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Statin-related muscle side effects are a constant healthcare problem since patient compliance is dependent on side effects. Statins reduce plasma cholesterol levels and can prevent secondary cardiovascular diseases. Although statin-induced muscle damage has been studied, preventive or curative therapies are yet to be reported. We exposed primary human muscle cell populations (n = 22) to a lipophilic (simvastatin) and a hydrophilic (rosuvastatin) statin and analyzed their expressome. Data and pathway analyses included GOrilla, Reactome and DAVID. We measured mevalonate intracellularly and analyzed eicosanoid profiles secreted by human muscle cells. Functional assays included proliferation and differentiation quantification. More than 1800 transcripts and 900 proteins were differentially expressed after exposure to statins. Simvastatin had a stronger effect on the expressome than rosuvastatin, but both statins influenced cholesterol biosynthesis, fatty acid metabolism, eicosanoid synthesis, proliferation, and differentiation of human muscle cells. Cultured human muscle cells secreted ω-3 and ω-6 derived eicosanoids and prostaglandins. The ω-6 derived metabolites were found at higher levels secreted from simvastatin-treated primary human muscle cells. Eicosanoids rescued muscle cell differentiation. Our data suggest a new aspect on the role of skeletal muscle in cholesterol metabolism. For clinical practice, the addition of omega-n fatty acids might be suitable to prevent or treat statin-myopathy.

The function of caveolae, small invaginations of the plasma membrane, remains a matter of debate. We discuss endocytosis and compartmentalization of metabolic and signaling pathways. Caveolin 3 (CAV3) and polymerase I and transcript release factor (PTRF) are important proteins that ensure shaping of caveolae in muscle cells. We investigated caveolae morphologically by electron microscopy in myotubes obtained from patients with CAV3 mutations and performed functional analyses in fibroblasts from a patient with a mutation in PTRF. Despite the complete clinical picture of a caveolinopathy, we found that caveolae in the CAV3-deficient myotubes were normal in shape and number. Furthermore, we found a difference in uptake of cholera toxin B between PTRF-deficient fibroblasts devoid of caveolae and normal fibroblasts. However, after caveolae were rescued by transfection of PTRF, cholera toxin B uptake did not normalize. We conclude that the presence of caveolae as an anatomic structure is not sufficient to ensure their proper function. Alternatively, the functional properties assigned to caveolae might be mediated by different mechanisms that have yet to be resolved., (Copyright © 2015 the American Physiological Society.)

Skeletal muscle is continually subjected to microinjuries that must be repaired to maintain structure and function. Fluorescent dye influx after laser injury of muscle fibers is a commonly used assay to study membrane repair. This approach reveals that initial resealing only takes a few seconds. However, by this method the process of membrane repair can only be studied in part and is therefore poorly understood. We investigated membrane repair by visualizing endogenous and GFP-tagged repair proteins after laser wounding. We demonstrate that membrane repair and remodeling after injury is not a quick event but requires more than 20 min. The endogenous repair protein dysferlin becomes visible at the injury site after 20 seconds but accumulates further for at least 30 min. Annexin A1 and F-actin are also enriched at the wounding area. We identified a new participant in the membrane repair process, the ATPase EHD2. We show, that EHD2, but not EHD1 or mutant EHD2, accumulates at the site of injury in human myotubes and at a peculiar structure that develops during membrane remodeling, the repair dome. In conclusion, we established an approach to visualize membrane repair that allows a new understanding of the spatial and temporal events involved., (© 2012 John Wiley & Sons A/S.)

Objective: Intensive care unit-acquired weakness indicates increased morbidity and mortality. Nonexcitable muscle membrane after direct muscle stimulation develops early and predicts intensive care unit-acquired weakness in sedated, mechanically ventilated patients. A comparison of muscle histology at an early stage in intensive care unit-acquired weakness has not been done. We investigated whether nonexcitable muscle membrane indicates fast-twitch myofiber atrophy during the early course of critical illness., Design: Prospective observational study., Setting: Two intensive care units at Charité University Medicine, Berlin., Patients: Patients at increased risk for development of intensive care unit-acquired weakness, indicated by Sepsis-related Organ Failure Assessment scores ≥8 on 3 of 5 consecutive days within their first week in the intensive care unit., Interventions: None., Measurements and Main Results: Electrophysiological compound muscle action potentials after direct muscle stimulation and muscle biopsies were obtained at median days 7 and 5, respectively. Patients with nonexcitable muscle membranes (n = 15) showed smaller median type II cross-sectional areas (p < .05), whereas type I muscle fibers did not compared with patients with preserved muscle membrane excitability (compound muscle action potentials after direct muscle stimulation ≥3.0 mV; n = 9). We also observed decreased mRNA transcription levels of myosin heavy chain isoform IIa and a lower densitometric ratio of fast-to-slow myosin heavy chain protein content., Conclusion: We suggest that electrophysiological nonexcitable muscle membrane predicts preferential type II fiber atrophy in intensive care unit patients during early critical illness.

