Biology subjects

Castets, P.

Publications and source records attributed to Castets, P..

8 recordsLinked to original sources

bioRxiv2026

CONSTITUTIVE STIM1L DELETION ALTERS STORE-OPERATED CALCIUM ENTRY KINETICS BUT DOES NOT PERTURB THE DEVELOPMENT AND FUNCTION OF MOUSE SKELETAL MUSCLE

Store-operated calcium entry (SOCE) is a ubiquitous calcium (Ca2+) signalling mechanism that replenishes endoplasmic and sarcoplasmic reticulum Ca2+ stores. We previously identified STIM1L, a skeletal muscle-enriched STIM1 splice variant that enables rapid SOCE activation in human myotubes. To determine its physiological role in vivo, we generated a constitutive knockout mouse model that selectively abolishes STIM1L expression while preserving the canonical STIM1 isoform. Stim1l-KO mice developed normally and exhibited no overt abnormalities, but both sexes showed reduced voluntary wheel-running activity, suggesting neuromuscular perturbation. Skeletal muscle deprived of STIM1L did not show any histological alterations or changes in fibre- type and size. Likewise, force-frequency relationships and fatigue resistance measured ex vivo in isolated extensor digitorum longus and soleus muscles were indistinguishable from control muscles. This lack of difference may be explained by the increased expression of STIM1 in several skeletal muscles and suggests that changes in the voluntary running activity of Stim1l-KO mice may arise from STIM1L loss in non-muscular tissues, including the central nervous system. Notwithstanding, primary myotubes derived from Stim1l-KO mice displayed a marked delay in SOCE activation kinetics, whereas SOCE amplitude remained comparable to controls. This was consistent with a compensatory STIM1 upregulation maintaining overall Ca2+ entry capacity. Interestingly, electrically evoked Ca2+ transients in intact Stim1l-KO flexor digitorum brevis fibres exhibited significantly faster decay kinetics than controls. This revealed another role of STIM1L in Ca2+ handling in skeletal muscle that appears independent of its contribution to SOCE activation. Together, these findings establish STIM1L as a regulator of SOCE activation kinetics and indicate an additional role in myofibre Ca2+ clearance, while suggesting that compensatory upregulation of canonical STIM1 may preserve muscle structure and contractile function in its absence in mice.

physiology↗

bioRxiv2025

Harnessing distinct tissue-resident immune niches via S100A9/TLR4 improves ketone, lipid, and glucose metabolism

Immunometabolism contributes to the development of metabolic diseases. Yet, how certain metabolic disorders, such as insulin deficiency (ID), influence immune cell function is poorly understood. Here, we observe that ID rearranges the immune landscape of the liver, causing a decrease in T cells and an increase in Kupffer cells, accompanied by a shift in the transcriptome and polarization of the latter. Treating ID mice with the protein S100A9 rescues the polarization and lipid-related changes caused by ID in the KCs, and rescues hypertriglyceridemia and hyperketonemia in a TLR4-dependent manner. Additionally, S100A9 acts on other immune niches to increase glucose uptake in skeletal muscle, improving hyperglycemia. In summary, the S100A9-TLR4 axis is a new tool to harness immune cells for improving ID-related metabolic dysfunction.

physiology↗

bioRxiv2025

CtBP1 coordinates synaptic, metabolic and contractile changes induced by denervation in skeletal muscle

