Cell mechanics

T cell mechanics

Principal investigators: K. SENGUPTA

PhD Student: Celine Dinet (2014-2018), Farah Mustafa (2018-2022)

Postdocs: Astrid Wahl (2016-2018), Fabio Manca (2020-2022)

Collaborations: P-H. Puech, Laurent Limozin (LAI, Marseille)

Funding: ERC (SYNINTER 2013-2018), AMU ED 352 PhD grant (Celine Dinet 2014-2017), ATER AMU (Celine Dinet 2018), DOC2AMU PhD grant (Farah Mustafa 2018-2022), CENTURI Post Doc (Fabio Manca 2020-2022).

It is now well established that living cells respond to the mechanics of their microenvironment, and that they exert forces to do so. We have shown that unlike tissue-forming cells, which respond monotonically to increasing environmental stiffness, T cells have a biphasic response when they use their special receptor - the T cell receptor (TCR) - to adhere. Based on observations of the early interaction of T cells with soft and rigid substrates, we show how the mechanics of molecular ligands are amplified at the cellular level. In addition, we measured the weak forces exerted by T cells on ultra-soft substrates at early times - experiments that lay the foundation for a better understanding of T cell mechanics.

A multiphysics approach of cell confined migration

Principal investigator:  E. Helfer

PhD student : Pauline Lahure (2025-2027)

Collaborators: Rachele Allena (LJAD, Nice) ; Slimane Ait-si-Ali (EDC, Paris) ; Jean-Baptiste Manneville & Sylvie Hénon (MSC, Paris)

Funding: ANR MultiPhysC2M (2025-2028)

Mechanobiology studies the response of cells and tissues to their mechanical environment during different biological processes such as carcinogenesis or embryogenesis. Although major advances have made it possible to observe in vitro the behaviour of cells, observations are still often qualitative since it is very difficult to quantify the stresses, strains and mechanical parameters associated with a specific cellular behaviour. Mechanical and mathematical modelling are, therefore, fundamental to explore a large number of scenarios with less time and cost compared to laboratory assays. In this project we focus on cell migration under confinement, a mechanobiological process which can be observed during embryogenesis, immune response or tumor invasion. During confinement, cells migrate through sub-cellular (10–30 µm width) or sub-nuclear (2–10 µm width) pores. The nucleus, which is the largest and stiffest cellular organelle, plays a critical role in confined environments since it may inhibit, and gradually slow down, migration.

Our objective is to study the influence of the cellular and nuclear mechanical properties during migration under confinement. To do so we will develop a sophisticated numerical model coupling both the molecular and the mechanical framework of the migration under confinement process. The model will be fed with experimental data and employed to explore scenarios that are difficult to access in vitro. We will quantify both the stress and strain state in the cell and assess their correlation with the ability (or not) of the cell to migrate through constrictions of different sizes. Thus, our experimental and numerical approaches will not only generate new knowledge, but also pave the way to develop a consistent diagnostic tool to identify pathological cells.

Towards the understanding of tension generation mechanisms in wood

Principal investigators: A. CHARRIER

PhD Student: Aubin Normand (defended)

Collaborations: A. Lereu (Institut Fresnel, Marseille), A. Passian (Oak Ridge National Laboratory, USA), O. Arnould (Laboratoire de Mécanique et Génie Civil, Montpellier), Pépinière expérimentale de l’Etat à Cadarache, NEASPEC GMBH (Allemagne)

Funding: IDEX AMU(2018-2022), PICS CNRS (2019-2022), PhD grant: Aubin Normand (2018-2022)

With 3000 billion trees, wood is one of the most widespread materials on Earth, it is also renewable and biodegradable, and it plays an omnipresent role in the maintenance and shaping of human societies. Its great diversity is expressed in a wide variety of physical and bio-chemical properties giving it different functionalities involved in our daily life, for example operating functions for building, paper or energy... Surprisingly, this diversity is obtained only from three polymers: cellulose, hemicellulose and lignin representing more than 95% of wood constituents. The diversity comes from the arrangement and proportions of these polymers. Trees have a hierarchical structure, i.e. their macroscopic properties and appearances come from their structures at the micro and nanometric scales. This leads to the question of the relationship between chemical distribution, structural organization and physical properties at the nanoscale. How will nanoscale variations influence the overall response of the tree? And conversely how can external action modify the molecular arrangement and associated properties?

