Separating Water Content from Network Dynamics in Cell Nuclei with Brillouin Microscopy.

Area of Science:

• Cellular mechanics
• Biophysics
• Mechanobiology

Background:

• Cellular mechanical properties are crucial in mechanobiology.
• Traditional methods involve deforming cells and measuring forces.
• Brillouin light scattering (BLS) offers an alternative by measuring acoustic parameters on picosecond timescales.

Purpose of the Study:

• To clarify the interpretation of hypersonic data from Brillouin light scattering (BLS) spectra.
• To differentiate contributions of water content and biopolymer network dynamics to cellular mechanical properties.
• To resolve confusion arising from the colloquial use of 'stiffness' in cell mechanics.

Main Methods:

• Applied osmotic compressions to single cells to vary intracellular water and solid network fractions.
• Utilized Brillouin light scattering (BLS) to measure sound velocity and attenuation.
• Compared BLS data with cell volume measurements and fitted results to a poroelastic model.

Main Results:

• Observed a nonlinear increase in sound velocity and attenuation in the nucleus with increasing osmotic pressure.
• Demonstrated that BLS shift is primarily sensitive to intracellular water content.
• Showed that BLS linewidth analysis reveals contributions from biopolymer network dynamics.

Conclusions:

• The study successfully differentiates between water content and biopolymer network contributions using BLS.
• Poroelastic modeling aids in interpreting hypersonic data from BLS.
• This work provides a clearer understanding of BLS applications in living cell mechanics.