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Results for “mtDNA copy number”

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PubMed2024

Age-induced changes in skeletal muscle mitochondrial DNA synthesis, quantity, and quality in genetically unique rats.

Mitochondrial genomic integrity is a key element of physiological processes and health. Changes in the half-life of the mitochondrial genome are implicated in the generation and accumulation of age-induced mitochondrial DNA (mtDNA) mutations, which are implicated in skeletal muscle aging and sarcopenia. There are conflicting data on the half-life of mtDNA, and there is limited information on how aging affects half-life in skeletal muscle. We hypothesized that skeletal muscle mtDNA synthesis rates would decrease with age in both female and male rats concomitant with changes in mtDNA integrity reflected in mtDNA copy number and mutation frequency. We measured mitochondrial genome half-life using stable isotope labeling over a period of 14 days and assessed mtDNA copy number and deletion mutation frequency using digital PCR in the quadriceps muscle of 9-month-old and 26-month-old male and female OKC-HET rats. We found a significant age-related increase in mtDNA half-life, from 132 days at 9 months to 216 days at 26 months of age in OKC-HET quadriceps. Concomitant with the increase in mtDNA half-life, we found an age-related increase in mtDNA deletion mutation frequency in both male and female rats. Notably, 26-month-old female rats had a lower mutation frequency than male rats, and there were no changes in mtDNA copy number with sex, age, or mitochondrial genotype. These data reveal several key findings: (1) mtDNA turnover in rat skeletal muscle decreases with age, (2) mtDNA half-lives in skeletal muscle are approximately an order of magnitude longer than what is reported for other tissues, and (3) muscle mtDNA turnover differs significantly from the turnover of other mitochondrial macromolecules including components of the mitochondrial nucleoid. These findings provide insight into the factors driving age-induced mtDNA mutation accumulation, which contribute to losses of mitochondrial genomic integrity and may play a role in skeletal muscle dysfunction.

Animals↗

PubMed2026

"Tissue-specific mitochondrial dysfunction in keratoconus: An integrated structural, genomic, and functional analysis".

PURPOSE: Keratoconus (KC) is a progressive corneal ectasia characterized by stromal thinning, conical protrusion, and irregular astigmatism, leading to visual impairment. Although oxidative stress is implicated in KC, the role of mitochondrial dysfunction remains unclear. We evaluated mitochondrial structural, genomic, and functional abnormalities in corneal tissues and blood from KC patients. METHODS: This prospective study enrolled 110 KC patients and 55 controls. Transmission electron microscopy (TEM) and immunohistochemistry (IHC) were performed on epithelial and stromal tissues from 10 KC to 5 control corneas assessing mitochondrial morphology, oxidative phosphorylation (OXPHOS) complexes and pro-apoptotic protein NOXA. Whole mitochondrial DNA (mtDNA) sequencing and relative mtDNA copy number analysis were performed on paired blood and corneal tissues from 50 KC patients and 35 controls including both epithelial and stromal samples. Gene expression of mitochondrial biogenesis and oxidative stress-related genes was analysed by qRT-PCR in corneal epithelium from independent 50 KC patients and 15 controls. RESULTS: TEM revealed cristolysis, membrane disruption, and reduced mitochondrial density in KC corneas. IHC showed reduced expression of OXPHOS complexes and increased NOXA expression (p < 0.05). Sequencing identified 1107 mtDNA variants, with more variants in corneal tissues than matched blood (929 vs. 576; p = 0.0002). Recurrent likely pathogenic variants were enriched in complex I-encoding genes (ND4, ND5). KC corneas showed reduced mtDNA copy number, downregulated POLRMT, upregulated NOX4, and significant downregulation of multiple antioxidant genes (p < 0.0001). CONCLUSION: KC patients exhibit tissue-specific mitochondrial abnormalities and impaired oxidative stress regulation, supporting a role for mitochondrial dysfunction in disease pathogenesis and highlighting potential therapeutic targets.

Corneal pathology↗

PubMed2026

Protocol for Duplex Sequencing of Mitochondrial DNA in Single Human Oocytes.

