Gene Expression Profiling of Fibroblast Growth Factor Ligands and their Receptors in Rat Hepatic Stellate Cells (HSC) and In In Vitro Transdifferentiated Myofibroblasts (MFB)

Abstract

Hepatic stellate cells (HSC) are pericytes of the sinusoidal compartment and represent the major site of vitamin A storage. After hepatic injury, HSC are activated and may play a key role in the regeneration of the liver. The liver has an amazing capacity to regenerate back to normal cell mass in a short time which requires a rise in cytokines and growth factors to promote proliferation and migration of various cell types. Activation of HSC is accompanied by morphological and metabolic changes including increased synthesis and secretion of cytokines and growth factors. FGFs and their receptors are important regulators of repair of various tissues and organs by stimulation of cell migration and proliferation. FGF signals are transduced via four related FGF receptor tyrosine kinases and their variants. In this study, we employed low density oligonucleotide arrays and reverse transcriptase-polymerase chain reaction (RT-PCR) to identify the expression profiles of different FGFs, their receptors and antagonists in hepatic stellate cells. The expression panel was compared with that obtained from in vitro transdifferentiated myofibroblasts (MFB). The expression analysis revealed that HSC and MFB express mRNA of four FGF ligands: FGF4, FGF5, FGF9 and FGF10. Freshly isolated HSC express FGF-R1(IIIc), FGF-R2(IIIc), FGF-R3(IIIc) and FGFR4–17 mRNA. Surprisingly, in vitro transdifferentiated MFB express the FGF-R1(IIIb) isoform in addition. Although HSC and MFB have the cognate receptors to the FGF ligands they express, both cell types are non-responsive to these FGF ligands, while the same FGF ligands induce proliferation and DNA synthesis in hepatocytes suggesting a paracrine function. The related Sprouty and Spred protein families are recently discovered negative regulators of FGF receptor signaling. Since HSC and MFB express mRNA of Sprouty 1, 2 and 4 and of Spred 1 and 2, our findings may suggest that members of both inhibitor families function in a negative feedback mechanism controlling the autocrine action of FGFs in HSC.