A systematic review on the association of mitochondrial DNA copy number (mtDNA-CN) with Alzheimer's disease (AD) and Parkinson disease (PD) is lacking and the causal relationship remains unclear.

We aimed to conduct a systematic review of observational studies on the association of mtDNA-CN with AD and PD and perform a bidirectional 2-sample Mendelian randomization (MR) study to investigate their causal relationships.

PubMed, Embase, and Web of Science were searched for eligible studies before Jan 2025. The causal links were conducted with inverse-variance weighted (IVW) method as the main analysis.

Fourteen case-control and 2 cohort studies investigated the association between mtDNA-CN and AD, with 13 reporting decreased mtDNA-CN associated with increased risk of AD and 3 showing no significant association. All the studies (9 case-control, 1 cross-sectional, 2 cohort studies) observed the relation between mtDNA-CN and PD except for 3 studies reporting no significant association. In MR analysis, genetically predicted mtDNA-CN was not associated with AD and PD, whereas genetically predicted AD (β -0.085, 95 % CI -0.156 to -0.013; P = 0.02) but not PD was associated with mtDNA-CN. Sensitivity and replication analyses showed a stable finding.

The systematic review found limited observational studies on mtDNA-CN and AD and PD and majority were case-control study. Findings of the bidirectional MR study did not support a causal effect of mtDNA-CN in the development of AD and PD but found that AD can lead to decreased levels of mtDNA-CN, which suggest mtDNA-CN as a potential biomarker of AD.

Mitochondria have their own genome (mtDNA), which in humans is a circular multi-copy genome consisting of 16 569 base pairs. Abnormalities in the mtDNA have been reported to correlate with various age-related pathophysiologies.

Based on a total of 182 DNA samples extracted from gastric cancer tissues, we measured mtDNA copy numbers (mtDNA-CN) using real-time polymerase chain reaction (PCR) and then examined alongside sex, age, tumor stage, Laurén classification, and the overexpression of Human Epidermal Growth Factor Receptor 2 (HER2).

We found no sex differences in mtDNA-CN and no correlation with age, but significant differences according to tumor stage. The mtDNAcn of intestinal type by Laurén classification was significantly larger than that of diffuse type. There was no significant difference in mtDNA-CN between HER2-positive and -negative tissues. Multiple regression analyses showed that only the tumor stage was a significant variable, while Laurén classification was not.

These results indicate that mitochondrial genomic abnormalities contribute the progression of gastric cancer independently of HER2 overexpression, and may shed light on the emerging role of mtDNA-CN in situ as a possible biomarker for estimating cancer progression.

Mitochondria are membrane-bound organelles of eukaryotic cells that play crucial roles in cell functioning and homeostasis, including ATP generation for cellular energy. Mitochondrial function is associated with several complex diseases and disorders, including cardiovascular, cardiometabolic, neurodegenerative diseases and some cancers. The risk for these diseases and disorders is often associated with mitochondrial dysfunction, particularly the quantitative and qualitative features of the mitochondrial genome. Emerging results implicate mito-nuclear crosstalk as the mechanism by which mtDNA variation affects complex disease outcomes. Experimental approaches are emerging for the targeting of mitochondria as a potential therapeutic for several of these diseases, particularly in the form of mitochondrial transplantation. Current approaches to mitochondrial transplantation generally involve isolating healthy mitochondria from donor cells and introducing them to diseased recipients towards amelioration of mitochondrial dysfunction. Using such a protocol, several reports have shown recovery of mitochondrial function and improved disease outcomes post-mitochondrial transplantation, highlighting its potential as a therapeutic method for several complex, severe and debilitating diseases. Additionally, the mitochondrial genome can be modified prior to transplantation to target disease-associated site-specific mutations and to reduce the ratio of mutant-to-WT alleles. These promising results may underlie the potential impact of mitochondrial transplantation on mito-nuclear genome interactions in the setting of the disease. Further, we recommend that mitochondrial transplantation experimentation include an assessment of potential impacts on remodelling of the nuclear genome, particularly the nuclear epigenome and transcriptome. Herein, we review these and other triumphs and challenges of mitochondrial transplantation as a potential novel therapeutic for mitochondria-associated diseases.

This study aims to investigate the causal relationship between Mitochondrial DNA (mtDNA) copy number and several common neurodegenerative diseases (NDs).

We conducted a bidirectional two-sample Mendelian randomization (MR) analysis using data from genome-wide association studies (GWAS) as instrumental variables (IVs). After screening for relevance and potential confounders, we estimated the association between mtDNA copy number and NDs, including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), and Multiple sclerosis (MS). Additionally, we validated our findings using GWAS data on mtDNA copy number from Longchamps et al., sourced from the Genetics Epidemiology Consortium and the UK Biobank (UKB) aging study cohort.

A GWAS analysis of 395,718 UKB participants found no significant association between mtDNA copy number and the risk of NDs, including AD (OR = 0.956, P = 0.708), PD (OR = 1.223, P = 0.179), ALS (OR = 0.972, P = 0.374), and MS (OR = 0.932, P = 0.789). Similarly, reverse MR analysis revealed no significant relationship between genetic predictions of NDs and mtDNA copy number: AD (OR = 0.987, P = 0.062), PD (OR = 0.997, P = 0.514), ALS (OR = 0.974, P = 0.706), and MS (OR = 1.003, P = 0.181).

Although mitochondrial dysfunction is implicated in the pathogenesis of NDs, no clear evidence supports a causal role for mtDNA copy number. The relationship between mtDNA copy number and NDs is likely mediated by more complex molecular regulatory mechanisms. Further research is required to elucidate these intricate interactions.

