1. Stiffness measurement is a biomarker of skin aging in vivo
Runel G, Cario M, Lopez-Ramirez N, Malbouyres M, Ruggiero F, Bernard L, Puisieux A, Caramel J, Chlasta J, Masse I.
Human skin is particularly vulnerable to age‐related deterioration and undergoes profound structural and functional changes, reflected in the external skin appearance. Skin aging is characterized by features such as wrinkling or loss of elasticity. Even if research advances have been done concerning the molecular mechanisms that underlie these changes, very few studies have been conducted concerning the structure stiffness of the skin organ as a whole. In this study, we showed, thanks to human skin reconstructs and the Japanese Medaka fish model, that biomechanics is a new biomarker of skin aging. We revealed that global stiffness measurement by Atomic Force Microscopy, since modulated through aging in these models, can be a new biomarker of skin aging, and reflects the profound reorganization of the dermis extracellular matrix, as shown by Transmission Electron Microscopy. Moreover, our data unveiled that the Japanese Medaka fish could represent a highly relevant integrated model to study skin aging in vivo.
2. Gene profile of zebrafish fin regeneration offers clues to kinetics, organization and biomechanics of basement membrane.
Nauroy P, Guiraud A, Chlasta J, Malbouyres M, Gillet B, Hughes S, Lambert E, Ruggiero F. Matrix Biology
How some animals regenerate missing body parts is not well understood. Taking advantage of the zebrafish caudal fin model, we performed a global unbiased time-course transcriptomic analysis of fin regeneration. Biostatistics analyses identified extracellular matrix (ECM) as the most enriched gene sets. Basement membranes (BMs) are specialized ECM structures that provide tissues with structural cohesion and serve as a major extracellular signaling platform. While the embryonic formation of BM has been extensively investigated, its regeneration in adults remains poorly studied. We therefore focused on BM gene expression kinetics and showed that it recapitulates many aspects of development. As such, the re-expression of the embryonic col14a1a gene indicated that col14a1a is part of the regeneration-specific program. We showed that laminins and col14a1a genes display similar kinetics and that the corresponding proteins are spatially and temporally controlled during regeneration. Analysis of our CRISPR/Cas9-mediated col14a1a knockout fish showed that collagen XIV-A contributes to timely deposition of laminins. As changes in ECM organization can affect tissue mechanical properties, we analyzed the biomechanics of col14a1a-/- regenerative BM using atomic force microscopy (AFM). Our data revealed a thinner BM accompanied by a substantial increase of the stiffness when compared to controls. Further AFM 3D-reconstructions showed that BM is organized as a checkerboard made of alternation of soft and rigid regions that is compromised in mutants leading to a more compact structure. We conclude that collagen XIV-A transiently acts as a molecular spacer responsible for BM structure and biomechanics possibly by helping laminins integration within regenerative BM.
3. Changes in nano-mechanical properties of human epidermal cornified cells depending on their proximity to the skin surface
Milani P, Chlasta J, Abdayem R, Kezic S, Haftek M. J Mol Recognit. 22 mai 2018;e2722.
During formation of the stratum corneum (SC) barrier, terminally differentiated keratinocytes continue their maturation process within the dead superficial epidermal layer. Morphological studies of isolated human corneocytes have revealed differences between cornified envelopes purified from the deep and superficial SC. We used atomic force microscopy to measure the mechanical properties of native human corneocytes harvested by tape‐stripping from different SC depths. Various conditions of data acquisition have been tested and optimized, in order to obtain exploitable and reproducible results. Probing at 200 nN allowed us to investigate the total stiffness of the cells (at 50 nm indentation) and that of the cornified envelopes (at 10 to15 nm), and lipid envelopes (at 5 to 10 nm). The obtained data indicated statistically significant differences between the superficial (more rigid) and deep (softer) corneocytes, thus confirming the existence of depth and maturation‐related morphological changes within the SC. The proposed approach can be potentially used for minimally invasive evaluation of various skin conditions such as aging, skin hydration, and pathologies linked to SC.
4. Variations in basement membrane mechanics are linked to epithelial morphogenesis
Chlasta J, Milani P, Runel G, Duteyrat JL, Arias L, Lamiré LA, Boudaoud A, Grammont M. Development 2017 : doi: 10.1242/dev.152652
The regulation of morphogenesis by the basement membrane (BM) may rely on changes in its mechanical properties. To test this, we developed an atomic force microscopy-based method to measure BM mechanical stiffness during two key processes in Drosophila ovarian follicle development. First, follicle elongation depends on epithelial cells that collectively migrate, secreting BM fibrils perpendicularly to the anteroposterior axis. Our data show that BM stiffness increases during this migration and that fibril incorporation enhances BM stiffness. In addition, stiffness heterogeneity, due to oriented fibrils, is important for egg elongation. Second, epithelial cells change their shape from cuboidal to either squamous or columnar. We prove that BM softens around the squamous cells and that this softening depends on the TGFβ pathway. We also demonstrate that interactions between BM constituents are necessary for cell flattening. Altogether, these results show that BM mechanical properties are modified during development and that, in turn, such mechanical modifications influence both cell and tissue shapes.
5. Stromal protein βig-h3 reprogrammes tumour microenvironment in pancreatic cancer
Goehrig D, Nigri J, Samain R, Wu Z, Cappello P, Gabiane G, Zhang X, Zhao Y, Kim IS, Chanal M, Curto R, Hervieu V, de la Fouchardière C, Novelli F, Milani P, Tomasini R, Bousquet C, Bertolino P, Hennino A.
OBJECTIVE : Pancreatic cancer is associated with an abundant stromal reaction leading to immune escape and tumour growth. This massive stroma drives the immune escape in the tumour. We aimed to study the impact of βig-h3 stromal protein in the modulation of the antitumoural immune response in pancreatic cancer.
