PPAR?1 synthesis and adipogenesis in C3H10T1/2 cells depends on S-phase progression, but does not require mitotic clonal expansion

Low lysine stimulates adipogenesis through ZFP423 upregulation in bovine stromal vascular cells

Adipogenesis is a complex process comprising commitment and a differentiation stages. Through research, many different transcriptional factors were found to mediate preadipocyte commitment and differentiation. Lysine has a potential of regulating the commitment and differentiation of preadipocytes. In the present study, intramuscular stromal vascular cells (SVC) isolated from Hanwoo beef cattle were used to elucidate the effects of low lysine level on adipogenesis. SVC were isolated and incubated with various concentrations of lysine (0, 37.5, 75, 150 and 300 µg/mL). No significant difference were observed in the proliferation of SVC after 24 and 48 h of incubation with different concentration of lysine. On preadipocyte determination, reducing the level of lysine significantly increased the expression of preadipocyte commitment gene Zinc finger protein 423 and Preadipocyte factor-1. Upon differentiation, Oil Red O staining revealed that lipid accumulation and triglyceride content significantly increased with the decreasing lysine levels in the media. Expression levels of peroxisome proliferator-activated receptor-γ, CCAAT enhancer binding protein-α, sterol regulatory element binding protein-1c, Fatty Acid Binding Protein 4 and stearoyl CoA desaturase were upregulated by the decreased level of lysine. These data suggest the potential mechanism of action for the improved preadipocyte commitment and adipocyte differentiation in bovine intramuscular SVC upon treatment with low levels of lysine. These findings may be valuable in developing feed rations that promote deposition of intramuscular fat in beef cattle through lysine level modification.

Effects of 4-nonylphenol on adipogenesis in 3T3-L1 preadipocytes and C3H/10T1/2 mesenchymal stem cells

Obesogens are a subset of endocrine disruptor chemicals (EDCs) that cause obesity. The typical EDC 4-nonylphenol (4-NP) has been identified as an obesogen. However, the in vitro effects of 4-NP on adipogenesis remain unclear. In this study, 3T3-L1 preadipocytes and C3H/10T1/2 mesenchymal stem cells (MSCs) were used to investigate the influence of 4-NP on adipogenesis. The differentiation protocols for 3T3-L1 preadipocytes and C3H/10T1/2 MSCs took 8 and 12 days, respectively, beginning at Day 0. In differentiated 3T3-L1 preadipocytes, 20 μM 4-NP decreased cell viability on Days 4 and 8. Exposure to 4-NP inhibited triglyceride (TG) accumulation and adipogenic marker expression on Days 0-8, but the inhibitory effects were weaker on Days 2-8. The protein expression of pSTAT3 or STAT3 decreased on Days 0-8 and 2-8. Conversely, 4-NP promoted TG accumulation and the adipogenic marker expression in C3H/10T1/2 adipocytes. The opposing effects were attributed to physiological differences between the two cell lines. The 3T3-L1 preadipocytes are dependent on mitotic clonal expansion (MCE) to drive differentiation, while C3H/10T1/2MSCs and human preadipocytes are not. Additionally, 4-NP downregulated β-catenin expression in C3H/10T1/2 adipocytes. Accordingly, we hypothesized that 4-NP promotes adipogenesis. The role of the canonical Wnt pathway in the promotion of adipogenesis by 4-NP requires further validation. This study provides new insights into the mechanisms and appropriate risk management of 4-NP.

Zyflamend, a unique herbal blend, induces cell death and inhibits adipogenesis through the coordinated regulation of PKA and JNK

The prevalence of obesity and its comorbidities has sparked a worldwide concern to address rates of adipose tissue accrual. Recent studies have demonstrated a novel role of Zyflamend, a blend of natural herbal extracts, in regulating lipid metabolism in several cancer cell lines through the activation of the AMPK signalling pathway. Yet, the role of Zyflamend in adipogenic differentiation and lipid metabolism remains largely unexplored. The objective of this study is to investigate the effects of Zyflamend on white 3T3-MBX pre-adipocyte differentiation and elucidate the molecular mechanisms. We demonstrate that Zyflamend treatment altered cell cycle progression, attenuated proliferation, and increased cell death of 3T3-MBX pre-adipocytes. In addition, treatment with Zyflamend inhibited lipid accumulation during the differentiation of 3T3-MBX cells, consistent with decreased expression of lipogenic genes and increased lipolysis. Mechanistically, Zyflamend-induced alterations in adipogenesis were mediated, at least in part, through the activation of AMPK, PKA, and JNK. Inhibition of AMPK partially reversed Zyflamend-induced inhibition of differentiation, whereas the inhibition of either JNK or PKA fully restored adipocyte differentiation and decreased lipolysis. Taken together, the present study demonstrates that Zyflamend, as a novel anti-adipogenic bioactive mix, inhibits adipocyte differentiation through the activation of the PKA and JNK pathways.

Abbreviation: 7-AAD: 7-amino-actinomycin D; ACC: acetyl-CoA carboxylase; AKT: protein kinase B; AMPK: AMP-activated protein kinase; ATGL: adipose triglyceride lipase; C/EBPα: CCAAT-enhancer binding protein alpha; DMEM: Dulbecco’s Modified Eagle Medium; DMSO: dimethyl sulphoxide; DTT: dithiothreitol; EGTA: ethylene glycol-bis-(2-aminoethyl)-N,N,N’,N’-tetraacetic acid; ERK: extracellular signal–regulated kinases; FASN: fatty acid synthase; FBS: foetal bovine serum; GLUT: glucose transporter; HSL: hormone-sensitive lipase; IR: insulin receptor; IRS: insulin receptor substrate; JNK: c-JUN N-terminal kinase; MGL: monoacylglycerol lipase; NaF: sodium fluoride; NF-κB: nuclear factor kappa-light-chain-enhancer of activated B cells; PBS: phosphate buffered- saline; PCB: pyruvate carboxylase; PDE: phosphodiesterase; PKA: protein kinase cAMP-dependent; PMSF: phenylmethylsulfonyl fluoride; PPARγ: perilipin peroxisome proliferator-activated receptor gamma; PREF-1: pre-adipocyte factor 1; PVDF: polyvinylidene fluoride; RIPA: radio-immunoprecipitation assay; SDS-PAGE: sodium dodecyl sulphate polyacrylamide gel electrophoresis; SEM: standard error of the mean; SOX9: suppressor of cytokine signalling 9; TGs: triacylglycerols.

