bims-inflin 2024-01-28 papers

Issue of 2024‒01‒28
four papers selected by
Juliane Cristina Ribeiro Fernandes, Faculdade de Medicina de Ribeirão Preto

Nat Commun. 2024 Jan 26. 15(1): 786

A cytomegalovirus inflammasome inhibitor reduces proinflammatory cytokine release and pyroptosis.

Yingqi Deng, Eleonore Ostermann, Wolfram Brune.

In response to viral infection, cells can initiate programmed cell death (PCD), leading to a reduction in the release of viral progeny. Viruses have therefore evolved specific mechanisms to curb PCD. Cytomegaloviruses (CMVs) are sophisticated manipulators of cellular defenses and encode potent inhibitors of apoptosis and necroptosis. However, a CMV inhibitor of pyroptosis has not been clearly identified and characterized. Here we identify the mouse cytomegalovirus M84 protein as an inhibitor of pyroptosis and proinflammatory cytokine release. M84 interacts with the pyrin domain of AIM2 and ASC to inhibit inflammasome assembly. It thereby prevents Caspase-1-mediated activation of interleukin 1β (IL-1β), IL-18, and Gasdermin D. Growth attenuation of an M84-deficient MCMV in macrophages is rescued by knockout of either Aim2 or Asc or by treatment with a Caspase-1 inhibitor, and its attenuation in infected mice is partially rescued in Asc knockout mice. Thus, viral inhibition of the inflammasome-pyroptosis pathway is important to promote viral replication in vivo.

DOI: https://doi.org/10.1038/s41467-024-45151-z

Mol Med Rep. 2024 Mar;pii: 48. [Epub ahead of print]29(3):

Excess phosphate promotes SARS‑CoV‑2 N protein‑induced NLRP3 inflammasome activation via the SCAP‑SREBP2 signaling pathway.

Mi-Hua Liu, Xiao-Long Lin, Le-Le Xiao.

Hyperphosphatemia or severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) infection can promote cardiovascular adverse events in patients with chronic kidney disease. Hyperphosphatemia is associated with elevated inflammation and sterol regulatory element binding protein 2 (SREBP2) activation, but the underlying mechanisms in SARS‑CoV‑2 that are related to cardiovascular disease remain unclear. The present study aimed to elucidate the role of excess inorganic phosphate (PI) in SARS‑CoV‑2 N protein‑induced NLRP3 inflammasome activation and the underlying mechanisms in vascular smooth muscle cells (VSMCs). The expression levels of SARS‑CoV‑2 N protein, SREBP cleavage‑activating protein (SCAP), mature N‑terminal SREBP2, NLRP3, procaspase‑1, cleaved caspase‑1, IL‑1β and IL‑18 were examined by western blotting. The expression levels of SREBP2, HMG‑CoA reductase, HMGCS1, low density lipoprotein receptor, proprotein convertase subtilisin/kexin type 9 (PCSK9), SREBP1c, fatty acid synthase, stearyl coenzyme A desaturase 1, acetyl‑CoA carboxylase α and ATP‑citrate lyase were determined by reverse transcription‑quantitative PCR. The translocation of SCAP or NLRP3 from the endoplasmic reticulum to the Golgi was detected by confocal microscopy. The results showed that excess PI promoted SCAP‑SREBP and NLRP3 complex translocation to the Golgi, potentially leading to NLRP3 inflammasome activation and lipogenic gene expression. Furthermore, PI amplified SARS‑CoV‑2 N protein‑induced inflammation via the SCAP‑SREBP pathway, which facilitates NLRP3 inﬂammasome assembly and activation. Inhibition of phosphate uptake with phosphonoformate sodium alleviated NLRP3 inflammasome activation and reduced SREBP‑mediated lipogenic gene expression in VSMCs stimulated with PI and with SARS‑CoV‑2 N protein overexpression. Inhibition of SREBP2 or small interfering RNA‑induced silencing of SREBP2 effectively suppressed the effect of PI and SARS‑CoV‑2 N protein on NLRP3 inflammasome activation and lipogenic gene expression. In conclusion, the present study identified that PI amplified SARS‑CoV‑2 N protein‑induced NLRP3 inflammasome activation and lipogenic gene expression via the SCAP‑SREBP signaling pathway.

