Mitochondrial DNA Abnormalities Research Articles

Lysosomal dysfunction and overload of nucleosides in thymidine phosphorylase deficiency of MNGIE

Inherited deficiency of thymidine phosphorylase (TP), encoded by TYMP, leads to a rare disease with multiple mitochondrial DNA (mtDNA) abnormalities, mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). However, the impact of TP deficiency on lysosomes remains unclear, which are important for mitochondrial quality control and nucleic acid metabolism. Muscle biopsy tissue and skin fibroblasts from MNGIE patients, patients with m.3243 A > G mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and healthy controls (HC) were collected to perform mitochondrial and lysosomal functional analyses. In addition to mtDNA abnormalities, compared to controls distinctively reduced expression of LAMP1 and increased mitochondrial content were detected in the muscle tissue of MNGIE patients. Skin fibroblasts from MNGIE patients showed decreased expression of LAMP2, lowered lysosomal acidity, reduced enzyme activity and impaired protein degradation ability. TYMP knockout or TP inhibition in cells can also induce the similar lysosomal dysfunction. Using lysosome immunoprecipitation (Lyso- IP), increased mitochondrial proteins, decreased vesicular proteins and V-ATPase enzymes, and accumulation of various nucleosides were detected in lysosomes with TP deficiency. Treatment of cells with high concentrations of dThd and dUrd also triggers lysosomal dysfunction and disruption of mitochondrial homeostasis. Therefore, the results provided evidence that TP deficiency leads to nucleoside accumulation in lysosomes and lysosomal dysfunction, revealing the widespread disruption of organelles underlying MNGIE.Graphical

Transfer of cGAMP from neuron to microglia activates microglial type I interferon responses after subarachnoid hemorrhage

Primary subarachnoid hemorrhage (SAH) is a type of acute stroke, accounting for approximately 10% of cases, with high disability and mortality rate. Early brain injury (EBI) is a critical factor in determining SAH mortality; however, there are no effective treatment interventions for EBI. Based on our results, the transmission of cyclic GMP-AMP (cGAMP) from neurons to microglia is a key molecular event that triggers type I interferon response, amplifies neuroinflammation, and leads to neuronal apoptosis. Abnormal intracytoplasmic mitochondrial DNA (mtDNA) is the initiating factor of the cGAS-cGAMP-STING signaling axis. Overall, the cGAS-cGAMP-STING signaling axis is closely associated with neuroinflammation after subarachnoid hemorrhage. Targeting cGAS triggered by cytoplasmic mtDNA may be useful for comprehensive clinical treatment of patients after SAH. Further studies targeting cGAS-specific antagonists for treating SAH are warranted.7PSVyjnQMobdwLpgGMHbxKVideo

The clinical, myopathological, and genetic analysis of 155 Chinese mitochondrial ophthalmoplegia patients with mitochondrial DNA single large deletions.

Progressive external ophthalmoplegia (PEO) is a common subtype of mitochondrial encephalomyopathy. The study aimed to investigate the relationship between mitochondrial DNA (mtDNA) abnormalities, muscle pathology, and clinical manifestations in Chinese patients with single large-scale mtDNA deletion presenting with PEO. This is a retrospective single-center study. Patients with PEO who had a single large deletion in mitochondrial DNA were included in this study. The associations were analyzed between mtDNA deletion patterns, myopathological changes, and clinical characteristics. In total, 155 patients with mitochondrial PEO carrying single large-scale mtDNA mutations were enrolled, including 137 chronic progressive external ophthalmoplegia (CPEO) and 18 Kearns-Sayre syndrome (KSS) patients. The onset ages were 9.61 ± 4.12 in KSS and 20.15 ± 9.06 in CPEO. The mtDNA deletions ranged from 2225 bp to 9131 bp, with m.8470_13446del being the most common. The KSS group showed longer deletions than the CPEO group (p = 0.004). Additionally, a higher number of deleted genes encoding respiratory chain complex subunits (p = 0.001) and tRNA genes (p = 0.009) were also observed in the KSS group. A weak negative correlation between the mtDNA deletion size and ages of onset (p < 0.001, r = -0.369) was observed. The proportion of ragged red fibers, ragged blue fibers, and cytochrome c negative fibers did not correlate significantly with onset ages (p > 0.05). However, a higher percentage of abnormal muscle fibers corresponds to an increased prevalence of exercise intolerance, limb muscle weakness, dysphagia, and cerebellar ataxia. We reported a large Chinese cohort consisting of mitochondrial PEO patients with single large-scale mtDNA deletions. Our results demonstrated that the length and locations of mtDNA deletions may influence onset ages and clinical phenotypes. The severity of muscle pathology could not only indicate diagnosis but also may be associated with clinical manifestations beyond the extraocular muscles.

