Becoming fat

Involvement of a battery of investigated genes in lipid droplet pathophysiology and associated comorbidities

Lipid droplets (LDs) are highly specialized energy storage organelles involved in the maintenance of lipid homoeostasis by regulating lipid flux within white adipose tissue (WAT). The physiological function of adipocytes and LDs can be compromised by mutations in several genes, leading to NEFA-induced lipotoxicity, which ultimately manifests as metabolic complications, predominantly in the form of dyslipidemia, ectopic fat accumulation, and insulin resistance. In this review, we delineate the effects of mutations and deficiencies in genes - CIDEC, PPARG, BSCL2, AGPAT2, PLIN1, LIPE, LMNA, CAV1, CEACAM1, and INSR - involved in lipid droplet metabolism and their associated pathophysiological impairments, highlighting their roles in the development of lipodystrophies and metabolic dysfunction.

Efficacy and Safety of Cell-Assisted Acellular Adipose Matrix Transfer for Volume Retention and Regeneration Compared to Hyaluronic Acid Filler Injection

BACKGROUND

Cell-assisted acellular adipose matrix (AAM) transfer is a novel technique for soft tissue volume restoration, where AAM acts as a scaffold for tissue proliferation and promotes host cell migration, vascularization, and adipogenesis. This study aimed to evaluate the efficacy and safety of in vivo cell-assisted AAM transfer compared to hyaluronic acid (HA) filler injection.

METHODS

Human adipose tissue was used to manufacture AAM, and murine adipose-derived stem cells (ASCs) were prepared. Nude mice were divided into four groups: AAM transfer (AT), ASC-assisted AAM transfer (CAT), HA filler injection (HI), and ASC-assisted HA filler injection (CHI). Eight weeks post-transfer, in vivo graft volume/weight, histology, and gene expression were analyzed to assess efficacy and safety.

RESULTS

The AAM retained its three-dimensional scaffold structure without cellular components. AT/CAT showed lower volume retention than HA/CHA; however, CAT maintained a similar volume to HA. Histologically, adipogenesis and collagen formation were increased in AT/CAT compared to HA/CHA, with CAT showing the highest levels. CAT also demonstrated superior angiogenesis, adipogenesis, and gene expression (Vegf and Pparg), along with lower Il-6 expression, higher Il-10 expression, and reduced capsule formation, indicating better biocompatibility.

CONCLUSIONS

Cell-assisted AAM transfer is a promising technique for volume retention and tissue regeneration, offering a safe and effective alternative to HA filler injections.

LEVEL OF EVIDENCE III

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Effect of Vitamin D Supplementation in Early Life on Children's Growth and Body Composition: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Vitamin D deficiency during pregnancy or infancy is associated with adverse growth in children. No systematic review has been conducted to summarize available evidence on the effect of vitamin D supplementation in pregnancy and infancy on growth and body composition in children. Objective: We aim to summarize the available evidence on the effect of vitamin D supplementation in pregnancy and infancy on child growth and body composition. Method: A systematic review and meta-analysis were performed on the effects of vitamin D supplementation during early life on children’s growth and body composition (bone, lean and fat). A literature search of randomized controlled trials (RCTs) was conducted to identify relevant studies on the effects of vitamin D supplementation during pregnancy and infancy on children’s body composition (bone, lean and fat) in PubMed, EMBASE and Cochrane Library from inception to 31 December 2020. A Cochrane Risk Assessment Tool was used for quality assessment. The comparison was vitamin D supplementation vs. placebo or standard care. Random-effects and fixed-effect meta-analyses were conducted. The effects are presented as mean differences (MDs) or risk ratios (RRs) with 95% confidence intervals (CIs). Results: A total of 3960 participants from eleven randomized controlled trials were eligible for inclusion. Vitamin D supplementation during pregnancy was associated with higher triceps skinfold thickness (mm) (MD 0.33, 95% CI, 0.12, 0.54; I² = 34%) in neonates. Vitamin D supplementation during pregnancy or infancy was associated with significantly increased length for age z-score in infants at 1 year of age (MD 0.29, 95% CI, 0.03, 0.54; I² = 0%), and was associated with lower body mass index (BMI) (kg/m²) (MD −0.19, 95% CI −0.34, −0.04; I² = 0%) and body mass index z-score (BMIZ) (MD −0.12, 95% CI −0.21, −0.04; I² = 0%) in offspring at 3–6 years of age. Vitamin D supplementation during early life was not observed to be associated with children’s bone, lean or fat mass. Conclusion: Vitamin D supplementation during pregnancy or infancy may be associated with reduced adiposity in childhood. Further large clinical trials of the effects of vitamin D supplementation on childhood body composition are warranted.

Hepatic Interferon Regulatory Factor 6 Alleviates Liver Steatosis and Metabolic Disorder by Transcriptionally Suppressing Peroxisome Proliferator-Activated Receptor γ in Mice

Nonalcoholic fatty liver disease (NAFLD) has become a worldwide epidemic. A large and growing unmet therapeutic need has inspired numerous studies in the field. Integrating the published genomic data available in the Gene Expression Omnibus (GEO) with NAFLD samples from rodents, we discovered that interferon regulatory factor 6 (IRF6) is significantly downregulated in high-fat diet (HFD)-induced fatty liver. In the current study, we identified IRF6 in hepatocytes as a protective factor in liver steatosis (LS). During HFD challenge, hepatic Irf6 was suppressed by promoter hypermethylation. Severity of HFD-induced LS was exacerbated in hepatocyte-specific Irf6 knockout mice, whereas hepatocyte-specific transgenic mice overexpressing Irf6 (IRF6-HTG) exhibited alleviated steatosis and metabolic disorder in response to HFD feeding. Mechanistic studies in vitro demonstrated that hepatocyte IRF6 directly binds to the promoter of the peroxisome proliferator-activated receptor γ (PPARγ) gene and subsequently halts the transcription of Pparγ and its target genes (e.g., genes that regulate lipogenesis and lipid acid uptake) under physiological conditions. Conclusion: Irf6 is downregulated by promoter hypermethylation upon metabolic stimulus exposure, which fail to inhibit Pparγ and its targets, driving abnormalities of lipid metabolism.

Nutritional Regulation of Gene Expression: Carbohydrate-, Fat- and Amino Acid-Dependent Modulation of Transcriptional Activity

The ability to detect changes in nutrient levels and generate an adequate response to these changes is essential for the proper functioning of living organisms. Adaptation to the high degree of variability in nutrient intake requires precise control of metabolic pathways. Mammals have developed different mechanisms to detect the abundance of nutrients such as sugars, lipids and amino acids and provide an integrated response. These mechanisms include the control of gene expression (from transcription to translation). This review reports the main molecular mechanisms that connect nutrients’ levels, gene expression and metabolism in health. The manuscript is focused on sugars’ signaling through the carbohydrate-responsive element binding protein (ChREBP), the role of peroxisome proliferator-activated receptors (PPARs) in the response to fat and GCN2/activating transcription factor 4 (ATF4) and mTORC1 pathways that sense amino acid concentrations. Frequently, alterations in these pathways underlie the onset of several metabolic pathologies such as obesity, insulin resistance, type 2 diabetes, cardiovascular diseases or cancer. In this context, the complete understanding of these mechanisms may improve our knowledge of metabolic diseases and may offer new therapeutic approaches based on nutritional interventions and individual genetic makeup.

