Biology subjects

Relaix, F.

Publications and source records attributed to Relaix, F..

16 recordsLinked to original sources

bioRxiv2026

Metabolic Heterogeneity of Muscle Stem Cells is Controlled by the Myofiber Niche

Metabolic pathways support biomass synthesis and provide substrates for epigenetic modifications of histones and DNA. These findings are particularly relevant for adult stem cells, where metabolic changes significantly impact functional behavior. However, assessing the metabolism of these cells in their native microenvironment is challenging as this typically necessitates dissociation prior to metabolic analysis. In this study, we focus on muscle stem cells (MuSCs) and show that removing these cells from the niche significantly alters their metabolic profile. To overcome this issue, we developed a novel enzymatic staining method for in situ metabolic profiling at a single-cell resolution. This approach reveals unexpected metabolic heterogeneity of MuSCs, identifying oxidative and glycolytic subsets, and demonstrates that their metabolism is directly modulated by adjacent myofibers. Accordingly, perturbing myofiber metabolism remodels the MuSC niche and drives metabolic adaptation in MuSCs. Finally, we define the kinetics by which myofiber-dependent metabolic regulation of MuSCs is re-established during muscle regeneration, thereby revealing how niche-imposed metabolic cues shape stem cell identity in vivo.

physiology↗

bioRxiv2026

Postnatal Pax7-expressing limb cells are multipotent and generate non-myogenic lineages that persist into adulthood.

Organs are composed of a complex arrangement of diverse cell types that can originate from independent cell lineages or shared progenitors. Skeletal muscle is derived from mesodermal Pax7+ stem/progenitor cells that can differentiate into myoblasts to form muscle fibers. During embryogenesis, however, somitic Pax7+ cells can also give rise to non-muscle cell types, including dermis and adipocytes. Here, we asked whether Pax7+ cells retain such multipotency during early postnatal growth of limb muscles. Using lineage tracing, we uncovered unexpected plasticity at early postnatal days, leading to the generation of multiple non-myogenic lineages, including a previously unrecognized Pax7-derived subpopulation of fibro-adipogenic progenitors that we termed Pax7FAPs and further investigated. Using mouse models, we further show that Notch signaling primes neonatal Pax7+ cells toward a fibrogenic molecular identity at the expense of myogenic differentiation, thereby biasing their trajectory toward a fibrogenic fate. In the adult muscle, long-term tracing revealed that neonatally produced Pax7FAPs persist into adulthood. In addition, injury in adult muscle triggered de novo generation of Pax7FAPs, which displayed higher proliferative capacity than resident stromal cells. This newfound multipotency of postnatal Pax7+ cells adds a new dimension to our understanding of cellular contributions during postnatal muscle development and regeneration.

developmental biology↗

bioRxiv2025

CRISPR/Cas13-mediated Dynamin 2 reduction therapy in a canine model of DNM2-related centronuclear myopathy

We determined the potential of CRISPR/Cas13 technology as a therapeutic approach for centronuclear myopathies (CNMs) by reducing the expression of a single protein, DNM2. CNMs are severe congenital rare muscle disorders that result in muscle hypotrophy and weakness, with no cure. CNMs frequently result from mutations in either BIN1, MTM1, or DNM2 genes, with DNM2 being a key GTPase that plays a pivotal role in muscle membrane interactions with MTM1 and BIN1. Previous studies indicate that reducing DNM2 transcript expression by half could correct CNM phenotypes regardless the genetic forms, paving the way for a broad-spectrum CNM-therapy. We evaluated CRISPR/Cas13X.1-mediated DNM2 transcript knockdown, as a therapeutic application in a unique naturally-occurring canine CNM model harboring the DNM2R465W/+ mutation, the most frequent pathogenic variant in patients. We show that in vivo intramuscular AAV-mediated CRISPR/Cas13X.1 injections, led to a reduction in DNM2 transcript and protein levels at one and two months post-treatment. Our results demonstrate the feasibility of CRISPR/Cas13-based therapy for CNM in a large animal model, paving the way for advancing this approach towards clinical trials.

molecular biology↗

bioRxiv2025

Muscle stem cells produce a protective Fibrillin-1 matrix to prevent precocious activation.

