title: Streptococcus gordonii induces nitric oxide production through its lipoproteins stimulating Toll-like receptor 2 in murine macrophages.
abstract: Streptococcus gordonii, a Gram-positive commensal in the oral cavity, is an opportunistic pathogen that can cause endodontic and systemic infections resulting in infective endocarditis. Lipoteichoic acid (LTA) and lipoprotein are major virulence factors of Gram-positive bacteria that are preferentially recognized by Toll-like receptor 2 (TLR2) on immune cells. In the present study, we investigated the effect of S. gordonii LTA and lipoprotein on the production of the representative inflammatory mediator nitric oxide (NO) by the mouse macrophages. Heat-killed S. gordonii wild-type and an LTA-deficient mutant (ΔltaS) but not a lipoprotein-deficient mutant (Δlgt) induced NO production in mouse primary macrophages and the cell line, RAW 264.7. S. gordonii wild-type and ΔltaS also induced the expression of inducible NO synthase (iNOS) at the mRNA and protein levels. In contrast, the Δlgt mutant showed little effect under the same condition. Furthermore, S. gordonii wild-type and ΔltaS induced NF-κB activation, STAT1 phosphorylation, and IFN-β expression, which are important for the induction of iNOS gene expression, with little activation by Δlgt. S. gordonii wild-type and ΔltaS showed an increased adherence and internalization to RAW 264.7 cells compared to Δlgt. In addition, S. gordonii wild-type and ΔltaS, but not Δlgt, substantially increased TLR2 activation while none of these induced NO production in TLR2-deficient macrophages. Triton X-114-extracted lipoproteins from S. gordonii were sufficient to induce NO production. Collectively, we suggest that lipoprotein is an essential cell wall component of S. gordonii to induce NO production in macrophages through TLR2 triggering NF-κB and STAT1 activation.
authors.affiliation: Department of Oral Microbiology and Immunology, DRI and BK21 Plus Program, School of Dentistry, Seoul National University, Seoul 08826, Republic of Korea.
authors.forename: Hyun Young
authors.initials: HY
authors.lastname: Kim
authors.affiliation: Department of Oral Microbiology and Immunology, DRI and BK21 Plus Program, School of Dentistry, Seoul National University, Seoul 08826, Republic of Korea.
authors.forename: Jung Eun
authors.initials: JE
authors.lastname: Baik
authors.affiliation: Department of Oral Microbiology and Immunology, DRI and BK21 Plus Program, School of Dentistry, Seoul National University, Seoul 08826, Republic of Korea.
authors.forename: Ki Bum
authors.initials: KB
authors.lastname: Ahn
authors.affiliation: Radiation Biotechnology Research Division, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup 34057, Republic of Korea.
authors.forename: Ho Seong
authors.initials: HS
authors.lastname: Seo
authors.affiliation: Department of Agricultural Biotechnology and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 08826, Republic of Korea.
authors.forename: Cheol-Heui
authors.initials: CH
authors.lastname: Yun
authors.affiliation: Department of Oral Microbiology and Immunology, DRI and BK21 Plus Program, School of Dentistry, Seoul National University, Seoul 08826, Republic of Korea. Electronic address: shhan-mi@snu.ac.kr.
authors.forename: Seung Hyun
authors.initials: SH
authors.lastname: Han
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000276:immunology*; D015153:Blotting, Western; D004195:Disease Models, Animal; D008074:Lipoproteins / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D009569:Nitric Oxide / Q000096:biosynthesis; D000067996:RAW 264.7 Cells; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology; D013290:Streptococcal Infections / Q000276:immunology* / Q000378:metabolism; D054773:Streptococcus gordonii / Q000276:immunology; D051195:Toll-Like Receptor 2 / Q000276:immunology* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008074:Lipoproteins; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; D009569:Nitric Oxide
keywords: Lipoprotein; Lipoteichoic acid; Macrophage; Nitric oxide; Streptococcus gordonii