Morphologic features of hypermetabolic mitochondrial disease. A light microscopic, histochemical and electron microscopic study

Megamitochondria formation - physiology and pathology

Mitochondria undergo structural changes simultaneously with their functional changes in both physiological and pathological conditions. These structural changes of mitochondria are classified into two categories: simple swelling and the formation of megamitochondria (MG). Data have been accumulated to indicate that free radicals play a crucial role in the mechanism of the MG formation induced by various experimental conditions which are apparently various. These include ethanol-, chloramphenicol- and hydrazine-induced MG formation. Involvement of free radicals in the mechanism of MG formation is showed by the fact that MG formation is successfully suppressed by free radical scavengers such as alpha-tocopherol, coenzyme Q(10), and 4-OH-TEMPO. Detailed mechanisms and pathophysiological meanings of MG formation still remain to be investigated. However, a body of evidence strongly suggests that enormous changes in physicochemical and biochemical properties of the mitochondrial membranes during MG formation take place and these changes are favorable for membrane fusion. A recent report showed that continous exposure of cells with MG to free radicals induces apoptosis, finding which suggests that MG formation is an adaptative process to unfavorable environments at the level of intracellular organelles. Mitochondria try to decrease intracellular reactive oxygen species (ROS) levels by decreasing the consume of oxygen via MG formation. If mitochondria succeed to suppress intracellular ROS levels, MG return to normal both structurally and functionally, and they restore the ability to actively synthesize ATP. If cells are additionally exposed to excess amounts of free radicals, MG become swollen, membrane potential of mitochondria (DeltaPsim) decreases, cytochrome c is released from mitochondria, leading to activation of caspases and apoptosis is induced.

Mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes (MELAS): clinical, radiological, pathological, and genetic observations

We reviewed 10 patients (5 males, 5 females) with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes. The age of symptom onset ranged from 3 months to 12 years. All had lactic acidosis, multiple stroke-like events with secondary neurological deficits, radiological changes of progressive brain infarction, and muscle biopsy showing ragged-red fibers. In patients with earlier onset of symptoms (< 2 yr), involvement tended to be more diffuse, with failure to thrive and early onset of delayed development. Patients whose symptoms appeared later tended to have focal neurological deficits with migraine-like headache, and a rate of cognitive regression reflecting the rapidity of disease progression. Radiological changes included multiple areas of infarction with initial predilection for parietal occipital areas, progressing to generalized atrophy. Pathological findings in muscle biopsies included type 1 fiber predominance, ragged-red fibers, increased intermyofibrillar lipid deposition, and abnormal mitochondria. Four patients showed mitochondrial DNA tRNA mutation at position 3,243. No difference was noted in clinical, radiological, or pathological findings in patients with and without this mutation, suggesting that multiple sites of point mutation may give rise to mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes.

Distribution of the ATPase inhibitor proteins of mitochondria in mammalian tissues including fibroblasts from a patient with Luft's disease

The mitochondrial ATPase inhibitor proteins--the Pullman-Monroy inhibitor (PMI) and the Ca(2+)-binding protein (CaBI)--have a wide distribution, both being present in mitochondria of bovine heart and kidney, rat liver and brain, two mitochondrial populations of rabbit skeletal muscle, and mitochondria from human fibroblasts and the human breast cancer cell line T-47-D. The ratio of CaBI to PMI was highest in heart and skeletal muscle mitochondria. The subsarcolemmal fraction of skeletal muscle had 2.6-times as much CaBI as did the intermyofibrillar. The ratio of CaBI to PMI in the mitochondria of the other normal tissues and fibroblasts was close to 1. In contrast, mitochondria from T-47D cells had 1.5-times as much PMI as CaBI whilst mitochondria from fibroblasts from a patient with Luft's disease showed a virtual lack of PMI. The specific ATPase, ATP-synthetase and succinate dehydrogenase activities of the Luft's mitochondria were, however, in the normal range. The specific ATP synthetase activity of the T-47D cells was significantly higher than normal. We conclude that tissues like heart and skeletal muscle which experience wide fluctuations in intracellular Ca2+ have a greater need for CaBI. Why lack of PMI could lead to 'loose' coupling of oxidative phosphorylation in skeletal muscle of Luft's patients, but not in fibroblasts is discussed.

