Clinical and molecular heterogeneity of cytochromec oxidase deficiency in the newborn

Summary We report 8 cases of severe cytochromec oxidase deficiency with onset in the neonatal period. Clinical symptoms were heterogeneous: antenatal cerebral malformations, neurological distress with ketoacidosis, severe myopathy, or isolated respiratory control failure. Lactic acid was elevated in blood and/or CSF in 7 cases. Muscle biopsy (7 patients), liver biopsy (4 patients), and cultured skin fibroblasts (7 patients) were used to assess the cytochromec oxidase deficiency. Among the patients, the enzymatic defect differed in the level of residual activity, expression in different tissues and subunit composition in muscle (as analysed by immunohistochemistry). Southern blot analysis of the mitochondrial DNA was normal in 7 patients. The heterogeneity of cytochromec oxidase deficiency was therefore demonstrated by these clinical presentations and by the biochemical assessment of the enzyme defect. This reflects, most probably, the diverse nature of the causal mutations.     

Prenatal diagnosis of systemic disorders of the respiratory chain in cultured amniocytes and chorionic villus fibroblasts by studying the formation of lactate and pyruvate from glucose

Summary Formation of lactate and pyruvate from glucose was studied in cultured amniocytes and chorionic villus fibroblasts from controls, either untreated or treated with azide, an inhibitor of cytochromec oxidase, or other inhibitors of the mitochondrial respiratory chain. Amniocytes with an established cytochromec oxidase deficiency were also investigated.Control amniocytes treated with azide as well as cytochromec oxidase deficient amniocytes displayed strongly increased lactate-to-pyruvate ratios after incubation with glucose, compared to control cells. Elevated lactate-to-pyruvate ratios were also found in chorionic villus fibroblasts in which complexes I, III or IV were inhibited by rotenone, antimycin or azide, respectively. We conclude that measurement of lactate and pyruvate production from glucose in cultured amniocytes and/or chorionic villus fibroblasts allows adequate prenatal diagnosis of systemic cytochromec oxidase deficiency and presumably of other systemic deficiencies of mitochondrial respiratory chain enzymes.     

病毒性心肌炎小鼠心肌与骨骼肌细胞线粒体损伤及其相关性

目的探讨病毒性心肌炎（VMC）小鼠心肌与骨骼肌细胞线粒体损伤（线粒体膜磷脂脱失和线粒体DNA3867缺失）程度及二者的相关性。方法50只BALB/c小鼠随机分为2组,实验组（40只）腹腔注射内含柯萨奇B3病毒（Coxsackievirus B3,CVB3,TCID50=108）的Eagle液制备VMC小鼠模型,另10只为对照组。分别于病毒感染后3、11和24 d行心肌和骨骼肌细胞线粒体膜磷脂脱失程度和mtDNA3867缺失率的测定,并用Spearman法对其进行相关分析。结果实验组小鼠在病毒感染后3 d,可见心肌和骨骼肌细胞mtDNA3867缺失率显著高于对照组（P<0.05）,而线粒体膜磷脂脱失程度与对照组相比无显著性差异;病毒感染后11 d,心肌和骨骼肌细胞mtDNA3867缺失性损伤达高峰（P<0.05）,线粒体膜磷脂脱失程度亦显著高于对照组（P<0.05）;病毒感染后24 d,心肌和骨骼肌细胞线粒体膜磷脂脱失和mtDNA3867缺失程度与感染后11 d组比较无显著性差异,但与对照组和病毒感染后3 d组比较,仍有显著性差异（P<0.05）。线粒体的上述损伤性改变在心肌和骨骼肌细胞呈一致性同步变化,且具有良好相关性（P<0.05）。结论CVB3可显著损伤心肌和骨骼肌线粒体DNA和膜磷脂,两者损伤具有相关性,提示骨骼肌有望成为反映心肌细胞线粒体损伤的外周细胞“窗口”。     

Biochemical and molecular investigation of mitochondrial disease: an illustrative case showing the value of a multifaceted approach

