ECM Regulation of Ocular Surface Disease

摘要 细菌性角膜炎是一种严重的公共卫生威胁，与显著的眼部发病率相关，并且是 世界范围内失明的主要原因。据估计，细菌性角膜炎的年发病率为 全球约50万患者。即使使用现代治疗，角膜感染也会导致 50%的患者视力差，12%的患者接受手术干预。几种革兰氏阳性和阴性 细菌病原体可感染角膜并引起角膜炎。细菌病原体利用一切可用资源 在恶劣的宿主环境中生存宿主细胞外基质（ECM）成分的颠覆及其对细胞的影响 受体作为附着位点被认为是许多细菌共有的常见毒力机制。 然而，在体内很少有数据明确支持这一观点。我们在初步研究中发现 syndecan-1（Sdc 1）是上皮细胞的主要细胞表面硫酸乙酰肝素蛋白聚糖（HSPG）， 在划痕角膜感染的小鼠模型中获得功能，其中Sdc 1-/-角膜显著较少 易受肺炎链球菌感染。局部施用过量的Sdc 1胞外域或 硫酸乙酰肝素（HS）对S.肺炎克雷伯氏菌角膜感染，表明Sdc 1的HS链 作为细胞表面附着受体促进感染。然而，S.肺炎克雷伯氏菌不与Sdc 1相互作用 Sdc 1在S上脱落。pneumoniae感染，表明Sdc 1不直接支持S.肺炎 粘连相反，Sdc 1促进S.通过驱动纤连蛋白（FN）原纤维的组装来促进肺炎链球菌粘附 在角膜基底膜中，S.当感染受伤的角膜时肺炎会附着。过量 Sdc1胞外域抑制S.通过与FN中的肝素结合结构域结合而抑制肺炎性角膜感染，以及 干扰S. pneumoniae结合FN。根据这些数据，本提案将审查 假设特定的ECM相互作用协调角膜基底膜的组装， 眼表面的某些细菌病原体利用这些正常的生物过程来促进它们的 发病机制这一假设将在3个特定目标中进行检验。目标1将确定协调制度的结构基础， 抑制细菌性角膜感染。目的2将确定细菌诱导的 Sdc 1在角膜感染中的脱落，目的3将阐明Sdc 1如何调节 角膜基底膜FN纤维形成。这些研究预计将揭示以前 ECM在角膜中的未知功能，并建立一个新的细菌整合毒力途径， 角膜炎。

ABSTRACT Bacterial keratitis is a serious public health threat associated with significant ocular morbidity and is one of the major causes of blindness worldwide. By one estimate, the annual incidence of bacterial keratitis is approximately 500,000 patients worldwide. Even with modern day treatment, corneal infections can result in poor vision in 50% and surgical intervention in 12% of patients. Several Gram-positive and Gram-negative bacterial pathogens can infect the cornea and cause keratitis. Bacterial pathogens use all resources available to survive in the hostile host environment. Subversion of host extracellular matrix (ECM) components and their receptors as attachment sites is thought to be a common virulence mechanism shared by many bacteria. However, there are few data that clearly support this idea in vivo. We found in preliminary studies that deletion of syndecan-1 (Sdc1), a major cell surface heparan sulfate proteoglycan (HSPG) of epithelial cells, causes a gain of function in a mouse model of scarified corneal infection, where Sdc1-/- corneas are significantly less susceptible to Streptococcus pneumoniae infection. Topical administration of excess Sdc1 ectodomains or heparan sulfate (HS) significantly inhibits S. pneumoniae corneal infection, suggesting that HS chains of Sdc1 promote infection as a cell surface attachment receptor. However, S. pneumoniae does not interact with Sdc1 and Sdc1 is shed upon S. pneumoniae infection, indicating that Sdc1 does not directly support S. pneumoniae adhesion. Instead, Sdc1 promotes S. pneumoniae adhesion by driving the assembly of fibronectin (FN) fibrils in the corneal basement membrane to which S. pneumoniae attaches when infecting injured corneas. Excess Sdc1 ectodomains inhibit S. pneumoniae corneal infection by binding to the heparin-binding domain in FN, and interfering with S. pneumoniae binding to FN. Based on these data, this proposal will examine the overall hypothesis that specific ECM interactions coordinate the assembly of corneal basement membranes, and that certain bacterial pathogens of the ocular surface exploit these normal biological processes to promote their pathogenesis. This hypothesis will be tested in 3 Specific Aims. Aim 1 will define the structural basis of how HS inhibits bacterial corneal infection. Aim 2 will determine the significance and relevance of bacteria-induced Sdc1 shedding in corneal infection, and Aim 3 will elucidate the underlying mechanisms of how Sdc1 regulates FN fibrillogenesis in the corneal basement membrane. These studies are expected to uncover previously unknown functions of the ECM in the cornea and to establish a new integrated virulence pathway in bacterial keratitis.