Surface and volume modulation of fast deforming cells and organelles – SurVol
Surface and volume modulation of fast deforming cells and organelles
Cells are often described as almost spherical objects. However, the dense environment of the tissues keeps them away from this simple shape. Cells can undergo rapid deformation as they migrate through dense tissue and as they move through blood capillaries. In this project, we propose to study the large deformations of cells, the associated responses and their importance for the migration of immune cells.
Large deformations of cells and organelles
When cells proliferate in a tumor, because the tumor is often encapsulated in a stiff basement membrane, they are compressed by their own growth. Similarly, when cells escape primary tumors, the lack of space in surrounding tissues generates compressive forces that can induce strong deformations of the cell and the nucleus as they migrate. This is also true during physiological proliferation of epithelial cells, leading to crowding effects, or during normal migration of immune cells. Another well-described example of large cell deformation is cells circulating through blood capillaries. In all these examples, the capacity of cells to adapt and survive to large deformations is a key element of physiological and pathological processes. Nevertheless, there is so far very little knowledge on both the physics and the biology of large cell deformations. <br />Why is it important to study large cell deformations? Most studies that involve applying mechanical stresses to cells, such as stretching or AFM, always remain in the range of ~10 to 30% deformation. It is only in recent years that in vivo imaging has revealed that, in a variety of physiological and pathological contexts, cells undergo much larger deformations3, sometimes being squeezed to a tenth of their resting diameter, thus asking for new biophysics and cell biology studies addressing this range of deformation. Cell shape has been traditionally studied as the result of a morphogenetic process, the question being how cells achieve a given shape, and how it is genetically encoded (meaning which genes are needed to achieve this shape). Changes in cell shape and cell morphogenesis can also be viewed as the result of a series of deformations, thus generated from internally or externally applied forces. However, the tools to apply and measure precise forces on cells only emerged a few decades ago. Mechanical studies of biomolecules, cells and tissues have immensely clarified the physical properties of biological matter in the past two decades, but the question of large deformations was mostly left aside. <br />This project aims to integrate the accumulated knowledge in cell mechanics and mechanotransduction to better understand the mechanisms and consequences of large cell deformations, focusing on consequences for fast migrating immune cells. Our overarching aim is to understand how the cell and its organelles adapt and respond to these deformations and identify specific deformation thresholds or rates that elicit specific responses. We foresee important immediate consequences of this fundamental study to understand how immune cells efficiently migrate through dense normal and tumor associated tissues and how they can robustly adapt their gait to the rheology of the various environments they cross. Further impact can be anticipated concerning migrating and circulating tumor cells, but also cells growing in normal or pathological crowded tissues.
AIM 1: Understanding how cell and nuclear integrity are ensured during large deformations
Large shape changes often involve changes in volume or in surface area. But whether cells and nuclei rather effectively behave like sponges (poroelastic balls losing volume when pressed) or like incompressible viscoelastic balls (extending their surface area at constant volume), or even have a negative Poisson ratio (increasing volume upon deformation) is currently unknown. Does the plasma membrane, like the nuclear envelope, also rupture and repair? Because rupture events are most likely due to excessive surface tension, potentially caused by friction of the membrane with the underlying cytoskeleton upon fast deformation, we aim at understanding how surface tension, surface area and volume are coupled. Focusing on the cell surface (actin cortex plus plasma membrane and the nuclear envelope (double membrane plus lamina), we will investigate how cell and nuclear volume and surface modulation ensure survival under large deformations (note that the part on the nucleus is the focus of another grant and we include it here only for coherency of the project). Deformations can be either experimentally imposed using specific devices (2D confinement or flow in a confining channel mimicking a blood capillary), or self-imposed by cells spreading and moving in well-defined environments – this introduces an important parameter: cell adhesion, which can cause self-deformation, but also induces a large number of already well-studied signalling pathways. We will thus systematically compare phenomena observed upon imposed deformation of non-adhesive cells and upon adhesion-mediated self-deformation.
AIM 2: Understanding how fast responses to large deformations allows migration through complex environments
Dendritic cells (DCs) are professional migratory cells, and their function highly depends on their migration capacity. Because they migrate through dense tissues without disrupting them, they constantly have to adapt their shape to the local environment and thus deform their body and their nucleus to very large extents. They display a migration speed of several microns per minute, which means their speed of deformation matches the range in which we observed volume modulation. We will focus on DCs navigating complex environments, and we will ask how they manage to rapidly adapt to the local topography, to be able to efficiently scan a tissue or follow a chemokine gradient, to reach a target (e.g. the closest lymph vessel). We will start from shape adaptation and signalling from the cell cortex and then consider intracellular signalling from deforming organelles. Our aim with this part of the project is to ask how dendritic cells rapidly adapt their migration machinery (acto-myosin), their shape and potentially their volume and surface tension to migrate efficiently through complex environments, potentially involving mechanisms identified in Aim1.
