Differential proteoglycan and hyaluronan distribution in calcified aortic valves

Abstract

Background: While the prevalence of calcified aortic valve disease continues to rise and no pharmacological treatments exist, little is known regarding the pathogenesis of the disease. Proteoglycans and the glycosaminoglycan hyaluronan are involved in calcification in arteriosclerosis and their characterization in calcified aortic valves may lend insight into the pathogenesis of the disease.

Methods: Fourteen calcified aortic valves removed during valve replacement surgery were immunohistochemically stained for the proteoglycans decorin, biglycan, and versican, as well as the glycosaminoglycan hyaluronan. Staining intensity was evaluated in the following regions of interest: center of calcified nodule, edge of nodule, tissue directly surrounding the nodule; center and tissue surrounding small "prenodules"; and fibrosa layer of normal regions of the leaflet distanced from the nodule.

Results: Decorin, biglycan, and versican, as well as hyaluronan, were abundantly present immediately surrounding the calcified nodules, but minimally within the nodule itself. Expression of decorin and biglycan in and surrounding prenodules was greater than in the edge and center regions of mature nodules. The levels of expression of the proteoglycans and hyaluronan were highly correlated with one another in the different regions of the valve.

Conclusions: The three proteoglycans and hyaluronan demonstrated distinctive localization relative to nodules within calcified aortic valves, where they likely mediate lipid retention, cell proliferation, and extracellular matrix remodeling, and motivate further study. Comparisons between expression of these components in mature nodules and prenodules suggest distinct roles for these components in nodule progression, especially in the tissues surrounding the nodules.

Figure 1

Upper two images: Movat pentachome stain of two calcified aortic valves showing large nodules at the distal end and small prenodules (indicated by arrows) more proximal to the annular edge of the leaflet. Asterisk indicates normal fibrosa. Lower two images: one of the same calcified valves stained for hyaluronan (HA) and versican. Scale bar = 1 mm.

Figure 2

Intensities of staining for PGs and HA in different regions of calcified aortic valves. Error bars indicate standard error of the mean. †p<0.05 compared to Nod Surr. *p<0.05 compared to Fibrosa. ‡p<0.05 compared to Prenod. Nod Ctr = innermost 2/3 of the large nodule. Nod Edge = outer 1/3 of the large nodule. Nod Surr = tissue immediately surrounding the large nodule. Prenod = prenodule. Prenod Surr = tissue immediately surrounding the prenodule.

Figure 3

Calcified valve stained with Movat pentachrome and histochemically stained for decorin, biglycan, hyaluronan (HA), and versican. Scale bar = 1 mm.

Figure 4

Calcified valve stained with Movat pentachrome and immunohistochemically stained for decorin and biglycan. Asterisk indicates normal fibrosa. Scale bar = 1 mm.