Cyclic Biaxial Strain of Pulmonary Artery Endothelial Cells Causes an Increase in Cell Layer-associated Fibronectin

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Abstract
Bovine pulmonary artery endothelial (PAE) cells were cultured on an artificial compliant substrate (Mitrathane) and were strained biaxially at a frequency of 1/s for 2, 4, 6, 7, or 24 h. Total protein synthesis, determined by estimating the incorporation of radiolabeled precursors into nondialyzable protein, was increased in cultures that had been biaxially strained for 6, 7, or 24 h, with differences more apparent in the cell layer fraction than in the medium fraction. Medium and cell layer-associated fibronectin were quantitated by enzyme-linked immunosorbent assay and by densitometric analysis of the autoradiograms of electrophoresed protein. Fibronectin levels in the medium of biaxially strained cells were initially depressed in comparison to nonstrained controls but, with time, began to approach control values. Cell layer-associated fibronectin of biaxially strained cultures was significantly elevated at 24 h, whereas DNA synthesis was not altered. Immunohistochemical localization of fibronectin and factor VIII-von Willebrand antigen revealed a more intense staining pattern in strained cultures. Distribution of stress fibers containing fibrous actin was visualized by staining with rhodamine-phalloidin and was altered in strained cultures. These observations indicate that cells respond to cyclic biaxial strain by selectively enhancing structural components associated with cell adhesion.