The mitochondrial T16189C polymorphism is associated with coronary artery disease in Middle European populations

Glioma grade and mortality in relation to sequence variation in the mitochondrial genome

PURPOSE

Glioma arises from glial cells and comprises ∼80 % of malignant adult brain tumors. The polymorphic mitochondrial genome plays a key role in maintaining redox homeostasis and generation of reactive oxygen species (ROS). ROS have a well-established role in glial tumors. We investigated associations between germline mtDNA variants and haplogroups with glioma grade and glioblastoma (GBM) survival.

METHODS

We conducted germline mtDNA sequencing for 388 patients (300 Caucasians, 88 African Americans [AA]) with incident glioma (105 non-GBM, 283 GBM). Across all patients we identified 1431 homoplasmic mtDNA variants, including 692 variants observed only in Caucasians, 474 only in AAs, and 265 in both groups. We estimated Odds Ratios (OR) and 95 % Confidence Intervals (CI) for mtDNA common variants, haplogroups, and gene variant burden in relation to glioma grade and tertiles of survival in GBM patients. Bonferroni and Benjamini-Hochberg correction were applied for multiple comparisons.

RESULTS

No mtDNA haplogroup was associated with glioma grade or patient survival in GBM. Common variants m.3010G>A, m.195T>C, and m.16189T>C were linked to lower-grade glioma risk. For GBM survival, m.1719G>A, m.14766T>C, m.16129G>A, and m.204T>C were associated with a poorer prognosis while variant m.73A>G was associated with an improved prognosis. A higher variant burden in MT-ND1 and MT-ND5 was associated with a better prognosis. No results remained statistically significant after correction.

CONCLUSION

This is the first comprehensive study of germline mtDNA sequence variation in relation to glioma grade at diagnosis and gliobastoma patient survival. Results warrant further study in larger populations and investigation of biologic mechanisms linking mtDNA polymorphism to these endpoints.

Novel blood and tissue-based mitochondrial D-loop mutations detected in an Iranian NAFLD patient cohort

Non-alcoholic fatty liver disease (NAFLD) is an increasingly prevalent chronic liver disease characterized by an elusive etiology. In its advanced stages, this condition can pose life-threatening implications. Mitochondrial dysfunction due to its impact on hepatic lipid homeostasis, cytokine release, ROS production, and cell death, contributes to the pathogenesis of NAFLD. Previous research reveals a direct link between NAFLD genetic predictors and mitochondrial dysfunction. The emphasis on the D-loop stems from its association with impaired mtDNA replication, underscoring its crucial role in NAFLD progression. We included 38 Iranian NAFLD patients (comprising 16 patients with non-alcoholic fatty liver [NAFL] and 22 patients with non-alcoholic steatohepatitis [NASH]), with matched blood and liver tissue samples collected from each to compare variations in the mitochondrial D-loop sequence within samples. The mitochondrial DNA (mtDNA) D-loop region was amplified using PCR, and variations were identified through sequencing. The resultant sequences were compared with the reference sequence of human mtDNA available in the MITOMAP Database for comparative analysis. In this study, 97 somatic mutations in the mtDNA D-loop region were identified in NAFLD patients. Our study revealed significant difference between the NAFLD patients and control group in 13 detected mutations (P ≤ 0.05). Novel mutations were discovered in hepatic tissues, while mutation 16220-16221ins C was found in both tissues and blood. A significant difference was found in the distribution of D310 and mt514-mt523 (CA)n repeat variations between NAFLD patients and the control group (P < 0.001). C to T and T to C transitions were the prevalent substitution among patients. Identification of the 16220-16221ins C mutation in both blood and tissue samples from NAFLD patients holds substantial promise as a potential diagnostic marker. However, further research is imperative to corroborate these findings.

Mitochondrial Dysfunction Associated with mtDNA in Metabolic Syndrome and Obesity

Metabolic syndrome (MetS) is a precursor to the major health diseases associated with high mortality in industrialized countries: cardiovascular disease and diabetes. An important component of the pathogenesis of the metabolic syndrome is mitochondrial dysfunction, which is associated with tissue hypoxia, disruption of mitochondrial integrity, increased production of reactive oxygen species, and a decrease in ATP, leading to a chronic inflammatory state that affects tissues and organ systems. The mitochondrial AAA + protease Lon (Lonp1) has a broad spectrum of activities. In addition to its classical function (degradation of misfolded or damaged proteins), enzymatic activity (proteolysis, chaperone activity, mitochondrial DNA (mtDNA)binding) has been demonstrated. At the same time, the spectrum of Lonp1 activity extends to the regulation of cellular processes inside mitochondria, as well as outside mitochondria (nuclear localization). This mitochondrial protease with enzymatic activity may be a promising molecular target for the development of targeted therapy for MetS and its components. The aim of this review is to elucidate the role of mtDNA in the pathogenesis of metabolic syndrome and its components as a key component of mitochondrial dysfunction and to describe the promising and little-studied AAA + LonP1 protease as a potential target in metabolic disorders.

Mitochondrial Heteroplasmy as a Marker for Premature Coronary Artery Disease: Analysis of the Poly-C Tract of the Control Region Sequence

Mitochondrial DNA (mtDNA) differs from the nuclear genome in many aspects: a maternal inheritance pattern; being more prone to acquire somatic de novo mutations, accumulative with age; and the possible coexistence of different mtDNA alleles (heteroplasmy). Mitochondria are key cellular organelles responsible for energy production and involved in complex mechanisms, including atherosclerosis. In this scenario, we aimed to evaluate mtDNA variants that could be associated with premature cardiovascular disease. We evaluated 188 consecutive patients presenting with premature myocardial infarction with ST elevation (STEMI) confirmed by coronary angiogram. mtDNA polymorphisms and clinical data were evaluated and compared with 271 individuals from the same population (control group). Tobacco consumption (80.85% vs. 21.21%, p < 0.01) and dyslipidemia (38.83% vs. 28.41%, p = 0.02) were significantly more frequent among STEMI patients. Moreover, C16223T mtDNA mutation and poly-C heteroplasmy were significantly more frequent among premature STEMI male patients than in controls. The OR associated C16223T mtDNA with the increased presence of cardiovascular risk factors. Our data suggest that mtDNA 16223T and heteroplasmy may be associated with unstable premature atherosclerosis disease in men. Moreover, the presence of cardiovascular risk factors (CVRFs) was associated with C16223T mtDNA, with a cumulative effect. Protective mitochondrial pathways are potential therapeutic targets. Preventing exposure to the damaging mechanisms associated with CVRFs is of utmost importance.

Precision mitochondrial medicine

Mitochondria play a key role in cell homeostasis as a major source of intracellular energy (adenosine triphosphate), and as metabolic hubs regulating many canonical cell processes. Mitochondrial dysfunction has been widely documented in many common diseases, and genetic studies point towards a causal role in the pathogenesis of specific late-onset disorder. Together this makes targeting mitochondrial genes an attractive strategy for precision medicine. However, the genetics of mitochondrial biogenesis is complex, with over 1,100 candidate genes found in two different genomes: the nuclear DNA and mitochondrial DNA (mtDNA). Here, we review the current evidence associating mitochondrial genetic variants with distinct clinical phenotypes, with some having clear therapeutic implications. The strongest evidence has emerged through the investigation of rare inherited mitochondrial disorders, but genome-wide association studies also implicate mtDNA variants in the risk of developing common diseases, opening to door for the incorporation of mitochondrial genetic variant analysis in population disease risk stratification.

