bims-inflin 2024-09-08 papers

mBio. 2024 Aug 29. e0168024

Seneca Valley virus circumvents Gasdermin A-mediated inflammation by targeting the pore-formation domain for cleavage.

Hongyan Yin, Zhenchao Zhao, Ya Yan, Ye Yuan, Weiyu Qu, Haiwei Wang, Cheng Zhu, Pingwei Li, Xin Li.

Members of the gasdermin (GSDM) family are critical for inducing programmable pyroptosis by forming pores on the cell membrane. GSDMB, GSDMC, GSDMD, and GSDME are activated by caspases or granzyme, leading to the release of their autoinhibitory domains. The protease SpeB from group A Streptococcus has been shown to cleave and activate GSDMA-mediated pyroptosis. Meanwhile, African Swine Fever Virus infection regulates pyroptosis by cleaving porcine GSDMA (pGSDMA) via active caspase-3 and caspase-4. However, it is not known whether virus-encoded proteases also target GSDMA. Here, we show that residues 1-252 of pGSDMA (pGSDMA1-252) is the pore-forming fragment that induces lytic cell death and pyroptosis. Interestingly, Seneca Valley Virus (SVV) infection induces the cleavage of both pGSDMA and human GSDMA and suppresses GSDMA-mediated cell death. Mechanistically, SVV protease 3C cleaves pGSDMA between Q187 and G188 to generate a shorter fragment, pGSDMA1-186, which fails to induce lytic cell death and lactate dehydrogenase release. Furthermore, pGSDMA1-186 does not localize to the plasma membrane and does not induce cell death, thereby promoting viral replication by suppressing host immune responses. These studies reveal a sophisticated evolutionary adaptation of SVV to bypass GSDMA-mediated pyroptosis, allowing it to overcome host inflammatory defenses.
IMPORTANCE: Gasdermin A (GSDMA) remains a protein shrouded in mystery, particularly regarding its regulation by virus-encoded proteases. Previous studies have identified human GSDMA (hGSDMA) as a sensor and substrate of the SpeB from group A Streptococcus, which initiates pyroptosis. However, it is not clear if viral proteases also cleave GSDMA. In this study, we show that a fragment of porcine GSDMA (pGSDMA) containing the first 252 residues constitutes the pore-forming domain responsible for inducing lytic cell death and pyroptosis. Interestingly, picornavirus Seneca Valley Virus (SVV) protease 3C cleaves both pGSDMA and hGSDMA, generating a shorter fragment that fails to associate with the plasma membrane and does not induce pyroptosis. This cleavage by SVV 3C suppresses GSDMA-mediated lactate dehydrogenase release, bactericidal activity, and lytic cell death. This study reveals how SVV subverts host inflammatory defense by disrupting GSDMA-induced pyroptosis, thereby advancing our understanding of antiviral immunity and opening avenues for treating GSDMA-associated autoimmune diseases.

Keywords: 3C protease; Gasdermin A; Seneca Valley Virus; cleavage; pyroptosis

DOI: https://doi.org/10.1128/mbio.01680-24

PLoS Pathog. 2024 Aug;20(8): e1012387

RVFV virulence factor NSs triggers the mitochondrial MCL-1-BAK axis to activate pathogenic NLRP3 pyroptosis.

Zhenqiong Guan, Huiling Li, Chongtao Zhang, Ziyan Huang, Meidi Ye, Yulan Zhang, Shufen Li, Ke Peng.

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.

DOI: https://doi.org/10.1371/journal.ppat.1012387

mBio. 2024 Sep 06. e0081024

Bystander monocytic cells drive infection-independent NLRP3 inflammasome response to SARS-CoV-2.

Leon L Hsieh, Monika Looney, Alexis Figueroa, Guido Massaccesi, Georgia Stavrakis, Eduardo U Anaya, Franco R D'Alessio, Alvaro A Ordonez, Andrew S Pekosz, Victor R DeFilippis, Petros C Karakousis, Andrew H Karaba, Andrea L Cox.

