RNA Binding Proteins Control Transdifferentiation of Hepatic Stellate Cells into Myofibroblasts

Abstract

Background/aims: Myofibroblasts (MF) derived from quiescent nonfibrogenic hepatic stellate cells (HSC) are the major sources of fibrous matrix in cirrhosis. Because many factors interact to regulate expansion and regression of MF-HSC populations, efforts to prevent cirrhosis by targeting any one factor have had limited success, motivating research to identify mechanisms that integrate these diverse inputs. As key components of RNA regulons, RNA binding proteins (RBPs) may fulfill this function by orchestrating changes in the expression of multiple genes that must be coordinately regulated to affect the complex phenotypic modifications required for HSC transdifferentiation.

Methods: We profiled the transcriptomes of quiescent and MF-HSC to identify RBPs that were differentially-expressed during HSC transdifferentiation, manipulated the expression of the most significantly induced RBP, insulin like growth factor 2 binding protein 3 (Igf2bp3), and evaluated transcriptomic and phenotypic effects.

Results: Depleting Igf2bp3 changed the expression of thousands of HSC genes, including multiple targets of TGF-β signaling, and caused HSCs to reacquire a less proliferative, less myofibroblastic phenotype. RNA immunoprecipitation assays demonstrated that some of these effects were mediated by direct physical interactions between Igf2bp3 and mRNAs that control proliferative activity and mesenchymal traits. Inhibiting TGF-β receptor-1 signaling revealed a microRNA-dependent mechanism that induces Igf2bp3.

Conclusions: The aggregate results indicate that HSC transdifferentiation is ultimately dictated by Igf2bp3-dependent RNA regulons and thus, can be controlled simply by manipulating Igf2bp3.

Keywords: Cirrhosis; Epithelial-mesenchymal transition (EMT); IMP3; Insulin-like growth factor 2 binding protein 3; Mesenchymal stem cells (MSCs); MicroRNA (miRNA); RNA binding protein; Transforming growth factor beta (TGF-β).