Comprehensive analysis of mitochondrial DNA variants, mitochondrial DNA copy number and oxidative damage in psoriatic arthritis.

Growing evidence suggests that abnormalities in mitochondrial DNA (mtDNA) are involved in the pathogenesis of various inflammatory and immuno-mediated diseases. The present study analysed the entire mitochondrial genome by next-generation sequencing (NGS) in 23 patients with psoriatic arthritis (PsA) and 20 healthy controls to identify PsA-related variants. Changes in mtDNA copy number (mtDNAcn) were also evaluated by quantitative polymerase chain reaction (qPCR) and mtDNA oxidative damage was measured using an 8-hydroxy-2'-deoxyguanosine assay. NGS analysis revealed a total of 435 variants including 187 in patients with PsA only and 122 in controls only. Additionally, 126 common variants were found, of which 2 variants differed significantly in their frequencies among patients and controls (P<0.05), and may be associated with susceptibility to PsA. A total of 33 missense variants in mtDNA-encoded genes for complexes I, III, IV and V were identified only in patients with PsA. Of them, 25 variants were predicted to be deleterious by affecting the functions and structures of encoded proteins, and 13 variants were predicted to affect protein's stability. mtDNAcn analysis revealed decreased mtDNA content in patients with PsA compared with controls (P=0.0001) but the decrease in mtDNAcn was not correlated with patients' age or inflammatory biomarkers (P>0.05). Moreover, a higher level of oxidative damage was observed in patients with PsA compared with controls (P=0.03). The results of the present comprehensive analysis of mtDNA in PsA revealed that certain mtDNA variants may be implicated in the predisposition/pathogenesis of PsA, highlighting the importance of NGS in the identification of mtDNA variants in PsA. The current results also demonstrated that decreased mtDNAcn in PsA may be a consequence of increased oxidative stress. These data provide valuable insights into the contribution of mtDNA defects to the pathogenesis of PsA. Additional studies in larger cohorts are needed to elucidate the role of mtDNA defects in PsA.

Reversible cardiac function and left ventricular hypertrophy in a Chinese man with mitochondrial myopathy: a case report

BackgroundMitochondrial myopathies (MMs) are a group of multi-system diseases caused by abnormalities in mitochondrial DNA (mtDNA) or mutations of nuclear DNA (nDNA). The diagnosis of mitochondrial myopathy (MM) is reliant on the combination of history and physical examination, muscle biopsy, histochemical studies, and next-generation sequencing. Patients with MMs have diverse clinical manifestations. In the contemporary literature, there is a paucity of reports on cardiac structure and function in this rare disease. We report a Chinese man with MM accompanied with both acute right heart failure and left ventricular hypertrophy.Case presentationA 49-year-old man presented with clinical features suggestive of MM, i.e., ophthalmoparesis, weakness of the pharyngeal and extremity muscles, and respiratory muscles which gradually progressed to respiratory insufficiency. He had a family history of mitochondrial myopathy. He had increased levels of serum creatine kinase and lactate. Muscle biopsy of left lateral thigh revealed 8% ragged red fibers (RRF) and 42% COX-negative fibers. Gene sequencing revealed a novel heterozygote TK2 variant (NM_001172644: c.584T>C, p.Leu195Pro) and another heterozygous variant (NM_004614.4:c.156+958G>A; rs1965661603) in the intron of TK2 gene. Based on these findings, we diagnosed the patient as a case of MM. Echocardiography revealed right heart enlargement, pulmonary hypertension, left ventricular hypertrophy, and thickening of the main pulmonary artery and its branches. The patient received non-invasive ventilation and coenzyme Q10 (CoQ10). The cardiac structure and function were restored at 1-month follow-up.ConclusionsThis is the first report of reversible cardiac function impairment and left ventricular hypertrophy in a case of adult-onset MM, nocturnal hypoxia is a potential mechanism for left ventricular hypertrophy in patients with MM.

