Homoplasmic Mutation Research Articles

Associations Between Maternal Lifetime Stress and Placental Mitochondrial DNA Mutations in an Urban Multiethnic Cohort

BackgroundDisrupted placental functioning due to stress can have lifelong implications. Cumulative stress and trauma are likely to have lasting impacts on maternal physiological functioning and offspring development, resulting in increased risk for later-life complex disorders for which racial disparities exist. MethodsThis study examined the association between maternal lifetime stress and placental mitochondrial DNA mutational load in an urban multiethnic cohort. Maternal lifetime exposure to stressful events was assessed using the validated Life Stressor Checklist–Revised. Whole mitochondrial DNA sequencing was performed and mutations were determined for 365 placenta samples with complete exposure and covariate data. Multivariable regression was used to model maternal lifetime stress in relation to placental mitochondrial DNA mutational load. Racial/ethnic differences were examined by cross-product terms and contrast statements. Gene-wise analyses were conducted. ResultsWe identified 13,189 heteroplasmies (Phred score > 10,000, minor allele frequency < 0.5, number of mutant reads > 1). Women experiencing increased psychosocial stress over their lifetime exhibited a higher number of total placental mitochondrial mutations (β = .23, 95% confidence interval = .03 to .42) and heteroplasmic mutations (β = .18, 95% confidence interval = .05 to .31) but not homoplasmic mutations (β = −.008, 95% confidence interval = −.03 to .01); the strongest associations were observed among Black women and genes coding for NADH dehydrogenase and cytochrome c oxidase subunits. ConclusionsCumulative maternal lifetime stress is associated with a greater mitochondrial mutational load, particularly among Black women. The impact of racial/ethnic differences in mutational load on placental function directly affecting offspring development and/or leading to chronic disease disparities warrants further investigation.

Homoplasmic deleterious MT-ATP6/8 mutations in adult patients

To address the frequency of complex V defects, we systematically sequenced MT-ATP6/8 genes in 512 consecutive patients.We performed functional analysis in muscle or fibroblasts for 12 out of 27 putative homoplasmic mutations and in cybrids for four. Fibroblasts, muscle and cybrids with known deleterious mutations underwent parallel analysis. It included oxidative phosphorylation spectrophotometric assays, western blots, structural analysis, ATP production, glycolysis and cell proliferation evaluation.We demonstrated the deleterious nature of three original mutations. Striking gradation in severity of the mutations consequences and differences between muscle, fibroblasts and cybrids implied a likely under-diagnosis of human complex V defects.

Generation of a human iPSC line, FINCBi001-A, carrying a homoplasmic m.G3460A mutation in MT-ND1 associated with Leber's Hereditary optic Neuropathy (LHON).

Leber's Hereditary Optic Neuropathy (LHON) is a maternally inherited disorder caused by homoplasmic mutations of mitochondrial DNA (mtDNA). LHON is characterized by the selective degeneration of the retinal ganglion cells (RGC). Almost all LHON maternal lineages are homoplasmic mutant (100%mtDNA copies are mutant) for one of three frequent mtDNA mutations now found in over 90% of patients worldwide (m.11778G>A/MT-ND4, m.3460G>A/MT-ND1, m.14484T>C/MT-ND6). Human induced pluripotent stem cells (hiPSCs) were generated from a patient carrying the homoplasmic m.3460G>A/MT-ND1 mutation using the Sendai virus non-integrating virus.

Homoplasmic mitochondrial tRNAPro mutation causing exercise-induced muscle swelling and fatigue.

