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.