Aging-associated genes and let-7 microRNAs: a contribution to myogenic program dysregulation in oculopharyngeal muscular dystrophy.

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset muscle disease caused by an abnormal (GCN) triplet expansion within the polyadenylate-binding protein nuclear 1 gene and consequent mRNA processing impairment and myogenic defects. Because a reduced cell proliferation potential and the consequent regeneration failure of aging muscle have been shown to be governed by lethal-7 (let-7) microRNA-mediated mechanisms, in the present study, we evaluated the role of let-7 in the pathogenesis of OPMD. By a multidisciplinary approach, including confocal microscopy, Western blot, and quantitative PCR analyses on muscle biopsies from patients and unaffected individuals, we found a significant increase in let-7 expression in OPMD muscles associated with an unusual high percentage of paired box 7-positive satellite cells. Furthermore, IL-6, a cytokine involved in the regulation of satellite cell proliferation and differentiation and a potential target of let-7, was found strongly down-regulated in OPMD compared with control muscles. The decrease in IL-6 transcript levels and protein content was also confirmed in vitro during differentiation of patients' and controls' muscle cells. Overall, our data suggest a key role of let-7 in the regeneration and degeneration process in OPMD muscle and pointed to IL-6 as a potential target molecule for new therapeutic approaches for this disorder.-Cappelletti, C., Galbardi, B., Bruttini, M., Salerno, F., Canioni, E., Pasanisi, M. B., Rodolico, C., Brizzi, T., Mora, M., Renieri, A., Maggi, L., Bernasconi, P., Mantegazza, R. Aging-associated genes and let-7 microRNAs: a contribution to myogenic program dysregulation in oculopharyngeal muscular dystrophy.

Botulinum toxin type A affects the transcriptome of cell cultures derived from muscle biopsies of controls and spastic patients.

Botulin toxin (BTX) is widely used for treating skeletal muscle spasticity. Experimental reports on BTX treatment were mainly focused on the neuromuscular junction, while relatively little is known about toxin effects on the muscle cell itself. We investigated possible impact of BTX type A on skeletal muscle cell transcriptome by microarray analysis in muscle-derived cell cultures (fibroblasts, myoblasts and myotubes) from controls and spastic patients, and results were then validated at transcript and protein level. BTX-A treatment of control cells induced major changes in the myogenic component of the transcriptome, whereas the same treatment had a negligible effect in the fibrogenic component. BTX-A treatment of cell cultures from spastic patients induced an increased number of genes differentially expressed both in the fibrogenic and myogenic components. Specifically, BTX-A had a major effect on cell cycle-related genes in myoblasts, on muscle contraction-related genes in myotubes, and on extracellular matrix-related genes in fibroblasts from spastic patients. Our findings show that in vitro BTX-A treatment differentially affects transcript expression in muscle cells from spastic patients compared to those from controls suggesting a direct effect of BTX-A on muscle-specific functional pathways.

SEPN1-related myopathy in three patients: novel mutations and diagnostic clues.

UNLABELLED: Mutations in SEPN1 cause selenoprotein N (SEPN)-related myopathy (SEPN-RM) characterized by early-onset axial and neck weakness, spinal rigidity, respiratory failure and histopathological features, ranging from mild dystrophic signs to a congenital myopathy pattern with myofibrillar disorganization. We report on clinical and instrumental features in three patients affected with a congenital myopathy characterized by prevalent neck weakness starting at different ages and mild myopathy, in whom we performed diagnosis of SEPN-RM. The patients presented myopathic signs since their first years of life, but the disease remained unrecognized because of a relatively benign myopathic course. In two cases, myopathic features were stable after 2 years of follow-up, but respiratory involvement worsened. The muscle MRI and muscle biopsy showed a typical pattern of SEPN-RM. Molecular diagnosis revealed two novel homozygous mutations in SEPN1, c.1176delA and c.726_727InsTCC. CONCLUSION: This report underlines the clinical diagnostic clues of early neck and axial weakness to suspect a SEPN-RM and the usefulness of muscle MRI in conjunction with clinical features to achieve the diagnosis. Our data confirm the slow progression of respiratory involvement in spite of the relatively stable course of myopathy. We report two previously undescribed mutations in SEPN1. WHAT IS KNOWN: • Mutations in SEPN1 cause myopathy characterized by early-onset axial and neck weakness spinal rigidity and respiratory failure. • SEPN-related myopathies have been initially associated with four distinct histopathological entities that however appear more mixed in recently described cases. What is New: • SEPN-related myopathies can remain unrecognized because of the normal early motor development and relatively benign myopathic course of the disease. • Our study adds two novel homozygous mutations to the number of reported pathogenic SEPN1 variants.

Fibrosis and inflammation are greater in muscles of beta-sarcoglycan-null mouse than mdx mouse.