Nerve injury triggers dramatic atrophy of skeletal muscle, accompanied with synaptic and metabolic changes. Regulation of denervation-induced muscle fiber remodeling involves several factors governing genetic reprogramming and proteostasis changes. Here, we demonstrate that the transcriptional co-repressor CtBP1 coordinates synaptic and metabolic changes in muscle fibers upon denervation. CtBP1 was present both in sub- and non-synaptic myonuclei in innervated muscle. Although CtBP1 levels remained unchanged in denervated muscle, CtBP1 accumulated transiently in myonuclei after 2 days of denervation. Ctbp1 knockdown perturbed the expression of a large set of activity-independent and -dependent genes in innervated and denervated skeletal muscles. CtBP1 loss had limited effect on the expression of most synaptic genes, but increased transcript levels of Chrne, encoding the adult {varepsilon} sub-unit of acetylcholine receptors (AChR). However, it did not affect AChR turnover or maintenance of the post-synaptic compartment upon denervation. Importantly, we uncovered that Ctbp1 knockdown promotes denervation-induced changes in metabolic gene expression, including most genes encoding proteins of the respiratory chain complexes. Consistently, it enhanced the switch towards slower, oxidative fibers in fast muscle after 2 weeks of denervation. Moreover, CtBP1 loss precipitated the profound ultrastructural remodeling of mitochondria network induced after denervation. Hence, our study unveils the role of CtBP1 in the integrated muscle response to denervation, with important implications for CtBP1-related muscle diseases. One-sentence summaryLoss of CtBP1 perturbs synaptic, metabolic and contractile changes induced by denervation in skeletal muscle

physiology↗

bioRxiv2025

Intracellular autofluorescence enables the isolation of viable, functional human muscle reserve cells with distinct Pax7 levels and stem cell states.

BackgroundHuman muscle reserve cells (MuRC) represent a quiescent MuSC population generated in vitro that exhibit heterogeneous Pax7 expression, with a Pax7High subset in a deeper quiescent state. However, conventional identification of Pax7High cells requires intracellular staining, limiting their viability for functional studies. This study investigates autofluorescence (AF) as a potential biomarker to identify functionally distinct human MuRC subpopulations. MethodsHuman myoblasts (MB) and MuRC were analysed for AF by fluorescence microscopy and flow cytometry. Cellular metabolic composition was assessed by NADH/NADPH quantification and lipid staining. Human MuRC subpopulations were sorted by AF intensity and analysed for Pax7 expression, cell cycle re-entry, proliferation, clonal expansion, and myogenic differentiation. In vivo transplantation of MuRC-AFHigh and MuRC-AFLow populations into immunodeficient mice assessed survival and regenerative potential using bioluminescence imaging and immunohistochemistry. ResultsHuman MuRC showed a 3-fold increase in mean fluorescence intensity compared to MB, with AF peak at 405 nm excitation. Lipid staining revealed a 1.6-fold increase in lipid content in MuRC, while NADH/NADPH levels were similar between MB and MuRC. Flow cytometry identified MuRC-AFHigh as a Pax7High-enriched subpopulation. Functionally, MuRC-AFHigh cells exhibited delayed cell cycle re-entry and slower proliferation but retained differentiation potential. In vivo, both MuRC-AFHigh and MuRC-AFLow survived transplantation with no significant differences in engraftment efficiency. They contributed to the generation of human Pax7 positives MuSC and both subpopulations retain their regenerative capacity upon re-injury. ConclusionAF allows the identification of human MuRC subsets, with the AFHigh subpopulation associated with increased lipid content. MuRC-AFHigh cells are enriched in Pax7High cells and show delayed activation, slower proliferation and comparable engraftment efficiency to the AFLow subpopulation. These findings provide a novel perspective on AF as a potential biomarker to identify functionally distinct muscle progenitor subsets and highlight its relevance in muscle regeneration research.

cell biology↗

bioRxiv2024

mTORC1-dependent SOCE activity regulates synaptic gene expression and muscle response to denervation

Neuromuscular junction (NMJ) instability is central in muscle dysfunction occurring in neuromuscular disorders and aging. NMJ maintenance requires regionalized regulation of synaptic genes, previously associated with Ca2+-dependent pathways. However, what sustains Ca2+ micro-domains in myofibers and allows a rapid response to denervation is not known. Here, we identify that Store-Operated Calcium Entry (SOCE) plays a critical role in synaptic gene regulation. SOCE components show differential enrichment in sub- and non-synaptic muscle regions. Especially, STIM1 accumulation at rough endoplasmic reticulum associates with functional SOCE at the endplate. Denervation increases SOCE in non- and sub-synaptic regions, together with reticulum remodeling. Stim1 knockdown hampers denervation-induced synaptic gene up-regulation, while STIM1 overexpression increases synaptic gene expression in innervated muscle. Finally, mTORC1 activation mimics the effect of denervation on SOCE capacity, STIM1 localization and reticulum remodeling. Together, our results reveal a decisive role of SOCE in sensing innervation and regulating muscle response to denervation. They further suggest that SOCE perturbation may contribute to neuromuscular integrity loss in pathological conditions associated with mTORC1 dysregulation.

