Selective Muscle Fiber Research Articles

The Clinical, Myopathological, and Genetic Analysis of 20 Patients With Non-dystrophic Myotonia

IntroductionNon-dystrophic myotonias (NDMs) are skeletal muscle ion channelopathies caused by CLCN1 or SCN4A mutations. This study aimed to describe the clinical, myopathological, and genetic analysis of NDM in a large Chinese cohort.MethodsWe reviewed the clinical manifestations, laboratory results, electrocardiogram, electromyography, muscle biopsy, genetic analysis, treatment, and follow-up of 20 patients (from 18 families) with NDM.ResultsCases included myotonia congenita (MC, 17/20) and paramyotonia congenita (PMC, 3/20). Muscle stiffness and hypertrophy, grip and percussion myotonia, and the warm-up phenomenon were frequently observed in MC and PMC patients. Facial stiffness, eye closure myotonia, and cold sensitivity were more common in PMC patients and could be accompanied by permanent weakness. Nine MC patients and two PMC patients had cardiac abnormalities, mainly manifested as cardiac arrhythmia, and the father of one patient died of sudden cardiac arrest. Myotonic runs in electromyography were found in all patients, and seven MC patients had mild myopathic changes. There was no difference in muscle pathology between MC and PMC patients, most of whom had abnormal muscle fiber type distribution or selective muscle fiber atrophy. Nineteen CLCN1 variants were found in 17 MC patients, among which c.795T>G (p.D265E) was a new variant, and two SCN4A variants were found in three PMC patients. The patients were treated with mexiletine and/or carbamazepine, and the symptoms of myotonia were partially improved.ConclusionsMC and PMC have considerable phenotypic overlap. Genetic investigation contributes to identifying the subtype of NDM. The muscle pathology of NDM lacks specific changes.

Efficacy of Botulinum Toxin Stereotype A and Its Relevant Mechanisms of Action in Both Cosmetic and Therapeutic Uses

Onabotulinumtoxin A (Botox®) is a parasympathetic autonomic blocking agent which acts as an inhibitor of the neuromuscular transmitter acetylcholine release and as a neuromuscular blocking agent, thereby inducing relaxation of selected muscle fibers for a duration of up to approximately 3 months duration. First approved by the FDA in 1989 and approved for further applications since 1991, the drug has now gained wide acceptance in cosmetic and other therapeutic applications, where the autonomic neurotransmitter acetylcholine blockade can bring about favorable cosmetic responses, particularly in the field of dermatology and cosmetic medicine. Since the original application of Onabotulinumtoxin A was approved for clinical use as a cosmetic agent, numerous additional applications have been approved by the FDA, all of which involve acetylcholine-mediated neuromuscular actions.

Treatment of convergence insufficiency exotropia in adults using a selective muscle fiber surgery algorithm

Treatment of convergence insufficiency exotropia in adults using a selective muscle fiber surgery algorithm

Treatment of convergence insufficiency exotropia in adults using a selective muscle fiber surgery treatment algorithm

Treatment of adults with convergence insufficiency (CI) exotropia is challenging as surgery frequently results in distance and lateral gaze esotropia. Recent evidence demonstrates differential compartmental function of extraocular muscle fiber groups. Selective surgery of muscle fiber groups may diminish distance–near disparities (NDD) while maintaining alignment at distance.

Histological characterization and biochemical analysis of paraspinal muscles in neuromuscularly healthy subjects

There are no generally accepted histopathological reference values in paraspinal skeletal muscle biopsies. We examined multifidii muscle biopsies from 20 neuromuscularly healthy subjects using routine histological stains and biochemical analyses of respiratory chain enzymes. Staining showed incomplete myopathic features, such as increased variability in fiber size, type 1 hypertrophy, rounded fiber shape, endomysial fibrosis, and replacement by adipose tissue. Acid phosphatase reaction was positive in up to 35% of the selected muscle fibers. Mitochondrial changes were obvious but revealed no selective age dependence. Reduced complex I, cytochrome c oxidase (COX), and citrate synthase (CS) could be observed. Because the increased variability in morphological details can easily be misinterpreted as myopathic changes, analysis of paraspinal muscles should take into consideration that incomplete myopathic features and reduced oxidative enzyme activities for complex I, COX, and CS are normal variations at this location.