Modulating mitochondrial DNA mutations: factors shaping heteroplasmy in the germ line and somatic cells

Until recently it was thought that most humans only harbor one type of mitochondrial DNA (mtDNA), however, deep sequencing and single-cell analysis has shown the converse - that mixed populations of mtDNA (heteroplasmy) are the norm. This is important because heteroplasmy levels can change dramatically during transmission in the female germ line, leading to high levels causing severe mitochondrial diseases. There is also emerging evidence that low level mtDNA mutations contribute to common late onset diseases such as neurodegenerative disorders and cardiometabolic diseases because the inherited mutation levels can change within developing organs and non-dividing cells over time. Initial predictions suggested that the segregation of mtDNA heteroplasmy was largely stochastic, with an equal tendency for levels to increase or decrease. However, transgenic animal work and single-cell analysis have shown this not to be the case during germ-line transmission and in somatic tissues during life. Mutation levels in specific mtDNA regions can increase or decrease in different contexts and the underlying molecular mechanisms are starting to be unraveled. In this review we provide a synthesis of recent literature on the mechanisms of selection for and against mtDNA variants. We identify the most pertinent gaps in our understanding and suggest ways these could be addressed using state of the art techniques.

Heteroplasmic mitochondrial DNA variants in cardiovascular diseases

Mitochondria are implicated in the pathogenesis of cardiovascular diseases (CVDs) but the reasons for this are not well understood. Maternally-inherited population variants of mitochondrial DNA (mtDNA) which affect all mtDNA molecules (homoplasmic) are associated with cardiometabolic traits and the risk of developing cardiovascular disease. However, it is not known whether mtDNA mutations only affecting a proportion of mtDNA molecules (heteroplasmic) also play a role. To address this question, we performed a high-depth (~1000-fold) mtDNA sequencing of blood DNA in 1,399 individuals with hypertension (HTN), 1,946 with ischemic heart disease (IHD), 2,146 with ischemic stroke (IS), and 723 healthy controls. We show that the per individual burden of heteroplasmic single nucleotide variants (mtSNVs) increases with age. The age-effect was stronger for low-level heteroplasmies (heteroplasmic fraction, HF, 5-10%), likely reflecting acquired somatic events based on trinucleotide mutational signatures. After correcting for age and other confounders, intermediate heteroplasmies (HF 10-95%) were more common in hypertension, particularly involving non-synonymous variants altering the amino acid sequence of essential respiratory chain proteins. These findings raise the possibility that heteroplasmic mtSNVs play a role in the pathophysiology of hypertension.

Mitochondria in tumour progression: a network of mtDNA variants in different types of cancer

Background

Mitochondrial participation in tumorigenesis and metastasis has been studied for many years, but several aspects of this mechanism remain unclear, such as the association of mitochondrial DNA (mtDNA) with different cancers. Here, based on two independent datasets, we modelled an mtDNA mutation-cancer network by systematic integrative analysis including 37 cancer types to identify the mitochondrial variants found in common among them.

Results

Our network showed mtDNA associations between gastric cancer and other cancer types, particularly kidney, liver, and prostate cancers, which is suggestive of a potential role of such variants in the metastatic processes among these cancer types. A graph-based interactive web tool was made available at www2.lghm.ufpa.br/mtdna. We also highlighted that most shared variants were in the MT-ND4, MT-ND5 and D-loop, and that some of these variants were nonsynonymous, indicating a special importance of these variants and regions regarding cancer progression, involving genomic and epigenomic alterations.

Conclusions

This study reinforces the importance of studying mtDNA in cancer and offers new perspectives on the potential involvement of different mitochondrial variants in cancer development and metastasis.

Evaluation of D-loop hypervariable region I variations, haplogroups and copy number of mitochondrial DNA in Bangladeshi population with type 2 diabetes

The profound impact of mitochondrion in cellular metabolism has been well documented. Since type 2 diabetes (T2D) is a metabolic disorder, mitochondrial dysfunction is intricately linked with the disease pathogenesis. Mitochondrial DNA (mtDNA) variants are involved with functional dysfunction of mitochondrion and play a pivotal role in the susceptibility to T2D. In this study, we opted to find the association of mtDNA variants within the D-loop hypervariable region I (HVI), haplogroups and mtDNA copy number with T2D in Bangladeshi population. A total of 300 unrelated Bangladeshi individuals (150 healthy and 150 patients with T2D) were recruited in the present study, their HVI regions were amplified and sequenced using Sanger chemistry. Haplogrep2 and Phylotree17 tools were employed to determine the haplogroups. MtDNA copy number was measured using primers of mitochondrial tRNALeu (UUR) gene and nuclear β2-microglobulin gene. Variants G16048A (OR:0.12, p = 0.04) and G16129A (OR: 0.42, p = 0.007) were found to confer protective role against T2D according to logistic regression analysis. However along with G16129A, two new variants C16294T and T16325C demonstrated protective role against T2D when age and gender were adjusted. Haplogroups A and H showed significant association with the risk of T2D after adjustments out of total 19 major haplogroups identified. The mtDNA copy numbers were stratified into 4 groups according to the quartiles (groups with lower, medium, upper and higher mtDNA copy numbers were respectively designated as LCN, MCN, UCN and HCN). Patients with T2D had significantly lower mtDNA copy number compared to their healthy counterparts in HCN group. Moreover, six mtDNA variants were significantly associated with mtDNA copy number in the participants. Thus, our study confers that certain haplogroups and novel variants of mtDNA are significantly associated with T2D while decreased mtDNA copy number (though not significant) has been observed in patients with T2D. However, largescale studies are warranted to establish association of novel variants and haplogroup with type 2 diabetes.

The Role of Mitochondria in Carcinogenesis

The mitochondria are essential for normal cell functioning. Changes in mitochondrial DNA (mtDNA) may affect the occurrence of some chronic diseases and cancer. This process is complex and not entirely understood. The assignment to a particular mitochondrial haplogroup may be a factor that either contributes to cancer development or reduces its likelihood. Mutations in mtDNA occurring via an increase in reactive oxygen species may favour the occurrence of further changes both in mitochondrial and nuclear DNA. Mitochondrial DNA mutations in postmitotic cells are not inherited, but may play a role both in initiation and progression of cancer. One of the first discovered polymorphisms associated with cancer was in the gene NADH-ubiquinone oxidoreductase chain 3 (mt-ND3) and it was typical of haplogroup N. In prostate cancer, these mutations and polymorphisms involve a gene encoding subunit I of respiratory complex IV cytochrome c oxidase subunit 1 gene (COI). At present, a growing number of studies also address the impact of mtDNA polymorphisms on prognosis in cancer patients. Some of the mitochondrial DNA polymorphisms occur in both chronic disease and cancer, for instance polymorphism G5913A characteristic of prostate cancer and hypertension.

Associations of Mitochondrial Variants With Lipidomic Traits in a Chinese Cohort With Coronary Artery Disease

Plasma lipids have been at the center stage of the prediction and prevention strategies for cardiovascular diseases (CVDs), and novel lipidomic traits have been recognized as reliable biomarkers for CVD risk prediction. The mitochondria serve as energy supply sites for cells and can synthesize a variety of lipids autonomously. Therefore, investigating the relationships between mitochondrial single nucleotide polymorphism (SNPs) and plasma lipidomic traits is meaningful. Here, we enrolled a total of 1,409 Han Chinese patients with coronary artery disease from three centers and performed linear regression analyses on the SNPs of mitochondrial DNA (mtDNA) and lipidomic traits in two independent groups. Sex, age, aspartate aminotransferase, estimated glomerular filtration rate, antihypertensive drugs, hypertension, and diabetes were adjusted. We identified three associations, namely, D-loop_m.16089T>C with TG(50:4) NL-16:0, D-loop_m.16145G>A with TG(54:5) NL-18:0, and D-loop_m.16089T>C with PC(16:0_16:1) at the statistically significant threshold of FDR < 0.05. Then, we explored the relationships between mitochondrial genetic variants and traditional lipids, including triglyceride, total cholesterol (TC), low-density lipoprotein cholesterol (LDLC), and high-density lipoprotein cholesterol. Two significant associations were found, namely MT-ND6_m.14178T>C with TC and D-loop_m.215A>G with LDLC. Furthermore, we performed linear regression analysis to determine on the SNPs of mtDNA and left ventricular ejection fraction (LVEF) and found that the SNP D-loop_m.16145G>A was nominally significantly associated with LVEF (P = 0.047). Our findings provide insights into the lipidomic context of mtDNA variations and highlight the importance of studying mitochondrial genetic variants related to lipid species.