Oocytes are densely packed with mitochondria, the energy-producing organelles that contain their own genome, mitochondrial DNA (mtDNA). Each cell contains multiple copies of mtDNA, with copy number varying among tissue types. Oocytes possess the highest mtDNA copy number, containing hundreds of thousands of mtDNA molecules per cell. Because mitochondria are inherited exclusively through the maternal lineage, accurate detection of mtDNA variants is essential for studies of inheritance, aging, and disease. The presence of multiple mtDNA copies allows wild-type and mutant molecules to coexist within the same cell, a condition known as heteroplasmy, in which low-frequency and de novo variants may occur at frequencies below 1%. Conventional next-generation sequencing (NGS) lacks sufficient accuracy to reliably distinguish these rare variants from errors introduced during library preparation and sequencing. Here, we present a protocol for enriching mtDNA from single human oocytes using Exonuclease V to remove linear DNA, followed by duplex sequencing library preparation for highly accurate mtDNA analysis. This workflow enables error-corrected sequencing of individual oocytes, facilitating reliable detection of low-frequency mtDNA variants and analysis of heteroplasmy and de novo mutagenesis. The protocol provides a reproducible approach for investigating mitochondrial genome variation in single oocytes using Illumina-compatible sequencing platforms.

Humans↗

PubMed2026

Mitochondrial Haplotype Shapes the Trajectory of Ovarian Aging in Genetically Heterogeneous Rats.

Ovarian aging leads to permanent reproductive senescence and systemic hormonal changes that predispose women to age-associated comorbidities. Despite these observations, the intrinsic mechanisms driving age-related ovarian decline are poorly defined. Mitochondrial DNA (mtDNA) mutations and instability are strongly associated with aging; however, it remains unknown if naturally occurring mitochondrial genetic variation influences the trajectory of ovarian aging. To address this, we compared two genetically heterogeneous rat cohorts (OKC-HETB and OKC-HETW) that differ in mitochondrial haplotype on a randomized but equivalently distributed nuclear background. The OKC-HETW haplotype was associated with accelerated loss of primordial follicles and pathological remodeling marked by fibrosis, macrophage infiltration, and multinucleated giant cells. These tissue-level pathologies were paralleled by mitochondrial dysfunction, characterized by decreased respiratory complex activity, ATP production, and mtDNA copy number. Mechanistically, we identified a haplotype-specific defect in mitochondrial genome maintenance. Although TFAM expression was normal, and total TFAM protein was elevated, OKC-HETW ovaries showed reduced mitochondrial TFAM abundance, TFAM-mtDNA binding, and TOMM20, suggesting that impaired TOMM20-mediated import is associated with compromised mitochondrial genomic stability. Longitudinal transcriptomic and proteomic analyses further indicate that mitochondrial haplotype influences the rate of ovarian aging, with OKC-HETW ovaries showing accelerated activation of inflammatory and fibrotic pathways alongside suppressed proteostasis and mitochondrial function. These defects corresponded to impairments in ovulation and a trend toward worsening oocyte quality. Collectively, our findings identify mitochondrial haplotype as a heritable modifier of ovarian aging rate that acts in concert with the nuclear genome, and a putative target for preserving ovarian function and female healthspan.

Animals↗

PubMed2026

Functional impact of Nth like DNA glycosylase 1 on mitochondrial dynamics.

Nth like DNA glycosylase 1 (NTHL1), a key base excision repair enzyme, has long been considered essential for nuclear and mitochondrial genome integrity. Combining in vitro biochemical assays, in cellulo molecular biology, and bioinformatic analyses, we investigated how NTHL1 loss affects mitochondrial DNA (mtDNA) stability and mitochondrial function. Contrary to the conventional view that mtDNA damage is solely detrimental, we find that NTHL1 loss confers a beneficial, mitochondria-initiated phenotype in human cells. Despite accumulating mtDNA lesions, NTHL1 loss unexpectedly increases mtDNA copy number, elevates oxidative phosphorylation protein levels, and enhances mitochondrial respiration. NTHL1-/- cells also show increased mitochondrial mass and higher levels of the biogenesis regulator PGC1α and the fusion protein OPA1, indicating an adaptive response that boosts mitochondrial function and capacity. Consequently, NTHL1-/- cells exhibit resistance to mitochondrial stress, accompanied by increased eIF2α phosphorylation and reduced MYC levels, converging on a broader transcriptional adaptive program. This phenotype depends on mitochondrial NTHL1 and reactive oxygen species (ROS) signaling, since treatment with ROS scavengers or mitochondria-specific reintroduction of NTHL1 rescues it. Together, these findings position NTHL1 as a key modulator of mtDNA stability and mitochondrial function, revealing that loss of this DNA repair enzyme shifts cellular metabolism toward a stress-adaptive state and enhances resilience to oxidative stress.