Mechanisms for fiber-type specificity of skeletal muscle atrophy

There are a variety of pathophysiologic conditions that are known to induce skeletal muscle atrophy. However, muscle wasting can occur through multiple distinct signaling pathways with differential sensitivity between selective skeletal muscle fiber subtypes. This review summarizes some of the underlying molecular mechanisms responsible for fiber-specific muscle mass regulation. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha protects slow-twitch oxidative fibers from denervation/immobilization (disuse)-induced muscle atrophies. Nutrient-related muscle atrophies, such as those induced by cancer cachexia, sepsis, chronic heart failure, or diabetes, are largely restricted to fast-twitch glycolytic fibers, of which the underlying mechanism is usually related to abnormality of protein degradation, including proteasomal and lysosomal pathways. In contrast, nuclear factor kappaB activation apparently serves a dual function by inducing both fast-twitch fiber atrophy and slow-twitch fiber degeneration. Fast-twitch glycolytic fibers are more vulnerable than slow-twitch oxidative fibers under a variety of atrophic conditions related to signaling transduction of Forkhead box O family, autophagy inhibition, transforming growth factor beta family, and nuclear factor-kappaB. The resistance of oxidative fibers may result from the protection of peroxisome proliferator-activated receptor gamma coactivator 1-alpha.

The study of muscle remodeling in Drosophila metamorphosis using in vivo microscopy and bioimage informatics

BackgroundMetamorphosis in insects transforms the larval into an adult body plan and comprises the destruction and remodeling of larval and the generation of adult tissues. The remodeling of larval into adult muscles promises to be a genetic model for human atrophy since it is associated with dramatic alteration in cell size. Furthermore, muscle development is amenable to 3D in vivo microscopy at high cellular resolution. However, multi-dimensional image acquisition leads to sizeable amounts of data that demand novel approaches in image processing and analysis.ResultsTo handle, visualize and quantify time-lapse datasets recorded in multiple locations, we designed a workflow comprising three major modules. First, the previously introduced TLM-converter concatenates stacks of single time-points. The second module, TLM-2D-Explorer, creates maximum intensity projections for rapid inspection and allows the temporal alignment of multiple datasets. The transition between prepupal and pupal stage serves as reference point to compare datasets of different genotypes or treatments. We demonstrate how the temporal alignment can reveal novel insights into the east gene which is involved in muscle remodeling. The third module, TLM-3D-Segmenter, performs semi-automated segmentation of selected muscle fibers over multiple frames. 3D image segmentation consists of 3 stages. First, the user places a seed into a muscle of a key frame and performs surface detection based on level-set evolution. Second, the surface is propagated to subsequent frames. Third, automated segmentation detects nuclei inside the muscle fiber. The detected surfaces can be used to visualize and quantify the dynamics of cellular remodeling. To estimate the accuracy of our segmentation method, we performed a comparison with a manually created ground truth. Key and predicted frames achieved a performance of 84% and 80%, respectively.ConclusionsWe describe an analysis pipeline for the efficient handling and analysis of time-series microscopy data that enhances productivity and facilitates the phenotypic characterization of genetic perturbations. Our methodology can easily be scaled up for genome-wide genetic screens using readily available resources for RNAi based gene silencing in Drosophila and other animal models.

Diaphragm Muscle Fiber Weakness in Pulmonary Hypertension

Recently it was suggested that patients with pulmonary hypertension (PH) suffer from inspiratory muscle dysfunction. However, the nature of inspiratory muscle weakness in PH remains unclear. To assess whether alterations in contractile performance and in morphology of the diaphragm underlie inspiratory muscle weakness in PH. PH was induced in Wistar rats by a single injection of monocrotaline (60 mg/kg). Diaphragm (PH n = 8; controls n = 7) and extensor digitorum longus (PH n = 5; controls n = 7) muscles were excised for determination of in vitro contractile properties and cross-sectional area (CSA) of the muscle fibers. In addition, important determinants of protein synthesis and degradation were determined. Finally, muscle fiber CSA was determined in diaphragm and quadriceps of patients with PH, and the contractile performance of single fibers of the diaphragm. In rats with PH, twitch and maximal tetanic force generation of diaphragm strips were significantly lower, and the force-frequency relation was shifted to the right (i.e., impaired relative force generation) compared with control subjects. Diaphragm fiber CSA was significantly smaller in rats with PH compared with controls, and was associated with increased expression of E3-ligases MAFbx and MuRF-1. No significant differences in contractility and morphology of extensor digitorum longus muscle fibers were found between rats with PH and controls. In line with the rat data, studies on patients with PH revealed significantly reduced CSA and impaired contractility of diaphragm muscle fibers compared with control subjects, with no changes in quadriceps muscle. PH induces selective diaphragm muscle fiber weakness and atrophy.

