The effects of disruption of cytoskeleton polymers on the rheological properties of cultured mammalian cells in the cortical and perinuclear regions

Researchers have long sought to characterize and understand mammalian cells\u27 physical response to mechanical stress as a prerequisite for understanding cells mechanical functions such as motility, contractility and mechano-sensing. The mechanical properties of the cell were quantified by either its mean squared displacement (MSD) or a complex shear modulus (G*(ω)). Here the frequency-dependent shear modulus of cultured mammalian cells was determined using four different methods. Non-Brownian driving forces were observed at lag time greater than 0.02 s, and were determined to be ATP-dependent. The multiple technique approach allowed the cell to be probed in two regions, cortical and perinuclear. Results clearly indicated two qualitatively similar but distinct mechanical responses, corresponding to the cortical and perinuclear networks, each having an unusual, weak power-law form at low frequency. Using several pharmacological interventions the effects of the three major cytoskeleton polymers, filamentous (F) actin, microtubules (MT) and intermediate filaments (IF), were also examined. F-actin plays a significant role in the mechanics of the cortical region of epithelial cells, but its disruption has no discernable effect on the rheology of the deeper interior. Moreover, we find that myosins do not contribute significantly to the rheology or ATP dependent, non-Brownian motion in the cell interior. It was found that IF removal actually caused the cytoskeleton to stiffen at low frequencies, with no change at high frequency. Finally, it was determined that for the perinuclear region of the cell stiffness is mostly controlled by some combination of microtubules and endomembranes. The most significant change in mechanics arose from either disruption of MT network, which is closely linked to stability of membranous structures, or from repartitioning of the golgi apparatus and endoplasmic reticulum. These findings presented here are compatible with a compartmentalized description of mechanical function: much of the cells bulk is contained in a central compartment that is mechanically passive, which is surrounded by an active, actin-dominated, contractile cortex essential for force production and motility