Iliac and mandible osteoblasts exhibit varied responses to LMHF vibration

The facial and long bones have distinct developmental origins, structures, and cellular compositions. This study aimed to compare the in vitro responses of human mandible and long bone osteoblasts to low-magnitude, high-frequency (LMHF) mechanical vibration in terms of expression of mediators of bone remodeling. Osteoblast-like cell cultures were prepared from iliac crest and mandibular bone specimens from three individuals and cultured in osteogenic induction media. Induction of mature osteoblastic phenotypes was confirmed by analysis of DNA content, alkaline phosphatase activity and gene expression every 3 days for 27 days. Based on gene expression, mature osteoblasts formed by day 15 of induction culture. After 15 days of culture in induction media, mature osteoblasts were subjected to vibration (0, 30, or 60 Hz) for 30 min every 24 h. After 48 h, RANKL, OPG, IL-1β, IL-6 and TGF-β gene, and protein expression were determined by real-time PCR analysis of total cellular mRNA and ELISAs of the cell supernatants. Both iliac and mandible osteoblasts responded to LMHF vibration: IL-1β and RANKL mRNA were downregulated and IL-6 mRNA was upregulated. However, TGF- β mRNA was unaltered and OPG mRNA was upregulated in iliac osteoblasts, whereas both TGF-β and OPG mRNA were downregulated in mandible osteoblasts. As a result, LMHF reduced the RANKL/OPG mRNA ratio in iliac osteoblasts but did not alter the RANKL/OPG mRNA ratio in mandible osteoblasts. This study suggests mature iliac osteoblasts exhibit a more potent anti-resorptive response to vibration, while this tendency was not obviously apparent in mature mandible osteoblasts.