Small-caliber skeletal muscle fibers do not suffer deleterious consequences of dystrophic gene expression

In Duchenne dystrophy and in the genetic dystrophies of CHF-147 hamsters and MDX mice, the fundamental deleterious consequence of dystrophic gene expression is segmental necrosis of skeletal muscle fibers. The nature of the gene defects and the pathogenesis of muscle fiber damage are not known. However, clinical and experimental evidence indicates that muscle fibers, whose girth is below a certain level (estimated at approximately 20-25 microns in diameter in dystrophic hamsters and MDX mice) are not susceptible to necrosis. This apparent "immunity" has been observed in muscle fibers that are naturally of small girth (such as those in extraocular muscles), and in fibers that were prevented from growing normally by experimental procedures (hamsters and mice) or by pathological processes (Duchenne patients). The cellular or molecular basis by which small-caliber muscle fibers are resistant to the necrotizing effect of the dystrophic gene expression remains unknown. In small-caliber muscle fibers, the normal contraction-related mechanical strains per unit surface area are relatively less than in larger fibers; this could explain their relative resistance to necrosis in some dystrophies.

Lysosomal storage in human skeletal muscle

Skeletal muscle is involved symptomatically in two lysosomal storage diseases, acid maltase deficiency and a similar condition in which enzyme levels are normal. Asymptomatic storage in skeletal muscle cells is found in Batten-Kufs' disease (ceroid lipofuscinosis), Fabry's disease, and mannosidosis, as well as in rare patients with an unidentified storage disease. Other cell types (vascular endothelium, smooth muscle, fibroblasts, satellite cells) within the confines of the biopsy specimen may reveal storage in other diseases. The differential diagnosis involves predominantly both normal and abnormal conditions in which acid phosphatase activity is prominent in cells.

Myopathy caused by a deficiency of Ca2+-adenosine triphosphatase in sarcoplasmic reticulum (Brody's disease)

Four male patients from two families were first seen with impaired skeletal muscle relaxation that rapidly worsened during exercise. Muscle biopsies from 2 patients were examined by appropriate biochemical and microscopic immunocytochemical techniques. The adenosine triphosphate (ATP)-dependent Ca2+ transport rate was extremely low in a particulate membrane fraction of skeletal muscle, and there was also a marked reduction of the concentration of 100-kD phosphoprotein, corresponding to Ca2+-ATPase of sarcoplasmic reticulum, in muscle microsomes. The concentration of immunoreactive Ca2+-ATPase of sarcoplasmic reticulum was markedly reduced on immunoblots. Evaluation by microscopic immunocytochemical techniques, using one polyclonal and two monoclonal antibodies against sarcoplasmic reticulum Ca2+ transport protein, revealed that the severe reduction of immunoreactive Ca2+-ATPase was limited to the histochemical type 2 fibers. The deficiency of the Ca2+ transport protein in the sarcoplasmic reticulum of type 2 fibers, which may be the primary expression of a presumed gene defect, can explain the impaired muscle relaxation of the patients. This disease appears to be a clinically, electromyographically, and biochemically distinct metabolic myopathy.

Calcium paradox in skeletal muscles: physiologic and microscopic observations

Immersion of rat hemidiaphragms in Ca2+-free Krebs solution (KS) containing Ca2+ chelator in vitro leads to separation of basal lamina from the plasma membrane, as well as transient contracture and rapid loss of twitch response [calcium paradox (CP) phase 1]. Subsequent immersion in regular KS results in necrosis of muscle fibers accompanied by slowly increasing contracture (CP phase 2). This contracture could be prevented or reduced by using either Ca2+-free KS or calcium channel blockers, but not by dantrolene sodium, implying that after drastic reduction of extracellular and sarcolemmal Ca2+ during CP phase 1, the sarcolemma has lost its ability to control normal Ca2+ fluxes. Contracture did not develop at 21 degrees C. CP is a convenient model to study calcium-induced muscle cell death and the role of Ca2+ in maintaining sarcolemmal integrity.

