Downregulated MicroRNA-195 in the Bicuspid Aortic Valve Promotes Calcification of Valve Interstitial Cells via Targeting SMAD7.

BACKGROUND/AIMS: Aortic stenosis caused by leaflet calcification in the bicuspid aortic valve (BAV) is more accelerative than that in the tricuspid aortic valve (TAV). MicroRNA-195 (miR-195) is downregulated more in stenotic than in insufficient BAVs, but its expression in BAVs compared with TAVs is unclear. We aimed to investigate the roles of miR-195 and its calcification-related target SMAD7 in stenotic BAVs compared with those in TAVs.

METHODS: Twenty-one stenotic BAV and 29 TAV samples were collected from surgical patients and examined for the expression of miR-195 and SMAD7 by RT-PCR. The samples were also assessed by western blotting and immunohistochemistry for the functional protein alteration associated with calcification. Dual-luciferase assay was performed to determine the putative target of miR-195 before the effects of miR-195 expression on osteogenic progression was demonstrated in cultured porcine valve interstitial cells (VICs).

RESULTS: Compared with TAV, the expression of miR-195 was remarkably lower in the BAV leaflet with higher expression of SMAD7, which was then validated as a direct target of miR-195. Their negative correlation was then confirmed in cultured VICs. Under an osteogenic environment, the cellular calcification was promoted in miR-195-repressed VICs expressing higher BMP-2 and Runx2 and higher activity of MMP-2 compared with the controls. Finally, higher MMP-2 and MMP-9 expression and more collagen distribution were observed in BAV than TAV samples.

CONCLUSIONS: miR-195 is downregulated more in stenotic BAV than TAV in this study. The downregulation of miR-195 is associated with valvular calcification via targeting SMAD7, which promotes the remodeling of the extracellular matrix.