Propagation of mechanical stress through the actin cytoskeleton
towards focal adhesions: model and experiment

Raja Paul, Patrick Heil, Joachim P. Spatz and Ulrich S. Schwarz

Biophys. J. 2008

We investigate both theoretically and experimentally how stress is
propagated through the actin cytoskeleton of adherent cells and
consequentially distributed at sites of focal adhesions (FAs). The
actin cytoskeleton is modelled as a two-dimensional cable network with
different lattice geometries. Both prestrain resulting from actomyosin
contractility and central application of external force leads to
finite forces at the FAs which are largely independent of the lattice
geometry, but strongly depend on the exact spatial distribution of the
FAs. The simulation results compare favorably with experiments with
adherent fibroblasts onto which lateral force is exerted using a
microfabricated pillar. For elliptical cells, central application of
external force along the long axis leads to two large stress regions
located obliquely opposite to the pulling direction. For elliptical
cells pulled along the short axis as well as for circular cells, there
is only one region of large stress opposite to the direction of
pull. If in the computer simulations FAs are allowed to rupture under
force for elliptically elongated and circular cell shapes, then
morphologies arise which are typical for migrating fibroblasts and
keratocytes, respectively.  The same effect can be obtained also by
internally generated force, suggesting a mechanism by which cells can
control their migration morphologies.