Inflammation and excess cytokine release are hallmarks of severe acute COVID-19 and underpin key aspects of long COVID. While programmed cell death is known to drive inflammation, its role in SARS-CoV-2 pathogenesis and post-acute sequelae of COVID (PASC) remains obscure as post-mortem or in vitro assays only allow for correlative analyses.
In order to untangle cause and effect of inflammation and cell death in vivo, we utilized our P21 mouse-adapted SARS-CoV-2 virus strain and infected a range of gene-targeted animals lacking key inflammatory mediators as well as upstream initiators and/or downstream effectors of the main programmed cell death pathways. This comprehensive in vivo screening approach, including viral load measurement, lung cytokine, spatial transcriptomic and proteomic analyses analysis found that while pyroptosis and necroptosis are redundant, caspase-8 is critical for cytokine release and inflammation. Loss of caspase-8 reduced disease severity and viral load in mice, and this occurred independently of its apoptotic function. Elevated expression of caspase-8 and its regulator cFLIP in infected lungs, alongside caspase-8 mediated cleavage of N4BP1, a suppressor of NF-kB signalling, indicates a role of this signalling axis in pathological inflammation, offering potential therapeutic intervention targets.
Notably, P21-infected mice develop key aspects of long COVID, including persistent lung inflammation and fibrosis, neuroinflammation, cognitive defects, gut inflammation and dysbiosis as well as heart issues. We identified caspase-8-mediated lung inflammatory signaling long after viral clearance and are now exploring its role in the development of PASC. Additionally, we are developing and evaluating tissue and cell type specific lipid nanoparticle RNA therapy platforms to target and restore aberrant lung inflammatory signaling to mitigate pathology.