IL-1beta in the Development of Hypoxemia in Acute Lung Injury

 描述(申请人提供)：急性呼吸窘迫综合征(ARDS)是一种急性肺损伤的临床综合征，其特征是发病突然，肺部严重无法给血液供氧(低氧血症)。ARDS的死亡率为30%，尽管进行了广泛的研究，但美国每年仍有7.5万人死于ARDS。脓毒症合并机械通气显著增加了发生ARDS的风险。因此，两次打击的急性肺损伤模型引起了广泛的兴趣，并在动物模型中得到了广泛的研究。然而，脓毒症和机械通气(MV)协同作用导致急性肺损伤的具体机制仍不清楚。白细胞介素1受体(IL-1β，IL-1β)参与了急性呼吸窘迫综合征的发病机制，其分泌受一种称为NLRP3炎症体的细胞内复合体的调节，我们最近发现该复合体是由线粒体功能障碍激活的巨噬细胞，并与细胞死亡有关。我们建立了一种MV诱发巨噬细胞线粒体功能障碍和细胞死亡的小鼠模型，吸入脂多糖和MV共同导致IL-1β的分泌和急性肺损伤的发生，表现为中性粒细胞浸润、肺泡水肿、趋化因子分泌和低氧血症。有趣的是，当IL-1β信号被Caspase-1或NLRP3的缺失或IL-1R拮抗剂Anakinra阻断时，我们观察到低氧血症的发生明显改善，而对中性粒细胞浸润和肺泡渗漏没有明显影响，表明导致肺损伤低氧血症的机制不依赖于肺炎症，而依赖于IL-1β信号转导。这些数据提示了IL-1β和NLRP3炎症小体的新作用，特别是在与急性肺损伤和急性呼吸窘迫综合征相关的低氧血症中。我们假设缺氧性肺血管收缩，即血液从气体交换不良的区域分流，有助于解释低氧血症的发展如何从机械上区别于炎症。文献表明，IL-1β可能通过影响肺内一氧化氮的产生来调节缺氧性肺血管收缩。事实上，我们发现MV增加了肺中一氧化氮合酶2(NOS2)的表达和一氧化氮的产生，并且NOS2缺陷小鼠免受急性肺损伤相关低氧血症的发展。基于这些数据，这项有指导的K08赠款申请的中心假设是，急性肺损伤中低氧血症的发生需要NLRP3炎症小体激活和IL-1β的分泌，低氧血症的机制主要是通过IL-1β对缺氧性肺血管收缩的影响。我们现在建议通过以下目的来验证我们的假设：目的1是确定肺泡巨噬细胞在急性肺损伤低氧血症中的作用；目的2是确定一氧化氮在急性肺损伤中IL-1β依赖的低氧血症中的作用；目的3是确定急性肺损伤中的NLRP3和IL-1β信号是否破坏了缺氧性肺血管收缩。

 DESCRIPTION (provided by applicant): Acute Respiratory Distress Syndrome (ARDS) is a clinical syndrome of acute lung injury characterized by a sudden onset and a profound inability of the lungs to oxygenate the blood (hypoxemia). ARDS has a mortality rate of 30% and is responsible for 75,000 deaths annually in the United States despite extensive research efforts. The combination of sepsis plus mechanical ventilation significantly increases the risk for developing ARDS. Therefore, a two-hit model of acute lung injury is of great interest and has been studied extensively in animal models. However, the specific mechanisms underlying the development of acute lung injury through synergy of sepsis and mechanical ventilation (MV) remain unknown. Interleukin 1β (IL-1β) is implicated in the pathogenesis of ARDS, and its secretion is regulated by an intracellular complex termed the NLRP3 inflammasome, which we recently demonstrated is activated in macrophages by mitochondrial dysfunction and is associated with cell death. We developed a mouse model in which MV triggers macrophage mitochondrial dysfunction and cell death, and inhaled lipopolysaccharide (LPS) and MV together lead to IL-1β secretion and the development of acute lung injury, as demonstrated by neutrophil infiltration, alveolar edema, chemokine secretion, and hypoxemia. Interestingly, when IL-1β signaling was disrupted by the absence of caspase-1 or NLRP3, or by the administration of IL-1R antagonist Anakinra, we observed significant improvement in the development of hypoxemia without significant effects on neutrophil infiltration or alveolar leakage, indicating that the mechanism causing hypoxemia in lung injury is independent of lung inflammation but dependent on IL- 1β signaling. These data suggest a novel role for IL-1β and the NLRP3 inflammasome, specifically in the hypoxemia associated with acute lung injury and ARDS. We hypothesize that hypoxic pulmonary vasoconstriction, in which blood is diverted away from areas of poor gas exchange, can help to explain how the development of hypoxemia can be mechanistically distinct from inflammation. Literature suggests that IL- 1β may modulate hypoxic pulmonary vasoconstriction by affecting nitric oxide production in the lung. Indeed, we found that MV increases expression of nitric oxide synthase 2 (NOS2) and nitric oxide production in the lung, and that Nos2-deficient mice were protected from the development of acute lung injury-related hypoxemia. Based on these data, the central hypothesis for this mentored K08 grant application is that the development of hypoxemia in acute lung injury requires NLRP3 inflammasome activation and IL-1β secretion, and that the mechanism of hypoxemia is primarily through IL-1β effects on hypoxic pulmonary vasoconstriction. We now propose to test our hypothesis through the following aims: Aim 1 is to determine the role of alveolar macrophages in the development of hypoxemia in acute lung injury; Aim 2 is to determine the role of nitric oxide in IL-1β-dependent hypoxemia in acute lung injury; and Aim 3 is to determine if NLRP3 and IL-1β signaling in acute lung injury disrupts hypoxic pulmonary vasoconstriction.