Background: Calcific aortic valve disease (CAVD) is an age-related and slowly progressive valvular disorder. Overexpression of matrix metalloproteinase 12 (MMP-12) has been found in atherosclerosis, stiffed vascular tissue, and calcified aortic valves. We hypothesized that MMP-12 may induce the pro-osteogenic responses in human aortic valve interstitial cells (AVICs).
Methods: Human AVICs were isolated from normal and calcified aortic valves. Cells were treated with MMP-12. The pro-osteogenic marker Runt-related transcription factor 2 (RUNX-2), bone morphogenetic protein 2 (BMP-2), and alkaline phosphatase (ALP), as well as MMP-12-associated signaling molecules, were analyzed.
Results: Human calcified aortic valves expressed significantly higher MMP-12 than normal human aortic valves. MMP-12-induced the expression of RUNX-2, BMP-2, ALP, and calcium deposit formation. Suppression of MMP-12 by its inhibitor decreased the expression of RUNX-2, BMP-2, and ALP. MMP-12-induced osteogenic responses were associated with higher levels of phosphorylation of p38 mitogen-activated protein kinases (MAPK), low density lipoprotein-related protein 6 (LRP-6), and β-catenin signaling molecules. Calcified aortic valves exhibited markedly higher levels of LRP-6 and β-catenin levels. Inhibition of either p38 MAPK or LRP-6 attenuated MMP-12-induced expression of RUNX-2, BMP-2, and ALP. Suppression of p38 MAPK abrogated MMP-12-induced activation of LRP-6 and β-catenin signaling pathways.
Conclusions: MMP-12 induces pro-osteogenic responses in AVICs by activation of p38 MAPK-mediated LRP-6 and β-catenin signaling pathways. The study revealed that the potential role of MMP-12 in the pathogenesis of CAVD and therapeutically targeting MMP-12 may suppress the development of CAVD.
Keywords: Aortic valve; MMP-12; Pro-osteogenic proteins; Signal transduction.
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