Single-cell transcriptomics has transformed our understanding of cellular diversity, yet noise from technical artifacts and low-quality cells can obscure key biological signals. A common practice is filtering out cells with a high percentage of mitochondrial RNA counts (pctMT), typically indicative of cell death. However, commonly used filtering thresholds, primarily derived from studies on healthy tissues, may be overly stringent for malignant cells, which often naturally exhibit higher baseline mitochondrial gene expression.

We examine nine public single-cell RNA-seq datasets from various cancers, including 441,445 cells from 134 patients, and public spatial transcriptomics data, assessing the viability of malignant cells with high pctMT. Our analysis reveals that malignant cells exhibit significantly higher pctMT than nonmalignant cells, without a notable increase in dissociation-induced stress scores. Malignant cells with high pctMT show metabolic dysregulation, including increased xenobiotic metabolism, relevant to therapeutic response. Analysis of pctMT in cancer cell lines further reveals links to drug resistance. We also observe associations between pctMT and malignant cell transcriptional heterogeneity, as well as patient clinical features.

This study provides insights into the functional characteristics of malignant cells with elevated pctMT, challenging current quality control practices in tumor single-cell RNA-seq analyses and offering potential improvements in data interpretation for future cancer studies.

Mitochondrial function influences Parkinson's disease (PD) through the accumulation of pathogenic alpha-synuclein, oxidative stress, impaired autophagy, and neuroinflammation. The mitochondrial DNA copy number (mtDNA-CN), representing the number of mitochondrial DNA copies within a cell, serves as an easily assessable proxy for mitochondrial function.

This study aimed to assess the diagnostic and prognostic capabilities of mtDNA-CN in PD.

We assessed mtDNA-CN in blood samples using whole genome sequencing from 405 patients with PD and 200 healthy controls (HC). We examined the relationship between mtDNA-CN levels and motor symptom severity in PD, as well as their association with dementia development in patients with early-PD (within 3 years of diagnosis).

mtDNA-CN levels were significantly lower in patients with PD compared with HC (P = 1.1 × 10-5). A negative correlation was discovered between mtDNA-CN level and motor severity in PD (correlation coefficient = -0.20; P = 0.008). Among 210 patients with early-PD, Cox regression analysis demonstrated an association between lower mtDNA-CN levels and a higher risk of developing dementia (hazard ratio [HR] = 0.41, 95% confidence interval: 0.20-0.86, P = 0.02), even after adjusting for age and blood cell count (HR = 0.41, 95% confidence interval: 0.18-0.92, P = 0.03). However, mtDNA-CN levels did not significantly correlate with motor progression in PD.

Our findings suggest that blood mtDNA-CN may function as a diagnostic biomarker for PD and a prognostic marker for dementia in patients with PD. © 2025 International Parkinson and Movement Disorder Society.

Mitochondria are multifaceted organelles with crucial roles in energy generation, cellular signalling and a range of synthesis pathways. The study of mitochondrial biology is complicated by its own small genome, which is matrilineally inherited and not subject to recombination, and present in multiple, possibly different, copies. Recent methodological developments have enabled the analysis of mitochondrial DNA (mtDNA) in large-scale cohorts and highlight the far-reaching impact of mitochondrial genetic variation. Genome-editing techniques have been adapted to target mtDNA, further propelling the functional analysis of mitochondrial genes. Mitochondria are finely tuned signalling hubs, a concept that has been expanded by advances in methodologies for studying the function of mitochondrial proteins and protein complexes. Mitochondrial respiratory complexes are of dual genetic origin, requiring close coordination between mitochondrial and nuclear gene-expression systems (transcription and translation) for proper assembly and function, and recent findings highlight the importance of the mitochondria in this bidirectional signalling.

Alzheimer's disease (AD) is a progressive degenerative disease that affects a growing number of elderly individuals worldwide. OAB-14, a novel chemical compound developed by our research group, has been approved by the China Food and Drug Administration (FDA) for clinical trials in patients with AD (approval no. YD-OAB-220210). Previous studies have shown that OAB-14 enhances cognitive function in APP/PS1 transgenic mice and ameliorates abnormal mitochondrial morphology in the hippocampus. Mitochondrial dysfunction is a major risk factor for the development of AD, and maintaining healthy mitochondrial morphology and function is essential for improving the pathological changes and symptoms of AD. However, the protective effects of OAB-14 on mitochondria in AD and the underlying mechanisms remain unclear. This study aimed to investigate the protective effects of OAB-14 on the mitochondria of APP/PS1 transgenic mice and N2a/APP cells. Treatment with OAB-14 restored impaired mitochondrial function, mitochondrial dynamics, mitophagy, and mitochondrial DNA (mtDNA) in APP/PS1 transgenic mice and N2a/APP cells. In APP/PS1 transgenic mice and N2a/APP cells, OAB-14-treated elevated the expression and activity of SIRT3, decreased mitochondrial acetylation, and reduced mitochondrial reactive oxygen species (mtROS) levels. OAB-14 also attenuated mitochondrial acetylation, improved mitochondrial dynamics and mitophagy, and mitigated mtDNA damage in a SIRT3-dependent manner. In addition, OAB-14 suppressed mitochondrial Aβ accumulation in the hippocampus of APP/PS1 transgenic mice. This study provides further clarification on the potential therapeutic mechanisms of OAB-14 in the treatment of AD and lays the groundwork for future drug applications.

