A disturbed regulation of multi-differentiation in human mesenchymal stem cells by dioxin and its mechanism

芳烃受体（Arylhydrocarbon receptor，AhR）是一种配体激活的转录因子，介导2，3，7，8-四氯-对-二恶英（TCDD）及其相关化合物的一系列毒理学和生物学效应。AhR基因敲除小鼠表现出肝脏中的脂质积聚和脊柱弯曲。因此，我们研究了TCDD处理对人骨髓间充质干细胞向脂肪细胞和骨细胞分化的影响。TCDD处理抑制人骨髓间充质干细胞向脂肪细胞的分化。另一方面，TCDD可促进细胞向骨细胞的分化。这些结果表明，脂肪组织质量的损失（消耗综合征）、骨发育不良和骨软骨病是由人骨髓间充质干细胞向多功能细胞分化的调控紊乱引起的。AhR蛋白水平为 ...更多信息 在脂肪形成过程中3 T3-L1细胞中受到抑制。蛋白体抑制剂对3 T3-L1细胞中前脂肪细胞和脂肪细胞的处理对AhR蛋白水平无影响。在AhR mRNA的表达中，与AhR蛋白水平类似，在脂肪形成过程中3 T3-L1细胞中AhR mRNA的水平被耗尽。接下来，为了理解AhR在脂肪形成过程中耗尽的机制，我们分析了3 T3-L1细胞脂肪分化过程中AhR启动子的活性。为了鉴定负责分化依赖性抑制AhR转录的AhR启动子区的序列，将一系列与CAT报告基因连接的缺失构建体转染到3 T3-L1细胞中。前脂肪细胞和脂肪细胞之间CAT活性的比较显示，-399/-339和-296/-217的序列是AhR启动子活性的分化依赖性下调的核心贡献者。使用核部分的凝胶位移分析显示存在与序列-399/-339和-296/-217结合的因子。前脂肪细胞中的结合活性高于脂肪细胞。因此，在脂肪分化过程中，反式作用因子的下调可能导致AhR基因转录的抑制。少

Arylhydrocarbon receptor(AhR) is a ligand-activated transcription factor that mediates a spectrum of toxicological and biological effects of 2,3,7,8-tetrachloro-p-dioxin(TCDD) and related compounds. AhR knockout mice exhibited a lipid accumulation in the liver and the curvature of the spinal column. Therefore, we investigated the effect of TCDD treatment on the differentiation of human mesenchymal stem cells to adipocytes and osteocytes. The differentiation to adipocytes in human mesenchymal stem cells was depressed by TCDD treatment. On the other hand, the differentiation to osteocytes in the cells was accumulated by TCDD. These results suggest that the loss of adipose tissue mass (wasting syndrome), osteodysplasia and osteochondrosis are induced by the disturbed regulation of the differentiation in the human mesenchymal stem cells to multi-functional cells.Furthermore, we examined the expression level of AhR in 3T3-L1 cells which have highly sensitivity to TCDD. AhR protein level was … More depressed in 3T3-L1 cells during adipogenesis. The treatment of proteosome inhibitors to preadipocytes and adipocytes in 3T3-L1 cells was no affected to the level of AhR protein. In the expression of AhR mRNA, the level was depleted in 3T3-L1 cells during adipogenesis as similarly the AhR protein level. Next, to understand the mechanism by which the AhR is depleted during adipogenesis, we analyzed the AhR promoter activity during adipose differentiation in 3T3-L1 cells. To identify the sequence of the AhR promoter region responsible for differentiation-dependent suppression of AhR transcription, a series of deletion constructs linked to the CAT reporter were transfected into 3T3-L1 cells. A comparison of CAT activity between preadipocytes and adipocytes revealed that the sequences of -399/-339 and -296/-217 are core contributor differentiation-dependent downregulation of AhR promoter activity. Gel shift analysis using the nuclear fraction showed the presence of the factor bound to the sequences of -399/-339 and -296/-217. The binding activity was higher in preadipocytes than in adipocytes. Consequently, the downregulation of the trans-acting factor may result in the suppression of AhR gene transcription during adipose differentiation. Less