Rôle des forces mécaniques au sein de l’épiderme durant la croissance du mélanome cutané

In recent years, many studies have sought to unravel the molecular mechanisms of cutaneous melanoma progression and to find new biomarkers for a better prognosis. However, the current data do not allow a complete understanding of melanoma progression and escape to therapies. The role of the microenvironment, with the remodeling of the extracellular matrix system but also of the immune environment, has been shown to play an important role in tumor progression and escape from control. However, both the biomechanical intrinsic properties of melanoma cells and the biomechanical characteristics related to the change of the microenvironment have not been extensively studied. During my PhD thesis, we have shown a modulation of the intrinsic stiffness of melanoma cells in culture by atomic force microscopy during tumor progression. We also showed that these biomechanical changes were correlated to morphological changes mediated by a reorganization of the cytoskeleton. Moreover, we were able to show that these phenotypic changes were also observed in integrated models such as reconstructed human skins with invasive or non-invasive melanoma and the Medaka fish model. We have also highlighted Tspan8 as an essential player in the modification of the biomechanical and morphological properties of the cells, after induction of expression by the transcription factors regulating the epithelial-to-mesenchymal transition. Finally, we were able to highlight a mechanical signature of melanoma in patients harboring cutaneous melanoma by using a prototype based on micro-indentation of the skin lesion.Au cours des dernières années, de nombreuses études ont cherché à décortiquer les mécanismes moléculaires qui sous-tendent le développement du mélanome cutané et à trouver notamment de nouveaux biomarqueurs permettant un meilleur pronostique. Cependant, les données actuelles ne permettent pas de comprendre dans l’intégralité la progression du mélanome vers des stades invasifs et l’échappement tumoral aux thérapies. Le rôle du micro-environnement, avec le remodelage de la matrice extracellulaire mais aussi de l’environnement immunitaire, a montré un rôle primordial dans ces mécanismes. Cependant les caractéristiques biomécaniques intrinsèques aux cellules cancéreuses et celles liées au changement du microenvironnement n’ont que très peu été étudiées. Au cours de ma thèse, nous avons montré une modulation de la rigidité intrinsèque des cellules par microscopie à force atomique au cours de la progression tumorale sur des cultures de cellules. Nous avons également mis en évidence que ces changements biomécaniques étaient corrélés à des changements morphologiques médiés par une réorganisation du cytosquelette. De plus, nous avons pu montrer que ces changements phénotypiques étaient également observés sur des modèles intégrés de peaux humaines reconstruites avec cellules de mélanome invasif ou non et in vivo dans le modèle de poisson Medaka. Nous avons également mis en évidence la protéine transmembranaire Tétraspanine 8 comme acteur indispensable de la modification des propriétés biomécaniques et morphologiques des cellules, et ce, via la transition phénotypique médiée par des facteurs de transcription de la transition épithélio-mésenchymateuse. Finalement, nous avons pu mettre en avant une signature mécanique des mélanomes cutanés directement chez les patients en utilisant un prototype basé sur la micro-indentation de la lésion cutanée

Biomechanical Properties of Cancer Cells

Since the crucial role of the microenvironment has been highlighted, many studies have been focused on the role of biomechanics in cancer cell growth and the invasion of the surrounding environment. Despite the search in recent years for molecular biomarkers to try to classify and stratify cancers, much effort needs to be made to take account of morphological and nanomechanical parameters that could provide supplementary information concerning tissue complexity adaptation during cancer development. The biomechanical properties of cancer cells and their surrounding extracellular matrix have actually been proposed as promising biomarkers for cancer diagnosis and prognosis. The present review first describes the main methods used to study the mechanical properties of cancer cells. Then, we address the nanomechanical description of cultured cancer cells and the crucial role of the cytoskeleton for biomechanics linked with cell morphology. Finally, we depict how studying interaction of tumor cells with their surrounding microenvironment is crucial to integrating biomechanical properties in our understanding of tumor growth and local invasion

Stem integrity in Arabidopsis thaliana requires a load-bearing epidermis

International audienceABSTRACT Because plant cells are glued to each other via their cell walls, failure to coordinate growth among adjacent cells can create cracks in tissues. Here, we find that the unbalanced growth of inner and outer tissues in the clavata3 de-etiolated3 (clv3 det3) mutant of Arabidopsis thaliana stretched epidermal cells, ultimately generating cracks in stems. Stem growth slowed before cracks appeared along clv3 det3 stems, whereas inner pith cells became drastically distorted and accelerated their growth, yielding to stress, after the appearance of cracks. This is consistent with a key role of the epidermis in restricting growth. Mechanical property measurements recorded using an atomic force microscope revealed that epidermal cell wall stiffness decreased in det3 and clv3 det3 epidermises. Thus, we hypothesized that stem integrity depends on the epidermal resistance to mechanical stress. To formally test this hypothesis, we used the DET3 gene as part of a tissue-specific strategy to complement cell expansion defects. Epidermis-driven DET3 expression restored growth and restored the frequency of stem cracking to 20% of the clv3 det3 mutant, demonstrating the DET3-dependent load-bearing role of the epidermis

