Background and aim of the study: A perimembranous ventricular septal defect (PMVSD) may be partially or completely occluded by aneurysms that originate from the tricuspid valve leaflets, though the exact mechanisms of closure remain unknown. It is hypothesized that valvar interstitial cells (VICs) mediate extracellular matrix (ECM) remodeling in aneurysms via the secretion of a serine proteinase and its inhibitor.
Methods: The functional characteristics of VICs in 15 aneurysms and in four normal tricuspid valve leaflets obtained at autopsy were evaluated by detecting the expression of urokinase plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1), and alpha-smooth muscle actin (alpha-SMA) in the specimens, using immunohistochemical methods.
Results: uPA and alpha-SMA were recognized predominantly in VICs located mainly in regions adjacent to the endothelium and smooth muscle cells of blood vessels. PAI-1 was identified in VICs found mainly in granulation tissues, and in endothelial cells. Two types of granulation tissue (myxoid and fibrous tissue) were associated with aneurysms. Nine aneurysms expressed a high uPA activity and a low PAI-1 activity (uPA/PAI-1 ratio 1.78), while six aneurysms expressed a low uPA activity and a high PAI-1 activity (uPA/PAI-1 ratio 0.14).
Conclusion: The expression of uPA, PAI-1 and alpha-SMA in VICs suggests that interactions among these molecules contribute to ECM remodeling during aneurysm formation and development. This provides a potential mechanism for defect closure in patients with PMVSD.