Apolipoprotein B and Control of S. aureus Quorum Sensing

描述(申请人提供)：在美国和世界各地，抗药性金黄色葡萄球菌感染正在成为一个主要的公共卫生威胁。尤其有问题的是USA300和USA400型耐甲氧西林金黄色葡萄球菌(MRSA)感染，它们会导致皮肤和肺部的坏死性感染。虽然在阐明导致感染的MRSA毒力因子以及通过群体感应操纵子agr控制这些毒力因子方面取得了进展，但对影响易感性的宿主因素知之甚少。通常情况下，金黄色葡萄球菌会在年龄最大和病情严重的人群中引起机会性感染。然而，USA300和USA400 MRSA感染出现在具有免疫能力的年轻成年人中，这表明以前未被认识到的障碍对于控制这些感染是必不可少的。金黄色葡萄球菌的群体感应部分由一个四基因操纵子agr调控，该操纵子包括一个硫代内酯多肽信息素(AIP)和一个双组分传感器调节因子，一旦激活，就会导致对160多个与毒力相关的不同基因的转录控制。我们发现载脂蛋白B是脂代谢的一种成分，是金黄色葡萄球菌皮肤侵袭性感染的重要屏障，其机制涉及对AGR信号的控制。具体地说，apoB结合并隔离AIP，从而阻止agr操纵子的激活。由于皮肤坏死性感染在这些MRSA感染中占主导地位，因此将血浆apoB渗入受感染的皮肤可以及早控制agr，从而限制毒力因子的产生，以逃避先天免疫杀死和细菌的清除。由于载脂蛋白B是极低密度脂蛋白和低密度脂蛋白的主要结构蛋白，脂蛋白代谢的某些方面，包括清道夫受体(如CD36)的清除，可能有助于这种宿主防御机制。因此，我们正在测试的假设是apoB的氨基末端结构域以及随后通过CD36的清除对于宿主抵御侵袭性MRSA感染是必不可少的。为了验证这一假说，我们将追求以下特定目标：1)定义apoB的结构域(S)在体外足以与AIP结合并产生功能拮抗作用；2)确定apoB在体内对来自最临床相关的社区获得性MRSA agr类型：USA300(Agr1)和USA400(Agr3)的依赖agr的侵袭性感染菌株的预后的贡献：3)确定apoB-aip复合体的CD36清除在对抗agr依赖的侵袭性MRSA感染方面的贡献。

DESCRIPTION (provided by applicant): Antibiotic resistant Staphylococcus aureus infections are emerging as a major public health threat in the US and around the world. Particularly problematic are methicillin resistant S. aureus (MRSA) infections of the USA300 and USA400 PFGE types that cause necrotic skin and lung infections. While progress has been made in elucidating the MRSA virulence factors that contribute to infection and their control by a quorum sensing operon, agr, very little is known about host factors that contribute to susceptibility. Typically, S. aureus causes opportunistic infections in those at the extremes of age and with serious medical conditions. However, USA300 and USA400 MRSA infections are presenting in young immunocompetent adults suggesting that barriers previously unrecognized are essential to control these infections. Quorum sensing in S. aureus is regulated in part by a four gene operon, agr, which includes a thiolactone peptide pheromone (AIP) and a two component sensor regulator that upon activation leads to transcriptional control of over 160 different genes involved in virulence. We identified apolipoprotein B, a component of lipid metabolism, as an essential barrier to invasive S. aureus skin infection and that the mechanism involves control of agr signaling. Specifically, apoB binds to and sequesters AIP thus preventing activation of the agr operon. Because dermonecrotic skin infections predominate in these MRSA infections, extravasation of plasma apoB into infected skin could provide early control of agr and thus limit the production of virulence factors required to evade innate immune killing and clearance of the bacteria. Because apoB is the major structural protein of both VLDL and LDL, aspects of lipoprotein metabolism, including clearance by scavenger receptors (e.g. CD36), could contribute to this host defense mechanism. Therefore, the hypothesis we are testing is that the amino terminal domain of apoB and subsequent clearance through CD36 are essential for host defense against invasive MRSA infection. To test this hypothesis we will pursue the following specific aims: 1) To define the domain(s) of apoB sufficient for binding and functional antagonism of AIP in vitro; 2) To determine the in vivo contribution of apoB to the outcome of agr-dependent invasive infections of strains from the most clinically relevant community-acquired MRSA agr types: USA300 (agr1) and USA400 (agr3): 3) To determine the contribution of CD36 clearance of apoB-AIP complexes to protection against agr dependent invasive MRSA infections.