Nanohydroxyapatite increases BMP-2 expression via a p38 MAP kinase dependent pathway in periodontal ligament cells

Objective: Bone morphogenetic protein (BMP)-2 promotes the osteoblastic differentiation of human periodontal ligament (PDL) cells, which play a pivotal role in periodontal regeneration. Recently, nano-sized hydroxyapatite (nano-HA) has been highlighted due to its advantageous features over micro-sized materials. Design and results: We investigated the effect of nano-HA on BMP-2 expression in human PDL cells. Real time PCR analysis revealed that the expression of BMP-2 increased upon stimulation with nano-HA in dose- and time-dependent manners. An immunofluorescence assay demonstrated the synthesis of BMP-2 proteins. Concentrations of Ca²⁺ as well as phosphate (Pi) in culture supernatants were unchanged, suggesting that nano-HA functioned as a nanoparticle rather than as a possible source for releasing Ca²⁺ and/or Pi extracellularly, which were shown to also enhance the expression of BMP-2. Nano-HA-induced BMP-2 expression was dependent on the p38 MAP kinase pathway because increases in BMP-2 expression were inhibited by treatment with SB203580, a p38 inhibitor, and phosphorylation of p38 was detected by Western blotting. Conclusions: This novel mechanism of nano-HA will be important for the rational design of future periodontal regeneration.