Molecular Mechanism of Stem Cell Differentiation into Adipocytes and Adipocyte Differentiation of Malignant Tumor

Adipogenesis is the process through which preadipocytes differentiate into adipocytes. During this process, the preadipocytes cease to proliferate, begin to accumulate lipid droplets, and develop morphologic and biochemical characteristics of mature adipocytes. Mesenchymal stem cells (MSCs) are a type of adult stem cells known for their high plasticity and capacity to generate mesodermal and nonmesodermal tissues. Many mature cell types can be generated from MSCs, including adipocyte, osteocyte, and chondrocyte. The differentiation of stem cells into multiple mature phenotypes is at the basis for tissue regeneration and repair. Cancer stem cells (CSCs) play a very important role in tumor development and have the potential to differentiate into multiple cell lineages. Accumulating evidence has shown that cancer cells can be induced to differentiate into various benign cells, such as adipocytes, fibrocytes, osteoblast, by a variety of small molecular compounds, which may provide new strategies for cancer treatment. Recent studies have reported that tumor cells undergoing epithelial-to-mesenchymal transition can be induced to differentiate into adipocytes. In this review, molecular mechanisms, signal pathways, and the roles of various biological processes in adipose differentiation are summarized. Understanding the molecular mechanism of adipogenesis and adipose differentiation of cancer cells may contribute to cancer treatments that involve inducing differentiation into benign cells.

A delayed proinflammatory response of human preadipocytes to PCB126 is dependent on the aryl hydrocarbon receptor

Inflammation in adipose tissue is recognized as a causative factor in the development of type II diabetes. Adipocyte hypertrophy as well as bacterial and environmental factors have been implicated in causing inflammation in mature adipocytes. Exposure to persistent organic pollutants such as polychlorinated biphenyls (PCBs) has been associated with the development of type II diabetes. We show here that PCB126, a dioxin-like PCB, activates a robust proinflammatory state in fat cell precursors (preadipocytes). The response was found to be dependent on aryl hydrocarbon receptor (AhR) activation, although induction of the response was delayed compared to upregulation of CYP1A1, a classic AhR-responsive gene. Treatment of preadipocytes with a nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) inhibitor partially attenuated the PCB126-induced inflammatory response and partly, but not completely, ameliorated disruption of adipogenesis caused by PCB126. Our results indicate a role for PCB126 in mediating an inflammatory response through AhR in preadipocytes that interferes with adipogenesis.

Shortcuts to a functional adipose tissue: The role of small non-coding RNAs

Metabolic diseases such as type 2 diabetes are a major public health issue worldwide. These diseases are often linked to a dysfunctional adipose tissue. Fat is a large, heterogenic, pleiotropic and rather complex tissue. It is found in virtually all cavities of the human body, shows unique plasticity among tissues, and harbors many cell types in addition to its main functional unit - the adipocyte. Adipose tissue function varies depending on the localization of the fat depot, the cell composition of the tissue and the energy status of the organism. While the white adipose tissue (WAT) serves as the main site for triglyceride storage and acts as an important endocrine organ, the brown adipose tissue (BAT) is responsible for thermogenesis. Beige adipocytes can also appear in WAT depots to sustain heat production upon certain conditions, and it is becoming clear that adipose tissue depots can switch phenotypes depending on cell autonomous and non-autonomous stimuli. To maintain such degree of plasticity and respond adequately to changes in the energy balance, three basic processes need to be properly functioning in the adipose tissue: i) adipogenesis and adipocyte turnover, ii) metabolism, and iii) signaling. Here we review the fundamental role of small non-coding RNAs (sncRNAs) in these processes, with focus on microRNAs, and demonstrate their importance in adipose tissue function and whole body metabolic control in mammals.

Nutrigenomics and Beef Quality: A Review about Lipogenesis

The objective of the present review is to discuss the results of published studies that show how nutrition affects the expression of genes involved in lipid metabolism and how diet manipulation might change marbling and composition of fat in beef. Several key points in the synthesis of fat in cattle take place at the molecular level, and the association of nutritional factors with the modulation of this metabolism is one of the recent targets of nutrigenomic research. Within this context, special attention has been paid to the study of nuclear receptors associated with fatty acid metabolism. Among the transcription factors involved in lipid metabolism, the peroxisome proliferator-activated receptors (PPARs) and sterol regulatory element-binding proteins (SREBPs) stand out. The mRNA synthesis of these transcription factors is regulated by nutrients, and their metabolic action might be potentiated by diet components and change lipogenesis in muscle. Among the options for dietary manipulation with the objective to modulate lipogenesis, the use of different sources of polyunsaturated fatty acids, starch concentrations, forage ratios and vitamins stand out. Therefore, special care must be exercised in feedlot feed management, mainly when the goal is to produce high marbling beef.

Development of mRuby2-Transfected C3H10T1/2 Fibroblasts for Musculoskeletal Tissue Engineering

Mouse C3H10T1/2 fibroblasts are multipotent, mesenchymal stem cell (MSC)-like progenitor cells that are widely used in musculoskeletal research. In this study, we have established a clonal population of C3H10T1/2 cells stably-transfected with mRuby2, an orange-red fluorescence reporter gene. Flow cytometry analysis and fluorescence imaging confirmed successful transfection of these cells. Cell counting studies showed that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells proliferated at similar rates. Adipogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for Oil Red O and showed increased expression of adipogenic genes including adiponectin and lipoprotein lipase. Chondrogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for Alcian Blue and showed increased expression of chondrogenic genes including aggrecan. Osteogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for alkaline phosphatase (ALP) as well as Alizarin Red and showed increased expression of osteogenic genes including alp, ocn and osf-1. When seeded on calcium phosphate-based ceramic scaffolds, mRuby2-transfected C3H10T1/2 cells maintained even fluorescence labeling and osteogenic differentiation. In summary, mRuby2-transfected C3H10T1/2 cells exhibit mRuby2 fluorescence and showed little-to-no difference in terms of cell proliferation and differentiation as untransfected C3H10T1/2 cells. These cells will be available from American Type Culture Collection (ATCC; CRL-3268™) and may be a valuable tool for preclinical studies.

