Angiogenesis and full thickness wound repair in a cell sheet-based vascularized skin substitute.

Skin tissue engineering is undergoing tremendous expansion as a result from clinical needs, mandatory replacement of animal models and development of new technologies. Many approaches have been used to produce vascularized skin substitutes for grafting purposes showing the presence of capillary-like structures but with limited analysis of their in vitro maturation and plasticity. Such knowledge is however important for the development of tissue substitutes with improved implantation success as well as for validation of vascularization in vitro models, including as a readout in pharmacological analyses. For optimal interactions of cells with microenvironment and vasculature, we here used a cell sheet approach consisting in the sole production of matrix by the cells. In this context, we limited the density of endothelial cells seeded for self-assembly and rather relied on the stimulation of angiogenesis for the development of an extensive connected microvascular-like network. After detailed characterization of this network, we challenged its plasticity both during and after establishment of the skin substitute. We show that fine tuning of VEGF concentration and time of application differentially affects formation of capillary-like structures and their perivascular coverage. Furthermore, we performed a deep wound assay that displayed tissue repair and angiogenesis with unique characteristics of the physiological process. These studies demonstrate the importance of cell-derived microenvironment for the establishment of mature yet dynamic vascularized skin models allowing a wide range of pharmacological and basic investigations. STATEMENT OF SIGNIFICANCE: The significant advancements in organ-on-chips and tissue engineering call for more relevant models including microvascularization with remodeling potential. While vascularized skin substitutes have been developed for years, focus has primarily been on the impact of microvascularization on implantation rather than on its in vitro characterization. We here developed a cell sheet-based vascularized skin substitute relying on angiogenesis, i.e. growth of vessel-like structures within the 3D model, rather than solely on endothelial cell self-assembly. We then characterized :1/ vascularization after modulation of angiogenic factor VEGF during the substitute construction; -2/ angiogenesis associated to tissue repair after deep mechanical wounding. These studies establish a solid physiologically relevant model for further investigation of skin cell interactions and in vitro wound healing.

Dual topologies of myotomal collagen XV and Tenascin C act in concert to guide and shape developing motor axons.

During development, motor axons are guided toward muscle target by various extrinsic cues including extracellular matrix (ECM) proteins whose identities and cellular source remain poorly characterized. Here, using single-cell RNAseq of sorted GFP+ cells from smyhc1:gfp-injected zebrafish embryos, we unravel the slow muscle progenitors (SMP) pseudotemporal trajectory at the single-cell level and show that differentiating SMPs are a major source of ECM proteins. The SMP core-matrisome was characterized and computationally predicted to form a basement membrane-like structure tailored for motor axon guidance, including basement membrane-associated ECM proteins, as collagen XV-B, one of the earliest core-matrisome gene transcribed in differentiating SMPs and the glycoprotein Tenascin C. To investigate how contact-mediated guidance cues are organized along the motor path to exert their function in vivo, we used microscopy-based methods to analyze and quantify motor axon navigation in tnc and col15a1b knock-out fish. We show that motor axon shape and growth rely on the timely expression of the attractive cue Collagen XV-B that locally provides axons with a permissive soft microenvironment and separately organizes the repulsive cue Tenascin C into a unique functional dual topology. Importantly, bioprinted micropatterns that mimic this in vivo ECM topology were sufficient to drive directional motor axon growth. Our study offers evidence that not only the composition of ECM cues but their topology critically influences motor axon navigation in vertebrates with potential applications in regenerative medicine for peripheral nerve injury as regenerating nerves follow their original path.

Identification of PCPE-2 as the endogenous specific inhibitor of human BMP-1/tolloid-like proteinases.

BMP-1/tolloid-like proteinases (BTPs) are major players in tissue morphogenesis, growth and repair. They act by promoting the deposition of structural extracellular matrix proteins and by controlling the activity of matricellular proteins and TGF-ß superfamily growth factors. They have also been implicated in several pathological conditions such as fibrosis, cancer, metabolic disorders and bone diseases. Despite this broad range of pathophysiological functions, the putative existence of a specific endogenous inhibitor capable of controlling their activities could never be confirmed. Here, we show that procollagen C-proteinase enhancer-2 (PCPE-2), a protein previously reported to bind fibrillar collagens and to promote their BTP-dependent maturation, is primarily a potent and specific inhibitor of BTPs which can counteract their proteolytic activities through direct binding. PCPE-2 therefore differs from the cognate PCPE-1 protein and extends the possibilities to fine-tune BTP activities, both in physiological conditions and in therapeutic settings.