Chronic progressive external ophthalmoplegia. II. A qualitative and quantitative electronmicroscopy study of skeletal muscles

This study quantifies the major electron microscopic changes in limb muscle biopsies from 31 out of 34 patients with the syndrome of chronic progressive external ophthalmoplegia. Patients were divided into three clinical groups -- A) 10 sporadic cases with muscle weakness only; B) 9 familial cases with muscle weakness only; C) 15 cases with muscle weakness and one or more of the following features: pigmentary retinopathy, cerebellar ataxia, pyramidal signs and peripheral neuropathy. Electron microscopic mitochondrial abnormalities were found in all groups (8 patients from group A, 3 from group B, 14 from group C). Quantitative measurements of certain muscle fibre constituents, using a point-counting technique, revealed decreased myofibril volume-fractions and increased volume-fractions of mitochondria, glycogen and lipid in some biopsies from each group. Mitochondrial volume-fractions correlated positively with lipid content, the proportion of type 1 fibres, and the percentage of fibres with increased oxidative enzyme activity. The three groups defined clinically showed no significant differences in terms of the relative proportions of these measured constituents.

The biochemical basis of mitochondrial diseases

Dysfunctioning of human mitochondria is found in a rapidly increasing number of patients. The mitochondrial system for energy transduction is very vulnerable to damage by genetic and environmental factors. A primary mitochondrial disease is caused by a genetic defect in a mitochondrial enzyme or translocator. More than 60 mitochondrial enzyme deficiencies have been reported. Secondary mitochondrial defects are caused by lack of compounds to enable a proper mitochondrial function or by inhibition of that function. This may result from malnutrition, circulatory or hormonal disturbances, viral infection, poisoning, or an extramitochondrial error of metabolism. Once mitochondrial ATP synthesis decreases, secondary mitochondrial lesions may be generated further, due to changes in synthesis and degradation of mitochondrial phospholipids and proteins, to mitochondrial antibody formation following massive degradation, to accumulation of toxic products as excess acyl-CoA, to the depletion of Krebs cycle intermediates, and to the increase of free radical formation and lipid peroxidation.

Early morphological changes in the striated muscles in normal and dystrophic chickens

Histological and histochemical analyses were performed on the anterior latissimus dorsi muscle (ALD, red muscle) and the posterior latissimus dorsi muscle (PLD, white muscle) in normal (line 412) and dystrophic chickens (line 413) from 19 day embryos to 6 weeks of age. PLD, the white muscle, in dystrophic chickens showed higher percentages of red and intermediate fibres than those of normal chickens during the early development of muscles. Increases of the oxidative enzyme activities and the numbers of NADH--TR formazan granules in the white fibres of PLD were already found at 1 week of age in dystrophic chicken. Fibre types, oxidative enzyme activities and NADH--TR formazan granules showed no differences in ALD between normal and dystrophic chickens. These results suggest that increases of oxidative enzyme activities and formazan granule numbers and incomplete fibre type differentiation in PLD of dystrophic chickens are early pathological processes in such birds.

Familial spinocerebellar degeneration with corneal dystrophy

We report on two sisters born to normal but consanguineous parents, with the unusual combination of spinocerebellar degeneration and corneal dystrophy. Their manifestations include mental subnormality, bilateral corneal opacification starting in the second year of life and leading to severe visual impairment, and slowly progressive cerebellar abnormalities with variable dorsal column and upper motor neuron involvement. A third sister had only minor spinocerebellar signs but no eye findings, and three other sibs were completely normal. Both affected sisters underwent penetrating keratoplasty and their vision improved. Histologic examination showed findings of corneal dystrophy including corneal edema, thickening of Descemet membrane, and degenerative pannus. High-resolution light and electron microscopy of muscle and sural nerve performed on both patients was abnormal. It is suggested that, in this family, the corneal dystrophy and spinocerebellar degeneration are pleiotropic manifestations of an autosomal-recessive disorder.

Mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes: a distinctive clinical syndrome

We report on two patients who have a mitochondrial myopathy, encephalopathy, lactic acidosis, and recurrent cerebral insults that resemble strokes (MELAS). These two and nine other reported patients share the following features: ragged red fibers evident on muscle biopsy, normal early development, short stature, seizures, and hemiparesis, hemianopia, or cortical blindness. Lactic acidemia is a common finding. We believe that MELAS represents a distinctive syndrome and that it can be differentiated from two other clinical disorders that also are associated with mitochondrial myopathy and cerebral disease: Kearns-Sayre syndrome and the myoclonus epilepsy ragged red fiber syndrome. Existing information suggests that MELAS is transmitted by maternal inheritance. The ragged red fibers suggest an abnormality of the electron transport system, but the precise biochemical disorders in these three clinical syndromes remain to be elucidated.

Mitochondrial cytochrome deficiency presenting as a myopathy with hypotonia, external ophthalmoplegia, and lactic acidosis in an infant and as fatal hepatopathy in a second cousin

Fatal infantile mitochondrial myopathy with lactic acidosis, morphologically abnormal mitochondria, deficient cytochromes aa3 and b, and a Fanconi-like aminoaciduria has been described. We report two infants, second cousins, with a similar fatal mitochondrial disorder, the cytochrome deficiency limited to skeletal muscle in one child and to liver in the other. The first child at 3 months of age had weight loss, hypotonia, external ophthalmoplegia, and a severe lactic acidosis with a high lactate/pyruvate ratio. Electron microscopy of muscle showed marked proliferation of enlarged mitochondria, many containing concentric rings of cristae. In skeletal muscle mitochondria, cytochromes aa3 and b were not detectable but cytochrome cc was found to be normal by spectroscopy. Cytochrome c oxidase activity was less than 1% of normal. Mitochondria from kidney, liver, heart, lung, and brain examined postmortem had normal cytochromes and preserved cytochrome c oxidase activity. The second cousin at 5 months of age had weight loss and hepatomegaly but no systemic lactic acidosis. Liver biopsy showed hepatocytes packed with enlarged mitochondria. The liver mitochondria showed deficient cytochromes aa3 and b postmortem, and cytochrome c oxidase activity was less than 10% of normal. Kidney mitochondria had normal cytochromes. Muscles was not studied. The mitochondrial abnormality in the two cousins presumably is related. Unexplained are the mode of genetic transmission or environmental exposure and the apparent involvement of a single different organ in each child.

Follow-up study of a myopathy with loosely coupled mitochondria

This communication deals with a clinical, histological, histochemical and biochemical follow-up study of a boy with an ameliorating myopathy with loosely coupled mitochondria who was studied earlier. In the course of about 15 years the clinical condition of the patient improved greatly. In a biopsy of skeletal muscle the same pathological features were found as before, but the pathological changes were much less severe. In contrast to earlier findings, the majority of the fibres with a loosely coupled state of the mitochondria belonged to the anaerobic type II fibres.

