Publications by authors named "Belinda S Cowling"

37 Publications

Common Pathogenic Mechanisms in Centronuclear and Myotubular Myopathies and Latest Treatment Advances.

Int J Mol Sci 2021 Oct 21;22(21). Epub 2021 Oct 21.

Department of Translational Medicine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67400 Illkirch, France.

Centronuclear myopathies (CNM) are rare congenital disorders characterized by muscle weakness and structural defects including fiber hypotrophy and organelle mispositioning. The main CNM forms are caused by mutations in: the gene encoding the phosphoinositide phosphatase myotubularin (myotubular myopathy), the gene encoding the mechanoenzyme dynamin 2, the gene encoding the membrane curvature sensing amphiphysin 2, and the gene encoding the skeletal muscle calcium release channel/ryanodine receptor. MTM1, BIN1, and DNM2 proteins are involved in membrane remodeling and trafficking, while RyR1 directly regulates excitation-contraction coupling (ECC). Several CNM animal models have been generated or identified, which confirm shared pathological anomalies in T-tubule remodeling, ECC, organelle mispositioning, protein homeostasis, neuromuscular junction, and muscle regeneration. Dynamin 2 plays a crucial role in CNM physiopathology and has been validated as a common therapeutic target for three CNM forms. Indeed, the promising results in preclinical models set up the basis for ongoing clinical trials. Another two clinical trials to treat myotubular myopathy by MTM1 gene therapy or tamoxifen repurposing are also ongoing. Here, we review the contribution of the different CNM models to understanding physiopathology and therapy development with a focus on the commonly dysregulated pathways and current therapeutic targets.
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http://dx.doi.org/10.3390/ijms222111377DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8583656PMC
October 2021

Mice with muscle-specific deletion of Bin1 recapitulate centronuclear myopathy and acute downregulation of dynamin 2 improves their phenotypes.

Mol Ther 2021 Aug 8. Epub 2021 Aug 8.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), CNRS UMR7104, INSERM U1258, Université de Strasbourg, 67404 Illkirch, France. Electronic address:

Mutations in the BIN1 (Bridging Interactor 1) gene, encoding the membrane remodeling protein amphiphysin 2, cause centronuclear myopathy (CNM) associated with severe muscle weakness and myofiber disorganization and hypotrophy. There is no available therapy, and the validation of therapeutic proof of concept is impaired by the lack of a faithful and easy-to-handle mammalian model. Here, we generated and characterized the Bin1 mouse through Bin1 knockout in skeletal muscle. Bin1 mice were viable, unlike the constitutive Bin1 knockout, and displayed decreased muscle force and most histological hallmarks of CNM, including myofiber hypotrophy and intracellular disorganization. Notably, Bin1 myofibers presented strong defects in mitochondria and T-tubule networks associated with deficient calcium homeostasis and excitation-contraction coupling at the triads, potentially representing the main pathomechanisms. Systemic injection of antisense oligonucleotides (ASOs) targeting Dnm2 (Dynamin 2), which codes for dynamin 2, a BIN1 binding partner regulating membrane fission and mutated in other forms of CNM, improved muscle force and normalized the histological Bin1 phenotypes within 5 weeks. Overall, we generated a faithful mammalian model for CNM linked to BIN1 defects and validated Dnm2 ASOs as a first translatable approach to efficiently treat BIN1-CNM.
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http://dx.doi.org/10.1016/j.ymthe.2021.08.006DOI Listing
August 2021

Hierarchical Bayesian modelling of disease progression to inform clinical trial design in centronuclear myopathy.

Orphanet J Rare Dis 2021 01 6;16(1). Epub 2021 Jan 6.

Division of Child Neurology, Centre de Référence Des Maladies Neuromusculaires, Department of Paediatrics, University Hospital of Liège and University of Liège, Liège, Belgium.

Background: Centronuclear myopathies are severe rare congenital diseases. The clinical variability and genetic heterogeneity of these myopathies result in major challenges in clinical trial design. Alternative strategies to large placebo-controlled trials that have been used in other rare diseases (e.g., the use of surrogate markers or of historical controls) have limitations that Bayesian statistics may address. Here we present a Bayesian model that uses each patient's own natural history study data to predict progression in the absence of treatment. This prospective multicentre natural history evaluated 4-year follow-up data from 59 patients carrying mutations in the MTM1 or DNM2 genes.

Methods: Our approach focused on evaluation of forced expiratory volume in 1 s (FEV1) in 6- to 18-year-old children. A patient was defined as a responder if an improvement was observed after treatment and the predictive probability of such improvement in absence of intervention was less than 0.01. An FEV1 response was considered clinically relevant if it corresponded to an increase of more than 8%.

Results: The key endpoint of a clinical trial using this model is the rate of response. The power of the study is based on the posterior probability that the rate of response observed is greater than the rate of response that would be observed in the absence of treatment predicted based on the individual patient's previous natural history. In order to appropriately control for Type 1 error, the threshold probability by which the difference in response rates exceeds zero was adapted to 91%, ensuring a 5% overall Type 1 error rate for the trial.

Conclusions: Bayesian statistical analysis of natural history data allowed us to reliably simulate the evolution of symptoms for individual patients over time and to probabilistically compare these simulated trajectories to actual observed post-treatment outcomes. The proposed model adequately predicted the natural evolution of patients over the duration of the study and will facilitate a sufficiently powerful trial design that can cope with the disease's rarity. Further research and ongoing dialog with regulatory authorities are needed to allow for more applications of Bayesian statistics in orphan disease research.
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http://dx.doi.org/10.1186/s13023-020-01663-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7789189PMC
January 2021

rAAV-related therapy fully rescues myonuclear and myofilament function in X-linked myotubular myopathy.

Acta Neuropathol Commun 2020 10 19;8(1):167. Epub 2020 Oct 19.

Centre of Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, Faculty of Life Sciences & Medicine, King's College London, London, UK.

