Intermembrane inclusions induced by anoxia in heart and skeletal muscle mitochondria

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.

Mitochondria-related encephalomyopathies

Owing to advances in morphological and biochemical techniques, the mitochondria-related myopathies and encephalomyopathies have emerged as a still rapidly growing group of primary and secondary metabolic disorders, which may extend from infancy to late adulthood. Impairment of the biochemically diversified mitochondria is reflected in an enormous number of deficiencies, often affecting several mitochondrial enzymes in the same patient; morphologically abnormal mitochondria are common and are thus not specific to individual mitochondrial enzyme deficiencies. Skeletal muscle biopsies have provided a wealth of data through histological and histochemical studies and from isolated mitochondria. As a similar abundance of biochemical and morphological findings has not been obtained from brain tissue in mitochondrial encephalomyopathies, investigation of these disorders is still in its infancy; interpretation of these conditions and their encephalopathic components has largely been based on comparison of data not derived from brain tissues. Therefore, it has been, and still is, largely the link between an encephalopathy and an associated mitochondrial myopathy that identifies the brain lesions as clinical and morphological expressions of a mitochondrial defect. As enzyme histochemical and electron microscopic investigations of mitochondrial encephalopathies have not yielded a comparable rich spectrum of morphological findings, it is conceivable that the spectrum of mitochondrial encephalopathies may be much larger than defined by the hitherto identified encephalomyopathies. This may be especially so when the myopathic component is of minor nosological significance.

Immunological abnormalities in a family with progressive external ophthalmoplegia

The authors report the muscular and humoral immunological abnormalities found in a family with progressive external ophthalmoplegia (PEO) of the "pure" form. Serum circulating immune complexes as determined by the polyethylen glycol (PEG) test and double radial immunodiffusion (DRID) were positive for IgG in both cases studied and for IgM and Clq for the propositus. In the latter circulating auto-antibodies against smooth muscle were also present. Immunohistochemical studies on striated muscle of the propositus showed positive perivascular IgG and IgM staining and IgG in the sarcolemma basement membrane complex. It is suggested that in this family a genetically inherited abnormal immune response to the muscular blood vessel wall has induced vascular injury and ultimately chronic ischemic muscular damage. This is consistent with the view that PEO is a clinical syndrome, i.e. the expression of various defects affecting primarily or secondarily the energy metabolism of the muscular tissue.

[Morphogenesis and micromorphology of epithelial tumors induced in the rat kidney by nitrosomorpholine. IV. Tubular lesions and basophilic tumors (author's transl)]

The genesis of basophilic cell kidney tumors was investigated stepwise by light and electron microscopy in rats treated with N-nitrosomorpholine for a limited time (stop experiment). Seven weeks after the beginning of the experiment the kidney tubules sometimes showed unusually large "chromophobic" and basophilic cells. After a lag period of 22-97 weeks more than 60% of the animals had developed these atypical tubules. Parallel to the appearance of chromophobic tubules 50% of the carcinogen-treated animals developed basophilic cell kidney tumors. All intermediate stages between chromophobic or basophilic cell tubules and tumors were found. During the neoplastic transformation chromophobic epithelia appeared to change into basophilic cells. Some of the chromophobic renal tubules and most of the renal tubules which consisted of chromophobic and basophilic epithelia stored acid mucopolysaccharides as demonstrated by histochemical methods. The fine structure of the basophilic epitheliomas was relatively uniform. The basophilia observed under the light microscope correlated with abundant membrane-bound and free ribosomes as seen under the electron microscope. The frequent appearance of brush borders and microbodies indicated the origin of the basophilic cell tumors from proximal renal tubules. In some tumor cells many mitochondria were found. These cells resembled oncocytes. However, in contrast to typical oncocytes the mitochondria of these cells were poor in cristae or showed tubular formations of the inner membrane. In some mitochondria homogeneous condensations could be detected in the intracristal space and tooth-like formations were seen on the surface of the cristae. In perpendicular sections these cristae resembled saw blades. Acute tubular lesions and cellular regeneration, as described earlier by other authors in early stages of the development of kidney tumors, were not found. It is suggested that the storage of acid mucopolysaccharides observed in many tubules and in some renal tumors indicates a disturbance of the cellular metabolism which plays an important role in tumor development.

Giant mitochondria in the human myocardium--morphogenesis and fate

Electron-microscopical examination of myocardial biopsy material obtained from a 58-year-old man revealed giant mitochondria having a length of 30 micron. Such giant mitochondria (also called megamitochondria) evolve by fusion of the membranes of numerous large individual organelles. Initially they are polymorphous and of diverse shapes, but later they are seen to be arranged among and parallel with the filaments of the myocardial fibres, where they present a smooth, cigar-like appearance. Deposits of glycogen in the giant mitochondria result from the accidental inclusion of glycogen granules during fusion. The abundance of cristae, which often form dense stacks in the megamitochondria, is evidence for the genuine synthesis of new cristal material. The aetiological and exact pathogenetic mechanisms of the evolution of giant mitochondria in the myocardium, as also their function, remain unclear. Particularly large specimens are obviously inefficient and disturbing to the cell. They are degraded by autophagy.

The occurrence of paracrystalline mitochondrial inclusions in normal human skeletal muscle

Two different types of paracrystalline mitochondrial inclusions identical with or very similar to those already described in the literature for a variety of muscle diseases were found in human skeletal muscle biopsies obtained under general anesthesia before ischemia and after various periods of anoxia up to 150 min. As these crystalloids could be observed in seven of 14 healthy subjects and occurred in five of these seven cases either before or only 10 min after onset of ischemia, it is suggested that such mitochondrial inclusions develop not only under the influence of variant noxious stimuli, but may also represent a normal constituent of human skeletal muscle mitochondria.