Abstract :Detailed biochemical and molecular investigations in a patient with Kearns-Sayre syndrome are presented. Polarographic studies in isolated mitochondria revealed a global impairment in respiratory capacity consistent with an admixture of functional and non-functional mitochondria. Cytochrome difference spectra revealed a selective deficiency in cytochrome aa₃. Western immunoblot studies revealed normal subunit content of Complexes 1, III and IV. Southern blot studies of mtDNA showed a deletion of approximately 5 Kb coexisting with wild type DNA. PCR analysis confirmed that this deletion lies between the ATPase8 and NAD coenzyme Q oxidoreductase subunit 5 (ND5) genes. Breakpoint sequencing revealed a 13 nucleotide direct repeat flanking sequence (ACCTCCCTCACCA) consistent with slippage in mtDNA during replication as the mechanism of deletion. Histochemical studies of skeletal muscle revealed many cytochrome oxidase negative fibres and immunocytochemical studies showed cytochrome oxidase negative areas with abundant respiratory complex protein suggesting upregulation. The value of a multifaceted approach in unravelling the pathophysiology of mitochondrial diseases is emphasised. (Aust NZ J Med 1991; 21: 837–843.)     

Genetic counselling and prenatal diagnosis in disorders of the mitochondrial energy metabolism

Summary Point mutations in mitochondrial DNA, as found in MELAS, MERRF, NARP and other syndromes, are inherited via the maternal lineage. Genetic counselling can be beneficial, but prenatal diagnosis is not advantageous in these syndromes. Empirical data about the recurrence risk can be applied in Leber disease (LHON). Mitochondrial disorders not associated with a point mutation have a sporadic nature (large deletions/duplications in mitochondrial DNA) or are transmitted according to Mendelian laws. Autosomal dominant inheritance is likely to be found in disorders with depletion of mitochondrial DNA. X-linked mode of inheritance is seen in Menkes disease, Barth syndrome, and in deficiencies of the E₁ subunit of the pyruvate dehydrogenase complex. Mutation analysis or linkage studies can be applied for carrier detection and prenatal diagnosis in these three types of mitochondriopathies. The majority of the disorders with a disturbed mitochondrial energy metabolism are likely inherited in an autosomal recessive mode. Prenatal diagnosis can be performed in the cases of cytochromec oxidase and NADH dehydrogenase deficiencies in chorionic villi in selected families.     

Case study of an inborn error manifested in the elderly: A woman with adult‐onset mitochondrial disease mimicking systemic vasculitis

Mitochondrial diseases are a group of disorders presenting mainly during infancy due to pathological dysfunction of the mitochondrial respiratory chain. We report a case of mitochondrial disease in an elderly woman complaining of generalized myalgia. A 69‐year‐old woman was admitted due to fatigue, general weakness, and a drowsy mental status. A brain magnetic resonance imaging (MRI) demonstrated multifocal lesions of increased T2 signal intensity, and laboratory findings were consistent with Fanconi syndrome. During her hospital course, she developed seizures, stress‐induced cardiomyopathy, and respiratory failure. A muscle biopsy demonstrated ragged‐red fibers in the muscle tissues seen in mitochondrial myopathy. We confirmed an 8 kb deletion in her mitochondrial DNA. Following treatment with l ‐carnitine, coenzyme Q10, and supportive measures, brain lesions on MRI scans disappeared, and the general symptoms gradually improved.     

A common mitochondrial DNA variant is associated with insulin resistance in adult life

Summary Mitochondrial DNA is maternally inherited. Mitochondrial DNA mutations could contribute to the excess of maternal over paternal inheritance of non-insulin-dependent diabetes mellitus (NIDDM). We therefore investigated the relationship between this variant, insulin resistance and other risk factors in a cohort which had been well characterised with respect to diabetes. Blood DNA was screened from 251 men born in Hertfordshire 1920–1930 in whom an earlier cohort study had shown that glucose tolerance was inversely related to birthweight. The 16 189 variant (T- > C transition) in the first hypervariable region of mitochondrial DNA was detected using the polymerase chain reaction and restriction digestion. DNA analysis showed that 28 of the 251 men (11 %) had the 16 189 variant. The prevalence of the 16 189 variant increased progressively with fasting insulin concentration (p < 0.01). The association was independent of age and body mass index and was present after exclusion of the patients with NIDDM or impaired glucose tolerance. We found that insulin resistance in adult life was associated with the 16 189 variant. This study provides the first evidence that a frequent mitochondrial variant may contribute to the phenotype in patients with a common multifactorial disorder. [Diabetologia (1998) 41: 54–58] Received: 20 May 1997 and in revised form: 7 August 1997     

Mitochondrial cytochrome <Emphasis Type="Italic">c</Emphasis> release: a factor to consider in mitochondrial disease?