ObjectiveTo demonstrate the causal role in disease of the MT-TP m.15992A>T mutation observed in patients from 5 independent families.MethodsLactate measurement, muscle histology, and mitochondrial activities in patients; PCR-based analyses of the size, amount, and sequence of muscle mitochondrial DNA (mtDNA) and proportion of the mutation; respiration, mitochondrial activities, proteins, translation, transfer RNA (tRNA) levels, and base modification state in skin fibroblasts and cybrids; and reactive oxygen species production, proliferation in the absence of glucose, and plasma membrane potential in cybrids.ResultsAll patients presented with severe exercise intolerance and hyperlactatemia. They were associated with prominent exercise-induced muscle swelling, conspicuous in masseter muscles (2 families), and/or with congenital cataract (2 families). MRI confirmed exercise-induced muscle edema. Muscle disclosed severe combined respiratory defect. Muscle mtDNA had normal size and amount. Its sequence was almost identical in all patients, defining the haplotype as J1c10, and sharing 31 variants, only 1 of which, MT-TP m.15992A>T, was likely pathogenic. The mutation was homoplasmic in all tissues and family members. Fibroblasts and cybrids with homoplasmic mutation had defective respiration, low complex III activity, and decreased tRNAPro amount. Their respiratory complexes amount and tRNAPro aminoacylation appeared normal. Low proliferation in the absence of glucose demonstrated the relevance of the defects on cybrid biology while abnormal loss of cell volume when faced to plasma membrane depolarization provided a link to the muscle edema observed in patients.ConclusionsThe homoplasmic MT-TP m.15992A>T mutation in the J1c10 haplotype causes exercise-induced muscle swelling and fatigue.

Associations of mitochondrial DNA 3777\u20134679 region mutations with maternally inherited essential hypertensive subjects in China

BackgroundNuclear genome or family mitochondrial screening system has become the hot focus of studies into essential hypertension. The role of mitochondrial DNA (mtDNA) in sporadic Chinese patients with hypertension has not been fully understood. The study was to evaluate the associations of mtDNA mutations with maternally inherited essential hypertensive subjects in China.MethodsFrom June 2009 to June 2016, a total of 800 gender-matched Chinese patients with maternally inherited essential hypertension (MIEH) and control group were 1:1 enrolled in this case-control study. Genomic DNA was extracted from each person’s peripheral blood cells. The main mtDNA locations for MIEH were screened with oligodeoxynucleotides 3777-4679 bp, analyzed and compared with the updated consensus Cambridge Sequence. Pathogenic mtDNA mutations were identified from the mitochondrial map.ResultsMIEH subjects presented significantly higher values than those of control group in abdominal circumference (AC), waist circumference (WC), body mass index (BMI), fasting blood glucose (FBG), triglyceride (TG), low-density lipoprotein cholesterol (LDL) and renal function (P < 0.05). MIEH subjects carried more amino acid changes and coding sequence variants (P < 0.01) than control group. The allele frequencies of the eight single nucleotide polymorphisms (SNPs) were significantly different between the two groups, including m.3970 C > T, m.4048G > A, m.4071C > T, m.4086C > T, m. 4164A > G and m.4248 T > C in ND1 gene, and m.4386 T > C and m.4394C > T in tRNAGln gene(P < 0.001). Fifty-five homoplasmic or heteroplasmic mutations were detected in 5 genes: ND1, tRNAIle, tRNAMet, tRNAGln and ND2 gene. The ND1 gene was the main mutation site, where the most mtDNA mutation was m.3970 C > T.ConclusionsThe mtDNA mutations were involved in the process of MIEH. We identified mitochondrial genetic characteristics in MIEH patients in China. The present research serves as a solid foundation for further detailed research on the association between MIEH and mitochondrial dysfunction, and their causal relationship in Chinese and other populations with a similar lifestyle.

Screening for mitochondrial 12S rRNA C1494T mutation in 655 patients with non-syndromic hearing loss: An observational study.