Keywords: NLRP3; excess phosphate; inflammasome; severe acute respiratory syndrome coronavirus 2 N protein; sterol regulatory element binding protein cleavage‑activating protein; vascular smooth muscle cell

DOI: https://doi.org/10.3892/mmr.2024.13173

J Immunol. 2024 Jan 22. pii: ji2300418. [Epub ahead of print]

Cutting Edge: Cytosolic Receptor AIM2 Is Induced by Peroxisome Proliferator-activated Receptor γ following Mycobacterium tuberculosis Infection of Human Macrophages but Does Not Contribute to IL-1β Release.

Eusondia Arnett, Jade Wolff, Chrissy M Leopold Wager, Jan Simper, Jeanine L Badrak, Carlos O Ontiveros, Bin Ni, Larry S Schlesinger.

AIM2 (absent in melanoma 2), an inflammasome component, mediates IL-1β release in murine macrophages and cell lines. AIM2 and IL-1β contribute to murine control of Mycobacterium tuberculosis (M.tb) infection, but AIM2's impact in human macrophages, the primary niche for M.tb, remains unclear. We show that M.tb, Mycobacterium bovis bacillus Calmette-Guérin (BCG), and M. smegmatis induce AIM2 expression in primary human macrophages. M.tb-induced AIM2 expression is peroxisome proliferator-activated receptor γ (PPARγ)-dependent and M.tb ESX-1-independent, whereas BCG- and M. smegmatis-induced AIM2 expression is PPARγ-independent. PPARγ and NLRP3, but not AIM2, are important for IL-1β release in response to M.tb, and NLRP3 colocalizes with M.tb. This is in contrast to the role for AIM2 in inflammasome activation in mice and peritoneal macrophages. Altogether, we show that mycobacteria induce AIM2 expression in primary human macrophages, but AIM2 does not contribute to IL-1β release during M.tb infection, providing further evidence that AIM2 expression and function are regulated in a cell- and/or species-specific manner.

DOI: https://doi.org/10.4049/jimmunol.2300418

Front Cell Infect Microbiol. 2023 ;13 1309128

Regulation and functions of the NLRP3 inflammasome in RNA virus infection.

Zhaoyang Yue, Xuelong Zhang, Yu Gu, Ying Liu, Lin-Miaoshen Lan, Yilin Liu, Yongkui Li, Ge Yang, Pin Wan, Xin Chen.

Virus infection is one of the greatest threats to human life and health. In response to viral infection, the host's innate immune system triggers an antiviral immune response mostly mediated by inflammatory processes. Among the many pathways involved, the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome has received wide attention in the context of viral infection. The NLRP3 inflammasome is an intracellular sensor composed of three components, including the innate immune receptor NLRP3, adaptor apoptosis-associated speck-like protein containing CARD (ASC), and the cysteine protease caspase-1. After being assembled, the NLRP3 inflammasome can trigger caspase-1 to induce gasdermin D (GSDMD)-dependent pyroptosis, promoting the maturation and secretion of proinflammatory cytokines such as interleukin-1 (IL-1β) and interleukin-18 (IL-18). Recent studies have revealed that a variety of viruses activate or inhibit the NLRP3 inflammasome via viral particles, proteins, and nucleic acids. In this review, we present a variety of regulatory mechanisms and functions of the NLRP3 inflammasome upon RNA viral infection and demonstrate multiple therapeutic strategies that target the NLRP3 inflammasome for anti-inflammatory effects in viral infection.

Keywords: NLRP3 inflammasome; RNA virus; inflammation; pyroptosis; therapeutic strategy

DOI: https://doi.org/10.3389/fcimb.2023.1309128