X-linked myotubular myopathy (XLMTM) is a life-threatening skeletal muscle disease caused by mutations in the MTM1 gene. XLMTM fibres display a population of nuclei mispositioned in the centre. In the present study, we aimed to explore whether positioning and overall distribution of nuclei affects cellular organization and contractile function, thereby contributing to muscle weakness in this disease. We also assessed whether gene therapy alters nuclear arrangement and function. We used tissue from human patients and animal models, including XLMTM dogs that had received increasing doses of recombinant AAV8 vector restoring MTM1 expression (rAAV8-cMTM1). We then used single isolated muscle fibres to analyze nuclear organization and contractile function. In addition to the expected mislocalization of nuclei in the centre of muscle fibres, a novel form of nuclear mispositioning was observed: irregular spacing between those located at the fibre periphery, and an overall increased number of nuclei, leading to dramatically smaller and inconsistent myonuclear domains. Nuclear mislocalization was associated with decreases in global nuclear synthetic activity, contractile protein content and intrinsic myofilament force production. A contractile deficit originating at the myofilaments, rather than mechanical interference by centrally positioned nuclei, was supported by experiments in regenerated mouse muscle. Systemic administration of rAAV8-cMTM1 at doses higher than 2.5 × 10vg kg allowed a full rescue of all these cellular defects in XLMTM dogs. Altogether, these findings identify previously unrecognized pathological mechanisms in human and animal XLMTM, associated with myonuclear defects and contractile filament function. These defects can be reversed by gene therapy restoring MTM1 expression in dogs with XLMTM.
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http://dx.doi.org/10.1186/s40478-020-01048-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7574461PMC
October 2020

Differential physiological roles for BIN1 isoforms in skeletal muscle development, function and regeneration.

Dis Model Mech 2020 11 24;13(11). Epub 2020 Nov 24.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Department of Translational Medicine, 67404 Illkirch, France

Skeletal muscle development and regeneration are tightly regulated processes. How the intracellular organization of muscle fibers is achieved during these steps is unclear. Here, we focus on the cellular and physiological roles of amphiphysin 2 (BIN1), a membrane remodeling protein mutated in both congenital and adult centronuclear myopathies (CNM), that is ubiquitously expressed and has skeletal muscle-specific isoforms. We created and characterized constitutive muscle-specific and inducible homozygous and heterozygous knockout mice targeting either ubiquitous or muscle-specific isoforms. Constitutive -deficient mice died at birth from lack of feeding due to a skeletal muscle defect. T-tubules and other organelles were misplaced and altered, supporting a general early role for BIN1 in intracellular organization, in addition to membrane remodeling. Although restricted deletion of in unchallenged adult muscles had no impact, the forced switch from the muscle-specific isoforms to the ubiquitous isoforms through deletion of the in-frame muscle-specific exon delayed muscle regeneration. Thus, ubiquitous BIN1 function is necessary for muscle development and function, whereas its muscle-specific isoforms fine tune muscle regeneration in adulthood, supporting that BIN1 CNM with congenital onset are due to developmental defects, whereas later onset may be due to regeneration defects.
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http://dx.doi.org/10.1242/dmm.044354DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7710016PMC
November 2020

Physiological impact and disease reversion for the severe form of centronuclear myopathy linked to dynamin.

JCI Insight 2020 09 17;5(18). Epub 2020 Sep 17.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

Classical dynamins are large GTPases regulating membrane and cytoskeleton dynamics, and they are linked to different pathological conditions ranging from neuromuscular diseases to encephalopathy and cancer. Dominant dynamin 2 (DNM2) mutations lead to either mild adult onset or severe autosomal dominant centronuclear myopathy (ADCNM). Our objectives were to better understand the pathomechanism of severe ADCNM and test a potential therapy. Here, we created the Dnm2SL/+ mouse line harboring the common S619L mutation found in patients with severe ADCNM and impairing the conformational switch regulating dynamin self-assembly and membrane remodeling. The Dnm2SL/+ mouse faithfully reproduces severe ADCNM hallmarks with early impaired muscle function and force, together with myofiber hypotrophy. It revealed swollen mitochondria lacking cristae as the main ultrastructural defect and potential cause of the disease. Patient analysis confirmed this structural hallmark. In addition, DNM2 reduction with antisense oligonucleotides after disease onset efficiently reverted locomotor and force defects after only 3 weeks of treatment. Most histological defects including mitochondria alteration were partially or fully rescued. Overall, this study highlights an efficient approach to revert the severe form of dynamin-related centronuclear myopathy. These data also reveal that the dynamin conformational switch is key for muscle function and should be targeted for future therapeutic developments.
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http://dx.doi.org/10.1172/jci.insight.137899DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7526554PMC
September 2020

Myostatin: a Circulating Biomarker Correlating with Disease in Myotubular Myopathy Mice and Patients.

Mol Ther Methods Clin Dev 2020 Jun 4;17:1178-1189. Epub 2020 May 4.

Dynacure, Illkirch, France.

Myotubular myopathy, also called X-linked centronuclear myopathy (XL-CNM), is a severe congenital disease targeted for therapeutic trials. To date, biomarkers to monitor disease progression and therapy efficacy are lacking. The mouse is a faithful model for XL-CNM, due to myotubularin 1 () loss-of-function mutations. Using both an unbiased approach (RNA sequencing [RNA-seq]) and a directed approach (qRT-PCR and protein level), we identified decreased levels in muscle, leading to low levels of myostatin in muscle and plasma. Myostatin ( or growth differentiation factor 8 []) is a protein released by myocytes and inhibiting muscle growth and differentiation. Decreasing by genetic cross with mice or by antisense oligonucleotides blocked or postponed disease progression and resulted in an increase in circulating myostatin. In addition, plasma myostatin levels inversely correlated with disease severity and with mRNA levels in muscles. Altered levels were associated with a generalized disruption of the myostatin pathway. Importantly, in two different forms of CNMs we identified reduced circulating myostatin levels in plasma from patients. This provides evidence of a blood-based biomarker that may be used to monitor disease state in XL-CNM mice and patients and supports monitoring circulating myostatin during clinical trials for myotubular myopathy.
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http://dx.doi.org/10.1016/j.omtm.2020.04.022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7267729PMC
June 2020

Translational medicine in neuromuscular disorders: from academia to industry.

Dis Model Mech 2019 10 24;13(2). Epub 2019 Oct 24.

Dynacure, Pôle API, 67400 Illkirch, France.

