Fibronectin biosynthesis and cell-surface expression by cardiac and non-cardiac endothelial cells

We examined the biosynthesis and surface expression of fibronectin, an adhesive glycoprotein, in several types of cultured porcine endothelial cells: pulmonary artery, thoracic aorta, coronary artery, aortic valve, and mitral valve. We used immunocytochemical staining to compare the levels of fibronectin present in these same tissues in vivo. Using endogenous radiolabeling, we found that all cell types except aortic valve endothelial cells synthesized and released into the culture media substantial quantities of fibronectin. Using radioiodination of intact cells, we found that, whereas both thoracic aorta and pulmonary artery cells had measurable fibronectin on the surface, aortic valve, mitral valve, and coronary artery cells had little cell-surface fibronectin present. Immunocytochemical staining showed that all endothelial regions except aortic valve had substantial quantities of immunoreactive fibronectin in vivo. These data suggest that the aortic valve endothelium may be distinct from other endothelia. Such differences could be important for the pathogenesis of valvular disease.