhanced expression of the adipose genes was observed. Moreover, adipocytes were markedly enlarged in the transgenic mice. Thus Mest appears to enlarge adipocytes and could be a novel marker of the size of adipocytes.

Maternal nutritional programming of fetal adipose tissue development: Long-term consequences for later obesity

As obesity reaches epidemic levels in the United States there is an urgent need to understand the developmental pathways leading to this condition. Obesity increases the risk of hypertension and diabetes, symptoms of which are being seen with increased incidence in children. Adipocyte development begins in the fetus and, in contrast to all other tissues whose growth ceases in late juvenile life, it has the capacity for "unlimited" growth. In normal healthy individuals, the increase in fat mass with age is accompanied by a parallel increase in cortisol sensitivity, i.e., increased glucocorticoid receptor abundance and increased activity of the enzyme 11beta hydroxysteroid dehydrogenase type 1. Enhanced adipocyte sensitivity to cortisol is promoted in offspring born to mothers that were nutrient-restricted in utero in conjunction with increased peroxisome proliferator activated receptor alpha. This adaptation only appears to be associated with greater fat mass in the offspring when maternal nutrient restriction is confined to late gestation, coincident with the period of maximal fetal growth. In these offspring, increased fat mass is accompanied by glucose intolerance and insulin resistance, in conjunction with an adipose tissue specific reduction in glucose transporter 4 abundance. In conclusion, changes in maternal and, therefore, fetal nutrient supply at specific stages of gestation have the potential to substantially increase the risk of those offspring becoming obese in later life. The extent to which changes in dietary habits, both during pregnancy and in later life, may act to contribute to the current explosion in childhood and adult obesity remains a scientific and public health challenge to us all.

Breast tissue engineering

Tissue engineering has the potential to redefine rehabilitation for the breast cancer patient by providing a translatable strategy that restores the postmastectomy breast mound while concomitantly obviating limitations realized with contemporary reconstructive surgery procedures. The engineering design goal is to provide a sufficient volume of viable fat tissue based on a patient's own cells such that deficits in breast volume can be abrogated. To be sure, adipose tissue engineering is in its infancy, but tremendous strides have been made. Numerous studies attest to the feasibility of adipose tissue engineering. The field is now poised to challenge barriers to clinical translation that are germane to most tissue engineering applications, namely scale-up, large animal model development, and vascularization. The innovative and rapid progress of adipose engineering to date, as well as opportunities for its future growth, is presented.

Progress in adipose tissue construct development

Although the field of tissue engineering has been the focus of a great deal of promise and study, only recently has significant attention been given to the engineering of soft tissues. The applicability of an engineered adipose construct as a basic science model and a reconstructive tool is unquestioned; yet, there have been limitations in previous work, specifically issues of construct size and maintenance over time. This article briefly overviews the pivotal factors necessary for adipocyte growth and differentiation, optimal scaffolds for the engineering of soft tissues, and a means of providing vascular support for these highly demanding cells. Clinical science and bioengineering concepts that may provide the foundation toward the successful in vivo engineering of an adipose tissue construct that maintains its complex three-dimensional shape over time are critically reviewed.

Modulatory role of testosterone in plasma leptin turnover in rats

We explored whether testosterone influences circulating leptin turnover in rats. Sham-operated male and female rats and 21-d gonadectomized rats treated or not treated with testosterone propionate were used. Anesthetized rats were implanted with an iv catheter, and then blood samples were drawn before and throughout a 60-min period following systemic leptin administration. Plasma testosterone, estradiol, and leptin concentrations were monitored. The results indicated that while gonadectomy blunted circulating concentrations of the homologous sex steroid, testosterone therapy, in gonadectomized rats, restored plasma testosterone concentrations to values found in normal male rats. Pharmacokinetic parameters evaluated during the test indicated the following: First, in the overall pharmacokinetic analyses, testosterone therapy in gonadectomized rats induced a more rapid disappearance of leptin from the circulation. Second, orchidectomy significantly enhanced the area under the curve (AUC) of circulating leptin, an effect fully reversed by testosterone treatment. Third, testosterone treatment in ovariectomized rats significantly decreased the AUC of leptin concentrations. Fourth, while gonadectomy alone did not modify circulating leptin half-life, conversely, testosterone therapy in gonadectomized rats decreased leptin halflife in the circulation. Finally, while orchidectomy reduced leptin body clearance, this parameter was increased by androgen therapy in gonadectomized rats. Our results strongly support that testosterone could play a main role in plasma leptin turnover by increasing leptin clearance rate and shortening plasma leptin half-life.