探討轉糖鏈球菌Phage Shock Protein C相似蛋白在感染性心內膜炎致病機轉中扮演的角色

Abstract

感染性心內膜炎是一種感染心血管系統並具有高復發率及致死率的的感染性疾病。人類口腔菌叢的轉糖鏈球菌是透過機會性感染引發感染性心內膜炎發生的主要致病菌之一。我們先前的成果指出，一種受LiaR調控的phage shock protein C相似蛋白在調控細菌於大鼠體內形成生物膜以造成感染性心內膜炎的能力中扮演重要角色；然而其中的機制並不清楚。在本篇研究中，我們發現phage shock protein C相似蛋白缺失突變株依賴胞外去氧核醣核酸以及依賴血小板形成體外生物膜的能力具有缺陷，其釋放胞外去氧核醣核酸及依靠纖維蛋白原的血小板結合能力也顯著變差。為了探討phage shock protein C相似蛋白的表現機制，血球凝集素標記的質體就此產生。人類血清迅速地刺激轉糖鏈球菌表現phage shock protein C相似蛋白，該刺激的效果呈現劑量效應且不需LiaSR雙分子系統的感應與調控。加熱去活化將使血清刺激phage shock protein C相似蛋白表現的能力變差，暗示著血清中負責進行調理作用的成分可能具有角色；然而抑制C3補體蛋白作用無法減少血清引起的phage shock protein C相似蛋白表現，於去除免疫球蛋白的血清中加入純化過的免疫球蛋白幾乎無法恢復血清的刺激效果，這些結果顯示C3補體蛋白和免疫球蛋白在血清引起的phage shock protein C相似蛋白表現中的角色並非最主要，可能有其他對溫度敏感的血清成分參與其中。總結而論，phage shock protein C相似蛋白是一種受人類血清刺激後所表現的蛋白，在轉糖鏈球菌引發之感染性心內膜炎致病機轉中調控細菌胞外去氧核醣核酸釋出、血小板黏附、生物膜形成。

Infective endocarditis (IE) is an infectious disease of cardiovascular system featuring high recurrence and mortality rate. Streptococcus mutans, an oral commensal flora, is the main cause of dental caries, and also one of the major opportunistic pathogens for IE. Our previous works indicated that phage shock protein C homolog protein (Pcp), a LiaR-regulated hypothetical protein of S. mutans, played important roles in modulating bacterial abilities to form biofilm in vivo for causing IE, but the mechanism remained unclear. In this study, we found that pcp-deficient mutant strain revealed defects in both of eDNA- and platelet-dependent biofilm formation in vitro. Pcp deficiency reduced the ability to release extracellular DNA and to bind the platelets in the fibrinogen-dependent manner. To investigate the mechanism of Pcp expression, the HA-tagged Pcp reporting plasmid was generated. Pcp expression was rapidly induced by human serum in a dose-dependent manner, which was independent of LiaSR sensing and regulation. Heat-inactivation of serum reduced the ability to induce Pcp expression, implying the role of serum opsonizing components. However, inhibition of complement C3 could not reduce and addition of purified IgG in Ig-depleted serum barely restored the serum-induced Pcp expression, suggesting the minor roles of IgG and C3 in serum-induced Pcp expression. These data indicated that other heat-sensitive serum component(s) is(are) involved in. Taken together, Pcp is a human serum-induced protein modulating bacterial eDNA release, platelet adhesion and biofilm formation in the pathogenesis of S. mutans-induced IE.