Role of C/EBPβ-LAP and C/EBPβ-LIP in early adipogenic differentiation of human white adipose-derived progenitors and at later stages in immature adipocytes

We investigated the role of the major isoforms of CCAAT enhancer binding protein β (C/EBPβ), C/EBPβ-LAP and C/EBPβ-LIP, in adipogenesis of human white adipose-derived stromal/progenitor cells (ASC). C/EBPβ gene expression was transiently induced early in adipogenesis. At later stages, in immature adipocytes, the C/EBPβ mRNA and protein levels declined. The C/EBPβ-LIP protein steady-state level decreased considerably stronger than the C/EBPβ-LAP level and the C/EBPβ-LIP half-life was significantly shorter than the C/EBPβ-LAP half-life. The turn-over of both C/EBPβ-isoforms was regulated by ubiquitin/proteasome-dependent degradation. These data suggest that the protein stability of the C/EBPβ-isoforms is differentially regulated in the course of adipogenesis and in immature adipocytes. Constitutive overexpression of C/EBPβ-LIP had antiadipogenic activity in human ASC. C/EBPβ-LAP, which promotes adipogenesis in mouse 3T3-L1 preadipocytes by directly activating expression of the adipogenic keyregulator PPARγ2, induced the expression of PPARγ2 and of the adipocyte differentiation gene product FABP4 in confluent ASC in the absence of adipogenic hormones. At later stages after hormone cocktail-induced adipogenesis, in immature adipocytes, constitutive overexpression of C/EBPβ-LAP led to reduced expression of PPARγ2 and FABP4, C/EBPα expression was downregulated and the expression of the adipocyte differentiation gene products adiponectin and leptin was impaired. These findings suggest that constitutive overexpression of C/EBPβ-LAP induces adipogenesis in human ASC and negatively regulates the expression of adipogenic regulators and certain adipocyte differentiation gene products in immature adipocytes. We conclude the regulation of both C/EBPβ gene expression and C/EBPβ-LIP and C/EBPβ-LAP protein turn-over plays an important role for the expression of adipogenic regulators and/or adipocyte differentiation genes in early adipogenic differentiation of human ASC and at later stages in human immature adipocytes.     

An Evi1-C/EBPβ complex controls peroxisome proliferator-activated receptor γ2 gene expression to initiate white fat cell differentiation

Fibroblastic preadipocyte cells are recruited to differentiate into new adipocytes during the formation and hyperplastic growth of white adipose tissue. Peroxisome proliferator-activated receptor γ (PPARγ), the master regulator of adipogenesis, is expressed at low levels in preadipocytes, and its levels increase dramatically and rapidly during the differentiation process. However, the mechanisms controlling the dynamic and selective expression of PPARγ in the adipocyte lineage remain largely unknown. We show here that the zinc finger protein Evi1 increases in preadipocytes at the onset of differentiation prior to increases in PPARγ levels. Evi1 expression converts nonadipogenic cells into adipocytes via an increase in the predifferentiation levels of PPARγ2, the adipose-selective isoform of PPARγ. Conversely, loss of Evi1 in preadipocytes blocks the induction of PPARγ2 and suppresses adipocyte differentiation. Evi1 binds with C/EBPβ to regulatory sites in the Pparγ locus at early stages of adipocyte differentiation, coincident with the induction of Pparγ2 expression. These results indicate that Evi1 is a key regulator of adipogenic competency.     

Berberine exerts anti-adipogenic activity through up-regulation of C/EBP inhibitors, CHOP and DEC2

Berberine exerts an anti-adipogenic activity that is associated with the down-regulation of C/EBPα and PPARγ. Stimulation of AMP-activated kinase (AMPK) caused by inhibition of mitochondrial respiration has been suggested to underlie such molecular regulation. In the present study, we show that berberine up-regulated the expression of two different sets of C/EBP inhibitors, CHOP and DEC2, while down-modulating C/EBPα, PPARγ and other adipogenic markers and effectors in differentiating 3T3-L1 preadipocytes and mature adipocytes. Data also suggested that the berberine-induced up-regulation of CHOP and DEC2 was attributable to selective activation of an unfolded protein response (UPR) and modified extracellular environment, respectively. As a result, the anti-adipogenic activity of berberine was diminished remarkably by adjusting the differentiation culture media and limitedly but consistently by knockdown of CHOP expression. Together, up-regulation of C/EBP inhibitors appears to underlie the berberine-induced repression of C/EBPα and PPARγ and, so, the inhibition of adipogenesis.     