Impact of Mitochondrial DNA Mutations on Carotid Intima-Media Thickness in the Novosibirsk Region

The search for markers of predisposition to atherosclerosis development is very important for early identification of individuals with a high risk of cardiovascular disease. The aim of the present study was to investigate the association of mitochondrial DNA mutations with carotid intima-media thickness and to determine the impact of mitochondrial heteroplasmy measurements in the prognosis of atherosclerosis development. This cross-sectional, population-based study was conducted in 468 subjects from the Novosibirsk region. It was shown that the mean (carotid intima-media thickness) cIMT correlated with the following mtDNA mutations: m.15059G>A (r = 0.159, p = 0.001), m.12315G>A (r = 0.119; p = 0.011), m.5178C>A (r = 0.114, p = 0.014), and m.3256C>T (r = 0.130, p = 0.011); a negative correlation with mtDNA mutations m.14846G>A (r = −0.111, p = 0.042) and m.13513G>A (r = −0.133, p = 0.004) was observed. In the linear regression analysis, the addition of the set of mtDNA mutations to the conventional cardiovascular risk factors increased the ability to predict the cIMT variability from 17 to 27%. Multi-step linear regression analysis revealed the most important predictors of mean cIMT variability: age, systolic blood pressure, blood levels of total cholesterol, LDL and triglycerides, as well as the mtDNA mutations m.13513G>A, m.15059G>A, m.12315G>A, and m.3256C>T. Thus, a high predictive value of mtDNA mutations for cIMT variability was demonstrated. The association of mutation m.13513G>A and m.14846G>A with a low value of cIMT, demonstrated in several studies, represents a potential for the development of anti-atherosclerotic gene therapy.

Association between mitochondrial DNA haplogroup variation and coronary artery disease

BACKGROUND AND AIMS

Mitochondrial DNA (mtDNA) haplogroups have been associated with the development of coronary artery disease (CAD) in European populations. However, the specific mtDNA haplogroups associated with CAD have not been investigated in Chinese populations.

METHODS AND RESULTS

Here, we carried out a case-control study including 1036 and 481 CAD patients and 973 and 511 geographically matched asymptomatic control subjects in southern and northern China, respectively. After adjusting for age and gender, our results indicated that mtDNA haplogroups are not associated with the occurrence of CAD and its subcategories, acute coronary syndromes and stable coronary heart disease, in both southern and northern Chinese populations. By focusing on the southern Chinese population, we further revealed that mtDNA haplogroups are not associated with CAD severity. Type 2 diabetes (T2D) and hypertension are two key driving factors for the development of CAD, nonetheless, we found that the frequencies of the 12 studied mtDNA haplogroups did not differ between patients with and without T2D or hypertension.

CONCLUSION

mtDNA haplogroups are not associated with the occurrence of CAD or its subcategories in Chinese populations. Other factors such as environment and nuclear genetic background may contribute to the occurrence of CAD.

African and Asian Mitochondrial DNA Haplogroups Confer Resistance Against Diabetic Stresses on Retinal Pigment Epithelial Cybrid Cells In Vitro

Diabetic retinopathy (DR) is the most common cause of blindness for individuals under the age of 65. This loss of vision can be due to ischemia, neovascularization, and/or diabetic macular edema, which are caused by breakdown of the blood-retina barrier at the level of the retinal pigment epithelium (RPE) and inner retinal vasculature. The prevalence of diabetes and its complications differ between Caucasian-Americans and certain minority populations, such as African-Americans and Asian-Americans. Individuals can be classified by their mitochondrial haplogroups, which are collections of single nucleotide polymorphisms (SNPs) in mitochondrial DNA (mtDNA) representing ancient geographic origins of populations. In this study, we compared the responses of diabetic human RPE cybrids, cell lines containing identical nuclei but mitochondria from either European (maternal European) or maternal African or Asian individuals, to hypoxia and high glucose levels. The African and Asian diabetic ([Afr+Asi]/DM) cybrids showed (1) resistance to both hyperglycemic and hypoxic stresses; (2) downregulation of pro-apoptotic indicator BAX; (3) upregulation of DNA methylation genes, such as DNMT3A and DNMT3B; and (4) resistance to DNA demethylation by the methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-dC) compared to European diabetic (Euro/DM) cybrids. Our findings suggest that mitochondria from African and Asian diabetic subjects possess a "metabolic memory" that confers resistance against hyperglycemia, hypoxia, and demethylation, and that this "metabolic memory" can be transferred into the RPE cybrid cell lines in vitro.

The alterations of mitochondrial DNA in coronary heart disease

Coronary heart disease (CHD) is the major cause of death in modern society. CHD is characterized by atherosclerosis, which could lead to vascular cavity stenosis or obstruction, resulting in ischemic cardiac conditions such as angina and myocardial infarction. In terms of the mitochondrion, the main function is to produce adenosine triphosphate (ATP) for cells. And the alterations (including mutations, altered copy number and haplogroups) of mitochondrial DNA (mtDNA) are associated with the abnormal expression of oxidative phosphorylation (OXPHOS) system, resulting in mitochondrial dysfunction, then leading to perturbation on the electron transport chain and increased ROS generation and reduction in ATP level, contributing to ATP-producing disorders and oxidative stress, which may further accelerate development or vulnerability of atherosclerosis and myocardial ischemic injury. Therefore, the mtDNA defects may play an important role in making an early diagnosis, identifying disease-specific biomarkers and therapeutic targets, and predicting outcomes for patients with atherosclerosis and CHD. In this review, we aim to summarize the contribution of mtDNA mutations, altered mtDNA copy number and mtDNA haplogroups on the occurrence and development of CHD.

The role of control region mitochondrial DNA mutations in cardiovascular disease: stroke and myocardial infarction

Recent studies associated certain type of cardiovascular disease (CVD) with specific mitochondrial DNA (mtDNA) defects, mainly driven by the central role of mitochondria in cellular metabolism. Considering the importance of the control region (CR) on the regulation of the mtDNA gene expression, the aim of the present study was to investigate the role of mtDNA CR mutations in two CVDs: stroke and myocardial infarction (MI). MtDNA CR mutations (both fixed and in heteroplasmy) were analysed in two demographically-matched case-control samples, using 154 stroke cases, 211 MI cases and their corresponding control individuals. Significant differences were found, reporting mutations m.16145 G > A and m.16311 T > C as potential genetic risk factors for stroke (conditional logistic regression: p = 0.038 and p = 0.018, respectively), whereas the m.72 T > C, m.73 A > G and m.16356 T > C mutations could act as possible beneficial genetic factors for MI (conditional logistic regression: p = 0.001, p = 0.009 and p = 0.016, respectively). Furthermore, our findings also showed a high percentage of point heteroplasmy in MI controls (logistic regression: p = 0.046; OR = 0.209, 95% CI [0.045-0.972]). These results demonstrate the possible role of mtDNA mutations in the CR on the pathogenesis of stroke and MI, and show the importance of including this regulatory region in genetic association studies.

Atherosclerosis Can Be Mitochondrial: A Review

One of the systems that are potentially affected in mitochondrial disorders, but hardly get systematically investigated, are the arteries. One of the phenotypic manifestations in arteries is atherosclerosis. This review focuses on the current knowledge and recent advances of mitochondrial atherosclerosis. We conducted a systematic literature review via PubMed using appropriate search terms.

Atherosclerosis in mitochondrial disorders may result from a primary pathomechanism or a secondary one due to mitochondrial diabetes, arterial hypertension, or hyperlipidemia. Anecdotal reports show that primary atherosclerosis can be a phenotypic feature of mitochondrial disorders. Predominantly, patients carrying mutations in mtDNA-located genes may develop primary mitochondrial atherosclerosis. Though not systematically investigated, it is conceivable that primary mitochondrial atherosclerosis results from increased oxidative stress, mitophagy, metabolic breakdown, or lactic acidosis. Mitochondrial disorder patients with primary mitochondrial atherosclerosis should receive not only antithrombotic medication but also antioxidants and cofactors.

