OBLIQUE ALIGNMENT OF STRESS FIBERS IN CELLS REDUCES THE MECHANICAL-STRESS IN CYCLICALLY DEFORMING FIELDS

The stress fiber (bundles of actin filaments) is one of the most promi nent cytoskeletal components that contributes to the maintenance of ce ll architecture. It has generally been believed that upon cyclic stret ching, both cells and their stress fibers become perpendicularly align ed to the direction of stretching. However, using our newly developed stretching device, we have recently found the contrary evidence that s tress fibers in endothelial cells rapidly become rearranged at a speci fic oblique angle relative to the direction of stretching [Takemasa, T ., K. Sugimoto, K. Yamashita: Exp. Cell Res. 230, 407-410 (1997)]. In light of this finding, we attempted to establish the explanation for s uch a phenomenon. First, we investigated the effects of possible modul ators on the angle of the stress fibers; those were, modification of t he stretching program, dependency of extracellular matrix types, and t heir reproducibility in other cell species. However, it seemed that th e orientation was solely depending on the stretching amplitude applied . Next, we analyzed alterations in stress fiber length during loading tests using two kinds of deforming experiment systems. It was thus rev ealed that stress fibers aligned at a particular angle so as to minimi ze their length alterations in cyclic deforming fields. Rearrangement of the stress fibers at this angle probably occurs as a result of avoi ding compressive stress and may be interpreted as a way of reducing th e mechanical stress to which they are subjected during the deformation . This hypothesis well explains the reason not only for the survival o f the stress fibers at a particular oblique angle, but also for the re duced numbers of stress fibers found at the other angles on cyclic def orming fields.