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Adipocytes are the key player in adipose tissue inflammation and subsequent systemic insulin resistance and its development involves complex process of proliferation and differentiation of preadipocytes. Fistein, a polyphenol flavonoid, is known to exert anti-inflammatory, anti-carcinogenic and anti-diabetic effects. In this study, we aimed to investigate the effect of fisetin on adipocyte proliferation and differentiation in 3T3-L1 preadipocyte cell line and its mechanism of action. We found that fisetin inhibits adipocyte differentiation in a concentration dependent manner, which were evidenced by Oil Red O staining and the protein expression of mature adipocyte marker genes fatty acid synthase and peroxisome proliferator-activated receptor γ. Moreover, the proliferation of preadipocytes was also markedly suppressed by treatment of fisetin for 24 and 48 h in the differentiation medium. We also found that fisetin inhibition of adipocyte differentiation was largely due to the effect on mitotic clonal expansion. Fisetin suppression of preadipocyte proliferation at early stage of differentiation was accompanied by the changes of expression of a series of cell cycle regulatory proteins. Altogether, our results suggest that the inhibition of adipocyte differentiation by fisetin may be at least in part mediated by cell cycle arrest during adipogenesis. [ABSTRACT FROM AUTHOR]

We have shown previously that the polyamine spermidine is indispensable for differentiation of 3T3-L1 preadipocytes. In the present study, we examined the mechanism of spermidine function by using the polyamine biosynthesis inhibitor a- difluoromethylornithine in combination with the metabolically stable polyamine analogues ? -methylspermidine or (R,R)- a,?-bismethylspermine. At the early phase of differentiation, spermidine-depleted 3T3-L1 cells showed decreased translation of the transcription factor C/EBPß (CCAAT/enhancer-binding protein ß), decreased PP2A (protein phosphatase 2A) activity and increased cytoplasmic localization of the RNA-binding protein HuR (human antigen R). The amount of HuR bound to C/EBPß mRNA was reduced, whereas the amount of bound CUGBP2, an inhibitor of C/EBPß translation, was increased. ANP32 (acidic nuclear phosphoprotein 32) proteins, which are known PP2A inhibitors and HuR ligands, bound more PP2A and HuR in spermidine-depleted than in control cells, whereas immunodepletion of ANP32 proteins from the lysate of spermidine-depleted cells restored PP2A activity. Taken together, our data shows that spermidine promotes C/EBPß translation in differentiating 3T3-L1 cells, and that this process is controlled by the interaction of ANP32 with HuR and PP2A. [ABSTRACT FROM AUTHOR]

In 3T3-L1 preadipocyte differentiation, the CCAAT/enhancer-binding protein-β (C/EBPβ) is an important early transcription factor that activates cell cycle genes during mitotic clonal expansion (MCE), sequentially activating peroxisome proliferator-activated receptor-γ (PPARγ) and C/EBPα during terminal differentiation. Although C/EBPβ acquires its DNA binding activity via dual phosphorylation at about 12-16 h postinduction, the expression of PPARγ and C/EBPα is not induced until 36-72 h. The delayed expression of PPARγ and C/EBPα ensures the progression of MCE, but the mechanism responsible for the delay remains elusive. We provide evidence that G9a, a major euchromatic methyltransferase, is transactivated by C/EBPβ and represses PPARγ and C/EBPα through H3K9 dimethylation of their promoters during MCE. Inhibitor- or siRNA-mediated G9a downregulation modestly enhances PPARγ and C/EBPα expression and adipogenesis in 3T3-L1 preadipocytes. Conversely, forced expression of G9a impairs the accumulation of triglycerides. Thus, this study elucidates an epigenetic mechanism for the delayed expression of PPARγ and C/EBPα. [ABSTRACT FROM AUTHOR]