Quantitative Image Analysis of Axonal Morphology in In Vivo Model.

Quantifying axonal branching is crucial for understanding neural circuit function, developmental and regeneration processes and disease mechanisms. Factors that regulate patterns of axonal arborization and tune neuronal circuits are investigated for their implication in various disorders in brain connectivity. The lack of a reliable and user-friendly method makes the quantitative analysis of axon morphology difficult. Specifically, methods to visualize and quantify the complex axon arborization are challenging to implement and apply practically. Our study was aimed at developing a robust but simple method of quantification that used ImageJ 2D analysis and compared it with Imaris visualization and analysis of 3D images. We used zebrafish fluorescent transgenic lines to perform in vivo imaging of developing motor neuron axons that adequately reflected the complexity of axonal networks. Our new method, developed on ImageJ, is easy and fast, giving access to new information such as collateral distribution along the axonal shaft. This study describes step-by-step procedures that can be easily applied to a variety of organisms and in vitro systems. Our study provides a basis for further exploration of neural circuits to gain new insights into neuronal disorders and potential therapeutic interventions.

A mechano- and heat-gated two-pore domain K+ channel controls excitability in adult zebrafish skeletal muscle.

TRAAK channels are mechano-gated two-pore-domain K+ channels. Up to now, activity of these channels has been reported in neurons but not in skeletal muscle, yet an archetype of tissue challenged by mechanical stress. Using patch clamp methods on isolated skeletal muscle fibers from adult zebrafish, we show here that single channels sharing properties of TRAAK channels, i.e., selective to K+ ions, of 56 pS unitary conductance in the presence of 5 mM external K+, activated by membrane stretch, heat, arachidonic acid, and internal alkaline pH, are present in enzymatically isolated fast skeletal muscle fibers from adult zebrafish. The kcnk4b transcript encoding for TRAAK channels was cloned and found, concomitantly with activity of mechano-gated K+ channels, to be absent in zebrafish fast skeletal muscles at the larval stage but arising around 1 mo of age. The transfer of the kcnk4b gene in HEK cells and in the adult mouse muscle, that do not express functional TRAAK channels, led to expression and activity of mechano-gated K+ channels displaying properties comparable to native zebrafish TRAAK channels. In whole-cell voltage-clamp and current-clamp conditions, membrane stretch and heat led to activation of macroscopic K+ currents and to acceleration of the repolarization phase of action potentials respectively, suggesting that heat production and membrane deformation associated with skeletal muscle activity can control muscle excitability through TRAAK channel activation. TRAAK channels may represent a teleost-specific evolutionary product contributing to improve swimming performance for escaping predators and capturing prey at a critical stage of development.

Papillary and reticular fibroblasts generate distinct microenvironments that differentially impact angiogenesis.

Papillary and reticular dermis show distinct extracellular matrix (ECM) and vascularization corresponding to their specific functions. These characteristics are associated with gene expression patterns of fibroblasts freshly isolated from their native microenvironment. In order to assess the relevance of these fibroblast subpopulations in a tissue engineering context, we investigated their contribution to matrix production and vascularization using cell sheet culture conditions. We first performed RNA-seq differential expression analysis to determine whether several rounds of cell amplification and high-density culture affected their gene expression profile. Bioinformatics analysis revealed that expression of angiogenesis-related and matrisome gene signatures were maintained, resulting in papillary and reticular ECMs that differ in composition and structure. The impact of secreted or ECM-associated factors was then assessed using two independent 3D angiogenesis assays: -1/ a fibrin hydrogel-based assay allowing investigation of diffusible secreted factors, -2/ a scaffold-free cell-sheet based assay for investigation of fibroblast-produced microenvironment. These analyses revealed that papillary fibroblasts secrete highly angiogenic factors and produce a microenvironment characterised by ECM remodelling capacity and dense and branched microvascular network, whereas reticular fibroblasts produced more structural core components of the ECM associated with less branched and larger vessels. These features mimick the characteristics of both the ECM and the vasculature of dermis subcompartments. In addition to showing that skin fibroblast populations differentially regulate angiogenesis via both secreted and ECM factors, our work emphasizes the importance of papillary and reticular fibroblasts for engineering and modelling dermis microenvironment and vascularization. STATEMENT OF SIGNIFICANCE: Recent advances have brought to the forefront the central role of microenvironment and vascularization in tissue engineering for regenerative medicine and microtissue modelling. We have investigated the role of papillary and reticular fibroblast subpopulations using scaffold-free cell sheet culture. This approach provides differentiated cells conditions allowing the production of their own microenvironment. Analysis of gene expression profiles and characterisation of the matrix produced revealed strong and specific angiogenic properties that we functionally characterized using 3D angiogenesis models targeting the respective role of either secreted or matrix-bound factors. This study demonstrates the importance of cell-generated extracellular matrix and questions the importance of cell source and the relevance of hydrogels for developing physio-pathologically relevant tissue engineered substitutes.

