Biology subjects

Mounier, R.

Publications and source records attributed to Mounier, R..

14 recordsLinked to original sources

bioRxiv2025

Defective plasticity in dermatomyositis patients muscle stem cells is associated with sustained intrinsic inflammatory signaling and disruption of the histone H3.3 chromatin loading pathway

Skeletal muscle regeneration is driven by muscle stem cells (MuSCs), which proliferate, differentiate and fuse to reform myofibers and restore muscle function. This myogenesis process is driven both by intrinsic MuSC properties and extrinsic cues. While coordinated inflammatory signals are necessary for healthy regeneration, chronic inflammation participates in various pathologies affecting the skeletal muscle. In the idiopathic inflammatory myopathy dermatomyositis (DM), MuSCs exhibit impaired myogenesis in vitro, indicating that they may have acquired intrinsic defects, contributing to the disease and providing a mechanism for sustained patient muscle weakness despite efficient anti-inflammatory treatments. Here, we investigated the transcriptomic regulation of DM-derived MuSCs, with a focus on the H3.3 histone variant which regulates myogenesis progression. DM-derived MuSCs were unable to effectively execute the myogenic transcriptional program during in vitro differentiation. They exhibited an activated canonical TNF- signaling. They also showed reduced expression of H3.3 and its chaperone genes, coupled with a decrease in H3.3 deposition across the entire genome, and particularly at myogenic regulatory factor loci. The loss of H3.3 combined with elevated TNF- signaling was associated with a failure of DM-derived MuSCs to achieve myogenesis, suggesting a mechanistic link between epigenetic dysregulation and defective muscle regeneration in humans.

molecular biology↗

bioRxiv2025

The AMPKa2/PHF2 axis is critical for turning over lipid droplets during muscle stem cell fate

Lipid metabolism is a key process required for muscle stem cell (MuSCs) function during regenerative myogenesis. However, the molecular pathway responsible of such regulation is still unknown. Studies of lysine demethylase PHF2 have reported its critical role in lipid metabolism in pathological processes, although there are no data regarding its role during MuSC fate transition. Here we show that PHF2 controls lipid droplet homeostasis in MuSCs during regenerative myogenesis, by promoting the contact between lipid droplets and mitochondria. Consistently, in absence of PHF2, myocytes accumulate lipid droplets, leading to mitochondrial dysfunction and impaired regeneration. Interestingly, such phenotype is rescued by AMPK2-PHF2 phospho-mimetic mutant expression. Our findings provide evidence that PHF2 is part of AMPK2 signaling and underscore the critical role of AMPK2/PHF2 axis in regulating lipid droplets homeostasis during MuSC fate.

cell biology↗

bioRxiv2024

Macrophage-derived RNAseT2 stimulates muscle stem cell fusion via SLK/N-WASP/actin bundling

Muscle stem cells (MuSCs) fuse to form myofibers to repair skeletal muscle after injury. Within the regenerative MuSC niche, restorative macrophages stimulate MuSC fusion, although the molecular mechanisms involved are largely unknown. Here, we show that restorative macrophages secrete ribonuclease T2 (RNAseT2) to stimulate MuSC fusion. RNAseT2 entered MuSCs via the mannose receptor and induced the formation of actin bundles in MuSCs, enabling cell/cell fusion. Mechanistically, RNAseT2 bound to Ste20-like kinase (SLK), which itself triggered the phosphorylation-mediated activation of N-WASP, through Paxillin phosphorylation, allowing actin bundling necessary for MuSC fusion. In vivo, overexpressing RNAseT2 in regenerating muscle increased fusion in newly formed myofibers in mouse and zebrafish while macrophages deficient for RNAseT2 gene led to fusion defect and smaller myofibers. This study reveals a new function for the highly conserved RNAseT2 and provides a new molecular mechanism by which restorative macrophages support MuSC fusion during muscle repair.

cell biology↗

bioRxiv2024

Immune aging impairs muscle regeneration via macrophage-derived anti-oxidant selenoprotein P

