Effect of Enterococcus faecalis on osteoclastogenesis under cobalt-mimicked hypoxia in vitro

Abstract

Objective: The bone destruction in persistent apical periodontitis associated with infection and a periapical hypoxic microenvironment is not well known. Thus, we aimed to investigate the effects of Enterococcus faecalis on osteoclastogenesis under cobalt-mimicked hypoxia.

Materials and methods: Mouse bone marrow-derived macrophages (BMMs) were isolated as osteoclast precursors and stimulated by heat-killed E. faecalis in an environment of cobalt-mimicked hypoxia environment. The cell proliferation and apoptosis were detected using CCK-8 and flow cytometry, respectively. Osteoclast differentiation was determined via tartrate-resistant acid phosphatase staining (TRAP) and immunofluorescence staining. The osteoclastogenic protein and gene expressions were measured by western blotting and real-time PCR.

Results: Under cobalt-mimicked hypoxia, E. faecalis markedly inhibited the proliferation of the BMMs and significantly promoted the apoptosis of the BMMs. The differentiation of the BMMs into osteoclasts was enhanced in the presence of the E. faecalis under hypoxia, and the expression of Blimp, c-Fos, and NFATc1 was up-regulated, while the expression of RBP-J was inhibited.

Conclusions: E. faecalis markedly promotes osteoclast differentiation under cobalt-mimicked hypoxia in vitro.

Keywords: Apoptosis; Bone marrow-derived macrophages; Enterococcus faecalis; Hypoxia; Osteoclasts.