Enterococcus faecalis attenuates osteogenesis through activation of p38 and ERK1/2 pathways in MC3T3‐E1 cells

Abstract

To explore the role of Enterococcus faecalis in the proliferation, apoptosis and differentiation of osteoblasts. Pre-osteoblastic MC3T3-E1 cells were treated with heat-killed E.faecalis ATCC 29212 and clinical E.faecalis P25RC strains, respectively. Cell proliferation, mineralized calcium deposition, alkaline phosphatase (ALP) activity and apoptosis were assessed at various time-points. The expression levels of osteogenic-related genes including ALP, osteocalcin (OC), runt-related protein 2 (Runx2) and collagen type 1 (COL1) were also analysed throughout the duration of the experiment. Additionally, the involvement of mitogen-activated protein kinases (MAPKs) signalling pathways was analysed by Western blotting. In the presence of culture supernatant from E.faecalis-treated murine macrophages, apoptosis of MC3T3-E1 cells was detected with flow cytometry. Data were analysed using analysis of variance (anova), and P<0.05 was considered significantly different. E.faecalis significantly inhibited proliferation (P<0.05) and also significantly induced apoptosis of MC3T3-E1 cells (P<0.05), whilst differentiation seemed to be unaffected after 7days of E.faecalis treatment. However, osteogenic differentiation was significantly inhibited with 21-day E.faecalis treatment (P<0.05). The p38 and ERK1/2 phosphorylation pathways associated with mineral deposition and apoptosis were significantly activated in MC3T3-E1 cells. The culture supernatants from E.faecalis-treated macrophages induced osteoblast apoptosis. E.faecalis exerted an inhibitory effect on osteogenesis in pre-osteoblastic MC3T3-E1 cells via phosphorylation of p38 and ERK1/2.