Multiple biological mechanisms have been uncovered to regulate muscle stem cell quiescence, including inhibition of differentiation, adhesion-dependent anchoring, and translational control, which can be broadly classified as intrinsic or extrinsic properties. Here, we identify the matrix glycoprotein Fibrillin-1 (FBN1) as a Notch-regulated, cell-autonomous effector, essential for maintaining quiescence in muscle stem cells. Known for its causal role in Marfan syndrome (MFS), a connective tissue disorder that also presents with skeletal muscle atrophy, our work positions FBN1 as a critical niche component that protects stem cells from aberrant growth factor signalling. We demonstrate that targeted deletion of Fbn1 in muscle stem cells leads to dose-dependent quiescence defects, characterized by loss of cellular projections, depletion of the stem cell pool, and progressive decline in muscle function. Consistently, human MFS muscle biopsies show abnormally activated satellite cells, implicating stem cell imbalance in the development of MFS-associated myopathy. Mechanistically, the loss of FBN1 upregulates TGF{beta} signalling, and pharmacological inhibition of this pathway using the Angiotensin Receptor blocker losartan restores the cellular and physiological defects of mutant muscles. These findings reveal a new quiescence-preserving mechanism through extracellular matrix-mediated shielding from mitogenic signals, and position stem cell dysfunction as a driver of MFS myopathy. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=159 SRC="FIGDIR/small/666604v1_ufig1.gif" ALT="Figure 1"> View larger version (64K): org.highwire.dtl.DTLVardef@1895e71org.highwire.dtl.DTLVardef@1974e87org.highwire.dtl.DTLVardef@a49979org.highwire.dtl.DTLVardef@5813c9_HPS_FORMAT_FIGEXP M_FIG C_FIG Model of Fibrillin-1 protective barrier in quiescent satellite cells.Satellite cells produce Fibrillin-1 (FBN1) to establish a localized extracellular matrix barrier that limits exposure to mitogenic signals. Mechanistically, FBN1 expression is induced by Notch signalling and serves to sequester latent TGF{beta} complexes in an inactive form, thereby preventing their activation within the immediate niche. This barrier is spatially restricted beneath the basal lamina and remains functionally independent from the abundant interstitial FBN1 produced by fibro-adipogenic progenitors (FAPs). The model describes a self-contained, satellite cell-derived ECM system that maintains quiescence by insulating the cells from activating cues.

cell biology↗

bioRxiv2025

Dual PAX3/7 transcriptional activities spatially encode spinal cell fates through distinct gene networks

Understanding how transcription factors regulate organized cellular diversity in developing tissues remains a major challenge due to their pleiotropic functions. We addressed this by monitoring and genetically modulating the activity of PAX3 and PAX7 during the specification of neural progenitor pools in the embryonic spinal cord. Using mouse models, we show that the balance between the transcriptional activating and repressing functions of these factors is modulated along the dorsoventral axis and is instructive to the patterning of spinal progenitor pools. By combining loss-of-function experiments with functional genomics in spinal organoids, we demonstrate that PAX-mediated repression and activation rely on distinct cis-regulatory genomic modules. This enables both the coexistence of their dual activity in dorsal cell progenitors and the specific control of two major differentiation programs. PAX promotes H3K27me3 deposition at silencers to repress ventral identities, while at enhancers, they act as pioneer factors, opening and activating cis-regulatory modules to specify dorsal-most identities. Finally, we show that this pioneer activity is restricted to cells exposed to BMP morphogens, ensuring spatial specificity. These findings reveal how PAX proteins, modulated by morphogen gradients, orchestrate neuronal diversity in the spinal cord, providing a robust framework for neural subtype specification.

developmental biology↗

bioRxiv2024

Targeted-SMN insufficiency in Skeletal Muscle Stem Cells mediates non-cell autonomous loss of motor neurons at long term

Spinal Muscular Atrophy (SMA) is due to a deficit in SMN protein encoded by the SMN1 gene. SMN-targeted disease modifying treatments have greatly improved the clinical outcomes of this neuromuscular disease. However, uncertainties remain regarding their long-term efficacy and non-neuronal tissue involvement in disease progression. We found that SMA type II patient muscles display a reduced number of quiescent PAX7+ Muscle Stem Cells (MuSC). In SMA mice, we showed that SMN is an important regulator of myogenic progenitor fate during early postnatal growth. In Pax7 Cre-driven conditional knockout mouse models, we demonstrated that high levels of SMN are required to ensure the maintenance of the quiescent MuSC pool in adult muscle. We further established that depletion of SMN-deficient MuSC yielded neuromuscular junctions remodeling followed by a non-cell autonomous loss of motor neurons in the long term. Overall, our findings demonstrate that MuSC are a crucial therapeutic target for SMA treatment. HIGHLIGHTSO_LISMN regulates myogenic lineage progression and quiescent MuSC pool establishment during postnatal growth C_LIO_LIBoth Smn alleles are necessary for the survival of quiescent MuSC in adult muscle C_LIO_LIDepletion of SMN-deficient MuSC leads to NMJ remodeling and non-cell autonomous loss of MN C_LI

pathology↗

bioRxiv2024

Transient hypoxia followed by progressive reoxygenation is required for efficient skeletal muscle repair through Rev-ERBalpha modulation