Mouse Cardiac Pde1C Is a Direct Transcriptional Target of Pparα

Phosphodiesterase 1C (PDE1C) is expressed in mammalian heart and regulates cardiac functions by controlling levels of second messenger cyclic AMP and cyclic GMP (cAMP and cGMP, respectively). However, molecular mechanisms of cardiac Pde1c regulation are currently unknown. In this study, we demonstrate that treatment of wild type mice and H9c2 myoblasts with Wy-14,643, a potent ligand of nuclear receptor peroxisome-proliferator activated receptor alpha (PPARα), leads to elevated cardiac Pde1C mRNA and cardiac PDE1C protein, which correlate with reduced levels of cAMP. Furthermore, using mice lacking either Pparα or cardiomyocyte-specific Med1, the major subunit of Mediator complex, we show that Wy-14,643-mediated Pde1C induction fails to occur in the absence of Pparα and Med1 in the heart. Finally, using chromatin immunoprecipitation assays we demonstrate that PPARα binds to the upstream Pde1C promoter sequence on two sites, one of which is a palindrome sequence (agcTAGGttatcttaacctagc) that shows a robust binding. Based on these observations, we conclude that cardiac Pde1C is a direct transcriptional target of PPARα and that Med1 may be required for the PPARα mediated transcriptional activation of cardiac Pde1C.

In utero vitamin D deficiency predisposes offspring to long-term adverse adipose tissue effects

The fetal period represents an important window of susceptibility for later obesity and metabolic disease. Maternal vitamin D deficiency (VDD) during pregnancy is a global concern that may have long-lasting consequences on offspring metabolic health. We sought to determine whether a VDD in utero environment affects fetal adipose tissue development and offspring metabolic disease predisposition in adulthood. Furthermore, we sought to explore the extent to which the VDD intrauterine environment interacts with genetic background or postnatal environment to influence metabolic health. Eight-week-old P₀ female C57BL/6J mice were fed either a VDD diet or sufficient diet (VDS) from four weeks before pregnancy (periconception) then bred to male A^vy/a mice. Females were maintained on the diets throughout gestation. At weaning, A^vy/a and a/a male F₁ offspring were randomized to low-fat (LFD) or high-fat diet (HFD) until 19 weeks of age, at which point serum and adipose tissue were harvested for analyses. Mice born to VDD dams weighed less at weaning than offspring born to VDS dams but experienced rapid weight gain in the four weeks post weaning, and acquired a greater ratio of perigonadal (PGAT) to subcutaneous (SQAT) than control offspring. Additionally, these mice were more susceptible to HFD-induced adipocyte hypertrophy. Offspring of VDD dams also had greater expression of Pparg transcript. These novel findings demonstrate that in utero VDD, an easily correctable but highly prevalent health concern, predisposes offspring to long-term adipose tissue consequences and possible adverse metabolic health complications.

Regulation of lipid deposition in farm animals: Parallels between agriculture and human physiology

For many years, clinically oriented scientists and animal scientists have focused on lipid metabolism and fat deposition in various fat depots. While dealing with a common biology across species, the goals of biomedical and food animals lipid metabolism research differ in emphasis. In humans, mechanisms and regulation of fat synthesis, accumulation of fat in regional fat depots, lipid metabolism and dysmetabolism in adipose, liver and cardiac tissues have been investigated. Further, energy balance and weight control have also been extensively explored in humans. Finally, obesity and associated maladies including high cholesterol and atherosclerosis, cardiovascular disease, insulin resistance, hypertension, metabolic syndrome and health outcomes have been widely studied. In food animals, the emphasis has been on regulation of fatty acid synthesis and lipid deposition in fat depots and deposition of intramuscular fat. For humans, understanding the regulation of energy balance and body weight and of prevention or treatment of obesity and associated maladies have been important clinical outcomes. In production of food animals lowering fat content in muscle foods while enhancing intramuscular fat (marbling) have been major targets. In this review, we summarize how our laboratories have addressed the goal of providing lean but yet tasty and juicy muscle food products to consumers. In addition, we here describe efforts in the development of a new porcine model to study regulation of fat metabolism and obesity. Commonalities and differences in regulation of lipid metabolism between humans, rodents and food animals are emphasized throughout this review.

Identification of Creb3l4 as an essential negative regulator of adipogenesis

Understanding the molecular networks that regulate adipogenesis is crucial for combating obesity. However, the identity and molecular actions of negative regulators that regulate the early development of adipocytes remain poorly understood. In this study, we investigated the role of CREB3L4, a member of the CREB3-like family, in the regulation of adiposity. Constitutive overexpression of CREB3L4 resulted in the inhibition of adipocyte differentiation, whereas knockdown of Creb3l4 expression caused differentiation of preadipocytes into mature adipocytes, bypassing the mitotic clonal expansion step. In 3T3-L1 preadipocytes, Creb3l4 knockdown resulted in increased expression of peroxisome proliferator-activated receptor γ (PPARγ2) and CCAAT/enhancer binding protein (C/EBPα), either by increasing the protein stability of C/EBPβ or by decreasing the expression of GATA3, a negative regulator of PPARγ2 expression. Consequently, increased PPARγ2 and C/EBPα levels induced adipocyte differentiation, even in the presence of minimal hormonal inducer. Thus, it can be speculated that CREB3L4 has a role as gatekeeper, inhibiting adipogenesis in 3T3-L1 preadipocytes. Moreover, adipocytes of Creb3l4-knockout mice showed hyperplasia caused by increased adipogenesis, and exhibited improved glucose tolerance and insulin sensitivity, as compared with littermate wild-type mice. These results raise the possibility that Creb3l4 could be a useful therapeutic target in the fight against obesity and metabolic syndrome.

Grain feeding coordinately alters expression patterns of transcription factor and metabolic genes in subcutaneous adipose tissue of crossbred heifers

The ability to improve meat quality and production efficiency in cattle is limited by an inability to enhance marbling and simultaneously limit undesirable adipose tissue accretion. The objective of this study was to examine expression of regulatory genes in subcutaneous (SCF) adipose tissue of heifers in response to increasing days on feed (DOF) and finishing strategy. Crossbred heifers (n = 24) were allotted as follows: Group 1 = 0 d, Group 2 = 99 d on winter annual ryegrass (grass; Lolium multiflorum Lam.), Group 3 = 218 g on grass, Group 4 = 99 d on grass followed by 119 d on grain. Adipose tissue samples were collected at time of harvest and frozen. Carcass characteristics were measured 24 h postharvest. As expected, HCW (P < 0.0001), ribeye area (REA; P < 0.0002), backfat (BF; P < 0.0001), KPH (P < 0.0001), and marbling score (P < 0.0009) increased with DOF though frame score was not different (P < 0.95). Average daily gain decreased with DOF (P < 0.0001). Yield grade increased (P < 0.0014) but cook loss percentage decreased (P < 0.001) with DOF without changes in 24-h pH (P < 0.31). Interestingly, Warner-Bratzler shear force (WBS) was decreased with DOF (P < 0.0089). Meanwhile, BF (P < 0.01) and KPH (P < 0.05) were greater, whereas marbling values trended greater in grain versus grass-finished heifers. Neither ADG (P < 0.89), HCW (P < 0.26), frame score (P < 0.85), nor REA (P < 0.38) were different between these groups. Grain finishing increased yield grade (P < 0.001) but did not affect 24-h pH (P < 0.88), cook loss percentage (P < 0.98), or WBS (P < 0.44) compared with grass-finished heifers. The expression of PPARγ, bone morphogenic protein 2 (BMP2), and SMAD family member 1 (SMAD1) mRNA was upregulated in response to DOF and grain finishing, whereas sterol regulatory element binding protein 1c (SREBP-1c), sonic hedgehog (SHH), chicken ovalbumin protein transcription factor 1 (COUP-TF1), chicken ovalbumin protein transcription factor 2 (COUP-TF2), and preadipocyte factor-1 (PREF-1) mRNA was decreased in response to DOF and grain finishing. These changes were associated with increased expression of lipoprotein lipase (LPL), stearoyl-coenzyme A desaturase (SCD), and fatty acid synthase (FAS) mRNA. In summary, increasing DOF was associated with improved meat quality whereas gene expression studies suggest several novel genes are associated with subcutaneous adipose tissue development in growing and finishing cattle.