Thyrotoxic myopathy. Pathomorphological observations of human material and experimentally induced thyrotoxicosis in rats

Proximal myopathy and different types of neuromuscular syndromes are frequently observed in hyperthyroid patients with complicated thyrotoxicosis. Conflicting reports on the changes seen in muscle biopsies range from no abnormalities to muscle necrosis with the fibers being replaced by connective tissue and fat. On the basis of 21 skeletal muscle biopsies from chronic thyrotoxic myopathic patients, coupled with studies in experimentally induced triiodothyronine myopathy in rats, the histological, histochemical, immunofluorescent, and electron-microscopic findings diagnostic for thyrotoxic myopathy are defined. These criteria include: clumping of nuclei, loss of cross-striation, vacuolar degeneration, and fatty infiltration of endo- and perimysium, presence of giant mitochondria, increased number of mitochondria, disorganization of contractile elements, swelling of transverse tubules, presence of microtubular aggregations, and a significant increase of lipofuscin granules. Both muscle fiber types or in some cases selective type II fibers display atrophy with signs of reinnervation. These alterations are polyfocal and polyphasic and, therefore, polychronous and stereotyped rather than pathognomonic. However, they are related to the severity of thyrotoxic myopathy and the duration of disease. The results of muscle biopsies have a predictive value in determining the reversibility of irreversibility of pathologic changes with therapeutic consequences.

Histochemical and ultrastructural analysis of the mitochondrial changes in a familial mitochondrial myopathy

Two familial cases of progressive external ophthalmoplegia with involvement of pharyngeal and distal muscles are presented. 'Ragged-red' fibres were found in both cases. Excessive amounts of RNA, as evidenced by the acridine orange-induced fluorescence, were noted in many muscle fibres, mostly in the 'ragged-red' fibres. At the ultrastructural level, numerous mitochondrial changes with paracrystalline formations were noted. Those formations were observed in three forms and three-dimensional reconstruction is proposed which suggests that the paracrystalline formations consist of undulating parallel leaflets joined along the top of the undulations. Small transverse bridges between neighbouring cristae and between cristae and paracrystalline formations are also emphasized. All those mitochondrial abnormalities are thought to represent the morphological expression of a biochemical deficiency in the inner membrane. They are interpreted thus: firstly, the biochemical defect leads to a multiplication of the mitochondria with increase in their volume and proliferation of the cristae in order to improve energy production; secondly, bridges between the modified inner membranes induce attachment of the neighbouring cristae and result in paracrystalline formations.

Neuropathy and mitochondrial myopathy

It has been stated that peripheral neuropathy can be a feature of so-called ophthalmoplegia-plus syndrome, but to date only one case of hypertrophic neuropathy has been reported. This study is concerned with the clinical, electrophysiological, and pathological observations in a 37-year-old man with progressive external ophthalmoplegia and a ragged-red fiber myopathy associated with severe sensorimotor neuropathy. Histological and morphometric studies of the sural nerve revealed a marked loss of large myelinated fibers and an occasional degenerating axon. Residual fibers had disproportionately thin myelin sheaths in relation to axon calibers. In contrast to the muscle biopsy findings, no mitochondrial paracrystalline inclusions were observed in the nerve. However, the number of mitochondria per square micron of Schwann cell cytoplasm was elevated when compared with values obtained from normal subjects and a patient with a chronic neuropathy. These findings may indicate an alteration of mitochondrial function common to muscle fibers and Schwann cells which, in nerves, could lead to axon loss and abnormality of myelination.

The histochemical characterization of the coupling state of skeletal muscle mitochondria

Isolated mitochondria from skeletal muscles of human and animals with neuromuscular diseases may reveal a loosely coupled state of oxidative phosphorylation, which is characterized by a normal phosphorylation in the presence of a phosphate acceptor and a maximal respiration in the absence of a phosphate acceptor. Moreover in these cases activity of mitochondrial Mg2+-stimulated ATPase is strongly increased and cannot be stimulated by the uncoupler 2,4-dinitrophenol. In this communication a histochemical technique for the demonstration of activity of mitochondrial Mg2+-stimulated ATPase to characterize the coupling state of muscle mitochondria in tissue sections, is described. This tissue-saving technique is especially suitable for the study of human skeletal muscle diseases.

