Centre for Medical Biotechnology, BioPark I, University of Regensburg, Regensburg, Germany.
J Cell Sci. 2013 Jul 1;126(Pt 13):2890-902. doi: 10.1242/jcs.124305. Epub 2013 Apr 19.
Sox9 is a key transcription factor in early chondrogenesis with distinct roles in differentiation processes and during embryonic development. Here, we report that Sox9 modulates cell survival and contributes to the commitment of mesenchymal stem cells (MSC) to adipogenic or osteogenic differentiation lineages. We found that the Sox9 activity level affects the expression of the key transcription factor in adipogenic differentiation, C/EBPβ, and that cyclin D1 mediates the expression of the osteogenic marker osteocalcin in undifferentiated adult bone-marrow-derived rat MSC. Introducing a stable Sox9 knockdown into undifferentiated rat MSC resulted in a marked decrease in proliferation rate and an increase in apoptotic activity. This was linked to a profound upregulation of p21 and cyclin D1 gene and protein expression accompanied by an induction of caspase 3/7 activity and an inhibition of Bcl-2. We observed that Sox9 silencing provoked a delayed S-phase progression and an increased nuclear localization of p21. The protein stability of cyclin D1 was induced in the absence of Sox9 presumably as a function of altered p38 signalling. In addition, the major transcription factor for adipogenic differentiation, C/EBPβ, was repressed after silencing Sox9. The nearly complete absence of C/EBPβ protein as a result of increased destabilization of the C/EBPβ mRNA and the impact on osteocalcin gene expression and protein synthesis, suggests that a delicate balance of Sox9 level is not only imperative for proper chondrogenic differentiation of progenitor cells, but also affects the adipogenic and probably osteogenic differentiation pathways of MSC. Our results identified Sox9 as an important link between differentiation, proliferation and apoptosis in undifferentiated adult rat mesenchymal stem cells, emphasizing the importance of the delicate balance of a precisely regulated Sox9 activity in MSC not only for proper skeletal development during embryogenesis but probably also for successful repair and regeneration of tissues and organs in adults.
Sox9 是早期软骨生成中的关键转录因子，在分化过程中和胚胎发育过程中具有不同的作用。在这里，我们报告 Sox9 调节细胞存活，并有助于间充质干细胞 (MSC) 向脂肪生成或成骨分化谱系的分化。我们发现 Sox9 的活性水平影响脂肪生成分化中的关键转录因子 C/EBPβ 的表达，并且细胞周期蛋白 D1 介导未分化的成年骨髓源性大鼠 MSC 中骨钙素的成骨标志物的表达。将稳定的 Sox9 敲低引入未分化的大鼠 MSC 中会导致增殖率显着降低和凋亡活性增加。这与 p21 和细胞周期蛋白 D1 基因和蛋白表达的深刻上调有关，伴随着 caspase 3/7 活性的诱导和 Bcl-2 的抑制。我们观察到 Sox9 沉默会引发 S 期进展延迟和 p21 的核内定位增加。在没有 Sox9 的情况下，细胞周期蛋白 D1 的蛋白稳定性被诱导，推测这是由于 p38 信号改变的功能。此外，脂肪生成分化的主要转录因子 C/EBPβ 在沉默 Sox9 后被抑制。由于 C/EBPβ mRNA 的不稳定性增加导致 C/EBPβ 蛋白几乎完全不存在，以及对骨钙素基因表达和蛋白质合成的影响，表明 Sox9 水平的精细平衡不仅对祖细胞的适当软骨生成分化至关重要，而且还影响 MSC 的脂肪生成和可能的成骨分化途径。我们的结果将 Sox9 鉴定为未分化成年大鼠间充质干细胞中分化、增殖和凋亡之间的重要联系，强调了精确调节的 Sox9 活性在 MSC 中的精细平衡不仅对胚胎发生期间适当的骨骼发育很重要，而且可能对组织和器官的成功修复和再生也很重要。