Abstract: Resveratrol is known as a potent antiobesity compound that acts partly through inhibition of adipogenesis. However, the direct targets responsible for its antiadipogenic action are unclear. Our hypothesis is that resveratrol inhibits adipogenesis through modulation of mitotic clonal expansion (MCE) and cell signaling pathways in the early phase of differentiation. To test this, we examined the effects of resveratrol on MCE and insulin signaling pathway in the early phase of adipogenesis in murine preadipocytes. We observed that the antiadipogenic action of resveratrol is largely limited to the early phase of adipogenesis. Specifically, the presence of resveratrol in the first 24 hours of adipogenesis was required for its antiadipogenic effect. During the first 24 hours of adipogenesis, resveratrol impaired the progression of MCE by suppressing the cell cycle entry of preadipocytes to G2/M phase, and expression of cell cycle regulators cyclin A and cyclin-dependent kinase 2. Concomitantly, resveratrol inhibited insulin signaling pathway in the early phase of adipogenesis. Furthermore, we revealed an inhibitory effect of resveratrol on insulin receptor (IR) activity, and this is likely through a direct physical interaction between resveratrol and IR. The antiadipogenic effect of resveratrol is through inhibition of the MCE and IR-dependent insulin signaling pathway in the early phase of adipogenesis. [Copyright &y& Elsevier]

Abstract: Adipocyte differentiation is a key process in determining the number of mature adipocytes in the development of obesity. Here, we examined the function of curcumin, a dietary polyphenol found in turmeric, and its underlying mechanisms in adipocyte differentiation. Our study reveals that curcumin exerts an anti-adipogenic function both in 3T3-L1 murine cells and in human primary preadipocytes as determined by intracellular lipid accumulation assay, quantitative analysis of adipocyte marker gene expression and a noninvasive multimodal Coherent Anti-Stokes Raman Scattering (CARS) microscopic analysis of intracellular curcumin. The inhibitory action of curcumin was largely limited to the early stage of adipocyte differentiation, where curcumin was found to inhibit mitotic clonal expansion (MCE) process as evidenced by impaired proliferation, cell-cycle entry into S phase and the S to G2/M phase transition of confluent cells, and levels of cell cycle-regulating proteins with no significant effect on cell viability and cytotoxicity. This, in turn, resulted in inhibition of mRNA levels of early adipogenic transcription factors, particularly Krüppel-like factor 5 (KLF5), CCAAT/enhancer binding proteinα (C/EBPα) and peroxisome proliferator-activated receptorγ (PPARγ), in the early stage of adipocyte differentiation. Supplementation with rosiglitazone, a PPARγ ligand, during the early stage of adipocyte differentiation partially rescued curcumin-inhibited adipocyte differentiation. Collectively, our results show that curcumin is an anti-adipogenic dietary bioactive component largely involved in the modulation of the MCE process during the early stage of adipocyte differentiation. [Copyright &y& Elsevier]

Abstract: Adipogenesis is stimulated in 3T3-L1 fibroblast by a combination of insulin, dexamethasone, and methylisobutylxanthine (MIX). Mitotic clonal expansion (MCE) precedes differentiation of 3T3-L1 fibroblast to adipocytes. MIX increases cAMP content, which is the activator of protein kinase A (PKA). However, PKA-independent cAMP signaling has also been described. In this paper, it was found that H89, an inhibitor of PKA, was able to block MCE but not differentiation of 3T3-L1 fibroblast. Consistently, MCE did not occur in the absence of MIX in the differentiation mixture but was recovered by overexpression of a catalytic subunit of PKA. In addition, the transfection of 3T3-L1 fibroblast with a dominant-negative mutant of PKA inhibited MCE. On the other hand, differentiation of 3T3-L1 fibroblast to adipocytes did not occur when MIX was not present in the differentiation mixture and it could not be recovered by overexpression of a catalytic subunit of PKA. Differentiation was restored by addition of either dibutyryl-cAMP (db-cAMP) or 8 CPT-2 Me-cAMP. The latter activates cAMP-EPAC but not PKA signaling. These results indicate that cAMP–PKA-independent signaling, is required for 3T3-L1 fibroblasts differentiation to adipocytes and MIX signaling through cAMP–PKA is necessary for MCE, although MCE is not essential for adipogenesis. [Copyright &y& Elsevier]