Ultrastructural study of globular inclusions in human skeletal muscle mitochondria

Limb muscle biopsies from a patient with Luft's disease and a patient with a slowly progressive neuromuscular disorder since infancy revealed by conventional electron microscopy the presence of globular inclusions in the mitochondria as one of the most prominent morphological findings. Electron cytochemical studies on fresh tissue blocks showed no cytochrome c oxidase activity within the globular inclusions. The study of strontium uptake supported by either NAD and flavo-protein linked substrates in freshly isolated mitochondria fractions showed no electron-dense needles within the globular inclusions. Attempts to remove the inclusions with pepsin and with pronase on ultrathin sections failed but they were partially and totally removed by treatment of the sections with hydrogen peroxide. Freeze fracture studies showed the globular inclusions consisted of amorphous and lamellar material. The results suggest that the globular inclusions in muscle mitochondria may consist primarily of lipid.

Mitochondrial abnormalities of late motor neuron degeneration following poliomyelitis and other neurogenic muscular atrophies

A case of late motor neuron degeneration following poliomyelitis with abnormal mitochondria in muscle fibers is presented with two additional cases of systemic neurogenic muscular atrophy (Charcot-Marie-Tooth disease). Muscle biopsy revealed a neurogenic pattern of variable severity in all cases. Subsarcolemmal zones of hyperactivity and hyperpositive intermyofibrillar collections of granular material present in a variable proportion of type I fibers were demonstrated by oxidative enzymes. Ultrastructurally they corresponded to abnormal mitochondria, with paracrystalline inclusions in one case. The finding is discussed in the light of the previous literature on mitochondrial myopathies. Mitochondrial alterations are not specific and their significance in neurogenic conditions is debated.

The early effects of ischemia upon skeletal muscle mitochondria

The effects of early ischemia were studied in the anterior tibial muscle of Sprague-Dawley rats after 2--24 hr of tourniquet compression at the thigh. Ragged-red fibers, moth-eaten fibers, cores and targets were seen in tissue examined by enzyme histochemistry and electron microscopy. Giant mitochondria, abnormalities of cristal arrangement, crystalloids, osmiophilic inclusion bodies and myeloid figures were dominant features of the mitochondrial reaction. The results of this experiment indicate that early ischemia induces a variety of changes described in other neuromuscular conditions such as dystrophy and the "mitochondrial myopathies". The pathogenesis of these changes and their relationship to human disease of muscle is discussed.

Skeletal muscle pathology in chronic heart block

Skeletal muscle samples, mainly from the deltoid, were studied morphologically and histochemically in 35 patients with chronic heart block and from nine elderly control subject. The average age of the first group was 67-7 (range 11-94) years. Abnormalities were present in 20 cases, no difference being found between patients with idiopathic and secondary heart block. In 15 samples there was increased oxidative enzyme activity in some muscle fibres, and in six there was fibre type grouping. Six had unexplained type 11 fibre atrophy and two had a predominance of type 1 fibres. Tubular aggregates were conspicuous in one biopsy specimen, and in another, rod bodies were found. Minor abnormalities were also seen in the control group. In the absence of any consistent pattern many of these changes were attributed to ageing.

Luft's disease. Further biochemical and ultrastructural studies of skeletal muscle in the second case

In the second known case of non-thyroidal hypermetabolism (Luft's disease), there were large areas of mitochondrial aggregates in all fibers. Many mitochondria were abnormally large and contained packed cristae. In isolated mitochondrial fractions, studies of oxidative phosphorylation showed defective respiratory control and normal phosphorylation capacity ("loose coupling"). Spectra and content of cytochromes were normal. Basal ATPase activity was seven times greater than normal and poorly stimulated by 2,4-dinitrophenol. The rate of energy-dependent calcium uptake by isolated mitochondria was normal, but the amount of calcium accumulated was much decreased. Calcium could not be retained and was spontaneously released into the medium within 30 seconds. "Recycling" of calcium between mitochondria and cytosol may take place in vivo and result in sustained stimulation of respiration and loose coupling.