Mutations in mitochondrial DNA, especially in 12S rRNA gene, are the most important causes for hearing loss. In particular, the A1555G and C1494T mutations have been found to be associated with both aminoglycoside-induced and non-syndromic hearing loss in many families worldwide. To determine the frequency of C1494T mutation in deaf patients, in the current study, we screened this mutation in 655 patients with non-syndromic hearing loss and 300 control subjects. After PCR amplification of mitochondrial 12S rRNA gene and direct sequence analysis, we found that there were 2 patients carrying the C1494T mutation; however, this mutation was not detected in 300 healthy subjects. Further genetic counseling suggested that only 1 patient had an obvious family history of hearing impairment. Clinical evaluation showed that 3 of 10 matrilineal relatives suffered from hearing loss, with different age at onset of hearing loss. Molecular analysis revealed the presence of homoplasmic 12S rRNA C1494T and ND5 T12338C mutations, together with a set of polymorphisms belonging to human mitochondrial haplogroup F2. Interestingly, T12338C mutation resulted in the replacement of the first amino acid, a translation-initiating methionine with a threonine, shortening 2 amino acids of ND5 polypeptide. Moreover, this mutation is located in 2 nucleotides adjacent to the 3’ end of the mt-tRNALeu(CUN) gene. Therefore, this mutation may alter ND5 mRNA metabolism and the processing of RNA precursors. Thus, the combination of T12338C and C1494T mutations may contribute to deafness expression in this family. Taken together, our data suggested that the C1494T mutation was the molecular basis for hearing loss, screening for the mitochondrial DNA pathogenic mutations was recommended for early detection, prevention, and diagnosis of mitochondrial deafness.

Fine-tuning of the respiratory complexes stability and supercomplexes assembly in cells defective of complex III

The respiratory complexes are organized in supramolecular assemblies called supercomplexes thought to optimize cellular metabolism under physiological and pathological conditions. In this study, we used genetically and biochemically well characterized cells bearing the pathogenic microdeletion m.15,649–15,666 (ΔI300-P305) in MT-CYB gene, to investigate the effects of an assembly-hampered CIII on the re-organization of supercomplexes. First, we found that this mutation also affects the stability of both CI and CIV, and evidences the occurrence of a preferential structural interaction between CI and CIII2, yielding a small amount of active CI+CIII2 supercomplex. Indeed, a residual CI+CIII combined redox activity, and a low but detectable ATP synthesis driven by CI substrates are detectable, suggesting that the assembly of CIII into the CI+CIII2 supercomplex mitigates the detrimental effects of MT-CYB deletion. Second, measurements of oxygen consumption and ATP synthesis driven by NADH-linked and FADH2-linked substrates alone, or in combination, indicate a common ubiquinone pool for the two respiratory pathways. Finally, we report that prolonged incubation with rotenone enhances the amount of CI and CIII2, but reduces CIV assembly. Conversely, the antioxidant N-acetylcysteine increases CIII2 and CIV2 and partially restores respirasome formation. Accordingly, after NAC treatment, the rate of ATP synthesis increases by two-fold compared with untreated cell, while the succinate level, which is enhanced by the homoplasmic mutation, markedly decreases. Overall, our findings show that fine-tuning the supercomplexes stability improves the energetic efficiency of cells with the MT-CYB microdeletion.

First description of an unusual novel double mutation in MECP2 co-occurring with the m.827A>G mutation in the MT-RNR1 gene associated with angelman-like syndrome

Mutations in Methyl-CpG-Binding protein 2 (MECP2), located on Xq28 and encoding a methyl CpG binding protein, are commonly related to Rett syndrome. However, MECP2 mutations have already been reported in patients with neurodevelopmental abnormalities such as X-linked mental retardation, severe neonatal encephalopathy and Angelman-like syndrome (AS-like). Accordingly, we report the clinical, molecular and bioinformatic analyses in a Tunisian patient with AS-like phenotype. In fact, the direct sequencing of MECP2 and cloning essay reveals the emergence of an unusual novel double mutation, including a de novo mutation c.397C > T (p.R133C) and an inherited one c.608C > T (p.T203 M) co-occurring in Trans. We also provide the molecular evidence of the c.608C > T transmission to the patient which was present in her father at somatic mosaicism state. To gain insight into the molecular basis of this disorder, we undertook, for the first time, a whole mitochondrial genome mutational analysis. Thus, the results showed the presence of several variations and a homoplasmic mutation m.827A > G in the MT-RNR1 gene, leading to the disruption of the 12S rRNA secondary structure. Our report is considered as the first to describe an unusual novel double mutation (c.397C > T in trans with c.608C > T) in MECP2 co-occurring with the mitochondrial m.827A > G mutation in the MT-RNR1 gene in a Tunisian patient with AS-like. Besides, our results highlight the importance of studying MECP2 and the significance of mDNA screening in AS-like disorder for a better understanding of its etiopathogenesis.

