The association between mitochondrial DNA abundance and stroke: A combination of multivariable-adjusted survival and Mendelian randomization analyse

Mitochondrial DNA copy number and Alzheimer's disease and Parkinson disease

INTRODUCTION

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.

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

DISCUSSION

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.

Investigating the genetic association of mitochondrial DNA copy number with neurodegenerative diseases

OBJECTIVE

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

METHODS

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.

RESULTS

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).

CONCLUSION

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.

Tapping natures rhythm: the role of season in mitochondrial function and genetics in the UK biobank

BACKGROUND

Mitochondria are small organelles inside our cells crucial for producing energy and heat, cell signaling, production and degradation of important molecules, as well as cell death. The number of mitochondria in each cell is a marker for mitochondrial function, which generally declines with increasing age. However, we found that there is also a considerable seasonal variation of mitochondrial abundance, which warrants further research.

METHODS

We leveraged data from individuals participating in the UK Biobank study and computed their mitochondrial abundance from Exome sequencing reads mapping to the mitochondrial genome. The seasonal effect was modelled as a sine-cosine function across the year and changes in amplitude, acrophase and displacement of mitochondrial abundance due to various demographic, lifestyle, genetic, proteomic, and metabolomic markers were investigated with multivariate regression.

RESULTS

We found that mitochondrial DNA (mtDNA) abundance was higher in winter than in summer. This difference is related to advanced age, a higher BMI and smoking behavior which resulted in a reduced amplitude of mtDNA abundance. A higher education reduced the acrophase (i.e., shifted the distribution to earlier in the year) and a higher BMI and lack of physical activity led to a later acrophase. Generally, increased immune cell count resulted in lower amplitude, and an increased platelet and lymphocyte count was found to increase the acrophase. Importantly, a reduced seasonal amplitude was associated with increased risk for cardiovascular, digestive, genitourinary, and respiratory diseases as well as all-cause mortality. Most of the metabolomic and proteomic markers were associated with mtDNA displacement (i.e., increase of the baseline level) but not acrophase or amplitude. Similarly, we found that there are multiple genetic variants influencing displacement, but none reached genome-wide significance when investigating acrophase or amplitude.

CONCLUSION

Seasonal variation of mtDNA abundance is influenced by environmental, lifestyle and immune parameters. Differences in the seasonal oscillation of mitochondrial abundance could potentially explain discrepancies of previous associations results and might be useful to improve future risk prediction.

Oxidative balance is associated with diabetic kidney disease and mortality in adults with diabetes mellitus: Insights from NHANES database and Mendelian randomization

OBJECTIVE

To explore and validate the association between the oxidative balance and prevalence of diabetic kidney disease (DKD) and mortality in patients with diabetes.

STUDY DESIGN

A large and representative sample from the National Health and Nutrition Examination Survey (NHANES) from 2013 to 2016 was analyzed to study the potential association between Oxidative Balance Score (OBS) and prognosis of DKD in adult diabetic patients. Weighted multivariate logistic regression analysis was conducted to examine the relationship between OBS and DKD risk. Subgroup analysis, sensitivity analysis, and mediation effect analysis were conducted to explore the effect of the covariates and assess the robustness of the findings. Mendelian randomization (MR) was employed to evaluate the correlated relationship between mitochondrial reactive oxygen species (ROS) levels and DKD at the genetic level.

RESULT

The highest OBS quartile showed the most significant negative correlation with DKD compared to the lowest OBS quartile (OR = 0.62, 95% CI 0.41-0.92, P = 0.017). Higher OBS was associated with a reduced risk of DKD (OR = 0.96; 95% CI = 0.93, 0.98; P < 0.001) and mortality (P = 0.021 by log-rank) in diabetic patients. This association remained robust even after excluding individual OBS components. Subgroup analysis revealed the interaction of metabolic syndrome on OBS was significant. Mediation analyses revealed that OBS's effect on DKD was independent of blood uric acid and cholesterol. Restricted cubic spline (RCS) analysis indicated a typical L-shaped relationship between OBS and DKD risk. The physical activity was identified as the core variable predicting DKD risk by two machine learning algorithms. MR showed a potential correlated relationship between ROS and microalbuminuria in DKD.

CONCLUSIONS

The high level of oxidative balance score was negatively correlated with the risk of DKD and mortality in diabetic patients.

Mitochondrial DNA abundance and circulating metabolomic profiling: Multivariable-adjusted and Mendelian randomization analyses in UK Biobank

BACKGROUND

Low leukocyte mitochondrial DNA (mtDNA) abundance has been associated with a higher risk of atherosclerotic cardiovascular disease, but through unclear mechanisms. We aimed to investigate whether low mtDNA abundance is associated with worse metabolomic profiling, as being potential intermediate phenotypes, using cross-sectional and genetic studies.