Atherosclerosis in mitochondrial disorders may occur even in the absence of classical atherosclerosis risk factors, suggesting that atherosclerosis can be a primary manifestation of the metabolic defect. Though primary atherosclerosis in mitochondrial disorders has not been systematically investigated, anecdotal data indicate that mitochondrial dysfunction can be a mechanism for the development of primary, mitochondrial atherosclerosis. These patients require antioxidants and cofactors in addition to antithrombotic medication.

Discovery of mitochondrial DNA variants associated with genome-wide blood cell gene expression: a population-based mtDNA sequencing study

The effect of mitochondrial DNA (mtDNA) variation on peripheral blood transcriptomics in health and disease is not fully known. Sex-specific mitochondrially controlled gene expression patterns have been shown in Drosophila melanogaster but in humans, evidence is lacking. Functional variation in mtDNA may also have a role in the development of type 2 diabetes and its precursor state, i.e. prediabetes. We examined the associations between mitochondrial single-nucleotide polymorphisms (mtSNPs) and peripheral blood transcriptomics with a focus on sex- and prediabetes-specific effects. The genome-wide blood cell expression data of 19 637 probes, 199 deep-sequenced mtSNPs and nine haplogroups of 955 individuals from a population-based Young Finns Study cohort were used. Significant associations were identified with linear regression and analysis of covariance. The effects of sex and prediabetes on the associations between gene expression and mtSNPs were studied using random-effect meta-analysis. Our analysis identified 53 significant expression probe-mtSNP associations after Bonferroni correction, involving 7 genes and 31 mtSNPs. Eight probe-mtSNP signals remained independent after conditional analysis. In addition, five genes showed differential expression between haplogroups. The meta-analysis did not show any significant differences in linear model effect sizes between males and females but identified the association between the OASL gene and mtSNP C16294T to show prediabetes-specific effects. This study pinpoints new independent mtSNPs associated with peripheral blood transcriptomics and replicates six previously reported associations, providing further evidence of the mitochondrial genetic control of blood cell gene expression. In addition, we present evidence that prediabetes might lead to perturbations in mitochondrial control.

Integrating Genes Affecting Coronary Artery Disease in Functional Networks by Multi-OMICs Approach

Coronary artery disease (CAD) and myocardial infarction (MI) remain among the leading causes of mortality worldwide, urgently demanding a better understanding of disease etiology, and more efficient therapeutic strategies. Genetic predisposition as well as the environment and lifestyle are thought to contribute to disease risk. It is likely that non-linear and complex interactions occur between these multiple factors, involving simultaneous pathological changes in diverse cell types, tissues, and organs, at multiple molecular levels. Recent technological advances have exponentially expanded the breadth of available -omics data, from genome, epigenome, transcriptome, proteome, metabolome to even the microbiome. Integration of multiple layers of information across several -omics domains, i.e., the so-called multi-omics approach, currently holds the promise as a path toward precision medicine. Indeed, a more meaningful interpretation of genotype-phenotype relationships and the development of successful therapeutics tailored to individual patients are urgently needed. In this review, we will summarize recent findings and applications of integrative multi-omics in elucidating the etiology of CAD/MI; with a special focus on established disease susceptibility loci sequentially identified in genome-wide association studies (GWAS) over the last 10 years. Moreover, in addition to the autosomal genome, we will also consider the genetic variation in our “second genome”—the mitochondrial genome. Finally, we will summarize the current challenges in the field and point to future research directions required in order to successfully and effectively apply these approaches for precision medicine.

Meta-analysis of mitochondrial T16189C polymorphism for cancer and Type 2 diabetes risk

AIM

Whereas many previous studies have revealed that mitochondrial DNA (mtDNA) polymorphism T16189C is associated with the risk of cancer and Type 2 diabetes mellitus (T2DM), there are others that have disputed the same. As a result, clarity on the role of mitochondrial T16189C in these disorders is missing. The aim of this study is to evaluate the association of T16189C polymorphism with the risk of cancer and T2DM development by pooling all case-control studies available.

METHODS

Published studies till November 2017 were searched from PubMed, Google scholar, Google and EMBASE and isolated a total of 36 studies having 44,203 subjects (20,439 cases and 23,764 controls) based on strict inclusion and exclusion criteria. We used the statistical software "R" to calculate the Pooled Odds Ratios and 95% confidence intervals to evaluate the association of T16189C polymorphism with a possible risk towards cancer and T2DM development.

RESULT

From the meta-analysis, we obtained Pooled Odds Ratios using Random effect model for cancer (OR: 1.20, 95% CI: 0.96-1.49, P = 0.104) and for T2DM (OR: 1.22, 95% CI: 1.09-1.36, P = 0.0004). In the subgroup analysis with Random effect model, we found that both Asians and Caucasians were at a statistically significant risk (OR: 1.25, P < 0.0001 and OR: 1.20, P < 0.0001, respectively) for the development of T2DM, whereas, a statistically non-significant risk (OR: 1.28 P = 0.1965 and OR: 1.16, P = 0.1148) emerged for the development of cancer. There was no evidence of a significant publication bias (Egger's and Begg's test) in this meta-analysis. Further sensitivity analysis also demonstrated that our meta-analysis was relatively stable and credible.

CONCLUSION

Individuals with 'C' allele at position 16,189 within the mitochondrial D-loop are seemingly at a higher risk of developing T2DM and cancer. However, before arriving at generalizations, it would be pertinent to conduct similar studies in different populations with larger numbers to corroborate these results, especially in cancer.

Mitochondrial T16189C Polymorphism Is Associated with Metabolic Syndrome in the Mexican Population

Genetic factors, such as the mitochondrial DNA (mtDNA) T16189C polymorphism, have been associated with metabolic syndrome (MetS), but this association has not been studied in Mexico to date. The aim of the present study was to determine whether this polymorphism contributes to MetS in the Mexican population. We recruited 100 unrelated volunteer subjects who were divided into 2 groups: with MetS (MetS group) and without MetS (control group). All subjects were genotyped for the mtDNA T16189C polymorphism by polymerase chain reaction and sequencing. The mitochondrial T16189C polymorphism was detected in 24 (24%) of 100 subjects analyzed. The frequency of the mtDNA T16189C polymorphism was higher in the MetS group with 21 (32.3%) of 65 testing positive compared to 3 (8.5%) of 35 in the control group, indicating that this polymorphism is a probable risk factor for MetS in the Mexican population (odds ratio 5.0909, 95% CI 1.3977–18.5424, P = 0.0136). Our results may contribute to early diagnosis of MetS, which is essential for establishing changes in early stages of the disease to avoid further complications and pathologies, thereby preventing the development of type 2 diabetes and cardiovascular disease in Mexico.

Association of mitochondrial copy number variation and T16189C polymorphism with colorectal cancer in North Indian population

Globally, colorectal cancer is the third most common type of cancer. Genetic instability leading to cancer development is one of the major causes for development of cancer. Alterations in mitochondrial genome, that is, mutations, single-nucleotide polymorphisms, and copy number variations are known to contribute in cancer development. The aim of our study was to investigate association of mitochondrial T16189C polymorphism and copy number variation with colorectal cancer in North Indian population. DNA isolated from peripheral blood of 126 colorectal cancer patients and 114 healthy North Indian subjects was analyzed for T16189C polymorphism and half of them for mitochondrial copy number variation. Genotyping was done using polymerase chain reaction-restriction fragment length polymorphism, and copy number variation was estimated using real-time polymerase chain reaction, numbers of mitochondrial copies and found to be significantly higher in colorectal cancer patients than healthy controls (88 (58-154), p = 0.001). In the regression analysis, increased mitochondrial copy number variation was associated with risk of colorectal cancer (odds ratio = 2.885, 95% confidence interval = 1.3-6.358). However, T16189C polymorphism was found to be significantly associated with the risk of rectal cancer (odds ratio = 5.213, p = 0.001) and non-significantly with colon cancer (odds ratio = 0.867, p = 0.791). Also, false-positive report probability analysis was done to validate the significant findings. Our results here indicate that mitochondrial copy number variation may be playing an important role in the development of colorectal cancer, and detection of mitochondrial copy number variation can be used as a biomarker for predicting the risk of colorectal cancer in North Indian subjects.

