Alveolus as Incubator: Functional Genomic Dissection of the Host Response to SARS-CoV-2 Infection.

PROJECT SUMMARY/ABSTRACT The host inflammatory response is a double-edged sword that must vigorously defend against pathogens, but also requires restraint to prevent unintended injury to the host. The Cytokine Storm Syndrome (CSS) represents a state of unbridled inflammation that can be triggered by infections, including Severe Acute Respiratory Syndrome-associated Coronavirus 2 (SARS-CoV-2). While evidence for dysregulated cytokine responses exists for the SARS-CoV-2-associated CSS (S-CSS), the precise cell types and viral factors that precipitate this response remain incompletely understood. Autophagy is a cytosol-to-lysosome degradative pathway that has important functions in host immunity. We have recently shown that autophagy genes in myeloid cells, preliminarily alveolar macrophages (aMΦ), confer protection in a murine model of CSS induced by intravenous TNF. We hypothesize that host autophagy may also have a pleiotropic role in limiting the S-CSS. We are motivated in this hypothesis since coronaviruses (CoVs) manipulate host autophagy-associated membranes for their own replication via the nonstructural protein 6 (nsp6). This proposal for the NIH Director's New Innovator Award will test the role of host autophagy and a viral antagonist in the triggering of S-CSS using both established and innovative methods. The project will utilize a model for SARS-CoV-2 infection in which the human ACE2 receptor (encoded by hAce2) is delivered to mouse lungs via adenovirus (AdV) vector. Additionally, we will determine the role of aMΦ-specific host pathways by utilizing mice deficient for GM-CSF signaling and devoid of aMΦ (Csf2rb-/-), that are durably restored with aMΦ by a single intranasal instillation of progenitor cells in neonates. The role of SARS-CoV-2 nsp6 in viral pathogenesis will be determined with recombinant viruses deleted for this factor or with naturally occurring point mutations hypothesized to facilitate infection. Moreover, we will develop an AdV-hAce2 vector system expressing sgRNAs to edit genes directly in susceptible respiratory cells in Cas9-transgenic recipient mice. We will generate pooled AdV sgRNA libraries via this method for in vivo screening approaches that may identify host pathways important for regulating infection not otherwise recapitulated by in vitro approaches. Further, we will reconstitute Csf2rb-/- mice with aMΦ cell progenitors containing pooled CRISPR libraries to identify host genes important for not only the aMΦ response to SARS- CoV-2 but also for fundamental aspects of aMΦ niche development. These studies have the potential to identify new areas for the development of host- and viral-directed therapies (e.g., the autophagy pathway and nsp6, respectively). The robust and versatile in vivo platforms established for functional genomic studies of a tissue site critical for the proximal response to SARS-CoV-2 have broader implications for the study of complex cell populations in diverse biological processes.