vignette|schéma fibronectine Fibronectine est le nom d'une classe de glycoprotéines présente dans la matrice extracellulaire et qui joue un rôle clé dans l'adhésion des cellules à la matrice extracellulaire. Son gène est le FN1 situé sur le chromosome 2 humain. De haut poids moléculaire, ces protéines sont retrouvées sous forme soluble dans le plasma sanguin et dans certains liquides biologiques. Elles sont aussi trouvées, alors sous forme insoluble dans les tissus. Divers types de cellules peuvent in vivo et in vitro (mise en culture) biosynthétiser la fibronectine. C'est le cas en particulier des cellules musculaires, des cellules de Schwann, des cellules de l'épithélium intestinal, des myoblastes, des chondrocytes, des hépatocytes, des fibroblastes et des macrophages. Typologie Deux principales formes de fibronectine sont distinguées qui diffèrent pour leurs structures et leurs fonctions :

la forme plasmatique ;

la form

Novel interventions to recover the regenerative capacity of aged skeletal muscle by targeting the interactions in the stem cell niche

Laura Lukjanenko

The remarkable ability of skeletal muscle to regenerate upon injury is conferred by tissue-resident stem cells called satellite cells. With age, the regenerative capacity of muscle stem cells (MuSCs) dramatically declines. Developing strategies to enhance muscle repair in elderly people is therefore required; in particular to accelerate their recovery from injuries following falls or from surgical interventions affecting muscle tissues. As the causes of MuSC dysfunction with age are multi-systemic, we decided to dissect age-related changes at different levels of the MuSC environment, in order to uncover synergistic ways to restore their regenerative capacities. This thesis describes three major interventions at the extracellular matrix, cell-cell interaction and tissue/systemic level that successfully restored skeletal muscle regeneration in aged mice. Using a proteomic screen, we identified fibronectin as a structural and signaling molecule of the extracellular matrix that is lost in the aged muscle niche. Loss of fibronectin in aged regenerating muscle primarily arises from perturbed cellular turnover of hematopoietic and endothelial cells which were shown to be the major fibronectin producers in muscle upon injury. Our work also uncovered that the function of old MuSCs is impaired by loss of adhesion and cell death by anoikis, and can be rescued by fibronectin treatment both ex vivo and in vivo. At the molecular level, loss of fibronectin is an upstream trigger leading to perturbed MuSC signaling. Fibronectin treatment rescues perturbations of pathways, such as p38 and ERK, that were previously known to be altered in aged MuSCs, as well as the newly discovered age-related perturbations of FAK signaling. Altogether we demonstrated that aging impairs the remodeling of the extracellular matrix of the MuSC niche, and thereby triggers multiple dysfunction of old MuSCs that can be rescued therapeutically. In a second project, we dissected the cellular cross-talk between MuSCs and non-myogenic support cells called Fibro-Adipogenic Progenitors (FAPs). We uncovered that the adipogenic fate of FAPs is tightly correlated to the muscle micro-environment and the myogenic regenerative capacity in different models of regeneration and aging. The function of FAPs and their cross-talk with MuSCs are impaired with age. We identified the secreted protein WISP1 as a paracrine communication factor between FAPs and MuSCs which is perturbed with age. Treating aged mice with WISP1 restored stem cell function and muscle regeneration, highlighting the possibility to target the cross-talk of MuSC with other cells of the niche to ameliorate their function. Our last project identified altered signaling of the small circulating peptide apelin in aged MuSCs through lowered circulating levels of apelin and down-regulation of its receptor APJ in aged MuSCs. We demonstrated that apelin treatment rescued muscle stem cell function and regeneration in aged mice, highlighting that MuSC dysfunction can also be targeted systemically. Taken together, these approaches reveal the multiple possibilities to ameliorate muscle repair by targeting MuSC interactions with their niche. Our results also pave the way to develop integrated therapeutic strategies to boost old MuSC function.

EPFL2016

ADAM17 Promotes Motility, Invasion, and Sprouting of Lymphatic Endothelial Cells

Witold Waldemar Kilarski, Renata Katarzyna Mezyk-Kopec, Melody Swartz

Tumor-associated lymphatic vessels actively participate in tumor progression and dissemination. ADAM17, a sheddase for numerous growth factors, cytokines, receptors, and cell adhesion molecules, is believed to promote tumor development, facilitating both tumor cell proliferation and migration, as well as tumor angiogenesis. In this work we addressed the issue of whether ADAM17 may also promote tumor lymphangiogenesis. First, we found that ADAM17 is important for the migratory potential of immortalized human dermal lymphatic endothelial cells (LEC). When ADAM17 was stably silenced in LEC, their proliferation was not affected, but: (i) single-cell motility, (ii) cell migration through a 3D Matrigel/collagen type I matrix, and (iii) their ability to form sprouts in a 3D matrix were significantly diminished. The differences in the cell motility between ADAM17-proficient and ADAM17-silenced cells were eliminated by inhibitors of EGFR and HER2, indicating that ADAM17-mediated shedding of growth factors accounts for LEC migratory potential. Interestingly, ADAM17 depletion affected the integrin surface expression/functionality in LEC. ADAM17-silenced cells adhered to plastic, type I collagen, and fibronectin faster than their ADAM17-proficient counterparts. The difference in adhesion to fibronectin was abolished by a cyclic RGD peptide, emphasizing the involvement of integrins in the process. Using a soluble receptor array, we identified BIG-H3 among several candidate proteins involved in the phenotypic and behavioral changes of LEC upon ADAM17 silencing. In additional assays, we confirmed the increased expression of BIG-H3, as well as TGF beta 2 in ADAM17-silenced LEC. The antilym-phangiogenic effects of ADAM17 silencing in lymphatic endothelial cells suggest further relevance of ADAM17 as a potential target in cancer therapy.

Public Library Science2015

Integrin-Mediated Adhesion in the Unicellular Holozoan Capsaspora owczarzaki

Omaya Pierre Dudin

In animals, cell-matrix adhesions are essential for cell migration, tissue organization, and differentiation, which have central roles in embryonic development [1-6]. Integrins are the major cell surface adhesion receptors mediating cell-matrix adhesion in animals. They are heterodimeric transmembrane proteins that bind extracellular matrix (ECM) molecules on one side and connect to the actin cytoskeleton on the other [7]. Given the importance of integrin-mediated cell-matrix adhesion in development of multicellular animals, it is of interest to discover when and how this machinery arose during evolution. Comparative genomic analyses have shown that core components of the integrin adhesome pre-date the emergence of animals [8-11]; however, whether it mediates cell adhesion in non-metazoan taxa remains unknown. Here, we investigate cell-substrate adhesion in Capsaspora owczarzaki, the closest unicellular relative of animals with the most complete integrin adhesome [11, 12]. Previous work described that the life cycle of C. owczarzaki (hereafter, Capsaspora) includes three distinct life stages: adherent; cystic; and aggregative [13]. Using an adhesion assay, we show that, during the adherent life stage, C. owczarzaki adheres to surfaces using actin-dependent filopodia. We show that integrin b2 and its associated protein vinculin localize as distinct patches in the filopodia. We also demonstrate that substrate adhesion and integrin localization are enhanced by mammalian fibronectin. Finally, using a specific antibody for integrin b2, we inhibited cell adhesion to a fibronectin-coated surface. Our results suggest that adhesion to the substrate in C. owczarzaki is mediated by integrins. Wethus propose that integrin-mediated adhesion pre-dates the emergence of animals.

CELL PRESS2020