Apolipoprotein B and Control of S. aureus Quorum Sensing

描述（由申请人提供）：耐抗生素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。特别有问题的是耐甲氧西林的S。金黄色葡萄球菌（MRSA）感染的USA 300和USA 400 PFGE型，导致坏死性皮肤和肺部感染。虽然已经取得了进展，阐明了MRSA的毒力因子，有助于感染和控制的群体感应操纵子，agr，很少有人知道的宿主因素，有助于易感性。典型地，S.金黄色葡萄球菌在年龄极端和有严重医疗条件的人中引起机会性感染。然而，USA 300和USA 400 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屏障对于控制这些感染至关重要。群体感应在S.金黄色葡萄球菌部分地由四基因操纵子agr调节，agr包括硫内酯肽信息素（AIP）和双组分传感器调节子，其在激活时导致超过160种不同的涉及毒力的基因的转录控制。我们确定载脂蛋白B是脂质代谢的一个组成部分，是侵袭性链球菌的重要屏障。金黄色葡萄球菌皮肤感染，其机制涉及控制agr信号传导。具体地，apoB结合并螯合AIP，从而防止agr操纵子的激活。由于皮肤坏死性皮肤感染在这些MRSA感染中占主导地位，血浆apoB外渗到感染的皮肤中可以提供对agr的早期控制，从而限制逃避先天免疫杀死和细菌清除所需的毒力因子的产生。由于载脂蛋白B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CD 36）的清除，可能有助于这种宿主防御机制。因此，我们正在检验的假设是apoB的氨基末端结构域和随后通过CD 36的清除对于宿主防御侵袭性MRSA感染是必不可少的。为了检验这一假设，我们将追求以下具体目标：1）定义apoB的结构域，其足以在体外结合AIP并具有AIP的功能拮抗作用; 2）确定apoB对来自最具临床相关性的社区获得性MRSA agr类型（USA 300（agr 1）和USA 400（agr 3））的菌株的agr依赖性侵入性感染的结果的体内贡献：3）确定CD 36清除apoB-AIP复合物对抵抗agr依赖性侵袭性MRSA感染的保护作用的贡献。

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.