Cytochrome c oxidase deficiencies in the muscle of patients with inflammatory myopathies

HiFi long-read amplicon sequencing for full-spectrum variants of human mtDNA

BACKGROUND

Mitochondrial diseases (MDs) can be caused by single nucleotide variants (SNVs) and structural variants (SVs) in the mitochondrial genome (mtDNA). Presently, identifying deletions in small to medium-sized fragments and accurately detecting low-percentage variants remains challenging due to the limitations of next-generation sequencing (NGS).

METHODS

In this study, we integrated targeted long-range polymerase chain reaction (LR-PCR) and PacBio HiFi sequencing to analyze 34 participants, including 28 patients and 6 controls. Of these, 17 samples were subjected to both targeted LR-PCR and to compare the mtDNA variant detection efficacy.

RESULTS

Among the 28 patients tested by long-read sequencing (LRS), 2 patients were found positive for the m.3243 A > G hotspot variant, and 20 patients exhibited single or multiple deletion variants with a proportion exceeding 4%. Comparison between the results of LRS and NGS revealed that both methods exhibited similar efficacy in detecting SNVs exceeding 5%. However, LRS outperformed NGS in detecting SNVs with a ratio below 5%. As for SVs, LRS identified single or multiple deletions in 13 out of 17 cases, whereas NGS only detected single deletions in 8 cases. Furthermore, deletions identified by LRS were validated by Sanger sequencing and quantified in single muscle fibers using real-time PCR. Notably, LRS also effectively and accurately identified secondary mtDNA deletions in idiopathic inflammatory myopathies (IIMs).

CONCLUSIONS

LRS outperforms NGS in detecting various types of SNVs and SVs in mtDNA, including those with low frequencies. Our research is a significant advancement in medical comprehension and will provide profound insights into genetics.

Oxidative stress, mitochondrial dysfunction, and respiratory chain enzyme defects in inflammatory myopathies

We investigated the relationship between oxidative stress and inflammatory myopathies. We searched in the current literature the role of mitochondria and respiratory chain defects as sources of oxidative stress and reactive oxygen species production that led to muscle weakness and fatigue. Different molecules and pathways contribute to redox milieu, reactive oxygen species generation, accumulation of misfolded and carbonylated proteins that lose their ability to fulfil cellular activities. Small peptides and physical techniques proved, in mice models, to reduce oxidative stress. We focused on inclusion body myositis, as a major expression of myopathy related to oxidative stress, where mitochondrial abnormalities are causative agents as well. We described the effect of physical exercise in inclusion body myositis that showed to increase strength and to reduce beta amyloid accumulation with subsequent improvement of the mitochondrial functions. We illustrated the influence of epigenetic control on the immune system by non-coding genetic material in the interaction between oxidative stress and inflammatory myopathies.

Rare forms of inflammatory myopathies - part I, generalized forms

INTRODUCTION

The idiopathic inflammatory myopathies traditionally comprise dermatomyositis, polymyositis, immune-mediated necrotizing myopathy, anti-synthetase syndrome, and inclusion body myositis. In this review, we aimed to cover the less common forms of generalized myositis.

AREAS COVERED

We identified rare forms of widespread myositis on the basis of list provided by the homepage of the Neuromuscular disease center of Washington University, USA and on the basis of the authors' knowledge. We searched PubMed® and EMBASE® for relevant articles on these forms with the aim of providing as much as possible information on their clinical manifestations as well as guidance on their work-up and treatment.

EXPERT OPINION

There is substantial heterogeneity among the various rare forms of generalized myositis in terms of their frequency and characterization. Some forms are reasonably well defined, while others may not represent truly well-defined diseases, but rather variants of other myopathies. The landscape of rare forms appears to have evolved over time, with some forms now being better characterized, while others, such as SARS-Cov-2- and immune checkpoint inhibitor-related myositis have come to the fore only in recent years. Knowledge about rare forms of myositis can aid in their recognition and treatment.

