Regulatory effects of bone morphogenetic protein-4 on tumour necrosis factor-α-suppressed Runx2 and osteoprotegerin expression in cementoblasts

Objectives: Root resorption is a common phenomenon presented in periodontitis and orthodontic treatment, both of which are accompanied by an elevated TNF-alpha expression level in the periodontal tissues. Previously, we proved that TNF-alpha showed an inhibitory effect on cementoblast differentiation, mineralization and proliferation. However, the effect of TNF-alpha on Runx2 and osteoprotegerin (OPG) expression remains undetermined. This study aimed to identify the influence of TNF-alpha on Runx2 and OPG expression in cementoblasts and to test whether BMP-2, -4, -6, -7 would affect TNF-alpha-regulated Runx2 and OPG. Materials and methods: An immortalized murine cementoblast cell line OCCM-30 was used in this study. The expression of Runx2 and OPG were examined by qRT-PCR after stimulating cells with TNF-alpha. The role of signalling pathways, including MAPK, PI3K-Akt and NF-kappa B,were studied with the use of specific inhibitors. Cells were treated with TNF-alpha in combination with BMP-2, -4, -6 or -7, then the expression of Runx2 and OPG, the activity of MAPK and NF-kappa B pathways, and the proliferation ability were evaluated by qRT-PCR, Western blot and MTS assay respectively. Results: TNF-alpha inhibited Runx2 and OPG mRNAs in OCCM-30 cells, and the inhibitory effects were further aggravated by blocking p38 MAPK or NF-kappa B pathway. TNF-alpha-inhibited Runx2 and OPG were up-regulated by BMP-4. The p38 MAPK and Erk1/2 pathways were further activated by the combined treatment of BMP-4 and TNF-alpha compared with TNF-alpha alone. Finally, the TNF-alpha-suppressed proliferation was not obviously affected by BMP-2, -4, -6 or -7. Conclusions: TNF-alpha inhibited Runx2 and OPG in cementoblasts, and the p38 MAPK and NF-kappa B pathways acted in a negative-feedback way to attenuate the inhibitory effects. TNF-alpha-inhibited Runx2 and OPG could be effectively up-regulated by BMP-4; however, further investigations are needed to fully elaborate the underlying mechanisms.