Sequence variations of mitochondrial DNA D-loop region in patients with acute myeloid leukemia

The aim of the present study was to explore variations of the displacement (D)-loop region in patients with acute myeloid leukemia (AML) and their possible associations with AML pathogenesis. Blood or bone marrow samples from 216 patients with AML (158 AML patients in the first stage, and 58 more patients with AML-M3 for further verification), and 146 healthy controls were collected. Sanger sequencing was performed for the D-loop region ranging between nucleotide (nt)15811 and nt 775. With the exception of mitochondrial microsatellite instability (mtMSI) variations, a total of 2,630 variations in 232 loci were identified with similar variation rates/person in patients with AML and controls when compared with the revised Cambridge reference sequence (8.54±2.14 vs. 8.77±2.15; P=0.366). A positive association between AML and variation-T152C was identified, which occurred more frequently in patients with AML compared with in controls [26.6 vs. 17.1%; P=0.048; odds ratio (OR), 1.752; 95% confidence interval (CI), 1.004-3.058]. Furthermore, T152C was identified to be associated with promyelocytic leukemia-retinoic acid receptor α(PML-RARα) and French-American-British AML subtypes, with a tendency to occur in patients with AML-M3. The AML-M3 sample size was extended by 58 cases, and it was identified that the T152C variation rate was significantly higher in patients with AML-M3 compared with that of controls (41.0 vs. 17.1%; P<0.001; OR, 3.228; 95% CI, 1.714-6.079). However, no association was identified between the T152C variation and clinical characteristics, or chemotherapy response in patients with AML-M3. In addition, the mtMSIs, including D310, mt514-523 (CA)_n and T16189C, demonstrated no association with AML risk. Together, the results of the present study suggest that the mitochondrial DNA D-loop region is high variable, and that T152C is associated with AML risk, particularly regarding the M3 subtype. T152C mayparticipate in AML pathogenesis and may be a diagnostic biomarker; however further studies with larger sample sizes are required in order to verify its value.

Detection of somatic mutations in the mitochondrial DNA control region D-loop in brain tumors: The first report in Malaysian patients

Although the role of nuclear-encoded gene alterations has been well documented in brain tumor development, the involvement of the mitochondrial genome in brain tumorigenesis has not yet been fully elucidated and remains controversial. The present study aimed to identify mutations in the mitochondrial DNA (mtDNA) control region D-loop in patients with brain tumors in Malaysia. A mutation analysis was performed in which DNA was extracted from paired tumor tissue and blood samples obtained from 49 patients with brain tumors. The D-loop region DNA was amplified using the PCR technique, and genetic data from DNA sequencing analyses were compared with the published revised Cambridge sequence to identify somatic mutations. Among the 49 brain tumor tissue samples evaluated, 25 cases (51%) had somatic mutations of the mtDNA D-loop, with a total of 48 mutations. Novel mutations that had not previously been identified in the D-loop region (176 A-deletion, 476 C>A, 566 C>A and 16405 A-deletion) were also classified. No significant associations between the D-loop mutation status and the clinicopathological parameters were observed. To the best of our knowledge, the current study presents the first evidence of alterations in the mtDNA D-loop regions in the brain tumors of Malaysian patients. These results may provide an overview and data regarding the incidence of mitochondrial genome alterations in Malaysian patients with brain tumors. In addition to nuclear genome aberrations, these specific mitochondrial genome alterations may also be considered as potential cancer biomarkers for the diagnosis and staging of brain cancers.

Pandora's Box: mitochondrial defects in ischaemic heart disease and stroke

Ischaemic heart disease and stroke are vascular events with serious health consequences worldwide. Recent genetic and epigenetic techniques have revealed many genetic determinants of these vascular events and simplified the approaches to research focused on ischaemic heart disease and stroke. The pathogenetic mechanisms of ischaemic heart disease and stroke are complex, with mitochondrial involvement (partially or entirely) recently gaining substantial support. Not only can mitochondrial reactive oxygen species give rise to ischaemic heart disease and stroke by production of oxidised low-density lipoprotein and induction of apoptosis, but the impact on pericytes contributes directly to the pathogenesis. Over the past two decades, publications implicate the causative role of nuclear genes in the development of ischaemic heart disease and stroke, in contrast to the potential role of mitochondrial DNA (mtDNA) in the pathophysiology of the disorders, which is much less understood, although recent studies do demonstrate that the involvement of mitochondria and mtDNA in the development of ischaemic heart disease and stroke is likely to be larger than originally thought, with the novel discovery of links among mitochondria, mtDNA and vascular events. Here we explore the molecular events and mtDNA alterations in relation to the role of mitochondria in ischaemic heart disease and stroke.

The association of the mitochondrial DNA oriB variants with metabolic syndrome

Different genes are involved in the development of pathology and formation the metabolic syndrome (MS) phenotype. In the literature, there is a data connection to the site oriB polymorphisms of mitochondrial DNA (mtDNA), known as 16184-16193 polycytosine tract, with insulin resistance, type 2 diabetes (T2DM) and other metabolic abnormalities in different ethnic populations. It is supposed that for certain polymorphisms at this site decreases mtDNA copy number in the cells. In this study, we have identified different allelic variants of the mtDNA oriB site in MS patients (n=106) and healthy individuals (n=71) using capillary sequencing, and determined the amount of mtDNA copy blood leukocytes by droplet digital polymerase chain reaction (ddPCR). The continuous polycytosine tract was significantly more common in MS patients, and such a link was particularly strong in MS patients with type 2 diabetes (p<0.01). No significant correlation has been found between mtDNA copy number and the oriB site variants, but in general there is a tendency to decreased mtDNA copy number in MS patients.

Association of mitochondrial displacement loop polymorphisms with risk of colorectal cancer in south Indian population

Mitochondrial displacement loop (D-loop) is the hot spot for mitochondrial DNA (mtDNA) alterations which influence the generation of cellular reactive oxygen species. In the present study, we sequenced the entire mitochondrial D-loop region (1124 bp) of colorectal cancer (CRC) patients (n = 174) and controls (n = 170) of south Indian origin to identify significant mutations/polymorphisms. Our results showed 152 polymorphisms in the D-loop region of patients and/or controls. Polymorphisms were predominantly located in hypervariable region I (54.6%) than in II (45.4%) of D-loop region. The frequencies of 310'C' insertion (p = 0.0078), T16189C (p = 0.0097) variants and 310'C'ins/16189C haplotype (p = 0.0029) were significantly higher in cases than in controls. Furthermore, strong linkage disequilibrium was observed between nucleotide position 310 and 16189 in cases (D'=0.68) as compared with controls (D'=0.27). In conclusion, mitochondrial D-loop sequence alterations may constitute inherent risk factor for CRC.

