Abstract 1331: Myocardial Function Alterations Correlate to Cardiac Fibrosis and Upregulation of Profibrotic Signaling in Plasminogen Activator Inhibitor-1 Deficient Mice
Cardiac fibrosis is a common sequelae of cardiac injury and has deleterious functional consequences impacting cardiac filling, function and rhythm. Plasminogen activator inhibitor-1 (PAI-1) has been implicated in the pathogenesis of tissue fibrosis in mice. To investigate the longitudinal effect of PAI-1 on cardiac structure and function, M-mode echocardiography was employed to examine cardiac function in PAI-1 deficient (PAI-1−/−) and wild-type (WT) control mice in four age groups (6,12,18, 24 months). Eighteen month old PAI-1−/− mice exhibited reduced left ventricular (LV) diastolic internal dimension (p=0.0118) and a trend towards increased LV posterior wall (LVPW) thickness, compared to WT. Two year old PAI-1−/− mice showed increased diastolic and systolic LVPW thickness (p=0.0127 and p=0.0212, respectively), reduced diastolic and systolic LV internal dimension (p=0.0486 and p=0.0124), but with preserved LV fractional shortening compared to WT. Histological examination of cardiac sections revealed fibrosis on the anterior epicardial surface of the hearts in 18 month old PKO, which in 26 month old mice had become confluent with extensive (10 –17% by area) epicardial, perivascular, and interstitial distribution (compared to none in WT). Real time polymerase chain reaction (RT-PCR) revealed upregulation of transforming growth factor beta (TGF-β) and fibroblast growth factor 2 in PAI-1−/− compared to WT (p=0.0234 and p=0.037, respectively). Immunofluoresence confirmed this finding with bright TGF-β staining localized in the media of intra-myocardial arterioles, and phosphorylated SMAD2/3, the downstream TGF-β signaling mediator, in areas of fibrosis. Thoracic aortic cells from aged (18 –24 month) PKO and WT mice were grown in culture, with RT-PCR revealing 4 fold increased TGF-β and 17 fold increased SMAD3 (p<0.05 for both) RNA levels in PAI-1−/−, supplying additional evidence for upregulation of a profibrotic TGF-β/SMAD tissue signaling pathway. The present study is one of the first to elucidate some of the functional consequences and relevant molecular signaling pathways related to aging and PAI-1 deficiency mediated cardiac fibrosis.