Determinants of susceptibility to SARS-CoV-2 infection in murine ACE2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) utilizes angiotensin-converting enzyme 2 (ACE2) as a receptor to enter host cells, and primary receptor recognition of the spike protein is a major determinant of the host range of SARS-CoV-2. Since the emergence of SARS-CoV-2, a considerable number of variants have emerged. However, the determinants of host tropism of SARS-CoV-2 remain elusive. We conducted infection assays with chimeric recombinant SARS-CoV-2 carrying the spike protein from 10 viral variants, assessing their entry efficiency using mammalian ACE2 orthologs from species that have close contact with humans. We found that only murine ACE2 exhibited different susceptibilities to infection with the SARS-CoV-2 variants. Moreover, we revealed that the mutation N501Y in the viral spike protein has a crucial role in determining the infectivity of cells expressing murine ACE2 and of mice in vivo. Next, we identified six amino acid substitutions at 24, 30, 31, 82, 83, and 353 in murine ACE2 that allowed for viral entry of the variants to which murine ACE2 was previously resistant. Furthermore, we showed that ACE2 from a species closely related to mice, Mus caroli, is capable of supporting entry of the viral variants that could not use murine ACE2. These results suggest that few ACE2 orthologs have different susceptibility to infection with SARS-CoV-2 variants as observed for murine ACE2. Collectively, our study reveals critical amino acids in ACE2 and the SARS-CoV-2 spike protein that are involved in the host tropism of SARS-CoV-2, shedding light on interspecies susceptibility to infection.IMPORTANCESARS-CoV-2 can infect many species besides humans, leading to the evolution of the virus and adaptation to other animal hosts, which could trigger a new COVID-19 wave. The SARS-CoV-2 spike protein utilizes ACE2 as a receptor for entry into host cells. The interaction of ACE2 with the spike protein determines the host range of SARS-CoV-2. In this study, using chimeric viruses carrying the spike protein of SARS-CoV-2 variants to infect cells expressing different ACE2 orthologs from species humans come in close contact with, we confirmed murine ACE2 alone showed different susceptibility to the variants. We identified residues in murine ACE2 and the viral spike that restrict viral entry. Furthermore, an ACE2 ortholog from a species genetically close to mice mediated entry of SARS-CoV-2 variants incapable of infecting mice. This research highlights the uniquely limited susceptibility of mice to different SARS-CoV-2 variants and provides invaluable insights into the host tropism of SARS-CoV-2.