Platelet-derived growth factor-D (PDGF-D) is one member of PDGF growth factors and known to signal by binding to and activating its cognate receptor type β (PDGFR-β). Beside PDGF-B, PDGF-D is a potent growth factor for stellate cell growth and proliferation and therefore potentiates the extracellular matrix deposition in liver fibrogenesis. We aimed to explore the signaling and molecular mechanisms of PDGF-D in liver fibrogenesis using the primary liver portal myofibroblasts and hepatic stellate cells. Unexpectedly we found PDGF-D to bind to PDGFR-α, thus inducing receptor endocytosis and decreasing the amount of PDGFR-α significantly. PDGF-D activates PDGFR-α specific tyrosine 754 and -1018 phosphorylation and CrkII, the adaptor protein that is specifically recruited by activated PDGFR-α. As a novel finding we could also demonstrate that recombinant PDGFR-α-Fc chimera homodimer is able to bind PDGF-D and thus prevent PDGF-D signaling. PDGF-D does induce individual PDGFR-β specific tyrosine phosphorylation similar to the PDGF-B. Additionally, PDGF-D enhances extracellular matrix accumulation comparable to the PDGF-B isoform.
Conclusion: PDGF-D signaling in pMF and HSC is identical to that of PDGF-B by binding to both PDGFR-α and -β.
Keywords: Hepatic stellate cells; MMP; PDGF-D; Portal myofibroblasts; TIMP-1.
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