Maternally Inherited Differences within Mitochondrial Complex I Control Murine Healthspan.

Mitochondrial complex I—the largest enzyme complex of the mitochondrial oxidative phosphorylation machinery—has been proposed to contribute to a variety of age-related pathological alterations as well as longevity. The enzyme complex-consisting proteins are encoded by both nuclear (nDNA) and mitochondrial DNA (mtDNA). While some association studies of mtDNA encoded complex I genes and lifespan in humans have been reported, experimental evidence and the functional consequence of such variants is limited to studies using invertebrate models. Here, we present experimental evidence that a homoplasmic mutation in the mitochondrially encoded complex I gene mt-Nd2 modulates lifespan by altering cellular tryptophan levels and, consequently, ageing-related pathways in mice. A conplastic mouse strain carrying a mutation at m.4738C > A in mt-Nd2 lived slightly, but significantly, shorter than the controls did. The same mutation led to a higher susceptibility to glucose intolerance induced by high-fat diet feeding. These phenotypes were not observed in mice carrying a mutation in another mtDNA encoded complex I gene, mt-Nd5, suggesting the functional relevance of particular mutations in complex I to ageing and age-related diseases.

Immortalization of Different Breast Epithelial Cell Types Results in Distinct Mitochondrial Mutagenesis.

Different phenotypes of normal cells might influence genetic profiles, epigenetic profiles, and tumorigenicities of their transformed derivatives. In this study, we investigate whether the whole mitochondrial genome of immortalized cells can be attributed to the different phenotypes (stem vs. non-stem) of their normal epithelial cell originators. To accurately determine mutations, we employed Duplex Sequencing, which exhibits the lowest error rates among currently-available DNA sequencing methods. Our results indicate that the vast majority of the observed mutations of the whole mitochondrial DNA occur at low-frequency (rare mutations). The most prevalent rare mutation types are C→T/G→A and A→G/T→C transitions. Frequencies and spectra of homoplasmic point mutations are virtually identical between stem cell-derived immortalized (SV1) cells and non-stem cell-derived immortalized (SV22) cells, verifying that both cell types were derived from the same woman. However, frequencies of rare point mutations are significantly lower in SV1 cells (5.79 × 10−5) than in SV22 cells (1.16 × 10−4). The significantly lower frequencies of rare mutations are aligned with a finding of longer average distances to adjacent mutations in SV1 cells than in SV22 cells. Additionally, the predicted pathogenicity for rare mutations in the mitochondrial tRNA genes tends to be lower (by 2.5-fold) in SV1 cells than in SV22 cells. While four known/confirmed pathogenic mt-tRNA mutations (m.5650 G>A, m.5521 G>A, m.5690 A>G, m.1630 A>G) were identified in SV22 cells, no such mutations were observed in SV1 cells. Our findings suggest that the immortalization of normal cells with stem cell features leads to decreased mitochondrial mutagenesis, particularly in RNA gene regions. The mutation spectra and mutations specific to stem cell-derived immortalized cells (vs. non-stem cell derived) have implications in characterizing the heterogeneity of tumors and understanding the role of mitochondrial mutations in the immortalization and transformation of human cells.

