Sequence of expression of MyoD1 and various cell surface and cytoskeletal proteins in regenerating mouse muscle fibers following treatment with sodium dihydrogen phosphate

Polystyrene-coated micropallets for culture and separation of primary muscle cells

Despite identification of a large number of adult stem cell types, current primary cell isolation and identification techniques yield heterogeneous samples, making detailed biological studies challenging. To identify subsets of isolated cells, technologies capable of simultaneous cell culture and cloning are necessary. Micropallet arrays, a new cloning platform for adherent cell types, hold great potential. However, the microstructures composing these arrays are fabricated from an epoxy photoresist 1002F, a growth surface unsuitable for many cell types. Optimization of the microstructures' surface properties was conducted for the culture of satellite cells, primary muscle cells for which improved cell isolation techniques are desired. A variety of surface materials were screened for satellite cell adhesion and proliferation and compared to their optimal substrate, gelatin-coated Petri dishes. A 1-μm thick, polystyrene copolymer was applied to the microstructures by contact printing. A negatively charged copolymer of 5% acrylic acid in 95% styrene was found to be equivalent to the control Petri dishes for cell adhesion and proliferation. Cells cultured on control dishes and optimal copolymer-coated surfaces maintained an undifferentiated state and showed similar mRNA expression for two genes indicative of cell differentiation during a standard differentiation protocol. Experiments using additional contact-printed layers of extracellular matrix proteins collagen and gelatin showed no further improvements. This micropallet coating strategy is readily adaptable to optimize the array surface for other types of primary cells.

Acetylcholine receptors and nerve terminal distribution at the neuromuscular junction of long-term regenerated muscle fibers

Mdx mice are deficient in dystrophin and show muscle fiber regeneration. Changes in the distribution of acetylcholine receptors have been reported at the neuromuscular junction of mdx mice and may be a consequence of muscle fiber regeneration. In this study, we examined whether the distribution of receptors was still altered in long-term, regenerated muscle fibers from C57Bl/10 mice. The left sternomastoid muscle of adult mice was injected with 60 microl of lidocaine hydrochloride to induce muscle degeneration-regeneration. In some mice, the sternomastoid muscle was denervated at the time of lidocaine injection. After 90 and 150 days, the nicotinic acetylcholine receptors were labeled with rhodamine-alpha-bungarotoxin for confocal microscopy. At both intervals studied, the receptors were distributed in spots. In denervated-regenerated fibers, the receptors were distributed as regular branches similar to denervated muscles without lidocaine treatment. These findings suggested that nerve-dependent mechanisms were involved in the changes in receptor distribution seen in regenerated muscle fibers after lidocaine treatment, and that a similar phenomenon could explain the changes in receptor distribution seen in dystrophic muscle fibers.

Diagnostic protein expression in human muscle biopsies

Using immunohistochemistry in diagnosing neuromuscular diseases is meant to enhance the diagnostic yield in two ways. The first application aims at visualizing molecules which are developmentally, neurally, and/or immunologically regulated and not expressed by normal muscle. They are upregulated in pathological conditions and may help assign a given muscular biopsy to one of the main diagnostic entities (muscular dystrophies, inflammatory myopathy, neurogenic atrophy). In the past, muscle-specific molecules with a defined expression pattern during fetal myogenesis served as antigens, with the rationale that the developmental program was switched on in new fibers. Recently, myofibers in diseased muscle are thought of as targets of stimuli which are released by macrophages in muscular dystrophy, by lymphocytes in inflammatory myopathies, or by a lesioned peripheral nerve in neurogenic atrophies. This has somewhat blurred the borders between the diagnostic groups, for certain molecules, e.g. cytokines, may be upregulated after experimental necrotization, denervation, and also in inflammatory myopathies. In the second part of this review we summarise the experiences of a Centre in the North of England that specialises in the diagnosis and clinical support of patients with muscular dystrophy. Emphasis is placed on the use of protein expression to guide mutation analysis, particularly in the limb-girdle muscular dystrophies (a group of diseases that are very difficult to differentiate on clinical grounds alone). We confirm that genetic analysis is essential to corroborate the results of protein analysis in certain conditions (particularly in calpainopathy). However, we conclude that analysing biopsies for abnormal protein expression is very useful in aiding the decision between alternative diagnoses.

Characterization of human muscle type cofilin (CFL2) in normal and regenerating muscle

Cofilins are actin binding proteins and regulate actin assembly in vivo. Numerous cofilin homologues have been characterized in various organisms including mammals. In mice, a ubiquitously expressed cofilin (CFL1) and a skeletal muscle specific cofilin (CFL2) have been described. In the present study, we identified and characterized a human CFL2 gene localized on chromosome 14, with high homology to murine CFL2. Furthermore, we provide evidence for differentially spliced CFL2 transcripts (CFL2a and CFL2b). CFL2b is expressed predominantly in human skeletal muscle and heart, while CFL2a is expressed in various tissues. Genetic defects of CFL2 were excluded for one human muscle disorder, the chromosome 14 linked distal myopathy MPD1, and shown to be only possible to be a rare cause of another, nemaline myopathy. In a mouse model of mechanically induced muscle damage the changes of cofilin expression were monitored during the first 10 days of regeneration, with dephosphorylated CFL2 being the major isoform at later stages of muscle regeneration. A similar predominance of dephosphorylated CFL2 was observed in chronically regenerating dystrophin-deficient muscles of Duchenne muscular dystrophy patients. Therefore, the CFL2 isoform may play an important role in normal muscle function and muscle regeneration.

Recovery recapitulates ontogeny

Several studies support the hypothesis that after stroke, specific features of brain function revert to those seen at an early stage of development, with the subsequent process of recovery recapitulating ontogeny in many ways. Many clinical characteristics of stroke recovery resemble normal development, particularly in the motor system. Consistent with this, brain-mapping studies after an ischemic insult suggest re-emergence of childhood organizational patterns: recovery being associated with a return to adult patterns. Experimental animal studies demonstrate increased levels of developmental proteins, particularly in the area surrounding an infarct, suggesting an active process of reconditioning in response to cerebral ischemia. Understanding the patterns of similarity between normal development and stroke recovery might be of value in its treatment.