Congenital oculoskeletal myopathy with abnormal muscle and liver mitochondria

We report a 22-year-old very thin man, who showed various symptoms and signs of oculoskeletal muscle weakness, episodes of myalgia, prolonged diarrhea, severe myopia, perceptive deafness, electrocardiographic and electroencephalographic abnormalities, and endocrinological abnormality. The onset was at about 3 months of age and a positive family history was strongly suggested. The light-microscopic, histochemical and electron-microscopic findings showed abnormal mitochondria not only in the skeletal muscle, but also in liver cells. From the clinical as well as morphological points of view, this case was suspected to be one of congenital oculoskeletal myopathy probably due to an unidentified systemic metabolic disorder.

Ragged-red fibers. A biochemical and morphological study

Histochemical, ultrastructural and biochemical studies were performed on muscle biopsy specimens from a 30-year-old man with proximal limb weakness. Modified Gomori trichome stains of anterior tibial muscle revealed accumulations of red-staining material in the subsarcolemmal and intermyofibrillar regions of virtually every fiber (ragged-red fibers); these accumulations were rich in oxidative enzymes. Electron microscopy of this muscle showed that the red-staining areas consisted of large collections of abnormal-appearing mitochondria. Mitochondria isolated from the quadriceps muscle showed lack of respiratory control with alpha-glycerophosphate as substrate. However, the lack of respiratory control with alpha-glycerophosphate must be interpreted with caution since the quadriceps muscle was severely degenerated, and biochemical alterations of mitochondria may occur secondary to muscle degeneration itself. Nevertheless, this is the second reported case of lack of respiratory control with alpha-glycerophosphate in a patient with ragged-red fibers. Further interpretation of this defect and its significance must await more studies to determine whether this muscle mitochondrial abnormality is a common finding in the disorders in which ragged-red fibers are encountered.

Idiopathic cardiomyopathy and skeletal muscle abnormality

The skeletal muscle of three cases presenting with idiopathic congestive cardiomyopathy has been studied, histologically, histochemically, ultramicroscopically, and electromyographically. In all three there is clinical evidence of skeletal muscle weakness, and in all three, pathologic changes were found in the muscle. These changes were different in each case and varied from mitochondrial myopathy to spinal atrophy to vacuolar myopathy. Other reported cases of cardiomyopathy demonstrating skeletal muscle pathology are discussed.

[Mitochondrial changes of the skeletal muscle in the peroneal muscular atrophy (Charcot-Marie-Tooth disease). Histological and electron microscopic studies (author's transl)]

This report deals with two sisters (38 and 44 years old) suffering from Charcot-Marie-Tooth disease. Muscle biopsies were taken from the deltoid and the rectus femoris. In one of the cases a sural nerve biopsy was also made. Light microscopy showed only slight myopathic changes. The histochemical reactions disclosed an increase in lipid deposition and in NADH-TR activity of type 1 fibres. Electron microscopy showed abnormal mitochondrial aggregates, which were surrounded inconstantly by glycogen deposits, especially in subsarcolemmal space. Many of the atypical mitochondria showed paracristalline inclusions within the cristae. The significance of these findings is discussed and compared with similar reports in the literature.

A possible role for electron microscopy in detection of carriers of Duchenne type muscular dystrophy

Five carriers of the gene of Duchenne type muscular dystrophy are described. Muscle histology was minimally to moderately abnormal in two and normal in three. Electron microscopy was abnormal in all five and showed massive aggregates of subsarcolemmal mitochondria, paracrystalline mitochondria, Z line streaming, central nuclei, dilated sacs of sarcoplasmic reticulum, focal loss of myofilaments, and lipid lysosome bodies. The electron microscopic literature on the carrier state is reviewed and analysed. The possible role of electron microscopy in detection of carriers is discussed.