Osteoblast Differentiation and Notch Signaling

Notch是一种跨膜受体，在干细胞分化过程中起着至关重要的作用。它在间充质组织形成中的作用也被提及，尽管详细的机制还没有被分析。为了阐明Notch信号在成骨过程中的作用，将具有结构活性的Notchi(Notch胞内域，NICD)基因导入两个不同的成骨细胞间充质细胞系Kusa-A1和Kusa-O，并建立了稳定的转化子(KusaANICD和KusaONICD)来检测Notch信号。NiCd普遍抑制Kusa-Al和KusaO成骨标志基因的表达、钙沉积、体外矿化、Cbfal和Ose2元件的启动子活性。NICD可显著抑制Kusa-Al的体内成骨。这些结果表明，Notch信号在成骨细胞分化中起负调控作用。为了证实这些结果，Notch信号被进化的…抑制更为保守的转录因子CBF1，也称为RBP-JIC。瞬时转染CBF1可显著提高Ose2和Cbfal的启动子活性，但可阻断NICD诱导的HESI启动子活性的升高。在稳定表达CBF1的Kusa-AI/CBF1细胞系中，其成骨特性包括钙沉积、体外矿化和RANKL表达均显著增强。Kusa-A1/CBFI可显著促进体内硬组织的形成。此外，Kusa-A1/CBF1形成的硬组织比Kusa-AI/HOST形成的硬组织更致密，类似于骨小梁组织。CBF1的表达普遍存在，但在骨组织和骨形成结构中的表达水平尤其高。这些结果表明，转录调节因子CBF1的过表达强烈地促进了间充质前体细胞的成骨分化。综上所述，Notch信号在成骨细胞分化过程中起着至关重要的作用，而对其信号的修饰将是控制成骨细胞矿化的关键。较少

Notch is a trausmembrane receptor that plays a crucial role in differentiation of stem cells. Its role in the formation of mesenchymal tissues has also been implicated although detailed mechanism has not yet been analyzed. To elucidate the function of Notch signaling in osteogenesis, the constitutively active Notchi (Notch intracellular domain, NICD) was transfected into two different osteoblastic mesenchymal cell lines, Kusa-Al and Kusa-O, and established stable transformants (KusaANICD and KusaONICD) to examine the Notch signaling. NICD generally suppressed the expression of osteogenic marker genes, calcium deposition, in vitro mineralization, the promoter activities of the Cbfal and the Ose2 element in both Kusa-Al and KusaO. In vivo bone formation of Kusa-Al was significantly suppressed by NICD. These results imply that Notch signaling functions as a negative regulator on osteoblast differentiation. In order to confirm these results, the Notch signaling was suppressed by an evoluti … More onarily conserved transcription factor CBF1, also known as RBP-Jic. Transient transfection of CBF1 remarkably increased the promoter activities of Ose2 and Cbfal, but blocked the elevation of Hesi promoter activity induced by NICD transfection. In Kusa-AI/CBF1 cell line, which is a CBF1 expressing stable cell line, the osteogenic properties, including calcium deposition, in vitro mineralization and the RANKL expression were significantly promoted. The in vivo hard tissue formation was greatly facilitated in Kusa-A1/CBFI. Furthermore, the hard tissues formed by Kusa-A1/CBF1 showed more compact structure similar to trabecular bone tissues than those by Kusa-AI/host. The expression of CBF1 was ubiquitous, but it was especially high in bone tissues and bone forming structures. These, results indicated that over-expression of transcription mediator CBF1 strongly promoted the osteogenic differentiation of mesenchymal progenitor cells. Taken together, the Notch signaling should be essential in the osteoblastic differentiation, and modification of its signaling would be key to control the mineralization. Less