Biophysics of cell adhesion

The mechanical properties of cellular micro-environment has been shown to influence basic cell functions, e.g. cell division, cell differentiation, transcriptional regulation, endocytosis or migration.
Our team focuses on developing new microdevices and approaches to characterize and exploit cell response to mechanical cues:

Characterization of the mechanics of human tissues
We demonstrated in human pituitary gland tissue that the micro-environment is mechanically textured down to the micron scale [2,5].

Fig. 1: Force indentation scan of a human pituitary resection. Color level in kPa

Rigidity patterned substrates
To mimic cell mechanical environment, we developed a grey lithography technique to polymerize UV sensitive hydrogels (WO2013079231,WO2019175177, WO2019166487).
With this technique, micron to millimeter-scaled patterns of rigidity are printed in the hydrogel. With appropriate surface chemistry, the cells move to the stiffer regions of the hydrogel. This technology is used for the basic understanding of cell adhesion and migration with normal and pathological models [3].

Rigidity patterned substrates are presently available for research use thanks to Cell&Soft .

Measurements of intra and extracellular forces
Cells are pulling on the extracellular matrix to probe its mechanical properties. Using traction force microscopy, we measure the stresses the cells exert on the extracellular matrix as a quantification of the strength of the interaction of the cells with their extracellular environment [6,7].
For instance, intercellular adhesions in Human Umbilical Vein Endothelial cells (HUVEC) limit the cell-to-matrix stresses, and HUVEC monolayers loose sensitivity to the mechanical properties of their matrix.

Fig. 3: 100µm diameter island of HUVEC on a soft polyacrylamide hydrogel. The cells pull with smaller forces on the hydrogel when the size of the island increases, leading to smaller deformations of the hydrogel. This size effect is maintained in the présence of Blebbistatin.

Intracellular stresses can also be assessed by the measurement of the deformation of the extracellular matrix. For single-cell, we showed that the stress tensor aligns with acto-myosin filaments at the periphery of the cell. This measurement allows visualizing the places of cellular contraction or dilatation and the anisotropy of cellular intracellular tension.

Fig. 3: 100µm diameter island of HUVEC on a soft polyacrylamide hydrogel. The cells pull with smaller forces on the hydrogel when the size of the island increases, leading to smaller deformations of the hydrogel. This size effect is maintained in the présence of Blebbistatin.

Publications:
[1] S. Palva, P. Joanne, C. Migdal, E. Lopez-Soler, Y. Hovhannisyan, A. Nicolas, and O. Agbulut. Polyacrylamide hydrogels with rigidity-independent surface chemistry show limited long-term maintenance of pluripotency of human induced pluripotent stem cells on soft substrate. ACS Biomat. Sci. Eng., 6:340-351, 2020.
[2] N. Bouchonville and A. Nicolas. Quantification of the elastic properties of soft and sticky materials using AFM. In N. C. Santos and F. A. Carvalho, editors, Meth. Mol. Biol., Atomic Force Microscopy : Methods and Protocols, 281–290, 2019.
[3] C. Migdal and A. Nicolas. De l’intérêt de cultiver des cellules sur des supports mous. Techniques Hospitalières, 768, 2018.
[4] A. Nicolas. Cell adhesion mechanosensitivity, an active biological process. comment on ”cellular mechanosensing of the biophysical microenvironment : A review of the mathematical models of biophysical regulation of cell responses” by bo cheng et al. Phys. Life Rev., 22-23 :123–126, 2017.
[5] N. Bouchonville, M. Meyer, C. Gaude, E. Gay, D. Ratel, and A. Nicolas. AFM mapping of the elastic properties of brain tissue reveals kpa/μm gradients of rigidity. Soft Matter, 12 :6232–6239, 2016.
[6] M. Moussus, C. der Loughian, D. Fuard, M. Courcon, D. Gulino-Debrac, H. Delanoe-Ayari, and A. Nicolas. Intracellular stresses in patterned cell assemblies. Soft Matter, 10 :2414–2423, 2014.
[7] M. Moussus, C. der Loughian, D. Fuard, M. Courçon, D. Gulino Debrac, H. Delanoë-Ayari, and A. Nicolas. Reply to the ’comment on “intracellular stresses in patterned cell assemblies”’ by D. Tambe et al., Soft Matter, 2014, 10, 7681. Soft Matter, 10 :7683–7684, 2014.
[8] B. Ladoux and A. Nicolas. Physical-based principles of cell adhesion mechanosensitivity in tissues. Rep. Prog. Phys., 75 :116601–116626, 2012.
[9] A. Chervin-Pétinot, M. Courçon, S. Almagro, A. Nicolas, A. Grichine, D. Grunwald, M.-H. Prandini, P. Huber, and D. Gulino-Debrac. Epithelial protein lost in neoplasm (eplin) interacts with α-catenin and actin filaments in endothelial cells and stabilizes vascular capillary network in vitro. J. Biol. Chem., 287 :7556–7572, 2012.
[10] P. Robert, A. Nicolas, S. Aranda-Espinoza, P. Bongrand, and L. Limozin. Minimal encounter time and separation determine ligand-receptor binding in cell adhesion. Biophys. J., 100 :2642 – 2651, 2011.
[11] T. Honegger, S. Sarla, O. Lecarme, K. Berton, A. Nicolas, and D. Peyrade. Selective grafting of proteins on janus particles : Adsorption and covalent coupling strategies. Microelectron. Eng., 88 :1852–1855, 2011.
[12] N. Broguière, T. Pinedo Rivera, B. Pépin-Donat, A. Nicolas, and D. Peyrade. Capillary force assembly of giant vesicles on a microstructured substrate. Microelectron. Eng., 88 :1821–1824, 2011.
[13] A. Nicolas, A. Besser, and S. A. Safran. Is the mechanics of cell-matrix adhesion amenable to physical modeling ? JAST, 24 :2203–2214, 2010.
[14] D. Fuard, M. Moussus, C. Tomba, D. Peyrade, and A. Nicolas. Fabrication of three-dimensional structures for the assessment of cell mechanical interactions within cell monolayers. J. Vac. Sci. Technol. B, 28 :C6K1, 2010.
[15] P. F. Lenne and A. Nicolas. Physics puzzles on membrane domains posed by cell biology. Soft Matter, 5 :2841–2848, 2009.
[16] A. Nicolas, A. Besser, and S. A. Safran. Dynamics of cellular focal adhesions on deformable substrates : consequences for cell force microscopy. Biophys. J., 95 :527–539, 2008.
[17] S. A. Safran, A. Nicolas, and U. S. Schwarz. Elastic interactions of biological cells. In W. Gutkowski and T. A. Kowalewski, editors, Mechanics of the 21st century, Proceedings of the 21st International Congress of Theoretical and Applied Mechanics, Warsaw, Poland, 329, 2004.
[18] A. Nicolas and S. A. Safran. Elastic deformations of grafted layers with surface stress. Phys. Rev. E, 69 :051902, 2004.
[19] A. Nicolas, B. Geiger, and S. A. Safran. Cell mechanosensitivity controls the anisotropy of focal adhesions. Proc. Nat. Acad. Sci. USA, 101 :12520–12525, 2004.