Role of Wnt10b and C/EBPalpha in spontaneous adipogenesis of 243 cells

This report examines the balance of positive and negative adipogenic factors in a line of immortalized 243 embryonic fibroblasts that undergo spontaneous preadipocyte differentiation. Control of adipogenesis reflects the interplay of factors that promote or inhibit expression of C/EBPalpha and PPARgamma. The 243 cells express C/EBPalpha early and at elevated levels compared to 3T3-F442A preadipocytes or adipocytes. Cell clones were derived from the heterogeneous 243 population for ability or inability to differentiate into adipocytes. Wnt10b, a secreted protein that inhibits adipogenesis, is expressed at high levels in cells with low adipogenic potential and is undetectable in preadipocytes that spontaneously differentiate. In contrast, C/EBPalpha is expressed at reduced levels in cells with low adipogenic potential, and is expressed at high levels in preadipocytes that spontaneously differentiate. These data are consistent with a model in which decreased Wnt10b, coupled with increased C/EBPalpha, results in induction of PPARgamma and spontaneous adipogenesis of 243 cells.     

Rehmannia inhibits adipocyte differentiation and adipogenesis

Rehmannia glutinosa, a Traditional Chinese Medicine (TCM), has been used to increase physical strength. Here, we report that Rehmannia glutinosa extract (RE) inhibits adipocyte differentiation and adipogenesis. RE impairs differentiation of 3T3-L1 preadipocytes in a dose-dependent manner. At the molecular level, treatment with RE inhibits expression of the key adipocyte differentiation regulator C/EBPβ, as well as C/EBPα and the terminal marker protein 422/aP2, during differentiation of preadipocytes into adipocytes. Additionally, RE inhibits the mitotic clonal expansion (MCE) process of adipocyte differentiation, and RE prevents localization of C/EBPβ to the centromeres. RE also prevents high fat diet (HFD) induced weight gain and adiposity in rats. Taken together, our results indicate that Rehmannia glutinosa extract inhibits preadipocyte differentiation and adipogenesis in cultured cells and in rodent models of obesity.     

The TBN protein, which is essential for early embryonic mouse development, is an inducible TAFII implicated in adipogenesis

Human TFIID contains the TATA-binding protein (TBP) and several TBP-associated factors (hTAFs) that have been shown to play important roles, within TFIID, both in core promoter recognition and as coactivators. Here we show that the human TAF(II)43 (TAF8) is an integral component of a functional TFIID and an apparent ortholog to the recently reported mouse TBN, which is essential for early embryonic mouse developmental events. Significantly, we also show that TAF8 is dramatically induced and sequestered within TFIID upon differentiation of 3T3-L1 preadipocytes to adipocytes, whereas the expression of all other TAFs tested is slightly reduced. Moreover, when ectopically expressed, the histone fold domain of TAF8 acts as a dominant-negative mutant and selectively inhibits 3T3-L1 adipogenic differentiation. Furthermore TAF8 acts as a positive regulator of adipogenesis and reverses the inhibitory effect of its histone fold. These data suggest a selective role for TAF8 in a specific cell differentiation process(es).     

Wnt信号通路与前体脂肪细胞

Wnt蛋白是一类分泌型蛋白生长因子,通过自分泌和旁分泌作用调节多种细胞的发生和发育.新近研究表明,Wnt信号通路在前体脂肪细胞的增殖分化中发挥着重要作用.Wnt蛋白的配基通过与细胞膜上的特异性受体Frizzled1/2/5及辅助受体LRP5/6结合,激活经典或非经典的Wnt信号通路,影响下游靶基因产物的磷酸化作用,进而抑制C/EBPα、PPARγ等脂肪细胞关键转录因子,使细胞保持未分化状态,从而抑制脂肪的形成.本文就Wnt信号通路的研究史和主要分支、作用方式及其抑制脂肪细胞的机制方面进行了综述,并对今后的研究方向和应用作了展望.