Increased expression of profibrotic neutral endopeptidase and bradykinin type 1 receptors in stenotic aortic valves.
OBJECTIVE
In aortic stenosis (AS), adverse remodelling of the valves may depend on altered local regulation of pro- and antifibrotic systems. We have recently shown that angiotensin-converting enzyme (ACE), which generates profibrotic angiotensin II and inactivates antifibrotic bradykinin (BK), is upregulated in stenotic aortic valves. Here, we analyse the expression of neutral endopeptidase (NEP), another profibrotic and BK-degrading enzyme, and of BK receptors in aortic valves in AS.


RESULTS
Stenotic aortic valves (n = 86) were obtained at valve replacement surgery and control valves (n = 13) at cardiac transplantation. Expression levels of NEP and BK type 1 and 2 receptors (BK-1R and BK-2R) in aortic valves and in isolated valvular myofibroblasts were analysed by real-time PCR and immunohistochemistry, and NEP activity was quantified by autoradiography. NEP, BK-1R, and BK-2R mRNA levels were higher in stenotic than in non-stenotic valves (P < 0.05 for each) and the respective proteins localized to valvular endothelial cells and myofibroblasts. In stenotic valves, the proteolytic activity of NEP was significantly increased (4.5-fold, P < 0.001), and tumour necrosis factor-alpha induced the expression of NEP in cultured myofibroblasts. Finally, treatment of cultured myofibroblasts with an NEP inhibitor (phosphoramidon) downregulated the expression of profibrotic transforming growth factor-beta1, whereas addition of BK decreased the expression of collagens I and III which was reversed by a BK-2R antagonist.


CONCLUSIONS
NEP activity is increased in stenotic aortic valves in parallel with increased expression of BK-receptors. The upregulation of NEP and BK-1R have the potential to promote valvular fibrosis and remodelling while the increase in BK-2R may represent a compensatory antifibrotic response. These findings add novel pathogenic insight and raise potential new therapeutic targets in AS.
Helske
Satu
S
Wihuri Research Institute, Kalliolinnantie 4, Fin-00140 Helsinki, Finland.
Laine
Mika
M
Kupari
Markku
M
Lommi
Jyri
J
Turto
Heikki
H
Nurmi
Laura
L
Tikkanen
Ilkka
I
Werkkala
Kalervo
K
Lindstedt
Ken A
KA
Kovanen
Petri T
PT
D000328:Adult; D000368:Aged; D001021:Aortic Valve / Q000473:pathology*; D001024:Aortic Valve Stenosis / Q000378:metabolism / Q000473:pathology*; D005260:Female; D005355:Fibrosis / Q000401:mortality / Q000503:physiopathology*; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D015260:Neprilysin / Q000096:biosynthesis* / Q000378:metabolism; D011446:Prospective Studies; D043783:Receptor, Bradykinin B1 / Q000096:biosynthesis* / Q000378:metabolism; D043782:Receptor, Bradykinin B2 / Q000096:biosynthesis* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D043783:Receptor, Bradykinin B1; D043782:Receptor, Bradykinin B2; D015260:Neprilysin