Diagnosis and Clinical Development of Sporadic Inclusion Body Myositis and Polymyositis With Mitochondrial Pathology: A Single-Center Retrospective Analysis

To review our diagnostic and treatment approaches concerning sporadic inclusion body myositis (sIBM) and polymyositis with mitochondrial pathology (PM-Mito), we conducted a retrospective analysis of clinical and histological data of 32 patients diagnosed as sIBM and 7 patients diagnosed as PM-Mito by muscle biopsy. Of 32 patients identified histologically as sIBM, 19 fulfilled the 2011 European Neuromuscular Center (ENMC) diagnostic criteria for "clinico-pathologically defined sIBM" at the time of biopsy. Among these, 2 patients developed sIBM after years of immunosuppressive treatment for organ transplantation. Of 11 patients fulfilling the histological but not the clinical criteria, including 3 cases with duration <12 months, 8 later fulfilled the criteria for clinico-pathologically defined sIBM. Of 7 PM-Mito patients, 4 received immunosuppression with clinical improvement in 3. One of these later developed clinico-pathologically defined sIBM; 1 untreated patient progressed to clinically defined sIBM. Thus, muscle histology remains important for this differential diagnosis to identify sIBM patients not matching the ENMC criteria and the PM-Mito group. In the latter, we report at least 50% positive, if occasionally transient, response to immunosuppressive treatments and progression to sIBM in a minority. The mitochondrial abnormalities defining PM-Mito do not seem to define the threshold to immunosuppression unresponsiveness.

Idiopathic inflammatory myopathy human derived cells retain their ability to increase mitochondrial function

Idiopathic Inflammatory Myopathies (IIMs) have been studied within the framework of autoimmune diseases where skeletal muscle appears to have a passive role in the illness. However, persiting weakness even after resolving inflammation raises questions about the role that skeletal muscle plays by itself in these diseases. "Non-immune mediated" hypotheses have arisen to consider inner skeletal muscle cell processes as trigger factors in the clinical manifestations of IIMs. Alterations in oxidative phosphorylation, ATP production, calcium handling, autophagy, endoplasmic reticulum stress, among others, have been proposed as alternative cellular pathophysiological mechanisms. In this study, we used skeletal muscle-derived cells, from healthy controls and IIM patients to determine mitochondrial function and mitochondrial ability to adapt to a metabolic stress when deprived of glucose. We hypothesized that mitochondria would be dysfunctional in IIM samples, which was partially true in normal glucose rich growing medium as determined by oxygen consumption rate. However, in the glucose-free and galactose supplemented condition, a medium that forced mitochondria to function, IIM cells increased their respiration, reaching values matching normal derived cells. Unexpectedly, cell death significantly increased in IIM cells under this condition. Our findings show that mitochondria in IIM is functional and the decrease respiration observed is part of an adaptative response to improve survival. The increased metabolic function obtained after forcing IIM cells to rely on mitochondrial synthesized ATP is detrimental to the cell’s viability. Thus, therapeutic interventions that activate mitochondria, could be detrimental in IIM cell physiology, and must be avoided in patients with IIM.