Although around half of US Food and Drug Administration (FDA)-approved drugs originate from discoveries made in academic research laboratories, the US National Institutes of Health (NIH) estimates that nearly 90% of therapies developed in preclinical stages never reach clinical trials. From those in clinical trials, only 10% obtain marketing approval. Despite the recent advances in our understanding and diagnosis of neuromuscular disease, and the development of rational therapies in clinical trials, these numbers have not changed dramatically over the past two decades. This article discusses the advantages and challenges for translational research initiated from academia, and the trend towards bridging the gap between discovery and translation to the clinic. A focus is made on recent advances in therapeutic development for neuromuscular disorders.
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http://dx.doi.org/10.1242/dmm.041434DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6906629PMC
October 2019

Different in vivo impacts of dynamin 2 mutations implicated in Charcot-Marie-Tooth neuropathy or centronuclear myopathy.

Hum Mol Genet 2019 12;28(24):4067-4077

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

Dynamin 2 (DNM2) is a ubiquitously expressed GTPase implicated in many cellular functions such as membrane trafficking and cytoskeleton regulation. Dominant mutations in DNM2 result in tissue-specific diseases affecting peripheral nerves (Charcot-Marie-Tooth neuropathy, CMT) or skeletal muscles (centronuclear myopathy, CNM). However, the reason for this tissue specificity is unknown, and it remains unclear if these diseases share a common pathomechanism. To compare the disease pathophysiological mechanisms in skeletal muscle, we exogenously expressed wild-type DNM2 (WT-DNM2), the DNM2-CMT mutation K562E or DNM2-CNM mutations R465W and S619L causing adult and neonatal forms, respectively, by intramuscular adeno-associated virus (AAV) injections. All muscles expressing exogenous WT-DNM2 and CNM or CMT mutations exhibited reduced muscle force. However, only expression of CNM mutations and WT-DNM2 correlated with CNM-like histopathological hallmarks of nuclei centralization and reduced fiber size. The extent of alterations correlated with clinical severity in patients. Ultrastructural and immunofluorescence analyses highlighted defects of the triads, mitochondria and costameres as major causes of the CNM phenotype. Despite the reduction in force upon expression of the DNM2-CMT mutation, muscle histology and ultrastructure were almost normal. However, the neuromuscular junction was affected in all DNM2-injected muscles, with the DNM2-CMT mutation inducing the most severe alterations, potentially explaining the reduction in force observed with this mutant. In conclusion, expression of WT and CNM mutants recreate a CNM-like phenotype, suggesting CNM mutations are gain-of-function. Histological, ultrastructural and molecular analyses pointed to key pathways uncovering the different pathomechanisms involved in centronuclear myopathy or Charcot-Marie-Tooth neuropathy linked to DNM2 mutations.
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http://dx.doi.org/10.1093/hmg/ddz249DOI Listing
December 2019

Allele-Specific CRISPR/Cas9 Correction of a Heterozygous DNM2 Mutation Rescues Centronuclear Myopathy Cell Phenotypes.

Mol Ther Nucleic Acids 2019 Jun 27;16:246-256. Epub 2019 Feb 27.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch 67404, France; INSERM U1258, Illkirch 67404, France; CNRS UMR7104, Illkirch 67404, France; Strasbourg University, Illkirch 67404, France. Electronic address:

Genome editing with the CRISPR/Cas9 technology has emerged recently as a potential strategy for therapy in genetic diseases. For dominant mutations linked to gain-of-function effects, allele-specific correction may be the most suitable approach. In this study, we tested allele-specific inactivation or correction of a heterozygous mutation in the Dynamin 2 (DNM2) gene that causes the autosomal dominant form of centronuclear myopathies (CNMs), a rare muscle disorder belonging to the large group of congenital myopathies. Truncated single-guide RNAs targeting specifically the mutated allele were tested on cells derived from a mouse model and patients. The mutated allele was successfully targeted in patient fibroblasts and Dnm2 mouse myoblasts, and clones were obtained with precise genome correction or inactivation. Dnm2 myoblasts showed an alteration in transferrin uptake and autophagy. Specific inactivation or correction of the mutated allele rescued these phenotypes. These findings illustrate the potential of CRISPR/Cas9 to target and correct in an allele-specific manner heterozygous point mutations leading to a gain-of-function effect, and to rescue autosomal dominant CNM-related phenotypes. This strategy may be suitable for a large number of diseases caused by germline or somatic mutations resulting in a gain-of-function mechanism.
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http://dx.doi.org/10.1016/j.omtn.2019.02.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6439232PMC
June 2019

Amphiphysin 2 modulation rescues myotubular myopathy and prevents focal adhesion defects in mice.

Sci Transl Med 2019 03;11(484)

IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), 67404 Illkirch, France.

Centronuclear myopathies (CNMs) are severe diseases characterized by muscle weakness and myofiber atrophy. Currently, there are no approved treatments for these disorders. Mutations in the phosphoinositide 3-phosphatase myotubularin (MTM1) are responsible for X-linked CNM (XLCNM), also called myotubular myopathy, whereas mutations in the membrane remodeling Bin/amphiphysin/Rvs protein amphiphysin 2 [bridging integrator 1 (BIN1)] are responsible for an autosomal form of the disease. Here, we investigated the functional relationship between MTM1 and BIN1 in healthy skeletal muscle and in the physiopathology of CNM. Genetic overexpression of human BIN1 efficiently rescued the muscle weakness and life span in a mouse model of XLCNM. Exogenous human BIN1 expression with adeno-associated virus after birth also prevented the progression of the disease, suggesting that human BIN1 overexpression can compensate for the lack of MTM1 expression in this mouse model. Our results showed that MTM1 controls cell adhesion and integrin localization in mammalian muscle. Alterations in this pathway in mice were associated with defects in myofiber shape and size. BIN1 expression rescued integrin and laminin alterations and restored myofiber integrity, supporting the idea that MTM1 and BIN1 are functionally linked and necessary for focal adhesions in skeletal muscle. The results suggest that BIN1 modulation might be an effective strategy for treating XLCNM.
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http://dx.doi.org/10.1126/scitranslmed.aav1866DOI Listing
March 2019

Tamoxifen prolongs survival and alleviates symptoms in mice with fatal X-linked myotubular myopathy.