Cell differentiation and matrix organization are differentially affected during bone formation in osteogenesis imperfecta zebrafish models with different genetic defects impacting collagen type I structure.

Osteogenesis imperfecta (OI) is a family of rare heritable skeletal disorders associated with dominant mutations in the collagen type I encoding genes and recessive defects in proteins involved in collagen type I synthesis and processing and in osteoblast differentiation and activity. Historically, it was believed that the OI bone phenotype was only caused by abnormal collagen type I fibrils in the extracellular matrix, but more recently it became clear that the altered bone cell homeostasis, due to mutant collagen retention, plays a relevant role in modulating disease severity in most of the OI forms and it is correlated to impaired bone cell differentiation. Despite in vitro evidence, in vivo data are missing. To better understand the physiopathology of OI, we used two zebrafish models: Chihuahua (Chi/+), carrying a dominant p.G736D substitution in the α1 chain of collagen type I, and the recessive p3h1-/-, lacking prolyl 3-hydroxylase (P3h1) enzyme. Both models share the delay of collagen type I folding, resulting in its overmodification and partial intracellular retention. The regeneration of the bony caudal fin of Chi/+ and p3h1-/- was employed to investigate the impact of abnormal collagen synthesis on bone cell differentiation. Reduced regenerative ability was evident in both models, but it was associated to impaired osteoblast differentiation and osteoblastogenesis/adipogenesis switch only in Chi/+. On the contrary, reduced osteoclast number and activity were found in both models during regeneration. The dominant OI model showed a more detrimental effect in the extracellular matrix organization. Interestingly, the chemical chaperone 4-phenylbutyrate (4-PBA), known to reduce cellular stress and increase collagen secretion, improved bone formation only in p3h1-/- by favoring caudal fin growth without affecting bone cell markers expression. Taken together, our in vivo data proved the negative impact of structurally abnormal collagen type I on bone formation but revealed a gene mutation-specific effect on bone cell differentiation and matrix organization in OI. These, together with the distinct ability to respond to the chaperone treatment, underline the need for precision medicine approaches to properly treat the disease.

NRF2 Shortage in Human Skin Fibroblasts Dysregulates Matrisome Gene Expression and Affects Collagen Fibrillogenesis.

NRF2 is a master regulator of the antioxidative response that was recently proposed as a potential regulator of extracellular matrix (ECM) gene expression. Fibroblasts are major ECM producers in all connective tissues, including the dermis. A better understanding of NRF2-mediated ECM regulation in skin fibroblasts is thus of great interest for skin homeostasis maintenance and aging protection. In this study, we investigate the impact of NRF2 downregulation on matrisome gene expression and ECM deposits in human primary dermal fibroblasts. RNA-sequencing‒based transcriptome analysis of NRF2 silenced dermal fibroblasts shows that ECM genes are the most regulated gene sets, highlighting the relevance of the NRF2-mediated matrisome program in these cells. Using complementary light and electron microscopy methods, we show that NRF2 deprivation in dermal fibroblasts results in reduced collagen I biosynthesis and impacts collagen fibril deposition. Moreover, we identify ZNF469, a putative transcriptional regulator of collagen biosynthesis, as a target of NRF2. Both ZNF469 silenced fibroblasts and fibroblasts derived from Brittle Corneal Syndrome patients carrying variants in ZNF469 gene show reduced collagen I gene expression. Our study shows that NRF2 orchestrates matrisome expression in human skin fibroblasts through direct or indirect transcriptional mechanisms that could be prioritized to target dermal ECM homeostasis in health and disease.

