Immunoproteasome-Mediated Inflammation in Coronavirus Respiratory Infection

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PROJECT SUMMARY Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel human coronavirus that has caused the coronavirus disease 2019 (COVID-19) pandemic. COVID-19 is associated with severe, frequently life-threatening respiratory illness in a substantial proportion of affected people. Severe COVID-19 is characterized by an exuberant systemic inflammatory response to SARS-CoV-2 infection. That response aids in control of viral replication during acute infection, but it also drives virus-induced pathology and disease manifestations. For reasons that remain incompletely understood, that deleterious inflammatory response is less likely to develop in children infected with SARS-CoV-2, and children are more likely than adults to have asymptomatic infection or mild disease. The immunoproteasome (IP), an inducible component of the ubiquitin- proteasome system, is more efficient than the constitutive proteasome in generating MHC class I epitopes for recognition by CD8 T cells. IP activity also exerts intrinsic effects on T cell, B cell, macrophage, and DC functions and contributes to inflammatory responses via mechanisms that include degradation of IκB and subsequent activation of NF-κB-mediated inflammatory pathways. No studies have addressed contributions of the IP to the pathogenesis of human or animal coronaviruses. Our published and preliminary data suggest that IP subunit activity is developmentally regulated in the lungs and other organs, increasing with age. IP subunit expression increases in mice during acute infection with a murine coronavirus, and IP inhibition suppresses virus-induced expression of pro-inflammatory cytokines but enhances weight loss and mortality. In this proposal, we will test the hypothesis that increased IP activity during coronavirus infection drives immunopathology in an age-dependent manner. We will use a tractable animal model with an animal coronavirus, murine hepatitis virus type 1 (MHV-1), to define the role of the IP in coronavirus pathogenesis and identify effects of IP inhibition on virus-induced inflammation and disease during acute infection. In Aim 1, we will define age-based differences in IP response, inflammation, and disease induced by acute MHV-1 respiratory infection. In Aim 2, we will use pharmacologic inhibition of IP subunit activity to define effects of IP activity on key immune cells and determine the extent to which the IP contributes to virus-induced inflammation and disease. There is a clear and pressing need to development effective preventative and therapeutic measures for COVID-19. Modulation of an inducible host factor, such as the IP, that is predominantly active during an inflammatory state such as infection would be an appealing strategy if it could facilitate reduction of detrimental inflammatory responses with minimal impact on essential constitutively active host processes.