Mitochondrial DNA copy number in whole blood and glioma risk: A case control study

Mitochondrial DNA Copy Number: Linking Diabetes and Cancer

Recent Advances: Various studies have suggested that mitochondrial DNA copy number (mtDNA-CN), a surrogate biomarker of mitochondrial dysfunction, is an easily quantifiable biomarker for chronic diseases, including diabetes and cancer. However, current knowledge is limited, and the results are controversial. This has been attributed mainly to methodology and study design. Critical Issues: The incidence of diabetes and cancer has increased significantly in recent years. Moreover, type 2 diabetes (T2D) has been shown to be a risk factor for cancer. mtDNA-CN has been associated with both T2D and cancer. However, it is not known whether mtDNA-CN plays any role in the association between T2D and cancer. Significance: In this review, we have discussed mtDNA-CN in diabetes and cancer, and reviewed the literature and methodology used in published studies so far. Based on the literature review, we have speculated how mtDNA-CN may act as a link between diabetes and cancer. Furthermore, we have provided some recommendations for reliable translation of mtDNA-CN as a biomarker. Future Directions: Further research is required to elucidate the role of mtDNA-CN in the association between T2D and cancer. If established, early lifestyle interventions, such as physical activity and diet control that improve mitochondrial function, may help preventing cancer in patients with T2D. Antioxid. Redox Signal. 37, 1168-1190.

Insights regarding mitochondrial DNA copy number alterations in human cancer (Review)

Mitochondria are the critical organelles involved in various cellular functions. Mitochondrial biogenesis is activated by multiple cellular mechanisms which require a synchronous regulation between mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). The mitochondrial DNA copy number (mtDNA-CN) is a proxy indicator for mitochondrial activity, and its alteration reflects mitochondrial biogenesis and function. Despite the precise mechanisms that modulate the amount and composition of mtDNA, which have not been fully elucidated, mtDNA-CN is known to influence numerous cellular pathways that are associated with cancer and as well as multiple other diseases. In addition, the utility of current technology in measuring mtDNA-CN contributes to its extensive assessment of diverse traits and tumorigenesis. The present review provides an overview of mtDNA-CN variations across human cancers and an extensive summary of the existing knowledge on the regulation and machinery of mtDNA-CN. The current information on the advanced methods used for mtDNA-CN assessment is also presented.

Association between telomere length and mitochondrial copy number and cancer risk in humans: A meta-analysis on more than 300,000 individuals

In the last decades the association of leukocyte telomere length (LTL) and mitochondrial copy number (mtDNAcn) with cancer risk has been the focus of many reports, however the relation is not yet completely understood. A meta-analysis of 112 studies including 64,184 cancer cases and 278,641 controls that analysed LTL and mtDNAcn in relation to cancer risk has been conducted to further our understanding of the topic. Stratified analyses for tumor type were also performed. Overall, no association was observed for all cancer combined neither for LTL nor mtDNAcn. Significant associations were detected for these biomarkers and specific cancer type; however, a large degree of heterogeneity was present, even within the same tumor type. Alternatives approaches based on polymorphic variants, such as polygenic risk scores and mendelian randomization, could be adopted to unravel the causal correlation of telomere length and mitochondrial copy number with cancer risk.

Mitochondrial DNA Alterations in Glioblastoma (GBM)

Glioblastoma (GBM) is an extremely aggressive tumor originating from neural stem cells of the central nervous system, which has high histopathological and genomic diversity. Mitochondria are cellular organelles associated with the regulation of cellular metabolism, redox signaling, energy generation, regulation of cell proliferation, and apoptosis. Accumulation of mutations in mitochondrial DNA (mtDNA) leads to mitochondrial dysfunction that plays an important role in GBM pathogenesis, favoring abnormal energy and reactive oxygen species production and resistance to apoptosis and to chemotherapeutic agents. The present review summarizes the known mitochondrial DNA alterations related to GBM, their cellular and metabolic consequences, and their association with diagnosis, prognosis, and treatment.

Mitochondrial DNA copy number in human disease: the more the better?

Most of the genetic information has been lost or transferred to the nucleus during the evolution of mitochondria. Nevertheless, mitochondria have retained their own genome that is essential for oxidative phosphorylation (OXPHOS). In mammals, a gene‐dense circular mitochondrial DNA (mtDNA) of about 16.5 kb encodes 13 proteins, which constitute only 1% of the mitochondrial proteome. Mammalian mtDNA is present in thousands of copies per cell and mutations often affect only a fraction of them. Most pathogenic human mtDNA mutations are recessive and only cause OXPHOS defects if present above a certain critical threshold. However, emerging evidence strongly suggests that the proportion of mutated mtDNA copies is not the only determinant of disease but that also the absolute copy number matters. In this review, we critically discuss current knowledge of the role of mtDNA copy number regulation in various types of human diseases, including mitochondrial disorders, neurodegenerative disorders and cancer, and during ageing. We also provide an overview of new exciting therapeutic strategies to directly manipulate mtDNA to restore OXPHOS in mitochondrial diseases.

