Role of the Staphylococcus aureus SaeR/S Regulatory System in Neutrophil Evasion

描述(申请人提供)：金黄色葡萄球菌(金黄色葡萄球菌)是全球人类感染的主要原因，导致从轻微到危及生命的各种疾病严重程度。近年来，社区相关耐甲氧西林金黄色葡萄球菌(CA-MRSA)感染在其他健康人群中的发病率有所增加，其基础在很大程度上尚不清楚。人类多形核白细胞(PMN或中性粒细胞)是抵御细菌感染的第一道防线。金黄色葡萄球菌逃避先天免疫破坏的能力包括吞噬PMN后的存活。金黄色葡萄球菌吞噬PMN后存活的能力取决于病原体感知和生存于恶劣PMN环境的能力。然而，金黄色葡萄球菌用来逃避PMN杀伤的具体机制还没有完全确定。我们假设，SAER/S双组分调控系统直接调控金黄色葡萄球菌因子，这些因子损害有效的中性粒细胞反应，导致病原体存活。这一假说基于以下已发表的和初步的观察结果：1)在多形核白细胞吞噬后，SAER和SAES的转录本上调；2)在人多形核白细胞吞噬后，SAER/S的缺失显著降低了金黄色葡萄球菌的存活率；3)转录检测发现在SAER/S中下调的胞外毒力基因并且重组的SAER直接与这些毒力基因启动子中的一个共同序列相结合。这些数据与体内研究很好地相关，这些研究表明，SAER/S调控了金黄色葡萄球菌引起的皮肤感染后发病率和侵袭性感染后死亡率的关键因素。为了确定SAER/S依赖表型背后的分子机制，我们将首先定义SAER/S调节的基因在中性粒细胞吞噬反应中的激活动力学。接下来，我们将确定单个SAER/S靶基因对金黄色葡萄球菌存活和中性粒细胞裂解的贡献。最后，我们将评估SAER/S靶基因在体内的表达，并确定SAER/S调控的单个基因在金黄色葡萄球菌致病中的作用。这项研究的完成将确定由Saer/S调控的负责PMN吞噬后存活的特定效应物，并将确定它们在PMN裂解和体内金黄色葡萄球菌致病中的作用。这些发现将提高我们对导致金黄色葡萄球菌感染的最初宿主-病原体相互作用的理解。这一知识预计将直接应用于葡萄球菌感染的新预防和治疗策略。

DESCRIPTION (provided by applicant): Staphylococcus aureus (S. aureus) is a leading cause of human infections worldwide, resulting in a diverse spectrum of disease severity from mild to life-threatening. Recently, there has been an increase in the incidence of community-associated methicillin-resistant S. aureus (CA-MRSA) infections in otherwise healthy individuals, the basis of which is largely unknown. Human polymorphonuclear leukocytes (PMNs or neutrophils) are the first line of defense against bacterial infections. The ability of S. aureus to circumvent destruction by innate immunity includes survival after PMN phagocytosis. The ability of S. aureus to survive following PMN phagocytosis is dependent on the pathogen's ability to sense and survive the hostile PMN environment. However, specific mechanisms used by S. aureus to evade PMN killing are incompletely defined. We hypothesize that the SaeR/S two-component regulatory system directly regulates S. aureus factors that impair an effective neutrophil response resulting in pathogen survival. This hypothesis is based on the following published and preliminary observations: 1) saeR and saeS transcripts were up-regulated following PMN phagocytosis; 2) deletion of saeR/S significantly decreased survival of S. aureus following human PMN phagocytosis; and 3) transcriptional assays identified extracellular virulence genes down- regulated in saeR/S and direct binding of recombinant SaeR to a consensus sequence within several of these virulence gene promoters. These data correlate well with in vivo studies that demonstrate SaeR/S regulates factors vital for S. aureus - induced morbidity following skin infections and mortality following invasive infections. To determine the molecular mechanisms behind the saeR/S-dependent phenotype we will first define the kinetics of activation of SaeR/S-regulated genes in response to PMN phagocytosis. Next, we will determine the contribution of individual SaeR/S-target genes to S. aureus survival and PMN lysis. Finally, we will assess expression of saeR/S-target genes in vivo and identify the contribution of individual genes regulated by saeR/S to S. aureus pathogenesis. Completion of this research will identify the specific effectors regulated by saeR/S responsible for survival following PMN phagocytosis and will define their contribution to PMN lysis and S. aureus pathogenesis in vivo. These findings will improve our understanding of the initial host-pathogen interactions that lead to S. aureus infection. This knowledge is predicted to have direct application for novel prevention and treatment strategies for staphylococcal infections.