Mitochondrial dysfunction and role of harakiri in the pathogenesis of myositis

The etiology of myositis is unknown. Although attempts to identify viruses in myositis skeletal muscle have failed, several studies have identified the presence of a viral signature in myositis patients. Here we postulate that in individuals with susceptible genetic backgrounds, viral infection alters the epigenome to activate the pathological pathways leading to disease onset. To identify epigenetic changes, methylation profiling of Coxsackie B infected human myotubes and muscle biopsies from polymyositis (PM) and dermatomyositis (DM) patients were compared to changes in global transcript expression induced by in vitro Coxsackie B infection. Gene and protein expression analysis and live cell imaging were performed to examine the mechanisms. Analysis of methylation and gene expression changes identified that a mitochondria-localized activator of apoptosis - harakiri (HRK) - is upregulated in myositis skeletal muscle cells. Muscle cells with higher HRK expression have reduced mitochondrial potential and poor ability to repair from injury as compared to controls. In cells from myositis patient toll-like receptor 7 (TLR7) activates and sustains high HRK expression. Forced over expression of HRK in healthy muscle cells is sufficient to compromise their membrane repair ability. Endurance exercise that is associated with improved muscle and mitochondrial function in PM and DM patients decreased TLR7 and HRK expression identifying these as therapeutic targets. Increased HRK and TLR7 expression causes mitochondrial damage leading to poor myofiber repair, myofiber death and muscle weakness in myositis patients and exercise induced reduction of HRK and TLR7 expression in patients is associated with disease amelioration. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Polymyositis with mitochondrial pathology or atypical form of sporadic inclusion body myositis: case series and review of the literature

Polymyositis with mitochondrial pathology (PM-Mito) is a rare form of idiopathic inflammatory myopathy with no definite diagnostic criteria and similarities to both PM and sporadic inclusion body myositis (s-IBM). The aim of this study is to address the dilemma of whether PM-Mito is a subtype of inflammatory myopathy or represents a disease falling into the spectrum of s-IBM. Herein, we report four female patients diagnosed with PM-Mito, highlighting their rather atypical clinical and histopathological characteristics that seem to indicate a diagnosis away from s-IBM. Muscle weakness was rather proximal and symmetrical and lacked the selective pattern observed in s-IBM. Patients had large-scale deletions in mtDNA, reflecting the mitochondrial component in the pathology of the disease. Conclusively, our study adds to the limited data in the literature on whether PM-Mito is a distinct form of myositis or represents a prodromal stage of s-IBM. Although the latter seems to be supported by a substantial body of evidence, there are, however, important differences, such as the different patterns of muscle weakness, and the good response to treatment observed in some patients. Larger-scale studies are certainly needed to clarify pathogenesis and clinical characteristics of PM-Mito patients, especially in therapeutic and prognostic terms.

IFN-β-induced reactive oxygen species and mitochondrial damage contribute to muscle impairment and inflammation maintenance in dermatomyositis

Dermatomyositis (DM) is an autoimmune disease associated with enhanced type I interferon (IFN) signalling in skeletal muscle, but the mechanisms underlying muscle dysfunction and inflammation perpetuation remain unknown. Transcriptomic analysis of early untreated DM muscles revealed that the main cluster of down-regulated genes was mitochondria-related. Histochemical, electron microscopy, and in situ oxygraphy analysis showed mitochondrial abnormalities, including increased reactive oxygen species (ROS) production and decreased respiration, which was correlated with low exercise capacities and a type I IFN signature. Moreover, IFN-β induced ROS production in human myotubes was found to contribute to mitochondrial malfunctions. Importantly, the ROS scavenger N-acetyl cysteine (NAC) prevented mitochondrial dysfunctions, type I IFN-stimulated transcript levels, inflammatory cell infiltrate, and muscle weakness in an experimental autoimmune myositis mouse model. Thus, these data highlight a central role of mitochondria and ROS in DM. Mitochondrial dysfunctions, mediated by IFN-β induced-ROS, contribute to poor exercise capacity. In addition, mitochondrial dysfunctions increase ROS production that drive type I IFN-inducible gene expression and muscle inflammation, and may thus self-sustain the disease. Given that current DM treatments only induce partial recovery and expose to serious adverse events (including muscular toxicity), protecting mitochondria from dysfunctions may open new therapeutic avenues for DM.

Mitochondrial dysfunction in myofibrillar myopathy

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Clonally expanded mtDNA deletions were found in a small number of patient fibres.

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Complex I and IV deficiency is higher than in control muscle.

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Mitochondrial mass is significantly reduced in patients relative to controls.

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No relationship between MFM protein aggregates and reduced mitochondrial mass.

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Negative correlations was detected between mitochondrial mass and muscle fibre area.

