Effect of BMP6 on Osteogenesis of Dental Follicle Stem Cells

Objectives: Tooth eruption requires osteogenesis in the base of the tooth crypt. It has been determined that the basal one-half of the dental follicle (DF) expresses higher levels of BMP6 than does the coronal one-half.  We proposed that dental follicle stem cells (DFSC) may contribute to osteogenesis needed for tooth eruption.  The aim of this study was to determine the expression of BMP6 in the DFSC and to elucidate if BMP6 is required for osteogenesis of DFSC. Methods: DFSC and their non-stem cell counterpart dental follicle cells (DFC) were obtained from the DF of 1^st mandibular molars of day 6 rat pups. Expression of BMP6 in the DFSC and DFC was determined by real-time RT-PCR. DFSC were induced for osteogenesis, and BMP6 expression was assessed during osteogenic induction. To determine if BMP6 was required for osteogenesis of DFSC, BMP6 expression in the DFSC was knocked down by siRNA, and then the cells were subjected to osteogenic induction to evaluate their osteogenic capability. Results: BMP6 expression in the DFSC was about 20-fold higher than in non-stem cells DFC. When subjected to osteogenic induction, the early passage DFSC showing strong osteogenesis expressed dramatically higher levels of BMP6 than the late passage DFSC that had reduced osteogenic capability. Moreover, when BMP6 expression in the DFSC was knocked down by siRNA, the osteogenesis capability of the DFSC diminished. However, the lost osteogenic capability caused by BMP6 knockdown could be restored by adding BMP6 protein to the osteogenic induction medium. Conclusion: DFSC express high levels of BMP6 for maintaining their osteogenic capability. DFSC also could contribute to the overall BMP6 production in the DF to stimulate the alveolar bone growth needed for tooth eruption.  Increased BMP6 expression in the basal one-half of the DF could be important in promoting osteogenesis of DFSC for tooth eruption.