283032 Control of Dorsal Ruffle Dynamics in Cells Through Substrate Stiffness

Monday, October 29, 2012: 9:06 AM
Somerset East (Westin )
Yukai Zeng1, Tanny Lai2, Philip R. LeDuc1 and Keng Hwee Chiam2, (1)Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, (2)Biophysics, A*STAR, Institute of High Performance Computing, Singapore, Singapore

Control of Dorsal Ruffle Dynamics in Cells through Substrate Stiffness

Yukai Zeng1,2, 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.


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