The effect of platelet-derived growth factor ligands in rat cardiac allograft vasculopathy and fibrosis

BACKGROUND: In chronic rejection, parenchymal fibrosis and cardiac allograft vasculopathy (CAV) characterized by neointimal growth are the leading causes of graft loss for heart transplant recipients. During alloimmune responses a variety of cytokines, adhesion proteins, and growth factors, such as platelet-derived growth factor (PDGF), are up-regulated. The PDGF family (AA, AB, BB, CC, DD), which acts mainly on connective tissue cells, is considered to be a potent mitogenic and chemotactic factor for fibroblasts and vascular smooth muscle cells. In this study, we evaluated the effects of PDGF ligands in chronic rejection. METHODS: Heterotopic heart transplantations were performed between fully major histocompatability complex-mismatched Dark Agouti to Wistar Furth rats receiving cyclosporine immunosuppression. Allograft coronary arteries were perfused with a recombinant adeno-associated virus (AAV) encoding enhanced green fluorescence protein (EGFP) as a control gene or PDGF-A, -B, -C, -D. Allografts were harvested at 100 days for morphometric analysis of CAV and fibrosis. RESULTS: AAV-mediated transgene expression was detected by EGFP immunoreactivity across the graft section (at 100 days) in AAV EGFP-perfused allografts. AAV PDGF-A, -C, and -D perfusion resulted in accelerated CAV and fibrosis. In contrast, AAV PDGF-B perfusion did not induce arteriosclerotic changes or fibrosis in cardiac allografts. CONCLUSIONS: AAV PDGF-A, -C, and -D overexpression accelerated the development of chronic rejection, whereas PDGF-B did not. Our results suggested that more targeted therapy with monoclonal antibodies blocking the active sites of PDGF-A, -C, and -D may produce beneficial effects on heart transplant survival.