Adipose tissue engineering with cells in engineered matrices

Tissue engineering has shown promise for the development of constructs to facilitate large volume soft tissue augmentation in reconstructive and cosmetic plastic surgery. This article reviews the key progress to date in the field of adipose tissue engineering. In order to effectively design a soft tissue substitute, it is critical to understand the native tissue environment and function. As such, the basic physiology of adipose tissue is described and the process of adipogenesis is discussed. In this article, we have focused on tissue engineering using a cell-seeded scaffold approach, where engineered extracellular matrix substitutes are seeded with exogenous cells that may contribute to the regenerative response. The strengths and limitations of each of the possible cell sources for adipose tissue engineering, including adipose-derived stem cells, are detailed. We briefly highlight some of the results from the major studies to date, involving a range of synthetic and naturally derived scaffolds. While these studies have shown that adipose tissue regeneration is possible, more research is required to develop optimized constructs that will facilitate safe, predictable and long-term augmentation in clinical applications.

Preventing and Treating Obesity in Girls and Young Women to Curb the Epidemic

Obesity and its serious comorbidities, type 2 diabetes, coronary heart disease, hypertension, and dyslipidemia, have reached epidemic proportions in adults and children. Female obesity is more prevalent and, thus, has greater epidemiological importance: mothers transmit the disease epigenetically and genetically. Maternal obesity affects maternal health, pregnancy outcome, and fetal, neonatal, childhood, and ultimately adult morbidity and mortality. Obesity is easy to diagnose, as are most of its risk factors, yet very little progress has been made in preventing the disease. During a brief period of rapid early growth, there is imprinting of antecedents of adult obesity and obesity-related disease. Because of the rapidity of this early growth and the relative brevity of the critical period, early recognition and prompt intervention are necessary and possibly sufficient to prevent the development of obesity. Identification of inappropriate rapid weight gain through frequent weighing should trigger immediate adjustment of energy intake, a simple intervention in bottle-fed infants, the ones at greatest risk for becoming obese. This review presents a step-care strategy with fail-safe action levels starting with maternal education and diet, exercise, and behavior modification for mother and child and progressing to drug treatment and, in selected cases, laparoscopic surgery for young women of childbearing age in whom other measures have failed. This approach is predicated on the assumption that careful monitoring and responsive supplementation of potential deficiencies is easier to achieve, more cost-effective, and safer than effectively treating manifest obesity and its comorbidities in adults.

The case for intraocular delivery of PPAR agonists in the treatment of diabetic retinopathy

Background

Systemic therapeutics targeting the peroxisome proliferator-activated receptors have been found to be beneficial in the treatment of diabetic retinopathy. In this paper, we provide a rationale for the use of these therapeutics as intraocular agents. In addition, we introduce the peroxisome proliferator-activated receptors and describe their functions in response to the drugs.

Discussion

Based on the evidence of large-scale clinical studies investigating the systemic administration of fenofibrate, this ligand for peroxisome proliferator-activated receptor-α is potentially a good candidate for intraocular delivery. Here, we describe the mechanisms by which it might be acting to improve diabetic retinopathy, its relative safety and we speculate on how it could be developed for intraocular delivery.

Summary

In this paper, we provide a rationale for the further investigation of peroxisome proliferator-activated receptor-α agonists as intraocular agents for the treatment of diabetic retinopathy.

Bisphenol A-mediated suppression of LPL gene expression inhibits triglyceride accumulation during adipogenic differentiation of human adult stem cells

The endocrine disrupting chemical, bisphenol A (BPA), has been shown to accelerate the rate of adipogenesis and increase the amount of triglyceride accumulation during differentiation of 3T3-L1 preadipocytes. The objective of this study was to investigate if that observation is mirrored in human primary cells. Here we investigated the effect of BPA on adipogenesis in cultured human primary adult stem cells. Continuous exposure to BPA throughout the 14 days of differentiation dramatically reduced triglyceride accumulation and suppressed gene transcription of the lipogenic enzyme, lipoprotein lipase (LPL). Results presented in the present study show for the first time that BPA can reduce triglyceride accumulation during adipogenesis by attenuating the expression of LPL gene transcription. Also, by employing image cytometric analysis rather than conventional Oil red O staining techniques we show that BPA regulates triglyceride accumulation in a manner which does not appear to effect adipogenesis per se.

The performance of decellularized adipose tissue microcarriers as an inductive substrate for human adipose-derived stem cells

With the aim of developing a clinically-translatable cell expansion and delivery vehicle for adipose tissue engineering, the adipogenic differentiation of human adipose-derived stem cells (ASCs) was investigated on microcarriers fabricated from human decellularized adipose tissue (DAT). ASCs seeded on the DAT microcarriers and cultured in adipogenic differentiation medium within a low-shear spinner culture system demonstrated high levels of adipogenic differentiation, as measured by the expression of adipogenic genes, glycerol-3-phosphate dehydrogenase (GPDH) enzyme activity, and intracellular lipid accumulation. In contrast, gelatin microcarrier controls did not demonstrate significant adipogenesis, emphasizing the role of the native matrix in mediating ASC differentiation. Interestingly, ASCs cultured on the DAT microcarriers in proliferation medium expressed elevated levels of the adipogenic markers, suggesting that the DAT provided an adipo-inductive substrate for the human ASCs. In vivo testing of the DAT and gelatin microcarriers in a subcutaneous Wistar rat model confirmed injectability and demonstrated stable volume retention over 28 days. Under histological analysis, the DAT microcarriers demonstrated no evidence of immunogenicity or cytotoxicity, with the DAT supporting cellular infiltration and tissue remodeling. Pre-seeding the DAT microcarriers with allogenic rat ASCs enhanced cellularity and angiogenesis within the implant region.

The effect of serial passaging on the proliferation and differentiation of bovine adipose-derived stem cells

Adipose-derived stem cells (ASCs) represent an excellent cell source for the development of regenerative therapies for a broad variety of tissue disorders. Commonly, in vitro expansion is necessary to obtain sufficient cell populations for research purposes and clinical applications. Although it has been demonstrated that human ASCs can maintain their adipogenic, chondrogenic and osteogenic potential in long-term culture (up to 15 passages), it is not guaranteed that a satisfactory level of differentiation is achievable in later passages. In this study, we investigated the self-renewal and multilineage differentiation capacity of bovine ASCs, isolated from the interdigital fat pad, and explored how serial passaging influences the cells. A proliferation study examined the changes in growth kinetics from passage 1 to 5, and multilineage (adipogenesis, chondrogenesis and osteogenesis) differentiation studies were conducted to compare the potential between passage 2 (P2) and passage 5 (P5). From the proliferation study, a statistically significant change in the doubling time did not appear until P5. In the differentiation study, both P2 and P5 ASCs could be stimulated to undergo multilineage differentiation under specific culturing conditions. However, adipogenic and chondrogenic cultures showed significantly lower levels of differentiation in the P5-induced cultures. In contrast, P5-induced osteogenic cultures had higher alkaline phosphatase enzyme activity than P2-induced cultures, suggesting an increase in the osteogenic response with serial passaging. Overall, bovine ASCs are capable of self-renewal and multilineage differentiation; however, long-term in vitro expansion has a negative effect on adipogenic and chondrogenic differentiation, while potentially favoring osteogenesis.