Mitochondrial dysfunction is linked to physical impairment and dementia. Mitochondrial DNA copy number (mtDNAcn) from blood may predict cognitive decline and dementia risk, but the effect of somatic mutations or frailty is unknown. We estimated mtDNAcn using fastMitoCalc and microheteroplasmies using mitoCaller, from Whole Genome Sequencing (WGS) data. In 189,566 participants free of dementia at study entry (mean age = 56 ± 8), we examined the association between mtDNAcn and subsequent dementia diagnosis using Cox regression. Cognition was assessed in a subset on average 8.9 years later. We examined the associations between mtDNAcn and cognitive measures using multivariable linear regression, adjusted for demographic factors, mtDNAcn-related parameters, and apolipoprotein E ε4 status. We further stratified by frailty and microheteroplasmies. Over an average follow-up of 13.2 years, 3533 participants developed dementia. Each SD higher mtDNAcn (16) was associated with 4.2% lower all-cause dementia hazard (HR = 0.958, p = 0.030), 6% lower non-AD dementia hazard (HR = 0.933, p = 0.022), and not-AD dementia hazard. The associations between mtDNAcn and all-cause dementia and non-AD dementia were stronger among those who were pre-frail or frail or with higher microheteroplasmies. Higher mtDNAcn was associated with higher DSST scores (p = 0.036) and significant only among those with higher microheteroplasmies or frailty (p = 0.029 and 0.048, respectively). mtDNAcn was also associated with delta TMT and paired associate learning only in pre-frail/frail participants (p = 0.007 and 0.045, respectively). Higher WGS-based mtDNAcn in human blood is associated with lower dementia risk, specifically non-AD dementia, and specific cognitive function. The relationships appear stronger in high somatic mutations or frailty. Future studies are warranted to investigate biological underpinnings.

Mitochondrial genomes are dynamically evolving and are shaped by somatic mutation and selection throughout the female germline. In this study, we investigated the radiation-induced impacts on mitochondrial DNA in vitro and in vivo, as well as the transgenerational inheritance.

Human cervical cancer HeLa cells and telomerase-immortalized normal fibroblast BJ1-hTERT cells were exposed to X-rays at 0.5-8 Gy. Also, we exposed 8-week-old female C57BL/6N mice to a single whole-body dose of 2 Gy of X-rays and mated them with healthy males 1 day after irradiation. We extracted DNA from the irradiated cells, female mice, and the 2-week-old pups, then examined the mitochondrial DNA copy numbers (mtDNAcns) and radiation-induced damage by real-time quantitative PCR.

The mtDNAcn levels in cells increased and the intact copy ratios decreased 24 h after irradiation, resulting in the delayed shift of heteroplasmy. Also, the peripheral blood-derived mtDNAcn levels in irradiated females increased 1 day after irradiation and the intact copy rates decreased, supporting the results in vitro. Furthermore, whole blood-derived mtDNAcn levels decreased in 2-week-old pups born from irradiated mothers, indicating the mitochondrial genomic instability.

We found the delayed induction of mtDNA damage in human cancer and noncancerous cells after irradiation, as well as the same trend in mice. Furthermore, to our knowledge, this is first to demonstrate the hereditary effects of radiation on the regulation of mitochondrial genome. These provide novel insights into the significance of radiation protection and preventive medicine for not only pre-pregnancy females but also the next generation.

Mitochondrial dysfunctions have been reported in bipolar disorder (BD), but their role in the etiopathogenesis of BD as well as their implications in modulating response to pharmacological treatments with psychotropic medications have been scarcely explored. Mitochondrial DNA copy number (mtDNA-cn) has been linked to mitochondria functioning, and, despite some degree of inconsistence, previous findings showed that BD patients present significant differences in mtDNA-cn compared to healthy controls. Here we measured mtDNA-cn in a sample of 89 patients with BD and 78 healthy controls (HC). Patients in the BD sample were treated either with lithium (n = 47) and characterized as responders (n = 22) or non-responders (n = 25), or with other mood stabilizers (n = 42). BD patients had larger mtDNA-cn compared to HC (adjusted model: F2=9.832; p = 0.000095; contribution of diagnosis F1= 10.798; p = 0.001). When the BD sample was stratified for treatment exposure, mtDNA-cn was lower in patients treated with lithium compared to those treated with other mood stabilizers (adjusted model: F4=23.770, p = 7.0929E-13; contribution of treatment: F1=54.300, p = 1.55E-10). Moreover mtDNA-cn was higher in patients treated with other mood stabilizers compared to controls and Li-treated BD patients (F3=28.125, p = 1.36E-14; contribution of groups F2=36.156, p = 1.25E-13). Finally, there was no difference in mtDNA-cn levels in lithium responders compared to non-responders and neither between the two diagnostic groups (BD type 1 and 2). Our findings suggest that BD may be associated with mitochondrial dysfunctions, and that exposure to lithium but not to other mood stabilizers may restore these abnormalities, though this does not appear correlated with the clinical efficacy of lithium.

Several studies evaluated peripheral and cerebrospinal fluid (CSF) mtDNA as a putative biomarker in neurodegenerative diseases, often yielding inconsistent findings. We systematically reviewed the current evidence assessing blood and CSF mtDNA levels and variant burden in Parkinson's disease (PD), Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS). Multiple sclerosis (MS) was also included as a paradigm of chronic neuroinflammation-driven neurodegeneration.

Medline, Embase, Scopus and Web of Science were searched for articles published from inception until October 2023. Studies focused on mtDNA haplogroups or hereditary pathogenic variants were excluded. Critical appraisal was performed using the Quality Assessment for Diagnostic Accuracy Studies criteria.

Fifty-nine original studies met our a priori-defined inclusion criteria. The majority of CSF-focused studies showed (i) decreased mtDNA levels in PD and AD; (ii) increased levels in MS compared to controls. No studies evaluated CSF mtDNA in ALS. Results focused on blood cell-free and intracellular mtDNA were contradictory, even within studies evaluating the same disease. This poor reproducibility is likely due to the lack of consideration of the many factors known to affect mtDNA levels. mtDNA damage and methylation levels were increased and reduced in patients compared to controls, respectively. A few studies investigated the correlation between mtDNA and disease severity, with conflicting results.

