Enterococcus faecalis promotes RANKL-dependent TRAP-positive osteoclastogenesis and semaphorin 4D expression

Abstract

OBJECTIVES: Enterococcus faecalis is a major bacterial pathogen associated with endodontic infections and contributes considerably to periapical periodontitis. This study aimed to investigate the potential mechanisms by which E. faecalis accounts for the bone destruction in periapical periodontitis in vitro. METHODS: The osteoclast precursor RAW264.7 cells and RANKL-primed RAW264.7 cells were infected by E. faecalis ATCC 29212 and E. faecalis strain derived from an infected root canal. RESULTS: This pathogen was unable to induce RAW264.7 cells to form tartrate-resistant acid phosphatase (TRAP)-positive multinuclear osteoclast-like cells, but up-regulated the expressions of IL-1β and COX-2 that are associated with osteoclastogenesis. E. faecalis markedly stimulated RAW264.7 cells to express semaphorin 4D that was previously shown to inhibit bone formation. Once RAW264.7 cells were primed by RANKL, E. faecalis could increase the production of TRAP-positive multinuclear cells and fully or partially up-regulated the expression of osteoclast-specific genes including TRAP, NFATc1 and cathepsin K. Meanwhile, the expression of Sema4D was highly increased, especially with treatment of the clinical E. faecalis strain. The p38 and ERK1/2 MAPK signaling pathways were activated by E. faecalis in RANKL-primed RAW264.7 cells.Conclusions: This pioneering study suggests that the clinical E. faecalis strain exhibited potent effects on osteoclast differentiation with reference to the ATCC standard strain. CONCLUSIVELY, E. faecalis may contribute to the bone resorption in periapical periodontitis by promoting RANKL-dependent TRAP-positive osteoclastogenesis and expression of Sema4D through activation of p38 and ERK1/2 MAPK signaling pathways.