The inhibitory effect of Lactobacillus plantarum KY1032 cell extract on the adipogenesis of 3T3-L1 Cells

Some probiotics and their cell components are known to modulate lipid metabolism in vitro and/or in vivo. This study was carried out to investigate possible anti-adipogenic action of a probiotic cell extract, Lactobacillus plantarum KY1032 cell extract (KY1032-CE), in vitro using 3T3-L1 cells. Lipid regulation in the cell culture system was assessed by AdipoRed assay and Oil red O staining of intracellular lipids and real-time polymerase chain reaction and western blot analysis of adipogenesis-related factors. AdipoRed assay revealed that KY1032-CE treatment significantly decreased lipid accumulation in maturing 3T3-L1 preadipocytes in a dose-dependent manner. Oil red O staining demonstrated that KY1032-CE reduced the number of lipid-containing rounded cells. KY1032-CE down-regulated the mRNA and protein expression of four adipocyte-specific genes: peroxisome proliferator-activated receptor-γ2, CCAAT/enhancer binding protein-α, fatty acid synthase, and adipocyte-fatty acid binding protein. Accordingly, these results indicate that KY1032-CE can reduce fat mass by modulating adipogenesis in maturing preadipocytes. Further studies are needed to elucidate its mode of actions in efficacy tests of KY1032-CE in vivo.

Effect of resveratrol on fat mobilization

Higher levels of body fat are associated with increased risk for development of numerous adverse health conditions. Phytochemicals are potential agents to inhibit differentiation of preadipocytes, stimulate lipolysis, and induce apoptosis of existing adipocytes, thereby reducing adipose tissue mass. Resveratrol decreased adipogenesis and viability in maturing preadipocytes; these effects were mediated not only through down-regulating adipocyte specific transcription factors and enzymes but also by genes that modulate mitochondrial function. Additionally, resveratrol increased lipolysis and reduced lipogenesis in mature adipocytes. In addition, combining resveratrol with other natural products produced synergistic activities from actions on multiple molecular targets in the adipocyte life cycle. Treatment of mice with resveratrol alone was shown to improve resistance to weight gain caused by a high-fat diet. Moreover, dietary supplementation of aged ovariectomized rats with a combination of resveratrol and vitamin D, quercetin, and genistein not only decreased weight gain but also inhibited bone loss. Combining several phytochemicals, including resveratrol, or using them as templates for synthesizing new drugs, provides a large potential for using phytochemicals to target adipocyte adipogenesis, apoptosis, and lipolysis.

Fabrication of porous extracellular matrix scaffolds from human adipose tissue

Adipose tissue is found over the whole body and easily obtained in large quantities with minimal risk by a common surgical operation, liposuction. Although liposuction was originally intended for the removal of undesired adipose tissue, it may provide an ideal material for tissue engineering scaffolds. Here we present novel, porous scaffolds prepared from human adipose tissues. The scaffolds were fabricated in a variety of macroscopic shapes such as round dishes, squares, hollow tubes, and beads. The microscopic inner porous structure was controlled by the freezing temperature, with a decrease in pore size as the freezing temperature decreased. The scaffold prepared from human adipose tissue contains extracellular matrix components including collagen. Preliminary in vitro studies showed that human adipose-derived stem cells attached to a human extracellular matrix scaffold and proliferated. This scaffold based on human adipose tissue holds great promise for many clinical applications in regenerative medicine, particularly in patients requiring soft-tissue regeneration.

Coactivators in PPAR-Regulated Gene Expression

Peroxisome proliferator-activated receptor (PPAR)alpha, beta (also known as delta), and gamma function as sensors for fatty acids and fatty acid derivatives and control important metabolic pathways involved in the maintenance of energy balance. PPARs also regulate other diverse biological processes such as development, differentiation, inflammation, and neoplasia. In the nucleus, PPARs exist as heterodimers with retinoid X receptor-alpha bound to DNA with corepressor molecules. Upon ligand activation, PPARs undergo conformational changes that facilitate the dissociation of corepressor molecules and invoke a spatiotemporally orchestrated recruitment of transcription cofactors including coactivators and coactivator-associated proteins. While a given nuclear receptor regulates the expression of a prescribed set of target genes, coactivators are likely to influence the functioning of many regulators and thus affect the transcription of many genes. Evidence suggests that some of the coactivators such as PPAR-binding protein (PBP/PPARBP), thyroid hormone receptor-associated protein 220 (TRAP220), and mediator complex subunit 1 (MED1) may exert a broader influence on the functions of several nuclear receptors and their target genes. Investigations into the role of coactivators in the function of PPARs should strengthen our understanding of the complexities of metabolic diseases associated with energy metabolism.

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.

Isolation and differentiation of chicken mesenchymal stem cells from bone marrow

Mesenchymal stem cells (MSCs) are multipotent progenitor cells found in bone marrow that have the capacity of differentiating into bone, cartilage, fat, muscle, and other tissues. Chicken MSCs were isolated from 1- to 14-day-old chickens. Microscopically, the cultured cells showed morphology resembling fibroblasts and divided actively. Chicken MSCs expressed the transcription factors PouV, Sox2, and Nanog, which have been shown to be critical for stem cell self-renewal and pluripotency. The multilineage differentiation potential of chicken MSCs was revealed by their ability to undergo adipogenic, osteogenic, and chondrogenic differentiation. Like mammalian MSCs, chicken MSCs also had immunoregulatory activity and inhibited in vitro mitogenic response of T cells. The inhibition of mitogenic response of T cells correlated with the production of nitric oxide (NO) in cultures containing MSCs and T cells. Our data show for the first time that MSCs can be isolated from postnatal chicken bone marrow and these cells are capable of in vitro multiplication and multilineage differentiation, thus making them a suitable model in the field of stem cell research.

Decreased PPAR gamma expression compromises perigonadal-specific fat deposition and insulin sensitivity

Mutations and polymorphisms in PPARG have been linked to adiposity and partial lipodystrophy in humans. However, how disturbances in PPARG lead to depot-specific effects on adipose tissue, as shown by the characteristic aberrant fat distribution in patients, remains unclear. By manipulating the 3'-untranslated region of the Pparg gene, we have generated mice with peroxisome proliferator-activated receptor gamma (PPAR gamma) gene expression ranging from 25% to 100% normal. Basal levels of PPAR gamma transcripts between 50% and approximately 100% had no significant effect on body weight, fat mass, and insulin sensitivity. In contrast, mice with 25% normal PPAR gamma expression exhibited reduced body weight and total fat mass, insulin resistance, and dyslipidemia. Interestingly, fat mass was selectively reduced in perigonadal depot without significant changes in inguinal and other depots. Expression of adipogenic factor CCAAT enhancer binding protein-alpha and some other metabolic genes containing peroxisome proliferator response element were reduced in a perigonadal depot-specific fashion. This was further associated with depot-specific reduction in the expression of adipokines, increased expression of TNFalpha, and increased ectopic lipid deposition in muscles. Together, these results underscore the differential sensitivity of the individual fat depots on PPAR gamma availability as an underlying mechanism of partial lipodystrophy.

