Temporal histological examination of C57/B6J mitral valves.
(A) 2 week old murine mitral valves contain similar fractional amounts of collagen and GAGs, with the majority of collagen near the attachment zones but mostly undefined architecture (Movat’s stain: yellow/orange = collagen, green/blue = GAGs). (B) More collagen relative to GAGs is present in 3 week old MV, with matrix stratification developing (Arrows). (C) At 4 months, murine mitral valves have nearly 3 times the amount of collagen to GAGs, are significantly more compact, and have well defined atrialis/fibrosa strata (Arrows). (D) At 12 months, murine mitral valves have significantly less collagen to GAGs, with dramatically increased thickening and reduced structural organization. (E) Digital quantification of matrix composition using color thresholding. Data compared as the ratio of collagen to GAGs within each valve leaflet. Magnification, ×4. Scale bars: 200 µm. Error bars show ±SD, n ≥3 valves per time point. Bars that do not share any letters are significantly different according to a one-way ANOVA with Tukey’s post hoc (p≤0.05).