Cell surface receptors transmit sufficient force to bend collagen fibrils

To better understand the dynamic interaction of cells with their surrounding extracellular matrix, chondrocytes and rat embryo fibroblasts were overlaid with individual collagen fibrils and observed with high-resolution video-enhanced differential interference contrast microscopy. Although the cells had a polygonal shape characteristic of nonmotile cells, they used processes usually associated with cell locomotion to acquire the collagen fibrils. Instead of being transported in a retrograde direction, fibrils on the dorsal cell surface were bent, and regions of the bent fibrils were shifted in diverse directions. A blocking antibody to the beta1 integrin subunit significantly inhibited collagen fibril acquisition and bending. Enhanced actin assembly was only occasionally associated with fibrils undergoing rearrangement. Considering that the relatively stiff collagen fibrils require the application of force to be bent, this study shows that cells with a polygonal morphology (as opposed to a polarized, motile shape) are capable of exerting force through the beta1 integrins on the dorsal surface of the cell. Analysis of the bending patterns indicates that fibril buckling was induced by retrograde force combined with regions held stationary and/or the fibrils were bent by forces acting in opposing directions.