Novel Alterations of Some Mitochondrial tRNA Genes in Vienamese Colorectal Cancer Patients

Some mutations of mt-DNA which encode tRNA (mt-tRNA) were previously reported to be associated with clinical manifestations of neuromuscular disorders syndrome. In addition, alterations of the mitochondrial genome have been suggested to contribute to mitochondrial dysfunction and tumorigenesis. Alterations in some mt-tRNA genes have also been identified in breast cancer, lung cancer and colorectal cancer. However, so far, we have not found any report on mt-tRNA gene alteration in the Vietnamese colorectal cancer patients. So that, in this study, we analyzed the alterations of some mt-tRNA genes in a group of Vietnamese colorectal cancer patients and predicted influence of the alterations to secondary structure of tRNA based on bioinformatic tools. PCR-RFLP and DNA sequencing methods were used to screening alterations, secondary structure of tRNA was predicted in silico by using a tool of the Vienna RNA Websuite. Results: both A12309G and A12310G of tRNALeu were identified together in two out of 98 patients, and both T12150G and C12154G of tRNAHis were indentified in one out of 19 patients. All of these alterations were heteroplasmic and have not been reported in cancer patients. In particular, the C12154G alteration in the DHR loop led to change of secondary structure of tRNAHis and may affect to function of this tRNA molecule.&#x0D; Keywords&#x0D; mt-tRNA, Vietnamese colorectal cancer, PCR-RFLP, DNA sequencing&#x0D; References&#x0D; [1] http://globocan.iarc.fr/Pages/online.aspx (30/11/2017).[2] M. Brandon, P. Baldi, D.C Wallace, Mitochodrial mutations in cancer, Oncogen 25(34) (2006) 4647.[3] G. Li, YX. Duan, XB. Zhang, F Wu, Mitochondrial RNA mutations may be infrequent in hepatocellular carcinoma patients, Genet Mol Res15(2) (2016) doi: 10.4238/gmr.15027665.[4] F. Mohammed, AR. Rezaee, E. Mosaieby, M. Houshmand, Mitochondrial A12308G alteration in RNA Leu (CUN)) in colorectal cancer samples, Diagn Pathol (2015) doi: 10.1186/s13000-015-0337-6.[5] S. Datta, M. Majumder, NK. Biswas, N. Sikdar, B. Roy, Increased risk of oral cancer in relation to common Indian mitochondrial polymorphisms and Autosomal GSTP1 locus, Cancer, 110 (2007) 1999.[6] L .Wang , ZJ. Chen , YK. Zhang , HB. Le, The role of mitochondrial RNA mutations in lung cancer, Int J Clin Exp Med 8(8) (2015) 13341.[7] AR. Gruber, R. Lorenz, SH. Bernhart, R. Neubock, IL Hofacker The Vienna ARN Websuite, Nucleic Acids Res 36 (2008) 70.[8] https://blast.ncbi.nlm.nih.gov/Blast.cgi (11/2017).[9] Y. Goto, I Nonaka, S Horai, A mutation in the RNALeu (UUR) gene associated with the MELAS subgroup of mitochondrial encephalomyopathies, Nature 348(6302 (1990) 651[10] http://www.mitomap.org/MITOMAP (11/2017).[11] A. Lorenc, J. Bryk Golik P, Homoplasmic MELAS A3243G mtDNA mutation in a colon cancer sample, Mitochondrion 3(2) (2003) 119.[12] EL. Blakely, J.W Yarham , C.L. Alston , K Craig , J. Poulton , C. Brierley , SM. Park , A. Dean , JH. Xuereb , KN. Anderson , A. Compston , C. Allen , S. Sharif , P. Enevoldson , M. Wilson , SR. Hammans , DM. Turnbull , R. McFarland , RW.Taylor , Pathogenic mitochondrial tRNA point mutations: nine novel mutations affirm their importance as a cause of mitochondrial disease, Hum Mutat 34(9) (2013) 1260.[13] S. DiMauro, Mitochondrial ADN medicine, Biosci Rep 27(3) (2007) 5.[14] DC. Wallace, D. Chalkia, Mitochondrial ADN genetics and the heteroplasmy conundrum in evolution and disease”, Cold Spring Harb Perspect Biol 5(11) (2013), doi:10.1101/cshperspect. a021220&#x0D;

Analysis of Inherited Optic Neuropathies.

