Abstract
Previous studies have described remodelling of the extracellular substratum by matrix metalloproteinases (MMPs) in aortic valves. However, involvement of the fibrinolytic system has not yet been analysed. We hypothesized that plasminogen and plasminogen activator(s) are present in aortic valves and that plasminogen activation could induce the degradation of adhesive proteins and apoptosis of the valvular myofibroblasts. We employed ELISA, western blotting, fibrin-agar zymography, and immunochemistry to detect components of the plasminogen activation system, in samples of aortic valves and valvular myofibroblasts in primary culture. Using myofibroblast cultures, real-time measurement of plasminogen activation was performed in the absence and presence of inhibitors (amiloride, epsilon-aminocaproic acid, and an MMP inhibitor); the degradation of fibronectin was visualized on western blots; and the apoptotic process was assessed by detection of phosphatidylserine exposure (binding of FITC-annexin V) and DNA fragmentation (TUNEL and ELISA). We demonstrate that a time- and plasminogen concentration-dependent generation of plasmin occurs on the surface of cultured valvular myofibroblasts expressing both u-PA and t-PA. Only u-PA appears to activate plasminogen as t-PA is essentially found in complex with PAI-1. Plasmin-dependent degradation of pericellular proteins, such as fibronectin, leads to cell detachment and apoptosis. In conclusion, various proteins of the fibrinolytic system are synthesized in vitro by cultured myofibroblasts from aortic valves, leading to plasmin-dependent cell detachment-induced apoptosis, a biological process named anoikis. The presence of plasminogen in aortic valves suggests that this process may be operating in vivo and may participate in valvular tissue remodelling, as also suggested by the finding of apoptotic cells in valvular tissue. This is the first demonstration of the presence and potential role of enzymes of the fibrinolytic system in aortic valves.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.