Intracellular Invasion by Streptococcus mutans: Significance in Disease

摘要 人类病原体变形链球菌是一种与龋齿有关的主要病原体， 感染性心内膜炎(IE)的常见病原体。最近出现的证据表明，S。 产生胶原结合蛋白CNM的突变株可能与更严重的IE病例和 其他口腔外病理的发展，包括出血性中风和IgA肾病。而当 产生CNM的菌株在口腔中并不普遍，横断面临床研究表明 CNM+变形链球菌感染，龋患率和严重程度增加。此外，在本港进行的研究 实验室已经证明，产生CNM的变形链球菌能够更有效地附着于富含胶原蛋白 体外存在于心脏瓣膜和牙齿(即牙本质)中的组织，并能够侵袭口腔上皮和心脏 体外培养内皮细胞。利用兔IE和大鼠龋病模型，我们证实了CNM是一种重要的 毒力因子表明产生CNM的变形链球菌可以是超强毒力的。所获得的数据 到目前为止表明，CNM赋予的特性使变形链球菌在口服中具有持久性和毒力 空洞也可能促进全身传播和感染。利用分子和生化 方法，我们发现CNM是由新发现的糖基化复合体在翻译后修饰的。 被命名为PGF。PGF系统的缺失通过影响CNM的稳定性而损害CNM的功能。我们还发现， CNM具有淀粉样变性，尽管CNM形成淀粉样蛋白对胶原结合和 相关功能目前尚不清楚。我们认为，糖基化状态和淀粉样蛋白的形成形式 CNM可能通过促进蛋白质稳定性(糖基化)或赋予新的 CNM的特性(淀粉样蛋白形成)。这一应用的首要假设是CNM+变形链球菌 菌株更适合定植于人体组织，包括口腔软组织和暴露的牙本质和牙齿。 牙根，因此可能与更具侵袭性和更严重的龋病有关，如那些 在儿童早期的龋齿中发现。我们推测，CNM+变形链球菌的口腔感染与大多数 侵袭性的龋病病例，以及无法用常规风险解释的龋病复发 含蔗糖食物摄入量高、口腔卫生差等因素。在此应用程序中，我们将 使用生化、分子、糖蛋白组学和结构方法来表征CNM 糖蛋白和淀粉样蛋白，以及大鼠龋齿模型揭示口腔中CNM的意义 殖民性、持久性和致龋性。这项研究的发现将揭示相关的其他方面 被不同菌株的变形链球菌感染，这可能导致当前评估范式的变化 龋齿有风险，并最终有助于设计新的抗菌疗法。

ABSTRACT The human pathogen Streptococcus mutans is a major etiological agent associated in dental caries and a common causative agent of infective endocarditis (IE). Evidence has recently emerged that strains of S. mutans producing the collagen binding protein Cnm may be associated with more severe cases of IE and with the development of other extra-oral pathologies including hemorrhagic stroke and IgA nephropathy. While Cnm-producing strains are not prevalent in the oral cavity, crosss-sectional clinical studies have linked infection with cnm+ S. mutans with increased caries incidence and severity. Moreover, studies conducted in our laboratory have showed that S. mutans strains producing Cnm can more efficiently adhere to collagen-rich tissues present in heart valves and in teeth (i.e. dentin) ex vivo, and are able to invade oral epithelial and heart endothelial cells in vitro. Using the rabbit IE and rat caries models, we confirmed that Cnm is an important virulence factor indicating that S. mutans strains that produce Cnm can be hypervirulent. The data obtained thus far indicate that the properties conferred by Cnm enables S. mutans persistence and virulence in the oral cavity that could also facilitate systemic dissemination and infection. Using molecular and biochemical approaches, we found that Cnm is posttranslationally modified by a newly identified glycosylation complex that was named Pgf. Loss of the Pgf system impaired Cnm function by affecting its stability. We also found that Cnm has amylodoigenic properties albeit the impact of amyloid formation by Cnm on collagen-binding and related functions is presently unknown. We propose that the glycosylation state and amyloidogenic form of Cnm may contribute to its function by promoting protein stability (glycosylation) or by conferring novel properties (amyloid formation) to Cnm. The overarching hypothesis of this application is that cnm+ S. mutans strains are better equipped to colonize human tissues, including oral soft tissues and exposed dentin and teeth roots, and, therefore may be associated with more aggressive and reincident cases of caries, such as those found in early childhood caries. We postulate that oral infection by cnm+ S. mutans are linked to the most aggressive cases of caries, as well as to caries recurrence that cannot be explained by conventional risk factors such as high intake of sucrose-containing foodstuffs and poor oral hygiene. In this application, we will use biochemical, molecular, glycoproteomic and structural approaches to characterize Cnm as both a glycoprotein and an amyloidogenic protein, and the rat caries model to uncover the significance of Cnm in oral colonization, persistence and cariogenicity. The findings of this study will reveal additional facets associated with infection by different strains of S. mutans, which could lead to changes in current paradigms for assessing caries risk and ultimately help devise novel antimicrobial therapies.