Sex-Dependent Regulation of Host Factors Influencing SARS-CoV-2 Infection and COVID-19 Disease

Project Summary COVID-19, the disease caused by the SARS-CoV-2 virus, commonly presents as pneumonia, with those most severely affected progressing to Acute Respiratory Distress Syndrome (ARDS). Notably, males seem to be at significantly higher risk for severe or fatal outcomes from COVID-19, and male-specific skewing was also observed with related coronaviruses SARS-CoV and MERS. The X chromosome is enriched for immunity-related genes, and females (XX) mount stronger immune responses than do males (XY). X-chromosome Inactivation (XCI) normalizes the gene dosage effect between the sexes and we have previously found that immune cells have novel and dynamic XCI mechanisms that allow for gene-specific transcriptional activation from the inactive X (Xi) in a cell-type specific manner. Notably, our preliminary data suggest the regulation of XCI in lung alveolar type 2 (AT2) cells, the predominant target of SARS-CoV-2 in the lung and a cell type critically involved in lung repair following viral injury, phenocopies that seen in immune cells. As such, we will test the novel hypothesis that X-linked genes, including immune genes and ACE2, escape XCI in a lineage-specific fashion and contribute to the relative resistance of females to COVID-19 (Aim 1). We will test the hypothesis that our novel humanized ACE2 mice, which are susceptible to SARS-CoV-2 infection, will exhibit sex differences with resulting lung pathologies in aged mice (Aim 2). Together, these studies will further our understanding of the mechanisms that predispose males to COVID-19 disease and will reveal novel strategies to reduce disease severity.