Abstract: AMP-activated protein kinase (AMPK) activation inhibits adipocyte differentiation. This study investigated the effect of compound C (CC), a widely used AMPK inhibitor, on differentiation of 3T3-L1 preadipocytes. CC treatment blocked hormone-induced preadipocyte differentiation due to inhibition of mitotic clonal expansion, which was accompanied by the failure of degradation of p21, a cyclin-dependent kinase inhibitor. CC increased the level of p21 protein, but not its mRNA, in preadipocytes incubated in a hormone-free medium. Cycloheximide decreased the basal p21 level, which was inhibited by CC treatment, supporting the stabilization of p21 by CC. Treatment of AICAR or metformin, AMPK activators, failed to induce p21 or inhibit the ability of CC to increase p21 level. In conclusion, CC inhibits proliferation of preadipocytes as a consequence of an increase in p21 content, which might result from p21 stabilization, and the increase in p21 level by CC might not be associated with AMPK inhibition. [Copyright &y& Elsevier]

Adipocytokines, bioactive molecules secreted from adipose tissues, play important roles in physiology, development, and disease. Recently, heparin-binding epidermal growth factor-like growth factor (HB-EGF) was identified as an adipocytokine whose expression correlates with obesity. However, the biological role of fat-secreted HB-EGF is still unclear. In this study, we investigated the effects of HB-EGF on the adipocyte differentiation of C3H10T1/2 pluripotent mesenchymal cells. Upon adipogenic conversion of C3H10T1/2 cells, HB-EGF displayed dynamic changes in expression where an initial decrease was followed by increased levels of expression at later stages. HB-EGF treatment during adipogenic induction inhibited lipid accumulation and decreased the expression of adipocyte molecular markers (fatty acid-binding protein, peroxisome proliferator-activated receptor γ, and CAAT enhancer-binding protein α) and lipogenic genes (glucose transporter, fatty acid synthetase, and lipoprotein lipase). Therefore, HB-EGF has an inhibitory effect on adipocyte differentiation. Administration of HB-EGF at various intervals during adipocyte differentiation revealed that HB-EGF acts during the early stages of adipocyte differentiation, but not at the later stages of differentiation. Furthermore, HB-EGF was able to block the commitment of pluripotent mesenchymal cells to the adipocyte lineage triggered by bone morphogenic protein 4 treatment. These data suggest that HB-EGF acts as a negative regulator of adipogenesis by inhibiting the commitment and early differentiation of the adipose lineage. The inhibitory role of HB-EGF on adipocyte differentiation of pluripotent mesenchymal cells sheds light on potential mechanisms that control adipose tissue homeostasis. [ABSTRACT FROM AUTHOR]

Upon induction of differentiation, growth-arrested (G1 phase) 3T3-L1 preadipocytes express CCAAT/enhancer binding protein-β (C/EBPβ), initiating a transcriptional cascade. C/EBPβ immediately undergoes a priming phosphorylation (on Thr188) by MAPK/ERK. However, the acquisition of DNA binding and transactivation capacity of C/EBPβ is delayed until further phosphorylation (on Ser184 or Thr179) by GSK3β occurs. Phosphorylation by glycogen synthase kinase-3β (GSK3β) induces S phase entry and thereby mitotic clonal expansion (MCE), a requirement for terminal differentiation. Because MAPK activity is down-regulated before S phase is completed, we sought to identify the kinase that maintains C/EBPβ in the primed phosphorylated state throughout S phase and MCE. We show here that cdk2/cyclinA, whose expression is activated at the onset of S phase, functions in this capacity. Ex vivo and in vitro experiments show that cdk2/cyclinA catalyzes this delayed priming phosphorylation. Mass spectrometric analysis revealed that cdk2/cyclinA phosphorylates C/EBPβ on Thr188 and is required for phosphorylation (on Ser184 or Thr179) of C/EBPβ by GSK3β and maintenance of DNA binding activity. Suppression of cdk2 activity by RNA interference or pharmacologic inhibitor disrupts subsequent events in the differentiation program. Thus, MAPK and cdk2/cyclinA act sequentially to maintain Thr188 of C/EBPβ in the primed phosphorylated state during MCE and thereby progression of terminal differentiation. [ABSTRACT FROM AUTHOR]