Superfast excitation-contraction coupling in adult zebrafish skeletal muscle fibers.

The zebrafish has emerged as a very relevant animal model for probing the pathophysiology of human skeletal muscle disorders. This vertebrate animal model displays a startle response characterized by high-frequency swimming activity powered by contraction of fast skeletal muscle fibers excited at extremely high frequencies, critical for escaping predators and capturing prey. Such intense muscle performance requires extremely fast properties of the contractile machinery but also of excitation-contraction coupling, the process by which an action potential spreading along the sarcolemma induces a change in configuration of the dihydropyridine receptors, resulting in intramembrane charge movements, which in turn triggers the release of Ca2+ from the sarcoplasmic reticulum. However, thus far, the fastest Ca2+ transients evoked by vertebrate muscle fibers has been described in muscles used to produce sounds, such as those in the toadfish swim bladder, but not in muscles used for locomotion. By performing intracellular Ca2+ measurements under voltage control in isolated fast skeletal muscle fibers from adult zebrafish and mouse, we demonstrate that fish fast muscle fibers display superfast kinetics of action potentials, intramembrane charge movements, and action potential-evoked Ca2+ transient, allowing fusion and fused sustained Ca2+ transients at frequencies of excitation much higher than in mouse fast skeletal muscle fibers and comparable to those recorded in muscles producing sounds. The present study is the first demonstration of superfast kinetics of excitation-contraction coupling in skeletal muscle allowing superfast locomotor behaviors in a vertebrate.

Lack of the myotendinous junction marker col22a1 results in posture and locomotion disabilities in zebrafish.

The myotendinous junction (MTJ) is essential for the integrity of the musculoskeletal unit. Here, we show that gene ablation of the MTJ marker col22a1 in zebrafish results in MTJ dysfunction but with variable degrees of expression and distinct phenotypic classes. While most individuals reach adulthood with no overt muscle phenotype (class 1), a subset of the progeny displays severe movement impairment and die before metamorphosis (class 2). Yet all mutants display muscle weakness due to ineffective muscle force transmission that is ultimately detrimental for class-specific locomotion-related functions. Movement impairment at the critical stage of swimming postural learning causes class 2 larval death by compromising food intake. In class 1 adults, intensive exercise is required to uncover a decline in muscle performance, accompanied by higher energy demand and mitochondrial adaptation. This study underscores COL22A1 as a candidate gene for myopathies associated with dysfunctional force transmission and anticipates a phenotypically heterogeneous disease.

[The role of extracellular matrix in the regeneration of motor nerves]. / Le rôle de la matrice extracellulaire dans la régénération des nerfs moteurs.

The motor neurons (MN) form the ultimate route to convey the commands from the central nervous system to muscles. During development, MN extend axons that follow stereotyped trajectories to their muscle targets, guided by various attractive and repulsive molecular cues. Extracellular matrix (ECM) is a major source of guidance cues, but its role in axonal development and regeneration remains poorly documented. Regenerating axons are able to return to their synaptic target following their original trajectory. The same guidance cues could be thus involved in motor nerve regeneration. Zebrafish has become a popular model system in understanding the development of the peripheral nervous system. Thanks to the generation of fluorescent transgenic lines and the optical transparency of embryos and larvae, it allows direct visualization of axonogenesis. Additionally, and contrary to humans, its remarkable capacity to regenerate makes it well suited for the study of nerve regeneration. A laser method to ablate nerves in living zebrafish larvae has been developed in our laboratory that, combined with the use of the fluorescent mnx1:gfp zebrafish transgenic line, allows the follow up of the dynamics of the nerve regeneration process. To study the role of ECM proteins present in the axonal path, mutant lines for different ECM proteins (already available in our laboratory or generated in mnx1:gfp fish using CRISPR-Cas9 method) will be used to analyze their role during the regeneration process. These mutant lines for ECM will be crossed with existing fluorescent transgenic lines to visualize different cell types involved in the nerve regeneration, such as macrophages (mfap4:mcherry), neutrophils (mpx:gfp) or even Schwann cells (sox10:mrfp). Overall, this study will depict the role of ECM in nerve regeneration and will provide essential knowledge for the development of new biomaterials to promote the regeneration of injured motor nerves.

