Identification of phenotypic and expression quantitative trait loci (p/eQTLs) affecting liver fibrosis by genome-wide association analysis in recombinant inbred mouse lines

Aims: Liver fibrosis is a complex disease mediated by multiple interacting genes and environmental factors. Our aim is to identify genetic loci that confer susceptibility to liver fibrosis. We now induced fibrosis in the genetically well characterised reference panel of BXD recombinant inbred lines and linked differences in liver fibrosis to the genetic variation segregating among the lines. Methods: In total, 30 BXD lines (392 mice) were analysed after fibrosis induction by CCl₄ (12 injections i.p.; 0.7mg/kg). Fibrosis progression was assessed by histological fibrosis staging, quantification of hepatic collagen and clinical-chemical assays. The hepatic expression profile in each line was generated using Affymetrix Mouse Gene 1.0 ST arrays (>34000 transcripts). Genome-wide interval-mapping analyses were performed to identify genomic loci influencing the fibrotic phenotypes (pQTLs) as well as loci regulating gene expression (eQTLs) during CCl₄-induced fibrogenesis. Results: Hepatic collagen concentrations are normally distributed among the mice, and line means of collagen contents range from 181 to 702µg hyp/g liver across the reference panel. Interval mapping identified several suggestive loci associated with the fibrotic phenotypes on chromosomes 6, 11, 12, and 17 (likelihood ratio statistics (LRS) > 12). Further suggestive peaks are localized by composite interval mapping on chromosomes 4, 16, and X. pQTL regions were further dissected by eQTL mapping, revealing several cis- and trans-regulated genes that are promising targets for functional studies. Conclusions: Genotype-phenotype correlation analysis in the BXD panel allowed us to identify potential profibrogenic genes and regulatory mechanisms. Our experimental set-up provides an experimental framework for modelling gene networks that regulate liver fibrogenesis.