Abstract 509: Early Pathogenesis of Murine Aortic Valve Disease is Marked by Versican-Rich Proteoglycan Synthesis

Abstract

Background: Aortic valve disease (AVD) is a cell-mediated pathology without pharmacotherapy whose early pathogenesis is poorly understood. In mice, the study of later-stage fibrotic & calcific AVD requires aggressive dietary/genetic induction unsuitable for the study of early AVD progression. Here, we examined the initial extracellular matrix & cellular changes induced in the mouse aortic valve by a mildly atherogenic diet. Methods: Male WT C57Bl/6J mice were fed control or high-fat (HF, BioServ F3282) diets for 4 or 16 months (n = 6-10 per group). Aortic valve function was assessed by echocardiography. Valve sections were (immuno)stained for Movat’s pentachrome, proteoglycans (PG), Sox9, & αSMA. Valve interstitial cells (VICs) from porcine aortic valves were cultured with 5 ng/ml TGF-β1 for 5 days. PG synthesis & mRNA levels were measured by g-HCL & qPCR, respectively. Results: At 4 months, valve function was unaffected by the HF diet (transvalvular velocity: 123.5 ± 8.5 vs. 128.2 ± 9.2 cm/s, p = 0.75), & no leaflets expressed αSMA. Distal tips of HF leaflets were thickened (84.4 ± 10.4 vs. 37.3 ± 2.7 μm) due to PG accumulation (11435 ± 1920 vs. 5448 ± 762 μm 2 , p < 0.01), not collagen deposition (1729 ± 815 vs. 1771 ± 663 μm 2 , p = 0.87). Versican was the only PG increased in HF leaflets (2.38-fold, p < 0.05), with no alterations in decorin or biglycan (p = 0.69 & 0.59). Chondrogenic processes were activated in HF leaflets, with a 3.42-fold increase in Sox9-positive leaflet area (p < 0.01). By 16 months, HF mice had elevated transvalvular velocities (169.7 ± 20.3 vs. 115.4 ± 3.6 cm/s, p < 0.05) & leaflets were αSMA-positive & myofibrogenic. Histology of 16-month mice for PGs & Sox9 is ongoing. Early PG expression patterns were recapitulated in culture: total PG production was increased 2.14-fold in TGF-β1-treated VICs (p < 0.05), while versican mRNA was solely elevated (1.53-fold, p < 0.05) & decorin & biglycan were decreased (-2.05-fold, p < 0.01 & -2.62-fold, p < 0.05 respectively). Conclusions: Diet-induced de novo PG synthesis is versican-rich, occurs along with increased Sox9 expression, & develops prior to myofibroblast activation, fibrosis, or deficits in valve function. These studies provide new insight into early AVD pathogenesis & the involvement of specific PGs therein.