Potential involvement of Streptococcus mutans possessing collagen binding protein Cnm in infective endocarditis

Abstract

AbstractStreptococcus mutans, a significant contributor to dental caries, is occasionally isolated from the blood of patients with infective endocarditis. We previously showed thatS. mutansstrains expressing collagen-binding protein (Cnm) are present in the oral cavity of approximately 10–20% of humans and that they can effectively invade human umbilical vein endothelial cells (HUVECs). Here, we investigated the potential molecular mechanisms of HUVEC invasion by Cnm-positiveS. mutans. The ability of Cnm-positiveS. mutansto invade HUVECs was significantly increased by the presence of serum, purified type IV collagen, and fibrinogen (p < 0.001). Microarray analyses of HUVECs infected by Cnm-positive or -negativeS. mutansstrains identified several transcripts that were differentially upregulated during invasion, including those encoding the small G protein regulatory proteinsARHGEF38andARHGAP9. Upregulation of these proteins occurred during invasion only in the presence of serum. Knockdown ofARHGEF38strongly reduced HUVEC invasion by Cnm-positiveS. mutans. In a rat model of infective endocarditis, cardiac endothelial cell damage was more prominent following infection with a Cnm-positive strain compared with a Cnm-negative strain. These results suggest that the type IV collagen–Cnm–ARHGEF38pathway may play a crucial role in the pathogenesis of infective endocarditis.