Localization and pattern of expression of extracellular matrix components in human heart valves

BACKGROUND AND AIM OF THE STUDY: The pattern of expression and distribution of extracellular matrix (ECM) components in human cardiac leaflets was analyzed. Additionally, interstitial cells (ICs) from the four different leaflets were isolated and studied. METHODS: Immunohistochemistry and immunocytochemistry were used for localization, and flow cytometric analysis to quantify the expression of specific markers on these ICs; the synthesis and expression of ECM components was assessed. RESULTS: Elastin was found predominantly on the inflow layer, but fine fibers were also present in the central and outflow layers. Collagen I was predominantly on the outflow layer but permeated throughout the leaflets. Collagen III was expressed ubiquitously. Proteoglycan expression was throughout the leaflet, but was predominant in the central layer. Fibronectin and vitronectin were expressed strongly in the inflow layer, moderately in the central layer, and weakly in the outflow layer. Biglycan expression was ubiquitous, with strong filamentous strands in the central layer. Keratan sulfate and decorin were ubiquitous. Chondroitin-4-sulfate and chondroitin-6-sulfate were strongly expressed in the outer layers, and laminin was restricted to the basal lamina of the endothelial cells. Cultured ICs showed synthesis and expression of various ECM components. CONCLUSION: This study of the pattern of expression of ECM components may provide a basis for a fingerprint on which to base future valve alternatives. The results provide useful information for valve tissue engineering and an understanding of the structural basis of some sophisticated functions of the valves.