A novel gene-by-environment quantitative trait locus on mouse chromosome 15 underlies susceptibility to acute ozone-induced lung injury

Respiratory toxicity caused by the common urban air pollutant ozone (O3) varies considerably within the human population and across inbred mouse strains, suggestive of gene-environment interactions (GxE). Though previous studies genetic mapping studies using classical inbred strains have identified several and quantitative trait locus (QTL) and candidate genes underlying responses to O3 exposure, precise mechanisms of susceptibility remain incompletely described. We sought to expand our understanding of the genetic architecture of O3 responsiveness using the Collaborative Cross (CC) recombinant inbred mouse panel, which contains more genetic diversity than previous inbred strain panels. We evaluated hallmark O3-induced respiratory phenotypes in 56 CC strains after exposure to filtered air or 2 ppm O3, and performed focused genetic analysis of variation in lung injury as measured by the total bronchoalveolar lavage protein concentration. Because animals were exposed in sex- and batch-matched pairs, we defined a protein response phenotype as the difference in lavage protein between the O3- and FA-exposed animal within a pair. The protein response phenotype was heritable, and QTL mapping revealed two novel loci on Chromosomes 10 (peak: 26.2 Mb; 80% CI: 24.6-43.6 Mb) and 15 (peak: 47.1 Mb; 80% CI: 40.2-54.9 Mb), the latter surpassing the 95% significance threshold. At the Chr. 15 locus, C57BL/6J and CAST/EiJ founder haplotypes were associated with higher protein responses compared to all other CC founder strain haplotypes. Using additional statistical analysis and high-density SNP data, we delimited the Chr. 15 QTL to a [~]2 Mb region containing 21 genes (10 protein coding). Using a weight of evidence approach that incorporated candidate variant analysis, functional annotations, and publicly available lung gene expression data, we nominated three candidate genes (Oxr1, Rspo2, and Angpt1). In summary, we have shown that O3-induced lung injury is modulated by genetic variation and demonstrated the value of the CC for uncovering and dissecting gene-environment interactions.