METHODS

Among 61,186 unrelated European participants from UK Biobank, we performed multivariable-adjusted linear regression analyses to examine the associations between mtDNA abundance and 168 NMR-based circulating metabolomic measures and nine metabolomic principal components (PCs) that collectively covered 91.5% of the total variation of individual metabolomic measures. Subsequently, we conducted Mendelian randomization (MR) to approximate the causal effects of mtDNA abundance on the individual metabolomic measures and their metabolomic PCs.

RESULTS

After correction for multiple testing, low mtDNA abundance was associated with 130 metabolomic measures, predominantly lower concentrations of some amino acids and higher concentrations of lipids, lipoproteins and fatty acids; moreover, mtDNA abundance was associated with seven out of the nine metabolomic PCs. Using MR, genetically-predicted low mtDNA abundance was associated with lower lactate (standardized beta and 95% confidence interval: -0.17; -0.26, -0.08), and higher acetate (0.15; 0.07,0.23), and unsaturation degree (0.14; 0.08,0.20). Similarly, genetically-predicted low mtDNA abundance was associated with lower metabolomic PC2 (related to lower concentrations of lipids and fatty acids), and higher metabolomic PC9 (related to lower concentrations of glycolysis-related metabolites).

CONCLUSION

Low mtDNA abundance is associated with metabolomic perturbations, particularly reflecting a pro-atherogenic metabolomic profile, which potentially could link low mtDNA abundance to higher atherosclerosis risk.

Mitochondrial DNA copy number and risk of cardiovascular disease and all-cause mortality: a systematic review and meta-analysis of observational studies

Increasing studies have explored the correlation of mitochondrial DNA copy number (mtDNA-CN) abnormalities with cardiovascular disease (CVD) and all-cause mortality; however, their findings are contradictory. This systematic review and meta-analysis sought to quantitatively summarize current studies to elucidate the impact of mtDNA-CN on CVD outcomes and all-cause mortality. Relevant studies were searched for in PubMed, Embase and Web of Science databases, up to 23 October 2023. Summary relative risks (RRs) and 95% confidence intervals (CIs) were calculated with the random-effects model. In total, 22 articles were included in the systematic review, 13 of which were included in the meta-analysis of CVD outcomes and 8 in all-cause mortality. Compared to the highest mtDNA-CN level, the summary RR (95% CI) for the lowest mtDNA-CN level was 2.09 (95% CI 1.59-2.75) for CVD, 1.70 (95% CI 1.29-2.24) for coronary heart disease (CHD), 1.43 (95% CI 1.15-1.79) for heart failure (HF), 1.88 (95% CI 1.08-3.28) for stroke and 1.33 (95% CI 1.21-1.47) for all-cause mortality. Lower mtDNA-CN may increase the risk of CVD, including CHD, HF and stroke, as well as all-cause mortality. MtDNA-CN is a potential predictor of CVD and all-cause mortality.

Subtype-Specific Association of Mitochondrial DNA Copy Number With Poststroke/TIA Outcomes in 10 241 Patients in China

BACKGROUND

Mitochondrial DNA copy number (mtDNA-CN) is associated with the severity and mortality in patients with stroke, but the associations in different stroke subtypes remain unexplored.

METHODS

We conducted an observational prospective cohort analysis on patients with ischemic stroke or transient ischemic attack enrolled in the Third China National Stroke Registry. We applied logistic models to assess the association of mtDNA-CN with functional outcome (modified Rankin Scale score, 3-6 versus 0-2) and Cox proportional hazard models to assess the association with stroke recurrence (treating mortality as a competing risk) and mortality during a 12-month follow-up, adjusting for sex, age, physical activity, National Institutes of Health Stroke Scale at admission, history of stroke and peripheral artery disease, small artery occlusion, and interleukin-6. Subgroup analyses stratified by age and stroke subtypes were conducted.

