Repressive effect of Sp1 on the C/EBPalpha gene promoter: role in adipocyte differentiation

SP1 regulates porcine primary adipocyte differentiation by modulating BAMBI transcriptional activity

Obesity is a critical metabolic disorder in modern society, necessitating urgent research and intervention. Compared to mice, pigs are increasingly been recognized as valuable model organisms for such studied due to their closer genetic similarity to humans. The BAMBI gene plays a pivotal role in adipocyte differentiation and adipose tissue development, rendering it a potent target for exploring the mechanisms of obesity and related metabolic disorders. This study conducted an in-depth exploration of the intricate regulatory mechanisms governing the BAMBI gene, with a particular emphasis on the transcription factor SP1. Our experiments strongly provided that SP1 modulates BAMBI transcription by directly binding to its promoter. Using primary porcine adipocytes, we further demonstrated that SP1 regulates adipocyte differentiation occurs via the BAMBI gene. These findings enhance understanding of the critical role played by the BAMBI gene in adipocyte differentiation and establish a theoretical foundation for novel therapeutic strategies targeting obesity and type 2 diabetes. Importantly, this study emphasizes the potential of SP-BAMBI pathways in interventions within the context of metabolic diseases, addressing the global challenges posed by obesity and its associated complications.

Mevalonate biosynthesis pathway regulates the development and survival of brown adipocytes

The high thermogenic activity of brown adipose tissue (BAT) has received considerable attention. Here, we demonstrated the role of the mevalonate (MVA) biosynthesis pathway in the regulation of brown adipocyte development and survival. The inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the rate-limiting enzyme in the MVA pathway and the molecular target of statins, suppressed brown adipocyte differentiation by suppressing protein geranylgeranylation-mediated mitotic clonal expansion. The development of BAT in neonatal mice exposed to statins during the fetal period was severely impaired. Moreover, statin-induced geranylgeranyl pyrophosphate (GGPP) deficiency led to the apoptosis of mature brown adipocytes. Brown adipocyte-specific Hmgcr knockout induced BAT atrophy and disrupted thermogenesis. Importantly, both genetic and pharmacological inhibition of HMGCR in adult mice induced morphological changes in BAT accompanied by an increase in apoptosis, and statin-treated diabetic mice showed worsened hyperglycemia. These findings revealed that MVA pathway-generated GGPP is indispensable for BAT development and survival.

Altered recruitment of Sp isoforms to HIV-1 long terminal repeat between differentiated monoblastic cell lines and primary monocyte-derived macrophages

Human immunodeficiency virus type 1 (HIV-1) transcription in cells of the monocyte-macrophage lineage is regulated by interactions between the HIV-1 long terminal repeat (LTR) and a variety of host cell and viral proteins. Binding of the Sp family of transcription factors (TFs) to the G/C box array of the LTR governs both basal as well as activated LTR-directed transcriptional activity. The effect of monocytic differentiation on Sp factor binding and transactivation was examined with respect to the HIV-1 LTR. The binding of Sp1, full-length Sp3 and truncated Sp3 to a high affinity HIV-1 Sp element was specifically investigated and results showed that Sp1 binding increased relative to the binding of the sum of full-length and truncated Sp3 binding following chemically-induced monocytic differentiation in monoblastic (U-937, THP-1) and myelomonocytic (HL-60) cells. In addition, Sp binding ratios from PMA-induced cell lines were shown to more closely approximate those derived from primary monocyte-derived macrophages (MDMs) than did ratios derived from uninduced cell lines. The altered Sp binding phenotype associated with changes in the transcriptional activation mediated by the HIV-1 G/C box array. Additionally, analysis of post-translational modifications on Sp1 and Sp3 revealed a loss of phosphorylation on serine and threonine residues with chemically-induced differentiation indicating that the activity of Sp factors is additionally regulated at the level of post-translational modifications (PTMs).

Suppressive Effect of Fraxetin on Adipogenesis and Reactive Oxygen Species Production in 3T3-L1 Cells by Regulating MAPK Signaling Pathways

Recent studies have identified obesity as one of the world’s most serious chronic disorders. Adipogenesis, in which preadipocytes are differentiated into mature adipocytes, has a decisive role in establishing the number of adipocytes and determining the lipid storage capacity of adipose tissue and fat mass in adults. Fat accumulation in obesity is implicated with elevated oxidative stress in adipocytes induced by reactive oxygen species (ROS). Adipogenesis regulation by inhibiting adipogenic differentiation and ROS production has been selected as the strategy to treat obesity. The conventional anti-obesity drugs allowed by the U.S. Food and Drug Administration have severe adverse effects. Therefore, various natural products have been developed as a solution for obesity, suppressing adipogenic differentiation. Fraxetin is a major component extracted from the stem barks of Fraxinus rhynchophylla, with various bioactivities, including anti-inflammatory, anticancer, antioxidant, and antibacterial functions. However, the effect of fraxetin on adipogenesis is still not clearly understood. We studied the pharmacological functions of fraxetin in suppressing lipid accumulation and its underlying molecular mechanisms involving 3T3-L1 preadipocytes. Moreover, increased ROS production induced by a mixture of insulin, dexamethasone, and 3-isobutylmethylxanthine (MDI) in 3T3-L1 was attenuated by fraxetin during adipogenesis. These effects were regulated by mitogen-activated protein kinase (MAPK) signaling pathways. Therefore, our findings imply that fraxetin possesses inhibitory roles in adipogenesis and can be a potential anti-obesity drug.

miRNA-22 deletion limits white adipose expansion and activates brown fat to attenuate high-fat diet-induced fat mass accumulation

BACKGROUND

Obesity, characterized by excessive expansion of white adipose tissue (WAT), is associated with numerous metabolic complications. Conversely, brown adipose tissue (BAT) and beige fat are thermogenic tissues that protect mice against obesity and related metabolic disorders. We recently reported that deletion of miR-22 enhances energy expenditure and attenuates WAT expansion in response to a high-fat diet (HFD). However, the molecular mechanisms involved in these effects mediated by miR-22 loss are unclear.

METHODS AND RESULTS

Here, we show that miR-22 expression is induced during white, beige, and brown adipocyte differentiation in vitro. Deletion of miR-22 reduced white adipocyte differentiation in vitro. Loss of miR-22 prevented HFD-induced expression of adipogenic/lipogenic markers and adipocyte hypertrophy in murine WAT. In addition, deletion of miR-22 protected mice against HFD-induced mitochondrial dysfunction in WAT and BAT. Loss of miR-22 induced WAT browning. Gain- and loss-of-function studies revealed that miR-22 did not affect brown adipogenesis in vitro. Interestingly, miR-22 KO mice fed a HFD displayed increased expression of genes involved in thermogenesis and adrenergic signaling in BAT when compared to WT mice fed the same diet.

CONCLUSIONS

Collectively, our findings suggest that loss of miR-22 attenuates fat accumulation in response to a HFD by reducing white adipocyte differentiation and increasing BAT activity, reinforcing miR-22 as a potential therapeutic target for obesity-related disorders.

Sulforaphene Suppresses Adipocyte Differentiation via Induction of Post-Translational Degradation of CCAAT/Enhancer Binding Protein Beta (C/EBPβ)

Adipocyte differentiation (adipogenesis) is a crucial process that determines the total number and size of mature adipocytes that will develop. In this study, the anti-adipogenic effect of sulforaphene (SFEN), a dietary isothiocyanate (ITC) derived from radish, is investigated both in 3T3-L1 pre-adipocytes and in human adipose tissue-derived stem cells. The results revealed that SFEN significantly inhibit adipogenic cocktail-induced adipocyte differentiation and lipid accumulation at the early stage of adipogenesis. Additionally, the effects are more potent compared to those of other ITCs derived from various cruciferous vegetables. As a related molecular mechanism of action, SFEN promotes the post-translational degradation of CCAAT/enhancer-binding protein (C/EBP) β by decreasing the stability of C/EBPβ, which is responsible for decreasing the expression of master regulatory proteins such as peroxisome proliferator-activated receptor γ and C/EBPα. Collectively, these results suggest that the intake of SFEN-enriched natural materials could be helpful as a strategy for preventing obesity.

