Study Of Osteocytic Smad4 Mechanism In Bone Development

Objective:To determine the mechanism of Smad4 via TGF?-BMP cell signaling pathway and the role of bone regeneration and formation.Methods;1.Conditional gene knockout technique Cre/loxp were used to make mice with osteocytic Smad4 specific knock Out(Smad4^otcko).2.Embryonic mouse skeletal growth was shown by whole mount skeletal staining of new pups.3.Bone mineral density differences were detected by X-ray in one-month-old mice.Changes in bone mass?trabecular number and osteoblast number were analyzed by static bone histomorphology.4.Osteoblastic marker ALP?Runx2,OSX,OCN?OPN?Collagen?and osteocytic marker DMP1?DKK1?MEPE?SOST were detected by qPCR.5.Osteoclastic marker RANKL,OPG M-CSF were evaluated by qPCRResults:1.Smad4^otcko mice displayed no gross skeletal abnormalities at birth.2.X-ray radiography showed reduced bone density in one month mice as compare with control mice,bone mass and osteoblast number in trabecular and cortical bone were decreased,osteocyte number was decreased in cortical bone,trabecular number was decreased in trabecular bone as compared to control mice and shows significant deference?p<0.05?,similarly the specific markers of osteoblastic differentiation Runx2?ALP?OCN?OPN?OSX?Collagen?and osteocytic mutration marker DMP1?DKK1?SOST?MEPE were decreased.3.The mRNA expression of RANKL was highly increased while OPG decreased,Thus,the radio of RANKL/OPG was significantly increased?p<0.05?.Conclusion:Smad4 in terminal differentiated osteocytes can regulate bone homeostasis through promoting osteoblastic differentiation and down regulation of osteoclastic resorption.