The role of acute kidney in the pathogenesis of sepsis from pneumonia

 描述（由申请人提供）：急性肾损伤（AKI）很常见，并会增加死亡率。AKI使高达20%的住院和30%至50%的ICU住院复杂化。40 - 45%的患者在AKI诊断后发生脓毒症，死亡率加倍。肺炎是住院患者败血症和感染相关死亡的最常见原因。当肺炎患者出现菌血症时，死亡率会加倍。由于绝大多数菌血症患者为脓毒症，因此菌血症可视为等同于脓毒症。在这项研究中，我们研究了AKI易患肺炎菌血症和脓毒症的机制。肺炎引起菌血症的机制知之甚少，通常认为是由于免疫抑制导致肺部细菌防御压倒性。在初步研究中，我们发现AKI小鼠的肺炎严重程度与肺炎对照组相似，但AKI中的菌血症更严重。因此，免疫抑制不能解释AKI期间的菌血症。事实上，我们的初步研究表明，对内毒素（革兰氏阴性菌的免疫活化成分）的反应是旺盛的，其特征是炎症反应增加，而不是免疫抑制反应。Claudin 4（一种肺上皮紧密连接蛋白）减少，表明在伴有肺炎的AKI中存在上皮通透性增加。因此，我们认为AKI引起肺的免疫启动，而不是免疫抑制。初步研究表明，AKI中的肺免疫启动与肺中性粒细胞募集一致。我们的总体假设是，当暴露于来自革兰氏阴性菌的内毒素或肺炎时，AKI引发肺产生旺盛的炎症反应。我们提出，旺盛的炎症反应介导了肺部炎症，紧密连接蛋白（例如，紧密连接蛋白4），以及增加的上皮渗透性，其促进细菌移位进入循环，导致菌血症和脓毒症。我们有三个具体目标：1）确定AKI是否引起肺免疫引发，2）确定细菌易位在具有肺炎的AKI中是否更大，3确定密蛋白4的损失是否介导具有肺炎的AKI中的细菌易位。在目的1中，我们试图表征免疫引发的应答，确定该应答是否对肺泡巨噬细胞特异，并鉴定AKI中导致免疫引发的因素（即，中性粒细胞募集和可透析循环因子（使用腹膜透析）。在目标2中，我们试图建立细菌易位增加解释AKI中的菌血症，使用活体共聚焦显微镜来跟踪和量化患有肺炎和AKI的活小鼠中GFP标记的细菌的易位。在目的三中，我们试图确定AKI引发的肺泡巨噬细胞的炎症反应通过下调claudin 4表达和增加肺上皮通透性来介导肺炎期间的菌血症。这项资助的实验将为开发预防肺炎败血症和改善AKI患者生存率的干预措施提供有用的线索。

 DESCRIPTION (provided by applicant): Acute kidney injury (AKI) is common and increases mortality. AKI complicates up to 20% of hospital admissions and 30 to 50% of ICU admissions. Sepsis occurs in 40-45% of patients after AKI diagnosis and doubles mortality. Pneumonia is the most common cause of sepsis and infection-related death in hospitalized patients. Mortality in pneumonia doubles when patients become bacteremic. Since the vast majority of patients with bacteremia are septic, bacteremia may be considered equivalent to sepsis. In this grant, we investigate the mechanisms by which AKI predisposes to bacteremia and sepsis from pneumonia. The mechanism by which pneumonia causes bacteremia is poorly understood and is generally considered to be due to immunosuppression leading to overwhelming of lung bacterial defenses. In preliminary studies, we found that mice with AKI had similar pneumonia severity to controls with pneumonia, yet bacteremia was greater in AKI. Thus, immunosuppression does not explain bacteremia during AKI. In fact, rather than an immunosuppressed response, our preliminary studies demonstrate that the response to endotoxin (the immune activating component of gram negative bacteria) was exuberant and characterized by an increased inflammatory response. Claudin 4, a lung epithelial tight junction protein, was reduced suggesting that increased epithelial permeability was present in AKI with pneumonia. Thus, we suggest that AKI causes immune priming, not immunosuppression, of the lung. Preliminary studies suggest the lung immune priming in AKI coincides with lung neutrophil recruitment. Our overall hypothesis is that AKI primes the lung to exert an exuberant inflammatory response when exposed to endotoxin or pneumonia from gram negative bacteria. We propose that the exuberant inflammatory response mediates lung inflammation, loss of tight junction proteins (e.g., claudin 4), and increased epithelial permeability which facilitates translocation of bacteria into the circulation resulting in bacteremia and sepsis. We have three Specific Aims: 1) Determine if AKI causes lung immune priming, 2) Determine if bacterial translocation is greater in AKI with pneumonia, 3 Determine if loss of claudin 4 mediates bacterial translocation in AKI with pneumonia. In Aim 1, we seek to characterize the immune primed response, determine if this response is specific to alveolar macrophages, and identify factors in AKI which lead to immune priming (i.e., neutrophil recruitment and dialyzable circulating factors (using peritoneal dialysis). In Aim 2, we seek to establish that increased translocation of bacteria explains bacteremia in AKI using intravital confocal microscopy to track and quantify translocation of GFP-labelled bacteria in live mice with pneumonia and AKI. In Aim three, we seek to establish that the inflammatory response of AKI-primed alveolar macrophages mediates bacteremia during pneumonia by down regulating claudin 4 expression and increasing lung epithelial permeability. The experiments in this grant will provide useful leads into the development of interventions to prevent sepsis from pneumonia and improve survival in patients with AKI.