Extracellular matrix remodeling in calcific aortic valve disease: Localized enrichment of type III collagen and...

Calcific aortic valve disease (CAVD) is characterized by progressive extracellular matrix (ECM) remodeling that promotes valve fibrosis and calcification. However, its molecular and structural basis remains unclear. In this study, we comprehensively analyzed ECM remodeling in human CAVD valves, focusing on collagen dynamics and key ECM-associated regulatory components. Histopathological analysis revealed fibrous layer thickening, collagen disorganization, and focal loss of the spongiosa in the CAVD group. Polarized picrosirius red staining demonstrated increased yellow-orange birefringence in the fibrotic and calcified regions, indicating altered collagen organization. Quantitative liquid chromatography-mass spectrometry analysis showed region-specific shifts toward an increased type III collagen proportion in fibrotic and calcific regions despite the reduced total collagen content in calcified areas. Collagen with improper triple-helical structure primarily accumulated around the calcified nodules, suggesting abnormal collagen turnover. Transmission electron microscopy revealed thinner and more heterogeneous collagen fibrils in lesioned regions than that in pre-lesional region. In normal valves, immunohistochemistry suggested that the hyaluronan-versican-fibrillin complex contributes to local regulation of Transforming growth factor-beta 1 (TGF-β1) activity via latent TGF-β binding proteins (LTBP); however, this regulatory structure was disrupted in CAVD. Notably, LTBP-4 showed strong, regionally restricted localization in the fibrotic and calcific regions and was positively correlated with collagen yellow-orange birefringence. Collectively, these findings indicate that CAVD is associated with a localized shift toward a structurally heterogeneous, type III collagen-enriched matrix, accompanied by collagen denaturation and abnormal accumulation of LTBP-4, highlighting ECM dysregulation as a key feature of disease progression.