Muscle stem cells (MuSCs) are essential for skeletal muscle repair. Following injury, MuSCs reside in low oxygen environments until muscle fibers and vascularization are restablished. The dynamics of oxygen levels during the regenerative process and its impact on muscle repair has been underappreciated. We confirm that muscle repair is initiated in a low oxygen environment followed by gradual reoxygenation. Strikingly, when muscle reoxygenation is limited by keeping mice under systemic hypoxia, muscle repair is impaired and leads to the formation of hypotrophic myofibers. In vivo, sustained hypoxia decreases the ability of MuSCs to differentiate and fuse independently of HIF-1. Prolonged hypoxia specifically affects the circadian clock by increasing Rev-erb expression in MuSCs. Using pharmacological tools, we demonstrate that Rev-ERB negatively regulates myogenesis by reducing late myogenic cell fusion under prolonged hypoxia. Our results underscore the critical role of progressive muscle reoxygenation after transient hypoxia in coordinating proper myogenesis through Rev-ERB.

physiology↗

bioRxiv2024

Non-canonical nuclear function of glutaminase cooperates with Wnt signaling to drive EMT during neural crest development

Metabolic reprograming has been linked to epithelial-to-mesenchymal transition (EMT) in cancer cells, but how it influences EMT in normal cells remains largely unknown. Here we explored how metabolism impacts delamination and migration of avian trunk neural crest cells, an important stem cell population of the vertebrate embryo. We report that delamination exhibits a quiescent metabolic phenotype whereas migration is characterized by OXPHOS-driven metabolism coupled to distinct expression of metabolic, EMT and developmental genes. While glucose and glutamine are required for delamination and migration, we uncover a novel role for glutamine and its catabolizing enzyme glutaminase in delamination. Specifically, glutamine is required for nuclear translocation of glutaminase, which interacts and cooperates with Wnt signaling to regulate EMT gene expression and cell cycle during delamination. Our data indicate that similarly to cancer cells, embryonic cells engage metabolic enzymes for non-canonical signaling functions to connect metabolism with EMT.

developmental biology↗

bioRxiv2023

Ambulatory electrocardiographic longitudinal monitoring in dystrophin-deficient dogs identifies decreased Very Low Frequency power as a hallmark of impaired Heart Rate Variability in Duchenne Muscular Dystrophy

BackgroundDuchenne muscular dystrophy (DMD) patients exhibit a late left ventricular systolic dysfunction preceded by an occult phase, during which myocardial fibrosis progresses and some early functional impairments can be detected. These latter include electrocardiographic (ECG) and heart rate variability (HRV) abnormalities. MethodsA longitudinal study aiming at describing the sequence of ECG and HRV abnormalities, relative to cardiac function degradation, using Holter ECG, was performed in the GRMD (Golden retriever muscular dystrophy) dog model, known to develop a DMD-like disease, including cardiomyopathy. ResultsMost of the known ECG and HRV abnormalities described in DMD patients were also found in GRMD dogs, and several of them could be detected months before the decrease of fractional shortening. One of the earliest evidenced abnormalities was a decrease in the very low frequency (VLF) component of the power spectrum, and this decrease was correlated with the further reduction of fractional shortening. Such decreased VLF probably reflects impaired autonomic function and abnormal vasomotor tone. ConclusionThis study provides new insights into the knowledge of the GRMD dog model and DMD cardiomyopathy and emphasizes the interest to monitor the VLF power in DMD patients, still unexplored in this disease, whilst it is highly predictive of deleterious clinical events in many other pathological conditions. Abbreviations

physiology↗

bioRxiv2022

Receptor interacting protein kinase-3 promotes both myopathy and cardiomyopathy in dystrophin-deficient mice

