Stiffening of the Cytoplasm in Response to Intracellularly Applied Forces

Cells constantly encounter mechanical forces that regulate various cellular functions, such as migration, division, and differentiation. Understanding how cells respond to forces at the intracellular level is essential for elucidating the mechanical adaptability of living cells. This study investigates how the cytoplasm alters its mechanical properties in response to forces applied inside a cell. The mechanical properties were measured through <i>in situ</i> characterization using magnetic tweezers to apply mechanical forces on magnetic beads internalized into cells. The findings reveal that the cytoplasm stiffens within seconds when force is applied to the cytoplasm. Macromolecular crowding and cytoskeletal structures, particularly F-actin, were found to significantly contribute to cytoplasm stiffening. The stiffening response was also observed across multiple length scales by using magnetic beads of varying diameters. These results highlight the rapid adaptation of the cytoplasm to mechanical forces applied to the inside of a cell.