Humans↗

PubMed2026

Transmitochondrial pigs reveal causal effects of mitochondrial DNA on backfat thickness via nuclear epigenetic reprogramming.

Mitochondrial DNA (mtDNA) polymorphisms have been associated with production traits in farm animals, including backfat thickness in pigs, yet direct in vivo evidence establishing a causal link between specific mtDNA haplotypes and fat deposition remains limited. In this study, we generated transmitochondrial pigs (mitopigs) by combining the Dapulian nuclear genome with Wuzhishan mtDNA via somatic cell nuclear transfer, introducing 23 mtDNA mutations relative to controls. Mitopigs exhibited significantly increased backfat thickness at 5 months, a difference that persisted in their offspring, without significant differences in body weight, body size, or litter size. Fibroblasts derived from mitopigs exhibited reduced mtDNA copy numbers, decreased expression of mitochondrial biogenesis genes (PPARA, PPARGC1A, RRM2B, and LRPPRC), impaired mitochondrial respiration, elevated reactive oxygen species (ROS), and upregulated adipogenic transcription factors (CEBPA, CEBPB, and PPARG). Consistent with these fibroblast findings, backfat tissue of mitopigs showed corresponding upregulation of adipogenic transcription factors and downregulation of mitochondrial biogenesis genes. Integrated transcriptomic and whole-genome bisulfite sequencing (WGBS) analyses revealed nuclear transcriptional reprogramming that was closely associated with differential DNA methylation, predominantly affecting mitochondrial function and lipid metabolism pathways. Mitopig fibroblasts also showed a pro-inflammatory response to lipopolysaccharide stimulation, with elevated expression of IL-12, NOS2, RELA, and TNF-α. Our findings provide direct in vivo evidence that mtDNA variants regulate adiposity in pigs through mitochondrial dysfunction, oxidative stress, and nuclear epigenetic modulation, highlighting the potential for incorporating mtDNA haplotype information into pig breeding programs as a complementary strategy to nuclear genomic selection.

Adipogenesis↗

PubMed2026

Age-related differences in semen quality in Holstein-Friesian bulls: a paired within-bull comparison of early and mature reproductive stages.

Genomic selection has changed dairy cattle breeding by increasing the use of young bulls for artificial insemination and shortening the reproductive lifespan of sires. Under these conditions, semen quality at the beginning of commercial use has become an important practical issue. Semen samples from 39 fertile Holstein-Friesian bulls used for commercial AI were collected between 2013 and 2016, during the introduction of genomic selection in Poland. This paired within-bull study compared semen collected from the same bulls at an early reproductive stage (13-20 months; young bulls, YB) and at full maturity (5-6 years; mature bulls, MB). The evaluation included conventional ejaculate traits, CASA-derived motility and kinematic descriptors, mtDNA copy number, and mitochondrial content per sperm cell. Importantly, all ejaculates met the quality requirements for commercial insemination. Ejaculate volume, sperm concentration, mitochondrial DNA copy number, and mitochondrial content did not differ significantly between age groups. The CASA-derived sperm movement profile, in contrast, differed with age. Semen from young bulls showed a higher proportion of progressively motile spermatozoa, whereas semen from mature bulls showed higher velocity-related parameters, including VSL, VCL, and STR. These findings indicate that bull age mainly affected sperm movement characteristics rather than semen output or mitochondrial content. Overall, the results support the use of young bulls in artificial insemination programs and show that age-related differences in semen quality are expressed mainly through changes in the post-thaw sperm motility and kinematic profile.

