Invasive Streptococcus mutans induces inflammatory cytokine production in human aortic endothelial cells via regulation of intracellular toll-like receptor 2 and nucleotide-binding oligomerization domain 2.

Abstract

Streptococcus mutans, the primary etiologic agent of dental caries, can gain access to the bloodstream and has been associated with cardiovascular disease. However, the roles of S.mutans in inflammation in cardiovascular disease remain unclear. The aim of this study was to examine cytokine production induced by S.mutans in human aortic endothelial cells (HAECs) and to evaluate the participation of toll-like receptors (TLRs) and cytoplasmic nucleotide-binding oligomerization domain (NOD) -like receptors in HAECs. Cytokine production by HAECs was determined using enzyme-linked immunosorbent assays, and the expression of TLRs and NOD-like receptors was evaluated by real-time polymerase chain reaction, flow cytometry and immunocytochemistry. The involvement of TLR2 and NOD2 in cytokine production by invaded HAECs was examined using RNA interference. The invasion efficiencies of S.mutans strains were evaluated by means of antibiotic protection assays. Five of six strains of S.mutans of various serotypes induced interleukin-6, interleukin-8 and monocyte chemoattractant protein-1 production by HAECs. All S.mutans strains upregulated TLR2 and NOD2 mRNA levels in HAECs. Streptococcus mutans Xc upregulated the intracellular TLR2 and NOD2 protein levels in HAECs. Silencing of the TLR2 and NOD2 genes in HAECs invaded by S.mutans Xc led to a reduction in interleukin-6, interleukin-8 and monocyte chemoattractant protein-1 production. Cytokine production induced by invasive S.mutans via intracellular TLR2 and NOD2 in HAECs may be associated with inflammation in cardiovascular disease.