RESULTS

The Third China National Stroke Registry enrolled 15 166 patients, of which 10 241 with whole-genome sequencing data were retained (mean age, 62.2 [SD, 11.2] years; 68.8% men). The associations between mtDNA-CN and poststroke/transient ischemic attack outcomes were specific to patients aged ≤65 years, with lower mtDNA-CN significantly associated with stroke recurrence in 12 months (subdistribution hazard ratio, 1.15 per SD lower mtDNA-CN [95% CI, 1.04-1.27]; P=5.2×10-3) and higher all-cause mortality in 3 months (hazard ratio, 2.19 [95% CI, 1.41-3.39]; P=5.0×10-4). Across subtypes, the associations of mtDNA-CN with stroke recurrence were specific to stroke of undetermined cause (subdistribution hazard ratio, 1.28 [95% CI, 1.11-1.48]; P=6.6×10-4). In particular, lower mtDNA-CN was associated with poorer functional outcomes in stroke of undetermined cause patients diagnosed with embolic stroke of undetermined source (odds ratio, 1.53 [95% CI, 1.20-1.94]; P=5.4×10-4), which remained significant after excluding patients with recurrent stroke (odds ratio, 1.49 [95% CI, 1.14-1.94]; P=3.0×10-3).

CONCLUSIONS

Lower mtDNA-CN is associated with higher stroke recurrence rate and all-cause mortality, as well as poorer functional outcome at follow-up, among stroke of undetermined cause, embolic stroke of undetermined source, and younger patients.

Rare and common genetic determinants of mitochondrial function determine severity but not risk of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving selective vulnerability of energy-intensive motor neurons (MNs). It has been unclear whether mitochondrial function is an upstream driver or a downstream modifier of neurotoxicity. We separated upstream genetic determinants of mitochondrial function, including genetic variation within the mitochondrial genome or autosomes; from downstream changeable factors including mitochondrial DNA copy number (mtCN). Across three cohorts including 6,437 ALS patients, we discovered that a set of mitochondrial haplotypes, chosen because they are linked to measurements of mitochondrial function, are a determinant of ALS survival following disease onset, but do not modify ALS risk. One particular haplotype appeared to be neuroprotective and was significantly over-represented in two cohorts of long-surviving ALS patients. Causal inference for mitochondrial function was achievable using mitochondrial haplotypes, but not autosomal SNPs in traditional Mendelian randomization (MR). Furthermore, rare loss-of-function genetic variants within, and reduced MN expression of, ACADM and DNA2 lead to ∼50 % shorter ALS survival; both proteins are implicated in mitochondrial function. Both mtCN and cellular vulnerability are linked to DNA2 function in ALS patient-derived neurons. Finally, MtCN responds dynamically to the onset of ALS independently of mitochondrial haplotype, and is correlated with disease severity. We conclude that, based on the genetic measures we have employed, mitochondrial function is a therapeutic target for amelioration of disease severity but not prevention of ALS.

The role of mitochondrial DNA copy number in cardiometabolic disease: a bidirectional two-sample mendelian randomization study

BACKGROUND

This study used a bidirectional 2-sample Mendelian randomization study to investigate the potential causal links between mtDNA copy number and cardiometabolic disease (obesity, hypertension, hyperlipidaemia, type 2 diabetes [T2DM], coronary artery disease [CAD], stroke, ischemic stroke, and heart failure).

METHODS

Genetic associations with mtDNA copy number were obtained from a genome-wide association study (GWAS) summary statistics from the UK biobank (n = 395,718) and cardio-metabolic disease were from largest available GWAS summary statistics. Inverse variance weighting (IVW) was conducted, with weighted median, MR-Egger, and MR-PRESSO as sensitivity analyses. We repeated this in the opposite direction using instruments for cardio-metabolic disease.

RESULTS

Genetically predicted mtDNA copy number was not associated with risk of obesity (P = 0.148), hypertension (P = 0.515), dyslipidemia (P = 0.684), T2DM (P = 0.631), CAD (P = 0.199), stroke (P = 0.314), ischemic stroke (P = 0.633), and heart failure (P = 0.708). Regarding the reverse directions, we only found that genetically predicted dyslipidemia was associated with decreased levels of mtDNA copy number in the IVW analysis (β= - 0.060, 95% CI - 0.044 to - 0.076; P = 2.416e-14) and there was suggestive of evidence for a potential causal association between CAD and mtDNA copy number (β= - 0.021, 95% CI - 0.003 to - 0.039; P = 0.025). Sensitivity and replication analyses showed the stable findings.

CONCLUSIONS

Findings of this Mendelian randomization study did not support a causal effect of mtDNA copy number in the development of cardiometabolic disease, but found dyslipidemia and CAD can lead to reduced mtDNA copy number. These findings have implications for mtDNA copy number as a biomarker of dyslipidemia and CAD in clinical practice.

Association between migraine and mitochondria: A Mendelian randomization study

BACKGROUND AND OBJECTIVE

Mitochondria are important organelles functioning in metabolic processes, inflammatory response and neurological disorders. Migraines are chronic and paroxysmal neurological disorders characterized by recurrent episodes of severe headache and other neurological symptoms. We explored whether mitochondria may be genetically and/or causally associated with migraine.