Summary  The pathogenesis of mitochondrial disorders has largely focused on the impairment of cellular energy metabolism. However, mitochondrial dysfunction has also been implicated as a factor in the initiation of apoptosis due to the translocation of cytochrome c, from mitochondria to the cytosol, and the subsequent cleavage of pro-caspase 3. In this study, we determined the cytochrome c content of cytosols (skeletal muscle) prepared from 22 patients with evidence of compromised mitochondrial electron transport chain enzyme activity and 26 disease controls. The cytochrome c content of the mitochondrial electron transport chain-deficient group was found to be significantly (p < 0.02) elevated when compared with the control group (63.7 ± 15.5 versus 27.7 ± 2.5 ng/mg protein). Furthermore, a relationship between the cytosolic cytochrome c content of skeletal muscle and complex I and complex IV activities was demonstrated. Such data raise the possibility that mitochondrial cytochrome c release may be a feature of mitochondrial disorders, particularly for those patients with marked deficiencies of respiratory chain enzymes. Whether initiation of apoptosis occurs as a direct consequence of this cytochrome c release has not been fully evaluated here. However, for one patient with the greatest documented cytosolic cytochrome c content, caspase 3 could be demonstrated in the cytosolic preparation. Further work is required in order to establish whether a relationship also exists between caspase 3 formation and the magnitude of respiratory chain deficiency. Competing interests: None declared     

Deletion of mitochondrial DNA in the endomyocardial biopsy sample from a patient with Kearns-Sayre syndrome.

A 15-year-old boy with Kearns-Sayre syndrome is reported. The deletion of mitochondrial DNA in the endomyocardial biopsy sample from the patient was confirmed by the polymerase chain reaction method, and was identified to that in the skeletal muscle.     

Different pathophysiological mechanisms of intramitochondrial iron accumulation in acquired and congenital sideroblastic anemia caused by mitochondrial DNA deletion

Sideroblastic anemias (SA) are characterized by iron accumulation in the mitochondria of erythroblasts. Although we have evidence of mitochondrial gene alterations in sporadic congenital cases, the origin of acquired forms [refractory anemia with ring sideroblasts (RARS)], is still largely unknown. Here, we report the analysis of respiratory chain function in a patient with a large mitochondrial deletion and in patients with RARS. A young boy with SA showed symptoms typical of a mitochondrial disease with metabolic acidosis, muscle weakness and cerebral involvement. His bone marrow DNA was analyzed for the presence of mitochondrial deletions. We found a new mitochondrial (mt)DNA deletion spanning 3,614 bp and including all the mt genes encoding complex IV, plus ATPase 6 and 8, and several transfer (t)RNAs. All tissues analyzed (liver, skeletal muscle, brain, pancreas) showed a heteroplasmic distribution of this mutant DNA. Bone marrow homogenates were obtained from five patients with RARS and from three patients with normal bone marrow and respiratory chain function assayed by spectrophotometric analysis. Cytochrome c oxidase (CCO) activity was greatly reduced in the patient's bone marrow. In contrast, CCO activity and global respiratory chain function were conserved in patients with RARS. We conclude that deficient CCO activity secondary to mtDNA deletions is related to intramitochondrial iron accumulation, as in our patient or in those with Pearson's syndrome, whereas other mechanisms, e.g. nuclear DNA mutations, have to be proposed to be involved in the acquired forms of SA.     

Caloric restriction delays aging-induced cellular phenotypes in rhesus monkey skeletal muscle

Sarcopenia is the age-related loss of skeletal muscle mass and function and is characterized by a reduction in muscle mass and fiber cross-sectional area, alterations in muscle fiber type and mitochondrial functional changes. In rhesus monkeys, calorie restriction (CR) without malnutrition improves survival and delays the onset of age-associated diseases and disorders including sarcopenia. We present a longitudinal study on the impact of CR on early stage sarcopenia in the upper leg of monkeys from ~ 16 years to ~ 22 years of age. Using dual-energy X-ray absorptiometry we show that CR delayed the development of maximum muscle mass and, unlike Control animals, muscle mass of the upper leg was preserved in CR animals during early phase sarcopenia. Histochemical analyses of vastus lateralis muscle biopsies revealed that CR opposed age-related changes in the proportion of Type II muscle fibers and fiber cross-sectional area. In contrast the number of muscle fibers with mitochondrial electron transport system enzyme abnormalities (ETS^ab) was not significantly affected by CR. Laser capture microdissection of ETS^ab fibers and subsequent PCR analysis of the mitochondrial DNA revealed large deletion mutations in fibers with abnormal mitochondrial enzyme activities. CR did not prevent stochastic mitochondrial deletion mutations in muscle fibers but CR may have contributed to the maintenance of affected fibers.     

