The Y498T499-SARS-CoV-2 spike (S) protein interacts poorly with rat ACE2 and does not affect the rat lung

The rat is a useful laboratory model for respiratory diseases. SARS-CoV-2 proteins, such as the spike (S) protein, can induce inflammation. This study has investigated the ability of the Q498Y, P499T (QP-YT) amino acid change, described in the S-protein of the mouse-adapted laboratory SARS-CoV-2 MA strain, to interact with rat angiotensin converting enzyme-2 (ACE2) and stimulate responses in rat lungs. A real-time S-ACE2 quantitative fusion assay shows that ancestral and L452R S-proteins fuse with human but not rat ACE2 expressed on HEK293 (human embryonic kidney-293) cells. The QP-YT S-protein retains the ability to fuse with human ACE2 and increases the binding to rat ACE2. Although lower lung of the rat contains both ACE2 and TMPRSS2 (transmembrane serine protease 2) target cells, intratracheal delivery of ancestral or QP-YT S-protein pseudotyped lentivirus did not induce measurable respiratory changes, inflammatory infiltration or innate mRNA responses. Isolation of primary cells from rat alveoli demonstrated the presence of cells expressing ACE2 and TMPRSS2. Infection of these cells, however, with ancestral or QP-YT S-protein pseudotyped lentivirus was not observed, and the QP-YT S-protein pseudotyped lentivirus poorly infected HEK293 cells expressing rat ACE2. Analysis of the amino acid changes across the S-ACE2 interface highlights not only the Y498 interaction with H353 as a likely facilitator of binding to rat ACE2 but also other amino acids that could improve this interaction. Thus, rat lungs contain cells expressing receptors for SARS-CoV-2, and the QP-YT S-protein variant can bind to rat ACE2, but this does not result in infection or stimulate responses in the lung. Further, amino acid changes in S-protein may enhance this interaction to improve the utility of the rat model for defining the role of the S-protein in driving lung inflammation.