Local Disassembly of Actin Stress Fibers Induced by Selected Release of Intracellular Tension in Osteoblastic Cell

In adherent cells, such as osteoblasts and endothelial cells, the actin stress fiber structure is dynamically reorganized under changes in the surrounding mechanical environment such as cyclic stretch deformation or extracellular fluid flow. Although many studies have been conducted to clarify the biochemical signaling pathways in the reorganization process, details of the reorganization mechanism are still not clearly understood. In addition, to known biochemical mediators, intracellular tension has been proposed as a candidate mechanical mediator for stress fiber reorganization. In previous studies, it was reported that the release of intracellular tension by contracting the cell body induced the disassembly of the stress fiber as an initial phase of the reorganization process. However, in these experimental systems, deformation or force was applied to the entire cell body, so that it was difficult to directly discuss the relationship between the individual mechanical condition of stress fibers and the disassembling phenomenon. In this study, we have designed a novel experimental system by which local contraction was applied to a single osteoblast-like cell and intracellular tension in the targeted stress fiber was selectively released. The dynamic change in stress fiber structure was observed in the EGFP-tagged actin expressed osteoblast-like cell MC3T3-E1. The results indicated that only tension-released stress fibers were selectively disassembled and disappeared in a single cell. This result suggests that the existence of intracellular tension is essential for the dynamical stability of the stress fibers in osteoblast-like cells.