Abnormal Proliferation Of Mitochondria Research Articles

Clinical, imaging, and pathological characteristics of 35 cases of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome

Objective: To summarize the clinical, imaging, and pathological characteristics of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome (MELAS) to improve the diagnosis of this rare disease. Methods: A retrospective case series was conducted to collect the clinical data and results of genetic testing, muscle biopsy, and imaging studies including computed tomography (CT), magnetic resonance imaging (MRI), and magnetic resonance spectroscopy (MRS) of 35 patients with MELAS admitted to the Nanjing Drum Tower Hospital from 2012 to 2021. Descriptive statistical analysis including mean, standard deviation, and frequency percentage were carried out. Results: The average age of onset of the patients was 30.2±2.3 years; the prevalence of family history was 20%. The two main initial symptoms were limb weakness and convulsions. The clinical manifestations of the neuromuscular system were proximal muscle weakness and exercise intolerance. The endocrine system is the most affected outside the neuromuscular system, with diabetes being the most common condition. Among the five patients who underwent brain CT, four showed hypodense lesions and two had calcified lesions. Brain MRI in 26 patients showed that the lesions more often affected the parietal lobe, basal ganglia, temporal lobe, occipital lobe, and frontal lobe than the infratentorial areas. Twelve of these individuals exhibited different levels of brain atrophy. Among the 10 patients who underwent 1H-MRS, nine showed a decrease in N-acetylaspartate (NAA) levels, eight exhibited abnormal lactate elevation (Lac peaks), whereas six had both reduced NAA levels and the presence of Lac peaks. Thirty-one patients underwent genetic testing; among them, 25 were found to have the mt.3243A>G mutation, while the remaining six exhibited rare gene alterations. Muscle biopsies were performed in 21 patients, and 15 showed abnormal mitochondrial proliferation manifested by ragged red fibers and defective oxidative phosphorylation manifested by cytochrome C oxidase (COX) enzyme-deficient muscle fibers. Conclusion: The clinical manifestations of MELAS syndrome are variable and complex, and early atypical symptoms could be missed or misdiagnosed. A detailed clinical history, imaging MRS analysis, muscle biopsy, and genetic testing are necessary to confirm the accurate diagnosis of MELAS.

Mitochondrial dysfunction and cerebral metabolic abnormalities in patients with mitochondrial encephalomyopathy subtypes: Evidence from proton MR spectroscopy and muscle biopsy.

Accumulated evidence indicates that cerebral metabolic features, evaluated by proton magnetic resonance spectroscopy (1 H-MRS), are sensitive to early mitochondrion dysfunction associated with mitochondrial encephalomyopathy (ME). The metabolite ratios of lactate (lac)/Cr, N-acetyl aspartate (NAA)/creatine (Cr), total choline (tCho)/Cr, and myoinositol (mI)/Cr are measured in the infarct-like lesions by 1 H-MRS and may reveal metabolic changes associated with ME. However, the application of this molecular imaging technique in the investigation of the pathology of ME subtypes is unknown. In this study, cerebral metabolic features of pathologically diagnosed ME cases, that is, 19 mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS); nine chronic progressive external ophthalmoplegia (CPEO); and 23 healthy controls, were investigated using 1 H-MRS. Receiver operating characteristics (ROC) analysis was used to evaluate the diagnostic power of the cerebral metabolites. Histochemical evaluation was carried out on muscle tissues derived from biopsy to assess the abnormal mitochondrial proliferation. The association between cerebral metabolic and mitochondrial cytopathy was examined by correlation analysis. Patients with MELAS or CPEO exhibited a significantly higher Lac/Cr ratio and a lower NAA/Cr ratio compared with controls. The ROC curve of Lac/Cr ratio indicated prominent discrimination between MELAS or CPEO and healthy control subjects, whereas the NAA/Cr ratio may present diagnostic power in the distinction of MELAS from CPEO. Lower NAA/Cr ratio was associated with higher Lac/Cr in MELAS, but not in CPEO. Furthermore, higher ragged-red fibers (RRFs) percentages were associated with elevated Lac/Cr and reduced NAA/Cr ratios, notably in MELAS. This association was not noted in the case of mI/Cr ratio. Mitochondrial cytopathy (lactic acidosis and RRFs on muscle biopsy) was associated with neuronal viability but not glial proliferation, notably in MELAS. Mitochondrial neuronopathy and neuronal vulnerability are considered significant causes in the pathogenesis of MELAS, particularly with regard to stroke-like episodes.