Additional well-designed studies are needed to evaluate CSF and blood mtDNA profiles as putative biomarkers in neurodegenerative diseases. The identification of "mitochondrial subtypes" of disease may enable novel precision medicine strategies to counteract neurodegeneration.

The mitochondrial cascade hypothesis of Alzheimer's disease (AD) has been portrayed through molecular, cellular, and animal studies; however large epidemiological studies are lacking. This study aimed to explore the association of mitochondrial DNA copy number (mtDNAcn), a marker representative of mtDNA abundance per cell, with risk of incident all-cause dementia, AD, and vascular dementia diagnosis within 17 years and dementia-related blood biomarkers (P-tau181, GFAP, and NfL). Additionally, sex-stratified analyses were completed. In this German population-based cohort study (ESTHER), 9940 participants aged 50-75 years were enrolled by general practitioners and followed for 17 years. Participants were included in this study if information on dementia status and blood-based mtDNAcn measured via real-time polymerase chain reaction were available. In a nested case-control approach, a subsample of participants additionally had measurements of P-tau181, GFAP, and NfL in blood samples taken at baseline. Of 4913 participants eligible for analyses, 386 were diagnosed with incident all-cause dementia, including 130 AD and 143 vascular dementia cases, while 4527 participants remained without dementia diagnosis within 17 years. Participants with low mtDNAcn (lowest 10%) experienced 45% and 65% percent increased risk of incident all-cause dementia and AD after adjusting for age and sex (all-cause dementia: HRadj, 95%CI:1.45, 1.08-1.94; AD: HRadj, 95%CI: 1.65, 1.01-2.68). MtDNAcn was not associated to vascular dementia diagnosis and was more strongly associated with all-cause dementia among women. In the nested case-control study (n = 790), mtDNAcn was not significantly associated with the dementia-related blood biomarkers (P-tau181, GFAP, and NfL) levels in blood from baseline before dementia diagnosis. This study provides novel epidemiological evidence connecting mtDNA abundance, measured via mtDNAcn, to incident dementia and AD at the population-based level. Reduced mitochondrial abundance may play a role in pathogenesis, especially among women.

Persistent cognitive challenges in bipolar disorder (BD) may be tied to insulin resistance, which crucially affects both metabolism and brain health. Additionally, mitochondrial DNA (mtDNA) copy number has emerged as an indicator of cognitive performance and response to treatment in BD. However, it remains unclear whether and how this indicator might serve as a bridge between metabolic dysfunction and cognitive capacity. In 68 study participants with euthymic BD, insulin resistance was assessed according to fasting glucose and insulin levels. mtDNA copy number was quantified from leukocytes, and executive function was measured with the Wisconsin card-sorting test (WCST). Mediation models were applied to explore the statistical relationship between insulin resistance, mtDNA copy number, and executive function. Both linear regression and Poisson distribution approaches with robust bootstrap simulations were used for significance testing. The results indicated that insulin resistance indirectly affects executive function via mtDNA copy number. This mediation relationship was statistically significant for both preservation errors and completion of categories in the WCST, although there were no significant direct effects of insulin resistance on the executive functions. We therefore concluded that insulin resistance is associated with reduced mtDNA copy number in blood, which may negatively impact executive functions in patients with euthymic BD. Further work is warranted to determine if improving metabolic and mitochondrial health may lead to better cognitive outcomes in BD.

Impaired muscle mitochondrial oxidative capacity is associated with future cognitive impairment, and higher levels of PET and blood biomarkers of Alzheimer's disease and neurodegeneration. Here, we examine its associations with up to over a decade-long changes in brain atrophy and microstructure. Higher in vivo skeletal muscle oxidative capacity via MR spectroscopy (post-exercise recovery rate, kPCr) is associated with less ventricular enlargement and brain aging progression, and less atrophy in specific regions, notably primary sensorimotor cortex, temporal white and gray matter, thalamus, occipital areas, cingulate cortex, and cerebellum white matter. Higher kPCr is also associated with less microstructural integrity decline in white matter around cingulate, including superior longitudinal fasciculus, corpus callosum, and cingulum. Higher in vivo muscle oxidative capacity is associated with preserved brain structure up to over a decade, particularly in areas important for cognition, motor function, and sensorimotor integration.

Cognitive frailty (CF), characterized by the coexistence of physical frailty and cognitive impairment, is linked to increased morbidity and mortality in older adults. While CF has been linked to multiple physiological and lifestyle factors, the underlying biological mechanisms remain poorly understood. This study investigated the risk factors for CF and explored the relationship between mitochondrial function and CF in hospitalized patients.

A total of 279 hospitalized individuals were recruited from December 2020 to August 2022, conducted comprehensive clinical assessments, and collected peripheral blood samples. CF was evaluated using the Physical Frailty Phenotype and Montreal Cognitive Assessment scales. Nutritional status was assessed with the Mini Nutritional Assessment, and depression was measured using the Geriatric Depression Scale. DNA was obtained from the peripheral blood and interrogated for mitochondrial DNA copy number (mtDNAcn). Peripheral blood mononuclear cells isolated from peripheral blood were examined for respiratory function and reactive oxygen species (ROS) levels. Additionally, plasma samples were analyzed for inflammatory markers and Carnitine Palmitoyltransferase II (CPT2).

Among the participants, 90 were classified as CF and 46 as non-CF. Logistic regression analysis revealed that increased age (OR 1.156, 95% CI 1.064-1.255), lower educational attainment (OR 0.115, 95% CI 0.024-0.550), malnutrition (OR 0.713, 95% CI 0.522-0.973), and higher depression scores (OR 1.345, 95% CI 1.065-1.699) were significantly associated with CF. The independent t tests and Mann-Whitney U tests showed the CF group exhibited impaired mitochondrial function, characterized by reduced mtDNAcn and respiratory activity, coupled with elevated ROS, interleukin-6, and CPT2 levels compared with the non-CF group. After adjusted for age, sex, and BMI, compared with non-CF group, the OR values for the CF group of mtDNAcn and ROS were 0.234 (95% CI = 0.065-0.849) (p = 0.027) and 1.203 (95% CI = 1.075-1.347) (p = 0.001), respectively. The Sensitive analysis showed that the area under curve values for mtDNAcn and ROS were 0.653 and 0.925.