PPARγ ligand production is tightly linked to clonal expansion during initiation of adipocyte differentiation

Adipocyte differentiation is orchestrated by the ligand-activated nuclear receptor PPARγ. Endogenous ligands comprise oxidized derivatives of arachidonic acid and structurally similar PUFAs. Although expression of PPARγ peaks in mature adipocytes, ligands are produced primarily at the onset of differentiation. Concomitant with agonist production, murine fibroblasts undergo two rounds of mitosis referred to as mitotic clonal expansion. Here we show that mouse embryonic fibroblasts deficient in either of two cell cycle inhibitors, the transcription factor p53 or its target gene encoding the cyclin-dependent kinase inhibitor p21, exhibit increased adipogenic potential. The antiadipogenic effect of p53 relied on its transcriptional activity and p21 expression but was circumvented by administration of an exogenous PPARγ agonist suggesting a linkage between cell cycling and PPARγ ligand production. Indeed, cell cycle inhibitory compounds decreased PPARγ ligand production in differentiating 3T3-L1 preadipocytes. Furthermore, these inhibitors abolished the release of arachidonic acid induced by the hormonal cocktail initiating adipogenesis. Collectively, our results suggest that murine fibroblasts require clonal expansion for PPARγ ligand production at the onset of adipocyte differentiation.

The PPARγ locus makes long-range chromatin interactions with selected tissue-specific gene loci during adipocyte differentiation in a protein kinase A dependent manner

Differentiation signaling results in reprogramming of cellular gene expression that leads to morphological changes and functional specialization of a precursor cell. This global change in gene expression involves temporal regulation of differentiation-specific genes that are located throughout the genome, raising the idea that genome structure may also be re-organized during cell differentiation to facilitate regulated gene expression. Using in vitro adipocyte differentiation as a model, we explored whether gene organization within the nucleus is altered upon exposure of precursor cells to signaling molecules that induce adipogenesis. The peroxisome proliferator-activated receptor gamma (PPARγ) nuclear hormone receptor is a master determinant of adipogenesis and is required for adipose differentiation. We utilized the chromosome conformation capture (3C) assay to determine whether the position of the PPARγ locus relative to other adipogenic genes is changed during differentiation. We report that the PPARγ2 promoter is transiently positioned in proximity to the promoters of genes encoding adipokines and lipid droplet associated proteins at 6 hours post-differentiation, a time that precedes expression of any of these genes. In contrast, the PPARγ2 promoter was not in proximity to the EF1α promoter, which drives expression of a constitutively active, housekeeping gene that encodes a translation elongation factor, nor was the PPARγ2 promoter in proximity to the promoter driving the expression of the C/EBPα regulatory protein. The formation of the long-range, intergenic interactions involving the PPARγ2 promoter required the regulatory factor C/EBPβ, elevated cyclic AMP (cAMP) levels, and protein kinase A (PKA) signaling. We conclude that genome organization is dynamically remodeled in response to adipogenic signaling, and we speculate that these transient inter-genic interactions may be formed for the purposes of selecting some of the transcriptionally silent tissue-specific loci for subsequent transcriptional activation.

Stimulation of mouse Cyp1b1 during adipogenesis: characterization of promoter activation by the transcription factor Pax6

Cytochrome P4501B1 (Cyp1b1) is expressed specifically in certain neural crest (NC) cells during embryogenesis. Mesenchymal progenitor cells that develop from NC cells are modeled here by mouse C3H10T1/2 and 3T3-L1 cells. Dexamethasone in combination with methylisobutylxanthine (DM) induces Cyp1b1 and a 6.7 kb mouse Cyp1b1 promoter-luciferase reporter in each cell type prior to adipogenesis. An 18 base sequence (at -6.11 kb) (PaxE) which was essential for this reporter stimulation in 3T3-L1 cells bound the transcription factor Pax6. This is shown by gel mobility shifts and sequence mutations. Heterologous vector expression of Pax6 in 3T3-L1 cells enhanced DM stimulated Cyp1b1 promoter activity through cooperation with two Sp1 sites in the proximal promoter region. Chromatin immunoprecipitation showed that DM stimulated binding of Pax6 adjacent to Sp1 in the proximal promoter more than in the PaxE region. The Cyp1b1 induction by DM in C3H10T1/2 cells was more rapid but independent of Pax6. The far upstream enhancer region (FUER) found in rat Cyp1b1 responded to DM but was inactive in the mouse promoter due to key sequence changes. The expression patterns of Pax6 and Cyp1b1 frequently overlap during mouse embryogenesis. The relationship between Pax6 and Cyp1b1 expression warrants further investigation, particularly in the NC.

Heavy metal lead exposure, osteoporotic-like phenotype in an animal model, and depression of Wnt signaling

BACKGROUND

Exposure to lead (Pb) from environmental and industrial sources remains an overlooked serious public health risk. Elucidating the effect of Pb on bone cell function is therefore critical for understanding its risk associated with diseases of low bone mass.

OBJECTIVES

We tested the hypothesis that Pb negatively affects bone mass. We also assessed the underlying mechanisms of Pb on bone signaling pathways.

METHODS

We used a model of low-level Pb exposure in a rodent beginning before conception and continuing over 18 months. We characterized the effect of Pb on bone quality using dual-energy X-ray absorptiometry (DXA), micro-computed tomography, Raman spectroscopy, and histology. We assessed the effect of Pb on bone and adipocyte formation by mineral deposition, lipid droplet formation, and Western blot and RNA analysis.

