In Situ Observation and Measurement of Actin Stress Fiber Deformation in Stretched Osteoblast like Cell

It is believed that mechanical stimuli, such as stretching of the extracellular matrix, are transmitted into cells via focal adhesion complexes and the actin cytoskeleton. Transmission dynamics of strain from the extracellular matrix into intracellular organelles is crucial to clarify the mechanosensing mechanisms of cells. In this study, we observed deformation behavior of actin stress fibers under uniaxial stretch using an originally developed cell-stretching microelectromechanical system (MEMS) device. It was difficult to conduct in situ observation of cells under stretch using conventional cell stretching devices, because motion artifacts such as rigid displacement during stretch application were not negligible. Our novel cell-stretching MEMS device suppressed rigid displacement while stretching, and we succeeded in obtaining time-lapse images of stretched cells. Uniaxial strain with a 10% magnitude and strain rate of 0.5%/sec was applied to cells. Deformation behaviors of the cells and actin stress fibers were recorded using a confocal laser scanning microscope. In time-lapse images of stretched cells, strains along each stress fiber were measured manually. As a result, in cells with a relatively homogeneous stress fiber structure oriented in one direction, distribution of the axial strain on stress fibers generally corresponded to deformation of the stretching sheet on which the cells had adhered. However, in cells with a heterogeneous stress fiber structure oriented in several directions, we found that the strain distribution along stress fibers was not homogeneous. In regions around the cell nucleus, there was a more complicated strain distribution compared with other regions. Our results suggest the cell nucleus with a stiff mechanical resistance yields such a complicated strain distribution in stress fibers.

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