Abstract 2316: Myocardial PAI-1 Over-expression Mediates Graft Sclerosis in Cardiac Transplant Recipients with Idiopathic Dilated Cardiomyopathy
Idiopathic dilated cardiomyopathy (DCM) is associated with reduced myocardial vascular density and increased collagen deposition with subsequent myocardial fibrosis and heart failure. The urokinase plasminogen activator (uPA)/plasminogen activator inhibitor (PAI) system plays an important role in extracellular matrix homeostasis as well as in preserving the integrity of the vascular endothelial cell (EC) intimal layer and EC regeneration, proliferation and motility. However, the involvement of the uPA/PAI system in DCM and graft remodeling following cardiac transplantation remains unclear. Gene expression of uPA, the uPA receptor uPAR and PAI-1 was examined in left ventricular (LV) biopsies of explanted hearts in 24 ischemic cardiomyopathy (ICM) and 60 DCM patients and 12 controls by real time RT-PCR and Western blotting. Vascular endothelial growth factor (VEGF) and uPA/PAI interplay was examined in stimulated DCM and ICM myocardium in vitro. Expression of uPA and PAI-1 mRNA was evaluated in endomyocardial biopsies (EMB) at 1, 2, 3, 4, 7, 12, 24 and 52 weeks post-transplant. The mRNA levels of uPA and uPAR were unchanged in both ICM and DCM patients compared to controls. PAI-1 mRNA and protein were up-regulated in DCM compared to ICM and controls (p<0.01). Active and inactive uPA protein was down-regulated in DCM and ICM compared to controls (p<0.05). VEGF stimulation in vitro did not affect uPA, uPAR or PAI-1 expression. Following transplantation, PAI-1 expression returned to baseline control levels in EMB from both patient groups, although PAI-1 expression increased at 24 and 52 weeks post-transplant in DCM patients (p<0.01 compared to post-transplant weeks 6 and 12). These data indicate a significant PAI-1 up-regulation associated with uPA down-regulation in DCM, independent of VEGF, which was temporarily corrected by cardiac transplantation. However, recurring up-regulation of myocardial PAI-1 levels at 6 and 12 months post-transplant suggest a persistent PAI-1-related molecular pathology in DCM. We have previously shown increased endothelin-1 expression and collagen deposition in grafts of DCM patients at 1 year post-transplant. The present data point to a previously unknown role of PAI-1 in mediating graft sclerosis.