Inherited optic neuropathies (IONs) cover a spectrum of clinically and genetically heterogenic conditions. Genetic evaluation of patients with IONs may enable their better clinico-diagnostic assessment and management of the disease. The aim of the present study was to determine the genetic condition related to the phenotype in patients with diverse inherited optic neuropathies. A retrospective study was performed in 12 adults and 8 children of 8 non-related families. Clinical phenotyping, supported by color fundus, FAF, and OCT imaging, was performed. Genetic testing was obtained for all family members suspected for ION. Identification of pathogenic mutations in eight non-related families helped to confirm the diagnosis of ION. Affected from ION were ten patients (eight adults and two children; four women and six men). Bilateral Leber's hereditary optic neuropathy (LHON) was linked to the m.11778G>A mutation in two families (two affected and five carriers). Secondary homoplasmic LHON mutations in MT-ND1 (m.4216T>C) and MT-CO3 genes (m.9804G>A) were confirmed in two families (each one subject, three eyes affected), without detection of a primary LHON mutation. One member presented a picture of right-sited optic neuropathy associated with a c.220C>G mutation in the ACO2 gene and a heterozygous c.185C>T mutation in the LDLR gene. Autosomal dominant optic atrophy was confirmed in three non-related families (five subjects with bilateral ION), where molecular genetic analyses confirmed four different heterozygous mutations in OPA1: c.1847+1G>T; c.2497-1G>A, 297A>G and c.(2983+1_2984-1)_(c.*3211) (2 splicing mutations, 1 missense mutation, and 1 gross deletion encompassing exons 30 and 31). Combining clinics and molecular genetics when evaluating patients with IONs helps in characterizing disease and, therefore, is strongly recommended for such patients.

Leigh Syndrome Due to mtDNA Pathogenic Variants

Abstract Leigh syndrome is a devastating neurodegenerative disease, typically manifesting in infancy or early childhood. Hallmarks of the disease are symmetrical lesions in the basal ganglia or brain stem on MRI, and a clinical course with rapid deterioration of cognitive and motor functions. It is genetically heterogeneous, causative mutations have been disclosed in mitochondrial DNA and nuclear genes involved in the process of energy production in the mitochondria .We investigated the whole mitochondrial DNA in three Brazilian patients with LS, based on their clinical and biochemical data, with the aim to identify the disease-causing mutations. In two of the patients, with complex I deficiency, a novel heteroplasmic variant m.4142G>T (p.R279L) in MT-ND1 and a recurrent homoplasmic mutation m.10197G>A (p.A47T) in MT-ND3 were identified. In the remaining patient, with complex IV deficiency, a de novo heteroplasmic variant in MT-CO1 m.6547T>C (p.L215P) was found. The molecular investigation in mitochondrial diseases have shifted their focus from mitochondrial DNA to nuclear DNA, however, mtDNA protein-coding genes are one of the important genetic causes of mitochondrial disorders for Leigh syndrome. This study expands the molecular and clinical spectrum associated with this disease.