Abstract: Hormonal induction triggers a cascade leading to the expression of CCAAT/enhancer-binding protein(C/EBP)α and peroxisome proliferator-activated receptor (PPAR) γ, C/EBPα, and PPARγ turns on series of adipocyte genes that give rise to the adipocyte phenotype. Previous findings indicate that C/EBPβ, a transcriptional activator of the C/EBPα and PPARγ genes, is rapidly expressed after induction, but lacks DNA-binding activity and therefore cannot activate transcription of the C/EBPα and PPARγ genes early in the differentiation program. Acquisition of DNA-binding activity of C/EBPβ occurs when CHOP-10, a dominant-negative form of C/EBP family members, is down-regulated and becomes hyperphosphorylated as preadipocytes traverse the G1–S checkpoint of mitotic clonal expansion. Evidences are presented in this report that lactacystin, a proteasome inhibitor, up-regulated the CHOP-10 expression, blocked the DNA-binding activity of C/EBPβ, and subsequently inhibited MCE as well as adipocyte differentiation. [Copyright &y& Elsevier]

CCAAT enhancer-binding protein (C/EBP)β, C/EBPα, and peroxisome proliferator activated receptor (PPAR)&#x03B3 act in a cascade where C/EBPβ activates expression of C/EBPα and PPAR&#x03B3, which then function as pleiotropic activators of genes that produce the adipocyte phenotype. When growth-arrested 3T3-L1 preadipocytes are induced to differentiate, C/EBPβ is rapidly expressed but still lacks DNA-binding activity. After a long (14-hour) lag, glycogen synthase kinase 3β enters the nucleus, which correlates with hyperphosphorylation of C/EBPβ and acquisition of DNA-binding activity. Concurrently, 3T3-L1 preadipocytes synchronously enter S phase and undergo mitotic clonal expansion, a prerequisite for terminal differentiation. Ex vivo and in vitro experiments with C/E8Pβ show that phosphorylation of Thr-188 by mitogen-activating protein kinase "primes" C/EBPβ for subsequent phosphorylation on Ser-184 and Thr-179 by glycogen synthase kinase 3β acquisition of DNA-binding function, and transactivation of the C/EBPα and PPAR&#x03B3 genes. The delayed transactivation of the C/EBPα and PPAR&#x03B3 genes by C/EBPβ appears necessary to allow mitotic clonal expansion, which would otherwise be prevented because C/EBPα and PPAR&#x03B3 are antimitotic. [ABSTRACT FROM AUTHOR]

In response to hormonal stimulation quiescent 3T3-L1 preadipocyte cells reenter the cell cycle and undergo a mitotic expansion phase prior to terminal differentiation. The cell cycle regulatory proteins p130 and p107 undergo dramatic changes in protein levels within 24 h of differentiation. The role of these proteins in regulating adipocyte mitotic clonal expansion and/or differentiation are unclear. It has recently been demonstrated that adipocyte proliferation can be uncoupled from adipocyte differentiation through the use of the pharmacological MEK inhibitor PD98059 or the tyrosine phosphatase inhibitor, sodium vanadate. We examined the expression of p130 and p107 in stimulated 3T3-L1 cells in the presence of either PD98059, U0126 or sodium vanadate. While inhibition of MEK blocked proliferation, the cells underwent differentiation normally. In contrast, vanadate blocked differentiation without affecting proliferation. Inhibition of MEK did not affect the increase in p107 expression in stimulated cells indicating that induction of p107 is independent of MAP kinase signaling. Vanadate treatment caused a significant delay in p107 expression in the first 24 h following stimulation. Under these conditions, p130 expression was relatively unchanged. Our results indicate that a rapid increase in p107 expression correlates with a commitment to undergo adipocyte differentiation. The data further suggest that the rapid induction of p107 is not required for cellular proliferation during the mitotic clonal expansion phase. Taken together, these findings provide correlative data that implicate p107 in the terminal differentiation, but not proliferation, of quiescent preadipocytes following hormonal stimulation. [Copyright &y& Elsevier]