Myofibrillar myopathies (MFM) are characterised by focal myofibrillar destruction and accumulation of myofibrillar elements as protein aggregates. They are caused by mutations in the DES, MYOT, CRYAB, FLNC, BAG3, DNAJB6 and ZASP genes as well as other as yet unidentified genes. Previous studies have reported changes in mitochondrial morphology and cellular positioning, as well as clonally-expanded, large-scale mitochondrial DNA (mtDNA) deletions and focal respiratory chain deficiency in muscle of MFM patients. Here we examine skeletal muscle from patients with desmin (n = 6), ZASP (n = 1) and myotilin (n = 2) mutations and MFM protein aggregates, to understand how mitochondrial dysfunction may contribute to the underlying mechanisms causing disease pathology. We have used a validated quantitative immunofluorescent assay to study respiratory chain protein levels, together with oxidative enzyme histochemistry and single cell mitochondrial DNA analysis, to examine mitochondrial changes. Results demonstrate a small number of clonally-expanded mitochondrial DNA deletions, which we conclude are due to both ageing and disease pathology. Further to this we report higher levels of respiratory chain complex I and IV deficiency compared to age matched controls, although overall levels of respiratory deficient muscle fibres in patient biopsies are low. More strikingly, a significantly higher percentage of myofibrillar myopathy patient muscle fibres have a low mitochondrial mass compared to controls. We concluded this is mechanistically unrelated to desmin and myotilin protein aggregates; however, correlation between mitochondrial mass and muscle fibre area is found. We suggest this may be due to reduced mitochondrial biogenesis in combination with muscle fibre hypertrophy.

Diagnostic evaluation of rhabdomyolysis

Rhabdomyolysis is characterized by severe acute muscle injury resulting in muscle pain, weakness, and/or swelling with release of myofiber contents into the bloodstream. Symptoms develop over hours to days after an inciting factor and may be associated with dark pigmentation of the urine. Serum creatine kinase and urine myoglobin levels are markedly elevated. Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing are useful tools for diagnosis of rhabdomyolysis, and they can help differentiate acquired from inherited causes of rhabdomyolysis. Acquired causes include substance abuse, medication or toxic exposures, electrolyte abnormalities, endocrine disturbances, and autoimmune myopathies. Inherited predisposition to rhabdomyolysis can occur with disorders of glycogen metabolism, fatty acid β-oxidation, and mitochondrial oxidative phosphorylation. Less common inherited causes of rhabdomyolysis include structural myopathies, channelopathies, and sickle-cell disease. This review focuses on the differentiation of acquired and inherited causes of rhabdomyolysis and proposes a practical diagnostic algorithm. Muscle Nerve 51: 793-810, 2015.

Functional relevance of mitochondrial abnormalities in sporadic inclusion body myositis

Cytochrome c oxidase (COX)-deficient fibers and multiple mitochondrial DNA (mtDNA) deletions are frequent findings in sporadic inclusion body myositis (s-IBM). However, the functional impact of these defects is not known. We investigated oxygen desaturation during exercise using the forearm exercise test, accumulation of lactate during exercise using a cycle ergometry test and mitochondrial changes (COX-deficient fibers, biochemical activities of respiratory chain complexes, multiple mtDNA deletions by long-range polymerase chain reaction) in 10 patients with s-IBM and compared the findings with age and sex-matched normal and diseased controls (without mitochondrial disorders) as well as patients with mitochondrial disorder due to nuclear gene defects resulting in multiple mtDNA deletions (MITO group). The mean age of the s-IBM patients was 68.2 ± 5.7 years (range: 56-75). Patients with s-IBM had statistically significantly reduced oxygen desaturation (ΔsO2) during the handgrip exercise (p<0.05) and elevated peak serum lactate levels during cycle ergometry compared to normal controls (p<0.05). The percentage of COX-deficient fibers in s-IBM and MITO patients was significantly increased compared to normal controls (p<0.01). Five out of nine s-IBM patients had multiple mtDNA deletions. Thirty-three percent of s-IBM patients showed an increased citrate synthase content and decreased activities of complex IV (COX). The biochemical pattern of respiratory chain complexes in patients with s-IBM and MITO was similar. Histopathological analysis showed similar changes in s-IBM and MITO due to nuclear gene defects. Functional tests reflecting mitochondrial impairment suggest a contribution of mitochondrial defects to disease-related symptoms such as fatigue and exertion-induced symptoms.