Mitochondrial DNA 7908\u20138816 region mutations in maternally inherited essential hypertensive subjects in China

BackgroundNuclear genes or family-based mitochondrial screening have been the focus of genetic studies into essential hypertension. Studies into the role of mitochondria in sporadic Chinese hypertensives are lacking. The objective of the study was to explore the relationship between mitochondrial DNA (mtDNA) variations and the development of maternally inherited essential hypertension (MIEH) in China.MethodsYangzhou residents who were outpatients or in-patients at the Department of Cardiology in Northern Jiangsu People’s Hospital (Jiangsu, China) from June 2009 to June 2015 were recruited in a 1:1 case control study of 600 gender-matched Chinese MIEH subjects and controls. Genomic DNA was isolated from whole blood cells. The most likely sites for hypertension were screened using oligodeoxynucleotides at positions 7908–8816, purified and subsequently analyzed by direct sequencing according to the revised consensus Cambridge sequence. The frequency, density, type and conservative evolution of mtDNA variations were comprehensively analyzed.ResultsWe found a statistical difference between the two groups for body mass index, waist circumference, abdominal circumference, triglyceride, low-density lipoprotein cholesterol, fasting blood glucose, uric acid, creatinine and blood urea nitrogen (P < 0.05). More amino-acid changes and RNA variants were found in MIEH subjects than the controls (P < 0.01). The detection system simultaneously identified 40 different heteroplasmic or homoplasmic mutations in 4 genes: COXII, tRNALys, ATP8 and ATP 6. The mtDNA variations were mainly distributed in regions of ATP6 binding sites, and the site of highest mutation frequency was m. 8414C > T. Three changes in single bases (C8414T in ATP8, A8701G in ATP6 and G8584A in ATP6) were significantly different in the MIEH patients and the controls (P < 0.001). The m.8273_8281del mutation was identified from 59 MIEH patients.ConclusionsOur results indicate that novel mtDNA mutations may be involved in the pathological process of MIEH, and mitochondrial genetic characteristics were identified in MIEH individuals.

Mitochondrial dysfunction caused by m.2336T>C mutation with hypertrophic cardiomyopathy in cybrid cell lines

Hypertrophic cardiomyopathy (HCM), affecting approximately 1 in 500 in the general population, is the most prominent cause of sudden heart disease-related mortality in the young. Mitochondrial DNA (mtDNA) mutations are among the primary causes of HCM. We previously identified a novel m.2336T>C homoplasmic mutation in the mitochondrial 16S rRNA gene (MT-RNR2) in a Chinese maternally inherited HCM family. However, the molecular mechanisms by which m.2336T>C mutation contributes to HCM remain elusive. Here we generated transferring mitochondria cell lines (cybrids) with a constant nuclear background by transferring mitochondria from immortalized lymphoblastoid cell lines carrying the HCM-associated m.2336T>C mutation into human mtDNA-less (ρ°) cells. Functional assays showed a decreased stability for 16S rRNA and the steady-state levels of its binding proteins in the mutant cybrids. This mutation impaired the mitochondrial translation capacity and resulted in many mitochondrial dysfunctions, including elevation of ROS generation, reduction of ATP production and impairment of mitochondrial membrane potential. Moreover, the mutant cybrids had poor physiological status and decreased survival ability. These results confirm that the m.2336T>C mutation leads to mitochondrial dysfunction and strongly suggest that this mutation may play a role in the pathogenesis of HCM.

Detection of homoplasmic MTDNA mutations by ngs method in patients with carotid atherosclerosis

Aim: The aim of the study was to identify homoplasmic mutations mtDNA associated with atherosclerotic lesions by the NGS (next-generation sequencing) method.

Widespread Chromosomal Losses and Mitochondrial DNA Alterations as Genetic Drivers in Hürthle Cell Carcinoma

Hürthle cell carcinoma of the thyroid (HCC) is a form of thyroid cancer recalcitrant to radioiodine therapy that exhibits an accumulation of mitochondria. We performed whole-exome sequencing on a cohort of primary, recurrent, and metastatic tumors, and identified recurrent mutations in DAXX, TP53, NRAS, NF1, CDKN1A, ARHGAP35, and the TERT promoter. Parallel analysis of mtDNA revealed recurrent homoplasmic mutations in subunits of complex I of the electron transport chain. Analysis of DNA copy-number alterations uncovered widespread loss of chromosomes culminating in near-haploid chromosomal content in a large fraction of HCC, which was maintained during metastatic spread. This work uncovers a distinct molecular origin of HCC compared with other thyroid malignancies.