FGF-2 promotes angiogenesis through a SRSF1/SRSF3/SRPK1-dependent axis that controls VEGFR1 splicing in endothelial cells.

BACKGROUND: Angiogenesis is the process by which new blood vessels arise from pre-existing ones. Fibroblast growth factor-2 (FGF-2), a leading member of the FGF family of heparin-binding growth factors, contributes to normal as well as pathological angiogenesis. Pre-mRNA alternative splicing plays a key role in the regulation of cellular and tissular homeostasis and is highly controlled by splicing factors, including SRSFs. SRSFs belong to the SR protein family and are regulated by serine/threonine kinases such as SRPK1. Up to now, the role of SR proteins and their regulators in the biology of endothelial cells remains elusive, in particular upstream signals that control their expression. RESULTS: By combining 2D endothelial cells cultures, 3D collagen sprouting assay, a model of angiogenesis in cellulose sponges in mice and a model of angiogenesis in zebrafish, we collectively show that FGF-2 promotes proliferation, survival, and sprouting of endothelial cells by activating a SRSF1/SRSF3/SRPK1-dependent axis. In vitro, we further demonstrate that this FGF-2-dependent signaling pathway controls VEGFR1 pre-mRNA splicing and leads to the generation of soluble VEGFR1 splice variants, in particular a sVEGFR1-ex12 which retains an alternative last exon, that contribute to FGF-2-mediated angiogenic functions. Finally, we show that sVEGFR1-ex12 mRNA level correlates with that of FGF-2/FGFR1 in squamous lung carcinoma patients and that sVEGFR1-ex12 is a poor prognosis marker in these patients. CONCLUSIONS: We demonstrate that FGF-2 promotes angiogenesis by activating a SRSF1/SRSF3/SRPK1 network that regulates VEGFR1 alternative splicing in endothelial cells, a process that could also contribute to lung tumor progression.

A dynamic and mosaic basement membrane controls cell intercalation in Drosophila ovaries.

Basement membranes (BM) are extracellular matrices assembled into complex and highly organized networks essential for organ morphogenesis and function. However, little is known about the tissue origin of BM components and their dynamics in vivo Here, we unravel the assembly and role of the BM main component, Collagen type IV (ColIV), in Drosophila ovarian stalk morphogenesis. Stalks are short strings of cells assembled through cell intercalation that link adjacent follicles and maintain ovarian integrity. We show that stalk ColIV has multiple origins and is assembled following a regulated pattern leading to a unique BM organisation. Absence of ColIV leads to follicle fusion, as observed upon ablation of stalk cells. ColIV and integrins are both required to trigger cell intercalation and maintain mechanically strong cell-cell attachment within the stalk. These results show how the dynamic assembly of a mosaic BM controls complex tissue morphogenesis and integrity.

Design of PEGylated Three Ligands Silica Nanoparticles for Multi-Receptor Targeting.

The synthesis of silica nanoparticles (SiNPs) decorated on their surface with a range of various elements (e.g., ligands, drugs, fluorophores, vectors, etc.) in a controlled ratio remains a big challenge. We have previously developed an efficient strategy to obtain in one-step, well-defined multifunctional fluorescent SiNPs displaying fluorophores and two peptides ligands as targeting elements, allowing selective detection of cancer cells. In this paper, we demonstrate that additional level of controlled multifunctionality can be achieved, getting even closer to the original concept of "magic bullet", using solely sol-gel chemistry to achieve conjugation of PEG chains for stealth, along with three different ligands. In addition, we have answered the recurrent question of the surface ungrafting by investigating the stability of different siloxane linkages with the ERETIC Method (Electronic Reference to Access In Vivo Concentrations) by 19F NMR quantification. We also compared the efficiency of the hybrid silylated fluorophore covalent linkage in the core of the SiNP to conventional methods. Finally, the tumor-cell-targeting efficiency of these multi-ligand NPs on human endothelial cells (HUVEC or HDMEC) and mixed spheroids of human melanoma cells and HUVEC displaying different types of receptors were evaluated in vitro.

Stiffness measurement is a biomarker of skin ageing in vivo.

Human skin is particularly vulnerable to age-related deterioration and undergoes profound structural and functional changes, reflected in the external skin appearance. Skin ageing 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 ageing. We revealed that global stiffness measurement by Atomic Force Microscopy, since modulated through ageing in these models, can be a new biomarker of skin ageing, 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 ageing in vivo.