Muscle regeneration is impaired in the aged organism, due to both intrinsic defects of muscle stem cells (MuSCs) and alterations of their environmental niche. However, the latter has still been poorly explored. Here, we compared and analyzed the time course of the various cell types constituting the MuSC niche during muscle generation in young and old mice. Aging altered the amplification of all niche cells with particularly prominent phenotypes in macrophages that impaired the resolution of inflammation in the old regenerating muscle. RNAsequencing of FACs-isolated MuSCs and non-myogenic niche cells during regeneration uncovered specific profiles and kinetics of genes and molecular pathways differentially regulated in old versus young regenerating muscle, indicating that each cell type responded to aging in a specific manner. Through this, we discovered that macrophages have a strong signature of aging with altered the activation of Selenoprotein P (Sepp1) expression in macrophages during the resolution of inflammation in regenerating muscle. Macrophage-specific deletion of Sepp1 gene was sufficient to impair the acquisition of the repair inflammatory profile, perturbed the support of macrophages to MuSCs in vitro and in vivo, and to cause inefficient skeletal muscle regeneration. When transplanted in aged mice, bone marrow from young WT mice, but not Sepp1 KOs, restored muscle regeneration to youthful levels. Altogether this work provides a unique resource to study the aging of the MuSC niche, reveals that aging of niche cells is asynchronous and establishes impaired macrophage dynamics/polarization and the anti-oxidant Selenoprotein P expression as drivers of age-related decline of muscle regeneration. Teaser: Cell profiling reveals asynchronicity of aging in the muscle stem cell niche and age-dependent macrophage/stem cell interactions through anti-oxidant selenoprotein P

physiology↗

bioRxiv2024

Polymeric nanoparticles delivery of AMPK activator 991 prevents its toxicity and improves muscle homeostasis in Duchenne Muscular Dystrophy

Muscular dystrophies, such as Duchenne muscular dystrophy (DMD), are caused by permanent muscle injuries leading to chronic inflammation. In that context, macrophages harbor an altered inflammatory profile that contributes to fibrosis through the secretion of the profibrotic cytokine TGF{beta}1. We previously showed that AMP-activated protein kinase (AMPK) activation reduces TGF{beta}1 secretion by macrophages and improves muscle homeostasis and muscle force in a mouse model of DMD. This makes AMPK an attractive therapeutic target for treating chronic inflammation and fibrosis in DMD. However, potent direct AMPK activators like compound 991 show strong adverse effects in vivo, preventing their direct use. Here, we encapsulated 991 into biodegradable polymeric poly(lactic-co-glycolic) acid (PLGA) nanoparticles for in vivo delivery, in an attempt to overcome toxicity issues. We show that 991-loaded PLGA nanoparticles retained drug activity on fibrotic macrophages in vitro, by reducing their secretion of TGF{beta}1. In the D2-mdx pre-clinical DMD mouse model, intravenously injected PLGA nanoparticles reached gastrocnemius and diaphragm muscles, which are the most affected muscles in this model. Chronic intravenous injections of 991-loaded PLGA nanoparticles decreased inflammation in both muscles, which was associated with fibrosis reduction and increase in myofiber size and muscle mass in the gastrocnemius. No impact on blood cell counts and liver enzymes was observed. These results demonstrate that nanomedicine is an efficient strategy to deliver AMPK activators in vivo to target inflammation and improve the dystrophic muscle phenotype.

pathology↗

bioRxiv2024

Impaired skeletal muscle regeneration induced by Cre recombinase activation in skeletal muscle stem cells