Resveratrol induces apoptosis and inhibits adipogenesis in 3T3-L1 adipocytes

Resveratrol, a phytoallexin, has recently been reported to slow aging by acting as a sirtuin activator. Resveratrol also has a wide range of pharmacological effects on adipocytes. In this study, we investigated the effects of resveratrol on adipogenesis and apoptosis using 3T3-L1 cells. In mature adipocytes, 100 and 200 microM resveratrol decreased cell viability dose-dependently by 23 +/- 2.7%, and 75.3 +/- 2.8% (p < 0.0001), respectively, after 48 h treatment, and 100 microM resveratrol increased apoptosis by 76 +/- 8.7% (p < 0.0001). Resveratrol at 25 and 50 microM decreased lipid accumulation in maturing preadipocytes significantly by 43 +/- 1.27% and 94.3 +/- 0.3% (p < 0.0001) and decreased cell viability by 25 +/- 1.3% and 70.4 +/- 1.6% (p < 0.0001), respectively. In order to understand the anti-adipogenic effects of resveratrol, maturing 3T3-L1 preadipocytes were treated with 25 microM resveratrol and the change in the expression of several adipogenic transcription factors and enzymes was investigated using real-time RT-PCR. Resveratrol down-regulated the expression of PPAR gamma, C/EBP alpha, SREBP-1c, FAS, HSL, LPL and up-regulated the expression of genes regulating mitochondrial activity (SIRT3, UCP1 and Mfn2). These results indicate that resveratrol may alter fat mass by directly affecting cell viability and adipogenesis in maturing preadipocytes and inducing apoptosis in adipocytes and thus may have applications for the treatment of obesity.

Cidea is associated with lipid droplets and insulin sensitivity in humans

Storage of energy as triglyceride in large adipose-specific lipid droplets is a fundamental need in all mammals. Efficient sequestration of fat in adipocytes also prevents fatty acid overload in skeletal muscle and liver, which can impair insulin signaling. Here we report that the Cide domain-containing protein Cidea, previously thought to be a mitochondrial protein, colocalizes around lipid droplets with perilipin, a regulator of lipolysis. Cidea-GFP greatly enhances lipid droplet size when ectopically expressed in preadipocytes or COS cells. These results explain previous findings showing that depletion of Cidea with RNAi markedly elevates lipolysis in human adipocytes. Like perilipin, Cidea and the related lipid droplet protein Cidec/FSP27 are controlled by peroxisome proliferator-activated receptor gamma (PPARgamma). Treatment of lean or obese mice with the PPARgamma agonist rosiglitazone markedly up-regulates Cidea expression in white adipose tissue (WAT), increasing lipid deposition. Strikingly, in both omental and s.c. WAT from BMI-matched obese humans, expression of Cidea, Cidec/FSP27, and perilipin correlates positively with insulin sensitivity (HOMA-IR index). Thus, Cidea and other lipid droplet proteins define a novel, highly regulated pathway of triglyceride deposition in human WAT. The data support a model whereby failure of this pathway results in ectopic lipid accumulation, insulin resistance, and its associated comorbidities in humans.

Isomer-specific regulation of differentiating pig preadipocytes by conjugated linoleic acids

Conjugated linoleic acids are a group of geometric and positional isomers of linoleic acid that decrease body fat in growing animals by a poorly understood mechanism. The objective of this study was to investigate the isomer-specific effect of CLA on the proliferation and differentiation of pig preadipocytes in primary culture. The effect of CLA on preadipocyte proliferation was determined using cleavage of the tetrazolium salt, WST-1, as a marker for proliferation. Preadipocyte number was decreased in a dose-dependent fashion by trans-12,cis-10 CLA (P < 0.05). No other fatty acid affected preadipocyte number. Differentiation was monitored on d 10 after induction morphologically, enzymatically, and by measuring the mRNA abundance of key adipogenic transcription factors. Both a crude CLA preparation containing a mixture of CLA isomers (CLA-mix) and the pure trans-10,cis-12 CLA isomer inhibited glycerol-3-phosphate dehydrogenase (GPDH) activity in a dose-dependent fashion, with trans-10,cis-12 CLA being more potent (P < 0.01) than the CLA-mix. Cis-9,trans-11 CLA failed to decrease GPDH activity; however, increasing concentrations of cis-9,trans-11 CLA tended to blunt the inhibitory effect of trans-10,cis-12 CLA on GPDH activity (P < 0.09), suggesting that cis-9,trans-11 CLA may antagonize the action of trans-10,cis-12 CLA in porcine adipocytes. Finally, the isomer-specific effect of CLA on adipogenic transcription factor gene expression was investigated. Trans-10,cis-12 CLA decreased expression of peroxisome proliferator-activated receptor gamma (PPAR gamma; P < 0.01) and sterol regulatory element-binding protein-1c (SREBP-1c; P < 0.05) mRNA, while failing to alter the expression of CCAAT/enhancer binding protein alpha (C/EBPalpha) mRNA. Interestingly, both the CLA-mix and the trans-10,cis-12 CLA isomer increased the mRNA abundance of chicken ovalbumin upstream promoter transcription factor 1 (COUP-TF; P < 0.002). No other fatty acid affected COUP-TF mRNA levels. Collectively these data support the concept that CLA decreases fat accretion in pigs, in part by inhibiting preadipocyte proliferation and differentiation, with trans-10,cis-12 CLA being an active isomer eliciting these effects. Furthermore, trans-10,cis-12 CLA inhibits porcine preadipocyte differentiation by a mechanism that involves the down-regulation of PPARgamma and SREBP-1c mRNA. This mechanism is independent of changes in C/EBPalpha mRNA abundance and may involve COUP-TF.

RNAi screens reveal novel metabolic regulators: RIP140, MAP4k4 and the lipid droplet associated fat specific protein (FSP) 27

Adipose tissue modulates whole body metabolism and insulin sensitivity by controlling circulating lipid levels and producing molecules that can regulate fatty acid metabolism in such tissues as muscle and liver. We have developed RNA interference (RNAi) screens to identify genes in cultured adipocytes that regulate insulin signalling and key metabolic pathways. These short interfering RNA (siRNA)-based screens identified the transcriptional corepressor receptor interacting protein 140 (RIP140) (J Clin Invest 116: 125, 2006) and the mitogen-activated protein kinase (MAP4k4) (Proc Natl Acad Sci USA 103: 2087, 2006) as negative regulators of insulin-responsive hexose uptake and oxidative metabolism. Gene expression profiling revealed that RIP140 depletion upregulates the expression of clusters of genes in the pathways of glucose uptake, glycolysis, tricarboxylic acid cycle, fatty acid oxidation, mitochondrial biogenesis and oxidative phosphorylation. RIP140-null mice resist weight gain on a high-fat diet and display enhanced glucose tolerance. MAP4k4 depletion in adipocytes increases many of the RIP140-sensitive genes, increases adipogenesis and mediates some actions of tumour necrosis factor-alpha (TNF-alpha). Remarkably, another hit in our RNAi screens was fat specific protein 27 (FSP27), a highly expressed isoform of Cidea. We discovered that FSP27 unexpectedly associates specifically with lipid droplets and regulates fat storage. We conclude that RIP140, MAP4k4 and the novel lipid droplet protein FSP27 are powerful regulators of adipose tissue metabolism and are potential therapeutic targets for controlling metabolic disease. The discovery of these novel proteins validates the power of RNAi screening for discovery of new therapeutic approaches to type 2 diabetes and obesity.

Chondrogenesis, osteogenesis and adipogenesis of canine mesenchymal stem cells: a biochemical, morphological and ultrastructural study

Musculoskeletal diseases with osteochondrotic articular cartilage defects, such as osteoarthritis, are an increasing problem for humans and companion animals which necessitates the development of novel and improved therapeutic strategies. Canine mesenchymal stem cells (cMSCs) offer significant promise as a multipotent source for cell-based therapies and could form the basis for the differentiation and cultivation of tissue grafts to replace damaged tissue. However, no comprehensive analysis has been undertaken to characterize the ultrastructure of in vitro differentiated cMSCs. The main goal of this paper was to focus on cMSCs and to analyse their differentiation capacity. To achieve this aim, bone marrow cMSCs from three canine patients were isolated, expanded in monolayer culture and characterized with respect to their ability for osteogenic, adipogenic and chondrogenic differentiation capacities. cMSCs showed proliferative potential and were capable of osteogenic, adipogenic and chondrogenic differentiation. cMSCs treated with the osteogenic induction medium differentiated into osteoblasts, produced typical bone matrix components, beta1-integrins and upregulated the osteogenic specific transcription factor Cbfa-1. cMSCs treated with the adipogenic induction medium showed typical adipocyte morphology, produced adiponectin, collagen type I and beta1-integrins, and upregulated the adipogenic specific transcription factor PPAR-gamma. cMSCs treated with the chondrogenic induction medium exhibited a round to oval shape, produced a cartilage-specific extracellular matrix, beta1-integrins and upregulated the chondrogenic specific transcription factor Sox9. These results demonstrate, at the biochemical, morphological and ultrastructural levels, the multipotency of cMSCs and thus highlight their potential therapeutic value for cell-based tissue engineering.