Animals↗

PubMed2026

Mitochondrial DNA in lung cancer: From biology to clinical implications.

Mitochondrial DNA (mtDNA) is emerging as a relevant component of the molecular landscape in non-small cell lung cancer (NSCLC). Due to its inherent vulnerability to environmental carcinogens, the mitochondrial genome accumulates alterations-such as D-loop and Electron Transport Chain variants- increasingly identified as potential mediators of tumor development and metabolic shifts. Recent findings highlight potential clinical applications of mtDNA. In diagnostics, emerging models based on cf-mtDNA fragmentomics and tRNA-derived fragments have shown promising capabilities for early-stage diagnosis. Prognostically, somatic variants in Complex I and specific mitochondrial lncRNA signatures have been evaluated as independent indicators of overall survival and metastatic risk. Furthermore, mitochondrial mass may potentially support chemotherapy election. Additionally, horizontal transfer of mitochondria to tumor-infiltrating lymphocytes offers a novel framework for understanding resistance to immunotherapy. While these preliminary results provide a promising roadmap for molecular stratification, their integration into routine practice remains a goal that requires further prospective validation in larger, multi-ethnic cohorts to ensure reproducibility and to distinguish functional drivers from passenger variants. Collectively, these emerging findings suggest that mtDNA analysis represents a valuable complementary approach to precision oncology in lung cancer.

Humans↗

PubMed2026

A Novel SLC25A4 Variant Causing Mitochondrial Dysfunction, Myopathy and Cardiomyopathy: A Functional and Molecular Characterization.

SLC25A4, solute carrier family 25 member 4, gene is a member of the mitochondrial carrier subfamily within the solute carrier protein family. Pathogenic variants in SLC25A4 are associated with a spectrum of mitochondrial disorders that exhibit variable inheritance patterns and clinical manifestations. Specifically, dominantly inherited variants are typically associated with progressive external ophthalmoplegia with mitochondrial DNA deletions, recessively inherited variants are linked to myopathy and cardiomyopathy, and de novo variants can result in early-onset fatal disease presentations. In this study, we aimed to identify and characterize the disease-causing mutation(s) in a nine-year-old female patient from a consanguineous Saudi family. The patient was asymptomatic until the age of 3 years, when she presented with cardiomyopathy and myopathy. Comprehensive genetic analysis inclusive of whole exome sequencing and segregation analysis using Sanger sequencing identified an SLC25A4 variant (NM_001151.4: exon 2: c.112-1G>C) as the most likely cause of the disease. To assess transcript-level effects, we performed RT-PCR on RNA extracted from the patient's cultured lymphoblast cell lines (LCLs) and fibroblast cell lines (FCLs). RT-PCR analysis demonstrated that the variant causes aberrant splicing, resulting in a 6 bp in-frame deletion (p.Gln37_Val38del) in the ANT1 protein. Quantitative RT-PCR demonstrated reduced SLC25A4 transcript levels in both FCLs and LCLs. Quantitative PCR analysis of mitochondrial DNA demonstrated a trend toward increased mtDNA copy number in patient-derived FCLs compared with controls, suggesting a possible compensatory response to mitochondrial dysfunction. Furthermore, Seahorse assays revealed marked reductions in both oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in patient-derived FCLs compared with controls. These findings expand the molecular and functional spectrum of SLC25A4-associated disease and may inform clinical practice, including genetic interventions such as preimplantation genetic diagnosis, premarital genetic screening, targeted genetic counseling, and cascade testing of at-risk family members.

Humans↗

PubMed2026

Accurate quantification of canine mitochondrial DNA copy number from canine blood and brain samples.