Mitochondria in Human Fertility and Infertility.

In human spermatozoa and oocytes (and their surrounding granulosa cells), mitochondria carry out important functions relating to human fertility and infertility. Sperm mitochondria are not transmitted to the future embryo, but are closely related to the generation of energy needed for sperm movement, capacitation, and acrosome reactions, as well as for sperm-oocyte fusion. On the other hand, oocyte mitochondria produce energy required for oocyte meiotic division and their abnormalities can thus cause oocyte and embryo aneuploidy. In addition, they play a role in oocyte calcium metabolism and in essential epigenetic events during the oocyte-to-embryo transition. They are transmitted to the future embryos and may thus cause hereditary diseases in the offspring. Due to the long life span of the female germ cells, the accumulation of mitochondrial DNA abnormalities often causes ovarian aging. Mitochondrial substitution therapy is the only way of dealing with these issues nowadays. New therapies based on mitochondrial DNA editing are under investigation.

Sperm telomere length is associated with sperm nuclear DNA integrity and mitochondrial DNA abnormalities among healthy male college students in Chongqing, China.

Is sperm telomere length (STL) associated with sperm nuclear DNA damage and mitochondrial DNA abnormalities? Sperm telomere length is related to sperm nuclear DNA integrity and mitochondrial DNA abnormalities in healthy young college students. Many studies have revealed the correlations between sperm genetic alterations in both the nucleus and mitochondria and sperm functionality, however, the possible associations between the telomere, an important component of chromosome, and conventional indicators of mitochondrial DNA and nuclear DNA changes have not been investigated. A prospective cohort study, Male Reproductive Health in Chongqing College Students (MARHCS), was conducted from June 2013 to June 2015. We pooled data collected from the follow-up study in 2014 and a total of 444 participants were included. STL was measured by quantitative (Q)-PCR. Sperm nuclear DNA integrity was determined using sperm chromatin structure assay (SCSA) and comet assay. Mitochondrial DNA damage was assessed by mitochondrial DNA copy number (mtDNAcn) evaluated with Q-PCR, and mtDNA integrity was determined with long PCR. The univariable-linear regression analysis revealed that STL was significantly positively correlated with markers of sperm nuclear DNA damage including the DNA fragmentation index (DFI) and comet parameters (the percentage of DNA in the tail, tail length, comet length, and tail moment). Additionally, STL was also significantly positively correlated with mtDNAcn and significantly negatively correlated with mtDNA integrity. After adjustment for potential confounders, these relationships remained appreciable. Moreover, we investigated potential effects of biometric factors, including age, parental age at conception, and BMI on STL and found that STL was increased with paternal age at conception. A mechanistic explanation of the correlation between STL, sperm nuclear DNA integrity, and mtDNA abnormalities cannot be provided with a cross-sectional study design, so well-designed longitudinal studies are still necessary. In addition, a single semen samples were provided and were not all obtained at the same time point, which may increase the intraindividual bias in this study. The findings extend the literature including assessment of mitochondrial dysfunction, sperm nuclear DNA damage, and telomere length and provide new insights into the relevance of STL in male reproduction. This work was supported by the National Natural Science Foundation of China (No. 82073590), the National Natural Science Foundation of China (No. 81903363), the National Natural Science Foundation of China (No. 82130097), and the National Key R&D Program of China (2022YFC2702900). The authors declare no conflicts of interest. N/A.

Mitochondrial DNA abnormalities and metabolic syndrome.

