Apolipoprotein B and Control of S. aureus Quorum Sensing

描述（由申请人提供）：抗生素耐药金黄色葡萄球菌感染正在成为美国和世界各地的主要公共卫生威胁。尤其成问题的是USA300和USA400 PFGE类型的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坏死感染。虽然在阐明MRSA引起感染的毒力因子及其通过群体感应操纵子agr控制方面取得了进展，但对导致易感性的宿主因子知之甚少。通常情况下，金黄色葡萄球菌引起机会性感染的人在极端年龄和严重的医疗条件。然而，USA300和USA400 MRSA感染出现在年轻的免疫功能正常的成年人中，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，其中包括一个硫代内酯肽信息素（AIP）和一个双组分传感器调节子，激活后可导致160多个不同毒力基因的转录控制。我们发现载脂蛋白B（脂质代谢的一个组成部分）是侵袭性金黄色葡萄球菌皮肤感染的重要屏障，其机制涉及agr信号的控制。具体来说，载脂蛋白ob结合并隔离AIP，从而阻止agr操纵子的激活。由于在这些MRSA感染中皮肤腐蚀感染占主导地位，血浆载脂蛋白ob外渗到感染皮肤中可以提供agr的早期控制，从而限制了逃避先天免疫杀死和清除细菌所需的毒力因子的产生。由于载脂蛋白ob是VLDL和LDL的主要结构蛋白，脂蛋白代谢的各个方面，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，我们正在验证的假设是载脂蛋白ob的氨基末端结构域和随后通过CD36的清除对于宿主防御侵袭性MRSA感染至关重要。为了验证这一假设，我们将追求以下具体目标：1)确定载脂蛋白ob在体外足以结合和功能拮抗AIP的结构域；2)确定apoB对临床上最相关的社区获得性MRSA agr型USA300 （agr1）和USA400 （agr3）菌株agr依赖性侵袭性感染结果的体内贡献：3)确定CD36清除apoB- aip复合物对agr依赖性侵袭性MRSA感染的保护作用。

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.