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Infection by Streptococcus pyogenes induces the receptor activator of NF-kappaB ligand expression in mouse
Nobuo Okahashi1, Atsuo Sakurai, Ichiro Nakagawa
1Department of Oral and Molecular Microbiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Japan. okahashi@dent.osaka-u.ac.jp
Abstract:
Group A Streptococcus pyogenes is known to induce nongonococcal septic arthritis in addition to pharyngitis, scarlet fever, and poststreptococcal sequelae. However, little is known about the interaction between S. pyogenes and bone cells. We report here that S. pyogenes strain JRS4 (M6) attached to and invaded mouse primary osteoblasts. Reverse transcription-PCR demonstrated that S. pyogenes infection of osteoblasts stimulated expression of mRNA for the receptor activator of NF-kappaB ligand (RANKL). Western blot analysis followed by ligand precipitation with the receptor activator of NF-kappaB receptor showed that there was an increase in RANKL protein in infected osteoblasts. Production of interleukin-6 was also stimulated, but no production of interleukin-1beta or tumor necrosis factor alpha was observed. Stimulation of RANKL production was not observed in osteoblasts stimulated with heat-inactivated S. pyogenes, suggesting that an active interaction of S. pyogenes with osteoblasts is essential for this phenomenon. A Western blot analysis performed with antibodies specific for phosphorylated signal transduction proteins demonstrated that S. pyogenes infection induces phosphorylation of p38 mitogen-activated protein kinase. A specific inhibitor of this kinase, SB203580, inhibited RANKL production by infected osteoblasts. These results suggest that infection of osteoblasts by S. pyogenes stimulates RANKL production and may trigger bone destruction in infected bone tissue.
Insights
Group A Streptococcus pyogenes invades bone cells, stimulating receptor activator of NF-kappaB ligand (RANKL) production. This process, mediated by p38 kinase, suggests a mechanism for S. pyogenes-induced bone destruction in septic arthritis.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Group A Streptococcus pyogenes (GAS) causes various infections, including septic arthritis.
- The interaction between S. pyogenes and bone cells, particularly osteoblasts, remains poorly understood.
- Understanding this interaction is crucial for elucidating the pathogenesis of S. pyogenes-induced bone disease.
Purpose of the Study:
- To investigate the interaction between S. pyogenes and primary osteoblasts.
- To determine if S. pyogenes infection influences the expression of key bone remodeling factors.
- To elucidate the signaling pathways involved in the osteoblast response to S. pyogenes.
Main Methods:
- Co-culture of mouse primary osteoblasts with live S. pyogenes strain JRS4 (M6).
- Reverse transcription-PCR to assess mRNA expression of RANKL and cytokines.
- Western blot analysis to detect protein levels of RANKL and phosphorylated signaling proteins.
- Inhibition studies using SB203580, a p38 mitogen-activated protein kinase inhibitor.
Main Results:
- S. pyogenes attached to and invaded osteoblasts.
- Infection significantly increased mRNA and protein expression of RANKL in osteoblasts.
- Interleukin-6 production was stimulated, but not interleukin-1beta or tumor necrosis factor alpha.
- S. pyogenes infection induced phosphorylation of p38 mitogen-activated protein kinase, which was essential for RANKL production.
Conclusions:
- S. pyogenes infection of osteoblasts stimulates RANKL production via the p38 mitogen-activated protein kinase pathway.
- This mechanism may contribute to bone destruction observed in S. pyogenes-associated septic arthritis.
- Live bacterial interaction is essential for stimulating RANKL production, highlighting the importance of active infection.