Shockwaves Suppress Adipocyte Differentiation via Decrease in PPARγ

Adipogenesis is a crucial cellular process that contributes to the expansion of adipose tissue in obesity. Shockwaves are mechanical stimuli that transmit signals to cause biological responses. The purpose of this study is to evaluate the effects of shockwaves on adipogenesis. We treated 3T3L-1 cells and human primary preadipocytes for differentiation with or without shockwaves. Western blots and quantitative real-time reverse transcriptase PCR (qRT-PCR) for adipocyte markers including peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT-enhancer-binding proteins (C/EBPα) were performed. Extracellular adenosine triphosphate (ATP) and intracellular cyclic adenosine monophosphate (cAMP) levels, which are known to affect adipocyte differentiation, were measured. Shockwave treatment decreased intracellular lipid droplet accumulation in primary human preadipocytes and 3T3-L1 cells after 11–12 days of differentiation. Levels of key adipogenic transcriptional factors PPARγ and/or C/EBPα were lower in shockwave-treated human primary preadipocytes and 3T3L-1 cells after 12–13 days of differentiation than in shockwave-untreated cells. Shockwave treatment induced release of extracellular ATP from preadipocytes and decreased intracellular cAMP levels. Shockwave-treated preadipocytes showed a higher level of β-catenin and less PPARγ expression than shockwave-untreated cells. Supplementation with 8-bromo-cAMP analog after shockwave treatment rescued adipocyte differentiation by preventing the effect of shockwaves on β-catenin, Wnt10b mRNA, and PPARγ expression. Low-energy shockwaves suppressed adipocyte differentiation by decreasing PPARγ. Our study suggests an insight into potential uses of shockwave-treatment for obesity.

Identification of Candidate Genes and Regulatory Factors Underlying Intramuscular Fat Content Through Longissimus Dorsi Transcriptome Analyses in Heavy Iberian Pigs

One of the most important determinants of meat quality is the intramuscular fat (IMF) content. The development of high-throughput techniques as RNA-seq allows identifying gene pathways and networks with a differential expression (DE) between groups of animals divergent for a particular trait. The Iberian pig is characterized by having an excellent meat quality and a high content of intramuscular fat. The objectives of the present study were to analyze the longissimus dorsi transcriptome of purebred Iberian pigs divergent for their IMF breeding value to identify differential expressed genes and regulatory factors affecting gene expression. RNA-seq allowed identifying ∼10,000 of the 25,878 annotated genes in the analyzed samples. In addition to this, 42.46% of the identified transcripts corresponded to newly predicted isoforms. Differential expression analyses revealed a total of 221 DE annotated genes and 116 DE new isoforms. Functional analyses identified an enrichment of overexpressed genes involved in lipid metabolism (FASN, SCD, ELOVL6, DGAT2, PLIN1, CIDEC, and ADIPOQ) in animals with a higher content of IMF and an enrichment of overexpressed genes related with myogenesis and adipogenesis (EGR1, EGR2, EGR3, JUNB, FOSB, and SEMA4D) in the animals with a lower content of IMF. In addition to this, potential regulatory elements of these DE genes were identified. Co-expression networks analyses revealed six long non-coding RNAs (lncRNAs) (ALDBSSCG0000002079, ALDBSSCG0000002093, ALDBSSCG0000003455, ALDBSSCG0000004244, ALDBSSCG0000005525, and ALDBSSCG0000006849) co-expressed with SEMA4D and FOSB genes and one (ALDBSSCG0000004790) with SCD, ELOVL6, DGAT2, PLIN1, and CIDEC. Analyses of the regulatory impact factors (RIFs) revealed 301 transcriptionally regulatory factors involved in expression differences, with five of them involved in adipogenesis (ARID5B, CREB1, VDR, ATF6, and SP1) and other three taking part of myogenesis and development of skeletal muscle (ATF3, KLF11, and MYF6). The results obtained provide relevant insights about the genetic mechanisms underlying IMF content in purebred Iberian pigs and a set of candidate genes and regulatory factors for further identification of polymorphisms susceptible of being incorporated in a selection program.

Potential miRNA involvement in the anti-adipogenic effect of resveratrol and its metabolites

OBJECTIVE

Scientific research is constantly striving to find molecules which are effective against excessive body fat and its associated complications. Taking into account the beneficial effects that resveratrol exerts on other pathologies through miRNA, the aim of the present work was to analyze the possible involvement of miRNAs in the regulation of adipogenic transcription factors peroxisome proliferator-activated receptor γ (pparγ), CCAAT enhancer-binding proteins α and β (cebpβ and cebpα) induced by resveratrol and its metabolites.

METHODS

3T3-L1 maturing pre-adipocytes were treated during differentiation with 25 μM of trans-resveratrol (RSV), trans-resveratrol-3-O-sulfate (3S), trans-resveratrol-3'-O-glucuronide (3G) and trans-resveratrol-4'-O-glucuronide (4G). After computational prediction and bibliographic search of miRNAs targeting pparγ, cebpβ and cebpα, the expression of microRNA-130b-3p (miR-130b-3p), microRNA-155-5p (miR-155-5p), microRNA-27b-3p (miR-27b-3p), microRNA-31-5p (miR-31-5p), microRNA-326-3p (miR-326-3p), microRNA-27a-3p (miR-27a-3p), microRNA-144-3p (miR-144-3p), microRNA-205-5p (miR-205-5p) and microRNA-224-3p (miR-224-3p) was analyzed. Moreover, other adipogenic mediators such as sterol regulatory element binding transcription factor 1 (srebf1), krüppel-like factor 5 (klf5), liver x receptor α (lxrα) and cAMP responding element binding protein 1 (creb1), were measured by Real Time RT-PCR. As a confirmatory assay, cells treated with RSV were transfected with anti-miR-155 in order to measure cebpβ gene and protein expressions.

RESULTS

Of the miRNAs analyzed only miR-155 was modified after resveratrol and glucuronide metabolite treatment. In transfected cells with anti-miR-155, RSV did not reduce cebpβ gene and protein expression. 3S decreased gene expression of creb1, klf5, srebf1 and lxrα.

CONCLUSIONS

While RSV and glucuronide metabolites exert their inhibitory effect on adipogenesis through miR-155 up-regulation, the anti-adipogenic effect of 3S is not mediated via miRNAs.

The Inhibitory Effect of Tartary Buckwheat Extracts on Adipogenesis and Inflammatory Response

Tartary buckwheat (Fagopyrum tataricum) has been established globally as a nutritionally important food item, particularly owing to high levels of bioactive compounds such as rutin. This study investigated the effect of tartary buckwheat extracts (TBEs) on adipogenesis and inflammatory response in 3T3-L1 cells. TBEs inhibited lipid accumulation, triglyceride content, and glycerol-3-phosphate dehydrogenase (GPDH) activity during adipocyte differentiation of 3T3 L1 cells. The mRNA levels of genes involved in fatty acid synthesis, such as peroxisome proliferator-activated receptor-γ (PPAR-γ), CCAAT/enhancer binding protein-α (CEBP-α), adipocyte protein 2 (aP2), acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), and stearoylcoenzyme A desaturase-1 (SCD-1), were suppressed by TBEs. They also reduced the mRNA levels of inflammatory mediators such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), monocyte chemoattractant protein 1 (MCP-1), and inducible nitric oxide synthase (iNOS). In addition, TBEs were decreased nitric oxide (NO) production. These results suggest that TBEs may inhibit adipogenesis and inflammatory response; therefore, they seem to be beneficial as a food ingredient to prevent obesity-associated inflammation.

Hepatocyte nuclear factor 1b is a novel negative regulator of white adipocyte differentiation

Hepatocyte nuclear factor 1b (HNF1b) is a transcription factor belonging to the HNF family. We aimed to investigate the role of HNF1b in white adipocyte differentiation. The expression of HNF1b was reduced in white adipose tissue (WAT) of both diet-induced and genetic obese mice and decreased during the process of 3T3-L1 adipocyte differentiation. Downregulation of HNF1b enhanced 3T3-L1 adipocyte differentiation and upregulation of HNF1b inhibited this process. Upregulation of HNF1b inhibited peroxisome proliferator-activated receptor γ (PPARγ) and its target gene expression, while downregulation of HNF1b increased those genes expression. Overexpression of PPARγ suppressed HNF1b upregulation-induced inhibition of adipocyte differentiation. HNF1b can directly bind with the promoter of PPARγ in 3T3-L1 cells, which was decreased after adipogenic differentiation. HNF1b promoted apoptotic and autophagic cell death in early differentiated adipocytes through regulation of cell cycle progress and cell death-related factors, and thus inhibited the process of mitotic clonal expansion (MCE). HNF1b acted as an antioxidant regulator through regulating various antioxidant enzymes via binding with antioxidant response element. Oxidant treatment suppressed HNF1b upregulation-induced inhibition of adipocyte differentiation. Overall, our results suggest that HNF1b is a novel negative regulator of adipocyte differentiation through regulation of PPARγ signaling, MCE and redox state.