Effects of RXRalpha gene silencing on the porcine adipocyte differentiation in vitro

The elucidation of the molecular mechanism of porcine adipocyte differentiation is important not only to domestic animal industry, but also to medical science because of the similarities in the trait of body lipid deposition between human and pigs. In this study, we investigated the roles of RXRalpha in porcine (Sus scrofa) adipocyte differentiation by using RNAi method and primary cultured porcine adipocytes. With the transfection of RXRalpha-siRNA, the gene and protein expressions of RXRalpha were successfully inhibited in differentiating porcine adipocytes. By the RXRalpha gene silencing, the adipocyte differentiation, as characterized by lipid accumulation and GPDH activity, was suppressed. Furthermore, in association with the decrease in RXRalpha gene expression level, PPARgamma and C/EBPalpha genes expression level also decreased, suggesting that RXRalpha is involved in their expression. Thus, our study clearly demonstrated the pivotal roles of RXRalpha in porcine adipocyte differentiation.

Pathophysiological roles of ASK1-MAP kinase signaling pathways

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogenactivated protein kinase (MAPK) kinase kinase that activates JNK and p38 kinases. ASK1 is activated by various stresses, such as reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, lipopolysaccharide (LPS) and calcium influx which are thought to be responsible for the pathogenesis or exacerbations of various human diseases. Recent studies revealed the involvement of ASK1 in ROS- or ER stressrelated diseases, suggesting that ASK1 may be a potential therapeutic target of various human diseases. In this review, we focus on the current findings for the relationship between pathogenesis and ASK1-MAPK pathways.

Adipogenesis of murine embryonic stem cells in a three-dimensional culture system using electrospun polymer scaffolds

A mechanistic understanding of adipose tissue differentiation is critical for the treatment and prevention of obesity and type 2 diabetes. Conventional in vitro models of adipogenesis are preadipocytes or freshly isolated adipocytes grown in two-dimensional (2D) cultures. Optimal results using in vitro tissue culture models can be expected only when adipocyte models closely resemble adipose tissue in vivo. Thus the design of an in vitro three-dimensional (3D) model which faithfully mimics the in vivo environment is needed to effectively study adipogenesis. Pluripotent embryonic stem (ES) cells are a self-renewing cell type that can readily be differentiated into adipocytes. In this study, a 3D culture system was developed to mimic the geometry of adipose tissue in vivo. Murine ES cells were seeded into electrospun polycaprolactone scaffolds and differentiated into adipocytes in situ by hormone induction as demonstrated using a battery of gene and protein expression markers along with the accumulation of neutral lipid droplets. Insulin-responsive Akt phosphorylation, and beta-adrenergic stimulation of cyclic AMP synthesis were demonstrated in ES cell-derived adipocytes. Morphologically, ES cell-derived adipocytes resembled native fat cells by scanning electron and phase contrast microscopy. This tissue engineered ES cell-matrix model has potential uses in drug screening and other therapeutic developments.

A pericellular collagenase directs the 3-dimensional development of white adipose tissue

White adipose tissue (WAT) serves as the primary energy depot in the body by storing fat. During development, fat cell precursors (i.e., preadipocytes) undergo a hypertrophic response as they mature into lipid-laden adipocytes. However, the mechanisms that regulate adipocyte size and mass remain undefined. Herein, we demonstrate that the membrane-anchored metalloproteinase, MT1-MMP, coordinates adipocyte differentiation in vivo. In the absence of the protease, WAT development is aborted, leaving tissues populated by mini-adipocytes which render null mice lipodystrophic. While MT1-MMP preadipocytes display a cell autonomous defect in vivo, null progenitors retain the ability to differentiate into functional adipocytes during 2-dimensional (2-D) culture. By contrast, within the context of the 3-dimensional (3-D) ECM, normal adipocyte maturation requires a burst in MT1-MMP-mediated proteolysis that modulates pericellular collagen rigidity in a fashion that controls adipogenesis. Hence, MT1-MMP acts as a 3-D-specific adipogenic factor that directs the dynamic adipocyte-ECM interactions critical to WAT development.

Statins and bone metabolism

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are potent inhibitors of cholesterol biosynthesis. Cholesterol-lowering therapy using statins significantly reduces the risk of coronary heart disease. However, extensive use of statins leads to increases of other undesirable as well as beneficial effects, so-called pleiotropic effects. With respect to these effects, statins augment the expression of bone morphogenetic protein-2, a potent simulator of osteoblast differentiation and its activity, and promote mineralization by cultured osteoblasts, indicating that statins have an anabolic effect on bone. Chronic administration of statins in ovariectomized (OVX) rats modestly increases bone mineral density (BMD) of cancellous bone but not of compact bone. In clinical studies, there are conflicting results regarding the clinical benefits of this therapy for the treatment of osteoporosis. Observational studies suggest an association between statin use and reduction in fracture risk. Clinical trials reported no effect of statin treatment on BMD in hip and spine, and on bone turnover. Statins also may influence oral osseous tissues. Administration of statins in combination with osteoporosis therapy appears to improve alveolar bone architecture in the mandibles of OVX rats with maxillary molar extraction. Statins continue to be considered as potential therapeutic agents for patients with osteoporosis and possibly with periodontal disease. Development of new statins that are more specific and potent for bone metabolism will greatly increase the usefulness of these drugs for the treatment of bone diseases.

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.

Differentiation-dependent regulation of the cyclooxygenase cascade during adipogenesis suggests a complex role for prostaglandins

AIM

A thorough understanding of the mechanisms of adipocyte differentiation and metabolism is important for the prevention and/or treatment of obesity and its complications, including type 2 diabetes mellitus. A complex role for prostaglandins (PGs) in adipogenesis is suggested. We examined the expression and cellular localization of enzymes in the cyclooxygenase (COX) cascade that synthesize PGs as well as the PG profile as a function of differentiation status in 3T3-L1 cells.

METHODS

Murine 3T3-L1 preadipocytes were used as a model for studies of adipocyte differentiation induced by a hormone cocktail and compared with the parental fibroblastic line NIH 3T3. Both cell lines were incubated in maintenance medium or differentiation medium. Nine days after differentiation, the expression of enzymes in the COX cascade was evaluated by immunoblot analysis, reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry, and PG formation was examined using enzyme immunoassay.

RESULTS

A differentiation-dependent diminution of COX-1 and COX-2 mRNA and cognate proteins in 3T3-L1 cells was observed. PG release, including PGE(2), 6-keto PGF(1alpha), PGD(2) and 15d-PGJ(2), significantly decreased following differentiation in 3T3-L1 cells (anova/Tukey, p < 0.05). However, microsomal PGE synthase (mPGES) and lipocalin-type PGD synthase (L-PGDS) were selectively upregulated. Immunocytochemistry revealed that COX-1 and COX-2 became intracellularly more diffuse upon differentiation, whereas mPGES was redistributed to the nuclear compartment.

CONCLUSIONS

Regulation of PG formation and COX-2 expression in 3T3-L1 cells is differentiation-dependent and involves changes in the levels of gene expression of the individual isoforms as well as redistribution of the enzymes within cellular compartments.