Acute brain injury is difficult to evaluate in veterinary medicine and tools to investigate the potential involvement of mitochondrial involvement are limited. The brain is highly enriched in mitochondria and contains thousands of copies of mitochondrial DNA (mtDNA) per cell, but robust methods for quantifying mitochondrial DNA copy number (mtDNA-CN) in canine tissues are lacking. We describe the development of a quantitative real-time PCR assay for absolute measurement of mtDNA-CN which was validated in canine blood and brain tissue. To minimize amplification of nuclear mitochondrial insertion sequences (NumtS) and repetitive regions, species-specific oligonucleotide primers were designed following in silico genomic filtering. The assay was applied to a small pilot cohort comprising blood samples from dogs with and without acute brain injury (n = 4-6 per group) and cerebral cortex samples (n = 1 per group) to assess feasibility and biological plausibility. In non-brain injury dogs, blood mtDNA-CN ranged from 98 to 288 copies per nuclear genome (mean 193 ± 72), while values in brain-injured cases ranged from 163 to 228 copies per genome (mean 200 ± 33). Cerebral cortex samples exhibited higher mtDNA-CN than blood, consistent with known tissue-specific mitochondrial enrichment. In a single brain-injured case with serial sampling, mtDNA-CN increased over five days. This study presents a validated assay and pilot data for mtDNA-CN quantification in canine samples. While not powered for biomarker evaluation, this method may enable future studies of mitochondrial dynamics in canine brain injury and metabolic disease.

Animals↗

PubMed2025

Absolute Quantification of Cellular and Cell-Free Mitochondrial DNA Copy Number from Human Blood and Urinary Samples Using Real Time Quantitative PCR.

Mitochondrial DNA copy number (mtDNA-CN) in human body fluids is widely used as a biomarker of mitochondrial dysfunction in common metabolic diseases. Here we describe protocols to measure cellular and/or cell free (cf)-mtDNA-CN in human peripheral blood and urine. Cellular mtDNA is located inside the mitochondria where it encodes key subunits of the respiratory complexes in mitochondria and is usually normalized with reference to the nuclear genome as the mitochondrial genome to nuclear genome ratio (Mt/N) in either whole blood, peripheral blood mononuclear cells (PBMCs), or whole urine. Cf -mtDNA is usually found outside of the mitochondria, often released following mitochondrial damage, can trigger inflammatory pathways, and is usually measured as mtDNA-CN per volume of the starting material. Here we describe how to (1) separate whole blood into PBMCs, plasma, and serum fractions and whole urine into urinary supernatant and pellet, (2) prepare DNA from each of these fractions, (3) prepare reference standards for absolute quantification, (4) carry out qPCR for either relative or absolute quantification from test samples, (5) analyze qPCR data, and (6) calculate the sample size to adequately power studies. The protocol presented here is suitable for high throughput use and can be modified to quantify mtDNA from other body fluids, human cells, and tissues.

Humans↗

PubMed2025

Multiple features of cell-free mtDNA for predicting transarterial chemoembolization response in hepatocellular carcinoma.

BACKGROUND: Transarterial chemoembolization (TACE) is the primary treatment modality for advanced HCC, yet its efficacy assessment and prognosis prediction largely depend on imaging and serological markers that possess inherent limitations in terms of real-time capability, sensitivity, and specificity. Here, we explored whether multiple features of cell-free mitochondrial DNA (cf-mtDNA), including copy number, mutations, and fragmentomics, could be used to predict the response and prognosis of patients with HCC undergoing TACE treatment. METHODS: A total of 60 plasma cell-free DNA samples were collected from 30 patients with HCC before and after the first TACE treatment and then subjected to capture-based mtDNA sequencing and whole-genome sequencing. RESULTS: Comprehensive analyses revealed a clear association between cf-mtDNA multiple features and tumor characteristics. Based on cf-mtDNA multiple features, we also developed HCC death and progression risk prediction models. Kaplan-Meier curve analyses revealed that the high-death risk or high-progression-risk group had significantly shorter median overall survival (OS) and progression-free survival than the low-death risk or low-progression-risk group (all p<0.05). Moreover, the change in cf-mtDNA multiple features before and after TACE treatment exhibited an exceptional ability to predict the risk of death and progression in patients with HCC (log-rank test, all p<0.01; HRs: 0.36 and 0.33, respectively). Furthermore, we observed the consistency of change between the cf-mtDNA multiple features and copy number variant burden before and after TACE treatment in 40.00% (12/30) patients with HCC. CONCLUSIONS: Altogether, we developed a novel strategy based on profiling of cf-mtDNA multiple features for prognosis prediction and efficacy evaluation in patients with HCC undergoing TACE treatment.

