Terminal differentiation of stem cells is characterized by cessation of cell proliferation as well as changes in cell morphology associated with the differentiated state. For adipocyte differentiation, independent lines of evidence show that the transcription factors peroxisome proliferator activated receptor gamma (PPARgamma) and CCAAT/enhancer-binding protein alpha (C/EBPalpha) as well as the tumor suppressor retinoblastoma (Rb) protein are essential. How these proteins promote adipocyte conversion and how they function cooperatively during the differentiation process remain unclear. We have used retinoic acid (RA) inhibition of adipogenesis to investigate these issues. RA blocked adipogenesis of 3T3-L1 cells induced to differentiate by ectopic expression of PPARgamma and C/EBPalpha independently or together. However, under these circumstances RA was only effective at preventing adipogenesis when added prior to confluence, suggesting that factors involved in regulation of the cell cycle might play a role in establishing the commitment state of adipogenesis that is insensitive to RA. During differentiation of wild type 3T3 L1 preadipocytes, we found that Rb protein is hyperphosphorylated early in adipogenesis, corresponding to previously quiescent cells re-entering the cell cycle, and later becomes hypophosphorylated. The data suggest that, together with the coexpression of PPARgamma and C/EBPalpha, permanent exit from the cell cycle establishes the irreversible commitment to adipocyte differentiation.
"Because the expression of both isoforms of PPARγ, but not C/EBPα, is partially dependent on Nrf2 (Hou et al., 2012; Pi et al., 2010a), INH-induced downregulation of PPARγ during adipogenesis may be attributed, at least in part, to the suppression of Nrf2-ARE activity. It has been well documented that PPARγ and C/EBPα form a positive feedback loop by activating each other's expression and play roles at a later stage by inducing and maintaining expression of adipocyte-specific genes (Shao and Lazar, 1997; Wu et al., 1999). Thus, the reduction of C/EBPα during adipogenesis caused by INH treatment could be a secondary consequence of reduced expression and activity of PPARγ. "
[Show abstract][Hide abstract] ABSTRACT: Transcriptional signaling through the antioxidant response element (ARE), orchestrated by the Nuclear factor E2-related factor 2 (Nrf2), is a major cellular defense mechanism against oxidative or electrophilic stress. Here, we reported that isoniazid (INH), a widely used antitubercular drug, displays a substantial inhibitory property against ARE activities in diverse mouse and human cells. In 3T3-L1 preadipocytes, INH concentration-dependently suppressed the ARE-luciferase reporter activity and mRNA expression of various ARE-dependent antioxidant genes under basal and oxidative stressed conditions. In keeping with our previous findings that Nrf2-ARE plays a critical role in adipogenesis by regulating expression of CCAAT/enhancer-binding protein β (C/EBPβ) and peroxisome proliferator-activated receptor γ (PPARγ), suppression of ARE signaling by INH hampered adipogenic differentiation of 3T3-L1 cells and human adipose-derived stem cells (ADSCs). Following adipogenesis induced by hormonal cocktails, INH-treated 3T3-L1 cells and ADSCs displayed significantly reduced levels of lipid accumulation and attenuated expression of C/EBPα and PPARγ. Time-course studies in 3T3-L1 cells revealed that inhibition of adipogenesis by INH occurred in the early stage of terminal adipogenic differentiation, where reduced expression of C/EBPβ and C/EBPδ was observed. To our knowledge, the present study is the first to demonstrate that INH suppresses ARE signaling and interrupts with the transcriptional network of adipogenesis, leading to impaired adipogenic differentiation. The inhibition of ARE signaling may be a potential underlying mechanism by which INH attenuates cellular antioxidant response contributing to various complications.
"Adipogenesis in mammals is regulated both genetically and hormonally. It has been demosntrated that adipogenic transcription factors, such as proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer-binding proteins (C/EBPs), Krüppel-like factors (KLFs) and sterol regulatory element-binding protein (SREBP) are involved in the differentiation of adipocytes [4–6]. "
[Show abstract][Hide abstract] ABSTRACT: Adipogenesis is tightly regulated by altering gene expression, and TNF-α is a multifunctional cytokine that plays an important role in regulating lipogenesis. MicroRNAs are strong post-transcriptional regulators of cell differentiation. In our previous work, we found high expression of miR-181a in a fat-rich pig breed. Using bioinformatic analysis, miR-181a was identified as a potential regulator of TNF-α. Here, we validated TNF-α as the target of miR-181a by a dual luciferase assay. In response to adipogenesis, a mimic or inhibitor was used to overexpress or reduce miR-181a expression in porcine pre-adipocytes, which were then induced into mature adipocytes. Overexpression of miR-181a accelerated accumulation of lipid droplets, increased the amount of triglycerides, and repressed TNF-α protein expression, while the inhibitor had the opposite effect. At the same time, TNF-alpha rescued the increased lipogenesis by miR181a mimics. Additionally, miR-181a suppression decreased the expression of fatty synthesis associated genes PDE3B (phosphodiesterase 3B), LPL (lipoprotein lipase), PPARγ (proliferator-activated receptor-γ), GLUT1(glucose transporter), GLUT4, adiponectin and FASN (fatty acid synthase), as well as key lipolytic genes HSL (hormone-sensitive lipase) and ATGL (adipose triglyceride lipase) as revealed by quantitative real-time PCR. Our study provides the first evidence of the role of miR-181a in adipocyte differentiation by regulation of TNF-α, which may became a new therapeutic target for anti-obesity drugs.
PLoS ONE 10/2013; 8(10):e71568. DOI:10.1371/journal.pone.0071568 · 3.23 Impact Factor
"The results are shown in Figure 2(c). These results suggest that PG has inhibitory effects on PPARγ and C/EBPα, which are found almost exclusively in adipose tissues and play crucial roles in the induction of adipose-specific genes and in the manifestation of the mature adipose phenotype . In order to confirm the effects of PG on PPARγ and C/EBPα, a Western blot analysis was carried out. "
[Show abstract][Hide abstract] ABSTRACT: Obesity has become a major health threat in developed countries. However, current medications for obesity are limited because of their adverse effects. Interest in natural products for the treatment of obesity is thus rapidly growing. Korean Medicine (KM) is characterized by the wide use of herbal formulas. However, the combination rule of herbal formulas in KM lacks experimental evidence. According to Shennong's Classic of Materia Medica, the earliest book of herbal medicine, Veratrum nigrum (VN) has antagonistic features against Panax ginseng (PG), and the PG-VN pair is strictly forbidden. In this study, we have shown the effects of PG, VN, and their combination on obesity in high-fat (HF) diet-induced obese mice and in 3T3-L1 cells. PG, VN, and PG-VN combination significantly reduced weight gain and the fat pad weight in HF diet-induced obese mice. They also significantly decreased lipid accumulation and the expressions of two major adipogenesis factors, PPAR γ and C/EBP α , in 3T3-L1 cells. In addition, the PG-VN combination had synergistic effects compared with the mixture of extracts of PG and VN on inhibition of PPAR γ and C/EBP α expressions at lower doses. These results indicate a new potential anti-obese pharmacotherapy and also provide scientific evidence supporting the usage of herbal combinations instead of mixtures in KM.
Evidence-based Complementary and Alternative Medicine 09/2013; 2013(9115):732126. DOI:10.1155/2013/732126 · 1.88 Impact Factor
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