Identification of new acyl-CoA binding protein transcripts in human and mouse

The ubiquitously expressed acyl-CoA binding protein (ACBP) is involved in lipid metabolism and is regulated by hormones and feeding status via transcription factors such as sterol regulatory element-binding protein 1 and peroxisome proliferator-activated receptor-gamma (PPARgamma). In humans, two transcripts encoding proteins of 86 and 104 amino acids are known, whereas in mouse only one protein of 86 amino acids is described. We identified new transcripts in human and mouse tissues, that had been generated by alternative first exon usage. Quantitative RT-PCR analyses showed a high expression of the new human transcript, ACBP-1c, in adipose tissue. By promoter reporter gene assays, specific regulation of this transcript by PPARgamma2 was revealed, implicating the usage of an alternative promoter that contains a PPARgamma responsive element. Subcellular localizations of the known human proteins and the new variant showed an occurrence in cytoplasma and nucleus. Reported studies concerning ACBP gene regulation should be re-evaluated with respect to a new ACBP gene model. Given the fact that the new variant is highly expressed in adipose tissue and a PPARgamma target, it might be relevant for diseases like diabetes and obesity.

Anti-adipogenic effect of PDGF is reversed by PKC inhibition

Healthy adipose tissue function depends on adipogenesis. The capacity to form new adipocytes prevents the emergence of insulin-resistant hypertrophied adipocytes, as well as the deleterious lipid deposition in muscle, liver, and pancreas. It is therefore important to understand how adipogenesis is modulated. Platelet-derived growth factor (PDGF) is anti-adipogenic, but the stage of differentiation that it targets, and the signaling pathways that it triggers, are not defined. We have studied the inhibitory effect of PDGF on murine 3T3-L1 preadipocyte and human preadipocyte differentiation. There was a significant attenuation in the protein expression of the adipogenic transcription factors, PPARgamma and C/EBPalpha, as well as in the levels of later differentiation markers, including adiponectin, aP2, and fatty acid synthase. PDGF treatment resulted in the persistence of PDGF receptor and PKCalpha expression, in contrast to the expected downregulation of both proteins that occurs during differentiation. Inactivation of conventional PKC isoforms, by bisindolylmaleimide I or PKC pseudosubstrate M20-28, partially reversed the inhibition of 3T3-L1 and human preadipocyte differentiation by PDGF, as assessed by fatty acid synthase expression and morphological appearance.

Adipose tissue model using three-dimensional cultivation of preadipocytes seeded onto fibrous polymer scaffolds

A better understanding of the mechanism of adipose tissue differentiation is of paramount importance in the development of therapeutic strategies for the treatment and prevention of obesity and type 2 diabetes mellitus. Optimal results using tissue culture models can be expected only when the in vitro adipocyte resembles adipose tissue in vivo as closely as possible. In this study, we used tissue-engineering principles to develop a three-dimensional (3-D) culture system to mimic the geometry of adipose tissue in vivo. Mouse preadipocyte 3T3-L1 cells were seeded onto nonbiodegradable fibrous polyethylene terephthalate scaffolds and differentiated with a hormone cocktail consisting of insulin, dexamethasone, isobutylmethylxanthine, and fetal calf serum. Cell morphology, growth, differentiation, and function were studied by immunocytochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, enzyme-linked immunosorbent assay, and oil red O staining. Cells grown on 3-D fibrous scaffolds were differentiated in situ by hormone induction with high efficiency (approximately 90%) as shown by scanning electron microscopy. Immunocytochemistry, immunoblot analysis, and RT-PCR revealed that the 3-D constructs expressed adipocyte-specific genes, including peroxisome proliferator-activated receptor gamma, leptin, adipsin, aP2, adiponectin, GLUT4, and resistin. Adipocytes matured on 3-D constructs secreted leptin at levels even greater than that of fully differentiated adipocytes in 2-D conventional cell cultures. Finally, adipocyte-specific phenotypic function was demonstrated by accumulation of neutral lipids in larger fat droplets. In conclusion, preadipocytes grown on 3-D matrices acquire morphology and biological features of mature adipocytes. This new culture model should have significant utility for in vitro studies of adipocyte cell biology and development.

Removal of serum factors by charcoal treatment promotes adipogenesis via a MAPK-dependent pathway

In vitro differentiation of the progenitor cells or preadipocytes into adipocytes is usually achieved by adding an adipogenic mixture (isobutylmethylxanthine, dexamethasone, and insulin, IDI) to medium supplemented with fetal bovine serum (FBS). To study the effects of steroid hormones in vitro, endogenous hormones, growth factors and cytokines are removed by charcoal stripping of serum. However, the effects of charcoal-stripped serum (CS-FBS) per se on adipogenesis have been ignored. Here, we showed that alkaline phosphate activity and nodule formation of osteoprogenitor KS483 cells were lower in CS-FBS than in FBS. Concurrently, abundant amounts of adipocytes were only observed in KS483 cells cultured with CS-FBS, irrespective of the brands of serum used. Inhibition of the p42/44 MAPK pathway by its specific inhibitor PD98059 increased adipogenesis of KS483 cells with FBS, whereas activation of this signalling pathway by EGF blocked adipogenesis of these cells with CS-FBS. Furthermore, the p42/44 MAPK phosphorylation of KS483 cells cultured with CS-FBS was decreased compared with FBS. We concluded that charcoal-stripping of serum removed stimulators of the MAPK signalling pathway and in turn led to downregulation of osteogenesis and upregulation of adipogenesis. Interestingly, the adipogenic mixture IDI stimulated adipogenesis of KS483 cells cultured with CS-FBS, but not with FBS. Furthermore, differential effects of genistein on adipogenesis were observed in KS483 cells cultured with FBS or CS-FBS in combination with IDI. Our results showed that charcoal stripping of serum affected the commitment of KS483 cells and therefore differentially regulated adipogenesis influenced by IDI alone and in combination with genistein.

Regulation of differentiating pig preadipocytes by retinoic acid

All-trans retinoic acid (ATRA) potently inhibits the differentiation of porcine preadipocytes in primary culture; however, the mechanism by which ATRA exerts this effect in pigs is poorly understood. The objective of this study was to use retinoid receptor-specific ligands to investigate the mechanism underlying the antiadipogenic action of retinoids in cultured pig preadipocytes by identifying the retinoid receptor mediating this action and examining the effect of retinoids on the expression of key adipogenic transcription factors. Stromal-vascular cells were harvested from porcine adipose tissue and cultured in serum-free medium. Glycerol-3-phoshphate dehydrogenase (GPDH) activity, a late marker of preadipocyte differentiation, was decreased (P < 0.01) by the addition of 0 to 10 microM of either ATRA, a nonspecific agonist for both the retinoic acid receptor (RAR) and the retinoid X receptor (RXR) or the selective RAR agonist, 4-(E-2-[5,6,7,8-tet-rahydro-5,5,8,8-tetramethyl-2-naphthalenyl]-1-propenyl) benzoic acid (TTNPB). Addition of increasing amounts of Ro-61, a RAR-specific antagonist (0 to 10 microM) prevented ATRA and TTNBP from decreasing GPDH activity. Addition of methoprene acid, an RXR-specific agonist, increased (P < 0.01) GPDH activity. Preadipocytes were then continuously treated with 10 nM of TTNPB in the presence or absence of 1 microM Ro-61, and mRNA was isolated on d 2 and 8. Addition of TTNPB decreased (P < 0.001) the expression of peroxisome proliferator-activated receptor gamma (PPARgamma), sterol regulatory element-binding protein-1c (SREBP-1c), retinoid X receptor alpha (RXRalpha), and adipocyte fatty acid binding protein (aP2) mRNA transcripts, whereas these effects were prevented by the presence of Ro-61. Interestingly, TTNBP increased (P < 0.001) the mRNA abundance of the orphan nuclear receptor chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1), whereas Ro-61 prevented this increase. These changes were independent of alterations in the mRNA abundances of the retinoic acid receptor alpha, and CCAAT/enhancer binding protein alpha and beta (C/EBPbeta; C/EBPalpha) genes. These results indicate that retinoic acid inhibits porcine preadipocyte differentiation by a mechanism that involves activation of the RAR and downregulation of PPARgamma, RXRalpha, and SREBP-1C mRNA. This mechanism is independent of changes in C/EBPbeta and C/EBPalpha mRNA abundance and may involve COUP-TF.

