ber die Feinstruktur und Topochemie von Riesenmitochondrien und deren Einlagerungen bei Myopathien

Megamitochondria in Cardiomyocytes of a Knockout (Klf15-/-) Mouse

The Kruppel-like factors (KLF) family of zinc-finger transcriptional regulators control many aspects of cardiomyocyte structure and function. Deletion of Klf15 from the nuclear genome in mice affects cardiac mitochondria. Some become grossly enlarged, extending many sarcomeres in length. These display many sites of incipient pinching, but there is little attenuation of the megamitochondria at these sites; there are no examples of organelles that clearly have reached the point where further membrane encroachment will cause separation into smaller daughter mitochondria. It is clear that deletion of Klf15 interferes with nuclear control of mitochondrial fission, whereas fusion appears to be unaffected.

Two types of mitochondrial crystals in diseased human skeletal muscle fibers

Mitochondrial crystalline inclusions, frequently found in mitochondrial myopathies, were analyzed by crystallographic techniques and computer-aided image processing. It could be shown that these structures were real crystals. There are two distinct types of crystal, which can be distinguished by shape, size, and pattern. So-called type I crystals are usually present in the intracristal space, whereas the type II crystals are preferentially located in the intermembrane space between outer and inner mitochondrial membranes. The unit cell dimensions were found to be 38 x 34 x 8 nm for the type I crystals and 20 x 17 x 8 nm for the type II crystals. These results strongly suggest that the crystals are composed of macromolecules, presumably proteins. Arguments are presented that indicate that type I crystals occur only in type 1 muscle fibers and type II crystals in type 2 muscle fibers.

Morphological observations in skeletal muscle from patients with a mitochondrial myopathy

Mitochondrial metabolic dysfunction is considered to be the cause of certain congenital myopathies and a number of multisystem disorders in humans. The morphological hallmark of these diseases is the 'ragged red' fibre, which shows abnormally intensive oxidative enzyme reactions. Electron microscopy reveals that the numerically increased mitochondria in these fibres are often markedly enlarged and possess aberrant configurations of cristae. The mitochondrial matrix often contains lipid-like inclusions or shows vacuolation. The most characteristic mitochondrial abnormality is the occurrence of highly ordered inclusions in the intracristal or intermembrane space. These inclusions appear to be true crystals, composed of proteinaceous material. It is argued that the activity of accumulation of proteins in the mitochondria is related to the nuclear and nucleolar hypertrophy noticeable in the ragged red fibres. Since protein crystals in mitochondria in particular occur when an increased capillary density around the ragged red fibres is present, it is suggested that oxygen free radicals and lipid peroxidation processes are involved in the ragged red fibre pathology.

Myopathy with mitochondrial abnormalities and rimmed vacuoles

A man of 44 years suffering from an exercise-induced neuromuscular disease with mitochondrial abnormalities and rimmed vacuoles is reported. The mitochondrial abnormalities and rimmed vacuoles (autophagic vacuoles) are interpreted as sequential changes of the same pathogenetic process depending on the degree of energy deficiency.

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.

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.

Light and electron microscopic studies of intramitochondrial bodies in bovine adrenocortical cells by proteolytic digestion

The nature of the intramitochondrial bodies in bovine adrenocortical cells was investigated both light and electron microscopically, by applying enzymatic digestion on paraffin and epon sections. The result that these bodies were extracted completely either by pepsin or by trypsin strengthened the validity of the previous conclusion that their nature is proteinaceous.