Universal and Radiation-specific Loci Influence Murine Susceptibility to Radiation-induced Pulmonary Fibrosis

Susceptibility to radiation-induced pulmonary fibrosis is a heritable trait in mice. In a prior study of C57BL/6J (susceptible), C3Hf/Kam (resistant), and F1 and F2 mice derived from these strains, we estimated that ∼38% of the measured phenotypic variation could be attributed to effects from a few genetic factors. In addition, we identified one genetic factor on chromosome 17 in the MHC region. To identify any additional genetic loci that might influence interstrain variability, we conducted a genome-wide linkage scan using 214 markers and the phenotypically extreme 94 (of 268) F2 mice. In regions exceeding suggestive linkage (LOD = 2.8), we followed up with additional markers. This scan revealed evidence for quantitative trait locus (QTL) on chromosomes 17 (LOD = 4.2), 1 (LOD = 4.5), and 18 (LOD = 3.9), which influence susceptibility to radiation-induced pulmonary fibrosis. An additional region containing a QTL on chromosome 6, LOD = 4.6, showed linkage in female mice only. The evidence for linkage to chromosome 18 weakened when it was analyzed jointly with other markers. These four loci are estimated to account for 70% of the genetic contribution to this trait with chromosome 17 and 1 accounting for 28 and 24%, respectively. To confirm and better define the influence of the chromosome 17-linked QTL on radiation sensitivity, we conducted studies on congenic mice in which the linked region on chromosome 17 had been transferred onto a B6.AKR or a C3.SW background. The chromosome 17-linked QTL was confirmed to influence the phenotype as the fibrotic radiation response of B6.AKR- H2 k mice was significantly less than that of B6 mice ( P = 0.0001). The QTL on chromosome 17 for radiation-induced lung fibrosis is within the same region as QTLs identified for lung damage after other insults, including bleomycin, ozone, and particle exposure, as well as for asthma, suggesting that this region of chromosome 17 may harbor a “universal” lung injury gene.