RESULTS

Pb-exposed animals had decreased bone mass that resulted in bones that were more susceptible to fracture. Pb decreased osteoblastic cell number leading to a depression of bone formation. Accompanying this, Pb exposure elevated sclerostin protein levels in the skeleton, and correspondingly reduced levels of β-catenin and Runx2 in stromal precursor cells. Pb also increased skeletal expression of peroxisome proliferator-activated receptor-γ (PPAR-γ). These results indicate a shift in mesenchymal differentiation wherein Pb promoted enhanced adipogenesis and decreased osteoblastogenesis. Substantial differences in bone marrow composition were observed, highlighted by an increase in adipocytes.

CONCLUSIONS

The disruption Pb has on bone mass and bone homeostasis is principally explained by inhibition of the Wnt/β-catenin pathway, which may provide a molecular basis for novel therapeutic strategies to combat Pb-induced bone pathologies.

The clock gene, brain and muscle Arnt-like 1, regulates adipogenesis via Wnt signaling pathway

Circadian clocks in adipose tissue are known to regulate adipocyte biology. Although circadian dysregulation is associated with development of obesity, the underlying mechanism has not been established. Here we report that disruption of the clock gene, brain and muscle Arnt-like 1 (Bmal1), in mice led to increased adipogenesis, adipocyte hypertrophy, and obesity, compared to wild-type (WT) mice. This is due to its cell-autonomous effect, as Bmal1 deficiency in embryonic fibroblasts, as well as stable shRNA knockdown (KD) in 3T3-L1 preadipocyte and C3H10T1/2 mesenchymal stem cells, promoted adipogenic differentiation. We demonstrate that attenuation of Bmal1 function resulted in down-regulation of genes in the canonical Wnt pathway, known to suppress adipogenesis. Promoters of these genes (Wnt10a, β-catenin, Dishevelled2, TCF3) displayed Bmal1 occupancy, indicating direct circadian regulation by Bmal1. As a result, Wnt signaling activity was attenuated by Bmal1 KD and augmented by its overexpression. Furthermore, stabilizing β-catenin through Wnt ligand or GSK-3β inhibition achieved partial restoration of blunted Wnt activity and suppression of increased adipogenesis induced by Bmal1 KD. Taken together, our study demonstrates that Bmal1 is a critical negative regulator of adipocyte development through transcriptional control of components of the canonical Wnt signaling cascade, and provides a mechanistic link between circadian disruption and obesity.

Reactive oxygen species mediate adipocyte differentiation in mesenchymal stem cells

AIMS

Mesenchymal stem cells (MSC) have the potential to differentiate into various cell lineages, including adipocytes and osteoblasts. The formation of adipose tissue involves the commitment of MSC to the preadipocyte lineage and the differentiation of preadipocytes into mature adipocytes. In the present study, we investigated the involvement of reactive oxygen species (ROS) in adipocyte differentiation from MSC.

MAIN METHODS

ROS signaling was evaluated by the effects of antioxidant N-acetyl-l-cysteine (NAC) or shRNA against NAD(P)H oxidase in the multipotent mesenchymal stem cell line 10T1/2 cells. Intracellular ROS was measured using an H(2)DCF dye.

KEY FINDINGS

We found that NAC blocked adipocyte differentiation in MSC. An H(2)DCF assay revealed that differentiation-inducing agents induced ROS generation. These data suggest that ROS is involved in adipocyte differentiation in MSC. Next, we examined the source of ROS. Knockdown of NAD(P)H oxidase 4 (Nox4) by RNA interference inhibited ROS production and adipocyte differentiation by differentiation-inducing agents. Furthermore, treatment with NAC blocked the transcriptional activation of CREB, and the expression of dominant-negative mutants of CREB inhibited adipocyte differentiation.

SIGNIFICANCE

The findings suggest that the increase in the intracellular ROS level via Nox4 mediates adipocyte differentiation through CREB in MSC. This data will provide new insight into the drug development for obesity.

A putative role for endogenous FGF-2 in FGF-1 mediated differentiation of human preadipocytes

The defining characteristic of obesity is increased adipose tissue (AT) mass following chronic positive energy supply. AT mass is determined by adipocyte number and size, which reflect proliferation and differentiation of preadipocytes and hypertrophy of pre-existing adipocytes. The molecular pathways governing AT expansion are incompletely defined. We previously reported that FGF-1 primes proliferating primary human preadipocytes (phPA), thereby increasing adipogenesis. Here we examined whether FGF-1's adipogenic actions were due to modulation of other FGFs. Treatment of phPA with FGF-1 reduced FGF-2 mRNA/protein by 80%. To examine a putative functional role we performed siRNA knockdown studies. Following FGF-2 knockdown preadipocyte proliferation was decreased and expression of adipogenic genes (PPARγ, G3PDH and adiponectin) was increased at day 1 of differentiation. These results suggest that changes in endogenous FGF-2 levels contribute to FGF-1's early adipogenic effects and highlight the complexity of the paracrine interplay between FGFs within human AT.

Chemerin, a novel peroxisome proliferator-activated receptor gamma (PPARgamma) target gene that promotes mesenchymal stem cell adipogenesis

Chemerin is an adipocyte-secreted protein that regulates adipogenesis and the metabolic function of mature adipocytes via activation of chemokine-like receptor 1 (CMKLR1). Herein we report the interaction of peroxisome proliferator-activated receptor γ (PPARγ) and chemerin in the context of adipogenesis. Knockdown of chemerin or CMKLR1 expression or antibody neutralization of secreted chemerin protein arrested adipogenic clonal expansion of bone marrow mesenchymal stem cells (BMSCs) by inducing a loss of G(2)/M cyclins (cyclin A2/B2) but not the G(1)/S cyclin D2. Forced expression of PPARγ in BMSCs did not completely rescue this loss of clonal expansion and adipogenesis following chemerin or CMKLR1 knockdown. However, forced expression and/or activation of PPARγ in BMSCs as well as non-adipogenic cell types such as NIH-3T3 embryonic fibroblasts and MCA38 colon carcinoma cells significantly induced chemerin expression and secretion. Sequence analysis revealed a putative PPARγ response element (PPRE) sequence within the chemerin promoter. This PPRE was able to confer PPARγ responsiveness on a heterologous promoter, and mutation of this sequence abolished activation of the chemerin promoter by PPARγ. Chromatin immunoprecipitation confirmed the direct association of PPARγ with this PPRE. Treatment of mice with rosiglitazone elevated chemerin mRNA levels in adipose tissue and bone marrow coincident with an increase in circulating chemerin levels. Together, these findings support a fundamental role for chemerin/CMKLR1 signaling in clonal expansion during adipocyte differentiation as well as a role for PPARγ in regulating chemerin expression.

