Mitochondrial DNA Instability Research Articles

The immunology of rheumatoid arthritis.

The immunopathogenesis of rheumatoid arthritis (RA) spans decades, beginning with the production of autoantibodies against post-translationally modified proteins (checkpoint 1). After years of asymptomatic autoimmunity and progressive immune system remodeling, tissue tolerance erodes and joint inflammation ensues as tissue-invasive effector T cells emerge and protective joint-resident macrophages fail (checkpoint 2). The transition of synovial stromal cells into autoaggressive effector cells converts synovitis from acute to chronic destructive (checkpoint 3). The loss of T cell tolerance derives from defective DNA repair, causing abnormal cell cycle dynamics, telomere fragility and instability of mitochondrial DNA. Mitochondrial and lysosomal anomalies culminate in the generation of short-lived tissue-invasive effector T cells. This differentiation defect builds on a metabolic platform that shunts glucose away from energy generation toward the cell building and motility programs. The next frontier in RA is the development of curative interventions, for example, reprogramming T cell defects during the period of asymptomatic autoimmunity.

Drug repositioning as a therapeutic strategy for neurodegenerations associated with OPA1 mutations.

OPA1 mutations are the major cause of dominant optic atrophy (DOA) and the syndromic form DOA plus, pathologies for which there is no established cure. We used a ‘drug repurposing’ approach to identify FDA-approved molecules able to rescue the mitochondrial dysfunctions induced by OPA1 mutations. We screened two different chemical libraries by using two yeast strains carrying the mgm1I322M and the chim3P646L mutations, identifying 26 drugs able to rescue their oxidative growth phenotype. Six of them, able to reduce the mitochondrial DNA instability in yeast, have been then tested in Opa1 deleted mouse embryonic fibroblasts expressing the human OPA1 isoform 1 bearing the R445H and D603H mutations. Some of these molecules were able to ameliorate the energetic functions and/or the mitochondrial network morphology, depending on the type of OPA1 mutation. The final validation has been performed in patients’ fibroblasts, allowing to select the most effective molecules. Our current results are instrumental to rapidly translating the findings of this drug repurposing approach into clinical trial for DOA and other neurodegenerations caused by OPA1 mutations.

MRE11-Dependent Instability in Mitochondrial DNA Fork Protection Activates cGAS Inflammation

Mitochondrial DNA instability activates cGAS and the innate immune system by unknown mechanisms. Here, we find that Fanconi anemia suppressor genes are acting in the mitochondria to protect mitochondrial DNA replication forks from instability. Specifically, Fanconi anemia patient cells show a loss of nascent mitochondrial DNA through MRE11 nuclease degradation. In stark contrast to DNA replication stability in the nucleus, which requires pathway activation by FANCD2 mono ubiquitination and upstream FANC core complex genes, mitochondrial replication fork protection does not, uncovering a mechanistic and genetic separation between mitochondrial and nuclear genome stability pathways. The degraded mitochondrial DNA causes a hyperactivation of the cGAS dependent unphosphorylated ISG3 interferon type-1 response. Importantly, chemical inhibition of MRE11 suppresses this type of inflammation, identifying MRE11 as the nuclease responsible for activating the mitochondrial DNA-dependent cGAS/STING inflammation pathway. Overall, collective results establish a previously unknown molecular pathway for mitochondrial DNA replication stability and show how defects in tumor suppressor proteins cause diverse disease phenotypes including inflammation. Specifically, these findings reveal a molecular handle to control mitochondrial DNA-dependent cGAS activation by inhibiting MRE11 nuclease, relevant to future targeted pharmacological control of specific inflammation responses.

Altered Mitochondrial Dynamics in Motor Neuron Disease: An Emerging Perspective.

