Abstract
Illumination can have adverse effects on live cells. However, many experiments, e.g. traction force microscopy, rely on fluorescence microscopy. Current methods to assess undesired photo-induced cell changes rely on qualitative observation of changes in cell morphology. Here we utilize a quantitative technique to identify the effect of light on cell contractility prior to morphological changes. Fibroblasts were cultured on soft elastic hydrogels embedded with fluorescent beads. The adherent cells generated contractile forces that deform the substrate. Beads were used as fiducial markers to quantify the substrate deformation over time, which serves as a measure of cell force dynamics. We find that cells exposed to moderate fluorescence illumination (λ = 540–585 nm, I = 12.5 W/m2, duration = 60 s) exhibit rapid force relaxation. Strikingly, cells exhibit force relaxation after only 2 s of exposure, suggesting that photo-induced relaxation occurs nearly immediately. Evidence of photo-induced morphological changes were not observed for 15–30 min after illumination. Force relaxation and morphological changes were found to depend on wavelength and intensity of excitation light. This study demonstrates that changes in cell contractility reveal evidence of a photo-induced cell response long before any morphological cues.
Highlights
Fluorescence exposure on fibroblasts cultured on elastic polyacrylamide (PA) gels embedded with fluorescent beads
Adherent cells continuously pull on their underlying substrate[22,23] and bead motion allows quantification of substrate deformation, which serves as a measure of cell force dynamics[24,25]
As cell morphology is commonly used to assess cell health during illumination, we explored photo-induced cell contractility changes revealed by the cell force dipole model
Summary
Fluorescence exposure on fibroblasts cultured on elastic polyacrylamide (PA) gels embedded with fluorescent beads. We observe a transition from the natural contractile state of the cell to relaxation, which we use to characterize cell sensitivity to light. This technique is applicable to any study that utilizes fiducial markers in substrates to track cell behavior, such as PDMS26, microposts and pillars[27], and three-dimensional culture systems[28,29]. We observe this transition prior to distinct morphological changes due to exposure
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