physiology↗

bioRxiv2023

Destabilization of neuromuscular junctions and deregulation of activity-dependent signalling pathways in Myotonic Dystrophy type I

Myotonic Dystrophy type I (DM1) is the most common muscular dystrophy in adults. Previous reports have highlighted that neuromuscular junctions (NMJs) deteriorate in skeletal muscle from DM1 patients and mouse models thereof. However, the underlying pathomechanisms and their contribution to muscle dysfunction remain unknown. We compared changes in NMJs and activity-dependent signalling pathways in HSALR and Mbnl1{Delta}E3/{Delta}E3 mice, two established mouse models for DM1. DM1 muscle showed major deregulation of calcium/calmodulin-dependent protein kinases II (CaMKIIs), which are key activity sensors regulating synaptic gene expression and acetylcholine receptor (AChR) recycling at the NMJ. Both mouse models displayed increased fragmentation of the endplate, which preceded muscle degeneration. Endplate fragmentation was not accompanied by changes in AChR turnover at the NMJ. However, expression of synaptic genes was up-regulated in DM1 muscle, which may be linked to the abnormally high activity of histone deacetylase 4 (HDAC4), a known target of CaMKII. Consistently, expression of myosin heavy chains was deregulated as well, leading to a major switch to type IIA fibres in Mbnl1{Delta}E3/{Delta}E3 muscle, and to a lesser extent in HSALR muscle. Interestingly, although HDAC4 was efficiently induced upon nerve injury, synaptic gene up-regulation was abrogated in DM1 muscle, together with a reduced increase in AChR turnover. This suggested that HDAC4-independent mechanisms lead to the defective response to denervation in DM1 muscle. Our study shows that activity-dependent signalling pathways are disturbed in DM1 muscle, which may contribute to NMJ destabilization and muscle dysfunction in DM1 patients.

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↗

bioRxiv2020

Low expression of ANT1 confers oncogenic properties to rhabdomyosarcoma tumor cells via modulating metabolism and death pathways.

Rhabdomyosarcoma (RMS) is the most frequent form of pediatric soft-tissue sarcoma. It is divided into 2 main subtypes: ERMS (embryonal) and ARMS (alveolar). Current treatments are based on chemotherapy, surgery and radiotherapy. 5-year survival rate remains of 70% since 2000, despite several clinical trials. RMS cells are thought to derive from muscle lineage precursors. During development, myogenesis is characterized by primary expansion of myoblasts, elimination of those in excess by cell death and the differentiation of the remaining ones into myotubes and myofibers. The idea that these processes could be hijacked by tumor cells to sustain their oncogenic transformation has emerged, while RMS is being considered as the Mister Hydes side of myogenesis. Thus, focusing on myogenic developmental programs could help understanding RMS molecular aetiology. Following this idea, we decided to concentrate on ANT1, which is involved in myogenesis and is the underlying cause of genetic disorders associated with muscle degeneration. ANT1 is a mitochondrial protein, which has a functional duality, as it is involved both in metabolism via regulation of ATP/ADP release from mitochondria, but also in apoptosis as part as the mitochondria Permeability Transition Pore (mPTP). By bioinformatic analysis of transcriptomic datasets, we observed that ANT1 is expressed at low levels in RMS. Using CRISPR-Cas9 technology, we showed that decreased ANT1 expression confers selective advantages to RMS cells in terms of proliferation and resistance to stress-induced death. These effects result notably from a metabolic switch. Restoration of ANT1 expression using a Tet-On system is sufficient to prime tumor cells to death and to increase their sensitivity to chemotherapies. Thus, modulation of ANT1 activity could appear as an appealing therapeutic approach in RMS management.

cancer biology↗