Involvement of mitochondria in myasthenia gravis complicated with dermatomyositis and rheumatoid arthritis: a case report

We report a 57-year-old male with myasthenia gravis complicated with dermatomyositis and rheumatoid arthritis without evidence of thymoma. He showed prominent muscle wasting and weakness in the four extremities and trunk in addition to swallowing disturbance. He showed intolerance to exercise on a bicycle ergometer, and muscle biopsy specimens demonstrated ragged-red fibers. An anti-acetylcholine receptor (AChR) antibody was detected in his serum but no anti-mitochondrial M2 component antibody was found. In contrast, results of immunohistochemical study indicated that his serum sample reacted to muscle mitochondria as well as AChR. These results indicate the presence of an unidentified anti-mitochondrial antibody that may be involved in the development of mitochondrial dysfunction in skeletal muscle of the present patient.

Mitochondrial abnormalities in dermatomyositis: characteristic pattern of neuropathology

The objective of the work described in this paper was to evaluate mitochondrial abnormalities in perifascicular atrophic fibers in muscle biopsies from patients with dermatomyositis (DM). We localized cytochrome c oxidase (COX) and succinate dehydrogenase (SDH) histochemically in muscle biopsies of 12 patients with DM, and 12 control patients with neurogenic atrophy. These two histochemical techniques were also combined on single tissue sections in order to accentuate any COX-negative fibers. Eleven out of 12 patients (91.6%) with DM showed histochemical evidence of mitochondrial dysfunction in perifascicular distribution. Similar abnormalities in histochemical staining were not seen in comparably sized myofibers that were atrophic due to denervation. It is concluded that abnormal SDH and COX histochemical activities in atrophic perifascicular fibers are characteristic of dermatomyositis. These abnormal staining characteristics could not be accounted for solely by myofiber atrophy, or by generalized abnormalities in histochemical staining.

Tau aggregates are abnormally phosphorylated in inclusion body myositis and have an immunoelectrophoretic profile distinct from other tauopathies

Sporadic inclusion body myositis (s-IBM) is the most frequent progressive acquired inflammatory myopathy in people older than 50 years. Abnormal aggregates of 'Alzheimer's proteins', including tau proteins, have been previously demonstrated in s-IBM. In the present study, we have investigated by immunohistochemistry and immunoblotting analysis the presence of tau proteins in muscle biopsy samples from patients with s-IBM and other myopathies with rimmed vacuoles, using newly developed antibodies raised against tau protein epitopes found in Alzheimer's disease brain. Tau immunoreactivity was shown in rimmed vacuoles or inclusions, preferentially with antibodies directed against phosphorylated carboxy-terminal epitopes of tau proteins. Cytoplasmic reactivity was also demonstrated in atrophic, nonvacuolated fibres, as well as in non-necrotic fibres invaded by inflammatory cells. Abnormally phosphorylated tau aggregates were also found in other compartments of the muscle fibre in s-IBM and other myopathies. Tau immunoblotting showed an electrophorectic profile of a doublet within the range of 60-62 kDa isovariants, which was different from tauopathies of the central nervous system. Finally, the unique pattern of immunoreactivity of s-IBM samples towards anti-tau antibodies is a new clue to a possible distinct subclass of peripheral tauopathy, different from the tauopathies of the central nervous system.

