Transcriptional Profiling Reveals Novel Markers of Liver Fibrogenesis

Abstract

Activated hepatic stellate cells (HSC) that transdifferentiate to myofibroblasts in the injured liver are responsible for scar forma- tion that leads to fibrosisandeventually cirrhosis.Toinvestigate the gene expression profile during different stages of this process, we performed serial analysis of gene expression, representing a quan- titative and qualitative description of all expressed genes. Stellate cells were isolatedfromhumanliversandcultured. Serial analysis of gene expression was performed on RNA isolated from quiescent, activated, and transdifferentiated HSC. Comparison of the three resulting transcriptomes showed that less than 5% of all genes changed significantly in expression. Established markers of liver fibrosis showed enhanced expression in accordance with the trans- differentiation process. In addition, induction was seen for several genes not yet recognized to be involved in liver fibrosis, such as insulin-like growth factor-binding proteins (IGFBP) and antago- nists of bone morphogenic proteins: follistatin and gremlin. The induction of these genes was validated in vivo in mice developing liver fibrosis. The expression of IGFBPs and gremlin was measura- ble in the livers of these mice, whereas it was low or undetectable in control mice without liver fibrosis. Since gremlin modulates the activity of bone morphogenic growth factors, it may represent a novel pathway and a target for therapeutic intervention and together with IGFBPs it could be a specific marker of liver fibrosis. In conclusion, the comparison of the three transcriptomes of (acti- vated) stellate cells reveals novel genes involved in fibrogenesis and provides an appreciation of the sequence and timing of the fibrotic process in liver