Nat Commun 2018 11 19;9(1):4848. Epub 2018 Nov 19.

Pharmaceutical Biochemistry Group, School of Pharmaceutical Sciences, University of Lausanne, University of Geneva, CMU 5-6, Rue Michel-Servet 1, Geneva, 1211, Switzerland.

X-linked myotubular myopathy (XLMTM, also known as XLCNM) is a severe congenital muscular disorder due to mutations in the myotubularin gene, MTM1. It is characterized by generalized hypotonia, leading to neonatal death of most patients. No specific treatment exists. Here, we show that tamoxifen, a well-known drug used against breast cancer, rescues the phenotype of Mtm1-deficient mice. Tamoxifen increases lifespan several-fold while improving overall motor function and preventing disease progression including lower limb paralysis. Tamoxifen corrects functional, histological and molecular hallmarks of XLMTM, with improved force output, myonuclei positioning, myofibrillar structure, triad number, and excitation-contraction coupling. Tamoxifen normalizes the expression level of the XLMTM disease modifiers DNM2 and PI3KC2B, likely contributing to the phenotypic rescue. Our findings demonstrate that tamoxifen is a promising candidate for clinical evaluation in XLMTM patients.
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http://dx.doi.org/10.1038/s41467-018-07058-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6243013PMC
November 2018

Reducing dynamin 2 (DNM2) rescues -related dominant centronuclear myopathy.

Proc Natl Acad Sci U S A 2018 10 5;115(43):11066-11071. Epub 2018 Oct 5.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67404 Illkirch, France;

Centronuclear myopathies (CNM) are a group of severe muscle diseases for which no effective therapy is currently available. We have previously shown that reduction of the large GTPase DNM2 in a mouse model of the X-linked form, due to loss of myotubularin phosphatase MTM1, prevents the development of the skeletal muscle pathophysiology. As is mutated in autosomal dominant forms, here we tested whether DNM2 reduction can rescue -related CNM in a knock-in mouse harboring the p.R465W mutation ( ) and displaying a mild CNM phenotype similar to patients with the same mutation. A single intramuscular injection of adeno-associated virus-shRNA targeting resulted in reduction in protein levels 5 wk post injection, with a corresponding improvement in muscle mass and fiber size distribution, as well as an improvement in histopathological CNM features. To establish a systemic treatment, weekly i.p. injections of antisense oligonucleotides targeting were administered to mice for 5 wk. While muscle mass, histopathology, and muscle ultrastructure were perturbed in mice compared with wild-type mice, these features were indistinguishable from wild-type mice after reducing DNM2. Therefore, DNM2 knockdown via two different strategies can efficiently correct the myopathy due to mutations, and it provides a common therapeutic strategy for several forms of centronuclear myopathy. Furthermore, we provide an example of treating a dominant disease by targeting both alleles, suggesting that this strategy may be applied to other dominant diseases.
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http://dx.doi.org/10.1073/pnas.1808170115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6205463PMC
October 2018

Centronuclear myopathies under attack: A plethora of therapeutic targets.

J Neuromuscul Dis 2018 ;5(4):387-406

Centronuclear myopathies are a group of congenital myopathies characterized by severe muscle weakness, genetic heterogeneity, and defects in the structural organization of muscle fibers. Their names are derived from the central position of nuclei on biopsies, while they are at the fiber periphery under normal conditions. No specific therapy exists yet for these debilitating diseases. Mutations in the myotubularin phosphoinositides phosphatase, the GTPase dynamin 2, or amphiphysin 2 have been identified to cause respectively X-linked centronuclear myopathies (also called myotubular myopathy) or autosomal dominant and recessive forms. Mutations in additional genes, as RYR1, TTN, SPEG or CACNA1S, were linked to phenotypes that can overlap with centronuclear myopathies. Numerous animal models of centronuclear myopathies have been studied over the last 15 years, ranging from invertebrate to large mammalian models. Their characterization led to a partial understanding of the pathomechanisms of these diseases and allowed the recent validation of therapeutic proof-of-concepts. Here, we review the different therapeutic strategies that have been tested so far for centronuclear myopathies, some of which may be translated to patients.
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http://dx.doi.org/10.3233/JND-180309DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6218136PMC
January 2019

Single Intramuscular Injection of AAV-shRNA Reduces DNM2 and Prevents Myotubular Myopathy in Mice.

Mol Ther 2018 04 14;26(4):1082-1092. Epub 2018 Feb 14.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch 67400, France; INSERM U964, Illkirch 67400, France; CNRS UMR7104, Illkirch 67400, France; Strasbourg University, Illkirch 67400, France. Electronic address:

Myotubular myopathy, or X-linked centronuclear myopathy, is a severe muscle disorder representing a significant burden for patients and their families. It is clinically characterized by neonatal and severe muscle weakness and atrophy. Mutations in the myotubularin (MTM1) gene cause myotubular myopathy, and no specific curative treatment is available. We previously found that dynamin 2 (DNM2) is upregulated in both Mtm1 knockout and patient muscle samples, whereas its reduction through antisense oligonucleotides rescues the clinical and histopathological features of this myopathy in mice. Here, we propose a novel approach targeting Dnm2 mRNA. We screened and validated in vitro and in vivo several short hairpin RNA (shRNA) sequences that efficiently target Dnm2 mRNA. A single intramuscular injection of AAV-shDnm2 resulted in long-term reduction of DNM2 protein level and restored muscle force, mass, histology, and myofiber ultrastructure and prevented molecular defects linked to the disease. Our results demonstrate a robust DNM2 knockdown and provide an alternative strategy based on reduction of DNM2 to treat myotubular myopathy.
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http://dx.doi.org/10.1016/j.ymthe.2018.02.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6080128PMC
April 2018

Amphiphysin (BIN1) negatively regulates dynamin 2 for normal muscle maturation.

