Co-regulation of cell adhesion by nanoscale RGD organization and mechanical stimulus
Lily Y. Koo1,
Darrell J. Irvine2,
Anne M. Mayes2,
Douglas A. Lauffenburger1,3,4 and
Linda G. Griffith1,3,4,*
1 Department of Chemical Engineering, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, USA
2 Department of Material Science and Engineering, Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139, USA
3 Division of Bioengineering and Environmental Health, Massachusetts Institute
of Technology, Cambridge, Massachusetts 02139, USA
4 Biotechnology Process Engineering Center, Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139, USA
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Fig. 1. (A) A schematic of RGD-comb structure at the polymer-water interface.
Adhesion peptides (pink) are tethered to the comb backbone (blue) via short
poly(ethylene oxide) side chains (yellow) that protrude into the aqueous phase
owing to their favorable interaction with water. (B) Quasi-2D configuration of
an RGD-comb island at the polymer-water interface.
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Fig. 2. At higher RGD cluster sizes, WT NR6 cell adhesion is reinforced in response
to the increased detachment force in the range of 70-150 pN/cell, followed by
a monotonic decrease and a density-dependent plateau at higher forces. When
cluster size remains unchanged, cell adhesion strength increases with
increasing average RGD density. Each graph illustrates adhesion profiles
obtained from substrates presenting RGD peptides in various cluster sizes: (A)
5.4 RGD/cluster; (B) 3.6 RGD/cluster; (C) 1.7 RGD/cluster.
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Fig. 3. WT NR6 cell adhesion is enhanced through nanoscale RGD clustering even when
average peptide density remains the same. Cell adhesion strengths on most
clustered (5.4 RGD/comb) and least clustered RGD (1.7 RGD/comb) substrates are
compared at three comparable RGD surface densities. (A) 5.4 RGD/comb: 1050
RGD/µm2; 1.7 RGD/comb: 1660 RGD/µm2. (B) 5.4
RGD/comb: 530 RGD/µm2; 1.7 RGD/comb: 830 RGD/µm2.
(C) 5.4 RGD/comb: 260 RGD/µm2; 1.7 RGD/comb: 330
RGD/µm2.
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Fig. 4. WT NR6 cell adhesion strength on fibronectin-coated for BSA-coated
substrates was measured after a 12 hour incubation in serum-free medium
followed by an 8 hour incubation in medium containing 1% dialyzed serum.
Adhesion dependence on ligand density and ligand specificity is greatly
diminished, and cell detachment is insensitive to the range of detachment
forces applied.
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Fig. 5. WT NR6 cell adhesion strength on fibronectin-coated substrates was measured
after a 12 hour incubation in serum-free medium to avoid non-specific
adsorption of serum-derived adhesion proteins. Cell adhesion depends on ligand
density, and monotonically decreases with increasing detachment force.
Adhesion is not reinforced on fibronectin surfaces in the absence of
serum.
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Fig. 6. Ligand-clustering-dependent model for adhesion reinforcement. In the top
panel, the blue solid line depicts the physical response of objects undergoing
detachment. No peak is observed in this purely physical process; more objects
are removed as detaching force is increased. However, on an RGD-clustered
substrate, a living cell may be able to transduce the mechanical stimulus into
intracellular signals (pink solid line) that result in the strengthening of
ligand-receptor and/or receptor-cytoskeleton linkages. The outcome of
combining physical detachment with signaling-mediated adhesion reinforcement
is a characteristic peak in the resultant adhesion profile (red line, region
A). At a higher threshold of mechanical stimulus (region B), the primary
signal (pink solid line) is itself reinforced by a secondary signal (pink
dotted line), resulting in a non-zero plateau in the observed adhesion profile
(red line, region B).
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© The Company of Biologists Ltd 2002
