The aim of this work was to identify micro‐RNAs (miRNAs) involved in the pathological pathways activated in skeletal muscle damage and regeneration by both dystrophin absence and acute ischemia. Eleven miRNAs were deregulated both in MDX mice and in Duchenne muscular dystrophy patients (DMD signature). Therapeutic interventions ameliorating the mdx ‐phenotype rescued DMD‐signature alterations. The significance of DMD‐signature changes was characterized using a damage/regeneration mouse model of hind‐limb ischemia and newborn mice. According to their expression, DMD‐signature miRNAs were divided into 3 classes. 1 ) Regeneration miRNAs, miR‐31, miR‐34c, miR‐206, miR‐335, miR‐449, and miR‐494, which were induced in MDX mice and in DMD patients, but also in newborn mice and in newly formed myofibers during postischemic regeneration. Notably, miR‐206, miR‐34c, and miR‐335 were up‐regulated following myoblast differentiation in vitro. 2 ) Degenerative‐miRNAs, miR‐1, miR‐29c, and miR‐135a, that were down‐modulated in MDX mice, in DMD patients, in the degenerative phase of the ischemia response, and in newborn mice. Their down‐modulation was linked to myofiber loss and fibrosis. 3 ) Inflammatory miRNAs, miR‐222 and miR‐223, which were expressed in damaged muscle areas, and their expression correlated with the presence of infiltrating inflammatory cells. These findings show an important role of miRNAs in physiopathological pathways regulating muscle response to damage and regeneration.—Greco, S., De Simone, M., Colussi, C., Zaccagnini, G., Fasanaro, P., Pescatori, M., Cardani, R., Perbellini, R., Isaia, E., Sale, P., Meola, G., Capogrossi, M. C., Gaetano, C., Martelli, F. Common micro‐RNA signature in skeletal muscle damage and regeneration induced by Duchenne muscular dystrophy and acute ischemia. FASEB J . 23, 3335–3346 (2009). www.fasebj.org

A severe mitochondrial protein synthesis defect in myoblasts from a patient with mitochondrial myopathy was transferred with myoblast mitochondria into two genetically unrelated mitochondrial DNA (mtDNA)-less human cell lines, pointing to an mtDNA alteration as being responsible and sufficient for causing the disease. The transfer of the defect correlated with marked deficiencies in respiration and cytochrome c oxidase activity of the transformants and the presence in their mitochondria of mtDNA carrying a tRNA(Lys) mutation. Furthermore, apparently complete segregation of the defective genotype and phenotype was observed in the transformants derived from the heterogeneous proband myoblast population, suggesting that the mtDNA heteroplasmy in this population was to a large extent intercellular. The present work thus establishes a direct link between mtDNA alteration and a biochemical defect.

Background: Several missense mutations of CACNA1S and SCN4A genes occur in hypokalemic periodic paralysis. These mutations affect arginine residues in the S4 voltage sensors of the channel. Approximately 20% of cases remain genetically undefined. Methods: We undertook direct automated DNA sequencing of the S4 regions of CACNA1S and SCN4A in 83 cases of hypokalemic periodic paralysis. Results: We identified reported CACNA1S mutations in 64 cases. In the remaining 19 cases, mutations in SCN4A or other CACNA1S S4 segments were found in 10, including three novel changes and the first mutations in channel domains I (SCN4A) and III (CACNA1S). Conclusions: All mutations affected arginine residues, consistent with the gating pore cation leak hypothesis of hypokalemic periodic paralysis. Arginine mutations in S4 segments underlie 90% of hypokalemic periodic paralysis cases.