J Clin Invest 2017 12 13;127(12):4477-4487. Epub 2017 Nov 13.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

Regulation of skeletal muscle development and organization is a complex process that is not fully understood. Here, we focused on amphiphysin 2 (BIN1, also known as bridging integrator-1) and dynamin 2 (DNM2), two ubiquitous proteins implicated in membrane remodeling and mutated in centronuclear myopathies (CNMs). We generated Bin1-/- Dnm2+/- mice to decipher the physiological interplay between BIN1 and DNM2. While Bin1-/- mice die perinatally from a skeletal muscle defect, Bin1-/- Dnm2+/- mice survived at least 18 months, and had normal muscle force and intracellular organization of muscle fibers, supporting BIN1 as a negative regulator of DNM2. We next characterized muscle-specific isoforms of BIN1 and DNM2. While BIN1 colocalized with and partially inhibited DNM2 activity during muscle maturation, BIN1 had no effect on the isoform of DNM2 found in adult muscle. Together, these results indicate that BIN1 and DNM2 regulate muscle development and organization, function through a common pathway, and define BIN1 as a negative regulator of DNM2 in vitro and in vivo during muscle maturation. Our data suggest that DNM2 modulation has potential as a therapeutic approach for patients with CNM and BIN1 defects. As BIN1 is implicated in cancers, arrhythmia, and late-onset Alzheimer disease, these findings may trigger research directions and therapeutic development for these common diseases.
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http://dx.doi.org/10.1172/JCI90542DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5707152PMC
December 2017

Expression of the neuropathy-associated MTMR2 gene rescues MTM1-associated myopathy.

Hum Mol Genet 2017 10;26(19):3736-3748

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67404 Illkirch, France.

Myotubularins (MTMs) are active or dead phosphoinositides phosphatases defining a large protein family conserved through evolution and implicated in different neuromuscular diseases. Loss-of-function mutations in MTM1 cause the severe congenital myopathy called myotubular myopathy (or X-linked centronuclear myopathy) while mutations in the MTM1-related protein MTMR2 cause a recessive Charcot-Marie-Tooth peripheral neuropathy. Here we aimed to determine the functional specificity and redundancy of MTM1 and MTMR2, and to assess their abilities to compensate for a potential therapeutic strategy. Using molecular investigations and heterologous expression of human MTMs in yeast cells and in Mtm1 knockout mice, we characterized several naturally occurring MTMR2 isoforms with different activities. We identified the N-terminal domain as responsible for functional differences between MTM1 and MTMR2. An N-terminal extension observed in MTMR2 is absent in MTM1, and only the short MTMR2 isoform lacking this N-terminal extension behaved similarly to MTM1 in yeast and mice. Moreover, adeno-associated virus-mediated exogenous expression of several MTMR2 isoforms ameliorates the myopathic phenotype owing to MTM1 loss, with increased muscle force, reduced myofiber atrophy, and reduction of the intracellular disorganization hallmarks associated with myotubular myopathy. Noteworthy, the short MTMR2 isoform provided a better rescue when compared with the long MTMR2 isoform. In conclusion, these results point to the molecular basis for MTMs functional specificity. They also provide the proof-of-concept that expression of the neuropathy-associated MTMR2 gene improves the MTM1-associated myopathy, thus identifying MTMR2 as a novel therapeutic target for myotubular myopathy.
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http://dx.doi.org/10.1093/hmg/ddx258DOI Listing
October 2017

Antisense oligonucleotide-mediated Dnm2 knockdown prevents and reverts myotubular myopathy in mice.

Nat Commun 2017 06 7;8:15661. Epub 2017 Jun 7.

Department of Translational Medicine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch 67404, France.

Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy is currently available. The most severe form, X-linked CNM, is caused by myotubularin 1 (MTM1) loss-of-function mutations, while the main autosomal dominant form is due to dynamin2 (DNM2) mutations. We previously showed that genetic reduction of DNM2 expression in Mtm1 knockout (Mtm1KO) mice prevents development of muscle pathology. Here we show that systemic delivery of Dnm2 antisense oligonucleotides (ASOs) into Mtm1KO mice efficiently reduces DNM2 protein level in muscle and prevents the myopathy from developing. Moreover, systemic ASO injection into severely affected mice leads to reversal of muscle pathology within 2 weeks. Thus, ASO-mediated DNM2 knockdown can efficiently correct muscle defects due to loss of MTM1, providing an attractive therapeutic strategy for this disease.
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http://dx.doi.org/10.1038/ncomms15661DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5467247PMC
June 2017

WANTED - Dead or alive: Myotubularins, a large disease-associated protein family.

Adv Biol Regul 2017 Jan 15;63:49-58. Epub 2016 Sep 15.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 1 Rue Laurent Fries, BP10142, 67404 Illkirch, France; INSERM U964, 67404 Illkirch, France; CNRS, UMR7104, 67404 Illkirch, France; Fédération de Médecine Translationnelle de Strasbourg (FMTS), Université de Strasbourg, 67404 Illkirch, France. Electronic address:

Myotubularins define a large family of proteins conserved through evolution. Several members are mutated in different neuromuscular diseases including centronuclear myopathies and Charcot-Marie-Tooth (CMT) neuropathies, or are linked to a predisposition to obesity and cancer. While some members have phosphatase activity against the 3-phosphate of phosphoinositides, regulating the phosphorylation status of PtdIns3P and PtdIns(3,5)P implicated in membrane trafficking and autophagy, and producing PtdIns5P, others lack key residues in the catalytic site and are classified as dead-phosphatases. However, these dead phosphatases regulate phosphoinositide-dependent cellular pathways by binding to catalytically active myotubularins. Here we review previous studies on the molecular regulation and physiological roles of myotubularins. We also used the recent myotubularins three-dimensional structures to underline key residues that are mutated in neuromuscular diseases and required for enzymatic activity. In addition, through database mining and analysis, expression profile and specific isoforms of the different myotubularins are described in depth, as well as a revisited protein interaction network. Comparison of the interactome and expression data for each myotubularin highlights specific protein complexes and tissues where myotubularins should have a key regulatory role.
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http://dx.doi.org/10.1016/j.jbior.2016.09.001DOI Listing
January 2017

Reciprocal Effects on Neurocognitive and Metabolic Phenotypes in Mouse Models of 16p11.2 Deletion and Duplication Syndromes.