Skeletal muscle endurance: the effect of increased availability of endogenous long-chain fatty acid fuel

A possible role of intramuscularly derived fatty acid fuel on muscle endurance was investigated in curarized diaphragms of fasted rats. These showed significantly improved endurance during 60 min of intermittent stimulation at 20 Hz in vitro compared with diaphragms of fed control animals. The improved endurance appeared to be related to an increased availability and utilization of fatty acid fuel derived from greatly increased numbers of lipid globules in muscle fibers of fasted animals. The pH of muscles with improved endurance (fasted rats) was not different from that of muscles from fed controls at rest. After 60 min of intermittent stimulation, the muscle pH diminished to the same extent in both groups. Diaphragms of fasted rats that were refed 12 h before testing did not show improved endurance. Epinephrine in the bath abolished the improved endurance of diaphragms of fasted rats. Diaphragms of fasted guinea pigs did not show significantly improved endurance (despite abundant intracellular lipid globules), possibly because of a reduced intracellular carnitine.

Calcium-induced damage of skeletal muscle fibers is markedly reduced by calcium channel blockers

Vascular perfusion of rat hind limbs with a Ca2+-free physiological solution containing ethylenediaminetetraacetate, when followed by a physiological solution with normal concentration of Ca2+, caused a marked rise of creatine kinase (CK) in the venous effluent. When calcium channel blockers were present in the perfusing solutions, no rise of CK occurred. On histological sampling of perfused muscles, CK rise was roughly correlated with muscle fiber damage of the appropriate muscles. Removal of calcium from the plasmalemma of muscle fibers appears to prevent closure of calcium channels, making the muscle fibers susceptible to a deleterious influx of extracellular calcium. This influx can be prevented by the presence of calcium channel blockers in the perfusates.

Hexosaminidase-A deficiency presenting as atypical juvenile-onset spinal muscular atrophy

Three patients from two families had an unusual phenotypical variant of late-onset hexosaminidase-A deficiency. The clinical picture was dominated by spinal motor neuron involvement mimicking juvenile-onset spinal muscular atrophy. Atypical features included prominent muscle cramps, postural and action tremor, recurrent psychosis, incoordination, corticospinal and corticobulbar involvement, and dysarthria. The presence of these atypical features in patients whose lower motor neuron involvement would otherwise be consistent with juvenile-onset spinal muscular atrophy should raise the suspicion of the presence of hexosaminidase-A deficiency and GM2 gangliosidosis that can be proved by appropriate enzyme assays.

New observations in reducing body myopathy

Numerous autofluorescent reducing bodies were found in deltoid and biceps muscle biopsies of a 7-year-old girl with progressive, asymmetric muscle weakness. The structures were composed of tubular filaments as seen by electronmicroscopy. They seemed to have formed around nuclei. An excess of two unidentified proteins was found in muscle homogenates. This patient, like one previously reported, had high serum titers of antibodies to coxsackievirus, but her serum, when tested by indirect immunocytochemistry, did not react with the reducing bodies.

Hypophysectomy mitigates skeletal muscle fiber damage in hamster dystrophy

Ablation of the pituitary gland by a radiofrequency lesion markedly retarded the musculoskeletal growth of young dystrophic hamsters. The prevalence of centronucleated muscle fibers, which is a reliable cumulative index of the microscopic pathological expression of dystrophy, was drastically reduced in quadriceps muscles of 35- and 45-day-old hypophysectomized dystrophic hamsters, compared with sham-operated controls. Mitigation of skeletal muscle fiber damage by musculoskeletal growth retardation may also occur in human dystrophy.

Neurofilament subunit--related proteins in neuronal intranuclear inclusions

Well-preserved nuclei were isolated from the brain of a patient with neuronal intranuclear inclusion disease ( NIID ). The inclusions in situ stained for proteins and, by immunohistochemical techniques, for the 200K and 68K components of the neurofilament protein triplet but were negative for the 145K neurofilament protein. At the electron microscopic level the inclusions were seen to consist of straight, randomly arranged tubular filaments 8.5 to 9.5 nm in diameter. They were resistant to extraction with hot buffer containing sodium dodecyl sulfate (SDS) and 2-mercaptoethanol, indicating that the proteins of NIID inclusions are probably cross-linked by covalent bonds other than disulfide. This feature is also exhibited by the paired helical filaments occurring in brain in Alzheimer's disease. No major differences were found in the polypeptide composition of nuclei in NIID and control nuclei resolved by SDS-polyacrylamide gel electrophoresis. The inclusions isolated from SDS-extracted nuclei were shown by immunohistochemical techniques to stain for all three neurofilament subunits, indicating that 145K -related antigenic sites were uncovered during the extraction procedure.