Quantitative Assessment of Laryngeal Muscle Morphology After Recurrent Laryngeal Nerve Injury: Right vs. Left Differences

Reports of laryngeal response to denervation are inconsistent. Some document atrophy and fibrosis in denervated laryngeal muscles, whereas others indicate resistance to atrophy. Spontaneous reinnervation has also been documented. The goal of this study was to clarify the effects of nerve injury and reinnervation on thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles. Laboratory experiment. TA and PCA muscles of cats were harvested 5 to 6 months after transecting right or left recurrent laryngeal nerve (RLN). Images of muscle cross-sections were acquired and studied using an image analysis workstation. Cross-sectional areas as well as total cross-sectional area of randomly selected muscle fibers were recorded. TA reinnervation was robust on both sides, but there was less reinnervation of the PCA muscle after left-sided RLN lesion than after right-sided injury. Differences in reinnervation after RLN injury could contribute to the higher clinical incidence of left- vs. right-sided laryngeal paralysis.

Abstracts

Epidermolysis bullosa simplex (EBS) associated with muscular dystrophy (MD, MIM#226670) is a disorder involving defects in certain isoforms of the cytoskeletal protein plectin expressed in skin and muscle. Immunoperoxidase staining was performed using previously reported EBS-MD patients skeletal muscle (n=3) together with control muscle (n=4) to determine the pathogenesis of muscular dystrophy. While plectin monoclonal antibodies 10F6 and HD1-121 both localized to the plasma membrane (PM) in control skeletal muscle, 10F6 also stained the center of type II muscle fibers. Conversely, HD1-121 stained the center of type I fibers. EBS-MD muscle demonstrated a loss of all membrane HD1-121 and 10F6 staining (in 3 cases) but retained some HD1-121 (in 1 case) and 10F6 staining (in 3 cases) within the center of selected muscle fibers. There was normal staining for dystrophin, β spectrin, vinculin and β1 integrin in all 3 cases of EBS-MD muscle. However, α actinin and desmin staining in 2 EBS-MD cases was disorganized and lacked the sharp, striated appearance of control muscle. Electron microscopy showed a widening of the space immediately beneath the PM with abnormal vacuolization and variation in the number, size and parallel organization of Zlines in 2 cases. Postembedding immunogold electron microscopy of control muscle colocalized plectin and desmin to two main sites: filamentous bridges between Z-lines and to the inner surface of the PM, in contrast to dystrophin labeling that was restricted to focal densities on the membrane. We therefore conclude that multiple, distinct fiber-specific plectin isoforms play a role in linking cytoskeletal elements to Z-lines and more critically to the myocyte PM, analogous to epidermal hemidesmosome-cytoskeletal anchorage in skin.

Physical Training of Children with Juvenile Chronic Arthritis: Effects on Force, Endurance and EMG Response to Localized Muscle Fatigue

We examined force, endurance and the electromyographic response to muscle fatigue in ten children with juvenile chronic arthritis (JCA) and ten age-matched healthy controls before and after physical training. Our main finding was a reduced electromyographic response to localized muscle fatigue in the patient group. After training there was a tendency towards a normalized response pattern. A possible explanation may be selective type-II muscle fiber atrophy, and recovery of these fibers after training.

Mitochondrial size and shape in equine skeletal muscle: a three-dimensional reconstruction study.

Individual mitochondria were reconstructed from ultrathin serial sections of selected muscle fibers in the M. semitendinosus of a horse, over a length of nearly two sarcomeres. Mitochondria were found to be highly variable, with size and complexity of single mitochondria increasing with the fractional part of a fiber occupied by mitochondria. In fibers with a mitochondrial volume density of less than 4%, corresponding to the mitochondrial content of fast-twitch glycolytic fibers, mitochondria were generally rather simple cylindrical shapes, oriented parallel to the myofibrils. In fibers with a mitochondrial volume density of more than 7%, corresponding to the mitochondrial content of slow-oxidative or fast-oxidative glycolytic fibers, mitochondria were generally cylindrical at the A-band and Z-plate level of the muscle sarcomeres. However, these mitochondria often had transverse extensions or interconnections that occurred at the I-band level. Volumes of individual mitochondria ranged from as small as a few thousandths of a micron3 up to several micron3 for the incompletely reconstructed portions of the largest mitochondria. Mitochondrial profiles that one would classify from single sections as subsarcolemmal were found to interconnect with other profiles deeper within the fiber. This suggests that it is unlikely that subsarcolemmal and interfibrillar mitochondria are two structurally distinct populations. However, we found no evidence of a reticulum completely interlinking all mitochondrial material in a muscle fiber.

Effects of age on the number and histochemical properties of muscle fibers and motoneurons in the rat extensor digitorum longus muscle

The number and histochemical properties of muscle fibers and motoneurons were studied in the extensor digitorum longus muscle in female albino rats at the ages of 10, 60 and 120 weeks. The number of fast twitch glycolytic (FG) fibers was decreased at 60 weeks, while that of fast twitch oxidative glycolytic (FOG) fibers was decreased at 120 weeks. The number and oxidative enzyme activity of motoneurons were decreased later at 120 weeks. Thus, it is suggested that the decrease in FG fibers at 60 weeks was due to selective muscle fiber atrophy or to degeneration of neuromuscular junctions, while on the other hand, the decrease in FOG fibers at 120 weeks was due mainly to both a decrease in motoneurons and a type shift of fibers from FOG to FG.