Adipogenesis is a complex process in which cell commitment and mitotic clonal expansion (MCE) are in-sequence crucial events leading to terminal adipocyte differentiation. The molecules able to block some key signals in this cascade can hamper adipogenesis becoming promising agents to counteract hyperplasia and hypertrophy of adipose tissue. Mono- and di-caffeoylquinic acid isomers are biologically active polyphenols, displaying in vitro and in vivo antioxidant, hepatoprotective, anti-diabetic and anti-obesity properties. Among these isomers, 3,5-dicaffeoylquinic acid (DCQA) has been reported to inhibit lipid accumulation in adipose cells more successfully than others. Thus, we investigated DCQA effects and molecular mechanisms on 3T3-L1 pre-adipocytes induced to differentiate with a hormonal cocktail (MDI). Oil Red O incorporation assessed that DCQA pre-treatment inhibited lipid accumulation in 3T3-L1 cells induced to differentiate for 10 days. At this time, an increased phosphorylation of both AMP-activated kinase and acetyl-CoA carboxylase, as well as a strong decrease in fatty acid synthase protein level, were registered by immunoblotting, thereby suggesting that DCQA treatment can reduce fatty acid anabolism in 3T3-L1 adipocytes. Furthermore, BrdU incorporation assay, performed 48 h after hormonal stimulation, revealed that DCQA treatment was also able to hinder the 3T3-L1 cell proliferation during the MCE, which is an essential step in the adipogenic process. Thus, we focused our attention on early signals triggered by the differentiation stimuli. In the first hours after hormonal cocktail administration, the activation of ERK1/2 and Akt kinases, or CREB and STAT3 transcription factors, was not affected by DCQA pre-treatment. Whereas 24 h after MDI induction, DCQA pre-treated cells showed increased level of the transcription factor Nrf2, that induced the expression of the antioxidant enzyme heme oxygenase 1 (HO-1). In control samples, the expression level of HO-1 was reduced 24 h after MDI induction in comparison with the higher amount of HO-1 protein found at 2 h. The HO-1 decrease was functional by allowing reactive oxygen species to boost and allowing cell proliferation induction at the beginning of MCE phase. Instead, in DCQA-treated cells the HO-1 expression was maintained at high levels for a further 24 h; in fact, its expression decreased only 48 h after MDI stimulation. The longer period in which HO-1 expression remained high led to a delay of the MCE phase, with a subsequent inhibition of both C/EBP-α expression and adipocyte terminal differentiation. In conclusion, DCQA counteracting an excessive adipose tissue expansion may become an attractive option in obesity treatment. [ABSTRACT FROM AUTHOR]

The flower of Inula britannica contains various phenolic compounds with prophylactic properties. This study aimed to determine the anti-adipogenic effect of an I. britannica flower aqueous extract (IAE) and its underlying mechanisms in the 3T3-L1 preadipocytes and to identify the phenolic compounds in the extract. Treatment with IAE inhibited the adipogenesis of 3T3-L1 preadipocytes by showing a dose-dependently suppressed intracellular lipid accumulation and significantly mitigated expression levels of lipogenesis- and adipogenesis-associated biomarkers including transcription factors. IAE exerted an anti-adipogenic effect through the modulation of the early phases of adipogenesis including mitotic clonal expansion (MCE). Treatment with IAE inhibited MCE by arresting the cell cycle at the G0/G1 phase and suppressing the activation of MCE-related transcription factors. Furthermore, IAE inhibited adipogenesis by regulating the extracellular signal-regulated kinase 1/2 and Akt signaling pathways. Protocatechuic acid, chlorogenic acid, kaempferol-3-O-glucoside, and 6-methoxyluteolin, which are reported to exhibit anti-adipogenic properties, were detected in IAE. Therefore, modulation of early phases of adipogenesis, especially MCE, is a key mechanism underlying the anti-adipogenic activity of IAE. In summary, the anti-obesity effects of IAE can be attributed to its phenolic compounds, and hence, IAE can be used for the development of anti-obesity products. [ABSTRACT FROM AUTHOR]

