Identifying genetic modifiers of the TGF-β response in mouse hepatocytes: potential candidate genes for fibrosis susceptibility

Aims: TGF-beta is the central cytokine in liver fibrogenesis, and hepatocytes might play an important role through recruitment and activation of Kupffer cells, HSCs and lymphocytes (Dooley et al. 2008). To assess the role of genetic variation in fibrosis susceptibility, we will delineate differences in hepatocellular damage in response to TGF-beta signalling in the BXD genetic reference population (GRP). Differences in damage susceptibility and gene expression will be measured in C57BL/6J, DBA/2J and their recombinant inbred (RI) offspring. Quantification of cellular damage or expression levels in the GRP allows localisation of loci underlying these differences by QTL or eQTL analysis (Gatti et al. 2007).

Methods: Hepatocytes from C57BL/6J and DBA/2J were treated with TGF-beta and cellular damage quantified by lactate dehydrogenase (LDH) release assay. Transcript levels in normal liver (Gatti et al. 2007) were analysed by interval mapping.

Results: Treatment with 5 ng/ml TGF-beta for 48 hours led to an 80–200% increase in cellular damage levels in primary hepatocytes from DBA/2J. In contrast, C57BL/6J hepatocytes show a mere 10–20% increase in LDH release. Expression of TGF-beta receptor II differs in the normal liver of the two parental strains. Interval mapping revealed a significant eQTL on chromosome 18p (LRS >18).

Conclusions: The BXD parental strains differ in sensitivitiy to TGF-beta induced hepatocellular damage. Quantitative analysis in BXD RI strains and interval mapping will identify the corresponding variant genomic loci. Comparative transcription profiling of both parental strains will reveal underlying expression differences. This will provide insights into which parts and targets of the TGF-beta signalling pathway are subject to modulation by individual variation. Genetic factors that modulate fibrosis susceptibility in mice are potential candidate genes for fibrosis susceptibility in humans (Hillebrandt et al. 2005)

Literatur: [1] Dooley et al.: Hepatocyte-specific Smad7 expression attenuates TGF-beta mediated fibrogenesis and protects against liver damage, Gastroenterology 135 (2008). [2] Gatti et al.: Genome-Level Analysis of Genetic Regulation of Liver Gene Expression Networks, Hepatology (2007). [3] Hillebrandt et al.: Complement factor 5 is a quantitative trait gene that modifies liver fibrogenesis in mice and humans, Nature Genetics 37 (2005)

TGF-beta - cell damage - fibrosis - gene expression - hepatocytes - mouse genetics