Manganese-superoxide dismutase (Mn-SOD) overexpression is a common event in colorectal cancers with mitochondrial microsatellite instability

Mitochondrial displacement loop (D-loop) is a hot spot for mitochondrial DNA (mtDNA) alterations that effects cellular reactive oxygen species (ROS) generation. Manganese-superoxide dismutase (Mn-SOD) is a major antioxidant enzyme that protects cells from ROS-mediated damage. In the present study, we investigated the relationship between sequence alterations of mitochondrial D-loop and Mn-SOD expression in colorectal cancer (CRC). Genotyping of entire mitochondrial D-loop (1124 bp) was carried out on mtDNA of analogous tumor and normal tissues from 35 CRC patients of south Indian origin by PCR-sequencing analysis. Tumor-specific large-scale mtDNA deletions and Mn-SOD expression was analyzed by PCR and Western blot analysis, respectively. We identified 87 polymorphisms in the D-loop region of tumor and/or control tissues. Polymorphisms were predominantly located in hypervariable region I (67.9 %) than in II (32.1 %) of D-loop. Significantly increased mtDNA microsatellite instability (mtMSI) [310'C' insertion (P = 0.00001) and T16189C (P = 0.0007)] and elevated Mn-SOD expression was observed in tumor tissues compared with controls. Interestingly, mtMSI was significantly high in tumors with Mn-SOD overexpression. Tumor-specific large-scale mtDNA deletions were not observed in CRC tissues. In conclusion, mtMSI and Mn-SOD overexpression are a common event in CRC. The analysis of mtMSI and/or Mn-SOD expression might help to identify patients at high risk for disease outcome, thereby helping to refine therapeutic decisions in CRC.

Oxidative Stress Genes, Antioxidants and Coronary Artery Disease in Type 2 Diabetes Mellitus

The worldwide increasing prevalence of obesity and sedentary lifestyle is the main cause of the rising incidence of T2DM. Due to chronic macrovascular and microvascular complications, T2DM represent a huge socioeconomic burden in the world. Oxidative stress is a key pathogenic mechanism implicated in diabetic coronary artery disease (CAD). Polymorphisms of oxidative stress genes are known to influence oxidative stress levels and are therefore thought to impact CAD pathogenesis. Identifying higher risk groups would be rational, since it would allow better sample selection and thus better results in antioxidant trials. In this review, we summarize the evidence of oxidative stress gene polymorphisms related to the pathogenesis of CAD. Moreover, we provide a review of antioxidants tested in subjects with CAD.

Mitochondrial Haplogroup T Is Associated with Obesity in Austrian Juveniles and Adults

Background

Recent publications have reported contradictory data regarding mitochondrial DNA (mtDNA) variation and its association with body mass index. The aim of the present study was to compare the frequencies of mtDNA haplogroups as well as control region (CR) polymorphisms of obese juveniles (n = 248) and obese adults (n = 1003) versus normal weight controls (n_juvenile = 266, n_adults = 595) in a well-defined, ethnically homogenous, age-matched comparative cohort of Austrian Caucasians.

Methodology and Principal Findings

Using SNP analysis and DNA sequencing, we identified the nine major European mitochondrial haplogroups and CR polymorphisms. Of these, only the T haplogroup frequency was increased in the juvenile obese cohort versus the control subjects [11.7% in obese vs. 6.4% in controls], although statistical significance was lost after adjustment for sex and age. Similar data were observed in a local adult cohort, in which haplogroup T was found at a significantly higher frequency in the overweight and obese subjects than in the normal weight group [9.7% vs. 6.2%, p = 0.012, adjusted for sex and age]. When all obese subjects were considered together, the difference in the frequency of haplogroup T was even more clearly seen [10.1% vs. 6.3%, p = 0.002, OR (95% CI) 1.71 (1.2–2.4), adjusted for sex and age]. The frequencies of the T haplogroup-linked CR polymorphisms C16294T and the C16296T were found to be elevated in both the juvenile and the adult obese cohort compared to the controls. Nevertheless, no mtDNA haplogroup or CR polymorphism was robustly associated with any of several investigated metabolic and cardiovascular parameters (e.g., blood pressure, blood glucose concentration, triglycerides, cholesterol) in all obese subjects.

Conclusions and Significance

By investigation of this large ethnically and geographically homogenous cohort of Middle European Caucasians, only mtDNA haplogroup T was identified as an obesity risk factor.

Single nucleotide polymorphisms in the D-loop region of mitochondrial DNA is associated with the kidney survival time in chronic kidney disease patients

BACKGROUND

The mitochondrial displacement loop (D-loop) is known to accumulate mutations and SNPs at a higher frequency than other regions of mitochondrial DNA (mtDNA). We had identified chronic kidney disease (CKD) risk-associated SNPs in the D-loop of CKD patients previously. In this study, we investigated the association of SNPs in the D-loop of mtDNA with the kidney survival of CKD.

METHODS

The D-loop region of mtDNA was sequenced for 119 CKD patients from the inpatient of the Fourth Hospital of Hebei Medical University. The Kaplan-Meier method was used to identify disease outcome-associated SNPs in the D-loop of CKD patients. The Cox proportional hazards model was used to identify risk factors for the kidney survival of CKD.

RESULTS

In the present study, we identified 20 SNPs with a frequency higher than 5% and assessed the relationship of these SNPs with kidney survival time in CKD patients, a SNP of 146 was identified by log-rank test for statistically significant prediction of the kidney survival time. In an overall multivariate analysis, allele 146 was identified as an independent predictor of kidney survival time in CKD patients. The survival time of kidney in the CKD patients with 146C was significantly shorter than that of kidney in CKD patients with 146T (relative risk, 2.336; 95% CI, 1.319-3.923; p = 0.001).

CONCLUSION

SNPs in the D-loop can predict the kidney survival of CKD patients. Analysis of genetic polymorphisms in the mitochondrial D-loop can help to identify CKD patient subgroup at high risk of a poor disease outcome.

Association of genetic variations in the mitochondrial D-loop with β-thalassemia

Beta-thalassemia, one of the most common single-gene disorders, is the result of reduced or absent production of β-globin chains. Patients with β-thalassemia show weak genotype-phenotype correlations. Mitochondrial DNA polymorphisms are a potential source for different physiological and pathological characteristics and have been found to be associated as genetic modifiers with various pathophysiologies, including cancers and neurodegenerative diseases. A group of 35 patients with β-thalassemia was investigated for the presence of mtDNA D-loop polymorphisms in comparison with 504 normal controls. We found four mtDNA D-loop polymorphisms at nucleotides 16,069C > T, 16,189T > C, 16,319G > A, and 16,519T > C that showed significant differences between patients and normal subjects. There is no strong proof for the association of these polymorphisms with β-thalassemia. It is hypothesized that iron overload or its effects on sequestration of calcium or zinc can lead to oxidative stress and ROS production inside the mitochondria. Therefore, possible accompanying of mtDNA polymorphisms with β-thalassemia disease may complicate the genotype-phenotype correlation and could affect the clinical outcomes in the patients.

Quantitative assessment of heteroplasmy of mitochondrial genome: perspectives in diagnostics and methodological pitfalls

The role of alterations of mitochondrial DNA (mtDNA) in the development of human pathologies is not understood well. Most of mitochondrial mutations are characterized by the phenomenon of heteroplasmy which is defined as the presence of a mixture of more than one type of an organellar genome within a cell or tissue. The level of heteroplasmy varies in wide range, and the expression of disease is dependent on the percent of alleles bearing mutations, thus allowing consumption that an upper threshold level may exist beyond which the mitochondrial function collapses. Recent findings have demonstrated that some mtDNA heteroplasmic mutations are associated with widely spread chronic diseases, including atherosclerosis and cancer. Actually, each etiological mtDNA mutation has its own heteroplasmy threshold that needs to be measured. Therefore, quantitative evaluation of a mutant allele of mitochondrial genome is an obvious methodological challenge, since it may be a keystone for diagnostics of individual genetic predisposition to the disease. This review provides a comprehensive comparison of methods applicable to the measurement of heteroplasmy level of mitochondrial mutations associated with the development of pathology, in particular, in atherosclerosis and its clinical manifestations.

Association of sequence polymorphism in the mitochondrial D-loop with chronic kidney disease

BACKGROUND

The mitochondrial displacement loop (D-loop) is known to accumulate mutations and single nucleotide polymorphisms (SNPs) at a higher frequency than other regions of mitochondrial DNA (mtDNA).

