Mitochondrial Mechanics

Mitochondria constantly undergo fission and fusion events. These dynamical processes regulate mitochondrial morphology and are essential for cell physiology. We propose an elastocapillary mechanical instability as a mechanism for mitochondrial fission. We induce mitochondrial fission by rupturing the cell’s plasma membrane with a micropipette. We present a stability analysis that successfully explains the observed fission wavelength and the role of mitochondrial morphology in the occurrence of fission events.

PRL 2015;115:088102. Gonzalez-Rodriguez D, Sart S, Babataheri A, Tareste D, Barakat AI, Clanet C, Husson J. Elastocapillary Instability in Mitochondrial Fission


Mechanics of Endothelial Cells

Characterizing Cell Adhesion

We have developed a technique to quantify cell-substrate adhesion force using micropipette aspiration. We position a micropipette perpendicular to the surface of an adherent cell and we apply a constant-rate aspiration pressure.

Biophys J. 2015; 109(2):209-19. Hogan B, Babataheri A, Hwang Y, Barakat AI, Husson J. Characterizing Cell Adhesion by Using Micropipette Aspiration.


Profile Microindentation

We have developed a system to visualize adherent cells in profile while measuring their mechanical properties using microindentation. We can simultaneously control the cell microenvironment by introducing a micropipette for the delivery of soluble factors or other cell types. This technique can be used to monitor cell mechanical properties and their time evolution as the cell is subjected to external stimuli.

Scientific Reports. 2016;6:21529. Dynamic monitoring of cell mechanical properties using profile microindentation. Guillou L, Babataheri A, Puech P-H, Barakat AI, and Husson J

 


A glass micropipette is modified with a microforge to form a microindenter. The micropipette (left, typically 2 µm in diameter) is dipped into a glass in fusion (right) to form a microbead at its tip.


Mechanics of Cell Injury

We are interested in understanding the mechanics of endothelial cells submitted to large stresses or strains. These situations occur for instance during apposition of a stent on an atherosclerotic plaque, or during the transmigration of a leukocyte across the endothelium. We developed a new type of microindenter that allows us to characterize the rupture of endothelial cell membrane under a compressive force.

Biophysical Journal, 20 Dec 2016; 111(12):2711-2721. D. Gonzalez-Rodriguez*, L. Guillou*, F. Cornat, J. Lafaurie-Janvore, A. Babataheri, E. de Langre, A. I. Barakat, and J. Husson. Mechanical criterion for the rupture of a cell membrane under compression.


In this "magic wand" experiments, endothelial cells are loaded with the calcium probe Fluo-4. Cells are pressed with a glass microindenter, provoking a rupture of their plasma membrane. This induces a large calcium influx from the extracellular medium. This calcium flux then propagates to neighboring cells. Credit: Julien Husson, LadHyX, Ecole Polytechnique.

Endothelial cells are loaded with the calcium probe Fluo-4. The center cell is pressed with a glass microindenter, until its plasma membrane breaks, inducing a large calcium influx from the extracellular medium. This calcium flux then propagates to neighboring cells. Credit: Julien Husson, LadHyX, Ecole Polytechnique.


Leukocyte-Endothelium Interactions

We are interested in understanding the mechanics of leukocytes, endothelial cells, and their interactions. We study these mechanical aspects in different biological contexts : T cell activation and cytotoxic function, and atherosclerosis.  To do so, we use optical microscopy and single-cell micromanipulation techniques that enable us to measure forces, cell stiffnesses, and their changes over time.

 

Mechanics of T Cells

We develop a micropipette force probe that allows us to measure piconewton to nanonewton-forces. We measure forces generated by T lymphocytes in contact with antibody-covered microbeads that mimick antigen presenting cells or targets for cytotoxic T cells. The technique allows us to dissect the mechanical response of leukocytes depending on the engaged receptors and on T cell type and/or modification. This tool also allows probing how leukocytes are sensitive to the mechanical properties of their environment.

Cell. 2016;165(1):100-110. Cytotoxic T cells use mechanical force to potentiate target cell killing. Basu R*, Whitlock BM*, Husson J*, Le Floc’h A, Jin W, Dotiwala F, Giannone G, Hivroz C, Lieberman J, Kam LC, and Huse M. (* co-first authors)


Molecular Biology of the Cell 2016; 27(22): 3574-3582. Guillou L, Babataheri A, Saitakis M, Bohineust A, Dogniaux S, Hivroz C, Barakat AI, and Husson J. T lymphocyte passive deformation is controlled by unfolding of membrane surface reservoirs.


PLoS One. 2011 May 10;6(5):e19680.

Force generation upon T cell receptor engagement.

Husson J, Chemin K, Bohineust A, Hivroz C, Henry N.


Langmuir. 2012 Apr 10;28(14):6106-13. Biomimetic droplets for artificial engagement of living cell surface receptors: the specific case of the T-cell. Bourouina N, Husson J, Hivroz C, Henry N.

Soft Matter. 2011;7:9130-9139. Formation of specific receptor–ligand bonds between liquid interfaces. Bourouina N, Husson J, Waharte F, Pansu RB, Henry N.

Microtubule Mechanics

We are interested in the study of microtubule mechanics. Microtubules are biopolymers that can generate forces when growing or shrinking. Their dynamics can be regulated by specific proteins, but also by the biochemical properties of their environement, such as molecular crowding.


Cell 2012; 148(3):502-14. Laan L, Pavin N, Husson J, Romet-Lemonne G, van Duijn M, López MP, Vale RD, Jülicher F, Reck-Peterson SL, Dogterom M. Cortical dynein controls microtubule dynamics to generate pulling forces that position microtubule asters.

Biophysical Reviews and Letters. 2009; 4:33-44. Husson J, Laan L, Dogterom M. Force-generation by microtubule bundles.

PNAS 2008; 105(26):8920-5. Laan L, Husson J, Munteanu EL, Kerssemakers JW, Dogterom M. Force-generation and dynamic instability of microtubule bundles.

Single-Molecule Mechanics

Cell adhesion involves the formation of specific biological, non-covalent, ligand-receptor bonds. One way to understand the mechanics of these bonds is to pull on them and measure the force necessary to break them. The strength of a bond depends on how fast one pulls on them, a property described by dynamic force spectroscopy theory. We used a micropipette-based device, the Biomembrane Force Probe, to measure the rupture force of streptavidin-biotin single bonds.

Biophys J. 2005; 89(6):4374-81. Pincet F, Husson J. The solution to the streptavidin-biotin paradox: the influence of history on the strength of single molecular bonds.


The Journal of chemical physics 2009; 130(5):051103. Husson J, Dogterom M, Pincet F. Force spectroscopy of a single artificial biomolecule bond: the Kramers’ high-barrier limit holds close to the critical force.

Cellular and Molecular Bioengineering 2008; 1(4):263-275. Gourier C, Jegou A, Husson J, Pincet F. A Nanospring Named Erythrocyte. The Biomembrane Force Probe.

PRE 2008; 77(2 Pt 2):026108. Husson J, Pincet F. Analyzing single-bond experiments: influence of the shape of the energy landscape and universal law between the width, depth, and force spectrum of the bond.