Biology subjects

Bitoun, M.

Publications and source records attributed to Bitoun, M..

5 recordsLinked to original sources

bioRxiv2024

Early endosome disturbance and endolysosomal pathway dysfunction in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal dystrophy characterized by the progressive loss of muscle fibers caused by mutations in DMD gene and absence of the dystrophin protein. While autophagy and lysosome biogenesis defects have been described in DMD muscles, the endosomal pathway has never been studied. Here, we showed that impaired lysosome formation is associated with altered acidification and reduced degradative function of the endolysosomal pathway in muscle cells derived from DMD patients. Our data demonstrated that early endosomes are increased in these cells as well as in muscle biopsies from DMD patients and two animal models of DMD, mdx mice and GRMD dogs. We determined that these abnormalities are due to the lack of dystrophin per se and could be correlated with disease progression and severity. We further identified an abnormal upregulation of the Rab5 GTPase protein, one key actor of early endosomal biogenesis and fusion, in the three DMD models which may underlie the endosomal defects. Finally, we demonstrated that Rab5 knock-down in human DMD muscle cells as well as dystrophin restoration in GRMD dogs, normalize Rab5 expression levels and rescue endosomal abnormalities. This study unveils a defect in a pathway essential for muscle homeostasis and for efficacy of adeno associated virus vectors and antisense oligonucleotides-mediated therapies.

pathology↗

bioRxiv2022

Caveolae and Bin1 form ring-shaped platforms for T-tubule initiation

Excitation-contraction coupling requires a highly specialized membrane structure, the triad, composed of a plasma membrane invagination, the T-tubule, surrounded by two sarcoplasmic reticulum terminal cisternae. Although the precise mechanisms governing T-tubule biogenesis and triad formation remain largely unknown, studies have shown that caveolae participate in T-tubule formation and mutations of several of their constituents induce muscle weakness and myopathies. Here, we demonstrate that, at the plasma membrane, caveolae composed of caveolin-3 and Bin1 assemble into ring-like structures from which emerge tubes enriched in the dihydropyridine receptor. Overexpression of Bin1 lead to the formation of both rings and tubes and we show that Bin1 forms scaffolds on which caveolae accumulate to form the initial T-tubule. Cav3 deficiency caused by either gene silencing or pathogenic mutations cause defective ring formation and perturbed Bin1-mediated tubulation that may explain defective T-tubule organization in mature muscles. Our results uncover new pathophysiological mechanisms that may prove relevant to myopathies caused by Cav3 or Bin1.

cell biology↗

bioRxiv2021

A centronuclear myopathy-causing mutation in dynamin-2 perturbs the actin-dependent structure of dendritic spines leading to excitatory synaptic defects in a murine model of the disease

Dynamin-2 is a large GTP-ase, member of the dynamin superfamily, that regulates membrane remodeling and cytoskeleton dynamics. In the mammalian nervous system dynamin-2 modulates synaptic vesicle (SV)-recycling at the nerve terminals and receptor-trafficking to and from postsynaptic densities (PSDs). Mutations in dynamin-2 cause autosomal dominant centronuclear myopathy (CNM), a congenital neuromuscular disorder characterized by progressive weakness and atrophy of distal skeletal muscles. Cognitive defects have also been reported in dynamin-2-linked CNM patients suggesting a concomitant impairment of the central nervous system. Here we addressed the mechanisms that lead to cognitive defects in dynamin-2-linked CNM using a knock-in mouse model that harbors the p.R465W mutation in dynamin-2, the most common causing CNM. Our results show that these mice exhibit reduced capability to learn and acquire spatial and recognition memory, impaired long-term potentiation of the excitatory synaptic strength and perturbed dendritic spine morphology, which seem to be associated with actin defects. Together, these data reveal for the first time that structural and functional synaptic defects underlie cognitive defects in the CNM context. In addition our results contribute to the still scarce knowledge about the importance of dynamin-2 at central synapses.

neuroscience↗

bioRxiv2020

SH3KBP1 scaffolds endoplasmic reticulum and controls skeletal myofibers architecture and integrity

The building block of skeletal muscle is the multinucleated muscle fiber, formed by the fusion of hundreds of mononucleated precursor cells, myoblasts. In the normal course of muscle fiber development or regeneration, myonuclei are actively positioned throughout muscular development and adopt special localization in mature fibers: regular spacing along muscle fibers periphery, raising the notion of MyoNuclear Domains (MNDs). There is now growing support for a direct connection between myonuclear positioning and normal function of muscles, but how myonuclei affects muscle function remains poorly characterized. To identify new factors regulating forces applied on myonuclei in muscles fibers, we performed a siRNA screen and identified SH3KBP1 as a new factor controlling myonuclear positioning in early phases of myofibers formation. Depletion of SH3KBP1 induces a reset of MNDs establishment in mature fibers reflected by a dramatic reduction in pairwise distance between myonuclei. We show that SH3KBP1 scaffolds Endoplasmic Reticulum (ER) in myotubes that in turn controls myonuclei velocity and localization and thus myonuclear domains settings. Additionally, we show that in later phases of muscle maturation, SH3KBP1 contributes to the formation and maintenance of Sarcoplasmic Reticulum (SR) and Transverse-tubules (T-tubules). We also demonstrate that in muscle fibers, GTPase dynamin-2 (DNM2) binds to SH3 domains of SH3KBP1. Interestingly, we observed that Sh3kbp1 mRNA is up regulated in a mouse model harboring the most frequent mutation for Autosomal Dominant CentroNuclear Myopathy (AD-CNM): Dnm2+/R465W. SH3KBP1 thus appears as a compensation mechanism in this CNM model since its depletion contributes to an increase of CNM-like phenotypes (reduction of muscle fibers Cross-section Areas (CSA) and increase in slow fibers content). Altogether our results identify SH3KBP1 as a new regulator of myonuclear domains establishment in the early phase of muscle fibers formation through ER scaffolding and later in myofibers integrity through T-tubules scaffolding/maintenance. SummaryMyonuclei are actively positioned throughout muscular development. Guiraud, Christin, Couturier et al show that SH3KBP1 scaffolds the ER through Calnexin interaction and controls myonuclei motion during early steps of muscle fibers formation. Besides SH3KBP1 participates in cell fusion and T-tubules formation/maintenance in mature skeletal muscle fibers and contributes to slow-down CNM-like phenotypes.

cell biology↗

bioRxiv2018

Clathrin plaques form mechanotransducing platforms

Large flat clathrin plaques are stable features of the plasma membrane associated with sites of strong adhesion suggesting that they could also play a role in force transduction. Here, we analyzed how clathrin plaques interact with the cytoskeleton and how they respond to mechanical cues in skeletal muscle myotubes. We show that branched actin networks surrounding clathrin plaques are directly regulated by dynamin 2, anchor intermediate filaments and sequester YAP at the plasma membrane. Dynamin 2, clathrin and desmin intermediate filaments are all required for basal YAP nucleocytoplasmic distribution and efficient nuclear translocation in response to mechanical stimuli. Dynamin 2 mutations that are responsible for centronuclear myopathy in humans disorganize the desmin network and deregulate YAP signaling both in vitro and in vivo. Thus, clathrin plaques and associated dynamin 2 are defined here as a new sensor conveying mechanical cues and integrate cell signaling with cytoskeletal regulation.

cell biology↗