Mitochondria plays privotal role in diverse pathways that regulate cellular function and survival, and have emerged as a prime focus in aging and age-associated motor neuron diseases (MNDs), such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Accumulating evidence suggests that many amyloidogenic proteins, including MND-associated RNA/DNA-binding proteins fused in sarcoma (FUS) and TAR DNA binding protein (TDP)-43, are strongly linked to mitochondrial dysfunction. Animal model and patient studies have highlighted changes in mitochondrial structure, plasticity, replication/copy number, mitochondrial DNA instability, and altered membrane potential in several subsets of MNDs, and these observations are consistent with the evidence of increased excitotoxicity, induction of reactive oxygen species, and activation of intrinsic apoptotic pathways. Studies in MND rodent models also indicate that mitochondrial abnormalities begin prior to the clinical and pathological onset of the disease, suggesting a causal role of mitochondrial dysfunction. Our recent studies, which demonstrated the involvement of specific defects in DNA break-ligation mediated by DNA ligase 3 (LIG3) in FUS-associated ALS, raised a key question of its potential implication in mitochondrial DNA transactions because LIG3 is essential for both mitochondrial DNA replication and repair. This question, as well as how wild-type and mutant MND-associated factors affect mitochondria, remain to be elucidated. These new investigation avenues into the mechanistic role of mitochondrial dysfunction in MNDs are critical to identify therapeutic targets to alleviate mitochondrial toxicity and its consequences. In this article, we critically review recent advances in our understanding of mitochondrial dysfunction in diverse subgroups of MNDs and discuss challenges and future directions.

Immunometabolism in the development of rheumatoid arthritis.

In rheumatoid arthritis (RA), breakdown of self-tolerance and onset of clinical disease are separated in time and space, supporting a multi-hit model in which emergence of autoreactive T cells is a pinnacle pathogenic event. Determining factors in T cell differentiation and survival include antigen recognition, but also the metabolic machinery that provides energy and biosynthetic molecules for cell building. Studies in patients with RA have yielded a disease-specific metabolic signature, which enables naive CD4 T cells to differentiate into pro-inflammatory helper T cells that are prone to invade into tissue and elicit inflammation through immunogenic cell death. A typifying property of RA CD4 T cells is the shunting of glucose away from glycolytic breakdown and mitochondrial processing toward the pentose phosphate pathway, favoring anabolic over catabolic reactions. Key defects have been localized to the mitochondria and the lysosome; including instability of mitochondrial DNA due to the lack of the DNA repair nuclease MRE11A and inefficient lysosomal tethering of AMPK due to deficiency of N-myristoyltransferase 1 (NMT1). The molecular taxonomy of the metabolically reprogrammed RA T cells includes glycolytic enzymes (glucose-6-phosphate dehydrogenase, phosphofructokinase), DNA repair molecules (MRE11A, ATM), regulators of protein trafficking (NMT1), and the membrane adapter protein TSK5. As the mechanisms determining abnormal T cell behavior in RA are unraveled, opportunities will emerge to interject autoimmune T cells by targeting their metabolic checkpoints.

Impaired lysosomal acidification triggers iron deficiency and inflammation in vivo.

Lysosomal acidification is a key feature of healthy cells. Inability to maintain lysosomal acidic pH is associated with aging and neurodegenerative diseases. However, the mechanisms elicited by impaired lysosomal acidification remain poorly understood. We show here that inhibition of lysosomal acidification triggers cellular iron deficiency, which results in impaired mitochondrial function and non-apoptotic cell death. These effects are recovered by supplying iron via a lysosome-independent pathway. Notably, iron deficiency is sufficient to trigger inflammatory signaling in cultured primary neurons. Using a mouse model of impaired lysosomal acidification, we observed a robust iron deficiency response in the brain, verified by in vivo magnetic resonance imaging. Furthermore, the brains of these mice present a pervasive inflammatory signature associated with instability of mitochondrial DNA (mtDNA), both corrected by supplementation of the mice diet with iron. Our results highlight a novel mechanism linking impaired lysosomal acidification, mitochondrial malfunction and inflammation in vivo.