Mitochondrial myopathy with autophagic vacuoles in patients with the m.8344A>G mutation

Background and aimsIn mitochondrial myopathy, autophagy is presumed to play an important role in mitochondrial dysfunction. Rimmed vacuoles (RVs), a sign of autophagy, can be seen as a secondary phenomenon...

A TAT–Frataxin fusion protein increases lifespan and cardiac function in a conditional Friedreich's ataxia mouse model

Friedreich's ataxia (FRDA) is the most common inherited human ataxia and results from a deficiency of the mitochondrial protein, frataxin (FXN), which is encoded in the nucleus. This deficiency is associated with an iron-sulfur (Fe-S) cluster enzyme deficit leading to progressive ataxia and a frequently fatal cardiomyopathy. There is no cure. To determine whether exogenous replacement of the missing FXN protein in mitochondria would repair the defect, we used the transactivator of transcription (TAT) protein transduction domain to deliver human FXN protein to mitochondria in both cultured patient cells and a severe mouse model of FRDA. A TAT-FXN fusion protein bound iron in vitro, transduced into mitochondria of FRDA deficient fibroblasts and reduced caspase-3 activation in response to an exogenous iron-oxidant stress. Injection of TAT-FXN protein into mice with a conditional loss of FXN increased their growth velocity and mean lifespan by 53% increased their mean heart rate and cardiac output, increased activity of aconitase and reversed abnormal mitochondrial proliferation and ultrastructure in heart. These results show that a cell-penetrant peptide is capable of delivering a functional mitochondrial protein in vivo to rescue a very severe disease phenotype, and present the possibility of TAT-FXN as a protein replacement therapy.

Calcium entry in skeletal muscle

Calcium entry in skeletal muscle

Novel germline variants identified in the inner mitochondrial membrane transporter TIMM44 and their role in predisposition to oncocytic thyroid carcinomas

Familial Non-Medullary Thyroid Carcinoma (fNMTC) represents 3–7% of all thyroid tumours and is associated with some of the highest familial risks among all cancers, with an inheritance pattern compatible with an autosomal dominant model with reduced penetrance. We previously mapped a predisposing locus, TCO (Thyroid tumour with Cell Oxyphilia) on chromosome 19p13.2, for a particular form of thyroid tumour characterised by cells with an abnormal proliferation of mitochondria (oxyphilic or oncocytic cells). In the present work, we report the systematic screening of 14 candidate genes mapping to the region of linkage in affected TCO members, that led us to identify two novel variants respectively in exon 9 and exon 13 of TIMM44, a mitochondrial inner membrane translocase for the import in the mitochondria of nuclear-encoded proteins. These variants were co-segregating with the TCO phenotype, were not present in a large group of controls and were predicted to negatively affect the protein (exon 9 change) or the transcript (exon 13 change). Functional analysis was performed in vitro for both changes and although no dramatic loss of function effects were identified for the mutant alleles, subtler effects might still be present that could alter Timm44 function and thus promote oncocytic tumour development. Thus we suggest that TIMM44 should be considered for further studies in independent samples of affected individuals with TCO.

Zidovudine Administration during Pregnancy and Mitochondrial Disease in the offspring

Prophylactic administration of zidovudine (ZDV) to mother-child pairs reduces HIV transmission. ZDV can impair mitochondrial (mt) DNA polymerase gamma, leading to mtDNA depletion. Signs of mitochondrial dysfunction have been observed in a few children with prenatal exposure to nucleoside analogues, although no mtDNA depletion was demonstrated. Other studies failed to confirm mitochondrial disorders in children who were exposed to antiretroviral agents in utero. A child, whose HIV-infected mother received ZDV from the fourth month of pregnancy, developed neonatal encephalomyopathy, anaemia and hyperlactataemia. At 2 weeks of age, a muscle biopsy exhibited red-ragged-like fibres, proliferation of abnormal mitochondria and a 90% depletion of mtDNA without qualitative abnormalities. At 6 months, the depletion was less profound (about 50% of normal values). Severe psychomotor delay and visual disturbances persisted at 30 months, but they were greatly reduced at 5-year follow-up. These laboratory and clinical findings clearly demonstrated that mtDNA alteration was acquired and not consequent to an inherited disorder. Fetal exposure to ZDV may have caused the mtDNA depletion, which, although temporary, led to irreversible but not progressive brain damage.

