Department of Medicine, Department of Microbiology and Immunology, Department of Pathology, McGill University Health Centre, McGill International TB Centre, Meakins-Christie Laboratories, McGill University, Montreal, QC, Canada H2X 2P2;
Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada M5S 1A8;
Proc Natl Acad Sci U S A. 2014 May 20;111(20):E2110-9. doi: 10.1073/pnas.1322118111. Epub 2014 May 5.
To subvert host immunity, influenza A virus (IAV) induces early apoptosis in innate immune cells by disrupting mitochondria membrane potential via its polymerase basic protein 1-frame 2 (PB1-F2) accessory protein. Whether immune cells have mechanisms to counteract PB1-F2-mediated apoptosis is currently unknown. Herein, we define that the host mitochondrial protein nucleotide-binding oligomerization domain-like receptor (NLR)X1 binds to viral protein PB1-F2, preventing IAV-induced macrophage apoptosis and promoting both macrophage survival and type I IFN signaling. We initially observed that Nlrx1-deficient mice infected with IAV exhibited increased pulmonary viral replication, as well as enhanced inflammatory-associated pulmonary dysfunction and morbidity. Analysis of the lungs of IAV-infected mice revealed markedly enhanced leukocyte recruitment but impaired production of type I IFN in Nlrx1(-/-) mice. Impaired type I IFN production and enhanced viral replication was recapitulated in Nlrx1(-/-) macrophages and was associated with increased mitochondrial mediated apoptosis. Through gain- and loss-of-function strategies for protein interaction, we identified that NLRX1 directly bound PB1-F2 in the mitochondria of macrophages. Using a recombinant virus lacking PB1-F2, we confirmed that deletion of PB1-F2 abrogated NLRX1-dependent macrophage type I IFN production and apoptosis. Thus, our results demonstrate that NLRX1 acts as a mitochondrial sentinel protecting macrophages from PB1-F2-induced apoptosis and preserving their antiviral function. We further propose that NLRX1 is critical for macrophage immunity against IAV infection by sensing the extent of viral replication and maintaining a protective balance between antiviral immunity and excessive inflammation within the lungs.
为了颠覆宿主的免疫，甲型流感病毒（IAV）通过其聚合酶碱性蛋白 1 框 2（PB1-F2）辅助蛋白破坏线粒体膜电位，从而诱导先天免疫细胞的早期凋亡。目前尚不清楚免疫细胞是否有机制来对抗 PB1-F2 介导的细胞凋亡。在此，我们定义宿主线粒体蛋白核苷酸结合寡聚化结构域样受体（NLR）X1 与病毒蛋白 PB1-F2 结合，防止 IAV 诱导的巨噬细胞凋亡，促进巨噬细胞存活和 I 型干扰素信号转导。我们最初观察到，感染 IAV 的 Nlrx1 缺陷型小鼠表现出肺部病毒复制增加，以及炎症相关的肺部功能障碍和发病率增加。对感染 IAV 的小鼠肺部的分析显示，在 Nlrx1(-/-) 小鼠中，白细胞募集明显增强，但 I 型 IFN 的产生受损。在 Nlrx1(-/-) 巨噬细胞中，IFN 产生受损和病毒复制增强得到了重现，并且与线粒体介导的凋亡增加有关。通过蛋白相互作用的增益和缺失功能策略，我们确定 NLRX1 直接在巨噬细胞的线粒体中与 PB1-F2 结合。使用缺乏 PB1-F2 的重组病毒，我们证实了 PB1-F2 的缺失消除了 NLRX1 依赖性巨噬细胞 I 型 IFN 产生和凋亡。因此，我们的结果表明 NLRX1 作为一种线粒体监测器，可防止 PB1-F2 诱导的巨噬细胞凋亡并维持其抗病毒功能。我们进一步提出，NLRX1 通过感知病毒复制的程度并在肺部抗病毒免疫和过度炎症之间保持保护性平衡，对巨噬细胞针对 IAV 感染的免疫至关重要。
