Inflammatory cytokines and pyroptosis in Coronavirus infection

SUMMARYHuman Coronaviruses (hCoV) cause severe respiratory syndromes like SARS, MERS, and the ongoingpandemic of Covid-19 caused by the recently identified SARS-Cov2. Human and murine studies indicate thatexcessive inflammation, rather than viral replication, may precipitate these infections into lethal diseases. Theoverarching hypothesis of this proposal is that the excessive inflammation and neutrophil recruitmenttriggered by IL-1β and pyroptotic cell lysis severely impair the host ability to control infection and maintainhomeostasis. The corollary of this hypothesis, if proven correct, is that carefully timed inhibition of IL-1β,pyroptosis, and neutrophil proteases should be beneficial to treat Covid-19 and other hCoV infections.Increasing the significance of our study, these therapies are already approved to treat a number of humandiseases, a fact that bodes well for a rapid approval to treat Covid-19 and other hCoV infections. The mouseCoV MHV-1 provides an excellent model of CoV lung infections and will be used to test our hypothesis inthese specific aims: AIM 1. Is IL-1β deleterious during CoV infection and through which mechanisms? We willtest the hypothesis that excessive production of IL-1β drives neutrophil recruitment to the infected lung withconsequent tissue damage. The ability of IL-1β to exacerbate the pathogenesis of MHV-1 lung infection willbe studied in susceptible and resistant mouse strains treated with pharmacological inhibitors of IL-1β or instrains deficient in IL-1β. We will determine whether excessive neutrophil recruitment damages lung tissuethrough release of neutrophil elastase. We will also test the hypothesis that IL-1β inhibits type I and type IIIIFN production by stimulation of PGE2 synthesis. We will use genetic and pharmacological approaches toexamine how inhibition of PGE2 production affects IFN-I and IFN-III production during MHV-1 infection. Wewill test whether interventions to regulate IFN-I or PGE2 in the early or late phases of the infection haveopposite effect on the disease outcome. AIM 2. Is pyroptosis beneficial or deleterious in MHV-1 infection andwhich inflammasome triggers cell death? We will test the hypothesis that gasdermin D-dependent pyroptosisof lung cells may affect pathogenesis of coronavirus infection in opposite ways by either restricting viralreplication or exacerbating inflammation. We will test the hypothesis that pyroptosis of CoV-infected lungepithelial or endothelial cells is mediated by caspase-11. Mouse strains that lack expression of caspase-11 inlung epithelial or endothelial cells have been generated in our lab and will be used to test tissue-specific roleof caspase-11 during MHV-1 infection.