BackgroundDuchenne muscular dystrophy (DMD) is a progressive muscle degenerative disorder, culminating in a complete loss of ambulation, hypertrophic cardiomyopathy and a fatal cardiorespiratory failure. Necroptosis is the form of necrosis that is dependent upon the receptor-interacting protein kinase (RIPK) 3; it is involved in several inflammatory and neurodegenerative conditions. We previously identified RIPK3 as a key player in the acute myonecrosis affecting the hindlimb muscles of the dystrophic mouse model, mdx. Whether necroptosis also mediates respiratory and heart disorders in DMD is currently unknown. MethodsEvidence of activation of the necroptotic axis was examined in dystrophic tissues from Golden retriever muscular dystrophy (GRMD) dogs and R-DMDdel52 rats. A functional assessment of the involvement of necroptosis in dystrophic animals was performed on mdx mice that were genetically depleted for RIPK3. Dystrophic mice aged from 12 to 18 months were analyzed by histology and molecular biology to compare the phenotype of muscles from mdxRipk3+/+ and mdxRipk3-/- mice. Heart function was also examined by echocardiography in 40-week-old mice. ResultsQuantification of RIPK3 transcripts in sartorius and biceps femoris muscles from GRMD dogs positively correlated to myonecrosis levels (r=0.81; p=0.0076). RIPK3 was also found elevated in the diaphragm (p=0<0.05). In the slow progressing heart phenotype of GRMD dogs, the phosphorylated form of RIPK1 at the Serine 161 site was dramatically increased in cardiomyocytes. A similar p-RIPK1 upregulation characterized the cardiomyocytes of R-DMDdel52 rats, associated with a marked overexpression of Ripk1 (p=0.007) and Ripk3 (p=0.008), indicating primed activation of the necroptotic pathway in the dystrophic heart. MdxRipk3-/- mice displayed decreased compensatory hypertrophy of the heart (p=0.014), and echocardiography showed a 19% increase in the relative wall thickness (p<0.05) and 29% reduction in the left ventricle mass (p=0.0144). Besides, mdxRipk3-/- mice presented no evidence of a regenerative default or sarcopenia in skeletal muscles, moreover around 50% less affected by fibrosis (p<0.05). ConclusionsOur data provide evidence of the activation of the necroptotic pathway in degenerative tissues from dystrophic animal models, including the diaphragm and the heart. The genetic inhibition of necroptosis in dystrophic mice improves both cardiac function and histological features of muscles, suggesting that prevention of necroptosis is susceptible to providing multiorgan beneficial effects for DMD.

cell biology↗

bioRxiv2021

Interferon-gamma mediates skeletal muscle lesions through JAK/STAT pathway activation in inclusion body myositis

Dysimmune and Inflammatory Myopathies (DIMs) are acquired idiopathic myopathy associated with immune response dysregulation. Inclusion Body Myositis (IBM), the most common DIMs, is characterized by endomysial infiltrates of cytotoxic T lymphocytes CD8, muscle type II-interferon (IFN{gamma}) signature, and by the lack of response to immunomodulatory therapies. We showed that IBM was pathologically characterized by the presence of chronic degenerative myopathic features including myofiber atrophy, fibrosis, adipose involution, and the altered functions of skeletal muscle stem cells. Here, we demonstrated that protracted systemic exposure to IFN{gamma} delayed muscle regeneration and led to IBM-like muscular degenerative changes in mice. In vitro, IFN{gamma} treatment inhibited the activation, proliferation, migration, differentiation, and fusion of myogenic progenitor cells and promoted their senescence through JAK-STAT-dependent activation. Finally, JAK-STAT inhibitor, ruxolitinib abrogated the deleterious effects of IFN{gamma} on muscle regeneration, suggesting that the JAK-STAT pathway could represent a new therapeutic target for IBM.

cell biology↗

bioRxiv2021

A fast Myh super enhancer dictates adult muscle fiber phenotype through competitive interactions with the fast Myh genes

The contractile properties of adult myofibers are shaped by their Myosin heavy chain (MYH) isoform content. We identify by snATAC-seq a 42kb super-enhancer (SE) at the locus regrouping the fast Myh (fMyh) genes. By 4C-seq we show that active fMyh promoters interact with the SE by DNA looping, leading to the activation of a single promoter per nucleus. A rainbow mouse transgenic model of the locus including the SE recapitulates the endogenous spatio-temporal expression of adult fMyh genes. In situ deletion of the SE by CRISPR/Cas9 editing demonstrates its major role in the control of associated fMyh genes, and deletion of two fMyh genes at the locus reveals an active competition of the promoters for the shared SE. Last, by disrupting the organization of fMyh, we uncover positional heterogeneity within limb skeletal muscles that may underlie selective muscle susceptibility to damage in certain myopathies.

