Cellular orientational fluctuations, rotational diffusion and nematic order under periodic driving.

Area of Science:

• Cellular mechanobiology
• Biophysics
• Soft matter physics

Background:

• Cells dynamically sense and respond to their physical microenvironment, crucial for regulating cellular structure, function, and fate.
• Physiological processes like heart beating and breathing involve cellular responses to periodic forces in noisy environments.

Purpose of the Study:

• To test and validate a mean-field theory for cellular reorientation under periodic driving forces.
• To extend the theory to include nonequilibrium fluctuations and quantitatively analyze cell orientation dynamics.
• To investigate intracellular nematic order and its relationship with external driving forces.

Main Methods:

• Validation of a mean-field theory combining elastic energy minimization and active remodeling forces.
• Extension of the theory to incorporate additive nonequilibrium fluctuations.
• Experimental measurements of cell body orientation probability distributions and intracellular actin stress fiber order under biaxial periodic driving forces.

Main Results:

• The extended mean-field theory quantitatively matches experimental cell orientation distributions under periodic driving.
• The theory enables extraction of active noise amplitude and rotational diffusion coefficients for different cell types.
• Intracellular nematic order increases with driving force magnitude and biaxiality, explained by applying the theory to actin stress fiber domains.

Conclusions:

• A robust theoretical framework quantitatively describes cell reorientation and intracellular order under periodic forces and noise.
• The findings provide a method to quantify cell mechanosensitivity and active noise.
• Cellular orientational fluctuations are significantly larger than thermal energy, highlighting active cellular processes.