Investigation of frequent somatic mutations of MTND5 gene in gastric cancer cell lines and tissues

The present study investigated the single nucleotide variants (SNVs) in mitochondrial DNA (mtDNA) of 13 paired gastric cancer tissue samples and seven gastric cancer cell lines using direct sequencing analysis of the MTND5 region. Results showed that nuclear mitochondrial pseudogenes (NUMTs) and mitochondrial copy number affected the detection of the SNV frequency in gastric cancer tissue and cell line samples using high-throughput sequencing technique. The heteroplasmic point mutation C12474T and G12835A happened in AGS and BGC823 cell lines, respectively. A total of seven SNVs were found in three paired gastric cancer tissue samples, including five heteroplasmic point mutations (A12406G, C12705T, T12882C, G12501A, and A12584G) and two homoplasmic point mutations (G12561A and C13590T). Gastric cancer tissue sample 16 exhibited the highest SNVs frequency with four SNVs (np 12406, np 12705, np 12882, and np 12501), whereas no SNVs or SNPs were detected in the tissue sample 4. SNP 12705 turned out to be an SNV in gastric cancer tissue sample 16. SNV 12338 detected by exome sequencing approach appeared to be an SNP in this study.

First description of a novel mitochondrial mutation in the MT-TI gene associated with multiple mitochondrial DNA deletion and depletion in family with severe dilated mitochondrial cardiomyopathy

Mitochondria are essential for early cardiac development and impaired mitochondrial function was described associated with heart diseases such as hypertrophic or dilated mitochondrial cardiomyopathy.In this study, we report a family including two individuals with severe dilated mitochondrial cardiomyopathy. The whole mitochondrial genome screening showed the presence of several variations and a novel homoplasmic mutation m.4318-4322delC in the MT-TI gene shared by the two patients and their mother and leading to a disruption of the tRNAIle secondary structure. In addition, a mitochondrial depletion was present in blood leucocyte of the two affected brother whereas a de novo heteroplasmic multiple deletion in the major arc of mtDNA was present in blood leucocyte and mucosa of only one of them. These deletions in the major arc of the mtDNA resulted to the loss of several protein-encoding genes and also some tRNA genes. The mtDNA deletion and depletion could result to an impairment of the oxidative phosphorylation and energy metabolism in the respiratory chain in the studied patients.Our report is the first description of a family with severe lethal dilated mitochondrial cardiomyopathy and presenting several mtDNA abnormalities including punctual mutation, deletion and depletion.

Mitochondrial Dysfunctions Contribute to Hypertrophic Cardiomyopathy in Patient iPSC-Derived Cardiomyocytes with MT-RNR2 Mutation.

SummaryHypertrophic cardiomyopathy (HCM) is the most common cause of sudden cardiac death in young individuals. A potential role of mtDNA mutations in HCM is known. However, the underlying molecular mechanisms linking mtDNA mutations to HCM remain poorly understood due to lack of cell and animal models. Here, we generated induced pluripotent stem cell-derived cardiomyocytes (HCM-iPSC-CMs) from human patients in a maternally inherited HCM family who carry the m.2336T>C mutation in the mitochondrial 16S rRNA gene (MT-RNR2). The results showed that the m.2336T>C mutation resulted in mitochondrial dysfunctions and ultrastructure defects by decreasing the stability of 16S rRNA, which led to reduced levels of mitochondrial proteins. The ATP/ADP ratio and mitochondrial membrane potential were also reduced, thereby elevating the intracellular Ca2+ concentration, which was associated with numerous HCM-specific electrophysiological abnormalities. Our findings therefore provide an innovative insight into the pathogenesis of maternally inherited HCM.