PLoS Genet 2016 Feb 12;12(2):e1005709. Epub 2016 Feb 12.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

The 16p11.2 600 kb BP4-BP5 deletion and duplication syndromes have been associated with developmental delay; autism spectrum disorders; and reciprocal effects on the body mass index, head circumference and brain volumes. Here, we explored these relationships using novel engineered mouse models carrying a deletion (Del/+) or a duplication (Dup/+) of the Sult1a1-Spn region homologous to the human 16p11.2 BP4-BP5 locus. On a C57BL/6N inbred genetic background, Del/+ mice exhibited reduced weight and impaired adipogenesis, hyperactivity, repetitive behaviors, and recognition memory deficits. In contrast, Dup/+ mice showed largely opposite phenotypes. On a F1 C57BL/6N × C3B hybrid genetic background, we also observed alterations in social interaction in the Del/+ and the Dup/+ animals, with other robust phenotypes affecting recognition memory and weight. To explore the dosage effect of the 16p11.2 genes on metabolism, Del/+ and Dup/+ models were challenged with high fat and high sugar diet, which revealed opposite energy imbalance. Transcriptomic analysis revealed that the majority of the genes located in the Sult1a1-Spn region were sensitive to dosage with a major effect on several pathways associated with neurocognitive and metabolic phenotypes. Whereas the behavioral consequence of the 16p11 region genetic dosage was similar in mice and humans with activity and memory alterations, the metabolic defects were opposite: adult Del/+ mice are lean in comparison to the human obese phenotype and the Dup/+ mice are overweight in comparison to the human underweight phenotype. Together, these data indicate that the dosage imbalance at the 16p11.2 locus perturbs the expression of modifiers outside the CNV that can modulate the penetrance, expressivity and direction of effects in both humans and mice.
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http://dx.doi.org/10.1371/journal.pgen.1005709DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4752317PMC
February 2016

The caveolin-cavin system plays a conserved and critical role in mechanoprotection of skeletal muscle.

J Cell Biol 2015 Aug;210(5):833-49

Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia Center for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland 4072, Australia

Dysfunction of caveolae is involved in human muscle disease, although the underlying molecular mechanisms remain unclear. In this paper, we have functionally characterized mouse and zebrafish models of caveolae-associated muscle disease. Using electron tomography, we quantitatively defined the unique three-dimensional membrane architecture of the mature muscle surface. Caveolae occupied around 50% of the sarcolemmal area predominantly assembled into multilobed rosettes. These rosettes were preferentially disassembled in response to increased membrane tension. Caveola-deficient cavin-1(-/-) muscle fibers showed a striking loss of sarcolemmal organization, aberrant T-tubule structures, and increased sensitivity to membrane tension, which was rescued by muscle-specific Cavin-1 reexpression. In vivo imaging of live zebrafish embryos revealed that loss of muscle-specific Cavin-1 or expression of a dystrophy-associated Caveolin-3 mutant both led to sarcolemmal damage but only in response to vigorous muscle activity. Our findings define a conserved and critical role in mechanoprotection for the unique membrane architecture generated by the caveolin-cavin system.
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http://dx.doi.org/10.1083/jcb.201501046DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4555827PMC
August 2015

Amphiphysin 2 (BIN1) in physiology and diseases.

J Mol Med (Berl) 2014 May 5;92(5):453-63. Epub 2014 Mar 5.

IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Illkirch, France.

Amphiphysin 2, also named bridging integrator-1 (BIN1) or SH3P9, has been recently implicated in rare and common diseases affecting different tissues and physiological functions. BIN1 downregulation is linked to cancer progression and also correlates with ventricular cardiomyopathy and arrhythmia preceding heart failure. Increased BIN1 expression is linked to increased susceptibility for late-onset Alzheimer's disease. In addition, altered splicing may account for the muscle component of myotonic dystrophies, while recessive germinal mutations cause centronuclear myopathy. Despite undoubtedly underlining the relevance of BIN1 in human diseases, the molecular and cellular bases leading to such different diseases are unclear at present. BIN1 is a key regulator of endocytosis and membrane recycling, cytoskeleton regulation, DNA repair, cell cycle progression, and apoptosis. In light of the recent findings on the molecular, cellular, and physiological roles of BIN1, we discuss potential pathological mechanisms and highlight common disease pathways and also tissue-specific regulation. Next challenges will be to validate BIN1 both as a prognostic marker for the related diseases and as a potential therapeutic target.
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http://dx.doi.org/10.1007/s00109-014-1138-1DOI Listing
May 2014

Reducing dynamin 2 expression rescues X-linked centronuclear myopathy.

J Clin Invest 2014 Mar 24;124(3):1350-63. Epub 2014 Feb 24.

Centronuclear myopathies (CNM) are congenital disorders associated with muscle weakness and abnormally located nuclei in skeletal muscle. An autosomal dominant form of CNM results from mutations in the gene encoding dynamin 2 (DNM2), and loss-of-function mutations in the gene encoding myotubularin (MTM1) result in X-linked CNM (XLCNM, also called myotubular myopathy), which promotes severe neonatal hypotonia and early death. Currently, no effective treatments exist for XLCNM. Here, we found increased DNM2 levels in XLCNM patients and a mouse model of XLCNM (Mtm1(-/y)). Generation of Mtm1(-/y) mice that were heterozygous for Dnm2 revealed that reduction of DNM2 in XLCNM mice restored life span, whole-body strength, and diaphragm function and increased muscle strength. Additionally, classic CNM-associated histological features, including fiber atrophy and nuclei mispositioning, were absent or reduced. Ultrastructural analysis revealed improvement of sarcomere organization and triad structures. Skeletal muscle-specific decrease of Dnm2 during embryogenesis or in young mice after disease onset revealed that the rescue associated with downregulation of Dnm2 is cell autonomous and is able to stop and potentially revert XLCNM progression. These data indicate that MTM1 and DNM2 regulate muscle organization and force through a common pathway. Furthermore, despite DNM2 being a key mechanoenzyme, its reduction is beneficial for XLCNM and represents a potential therapeutic approach for patients.
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http://dx.doi.org/10.1172/JCI71206DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3938268PMC
March 2014

Identification of FHL1 as a therapeutic target for Duchenne muscular dystrophy.

Hum Mol Genet 2014 Feb 18;23(3):618-36. Epub 2013 Sep 18.

Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia.

