Pneumococcal Cardiotoxicity During Invasive Pneumococcal Disease

描述(申请人提供)：肺炎链球菌(肺炎球菌)是一种革兰氏阳性细菌，约占所有社区获得性肺炎(CAP)病例的40%，是菌血症和败血症的主要原因。因侵袭性肺炎球菌病(IPD)住院的人因不良心脏事件，特别是新的或恶化的充血性心力衰竭而猝死的风险增加。因此，在这些感染发作期间，似乎会发生某种形式的心脏损伤。在此，我们描述了IPD脓毒症小鼠心肌内形成的心脏损害的新观察。病变的形成与血液中的细菌负荷以及血清心肌肌钙蛋白水平呈正相关，心肌肌钙蛋白是心脏损伤的临床标志物。病变的形成也伴随着电生理的改变，这表明心脏收缩能力的进行性丧失。在感染期间，皮损的严重性增加，明显缺乏浸润性免疫细胞，这与其他革兰氏阳性细菌通常所形成的脓肿形成了鲜明的对比。重要的是，心脏损伤的形成与细菌和小鼠的菌株无关。值得注意的是，肺炎球菌可在病变内可见，并在气管内和静脉攻击后局限于心脏。这些心脏损害可能解释了严重CAP患者心脏不良事件发生率高的原因。为了研究肺炎球菌引起心肌细胞死亡的机制(S)，并探索通过免疫预防肺炎溶血素的可能性，我们提出了以下具体目标：目的1：确定肺炎球菌细胞壁和肺炎溶血素对心肌细胞死亡和病变形成的影响。我们观察了TUNEL阳性细胞、肺溶血素和IL-1？存在于心脏病变中，提示可能正在发生炎症性细胞凋亡。为了确定心肌细胞死亡的机制(S)，我们将检查基因敲除(KO)和半胱氨酸天冬氨酸氨基转移酶(Caspase)抑制剂治疗的小鼠的损伤形成，这些小鼠缺乏已建立的凋亡途径的关键调节因子。使用HL-1心肌细胞的补充体外研究将使用半胱氨酸天冬氨酸氨基转移酶抑制剂检测外源性和内源性的细胞凋亡。进一步的研究将确定肺炎球菌细胞壁和肺炎毒素在细胞死亡上是独立作用还是协同作用。目的2：检测抗体中和肺炎溶血素活性是否能保护小鼠免受病变形成。溶气素在心脏病变中被检测到，并可能对心肌细胞造成损害。由于抗肺炎溶血素的抗体具有中和性，对肺炎链球菌具有显著的保护作用，因此我们推测，肺炎溶血素的免疫应能防止细菌攻击后心脏损伤的形成。

DESCRIPTION (provided by applicant): Streptococcus pneumoniae (the neumococcus), a Gram-positive bacterium, accounts for approximately 40% of all cases of community-acquired pneumonia (CAP) and is a leading cause of bacteremia and sepsis. Individuals hospitalized for invasive pneumococcal disease (IPD) are at an increased risk for sudden death as a result of adverse cardiac events, in particular new or worsened congestive heart failure. Thus, some form of cardiac damage seems to occur during these infectious episodes. Herein we describe the novel observation of cardiac lesions formed within the myocardium of septic mice with IPD. Lesion formation was positively correlated with bacterial burden in the blood as well as serum levels of cardiac troponin, a clinical marker for cardiac damage. Lesion formation was also concomitant with changes in electrophysiology, which indicated a progressive loss of cardiac contractility. Lesions increased in severity during the infection, and had a marked absence of infiltrated immune cells, which stands in stark contrast to abscesses typically seen formed by other Gram-positive bacteria. Importantly, cardiac lesion formation were both bacterial and mouse strain independent. Notably, pneumococci could be visualized within the lesions, and were confined to the heart following both intratracheal and intravenous challenge. These cardiac lesions may explain the high incidence of adverse cardiac events in humans with severe CAP. To examine the mechanism(s) responsible for cardiomyocyte death and to explore the potential for protection by immunization against pneumolysin we propose the following Specific Aims: Aim 1: Determine the impact of pneumococcal cell wall and pneumolysin on cardiomyocyte death and lesion formation. We have observed the presence of TUNEL positive cells, pneumolysin, and IL-1? present within cardiac lesions suggesting that inflammasome-dependent apoptosis may be occurring. To determine the mechanism(s) of cardiomyocyte death we will examine lesion formation in knockout (KO) and caspase inhibitor treated mice that are deficient in key regulators of established apoptosis pathways. Complementary in vitro studies using HL-1 cardiomyocytes will examine extrinsic and intrinsic apoptosis using caspase inhibitors. Additional studies will determine if pneumococcal cell wall and the toxin pneumolysin act independently or synergistically on cell death. Aim 2: Test if neutralization of pneumolysin activity with antibody protects mice against lesion formation. Pneumolysin is detected within cardiac lesions and is presumably damaging to cardiomyocytes. Since antibodies against pneumolysin are neutralizing and confer significant protection against S. pneumoniae, we hypothesize that immunization against pneumolysin should prevent cardiac lesion formation following bacterial challenge.