METHODS

This is a case-control study. We sequenced SNPs in the D-loop of mtDNA and investigated their association with the risk of chronic kidney disease (CKD).

RESULTS

A total of 144 SNPs referring to the positions of the Revised Cambridge Reference Sequence (rCRS) for mitochondrial genome were identified in a case-control study. The minor alleles of nucleotides 73G, 146C, 150T, 194T, 195C and 310C were associated with an increased risk for CKD patients.

CONCLUSION

Analysis of genetic polymorphisms in the mitochondrial D-loop can help identify the people who are at a high risk of developing chronic kidney disease. These SNPs can be considered as potential predictors for CKD.

Mitochondrial control region alterations and breast cancer risk: a study in South Indian population

Background

Mitochondrial displacement loop (D-loop) is the hot spot for mitochondrial DNA (mtDNA) alterations which influence the generation of cellular reactive oxygen species (ROS). Association of D-loop alterations with breast cancer has been reported in few ethnic groups; however none of the reports were documented from Indian subcontinent.

Methodology

We screened the entire mitochondrial D-loop region (1124 bp) of breast cancer patients (n = 213) and controls (n = 207) of south Indian origin by PCR-sequencing analysis. Haplotype frequencies for significant loci, the standardized disequilibrium coefficient (D′) for pair-wise linkage disequilibrium (LD) were assessed by Haploview Software.

Principal Findings

We identified 7 novel mutations and 170 reported polymorphisms in the D-loop region of patients and/or controls. Polymorphisms were predominantly located in hypervariable region I (60%) than in II (30%) of D-loop region. The frequencies of 310‘C’ insertion (P = 0.018), T16189C (P = 0.0019) variants and 310‘C’ins/16189C (P = 0.00019) haplotype were significantly higher in cases than in controls. Furthermore, strong LD was observed between nucleotide position 310 and 16189 in controls (D′ = 0.49) as compared to patients (D′ = 0.14).

Conclusions

Mitochondrial D-loop alterations may constitute inherent risk factors for breast cancer development. The analysis of genetic alterations in the D-loop region might help to identify patients at high risk for bad progression, thereby helping to refine therapeutic decisions in breast cancer.

Mitochondrial tRNA variants in Chinese subjects with coronary heart disease

BACKGROUND

Coronary heart disease is the leading cause of death worldwide. Mitochondrial genetic determinants for the development of this disorder remain less explored.

METHODS AND RESULTS

We performed a clinical and genetic evaluation and mutational screening of 22 mitochondrial tRNA genes in a cohort of 80 genetically unrelated Han Chinese subjects and 125 members of 4 families with coronary heart disease and 512 Chinese control subjects. This analysis identified 16 nucleotide changes among 9 tRNA genes. Of these, the T5592C mutation creates a highly conservative base pairing (5G-68C) on the acceptor stem of tRNA(Gln), whereas the G15927A mutation destabilizes a highly conserved base pairing (28C-42G) in the anticodon stem of tRNA(Thr). However, the other tRNA variants were polymorphisms. The pedigrees of BJH24 carrying the T5592C mutation, BJH15, and BJH45 harboring the G15927A mutation exhibited maternal transmission of coronary heart disease. Sequence analysis of their mitochondrial genomes revealed the presence of T5592C or G15927A mutation but the absence of other functionally significant mutations in all matrilineal relatives of these families.

CONCLUSIONS

Our previous observations showed that altered structures of tRNAs by these mtDNA mutations caused mitochondrial dysfunction. These may be the first evidence that mtDNA mutations increase the risk of coronary heart disease. Our findings may provide new insights into the pathophysiology of this disorder.

Identification of sequence polymorphisms in the mitochondrial displacement loop as risk factors for sporadic and familial breast cancer

The accumulation of single nucleotide polymorphisms (SNPs) in the displacement loop (D-loop) of mitochondrial DNA (mtDNA) has been described for different types of cancers, and the association of these SNPs with cancer risk and disease outcome has been exhaustively studied. We sequenced a region of approximately 1 kb flanking the majority of the D-Loop in the DNA from the blood of breast cancer patients and the controls to identify cancer risk-associated D-loop SNPs. The D-loop region of mtDNA was sequenced from 92 sporadic breast cancer patients, 60 familial breast cancer patients and 41 relatives, and 93 healthy controls. Paired and unpaired Student's t tests were used as appropriate to determine the differences in SNP distribution within the D-loop region and in the number of SNPs per patient among the groups. The χ (2) test was used to analyze dichotomous values, such as the presence or absence of an individual SNP among each group, and the clinical characteristics between every two groups. The distribution frequencies of 315C/Cinsert, 524C/del, 16247A/del, 16248C/del, 16249T/C, 16257C/A, 16258A/del, 16259C/del, 16262C/del, 16268C/del, 16279C/del, 16280A/del, 16297T/C, and 16300A/del were significantly different between sporadic breast cancer patients and the normal controls. The SNP sites at nucleotides 310, 315, and 16362 were identified as cancer risk-associated SNPs specific for familial breast cancer. The N haplogroup, defined as 489T, was identified as a specific risk-associated SNP for families of breast cancer patients by comparing familial breast cancer patients with their relatives. The analysis of genetic polymorphisms in the D-loop may help to predict cancer risk for familial breast cancer and thereby help to detect and refine therapeutic decisions earlier.

The association of the mitochondrial DNA OriB variant (16184-16193 polycytosine tract) with type 2 diabetes in Europid populations

AIMS/HYPOTHESIS

The association between the mitochondrial DNA 16181-16193 polycytosine variant (known as the OriB variant as it maps to the OriB origin of replication) and type 2 diabetes has not been reliably characterised, with studies reporting conflicting results. We report a systematic review of published literature in Europid populations, new data from the Norfolk Diabetes Case-Control Study and a meta-analysis to help quantify this association.

METHODS

We performed a systematic review identifying all the studies of the OriB variant and type 2 diabetes in Europid populations published before January 2013. We typed the OriB variant by pyrosequencing and sequencing in the Norfolk Diabetes Case-Control Study, which comprised 5,574 type 2 diabetes cases and 6,950 population-based controls.

RESULTS

Overall, the meta-analysis included eight published studies plus the current new results, with a total of 11,794 type 2 diabetes cases and 14,465 controls. In the Norfolk Diabetes Case-Control Study, the OR for type 2 diabetes for the OriB variant was 1.09 (95% CI 0.96, 1.24). In a combined analysis, the relative risk for type 2 diabetes for the OriB variant in Europid populations was 1.10 (95% CI 1.01, 1.20; p = 0.03) CONCLUSIONS/INTERPRETATION: Results from this systematic review and meta-analysis suggest that the mitochondrial DNA OriB variant is modestly associated with an increased risk of type 2 diabetes in Europid populations, with an effect size comparable with that of recently identified variants from genome-wide association studies.

A novel heteroplasmic mitochondrial DNA mutation, A8890G, in a patient with juvenile‑onset metabolic syndrome: a case report

Metabolic syndrome (MS) is a complex disorder characterized by a group of metabolic abnormalities. In the present study, the case of an 18‑year‑old male who presented with MS characteristics with central obesity (overweight and a waist circumference of 95 cm) and dyslipidemia (high TG, low HDL levels and low apoA‑I/apoB‑100) was reported. The patient's family has maternally inherited diabetes and a number of the patient's maternal relatives present MS features. For the investigation of the mitochondrial DNA variants in the patient and the patient's family, genomic DNA of all the family members were extracted from peripheral blood using routine methods. Amplification of mitochondrial DNA in 24 overlapping fragments by PCR, direct sequencing and denaturing high‑performance liquid chromatography was utilized for genetic analysis. Sequences were compared to the reference sequence to identify variants. Bioinformatic methods and databases were used to analyze conservation of the variants and to predict the protein secondary structure. With the exception of the patient, five relatives were diagnosed with MS. Moreover, 5 of the 8 family members had been diagnosed with diabetes, hearing loss and mild kidney impairment according to serum biochemical analysis. Further molecular genetic analysis indicated that the MS‑associated variant T16189C was detected in this family. Notably, a heteroplasmic mutation A8890G was detected in the patient in the mitochondrial ATP6 gene, which codes the ATP synthase subunit 6 (ATPase6). A8890G changed the highly conserved ATPase6 Lys122 into Glu122 in the mitochondrial inner membrane. However, this mutation was not detected in other family members. In conclusion, the mutation A8890G may affect the function of ATPase 6 and the production of ATP, thus contributing to juvenile‑onset MS. It was not detected in other family members possibly due to the mitochondrial genetic segregation or production of a new germline mutation in the juvenile‑onset patient.

