Experiment
Linkage analysis was performed on 629 animals from an (A/J x BALB/cJ)F2 intercross to confirm a previously identified QTL influencing hepatic fibrosis and hepatic collagen concentrations on proximal mouse Chromosome 2. Parental strain BALB/cJ is susceptible to hepatic fibrosis whereas parental strain A/J is resistant. The QTL was confirmed and is named Hfib2 (hepatic fibrosis 2.) In silico mapping was performed to refine Hfib2. SNP haplotypes between D2Mit6 (12.5 cM; 20.9 Mb) and D2Mit90 (37 cM; 65.5Mb) were analyzed. Hfib2 mapped to an interval between 30.4 Mb and 35 Mb. The candidate gene Hc (23.5 cM; 34.9 Mb) is found at the distal end of the Hfib2 interval.
Candidate gene Hc is significantly associated with hepatic collagen concentration (LOD=3.4) and histological stage of fibrosis (LOD=2.3) in F2 animals. Fibrosis resistant inbred strains, such as A/J, AKR/J, DBA/2, and FVB/NJ, carry a 2 base-pair deletion in exon 6 of Hc that results in Hc deficiency whereas fibrosis susceptible inbred strains,such as BALB/cJ, C3H/HeJ, and C57BL/6, are not Hc deficient.
Several other lines of evidence support Hc as the gene responsible for Hfib2. A congenic line was constructed carrying Hc deficient alleles from resistant strain DBA/2J on the genetic background of susceptible strain C57BL/10SnJ (B10.D2-Hc0). Following CCl4 challenge the congenic displays significantly lower hepatic collagen concentrations and less advanced liver fibrosis compared to C57BL/10SnJ controls. A 118 kb BAC transgene carrying the wild type Hc sequence from susceptible strain C57BL/6J was able to reconstitute the hepatic fibrosis phenotype in resistant strain FVB/NJ. In addition, in vivo administration of Hc agonists in fibrosis susceptible strain BALB/cJ significantly reduced hepatic collagen levels and the stage of fibrosis. Hc haplotypes in humans also show association to end stage liver fibrosis caused by chronic hepatitis C infection.
Analysis Tools