Mitochondrial dysfunction and heart disease

Several inherited and acquired disorders of mitochondria lead to defects in cardiac function as reflected in exercise intolerance, arrhythmias and heart failure. Manifestations of mitochondrial dysfunction is reflected in the abnormal mitochondrial proliferation, structure and ultimately as cytochrome C-induced apoptosis. How these defects are associated with disordered cytosolic events including SR calcium release and transcription has suggested a cross talk of mitochondria and cytosolic events that drive cardiomyocytes dysfunction.

Transcriptional profiling reveals coordinated up-regulation of oxidative metabolism genes in thyroid oncocytic tumors.

Oncocytomas are large cell tumors characterized by an abnormal proliferation of mitochondria. To investigate this phenomenon in thyroid oncocytomas, we determined gene expression profiles of 87 samples using microarrays of 6720 PCR products from cDNA clones. Samples included 29 thyroid oncocytomas and six papillary carcinomas, the remainder representing other thyroid pathologies or mitochondria-rich tumor samples, normal thyroid samples, and two thyroid cell lines. Hierarchical clustering and supervised analysis identified two specific oncocytic clusters and 163 distinctly regulated genes between oncocytoma and normal thyroid. Differential expression of five selected genes (APOD, BCL-2, COX, CTSB, and MAP2) was confirmed by immunohistochemistry. The two specific oncocytic clusters were rich in mitochondrial genes and revealed coordinated expression of nuclear and mitochondrial respiratory chain genes. We also observed the up-regulation of genes involved in mitochondrial biogenesis, such as nuclear respiratory factor 1 and the endothelial nitric oxide synthase. Several oxidative metabolism genes were overexpressed in oncocytomas, including those from the tricarboxylic acid cycle (MDH1) and cytosolic glycolysis (GAPD, ENO1, and GPI). On the contrary, the lactate dehydrogenase A gene, involved in anaerobic metabolism, was down-regulated. Our results suggest that, unlike a large number of solid tumors, thyroid oncocytomas produce energy through an aerobic pathway.

Revelation of a New Mitochondrial DNA Mutation (G12147A) in a MELAS/MERFF Phenotype

A 26-year-old man presented at onset with the syndrome of mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) and later with a phenotype for MELAS and myoclonic epilepsy and ragged red fiber disease (MELAS/MERRF). To identify the possible defects in the mitochondrial genome in blood and muscle samples of the patient. Case study of a patient clinically exhibiting strokelike episodes and then epilepsy with myoclonic features, ataxia, and dementia. Research unit of a university hospital. Electromyographic, morphologic, and biochemical studies of muscle and molecular analysis of blood and muscle to investigate mitochondrial DNA (mtDNA) size and quantity. Morphologically, we found abnormal mitochondrial proliferation with several cytochrome-c oxidase (COX)-negative fibers in muscle biopsy specimens; the analysis of serial sections showed a decreased immunoreactivity for the mtDNA-encoded subunits COXII and, partially, COXI. Biochemically, we found a partial and isolated COX deficiency. The complete mtDNA sequence analysis identified 3 sequence changes, 2 of which were reported polymorphisms. The remaining change, a G12147A transition in the transfer RNA(His) gene, appeared to be the likely pathogenic mutation. Our data propose that the G12147A change, the first mutation in the transfer RNA(His) gene associated with an overlapped MELAS/MERFF phenotype, is the cause of the encephalomyopathy in this patient interfering with the overall mitochondrial protein synthesis.

Bcl-2 prevents abnormal mitochondrial proliferation duringetoposide-induced apoptosis

At the late stage of etoposide-induced apoptosis in HL-60 cells, marked by condensation of chromatin, mitochondria increase in numbers. There is also a drastic increase in mitochondrial DNA content. This increase in mitochondrial numbers and DNA content is an indicator of mitochondrial proliferation during apoptosis. These proliferating mitochondria exhibit abnormal morphology and are impaired, which is demonstrated by decrease in mitochondrial membrane potential and ATP content. The described apoptosis-induced abnormal mitochondrial proliferation was inhibited by overexpression of Bcl-2 protein, which also diminishes mitochondrial impairment. The increase in mitochondrial DNA levels correlated with elevated expression of one of the regulators of mitochondrial DNA replication, mtSSB. Our data suggest that proliferation of mitochondria may be an integral part of a cascade of apoptotic events.