Metabolic syndrome (MetS) is a complex pathological condition that involves disrupted carbohydrate, protein, and fat metabolism in the human body, and is a major risk factor for several chronic diseases, including diabetes, cardiovascular disease, and cerebrovascular disease. While the exact pathogenesis of metabolic syndrome is not yet fully understood, there is increasing evidence linking mitochondrial dysfunction, which is closely related to the mitochondrial genome and mitochondrial dynamics, to the development of this condition. Recent advancements in genetic sequencing technologies have allowed for more accurate detection of mtDNA mutations and other mitochondrial abnormalities, leading to earlier diagnosis and intervention in patients with metabolic syndrome. Additionally, the identification of specific mechanisms by which reduced mtDNA copy number and gene mutations, as well as abnormalities in mtDNA-encoded proteins and mitochondrial dynamics, contribute to metabolic syndrome may promote the development of novel therapeutic targets and interventions, such as the restoration of mitochondrial function through the targeting of specific mitochondrial defects. Additionally, advancements in genetic sequencing technologies may allow for more accurate detection of mtDNA mutations and other mitochondrial abnormalities, leading to earlier diagnosis and intervention in patients with MetS. Therefore, strategies to promote the restoration of mitochondrial function by addressing these defects may offer new options for treating MetS. This review provides an overview of the research progress and significance of mitochondrial genome and mitochondrial dynamics in MetS.

Polymorphism of mitochondrial DNA genes involved in asthenozoospermia in infertile patients of Côte d’Ivoire

Objective: The relationship between mitochondrial DNA (mtDNA) polymorphisms and abnormalities in sperm quality has been the subject of several studies, with the objective of improving the treatment of male infertility. This study, which contributes to the identification of genetic markers of sperm abnormalities, was conducted to study mtDNA mutations in the asthenozoospermia profile. Methods: This case-control study included 30 patients with asthenozoospermia and 28 with normospermia after spermogram and spermocytogram analyses. After the extraction of total DNA from the spermatozoa of 58 ejaculates from these individuals using the phenol-chloroform method, the amplification of genes of interest in mtDNA using specific primers was performed by conventional polymerase chain reaction, and sequencing was used to detect mutations. Results: Male patients with asthenozoospermia in the tertiary sector had significantly more mutant- than wild-type (P = 0.0005) MT-CO II genes. Similarly, for the same gene, males with asthenozoospermia and primary infertility had significantly more mutants than the wild-type (P = 0.001). Sequencing revealed 29 mutations that were observed only with asthenozoospermia, which could be the basis for low sperm mobility. Conclusion: This study identified several mutations in mtDNA genes that could be considered genetic markers of asthenozoospermia if confirmed in a deeper study.

Neuropathic Pain as Main Manifestation of POLG-Related Disease: A Case Report

Mutations in nuclear-encoded genes that are involved in mitochondrial DNA replication and maintenance (e.g., POLG) have been associated with chronic progressive external ophthalmoplegia (CPEO) phenotype. These nuclear genome mutations may lead to multiple mitochondrial DNA deletions or mitochondrial DNA depletion. On the other hand, primary genetic defects of mitochondrial DNA (such as single large-scale deletion or point mutations) have also been associated with the CPEO phenotype. Chronic progressive external ophthalmoplegia (CPEO) may be a manifestation of specific syndromes that, when clinically recognized, prompt clinicians to investigate specific genetic defects. Thus, CPEO, as part of Kearns Sayre syndrome, suggests the presence of a large-scale deletion of mitochondrial DNA. However, in pure CPEO or CPEO plus phenotypes, it is more difficult to know whether causative genetic defects affect the nuclear or mitochondrial DNA. Here, we present a patient with a long-standing history of CPEO plus phenotype, in whom the sequencing of mitochondrial DNA from skeletal muscle was normal, and no other genetic defect was suspected at first. At the time of our evaluation, the presence of polyneuropathy and neuropathic pain prompted us to investigate nuclear genetic defects and, specifically, mutations in the POLG gene. Thus, the sequencing of the POLG gene revealed p.Thr251Ile and p.Pro587Leu mutations in one allele, and p.Ala467Thr mutation in another allele. Although one would expect that mutations in POLG lead to multiple mitochondrial DNA deletions or depletion (loss of copies), the absence of mitochondrial DNA abnormalities in tissue may be explained by heteroplasmy, a lack or no significant involvement of biopsied tissue, or a sampling bias. So, the absence of secondary mitochondrial DNA alterations should not discourage clinicians from further investigating mutations in nuclear-encoded genes. Lastly, mitochondrial point mutations and single mitochondrial DNA deletions very rarely cause CPEO associated with polyneuropathy and neuropathic pain, and POLG-related disease should be considered in this scenario, instead.

Changes in Nuclear Gene Expression Related to Mitochondrial Function Affect Extracellular Matrix, Collagens, and Focal Adhesion in Keratoconus.