DESIGN : We performed studies with p48-Cre;Kras, pdx1-Cre;Kras;Ink4a/Arf , pdx1-Cre;Kras; p53 mice and tumour tissues from patients with pancreatic ductal adenocarcinoma (PDA). Some transgenic mice were given injections of anti-βig-h3, anti-CD8, anti-PD1 depleting antibodies. Tumour growth as well as modifications in the activation of local immune cells were analysed by flow cytometry, immunohistochemistry and immunofluorescence. Tissue stiffness was measured by atomic force microscopy.
RESULTS : We identified βig-h3 stromal-derived protein as a key actor of the immune paracrine interaction mechanism that drives pancreatic cancer. We found that βig-h3 is highly produced by cancer-associated fibroblasts in the stroma of human and mouse. This protein acts directly on tumour-specific CD8+ T cells and F4/80 macrophages. Depleting βig-h3 in vivo reduced tumour growth by enhancing the number of activated CD8+ T cell within the tumour and subsequent apoptotic tumour cells. Furthermore, we found that targeting βig-h3 in established lesions released the tissue tension and functionally reprogrammed F4/80 macrophages in the tumour microenvironment.
CONCLUSIONS : Our data indicate that targeting stromal extracellular matrix protein βig-h3 improves the antitumoural response and consequently reduces tumour weight. Our findings present βig-h3 as a novel immunological target in pancreatic cancer.
6. Mechanical Shielding in Plant Nuclei
Goswami R, Asnacios A, Milani P, Graindorge S, Houlné G, Mutterer J, Hamant O, Chabouté M-E.
In animal cells in culture, nuclear geometry and stiffness can be affected by mechanical cues, with important consequences for chromatin status and
gene expression. This calls for additional investigation into the corresponding physiological relevance in a multicellular context and in different mechanical environments. Using the Arabidopsis root as a model system, and combining morphometry and micro-rheometry, we found that hyperosmotic stress decreases nuclear circularity and size and increases nuclear stiffness in meristematic cells. These changes were accompanied by enhanced expression of touch response genes. The nuclear response to hyperosmotic stress was rescued upon return to iso-osmotic conditions and could even lead to opposite trends upon hypo-osmotic stress. Interestingly, nuclei in a mutant impaired in the functions of the gamma-tubulin complex protein 3 (GCP3) interacting protein (GIP)/MZT1 proteins at the nuclear envelope were almost insensitive to such osmotic changes.
The gip1gip2 mutant exhibited constitutive hyperosmotic stress response with stiffer and deformed nuclei, as well as touch response gene induction.
The mutant was also resistant to lethal hyperosmotic conditions. Altogether, we unravel a stereotypical geometric, mechanical, and genetic nuclear
response to hyperosmotic stress in plants. Our data also suggest that chromatin acts as a gel that stiffens in hyperosmotic conditions and that the nuclear-envelope-associated protein GIPs act as negative regulators of this response.
7. Changes in nano-mechanical properties of human epidermal cornified cells in children with atopic dermatitis
Haftek M, McAleer MA, Jakasa I, Irwin McLean WH, Kezic S, Irvine AD.
Background: Impaired skin barrier is an important etiological factor in atopic dermatitis (AD). The structural protein filaggrin (FLG) plays a major
role in maintenance of the competent skin barrier and its deficiency is associated with enhanced susceptibility to mechanical injury. Here we examined biomechanical characteristics of the corneocytes in children with AD and healthy controls.
Methods: We recruited 20 children with AD and 7 healthy children. They were genotyped for filaggrin gene (FLG) loss-of-function mutations. Stratum corneum was collected from clinically unaffected skin by adhesive tapes. Cell stiffness (apparent elastic modulus, Ea) was determined by atomic force microscopy and filaggrin degradation products (NMF) by liquid chromatography. Skin barrier function was assessed through trans-epidermal water loss (TEWL) and disease severity by the SCORing Atopic Dermatitis (SCORAD) tool.
Results: Corneocytes collected from AD patients showed a decreased elastic modulus which was strongly correlated with NMF and TEWL, but not with SCORAD. As compared with healthy controls, AD patients had reduced TEWL and NMF levels regardless of FLG mutations. NMF was strongly correlated with TEWL.
Conclusion: Our findings demonstrate that AD patients have decreased corneocyte stiffness which correlates with reduced levels of filaggrin degradation products, NMF and skin barrier function. Altered mechanical properties of the corneocytes likely contribute to the loss of mechanical integrity of the SC and to reduced skin barrier function in AD.
8. KATANIN-dependent mechanical properties of the stigmatic cell wall mediate the pollen tube path in Arabidospis
Riglet L, Rozier F, Kodera C, Bovio S, Sechet J, Fobis-Loisy I, Gaude T.
Successful fertilization in angiosperms depends on the proper trajectory of pollen tubes through the pistil tissues to reach the ovules. Pollen tubes first grow within the cell wall of the papilla cells, applying pressure to the cell. Mechanical forces are known to play a major role in plant cell shape by controlling the orientation of cortical microtubules (CMTs), which in turn mediate deposition of cellulose microfibrils (CMFs). Here, by combining imaging, genetic and chemical approaches, we show that isotropic reorientation of CMTs and CMFs in aged Col-0 and katanin1-5 (ktn1-5) papilla cells is accompanied by a tendency of pollen tubes to coil around the papillae. We show that this coiled phenotype is associated with specific mechanical properties of the cell walls that provide less resistance to pollen tube growth. Our results reveal an unexpected role for KTN1 in pollen tube guidance on the stigma by ensuring mechanical anisotropy of the papilla cell wall.