A particularly interesting example is the ability of trees to straighten and align themselves with the direction of gravity, to control the angle of growth of branches, or to improve their resistance to wind, while optimizing the proportion of biomass allocated to these functions. Thus, trees have an active motor mechanism, analogous to muscles in animals, in the form of internal stresses generated during secondary (radial) tree growth. In this project, our objective is to provide insight into the mechanisms leading to the creation of these stresses by providing quantitative correlated data on the chemical distribution of the different wood constituents and on the mechanical properties at the cell wall scale.

See the movie: Expérimenter l’avenir : Le bois de tension, matériau renouvelable et biodégradable, Collection AMIDEX, https://www.youtube.com/watch?v=JLDRaEduz1U

Physics of cellular senescence

Principal investigator:  E. Helfer

PhD student: Cécile Jebane (2018-2022)

Collaborators: Catherine Badens (MMG, Marseille, France); Jean-François Rupprecht (CPT, Marseille, France)

Funding: AMIDEX MecaLam (2018-2022)

Cellular aging, named senescence, is a normal process during which cell functions progresseively degrade, until cell death. Senescence can also occur prematurely, for example in laminopathies, genetic diseases associated with mutations in proteins of the lamina, a key component of the nuclear envelope (NE). While the consequences of these diseases are known, the relationship between their severity, mutations and mechanical alterations at the cellular/nuclear level is still unknown. Here, we focused on mechanical alterations specifically related to defects in lamin A/C, one of the components of the lamina. Lamin A/C is a well-established key contributor to nuclear stiffness and its role in nucleus mechanical properties has been extensively studied. However, its impact on whole-cell mechanics has been poorly addressed, particularly concerning measurable physical parameters. In this study, we combined microfluidic experiments with theoretical analyses to quantitatively estimate the whole-cell mechanical properties. This allowed us to characterize the mechanical changes induced in cells by lamin A/C alterations and prelamin A accumulation resulting from atazanavir treatment or lipodystrophy (FPLD2)-associated mutation. Our results reveal an increase in long-time viscosity as a signature of cells affected by lamin A/C alterations. Furthermore, we show that the whole-cell response to mechanical stress is driven not only by the nucleus but also by the nucleo-cytoskeleton links and the microtubule network. The enhanced cell viscosity assessed with our microfluidic assay could serve as a valuable diagnosis marker for lamin-related diseases.

Signalling crosstalk on cell differentiation.

Principal investigator:  E. Helfer

Postdoc: Jack Llewellyn (2022-2023)

Collaborator: Rosana Dono (IBDM, Marseille, France)

Funding: CENTURI postdoctoral fellowship (2022-2023)

Stem cells, capable of differentiating into any tissue in the human body, are an essential tool for studying human development and could hold the key to personalized regenerative treatments. A precise symphony of chemical cues is required to direct the differentiation of these cells. Here, we studied how human-induced pluripotent stem cells (hiPSCs) undergo differentiation in response to inductive signals and how this is modulated by substrates stiffness. We showed that Activin A-induced hiPSC differentiation into mesendoderm and its derivative, definitive endoderm, is enhanced on gel-based substrates softer than glass. The enhanced response was due to changes in tight junction formation and extensive cytoskeletal remodeling. Live imaging  suggests that changes in cell motility and interfacial contacts underlie hiPSC layer reshaping on soft substrates.   Our results provide mechanistic insight into how epithelial mechanics dictate the hiPSC response to chemical signand and a foundation to further investigate the effects of combined mechanical and chemical signalling during early human development.

Substrate stiffness alters layer architecture and biophysics of human induced pluripotent stem cells to modulate their differentiation potential. J. Llewellyn, A. Charrier, R. Cuciniello, E. Helfer, R. Dono. iScience 27, 110557 (2024). https://doi.org/10.1016/j.isci.2024.110557

https://www.inp.cnrs.fr/fr/cnrsinfo/une-touche-de-souplesse-pour-faciliter-la-differenciation-des-cellules-souches