Rosenbaum S E, Greenberg A S
The USDA Human Nutrition Research Center on Aging at Tufts University, Tupper Medical Research Institute, New England Medical Center, Boston, Massachusetts 02111, USA.
Mol Endocrinol. 1998 Aug;12(8):1150-60. doi: 10.1210/mend.12.8.0151.
Expression of tumor necrosis factor-alpha(TNFalpha) in adipocytes has been reported to correlate with insulin resistance associated with obesity. The thiazolidinediones such as BRL 49653 have been reported to improve insulin sensitivity in obese animals and humans. Although its exact mechanism of action is not known, BRL 49653 has been shown to antagonize some of the inhibitory actions of TNFalpha. BRL 49653 binds and activates the peroxisome proliferator-activated receptor (PPARgamma2), an important nuclear transcription factor in adipocyte differentiation; however, its regulation of PPARgamma2 in differentiated adipocytes is unknown. In this paper, we find that BRL 49653 blocked the ability of TNFalpha to down-regulate the expression and transcription of several adipocyte genes, but BRL 49653 did not prevent TNFalpha from down-regulating PPARgamma2. Moreover, BRL 49653 alone initially decreased the expression of PPARgamma2 mRNA and protein greatly. After 24 h of treatment in 3T3-L1 adipocytes, BRL 49653 down-regulated PPARgamma2 by greater than 90% and potentiated the decrease of PPARgamma2 mRNA by TNFalpha at this time. These unexpected results prompted us to repeat the experiments for a longer time to determine whether BRL 49653 would continue to down-regulate PPARgamma2. With prolonged BRL 49653 treatment, PPARgamma2 mRNA expression was not decreased as greatly, and the protein levels were decreased 20-30% below control at 72 h compared to 90% at 24 h. Although BRL 49653 continued to prevent the inhibitory effects of TNFgamma on perilipin and aP2 mRNA, by 72 h, BRL 49653 was not as potent an inhibitor of TNFalpha's down-regulation of perilipin protein. Since PPARgamma2 protein was more abundant at this time, these results suggest that the level of PPARgamma2 protein is not the sole factor that regulates the transcriptional control by BRL 49653.
据报道，脂肪细胞中肿瘤坏死因子-α（TNFα）的表达与肥胖相关的胰岛素抵抗有关。噻唑烷二酮类药物如BRL 49653已被报道可改善肥胖动物和人类的胰岛素敏感性。尽管其确切作用机制尚不清楚，但BRL 49653已被证明可拮抗TNFα的一些抑制作用。BRL 49653结合并激活过氧化物酶体增殖物激活受体（PPARγ2），这是脂肪细胞分化中的一种重要核转录因子；然而，其在分化脂肪细胞中对PPARγ2的调节尚不清楚。在本文中，我们发现BRL 49653可阻断TNFα下调几种脂肪细胞基因表达和转录的能力，但BRL 49653并不能阻止TNFα下调PPARγ2。此外，单独使用BRL 49653最初会大幅降低PPARγ2 mRNA和蛋白质的表达。在3T3-L1脂肪细胞中处理24小时后，BRL 49653使PPARγ2下调超过90%，并在此时增强了TNFα对PPARγ2 mRNA的降低作用。这些意外结果促使我们延长实验时间，以确定BRL 49653是否会继续下调PPARγ2。随着BRL 49653处理时间的延长，PPARγ2 mRNA表达的降低幅度没有那么大，与24小时时降低90%相比，72小时时蛋白质水平比对照降低20 - 30%。尽管BRL 49653继续阻止TNFγ对周脂素和aP2 mRNA的抑制作用，但到72小时时，BRL 49653对TNFα下调周脂素蛋白的抑制作用不再那么有效。由于此时PPARγ2蛋白更为丰富，这些结果表明PPARγ2蛋白水平不是调节BRL 49653转录控制的唯一因素。