Statins interfere with the attachment of S. cerevisiae mtDNA to the inner mitochondrial membrane

The 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme of the mevalonate pathway for the synthesis of cholesterol in mammals (ergosterol in fungi), is inhibited by statins, a class of cholesterol lowering drugs. Indeed, statins are in a wide medical use, yet statins treatment could induce side effects as hepatotoxicity and myopathy in patients. We used Saccharomyces cerevisiae as a model to investigate the effects of statins on mitochondria. We demonstrate that statins are active in S.cerevisiae by lowering the ergosterol content in cells and interfering with the attachment of mitochondrial DNA to the inner mitochondrial membrane. Experiments on murine myoblasts confirmed these results in mammals. We propose that the instability of mitochondrial DNA is an early indirect target of statins.

Instability of Mitochondrial DNA D-loop Region Genes in Patients with Leukemia

To study the instability of mitochondrial DNA（mt DNA） D-loop region genes in patients with Leukemia. The HV-1 and HV-2 regions of D-loop region in 24 patients with leukemia were amplificated and sequenced, then their results were compared with revised Cambridge reference sequence (rCRS) and Databank mtDB. The mutation rate was detected by SPSS 22.0 statistics software. The total mutation rate in patients was 95.83% (23/24), the detection showed 82 mutated genes, out of which 47 (57.32%) mutated genes located in HV-1 region, 35 (42.68%) mutated genes in HV-2 region. The comparison showed that the mutation rate in untreated (UT) group and treated (T) group of AML patients was (2.37±0.82)×10-3 and (4.76±2.45)×10-3 respectively(P＜0.01), the mutation rate in PR and CR groups of treated AML patients was (5.10±2.56)×10-3 and (4.51±2.51)×10-3 respectively (P＜0.05), the comparison among M3 group showed that the mutation rates in UT, PR and CR groups were (2.55±0.63)×10-3, (5.37±3.41)×10-3 and (3.71±1.65)×10-3 respectively (P＞0.05). The more high mutation rate and many kinds of mutation types exist in D-loop region, suggesting that the genes in D-loop region display the more strong instability, the chemotherapy may aggravate the instability of genes in D-loop region.

Mitochondrial transcription factor A (TFAM) shapes metabolic and invasion gene signatures in melanoma

Mitochondria are central key players in cell metabolism, and mitochondrial DNA (mtDNA) instability has been linked to metabolic changes that contribute to tumorigenesis and to increased expression of pro-tumorigenic genes. Here, we use melanoma cell lines and metastatic melanoma tumors to evaluate the effect of mtDNA alterations and the expression of the mtDNA packaging factor, TFAM, on energetic metabolism and pro-tumorigenic nuclear gene expression changes. We report a positive correlation between mtDNA copy number, glucose consumption, and ATP production in melanoma cell lines. Gene expression analysis reveals a down-regulation of glycolytic enzymes in cell lines and an up-regulation of amino acid metabolism enzymes in melanoma tumors, suggesting that TFAM may shift melanoma fuel utilization from glycolysis towards amino acid metabolism, especially glutamine. Indeed, proliferation assays reveal that TFAM-down melanoma cell lines display a growth arrest in glutamine-free media, emphasizing that these cells rely more on glutamine metabolism than glycolysis. Finally, our data indicate that TFAM correlates to VEGF expression and may contribute to tumorigenesis by triggering a more invasive gene expression signature. Our findings contribute to the understanding of how TFAM affects melanoma cell metabolism, and they provide new insight into the mechanisms by which TFAM and mtDNA copy number influence melanoma tumorigenesis.

Unravelling the Power of Omics for the Infertile Aging Male.

