Linkage analysis was performed on a population of 299 (BALB/cByJ x DBA/2J)F2 animals to identify loci associated with pulmonary tolerance to repeated inhalation of zinc oxide. Parental strain BALB/cByJ is tolerant to repeated zinc oxide exposure comparedto parental strain DBA/2J. Tolerance was measured by the level of bronchoalveolar lavage (BAL) proteins, polymorphonuclear monocytes (PMNs), and macrophages after repeated zinc oxide inhalation.
Selective genotyping of the 15 most tolerant and 15 most non-tolerant F2 animals was performed for an initial genome scan using 86 polymorphic markers. Linkage to BAL proteins was detected on mouse Chromosome 1 and the remaining animals were genotyped to confirm this locus. Zit1 (zinc induced tolerance 1) maps to distal mouse Chromosome 1 between 101 cM (D1Mit426) and 109.6 cM (D1Mit293). Peak linkage to BAL protein levels occurs at 101.5 cM (D1Mit291). F2 animals homozygous for DBA/2J-derived alleles at Zit1 exhibit increased BAL proteins compared to F2 animalshomozygous for BALB/cByJ-derived alleles. Potential candidate genes mapping to the Zit1 locus include Darc (94 cM), Tlr5 (98 cM), Parp1 (formerly Adprt1; 98.6 cM), Tgfb2 (101.5 cM), Traf5 (105 cM), and Slc30a1 (106 cM). Of particular interest is Tlr5 because inbred strain MOLF/Ei carries non-conservative sequence changes in Tlr5 and is tolerant to inhaled zinc oxide exposure.
Suggestive linkage to BAL proteins was detected on mouse Chromosome 4 between 53.6 cM (D4Mit146) and 82.5 cM (D4Mit254), and on mouse Chromosome 5 between 1 cM (D5Mit193) and 18 cM (D5Mit148). Potential candidate genes mapping to the chromosome 4 interval are Ptafr (62.4 cM), Slc30a2 (65.7 cM), Pla2g2a (75.5 cM), Tnfrsf1b (75.5 cM), and Tnfrsf4 (79.4 cM). Potential candidate genes mapping to the chromosome 5 interval are Slc4a2 (14 cM), Il6 (17 cM), and Slc30a3 (18 cM). Haplotype analyis suggests that suggestive loci on chromosomes 4 and 5 interact with Zit1 to influence zinc-oxide induced BAL protein levels.
Suggestive linkage to PMN levels following repeated zinc oxide inhalation mapped to mouse Chromosome 1 between 51 cM - 73 cM. Potential candidate genes in this region include Ccl20 (52 cM), Cxcr4 (67.4 cM), and Il10 (69.9 cM).
Suggestive linkage to PMN levels following repeated zinc oxide inhalation mapped to mouse Chromosome 5 between 43 cM - 58 cM. Potential candidate genes in this region include Areg (51 cM), Btc (51 cM), Cxcl1 (51 cM), Cxcl2 (51 cM), Cxcl5 (51.5 cM), Cxcl9 (53 cM), Cxcl10 (53 cM), and Spp1 (56 cM).