The pathogenesis of COVID-19 is associated with a hyperinflammatory immune response. Monocytes and macrophages play a central role in this hyperinflammatory response to SARS-CoV-2. NLRP3 inflammasome activation has been observed in monocytes of patients with COVID-19, but the mechanism and consequences of inflammasome activation require further investigation. In this study, we inoculated a macrophage-like THP-1 cell line, primary differentiated human nasal epithelial cell (hNEC) cultures, and primary monocytes with SARS-CoV-2. We found that the activation of the NLRP3 inflammasome in macrophages does not rely on viral replication, receptor-mediated entry, or actin-dependent entry. SARS-CoV-2 productively infected hNEC cultures without triggering the production of inflammasome cytokines IL-18 and IL-1β. Importantly, these cytokines did not inhibit viral replication in hNEC cultures. SARS-CoV-2 inoculation of primary monocytes led to inflammasome activation and induced a macrophage phenotype in these cells. Monocytic cells from bronchoalveolar lavage (BAL) fluid, but not from peripheral blood, of patients with COVID-19, showed evidence of inflammasome activation, expressed the proinflammatory marker CD11b, and displayed oxidative burst. These findings highlight the central role of activated macrophages, as a result of direct viral sensing, in COVID-19 and support the inhibition of IL-1β and IL-18 as potential therapeutic strategies to reduce immunopathology without increasing viral replication.
IMPORTANCE: Inflammasome activation is associated with severe COVID-19. The impact of inflammasome activation on viral replication and mechanistic details of this activation are not clarified. This study advances our understanding of the role of inflammasome activation in macrophages by identifying TLR2, NLRP3, ASC, and caspase-1 as dependent factors in this activation. Further, it highlights that SARS-CoV-2 inflammasome activation is not a feature of nasal epithelial cells but rather activation of bystander macrophages in the airway. Finally, we demonstrate that two pro inflammatory cytokines produced by inflammasome activation, IL-18 and IL-1β, do not restrict viral replication and are potential targets to ameliorate pathological inflammation in severe COVID-19.

Keywords: NLRP3; SARS-CoV-2; cytokines; inflammasome; macrophages

DOI: https://doi.org/10.1128/mbio.00810-24

Exp Mol Med. 2024 Sep 02.

STAT3 promotes NLRP3 inflammasome activation by mediating NLRP3 mitochondrial translocation.

Ling Luo, Fupeng Wang, Xueming Xu, Mingliang Ma, Guangyan Kuang, Yening Zhang, Dan Wang, Wei Li, Ningjie Zhang, Kai Zhao.

Recognition of the translocation of NLRP3 to various organelles has provided new insights for understanding how the NLRP3 inflammasome is activated by different stimuli. Mitochondria have already been demonstrated to be the site of NLRP3 inflammasome activation, and the latest research suggests that NLRP3 is first recruited to mitochondria, then disassociated, and subsequently recruited to the Golgi network. Although some mitochondrial factors have been found to contribute to the recruitment of NLRP3 to mitochondria, the detailed process of NLRP3 mitochondrial translocation remains unclear. Here, we identify a previously unknown role for Signal transducer and activator of transcription-3 (STAT3) in facilitating the translocation of NLRP3 to mitochondria. STAT3 interacts with NLRP3 and undergoes phosphorylation at Ser727 in response to several NLRP3 agonists, enabling the translocation of STAT3 and thus the bound NLRP3 to mitochondria. Disruption of the interaction between STAT3 and NLRP3 impairs the mitochondrial localization of NLRP3, specifically suppressing NLRP3 inflammasome activation both in vitro and in vivo. In summary, we demonstrate that STAT3 acts as a transporter for mitochondrial translocation of NLRP3 and provide new insight into the spatial regulation of NLRP3.

DOI: https://doi.org/10.1038/s12276-024-01298-9