527 Analysis of stress fiber reorientation in osteoblast-like cells induced with cyclic stretch : The effects of cyclic stretch waveform and cell junctions
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It has been reported that the stress fibers (SFs) of cells on elastic substrate aligned at a particular angle so as to minimize their strain magnitude caused by cyclic deformation of the substrate. However, little is known about the mechanism of their alignment. In this study, we investigated the effects of cyclic stretch waveform and intercellular junctions on the SF alignment in MC3T3-E1 osteoblast-like cells. The cells were cultured on silicone membranes under a sparse (15 cells/mm^2) or dense (300 cells/mm^2) condition, and subjected to cyclic uniaxial stretch having either one of the following wave forms with an amplitude of 8%: triangular; trapezoid, bottom hold, or peak hold for 24 h. Alignment of their SFs were then analyzed with a two-dimensional Fourier transformation analysis. In the sparse condition, no orientation was observed for the triangular and the peak hold waveforms, while SFs aligned mostly in the direction in which normal strain of substrate becomes zero (〜54°) with other waveforms, especially with the trapezoid waveform which had a hold time both at the maximum strain and the zero-strain state. Intracellular SFs generate a prestress, and they depolymerize with release of their prestress. They are also viscoelastic. Thus our results indicate that depolymerization and reorientation of SFs were significantly accelerated with the release of their prestress caused by the stress relaxation of SFs during the hold times in the trapezoid waveform. In the dense condition, in which cells have intercellular junctions, SFs aligned in perpendicular to and/or parallel to the stretch direction with the triangle waveform and in perpendicular to the stretch direction with other waveforms, as if the cells avoided shear deformation causing breakdown of cell-cell junctions. These results indicate that time history of stress applied to the SFs as well as intercellular junctions may have profound effects on cell alignment in MC3-3-E1 cells.