Stiffness measurement is a biomarker of skin ageing in vivo

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Gradient in cytoplasmic pressure in germline cells controls overlying epithelial cell morphogenesis

International audienceIt is unknown how growth in one tissue impacts morphogenesis in a neighboring tissue. To address this, we used the Drosophila ovarian follicle, in which a cluster of 15 nurse cells and a posteriorly located oocyte are surrounded by a layer of epithelial cells. It is known that as the nurse cells grow, the overlying epithelial cells flatten in a wave that begins in the anterior. Here, we demonstrate that an anterior to posterior gradient of decreasing cytoplasmic pressure is present across the nurse cells and that this gradient acts through TGFβ to control both the triggering and the progression of the wave of epithelial cell flattening. Our data indicate that intrinsic nurse cell growth is important to control proper nurse cell pressure. Finally, we reveal that nurse cell pressure and subsequent TGFβ activity in the stretched cells combine to increase follicle elongation in the anterior, which is crucial for allowing nurse cell growth and pressure control. More generally, our results reveal that during development, inner cytoplasmic pressure in individual cells has an important role in shaping their neighbors

Cancer Cell Biomechanical Properties Accompany Tspan8-Dependent Cutaneous Melanoma Invasion

The intrinsic biomechanical properties of cancer cells remain poorly understood. To decipher whether cell stiffness modulation could increase melanoma cells’ invasive capacity, we performed both in vitro and in vivo experiments exploring cell stiffness by atomic force microscopy (AFM). We correlated stiffness properties with cell morphology adaptation and the molecular mechanisms underlying epithelial-to-mesenchymal (EMT)-like phenotype switching. We found that melanoma cell stiffness reduction was systematically associated with the acquisition of invasive properties in cutaneous melanoma cell lines, human skin reconstructs, and Medaka fish developing spontaneous MAP-kinase-induced melanomas. We observed a systematic correlation of stiffness modulation with cell morphological changes towards mesenchymal characteristic gains. We accordingly found that inducing melanoma EMT switching by overexpressing the ZEB1 transcription factor, a major regulator of melanoma cell plasticity, was sufficient to decrease cell stiffness and transcriptionally induce tetraspanin-8-mediated dermal invasion. Moreover, ZEB1 expression correlated with Tspan8 expression in patient melanoma lesions. Our data suggest that intrinsic cell stiffness could be a highly relevant marker for human cutaneous melanoma development

Rilpivirine in HIV-1-positive women initiating pregnancy: to switch or not to switch?

International audienceBackgroundSafety data about rilpivirine use during pregnancy remain scarce, and rilpivirine plasma concentrations are reduced during second/third trimesters, with a potential risk of viral breakthroughs. Thus, French guidelines recommend switching to rilpivirine-free combinations (RFCs) during pregnancy.ObjectivesTo describe the characteristics of women initiating pregnancy while on rilpivirine and to compare the outcomes for virologically suppressed subjects continuing rilpivirine until delivery versus switching to an RFC.MethodsIn the ANRS-EPF French Perinatal cohort, we included women on rilpivirine at conception in 2010–18. Pregnancy outcomes were compared between patients continuing versus interrupting rilpivirine. In women with documented viral suppression (<50 copies/mL) before 14 weeks of gestation (WG) while on rilpivirine, we compared the probability of viral rebound (≥50 copies/mL) during pregnancy between subjects continuing rilpivirine versus those switching to RFC.ResultsAmong 247 women included, 88.7% had viral suppression at the beginning of pregnancy. Overall, 184 women (74.5%) switched to an RFC (mostly PI/ritonavir-based regimens) at a median gestational age of 8.0 WG. Plasma HIV-1 RNA nearest delivery was <50 copies/mL in 95.6% of women. Among 69 women with documented viral suppression before 14 WG, the risk of viral rebound was higher when switching to RFCs than when continuing rilpivirine (20.0% versus 0.0%, P = 0.046). Delivery outcomes were similar between groups (overall birth defects, 3.8/100 live births; pregnancy losses, 2.0%; preterm deliveries, 10.6%). No HIV transmission occurred.ConclusionsIn virologically suppressed women initiating pregnancy, continuing rilpivirine was associated with better virological outcome than changing regimen. We did not observe a higher risk of adverse pregnancy outcomes