Mechano-signalling: force transmission from the membrane down to the nucleus
The 2021 Nobel prize celebrated the discovery of PIEZO channels in mechano-sensation and mechano-transduction. Mechano-transduction appeared around the 90s when it was proven that gene expression can be activated by an external mechanical action. However, the mechanisms of force transmission from the outside down to the nucleus are still far from being completely understood. A crucial player is the cell cytoskeleton which interacts with many components of the cell, including the plasma membrane and the nucleus. The mechano-transmission process also involves biochemical signalling as mechanical stress is known to activate mechano-sensitive molecules at various cell locations. Indeed, on the one hand, recent studies have shown the crucial role of mechano-sensitive channels like PIEZO1, located at the plasma membrane, in embryo development or red cell hydration. On the other hand, nuclear envelop components such as lamin A/C are involved in maintaining chromatin organization integrity and cell adaptive response with modified gene expression profile. In this project, we aim at understanding the role of PIEZO1 and lamin A/C at the cellular level in mechano-transduction, and how they impact the cytoskeleton reorganization during the process.
Cell mechanics, mechano-transduction, viscoelasticity, theory and numerical simulations, microfluidics, videomicroscopy, image analysis, machine learning
The links between the mechanical stress at cell surface, the biological response to it, including signalling pathways activated by it, cytoskeleton re-organization and in fine nuclear consequences in terms of chromatin remodelling and gene expression are strongly lacking so far. We aim to understand the process of rapid cytoskeleton meshwork restructuration following cell mechanical stimulation, that leads to efficient mechano-transmission.
Proposed approach (experimental / theoretical / computational)
Fibroblast cell lines with deficient functions in PIEZO1 channel and lamin A/C will be provided by biology collaborators (C. Badens, MMG, Marseille, and Loïc Garçon, HEMATIM, Amiens).
Experiments (CINAM) – Microfluidic experiments on single cells will be conducted to assess cell and nucleus shape, fragility and deformability, and correlate their rheological properties with defects in lamina and PIEZO channel. Respective contributions of the cell components will be discriminated by destabilizing the cytoskeleton or extracting nuclei. Additionally, we will track various fluorescent markers of cellular dynamics (probe of Ca entry, chromatin dye for nucleus integrity) using a high-speed camera sensitive to fluorescence.
Modelling and computing (CPT) – We will apply a rheological model to the experimental data to extract the cell mechanical parameters and build a finite element model to simulate the behavior of different cell phenotypes inside the constrictions.
The project is based on a tight collaboration between the groups of Emmanuèle Helfer, biophysicist at CINaM, and Jean-François Rupprecht, theoretician at CPT, and includes collaborations with biologists C. Badens and L. Garçon, and computational scientist R. Allena (Nice). This interdisciplinary consortium provides a combination of techniques, expertise and knowledge from different scientific fields and cultures. The project involves microfluidic device design and fabrication, cell senescence and ion channel mechanosensitivity characterization, use of high-speed videomicroscopy, development of deep learning image analysis, and interpretation of experimental data using theoretical arguments and numerical simulations. The collaborating groups will continuously interact to confront experimental results and theoretical approaches, leading to establishment of a mechano-transduction model involving PIEZO1 channel, cytoskeleton reorganization and nuclear lamina.
The PhD candidate should preferentially be a physicist with some knowledge in programming. She or he must be motivated to work at the interface of physics and biology as she/he will handle biological samples and perform both experiments and computations.
Is this project the continuation of an existing project or an entirely new one? In the case of an existing project, please explain the links between the two projects
E. Helfer, JF Rupprecht and C. Badens already collaborate to study cell mechanics alterations due to nuclear envelope defects in the frame of premature ageing diseases. The CENTURI project now aims at understanding the transmission process of external mechanical stress down to the nucleus and its chromatin content.
2 to 5 references related to the project
- Cao et al., Chemomechanical model for nuclear morphology and stresses during cell transendothelial migration. Biophysical Journal 111, 1541 (2016).
- Isermann and Lammerding. Nuclear mechanics and mechanotransduction in health and disease. Current Biology 23, R1113 (2013).
- Ranade et al., Piezo2 is the major transducer of mechanical forces for touch sensation in mice. Nature 516, 121 (2014).
- Zeng et al., PIEZOs mediate neuronal sensing of blood pressure and the baroreceptor reflex. Science 362, 464 (2018).
- Zarychanski et al., Mutations in the mechanotransduction protein PIEZO1 are associated with hereditary xerocytosis, Blood 120, 1908 (2012).
3 main publications from each PI over the last 5 years
- A.-A. Varlet, E. Helfer#, and C. Badens#. Molecular and mechanobiological pathways related to the physiopathology of FPLD2. Cells 9, 1947 (2020) – Special Issue ‘Molecular Mechanisms in Metabolic Disease’. Review.
- J. Dupire, P.-H. Puech, E. Helfer, and A. Viallat. Mechanical adaptation of monocytes in model lung capillary networks. Proceedings of the National Academy of Sciences 117, 14798 (2020).
- C. Iss, D. Midou, A. Moreau, D. Held, A. Charrier, S. Mendez, A. Viallat#, and E. Helfer#. Self-organization of red blood cell suspensions under confined 2D flows. Soft Matter 15, 2971 (2019).
- A. P. Le, J.-F. Rupprecht, et al. Adhesion-mediated heterogeneous actin organization governs apoptotic cell extrusion. Nature Communications (2020).
- J. Lohner, J.-F. Rupprecht, et al. Large and reversible myosin-dependent forces in rigidity sensing. Nature Physics 15, 689 (2019).
- A. Singh, J.-F. Rupprecht, et al. Soft inclusion in a confined fluctuating active fluid. Physical Review E 97, 032602 (2018).