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T-tubule disorganization and defective excitation-contraction coupling in muscle fibers lacking myotubularin lipid phosphatase

2009; National Academy of Sciences; Volume: 106; Issue: 44 Linguagem: Inglês

10.1073/pnas.0900705106

1091-6490

Lama Al‐Qusairi, Norbert Weiss, Anne Toussaint, Céline Berbey, Nadia Messaddeq, Christine Kretz, Despina Sanoudou, Alan H. Beggs, Bruno Allard, Jean‐Louis Mandel, Jocelyn Laporte, Vincent Jacquemond, Anna Buj‐Bello,

Erythrocyte Function and Pathophysiology

Skeletal muscle contraction is triggered by the excitation-contraction (E-C) coupling machinery residing at the triad, a membrane structure formed by the juxtaposition of T-tubules and sarcoplasmic reticulum (SR) cisternae. The formation and maintenance of this structure is key for muscle function but is not well characterized. We have investigated the mechanisms leading to X-linked myotubular myopathy (XLMTM), a severe congenital disorder due to loss of function mutations in the MTM1 gene, encoding myotubularin, a phosphoinositide phosphatase thought to have a role in plasma membrane homeostasis and endocytosis. Using a mouse model of the disease, we report that Mtm1-deficient muscle fibers have a decreased number of triads and abnormal longitudinally oriented T-tubules. In addition, SR Ca(2+) release elicited by voltage-clamp depolarizations is strongly depressed in myotubularin-deficient muscle fibers, with myoplasmic Ca(2+) removal and SR Ca(2+) content essentially unaffected. At the molecular level, Mtm1-deficient myofibers exhibit a 3-fold reduction in type 1 ryanodine receptor (RyR1) protein level. These data reveal a critical role of myotubularin in the proper organization and function of the E-C coupling machinery and strongly suggest that defective RyR1-mediated SR Ca(2+) release is responsible for the failure of muscle function in myotubular myopathy.