Fibrogenic genotype-phenotype correlations in selected BXD recombinant inbred mouse lines: Closer to life?!

BxD mice are inbred F2 lines derived from a cross of laboratory strains C57BL/6J and DBA/2J. Array analyses in untreated livers reveal a normal distribution of gene expression among the >30 lines, reflecting the expected distribution in populations resulting from complex gene regulation (Figure 1). We hypothesised that "extreme expressors" (high or low) of fibrosis-relevant genes represent a better reflection of real-life gene expression variation than knockout animals. Thus they may offer more realistic models to study the consequences of long-term dysregulated expression of fibrogenic or cancerogenic genes. To test this hypothesis, we subjected BxD animals showing extremely high or low expression values for TGF-beta receptor type 2 (TGFbR2) to a short course of CCl4 intoxication and analysed parameters associated with tissue-damage and -repair in the liver. TGFbR2 is the rate-limiting receptor in TGF-beta signal transduction, and we expected to detect subtle differences highlighting a role during fibrosis initiation. Animals at 8–12 weeks of age were subjected to ip injections of CCl4 (3 injections over the course of 7 days) and the resulting damage analysed by Sirius red-, TUNEL- and Ki67-staining followed by quantification of positive areas. No significant differences were detectable in collagen deposition as detected by Sirius red and levels of apoptosis as revealed by TUNEL-staining. Significant quantitative differences between groups of animals belonging to different strains were detectable in Ki67 staining reflecting increased proliferation in animals with high TGFbR2 expression values. These results show that differential gene expressionis reflected by phenotypic differences in response to tissue damage. BXD lines represent a basic experimental framework to study the consequences of expression differences in a setting far more similar to natural variation than knockout or knock-down animals.

TGF-beta - fibrogenesis - gene expression - proliferation - wound healing