Analysis of age-associated mitochondrial DNA deletion breakpoint regions from mice suggests a novel model of deletion formation

Mitochondrial genomes with multiple types of DNA deletions have been shown to accumulate with age in various tissues from humans, monkeys, rats, mice, and C. elegans. The deleted genomes have been classified based on characteristics of the deletion breakpoints such as the presence (or absence) of direct repeat sequences. The prevalence of direct repeats located precisely at deletion breakpoints in human mitochondrial DNA deleted genomes has led several investigators to propose slip replication or recombination as mechanisms of deletion formation. Other sequence motifs such as topoisomerase II cleavage recognition sites and secondary or tertiary structures have also been implicated in aiding deletion formation. We have characterized, from mouse skeletal muscle and brain tissues, the breakpoint regions from 36 mitochondrial genomes with deletions. Based on the large number of deletion breakpoints precisely flanked by small (2–4 nucleotides) direct repeats, we propose “replication jumping” as an important mechanism of deletion formation. In this model, the polymerase stutters during replication, possibly in an area that has been oxidatively modified. The nascent strand then anneals to a complementary downstream region and replication continues after the removal of any single-stranded “excess” DNA up to a double-stranded region, resulting in a mutant genome.     

Batteries not included: diagnosis and management of mitochondrial disease

In 1998, Wallace et al. (Science 1988; 242 : 1427–30) published evidence that the mutation m.11778G>A was responsible for causing Leber’s hereditary optic neuropathy. This was the first account of a mitochondrial DNA mutation being irrefutably linked with a human disease and was swiftly followed by a report from Holt et al. (Nature 1988; 331 : 717–9) identifying deletions in mitochondrial DNA as a cause for myopathy. During the subsequent 20 years there has been an exponential growth in ‘mitochondrial medicine’, with clinical, biochemical and genetic characterizations of a wide range of mitochondrial diseases and evidence implicating mitochondria in a host of many other clinical conditions including ageing, neurodegenerative illness and cancer. In this review we shall focus on the diagnosis and management of mitochondrial diseases that lead directly or indirectly to disruption of the process of oxidative phosphorylation.     

The mitochondrial tRNALeu(UUR) A to G 3243 mutation is associated with insulin-dependent and non-insulin-dependent diabetes in a Chinese population

The mitochondrial DNA tRNA^Leu(UUR) A to G 3243 mutation is associated with maternally inherited diabetes in Caucasians and Japanese. In a Hong Kong Chinese population we have detected the 3243 mutation in 2 of 74 unrelated subjects with well characterized insulin-dependent (Type 1) diabetes mellitus (IDDM) and 2 of 75 unrelated subjects with young onset (<35 years) non-insulin-dependent diabetes (NIDDM). The 3243 mutation has only previously been associated with IDDM in Japanese. Racial differences in association of the mitochondrial 3243 mutation with IDDM suggest the influence of other genes that may increase its diabetogenic pathogenicity in Oriental races. We also found a significant excess of maternal inheritance of diabetes in the young onset NIDDM cohort, with a ratio of diabetic mothers to fathers of 2.4:1, p < 0.005. The 3243 mutation, however, only accounts for a small proportion of the observed excess maternal inheritance, and further study is needed to search for other diabetes associated mitochondrial DNA mutations. © 1997 John Wiley & Sons, Ltd.     

Diagnostic value of succinate ubiquinone reductase activity in the identification of patients with mitochondrial DNA depletion

Mitochondrial DNA (mtDNA) depletion syndrome (McKusick 251880) is characterized by a progressive quantitative loss of mtDNA resulting in severe mitochondrial dysfunction. A diagnosis of mtDNA depletion can only be confirmed after Southern blot analysis of affected tissue. Only a limited number of centres have the facilities to offer this service, and this is frequently on an irregular basis. There is therefore a need for a test that can refine sample selection as well as complementing the molecular analysis. In this study we compared the activities of the nuclear-encoded succinate ubiquinone reductase (complex II) to the activities of the combined mitochondrial and nuclear-encoded mitochondrial electron transport chain (ETC) complexes; NADH:ubiquinone reductase (complex I), ubiquinol-cytochrome-c reductase (complex III), and cytochrome-c oxidase (complex IV), in skeletal muscle biopsies from 7 patients with confirmed mtDNA depletion. In one patient there was no evidence of an ETC defect. However, the remaining 6 patients exhibited reduced complex I and IV activities. Five of these patients also displayed reduced complex II[ndash ]III (succinate:cytochrome-c reductase) activity. Individual measurement of complex II and complex III activities demonstrated normal levels of complex II activity compared to complex III, which was reduced in the 5 biopsies assayed. These findings suggest a possible diagnostic value for the detection of normal levels of complex II activity in conjunction with reduced complex I, III and IV activity in the identification of likely candidates for mtDNA depletion syndrome     