Ahnak1 is a giant, ubiquitously expressed, plasma membrane support protein whose function in skeletal muscle is largely unknown. Therefore, we investigated whether ahnak would be influenced by alterations of the sarcolemma exemplified by dysferlin mutations known to render the sarcolemma vulnerable or by mutations in calpain3, a protease known to cleave ahnak. Human muscle biopsy specimens obtained from patients with limb girdle muscular dystrophy (LGMD) caused by mutations in dysferlin (LGMD2B) and calpain3 (LGMD2A) were investigated for ahnak expression and localization. We found that ahnak1 has lost its sarcolemmal localization in LGMD2B but not in LGMD2A. Instead ahnak1 appeared in muscle connective tissue surrounding the extracellular site of the muscle fiber in both muscular dystrophies. The entire giant ahnak1 molecule was present outside the muscle fiber and did only partially colocalize with CD45-positive immune cell infiltration and the extracelluar matrix proteins fibronectin and collagenVI. Further, vesicles shedded in response to Ca(2+) by primary human myotubes were purified and their protein content was analysed. Ahnak1 was prominently present in these vesicles. Electron microscopy revealed a homogenous population of vesicles with a diameter of about 150 nm. This is the first study demonstrating vesicle release from human myotubes that may be one mechanism underlying abnormally localized ahnak1. Taken together, our results define ahnak1 in muscle connective tissue as a novel feature of two genetically distinct muscular dystrophies that might contribute to disease pathology.

Objectives: : To investigate the predictive value of electrophysiological measurements including validation of muscle membrane excitability on the development of intensive care unit (ICU)-aquired paresis., Design: : Prospective observational study., Setting: : University ICU., Patients: : Surgical ICU patients selected upon a simplified acute physiology score > or =20 on three successive days within 1 wk after ICU admission., Interventions: : We performed serial electrophysiological measurements with onset of critical illness including conventional electrophysiological parameters and compound muscle action potentials after direct muscle stimulation (dmCMAP). Patients' awareness and muscle strength were measured sequentially by Ramsay sedation scale and an additional questionnaire and by Medical Research Council score, respectively., Measurements and Main Results: : Among 56 sedated patients 34 patients revealed reduced dmCMAP values <3 mV indicating a myopathic process within 7.5 (5 of 11) days after admission to the ICU. Abnormal dmCMAP anticipated ICU-acquired paresis upon emergence from sedation with a sensitivity and specificity of 83.3% and 88.8%, respectively (positive predictive value of 0.91). Multivariate logistic regression analyses revealed that validating dmCMAP during early course of critical illness had significant diagnostic utility to anticipate ICU-acquired paresis (p = .004; odds ratio = .47; 95% confidence interval = .28-.79)., Conclusions: : Abnormal dmCMAP occurred within the first week after admission to the ICU and pointed towards a myopathic process as the primary cause of ICU-acquired paresis. Validation of dmCMAP with onset of critical illness allows an early prediction of ICU-acquired paresis and adds important information to clinical estimation of the patients' motor function.

Dysferlin is expressed in skeletal and cardiac muscles. However, dysferlin deficiency results in skeletal muscle weakness, but spares the heart. We compared intraindividual mRNA expression profiles of cardiac and skeletal muscle in dysferlin-deficient SJL/J mice and found down-regulation of the complement inhibitor, decay-accelerating factor/CD55, in skeletal muscle only. This finding was confirmed on mRNA and protein levels in two additional dysferlin-deficient mouse strains, A/J mice and Dysf-/- mice, as well as in patients with dysferlin-deficient muscular dystrophy. In vitro, the absence of CD55 led to an increased susceptibility of human myotubes to complement attack. Evidence is provided that decay-accelerating factor/CD55 is regulated via the myostatin-SMAD pathway. In conclusion, a novel mechanism of muscle fiber injury in dysferlin-deficient muscular dystrophy is demonstrated, possibly opening therapeutic avenues in this to date untreatable disorder.

Antibody-dependent complement-mediated muscle fiber injury is a hypothetical immune effector response in inflammatory muscle diseases. Moreover, a sarcolemmal alteration in muscular dystrophies might trigger antibody-independent activation of the alternative complement pathway. We therefore searched for C5b9 complement membrane attack complex (MAC), immunoglobulin (Ig)G, and IgM deposits on nonnecrotic muscle fibers in muscle specimens from 81 patients with inflammatory myopathies, 45 patients with muscular dystrophies, and 19 patients with necrotizing myopathies. Sarcolemmal MAC deposits were present on nonnecrotic fibers (C+ fibers) in only two unusual types of inflammatory myopathy. By contrast, seven of 17 facioscapulohumeral dystrophy, four of nine limb-girdle dystrophy, and three of six merosin (laminin-alpha-2)-positive congenital muscular dystrophy but none of the Becker or Duchenne dystrophy specimens harbored C+ fibers. None of the C+ fibers immunostained for IgG or IgM, and none failed to immunostain for CD59 or CD46-inhibitors of the complement cascade. Our findings do not support a role for antibody-dependent complement-mediated muscle fiber injury in the major inflammatory muscle diseases. The cause and pathogenetic significance of the C+ fibers in the different types of muscular dystrophies remains to be elucidated.