Depletion of muscle mitochondrial DNA in AIDS patients with zidovudine-induced myopathy

Long-term zidovudine therapy in patients with human immunodeficiency virus (HIV) infection can cause a destructive mitochondrial myopathy with histological features of ragged-red fibres (RRF) and proliferation of abnormal mitochondria. In 9 zidovudine-treated patients with this myopathy we found severely reduced amounts (up to 78% reduction vs normal adult controls) of mitochondrial DNA (mtDNA) in muscle biopsy specimens by means of Southern blotting. In 2 HIV-positive patients who had not received zidovudine, muscle mtDNA content did not differ from that in the 4 controls. Depletion of mtD NA seems to be reversible, since 1 patient showed a substantial reduction in RRF and a concomitant pronounced increase in muscle mtDNA content after zidovudine therapy was discontinued. Depletion of muscle mtDNA is probably due to zidovudine-induced inhibition of mtDNA replication by DNA polymerase gamma and is not a secondary effect of HIV infection.

Replication-competent human mitochondrial DNA lacking the heavy-strand promoter region.

We identified two patients with progressive external ophthalmoplegia, a mitochondrial disease, who harbored a population of partially deleted mitochondrial DNA (mtDNA) with unusual properties. These molecules were deleted from mtDNA positions 548 to 4,442 and encompassed not only rRNA sequences but the heavy-strand promoter region as well. A 13-bp direct repeat was found flanking the breakpoint precisely, with the repeat at positions 535 to 547 located within the binding site for mitochondrial transcription factor 1 (mtTF1). This is the second mtDNA deletion involving a 13-bp direct repeat reported but is at least 10 times less frequent in the patient population than the former one. In situ hybridization studies showed that transcripts under the control of the light-strand promoter were abundant in muscle fibers with abnormal proliferation of mitochondria, while transcripts directed by the heavy-strand promoter, whether of genes residing inside or outside the deleted region, were not. The efficient transcription from the light-strand promoter implies that the major heavy-and light-strand promoters, although physically close, are functionally independent, confirming previous in vitro studies.

Replication-Competent Human Mitochondrial DNA Lacking the Heavy-Strand Promoter Region

We identified two patients with progressive external ophthalmoplegia, a mitochondrial disease, who harbored a population of partially deleted mitochondrial DNA (mtDNA) with unusual properties. These molecules were deleted from mtDNA positions 548 to 4,442 and encompassed not only rRNA sequences but the heavy-strand promoter region as well. A 13-bp direct repeat was found flanking the breakpoint precisely, with the repeat at positions 535 to 547 located within the binding site for mitochondrial transcription factor 1 (mtTF1). This is the second mtDNA deletion involving a 13-bp direct repeat reported but is at least 10 times less frequent in the patient population than the former one. In situ hybridization studies showed that transcripts under the control of the light-strand promoter were abundant in muscle fibers with abnormal proliferation of mitochondria, while transcripts directed by the heavy-strand promoter, whether of genes residing inside or outside the deleted region, were not. The efficient transcription from the light-strand promoter implies that the major heavy-and light-strand promoters, although physically close, are functionally independent, confirming previous in vitro studies.

Zellweger syndrome. Lenticular opacities indicating carrier status and lens abnormalities characteristic of homozygotes.

Cataracts were found in four patients with pathologically confirmed Zellweger syndrome. By careful slitlamp examination with the pupil completely dilated, there is a denser cortex that produces a cortical-nuclear interface. These opacities have ultrastructural analogues, which are inclusion bodies restricted to the cortical lens fibers. The lens epithelium shows abnormal mitochondrial proliferation that is age dependent. The parents of these four infants with Zellweger syndrome have lenticular opacities that are seen only biomicroscopically after maximal pupillary dilation. These changes consist of curvilinear condensations in the cortical region corresponding to the locus of the cataractous changes in the homozygous state. In the clinical setting of an infant who is failing to thrive, has the Zellweger facies, and demonstrates an absent electroretinogram, these heterozygote lens opacities are useful in making the diagnosis of Zellweger syndrome before pathologic substantiation.