Cytoskeleton rheology

A cell’s behavior is often closely linked to its mechanical state—for example, how it adheres to a surface or to other cells. And its mechanical state is determined largely by its cytoskeleton—a scaffolding of three distinct stiff polymers that permeates most cells (see Physics Today, February 2010, page 60 ). As part of her PhD work at Stanford University, Claire Elkins (now at Abbott Vascular) developed a linear cell-monolayer rheometer (LCMR, shown here) to both image and quantitatively measure mechanical properties of living cells. She and her Stanford colleagues have now used the device to elucidate the roles of the three cytoskeletal polymers. A monolayer of live cells was placed in the LCMR between two glass plates, about 5 microns apart, and allowed to adhere to the plates. Elkins and company then imparted a shear strain to the adhered cells by sliding the top plate relative to the fixed bottom one for a given distance at a given rate. By closely monitoring the force on the top plate, they could determine a time-dependent quantity called the relaxation modulus G_r. The researchers inhibited the function of each of the three cytoskeletal polymers in turn and systematically studied the resulting cells’ relaxation moduli. The results corroborated earlier single-cell studies: Inhibiting tubulin roughly doubled the maximum G_r relative to untreated cells, which means the cells stiffened appreciably; inhibiting either of the other two polymers halved G_r. Thus validated, the LCMR could become a useful biophysical tool, given the ease with which it can obtain average mechanical properties of an entire cell population. (C. M. Elkins et al., J. Rheol. 59, 33, 2015, doi: 10.1122/1.4902437 .)