Strain-Induced Calcium Response and Chromatin Condensation of Osteoblasts Via Direct Vibration of Focal Adhesion Sites Using Magnetic Micropillars

Abstract

Abstract. Cultured cells exhibit varied biochemical responses to mechanical vibration depending on the frequency and amplitude. However, the mechanisms by which cells sense, transmit, and respond biochemically to mechanical vibration remain unclear, particularly with respect to specific intracellular locations. In this study, vibration stimuli were applied directly to focal adhesion sites of osteoblastic cells using magnetic micropillars actuated at tens of hertz—the first such application to probe dynamic mechanosensing at focal adhesions—and generating cyclic strain of up to 60% in localized regions of the cells. We analyzed the calcium responses and chromatin condensation dynamics with respect to strain amplitude and vibration frequency. The initiation sites of calcium responses were statistically concentrated in regions of high local strain, suggesting a strain-dependent mechanism for calcium signaling.The correlation between local strain and calcium response tended to decrease with increasing vibration frequency, particularly at 12.5, 25, and 50 Hz. Similarly, the coefficient of variation in the number of chromatin condensates over time tended to decrease at these higher frequencies, suggesting a potential reduction in temporal fluctuations of chromatin condensation dynamics. While these tendencies were not statistically significant, they may reflect frequency-related modulation of chromatin condensation dynamics in the nucleus in response to dynamic mechanical stimulation. These findings provide new insights into how cells spatially and temporally decode mechanical vibration at the subcellular level, contributing to our understanding of the mechanisms underlying cell mechanotransduction.