Age, lower educational attainment, malnutrition, and depression are significant risk factors for CF. Moreover, mitochondrial dysfunction, characterized by decreased mtDNAcn, impaired respiratory function and increased ROS levels appears to be a critical phenotype of CF.

Abnormalities in mitochondrial energy homeostasis can lead to various disorders, including ocular motility aberrations. Previous studies have suggested the involvement of mitochondrial aberrations in strabismus etiology. We compared the blood-derived mitochondrial DNA (mtDNA) copy number from comitant strabismus patients with that from age-matched controls, and also compared expression of mitochondrial biogenesis genes in a separate set of extraocular muscle samples from strabismic and control subjects.

Blood samples from 93 strabismic (39 esotropic, 54 exotropic) and 93 control subjects were analyzed for mtDNA copy number through quantitative polymerase chain reaction. We also examined the expression of 6 genes involved in mitochondrial biogenesis in cDNA obtained from extraocular muscles of a separate group of 26 strabismus patients and 4 healthy controls.

The mtDNA content was significantly higher in strabismus patients as compared to the control group, both overall (fold change, 1.39; Z = -2.43 [P = 0.01]) and in strabismus subgroups (esotropia: fold change,1.42; Z = 2.59 [P = 0.0096]; exotropia: fold change, 1.41, Z = 3.35 [P = 0.00078]). No significant difference was observed in the expression of the examined biogenesis genes between strabismus and control groups.

Our results suggest an association between mtDNA copy number and strabismus; however, further studies are required to elucidate the significance of altered mtDNA in strabismus and its possible significance with regard to the etiology of strabismus.

Mitochondrial dysfunction plays an important role in Parkinson's disease (PD), with mitochondrial DNA copy number (mtDNA-CN) emerging as a potential marker for mitochondrial health. We investigated the links between blood mtDNA-CN and PD severity and risk using the Accelerating Medicines Partnership program for Parkinson's Disease dataset, replicating our results in the UK Biobank. Our findings reveal that reduced blood mtDNA-CN levels are associated with heightened PD risk and increased severity of motor symptoms and olfactory dysfunction. We estimated blood cell composition using complete blood cell profile when available or RNA-sequencing data as a surrogate. After adjusting for blood cell composition, the associations between mtDNA-CN and PD risk and clinical symptoms became non-significant. Bidirectional Mendelian randomization analysis also found no evidence of a direct causal relationship between blood mtDNA-CN and PD susceptibility. Hence peripheral inflammatory immune responses rather than mitochondrial dysfunction underpin these previously identified associations in PD.

Blood-derived mitochondrial DNA copy number (mtDNA-CN) is a proxy measurement of mitochondrial function in the peripheral and central systems. Abnormal mtDNA-CN not only indicates impaired mtDNA replication and transcription machinery but also dysregulated biological processes such as energy and lipid metabolism. However, the relationship between mtDNA-CN and Alzheimer disease (AD) is unclear.

We performed two-sample Mendelian randomization (MR) using publicly available summary statistics from GWAS for mtDNA-CN and AD to investigate the causal relationship between mtDNA-CN and AD. We estimated mtDNA-CN using whole-genome sequence data from blood and brain samples of 13,799 individuals from the Alzheimer's Disease Sequencing Project. Linear and Cox proportional hazards models adjusting for age, sex, and study phase were used to assess the association of mtDNA-CN with AD. The association of AD biomarkers and serum metabolites with mtDNA-CN in blood was evaluated in Alzheimer's Disease Neuroimaging Initiative using linear regression. We conducted a causal mediation analysis to test the natural indirect effects of mtDNA-CN change on AD risk through the significantly associated biomarkers and metabolites.

MR analysis suggested a causal relationship between decreased blood-derived mtDNA-CN and increased risk of AD (OR = 0.68; P = 0.013). Survival analysis showed that decreased mtDNA-CN was significantly associated with higher risk of conversion from mild cognitive impairment to AD (HR = 0.80; P = 0.002). We also identified significant associations of mtDNA-CN with brain FDG-PET (β = 0.103; P = 0.022), amyloid-PET (β = 0.117; P = 0.034), CSF amyloid-β (Aβ) 42/40 (β=-0.124; P = 0.017), CSF t-Tau (β = 0.128; P = 0.015), p-Tau (β = 0.140; P = 0.008), and plasma NFL (β=-0.124; P = 0.004) in females. Several lipid species, amino acids, biogenic amines in serum were also significantly associated with mtDNA-CN. Causal mediation analyses showed that about a third of the effect of mtDNA-CN on AD risk was mediated by plasma NFL (P = 0.009), and this effect was more significant in females (P < 0.005).

Our study indicates that mtDNA-CN measured in blood is predictive of AD and is associated with AD biomarkers including plasma NFL particularly in females. Further, we illustrate that decreased mtDNA-CN possibly increases AD risk through dysregulation of mitochondrial lipid metabolism and inflammation.

