Statins block calcific nodule formation of valvular interstitial cells by inhibiting alpha-smooth muscle actin expression.

OBJECTIVE: Calcific aortic stenosis, characterized by excessive fibrosis and deposition of bone-like calcified tissue, affects roughly 2% to 3% of the U.S. population over the age of 65. Recent studies have suggested that statins have a positive effect on the progression of aoritic stenosis, likely because of their ability to affect the resident cell population, known as valvular interstitial cells (VICs). VICs are fibroblastic cells that can differentiate to form activated myofibroblasts, displaying increased alpha smooth muscle actin (alphaSMA) expression, contractility, and collagen production. METHODS AND
RESULTS: In culture, VICs spontaneously form multicellular aggregates that subsequently develop into calcified nodules, providing an in vitro model for aortic stenosis. Using real-time microscopic tracking, we observed that confluent VIC monolayers spontaneously contract into rounded nodules, suggesting that myofibroblastic contractility is a critical step in the process of nodule formation. Overexpression of alphaSMA increased VIC calcific nodule formation and contractility, whereas knockdown of alphaSMA with siRNAs reduced these phenotypes, suggesting that the expression and contractile properties of alphaSMA are essential to the formation of nodules. Statin treatment of VICs reduced alphaSMA expression, inhibited contractility, and decreased nodule formation. When statins were used to treat preformed nodules, no decrease in the number of calcified nodules was observed, suggesting that statins may play more of a preventative role in aortic stenosis than a cure.
CONCLUSIONS: Our studies provide evidence of a causal relationship between VIC myofibroblastic activity and initial VIC calcific nodule formation. Furthermore, we demonstrate that pravastatin inhibition of calcific nodule formation is related to inhibition of myofibroblastic activity.