Toll-Like Receptor 2 Stimulation of Osteoblasts Mediates Staphylococcus Aureus Induced Bone Resorption and Osteoclastogenesis through Enhanced RANKL

PLoS One. 2016 Jun 16;11(6):e0156708. doi: 10.1371/journal.pone.0156708. eCollection 2016.

Abstract

Severe Staphylococcus aureus (S. aureus) infections pose an immense threat to population health and constitute a great burden for the health care worldwide. Inter alia, S. aureus septic arthritis is a disease with high mortality and morbidity caused by destruction of the infected joints and systemic bone loss, osteoporosis. Toll-Like receptors (TLRs) are innate immune cell receptors recognizing a variety of microbial molecules and structures. S. aureus recognition via TLR2 initiates a signaling cascade resulting in production of various cytokines, but the mechanisms by which S. aureus causes rapid and excessive bone loss are still unclear. We, therefore, investigated how S. aureus regulates periosteal/endosteal osteoclast formation and bone resorption. S. aureus stimulation of neonatal mouse parietal bone induced ex vivo bone resorption and osteoclastic gene expression. This effect was associated with increased mRNA and protein expression of receptor activator of NF-kB ligand (RANKL) without significant change in osteoprotegerin (OPG) expression. Bone resorption induced by S. aureus was abolished by OPG. S. aureus increased the expression of osteoclastogenic cytokines and prostaglandins in the parietal bones but the stimulatory effect of S. aureus on bone resorption and Tnfsf11 mRNA expression was independent of these cytokines and prostaglandins. Stimulation of isolated periosteal osteoblasts with S. aureus also resulted in increased expression of Tnfsf11 mRNA, an effect lost in osteoblasts from Tlr2 knockout mice. S. aureus stimulated osteoclastogenesis in isolated periosteal cells without affecting RANKL-stimulated resorption. In contrast, S. aureus inhibited RANKL-induced osteoclast formation in bone marrow macrophages. These data show that S. aureus enhances bone resorption and periosteal osteoclast formation by increasing osteoblast RANKL production through TLR2. Our study indicates the importance of using different in vitro approaches for studies of how S. aureus regulates osteoclastogenesis to obtain better understanding of the complex mechanisms of S. aureus induced bone destruction in vivo.

MeSH terms

  • Animals
  • Animals, Newborn
  • Bone Marrow Cells / immunology
  • Bone Marrow Cells / microbiology
  • Bone Resorption / immunology*
  • Bone Resorption / microbiology
  • Bone Resorption / pathology
  • Gene Expression Regulation, Developmental
  • Macrophages / immunology
  • Macrophages / microbiology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Osteoblasts / immunology
  • Osteoblasts / microbiology
  • Osteoclasts / immunology
  • Osteoclasts / microbiology
  • Osteogenesis / genetics
  • Osteogenesis / immunology*
  • Osteoprotegerin / genetics
  • Osteoprotegerin / immunology
  • Parietal Bone / growth & development
  • Parietal Bone / immunology*
  • Parietal Bone / microbiology
  • Primary Cell Culture
  • Prostaglandins / biosynthesis
  • RANK Ligand / genetics*
  • RANK Ligand / immunology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Signal Transduction
  • Staphylococcal Infections / immunology*
  • Staphylococcal Infections / microbiology
  • Staphylococcal Infections / pathology
  • Staphylococcus aureus / immunology
  • Staphylococcus aureus / pathogenicity
  • Toll-Like Receptor 2 / deficiency
  • Toll-Like Receptor 2 / genetics*
  • Toll-Like Receptor 2 / immunology

Substances

  • Osteoprotegerin
  • Prostaglandins
  • RANK Ligand
  • RNA, Messenger
  • Tlr2 protein, mouse
  • Tnfrsf11b protein, mouse
  • Tnfsf11 protein, mouse
  • Toll-Like Receptor 2

Grants and funding

This work was supported by The Swedish Research Council, the County Council of Västerbotten, the Swedish National Graduate School in Odontological Sciences, the Swedish Rheumatism Association, the Royal 80-Year Fund of King Gustav V, COMBINE, ALF/LUA research grant from Sahlgrenska University Hospital in Gothenburg and the Lundberg Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.