Possible pathogenic mechanisms in inflammatory myopathies

The limitations associated with the different approaches into the pathogenesis of the IIM have resulted in incomplete knowledge of disease mechanisms in myositis. In most research, in which muscle tissue was used to study the different aspects of disease, biopsies with inflammatory infiltrates have been selected. Although inflammatory cell infiltrates are a characteristic feature of myositis, selecting patients with inflammatory cell infiltrates for investigations naturally introduces a selection bias. Only a few studies have been published on patients without inflammatory infiltrates but with muscle weakness, and few studies have included follow-up biopsies after different therapies. The heterogeneity of the population of patients with myositis is another limitation of the studies of pathogenic mechanisms. Although most studies classify patients according to the Bohan and Peter criteria [118, 119], some studies used histopathologic criteria [6], and only a few studies included characterization with myositis-specific autoantibodies. Because myositis-specific autoantibodies are often associated with certain clinical profiles, classification according to autoantibody profiles could be important to define differences in the pathogenesis of different phenotypes [3]. From available data on pathogenic mechanisms it is evident that cellular and humoral immune responses are involved in disease mechanisms of myositis, but whether there is a muscle-specific immune response cannot be answered by current studies. It is likely that other mechanisms are important for development of muscle weakness, including metabolic disturbances, and muscle weakness could be caused by different mechanisms in different IIM subsets or in patients in different phases of the disease. There could be early changes, which reversibly affect the metabolism, and later, irreversible changes, that could be dependent on muscle fiber damage and replacement of muscle tissue by connective tissue and fat. Current findings suggest that cytokines, which are produced in muscle tissue from different cell sources including inflammatory cells, endothelial cells, and muscle fibers, could affect muscle function. Careful follow-up studies, including the effect of therapies targeting different molecules on molecular expression in muscle tissue, are likely to increase our knowledge on disease mechanisms. A better understanding of which molecules and mechanisms affect muscle function is likely to lead to improved, less toxic therapies in patients with myositis. Many possible target molecules for blocking therapies, especially the proinflammatory cytokines IL-1 and TNF-alpha, have been identified and should be studied in appropriate clinical settings given the currently poor outcomes of many patients with IIM.

Impaired redox status and cytochrome c oxidase deficiency in patients with polymyalgia rheumatica

OBJECTIVE

To evaluate redox status and muscular mitochondrial abnormalities in patients with polymyalgia rheumatica (PMR).

METHODS

Prospective evaluation of deltoid muscle biopsy in 15 patients with PMR. Fifteen subjects matched for age and sex, with histologically normal muscle and without clinical evidence of myopathy, were used as controls. Cryostat sections of muscle were processed for conventional dyes, cytochrome c oxidase (COX), usual histochemical reactions, and Sudan black. A total of 300-800 fibres was examined in each case. Blood lactate, pyruvate, and lactate/pyruvate ratio were determined in all patients.

RESULTS

Ragged red fibres were found in eight patients with PMR and accounted for 0-0.5% of fibres. Focal COX deficiency was found in 14 (93%) of 15 patients and in nine (60%) of 15 controls. COX deficient fibres were more common in patients with PMR (range 0-2.5%; mean 0.9%) than in controls (range 0-1.2%; mean 0.3%) (paired t test, p=0.001). Seven (47%) of 15 patients had high blood lactate levels (1.50-2.60 mmol/l) or high blood lactate/pyruvate ratios (22-25).

CONCLUSIONS

PMR is associated with mitochondrial abnormalities not solely related to the aging process.

