Activated Blood Coagulation Factor X (FXa) Induces Angiogenic Growth Factor Expression in Human Retinal Pigment Epithelial Cells

Abstract

To determine the transcriptional regulation of the blood coagulation factor X (FX) in cultured human retinal pigment epithelial (RPE) cells, and whether the effects of FXa on the chemotaxis and expression of angiogenic growth factors are mediated by autocrine growth factor signaling. Alterations in gene expression and secretion of growth factors were determined by real-time RT-PCR and ELISA, respectively. Cellular proliferation and chemotaxis were investigated with a bromodeoxyuridine immunoassay and a Boyden chamber assay, respectively. The gene expression of FX in RPE cells was increased by hypoxia and prostaglandin E(2), and decreased by blood serum, FXa, thrombin, transforming growth factor beta (TGF-β1), and platelet-derived growth factor (PDGF). The serum-induced downregulation of FX was mediated by thrombin and TGF-β signaling. FXa induced chemotaxis of RPE cells via activation of the p38 mitogen-activated protein kinase signal transduction pathway. FXa also induced expression of vascular endothelial growth factor (VEGF), heparin-binding epidermal growth factor-like growth factor (HB-EGF), and basic fibroblast growth factor (bFGF), as well as release of VEGF, bFGF, and TGF-β1 from RPE cells. The stimulatory effects of FXa on the expression of growth factors and secretion of VEGF were prevented by inhibition of the TGF-β activin receptor-like kinase, but not by the thrombin inhibitor hirudin. FXa induced phosphorylation of ERK1/2, p38, and Akt proteins. FXa induces chemotaxis of RPE cells, as well as expression and release of angiogenic growth factors from RPE cells, including VEGF. The effects of FXa on the expression and secretion of VEGF are mediated by autocrine/paracrine TGF-β signaling.