rAAV-related therapy fully rescues myonuclear and myofilament function in X-linked myotubular myopathy
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RESEARCH
rAAV‑related therapy fully rescues myonuclear and myofilament function in X‑linked myotubular myopathy Jacob A. Ross1,2, Hichem Tasfaout3, Yotam Levy1, Jennifer Morgan4,5, Belinda S. Cowling3, Jocelyn Laporte3, Edmar Zanoteli6, Norma B. Romero7, Dawn A. Lowe8, Heinz Jungbluth9,10,11, Michael W. Lawlor12, David L. Mack13,14 and Julien Ochala1,9,15*
Abstract 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 × 1013 vg kg−1 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. Keywords: Skeletal muscle, Congenital myopathy, Myotubularin, Myonuclear domain, Myofilament, Force production
*Correspondence: [email protected] 1 Centre of Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, Faculty of Life Sciences & Medicine, King’s College London, London, UK Full list of author information is available at the end of the article
Introduction The centronuclear myopathies (CNM) are a group of genetically and clinically heterogeneous early-onset muscle disorders, with phenotypes varying from severe cases with antenatal/neonatal onset and death in infancy if untreated, to mild cases with onset in adolescence or adulthood and a stable or only slowly progressive course. The severe X-linked form of CNM (also termed X-linked myotubular myopathy or XLMTM, OMIM 310,400) is
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