MECHANICAL-PROPERTIES OF THE EXTRACELLULAR-MATRIX INFLUENCE FIBRONECTIN FIBRIL ASSEMBLY IN-VITRO

Mechanical properties of the extracellular matrix (ECM) are proposed t o influence cell behavior and biological activity. The influence of th e mechanical environment on fibronectin fibril assembly was evaluated. Fibroblasts were cultured in hydrated collagen gels with two distinct ly different mechanical properties. Cells cultured within a stabilized collagen gel generate stress that is transmitted throughout the matri x (stressed gel). In contrast, cells that are cultured within a collag en gel that is floating freely in media do not generate stress (relaxe d gel). Fibroblasts in the stressed collagen gel develop large bundles of actin microfilaments and associated fibronectin fibrils, while fib roblasts within relaxed gels do not form stress fibers or assemble fib ronectin into fibrils. In addition, we have evaluated the mechanism of fibronectin fibril assembly employed by fibroblasts cultured within a stressed three-dimensional collagen matrix and the role of fibronecti n fibrils in transmission of cell-generated forces to the surrounding matrix. Fibronectin fragments (70-kDa amino terminal fragment, 110-kDa cell-adhesive fragment, and GRGDS peptide) and a monoclonal antibody blocked fibronectin fibril assembly in stressed three-dimensional coll agen gels. These results suggest that the features of fibronectin requ ired for fibronectin fibril assembly by cells in collagen gels is simi lar to those required by cells cultured on a planar substratum. Althou gh fibronectin fibril assembly was blocked by these inhibiting fragmen ts and antibody, the cells displayed prominent actin bundles and devel oped isometric tension, indicating that stress fiber formation and con tractile force transmission is not dependent on the presence of fibron ectin fibrils. (C) 1995 Academic Press, Inc.