Genetic investigation of SARS-CoV-2 infection in oral and nasal tissues

Project Summary/Abstract The COVID-19 pandemic has produced a global health and economic crisis. While the pandemic is gradually being lessened by mass vaccinations, full control of this disaster is hampered by several ongoing problems including: (i) resistance or poor access to vaccination; (ii) emergence of new more infectious viral variants; (iii) "long COVID" symptoms in some patients; and (iv) incomplete understanding of the mechanisms of viral entry. Thus, it remains important to identify additional methods of blocking infection and to improve understanding of long-lasting symptoms so that these can be prevented and/or treated more effectively. SARS-CoV-2 infection is transmitted via airborne droplets, and loss or alterations of taste and smell appear early in disease progression, can occur in the absence of other symptoms, and serve as a diagnostic tool for COVID-19, suggesting oral and nasal epithelia as primary viral targets. However, functional evidence for these epithelia as primary infection sites is lacking, and the basis for chemosensory symptoms, and why these can persist after disease recovery, remains poorly understood. In particular, whether COVID-19-associated taste abnormalities are secondary to anosmia, infection of associated oral epithelia, and/or altered salivary secretion, or result from direct or secondary infection of taste buds or nerves, is currently unclear. Addressing these questions in vivo at the mechanistic level requires robust and genetically manipulable model systems. Mice provide an excellent genetic system for human disease modeling, but cannot be robustly infected by wild-type SARS-CoV-2 because its spike protein does not efficiently bind the mouse ACE2 receptor. Existing human (h)ACE2- expressing mice either express hACE2 in a transgenic, non-endogenous manner, or exhibit relatively weak expression of hACE2 following knockin to the mouse Ace2 allele resulting in absence of clinical disease after SARS-CoV-2 infection, limiting their use in mechanistic studies. The proposed studies will utilize powerful new hACE2 conditional knockin mouse lines that support lethal SARS-CoV-2 infection and permit tissue-specific Cre-mediated loss and gain of hACE2 function. Using these tools, we will: (i) determine whether hACE2 expression in oral and nasal epithelia is required and/or sufficient for lethal COVID-19 disease; and (ii) elucidate the oral and nasal cellular mechanisms underlying taste dysfunction in COVID-19 disease. Combined with human tissue validation, these studies will define the role of oral and nasal cells in COVID-19 disease and reveal strategies to prevent or treat the disease by targeting these cells.