Stem cells hold great potential in tissue engineering. Future hopes for the regeneration of diseased or damaged tissue lie in part with the use of intricate combinations of scaffolds, growth factors and stem cells. Mimicking natural tissue development in vitro requires appropriate biochemical and topographical cues to be provided in a spatially controlled manner. Our studies utilize nanotopography to influence cellular behaviors, ranging from attachment to proliferation and differentiation – all of which are key processes in tissue engineering.
Much of our research focuses on understanding how cell adhesion, biomechanical and biochemical signals cooperate to allow cells, tissues and ultimately living organisms to adapt to changes in the environment. Mechanical forces are transduced in a multicellular context through multiple means. These include, but are not limited to, mechanosensing through a compliant substratum, cell proliferation, cell-cell and cell-matrix adhesions. By controlling the mechanical and physical properties of the cellular environment, through the use of different micro- and nano-fabrication tools, we aim to understand how these multiple processes allow cells to respond appropriately to their ever-changing environments.
Nuclear morphology and size are emerging as potential mechanistic regulators of genome function and as such forms one of our key areas of investigation. Physical connections bridging the nucleus and cytoplasm govern the size and shape of a pre-stressed eukaryotic nucleus. During the process of cellular differentiation mechanical properties of the nucleus are known to change. Differentiation is known to be governed in part by physical aspects of the microenvironment, which is increasingly linked to gene expression and protein organization, as we and others have shown.
Numerous regulatory interactions occur from the point of detection of a mechanical force to the transduction of this information along a biochemical signaling pathway. The proteins responsible for detecting these forces, such as integrins and cadherins, play a key role in transmitting the information through to the necessary effector molecules that can then elicit a mechanoresponse. We utilize a range of different model systems including bacteria, yeast, C.elegans and human cells to study the various interactions between proteins involved in this cascade of events at cell-cell and cell-matrix adhesions. The results of these studies feed into the development of new paradigms in tissue engineering methods.
Tools of the Trade
The development of several new tools and protocols for measuring cell forces at the molecular level has revolutionized our understanding of how cells can both generate and respond to external forces. This is exemplified by our application of advanced microfluidics to explore the frequency response of single cells subjected to periodically changing environments. Advances in micro- and nanotechnology have also led us to study changes in the mechanical properties of not only individual cells but also molecules. Results from such work will help us better understand the relationship between mechanical properties and cellular functions.
Lim, C.T., S.J. Tan S, W.T. Lim, M.H. Tan. Biomechanics Based Microfluidic Biochip for the Label-free Isolation and Retrieval of Circulating Tumour Cells. European Journal of Cancer; 47, S48(2011)
Hou, H. W., W. C. Lee, M. C. Leong, S. Sonam, S. R. K. Vedula, C.T. Lim .Microfluidics for applications in cell mechanics and mechanobiology. Cellular and Molecular Bioengineering, (2011) [in press]
Cheng-han Yu, Jaslyn Bee Khuan Law, Mona Suryana, Hong Yee Low, Michael P. Sheetz. Early Integrin Binding to RGD Activates Actin Polymerization and Contractile Movement that Stimulates Outward Translocation. PNAS (2011) [in press]
Zhang X., Jiang G., Cai Y., Monkley S.J., Critchley D.R., Sheetz M.P. Talin depletion reveals independence of initial cell spreading from integrin activation and traction. Nat Cell Biol. Sep; 10(9); 1062-8(2008)
Y. Cai, O. Rossier, N. Gauthier, N. Biais, L. W. Miller, M. Fardin, B. Ladoux, V. W. Cornish & M. P. Sheetz. Cytoskeletal coherence depends on myosin IIA contractility. Journal of Cell Science, 123; 413-423 (2010)
B. Ladoux, E. Anon, M. Lambert, A. Rabodzey, P. Hersen, A. Buguin, P. Silberzan & R-M. Mège. Strength dependence of cadherins mediated adhesions. Biophysical Journal , 98, 534-542 (2010)
Evelyn K.F. Yim, Eric M. Darling, Karina Kulangara, Farshid Guilak and Kam W. Leong. Nanotopography-induced changes in focal adhesions, cytoskeletal organization, and mechanical properties of human mesenchymal stem cells. Biomaterials, 31: 1299-1306 (2010)
del Rio A., Perez-Jimenez R., Liu R, Roca-Cusachs P., Fernandez J.M., Sheetz M.P. Stretching single talin rod molecules activates vinculin binding. Science, 323(5914):638-41(2009)
Zhang, C., Zhao, Z., Abdul Rahim, N.A., van Noort, D., and Yu, H. Towards a Human-on-Chip: Culturing Multiple Cell Types on a Chip with Compartmentalized Microenvironments. Lab on a chip, 9(22):3185-3192(2009)
G.V.Shivashankar. Mechanosignaling to cell nucleus and genome regulation. Annual Reviews of Biophysics; 40, 361-378(2011)
Zaidel-Bar R., Joyce M.J., Lynch A.M., Witte K., Audhya A., Hardin J.D. The F-BAR domain of SRGP-1 facilitates cell-cell adhesion during C. elegans morphogenesis. J. Cell. Biol. 191(4);761-769(2010)
Zaidel-Bar R. Evolution of Complexity in the Integrin Adhesome. J. Cell. Biol. 186(3); 317-21(2009)
Yukai Zeng , Tanny Lai , Cheng Gee Koh , Philip R. LeDuc, K.H. Chiam Investigating Circular Dorsal Ruffles through Varying Substrate Stiffness and Mathematical Modeling. Biophysical Journal, 101; 9, 2122-2130, (2011)
C Meghana, Nisha Ramdas, Feroz Hameed, Madan Rao, G.V. Shivashankar & Maithreyi Narasimha. Integrin adhesion drives the emergent polarisation of active cytoskeletal stresses to pattern cell delamination. PNAS, 108; 9107-9112(2011)