Roscovitine inhibits EBNA1 serine 393 phosphorylation, nuclear localization, transcription, and episome maintenance

Latent Epstein-Barr virus (EBV) infection causes human lymphomas and carcinomas. EBV usually persists as an episome in malignant cells. EBV episome persistence, replication, and gene expression are dependent on EBNA1 binding to multiple cognate sites in oriP. To search for inhibitors of EBNA1- and oriP-dependent episome maintenance or transcription, a library of 40,550 small molecules was screened for compounds that inhibit EBNA1- and oriP-dependent transcription and do not inhibit EBNA1- and oriP-independent transcription. This screening identified roscovitine, a selective inhibitor of cyclin-dependent kinase 1 (CDK1), CDK2, CDK5, and CDK7. Based on motif predictions of EBNA1 serine 393 as a CDK phosphorylation site and (486)RALL(489) and (580)KDLVM(584) as potential cyclin binding domains, we hypothesized that cyclin binding to EBNA1 may enable CDK1, -2, -5, or -7 to phosphorylate serine 393. We found that Escherichia coli-expressed EBNA1 amino acids 387 to 641 were phosphorylated in vitro by CDK1-, -2-, -5-, and -7/cyclin complexes and serine 393 phosphorylation was roscovitine inhibited. Further, S393A mutation abrogated phosphorylation. S393A mutant EBNA1 was deficient in supporting EBNA1- and oriP-dependent transcription and episome persistence, and roscovitine had little further effect on the diminished S393A mutant EBNA1-mediated transcription or episome persistence. Immunoprecipitated FLAG-EBNA1 was phosphorylated in vitro, and roscovitine inhibited this phosphorylation. Moreover, roscovitine decreased nuclear EBNA1 and often increased cytoplasmic EBNA1, whereas S393A mutant EBNA1 was localized equally in the nucleus and cytoplasm and was unaffected by roscovitine treatment. These data indicate that roscovitine effects are serine 393 specific and that serine 393 is important in EBNA1- and oriPCp-dependent transcription and episome persistence.

Culture conditions allow selection of different mesenchymal progenitors from adult mouse bone marrow

The use of adult stem cells in tissue engineering approaches will benefit from the establishment of culture conditions that allow the expansion and maintenance of cells with stem cell-like activity and high differentiation potential. In the field of adult stem cells, bone marrow stromal cells (BMSCs) are promising candidates. In the present study, we define, for the first time, conditions for optimizing the yields of cultures enriched for specific progenitors of bone marrow. Using four distinct culture conditions, supernatants from culture of bone fragments, marrow stroma cell line MS-5, embryonic fibroblast cell line NIH3T3, and a cocktail of epidermal growth factor (EGF) and platelet-derived growth factor (PDGF), we isolated four different sub-populations of murine BMSCs (mBMSCs). These cells express a well-known marker of undifferentiated embryonic stem cells (Nanog) and show interesting features in immunophenotype, self-renewal ability, and differentiation potency. In particular, using NIH3T3 conditioned medium, we obtained cells that showed impairment in osteogenic and chondrogenic differentiation while retaining high adipogenic potential during passages. Our results indicate that the choice of the medium used for isolation and expansion of mBMSCs is important for enriching the culture of desired specific progenitors.

Maternal obesity, inflammation, and fetal skeletal muscle development

Maternal obesity coupled with Western-style high-energy diets represents a special problem that can result in poor fetal development, leading to harmful, persistent effects on offspring, including predisposition to obesity and type 2 diabetes. Mechanisms linking maternal obesity to the increased incidence of obesity and other metabolic diseases in offspring remain poorly defined. Because skeletal muscle is the principal site for glucose and fatty acid utilization and composes 40%-50% of total body mass, changes in the properties of offspring skeletal muscle and its mass resulting from maternal obesity may be responsible for the increase in type 2 diabetes and obesity. Fetal stage is crucial for skeletal muscle development because there is no net increase in the muscle fiber number after birth. Fetal skeletal muscle development involves myogenesis, adipogenesis, and fibrogenesis, which are all derived from mesenchymal stem cells (MSCs). Shifting commitment of MSCs from myogenesis to adipogenesis and fibrogenesis will result in increased intramuscular fat and connective tissue, as well as reduced numbers of muscle fiber and/or diameter, all of which have lasting negative effects on offspring muscle function and properties. Maternal obesity leads to low-grade inflammation, which changes the commitment of MSCs in fetal muscle through several possible mechanisms: 1) inflammation downregulates wingless and int (WNT) signaling, which attenuates myogenesis; 2) inflammation inhibits AMP-activated protein kinase, which promotes adipogenesis; and 3) inflammation may induce epigenetic modification through polycomb group proteins. More studies are needed to further explore the underlying mechanisms associated with maternal obesity, inflammation, and the commitment of MSCs.