The aging phenomenon is intrinsically responsible for diseases and lifestyle-associated conditions afflicting the aging male. In particular, male infertility seems to result from deleterious lifestyle choices. However, the aging effect at the individual gene/protein level is poorly discussed and valuable information is certainly missing. We have thus used an omics approach to identify differentially expressed proteins and genes from spermatozoa and seminal plasma samples across several conditions affecting adult male fertility. Our search resulted in 400 differentially expressed proteins in seminal plasma and 409 differentially expressed proteins in spermatozoa as well as, almost 6,000 differentially expressed spermatozoa mRNAs. We have functionally analyzed these proteins and genes to understand and discuss how biological processes and signaling pathways associated with aging might affect male fertility. Sperm and seminal fluid proteins from infertile males display significant alterations in i) processes previously implicated in the aging phenomena, such as mitochondrial dysfunction, DNA instability, oxidative stress, protein misfolding and intracellular mistrafficking, and ii) processes specifically involved in reproductive phenomena, such as sperm-egg recognition/acrosome reaction, embryo and morula development, blastocyst implantation and DNA methylation involved in embryo development. These proteins display a widespread distribution and seem to be significantly influenced by deleteriously lifestyle choices. Conventional assays to assess male fertility are inadequate to comprehensively reveal the broad-spectrum of alterations at the transcriptional and translational levels afflicting the infertile aging male. In turn, proteomics and transcriptomics are suitable options for addressing these key issues that may explain many poorly understood fertility-associated phenomena resulting from the aging process.

Dominance of yeast aac2R96H and aac2R252G mutations, equivalent to pathological mutations in ant1, is due to gain of function

The mitochondrial ADP/ATP carrier is a nuclear encoded protein, which catalyzes the exchange of ATP generated in mitochondria with ADP produced in the cytosol. In humans, mutations in the major ADP/ATP carrier gene, ANT1, are involved in several degenerative mitochondrial pathologies, leading to instability of mitochondrial DNA. Recessive mutations have been associated with mitochondrial myopathy and cardiomyopathy whereas dominant mutations have been associated with autosomal dominant Progressive External Ophtalmoplegia (adPEO). Recently, two de novo dominant mutations, R80H and R235G, leading to extremely severe symptoms, have been identified. In order to evaluate if the dominance is due to haploinsufficiency or to a gain of function, the two mutations have been introduced in the equivalent positions of the AAC2 gene, the yeast orthologue of human ANT1, and their dominant effect has been studied in heteroallelic strains, containing both one copy of wild type AAC2 and one copy of mutant aac2 allele. Through phenotypic characterization of these yeast models we showed that the OXPHOS phenotypes in the heteroallelic strains were more affected than in the hemiallelic strain indicating that the dominant trait of the two mutations is due to gain of function.

Three mitochondrial transporters of Saccharomyces cerevisiae are essential for ammonium fixation and lysine biosynthesis in synthetic minimal medium.

The nuclear genes of Saccharomyces cerevisiae YHM2, ODC1 and ODC2 encode three transporters that are localized in the inner mitochondrial membrane. In this study, the roles of YHM2, ODC1 and ODC2 in the assimilation of nitrogen and in the biosynthesis of lysine have been investigated. Both the odc1Δodc2Δ double knockout and the yhm2Δ mutant grew similarly as the YPH499 wild-type strain on synthetic minimal medium (SM) containing 2% glucose and ammonia as the main nitrogen source. In contrast, the yhm2Δodc1Δodc2Δ triple knockout exhibited a marked growth defect under the same conditions. This defect was fully restored by the individual expression of YHM2, ODC1 or ODC2 in the triple deletion strain. Furthermore, the lack of growth of yhm2Δodc1Δodc2Δ on 2% glucose SM was rescued by the addition of glutamate, but not glutamine, to the medium. Using lysine-prototroph YPH499-derived strains, the yhm2Δodc1Δodc2Δ knockout (but not the odc1Δodc2Δ and yhm2Δ mutants) also displayed a growth defect in lysine biosynthesis on 2% glucose SM, which was rescued by the addition of lysine and, to a lesser extent, by the addition of 2-aminoadipate. Additional analysis of the triple mutant showed that it is not respiratory-deficient and does not display mitochondrial DNA instability. These results provide evidence that only the simultaneous absence of YHM2, ODC1 and ODC2 impairs the export from the mitochondrial matrix of i) 2-oxoglutarate which is necessary for the synthesis of glutamate and ammonium fixation in the cytosol and ii) 2-oxoadipate which is required for lysine biosynthesis in the cytosol. Finally, the data presented allow one to suggest that the yhm2Δodc1Δodc2Δ triple knockout is suitable in complementation studies aimed at assessing the pathogenic potential of human SLC25A21 (ODC) mutations.