PurposeMitochondrial DNA (mtDNA) abnormalities were previously found to be causative in the pathogenesis of various diseases. Here, comprehensive mitochondrial and nuclear sequence and transcript analyses, along with analyses of the methylation aspects of nuclear genes related to mitochondrial function, were performed in patients with keratoconus (KTCN) to evaluate their contribution to the KTCN pathogenesis.MethodsBlood mtDNA of 42 KTCN and 51 non-KTCN individuals was Sanger sequenced and analyzed along with the previously obtained corneal RNA-sequencing data of 20 KTCN and 21 non-KTCN individuals. In addition, the expression and methylation of mtDNA genes and 1223 mitochondria-related nuclear genes were evaluated.ResultsThe mtDNA sequence alterations detected in blood coincided with variants identified in transcripts of the matched corneal tissues. In KTCN corneas, 97 mitochondria-related genes were deregulated, including TGFB1, P4HB, and BCL2, which are involved in the extracellular matrix (ECM) organization, collagen formation, and focal adhesion pathways. No changes in the expression of mtDNA transcripts and no differentially methylated genes among the assessed mitochondrial–nuclear gene sets were found.ConclusionsThe absence of corneal-specific mtDNA variants indicates that there is no direct relationship between mitochondrial sequence variability and KTCN phenotype in the studied individuals. However, the identified KTCN-specific transcriptomic alterations of the nuclear genes directly related to the mitochondria functioning point to their possible involvement in the ECM organization, collagen formation, and focal adhesion.Translational RelevanceThe identification of abnormalities within nuclear genes regulating ECM formation, collagen synthesis, and/or focal adhesion may form the basis of future treatment strategies or predict the progression of corneal changes in KTCN.

Mitochondrial DNA abnormalities provide mechanistic insight and predict reactive oxygen species-stimulating drug efficacy

BackgroundAssociations between mitochondrial genetic abnormalities (variations and copy number, i.e. mtDNAcn, change) and elevated ROS have been reported in cancer compared to normal cells. Since excessive levels of ROS can trigger apoptosis, treating cancer cells with ROS-stimulating agents may enhance their death. This study aimed to investigate the link between baseline ROS levels and mitochondrial genetic abnormalities, and how mtDNA abnormalities might be used to predict cancer cells’ response to ROS-stimulating therapy.MethodsIntracellular and mitochondrial specific-ROS levels were measured using the DCFDA and MitoSOX probes, respectively, in four cancer and one non-cancerous cell lines. Cells were treated with ROS-stimulating agents (cisplatin and dequalinium) and the IC50s were determined using the MTS assay. Sanger sequencing and qPCR were conducted to screen the complete mitochondrial genome for variations and to relatively quantify mtDNAcn, respectively. Non-synonymous variations were subjected to 3-dimensional (3D) protein structural mapping and analysis.ResultsOur data revealed novel significant associations between the total number of variations in the mitochondrial respiratory chain (MRC) complex I and III genes, mtDNAcn, ROS levels, and ROS-associated drug response. Furthermore, functional variations in complexes I/III correlated significantly and positively with mtDNAcn, ROS levels and drug resistance, indicating they might mechanistically influence these parameters in cancer cells.ConclusionsOur findings suggest that mtDNAcn and complexes I/III functional variations have the potential to be efficient biomarkers to predict ROS-stimulating therapy efficacy in the future.

Mitochondrial Dysfunction in Polycystic Ovary Syndrome.

Polycystic ovary syndrome (PCOS) is one of the most common female reproductive metabolisms. It is an endocrine disease that affects reproductive women and often exhibits with hyperandrogenemia, insulin resistance (IR), low inflammation, and an increased risk of type 2 diabetes mellitus, metabolic syndrome, and cardiovascular events such as hypertension and dyslipidemia in patients. However, the molecular mechanism of PCOS is still unclear. Recently, an increasing number of studies have shown that the oxidative stress induced by mitochondrial dysfunction has negative effects on IR, lipid metabolism, and follicular development, suggesting that mitochondrial dysfunction plays an essential role in the development of PCOS. Abnormal mitochondrial DNA copy number in patients with PCOS, and mitochondrial gene mutations, has been the focus of research in recent years, and functional mitochondrial diseases have been gradually accepted as a related factor in PCOS. This review is intended to summarize and discuss previous and recent studies and findings on the connections between mitochondrial dysfunction and PCOS.

