Stress Clamp Experiments on Multicellular Tumor Spheroids

The precise role of the microenvironment on tumor growth is poorly understood. Whereas the tumor is in constant competition with the surrounding tissue, little is known about the mechanics of this interaction. Using a novel experimental procedure, we study quantitatively the effect of an applied mechanical stress on the long-term growth of a spheroid cell aggregate. We observe that a stress of 10 kPa is sufficient to drastically reduce growth by inhibition of cell proliferation mainly in the core of the spheroid. We compare the results to a simple numerical model developed to describe the role of mechanics in cancer progression.Comment: 5 pages, 4 figure

Pi-stacking functionalization through micelles swelling: Application to the synthesis of single wall carbon nanotube/porphyrin complexes for energy transfer

We report on a new, orginal and efficient method for "pi-stacking" functionalization of single wall carbon nanotubes. This method is applied to the synthesis of a high-yield light-harvesting system combining single wall carbon nanotubes and porphyrin molecules. We developed a micelle swelling technique that leads to controlled and stable complexes presenting an efficient energy transfer. We demonstrate the key role of the organic solvent in the functionalization mechanism. By swelling the micelles, the solvent helps the non water soluble porphyrins to reach the micelle core and allows a strong enhancement of the interaction between porphyrins and nanotubes. This technique opens new avenues for the functionalization of carbon nanostructures.Comment: 6 pages, 5 figure

mTORC1 Controls Phase Separation and the Biophysical Properties of the Cytoplasm by Tuning Crowding

International audienceMacromolecular crowding has a profound impact on reaction rates and the physical properties of the cell interior, but the mechanisms that regulate crowding are poorly understood. We developed genetically encoded multimeric nanoparticles (GEMs) to dissect these mechanisms. GEMs are homomultimeric scaffolds fused to a fluorescent protein that self-assemble into bright, stable particles of defined size and shape. By combining tracking of GEMs with genetic and pharmacological approaches, we discovered that the mTORC1 pathway can modulate the effective diffusion coefficient of particles ≥20 nm in diameter more than 2-fold by tuning ribosome concentration, without any discernable effect on the motion of molecules ≤5 nm. This change in ribosome concentration affected phase separation both in vitro and in vivo. Together, these results establish a role for mTORC1 in controlling both the mesoscale biophysical properties of the cytoplasm and biomolecular condensation

Dietary Supplementation with Conjugated Linoleic Acid Plus n-3 Polyunsaturated Fatty Acid Increases Food IntakeBrown Adipose Tissue in Rats

The effect of supplementation with 1% conjugated linoleic acid and 1% n-3 long chain polyunsaturated fatty acids (CLA/n-3) was assessed in rats. Food intake increased with no difference in body weights. White adipose tissue weights were reduced whereas brown adipose tissue and uncoupling protein-1 expression were increased. Plasma adiponectin, triglyceride and cholesterol levels were reduced while leptin, ghrelin and liver weight and lipid content were unchanged. Hypothalamic gene expression measurements revealed increased expression of orexigenic and decreased expression of anorexigenic signals. Thus, CLA/n-3 increases food intake without affecting body weight potentially through increasing BAT size and up-regulating UCP-1 in rats

A simple molecular mechanism explains multiple patterns of cell-size regulation

International audienceIncreasingly accurate and massive data have recently shed light on the fundamental question of how cells maintain a stable size trajectory as they progress through the cell cycle. Microbes seem to use strategies ranging from a pure sizer, where the end of a given phase is triggered when the cell reaches a critical size, to pure adder, where the cell adds a constant size during a phase. Yet the biological origins of the observed spectrum of behavior remain elusive. We analyze a molecular size-control mechanism, based on experimental data from the yeast S. cerevisiae, that gives rise to behaviors smoothly interpolating between adder and sizer. The size-control is obtained from the accumulation of an activator protein that titrates an inhibitor protein. Strikingly, the size-control is composed of two different regimes: for small initial cell size, the size-control is a sizer, whereas for larger initial cell size, it is an imperfect adder, in agreement with recent experiments. Our model thus indicates that the adder and critical size behaviors may just be different dynamical regimes of a single simple biophysical mechanism