Identification of transcription factors potentially involved in human adipogenesis in vitro

BACKGROUND

Increased adiposity in humans leads to obesity, which is a major risk factor for cardiovascular disease, type 2 diabetes, and cancer. We previously conducted an extensive unbiased in vitro transcriptomic analysis of adipogenesis, using human adipose-derived stromal cells (ASCs). Here, we have applied computational methods to these data to identify transcription factors (TFs) that constitute the upstream gene regulatory networks potentially, driving adipocyte formation in human ASCs.

METHODS

We used Affymetrix Transcription Analysis Console™ v3.0 for calculating differentially expressed genes. MATCH™ and F-MATCH™ algorithms for TF identification. STRING v10 to predict protein-protein interactions between TFs.

RESULTS

A number of TFs that were reported to have a significant role in adipogenesis, as well as novel TFs that have not previously been described in this context, were identified. Thus, 32 upstream TFs were identified, with most belonging to the C2H2-type zinc finger and HOX families, which are potentially involved in regulating most of the differentially expressed genes observed during adipocyte differentiation. Furthermore, 17 important upstream TFs were found to have increased regulatory effects on their downstream target genes and were consistently up-regulated during the differentiation process. A strong hypothetical functional interaction was observed among these TFs, which supports their common role in the downstream regulation of gene expression during adipogenesis.

CONCLUSION

Our results support several previous findings on TFs involved in adipogenesis and thereby validate the comprehensive and systematic in silico approach described in this study. In silico analysis also allowed for the identification of novel regulators of adipocyte differentiation.

Potential Application of p-Coumaric Acid on Differentiation of C2C12 Skeletal Muscle and 3T3-L1 Preadipocytes-An in Vitro and in Silico Approach

Coumaric acid (CA) is a phenolic acid of the hydroxycinnamic acid family, and it has many biological functions such as anti-oxidant, anti-inflammatory, antidiabetic, anti-ulcer, anti-platelet, anti-cancer activities, etc. In the present study, we planned to analyse the potential molecular function of CA on skeletal muscle and preadipocytes differentiation using PCR and Western blot techniques. First, we analysed the impact of CA on C2C12 skeletal muscle differentiation. It revealed that CA treatment inhibited horse serum-induced skeletal muscle differentiation as evidenced by the decreased expression of early myogenic differentiation markers such as Myogenin and myoD via the AMP activated protein kinase- alpha AMPK-α mediated pathway. Furthermore, the level of lipid accumulation and changes in genes and protein expressions that are associated with lipogenesis and lipolysis were analyzed in 3T3-L1 cells. The Oil Red O staining evidenced that CA treatment inhibited lipid accumulation at the concentration of 0.1 and 0.2 mM. Furthermore, coumaric acid treatment decreased the expression of main transcriptional factors such as CCAAT/enhancer binding protein-alpha (C/EBP-α) and peroxisome proliferator-activated receptor gamma-2 (PPAR-γ2). Subsequently, CA treatment decreased the expression of sterol regulatory element binding protein-1 (SREBP-1), fatty acid synthase (FAS), acetyl CoA carboxylase (ACC) and adiponectin. Finally, we identified conformational changes induced by CA in PPAR-γ2 using computational biology tools. It revealed that CA might downregulate the PPAR-γ2 expression by directly binding with amino acids of PPAR-γ2 by hydrogen at 3.26 distance and hydrophobic interactions at 3.90 contact distances. These data indicated that CA suppressed skeletal muscle and preadipocytes differentiation through downregulation of the main transcriptional factors and their downstream targets.

Inhibition of SP1 by the mithramycin analog EC-8042 efficiently targets tumor initiating cells in sarcoma

Tumor initiating cells (TICs), responsible for tumor initiation, and cancer stem cells (CSCs), responsible for tumor expansion and propagation, are often resistant to chemotherapeutic agents. To find therapeutic targets against sarcoma initiating and propagating cells we used models of myxoid liposarcoma (MLS) and undifferentiated pleomorphic sarcoma (UPS) developed from human mesenchymal stromal/stem cells (hMSCs), which constitute the most likely cell-of-origin for sarcoma. We found that SP1-mediated transcription was among the most significantly altered signaling. To inhibit SP1 activity, we used EC-8042, a mithramycin (MTM) analog (mithralog) with enhanced anti-tumor activity and highly improved safety. EC-8042 inhibited the growth of TIC cultures, induced cell cycle arrest and apoptosis and upregulated the adipogenic factor CEBPα. SP1 knockdown was able to mimic the anti-proliferative effects induced by EC-8042. Importantly, EC-8042 was not recognized as a substrate by several ABC efflux pumps involved in drug resistance, and, opposite to the chemotherapeutic drug doxorubicin, repressed the expression of many genes responsible for the TIC/CSC phenotype, including SOX2, C-MYC, NOTCH1 and NFκB1. Accordingly, EC-8042, but not doxorubicin, efficiently reduced the survival of CSC-enriched tumorsphere sarcoma cultures. In vivo, EC-8042 induced a profound inhibition of tumor growth associated to a strong reduction of the mitotic index and the induction of adipogenic differentiation and senescence. Finally, EC-8042 reduced the ability of tumor cells to reinitiate tumor growth. These data suggest that EC-8042 could constitute an effective treatment against both TIC and CSC subpopulations in sarcoma.

Rubus crataegifolius Bunge regulates adipogenesis through Akt and inhibits high-fat diet-induced obesity in rats

Background

Obesity is one of the greatest public health problems and major risk factors for serious metabolic diseases and significantly increases the risk of premature death. The aim of this study was to determine the inhibitory effects of Rubus crataegifolius Bunge (RCB) on adipocyte differentiation in 3 T3-L1 cells and its anti-obesity properties in high fat diet (HFD)-induced obese rats.

Methods

3 T3-L1 adipocytes and HFD-induced obese rats were treated with RCB, and its effect on gene expression was analyzed using RT-PCR and Western blotting experiments.

Results

RCB treatment significantly inhibited adipocyte differentiation by suppressing the expression of C/EBPβ, C/EBPα, and PPARγ in the 3 T3-L1 adipocytes. Subsequently, the expression of the PPARγ target genes aP2 and fatty acid synthase (FAS) decreased following RCB treatment during adipocyte differentiation. In uncovering the specific mechanism that mediates the effects of RCB, we demonstrated that the insulin-stimulated phosphorylation of Akt strongly decreased and that its downstream substrate phospho-GSK3β was downregulated following RCB treatment in the 3 T3-L1 adipocytes. Moreover, LY294002, an inhibitor of Akt phosphorylation, exerted stronger inhibitory effects on RCB-mediated suppression of adipocyte differentiation, leading to the inhibition of adipocyte differentiation through the downregulation of Akt signaling. An HFD-induced obesity rat model was used to determine the inhibitory effects of RCB on obesity. Body weight gain and fat accumulation in adipose tissue were significantly reduced by the supplementation of RCB. Moreover, RCB treatment caused a significant decrease in adipocyte size, associated with a decrease in epididymal fat weight. The serum total cholesterol (TC) and triglyceride (TG) levels decreased in response to RCB treatment, whereas HDL cholesterol (HDL-C) increased, indicating that RCB attenuated lipid accumulation in adipose tissue in HFD-induced obese rats.

Conclusion

Our results demonstrate an inhibitory effect of RCB on adipogenesis through the reduction of the adipogenic factors PPARγ, C/EBPα, and phospho-Akt. RCB had a potent anti-obesity effect, reducing body weight gain in HFD-induced obese rats.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0091-0) contains supplementary material, which is available to authorized users.

