Cells on gels: smooth and skeletal muscle cell responses to substrate compliance

Cell adhesion has been recognized as being regulated by receptor-ligand interactions, but substrate compliance is emerging as an equally important determinant of adhesion, structure, and ultimately cell state. For contractile cells, such as the Smooth Muscle Cell line A7r5, spreading was investigated as a function of both adsorbed collagen and substrate compliance. Collagen levels of 10³ng/cm² produce a significant short term increase in cell spreading on rigid substrates. Longer-term spreading was dependent, however, on substrate compliance (controlled by a variably crosslinked polyacrylamide gel), in which cell area increased two-fold on stiff substrates (8 kPa) versus soft gels (1 kPa). To investigate their influence on cytoskeletal function, cells transfected with GFP-actin and - paxillin were controllably peeled using a translating micropipette and a shear fluid force. F-actin remodeling on stiff surfaces caused fracturing of the cytoskeleton during peeling, with the residual actin co-localized with paxillin. Preliminary results of fluorescent AFM on F-actin also show a change in assembly that marginally translates to a change in rigidity on stiff substrates. Results were also obtained with the skeletal muscle line C2C12 and indicated only a short term dependence on substrate compliance. This study suggests that the coupling of short-term chemical signaling and long-term mechanical signaling contributes to contractile cell mechanotransduction, ultimately affecting cell remodeling.