Sequential release of IL-1alpha and IL-1beta leads to a two-hit model of acute lung injury

 描述(申请人提供)：急性呼吸窘迫综合征(ARDS)是急性肺损伤(ALI)的一种临床综合征，其特征是发病突然，肺部严重无法为血液供氧(低氧血症)。目前还没有已知的治疗ARDS的方法，除了使用低容量的机械通气(MV)，这种方法的死亡率仍然高达30%，令人无法接受。白介素1α(IL-1α)和IL-1β参与了急性呼吸窘迫综合征的发病过程。虽然IL-1α和IL-1β都是以前体形式产生的，但其分泌和激活需要IL-1β的裂解，而IL-1α的裂解和前型都是活性的。我们的初步数据表明，前IL-1α是从坏死中释放出来的 MΦ吸入脂多糖后，导致血管渗漏和中性粒细胞重新聚集到肺内。然而，为了成熟和释放IL-1β，需要激活炎性小体。我们发现，在MΦ中，NLRP3炎症体是通过线粒体(Mt)功能障碍和氧化mtDNA与NLRP3结合而激活的。MT损伤同时导致自噬和有丝分裂等反对细胞死亡的修复系统的激活。最近的报道表明，吞丝分裂和线粒体生物发生都可能在脓毒症中起到保护作用，并减轻ALI。我们建立了一种MV诱发M-Φ-mt功能障碍和细胞死亡的小鼠模型，MV后气管内注射脂多糖导致IL-1α和IL-1β分泌的顺序释放，并发展为ALI，并伴有中性粒细胞浸润、肺泡水肿、趋化因子分泌和低氧血症。当IL-1信号被Caspase-1、NLRP3或IL-1R拮抗剂干扰时，小鼠表现出与对照组相同水平的炎症反应，但没有出现低氧血症，这表明ALI低氧血症的机制依赖于IL-1信号转导。血管内皮细胞(EC)和平滑肌细胞(SMC)均参与了ALI所致低氧血症的发病机制，是IL-1信号转导的靶点。这些观察结果使我们推测，ALI和低氧血症的发生需要从内毒素诱导的坏死性Mα中依次释放IL-1Φ，然后在MV过程中AM中的NLRP3炎性小体激活产生IL-1。吞丝和线粒体生物合成通过抑制炎性小体激活和保护组织功能来对抗内毒素+MV所致的急性肺损伤和低氧血症。为了验证这些假说，我们提出了以下具体目标：1)确定IL-1α在内毒素+MV急性肺损伤低氧血症发生中的作用。2)探讨IL-1信号在内毒素+MV诱导的低氧血症中的作用。3)探讨线粒体吞噬和线粒体生物发生在LPS+MV急性肺损伤中的作用。这些研究将有助于确定ALI和ARDS中IL-1α和依赖的低氧血症的新机制，并将确定一个新的潜在治疗领域，用于MV上患有ARDS的脓毒症患者，这种疾病目前仍有超过30%的死亡率，目前尚无治疗方法。

 DESCRIPTION (provided by applicant): Acute Respiratory Distress Syndrome (ARDS) is a clinical syndrome of acute lung injury (ALI) characterized by a sudden onset and a profound inability of the lungs to oxygenate the blood (hypoxemia). There are no known therapies for ARDS except using low volumes on mechanical ventilation (MV), which still has an unacceptably high mortality rate of 30%. The combination of sepsis plus MV (`two-hit") significantly increases the risk for developing ARDS. Interleukin-1α (IL-1α) and IL-1β are implicated in the pathogenesis of ARDS. While both IL-1α and IL-1β are produced in a pro form, cleavage of IL-1β is required for its secretion and activation, while both the cleaved and pro-form of IL-1α are active. Our preliminary data indicate that pro- IL-1α is released from necrotic MΦ after LPS inhalation, which leads to vascular leakage and PMN recruitment into the lungs. However, for maturation and release of IL-1β, activation of the inflammasome is required. We showed that NLRP3 inflammasome is activated in MΦ by mitochondrial (Mt) dysfunction followed by oxidized MtDNA binding to NLRP3. Mt damage simultaneously leads to activation of repair systems such as autophagy and mitophagy that oppose cell death. Recent reports suggest that both mitophagy and Mt biogenesis may serve a protective role in sepsis and mitigate ALI. We developed a mouse model in which MV triggers MΦ Mt dysfunction and cell death, and intratracheal LPS followed by MV lead to sequential release of IL-1α and IL-1β secretion and the development of ALI, with PMN infiltration, alveolar edema, chemokine secretion, and hypoxemia. When IL-1 signaling was disrupted by the absence of caspase-1 or NLRP3, or by IL-1R antagonist, mice demonstrated equal levels of inflammation compared to controls, but failed to develop hypoxemia, indicating that the mechanism of hypoxemia in ALI is dependent on IL-1 signaling. Both endothelial cells (EC) and smooth muscle cells (SMC) have been implicated in the mechanism of ALI-induced hypoxemia and are targets of IL-1 signaling. These observations lead us to hypothesize that the development of ALI and hypoxemia in LPS+MV requires sequential release of IL-1α from LPS-induced necrotic MΦ, followed by IL-1 secretion by NLRP3 inflammasome activation in AM during MV. Mitophagy and mitochondrial biogenesis oppose LPS+MV induced acute lung injury and hypoxemia by inhibiting inflammasome activation and preserving tissue function. To test these hypotheses we propose the following specific aims: 1) Determine the role of IL-1α in the development of hypoxemia in LPS+MV acute lung injury. 2) Determine the role of IL-1 signaling in LPS+MV-induced hypoxemia. 3) Determine the role of mitophagy and mitochondria biogenesis in LPS+MV acute lung injury. These studies will help determine novel mechanisms underlying IL-1α and dependent hypoxemia in ALI and ARDS, and will identify a new area of potential therapeutics for sepsis patients with ARDS on MV, a condition that still carries over 30% mortality rate for which no treatments currently exist.