AIM2 Inflammasome-Mediated Pyroptosis in Enterovirus A71-Infected Neuronal Cells Restricts Viral Replication

Abstract

Encephalomyelitis is a well-known complication of hand, foot, and mouth disease (HFMD) due to Enterovirus 71 (EV71) infection. Viral RNA/antigens could be detected in the central nervous system (CNS) neurons in fatal encephalomyelitis but the mechanisms of neuronal cell death is not clearly understood. We investigated the role of absent in melanoma 2 (AIM2) inflammasome in neuronal cell death, and its relationship to viral replication. Our transcriptomic analysis, RT-qPCR, Western blot, immunofluorescence and flow cytometry studies consistently showed AIM2 gene up-regulation and protein expression in EV-A71-infected SK-N-SH cells. Downstream AIM2-induced genes, CARD16, caspase-1 and IL-1β were also up-regulated and caspase-1 was activated to form cleaved caspase-1 p20 subunits. As evidenced by 7-AAD positivity, pyroptosis was confirmed in infected cells. Overall, these findings have a strong correlation with decreases in viral titers, copy numbers and proteins, and reduced proportions of infected cells. AIM2 and viral antigens were detected by immunohistochemistry in infected neurons in inflamed areas of the CNS in EV-A71 encephalomyelitis. In infected AIM2-knockdown cells, AIM2 and related downstream gene expressions, and pyroptosis were suppressed, resulting in significantly increased virus infection. These results support the notion that AIM2 inflammasome-mediated pyroptosis is an important mechanism of neuronal cell death and it could play an important role in limiting EV-A71 replication.

The AIM2 inflammasome: Sensor of pathogens and cellular perturbations

“…AIM2 has also been described to control RNA viruses including Chikungunya virus (CHINKV), West Nile virus (WNV), and Enterovirus A71 (EV‐A71) . AIM2 and CASP1 genes were highly upregulated in primary human dermal fibroblasts upon infection with CHINKV and WNV.…”

“…Likewise, EV‐A71 promoted upregulation of genes encoding for AIM2 inflammasome components in SK‐N‐SH human neural cell line and AIM2 was found highly expressed in the central nervous system of patients infected with EV‐A71. Downregulation of AIM2 in SK‐N‐SH cells decreased pyroptosis upon infection with EV‐A71 and augmented viral replication . In contrast AIM2 did not control the replication of Influenza A virus (IAV) in murine models .…”

“…Downregulation of AIM2 in SK-N-SH cells decreased pyroptosis upon infection with EV-A71 and augmented viral replication. 129 In contrast AIM2 did not control the replication of Influenza A virus (IAV) in murine models. 81 However, mice lacking AIM2 had reduced lung inflammation and injury after (IAV) infection as illustrated by decreased inflammatory cells infiltrate and decreases lung tissue damage.…”

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

“…This form of cell death is evoked by intracellular pathogens, mainly bacteria, as a means of escaping the inflammatory response of the host (Fink and Cookson, 2006;Cunha and Zamboni, 2013). Pyroptosis has been observed in EV-A71 infected neuroblastoma cell lines (Yogarajah et al, 2017a;Zhu et al, 2018). The mechanism of EV induced pyroptosis was found to involve upregulation of a major inflammasome gene called AIM2, along with several AIM2-mediated pyroptosis-associated genes including caspase-1 causing a decrease in EV-A71 replication within neurons (Yogarajah et al, 2017a).…”

The involvement of regulated cell death forms in modulating the bacterial and viral pathogenesis

“…3). In natural situations, AIM2 dependent pyroptosis is observed in response to MCMV, Vaccinia virus (Rathinam et al, 2010) and EV71 infections (Yogarajah et al, 2017). Zika virus (ZIKV), an RNA virus, has gained increased attention over the last years due to its association with severe birth defects, including microcephaly.…”