Cell Prestress, Stiffness, and Density
In recent years, mechanotransduction in cells has been a topic of great interest. In cultures of fibroblasts and endothelial cells, for example, it has been shown that cell morphology and motility are sensitive to substrate elasticity1 and are related to the tractional forces that cells exert on substrates.2,3 It was shown that in human airway soft muscle cells, the stiffness of the cell itself increases in proportion to the tractional forces the cell exerts on the substrate.4 It has also been observed that cell rigidity changes when the cultured cell population reaches confluence. Taken together, these observations suggest a close relationship between cell elasticity and cytoskeletal prestress, possibly related to cell density. However, no direct measurements exist showing such a relationship.
Cells preferentially grow on rigid substrates, as illustrated here. On the left we see a confluent layer of cells covering a 256 micron x 256 micron island of ridid PDMS (left), while the continuous regions of soft PDMS are vacant. We see similar behavior for slightly smaller islands, shown on the right (128 microns x 128 microns).
To explore the prestress mechanism of cell elasticity we have cultured adherent cos-7 cells on PDMS substrates with periodic patterns of varying stiffness and constant chemical environment, following the method of Gray, et al.5 We have varied the moduli and the ‘wavelengths’ of the patterned regions, and have observed the expected preferred growth of cells on stiffer regions (see Figure 1).
We will employ magnetic twisting cytometry6 (MTC) to characterize the elasticity of cells plated on a variety of patterned substrates, such as those shown in Figure 2. Traction force measurements on the different regions of patterned substrates of stationary and migrating cells, as well as isolated versus confluent cells, will allow us to search for the conditions under which, and the manner in which, cell elasticity and cytoskeletal prestress are related.
On the left we see a single lane of cells growing on a 64 micron wide strip of stiff PDMS, confined between two 16 micron wide regions of soft PDMS. On the right we see a confluent sheet of cells growing on a 256 micron wide strip of stiff PDMS confined between 16 um wide strips of soft PDMS.
For more information, contact:
Thomas E. Angelini
McKay Laboratory 525
9 Oxford St.
Cambridge, MA 02138
Tel: (617) - 495 - 3705
Fax: (617) - 496 - 3088
angelini@deas.harvard.edu
References:
1. Pelham, R. J., Jr. & Wang, Y. Cell locomotion and focal adhesions are regulated by substrate flexibility. Proc Natl Acad Sci U S A 94, 13661-5 (1997).
2. Harris, A. K., Wild, P. & Stopak, D. Silicone rubber substrata: a new wrinkle in the study of cell locomotion. Science 208, 177-9 (1980).
3. Tan, J. L. et al. Cells lying on a bed of microneedles: an approach to isolate mechanical force. Proc Natl Acad Sci U S A 100, 1484-9 (2003).
4. Wang, N. et al. Cell prestress. I. Stiffness and prestress are closely associated in adherent contractile cells. Am J Physiol Cell Physiol 282, C606-16 (2002).
5. Gray, D. S., Tien, J. & Chen, C. S. Repositioning of cells by mechanotaxis on surfaces with micropatterned Young's modulus. J Biomed Mater Res A 66, 605-14 (2003).
6. Wang, N., Butler, J. P. & Ingber, D. E. Mechanotransduction across the cell surface and through the cytoskeleton. Science 260, 1124-7 (1993).
