Denervation in murine dystrophy

Age-related Differences in Dystrophin: Impact on Force Transfer Proteins, Membrane Integrity, and Neuromuscular Junction Stability

The loss of muscle strength with age has been studied from the perspective of a decline in muscle mass and neuromuscular junction (NMJ) stability. A third potential factor is force transmission. The purpose of this study was to determine the changes in the force transfer apparatus within aging muscle and the impact on membrane integrity and NMJ stability. We measured an age-related loss of dystrophin protein that was greatest in the flexor muscles. The loss of dystrophin protein occurred despite a twofold increase in dystrophin mRNA. Importantly, this disparity could be explained by the four- to fivefold upregulation of the dystromir miR-31. To compensate for the loss of dystrophin protein, aged muscle contained increased α-sarcoglycan, syntrophin, sarcospan, laminin, β1-integrin, desmuslin, and the Z-line proteins α-actinin and desmin. In spite of the adaptive increase in other force transfer proteins, over the 48 hours following lengthening contractions, the old muscles showed more signs of impaired membrane integrity (fourfold increase in immunoglobulin G-positive fibers and 70% greater dysferlin mRNA) and NMJ instability (14- to 96-fold increases in Runx1, AchRδ, and myogenin mRNA). Overall, these data suggest that age-dependent alterations in dystrophin leave the muscle membrane and NMJ more susceptible to contraction-induced damage even before changes in muscle mass are obvious.

Origin of predominance of cementite among iron carbides in steel at elevated temperature

A long-standing challenge in physics is to understand why cementite is the predominant carbide in steel. Here we show that the prevalent formation of cementite can be explained only by considering its stability at elevated temperature. A systematic highly accurate quantum mechanical study was conducted on the stability of binary iron carbides. The calculations show that all the iron carbides are unstable relative to the elemental solids, α-Fe and graphite. Apart from a cubic Fe23C6 phase, the energetically most favorable carbides exhibit hexagonal close-packed Fe sublattices. Finite-temperature analysis showed that contributions from lattice vibration and anomalous Curie-Weis magnetic ordering, rather than from the conventional lattice mismatch with the matrix, are the origin of the predominance of cementite during steel fabrication processes.

Myosin isoforms in hindlimb muscles of normal and dystrophic (ReJ129 dy/dy) mice

Myosin isoform expression was studied in hindlimb muscles of control (Dy/Dy) and dystrophic (dy/dy) mice of the ReJ129 strain during postnatal development. Three myosin heavy chain isoforms (fast II-B MHC, neonatal MHC, and slow or I MHC) were identified using monoclonal antibodies. Only original fibers, i.e., fibers formed during fetal life, were studied. Necrotic and regenerating fibers were excluded. The disappearance of neonatal MHC was found to be delayed in all muscles of dystrophic mice, except the soleus. The fraction of fibers containing I MHC was similar in control and dystrophic animals at all ages, except during the third postnatal week. The developmental increase in the fraction of fibers expressing II-B MHC was interrupted in dystrophic mice by two marked declines. The first occurred during the second postnatal week at the beginning of the main wave of fiber necrosis, and the second occurred at between 30 and 90 postnatal days.

Direct effects of serotonin and ketanserin on the functional morphology of embryonic chick skin in vitro

Different organotypical culture methods are used to test direct effects of serotonin and ketanserin, a S2, alpha 1, and H1 receptor antagonist in vascular tissue, on fibroblasts and epidermal cells of embryonic chick skin in vitro. From light microscopic and electron microscopic analyses, we learn that serotonin enhances keratinization and differentiation, whereas ketanserin reduces differentiation in comparison to the control cultures. Incorporation data of fragments cultured with [3H]thymidine show that ketanserin, within a dose range from 0.05 to 5 micrograms/ml, stimulates proliferation. Serotonin at a concentration of 10 micrograms/ml slightly slows down proliferation, whereas lower doses of 0.1 and 1 microgram/ml result in tritium activities that do not differ from control cultures.