Inherited eye-related disorders due to mitochondrial dysfunction.

Genetic disorders due to mitochondrial dysfunction are not uncommon and the majority of these patients will have eye-related manifestations, including visual loss from the optic nerve and retinal disease, visual field loss from retrochiasmal visual pathway damage, and ptosis and ocular dysmotility from extraocular muscle involvement. Defects in both the nuclear and mitochondrial genomes cause mitochondrial dysfunction via several mechanisms, including impaired mitochondrial energy production, oxidative stress, mitochondrial DNA instability, abnormalities in the regulation of mitochondrial dynamics and mitochondrial quality control, and disturbed cellular interorganellar communication. Advances in our understanding of the molecular genetic basis of mitochondrial disease have not only improved genetic diagnosis, but they have provided important insights into the pathophysiologic basis of these disorders and potential therapeutic targets. In parallel, more sophisticated techniques for genetic manipulation are facilitating the development of animal and in vitro models that should prove powerful and versatile tools for disease modelling and therapeutic experimentation. Effective therapies for mitochondrial disorders are beginning to translate from bench to bedside along the paths of neuroprotection, gene replacement and stem cell-based regenerative paradigms. Additionally, preventing the transmission of pathogenic mtDNA mutations from mother to child is now a reality with in vitro fertilization mitochondrial replacement techniques.

Role of Tim17 Transmembrane Regions in Regulating the Architecture of Presequence Translocase and Mitochondrial DNA Stability.

Mitochondrial life cycle and protein import are intricate cellular processes, which require precise coordination between the transport machineries of outer and inner mitochondrial membranes. Presequence translocase performs the indispensable function of translocating preproteins having N-terminal targeting sequences across the inner membrane. Tim23 forms the core of the voltage-gated import channel, while Tim17 is presumed to maintain the stoichiometry of the translocase. However, mechanistic insights into how Tim17 coordinates these regulatory events within the complex remained elusive. We demonstrate that Tim17 harbors conserved G/AXXXG/A motifs within its transmembrane regions and plays an imperative role in the translocase assembly through interaction with Tim23. Tandem motifs are highly essential, as most of the amino acid substitutions lead to nonviability due to the complete destabilization of the TIM23 channel. Importantly, Tim17 transmembrane regions regulate the dynamic assembly of translocase to form either the TIM23 (PAM)-complex or TIM23 (SORT)-complex by recruiting the presequence translocase-associated motor (PAM) machinery or Tim21, respectively. To a greater significance, tim17 mutants displayed mitochondrial DNA (mtDNA) instability, membrane potential loss, and defective import, resulting in organellar dysfunction. We conclude that the integrity of Tim17 transmembrane regions is critical for mitochondrial function and protein turnover.

Ovarian ageing: the role of mitochondria in oocytes and follicles.