Melatonin prevents cell death and mitochondrial dysfunction via a SIRT1‐dependent mechanism during ischemic‐stroke in mice

Silent information regulator 1 (SIRT1), a type of histone deacetylase, is a highly effective therapeutic target for protection against ischemia reperfusion (IR) injury (IRI). Previous studies showed that melatonin preserves SIRT1 expression in neuronal cells of newborn rats after hypoxia–ischemia. However, the definite role of SIRT1 in the protective effect of melatonin against cerebral IRI in adult has not been explored. In this study, the brain of adult mice was subjected to IRI. Prior to this procedure, the mice were given intraperitoneal with or without the SIRT1 inhibitor, EX527. Melatonin conferred a cerebral‐protective effect, as shown by reduced infarct volume, lowered brain edema, and increased neurological scores. The melatonin‐induced upregulation of SIRT1 was also associated with an increase in the anti‐apoptotic factor, Bcl2, and a reduction in the pro‐apoptotic factor Bax. Moreover, melatonin resulted in a well‐preserved mitochondrial membrane potential, mitochondrial Complex I activity, and mitochondrial cytochrome c level while it reduced cytosolic cytochrome c level. However, the melatonin‐elevated mitochondrial function was reversed by EX527 treatment. In summary, our results demonstrate that melatonin treatment attenuates cerebral IRI by reducing IR‐induced mitochondrial dysfunction through the activation of SIRT1 signaling.     

Cardiac dysfunction in patients with chronic progressive external ophthalmoplegia

Background: Chronic progressive external ophthalmoplegia (CPEO), which includes Kearns-Sayre syndrome, is a mitochondrial disorder with large deletions of mitochondrial DNA. Recently, mtDNA deletions in cardiac muscle cells were thought to be a cause of dilated cardiomyopathy. However, the cardiac involvement in patients with CPEO is generally considered to be limited to the cardiac conduction system. Hypothesis: The purpose of this study was to evaluate left ventricular function in patients with CPEO. Methods: We evaluated the cardiac function of five patients with CPEO by means of carotid pulse recording and Doppler echocardiography. Results: The ratio of the pre-ejection period to ejection time was increased to 0.67 in one patient and to 0.50 in another. Echocardiography showed left ventricular dilatation and diffuse hypokinetic wall motion in both cases. Left ventricular fractional shortening was decreased to 5 and 19%, respectively, and the mean rate of circumferential shortening was decreased to 0.12 and 0.63 circ/s, respectively. One of the two patients died of congestive heart failure 2 months after the study. The Doppler pattern of left ventricular filling in the three remaining patients showed a decrease in the ratio of peak flow velocity in early diastole to that in late diastole, with an increase in deceleration time. Conclusion: Although cardiac involvement in patients with CPEO is generally considered to be limited to the cardiac conduction system, left ventricular dysfunction may be present and should receive more attention in the management of patients with CPEO.     

线粒体DNA与心肌病的关系

人类线粒体DNA（mtDNA）是细胞内唯一存在于细胞核外的遗传物质,参与了转录、编码2个rRNA,22个tRNA及线粒体呼吸链中的13种蛋白多肽亚单位。人类某些疾病与线粒体DNA缺陷有关。心肌病是一类原因不明的伴随心脏功能障碍的心肌疾病。研究显示,线粒体产生的大量活性氧可导致mtDNA缺失或突变,tRNA基因保守序列突变影响肌肉收缩蛋白合成,造成氧化磷酸化缺陷,影响能量代谢。因此,线粒体的功能缺陷可能在心肌病的发生发展中起一定的作用。本文探讨了mtDNA突变与心肌病的关系,对mtDNA的深入研究将为临床寻找病因以及预防、诊断、治疗心肌病提供新思路。