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

Abstract Objectives Root resorption is a common phenomenon presented in periodontitis and orthodontic treatment, both of which are accompanied by an elevated TNF ‐α expression level in the periodontal tissues. Previously, we proved that TNF ‐α showed an inhibitory effect on cementoblast differentiation, mineralization and proliferation. However, the effect of TNF ‐α on Runx2 and osteoprotegerin ( OPG ) expression remains undetermined. This study aimed to identify the influence of TNF ‐α on Runx2 and OPG expression in cementoblasts and to test whether BMP ‐2,‐4,‐6,‐7 would affect TNF ‐α‐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 ‐α. The role of signalling pathways, including MAPK , PI 3K‐Akt and NF ‐κB, were studied with the use of specific inhibitors. Cells were treated with TNF ‐α in combination with BMP ‐2,‐4,‐6 or ‐7, then the expression of Runx2 and OPG , the activity of MAPK and NF ‐κB pathways, and the proliferation ability were evaluated by qRT ‐ PCR , Western blot and MTS assay respectively. Results TNF ‐α inhibited Runx2 and OPG mRNA s in OCCM ‐30 cells, and the inhibitory effects were further aggravated by blocking p38 MAPK or NF ‐κB pathway. TNF ‐α‐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 ‐α compared with TNF ‐α alone. Finally, the TNF ‐α‐suppressed proliferation was not obviously affected by BMP ‐2,‐4,‐6 or ‐7. Conclusions TNF ‐α inhibited Runx2 and OPG in cementoblasts, and the p38 MAPK and NF ‐κB pathways acted in a negative‐feedback way to attenuate the inhibitory effects. TNF‐α‐inhibited Runx2 and OPG could be effectively up‐regulated by BMP ‐4; however, further investigations are needed to fully elaborate the underlying mechanisms.