Influence de contrainte mécaniques sur le développement du cancer

In 1889, the clinician Stefen Paget came up with the " seed and soil " hypothesis, to explain tumor progression. The seed - the tumor - can only grow in the right soil - the tumor microenvironment. During cancer development, the tumor and the microenvironment are in a constant biochemical crosstalk. We studied during this thesis the seed and soil hypothesis in a mechanical perspective: can the mechanical soil influence tumor progression? We chose an in vitro approach to decouple the biochemistry from the mechanics. We worked with multicellular spheroids, which are small balls of tumor cells that remarkably mimic a tumor. We developed a methodology that enables us to exert mechanical stresses on spheroids, and we studied the influence of such stresses. We show that mechanical stress can indeed have an influence on tumor development. First, the growth rate of a spheroid under mechanical stress is drastically but reversibly reduced. The cells in the center of a spheroid show a decreased volume, and it seems that this volume reduction triggers a proliferation arrest. Second, we show that a cell flow originates from cell division, and that this flow is reduced under mechanical stress. Eventually, we report that a spheroid embedded in a collagen gel invades the latter under mechanical stress. In conclusion, whether mechanical crosstalk restrains or promotes tumor progression, it is an intrinsic element of tumor development, superimposed to the biochemical crosstalk.En 1889, le clinicien Stefen Paget proposa l'hypothèse de " la graine et du terroir " pour expliquer la progression tumorale. La graine - la tumeur - ne peut pousser que dans le bon terroir - le microenvironnement tumoral. Durant le développement du cancer, la tumeur et ce microenvironnement sont en constant dialogue biochimique. Nous nous sommes intéressés durant cette thèse à l'hypothèse de Paget d'un point de vue mécanique : le terroir mécanique peut-il influencer la progression tumorale ? Nous avons choisi une approche in vitro afin de découpler les influences biochimiques et mécaniques. Nous avons travaillé avec des sphéroïdes multicellulaires, petites boules de cellules tumorales qui imitent remarquablement bien une tumeur. Nous avons développé une méthodologie nous permettant d'exercer des contraintes mécaniques sur des sphéroïdes, et nous avons étudié l'influence de telles contraintes. Nous avons montré qu'une contrainte mécanique influence le développement tumoral. Une contrainte mécanique réduit fortement la croissance d'un sphéroïde, et ce de manière réversible. Le volume des cellules au centre est diminué, ce qui semble déclencher un arrêt de la prolifération. Nous avons également montré que la division cellulaire est source de flux cellulaires à l'intérieur d'un sphéroïde, et que ces flux peuvent être inhibés par l'application d'une contrainte. Enfin, nous avons observé qu'une contrainte mécanique peut promouvoir l'envahissement d'une matrice de collagène par un sphéroïde. En conclusion, qu'un dialogue mécanique restreigne la progression tumorale ou la promeuve, il en est un élément intrinsèque

Macromolecular crowding: Sensing without a sensor

International audienceAll living cells are crowded with macromolecules. Crowding can directly modulate biochemical reactions to various degrees depending on the sizes, shapes, and binding affinities of the reactants. Here, we explore the possibility that cells can sense and adapt to changes in crowding through the widespread modulation of biochemical reactions without the need for a dedicated sensor. Additionally, we explore phase separation as a general physicochemical response to changes in crowding, and a mechanism to both transduce information and physically restore crowding homeostasis

Les « systèmes micro-physiologique » : des outils pour modéliser le vivant

National audienceLes "systèmes micro-physiologiques" sont adaptés à l'étude de l'initiation, de la propagation ou du traitement de pathologies telles que le cancer, mais également à des études sur la régénération de tissus, ou à la compréhension d'affections neuronales