The Effect Of TGFβI Type Receptor-ALK1 And ALK2 On The BMP9 Induced Osteogenesis Of C3H10

BMPs(Bone Morphogenetic Proteins)belong to the transforming growth factorb (TGFβ) superfamily, Originally isolated as proteins that induce bone and cartilage formation in vivo. More than 20 BMPs have been identified. Bone Morphogenetic Proteins (BMPs) play an important role during organ development and during regeneration after tissue damage. Prior works show that BMP2, BMP4, BMP7 has potent osteogenic activity. Presently, it has been found that BMP9 is the strongest factor to induce bone formation. But the mechanism under the bone formation induced by BMP9 reamins unclear.BMPs signal via transmembrane serine/threonine kinase receptors, termed TGFβtype I and type II receptor,and then, the activated receptor subsequently phosphorylates transcriptional factors, called Smads, which activate the expression of target genes in concert with coactivators. Therefore, in this signal pathway, TGFβreceptors act as a key point which can bind BMPs and activate Smads.TGFβreceptors are the most important molecular in early signal transduction of BMPs, and involve in osteogenic activity of BMPs. Among, TGFβtype I receptor, which is the connecting link of BMPs pathway, plays an important role.In our lab's previous study, we use TGFβtype I dn-receptor virus and BMP9 to co-stimulate stem cell and nude mouse, preliminary screening TGFβtypeⅠreceptor ALK1 and ALK2 which can inhibit the osteogenesis of BMP9. According to the experimental result, it is very probable for ALK1 and ALK2 to concern with osteogenesis of BMP9. Based on this background, our study further identify and validate the effect of ALK1 and ALK2 on the osteogenesis of BMP9.We apply a special siRNA screening system—pSOS designed by T-C He to successfully construct and screen siALK1 and siALK2 adenovirus which have potent effect to interfere the expression of ALK1 and ALK2, validating the impact of ALK1 and ALK2 on osteogenesis of BMP9 in vitro and vivo. In vitro, we have found siALK1 and siALK2 can inhibit the activity of alkaline phosphatase, luciferase and calcium salts which are the most important signaling and osteoblast markers. The experimental result shows that siALK1 and siALK2 inhibit osteogenesis of BMP9 in vitro. In vivo, siALK1 and siALK2 inhibit the subcutaneous bulb's size in nude. Bone matirx exhibits less while cartilage matrix more, indicating inactive and hysteretic osteogenesis. These show siALK1 and siALK2 inhibit osteogenesis of BMP9 in vivo. From the above, we identify and validate the potent effect of ALK1 and ALK2 on the osteogenesis of BMP9, which can provide virtual evidence to elucidate the mechanism under BMP9 induced osteogenesis.