ACE2-independent alternative receptors for SARS-CoV-2 at the oral mucosa

PROJECT SUMMARY Coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been a major challenge for public health since the first case was reported in December 2019. In May 2023, the WHO and CDC marked the end of the COVID-19 public health emergency. However, COVID-19 remains a threat due to continuously evolving new variants, and fully vaccinated people remain susceptible to infection by the newer variants of the virus. SARS-CoV-2 entry is primarily mediated by binding of the SARS-CoV-2 spike protein (receptor-binding domain, RBD) to the human angiotensin-converting enzyme 2 (ACE2) receptor. Although ACE2-expressing cells support robust SARS-CoV-2 viral replication, ACE2 expression profiles are not completely associated with clinical manifestations or immune responses. Furthermore, SARS-CoV-2 infects organs or cells that do not express ACE2, suggesting the involvement of alternative receptors for SARS-CoV-2. Our and other laboratories have identified ACE2-independent alternative receptors for SARS-CoV-2, and infection via alternative receptors (e.g. CD147) is resistant to monoclonal antibodies against spike RBD, which is the target for several SARS-CoV-2 vaccines to block ACE2 binding. Our preliminary data show that oral epithelial, salivary gland, and gingival epithelial cells are susceptible to the replication-competent SARS-CoV-2 and pseudotyped SARS-CoV-2 Omicron variant despite low or undetectable expression of ACE2. These oral epithelial cells do however express high levels of alternative receptors CD147 or AXL, suggesting the role of alternative receptors in SARS-CoV-2 infection of oral epithelial cells. We hypothesize that these alternative receptors play a critical role in SARS-CoV-2 infection and virus-mediated immune activation in region-specific oral epithelial cells. In Aim 1, we will determine repertories of receptors for SARS-CoV-2 and infection profiles in region-specific oral epithelial cells and tissues from healthy subjects and subjects with oral inflammation pre- and post-treatment. In Aim 2, we will determine the contribution of specific receptors to SARS-CoV-2 infection and virus-mediated immune activation in oral epithelial cells. Considering that the virus will continue to infect humans regularly, it is critical to understand the role of alternative receptors for SARS-CoV-2 in the oral mucosa, the potential portal of SARS-CoV-2 entry, to develop anti-viral therapeutics and strategies to dampen virus-mediated immune activation and disease outcomes, especially as regards emerging variants.