Nuclear receptor corepressor RIP140 regulates fat accumulation

Nuclear receptors and their coactivators have been shown to function as key regulators of adipose tissue biology. Here we show that a ligand-dependent transcriptional repressor for nuclear receptors plays a crucial role in regulating the balance between energy storage and energy expenditure. Mice devoid of the corepressor protein RIP140 are lean, show resistance to high-fat diet-induced obesity and hepatic steatosis, and have increased oxygen consumption. Although the process of adipogenesis is unaffected, expression of certain lipogenic enzymes is reduced. In contrast, genes involved in energy dissipation and mitochondrial uncoupling, including uncoupling protein 1, are markedly increased. Therefore, the maintenance of energy homeostasis requires the action of a transcriptional repressor in white adipose tissue, and ligand-dependent recruitment of RIP140 to nuclear receptors may provide a therapeutic target in the treatment of obesity and related disorders.

The balance between concurrent activation of ERs and PPARs determines daidzein-induced osteogenesis and adipogenesis

The soy phytoestrogen daidzein has biphasic dose responses, but the underlying mechanisms are not yet clear. Transcriptional and biochemical data show that PPARs, in addition to ERs, are molecular targets of daidzein, which divergently regulates osteogenesis and adipogenesis. Dose responses are the result of a balance among PPARs and between ERs and PPARs.

INTRODUCTION

Soy phytoestrogens have been used for the purposes of treatment and prevention of osteoporosis. Biphasic dose responses of daidzein, one of the main soy phytoestrogens, have long been recognized, but the underlying molecular mechanisms of action are not yet clear.

MATERIALS AND METHODS

Mouse bone marrow cells and mouse osteoprogenitor KS483 cells that concurrently differentiate into osteoblasts and adipocytes were cultured. Biochemical measurement of alkaline phosphatase (ALP) activity, RT-PCR, and gene reporter assays were used in this study.

RESULTS

Daidzein, one of the major soy phytoestrogens, had biphasic effects on osteogenesis and adipogenesis. Daidzein stimulated osteogenesis (ALP activity and nodule formation) and decreased adipogenesis (the number of adipocytes) at concentrations below 20 microM, whereas it inhibited osteogenesis and stimulated adipogenesis at concentrations higher than 30 microM. When estrogen receptors (ERs) were blocked by ICI182,780, daidzein-induced effects were not biphasic. A decrease in osteogenesis and an increase in adipogenesis were observed at the concentrations higher than 20 and 10 microM, respectively. In addition to ERs, daidzein transactivated not only peroxisome proliferator-activate receptor gamma (PPARgamma), but also PPARalpha and PPARdelta at micromolar concentrations. Activation of PPARalpha had no direct effects on osteogenesis and adipogenesis. In contrast, activation of PPARdelta stimulated osteogenesis but had no effects on adipogenesis, whereas PPARgamma inhibited osteogenesis and stimulated adipogenesis. Transfection experiments show that an activation of PPARalpha or PPARgamma by daidzein downregulated its estrogenic transcriptional activity, whereas activation of PPARdelta upregulated its estrogenic transcriptional activity. Activation of ERalpha or ERbeta by daidzein downregulated PPARgamma transcriptional activity but had no influence on PPARalpha or PPARdelta transcriptional activity.

CONCLUSIONS

Daidzein at micromolar concentrations concurrently activates different amounts of ERs and PPARs, and the balance of the divergent actions of ERs and PPARs determines daidzein-induced osteogenesis and adipogenesis.

Differential effects of PD98059 and U0126 on osteogenesis and adipogenesis

PD98059 and U0126 are considered as specific inhibitors of the p42/44 mitogen-activated protein kinases (MAPK) pathway, which affects osteogenesis and adipogenesis. Here, we show unexpected differential effects of PD98059 and U0126 on osteogenesis and adipogenesis as well as on estrogen (E2)-induced actions in osteoprogenitor KS483 cells. PD98059 dose-dependently inhibited osteogenesis indicated by cellular alkaline phosphatase (ALP) activity and nodule formation, but stimulated adipogenesis shown by the number of adipocytes. In contrast, U0126 slightly decreased osteogenesis but had no effects on adipogenesis, although it inhibited p42/44 MAPK more potently than PD98059. Furthermore, PD98059, but not U0126, counteracted E2-induced osteogenesis and adipogenesis. Transfection experiments showed that PD98059, but not U0126, had estrogenic transcriptional activity. Interestingly, both PD98059 and U0126 potentiated E2-induced estrogenic transcriptional activity in KS483 cells, which is opposite to the response in MCF7 breast cancer cells. Our data indicate that the cross-talk between growth factors and estrogen receptor (ER)-mediated pathways in KS483 cells is different from that in MCF7 cells. In summary, the differential effects of PD98059 and U0126 indicate their actions are not exclusively due to an inhibition of MAPK pathway. Caution should be taken in the interpretation of the results obtained using these inhibitors.

Resistin: molecular history and prognosis

Obesity and diabetes have reached epidemic proportions worldwide. The antidiabetic thiazolidinedione (TZD) drugs are insulin-sensitizing agents now widely used in the treatment of type 2 diabetes. TZDs are ligands for the nuclear hormone receptor peroxisome proliferator activated receptor gamma, which is a master regulator of adipogenesis and adipocyte metabolism. The molecular mechanisms by which TZDs improve insulin sensitivity have not been fully identified. Here we consider a novel secreted factor first identified as a TZD-suppressible gene in mouse adipocytes, called resistin, and discuss what is currently known about resistin regulation and function in mouse and human.

Peroxisome proliferator-activated receptor gamma (PPARgamma ) as a molecular target for the soy phytoestrogen genistein

The principal soy phytoestrogen genistein has an array of biological actions. It binds to estrogen receptor (ER) alpha and beta and has ER-mediated estrogenic effects. In addition, it has antiestrogenic effects as well as non-ER-mediated effects such as inhibition of tyrosine kinase. Because of its complex biological actions, the molecular mechanisms of action of genistein are poorly understood. Here we show that genistein dose-dependently increases estrogenic transcriptional activity in mesenchymal progenitor cells, but its biological effects on osteogenesis and adipogenesis are different. At low concentrations (< or =1 microm), genistein acts as estrogen, stimulating osteogenesis and inhibiting adipogenesis. At high concentrations (>1 microm), however, genistein acts as a ligand of PPARgamma, leading to up-regulation of adipogenesis and down-regulation of osteogenesis. Transfection experiments show that activation of PPARgamma by genistein at the micromolar concentrations down-regulates its estrogenic transcriptional activity, while activation of ERalpha or ERbeta by genistein down-regulates PPARgamma transcriptional activity. Genistein concurrently activates two different transcriptional factors, ERs and PPARgamma, which have opposite effects on osteogenesis or adipogenesis. As a result, the balance between activated ERs and PPARgamma determines the biological effects of genistein on osteogenesis and adipogenesis. Our findings may explain distinct effects of genistein in different tissues.