Disordered Proteostasis as a Driver of Disease in the Aging Lung

Pneumonia is the leading cause of death in patients with COVID-19 infection and disproportionately affects olderindividuals. In addition to the diffuse patchy alveolar infiltrates and acute hypoxemic respiratory failure typical ofviral pneumonia, patients with COVID-19 often develop hypotension requiring alpha-adrengergic agonists, veryhigh serum levels of IL-6 and its transcriptional target C-Reactive Protein (CRP) and display evidence ofintravascular coagulation. This is accompanied by the death of cells in multiple tissues including the kidney,muscle, liver and occasionally the heart. This end-organ injury is an important driver of morbidity and perhapsmortality in COVID-19 patients. These unusual clinical features suggest a virus-induced cytokine storm, but theunderlying mechanisms are unknown and these clinical features are not recapitulated in rodent or primatemodels of the disease.Our early analysis of bronchoalveolar lavage fluid collected from the alveolar space ofpatients with severe COVID-19 pneumonia requiring mechanical ventilation challenge the existing paradigm thatIL-6 originates in immune cells within the alveolar space. Specifically, we found that at the time of intubation, thealveolar space in the majority of patients with severe COVID-19-induced ARDS harbors mature alveolarmacrophages and lymphocytes none of which produce IL-6. Instead, a subset of resident alveolar macrophagesproduce IL-1? and appear to support replication of SARS-CoV-2.We hypothesize that disordered proteostasis in alveolar macrophages from aged individuals prevents viral killing after uptake of SARS-CoV-2. Replicating virus activates the inflammasome to induce IL-1? release in the lung, which in turn inducesthe release of IL-6 from endothelial cells in the lung and distant organs. We will test this hypothesis in two relatedexperiments. Experiment 1. To determine whether activation of the inflammasome in response to COVID-19 infection is necessary for the release of IL-6 from the lung endothelium. We will infect lung slices fromnormal human donors with SARS-CoV-2 in the presence or absence of an IL-1? inhibitor that is under evaluationas a therapy for patients with COVID-19 associate pneumonia (canakinumab). We will examine the lung slicesafter infection using single cell RNA-Seq and RNAscope. Experiment 2. To determine whether endothelialcells in tissues outside the lung express IL6 in patients with severe COVID-19. We will perform RNAscopeon fixed tissues harvested from 9 patients who have undergone autopsy after COVID-19 at Northwestern andRNAscope plus single cell RNA-Seq on lung, kidney, spleen and lymph nodes from 5 patients who undergo post-mortem biopsy in our ICU.