The physiology of inflammatory myopathies: an overview

The idiopathic inflammatory myopathies (IIMs) encompass a group of muscle disorders of unknown origin and pathogenesis characterized by symmetrical, proximal muscle weakness and by inflammatory infiltrates in muscle tissue. The mechanisms behind the loss of muscle function are largely unknown. It is often anticipated that the muscle weakness is caused by the inflammatory cells. However, inflammatory infiltrates are not always present in the muscle tissue and the infiltrates sometimes have a patchy distribution, which makes it difficult to explain the generalized muscle weakness merely by infiltration of inflammatory cells. We investigated patients at different stages of myositis: early myositis without detectable inflammatory infiltrates, active myositis with pronounced inflammatory infiltrates and chronic myositis with persisting muscle weakness but without detectable inflammatory cells in muscle tissues. In these studies, a better correlation was observed between the clinical symptoms and involvement of the capillaries with expression of the cytokine interleukin (IL)-1alpha and by the presence of major histocompatibility complex (MHC) class I expression on muscle fibres. Whether these molecules could affect muscle function is not known. Using phosphorus P-31 magnetic resonance spectroscopy decreased values of adenosine triphosphate (ATP) and phosphocreatine (PCr) levels were observed at rest. These metabolic abnormalities were further accentuated by exercise and increased PCr levels correlated with improved clinical status. The underlying mechanisms responsible for these biochemical abnormalities have not been defined but could be related to a disturbed tissue oxygenation.

Mitochondrial DNA deletion mutations colocalize with segmental electron transport system abnormalities, muscle fiber atrophy, fiber splitting, and oxidative damage in sarcopenia

The in vivo cellular impact of age-associated mitochondrial DNA mutations is unknown. We hypothesized that mitochondrial DNA deletion mutations contribute to the fiber atrophy and loss that cause sarcopenia, the age-related decline of muscle mass and function. We examined 82,713 rectus femoris muscle fibers from Fischer 344 x Brown Norway F1 hybrid rats of ages 5, 18, and 38 months through 1000 microns by serial cryosectioning and histochemical staining for cytochrome c oxidase and succinate dehydrogenase. Between 5 and 38 months of age, the rectus femoris muscle in the hybrid rat demonstrated a 33% decrease in mass concomitant with a 30% decrease in total fibers at the muscle mid-belly. We observed significant increases in the number of mitochondrial abnormalities with age from 289 +/- 8 ETS abnormal fibers in the entire 5-month-old rectus femoris to 1094 +/- 126 in the 38-month-old as calculated from the volume density of these abnormalities. Segmental mitochondrial abnormalities contained mitochondrial DNA deletion mutations as revealed by laser capture microdissection and whole mitochondrial genome amplification. Muscle fibers harboring mitochondrial deletions often displayed atrophy, splitting and increased steady-state levels of oxidative nucleic damage. These data suggest a causal role for age-associated mitochondrial DNA deletion mutations in sarcopenia.

Cellular phenotypes of age-associated skeletal muscle mitochondrial abnormalities in rhesus monkeys

Rhesus monkey vastus lateralis muscle was examined histologically for age-associated electron transport system (ETS) abnormalities: fibers lacking cytochrome c oxidase activity (COX(-)) and/or exhibiting succinate dehydrogenase hyperreactivity (SDH(++)). Two hundred serial cross-sections (spanning 1600 microm) were obtained and analyzed for ETS abnormalities at regular intervals. The abundance and length of ETS abnormal regions increased with age. Extrapolating the data to the entire length of the fiber, up to 60% of the fibers were estimated to display ETS abnormalities in the oldest animal studied (34 years) compared to 4% in a young adult animal (11 years). ETS abnormal phenotypes varied with age and fiber type. Middle-aged animals primarily exhibited the COX(-) phenotype, while COX(-)/SDH(++) abnormalities were more common in old animals. Transition region phenotype was affected by fiber type with type 2 fibers first displaying COX(-) and then COX(-)/SDH(++) while type 1 fibers progressed from normal to SDH(++) and then to COX(-)/SDH(++). In situ hybridizations studies revealed an association of ETS abnormalities with deletions of the mitochondrial genome. By measuring cross-sectional area along the length of ETS abnormal fibers, we demonstrated that some of these fibers exhibit atrophy. Our data suggest mitochondrial (mtDNA) deletions and associated ETS abnormalities are contributors to age-associated fiber atrophy.