There is a great inter-individual variability of ovarian ageing, and almost 20% of patients consulting for infertility show signs of premature ovarian ageing. This feature, taken together with delayed childbearing in modern society, leads to the emergence of age-related ovarian dysfunction concomitantly with the desire for pregnancy. Assisted reproductive technology is frequently inefficacious in cases of ovarian ageing, thus raising the economic, medical and societal costs of the procedures. Ovarian ageing is characterized by quantitative and qualitative alteration of the ovarian oocyte reserve. Mitochondria play a central role in follicular atresia and could be the main target of the ooplasmic factors determining oocyte quality adversely affected by ageing. Indeed, the oocyte is the richest cell of the body in mitochondria and depends largely on these organelles to acquire competence for fertilization and early embryonic development. Moreover, the oocyte ensures the uniparental transmission and stability of the mitochondrial genome across the generations. This review focuses on the role played by mitochondria in ovarian ageing and on the possible consequences over the generations. PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews concerning mitochondria and ovarian ageing, in animal and human species. Searches were performed using keywords belonging to three groups: 'mitochondria' or 'mitochondrial DNA'; 'ovarian reserve', 'oocyte', 'ovary' or 'cumulus cells'; and 'ageing' or 'ovarian ageing'. These keywords were combined with other search phrases relevant to the topic. References from these articles were used to obtain additional articles. There is a close relationship, in mammalian models and humans, between mitochondria and the decline of oocyte quality with ageing. Qualitatively, ageing-related mitochondrial (mt) DNA instability, which leads to the accumulation of mtDNA mutations in the oocyte, plays a key role in the deterioration of oocyte quality in terms of competence and of the risk of transmitting mitochondrial abnormalities to the offspring. In contrast, some mtDNA haplogroups are protective against the decline of ovarian reserve. Quantitatively, mitochondrial biogenesis is crucial during oogenesis for constituting a mitochondrial pool sufficiently large to allow normal early embryonic development and to avoid the untimely activation of mitochondrial biogenesis. Ovarian ageing also seriously affects the dynamic nature of mitochondrial biogenesis in the surrounding granulosa cells that may provide interesting alternative biomarkers of oocyte quality. A fuller understanding of the involvement of mitochondria in cases of infertility linked to ovarian ageing would contribute to a better management of the disorder in the future.

Cancer-associated isocitrate dehydrogenase mutations induce mitochondrial DNA instability.

A major advance in understanding the progression and prognostic outcome of certain cancers, such as low-grade gliomas, acute myeloid leukaemia, and chondrosarcomas, has been the identification of early-occurring mutations in the NADP+-dependent isocitrate dehydrogenase genes IDH1 and IDH2 These mutations result in the production of the onco-metabolite D-2-hydroxyglutarate (2HG), thought to contribute to disease progression. To better understand the mechanisms of 2HG pathophysiology, we introduced the analogous glioma-associated mutations into the NADP+ isocitrate dehydrogenase genes (IDP1, IDP2, IDP3) in Saccharomyces cerevisiae Intriguingly, expression of the mitochondrial IDP1R148H mutant allele results in high levels of 2HG production as well as extensive mtDNA loss and respiration defects. We find no evidence for a reactive oxygen-mediated mechanism mediating this mtDNA loss. Instead, we show that 2HG production perturbs the iron sensing mechanisms as indicated by upregulation of the Aft1-controlled iron regulon and a concomitant increase in iron levels. Accordingly, iron chelation, or overexpression of a truncated AFT1 allele that dampens transcription of the iron regulon, suppresses the loss of respirative capacity. Additional suppressing factors include overexpression of the mitochondrial aldehyde dehydrogenase gene ALD5 or disruption of the retrograde response transcription factor RTG1 Furthermore, elevated α-ketoglutarate levels also suppress 2HG-mediated respiration loss; consistent with a mechanism by which 2HG contributes to mtDNA loss by acting as a toxic α-ketoglutarate analog. Our findings provide insight into the mechanisms that may contribute to 2HG oncogenicity in glioma and acute myeloid leukaemia progression, with the promise for innovative diagnostic and prognostic strategies and novel therapeutic modalities.

CHCHD10 mutations promote loss of mitochondrial cristae junctions with impaired mitochondrial genome maintenance and inhibition of apoptosis.