Related to AIM 1.1 : We studied how cell volume changes when cell shape changes. We used a variety of ways to modulate cell shape and we found that what matters is not the shape of the cell but the speed at which the shape changes. Fast shape changes are accompanied by volume changes while slow shape changes happen at constant volume. We found that this is due to a mecano-osmotic coupling occurring at the cell membrane, linking ion fluxes to plasma membrane tension. We also showed that this could explain the fluctuation of volume that we observed in fast migrating immune cells in complex environments such as collagen gels.
Related to AIM 1.2 : We discovered that cell confinement leads to nuclear envelope rupture and to TREX1 dependent DNA damage, eventually inducing a partial EMT and collagen degradation. We showed that in the context of breast cancer, this process could contribute to promote the transition from an in situ to an invasive tumor.
Related to AIM 2.1: We studied the mechanism by which confinement induces changes in cell shape, leading to an amoeboid mode of migration. We identified a novel process related to the formation of stable blebs, based on a sequence of transitions in the physical properties of the acto-myosin cytoskeleton.
Related to AIM 2.2 : We finalized a major piece of work which had been presented as preliminary data when we applied for the project, showing that the cell nucleus and its deformations serve as a ruler/sensor for cell shape, leading to specific cellular responses by activation of the cPLA2 enzyme. We demonstrated the fundamental aspects of this process in HeLa and in dendritic cells and studied it short term effect on cell migration. We are also now finalizing a second part of the study for the longer term effects on dendritic cell behavior. We found that the same nuclear ruler pathway is activated in confined dendritic cells and leads to the production of tolerogenic cells, with a potential relevance in the regulation of autoimmunity.
- AIM 1.1 : Modulation of cell volume upon cell shape changes : discovery of a novel cell surface tension homeostasis mechanism based on a mechano-osmotic coupling at the plasma membrane. An article is currently in revision at ELife and available in bioRxiv (Venkova et al. 2021)
- AIM 1.2 :(not that for this part of the project no funding was asked to ANR). We discovered that nuclear envelope ruptures promote an epithelial to mesenchymal transition and favor an invasive behavior in mammary tumors. Published in Nader et al. Cell, 2021
- AIM 2.1: We developed a novel method to measure the physical properties of the actin cortex in live cells. Published in Laplaud et al. Science Advances 2021. We discovered that a rigidity percolation transition in the actomyosin cortex drives motility and morphogenesis of minimal amoeboid systems, and could consitute the basis of morphogenesis and motility of fast immune cells. An article is in preparation (Garcia Arcos et al.)
- AIM 2.2 : We discovered that the nucleus senses cell deformation and adapts the cell motile machinery to the environment. Published in Lomakin et al. Science, 2020
- AIM 2.2 : We discovered that nuclear deformations, in dendritic cells, induce a tolerogenic maturation process, via the activation of the nuclear ruler/cPLA2 pathway. An article is in preparation. (Alraies et al.).
1. Laplaud V, … Lennon-Duménil AM, …, Piel M, Heuvingh J. Pinching the cortex of live cells reveals thickness instabilities caused by myosin II motors. Sci Adv. 2021
2. Lomakin AJ, …, Lennon-Duménil AM, …, Piel M. The nucleus acts as a ruler tailoring cell responses to spatial constraints. Science. 2020
3. Dolega, M. E., …, Recho, P., & Cappello, G. (2021). Extracellular matrix in multicellular aggregates acts as a pressure sensor controlling cell proliferation and motility. Elife, 10, e63258
4. Rivera C, …, Lennon-Duménil AM*. Epithelial Colonization promotes the Functional Diversification of Gut Dendritic Cells. Immunity, Accepted in Principle
5. Venkova L, …, Piel M. A mechano-osmotic feedback couples cell volume to the rate of cell deformation. 2021. bioRxiv. In revision at ELife
6. Nader GPF, … Piel M. Compromised nuclear envelope integrity drives TREX1-dependent DNA damage and tumor cell invasion. Cell. 2021
Cells are often depicted as irregular spherical objects, however, the dense environment of tissues pushes them very far from this simple shape. Large cell deformations can result from cell crowding in epithelia and tumours, from cell migration through dense tissues and from circulation in blood capillaries. However, very little is known about the physics or biology of such large cell deformations. Our preliminary experiments show that most cells survive surprisingly well even when deformed to a tenth of their resting diameter in less than a second, and that large deformations induce fast, time-delimited cell responses, such as volume loss and activation of myosin contractility. In this project, we propose to establish the physical principles and biological mechanisms that enable cells to undergo and survive large deformations. We then propose investigating the fast cell responses to deformation and their consequences for immune cells navigating through complex and dense tissues.
Project coordination
Matthieu PIEL (INSTITUT CURIE - SECT DE RECHERCHE)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partner
IC INSTITUT CURIE - SECT DE RECHERCHE
LJP Laboratoire Jean PERRIN
LIPHY Laboratoire Interdisciplinaire de Physique
IC INSTITUT CURIE - SECT DE RECHERCHE
Help of the ANR 656,280 euros
Beginning and duration of the scientific project:
December 2019
- 36 Months
