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

 描述（由申请人提供）：急性呼吸窘迫综合征（ARDS）是急性肺损伤（ALI）的临床综合征，其特征为突然发作和肺严重不能吸收血液（低氧血症）。除了使用低容量机械通气（MV）外，没有已知的ARDS治疗方法，其死亡率仍高达30%。脓毒症加上MV（“两次打击”）的组合显著增加了发展为ARDS的风险。白细胞介素-1 α（IL-1α）和IL-1β参与了ARDS的发病机制。虽然IL-1α和IL-1β均以前体形式产生，但IL-1β的分泌和活化需要IL-1β的切割，而IL-1α的切割形式和前体形式均具有活性。我们的初步数据表明，IL-1α前体从坏死的 LPS吸入后，MΦ增加，导致血管渗漏和PMN募集到肺中。然而，为了成熟和释放IL-1β，需要激活炎性小体。我们表明，NLRP 3炎性体在MΦ中通过线粒体（Mt）功能障碍被激活，随后氧化的MtDNA与NLRP 3结合。线粒体损伤同时导致修复系统的激活，如自噬和线粒体自噬，对抗细胞死亡。最近的报道表明，线粒体自噬和线粒体生物发生可能在脓毒症中起保护作用，并减轻ALI。我们建立了一种小鼠模型，其中MV触发MΦ Mt功能障碍和细胞死亡，并且肺内LPS随后MV导致IL-1α和IL-1β分泌的顺序释放和ALI的发展，伴随PMN浸润、肺泡水肿、趋化因子分泌和低氧血症。当IL-1 R信号被caspase-1或NLRP 3的缺失或IL-1 R拮抗剂破坏时，小鼠表现出与对照组相同的炎症水平，但未发生低氧血症，表明ALI中低氧血症的机制依赖于IL-1信号。内皮细胞（EC）和平滑肌细胞（SMC）都参与了ALI诱导的低氧血症的机制，并且是IL-1信号转导的靶点。这些观察结果使我们推测，LPS+MV中ALI和低氧血症的发生需要LPS诱导的坏死MΦ中IL-1α的顺序释放，随后在MV期间AM中NLRP 3炎性小体激活产生IL-1 α分泌。线粒体自噬和线粒体生物合成通过抑制炎性小体活化和保护组织功能对抗LPS+MV诱导的急性肺损伤和低氧血症。为了验证这些假设，我们提出了以下具体目标：1）确定IL-1α在LPS+MV急性肺损伤低氧血症发展中的作用。2)确定IL-1信号在LPS+ MV诱导的低氧血症中的作用。3)确定线粒体自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β-内酰胺酶依赖性低氧血症的新机制，并将确定MV中伴有ARDS的脓毒症患者的潜在治疗新领域，这种疾病的死亡率仍超过30%，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.