Actomyosin Cortical Mechanical Properties in Nonadherent Cells Determined by Atomic Force Microscopy

Area of Science:

• Cell Biology
• Biophysics
• Biomechanics

Background:

• Cellular mechanical properties are crucial for cell function.
• The actomyosin cytoskeleton, comprising actin and myosin, dictates these properties.
• Quantifying the mechanical characteristics of the cell cortex is challenging, especially in nonadherent cells.

Purpose of the Study:

• To develop and validate a novel force spectroscopy method for measuring cell cortical tension, elastic modulus, and intracellular pressure.
• To investigate the effects of actomyosin components and perturbations on the mechanical properties of nonadherent cell cortices.
• To provide a physically relevant parameter-based characterization of cell mechanical regulation.

Main Methods:

• Utilized force spectroscopy with tipless cantilevers to perform approach curve measurements on nonadherent cells.
• Validated the method by measuring the surface tension of water microdrops.
• Applied the technique to human foreskin fibroblasts and THP-1 monocytes, assessing changes after pharmacological interventions targeting actomyosin activity.

Main Results:

• The method accurately measured water surface tension, validating its precision.
• Myosin II activity and actin polymerization were found to increase cortical tension and intracellular pressure.
• Myosin II activity stiffened the cell cortex, while branched actin networks softened it; actin polymerization did not affect stiffness.

Conclusions:

• The developed force spectroscopy method offers a robust approach to quantify cell cortical mechanical properties in nonadherent cells.
• Actomyosin contractility and organization play significant roles in modulating cell tension, pressure, and stiffness.
• This technique has broad applicability for understanding the molecular regulation of cell mechanics and cytoskeleton dynamics.