Mitochondria play a crucial role in numerous biological processes; however, limited methods and research have focused on revealing mitochondrial heterogeneity at the single-cell level. In this study, we optimized the DNBelab C4 single-cell ATAC (assay for transposase-accessible chromatin) sequencing workflow for single-cell mitochondrial sequencing (C4_mtscATAC-seq). We validated the effectiveness of our C4_mtscATAC-seq protocol by sequencing the HEK-293T cell line with two biological replicates, successfully capturing both mitochondrial content (~68% of total sequencing data) and open chromatin status simultaneously. Subsequently, we applied C4_mtscATAC-seq to investigate two mouse tissues, spleen and bone marrow, obtained from two mice aged 2 months and two mice aged 23 months. Our findings revealed higher mitochondrial DNA (mtDNA) content in young tissues compared to more variable mitochondrial content in aged tissues, consistent with higher activity scores of nuclear genes associated with mitochondrial replication and transcription in young tissues. We detected a total of 22, 15, and 21 mtDNA mutations in the young spleen, aged spleen, and bone marrow, respectively, with most variant allele frequencies (VAF) below 1%. Moreover, we observed a higher number of mtDNA mutations with higher VAF in aged tissues compared to young tissues. Importantly, we identified three mtDNA variations (m.9821A>T, m.15219T>C, and m.15984C>T) with the highest VAF in both aged spleen and aged bone marrow. By comparing cells with and without these mtDNA variations, we analyzed differential open chromatin status to identify potential genes associated with these mtDNA variations, including transcription factors such as KLF15 and NRF1. Our study presents an alternative single-cell mitochondrial sequencing method and provides crude insights into age-related single-cell mitochondrial variations.

The extent of cell-to-cell variation in tumor mitochondrial DNA (mtDNA) copy number and genotype, and the phenotypic and evolutionary consequences of such variation, are poorly characterized. Here we use amplification-free single-cell whole-genome sequencing (Direct Library Prep (DLP+)) to simultaneously assay mtDNA copy number and nuclear DNA (nuDNA) in 72,275 single cells derived from immortalized cell lines, patient-derived xenografts and primary human tumors. Cells typically contained thousands of mtDNA copies, but variation in mtDNA copy number was extensive and strongly associated with cell size. Pervasive whole-genome doubling events in nuDNA associated with stoichiometrically balanced adaptations in mtDNA copy number, implying that mtDNA-to-nuDNA ratio, rather than mtDNA copy number itself, mediated downstream phenotypes. Finally, multimodal analysis of DLP+ and single-cell RNA sequencing identified both somatic loss-of-function and germline noncoding variants in mtDNA linked to heteroplasmy-dependent changes in mtDNA copy number and mitochondrial transcription, revealing phenotypic adaptations to disrupted nuclear/mitochondrial balance.

Lower skeletal muscle mitochondrial function is associated with future cognitive impairment and mobility decline, but the biological underpinnings for these associations are unclear. We examined metabolomic markers underlying skeletal muscle mitochondrial function, cognition and motor function.

We analysed data from 560 participants from the Baltimore Longitudinal Study of Aging (mean age: 68.4 years, 56% women, 28% Black) who had data on skeletal muscle oxidative capacity (post-exercise recovery rate of phosphocreatine, kPCr) via 31P magnetic resonance spectroscopy and targeted plasma metabolomics using LASSO model. We then examined which kPCr-related markers were also associated with cognition and motor function in a larger sample (n = 918, mean age: 69.4, 55% women, 27% Black).

The LASSO model revealed 24 metabolites significantly predicting kPCr, with the top 5 being asymmetric dimethylarginine, lactic acid, lysophosphatidylcholine a C18:1, indoleacetic acid and triacylglyceride (17:1_34:3), also significant in multivariable linear regression. The kPCr metabolite score was associated with cognitive or motor function, with 2.5-minute usual gait speed showing the strongest association (r = 0.182). Five lipids (lysophosphatidylcholine a C18:1, phosphatidylcholine ae C42:3, cholesteryl ester 18:1, sphingomyelin C26:0, octadecenoic acid) and 2 amino acids (leucine, cystine) were associated with both cognitive and motor function measures.

Our findings add evidence to the hypothesis that mitochondrial function is implicated in the pathogenesis of cognitive and physical decline with aging and suggest that targeting specific metabolites may prevent cognitive and mobility decline through their effects on mitochondria. Future omics studies are warranted to confirm these findings and explore mechanisms underlying mitochondrial dysfunction in aging phenotypes.

Mitochondrial DNA copy number (mtDNA-CN) is associated with several age-related chronic diseases and is a predictor of all-cause mortality. Here, we examine site-specific differential nuclear DNA (nDNA) methylation and differential gene expression resulting from in vitro reduction of mtDNA-CN to uncover shared genes and biological pathways mediating the effect of mtDNA-CN on disease. Epigenome and transcriptome profiles were generated for three independent human embryonic kidney (HEK293T) cell lines harbouring a mitochondrial transcription factor A (TFAM) heterozygous knockout generated via CRISPR-Cas9, and matched control lines. We identified 4,242 differentially methylated sites, 228 differentially methylated regions, and 179 differentially expressed genes associated with mtDNA-CN. Integrated analysis uncovered 381 Gene-CpG pairs. GABAA receptor genes and related pathways, the neuroactive ligand receptor interaction pathway, ABCD1/2 gene activity, and cell signalling processes were overrepresented, providing insight into the underlying biological mechanisms facilitating these associations. We also report evidence implicating chromatin state regulatory mechanisms as modulators of mtDNA-CN effect on gene expression. We demonstrate that mitochondrial DNA variation signals to the nuclear DNA epigenome and transcriptome and may lead to nuclear remodelling relevant to development, aging, and complex disease.

Mitochondrial dysfunction may contribute to brain and muscle health through inflammation or fat infiltration in the muscle, both of which are associated with cognitive function and mobility. We aimed to examine the association between skeletal muscle mitochondrial function and cognitive and mobility outcomes and tested the mediation effect of inflammation or fat infiltration.

