Inhibition of PDGF signaling promotes hepatic differentiation of stellate cells from rat liver

Hepatic stellate cells (HSC) are liver-resident mesenchymal stem cells (MSC) with high developmental potential. They differentiate not only into adipocytes and osteocytes as known for typical MSC, but also into liver epithelial cells such as hepatocytes and bile duct cells. During stem cell-based liver regeneration in rats (partial hepatectomy/2-acetylaminoflourene injury model) a significant upregulation of the MSC-marker platelet-derived growth factor receptor β (Pdgfrβ) and its ligands (Pdgf-b and -d chains) were observed. To investigate the relevance of Pdgf signaling for developmental fate decisions, HSC were isolated from rat liver and treated with the Pdgf receptor inhibitor Crenolanib or natural Pdgfr ligands such as Pdgf-bb and dd. Both ligands increased HSC proliferation and the inhibitor Crenolanib diminished ligand-induced cell expansion significantly. Interestingly, Crenolanib treatment (100 nM) induced hepatic differentiation in HSC as indicated by the upregulation of epithelial progenitor (cytokeratin 19, epithelial cell adhesion molecule, α-fetoprotein) and hepatocyte markers (cytokeratin 18, albumin, bile salt export pump, hepatocyte nuclear factor 4α).

Similar results were obtained, if clonally expanded rat HSC or human induced pluripotent stem cells-derived MSC were treated with Crenolanib. Initiation of hepatic differentiation by Crenolanib was found to be dependent, at least in part, by mitogen-activated protein kinase (MAPK) p38 as investigated by application of the p38 MAPK inhibitor SB203580. Crenolanib elevated also the expression of fibroblast growth factors such as Fgf7 and Fgf10 in rat HSC known to support hepatic differentiation of stem/progenitor cells as well as increased the expression of the receptor Fgfr3, which most likely supported differentiation. In contrast to this, proliferative signals via Pdgf ligands impeded epithelial cell marker expression in HSC.

In conclusion, Pdgfr signaling is pivotal for balancing the opposing processes cell proliferation and differentiation in HSC. Therefore, Pdgfr signaling is essential for the regulation of developmental fate decisions in HSC and stem cell-based liver regeneration.