CHCHD10-related diseases include mitochondrial DNA instability disorder, frontotemporal dementia-amyotrophic lateral sclerosis (FTD-ALS) clinical spectrum, late-onset spinal motor neuropathy (SMAJ), and Charcot-Marie-Tooth disease type 2 (CMT2). Here, we show that CHCHD10 resides with mitofilin, CHCHD3 and CHCHD6 within the "mitochondrial contact site and cristae organizing system" (MICOS) complex. CHCHD10 mutations lead to MICOS complex disassembly and loss of mitochondrial cristae with a decrease in nucleoid number and nucleoid disorganization. Repair of the mitochondrial genome after oxidative stress is impaired in CHCHD10 mutant fibroblasts and this likely explains the accumulation of deleted mtDNA molecules in patient muscle. CHCHD10 mutant fibroblasts are not defective in the delivery of mitochondria to lysosomes suggesting that impaired mitophagy does not contribute to mtDNA instability. Interestingly, the expression of CHCHD10 mutant alleles inhibits apoptosis by preventing cytochromec release.

Understanding the role of mtDNA in tumor progression

Metabolic reprogramming mediated by nuclear and mitochondrial DNA instability of tumor cells has been pointed as a hallmark of cancer progression. Next-generation sequencing (NGS) platforms have become a powerful tool to explore the impact of genomic instability in the metabolic reprogramming of tumor cells. Here, we propose that the usage of NGS technology can accurately quantify mitochondrial genome instability by assessing some features as mitochondrial mutations, heteroplasmy levels, and mtDNA copy number variations. The evaluation of those parameters joined with nDNA information can improve the understanding of the mitochondrial role in cancer.

Genes and Pathways Involved in Adult Onset Disorders Featuring Muscle Mitochondrial DNA Instability

Replication and maintenance of mtDNA entirely relies on a set of proteins encoded by the nuclear genome, which include members of the core replicative machinery, proteins involved in the homeostasis of mitochondrial dNTPs pools or deputed to the control of mitochondrial dynamics and morphology. Mutations in their coding genes have been observed in familial and sporadic forms of pediatric and adult-onset clinical phenotypes featuring mtDNA instability. The list of defects involved in these disorders has recently expanded, including mutations in the exo-/endo-nuclease flap-processing proteins MGME1 and DNA2, supporting the notion that an enzymatic DNA repair system actively takes place in mitochondria. The results obtained in the last few years acknowledge the contribution of next-generation sequencing methods in the identification of new disease loci in small groups of patients and even single probands. Although heterogeneous, these genes can be conveniently classified according to the pathway to which they belong. The definition of the molecular and biochemical features of these pathways might be helpful for fundamental knowledge of these disorders, to accelerate genetic diagnosis of patients and the development of rational therapies. In this review, we discuss the molecular findings disclosed in adult patients with muscle pathology hallmarked by mtDNA instability.

Reactive Oxygen Species and Mitochondrial DNA Damage and Repair in BCR-ABL1 Cells Resistant to Imatinib.

Imatinib revolutionized the therapy of chronic myeloid leukemia (CML), but the resistance to it became an emerging problem. We reported previously that CML cells expressing the BCR/ABL1 fusion gene, accumulated a high level of reactive oxygen species (ROS) due to deregulated mitochondrial electron transport chain, which in turn led to genomic instability, resulting in imatinib resistance. In the present work, we hypothesize that imatinib-resistant cells may show higher instability of mitochondrial DNA (mtDNA) than their sensitive counterparts. To verify this hypothesis, we checked the ROS level and mtDNA damage and repair in model CML cells sensitive and resistant to imatinib and exposed to doxorubicin (DOX), a DNA-damaging agent. The extent of endogenous ROS in imatinib-resistant cells was higher than in their sensitive counterparts and DOX potentiated this relationship. ROS level in cells with primary resistance, which resulted from the T315I mutation in BCR/ABL1, was higher than in cells with acquired resistance. DOX-induced mtDNA damage in T315I imatinib-resistant cells was more pronounced than in imatinib-sensitive cells. All kinds of cells were repairing mtDNA damage with similar kinetics. In conclusion, imatinib-resistant cells can show increased instability of mtDNA, which can result from increased ROS production.