Abstract : Adherent cells can control their mechanical properties in order to perform crucial biological functions, like division, migration or differenciation. It has now been proved that cells are very sensitive to the mechanical properties of their substrate, which they sense through integrins. Integrins are transmembrane proteins that link the actin cytoskeleton to the extracellular matrix through scaffolding proteins.
We designed an optical tweezers setup controlled by a feedback loop, which allows the application of a constant local force via microbeads bound to the cell integrins. We can thus measure the creep function of a single cell and retrieve an estimate of its rigidity. Simultaneous fluorescence observations allow us to evaluate the impact of force application on the actin repartition within the cell.
We observed that cells stiffen under force application but keep the same rheological response - the creep function still exhibits a power law behavior : J(t) = At^(alpha), in which A decreases on a long time range. Stiffening is coupled to actin recruitment both in the contacts and in the cytoskeleton networtk - up to several µm from the force application point. Stiffening and recruitment dynamics seem strongly correlated.
This work presents an evaluation of the dynamics of cell stiffening under stress, which is a novel insight into the elucidation of the more general phenomenon of mechanotransduction.