Reinnervation is followed by necrosis in previously denervated skeletal muscles of dystrophic hamsters

Hind leg muscles of dystrophic hamsters were continually denervated by multiple crushes of the sciatic nerve to as long as 93 days of age. In these muscles, the prevalence of centronucleated fibers which is a cumulative index of prior necrosis, remained very low. In control dystrophic muscles the prevalence of centronucleated fibers increased steadily to approximately 80% where it leveled off. By omitting further crushes in other groups of animals, previously denervated muscles became adequately reinnervated. In the reinnervated muscles the prevalence of centronucleated fibers steadily increased throughout the necrotic phase of dystrophy at a rate that was comparable to corresponding stages of the natural history of the disease. These experiments indicated that continued denervation was effective in negating skeletal muscle fiber necrosis throughout the necrotic phase and that the electromechanical activity of muscle fibers which allows muscle fiber necrosis was not a time-locked factor.

Prevention of skeletal muscle fiber necrosis in hamster dystrophy

Necrosis and widespread central nucleation of skeletal muscle cells, which are the main features of skeletal muscle pathology in genetically dystrophic hamsters (UMX-7.1 strain), were not present in muscles of 45- to 65-day-old animals which had been surgically denervated at 15 to 18 days of age. Necrosis and widespread central nucleation were also absent in hind leg muscles at 30 to 60 days of age after transection of the high thoracic spinal cord at 15 to 18 days. Normal excitation or contraction of the skeletal muscle fibers in early age appears necessary for the microscopic pathological expression of the dystrophic gene in skeletal muscles in the UMX-7.1 strain hamsters. These experiments constitute a rare and clear example of consistent prevention of skeletal muscle cell destruction in vivo in an inherited myopathy.

Necrosis of capillaries in denervation atrophy of human skeletal muscle

Gastrocnemius muscles from eight adults with moderate to severe denervation of various causes (excluding vascular diseases), along with biopsy specimens from seven controls, were studies in semithin epoxy resin sections and by electron microscopy. Morphometry showed diminution in the number of capillaries per muscle fiber roughly proportional to the degree of muscle fiber atrophy. The number of capillaries per transverse muscle fiber area tended to increase. By phase microscopy, destroyed capillaries were found in all denervated muscle specimens. Denervated muscle becomes relatively overvascularized, and probably as a result, some capillaries become necrotic. This tends to restore the normal equilibrium between muscle mass and blood supply. The capillary changes of denervation can be distinguished from those in dermatomyositis.

Sweat gland duct cells in Lafora disease: diagnosis by skin biopsy

Skin biopsies of three patients with Lafora disease (clinically typical and proven by liver biopsy) showed PAS-positive inclusions in numerous peripheral cells of eccrine sweat ducts. By electronmicroscopy, the inclusions consisted of polyglucosan-type material; they were not bounded by a membrane. Skin biopsy should be a convenient method of diagnosing Lafora disease.

Lectin histochemistry of human skeletal muscle

Biotinyl derivatives of seven plant lectins-concanavalin A (Con A), peanut agglutinin (PNA), Ricinus communis agglutinin I (RCA I), Ulex europeus agglutinin I (UEA I), soybean agglutinin (SBA), Dolichos biflorus agglutinin (DBA), and wheat germ agglutinin (WGA)-were bound to cryostat sections of biopsied normal human muscle and visualized with avidin-horseradish peroxidase conjugates. A distinct staining pattern was observed with each lectin. The most general staining was observed with Con A, RCA I, and WGA, which permitted strong visualization of the plasmalemma-basement membrane unit, tubular profiles in the interior of muscle fibers, blood vessels, and connective tissue. PNA gave virtually no intracellular staining, while SBA and UEA I selectively stained blood vessels. DBA was unique in providing good visualization of myonuclei. In each case, lectin staining could be blocked by appropriate sugar inhibitors. Neuraminidase pretreatment of the cryostat sections altered the pattern of staining by all lectins except UEA I and Con A; staining with RCA I became stronger and that with WGA became less intense, while staining with PNA, SBA and DBA became stronger and more generalized, resembling that of RCA I. These effects of neuraminidase pretreatment are in conformity with the known structure of the oligosaccharide chains of membrane glycoproteins and specificities of the lectins involved.

