Source data used to generate graphs in Fig 3C.

Infection of Rift Valley fever virus (RVFV), a highly pathogenic mosquito-borne zoonotic virus, triggers severe inflammatory pathogenesis but the underlying mechanism of inflammation activation is currently unclear. Here, we report that the non-structural protein NSs of RVFV triggers mitochondrial damage to activate the NLRP3 inflammasome leading to viral pathogenesis in vivo. It is found that the host transcription inhibition effect of NSs causes rapid down-regulation of myeloid cell leukemia-1(MCL-1), a pro-survival member of the Bcl-2 (B-cell lymphoma protein 2) protein family. MCL-1 down-regulation led to BAK activation in the mitochondria, which triggered mtROS production and release of oxidized mitochondrial DNA (ox-mtDNA) into the cytosol. Cytosolic ox-mtDNA binds and activates the NLRP3 inflammasome triggering NLRP3-GSDMD pyroptosis in RVFV infected cells. A NSs mutant virus (RVFV-NSsRM) that is compromised in inducing transcription inhibition did not trigger MCL-1 down-regulation nor NLRP3-GSDMD pyroptosis. RVFV infection of the Nlrp3-/- mouse model demonstrated that the RVFV-triggered NLRP3 pyroptosis contributed to RVFV inflammatory pathogenesis and fatal infection in vivo. Infection with the RVFV-NSsRM mutant virus similarly showed alleviated inflammatory pathogenesis and reduced fatality rate. Taken together, these results revealed a mechanism by which a virulence factor activates the mitochondrial MCL-1-BAK axis through inducing host transcription inhibition to trigger NLRP3-dependent inflammatory pathogenesis.

裂谷热病毒（Rift Valley fever virus, RVFV）是一种高致病性蚊媒人畜共患病毒，其感染可引发严重的炎症性致病过程，但目前炎症激活的潜在分子机制尚不明确。本研究证实，RVFV编码的非结构蛋白NSs（non-structural protein NSs）可诱导线粒体损伤，进而激活NLRP3炎症小体（NLRP3 inflammasome），最终在体内介导病毒的致病进程。研究发现，NSs的宿主转录抑制效应可快速下调髓系细胞白血病-1（myeloid cell leukemia-1, MCL-1）的表达，该蛋白属于B细胞淋巴瘤蛋白2（B-cell lymphoma protein 2, Bcl-2）家族的促存活成员。MCL-1表达下调可诱导线粒体BAK活化，进而触发线粒体活性氧（mtROS）生成以及氧化型线粒体DNA（oxidized mitochondrial DNA, ox-mtDNA）向细胞质的释放。细胞质内的氧化型线粒体DNA可结合并激活NLRP3炎症小体，从而在RVFV感染的细胞中触发NLRP3-GSDMD细胞焦亡。一种丧失转录抑制能力的NSs突变毒株（RVFV-NSsRM），既无法诱导MCL-1表达下调，也不能触发NLRP3-GSDMD细胞焦亡。通过对Nlrp3基因敲除小鼠模型开展RVFV感染实验，结果证实RVFV诱导的NLRP3细胞焦亡可在体内介导RVFV的炎症性致病过程与致死性感染。感染RVFV-NSsRM突变毒株的小鼠同样表现出炎症性致病过程减轻、病死率降低的表型。综上，本研究揭示了一种病毒毒力因子通过诱导宿主转录抑制，激活线粒体MCL-1-BAK信号轴，进而触发NLRP3依赖性炎症性致病过程的分子机制。