The Sgcb-null mouse, with knocked-down ß-sarcoglycan, develops severe muscular dystrophy as in type 2E human limb girdle muscular dystrophy. The mdx mouse, lacking dystrophin, is the most used model for Duchenne muscular dystrophy (DMD). Unlike DMD, the mdx mouse has mild clinical features and shows little fibrosis in limb muscles. To characterize ECM protein deposition and the progression of muscle fibrosis, we evaluated protein and transcript levels of collagens I, III and VI, decorin, and TGF-ß1, in quadriceps and diaphragm, at 2, 4, 8, 12, 26, and 52 weeks in Sgcb-null mice, and protein levels at 12, 26, and 52 weeks in mdx mice. In Sgcb-null mice, severe morphological disruption was present from 4 weeks in both quadriceps and diaphragm, and included conspicuous deposition of extracellular matrix components. Histopathological features of Sgcb-null mouse muscles were similar to those of age-matched mdx muscles at all ages examined, but, in the Sgcb-null mouse, the extent of connective tissue deposition was generally greater than mdx. Furthermore, in the Sgcb-null mouse, the amount of all three collagen isoforms increased steadily, while, in the mdx, they remained stable. We also found that, at 12 weeks, macrophages were significantly more numerous in mildly inflamed areas of Sgcb-null quadriceps compared to mdx quadriceps (but not in highly inflamed regions), while, in the diaphragm, macrophages did not differ significantly between the two models, in either region. Osteopontin mRNA was also significantly greater at 12 weeks in laser-dissected highly inflamed areas of the Sgcb-null quadriceps compared to the mdx quadriceps. TGF-ß1 was present in areas of degeneration-regeneration, but levels were highly variable and in general did not differ significantly between the two models and controls. The roles of the various subtypes of macrophages in muscle repair and fibrosis in the two models require further study. The Sgcb-null mouse, which develops early fibrosis in limb muscles, appears more promising than the mdx mouse for probing pathogenetic mechanisms of muscle fibrosis and for developing anti-fibrotic treatments. Highlights • The Sgcb-null mouse develops severe muscular dystrophy, the mdx mouse does not. • Fibrosis developed earlier in Sgcb-null quadriceps and diaphragm than mdx. • Macrophages were commoner in mildly inflamed parts of Sgcb-null quadriceps than mdx. • The Sgcb-null model appears more useful than mdx for studying fibrotic mechanisms. • The Sgcb-null model also appears more useful for developing anti-fibrotic treatments.

Familial adult-onset Pompe disease associated with unusual clinical and histological features.

The adult-onset form of Pompe disease had a wide clinical spectrum, ranging from asymptomatic patients with increased CK to muscle cramps and pain syndrome or rigid-spine syndrome. In addition clinical severity and disease progression are greatly variable. We report on a family with 3 siblings characterized by an unusual adult-onset Pompe disease including dysphagia and weakness of tongue, axial and limb-girdle muscles, in association with atypical globular inclusions in muscle fibres. Our study confirms the great clinical and histological variability of adult-onset Pompe disease and further supports the need of careful evaluation of bulbar function in patients affected by this pathology.

Complete stable remission and autoantibody specificity in myasthenia gravis.

OBJECTIVES: Patients with myasthenia gravis (MG) are subgrouped as acetylcholine receptor (AChR)-positive, muscle-specific kinase (MuSK)-positive, and AChR/MuSK-negative MG (or double negative [DN]) on the basis of autoantibody assay. We investigated the relationships between autoantibody specificity, main clinical features, and outcome of the disease, in particular the occurrence of complete stable remission (CSR), by means of a retrospective study on a cohort of 677 Italian patients with MG. METHODS: A total of 517 (76%) patients with AChR-positive MG, 55 (8%) patients with MuSK-positive MG, and 105 (16%) patients with DN MG were included in the study. Kaplan-Meier and Cox proportional hazard regression analyses were used to evaluate associations between baseline characteristics, antibody specificity, and CSR. RESULTS: Clinical stage at onset and at maximal worsening was more severe for MuSK-positive patients: bulbar impairment at maximal worsening was found in 83.6% of MuSK-positive patients compared with 58.6% of AChR-positive patients and 43.8% of DN patients (p < 0.001). Baseline characteristics of AChR-positive and DN patients were similar. CSR was observed in 3.6% of MuSK-positive patients compared with 22.2% of AChR-positive and 21.9% of DN patients. In the whole MG cohort, onset before age 40 (hazard ratio [HR] = 1.96, 95% confidence interval [CI] 1.27-3.02, p = 0.002) and ocular and generalized clinical stages at maximal worsening were associated with CSR (ocular, HR = 8.05, 95% CI 1.88-34.53, p = 0.005; generalized, HR = 3.71, 95% CI 1.16-11.90, p = 0.023; bulbar, HR = 3.16, 95% CI 1.00-10.05, p = 0.051). CONCLUSIONS: MuSK antibodies identify a clinically distinguishable, more severe form of MG since the disease onset, with a lower occurrence of CSR. These features should be considered by the clinician in the management of this particular form of MG.