Quercetin prevents adipogenesis by regulation of transcriptional factors and lipases in OP9 cells

With the industrialization of society, the increase in the prevalence of obesity and metabolic disorders has become an important health concern in a number of countries. Quercetin (3,30,40,5,7-pentahydroxyflavone) is well known as a bioactive flavonoid in a variety of biological resources. The aim of the present study was to explore the machanisms responsible for the anti-adipogenic activity of quercetin and its effects on the lipolysis in OP9 mouse stromal cells which rapidly differentiate into adipocytes. The differentiation of OP9 cells into adipocytes was evaluated by the measurement of lipid accumulation by Oil Red O (ORO) staining; lipid accumulation was significantly impaired by treatment with quercetin. Reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis were used to measure the expression levels of CCAAT/enhancer binding protein α (C/EBPα), proliferator-activated receptor γ (PPARγ), sterol regulatory element-binding protein-1 (SREBP-1) and fatty acid synthase (FAS). The mRNA expression levels of lipases, such as adipose triglyceride lipase (ATGL), hormone sensitive lipase (HSL) and lipoprotein lipase (LPL) were also measured by RT-PCR. Quercetin significantly decreased the expression of transcription factors, including C/EBPα, PPARγ and SREBP-1c both at the protein and mRNA level. The results from the present study demonstrate that quercetin prevents adipogenesis by upregulating ATGL and HSL expression and downregulating FAS, LPL and adipocyte fatty acid-binding protein (aP2) expression, as well as the expression of transcription factors. Our data suggest that quercetin has therapeutic potential by regulating the expression of transcriptional factors and enzymes associated with adipogenesis.

RhoGTPases as key players in mammalian cell adaptation to microgravity

A growing number of studies are revealing that cells reorganize their cytoskeleton when exposed to conditions of microgravity. Most, if not all, of the structural changes observed on flown cells can be explained by modulation of RhoGTPases, which are mechanosensitive switches responsible for cytoskeletal dynamics control. This review identifies general principles defining cell sensitivity to gravitational stresses. We discuss what is known about changes in cell shape, nucleus, and focal adhesions and try to establish the relationship with specific RhoGTPase activities. We conclude by considering the potential relevance of live imaging of RhoGTPase activity or cytoskeletal structures in order to enhance our understanding of cell adaptation to microgravity-related conditions.

Negative regulation of DsbA-L gene expression by the transcription factor Sp1

Disulfide-bond A oxidoreductase-like protein (DsbA-L) possesses beneficial effects such as promoting adiponectin multimerization and stability, increasing insulin sensitivity, and enhancing energy metabolism. The expression level of DsbA-L is negatively correlated with obesity in mice and humans, but the underlying mechanisms remain unknown. To address this question, we generated reporter gene constructs containing the promoter sequence of the mouse DsbA-L gene. Deletion analysis showed that the proximal promoter of mouse DsbA-L is located between -186 and -34 bp relative to the transcription start site. In silico analysis identified a putative Sp1 transcription factor binding site in the first intron of the DsbA-L gene. Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis indicated that Sp1 bound to this intron region in vitro and in intact cells. Overexpression of Sp1 or suppressing Sp1 expression by siRNA reduced or increased DsbA-L promoter activity, respectively. The binding activity of Sp1 was gradually decreased during 3T3-L1 cell differentiation and was significantly increased in adipose tissues of obese mice. Our results identify Sp1 as an inhibitor of DsbA-L gene transcription, and the Sp1-mediated inhibition of DsbA-L gene expression may provide a mechanism underlying obesity-induced adiponectin downregulation and insulin resistance.

Novel inhibitors of nuclear transport cause cell cycle arrest and decrease cyst growth in ADPKD associated with decreased CDK4 levels

Autosomal-dominant polycystic kidney disease (ADPKD) is a progressive, proliferative renal disease. Kidneys from ADPKD patients are characterized by the presence of cysts that are marked by enhanced proliferation and apoptosis of renal tubular epithelial cells. Current treatment of this disease is supportive, as there are few if any clinically validated targeted therapeutics. Given the parallels between cystic disease and cancer, and in light of our findings of the efficacy of the nuclear transport inhibitors in kidney cancer, which has similarities to ADPKD, we asked whether such inhibitors show utility in ADPKD. In this study, we tested selective inhibitors of nuclear export (SINE) in two human ADPKD cell lines and in an in vivo mouse model of ADPKD. After effective downregulation of a nuclear exporter, exportin 1 (XPO1), with KPT-330, both cell lines showed dose-dependent inhibition of cell proliferation through G₀/G₁ arrest associated with downregulation of CDK4, with minimal apoptosis. To analyze mechanisms of CDK4 decrease by XPO1 inhibition, localization of various XPO1 target proteins was examined, and C/EBPβ was found to be localized in the nucleus by XPO1 inhibition, resulting in an increase of C/EBPα, which activates degradation of CDK4. Furthermore, inhibition of XPO1 with the parallel inhibitor KPT-335 attenuated cyst growth in vivo in the PKD1 mutant mouse model Pkd1(v/v). Thus, inhibition of nuclear export by KPT-330, which has shown no adverse effects in renal serum chemistries and urinalyses in animal models, and which is already in phase 1 trials for cancers, will be rapidly translatable to human ADPKD.

Proteome profiling of mitotic clonal expansion during 3T3-L1 adipocyte differentiation using iTRAQ-2DLC-MS/MS

Mitotic clonal expansion (MCE) is one of the important events taking place at the early stage during 3T3-L1 adipocyte differentiation. To investigate the mechanism underlying this process, we carried out a temporal proteomic analysis to profile the dynamic changes in MCE. Using 8-plex-iTRAQ-2DLC-MS/MS analysis, 3152 proteins were quantified during the initial 28 h of 3T3-L1 adipogenesis. Functional analysis was performed on 595 proteins with maximum or minimum quantities at 20 h of adipogenic induction that were potentially involved in MCE, which identified PI3K/AKT/mTOR as the most relevant pathway. Among the 595 proteins, PKM2 (Pyruvate kinase M2), a patterned protein identified as a potential target gene of C/EBPβ in our previous work, was selected for further investigation. Network analysis suggested positive correlations among C/EBPβ, PIN1, and PKM2, which may be related with the PI3K-AKT pathway. Knockdown of PKM2 with siRNA inhibited both MCE and adipocyte differentiation of 3T3-L1 cells. Moreover, PKM2 was down-regulated at both the mRNA level and the protein level upon the knockdown of C/EBPβ. And overexpressed PKM2 can partially restore MCE, although it did not restore terminal adipocyte differentiation, which was inhibited by siC/EBPβ. Thus, PKM2, potentially regulated by C/EBPβ, is involved in MCE during adipocyte differentiation. The dynamic proteome changes quantified here provide a promising basis for revealing molecular mechanism regulating adipogenesis.

Emerging roles of zinc finger proteins in regulating adipogenesis

Proteins containing the zinc finger domain(s) are named zinc finger proteins (ZFPs), one of the largest classes of transcription factors in eukaryotic genomes. A large number of ZFPs have been studied and many of them were found to be involved in regulating normal growth and development of cells and tissues through diverse signal transduction pathways. Recent studies revealed that a small but increasing number of ZFPs could function as key transcriptional regulators involved in adipogenesis. Due to the prevalence of obesity and metabolic disorders, the investigation of molecular regulatory mechanisms of adipocyte development must be more completely understood in order to develop novel and long-term impact strategies for ameliorating obesity. In this review, we discuss recent work that has documented that ZFPs are important functional contributors to the regulation of adipogenesis. Taken together, these data lead to the conclusion that ZFPs may become promising targets to combat human obesity.

p300-dependent acetylation of activating transcription factor 5 enhances C/EBPβ transactivation of C/EBPα during 3T3-L1 differentiation

Adipogenesis is a multistep process by which 3T3-L1 preadipocytes differentiate into mature adipocytes through mitotic clonal expansion (MCE) and terminal differentiation. The CCAAT/enhancer-binding protein β (C/EBPβ) is an important transcription factor that takes part in both of these processes. C/EBPβ not only transactivates C/EBPα and the peroxisome proliferator-activated receptor γ (PPARγ), which cause 3T3-L1 preadipocytes to enter terminal adipocyte differentiation, but also is required to activate cell cycle genes necessary for MCE. The identification of potential cofactors of C/EBPβ will help to explain how C/EBPβ undertakes these specialized roles during the different stages of adipogenesis. In this study, we found that activating transcription factor 5 (ATF5) can bind to the promoter of C/EBPα via its direct interaction with C/EBPβ (which is mediated via the p300-dependent acetylation of ATF5), leading to enhanced C/EBPβ transactivation of C/EBPα. We also show that p300 is important for the interaction of ATF5 with C/EBPβ as well as for the binding activity of this complex on the C/EBPα promoter. Consistent with these findings, overexpression of ATF5 and an acetylated ATF5 mimic both promoted 3T3-L1 adipocyte differentiation, whereas short interfering RNA-mediated ATF5 downregulation inhibited this process. Furthermore, we show that the elevated expression of ATF5 is correlated with an obese phenotype in both mice and humans. In summary, we have identified ATF5 as a new cofactor of C/EBPβ and examined how C/EBPβ and ATF5 (acetylated by a p300-dependent mechanism) regulate the transcription of C/EBPα.