Tanshinone I (Tan I) is a diterpenoid isolated from Salvia miltiorrhiza Bunge and exhibits antitumor effects in several cancers. However, the anti-obesity properties of Tan I remain unexplored. Here, we evaluated the anti-obesity effects of Tan I in high-fat-diet (HFD)-induced obese mice and investigated the underlying molecular mechanisms in 3T3-L1 cells. HFD-induced obese mice were orally administrated Tan I for eight weeks, and body weight, weight gain, hematoxylin and eosin staining and serum biological parameters were examined. The adipogenesis of 3T3-L1 preadipocytes was assessed using Oil Red O staining and measurement of intracellular triglyceride (TG) levels, and mitotic clonal expansion (MCE) and its related signal molecules were analyzed during early adipogenesis of 3T3-L1 cells. The administration of Tan I significantly reduced body weight, weight gain, and white adipocyte size, and improved obesity-induced serum levels of glucose, free fatty acid, total TG, and total cholesterol in vivo in HFD-induced obese mice. Furthermore, Tan I-administered mice demonstrated improvement of glucose metabolism and insulin sensitivity. Treatment with Tan I inhibited the adipogenesis of 3T3-L1 preadipocytes in vitro, with this inhibition mainly occurring at an early phase of adipogenesis through the attenuation of MCE via cell cycle arrest at the G1/S phase transition. Tan I inhibited the phosphorylation of p38, extracellular signal-regulated kinase (ERK), and Akt during the process of MCE, while it stimulated the phosphorylation of AMP-activated protein kinase. Furthermore, Tan I repressed the expression of CCAAT-enhancer-binding protein β (C/EBPβ), histone H3K9 demethylase JMJD2B, and subsequently cell cycle genes. Moreover, Tan I regulated the expression of early adipogenic transcription factors including GATAs and Kruppel-like factor family factors. These results indicate that Tan I prevents HFD-induced obesity via the inhibition of early adipogenesis, and thus improves glucose metabolism and insulin sensitivity. This suggests that Tan I possesses therapeutic potential for the treatment of obesity and obesity-related diseases. [ABSTRACT FROM AUTHOR]

Background: White adipose tissue includes subcutaneous and visceral adipose tissue (SAT and VAT) with different metabolic features. SAT protects from metabolic disorders, while VAT promotes them. The proliferative and adipogenic potentials of adipose-derived stem cells (ADSCs) are critical for maintaining adipose tissue homeostasis through driving adipocyte hyperplasia and inhibiting pathological hypertrophy. However, it remains to be elucidated the critical molecules that regulate different potentials of subcutaneous and visceral ADSCs (S-ADSCs, V-ADSCs) and mediate distinct metabolic properties of SAT and VAT. CD90 is a glycosylphosphatidylinositol-anchored protein on various cells, which is also expressed on ADSCs. However, its expression patterns and differential regulation on S-ADSCs and V-ADSCs remain unclear. Methods: S-ADSCs and V-ADSCs were detected for CD90 expression. Proliferation, colony formation, cell cycle, mitotic clonal expansion, and adipogenic differentiation were assayed in S-ADSCs, V-ADSCs, or CD90-silenced S-ADSCs. Glucose tolerance test and adipocyte hypertrophy were examined in mice after silencing of CD90 in SAT. CD90 expression and its association with CyclinD1 and Leptin were analyzed in adipose tissue from mice and humans. Regulation of AKT by CD90 was detected using a co-transfection system. Results: Compared with V-ADSCs, S-ADSCs expressed high level of CD90 and showed increases in proliferation, mitotic clonal expansion, and adipogenic differentiation, together with AKT activation and G1-S phase transition. CD90 silencing inhibited AKT activation and S phase entry, thereby curbing proliferation and mitotic clonal expansion of S-ADSCs. In vivo CD90 silencing in SAT inhibited S-ADSC proliferation, which caused adipocyte hypertrophy and glucose intolerance in mice. Furthermore, CD90 was highly expressed in SAT rather than in VAT in human and mouse, which had positive correlation with CyclinD1 but negative correlation with Leptin. CD90 promoted AKT activation through recruiting its pleckstrin homology domain to plasma membrane. Conclusions: CD90 is differentially expressed on S-ADSCs and V-ADSCs, and plays critical roles in ADSC proliferation, mitotic clonal expansion, and hemostasis of adipose tissue and metabolism. These findings identify CD90 as a crucial modulator of S-ADSCs and V-ADSCs to mediate distinct metabolic features of SAT and VAT, thus proposing CD90 as a valuable biomarker or target for evaluating ADSC potentials, monitoring or treating obesity-associated metabolic disorders. [ABSTRACT FROM AUTHOR]