The value of the Cre-lox system in biology is well-recognized, which is reflected by its widespread use to assess the role of a gene in a specific tissue or cell-type. Not in the least, Cre recombinase expressed under the Pax7 promotor has been invaluable for the study of skeletal muscle stem cell (MuSC) biology. In this study, we aimed to systematically assess the effects of the genetic makeup of Pax7Cre mice and Tamoxifen (Tx) treatment on skeletal muscle regeneration. We demonstrate that Tx treatment per se does not affect skeletal muscle regeneration at 14 days post injury (d.p.i.) induced by cardiotoxin, but specifically worsened regeneration in two Pax7CreERT2 lines. Pax7 heterozygosity in Pax7CreERT2(FAN) mice resulted in a lower body mass and Tibialis Anterior (TA) mass, a higher number of fibers per section, and a lower number of Pax7+ cells than in Pax7CreERT2(GAKA) mice, but Tx treatment did not worsen these effects caused by Pax7 haploinsufficiency. In vitro, proliferation of Pax7CreERT2(FAN) MuSCs was impaired after 4-Hydrotamoxifen (4-OHT) treatment, while cell survival and differentiation remained unaffected. Together with a lower number of nuclei per fiber after Tx treatment in Pax7CreERT2(FAN) and male Pax7CreERT2(GAKA) mice, this may suggest an impaired MuSC pool expansion upon Cre activation. Yet, the in vivo MuSC pool was maintained in Pax7Cre mice at 14 d.p.i. Overall, our results directly show that Cre recombinase activity has an off-target effect on MuSCs, which warrants the use of Tx-treated Pax7CreERT2 mice as experimental controls in future studies, and demand caution in interpreting data using other controls in previous studies.

cell biology↗

bioRxiv2024

Metformin protects the heart against chronic intermittent hypoxia through AMPK-dependent phosphorylation of HIF-1α

Chronic intermittent hypoxia (IH), a major feature of obstructive sleep apnea syndrome (OSA), is associated with a more severe myocardial infarction. In this study, we performed RNA sequencing of cardiac samples from mice exposed to IH, which reveals a specific transcriptomic signature of the disease, relative to mitochondrial remodeling and cell death. Corresponding to its activation under chronic IH, we stabilized the Hypoxia Inducible Factor-1 (HIF-1) in cardiac cells in vitro, and observed its association with an increased autophagic flux. In accordance, IH induced autophagy and mitophagy that is decreased in HIF-1+/_ mice compared to wild-type animals suggesting that HIF-1 plays a significant role in IH-induced mitochondrial remodeling. Next, we showed that the AMPK metabolic sensor, typically activated by mitochondrial stress, is inhibited after 3 weeks of IH in hearts. Therefore, we assessed the effect of metformin, an anti-diabetic drug and potent activator of AMPK, on myocardial response to ischemia-reperfusion (I/R) injury. Daily administration of metformin significantly decreases infarct size without any systemic beneficial effect on insulin-resistance under IH conditions. The cardioprotective effect of metformin is lost in AMPK2 knock-out mice demonstrating that AMPK2 isoform promotes metformin-induced cardioprotection in mice exposed to IH. Mechanistically, we found that metformin inhibits IH-induced mitophagy in myocardium and decreases HIF-1 nuclear expression in mice subjected to IH. In vitro demonstrated that metformin induces HIF-1 phosphorylation, decreases its nuclear localization and subsequently HIF-1 transcriptional activity. Collectively, these results identify the AMPK2 metabolic sensor as a novel modulator of HIF-1 activity. Our data suggest that metformin could be considered as a cardioprotective drug in OSA patients independently of their metabolic status.

physiology↗

bioRxiv2023

Alterations of the TGFb-sequestration complex member ADAMTSL1 levels are associated with muscular defects and rhabdomyosarcoma aggressiveness

