Abstract 340: Circulating TGF-ß1 Correlates with Increased Wall Shear Stress in a Hypercholesterolemic Murine Model of Spontaneous Aortic Valve Stenosis
Aortic valve stenosis (AS) is a chronic disorder involving fibrosis and calcification of the aortic valve (AV), leading to a decrease in AV orifice area and an increase in wall shear stress (WSS) across the valves. We previously demonstrated that the pro-fibrotic cytokine TGF-β1, which is secreted as a latent complex, can be activated by shear both in vitro and in vivo. Thus, we hypothesize that shear-induced TGF-β1 activation contributes to the pathophysiology of AS. In this study, we used Ldlr-/-Apob100/100/Mttpfl/fl/Mx1Cre+/+ mice (“Reversa”, kindly provided by Dr. Heistad), which spontaneously develop AS after 6 months of a high fat diet, to test this hypothesis.
Treating Reversa mice with a high fat diet for 6 months was associated with a significant decrease in AV cusp separation distance (median [IQR] from 0.85 [0.64-0.97] to 0.46 [0.37-0.65] mm) and significant increases in plasma cholesterol (mean±SD from 273±27 to 837±98 mg/dl), WSS across the AV (from 189 [152-235] to 308 [236-568] dyn/cm2), and plasma total TGF-β1 levels (from 1.24 [1.08-0.38] to 1.66 [1.34-2.10] ng/ml) (all p<0.01). In contrast, no change in AV cusp separation distance, WSS, or plasma total TGF-β1 levels were observed in mice on a chow diet (n=14, all p>0.05). The increase in plasma total TGF-β1 levels in mice on a high fat diet correlated with the increase in WSS (r=0.32, p=0.04). Immunofluorescence staining showed increased Smad2/3 phosphorylation and α-smooth muscle actin (α-SMA) expression in the stenotic valves. We tested the effect of TGF-β1 (1ng/ml) on cultured porcine AV interstitial cells and found increased Smad2/3 phosphorylation and increased expression of α-SMA after 12 or 24 hours treatment.
We conclude that AS progression is associated with both an increase in total plasma TGF-β1 levels and evidence of TGF-β1-induced cellular activation in this hypercholesterolemic murine model of spontaneous AS. These data are consistent with a model in which cellular release of TGF-β1 results in increased plasma TGF-β1, activation of latent TGF-β1 by the increased WSS across the AV, and TGF-β1 induces fibrosis and calcification of the AV. Since WSS increases with AS progression, a feed-forward mechanism may lead to accelerated AS progression.
- © 2013 by American Heart Association, Inc.