Humans↗

PubMed2024

Effects of particulate air pollution on BPDE-DNA adducts, telomere length, and mitochondrial DNA copy number in human exhaled breath condensate and BEAS-2B cells.

Traffic-related particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) have been linked to respiratory diseases and cancer risk in humans. Genomic damage, including benzo[a]pyrene diolepoxide (BPDE)-DNA adducts as well as alterations in telomere length (TL) and mitochondrial DNA copy number (mtDNA-CN) are associated with respiratory diseases. This study aimed to investigate the association between exposure to traffic-related particulate pollutants and genomic damage in exhaled breath condensate (EBC) in human subjects and a bronchial epithelial cell line (BEAS-2B). Among the 60 healthy recruited subjects, residents living in high-traffic-congested areas were exposed to higher concentrations of PM2.5 (1.66-fold, p < 0.01), UFPs (1.79-fold, p < 0.01), PM2.5-PAHs (1.50-fold, p < 0.01), and UFPs-PAHs (1.35-fold, p < 0.05), than those in low-traffic-congested areas. In line with increased exposure to particulate air pollution, the high-traffic-exposed group had significantly increased BPDE-DNA adducts (1.40-fold, p < 0.05), TL shortening (1.24-fold, p < 0.05), and lower mtDNA-CN (1.38-fold, p < 0.05) in EBC. The observations in the human study linking exposure to PM2.5, UFPs, PM2.5-PAHs, and UFPs-PAHs with the aforementioned biological effects were confirmed by an in vitro cell-based study, in which BEAS-2B cells were treated with diesel exhaust particulate matter (DEP) containing fine and ultrafine PM and PAHs. Increased BPDE-DNA adducts levels, shortened TL, and decreased mtDNA-CN were also found in treated BEAS-2B cells. The shortened TL and decreased mtDNA-CN were in part mediated by decreased transcript levels of hTERT, and SIRT1, which are involved in telomerase activity and mitochondrial biogenesis, respectively. These results suggest that exposure to traffic-related particulate pollutants can cause genomic instability in respiratory cells, which may increase the health risk of respiratory diseases and the development of cancer.

Humans↗

PubMed2026

Alterations of endothelial cell bioenergetics in congenital diaphragmatic hernia.

BACKGROUND: Pulmonary vascular development in congenital diaphragmatic hernia (CDH) is characterized by impaired angiogenesis and pathologic remodeling that contribute to pulmonary hypertension/hypoplasia. Mitochondria regulate endothelial energy, redox balance, and angiogenic signaling, suggesting a role in CDH vascular disease. METHODS: Endothelial cells (ECs) were isolated from umbilical veins of healthy and CDH newborns. Mitochondrial bioenergetics and glycolytic acidification were assessed by extracellular flux. Oxidative stress, mitochondrial membrane potential, and mitochondrial mass were measured by flow cytometry, while mitochondrial DNA copy number (mtDNA-CN) and morphology were evaluated by qPCR and microscopy. RESULTS: CDH ECs exhibited increased maximal respiratory capacity with elevated proton leak and reduced ATP coupling efficiency. Basal glycolytic activity was elevated. These changes were accompanied by increased mitochondrial superoxide and cellular reactive oxygen species and by severity-associated loss of membrane potential. Despite reduced MitoTracker Green, mtDNA-CN was unchanged, and confocal imaging revealed a highly branched, peripherally distributed network. CONCLUSIONS: These data define a distinct endothelial mitochondrial phenotype marked by metabolic activation, bioenergetic inefficiency, and oxidative stress, with concurrent upregulation of glycolysis and oxidative phosphorylation rather than a glycolytic shift. Structural remodeling with preserved mitochondrial content further indicates qualitative changes. Collectively, these findings link mitochondrial dysfunction to vascular pathology in CDH. IMPACT: Defines a distinct mitochondrial state in CDH endothelium, characterized by metabolic activation with inefficient oxidative phosphorylation, redox imbalance, and structural reorganization in primary human cells. Demonstrates that mitochondrial alterations in CDH occur without changes in mitochondrial content, supporting a model of qualitative remodeling. Provides rare human, cell-based data in CDH, addressing a major gap in a field largely reliant on animal models and indirect measures. Links mitochondrial alterations to clinical severity, supporting relevance to disease burden and heterogeneity. Establishes a framework for mitochondrial involvement in CDH vascular disease, with potential implications for future biomarker development and therapeutic targeting.

