Effect of bone morphogenetic protein-7 on gene expression of bone morphogenetic protein-4, dentin matrix protein-1, insulin-like growth factor-I and -II in cementoblasts in vitro

Formation of root cementum is a crucial moment in the development of the periodontium. Cells that produce the cementum are named cementoblasts and they posses some unique characteristics, which differentiates them from osteoblasts. Bone morphogenetic proteins (BMPs) are crucial regulators of both bone and tooth formation. In animal studies BMPs have shown to induce periodontal regeneration, however the molecular mechanism as how BMP-7 induces cementogenesis is largely unknown. We have investigated how BMP-7 regulates gene expression of BMP-4, Dentin matrix protein-1 (DMP-1), Insulin-like growth factor-I (IGF-I) and -II (IGF-II) in cementoblasts. BMP-7 induced proliferation, and mineralized nodule formation of cementoblasts. Our results show that gene expression was influenced by the BMP-7 concentration used, with 75 ng/mL generally down-regulating gene expression at 6 hours and then up-regulating after 24 hours. The 300 ng/mL concentration had an opposite effect while the 150 ng/mL concentration generally up-regulated gene expression after 6 hours and then after 24 hours maintained this up-regulation or had no effect compared to control, depending on the examined gene. The results show that BMP-7 down-regulated BMP-4 expression in cementoblasts but still up-regulated DMP-1 gene expression suggesting that BMP-7 can, in a paracrine manner, functionally substitute for BMP-4. Furthermore, it seems that BMP-7 exerts its effect more through the IGF-II than the IGF-I pathway as shown by an up-regulation of IGF-II and down-regulation of IGF-I. These results suggest that a combination of BMP-7/IGF-II could have a potential therapeutical significance in inducing cementogenesis and periodontal regeneration.