Abstract: Objective To study the regulation of BMP9 on P38 MAPK signaling pathway and its effect on autophagy and apoptosis in osteoblasts. Methods The osteoblast cell line MC3T3-E1 was cultured in vitro and was induced to undergo autophagy with rapamycin. The expressions of BMP9, P38 and p-P38 were detected by Western blotting. The MC3T3-E1 cells were divided into 7 groups: pcDNA3. 1-BMP9 group ( pcDNA3. 1-BMP9 ), BMP9 siRNA group ( BMP9 siRNA), P38 activation group ( anisomycin, 10 μmol / L), P38 inhibition group ( SB-202190, 10 μmol / L), pcDNA3. 1-BMP9 + P38 inhibition group ( pcDNA3. 1-BMP9 + SB-202190, 10 μmol / L), BMP9 siRNA + P38 activation group ( BMP9 siRNA + anisomycin, 10 μmol / L) and control group. The expression levels of autophagy-related proteins LC3-Ⅱ, Beclin-1 and P62 were detected by Western blotting, and the cell proliferation and apoptosis were measured by CCK-8 and flow cytometry. Results The expression levels of LC3-Ⅱ, Beclin-1, BMP9 and p-P38 were increased (P< 0. 05) while the expression level of P62 was decreased ( P < 0. 05) after MC3T3-E1 cells were treated with rapamycin. The expression levels of LC3-Ⅱ and Beclin-1 in the pcDNA3. 1-BMP9 group and the P38 activation group were increased (P< 0. 05), and the expression level of P62 in those two groups was decreased (P < 0. 05). The expression levels of LC3-Ⅱ and Beclin-1 in the BMP9 siRNA group and the P38 inhibition group were decreased (P < 0. 05), and the expression level of P62 in those two groups was increased (P< 0. 05). No significant differences in the expression levels of LC3-Ⅱ, Beclin-1 and P62 were found between the pcDNA3. 1-BMP9 + P38 inhibition group, the BMP9 siRNA + P38 activation group and the control group (all P> 0. 05). The cell proliferation rates of the pcDNA 3. 1-BMP9 group and the P38 activation group were increased, and the apoptosis rates of those two groups were decreased (all P< 0. 05). The cell proliferation rates of the BMP9 siRNA group and the P38 inhibition group were decreased, and the apoptosis rates of those two groups were increased (all P< 0. 05). No significant differences in the proliferation and apoptosis rates were found between the pcDNA 3. 1-BMP9 + P38 inhibition group, the BMP9 siRNA + P38 activation group and the control group (all P> 0. 05). Conclusion BMP9 activates the P38 MAPK pathway, induces autophagy and reduces apoptosis in osteoblasts.

Key words: costeoblasts, bone morphogenetic protein, P38 MAPK pathway, autophagy, apoptosis