Distribution of Vitronectin and Its Receptor in Embryonic Human Heart

Fibulin-1, vitronectin, and fibronectin expression during avian cardiac valve and septa development

BACKGROUND

Extracellular matrix (ECM) proteins have been implicated as mediators of events important to valvuloseptal development (reviewed by Little and Rongish, Experentia, 51:873-882, 1995). The aim of this study was to identify connective tissue ECM proteins present at sites of valvuloseptal morphogenesis, and to determine how their patterns of expression change during the developmental process.

METHODS

Immunofluorescence microscopy was used to examine the distribution of fibulin-1, vitronectin, and fibronectin in the embryonic chicken heart over a broad developmental time frame (Hamburger and Hamilton stages 14 to 44), emphasizing stages that illustrate endocardial cushion formation, growth, fusion, and development into valvuloseptal components.

RESULTS AND CONCLUSIONS

Fibulin-1 immunolabeling was concentrated in endocardial cushions, notably at boundaries with the myocardium, during stages when the cushions are differentiating into valvular and septal components. Fibulin-1 was detected in the endocardial cushions prior to their seeding with cushion cells, but became undetectable by early midgestation. Vitronectin expression was similar to fibulin-1, but less restricted in its distribution. Vitronectin was observed before endocardial cushion cell migration commenced and persisted until the formation of prevalvular structures (early midgestation) in the atrioventricular cushions. Vitronectin remained detectable in the semilunar valves until late midgestation. Fibronectin was present in the endocardial cushion region and in portions of the endocardium and myocardium throughout the stages presented. Our data suggests that the ECM of the endocardial cushions undergoes remodelling in a regionally and temporally specific manner which corresponds with morphogenetic changes during valvuloseptal development.

Role of vitronectin in embryonic rat endocardial cell migration in vitro

Vitronectin is one of the extracellular matrices that mediate cell spreading and attachment in vitro. In the present paper, we demonstrate the involvement of vitronectin in the migration of cushion mesenchymal cells of the embryonic rat heart. Immunohistochemistry established the localization of vitronectin in the myocardial cells and in some of the cushion mesenchymal cells of the truncus arteriosus and atrioventricular canal. In vitro, vitronectin, fibronectin, and collagen type-I revealed significant stimulating activity for cushion mesenchymal cell migration. The distance migrated by cushion mesenchymal cells cultured on vitronectin, collagen type-I, or both vitronectin and fibronectin was similar, but that on fibronectin was significantly shorter. Following the addition of anti-vitronectin IgG to the medium, the migration distance of cushion mesenchymal cells on fibronectin was remarkably increased. Most explants on vitronectin or on both vitronectin and fibronectin became detached from dishes after the addition of the antivitronectin antibody. Immunostaining revealed that cushion mesenchymal cells cultured on substrata other than vitronectin synthesized vitronectin. From these results, it is suggested that vitronectin is synthesized by myocardial cells and some cushion mesenchymal cells, and that vitronectin inhibits cell movement on fibronectin. This feature of vitronectin may be important in the regulation of the migration of cushion mesenchymal cell in vivo.