Abstract 3113: Increased Expression of Profibrotic Neutral Endopeptidase and Bradykinin Type 1 Receptors in Stenotic Aortic Valves
Objectives- Adverse remodeling of the aortic valves, a pathogenic mechanism of aortic stenosis (AS), may depend on altered local regulation of pro- and antifibrotic systems, such as angiotensin II (Ang II) and bradykinin (BK). We have recently shown that the angiotensin-converting enzyme (ACE), which activates Ang II and inactivates BK, is significantly upregulated in stenotic aortic valves. Here we analyzed the expression of the neutral endopeptidase (NEP), a BK-inactivating enzyme, and of BK receptors in normal and stenotic aortic valves.
Methods-Stenotic aortic valves (n=84) were obtained at valve replacement surgery and control valves (n=13) at cardiac transplantations. Myofibroblasts were isolated from both stenotic and control aortic valves. The expression levels of neutral endopeptidase (NEP) and BK type 1 and 2 receptors (BK-1R and BK-2R) mRNA were analyzed by real-time PCR. Translation products were localized by immunohistochemistry and double immunofluorescence, using normal and confocal microscopy. NEP activity in aortic valves was quantified by autoradiography.
Results-In comparison to control valves, the mRNA expression levels of NEP, BK-1R, and BK-2R were significantly upregulated in stenotic valves (p<0.05 for each). Autoradiography showed a 4.5-fold increase in active NEP in stenotic vs. control valves (p<0.001), which associated inversely with the aortic valve area (p=0.06). Immunohistochemical staining of stenotic valves localized NEP, BK1Rs, and BK-2Rs to endothelial cells and myofibroblasts. Isolated human myofibroblasts expressed NEP, BK1R, and BK2R mRNA, and confocal microscopy localized these proteins to the cell surface. TNF-alpha induced a significant increase in NEP and BK1R expression in cultured myofibroblasts, whereas treatment with statin increased their BK2R expression.
Conclusions- Enzymatically active NEP is increased in stenotic aortic valves in parallel with an upregulation of BK-1Rs and BK-2Rs. BK-1R upregulation is a result of ongoing inflammation and may promote fibrosis and angiogenesis. These findings suggest that NEP and BK-1Rs may participate in the adverse remodeling of aortic valves and may represent therapeutic targets in treating AS.