Do mitochondria contribute to left ventricular non-compaction cardiomyopathy? New findings from myocardium of patients with left ventricular non-compaction cardiomyopathy

BACKGROUND

Left ventricular non-compaction cardiomyopathy (LVNC) is a rare congenital cardiomyopathy that is associated with mutations in mitochondrial DNA (mtDNA), however, no study of myocardium mtDNA of LVNC patients has been reported. To identify novel candidate mtDNA variants that may be responsible for the pathogenesis of LVNC, myocardial specimens were examined to investigate pathogenic mtDNA variants.

MATERIALS AND METHODS

Samples from six patients who were diagnosed with LVNC and underwent heart transplantation were analyzed. The sequence and copy number of mtDNA from these samples were determined by Sanger sequencing and fluorescence-based quantitative polymerase chain reaction, respectively.

RESULTS

Myocardial mtDNA sequences analysis revealed 227 substitution variants, including 157 coding variants and 70 non-coding variants. An m.9856T>C (Ile217Thr) mutation in MT-CO3 from one LVNC patient was found to be a non-haplogroup associated variant, and was rare in the mtDB Human Mitochondrial Genome Database, suggesting that the variant may be pathogenic. And there was statistically significant difference in mtDNA copy number between LVNC patients and normal control subjects. Electron microscopy (EM) of left ventricular myocardium showed abnormality in mitochondrial morphology and disordered sarcomeric organization.

CONCLUSION

The identification of mtDNA sequence variants in myocardial specimens may be helpful for further investigation of the underlying pathogenic implications of myocardial mtDNA mutations in LVNC. However, measurement of mtDNA copy number showed that there was lower mtDNA content in myocardium of LVNC patients than in normal controls (P<0.01). Lower mtDNA copy number and morphological abnormalities of mitochondria suggested mitochondrial dysfunction that may be associated with etiology of LVNC.

Mitochondrial displacement loop alterations are associated with endometriosis

OBJECTIVE

To evaluate the association of mitochondrial displacement (D-) loop alterations with endometriosis in south Indian women.

DESIGN

Case-control study.

SETTING

Biochemistry and molecular biology laboratories.

PATIENT(S)

Women with (n = 152) and without (n = 150) endometriosis of south Indian origin.

INTERVENTION(S)

All women had a transvaginal ultrasound scan at screening followed by a laparoscopy to confirm the diagnosis (revised American Fertility Society stage III = 54; stage IV = 98).

MAIN OUTCOME MEASURE(S)

Genotyping of entire D-loop (1,124 bp) was carried out on genomic DNA of blood from cases and controls by polymerase chain reaction sequencing analysis.

RESULT(S)

Twelve novel mutations and 187 reported polymorphisms were identified in the D-loop region of cases and/or controls. The A189G, 310 C insertion, T16189C polymorphisms, and 189G/310TC/16189C haplotype have significantly higher frequency in cases compared with controls.

CONCLUSION(S)

Mitochondrial D-loop alterations may constitute an inheritable risk factor for endometriosis. The analysis of D-loop alterations may help to identify patients at high risk for disease outcome.

Sequence-based polymorphisms in the mitochondrial D-loop and potential SNP predictors for chronic dialysis

Background

The mitochondrial (mt) displacement loop (D-loop) is known to accumulate structural alterations and mutations. The aim of this study was to investigate the prevalence of single nucleotide polymorphisms (SNPs) within the D-loop among chronic dialysis patients and healthy controls.

Methodology and Principal Findings

We enrolled 193 chronic dialysis patients and 704 healthy controls. SNPs were identified by large scale D-loop sequencing and bioinformatic analysis. Chronic dialysis patients had lower body mass index, blood thiols, and cholesterol levels than controls. A total of 77 SNPs matched with the positions in reference of the Revised Cambridge Reference Sequence (CRS) were found in the study population. Chronic dialysis patients had a significantly higher incidence of 9 SNPs compared to controls. These include SNP5 (16108Y), SNP17 (16172Y), SNP21 (16223Y), SNP34 (16274R), SNP35 (16278Y), SNP55 (16463R), SNP56 (16519Y), SNP64 (185R), and SNP65 (189R) in D-loop of CRS. Among these SNPs with genotypes, SNP55-G, SNP56-C, and SNP64-A were 4.78, 1.47, and 5.15 times more frequent in dialysis patients compared to controls (P<0.05), respectively. When adjusting the covariates of demographics and comorbidities, SNP64-A was 5.13 times more frequent in dialysis patients compared to controls (P<0.01). Furthermore, SNP64-A was found to be 35.80, 3.48, 4.69, 5,55, and 4.67 times higher in female patients and in patients without diabetes, coronary artery disease, smoking, and hypertension in an independent significance manner (P<0.05), respectively. In patients older than 50 years or with hypertension, SNP34-A and SNP17-C were found to be 7.97 and 3.71 times more frequent (P<0.05) compared to patients younger than 50 years or those without hypertension, respectively.

Conclusions and Significance

The results of large-scale sequencing suggest that specific SNPs in the mtDNA D-loop are significantly associated with chronic dialysis. These SNPs can be considered as potential predictors for chronic dialysis.

Mitochondrial haplogroups and control region polymorphisms in age-related macular degeneration: a case-control study

BACKGROUND

Onset and development of the multifactorial disease age-related macular degeneration (AMD) are highly interrelated with mitochondrial functions such as energy production and free radical turnover. Mitochondrial dysfunction and overproduction of reactive oxygen species may contribute to destruction of the retinal pigment epithelium, retinal atrophy and choroidal neovascularization, leading to AMD. Consequently, polymorphisms of the mitochondrial genome (mtDNA) are postulated to be susceptibility factors for this disease. Previous studies from Australia and the United States detected associations of mitochondrial haplogroups with AMD. The aim of the present study was to test these associations in Middle European Caucasians.

METHODOLOGY/PRINCIPAL FINDINGS

Mitochondrial haplogroups (combinations of mtDNA polymorphisms) and mitochondrial CR polymorphisms were analyzed in 200 patients with wet AMD (choroidal neovascularization, CNV), in 66 patients with dry AMD, and in 385 controls from Austria by means of multiplex primer extension analysis and sequencing, respectively. In patients with CNV, haplogroup H was found to be significantly less frequent compared to controls, and haplogroup J showed a trend toward a higher frequency compared to controls. Five CR polymorphisms were found to differ significantly in the two study populations compared to controls, and all, except one (T152C), are linked to those haplogroups.

CONCLUSIONS/SIGNIFICANCE

It can be concluded that haplogroup J is a risk factor for AMD, whereas haplogroup H seems to be protective for AMD.

Physiology and pathophysiology of mitochondrial DNA

Mitochondria are the only organelles in animal cells which possess their own genomes. Mitochondrial DNA (mtDNA) alterations have been associated with various human conditions. Yet, their role in pathogenesis remains largely unclear. This review focuses on several major features of mtDNA: (1) mtDNA haplogroup, (2) mtDNA common deletion, (3) mtDNA mutations in the control region or D-loop, (4) mtDNA copy number alterations, (5) mtDNA mutations in translational machinery, (6) mtDNA mutations in protein coding genes (7) mtDNA heteroplasmy. We will also discuss their implications in various human diseases.