289O - Spectrum of mitochondrial genomic variation in parathyroid neoplasms by ultra-deep targeted DNA sequencing

BackgroundParathyroid neoplasms are characterized with hypersecretion of parathyroid hormone and potentially exhibit disruption of metabolic pathways. Mitochondria are essential for energy homeostasis and mitochondrial DNA (mtDNA) abnormalities are related to multiple types of malignancies. However, the status of mtDNA mutation and copy number variations in parathyroid carcinoma (PC) is not well known. MethodsUltra-deep targeted sequencing of mitochondrial genome was performed using tissues of 12 PCs and 12 parathyroid adenomas (PAs). Germline variants and somatic mutations in the mitochondrial genome were scanned and analysed in comparison with clinical features. The relative copy number of mtDNA in PCs and PAs was determined via quantitative real-time polymerase chain reaction. ResultsA total of 528 germline variants and 16 somatic mutations were identified in 24 samples of parathyroid neoplasms. All 62 non-synonymous germline variants in coding sequence (CDS) were predicted to be of low pathogenicity in PA and PC samples. Five somatic mutations with high pathogenicity in CDSs were identified in 4 (33.3%, 4/12) PC samples and 1 PA sample (8.3%, 1/12). A somatic mutation in a CDS was correlated with high mtDNA copy number in parathyroid neoplasm (p = 0.004), CDC73 gene mutation (p = 0.017) and PC recurrence (p = 0.024). More C-19 genotypes in the D310 region were found in PA than in the PC samples (3.5% vs 1.9%, p = 0.045). ConclusionsMore somatic CDS mutations with high pathogenicity were identified in PC than in PA. A high mtDNA copy number was found in parathyroid neoplasms with somatic CDS mutations and in PCs with CDC73 mutations and recurrence. Legal entity responsible for the studyThe authors. FundingThis work was supported by the Chinese Academy of Medical Sciences (CAMS) Initiative for Innovative Medicine (CAMS-I2M) (2017-I2M-1-001), Peking Union Medical College Innovative Team Development Program, the Non-profit Central Research Institute Fund of Chinese Academy of Medical Sciences (2018PT32014) and the 2016 Peking Union Medical College Hospital Science Foundation for Junior Faculty (pumch-2016.2.7). DisclosureAll authors have declared no conflicts of interest.

Parkinsonism and spastic paraplegia type 7: Expanding the spectrum of mitochondrial Parkinsonism.

Pathogenic variants in the spastic paraplegia type 7 gene cause a complicated hereditary spastic paraplegia phenotype associated with classical features of mitochondrial diseases, including ataxia, progressive external ophthalmoplegia, and deletions of mitochondrial DNA. To better characterize spastic paraplegia type 7 disease with a clinical, genetic, and functional analysis of a Spanish cohort of spastic paraplegia type 7 patients. Genetic analysis was performed in patients suspecting hereditary spastic paraplegia and in 1 patient with parkinsonism and Pisa syndrome, through next-generation sequencing, whole-exome sequencing, targeted Sanger sequencing, and multiplex ligation-dependent probe analysis, and blood mitochondrial DNA levels determined by quantitative polymerase chain reaction. Thirty-five patients were found to carry homozygous or compound heterozygous pathogenic variants in the spastic paraplegia type 7 gene. Mean age at onset was 40 years (range, 12-63); 63% of spastic paraplegia type 7 patients were male, and three-quarters of all patients had at least one allele with the c.1529C>T (p.Ala510Val) mutation. Eighty percent of the cohort showed a complicated phenotype, combining ataxia and progressive external ophthalmoplegia (65% and 26%, respectively). Parkinsonism was observed in 21% of cases. Analysis of blood mitochondrial DNA indicated that both patients and carriers of spastic paraplegia type 7 pathogenic variants had markedly lower levels of mitochondrial DNA than control subjects (228 per haploid nuclear DNA vs. 176 vs. 573, respectively; P < 0.001). Parkinsonism is a frequent finding in spastic paraplegia type 7 patients. Spastic paraplegia type 7 pathogenic variants impair mitochondrial DNA homeostasis irrespective of the number of mutant alleles, type of variant, and patient or carrier status. Thus, spastic paraplegia type 7 supports mitochondrial DNA maintenance, and variants in the gene may cause parkinsonism owing to mitochondrial DNA abnormalities. Moreover, mitochondrial DNA blood analysis could be a useful biomarker to detect at risk families. © 2019 International Parkinson and Movement Disorder Society.