Duplicated CCAAT/enhancer-binding protein β (C/EBPβ) gene: transcription and methylation changes in response to dietary betaine in Landes goose liver

The CCAAT/enhancer-binding protein β gene (C/EBPβ) is one of the key regulating factors of lipid metabolic balance in the liver. To better understand how C/EBPβ affects lipid accumulation in the Landes goose liver, its DNA was cloned. The goose C/EBPβ DNA sequence (2,075 bp) contains a 984-bp open reading frame and part of the 5'-flanking region, and shares 96.66 and 62.07% similarity with the chicken and human sequences at the amino acid level, respectively. Tissue expression profiling showed that the relative expression level was high in the liver and adipose tissue. To understand the effect of betaine on C/EBPβ in goose liver, the relative expression levels of C/EBPβ were detected under different treatments. Compared with the control group, C/EBPβ expression increased in the high-carbohydrate group (P < 0.01) and decreased in the betaine treatment group (P > 0.05). Using bisulfite sequencing PCR, the gene methylation status was analyzed among the different treatment groups. None of the 54 CpG sites in the promoter region or the 28 CpG sites in the structural domain of the coding region showed any significantly different methylation patterns among the groups. Taken together, the results showed that betaine decreased the goose C/EBPβ gene expression, but did not directly regulate its methylation. The data may form the basis for further investigation of the mechanisms of the effect of C/EBPβ on the regulation of lipometabolism in the goose liver and the effect of betaine on lipid metabolic genes at the molecular level.

Blueberry peel extracts inhibit adipogenesis in 3T3-L1 cells and reduce high-fat diet-induced obesity

This study examined the anti-obesity effect and mechanism of action of blueberry peel extracts (BPE) in 3T3-L1 cells and high-fat diet (HFD)-induced obese rats. The levels of lipid accumulation were measured, along with the changes in the expression of genes and proteins associated with adipocyte differentiation in 3T3-L1 cells. Evidenced by Oil-red O staining and triglyceride assay, BPE dose-dependently inhibited lipid accumulation at concentrations of 0, 50, and 200 µg/ml. BPE decreased the expression of the key adipocyte differentiation regulator C/EBPβ, as well as the C/EBPα and PPARγ genes, during the differentiation of preadipocytes into adipocytes. Moreover, BPE down-regulated adipocyte-specific genes such as aP2 and FAS compared with control adipocytes. The specific mechanism mediating the effects of BP revealed that insulin-stimulated phosphorylation of Akt was strongly decreased, and its downstream substrate, phospho-GSK3β, was downregulated by BPE treatment in 3T3-L1 cells. Together, these data indicated that BP exerted anti-adipogenic activity by inhibiting the expression of PPARγ and C/EBPβ and the Akt signaling pathway in 3T3-L1 adipocytes. Next, we investigated whether BP extracts attenuated HFD-induced obesity in rats. Oral administration of BPE reduced HFD-induced body weight gain significantly without affecting food intake. The epididymal or perirenal adipose tissue weights were lower in rats on an HFD plus BPE compared with the tissue weights of HFD-induced obese rats. Total cholesterol and triglyceride levels in the rats fed BPE were modestly reduced, and the HDL-cholesterol level was significantly increased in HFD plus BP-fed rats compared with those of HFD-fed rats. Taken together, these results demonstrated an inhibitory effect of BP on adipogenesis through the down-regulation of C/EBPβ, C/EBPα, and PPARγ and the reduction of the phospho-Akt adipogenic factor in 3T3-L1 cells. Moreover, BPE reduced body weight gain and inhibited fat accumulation in an HFD-induced animal model of obesity.

Epigenetic regulation of adipogenesis by PHF2 histone demethylase

PHF2 is a JmjC family histone demethylase that removes the methyl group from H3K9me2 and works as a coactivator for several metabolism-related transcription factors. In this study, we examined the in vivo role of PHF2 in mice. We generated Phf2 floxed mice, systemic Phf2 null mice by crossing Phf2 floxed mice with CMV-Cre transgenic mice, and tamoxifen-inducible Phf2 knockout mice by crossing Phf2 floxed mice with Cre-ERT2 transgenic mice. Systemic Phf2 null mice had partial neonatal death and growth retardation and exhibited less adipose tissue and reduced adipocyte numbers compared with control littermates. Tamoxifen-induced conditional knockout of PHF2 resulted in impaired adipogenesis in stromal vascular cells from the adipose tissue of tamoxifen-inducible Phf2 knockout mice as well as of Phf2 knocked-down 3T3-L1 cells. PHF2 interacts with CEBPA and demethylates H3K9me2 in the promoters of CEBPA-regulated adipogenic genes. These findings suggest that PHF2 histone demethylase potentiates adipogenesis through interaction with CEBPA in vivo. Taken together, PHF2 may be a novel therapeutic target in the treatment of obesity and the metabolic syndrome.

Krüppel-like factor KLF8 plays a critical role in adipocyte differentiation

KLF8 (Krüppel-like factor 8) is a zinc-finger transcription factor known to play an essential role in the regulation of the cell cycle, apoptosis, and differentiation. However, its physiological roles and functions in adipogenesis remain unclear. In the present study, we show that KLF8 acts as a key regulator controlling adipocyte differentiation. In 3T3-L1 preadipocytes, we found that KLF8 expression was induced during differentiation, which was followed by expression of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα). Adipocyte differentiation was significantly attenuated by the addition of siRNA against KLF8, whereas overexpression of KLF8 resulted in enhanced differentiation. Furthermore, luciferase reporter assays demonstrated that overexpression of KLF8 induced PPARγ2 and C/EBPα promoter activity, suggesting that KLF8 is an upstream regulator of PPARγ and C/EBPα. The KLF8 binding sites were localized by site mutation analysis to −191 region in C/EBPα promoter and −303 region in PPARγ promoter, respectively. Taken together, these data reveal that KLF8 is a key component of the transcription factor network that controls terminal differentiation during adipogenesis.

Paternally inherited gsα mutation impairs adipogenesis and potentiates a lean phenotype in vivo

Paternally inherited inactivating mutations of the GNAS gene have been associated with a rare and disabling genetic disorder, progressive osseous heteroplasia, in which heterotopic ossification occurs within extraskeletal soft tissues, such as skin, subcutaneous fat, and skeletal muscle. This ectopic bone formation is hypothesized to be caused by dysregulated mesenchymal progenitor cell differentiation that affects a bipotential osteogenic-adipogenic lineage cell fate switch. Interestingly, patients with paternally inherited inactivating mutations of GNAS are uniformly lean. Using a mouse model of Gsα-specific exon 1 disruption, we examined whether heterozygous inactivation of Gnas affects adipogenic differentiation of mesenchymal precursor cells from subcutaneous adipose tissues (fat pad). We found that paternally inherited Gsα inactivation (Gsα(+/p-) ) impairs adipogenic differentiation of adipose-derived stromal cells (ASCs). The Gsα(+/p-) mutation in ASCs also decreased expression of the adipogenic factors CCAAT-enhancer-binding protein (C/EBP)β, C/EBPα, peroxisome proliferator-activated receptor gamma, and adipocyte protein 2. Impaired adipocyte differentiation was rescued by an adenylyl cyclase activator, forskolin, and provided evidence that Gsα-cAMP signals are necessary in early stages of this process. Supporting a role for Gnas in adipogenesis in vivo, fat tissue weight and expression of adipogenic genes from multiple types of adipose tissues from Gsα(+/p-) mice were significantly decreased. Interestingly, the inhibition of adipogenesis by paternally inherited Gsα mutation also enhances expression of the osteogenic factors, msh homeobox 2, runt-related transcription factor 2, and osteocalcin. These data support the hypothesis that Gsα plays a critical role in regulating the balance between fat and bone determination in soft tissues, a finding that has important implications for a wide variety of disorders of osteogenesis and adipogenesis.