Rhabdomyosarcoma (RMS) is the most frequent form of paediatric soft-tissue sarcoma and remains a medical challenge, holding in failure current therapeutic strategies. RMS shares histological features with cells of the muscle lineage and this cancer is thought to arise from malignant transformation of myogenic precursors. It has been proposed that RMS and myogenesis could represent the "Jekyll and Hyde" of skeletal muscle. The underlying idea is that some early steps of myogenic differentiation are blocked in RMS, and that understanding how the normal process has gone awry could help to decipher the biological underpinnings of tumorigenesis and tumor escape. It is widely agreed that extracellular matrix (ECM) interferes in skeletal muscle regeneration and that defects in ECM components are clinically significant. The challenge is now to decipher actors and mechanisms responsible for the transmission of signals to muscle cells and the subsequent alterations that could be associated with RMS. Using an original transgenic mice model, we show here that ADAMTSL1 is involved in skeletal muscle regeneration. As previously reported for other members of its family, ADAMTSL1 is part of the TGF-{beta}-ECM-sequestering complex and likely positively regulates TGF-{beta}-pathway activity. Last, we observed that ADAMTSL1 expression behaves as a strong prognostic factor in the aggressive fusion-positive RMS and correlates with a neural-like phenotype of tumor cells, resulting from gain of SMAD2/3/4 targets.

cancer biology↗

bioRxiv2022

AMPKα2 is a skeletal muscle stem cell intrinsic regulator of myonuclear accretion

Due to the post-mitotic nature of skeletal muscle fibers, adult muscle maintenance relies on dedicated muscle stem cells (MuSCs). In most physiological contexts, MuSCs support myofiber homeostasis by contributing to myonuclear accretion, which requires a coordination of cell-type specific events between the myofiber and MuSCs. Here, we addressed the role of the kinase AMPK2 in the coordination of these events supporting myonuclear accretion. We demonstrate that AMPK2 deletion impairs skeletal muscle regeneration. Through in vitro assessments of MuSC myogenic fate and EdU-based cell tracing, we reveal a MuSC-specific role of AMPK2 in the regulation of myonuclear accretion, which is mediated by phosphorylation of the non-metabolic substrate BAIAP2. Similar cell tracing in vivo shows that AMPK2 knockout mice have a lower rate of myonuclear accretion during regeneration, and that MuSC-specific AMPK2 deletion decreases myonuclear accretion in response to myofiber contraction. Together, this demonstrates that AMPK2 is a MuSC-intrinsic regulator of myonuclear accretion.

cell biology↗

bioRxiv2022

Pharmacological inhibition of HDAC6 downregulates TGF-β via Smad2/3 acetylation and improves dystrophin-deficient muscles.

Abstract / SummaryThe absence of dystrophin in Duchenne muscular dystrophy (DMD) disrupts the dystrophin dystroglycan glycoprotein complex (DGC) resulting in fibers fragility and atrophy, associated with fibrosis and microtubules and neuromuscular junction (NMJ) disorganization. The specific non-conventional cytoplasmic histone deacetylase 6 (HDAC6) was previously shown to regulate acetylcholine receptor distribution and muscle atrophy. Here we show that administration of the HDAC6 specific inhibitor tubastatin A to the DMD mouse model mdx improves muscle strength, restores microtubules, NMJ and DGC organization, and reduces muscle atrophy and fibrosis. These effects involve the known action of HDAC6 on microtubules acetylation and muscle atrophy but also involve a yet undiscovered action of HDAC6 on transforming growth factor beta (TGF-{beta}) signaling. Conversely, to inhibitors of nuclear HDACs that regulate TGF-{beta} signaling via the activation of Follistatin expression, HDAC6 inhibition acts downstream of TGF-{beta} ligands and receptors by increasing Smad2/3 acetylation in the cytoplasm which in turn inhibits its phosphorylation and transcriptional activity.

physiology↗

bioRxiv2020

Myofiber / pro-inflammatory macrophage interplay controls muscle damage in mdx mice

Duchenne Muscular Dystrophy is a genetic muscle disease characterized by chronic inflammation and fibrosis, which is mediated by a pro-fibrotic macrophage population expressing pro-inflammatory markers. The aim of this study was to characterize cellular events leading to the alteration of macrophage properties, and to modulate macrophage inflammatory status using the gaseous mediator H2S. We first analyzed the relationship between myofibers and macrophages in the mdx mouse model of Duchenne Muscular Dystrophy using coculture experiments. We showed that normal myofibers derived from mdx mice strongly skewed the polarization of resting macrophages towards a pro-inflammatory phenotype. Treatment of mdx mice with NaHS, an H2S donor, reduced the number of pro-inflammatory macrophages in skeletal muscle, which was associated with a decrease in the number of nuclei per fiber, a reduction of myofiber branching and a reduced fibrosis. These results identify an interplay between myofibers and macrophages where dystrophic myofibers contribute to the maintenance of a highly inflammatory environment that skews the macrophage status, which in turn favors myofiber damage, myofiber branching and fibrosis establishment. They also identify H2S donors as a potential therapeutic strategy to improve dystrophic muscle phenotype by modulating macrophage inflammatory status.