Study of neurotrophism in normal/dystrophic parabiotic mice

The trophic influences of nerve and muscle on one another were studied in normal and dystrophic littermates of C57BL/6J dy2J mice parabiosed at 20 to 23 days after birth. Each parabiont had a soleus muscle cross-reinnervated by a tibial nerve of its partner. Ultrastructural abnormalities of muscle and endplate were quantified and compared 6 to 7 months postoperatively. The dystrophic nerve degenerated despite reinnervation to a normal muscle. The normal muscle did not prevent the dystrophic nerve from degenerating, and the dystrophic nerve induced degenerative changes in the reinnervated normal muscle. Normal nerve did not retard the genetically programmed degeneration of the dystrophic muscle. The dystrophic muscle, however, did not appear to cause normal nerve terminals to degenerate. We conclude that both nerve and muscle cells in dystrophic mice express characteristics of muscular dystrophy. Muscle fibers of a few motor units further suffer from abnormal neurotrophic influence because of the degeneration of the motor neurons. Myotrophic influence on nerve was not observed.

Osmotic fragility of erythrocytes in myopathies

Erythrocytes taken from patients with myopathy have previously been reported to have increased osmotic fragility. We have examined the osmotic fragility of erythrocytes from patients with various myopathies and from carriers. The osmotic fragility was the same as in unaffected controls.

Terminal motor innervation in myopathic hamsters

Terminal motor innervation and the histochemical profile of muscle fibers were investigated, before and after sciatic nerve crushing, in 1- to 150-day-old myopathic hamsters. The observed morphologic abnormalities in terminal motor innervation were of varying degree prior to the nerve injury. These abnormalities were found in close proximity to lesions of the myofibers, and became more pronounced with age and the progression of the disease process. Collateral ramification of healthy axons occurred in hamsters of 120 days of age with reinnervation of damaged muscle fibers. When submitted to sciatic nerve crushing, myopathic hamsters showed an ability to regenerate and reinnervate the subneural apparatuses. The regenerative process in these animals was essentially the same as in normal, sciatic nerve-crushed hamsters. Thus, it was concluded that the morphologic changes in terminal motor innervation were secondary to muscle cell degeneration.

Abnormalities expressed in long-term cultures of dorsal root ganglia from the dystrophic mouse

We have compared the development in long-term tissue culture of dorsal root ganglia taken from normal and dystrophic mice. Cultures were prepared from late fetal (15--20 days) or neonatal mice of either the C57BL/6 dy2j/dy2j dystrophic (dy) or C57BL/6J +/+ (control) strain and maintained until fully myelinated (5 weeks or more). Analysis by light and electron microscopy indicated that the substantial ensheathment failure present in certain dy nerve roots in vivo is not expressed in cultures; myelination and Schwann cell numbers are comparable to control cultures. On the other hand, many of the subtle abnormalities more recently described in distal parts of peripheral nerves of dystrophic mice are expressed in the dy cultures. These include: (a) discontinuity in the basal lamina surrounding both myelin-forming and non-myelinating Schwann cells: (b) elongated nodes of Ranvier occurring along otherwise well myelinated nerve fibers; (c) relatively short myelin internodes that are increased in thickness as well as irregularities of internode length along a nerve fiber; (d) Schwann cell nuclei substantially displaced from the central point of myelin internodes; and (e) occasional regions of incomplete ensheathment of unmyelinated nerve fibers. In discussing these observations, we present arguments that the dy nerve lesion may be explained by the presence of an abnormality in the extracellular matrix of the peripheral nerve tissues of the dy mouse.

The neuromuscular and vascular hypotheses of muscular dystrophy: a possible link via adenine nucleotides and phosphate

A hypothesis is presented that an abnormality of nucleotide synthesis or metabolism might be a primary functional defect underlying Duchenne muscular dystrophy. One aim of this hypothesis is to demonstrate that it is possible to explain a variety of observations in dystrophy, neuromuscular and vascular, on a single hypothesis.

Choline acetyltransferase and acetylcholinesterase in muscular dystrophic mice

The activities of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were assayed in various tissues of dystrophic (dy/dy) and normal mice of Bar Harbor strain 129. The brain weights of these dystrophic mice were not significantly different from those of normal mice, but the average body weight of these dystrophic mice was only 66.8% of that of the controls. The activity of CAT (expressed as unit activity per mg of protein) was very similar in the brains of both groups of animals, but the CAT activity (per mg of protein) in the hindlimb muscles of the dystrophic mice was significantly higher than that of the controls. The patterns of AChE activity, as separated by sucrose density gradient centrifugation, were distinctly different in extracts of dystrophic and normal muscle. Compared with controls, decreased activity of the 15-S and 10-S forms of AChE, with increased activity of a 4.3-S formed of AChE, was observed in dystrophic muscle.