Characterization of a proximal Sp1 response element in the mouse Dlk2 gene promoter

BACKGROUND

DLK2 is an EGF-like membrane protein, closely related to DLK1, which is involved in adipogenesis. Both proteins interact with the NOTCH1 receptor and are able to modulate its activation. The expression of the gene Dlk2 is coordinated with that of Dlk1 in several tissues and cell lines. Unlike Dlk1, the mouse Dlk2 gene and its locus at chromosome 17 are not fully characterized.

RESULTS

The goal of this work was the characterization of Dlk2 mRNA, as well as the analysis of the mechanisms that control its basal transcription. First, we analyzed the Dlk2 transcripts expressed by several mouse cells lines and tissues, and mapped the transcription start site by 5' Rapid Amplification of cDNA Ends. In silico analysis revealed that Dlk2 possesses a TATA-less promoter containing minimal promoter elements associated with a CpG island, and sequences for Inr and DPE elements. Besides, it possesses six GC-boxes, considered as consensus sites for the transcription factor Sp1. Indeed, we report that Sp1 directly binds to the Dlk2 promoter, activates its transcription, and regulates its level of expression.

CONCLUSIONS

Our results provide the first characterization of Dlk2 transcripts, map the location of the Dlk2 core promoter, and show the role of Sp1 as a key regulator of Dlk2 transcription, providing new insights into the molecular mechanisms that contribute to the expression of the Dlk2 gene.

Minireview: PPARγ as the target of obesogens

The peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of adipogenesis and is medically important for its connections to obesity and the treatment of type II diabetes. Activation of this receptor by certain natural or xenobiotic compounds has been shown to stimulate adipogenesis in vitro and in vivo. Obesogens are chemicals that ultimately increase obesity through a variety of potential mechanisms, including activation of PPARγ. The first obesogen for which a definitive mechanism of action has been elucidated is the PPARγ and RXR activator tributyltin; however, not all chemicals that activate PPARγ are adipogenic or correlated with obesity in humans. There are multiple mechanisms through which obesogens can target PPARγ that may not involve direct activation of the receptor. Ligand-independent mechanisms could act through obesogen-mediated post-translational modification of PPARγ which cause receptor de-repression or activation. PPARγ is active in multipotent stem cells committing to the adipocyte fate during fat cell development. By modifying chromatin structure early in development, obesogens have the opportunity to influence the promoter activity of PPARγ, or the ability of PPARγ to bind to its target genes, ultimately biasing the progenitor pool towards the fat lineage. Obesogens that act by directly or indirectly activating PPARγ, by increasing the levels of PPARγ protein, or enhancing its recruitment to promoters of key genes in the adipogenic pathway may ultimately play an important role in adipogenesis and obesity.

Effects of Atractylodes macrocephala Koidzumi rhizome on 3T3-L1 adipogenesis and an animal model of obesity

ETHNOPHARMACOLOGICAL RELEVANCE

Atractylodes macrocephala Koidzumi (AMK) is an herbal medicine traditionally used for treatment of abdominal pain, gastrointestinal disease, obesity, and related complications.

AIM OF THE STUDY

We investigated the effects and molecular mechanism of AMK rhizome water extract on 3T3-L1 adipogenesis and an animal model of obesity.

MATERIALS AND METHODS

To study the effect of AMK on adipogenesis in vitro, differentiating 3T3-L1 cells were treated every two days with AMK at various concentrations (1-25μg/ml) for eight days. Oil Red O staining was performed to determine the lipid accumulation in 3T3-L1 cells. To elucidate the inhibitory mechanism of AMK on adipogenesis, phosphorylation levels of Akt and expression of perilipin, were analyzed by Western blotting. AMK was administered orally to high fat diet (HFD)-induced obese rats to confirm its effect in vivo.

RESULTS

AMK inhibited 3T3-L1 adipocyte differentiation in a dose-dependent manner without cellular toxicity. Phospho-Akt expression was highly decreased by AMK treatment, whereas there was no significant change in perilipin expression. AMK administration significantly reduced the body weight of rats fed a HFD. Plasma triglyceride levels were significantly lower in the AMK-treated HFD group than those in the HFD control group or normal diet (ND) group, although serum total, HDL- and LDL-cholesterol levels did not differ between the groups.

CONCLUSION

These results demonstrate an inhibitory effect of AMK on adipogenesis through reduction of an adipogenic factor, phospho-Akt. AMK had a beneficial effect, reducing body weight gain in a HFD-induced animal model of obesity.

Water-soluble extract of Pacific Krill prevents triglyceride accumulation in adipocytes by suppressing PPARγ and C/EBPα expression

BACKGROUND

Pacific Krill (Euphausia pacifica) are small, red crustaceans, similar to shrimp, that flourish in the North Pacific and are eaten in Japan.

METHODS AND FINDINGS

We investigated the effect of a water-soluble extract of Pacific Krill on adipocytes and discovered that this extract suppressed triglyceride accumulation in adipocytes. Furthermore, the water-soluble extract of Pacific Krill suppressed the expression of two master regulators of adipocyte differentiation, peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT enhancer binding protein alpha (C/EBPα). C/EBPβ promotes PPARγ and C/EBPα expression, but the water-soluble extract of Pacific Krill did not inhibit the expression of C/EBPβ or C/EBPβ-mediated transcriptional activation. The Pacific Krill extract was more effective than a PPARγ antagonist in suppressing PPARγ and C/EBPα expression.

CONCLUSIONS

These results indicated that the water-soluble extract of Pacific Krill was not simply a PPARγ antagonist, but that it prevented triglyceride accumulation in adipocytes by suppression of PPARγ and C/EBPα via a pathway that is independent of C/EBPβ.

Liver-enriched inhibitory protein (LIP) actively inhibits preadipocyte differentiation through histone deacetylase 1 (HDAC1)

The CCAAT/enhancer-binding protein β (C/EBPβ) is expressed as three isoforms (LAP*, liver-enriched activating protein (LAP), and liver-enriched inhibitory protein (LIP)) that differentially regulate gene expression. The interplay between LAP*, LAP, and LIP in regulating cellular processes is largely unknown, and LIP has been largely regarded to repress transcription through a passive heterodimerization-dependent mechanism. Recently, we have shown that p300/GCN5 and mSin3A/HDAC1 differentially regulate the ability of C/EBPβ to stimulate preadipocyte differentiation through activation of C/ebpα transcription. Here, we have mapped requirements for binding of mSin3A/HDAC1 to LAP/LAP* and LIP to a 4-amino acid motif in the central region of LAP/LAP* (residues 153-156) and the N terminus of LIP. Reducing mSin3A/HDAC1 binding to LAP/LAP* and LIP through deletion of this motif reduced the recruitment of HDAC1 to the C/ebpα promoter and increased preadipocyte differentiation stimulated by insulin and 1-methyl-3-isobutylxanthine. Additional studies showed that the interaction of HDAC1 with LIP provides for active repression of C/ebpα transcription and is largely responsible for the ability of LIP and HDAC1 to repress preadipocyte differentiation. Thus, although mSin3A/HDAC1 interacted readily with LAP/LAP* in addition to LIP and that expression of LAP/LAP* was sufficient to recruit HDAC1 to the C/ebpα promoter, mutations in C/ebpβ that abrogated HDAC1 association to LAP/LAP* in the absence of LIP provided no additional stimulation of differentiation or transcription beyond the deletion of LIP alone. The implication of these results for the interaction between p300/GCN5 and mSin3A/HDAC1 in regulating C/EBPα transcription and preadipocyte differentiation are discussed.

Adipogenic differentiation of adult equine mesenchymal stromal cells

Equine adipose tissue-derived mesenchymal stem cells (ASCs) have only recently been investigated for their adipogenic, chondrogenic, and osteogenic differentiation potential. This chapter will briefly outline the molecular mechanisms leading to adipogenesis and the methods of equine adipose tissue harvest, ASC isolation, and adipogenic differentiation. The reader is also directed to other reported methods of adipogenesis for ASCs and mesenchymal stem cells (MSCs) from other tissues.