Utrophin is a potential therapeutic target for the fatal muscle disease, Duchenne muscular dystrophy (DMD). In adult skeletal muscle, utrophin is restricted to the neuromuscular and myotendinous junctions and can compensate for dystrophin loss in mdx mice, a mouse model of DMD, but requires sarcolemmal localization. NFATc1-mediated transcription regulates utrophin expression and the LIM protein, FHL1 which promotes muscle hypertrophy, is a transcriptional activator of NFATc1. By generating mdx/FHL1-transgenic mice, we demonstrate that FHL1 potentiates NFATc1 activation of utrophin to ameliorate the dystrophic pathology. Transgenic FHL1 expression increased sarcolemmal membrane stability, reduced muscle degeneration, decreased inflammation and conferred protection from contraction-induced injury in mdx mice. Significantly, FHL1 expression also reduced progressive muscle degeneration and fibrosis in the diaphragm of aged mdx mice. FHL1 enhanced NFATc1 activation of the utrophin promoter and increased sarcolemmal expression of utrophin in muscles of mdx mice, directing the assembly of a substitute utrophin-glycoprotein complex, and revealing a novel FHL1-NFATc1-utrophin signaling axis that can functionally compensate for dystrophin.
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http://dx.doi.org/10.1093/hmg/ddt449DOI Listing
February 2014

Regulation of the transcriptional coactivator FHL2 licenses activation of the androgen receptor in castrate-resistant prostate cancer.

Cancer Res 2013 Aug 25;73(16):5066-79. Epub 2013 Jun 25.

Department of Biochemistry and Molecular Biology and Immunology, Monash University, Clayton Victoria, Australia.

It is now clear that progression from localized prostate cancer to incurable castrate-resistant prostate cancer (CRPC) is driven by continued androgen receptor (AR), signaling independently of androgen. Thus, there remains a strong rationale to suppress AR activity as the single most important therapeutic goal in CRPC treatment. Although the expression of ligand-independent AR splice variants confers resistance to AR-targeted therapy and progression to lethal castrate-resistant cancer, the molecular regulators of AR activity in CRPC remain unclear, in particular those pathways that potentiate the function of mutant AR in CRPC. Here, we identify FHL2 as a novel coactivator of ligand-independent AR variants that are important in CRPC. We show that the nuclear localization of FHL2 and coactivation of the AR is driven by calpain cleavage of the cytoskeletal protein filamin, a pathway that shows differential activation in prostate epithelial versus prostate cancer cell lines. We further identify a novel FHL2-AR-filamin transcription complex, revealing how deregulation of this axis promotes the constitutive, ligand-independent activation of AR variants, which are present in CRPC. Critically, the calpain-cleaved filamin fragment and FHL2 are present in the nucleus only in CRPC and not benign prostate tissue or localized prostate cancer. Thus, our work provides mechanistic insight into the enhanced AR activation, most notably of the recently identified AR variants, including AR-V7 that drives CRPC progression. Furthermore, our results identify the first disease-specific mechanism for deregulation of FHL2 nuclear localization during cancer progression. These results offer general import beyond prostate cancer, given that nuclear FHL2 is characteristic of other human cancers where oncogenic transcription factors that drive disease are activated like the AR in prostate cancer.
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http://dx.doi.org/10.1158/0008-5472.CAN-12-4520DOI Listing
August 2013

Altered splicing of the BIN1 muscle-specific exon in humans and dogs with highly progressive centronuclear myopathy.

PLoS Genet 2013 Jun 6;9(6):e1003430. Epub 2013 Jun 6.

IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Illkirch, France.

Amphiphysin 2, encoded by BIN1, is a key factor for membrane sensing and remodelling in different cell types. Homozygous BIN1 mutations in ubiquitously expressed exons are associated with autosomal recessive centronuclear myopathy (CNM), a mildly progressive muscle disorder typically showing abnormal nuclear centralization on biopsies. In addition, misregulation of BIN1 splicing partially accounts for the muscle defects in myotonic dystrophy (DM). However, the muscle-specific function of amphiphysin 2 and its pathogenicity in both muscle disorders are not well understood. In this study we identified and characterized the first mutation affecting the splicing of the muscle-specific BIN1 exon 11 in a consanguineous family with rapidly progressive and ultimately fatal centronuclear myopathy. In parallel, we discovered a mutation in the same BIN1 exon 11 acceptor splice site as the genetic cause of the canine Inherited Myopathy of Great Danes (IMGD). Analysis of RNA from patient muscle demonstrated complete skipping of exon 11 and BIN1 constructs without exon 11 were unable to promote membrane tubulation in differentiated myotubes. Comparative immunofluorescence and ultrastructural analyses of patient and canine biopsies revealed common structural defects, emphasizing the importance of amphiphysin 2 in membrane remodelling and maintenance of the skeletal muscle triad. Our data demonstrate that the alteration of the muscle-specific function of amphiphysin 2 is a common pathomechanism for centronuclear myopathy, myotonic dystrophy, and IMGD. The IMGD dog is the first faithful model for human BIN1-related CNM and represents a mammalian model available for preclinical trials of potential therapies.
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http://dx.doi.org/10.1371/journal.pgen.1003430DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3675003PMC
June 2013

Myotubularin and PtdIns3P remodel the sarcoplasmic reticulum in muscle in vivo.

J Cell Sci 2013 Apr 26;126(Pt 8):1806-19. Epub 2013 Feb 26.

Department of Translational Medicine, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), INSERM U964, CNRS UMR7104, Université de Strasbourg, Collège de France, 67404 Illkirch, France.