Patients with metabolic syndrome are at an increased risk of developing type 2 diabetes and cardiovascular diseases. The principal risk factor for development of metabolic syndrome is obesity, defined as a state of pathological hyperplasia or/and hypertrophy of adipose tissue. The number of mature adipocytes is determined by adipocyte differentiation from preadipocytes. The purpose of the present study is to investigate the effects of curcumin on adipogenesis and the underlying mechanism. To examine cell toxicity of curcumin, 3T3-L1 preadipocytes were treated with 0–50 µM curcumin for 24, 48, or 72 h, then cell viability was measured using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The effect of curcumin on the cell cycle was determined by flow cytometry. Curcumin-induced cell apoptosis was determined by the TUNEL assay and curcumin-induced caspase activation was measured by immunoblotting. The effect of curcumin on adipocyte differentiation was determined by measuring mitotic clonal expansion (MCE), expression of adipogenic transcription factors, and lipid accumulation. Results showed the viability of preadipocytes was significantly decreased by treatment with 30 µM curcumin, a concentration that caused apoptosis in preadipocytes, as assessed by the TUNEL assay, and caused activation of caspases 8, 9, and 3. A non-cytotoxic dose of curcumin (15 µM) inhibited MCE, downregulated the expression of PPARγ and C/EBPα, prevented differentiation medium-induced β-catenin downregulation, and decreased the lipid accumulation in 3T3-L1 adipocytes. In conclusion, our data show that curcumin can induce preadipocyte apoptosis and inhibit adipocyte differentiation, leading to suppression of adipogenesis. [ABSTRACT FROM AUTHOR]

Obesity is becoming a global problem. Research into the detailed mechanism of adipocyte development is crucial for the treatment of excess fat. Zinc finger protein 217 plays roles in adipogenesis. However, the underlying mechanism remains unclear. Here, we demonstrated that ZFP217 knockdown prevented the mitotic clonal expansion process and caused adipogenesis inhibition. Depletion of ZFP217 increased the expression of the m 6 A methyltransferase METTL3, which upregulated the m 6 A level of cyclin D1 mRNA. METTL3 knockdown rescued the siZFP217-inhibited MCE and promoted CCND1 expression. YTH domain family 2 recognized and degraded the methylated CCND1 mRNA, leading to the downregulation of CCND1. Consequently, cell-cycle progression was blocked, and adipogenesis was inhibited. YTHDF2 knockdown relieved siZFP217-inhibited adipocyte differentiation. These findings reveal that ZFP217 knockdown-induced adipogenesis inhibition was caused by CCND1, which was mediated by METTL3 and YTHDF2 in an m 6 A-dependent manner. We have provided novel insight into the underlying molecular mechanisms by which m 6 A methylation is involved in the ZFP217 regulation of adipogenesis.

Objective: Kaempferide and 4,2'-dihydroxy-4',5',6'-trimethoxychalcone (DTMC) are two major flavonoids found in Chromolaena odorata Linn. leaf extract. The aim of this study was to elucidate the mechanism by which these two flavonoids exerted their effect on adipogenesis. The inhibitory effect of kaempferide and DTMC on adipocyte differentiation and their mechanisms involving mitotic clonal expansion (MCE) and apoptosis during the early stage of adipogenesis were investigated., Methods: Confluent 3T3-L1 preadipocytes were induced to differentiate and exposed to the flavonoids during various phases of differentiation. Intracellular lipid accumulation, cell density and expression of the transcription factors peroxisome proliferator-activated receptor γ and CCAAT/enhancer-binding proteins α were assessed using AdipoRed, Oil red O and Western blot assays. Effects of both flavonoids on cell proliferation and apoptosis were also determined by carboxyfluorescein diacetate succinimidyl ester and annexin V-fluorescein isothiocyanate/propidium iodide-staining assays, respectively., Results: Kaempferide and DTMC showed significant, concentration-dependent anti-adipogenic activity and effect on cell density in the early phase of adipogenesis. The expression of the transcription factors seemed to be reduced when the treatment was prolonged or in the early phase of adipogenesis. These flavonoids interrupted MCE via inhibition of preadipocyte proliferation and induction of apoptosis. DTMC was nearly three times more potent than kaempferide in inducing apoptosis., Conclusion: Kaempferide and DTMC exerted their anti-adipogenic activity through inhibition of MCE, either by suppressing cell proliferation or by inducing apoptosis during the early phase of differentiation., (Copyright © 2019 Shanghai Changhai Hospital. Published by Elsevier B.V. All rights reserved.)