Mitochondrial Therapy for Disease Treatment and Prevention: What’s New?

Many diseases caused by mitochondrial dysfunction are caused by mitochondrial DNA abnormalities. The concept of mitochondrial therapy is based on the repair or removal of the existing anomaly. This can be done by replacing affected mitochondria by healthy ones, by in situ correction of the damaged mitochondrial DNA or by selective destruction of the affected mitochondria. In theory, all these concepts are applicable at the preconception stage, thus preventing the mother-to-child disease transmission, as well as at more advanced developmental stages (embryonic, fetal and postnatal) to alleviate disease symptoms in specific organs and tissues. Animal reasearch has paved the way to human therapies at all of these levels. So far, the only successful human application concerned the preconception stage and was based on replacement of diseased mitochondria in patients’ oocytes with healthy ones originating from oocytes donated by healthy women.

ATAD3 gene cluster deletions cause cerebellar dysfunction associated with altered mitochondrial DNA and cholesterol metabolism.

Although mitochondrial disorders are clinically heterogeneous, they frequently involve the central nervous system and are among the most common neurogenetic disorders. Identifying the causal genes has benefited enormously from advances in high-throughput sequencing technologies; however, once the defect is known, researchers face the challenge of deciphering the underlying disease mechanism. Here we characterize large biallelic deletions in the region encoding the ATAD3C, ATAD3B and ATAD3A genes. Although high homology complicates genomic analysis of the ATAD3 defects, they can be identified by targeted analysis of standard single nucleotide polymorphism array and whole exome sequencing data. We report deletions that generate chimeric ATAD3B/ATAD3A fusion genes in individuals from four unrelated families with fatal congenital pontocerebellar hypoplasia, whereas a case with genomic rearrangements affecting the ATAD3C/ATAD3B genes on one allele and ATAD3B/ATAD3A genes on the other displays later-onset encephalopathy with cerebellar atrophy, ataxia and dystonia. Fibroblasts from affected individuals display mitochondrial DNA abnormalities, associated with multiple indicators of altered cholesterol metabolism. Moreover, drug-induced perturbations of cholesterol homeostasis cause mitochondrial DNA disorganization in control cells, while mitochondrial DNA aggregation in the genetic cholesterol trafficking disorder Niemann-Pick type C disease further corroborates the interdependence of mitochondrial DNA organization and cholesterol. These data demonstrate the integration of mitochondria in cellular cholesterol homeostasis, in which ATAD3 plays a critical role. The dual problem of perturbed cholesterol metabolism and mitochondrial dysfunction could be widespread in neurological and neurodegenerative diseases.

Migration of mitochondrial DNA in the nuclear genome of colorectal adenocarcinoma

BackgroundColorectal adenocarcinomas are characterized by abnormal mitochondrial DNA (mtDNA) copy number and genomic instability, but a molecular interaction between mitochondrial and nuclear genome remains unknown. Here we report the discovery of increased copies of nuclear mtDNA (NUMT) in colorectal adenocarcinomas, which supports link between mtDNA and genomic instability in the nucleus. We name this phenomenon of nuclear occurrence of mitochondrial component as numtogenesis. We provide a description of NUMT abundance and distribution in tumor versus matched blood-derived normal genomes.MethodsWhole-genome sequence data were obtained for colon adenocarcinoma and rectum adenocarcinoma patients participating in The Cancer Genome Atlas, via the Cancer Genomics Hub, using the GeneTorrent file acquisition tool. Data were analyzed to determine NUMT proportion and distribution on a genome-wide scale. A NUMT suppressor gene was identified by comparing numtogenesis in other organisms.ResultsOur study reveals that colorectal adenocarcinoma genomes, on average, contains up to 4.2-fold more somatic NUMTs than matched normal genomes. Women colorectal tumors contained more NUMT than men. NUMT abundance in tumor predicted parallel abundance in blood. NUMT abundance positively correlated with GC content and gene density. Increased numtogenesis was observed with higher mortality. We identified YME1L1, a human homolog of yeast YME1 (yeast mitochondrial DNA escape 1) to be frequently mutated in colorectal tumors. YME1L1 was also mutated in tumors derived from other tissues. We show that inactivation of YME1L1 results in increased transfer of mtDNA in the nuclear genome.ConclusionsOur study demonstrates increased somatic transfer of mtDNA in colorectal tumors. Our study also reveals sex-based differences in frequency of NUMT occurrence and that NUMT in blood reflects NUMT in tumors, suggesting NUMT may be used as a biomarker for tumorigenesis. We identify YME1L1 as the first NUMT suppressor gene in human and demonstrate that inactivation of YME1L1 induces migration of mtDNA to the nuclear genome. Our study reveals that numtogenesis plays an important role in the development of cancer.