Journal Article↗

PubMed2026

A Cooperative Release of Mitochondrial DNA From Platelets and Neutrophils Drives an Interferon Signature in Systemic Sclerosis.

OBJECTIVE: Mitochondria are organelles with a hypomethylated circular genome. Mitochondrial DNA (mtDNA) in the systemic circulation has been implicated in inflammation. This study investigates the role of circulating DNA in systemic sclerosis (SSc) and the cellular mechanisms governing its release. METHODS: Total DNA was isolated from the plasma of healthy controls (HCs) and patients with SSc. Copy numbers were analyzed for mtDNA (ATP-6) and GAPDH abundance by quantitative real-time polymerase chain reaction. mtDNA was isolated from HCs and patients with SSc. Neutrophils and platelets were incubated with the plasma and mtDNA of patients with SSc, and neutrophil extracellular trap (NET) formation was assessed by SytoxGreen and immunostainings. Platelets were tested for mtDNA release propensity. DNA oxidation was evaluated by MitoSOX Red staining in vitro and 8-OHdG enzyme-linked immunosorbent assay (ELISA) of patient plasma. Plasma interferon (IFN) type 1 and chemokine (C-X-C motif) ligand 4 (CXCL4) were measured by ELISA. IFN signaling activation capacity was evaluated using THP-1 reporter cells and confirmed by a whole blood bulk RNA transcriptomic analysis. RESULTS: Median plasma mtDNA levels were 152-fold higher in patients with SSc compared with HCs, whereas nuclear DNA levels were similar. mtDNA from SSc plasma was highly oxidized. SSc-derived mtDNA efficiently promoted its own release by NETosis, most potently in the neutrophils of patients with SSc and by platelet activation. Oxidized mtDNA from SSc platelets in complex with CXCL4 further stimulated mtDNA release in both neutrophils and platelets. mtDNA plasma concentrations correlated with type I IFN concentrations in the blood of patients with SSc, and SSc blood exhibited elevated IFN-stimulated gene expression. SSc plasma-derived mtDNA-induced IFN signaling and NET formation via endosomal Toll-like receptors, cyclic GMP-AMP synthase/stimulator of IFN genes, and the JAK/STAT pathway. The type I IFN pathway further promoted NETosis and mtDNA release because IFN receptor and JAK inhibition antagonized the proNETotic effects of IFN. CONCLUSION: SSc plasma is characterized by highly abundant mtDNA, which drives feedback loops amplifying its own release from both neutrophils and platelets. Thus, mtDNA contributes to inflammation and tissue damage in SSc.

Humans↗

PubMed2026

Mechanism of age-related accumulation of mtDNA mutations in human blood.

Accumulation of mutant mitochondrial DNA (mtDNA) heteroplasmy is among the strongest signatures of ageing1. Here we investigated the underlying mechanism by calling mtDNA sequence, mtDNA abundance and mtDNA heteroplasmic variants in human blood using whole-genome sequences from approximately 750,000 individuals. We observed that mtDNA single-nucleotide variants (mtSNVs) accumulate sharply at age 60 years, occur at low levels of heteroplasmy, exhibit little evidence of positive selection and are likely to be predominantly neutral. The mutational spectrum of mtSNVs does not reflect oxidative lesions, as is commonly invoked, but is more consistent with mtDNA replication errors. To understand why mtSNVs become detectable with age, we performed a genome-wide association study for heteroplasmic mtSNV burden, identifying germline variants near TERT, TCL1A and SMC4, all of which have been linked to clonal haematopoiesis (CH)2. Rare-variant analysis also showed that high mtSNV burden is associated with mutations in numerous CH driver genes. These genetic associations persisted even after exclusion of individuals with known CH driver mutations. Our results support a model in which 'cryptic' mtDNA mutations initially arise randomly as replication errors but are undetectable in bulk. They then become apparent only through age-related expansion of cellular clones in blood. We propose that the high copy number and mutation rate of mtDNA make it a sensitive blood-based marker of somatic mosaicism due to CH. Our work mechanistically unifies three prominent signatures of ageing: common germline variants in TERT, CH and observed accrual of mtDNA mutations.