Adipose tissue stores energy and plays an important role in energy homeostasis. CCAAT/enhancer-binding protein β (C/EBPβ) is an important early transcription factor for 3T3-L1 preadipocyte differentiation, facilitating mitotic clonal expansion (MCE) and transactivating C/EBPα and peroxisome proliferator-activated receptor-γ (PPARγ) to promote adipogenesis. C/EBPβ is induced early, but the expression of antimitotic C/EBPα and PPARγ is not induced until ∼48 h. The delayed expression of C/EBPα and PPARγ is thought to ensure MCE progression, but the molecular mechanism for this delay remains elusive. Here, we show that the zinc-finger transcription factor Krüppel-like factor 10 (KLF10) is induced after adipogenic induction and that its expression positively correlates with that of C/EBPβ but inversely correlates with expression of C/EBPα and PPARγ. C/EBPβ bound to the KLF10 promoter and transactivated its expression during MCE. KLF10 overexpression in 3T3-L1 preadipocyte repressed adipogenesis and decreased C/EBPα and PPARγ expression, whereas siRNA-mediated down-regulation of KLF10 enhanced adipogenesis and increased C/EBPα and PPARγ expression. Luciferase assays revealed an inhibitory effect of KLF10 on C/EBPα promoter activity. Using promoter deletion and mutation analysis, we identified a KLF10-binding site within the proximal promoter region of C/EBPα. Furthermore, KLF10 interacted with and recruited histone deacetylase 1 (HDAC1) to the C/EBPα promoter, decreasing acetylated histone H4 on the C/EBPα promoter and inactivating C/EBPα transcription. Because C/EBPα can transactivate PPARγ, our results suggest a mechanism by which expression of C/EBPα and PPARγ is delayed via KLF10 expression and shed light on the negative feedback loop for C/EBPβ-regulated adipogenesis in 3T3-L1 preadipocyte., (© 2018 Liu et al.)

Adipogenesis is a key driver of the expansion of adipose tissue mass that causes obesity. Hirsutenone (HST) is an active botanical diarylheptanoid present in Alnus species. In this study, we evaluated the effects of HST on adipogenesis, its mechanisms of action and the molecular targets involved. Using Oil Red O staining, we observed that HST dose-dependently suppresses lipid accumulation during adipogenesis in 3T3-L1 preadipocytes, concomitant with a decrease in peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα) and fatty acid synthase (FAS) protein expression. This inhibitory effect was largely limited to the early stage of adipogenesis, which includes mitotic clonal expansion (MCE), as evidenced by delayed cell cycle entry of preadipocytes from G1 to S phase. Furthermore, the regulation of MCE was accompanied by suppression of phosphatidylinositol 3-kinase (PI3K) and extracellular-regulated kinase (ERK) activity. HST was also shown to bind directly to PI3K and ERK1 in a non-ATP competitive manner. Our results suggest that HST attenuates adipogenesis by directly targeting PI3K and ERK during MCE in 3T3-L1 preadipocytes, underscoring the potential therapeutic application of HST in preventing obesity., (© 2015 Wiley Periodicals, Inc.)

Intramuscular fat (IMF) is a crucial factor for the meat quality of chickens. With the aim of studying the molecular mechanisms underlying IMF deposition in chickens, the expression profiles of five candidate transcription factors involved in lipid metabolism in several tissues were examined in Beijing-You (BJY) chickens at five ages (0, 4, 8, 14 and 20 wk). Results showed that accumulation of IMF in breast (IMFbr), thigh (IMFth) and abdominal fat weight increased significantly (P<0.01) after 8 wk. Accumulation of both IMFbr and IMFth from 8 to 14 wk exceeded that from 14 to 20 wk; IMFth was 4-7 times of IMFbr. As for the expression profiles of key transcription factors: 1) expression of C/EBPα and PPARγ in abdominal fat was significantly higher than that in breast and thigh muscles at all ages. The expression of C/EBPα was positively correlated with PPARγ in both breast and thigh muscles, which indicated that both C/EBPα and PPARγ promoted fat deposition and might act through a unified pathway; 2) the expression of SREBP-1 in 0, 4, and 8 wk in thigh muscle was significantly higher than that in breast; 3) expression of C/EBPβ at 4 and 8 wk was significantly higher than that at 14 and 20 wk; and it was positively correlated with IMFth and IMFbr from 0 to 8 wk; 4) expression of PPARα in breast and thigh muscles was significantly higher than that in abdominal fat. Taken together, all five transcription factors studied play roles in lipid metabolism in chickens with C/EBPα and PPARγ being important effectors., (© 2013.)