METHODS

Summary-level statistics of mitochondrial DNA copy number (mtDNA-CN), 69 mitochondria related exposures and migraine with aura, migraine without aura, migraine with aura and triptan purchases, migraine with aura, drug-induced, migraine without aura and triptan purchases and migraine without aura, drug-induced, were collected from genome-wide association studies (GWAS). The analysis employed two-sample Mendelian randomization, utilizing various methods including MR-Egger, inverse-variance weighted (IVW), MR-PRESSO (MR-pleiotropy residual sum and outlier), maximum likelihood, and weighted median.

RESULTS

We observed a potential association with decreased levels of mtDNA-CN with the risk of migraine without aura (Odds ratio (OR) 1.517, 95% Confidence interval (CI) 1.072-2.147, p = 0.019). Besides, for every 1 unit in NAD-dependent protein deacylase sirtuin-5 (SIRT5), relative risk of migraine without aura increased by 16.4%. For every 1 unit increase in Phenylalanine-transfer RNA (tRNA) ligase, relative risk of migraine without aura increased by 13.5%. For every 1 unit increase in Apoptosis-inducing factor 1, relative risk of migraine without aura increased by 27.4%.

CONCLUSION

This study indicates fresh evidence of association between mtDNA-CN, mitochondrial related exposures and migraine especially migraine without aura. The findings may shed light on developing interventions targeting on the causal pathway from mitochondria to migraine.

Reduced Peripheral Blood Mitochondrial DNA Copy Number as Identification Biomarker of Suspected Arsenic-Induced Liver Damage

Arsenic (As) can cause liver damage and liver cancer and is capable of seriously affecting human health. Therefore, it is important to identify biomarkers of arsenic-induced liver damage. Mitochondria are key targets of hepatotoxicity caused by arsenic. The mitochondrial DNA copy number (mtDNAcn) is the number of mitochondrial DNA (mtDNA) copies in the genome. mtDNA is vulnerable to exogenous chemical attacks, thus causing mtDNAcn to change after exposure to environmental pollutants. Therefore, mtDNAcn can serve as a potential marker to identify and assess the risk of diseases caused by exposure to environmental pollutants. In this study, we selected 272 arsenicosis patients (155 cases without liver damage and 117 cases with liver damage) and 218 participants not exposed to arsenic (155 cases without liver damage and 63 cases with liver damage) as subjects to investigate the correlation between peripheral blood mtDNAcn and arsenic-induced liver damage, as well as the ability of peripheral blood mtDNAcn to identify and assess the risk of arsenic-induced liver damage. Peripheral blood mtDNAcn in patients with arsenic-induced liver damage is significantly decreased and negatively correlated with serum ALT, AST, and GGT levels. The decrease of peripheral blood mtDNAcn was associated with an increased risk of arsenic-induced liver damage. The receiver operating characteristic (ROC) curve analysis indicated that peripheral blood mtDNAcn could specifically identify patients with liver damage in the arsenicosis group. The decision tree C5.0 model was established to identify arsenicosis in all patients with liver damage. Peripheral blood mtDNAcn was included in the model and played the most important role in the identification of arsenic-induced liver damage. This study provided a basis for the identification and evaluation of arsenic-induced liver damage by peripheral blood mtDNAcn, indicating that peripheral blood mtDNAcn is expected to be a potential biomarker of arsenic-induced liver damage, and provides clues for exploring the mechanism of arsenic-induced liver damage from mitochondria damage.

Impact of peripheral mitochondrial DNA level on immune response after COVID-19 vaccination

The efficacy of vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the elderly is partially hindered by immunosenescence, resulting from decreased mtDNA levels. This study evaluated the correlation between mtDNA levels in peripheral leukocytes and immune response to the SARS-CoV-2 vaccine. Two hundred ten participants (median age 79.5 years), including 83 frail residents/inpatients and 70 robust outpatients, were analyzed. Anti-spike IgG antibody (IgG(S)) titers were serially measured from before the first vaccination to after the third vaccination. The mtDNA levels and cell-mediated immunity were measured in 45 elderly and 22 elderly individuals two months after the third vaccination. The robust group had consistently higher IgG(S) titers than the frail group. The mtDNA levels positively correlated with IgG(S) titers, as well as with cell-mediated immunity. These findings suggest that mtDNA levels positively impact vaccine-induced immunity. Further studies into maintaining mtDNA levels may provide insights into immunosenescence in the elderly.