Genome Wide Identification of SARS-CoV Susceptibility Loci Using the Collaborative Cross

Abstract

New systems genetics approaches are needed to rapidly identify host genes and genetic networks that regulate complex disease outcomes. Using genetically diverse animals from incipient lines of the Collaborative Cross mouse panel, we demonstrate a greatly expanded range of phenotypes relative to classical mouse models of SARS-CoV infection including lung pathology, weight loss and viral titer. Genetic mapping revealed several loci contributing to differential disease responses, including an 8.5Mb locus associated with vascular cuffing on chromosome 3 that contained 23 genes and 13 noncoding RNAs. Integrating phenotypic and genetic data narrowed this region to a single gene, Trim55, an E3 ubiquitin ligase with a role in muscle fiber maintenance. Lung pathology and transcriptomic data from mice genetically deficient in Trim55 were used to validate its role in SARS-CoV-induced vascular cuffing and inflammation. These data establish the Collaborative Cross platform as a powerful genetic resource for uncovering genetic contributions of complex traits in microbial disease severity, inflammation and virus replication in models of outbred populations.

Author Summary

New emerging pathogens are a significant threat to human health with at least six highly pathogenic viruses, including four respiratory viruses, having spread from animal hosts into the human population within the past 15 years. With the emergence of new pathogens, new and better animal models are needed in order to better understand the disease these pathogens cause; to assist in the rapid development of therapeutics; and importantly to evaluate the role of natural host genetic variation in regulating disease outcome. We used incipient lines of the Collaborative Cross, a newly available recombinant inbred mouse panel, to identify polymorphic host genes that contribute to SARS-CoV pathogenesis. We discovered new animal models that better capture the range of disease found in human SARS patients and also found four novel susceptibility loci governing various aspects of SARS-induced pathogenesis. By integrating statistical, genetic and bioinformatic approaches we were able to narrow candidate genome regions to highly likely candidate genes. We narrowed one locus to a single candidate gene, Trim55, and confirmed its role in the inflammatory response to SARS-CoV infection through the use of knockout mice. This work identifies a novel function for Trim55 and also demonstrates the utility of the CC as a platform for identifying the genetic contributions of complex traits.