The sarcoplasmic reticulum (SR) is a specialized form of endoplasmic reticulum (ER) in skeletal muscle and is essential for calcium homeostasis. The mechanisms involved in SR remodeling and maintenance of SR subdomains are elusive. In this study, we identified myotubularin (MTM1), a phosphoinositide phosphatase mutated in X-linked centronuclear myopathy (XLCNM, or myotubular myopathy), as a key regulator of phosphatidylinositol 3-monophosphate (PtdIns3P) levels at the SR. MTM1 is predominantly located at the SR cisternae of the muscle triads, and Mtm1-deficient mouse muscles and myoblasts from XLCNM patients exhibit abnormal SR/ER networks. In vivo modulation of MTM1 enzymatic activity in skeletal muscle using ectopic expression of wild-type or a dead-phosphatase MTM1 protein leads to differential SR remodeling. Active MTM1 is associated with flat membrane stacks, whereas dead-phosphatase MTM1 mutant promotes highly curved cubic membranes originating from the SR and enriched in PtdIns3P. Overexpression of a tandem FYVE domain with high affinity for PtdIns3P alters the shape of the SR cisternae at the triad. Our findings, supported by the parallel analysis of the Mtm1-null mouse and an in vivo study, reveal a direct function of MTM1 enzymatic activity in SR remodeling and a key role for PtdIns3P in promoting SR membrane curvature in skeletal muscle. We propose that alteration in SR remodeling is a primary cause of X-linked centronuclear myopathy. The tight regulation of PtdIns3P on specific membrane subdomains may be a general mechanism to control membrane curvature.
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http://dx.doi.org/10.1242/jcs.118505DOI Listing
April 2013

Phosphatase-dead myotubularin ameliorates X-linked centronuclear myopathy phenotypes in mice.

PLoS Genet 2012 11;8(10):e1002965. Epub 2012 Oct 11.

Department of Translational Medecine, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), INSERM U964, CNRS UMR7104, Université de Strasbourg, Collège de France, Illkirch, France.

Myotubularin MTM1 is a phosphoinositide (PPIn) 3-phosphatase mutated in X-linked centronuclear myopathy (XLCNM; myotubular myopathy). We investigated the involvement of MTM1 enzymatic activity on XLCNM phenotypes. Exogenous expression of human MTM1 in yeast resulted in vacuolar enlargement, as a consequence of its phosphatase activity. Expression of mutants from patients with different clinical progression and determination of PtdIns3P and PtdIns5P cellular levels confirmed the link between vacuolar morphology and MTM1 phosphatase activity, and showed that some disease mutants retain phosphatase activity. Viral gene transfer of phosphatase-dead myotubularin mutants (MTM1(C375S) and MTM1(S376N)) significantly improved most histological signs of XLCNM displayed by a Mtm1-null mouse, at similar levels as wild-type MTM1. Moreover, the MTM1(C375S) mutant improved muscle performance and restored the localization of nuclei, triad alignment, and the desmin intermediate filament network, while it did not normalize PtdIns3P levels, supporting phosphatase-independent roles of MTM1 in maintaining normal muscle performance and organelle positioning in skeletal muscle. Among the different XLCNM signs investigated, we identified only triad shape and fiber size distribution as being partially dependent on MTM1 phosphatase activity. In conclusion, this work uncovers MTM1 roles in the structural organization of muscle fibers that are independent of its enzymatic activity. This underlines that removal of enzymes should be used with care to conclude on the physiological importance of their activity.
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http://dx.doi.org/10.1371/journal.pgen.1002965DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3469422PMC
March 2013

Defective membrane remodeling in neuromuscular diseases: insights from animal models.

PLoS Genet 2012 5;8(4):e1002595. Epub 2012 Apr 5.

Department of Translational Medicine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France.

Proteins involved in membrane remodeling play an essential role in a plethora of cell functions including endocytosis and intracellular transport. Defects in several of them lead to human diseases. Myotubularins, amphiphysins, and dynamins are all proteins implicated in membrane trafficking and/or remodeling. Mutations in myotubularin, amphiphysin 2 (BIN1), and dynamin 2 lead to different forms of centronuclear myopathy, while mutations in myotubularin-related proteins cause Charcot-Marie-Tooth neuropathies. In addition to centronuclear myopathy, dynamin 2 is also mutated in a dominant form of Charcot-Marie-Tooth neuropathy. While several proteins from these different families are implicated in similar diseases, mutations in close homologues or in the same protein in the case of dynamin 2 lead to diseases affecting different tissues. This suggests (1) a common molecular pathway underlying these different neuromuscular diseases, and (2) tissue-specific regulation of these proteins. This review discusses the pathophysiology of the related neuromuscular diseases on the basis of animal models developed for proteins of the myotubularin, amphiphysin, and dynamin families. A better understanding of the common mechanisms between these neuromuscular disorders will lead to more specific health care and therapeutic approaches.
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http://dx.doi.org/10.1371/journal.pgen.1002595DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3320571PMC
September 2012

Increased expression of wild-type or a centronuclear myopathy mutant of dynamin 2 in skeletal muscle of adult mice leads to structural defects and muscle weakness.

Am J Pathol 2011 May;178(5):2224-35

Department of Translational Medicine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.

Dynamin 2 (DNM2) is a large GTPase implicated in many cellular functions, including cytoskeleton regulation and endocytosis. Although ubiquitously expressed, DNM2 was found mutated in two genetic disorders affecting different tissues: autosomal dominant centronuclear myopathy (ADCNM; skeletal muscle) and peripheral Charcot-Marie-Tooth neuropathy (peripheral nerve). To gain insight into the function of DNM2 in skeletal muscle and the pathological mechanisms leading to ADCNM, we introduced wild-type DNM2 (WT-DNM2) or R465W DNM2 (RW-DNM2), the most common ADCNM mutation, into adult wild-type mouse skeletal muscle by intramuscular adeno-associated virus injections. We detected altered localization of RW-DNM2 in mouse muscle. Several ADCNM features were present in RW-DNM2 mice: fiber atrophy, nuclear mislocalization, and altered mitochondrial staining, with a corresponding reduction in specific maximal muscle force. The sarcomere and triad structures were also altered. We report similar findings in muscle biopsy specimens from an ADCNM patient with the R465W mutation. In addition, expression of wild-type DNM2 induced some muscle defects, albeit to a lesser extent than RW-DNM2, suggesting that the R465W mutation has enhanced activity in vivo. In conclusion, we show the RW-DNM2 mutation acts in a dominant manner to cause ADCNM in adult muscle, and the disease arises from a primary defect in skeletal muscle rather than secondary to peripheral nerve involvement. Therefore, DNM2 plays important roles in the maintenance of adult muscle fibers.
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http://dx.doi.org/10.1016/j.ajpath.2011.01.054DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3081151PMC
May 2011
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