Decreased hippocampal metabolic activity in Alzheimer patients is not reflected in the immunoreactivity of cytochrome oxidase subunits

In the present study we have compared histochemically determined cytochrome oxidase activity with the levels of immunocytochemically stained cytochrome oxidase subunits (CO II and CO IV) and ATP synthase in the human hippocampus in relation with Alzheimer's disease. Cytochrome oxidase activity was significantly reduced in all hippocampal areas of Alzheimer patients. The protein levels of subunits II and IV were not different between control subjects and Alzheimer patients. Additionally, it was observed that the active cytochrome oxidase is evenly distributed over both cell bodies and neuropil, while a relatively large pool of inactive enzyme or precursors is limited to the neuronal somata. Further, in Alzheimer patients the CO IV immunoreactivity decreased with age, whereas in control subjects it increased with age. Our results suggest that the assembly of cytochrome oxidase or the processing of its subunits may be impaired.

The prevalences of cytochrome c oxidase negative and superpositive fibres and ragged-red fibres in the trapezius muscle of female cleaners with and without myalgia and of female healthy controls

The association of cytochrome c oxidase negative fibres (COX-negative) and ragged-red fibres (RR-fibres) with work related trapezius myalgia has been proposed. Hitherto studies have been small or without control groups. The aim of the present study was to investigate the prevalences of RR-fibres and COX-negative fibres in female cleaners with (n=25) and without (n=23) trapezius myalgia and in clinically healthy female teachers (n=21). The cleaners did mainly floor cleaning requiring monotonous loading on the trapezius muscle. A questionnaire covering background data and aspects of pain (prevalence, duration, intensity and influence on daily living) was answered. Biopsies were obtained from the trapezius muscle by an open surgical technique. The three groups did not differ in prevalence of COX-negative or COX-superpositive (i.e. type-I fibres with extremely strong brownish reaction in both the COX and SDH/COX stainings) fibres. The prevalence of COX-negative fibres was age dependent. Two subgroups of RR-fibres were present when stained for COX; COX-negative (73%) and COX-superpositive (26%) fibres. Forty-two percent of the COX-negative fibres were RR-fibres and 79% of the COX-superpositive were RR-fibres. A significantly (P=0.002) higher proportion of the COX-superpositive fibres in the cleaners were RR-fibres compared to the teachers. Multivariate regression analysis revealed that age, occupation as cleaner and a tender point in the trapezius were significantly associated with increased prevalences of RR-fibres; a cleaner with a tender point had a 4.35 higher prevalence of RR-fibres compared to a teacher without a tender point. No correlations between other pain related variables and prevalence of RR-fibres were noted. In conclusion, RR-fibres but not COX-negative or COX-superpositive fibres were correlated with cleaning work tasks and with a tender point in the trapezius.

Analysis of respiratory chain regulation in roots of soybean seedlings

Changes in the respiratory rate and the contribution of the cytochrome (Cyt) c oxidase and alternative oxidase (COX and AOX, respectively) were investigated in soybean (Glycine max L. cv Stevens) root seedlings using the 18O-discrimination method. In 4-d-old roots respiration proceeded almost entirely via COX, but by d 17 more than 50% of the flux occurred via AOX. During this period the capacity of COX, the theoretical yield of ATP synthesis, and the root relative growth rate all decreased substantially. In extracts from whole roots of different ages, the ubiquinone pool was maintained at 50% to 60% reduction, whereas pyruvate content fluctuated without a consistent trend. In whole-root immunoblots, AOX protein was largely in the reduced, active form at 7 and 17 d but was partially oxidized at 4 d. In isolated mitochondria, Cyt pathway and succinate dehydrogenase capacities and COX I protein abundance decreased with root age, whereas both AOX capacity and protein abundance remained unchanged. The amount of mitochondrial protein on a dry-mass basis did not vary significantly with root age. It is concluded that decreases in whole-root respiration during growth of soybean seedlings can be largely explained by decreases in maximal rates of electron transport via COX. Flux via AOX is increased so that the ubiquinone pool is maintained in a moderately reduced state.