Abnormalities of the sciatic nerves of dystrophic mice with reference to the large U-axons

A statistical study using regression analysis was used to evaluate the density of axonal organelles in dystrophic peripheral nerves. The slope of the density of neurotubules (NT) in myelinated (M-) axons was different from that in small unmyelinated (U-) axons. The slope of the density of NT in large U-axons (larger than 1.5 micron in diameter) was similar to that of the M-axons in both the dystrophic and control mice. There was a higher density of NT in the dystrophic M-axons than in the controls in the anterior, posterior and mixed nerves of the sciatic nerve. There was also a higher density of NT in the dystrophic small U-axons than in the controls. There was a higher density of neurofilaments (NF) of M-axons in the dystrophic mice than in the controls. On the contrary, the NF of small U-axons were lower in density in the dystrophic mice. These results were different from our previous reports, which were observed in the distal part, depending on when the groups of U-axons were divided (Okada, Mizuhira and Nakamura 1976a).

Dysmyelination in the sciatic nerves of dystrophic mice

Ultrastructural alterations were observed in the sciatic nerve of dystrophic mice. Myelin sheaths were abnormal in shape, abruptly ceased beyond a node of Ranvier, leaving the axon naked. These changes were seen in both afferent and efferent nerve fibres. Apparent embryonal Schwann cells and Schwann cells which were associated with increased lysosomes in the cytoplasm were observed in the proximal portion. There is a relative decrease in Schwann cells in the cross-section of the radicular parts, and a relative increase in the distal parts. The mean number of neurotubules per unit area was smaller while the mean number of the neurofilaments was larger in U-axons, in the dystrophic mice than in the controls. In M-fibres, neurotubules and neurofilaments showed no significant difference between systrophic and control mice.

Dystrophic spinal cord transplants induce abnormal thymidine kinase activity in normal muscles

The role of the neural tube in the pathogenesis of muscular dystrophy was tested directly. Neural tubes from chicken embryos with hereditary muscular dystrophy and from genetically normal embryos were transplanted into normal recipient embryos. Dystrophic neural tissue induced in muscles of normal hosts high thymidine kinase activity characteristic of dystrophic muscle; normal neural tubes did not. We propose an early inductive effect of the neural tube on the presumptive myoblasts that sets their subsequent course of development, either normal or dystrophic.

On the pathogenesis of duchenne muscular dystrophy

The relative merits of the three presently most active hypotheses (vascular, neurogenic, and myogenic) concerning the pathogenesis of Duchenne muscular dystrophy are analysed and discussed and the literature is comprehensively reviewed.

Investigation of cranial and other nerves in the mouse with muscular dystrophy

In the muscular dystrophic mouse mutant there is an absence of Schwann cells over circumscribed lengths of all cranial nerves except for II (I was not examined) and the lesion involves the sympathetic system. Where present, Schwann cells do not produce myelin of normal thickness. The lesion is similar to that described for the spinal roots. Causation is discussed.

A neurogenic component in muscular dystrophy

Evidence for a neurogenic component in mouse and human muscular dystrophy is briefly reviewed. Such evidence comes from certain clinical observations, electrophysiological studies, muscle pathology, nervous system pathology, transplantation experiments in animals, and tissue culture studies. The evidence is at present rather conflicting though the results of recent tissue culture experiments are more convincing. If there is a neurogenic component in dystrophy then the basic defect may have to be sought in the central nervous system rather than in the muscle itself. It is argued, however, that a neurogenic component in dystrophy cannot be simply a defect in the anterior horn cells of the spinal cord since the clinical features and the laboratory and pathological findings are quite different from those in spinal muscular atrophy.

Calcium transport and phospholipid composition of microsomal fractions from denervated rat gastrocnemius

Total calcium uptake, but not the initial rate, and non-calcium-stimulated (basic) adenosine triphosphatase activity of rat gastrocnemius microsomal fractions 3, 7 and 14 days after denervation increased compared with contralateral controls. Microsomal sphingomyelin also increased but phosphatidylcholine plus choline plasmalogen was unchanged in amount. These results are contrasted with those reported for vincristine myopathy.