cell biology↗

bioRxiv2020

GREM1 is epigenetically reprogrammed in muscle cells after exercise training and controls myogenesis and metabolism

Exercise training improves skeletal muscle function, notably through tissue regeneration by muscle stem cells. Here, we hypothesized that exercise training reprograms the epigenome of muscle cell, which could account for better muscle function. Genome-wide DNA methylation of myotube cultures established from middle-aged obese men before and after endurance exercise training identified a differentially methylated region (DMR) located downstream of Gremlin 1 (GREM1), which was associated with increased GREM1 expression. GREM1 expression was lower in muscle satellite cells from obese, compared to lean mice, and exercise training restored GREM1 levels to those of control animals. We show that GREM1 regulates muscle differentiation through the negative control of satellite cell self-renewal, and that GREM1 controls muscle lineage commitment and lipid oxidation through the AMPK pathway. Our study identifies novel functions of GREM1 and reveals an epigenetic mechanism by which exercise training reprograms muscle stem cells to improve skeletal muscle function.

cell biology↗

bioRxiv2020

AMPKα1 is essential for Glucocorticoid Receptor triggered anti-inflammatory macrophage activation

SummaryMacrophages are key immune cells which mediate both the acute inflammatory phase and the repair phase after tissue damage. Macrophages switch from pro-inflammatory to anti-inflammatory cells that sustain repair and return to tissue homeostasis. We show that the metabolic sensor, AMP-activated protein kinase (AMPK) is essential for glucocorticoid induction of an anti-inflammatory macrophage phenotype. While canonical gene regulation by glucocorticoids was not affected by loss of AMPK, we identified AMPK-dependent glucocorticoid-regulated genes in macrophages, related to efferocytosis. AMPK-deficient macrophages do not acquire phenotypic and functional anti-inflammatory features upon glucocorticoid exposure. We identified FOXO3 as an AMPK-dependent regulator of glucocorticoid activity in macrophages. Loss of AMPK in macrophages in vivo abrogates glucocorticoid anti-inflammatory actions during post-injury muscle regeneration and endotoxin induced acute lung injury. These data highlight that the glucocorticoid receptor is dependent on AMPK for its immunomodulatory actions in macrophages, linking their metabolic status to transcriptional control in resolving inflammation.Competing Interest StatementThe authors have declared no competing interest.View Full Text

physiology↗

bioRxiv2018

Annexin A1 drives macrophage skewing towards a resolving phenotype to accelerate the regeneration of muscle injury through AMPK activation

Understanding the circuits that promote an efficient resolution of inflammation is crucial to deciphering the molecular and cellular processes required to promote tissue repair. Macrophages play a central role in the regulation of inflammation, resolution and repair/regeneration. Using a model of skeletal muscle injury and repair, herein we identify Annexin A1 (AnxA1) as the extracellular trigger of macrophage skewing towards a pro-reparative phenotype. Brought into the injured tissue initially by migrated neutrophils, and then over-expressed in infiltrating macrophages, AnxA1 activates FPR2/ALX receptors and the downstream AMPK signalling cascade leading to macrophage skewing, dampening of inflammation and regeneration of muscle fibres. Mice lacking AnxA1 in all cells or in myeloid cells only display a defect in this reparative process. In vitro experiments recapitulated these properties, with AMPK null macrophages lacking AnxA1-mediated polarization. Collectively, these data identify the AnxA1/FPR2/AMPK axis as a novel pathway in skeletal muscle injury regeneration.

cell biology↗