Mutations in SARS-CoV-2 Nsp1 are critical determinants of viral pathogenicity in mice

<jats:p>Severe Acute Respiratory Coronavirus 2 (SARS-CoV-2) nonstructural protein 1 (Nsp1) dampens the host immune response by shutting off host gene expression, a strategy that has remained evolutionary conserved among a diverse range of coronaviruses (CoVs). Residues important for SARS-CoV-2 Nsp1 mediated host shutoff have been incompletely defined. We have generated and characterized the ability of four Nsp1 mutants to inhibit host gene expression in both plasmid-based overexpression assays and utilized reverse genetic approaches to generate recombinant (r)SARS-CoV-2 expressing each Nsp1 mutant to investigate their impact on viral infection. Infection of K18-hACE2 transgenic mice with the rSARS-CoV-2 Nsp1 mutants resulted in reduced pathogenicity as determined by body weight maintenance and survival, attenuated viral replication in lung and nasal turbinate, distinct immune signatures in lung, and less severe lung pathology in comparison to wild-type (WT) virus-infected mice. Our data suggests amino acid residues in the C-terminal domain, in addition to the linker domain, of SARS-CoV-2 Nsp1 are critical determinants of viral pathogenicity as a result of their role in disrupting host gene expression. The reduced pathogenicity of rSARS-CoV-2 Nsp1 mutants highlights the potential for targeting Nsp1 for rational design of viral inhibitors and development of live-attenuated vaccine strategies as effective prophylactic and therapeutic treatments, respectively, to combat SARS-CoV-2 and possibly other CoV infections.</jats:p>