We analysed data from 596 Baltimore Longitudinal Study of Aging participants who had concurrent data on skeletal muscle oxidative capacity and cognitive and mobility measures of interest (mean age: 66.1, 55% women, 24% Black). Skeletal muscle oxidative capacity was assessed as post-exercise recovery rate (kPCr) via P31 MR spectroscopy. Fat infiltration was measured as intermuscular fat (IMF) via CT scan and was available for 541 participants. Inflammation markers [IL-6, C-reactive protein (CRP), total white blood cell (WBC), neutrophil count, erythrocyte sedimentation rate (ESR), or albumin] were available in 594 participants. We examined the association of kPCr and cognitive and mobility measures using linear regression and tested the mediation effect of IMF or inflammation using the mediation package in R. Models were adjusted for demographics and PCr depletion.

kPCr and IMF were both significantly associated with specific cognitive domains (DSST, TMA-A, and pegboard dominant hand performance) and mobility (usual gait speed, HABCPPB, 400 m walk time) (all P < 0.05). IMF significantly mediated the relationship between kPCr and these cognitive and mobility measures (all P < 0.05, proportion mediated 13.1% to 27%). Total WBC, neutrophil count, and ESR, but not IL-6 or CRP, also mediated at least one of the cognitive and mobility outcomes (all P < 0.05, proportion mediated 9.4% to 15.3%).

Skeletal muscle mitochondrial function is associated with cognitive performance involving psychomotor speed. Muscle fat infiltration and specific inflammation markers mediate the relationship between muscle mitochondrial function and cognitive and mobility outcomes. Future studies are needed to confirm these associations longitudinally and to understand their mechanistic underpinnings.

Major depressive disorder (MDD) and bipolar disorder (BD), are globally prevalent, contributing to significant disease burden and adverse health outcomes. These mood disorders are associated with changes in many aspects of brain reward pathways, yet cellular and molecular changes in the brain are not readily available in clinical populations. Therefore, the use of biomarkers as proxies for changes in the brain are necessary. The proliferation of mitochondria in blood has emerged as a potentially useful biomarker, yet a clear consensus on how these mood disorders impact mitochondrial DNA copy number (mtDNAcn) has not been reached. To determine the current available consensus on the relationship of mood disorder diagnosis and blood mtDNcn, we performed a meta-analysis of available literature measuring this biomarker. Following PRISMA guidelines for a systematic search, 22 papers met inclusion criteria for meta-analysis (10 MDD, 10 BD, 2 both MDD and BD). We extracted demographic, disorder, and methodological information with mtDNAcn. Using the metafor package for R, calculated effect sizes were used in random effects or meta regression models for MDD and BD. Overall, our data suggest blood mtDNAcn may be a useful biomarker for mood disorders, with MDD and BD Type II associated with higher mtDNAcn, and BD Type I associated with lower mtDNAcn. Initially, we observed a trending increase in mtDNAcn in patients with MDD, which reached significance when one study with outlying demographic characteristics was excluded. Subgroup and meta-regression analysis indicated the relationship between mtDNAcn and diagnosis in patients with BD is dependent on BD type, while no relationship is detectable when BD types are mixed. Further study of blood mtDNAcn could predict downstream health outcomes or treatment responsivity in individuals with mood disorders.

Background The relationship between mitochondrial DNA copy number (mtDNA CN) and cardiovascular disease remains elusive. Methods and Results We performed cross-sectional and prospective association analyses of blood-derived mtDNA CN and cardiovascular disease outcomes in 27 316 participants in 8 cohorts of multiple racial and ethnic groups with whole-genome sequencing. We also performed Mendelian randomization to explore causal relationships of mtDNA CN with coronary heart disease (CHD) and cardiometabolic risk factors (obesity, diabetes, hypertension, and hyperlipidemia). P<0.01 was used for significance. We validated most of the previously reported associations between mtDNA CN and cardiovascular disease outcomes. For example, 1-SD unit lower level of mtDNA CN was associated with 1.08 (95% CI, 1.04-1.12; P<0.001) times the hazard for developing incident CHD, adjusting for covariates. Mendelian randomization analyses showed no causal effect from a lower level of mtDNA CN to a higher CHD risk (β=0.091; P=0.11) or in the reverse direction (β=-0.012; P=0.076). Additional bidirectional Mendelian randomization analyses revealed that low-density lipoprotein cholesterol had a causal effect on mtDNA CN (β=-0.084; P<0.001), but the reverse direction was not significant (P=0.059). No causal associations were observed between mtDNA CN and obesity, diabetes, and hypertension, in either direction. Multivariable Mendelian randomization analyses showed no causal effect of CHD on mtDNA CN, controlling for low-density lipoprotein cholesterol level (P=0.52), whereas there was a strong direct causal effect of higher low-density lipoprotein cholesterol on lower mtDNA CN, adjusting for CHD status (β=-0.092; P<0.001). Conclusions Our findings indicate that high low-density lipoprotein cholesterol may underlie the complex relationships between mtDNA CN and vascular atherosclerosis.

Alterations in mitochondrial DNA (mtDNA) levels have been observed in Alzheimer's disease and are an area of research that shows promise as a useful biomarker. It is well known that not only are the mitochondria a key player in producing energy for the cell, but they also are known to interact in other important intracellular processes as well as extracellular signaling and communication. BODY: This mini review explores how cells use mtDNA as a stress signal, particularly in Alzheimer's disease. We investigate the measurement of these mtDNA alterations, the mechanisms of mtDNA release, and the immunological effects from the release of these stress signals.

Literature indicates a correlation between the release of mtDNA in Alzheimer's disease and increased immune responses, showing promise as a potential biomarker. However, several questions remain unanswered and there is great potential for future studies in this area.

