Mechanical Behavior In Living Cells Consistent With The Tensegrity Model By Simpson
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The document summarizes a study that experimentally tested the tensegrity model of cell mechanics. The study used oscillatory magnetic twisting cytometry and traction force microscopy to measure cell stiffness and internal stresses. It found that microtubules bear compression within cells and that intracellular prestress is a major determinant of cell deformability, consistent with the predictions of the tensegrity model. The study provided support for the tensegrity model as a reasonable mechanical description of cells.
Mechanical Behavior In Living Cells Consistent With The Tensegrity Model By Simpson
- 1. Mechanical Behavior in Living Cells Consistent with the Tensegrity Model Ning Wang et al. PNAS 2001; 98:7765-7770 Presented by: David L. Simpson ARTNews- February 1981
- 2. Outline Background and Introduction Methods Results Strengths and Limitations Discussion Topics
- 3. Current Models of Cell Mechanics Simple Mechanical Continuum Porous Filament Gel Tensed Cortical Membrane Tensegrity Model
- 4. Tensegrity Model Continuous and intricate network of tensed and compressed filaments Deformability Depends on level of prestress Prestress dependent on active (actomyosin contractile apparatus) and passive (distension by cell adhesions to the ECM) elements
- 5. Intent of Selected Paper Demonstrate that the cytoskeleton (CSK) behaves as a discrete network of filaments Demonstrate that microtubules behave as compression struts Demonstrate that CSK prestress is a major determinant of cell deformability Experimental confirmation of the a priori predictions of model
- 6. Motivation for Study In vitro experimentation inadequate Limitations of other models suggest the need for a more accurate model which links mechanics to microstructure and molecular biochemistry
- 7. Oscillatory Magnetic Twisting Cytometry Bead Rotation and oscillatory pattern resisted by intrinsic stresses developed by the cell Ratio of specific torque and angular rotation of bead define Complex Elastic Modulus a. G(f) = T(f)/φ(f) b. G(f) = G’(f) + G”(f) Real and imaginary parts J. Appl. Physiol. Vol. 89, Issue 4, 1619-1632, October 2000
- 8. Traction Force Microscopy Cells cultured on flexible ECM-coated, PA gels with fluorescent beads inside Traction at the cell-gel interfaced obtained by solving the problem of Boussinesq using a Fourier transform
- 9. MLC Phosphorylation and Intracellular Calcium Immunoblotting with MLC mAbs Microfluormetric quantitation of intracelluar calcium Fig 3. PNAS 2001; 98:7765-7770
- 10. Internal Cell Deformation Depends on Molecular Connectivity Closed circles: RGD Beads Open circle: AcLDL Beads Fig 1. PNAS 2001; 98:7765-7770
- 11. Microtubules Bear Compression in Living Cells Fig 2. PNAS 2001; 98:7765-7770
- 12. Microtubules Bear Compression in Living Cells Prestress is transferred to external adhesions which increases traction. Fig 5. PNAS 2001; 98:7765-7770
- 13. Quantitative Measurements Support the Tensegrity Model Prestress as a function of histamine and colchicine concentration Shear Modulus as a function of histamine concentration Shear modulus as a function of prestress. Notice the linear relationship over specified range Fig 4. PNAS 2001; 98:7765-7770
- 14. An a priori Prediction Tensegrity predicts that the cells dynamic shear modulus can be decomposed into the product of a prestress-dependent component and a frequency-dependent component Models confirms prediction in that both the storage and loss moduli increase by 70% while hysteresivity coefficient remained constant with increased prestress ( J. of Appl. Physiol . 2000; 89:1619-1632)
- 15. Strengths and Limitations Model is able to accurately model a priori prediction offered by the authors Models and defines prestress as a major player in cell mechanics Tensegrity does not consider viscoelastic forces, thermal motions and polymer. Dynamics Authors find ways to test there predictions buy offer no alternatives to observations For example, the mitochondria moves away from and toward induced forced Is it possible that signaling plays a role as well as polymerization dynamics Focus of this paper is mainly surrounded around microtubules. Not much on other the CSK elements
- 16. Let’s Discuss Let’s look at the most obvious: Is tensegrity a reasonable model? Prestress is a major part of this model, is it accounted for in other models? Are there alternatives for the predictions verified by this model? Adam Smith may describe such a situation by the distribution of labor How would divide the tensegrity model Could more than one model be combined to achieve a final product
- 17. Critics to tensegrity indicate that only local responses occur w/ an induced forced If an advocate, why might these responses be occurring If a critic why does this hurt the concept of tensegrity Referring to the famous engineer Rene Descartes, he found the concept of “seeking certainty in an uncertain world.” In other words always ask questions, so…ANY QUESTIONS? Let’s Discuss AND I’M SPENT…THANKS FOR YOUR ATTENTION