Cardiovascular aging results in cardiac fibrosis, diastolic dysfunction, and attenuated wound healing post-myocardial infarction (MI). While numerous studies have correlated increases in plasminogen activator inhibitor-1 (PAI-1) with aging, none have directly examined possible mechanisms of PAI-1-mediated inhibition of collagen turnover. The proposed study seeks to identify a role of PAI-1 in regulating age-related cardiac fibrosis. Age-dependent increases of PAI-1 correlate with decreased matrix metalloprotease (MMP) activity, increased collagen deposition, and blunted inflammatory response. As a consequence of impaired ECM degradation and fibroblast migration, the reduction in MMP activity may cause ventricular fibrosis by increasing collagen deposition and diminished inflammatory responses post-MI. Isolated rat cardiac fibroblasts (CFs) will be used to investigate the relationship between PAI-1 release and potential effects on collagen deposition and CF migration.
The first aim of this study asks whether PAI-1 produced and released by CFs increases collagen deposition by inhibiting MMP activation. Total and active MMPs will be assayed in CFs by Western blotting, zymography, and ELISA.
The second aim compares PAI-1 expression in CFs isolated from young and aged rats to examine whether expression increases with age and is responsible for increased collagen accumulation. The increase of PAI-1 with age is hypothesized to attenuate MMP activity. This in turn decreases collagen degradation and may also inhibit CF migration. Finally, the third aim of the study will use an ex vivo rat ischemia-reperfusion model. This provides a system to ascertain whether PAI-1 expression is increased basally in aged hearts and whether PAI-1 is up-regulated in physiologically relevant concentrations following ischemic stress. Acute inhibition of MMP activity by PAI-1 may explain the attenuated inflammatory and wound healing responses post-MI seen in aged individuals. Together, these findings may identify a novel PAI-1 dependent mechanism in which aged hearts are more prone to both fibrosis and attenuated wound healing following ischemic damage.
Cardiac fibrosis leads to stiffening of the heart, fluid buildup in the lungs, and decreased cardiac efficiency and can interfere with proper wound healing after injury. Age is an important factor in the development of cardiac fibrosis as all aged hearts undergo collagen deposition and suffer from attenuated healing responses. This study seeks to investigate plasminogen activator inhibitor-1, a protein that increases with age and can negatively affect the heart by increasing the amount of fibrous protein deposition and decreasing the healing response after cardiac injury.
|Lu, David; Insel, Paul A (2014) Cellular mechanisms of tissue fibrosis. 6. Purinergic signaling and response in fibroblasts and tissue fibrosis. Am J Physiol Cell Physiol 306:C779-88|
|Lu, David; Aroonsakool, Nakon; Yokoyama, Utako et al. (2013) Increase in cellular cyclic AMP concentrations reverses the profibrogenic phenotype of cardiac myofibroblasts: a novel therapeutic approach for cardiac fibrosis. Mol Pharmacol 84:787-93|
|Lu, David; Insel, Paul A (2013) Hydrolysis of extracellular ATP by ectonucleoside triphosphate diphosphohydrolase (ENTPD) establishes the set point for fibrotic activity of cardiac fibroblasts. J Biol Chem 288:19040-9|
|Lu, David; Soleymani, Sahar; Madakshire, Rohit et al. (2012) ATP released from cardiac fibroblasts via connexin hemichannels activates profibrotic P2Y2 receptors. FASEB J 26:2580-91|