Humans↗

PubMed2024

An easy-to-use pipeline to analyze amplicon-based Next Generation Sequencing results of human mitochondrial DNA from degraded samples.

Genome and transcriptome examinations have become more common due to Next-Generation Sequencing (NGS), which significantly increases throughput and depth coverage while reducing costs and time. Mitochondrial DNA (mtDNA) is often the marker of choice in degraded samples from archaeological and forensic contexts, as its higher number of copies can improve the success of the experiment. Among other sequencing strategies, amplicon-based NGS techniques are currently being used to obtain enough data to be analyzed. There are some pipelines designed for the analysis of ancient mtDNA samples and others for the analysis of amplicon data. However, these pipelines pose a challenge for non-expert users and cannot often address both ancient and forensic DNA particularities and amplicon-based sequencing simultaneously. To overcome these challenges, a user-friendly bioinformatic tool was developed to analyze the non-coding region of human mtDNA from degraded samples recovered in archaeological and forensic contexts. The tool can be easily modified to fit the specifications of other amplicon-based NGS experiments. A comparative analysis between two tools, MarkDuplicates from Picard and dedup parameter from fastp, both designed for duplicate removal was conducted. Additionally, various thresholds of PMDtools, a specialized tool designed for extracting reads affected by post-mortem damage, were used. Finally, the depth coverage of each amplicon was correlated with its level of damage. The results obtained indicated that, for removing duplicates, dedup is a better tool since retains more non-repeated reads, that are removed by MarkDuplicates. On the other hand, a PMDS = 1 in PMDtools was the threshold that allowed better differentiation between present-day and ancient samples, in terms of damage, without losing too many reads in the process. These two bioinformatic tools were added to a pipeline designed to obtain both haplotype and haplogroup of mtDNA. Furthermore, the pipeline presented in the present study generates information about the quality and possible contamination of the sample. This pipeline is designed to automatize mtDNA analysis, however, particularly for ancient samples, some manual analyses may be required to fully validate results since the amplicons that used to be more easily recovered were the ones that had fewer reads with damage, indicating that special care must be taken for poor recovered samples.

DNA, Mitochondrial↗

PubMed2025

Ataxia and oculomotor apraxia caused by a large-scale deletion in the senataxin gene.

Senataxin, an RNA/DNA helicase, is a key protein providing genome stability and one of the best characterized R-loop-binding factors playing an important role in transcription and DNA repair processes. Pathogenic SETX gene variants cause autosomal recessive spinocerebellar ataxia with axonal neuropathy (AOA2, MIM #606002) and autosomal dominant juvenile amyotrophic lateral sclerosis (ALS4, MIM #602433), rare neurodegenerative disorders characterized by juvenile onset of progressive cerebellar ataxia, axonal sensorimotor peripheral neuropathy, combined upper and lower motor neuron symptoms, and increased serum alpha-fetoprotein (AFP; specific for AOA2). We report two cases of adult patients presenting with cerebellar syndrome, scanned speech, and exercise intolerance which started in the second/third decade of life and were followed by muscle weakness and impaired gait coordination. Whole exome sequencing (WES) was performed to analyze single nucleotide and copy number variants. A decreased coverage of a genomic region of around 16 kb on chromosome 9 (chr9:132,295,852-132,311,876), suggesting a deletion encompassing 5 exons of the SETX gene (exons 11-15, NM_015046.7) was observed. This homozygous SETX (9q34.13) deletion leads to a frame shift and consequently truncation of the helicase domain in the protein. Loss-of-function variants in the SETX gene are known to be pathogenic. Statistical analysis of NGS data from the Polish population identified a few heterozygous carriers, suggesting its region-specific origin.

Humans↗