RSV bronchiolitis causes significant infant mortality. Bronchiolitis is characterised by airway epithelial cell (AEC) death, however the mode of death remains unknown.
To determine whether necroptosis contributes to RSV bronchiolitis pathogenesis via high mobility group box 1 (HMGB1) release.
Nasopharyngeal samples were collected from children presenting to hospital with acute respiratory infection. Primary human AECs and neonatal mice were inoculated with RSV and murine pneumovirus respectively. Necroptosis was determined via viability assays and immunohistochemistry for receptor-interacting protein kinase-1 (RIPK1), mixed lineage kinase domain-like protein (MLKL) and caspase-3. Necroptosis was blocked using pharmacological inhibitors, and RIPK1 kinase-dead knock-in mice.
HMGB1 levels were elevated in nasopharyngeal samples of children with acute RSV infection. RSV-induced epithelial cell death was associated with increased pRIPK1 and pMLKL, but not active caspase-3 expression. Inhibition of RIPK1 or MLKL attenuated RSV-induced HMGB1 translocation and release, and lowered viral load. MLKL inhibition increased active caspase-3 expression in a caspase-8/9-dependent manner. In susceptible mice, Pneumovirus infection up-regulated RIPK1 and MLKL expression in the airway epithelium at 8-10 days post infection; coinciding with AEC sloughing, HMGB1 release, and neutrophilic inflammation. Genetic or pharmacological inhibition of RIPK1 or MLKL attenuated these pathologies, lowered viral load, and prevented type-2 inflammation and airway remodelling. Necroptosis inhibition in early-life ameliorated asthma progression induced by viral or allergen challenge in later-life.
Pneumovirus infection induces AEC necroptosis. Inhibition of necroptosis may be a viable strategy to limit the severity of viral bronchiolitis and break its nexus with asthma.