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W. Petroll, N. Lakshman, L. Ma; The Response of Corneal Fibroblasts to Changes in Extracellular Matrix Tension is Dependent on Cell Orientation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2989.
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Mechanical stimuli play a key role in regulating growth and function in a variety of cell types. We previously assessed the dynamic response of corneal fibroblasts to alterations in ECM tension parallel to the cell axis. The purpose of this study was to compare the response to changes in ECM tension along different directional axes.
Rabbit and human corneal fibroblasts were plated inside fibrillar collagen matrices. After 18–72 hours, a thin glass microneedle (Femtotip) was inserted into the ECM either parallel or perpendicular to the long axis of the cell (which are bipolar at these time points), and pushed toward the cell to reduce local ECM stress. Time–lapse DIC imaging was performed for 1 hour before and for 2–3 hours after needle micromanipulation. Changes in cell morphology and ECM displacements were assessed using MetaMorph.
Consistent with previous observations by us, pushing the ECM parallel to the cell axis induced rapid shortening (contraction), presumably since existing cellular forces were no longer counterbalanced by ECM tension. Pseudopodial extension (spreading) was then observed at both ends of the cell; the ECM was pulled inward during this secondary spreading. In contrast, compressing the ECM perpendicular to the cell axis had no appreciable effect on cell mechanical activity, with the exception of a few cases in which cell migration appeared to be stimulated. Cell spreading and/or migration generally occurred parallel to the cell axis, and shifts in cell orientation were rarely observed over the time course evaluated.
Overall, the data support a model in which cells respond to matrix perturbations only as needed to maintain constant cytoskeletal tension. Corneal fibroblasts are most sensitive to reductions in matrix stress parallel to the axis of cellular force generation, since this most effectively perturbs the balance between cytoskeletal and matrix tension. In contrast, matrix compression perpendicular to this axis does not significantly alter the balance of forces, and has less impact on cell behavior.
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