Directional differentiation of chicken spermatogonial stem cells in vitro

BACKGROUND

Mammalian spermatogonial stem cells (SSC) are able to differentiate into different cell types in vitro, which are valuable sources for regenerative medicine and gene transfer studies. We investigated the differentiation potential of chicken SSC into osteoblasts, neuron-like cells and adipocytes in vitro.

METHODS

Chicken SSC from the testes of 18- and 20-day-old chicken embryos were cultured in different induction media for three passages in vitro. For differentiation into osteoblasts, SSC were cultured in Dulbecco's modified Eagle medium (DMEM) supplemented with 1 x 10(-4) micromol/mL desamethasone, 10 micromol/mL (beta-sodium glycerophosphate and 0.05 mg/mL vitamin C, and examined by microscopy after Von Kossa's, cytochemical and immunohistochemical staining. For differentiation into neuron-like cells, SSC were cultured in DMEM supplemented with 1 x 10(-3) micromol/mL retinoic acid (RA), 5.0 micromol/mL 3-isobutyl-1-methylxanthine (IBMX) and examined by microscopy after toluidine blue or immunohistochemical staining. For differentiation into adipocytes, SSC were cultured in DMEM supplemented with 1 x 10(-3) micromol/mL dexamethasone, 0.01 mg/mL insulin, 0.5 micromol/mL IBMX and examined by microscopy after Oil red O staining and reverse transcriptase-polymerase chain reaction (RT-PCR) for gene expression of peroxisome proliferation activation receptor-gamma (PPAR-gamma).

RESULTS

After 15 and 21 days of culture in the induction medium for osteoblast differentiation, 75% and 80% chicken SSC differentiated into osteoblasts, as confirmed by Von Kossa's, calcium-cobalt and collagen I antibody staining. After 3 and 7 days of culture in the induction medium for neuron-like cell differentiation, 78% and 85% SSC became neuron-like cells, as confirmed by staining with toluidine blue and the monoclonal antibody against neuron-specific enolase, nestin and glial fibrillary acidic protein. After 7 days of culture in the induction for adipocyte differentiation, 85% SSC differentiated into adipocytes, as confirmed by Oil red O staining and RT-PCT for PPAR-gamma gene expression.

DISCUSSION

Our results show that chicken SSC can differentiate into osteoblasts, neuron-like cells and adipocytes under similar conditions as for directional differentiation of mammalian SSC in vitro. The findings show the feasibility of using SSC-derived cells for developmental biology and gene transfer studies in chickens.

Anti-adipogenesis by 6-thioinosine is mediated by downregulation of PPAR gamma through JNK-dependent upregulation of iNOS

Adipocyte dysfunction is associated with the development of obesity. This study shows that 6-thioinosine inhibits adipocyte differentiation. The mRNA levels of PPAR gamma and C/EBPalpha, but not C/EBPbeta and delta, were reduced by 6-thioinosine. Moreover, the mRNA levels of PPAR gamma target genes (LPL, CD36, aP2, and LXRalpha) were down-regulated by 6-thioinosine. We also demonstrated that 6-thioinosine inhibits the transactivation activity and the mRNA level of PPAR gamma. Additionally, attempts to elucidate a possible mechanism underlying the 6-thioinosine-mediated effects revealed that 6-thioinosine induced iNOS gene expression without impacting eNOS expression, and that this was mediated through activation of AP-1, especially, JNK. In addition, 6-thioinosine was found to operate upstream of MEKK-1 in JNK activation signaling. Taken together, these findings suggest that the inhibition of adipocyte differentiation by 6-thioinosine occurs primarily through the reduced expression of PPAR gamma, which is mediated by upregulation of iNOS via the activation of JNK.

Down-regulation of tissue inhibitor of metalloproteinase-3 (TIMP-3) expression is necessary for adipocyte differentiation

Matrix metalloproteinase activity is essential for proper extracellular matrix remodeling that takes place during adipose tissue formation. Four tissue inhibitors of matrix metalloproteinases (TIMPs) regulate their activity. However, the role of TIMPs in adipocyte differentiation is poorly understood. We found that the expression of all TIMPs was modified during adipocyte differentiation, but that of TIMP-3 was distinguished by its extreme down-regulation. TIMP-3 expression was closely linked to the differentiation process. Indeed, it remained low during the adipocyte differentiation but increased when cell differentiation was prevented. We identified the transcription factor Sp1 as being responsible for the regulation of TIMP-3 expression during adipocyte differentiation. Overexpression of TIMP-3 reduced adipocyte differentiation, underlining its active role in this process. TIMP-3 overexpression decreased the expression of the early and obligate key inductors of adipogenesis Krüppel-like factor 4 (Klf4), early growth response 2 (Egr2/Krox20), and CAAT/enhancer-binding protein beta (C/EBPbeta). Our results indicate that during preadipocyte differentiation, the Sp1-dependent decrease in TIMP-3 expression is required for the successful implementation of the adipocyte differentiation program.

C/EBP transcription factors regulate SREBP1c gene expression during adipogenesis

The transcription factor SREBP1c (sterol-regulatory-element-binding protein 1c) is highly expressed in adipose tissue and plays a central role in several aspects of adipocyte development including the induction of PPARgamma (peroxisome-proliferator-activated receptor gamma), the generation of an endogenous PPARgamma ligand and the expression of several genes critical for lipid biosynthesis. Despite its significance, the regulation of SREBP1c expression during adipogenesis is not well characterized. We have noted that in several models of adipogenesis, SREBP1c expression closely mimics that of known C/EBPbeta (CCAAT/enhancer-binding protein beta) targets. Inhibition of C/EBP activity during adipogenesis by expressing either the dominant-negative C/EBPbeta LIP (liver-enriched inhibitory protein) isoform, the co-repressor ETO (eight-twenty one/MTG8) or using siRNAs (small interfering RNAs) targeting either C/EBPbeta or C/EBPdelta significantly impaired early SREBP1c induction. Furthermore, ChIP (chromatin immunoprecipitation) assays identified specific sequences in the SREBP1c promoter to which C/EBPbeta and C/EBPdelta bind in intact cells, demonstrating that these factors may directly regulate SREBP1c expression. Using cells in which C/EBPalpha expression is inhibited using shRNA (short hairpin RNA) and ChIP assays we show that C/EBPalpha replaces C/EBPbeta and C/EBPdelta as a regulator of SREBP1c expression in maturing adipocytes. These results provide novel insight into the induction of SREBP1c expression during adipogenesis. Moreover, the findings of the present study identify an important additional mechanism via which the C/EBP transcription factors may control a network of gene expression regulating adipogenesis, lipogenesis and insulin sensitivity.

Protein kinase Cdelta stimulates proteasome-dependent degradation of C/EBPalpha during apoptosis induction of leukemic cells

Background

The precise regulation and maintenance of balance between cell proliferation, differentiation and death in metazoan are critical for tissue homeostasis. CCAAT/enhancer-binding protein alpha (C/EBPα) has been implicated as a key regulator of differentiation and proliferation in various cell types. Here we investigated the potential dynamic change and role of C/EBPα protein during apoptosis induction.

Methodology/Principal Findings

Upon onset of apoptosis induced by various kinds of inducers such as NSC606985, etoposide and others, C/EBPα expression presented a profound down-regulation in leukemic cell lines and primary cells via induction of protein degradation and inhibition of transcription, as assessed respectively by cycloheximide inhibition test, real-time quantitative RT-PCR and luciferase reporter assay. Applying chemical inhibition, forced expression of dominant negative mutant and catalytic fragment (CF) of protein kinase Cdelta (PKCδ), which was proteolytically activated during apoptosis induction tested, we showed that the active PKCδ protein contributed to the increased degradation of C/EBPα protein. Three specific proteasome inhibitors antagonized C/EBPα degradation during apoptosis induction. More importantly, ectopic expression of PKCδ-CF stimulated the ubiquitination of C/EBPα protein, while the chemical inhibition of PKCδ action significantly inhibited the enhanced ubiquitination of C/EBPα protein under NSC606985 treatment. Additionally, silencing of C/EBPα expression by small interfering RNAs enhanced, while inducible expression of C/EBPα inhibited NSC606985/etoposide-induced apoptosis in leukemic cells.