cell biology↗

bioRxiv2020

Direct contribution of skeletal muscle mesenchymal progenitors to bone repair

Tissue regeneration relies on the activation of tissue resident stem cells concomitant with a transient fibrous tissue deposition to allow functional tissue recovery. Bone regeneration involves skeletal stem/progenitors from periosteum and bone marrow, the formation of a fibrous callus followed by the deposition of cartilage and bone to consolidate the fracture. Here, we show that mesenchymal progenitors residing in skeletal muscle adjacent to the bone fracture play a crucial role in mediating the initial fibrotic response to bone injury and also participate in cartilage and bone formation in the fracture callus. Combined lineage and scRNAseq analyses reveal that skeletal muscle mesenchymal progenitors adopt a fibrogenic fate before they engage in a chondrogenic fate after fracture. In polytrauma, where bone and skeletal muscle are injured, skeletal muscle mesenchymal progenitors fail to undergo fibrogenesis and chondrogenesis. This leads to impaired healing and persistent callus fibrosis originating from skeletal muscle. Thus, essential bone-muscle interactions govern bone regeneration through the direct contribution of skeletal muscle as a source of mesenchymal progenitors driving the fibrotic response and fibrotic remodeling, and supporting cartilage and bone formation.

physiology↗

bioRxiv2020

BMP signalling directs a fibroblast-to-myoblast conversion at the connective tissue/muscle interface to pattern limb muscles

Positional information driving limb muscle patterning is contained in lateral plate mesoderm-derived tissues, such as tendon or muscle connective tissue but not in myogenic cells themselves. The long-standing consensus is that myogenic cells originate from the somitic mesoderm, while connective tissue fibroblasts originate from the lateral plate mesoderm. We challenged this model using cell and genetic lineage tracing experiments in birds and mice, respectively, and identified a subpopulation of myogenic cells at the muscle tips close to tendons originating from the lateral plate mesoderm and derived from connective tissue gene lineages. Analysis of single-cell RNA-sequencing data obtained from limb cells at successive developmental stages revealed a subpopulation of cells displaying a dual muscle and connective tissue signature, in addition to independent muscle and connective tissue populations. Active BMP signalling was detected in this junctional cell sub-population and at the tendon/muscle interface in developing limbs. BMP gain- and loss-of-function experiments performed in vivo and in vitro showed that this signalling pathway regulated a fibroblast-to-myoblast conversion. We propose that localised BMP signalling converts a subset of lateral plate mesoderm-derived fibroblasts to a myogenic fate and establishes a boundary of fibroblast-derived myonuclei at the muscle/tendon interface to control the muscle pattern during limb development.

developmental biology↗

bioRxiv2020

Single-nucleus RNA-seq and FISH reveal coordinated transcriptional activity in mammalian myofibers

Skeletal muscle fibers are large syncytia but it is currently unknown whether gene expression is coordinately regulated in their numerous nuclei. By snRNA-seq and snATAC-seq, we showed that slow, fast, myotendinous and neuromuscular junction myonuclei each have different transcriptional programs, associated with distinct chromatin states and combinations of transcription factors. In adult mice, identified myofiber types predominantly express either a slow or one of the three fast isoforms of Myosin heavy chain (MYH) proteins, while a small number of hybrid fibers can express more than one MYH. By snRNA-seq and FISH, we showed that the majority of myonuclei within a myofiber are synchronized, coordinately expressing only one fast Myh isoform with a preferential panel of muscle-specific genes. Importantly, this coordination of expression occurs early during post-natal development and depends on innervation. These findings highlight a unique mechanism of coordination of gene expression in a syncytium.

cell biology↗

bioRxiv2019

Alteration of cardiolipin-dependent mitochondrial coupling in muscle protects against obesity

The tubular shape of mitochondrial cristae depends upon a specific composition of the inner mitochondrial membrane, including cardiolipin that allows strong curvature and promotes optimal organization of ATP synthase. Here we identify Hacd1, which encodes an enzyme involved in very long chain fatty acid biosynthesis, as a key regulator of composition, structure and functional properties of mitochondrial membranes in muscle. In Hacd1-deficient mice, the reduced cardiolipin content was associated with dilation of cristae and caused defective phosphorylating respiration, characterized by absence of proton leak and oxidative stress.\n\nThe skeletal muscle-specific mitochondrial coupling defect produced a global elevation in basal energy expenditure with increased carbohydrate and lipid catabolism, despite decreased muscle mass and locomotor capacities. Mice were protected against diet-induced obesity despite reduced muscle activity, providing an in vivo proof of concept that reducing mitochondrial coupling efficiency in skeletal muscle might be an actionable mechanism in metabolic disease conditions.

cell biology↗