An experimental morphometric study of neutral lipid accumulation in skeletal muscles

The neutral lipid content of skeletal muscle fibers was determined by computing the lipid accumulation index (LAI) on transverse cryostat sections stained with Oil Red O. The LAI was defined as: (total area of neutral lipid droplets in a fiber) x 100/(total cross-sectional area of a fiber). The biceps, diaphragm, and soleus muscles were studied in 3 groups of guinea pigs: normal animals, animals fasted for 48 hours, and animals subjected to muscle denervation and then fasted for 48 hours. In normal animals, the highest mean LAI was found in the diaphragm (4.93) in comparison with lower values in the biceps (2.25) and soleus (2.09). After fasting, these values were markedly increased; there was also a concomitant increase in plasma free fatty acid (FFA) concentration. Prior denervation further increased the LAI in biceps and soleus but reduced it in the diaphragm. Type 2A fibers tended to show high lipid accumulation when the plasma FFA concentration was high. Type 2B fibers never accumulated much lipid under any circumstances. Type 1 fibers varied in their response in the different muscles.

A distinct form of adult polyglucosan body disease with massive involvement of central and peripheral neuronal processes and astrocytes: a report of four cases and a review of the occurrence of polyglucosan bodies in other conditions such as Lafora's disease and normal ageing

We have described 4 patients with progressive lower and upper motor neuron deficits, marked sensory loss in the legs, 'neurogenic bladder', and, in 2 of the 4, dementia. Autopsy of two revealed a profusion of microscopic bodies resembling corpora amylacea or Lafora bodies, but restricted to processes of neurons and astrocytes. Similar (but especially large) bodies were seen within axons of sural nerves taken at biopsy from the other two patients. A general term--'polyglucosan body'--is introduced to refer to these structures in all the circumstances in which they may occur, such as in Lafora's disease, in a syndrome of longstanding double athetosis, in some cases of amyotrophic lateral sclerosis, in type IV glycogenosis, in diabetic rats, and in the normal course of ageing. Except in type IV glycogenosis, the causes for accumulation of polyglucosan bodies are unknown. They may damage tissue by more than one mechanism--probably by impeding axonal flow and impairing perivascular diffusion of metabolites.

Cylindrical spirals in human skeletal muscle

Muscle biopsies from two patients revealed that numerous type 2 fibers contained large abnormal areas filled with cylindrical spirals. The cytochemical profile of these cylindrical spirals was sufficiently characteristic that they could be distinguished from tubular aggregates. Their electron microscopic appearance was unmistakable. Their origin and significance are uncertain. The diverse nature of the patients' conditions (cramps and malignancy, and an unusual form of spinocerebellar degeneration) indicate that these abnormal structures are not disease specific.

The effects of partial chronic denervation on forearm metabolism

Effects of chronic denervation upon in vivo forearm metabolism were studied in six patients and six controls. The diagnosis was amyotrophic lateral sclerosis in four patients, the neuronal form of Charcot-Marie Tooth disease in one patient, and an unclassified chronic disease of the lower motor neurons in one patient. In all cases the forearm muscles showed clinical weakness and electrical evidence of denervation, while muscle biopsy from a proximal muscle of the upper limb showed typical denervation atrophy. At rest there was increased oxygen utilization and lactate output as well as a tendency for increased uptake of glucose and long chain fatty acids from arterial blood per 100 ml of forearm tissue. During exercise the abnormally high lactate output increased further. An increased arterial lactate concentration was present during rest and exercise. Oxidation of fatty acids was not impaired. It is suggested that these abnormalities are consistent with an augmented utilization of blood borne fuels at rest by denervated muscles. A concurrent regional ischemia of muscles during rest and exercise, possibly due to defective autoregulation of skeletal muscle blood flow, may explain the abnormally high lactate generation.