Reactive oxygen species facilitate adipocyte differentiation by accelerating mitotic clonal expansion

Growth-arrested 3T3-L1 preadipocytes rapidly express CCAAT/enhancer-binding protein-beta (C/EBPbeta) upon hormonal induction of differentiation. However, the DNA binding activity of C/EBPbeta is not activated until the cells synchronously reenter S phase during the mitotic clonal expansion (MCE) phase of differentiation. In this period, C/EBPbeta is sequentially phosphorylated by MAPK and glycogen synthase kinase-3beta, inducing C/EBPbeta DNA binding activity and transcription of its target genes. Because the DNA binding activity of C/EBPbeta is further enhanced by oxidation in vitro, we investigated how redox state affects C/EBPbeta DNA binding and MCE during adipogenesis. When 3T3-L1 cells were treated with H(2)O(2) and hormonal stimuli, differentiation was accelerated with increased expression of peroxisome proliferator-activated receptor gamma. Interestingly, cell cycle progression (S to G(2)/M phase) was markedly enhanced by H(2)O(2), whereas antioxidants caused an S phase arrest during the MCE. H(2)O(2) treatment resulted in the early appearance of a punctate pattern observed by immunofluorescent staining of C/EBPbeta, which is a hallmark for C/EBPbeta binding to regulatory elements, whereas a short antioxidant treatment rapidly dispersed the centromeric localization of C/EBPbeta. Consistently, reactive oxygen species production was increased during 3T3-L1 differentiation. Our results indicate that redox-induced C/EBPbeta DNA binding activity, along with the dual phosphorylation of C/EBPbeta, is required for the MCE and terminal differentiation of adipocytes.

Methods that resolve different contributions of clonal expansion to adipogenesis in 3T3-L1 and C3H10T1/2 cells

The mouse embryo fibroblast cell lines 3T3-L1 and C3H10T1/2 differentiate to adipocytes that exhibit similar insulin regulation of lipogenesis. These cell lines, however, differ appreciably in the processes that produce the major regulator PPAR gamma. Each line is stimulated by a mixture of insulin, dexamethasone, and methylisobutylxanthine (IDM). In the first 24h, IDM activates each cell type to produce similar regulatory changes and cell contraction. However, the increase in PPARy is delayed by 24h in typical 3T3-L1 cells compared with C3H10T1/2 cells. This delay is caused by the need for one or two rounds of cell division (clonal expansion) for PPAR gamma synthesis in 3T3-L1 cells. This expansion also occurs in C3H10T1/2 cells, but is not needed for PPAR gamma synthesis and differentiation. Other 3T3-L1 sublines have been described that follow the C3H10T1/2 pattern of differentiation. Culture conditions and inhibitors are described here that remove clonal expansion in C3H10T1/2 cells. With these constraints the cells retain full commitment to differentiation. This distinction is significant because many agents suppress differentiation in 3T3-L1 cells through inhibition of clonal expansion. Other effects on differentiation may be seen in C3H10T1/2 cells that are obscured in 3T3-L1 cells due to this inhibition of proliferation. Human preadipocytes do not need clonal expansion for adipogenesis, thus paralleling C3H10T1/2 cells.

Characterization of ScAP-23, a new cell line from murine subcutaneous adipose tissue, identifies genes for the molecular definition of preadipocytes

The 3T3-L1 model of in vitro adipogenesis has provided key insights into the molecular nature of this process. However, given that 3T3-L1 are of an embryonic origin, it is not clear to what extent they represent adipogenesis as it occurs in white adipose tissue (WAT). With the goal of better defining preadipocytes and adipogenesis in WAT, we have generated a new cell culture model from adipocyte precursors present in C57BL/6 mouse subcutaneous WAT. ScAP-23 preadipocytes show fibroblastic morphology, and on treatment with dexamethasone, 3-methylisobutylxanthine, insulin, and indomethacin, convert to nearly 100% adipocyte morphology. ScAP-23 adipocytes contain abundant lipid droplets and express transcripts for PPARγ, C/EBP family, and SREBP-1c transcription factors, SCD1, aFABP, ATGL, GLUT4, FAS, LDL, and GPDH, and are insulin responsive. Differential screening of 1,176 genes using nylon DNA arrays identified 10 transcripts enriched in ScAP-23 adipocytes vs. preadipocytes and 26 transcripts enriched in ScAP-23 preadipocytes vs. adipocytes. Semiquantitative or real-time PCR analyses identified a common cohort of 14 transcripts markedly downregulated in both ScAP-23 and 3T3-L1 adipogenesis. These included catenin-β1, chemokine ligand-2, serine or cysteine peptidase inhibitor f1, aurora kinase B, thrombospondin2, and solute carrier-7a5. Five of these transcripts (Ccl2, Serpinf1, Aurkb, Thbs2, and Slc7a5) demonstrated at least a twofold increase in WAT from obese ( ob/ob) mice compared with that of wild-type mice. This suggests that comparative gene expression studies of ScAP-23 and 3T3-L1 adipogenesis may be particularly fruitful in identifying preadipocyte-expressed genes that play a role in adipose tissue physiology and/or pathophysiology.

Characterization of the transcriptional and functional effects of fibroblast growth factor-1 on human preadipocyte differentiation

We recently established that fibroblast growth factor (FGF)-1 promotes adipogenesis of primary human preadipocytes (phPA). In the current report, we have characterized the adipogenic effects of FGF-1 in phPA and also in a human PA strain derived from an individual with Simpson-Golabi-Behmel syndrome (SGBS PA), which exhibit an intrinsic capacity to differentiate with high efficiency. In further studies, we compared these models with the well-characterized murine 3T3-L1 preadipocyte cell line (3T3-L1 PA). FGF-1 up-regulated the adipogenic program in phPA, with increased expression of peroxisome proliferator-activated receptor-gamma in confluent PA prior to induction of differentiation and increased expression of adipocyte markers during differentiation. Moreover, phPA differentiated in the presence of FGF-1 were more insulin responsive and secreted increased levels of adiponectin. FGF-1 treatment of SGBS PA further enhanced differentiation. For the most part, the adipogenic program in phPA paralleled that observed in 3T3-L1 PA; however, we found no evidence of mitotic clonal expansion in the phPA. Finally, we investigated a role for extracellular regulated kinase 1/2 (ERK1/2) in adipogenesis of phPA. FGF-1 induced robust phosphorylation of ERK1/2 in early differentiation and inhibition of ERK1/2 activity significantly reduced phPA differentiation. These data suggest that FGF-1 treated phPA represent a valuable in vitro model for the study of adipogenesis and insulin action and indicate that ERK1/2 activation is necessary for human adipogenesis in the absence of mitotic clonal expansion.

