Processing and secretion of BMP-2 in fetal rat mandibular cells

Objectives: BMP-2 induces bone formation by activating the function of osteoblasts. BMP-2 is synthesized as a proprotein, which becomes glycosylated, proteolytically cleaved and dimerized. Noggin, a BMP -2/-4-binding antagonist, restricts the bioactivity of BMPs in bone development. In the present study, we studied the processing and secretion of mature BMP-2 in fetal rat mandibular cells. Methods: Cells, prepared from 20d-old gestation of F344 rats by neutral protease digestion, were incubated in either the presence or absence of dexamethasone (Dex; 10^-8 M), and then cultured without agents for 24 days. The number of bone nodule was counted after staining with alizarin red-S. Using Western blotting, we detected endogenous BMP-2 in the deglycosylated and immunoprecipitated culture media. Results: During days 3-6, BMP bands at 35kDa and mature BMP-2 at 26kDa presented with no additives. During days 3-6, the application of Dex promoted the secretion of precursors for BMP-2 at 55 and 68kDa. During days 9-12, BMP-2 turned into biologically active homodimers in both cultures. Noggin (30ng/ml) removed BMP-2 protein bands at 35kDa. However, 26kDa band had been remained, and whatsoever, uncleaved hemidimer at 68kDa brought out. These results had shown that processing of BMP-2 hemidimer contributed to endogenous BMP-2-mediated bone formation. Conclusion: The intertwined secretion or cleavage from BMP-2-precursors to mature BMP-2 connects and regulates the endogenous BMP-2-mediated bone nodule formation.