Conclusions/Significance

These observations indicate that the activation of PKCδ upon apoptosis results in the increased proteasome-dependent degradation of C/EBPα, which partially contributes to PKCδ-mediated apoptosis.

C/EBPalpha expression is partially regulated by C/EBPbeta in response to DNA damage and C/EBPalpha-deficient fibroblasts display an impaired G1 checkpoint

We observed that C/EBPα is highly inducible in primary fibroblasts by DNA damaging agents that induce strand breaks, alkylate and crosslink DNA as well as those that produce bulky DNA lesions. Fibroblasts deficient in C/EBPα (C/EBPα^-/-) display an impaired G₁ checkpoint as evidenced by inappropriate entry into S-phase in response to DNA damage and these cells also display an enhanced G₁ to S transition in response to mitogens. The induction of C/EBPα by DNA damage in fibroblasts does not require p53. EMSA analysis of nuclear extracts prepared from UVB- and MNNG-treated fibroblasts revealed increased binding of C/EBPβ to a C/EBP consensus sequence and ChIP analysis revealed increased C/EBPβ binding to the C/EBPα promoter. To determine whether C/EBPβ has a role in the regulation of C/EBPα we treated C/EBPβ^-/- fibroblasts with UVB or MNNG. We observed C/EBPα induction was impaired in both UVB- and MNNG- treated C/EBPβ^-/- fibroblasts. Our study reveals a novel role for C/EBPβ in the regulation of C/EBPα in response to DNA damage and provides definitive genetic evidence that C/EBPα has a critical role in the DNA damage G₁ checkpoint.

Heat stimulation reduces early adipogenesis in 3T3-L1 preadipocytes

In this study, we used 3T3-L1 preadipocytes as a model to investigate the effects of heat stimulation on adipogenesis, which is a key process in the development of obesity. Heat stimulation at 43 degrees C for 60 min significantly reduced lipid accumulation, as measured by Oil Red-O assay. In the early phase of adipogenesis, heat stimulation almost completely blocked the increase of CCAAT/enhancer binding protein delta (C/EBPdelta) gene expression and delayed the onset of the increase of C/EBPbeta gene expression. The expression of proliferator-activated receptor gamma (PPARgamma), which is regulated by these factors, was also reduced. In the later phase of adipogenesis, the induction of adipocyte-specific genes, such as C/EBPalpha, adipocyte protein 2 (aP2), lipoprotein lipase (LPL), adiponectin, and glucose transporter 4 (Glut4), which are regulated by PPARgamma, was reduced. However, adipogenesis was not significantly reduced if heat stimulation was carried out after the early phase of adipogenesis. These results suggest that heat stimulation reduces adipogenesis by decreasing the expression of adipogenesis-related transcriptional factors during early adipogenesis.

Isorhamnetin represses adipogenesis in 3T3-L1 cells

Adipocyte dysfunction is strongly associated with the development of obesity, which is a major risk factor for many disorders including diabetes, hypertension, and heart disease. It is generally accepted that the regulation of adipogenesis or adipokines expression prevents obesity. In this study, we show that isorhamnetin inhibits adipocyte differentiation, as evidenced by reduced triglyceride (TG) accumulation and glycerol-3-phosphate dehydrogenase (GPDH) activity. At the molecular level, the mRNA expression levels of peroxidase proliferator-activated receptor-gamma (PPAR-gamma) and CCAAT/enhancer-binding protein-alpha (C/EBP-alpha), which are the major adipogenic transcription factors, were markedly reduced by isorhamnetin. However, the mRNA levels of C/EBP-beta and -delta, the upstream regulators of PPAR-gamma and C/EBP-alpha, were not reduced by isorhamnetin. Moreover, the mRNA levels of PPAR-gamma target genes such as lipoprotein lipase (LPL), CD36, aP2, and liver X receptor-alpha (LXR-alpha) were downregulated by isorhamnetin. We also showed that isorhamnetin inhibits the expression and secretion of adiponectin, and the results of adiponectin promoter assays suggest the inhibition of PPAR-gamma expression as a possible mechanism underlying the isorhamnetin-mediated effects. Taken together, these results indicate that isorhamnetin inhibits adipogenesis through downregulation of PPAR-gamma and C/EBP-alpha.

Characterization of the transcriptional regulation of the regulator of G protein signaling 2 (RGS2) gene during 3T3-L1 preadipocyte differentiation

Adipocyte differentiation is a complex process involving several signaling pathways. Molecular mechanisms regulating the very early stage of adipocyte differentiation is not fully appreciated yet. Several inducible genes at the early stage of preadipocyte differentiation have been identified, including the regulator of G protein signaling 2 (RGS2), a member of the RGS protein superfamily. This study aimed to clarify the precise induction profile of RGS2 and to determine the essential transcription element(s) regulating RGS2 expression in differentiating 3T3-L1 preadipocytes. RGS2 mRNA expression was elevated immediately at 1 h after differentiation initiation and it remained high until the late stage of differentiation. The putative promoter sequence (approximately 3,000 bp) of the mouse RGS2 gene was isolated and the RGS2 promoter activity was significantly upregulated 3 h after inducing differentiation. The primary signaling pathway leading to RGS2 transcriptional activation appeared to be cAMP-dependent. Sequential deletion and site-directed mutagenesis strategies demonstrate that the RGS2 promoter sequence truncated down to 78 bp in size retained full inducibility by the differentiation stimuli. Mutation of a Sp1 site within the 78 bp region significantly blocked promoter activity. In addition, high expression of Sp1 transcription factor was noted prior to and paralleling the differentiation process. Taken together, our data suggest that RGS2 transcription is immediately induced via a cAMP-dependent pathway after initiation of 3T3-L1 differentiation and the RGS2 mRNA level remains consistently high throughout the differentiation progression. A Sp1 site within RGS2 promoter appeared to be a crucial response element to regulate RGS2 transcription.

O-GlcNAc modification of Sp1 inhibits the functional interaction between Sp1 and Oct1

Sp1 is a ubiquitous transcription factor that is modified by multiple O-linked N-acetylglucosamines (O-GlcNAc). Previously, O-GlcNAcylation of a specific site of Sp1 was shown to inhibit Sp1 transcriptional activity. Yet, how O-GlcNAc on other modification sites affects Sp1 function and how O-GlcNAcylation of Sp1 affects the transcriptional regulation of a target gene remains unknown. Here we show that O-GlcNAc within the second serine/threonine-rich region of Sp1 interrupts a known interaction between Sp1 and Oct1, and inhibits the cooperative activation of the U2 snRNA gene by Sp1 and Oct1.

Modulation of the expression of the invasion-suppressor CRMP-1 by cyclooxygenase-2 inhibition via reciprocal regulation of Sp1 and C/EBPalpha

Collapsin response mediator protein-1 (CRMP-1) controls neural development and axonal growth but also acts as a cancer invasion suppressor. In this study, we investigated the transcriptional regulation of CRMP-1 expression. Using a serial deletion strategy, we identified a basal promoter region between nucleotides -100 and -180 in the 5' flanking region of CRMP-1 (nucleotides -1,920 to +50) that contains multiple putative Sp1 and C/EBPalpha sites. Site-directed mutagenesis and deletion analysis revealed that the two C/EBPalpha sites, from nucleotides -122 to -133 and from nucleotides -101 to -113, are the most important regulatory elements. Gel-shift and antibody supershift assays showed that Sp1 protein was also present at this C/EBPalpha site, which overlaps with a Sp1 site. Overexpression of Sp1 decreased CRMP-1 promoter activity and protein expression, whereas overexpression of C/EBPalpha produced the opposite effect. Chromatin immunoprecipitation assays confirmed that Sp1 and C/EBPalpha compete for binding at the overlapping C/EBPalpha and Sp1 sites and reciprocally regulate CRMP-1 expression. Overexpression of cyclooxygenase-2 (COX-2) decreased CRMP-1 mRNA and protein expression. Conversely, the COX-2 inhibitor, celecoxib, induced a dose-dependent increase in CRMP-1 expression. COX-2 inhibition also decreased Sp1-DNA complex formation and inhibited cell invasion. We conclude that transcription of the invasion suppressor, CRMP-1, is reciprocally regulated at the promoter region by C/EBPalpha and Sp1. COX-2 inhibitors increase CRMP-1 expression by inhibiting Sp1-DNA complex formation and enhancing DNA binding of C/EBPalpha at the promoter.