Mechanism, Function, and Exploitation of Influenza A Virus-Activated Cell Death

项目摘要/摘要 甲型流感病毒(IAV)在培养和体内复制的大多数细胞类型都会引发死亡。在……里面 2016，我们描述了一种IAV激活的细胞死亡途径，它几乎解释了IAV激活的所有死亡 被感染的肺细胞。在过去的资金周期中，我们表明这条途径是在宿主 传感器蛋白ZBP1检测病毒Z-RNAs并激活RIPK3激酶。然后，RIPK3触发并行、冗余 程序性坏死(坏死性下垂)和细胞凋亡的途径。这些研究勾勒出了优势细胞 IAV在感染肺中激活的死亡途径。他们还证明了ZBP1是一种RNA感知 蛋白质，它识别的RNA结构是Z-RNAs，这是独特的左手双螺旋 以前从未被认为在自然界中存在的RNA物种。我们现在做了几件耐人寻味的事情 为这一应用奠定基础的新发现。首先，我们发现在IAV期间产生的Z-RNA 感染不仅是病毒的来源，也是宿主细胞的来源。第二，我们观察到在肺泡中 巨噬细胞(AM)，与所有其他类型的肺细胞不同，ZBP1的激活不会导致细胞死亡，但 取而代之的是在一个非细胞溶解的转录程序中，该程序对于预防IAV致死性是必不可少的。第三，我们发现 在IAV感染期间，坏死性下垂不是在细胞质中被激活，而是在细胞核中被激活，导致核 破裂。这种“核性坏死性下垂”是高度炎症性的，是导致本病发生的主要原因。 严重的流感。最后，我们对IAV与 死下垂机制在鸟类和蝙蝠这两种主要的自然宿主这些病毒。而鸟类根本不会 表达ZBP1，我们发现蝙蝠在RIPK3上有一个选择性的氨基酸改变 取消坏死性下垂(但不是细胞凋亡)信号，潜在地解释了这些生物如何耐受这种 IAV亚型的多样性很大。据我们所知，这些发现提供了第一个证据 内源性Z-RNAs可能是ZBP1在抗IAV免疫中的天然配体，ZBP1具有非溶细胞性 在IAV感染期间发挥作用，IAV激活一种独特的、高炎症形式的坏死性下垂 原子核。他们还提供了新的进化洞察力，以了解IAV毒株是如何在其天然的 但可以激活人类的致病性坏死性下垂。基于这些和其他观察，目标是 本建议的目的是(1)鉴定和鉴定ZBP1的内源性Z-RNA配体，并确定 它们在ZBP1激活IAV感染细胞死亡中的重要性；(2)阐明其机制和功能 非细胞溶解ZBP1信号在AM中的作用；以及(3)了解核坏死下垂在流感中的作用 发病机制和进化中。这些研究联合了两个在ZBP1信号方面具有专业知识的实验室(Balachandran) 和IAV致病(Thomas)，它们的成功完成将为我们提供对 ZBP1在IAV感染过程中启动细胞死亡的机制和功能，具有重要的临床和临床意义 进化的结果。

PROJECT SUMMARY/ABSTRACT Influenza A virus (IAV) triggers the death of most cell types in which it replicates, both in culture and in vivo. In 2016, we described an IAV-activated cell death pathway which accounts for almost all IAV-activated death in infected pulmonary cells. Over that past funding cycle, we showed that this pathway is initiated when the host sensor protein ZBP1 detects viral Z-RNAs and activates RIPK3 kinase. RIPK3 then triggers parallel, redundant pathways of programmed necrosis (necroptosis) and apoptosis. These studies have outlined the dominant cell death pathway activated by IAV in infected lungs. They have also demonstrated that ZBP1 is an RNA sensing protein, and that the RNA structures it recognizes are Z-RNAs, which are unique, left-handed double-helical RNA species that had not previously been thought to occur in nature. We have now made several intriguing new discoveries that set the stage for this application. First, we found that the Z-RNAs produced during IAV infections are not just viral in origin, but host cell-derived as well. Second, we observed that in alveolar macrophages (AMs), unlike in all other lung cell types tested, ZBP1 activation does not result in cell death, but instead in a non-cytolytic transcriptional program essential for protection against IAV lethality. Third, we found that necroptosis during IAV infections is activated not in the cytoplasm, but in the nucleus, resulting in nuclear rupture. Such `nuclear necroptosis' is highly inflammatory, and is a major driver of the pathogenesis during severe influenza. Finally, we have obtained important new insight into the coevolution of IAV with the necroptosis machinery in birds and bats, the two major natural hosts of these viruses. While birds simply do not express ZBP1, we have found that bats possess a single amino acid alteration in RIPK3 which selectively abrogates necroptosis (but not apoptosis) signaling, potentially explaining how these organisms tolerate such a large diversity of IAV subtypes. To our knowledge, these discoveries provide the first evidence that endogenous Z-RNAs may function as innate ligands for ZBP1 in anti-IAV immunity, that ZBP1 has non-cytolytic functions during IAV infections, and that a IAV activates a unique, hyper-inflammatory form of necroptosis from the nucleus. They also provide fresh evolutionary insight into how IAV strains are tolerated in their natural reservoirs, but can activate pathogenic necroptosis in humans. Based these and other observations, the goals of this proposal are to (1) to identify and characterize endogenous Z-RNA ligands for ZBP1, and to determine their importance to ZBP1 activated cell death in IAV-infected cells; (2) to delineate the mechanism and function of non-cytolytic ZBP1 signaling in AMs; and (3) to understand the role of nuclear necroptosis in influenza pathogenesis and in evolution. These studies unite two labs with expertise in ZBP1 signaling (Balachandran) and IAV pathogenesis (Thomas), and their successful completion stands to provide pioneering insight into the mechanism and function of ZBP1-initiated cell death during IAV infections, with important clinical and evolutionary ramifications.