(18c) Control of Dorsal Ruffle Dynamics in Cells Through Substrate Stiffness

Control of Dorsal Ruffle
Dynamics in Cells through Substrate Stiffness

Yukai Zeng^1,2,
Tanny Lai², Philip R. LeDuc¹ and K.-H Chiam²

¹ Mechanical Engineering, Carnegie Mellon
University, Pittsburgh, PA, 15213, USA

² A*STAR, Institute of High Performance Computing,
Singapore

Circular dorsal
ruffles (CDRs) are structures which are rich in actin, formed in many mammalian
cells after stimulation with various growth factors, such as platelet-derived
growth factor (PDGF). These structures and their chemical environment are
important in many areas such as PDGF playing a role in cell proliferation, angiogenesis
and cell migration. CDRs are hypothesized to aid in cell migration by
initiating large scale reorganization of the actin cytoskeleton in cells [1]
and form minutes after PDGF stimulation, before persisting and disappearing
within tens of minutes in fibroblasts [1,2]. In addition, cells which exhibit
CDRs are thought to show an increase in macropinocytosis activity [2],
suggesting this as a possible function of CDRs. From a mechanics standpoint,
cells seeded on varying substrate stiffnesses exhibit differences in cell
migration speed [3]. We used this knowledge to investigate the migration speed
of cells which exhibit CDRs and compare them to those which do not. The size of
the CDRs formed in cells were also quantified, since when cells are seeded on 2
dimensional substrates and observed under a fluorescence microscope after
staining for F-actin, the CDRs appear as circular rings of F-actin and thus
provide a basis for stimulation based comparisons.

      Our experiments show that although changing
substrate stiffness does not change the physical properties such as the size of
CDRs, their kinetics is changed [4]. This is based on the increase in
persistence time of these CDRs when substrate stiffness is increased. We
hypothesize that the CDRs transverse at a reduced speed below the cell membrane
with increasing substrate stiffness. In addition, the percentage of cells which
exhibit CDRs in a population, when stimulated with PDGF, decreases with
increasing substrate stiffness. The ability of the CDR formation model, based
on Rac-Rho antagonism, to replicate our experimental results suggest that the
system of reaction-diffusion reactions based on the PDGF stimulated cell
signaling cascade and cell compartmentalization are able to explain the
experimental observations of the spatiotemporal response. This indicates that
while the geometric alterations of the CDRs may not be directly related to
substrate stiffness, the kinetics of the response may be very important.

rEferences

1.     
Krueger,
E. W., Orth, J. D., Cao, H. & McNiven, M. A. A dynamin?cortactin?Arp2/3
complex mediates actin reorganization in growth factor-stimulated cells. Mol.
Biol. Cell 14, 1085?1096 (2003).

2.     
Buccione, R., Orth,
J.D. & McNiven, M.A. Foot and mouth: podosomes,
invadopodia and circular dorsal ruffles. Nat Rev
Mol Cell Bio. 5, 647?657 (2004).

3.     
Lo, C.M, Wang, H.B.,
Dembo, M & Wang, Y.L. Cell Movement Is Guided by the
Rigidity of the Substrate. Biophysical Journal 79, 144-152 (2000).

4.     
Zeng,
Y.*, Lai, T.*, Koh, C. G., LeDuc, P.R., & Chiam, K.-H. Investigating
Circular Dorsal Ruffles through Varying Substrate Stiffness and Mathematical
Modeling. Biophysical Journal 101, 2122?2130 (2011).

*Equal contribution from both
authors.