Identification of RARRES1 as a core regulator in liver fibrosis.

Genetic factors contribute to progression and modulation of hepatic fibrosis. High throughput genomics/transcriptomics approaches aiming at identifying key regulators of fibrosis development are tainted with the difficulty of separating essential biological "driver" from modifier genes. We applied a comparative transcriptomics approach and investigated fibrosis development in different organs to identify overlapping expression changes, since these genes may be part of core pathways in fibrosis development. Gene expression was analysed on publicly available microarray data from liver, lung and kidney fibrosis. RARRES1, AGER and S100A2 were differentially regulated in all fibrosis experiments. RARRES1 was extensively analysed by means of advanced bioinformatics analyses and functional studies. Microarray and Western Blot analysis of a standard liver fibrosis model (CCl(4)) demonstrated an early induction of RARRES1 mRNA and protein expression. In addition, quantitative RT-PCR in tissue samples from patients with advanced liver fibrosis showed higher expression as compared to non-fibrotic biopsies. Microarray analysis of RARRES1 overexpressing cells identified an enrichment of a major signature associated with fibrosis. Furthermore, RARRES1 expression increased during in vitro activation of hepatic stellate cells. To further verify the pro-fibrogenic role across organs, we demonstrated an increase in RARRES1 expression in a rat lung fibrosis model induced by adenoviral TGF-β1 induction. We have performed a comparative transcriptomics analysis in order to identify core pathways of liver fibrogenesis, confirmed a candidate gene and enlightened the up- and downstream mechanisms of its action leading to fibrosis across organs and species.