A collagen Vα1-derived fragment inhibits FGF-2 induced-angiogenesis by modulating endothelial cells plasticity through its heparin-binding site.

Type V collagen (ColV) is a component of the endothelial basement membrane zone. During angiogenesis, extracellular matrix remodelling results in the release of active protein fragments that display pro- or anti-angiogenic properties. The latter often exert their activity through their heparin-binding site. We previously characterized a ColVα1-derived fragment called HEPV that contains a high affinity-binding site for heparin and heparan sulphate chains. Here we show that HEPV binds to FGF2 through its heparin-binding site. Using in vitro and in vivo angiogenesis assays, we show that HEPV but not the HEPV mutant at the heparin-binding site, inhibits FGF2-dependant angiogenesis. On the opposite, HEPV does not bind to VEGFA and has no effect on VEGFA-mediated angiogenesis. In 3D collagen gels, the addition of HEPV abrogates endothelial cell invasion and sprouting induced by FGF2. Interestingly, in vivo experiments reveal that HEPV anti-angiogenic activity is associated with the appearance of endothelial to mesenchymal transition (EndMT) markers. Together, these findings indicate that the ColVα1-derived fragment HEPV functions as an anti-angiogenic factor that represses FGF2-mediated angiogenesis through the regulation of endothelial cell plasticity. Previous observations showing that ColV overexpression negatively regulates pathological angiogenesis were left unexplained. Our data provide insights into the possible molecular mechanisms.

Scavenger Receptor Cysteine-Rich domains of Lysyl Oxidase-Like2 regulate endothelial ECM and angiogenesis through non-catalytic scaffolding mechanisms.

Lysyl oxidases are major actors of microenvironment and extracellular matrix (ECM) remodeling. These cross-linking enzymes are thus involved in many aspects of physiopathology, including tumor progression, fibrosis and cardiovascular diseases. We have already shown that Lysyl Oxidase-Like 2 (LOXL2) regulates collagen IV deposition by endothelial cells and angiogenesis. We here provide evidence that LOXL2 also affects deposition of other ECM components, including fibronectin, thus altering structural and mechanical properties of the matrix generated by endothelial cells. LOXL2 interacts intracellularly and directly with collagen IV and fibronectin before incorporation into ECM fibrillar structures upon exocytosis, as demonstrated by TIRF time-lapse microscopy. Furthermore, surface plasmon resonance experiments using recombinant scavenger receptor cysteine-rich (SRCR) domains truncated for the catalytic domain demonstrated their direct binding to collagen IV. We thus used directed mutagenesis to investigate the role of LOXL2 catalytic domain. Neither enzyme activity nor catalytic domain were necessary for collagen IV deposition and angiogenesis, whereas the SRCR domains were effective for these processes. Finally, surface coating with recombinant SRCR domains restored deposition of collagen IV by LOXL2-depleted cells. We thus propose that LOXL2 SRCR domains orchestrate scaffolding of the vascular basement membrane and angiogenesis through interactions with collagen IV and fibronectin, independently of the enzymatic cross-linking activity.

Collagen XV, a multifaceted multiplexin present across tissues and species.

Type XV collagen is a non-fibrillar collagen that is associated with basement membranes and belongs to the multiplexin subset of the collagen superfamily. Collagen XV was initially studied because of its sequence homology with collagen XVIII/endostatin whose anti-angiogenic and anti-tumorigenic properties were subjects of wide interest in the past years. But during the last fifteen years, collagen XV has gained growing attention with increasing number of studies that have attributed new functions to this widely distributed collagen/proteoglycan hybrid molecule. Despite the cumulative evidence of its functional pleiotropy and its evolutionary conserved function, no review compiling the current state of the art about collagen XV is currently available. Here, we thus provide the first comprehensive view of the knowledge gathered so far on the molecular structure, tissue distribution and functions of collagen XV in development, tissue homeostasis and disease with an evolutionary perspective. We hope that our review will open new roads for promising research on collagen XV in the coming years.

Spatio-temporal expression and distribution of collagen VI during zebrafish development.

