Inclusions in aged mitochondria

Deletions of mitochondrial DNA in Kearns-Sayre syndrome and ocular myopathies: genetic, biochemical and morphological studies

Genetic, biochemical and morphological investigations were conducted on skeletal muscle mitochondria from 6 cases of ocular myopathy: 4 cases with Kearns-Sayre syndrome (KSS) and 2 with chronic progressive external ophthalmoplegia. All of these 6 cases showed mitochondrial DNA (mtDNA) deletions in addition to normal sized DNA in the quadriceps muscle. The deletions ranging from 3 to 8 kbp were also mapped between nucleotides 5500 and 16000 by Southern blot. The deleted genes encoded for some subunits of complexes I, IV, V and 5-10 tRNAS. The boundaries of the deletions have been sequenced in three patients. Five patients had mitochondrial respiratory chain deficiency in complex I as shown by the low oxygen consumption in isolated mitochondria using three NAD(+)-linked substrates. Mitochondria with an abnormal ultrastructure were also observed in 2 cases. A good relationship between the cytochrome c oxidase deficiency and the amount of deleted mtDNA was shown in our present investigations.

Intramitochondrial inclusions in maturing and senescent muscle cells of rat myocardium

Intramitochondrial myelin-like structures were found in ventricular myocardial cells of the rat heart. These inclusions were found in both the first 2 postnatal weeks and in senescent stages. The origin of such myelin-like structures could be related to an age-dependent metabolic change, specifically to an inability to oxidize long-chain fatty acids described in both periods.

Experimental production of "septa" and apparent subdivision of muscle mitochondria

The rapid formation (in less than 45 min) of internal septa and the apparent subdivision in situ of mitochondria for cardiac and skeletal muscle are described following a variety of experimental treatments. For example, the ionophore A23187, caffeine, DNP, ruthenium red, and the insecticide lindane have been applied to intact, glycerinated, and chemically skinned skeletal muscle fibers and to cardiac muscle strips from both amphibians and mammals. In some mitochondria, the two compartments are in the same configurations; in others they are different. The significance of these mitochondrial septa is discussed, and it is suggested that the findings are consistent with the hypothesis that a variety of experimental procedures can promote rapid mitochondrial division.

Intermembrane inclusions induced by anoxia in heart and skeletal muscle mitochondria

Heart and skeletal muscle from rats of different ages were incubated in vitro in an oxygen-free medium supplied with substrates in order to investigate the effect of anoxia on muscle fine structure, particulary on the mitochondria. In skeletal muscle fibers anoxia has been found to induce changes similar to those previously described in ischemic muscles in vivo namely giant mitochondria, apparently derived by mitochondrial fusion, and intermembrane inclusions with a paracrystalline structure. The plate-like inclusions are mostly located in the intracristal spaces and are closely associated to cristal membranes even in markedly swollen mitochondria. Identical inclusions have been observed in cardiac muscle cells following anoxic injury, whereas they are never found in non-muscle cells such as endothelia, fibroblasts and nerve fibers. Cardiac and skeletal muscle fibers from newborn rats maintained in an oxygen-free medium show mitochondrial swelling but no intermembrane inclusions. The different response of mitochondria from developing vs adult striated muscle to anoxia may be due to changes during postnatal development in the quality or quantity of the protein component(s) involved in paracrystal formation.