2,3,7,8-tetrachlorodibenzo-p-dioxin and epidermal growth factor cooperatively suppress peroxisome proliferator-activated receptor-gamma1 stimulation and restore focal adhesion complexes during adipogenesis: selective contributions of Src, Rho, and Erk distinguish these overlapping processes in C3H10T1/2 cells

Stimulation of PPARgamma1 and adipogenesis in multipotential C3H10T1/2 cells by the combination of dexamethasone and 3-isobutyl-1-methylxanthine (DM) is suppressed by 2,3,7,8 tetrachlorodibenzodioxin (TCDD) (10 nM). This suppression requires sustained activation of extracellular signal-regulated kinase (Erk)1/2. We show that it arises from an effect of TCDD on epidermal growth factor (EGF) signaling. DM initiates an early loss of cell adhesion that is reversed by this TCDD/EGF synergy. Src kinase activity was completely essential for adhesion restoration, sustained Erk activation, and suppression of peroxisome proliferator-activated receptor (PPAR)gamma1. MEK/Erk activity did not contribute, however, to TCDD-induced adhesion. Stimulation of adhesion may therefore precede elevation of Erk. Adhesion is produced by interaction of alphabeta integrins with extracellular matrix proteins and subsequent Src-mediated phosphorylation of focal adhesion kinase (FAK, Tyr576/577) and paxillin (Tyr118). TCDD enhanced the steady state Src-mediated phosphorylation of FAK but not of paxillin. Protein tyrosine phosphatase (PTPase) inhibition by orthovanadate (OVA) showed that this Src activity is highly restricted by PTPases. Partial inhibition of PTPases by OVA mimicked TCDD in producing EGF- and Src-dependent effects on cell adhesion and PPARgamma1 suppression. TCDD may therefore induce a protein that enhances Src effectiveness at adhesion sites. Rho kinase (ROCK) inhibition blocked TCDD/EGF stimulation of clustered focal adhesion complexes without affecting either sustained Erk activation or suppression of PPARgamma1. Thus, this ROCK-mediated clustering of integrin complexes is not needed for the effects of TCDD on Erk and PPARgamma1. A minimal cholesterol depletion with beta-methylcyclodextrin attenuated TCDD effects on PPARgamma1 and Erk activation. TCDD intervention is therefore linked to extracellular proteins. It indicates that TCDD-enhanced stimulation of EGF signaling to Erk may derive from the initial alphabeta integrin complexes.

OP9 mouse stromal cells rapidly differentiate into adipocytes: characterization of a useful new model of adipogenesis

Much knowledge of adipocyte biology has been learned from cell culture models, most notably 3T3-L1 cells. The 3T3-L1 model has several limitations, including the requirement of 2 weeks to generate adipocytes and the waning of adipogenic potential in culture. We have investigated the capacity of OP9 cells, a line of bone marrow-derived mouse stromal cells, to recapitulate adipogenesis. When OP9 cells are given any one of three adipogenic stimuli, they rapidly accumulate triacylglycerol, assume adipocyte morphology, and express adipocyte late marker proteins, including glucose transporter 4 and adiponectin. OP9 cells can differentiate into adipocytes within 2 days. This rapid rate of differentiation allows for the detection of transiently expressed proteins in mature OP9 adipocytes. Adipogenesis in OP9 cells involves the master transcriptional regulator of adipocyte differentiation, peroxisome proliferator-activated receptor gamma (PPARgamma). OP9 cells are late preadipocytes in that, before the addition of adipogenic stimuli, they express the adipocyte proteins CCAAT/enhancer binding proteins alpha and beta, PPARgamma, sterol-regulatory element binding protein-1, S3-12, and perilipin. OP9 differentiation is not diminished by maintenance in culture at high cell density or by long periods in continuous culture, thereby facilitating the generation of stable cell lines that retain adipogenic potential. Thus, the unique features of OP9 cells will expedite the study of adipocyte biology.

Microarray analysis of early adipogenesis in C3H10T1/2 cells: cooperative inhibitory effects of growth factors and 2,3,7,8-tetrachlorodibenzo-p-dioxin

C3H10T1/2 mouse embryo fibroblasts differentiate into adipocytes when stimulated by a standard hormonal mixture (IDMB). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), via the aryl hydrocarbon receptor (AhR), inhibits induction of the key adipogenic gene peroxisome proliferator-activated receptor gamma (PPARgamma) and subsequent adipogenesis. This TCDD-mediated inhibition requires activation of the extracellular signal-regulated kinase (ERK) pathway, which can be accomplished by serum, epidermal growth factor (EGF), or fibroblast growth factor (FGF). In the absence of serum or growth factors, IDMB induced adipogenesis without mitosis. Microarray analysis identified 200 genes that exhibited expression changes of at least twofold after 24 h of IDMB treatment. This time precedes most PPARgamma stimulation but follows the period of TCDD/ERK cooperation and periods of increased cell contraction and DNA synthesis. Functionally related gene clusters include genes associated with cell structure, triglyceride and cholesterol metabolism, oxidative regulation, and secreted proteins. In the absence of growth factors TCDD inhibited 30% of these IDMB responses without inhibiting the process of differentiation. A combination of EGF and TCDD that blocks differentiation cooperatively blocked a further 44 IDMB-responsive genes, most of which have functional links to differentiation, including PPARgamma. Cell cycle regulators that are stimulated by EGF were substantially inhibited by IDMB but these responses were unaffected by TCDD. By contrast, TCDD and EGF cooperatively reversed IDMB-induced changes in cell adhesion complexes immediately prior to increases in PPARgamma1 expression. Changes in adhesion-linked signaling may play a key role in TCDD affects on differentiation.

