Abstract
Purpose The involvement of oral mucosa cells in mechanical stress-induced bone resorption is unclear. The aim of this study was to investigate the effects of cyclic pressure-induced cytokines from oral mucosal cells (human gingival fibroblasts: hGFs) on osteoclast activity in vitro.Methods Cyclic pressure at 50 kPa, which represents high physiologic occlusal force of dentures on the molar area, was applied to hGFs. NFAT-reporter stable RAW264.7 preosteoclasts (NFAT/Luc-RAW cells) were cultured in conditioned medium collected from hGF cultures under cyclic pressure or static conditions. NFAT activity and osteoclast formation were determined by luciferase reporter assay and TRAP staining, respectively. Cyclic pressure-induced cytokines in hGF culture were detected by ELISA, real-time RT-PCR, and cytokine array analyses.Results Conditioned media from hGFs treated with 48 hours of cyclic pressure significantly induced NFAT activity and increased multinucleated osteoclast formation. Furthermore, the cyclic pressure significantly increased the bone resorption activity of RAW264.7 cells. Cyclic pressure significantly increased the expression of major inflammatory cytokines including IL-1β/IL-1β, IL-6/IL-6, IL-8/IL-8 and MCP-1/CCL2 in hGFs compared to hGFs cultured under static conditions, and it suppressed osteoprotegerin (OPG/OPG) expression. A cytokine array detected 12 cyclic pressure-induced candidates. Among them, IL-8, decorin, MCP-1 and ferritin increased, whereas IL-28A and PDGF-BB decreased, NFAT activation of NFAT/Luc-RAW cells.Conclusions These results suggest that cyclic pressure-induced cytokines from hGFs promote osteoclastogenesis, possibly including up-regulation of IL-1β, IL-6, IL-8 and MCP-1, and down-regulation of OPG. These findings introduce the possible involvement of GFs in mechanical stress-induced alveolar ridge resorption, such as in denture wearers.
Highlights
Mucosal overload due to chronic stress and movement of illfitting dentures often contributes to alveolar bone/residual ridge resorption [1,2]
Previous studies have reported that osteoclasts are localized along the external surface of the residual ridge interfacing with the oral mucosa, the trabecular bone in the edentulous jawbone appears to be undergoing remodeling, suggesting that bone resorption contributing to residual ridge atrophy is influenced by the edentulous oral mucosa [8,9]
Human normal osteoblasts, which were used for comparison with human gingival fibroblasts (hGFs) in response to cyclic pressure, were purchased from Lonza (Walkersville, MD, USA). hOBs were cultured in OGM Osteoblast Growth Medium SingleQuots Supplements and Growth Factors (Lonza)
Summary
Mucosal overload due to chronic stress and movement of illfitting dentures often contributes to alveolar bone/residual ridge resorption [1,2]. Previous studies have reported that osteoclasts are localized along the external surface of the residual ridge interfacing with the oral mucosa (gingiva), the trabecular bone in the edentulous jawbone appears to be undergoing remodeling, suggesting that bone resorption contributing to residual ridge atrophy is influenced by the edentulous oral mucosa [8,9]. It remains unclear how edentulous oral mucosa affects the residual ridge resorption
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