Abstract
A cell is a complex material whose mechanical properties are essential for its normal functions. Heating can have a dramatic effect on these mechanical properties, similar to its impact on the dynamics of artificial polymer networks. We investigated such mechanical changes by the use of a microfluidic optical stretcher, which allowed us to probe cell mechanics when the cells were subjected to different heating conditions at different time scales. We find that HL60/S4 myeloid precursor cells become mechanically more compliant and fluid-like when subjected to either a sudden laser-induced temperature increase or prolonged exposure to higher ambient temperature. Above a critical temperature of 52 ± 1°C, we observed active cell contraction, which was strongly correlated with calcium influx through temperature-sensitive transient receptor potential vanilloid 2 (TRPV2) ion channels, followed by a subsequent expansion in cell volume. The change from passive to active cellular response can be effectively described by a mechanical model incorporating both active stress and viscoelastic components. Our work highlights the role of TRPV2 in regulating the thermomechanical response of cells. It also offers insights into how cortical tension and osmotic pressure govern cell mechanics and regulate cell-shape changes in response to heat and mechanical stress.
Highlights
Cells exhibit a rich dynamic behaviour when subjected to mechanical stress
We introduced a modified version of a microfluidic optical stretcher with integrated heating components, which allowed us to probe cell mechanics when the cells were subjected to an extended period of heating or to a sudden increase in temperature
We find that the cell compliance of HL60 cells scales linearly with the temperature, independent of the time scales of thermal treatments, and exhibits more fluid-like behaviour at higher temperatures
Summary
Several theoretical approaches have been developed to describe cell mechanical properties, there is no unambiguously accepted theoretical description as of yet These approaches range from phenomenological models that picture cells as a suitable combination of spring and dashpot elements [1,2] to the scale-free power-law models that well characterize the physical stress response of a large class of living cells [3,4]. To this end, a vast array of experimental techniques have been developed to study cellular mechanics. The microfluidic optical stretcher has emerged as a standard tool to probe whole-cell mechanics in a non-invasive way [14], offering powerful insights into the dynamics of non-adherent cells, for example during amoeboid migration [15,16]
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