Differentiation of pluripotent C3H10T1/2 cells rapidly elevates CYP1B1 through a novel process that overcomes a loss of Ah Receptor

Stimulation of C3H10T1/2 cells by an adipogenic hormonal mixture (IDM) consisting of insulin (I), dexamethasone (D), and methylisobutylxanthine (M) substantially induces cytochrome P450 (CYP) 1B1 expression. This stimulation represents up to 40% of the level produced by maximum activation of the arylhydrocarbon receptor (AhR) with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Dexamethasone and methylisobutylxanthine in combination produced near maximum elevation of CYP1B1 along with a subsequent decline in AhR that paralleled the rise in peroxisome proliferator-activated receptorgamma1 (PPARgamma1). Inhibitors of AhR activity, which block TCDD induction, did not affect this increase of CYP1B1 expression, which was, therefore, independent of AhR activity. These responses were unaffected by inhibition of DNA synthesis, which was required for PPARgamma1 induction and terminal differentiation. Induction of CYP1B1 mRNA was paralleled by increased CYP1B1 promoter-luciferase reporter activity. The initial 0.8kb of promoter region, which was sufficient for 24h near maximum stimulation, did not contain either the key AhR-responsive elements that mediate the TCDD response or CREB and SF1 elements that mediate cAMP stimulation of rat CYP1B1 in steroidogenic cells. This reporter response to IDM stimulation, but not to TCDD, was maintained in AhR-null fibroblasts. CYP1B1 expression, unlike TCDD induction, was stimulated by IDM in only about half the cells. CYP1B1 expression partially overlapped with PPARgamma expression, which was also inversely related in clonal sub-lines. CYP1B1 expression may, therefore, represent an early stage of differentiation that requires factors associated with DNA synthesis to subsequently generate PPARgamma1.

Mesenchymal stem cells from the outer ear: a novel adult stem cell model system for the study of adipogenesis

Adipocytes arise from multipotent stem cells of mesodermal origin, which also give rise to the muscle, bone, and cartilage lineages. However, signals and early molecular events that commit multipotent stem cells into the adipocyte lineage are not well established mainly due to lack of an adequate model system. We have identified a novel source of adult stem cells from the external murine ears referred to here as an ear mesenchymal stem cells (EMSC). EMSC have been isolated from several standard and mutant strains of mice. They are self-renewing, clonogenic, and multipotent, since they give rise to osteocytes, chondrocytes, and adipocytes. The in vitro characterization of EMSC indicates very facile adipogenic differentiation. Morphological, histochemical, and molecular analysis after the induction of differentiation showed that EMSC maintain adipogenic potentials up to fifth passage. A comparison of EMSC to the stromal-vascular (S-V) fraction of fat depots, under identical culture conditions (isobutyl-methylxanthine, dexamethasone, and insulin), revealed much more robust and consistent adipogenesis in EMSC than in the S-V fraction. In summary, we show that EMSC can provide a novel, easily obtainable, primary culture model for the study of adipogenesis.

The extracellular signal-regulated kinase isoform ERK1 is specifically required for in vitro and in vivo adipogenesis

Hyperplasia of adipose tissue is critical for the development of obesity, but molecular mechanisms governing normal or pathological recruitment of new adipocytes remain unclear. The extracellular signal-regulated kinase (ERK) pathway plays a pivotal role in many essential cellular functions, such as proliferation and differentiation. Using ERK1(-/-) mice, we investigated the role of this isoform in adipose tissue development. Mice lacking ERK1 have decreased adiposity and fewer adipocytes than wild-type animals. Furthermore, ERK1(-/-) mice challenged with high-fat diet are resistant to obesity, are protected from insulin resistance, and have a higher postprandial metabolic rate. To get insights into cellular mechanisms implicated in reduced adiposity in ERK1(-/-) animals, we analyzed adipocyte differentiation in ERK1(-/-) cells. Compared with wild-type control cells, mouse embryo fibroblasts and cultures of adult preadipocytes isolated from ERK1(-/-) adult animals exhibit impaired adipogenesis. An inhibitor of the ERK pathway does not affect the residual adipogenesis of the ERK1(-/-) cells, suggesting that ERK2 is not implicated in adipocyte differentiation. Our results clearly link ERK1 to the regulation of adipocyte differentiation, adiposity, and high-fat diet-induced obesity. This suggests that a therapeutic approach of obesity targeting specifically the ERK1 isoform and not ERK2 would be of particular interest.

TCDD administration after the pro-adipogenic differentiation stimulus inhibits PPARgamma through a MEK-dependent process but less effectively suppresses adipogenesis

Hormone (IDMB)-induced adipogenesis in C3H10T1/2 cells is suppressed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via the aryl hydrocarbon receptor (AhR). We have previously reported that TCDD addition 48 h before the hormonal stimulation of IDMB suppresses a key mediator of adipogenesis, the peroxisome proliferator-activated receptor (PPARgamma), by a MEK/ERK dependent mechanism. Here we add to previous evidence that this synergism functions after IDMB addition but before increased PPARgamma1 transcription. Suppression remains effective and MEK/ERK dependent when TCDD is added 6-12 h after IDMB addition but not when delayed to 16-24 h, thus preceding the rise in PPARgamma mRNA. TCDD suppression of the number of committed adipocytes and of triglyceride formation is less effective with the delayed addition. TCDD therefore does not directly suppress the expression of the key mediator PPARgamma1. An alternative mediation of adipocyte commitment is apparently less sensitive to the 6-12 h of delayed TCDD addition. TCDD suppression potencies (EC(50) = 50 pM) match the potencies for stimulation of CYP1B1 protein and AhR-sensitive reporters. The AhR antagonist 3'-methoxy-4'-nitroflavone (3-MNF) inhibited both TCDD-mediated CYP1B1 induction and inhibition of PPARgamma protein expression. This antagonism was only effective when 3-MNF was present in the 24-h period after IDMB addition. TCDD activation of AhR in conjunction with MEK/ERK therefore generates PPARgamma1 suppression activity before the increase of PPARgamma1 synthesis. The potency and inhibition data are consistent with induction of one or more gene products that sustain suppression through the extended period of PPARgamma1 transcription.