Parkinson's disease (PD) pathophysiology includes mitochondrial dysfunction, neuroinflammation, and aging as its biggest risk factors. Mitochondrial DNA copy number (mtDNA-CN) and telomere length (TL) are biological aging markers with inconclusive results regarding their association with PD. A case-control study was used to measure TL and mtDNA-CN using qPCR in PBMCs. PD patients were naive at baseline (T0) and followed-up at one (T1) and two (T2) years after the dopaminergic treatment (DRT). Plasmatic cytokines were determined by ELISA in all participants, along with clinical parameters of patients at T0. While TL was shorter in patients vs. controls at all time points evaluated (p < 0.01), mtDNA-CN showed no differences. An increase in mtDNA-CN and TL was observed in treated patients vs. naive ones (p < 0.001). Our statistical model analyzed both aging markers with covariates, showing a strong correlation between them (r = 0.57, p < 0.01), and IL-17A levels positively correlating with mtDNA-CN only in untreated patients (r = 0.45, p < 0.05). TL and mtDNA-CN could be useful markers for monitoring inflammation progression or treatment response in PD. DRT might modulate TL and mtDNA-CN, reflecting a compensatory mechanism to counteract mitochondrial dysfunction in PD, but this needs further investigation.

Major depressive disorder (MDD) and bipolar disorder (BD), are globally prevalent, contributing to significant disease burden and adverse health outcomes. These mood disorders are associated with changes in many aspects of brain reward pathways, yet cellular and molecular changes in the brain are not readily available in clinical populations. Therefore, the use of biomarkers as proxies for changes in the brain are necessary. The proliferation of mitochondria in blood has emerged as a potentially useful biomarker, yet a clear consensus on how these mood disorders impact mitochondrial DNA copy number (mtDNAcn) has not been reached.

Following PRISMA guidelines for a systematic search, 22 papers met inclusion criteria for meta-analysis (10 MDD, 10 BD, 2 both MDD and BD). We extracted demographic, disorder, and methodological information with mtDNAcn. Using the metafor package for R, calculated effect sizes were used in random effects or meta regression models for MDD and BD.

Our results show a trending increase in mtDNAcn in patients with MDD, which reaches significance when one study with outlying demographic characteristics is excluded. Overall, there was no effect of BD on mtDNAcn, however, further subgroup and meta-regression analysis indicated the effects on mtDNAcn are dependent on BD type.

Together our data suggest whole blood/leukocyte mtDNAcn may be a useful biomarker for mood disorders, with MDD and BD Type II associated with higher mtDNAcn, and BD Type I associated with lower mtDNAcn. Further study of blood mtDNAcn could predict downstream health outcomes or treatment responsivity in individuals with mood disorders.

Healthy human longevity is a global goal of the world health system. Determining the causes and processes influencing human longevity is the primary fundamental goal facing the scientific community. Currently, the main efforts of the scientific community are aimed at identifying the qualitative characteristics of the genome that determine the trait. At the same time, when evaluating qualitative characteristics, there are many challenges that make it difficult to establish associations. Quantitative traits are burdened with such problems to a lesser extent, but they are largely overlooked in current genomic studies of aging and longevity. Although there is a wide repertoire of quantitative trait analyses based on genomic data, most opportunities are ignored by authors, which, along with the inaccessibility of published data, leads to the loss of this important information. This review focuses on describing quantitative traits important for understanding aging and necessary for analysis in further genomic studies, and recommends the inclusion of the described traits in the analysis. The review considers the relationship between quantitative characteristics of the mitochondrial genome and aging, longevity, and age-related neurodegenerative diseases, such as the frequency of extensive mitochondrial DNA (mtDNA) deletions, mtDNA half-life, the frequency of A>G replacements in the mtDNA heavy chain, the number of mtDNA copies; special attention is paid to the mtDNA methylation sign. A separate section of this review is devoted to the correlation of telomere length parameters with age, as well as the association of telomere length with the amount of mitochondrial DNA. In addition, we consider such a quantitative feature as the rate of accumulation of somatic mutations with aging in relation to the lifespan of living organisms. In general, it may be noted that there are quite serious reasons to suppose that various quantitative characteristics of the genome may be directly or indirectly associated with certain aspects of aging and longevity. At the same time, the available data are clearly insufficient for definitive conclusions and the determination of causal relationships.

To subgroup Chinese patients with newly diagnosed type 2 diabetes (T2D) by K-means cluster analysis on clinical indicators, and to explore whether these subgroups represent different genetic features and calculated cardiovascular risks.

The K-means clustering analysis was performed on two cohorts (n = 590 and 392), both consisting of Chinese participants with newly diagnosed T2D. To assess genetic risks, multiple polygenic risk scores (PRSs) and mitochondrial DNA copy numbers (mtDNA-CN) were calculated for all participants. Furthermore, Framingham risk scores (FRS) of cardiovascular diseases in two cohorts were also calculated to verify the genetic risks.

Four clusters were identified including the mild age-related diabetes (MARD)(35.08%), mild obesity-related diabetes (MOD) (34.41%), severe autoimmune diabetes (SAID) 19.15%, and severe insulin-resistant diabetes (SIRD) 11.36% subgroups in the MARCH (metformin, and acarbose in Chinese patients as the initial hypoglycemic treatment) cohort. There was a significant difference in PRS for cardiovascular diseases (CVD) across four subgroups in the MARCH cohort (p < 0.05). Compared with the SIDD and SIRD subgroups, patients in the MOD subgroup had a relatively lower PRS for CVD (p < 0.05) in the MARCH cohort. Females had a higher PRS compared to males, with no significant difference in FRS across the four clusters. The MOD subgroup had a significantly lower FRS which was consistent with the results of PRS. Similar results of PRS and FRS were also replicated in the CONFIDENCE (comparison of glycemic control and b-cell function among newly diagnosed patients with type 2 diabetes treated with exenatide, insulin or pioglitazone) cohort.

There are different CVD risks in diabetic subgroups based on clinical and genetic evidence which may promote precision medicine.