PDGF-A, -C, and -D but not PDGF-B Increase TGF-β1 and Chronic Rejection in Rat Cardiac Allografts

Abstract

OBJECTIVE-: Chronic rejection is the main reason for the poor long-term survival of heart transplant recipients and is characterized by cardiac allograft inflammation, fibrosis, and arteriosclerosis. We examined the specific roles of different platelet-derived growth factor (PDGF) ligands (A-D)-potent mesenchymal cell mitogens-in rat cardiac allografts. METHODS AND RESULTS-: PDGFR-α mRNA was upregulated in acutely-rejecting, and PDGF-A and PDGF-C mRNA in chronically-rejecting cardiac¢hatn allografts. In acute rejection, PDGFR-α immunoreactivity increased in the media of arteries. In chronically-rejecting allografts, immunoreactivity of all PDGF ligands and receptors-except that of PDGF-B ligand-was found in the intima of arteries, and the expression of PDGF-A and PDGF-C was seen in cardiomyocytes. Intracoronary adeno-associated virus-2 (AAV2)-mediated PDGF-A and -D gene transfer enhanced cardiac allograft inflammation. AAV2-PDGF-A, AAV2-PDGF-C, and AAV2-PDGF-D significantly upregulated profibrotic TGF-β1 mRNA and accelerated cardiac fibrosis and arteriosclerosis. In contrast, AAV2-PDGF-B did not aggravate chronic rejection. CONCLUSIONS-: We found that alloimmune response induces PDGF-A, PDGF-C, and PDGF-D expression in the graft vasculature. PDGF-A, PDGF-C, and PDGF-D mediated profibrotic and proarteriosclerotic effects in transplanted hearts involving the TGF-β1 pathway. Inhibition of signaling of all PDGF-ligands except that of PDGF-B may thus be needed to inhibit chronic rejection in cardiac allografts. © 2009 American Heart Association, Inc.