Nlrp9b inflammasome restricts rotavirus infection in intestinal epithelial cells

Abstract

Rotavirus, a leading cause of severe gastroenteritis and diarrhoea in young children, accounts for around 215,000 deaths annually worldwide1. Rotavirus specifically infects the intestinal epithelial cells in the host small intestine and has evolved strategies to antagonize interferon and NF-κB signalling2–5, raising the question as to whether other host factors participate in antiviral responses in intestinal mucosa. The mechanism by which enteric viruses are sensed and restricted in vivo, especially by NOD-like receptor (NLR) inflammasomes, is largely unknown. Here we uncover and mechanistically characterize the NLR Nlrp9b that is specifically expressed in intestinal epithelial cells and restricts rotavirus infection. Our data show that, via RNA helicase Dhx9, Nlrp9b recognizes short double-stranded RNA stretches and forms inflammasome complexes with the adaptor proteins Asc and caspase-1 to promote the maturation of interleukin (Il)-18 and gasdermin D (Gsdmd)-induced pyroptosis. Conditional depletion of Nlrp9b or other inflammasome components in the intestine in vivo resulted in enhanced susceptibility of mice to rotavirus replication. Our study highlights an important innate immune signalling pathway that functions in intestinal epithelial cells and may present useful targets in the modulation of host defences against viral pathogens.

Rotavirus infection

“…This interaction was illustrated by the report that antibiotic treatment can reduce rotavirus replication and the severity of disease in mice 80 . Rotavirus dsRNA can be recognized by TLR3 (a MYD88-independent TLR) and NACHT, LRR and PYD domains-containing protein 9B (a component of the nucleotide-binding oligomerization domain-like receptor inflammasome), and these PRRs are speculated to have a role in the age-dependent resistance to rotavirus disease in mice, as both proteins are expressed at higher levels in adult animals 81,82 . In vitro (with multiple cell types) and in vivo experiments in mice have shown that, depending on the tissue, virus strain and age of the animal, NSP1 or possibly other rotavirus proteins can inhibit the signalling pathways activated by PRRs, which might underlie the poor innate immune response to rotaviruses 78,83 (FIG.…”

NLRP9b: a novel RNA-sensing inflammasome complex

“…Indeed, the authors identified the human RNA helicase DHX9 as an interacting partner of both human NLRP9 and viral dsRNA. Furthermore, mouse intestinal organoids lacking DHX9 and infected with Rotavirus produced less IL-18 and were more resistant to pyroptosis compared with wild-type organoids, confirming a role for DHX9 in the activation of the NLRP9b inflammasome (Figure 1) [5].…”

“…In a recent study published in Nature, Zhu and colleagues identified a cytosolic inflammasome sensor for Rotavirus [5]. The authors first established that infection of suckling mice with Rotavirus induced robust activation of caspase-1 in the ileal tissue, indicating a role for inflammasomes in the pathogenesis of Rotavirus infection.…”

“…To elucidate the role of this enigmatic NLR, the authors utilized CRISPR-Cas9 technology to generate mouse strains lacking NLRP9b either in all cells or specifically in intestinal epithelial cells. They found that both Nlrp9b -/-strains were more susceptible to Rotavirus infection compared to wild-type mice, highlighting a crucial role of NLRP9b in controlling Rotavirus infection [5].…”

“…Similar to organoids lacking key inflammasome components, Nlrp9b -/-organoids produced lower levels of IL-18 and were more resistant to cell death compared with wild-type organoids. Interestingly, NLRP6, a highly expressed NLR in intestinal epithelial cells, also contributed to the host defense against Rotavirus infection [5], raising the possibility that NLRP6 and NLRP9b are co-activated and recruited to the same inflammasome complex, similar to the findings that NLRP3 and NLRC4 are co-recruited to the Salmonella-induced inflammasome in macrophages [6]. Although the role of NLRP6 was not investigated further, these findings collectively revealed, for the first time, that a signaling axis defined by NLRP9b-ASC-Caspase-1-Gasdermin D contributed to anti-Rotavirus immunity in intestinal epithelial cells [5].…”