title: Enterococcus faecalis attenuates osteogenesis through activation of p38 and ERK1/2 pathways in MC3T3-E1 cells.
abstract: OBJECTIVE
  To explore the role of Enterococcus faecalis in the proliferation, apoptosis and differentiation of osteoblasts.
  
  
  METHODS
  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.
  
  
  RESULTS
  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 7 days 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.
  
  
  CONCLUSIONS
  E. faecalis exerted an inhibitory effect on osteogenesis in pre-osteoblastic MC3T3-E1 cells via phosphorylation of p38 and ERK1/2.
authors.affiliation: Department of Endodontics, Comprehensive Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: S
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Endodontics, Comprehensive Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.|Shenzhen ENT Institute, Shenzhen, China.
authors.forename: Z
authors.initials: Z
authors.lastname: Deng
authors.affiliation: Department of Endodontics, Comprehensive Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.|School of Dentistry, Shandong University, Jinan, China.
authors.forename: X
authors.initials: X
authors.lastname: Ye
authors.affiliation: Department of Stomatology, Shenzhen Longgang Center Hospital, ENT Hospital, Shenzhen, China.
authors.forename: X
authors.initials: X
authors.lastname: Geng
authors.affiliation: Department of Endodontics, Comprehensive Dental Care, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: C
authors.initials: C
authors.lastname: Zhang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D049109:Cell Proliferation / Q000502:physiology; D013293:Enterococcus faecalis / Q000378:metabolism*; D016908:Gram-Positive Bacterial Infections / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D059467:Transcriptome
keywords: 
  Enterococcus faecalis
  ; MAPK signalling pathways; apoptosis; differentiation; mineralization; osteoblasts