A test for muscle lesions and their regeneration following intramuscular drug application.

A standard infiltration of the rat tibialis anterior muscle with 0.1 ml of local anesthetics was used as a model to help choose criteria for testing the intramuscular toxicity of drugs. Anesthetics used were 0.2% carbisocaine, 1% and 2% Lidocaine, 0.5% Marcaine, 1% and 2% Mesocaine, 1% and 2% Procaine. Increases in the serum levels of creatine kinase were monitored for 24 hours, and the weight, as well as macro- and microscopic changes in the muscle for a period of 1 month. Exposure of the muscle to local anesthetics resulted in 2 types of lesions. One was characterized by selective muscle fiber damage in the injected area. The other type of lesion was a generalized one that involved a number of cell types. To assess the intramuscular toxicity of drugs we defined the type of lesion, its size, and the rate of subsequent muscle regeneration. We recommend the following criteria for the assay of myotoxicity of new drugs being developed as pharmaceutical agents: 1) serum creatine kinase level 1 hour after intramuscular injection of the drug; 2) microscopic findings at 3, 7, and 21 days; 3) the cross-sectional area of the lesion at 3 days; and 4) the weight of the muscle at 7 and 21 days.

Determination of human muscle pH in needle-biopsy specimens.

The homogenate technique for the determination of muscle pH (pHm) has been studied to assess the influence of delayed freezing and the composition and volume of the homogenizing medium on human muscle pH at rest and after exhaustive exercise. It was concluded that resting muscle samples must be frozen within 2 s to prevent falsely high pHm values. Muscle specimens used for lactate determinations (HLam), on the other hand, can be delayed in freezing for up to 30 s without altering the HLam content. A 30- to 40-s delay in biopsying the muscle after the cessation of exhaustive exercise does not appear to alter pHm or HLam values. Although the homogenate method does not provide information relative to the status of selected muscle fibers, it does offer a reliable sensitive measure of mean changes in the acidification of muscle with intense exercise.

Myosin autoantibodies reacting with selective muscle fiber types.

Myosin in striated muscle exists in at least two immunologically distinct forms. Human autoantibodies specific for either form show selective muscle fiber reactivity. One group of antibodies reacts with type 2b (white) muscle fibers, the other with type 2a (red) and type 1 (intermediate) fibers. All of these antibodies react with the A band of glycerinated myofibrils. Both groups of antibodies react with cardiac muscle. Muscle-fiber-specific antibodies are detected in approximately 1% of sera submitted for diagnostic screening. Sera from eight patients were studied further. The two patients with antibodies against type 2b (white) muscle myosin had rheumatoid arthritis. The six patients with antibodies against type 2a (red) and type 1 (intermediate) myosin had clinical features which included various autoimmune and infectious disorders.

Selective muscle fiber type anomalies in neuromusclar disorders. An analysis of 124 consecutive muscle biopsies (author's transl)

The following parameters were measured and calculated in 124 consecutive muscle biopsies: mean fiber diameter, standard deviation, percentage of type I and Type II fibers, variability coefficient, hypertrophy and atrophy factor. Twenty percent of the histometrically analyzed biopsies showed a type II atrophy and four percent a type I atrophy. Type II atrophy was found particularly in the following disorders: collagen vascular diseases, steroid myopathies, cachexia and as a result of inactivity. Some neurogenic processes also demonstrated a selective type II atrophy. The combination of a grouped type II atrophy with a type I hypertrophy is characteristic of chronic and usually heredodegenerative disorders of the motoneurons. The presence of a selective type II atrophy argues against a genetically determined muscular dystrophy. A mixed atrophy classified here as strong or very strong primarily suggests a neuropathy. A selective type I hypertrophy has been found exclusively in neurogenic processes, and type II hypertrophy predominantly in the cases of chronic heredodegenerative neurogenic and primarily myopathic diseases. An increase of the variability coefficient of both types of muscle fibers is more frequent and pronounced in neurogenic processes than in myopathic syndromes. Type II fibers show a selective increase in the variability coefficient considerably more often than type I fibers. In contrast to other reports we seldom found a fiber type predominance or a pathological type-grouping. Only two out of five biopsies with pathological fiber type-grouping were definitely neurogenic. In special cases the histometric analysis of muscle fiber types improves the diagnostic efficiency of muscle biopsies.