Time-dependent dysregulation of autophagy: Implications in aging and mitochondrial homeostasis in the kidney proximal tubule

ABSTRACTAutophagy plays an essential role in cellular homeostasis through the quality control of proteins and organelles. Although a time-dependent decline in autophagic activity is believed to be involved in the aging process, the issue remains controversial. We previously demonstrated that autophagy maintains proximal tubular cell homeostasis and protects against kidney injury. Here, we extend that study and examine how autophagy is involved in kidney aging. Unexpectedly, the basal autophagic activity was higher in the aged kidney than that in young kidney; short-term cessation of autophagy in tamoxifen-inducible proximal tubule-specific autophagy-deficient mice increased the accumulation of SQSTM1/p62- and ubiquitin-positive aggregates in the aged kidney. By contrast, autophagic flux in response to metabolic stress was blunted with aging, as demonstrated by the observation that transgenic mice expressing a green fluorescent protein (GFP)-microtubule-associated protein 1 light chain 3B fusion construct, showed a drastic increase of GFP-positive puncta in response to starvation in young mice compared to a slight increase observed in aged mice. Finally, proximal tubule-specific autophagy-deficient mice at 24 mo of age exhibited a significant deterioration in kidney function and fibrosis concomitant with mitochondrial dysfunction as well as mitochondrial DNA abnormalities and nuclear DNA damage, all of which are hallmark characteristics of cellular senescence. These results suggest that age-dependent high basal autophagy plays a crucial role in counteracting kidney aging through mitochondrial quality control. Furthermore, a reduced capacity for upregulation of autophagic flux in response to metabolic stress may be associated with age-related kidney diseases.

MPV17 Loss Causes Deoxynucleotide Insufficiency and Slow DNA Replication in Mitochondria.

MPV17 is a mitochondrial inner membrane protein whose dysfunction causes mitochondrial DNA abnormalities and disease by an unknown mechanism. Perturbations of deoxynucleoside triphosphate (dNTP) pools are a recognized cause of mitochondrial genomic instability; therefore, we determined DNA copy number and dNTP levels in mitochondria of two models of MPV17 deficiency. In Mpv17 ablated mice, liver mitochondria showed substantial decreases in the levels of dGTP and dTTP and severe mitochondrial DNA depletion, whereas the dNTP pool was not significantly altered in kidney and brain mitochondria that had near normal levels of DNA. The shortage of mitochondrial dNTPs in Mpv17-/- liver slows the DNA replication in the organelle, as evidenced by the elevated level of replication intermediates. Quiescent fibroblasts of MPV17-mutant patients recapitulate key features of the primary affected tissue of the Mpv17-/- mice, displaying virtual absence of the protein, decreased dNTP levels and mitochondrial DNA depletion. Notably, the mitochondrial DNA loss in the patients’ quiescent fibroblasts was prevented and rescued by deoxynucleoside supplementation. Thus, our study establishes dNTP insufficiency in the mitochondria as the cause of mitochondrial DNA depletion in MPV17 deficiency, and identifies deoxynucleoside supplementation as a potential therapeutic strategy for MPV17-related disease. Moreover, changes in the expression of factors involved in mitochondrial deoxynucleotide homeostasis indicate a remodeling of nucleotide metabolism in MPV17 disease models, which suggests mitochondria lacking functional MPV17 have a restricted purine mitochondrial salvage pathway.