Inhibition of pathological differentiation of valvular interstitial cells by C-type natriuretic peptide.

OBJECTIVE: Calcific aortic valve disease is associated with the differentiation of valvular interstitial cells (VICs) to myofibroblast and osteoblast-like cells, particularly in the fibrosa layer of the valve. Previous studies suggested that C-type natriuretic peptide (CNP) protects against calcific aortic valve disease to maintain homeostasis. We aimed to determine whether CNP inhibits VIC pathological differentiation as a mechanism to explain its protective effects. METHODS AND
RESULTS: CNP expression was prominent in normal porcine aortic valves, particularly on the ventricular side, but reduced in sclerotic valves concomitant with the appearance of pathological VIC phenotypes in the fibrosa. In vitro, CNP inhibited calcified aggregate formation and bone-related transcript and protein expression by VICs grown in osteogenic conditions. Under myofibrogenic culture conditions, CNP reduced α-smooth muscle actin expression and cell-mediated gel contraction, indicating inhibition of myofibroblast differentiation. Similar to CNP, simvastatin inhibited VIC osteoblast and myofibroblast differentiation in vitro. Strikingly, simvastatin upregulated CNP expression in VICs cultured under myofibrogenic conditions, and small interfering RNA knockdown of natriuretic peptide receptor-b (a CNP receptor) significantly reduced the antifibrotic effect of simvastatin, suggesting that it acts in part via CNP/NPR-B autocrine/paracrine signaling.
CONCLUSIONS: CNP inhibits myofibroblast and osteoblast differentiation of VICs and is responsible in part for inhibition of VIC myofibroblast differentiation by statins, suggesting novel mechanisms to explain the protective effect of CNP and the pleiotropic effects of statins in the aortic valve.