Host-mediated zinc sequestration during Acinetobacter baumannii infection

描述(申请人提供)：鲍曼不动杆菌是一种重要的医院病原体，可引起一系列疾病，包括呼吸道和尿路感染、脑膜炎、心内膜炎、伤口感染和菌血症。事实上，鲍曼不动杆菌现在占世界某些地区所有重症监护病房感染的20%，肺炎是最常见的表现。鲍曼不动杆菌对几乎所有抗生素迅速产生抗药性，这推动了它的临床意义。这个 确定治疗干预的新靶点对于我们保护公众健康免受这一新出现的传染病威胁的能力至关重要。治疗开发的一个有希望的潜在领域涉及靶向细菌获取营养金属。这一策略是基于这样一个事实，即所有细菌病原体都需要营养金属来定植它们的宿主。尽管细菌病原体在脊椎动物的生长过程中需要多种金属，但铁的封存被认为是宿主在对感染的先天性免疫反应中主动封存的主要营养物质。在目前的应用中，我们提供了先天免疫因子钙保护素通过螯合营养锌(锌)来预防不动杆菌肺炎的证据。利用钙保护素作为探针，我们在鲍曼不动杆菌中发现了一个与钙保护素竞争锌的转运系统，该系统在转录水平上受锌依赖调节因子的控制。钙保护素在炎症部位大量存在，是一种已知的促炎分子，是晚期糖基化终产物受体(RAGE)的配体。尽管它明显参与，但钙保护素介导的金属隔离和RAGE结合对防御感染的贡献还没有得到彻底的评估。基于本申请中描述的初步数据，我们假设钙保护素介导的锌固定和RAGE结合是宿主与病原体相互作用的关键因素。为了验证这一中心假设，我们提出了一系列实验，旨在了解鲍曼不动杆菌肺炎期间钙保护素介导的锌固定和RAGE结合的机制和病理生理后果。在这些研究中，我们将(I)确定使其能够与锌等过渡金属络合并结合RAGE的钙保护素的结构特征，(Ii)阐明钙保护素和RAGE在鲍曼不动杆菌发病中的作用，以及(Iii)确定CP介导的锌螯合对鲍曼不动杆菌生理的影响。这些结果将为鲍曼不动杆菌如何在脊椎动物宿主中获取营养提供基本的见解，并为基于钙保护素支架的多肽疗法的创建奠定基础，该支架通过营养金属螯合抑制微生物生长。

DESCRIPTION (provided by applicant): Acinetobacter baumannii is an important nosocomial pathogen that causes a range of diseases, including respiratory and urinary tract infections, meningitis, endocarditis, wound infections, and bacteremia. In fact, A. baumannii is now responsible for up to 20% of all intensive care unit infections in some regions of the world with pneumonia being the most common presentation. The clinical significance of A. baumannii has been propelled by this organism's rapid acquisition of resistance to virtually all antibiotics. The identification of novel targets for therapeutic intervention is critical to our ability to protect he public health from this emerging infectious threat. One promising potential area of therapeutic development involves targeting bacterial access to nutrient metal. This strategy is based on the fact that all bacterial pathogens require nutrient metal in order to colonize their hosts. Despite the fact that a variety of metals are required by bacterial pathogens during growth within vertebrates, iron sequestration is considered to be the primary nutrient that is actively sequestered by the host during the innate immune response to infection. In the present application, we provide evidence that the innate immune factor calprotectin defends against Acinetobacter pneumonia by chelating nutrient zinc (Zn). Using calprotectin as a probe, we have identified a transport system in A. baumannii that competes with calprotectin for Zn and is transcriptionally controlled by a Zn-dependent regulator. Calprotectin is abundant at sites of inflammation and is a known pro- inflammatory molecule that is a ligand for the receptor for advanced glycation end products (RAGE). Despite its clear involvement, the contributions of calprotectin-mediated metal sequestration and RAGE binding to defense against infection have not been thoroughly evaluated. Based on preliminary data described in this application, we hypothesize that calprotectin-mediated Zn sequestration and RAGE binding are critical factors during the host-pathogen interaction. To test this central hypothesis, we propose a series of experiments aimed at understanding the mechanism and pathophysiological consequence of calprotectin-mediated Zn sequestration and RAGE binding during A. baumannii pneumonia. In these studies, we will (i) identify the structural features of calprotectin that enable it to chelae transition metals such as Zn and to bind RAGE, (ii) elucidate the impact of calprotectin and RAGE on A. baumannii pathogenesis, and (iii) determine the impact of CP-mediated Zn chelation on the physiology of A. baumannii. These results will provide fundamental insight into how A. baumannii acquires nutrients in the vertebrate host, and lay the foundation for the creation of peptide therapeutics based on a calprotectin scaffold that inhibit microbial growth through nutrient metal chelation.