Collagen VI (ColVI) is an extracellular matrix (ECM) protein involved in a range of physiological and pathological conditions. Zebrafish (Danio rerio) is a powerful model organism for studying vertebrate development and for in vivo analysis of tissue patterning. Here, we performed a thorough characterization of ColVI gene and protein expression in zebrafish during development and adult life. Bioinformatics analyses confirmed that zebrafish genome contains single genes encoding for α1(VI), α2(VI) and α3(VI) ColVI chains and duplicated genes encoding for α4(VI) chains. At 1 day post-fertilization (dpf) ColVI transcripts are expressed in myotomes, pectoral fin buds and developing epidermis, while from 2 dpf abundant transcript levels are present in myosepta, pectoral fins, axial vasculature, gut and craniofacial cartilage elements. Using newly generated polyclonal antibodies against zebrafish α1(VI) protein, we found that ColVI deposition in adult fish delineates distinct domains in the ECM of several organs, including cartilage, eye, skin, spleen and skeletal muscle. Altogether, these data provide the first detailed characterization of ColVI expression and ECM deposition in zebrafish, thus paving the way for further functional studies in this species.

[Unraveling the pathophysiology of Bethlem Myopathy using a unique zebrafish model for the disease]. / Étude physiopathologique de la myopathie de Bethlem à l'aide d'un modèle de poisson zèbre - 16es JSFM : Prix Master 2018.

Bethlem myopathy (BM) is a neuromuscular disease characterized by joint contractures and muscle weakness. BM is caused by mutations in one of the genes encoding one of the three α-chains of collagen VI (COLVI), a component of the skeletal muscle extracellular matrix. Nowadays, an unresolved question is to understand how alteration of COLVI located outside the muscle cells leads to functional modifications in muscle fibers. The zebrafish model col6a1Δex14 is currently the unique animal model of the disease since it is the only model to reproduce a mutation that is the most frequently found in BM patients. In patient and col6a1Δex14 zebrafish muscles, the structure of the sarcoplasmic reticulum has been found to be altered, thus suggesting dysfunction in intracellular Ca2+ handling and/or in ion channels that are known to control Ca2+ homeostasis and to play pivotal roles in muscle function and pathogenesis. Therefore, our project aims at exploring the properties of ion channels and intracellular Ca2+ regulation using electrophysiological approaches and intracellular Ca2+ measurement at rest and during activity in isolated muscle fibers from col6a1Δex14 zebrafish. On one hand, this project should contribute to decipher how alteration in an extracellular matrix component transduces pathogenic signals within muscle fiber and should possibly lead to identify therapeutic targets for this currently incurable disease. On the other hand, because functional studies on zebrafish muscle cells are scarce, this project will provide a sound database on the electrophysiological properties of this cell model.

TITLE: Étude physiopathologique de la myopathie de Bethlem à l'aide d'un modèle de poisson zèbre - 16es JSFM : Prix Master 2018. ABSTRACT: La myopathie de Bethlem (BM) est une maladie caractérisée par des rétractions et une faiblesse musculaires. Cette pathologie résulte de mutations dans un des gènes codant l'une des trois chaînes α du collagène VI (COLVI), un composant de la matrice extracellulaire musculaire squelettique. Aujourd'hui, une question non résolue est de comprendre comment l'altération de COLVI présent à l'extérieur des cellules musculaires conduit à des modifications fonctionnelles dans les fibres musculaires. Le modèle poisson zèbre col6a1Δex14 est actuellement un modèle animal unique de la BM puisqu'il est le seul à reproduire spécifiquement l'une des mutations la plus fréquemment retrouvée chez les patients. Chez les patients et le poisson col6a1Δex14, la structure du réticulum sarcoplasmique est altérée, suggérant une perturbation de l'homéostasie calcique musculaire et/ou des canaux ioniques qui, en contrôlant cette homéostasie, jouent un rôle crucial dans la fonction et la pathogenèse musculaire. Notre projet vise ainsi à étudier à l'aide de techniques électrophysiologiques et de mesure de Ca2+ les propriétés des canaux ioniques et la régulation du Ca2+ intracellulaire au repos et en activité dans la fibre musculaire du poisson col6a1Δex14. Nos recherches devraient contribuer à mieux comprendre comment la perturbation de la matrice influe sur la fonction musculaire et conduire à terme à identifier des cibles thérapeutiques pour traiter cette maladie actuellement incurable. Enfin, du fait de la rareté des études fonctionnelles sur la cellule musculaire de poisson zèbre, ce projet permettra de constituer une base de données de référence sur les propriétés électrophysiologiques de ce modèle.