Diagnostic value of circulating cell-free mtDNA in patients with suspected thyroid cancer: ND4/ND1 ratio as a new potential plasma marker

Thyroid cancer is the most common endocrine malignancy, and its incidence continues to rise. For clinicians with cancer patients, choosing and interpreting diagnostic laboratory studies has become increasingly important. Previously, changes in plasma free mitochondrial DNA levels have been found in colorectal, breast, lung, and urinary cancers, and have demonstrated diagnostic value. In this study, we investigated whether the occurrence and development of thyroid cancer might be predicted using mtDNA copy number (ND1), mtDNA integrity (ND4/ND1) and levels of cell-free nDNA (GAPDH). We analyzed ND1, ND4, and GAPDH levels in plasma and blood cells from 75 patients with thyroid cancer, 40 patients with nodular goiter, and 107 normal controls using real-time PCR. Although both the thyroid nodule and thyroid cancer patients had significantly increased ND1 levels, the ND4/ND1 ratio in the thyroid cancer group was higher than the thyroid nodule group (P < 0.05), and significantly higher than the normal control group (P < 0.01). Plasma levels of nuclear DNA (GAPDH) in the thyroid cancer group were also higher compared to normal (P < 0.05). These results indicate that increased intactness of plasma free mtDNA is associated with increased levels of plasma cell-free nDNA, and that the ND4/ND1 ratio has the potential to be a new detection indicator in thyroid cancer. Furthermore, we classified thyroid cancer patients according to clinical data including age, tumor size, and metastasis. We found significantly higher levels of GAPDH in malignant tissues. Because ND4/ND1 correlated with plasma GAPDH in the plasma studies, this also suggests a potential relationship between ND4 intactness and thyroid tumor tissue size. Taken together, our findings suggest a tumor-specific process involving increased release of intact mtDNA, detectable in the plasma, which differentiates normal patients from patients with thyroid cancer.

Leukocyte mitochondrial DNA copy number and built environment in Mexican Americans: a cross-sectional study

Mitochondrial DNA (mtDNA) copy number in leukocytes has been regarded as a biomarker for various environmental exposures and chronic diseases. Our previous study showed that certain demographic factors (e.g. age, gender, BMI, etc.) significantly affect levels of leukocyte mtDNA copy number in Mexican Americans. However, the effect of the built environment on leukocyte mtDNA copy number has not been studied previously. In this cross-sectional study, we examined the association between multiple components of the built environment with leukocyte mtDNA copy number among 5,502 Mexican American adults enrolled in Mano-A-Mano, the Mexican American Cohort Study (MACS). Based on the median levels of mtDNA copy number, the study population was stratified into low mtDNA copy number group (< median) and high mtDNA copy number group (≥ median). Among all built environment exposure variables, household density and road/intersection ratio were found to be statistically significant between groups with low and high mtDNA copy number (P < 0.001 and 0.002, respectively). In the multivariate logistic regression analysis, individuals living in areas with elevated levels of household density had 1.24-fold increased odds of having high levels of mtDNA copy number [Odds ratio (OR) = 1.24, 95% confidence interval (CIs) 1.08, 1.36]. Similarly, those living in areas with elevated levels of road/intersection ratio had 1.12-fold increased odds of having high levels of mtDNA copy number (OR = 1.12, 95% CI 1.01, 1.27). In further analysis, when both variables were analyzed together in a multivariate logistic regression model, the significant associations remained. In summary, our results suggest that selected built environment variables (e.g. population density and road/intersection ratio) may influence levels of mtDNA copy number in leukocytes in Mexican Americans.

Role of Mitochondrial DNA (mtDNA) Variations in Cancer Development: A Systematic Review

mtDNA is the closed circular, ds-DNA present in mitochondria of eukaryotic cells and are inherited maternally. Besides being the power house of the cell, mitochondria are also responsible for the regulation of redox homeostasis, signaling, metabolism, immunity, survival and apoptosis. Lack of a 'Systematic Review' on mtDNA variations and cancers encouraged us to perform the present study. Pubmed', 'Embase' and 'Cochrane Library' databases were searched using keywords 'Mitochondrial DNA' OR 'mtDNA' OR 'mDNA' AND 'polymorphism' AND 'cancer' AND 'risk' to retrieve literature. Polymorphisms occupy first rank among mtDNA variations followed by CNV, MSI, mutations and hold a great potential to emerge as key predictors for human cancers.

Is mitochondrial DNA copy number a good prognostic marker in resectable pancreatic cancer?

BACKGROUND

The aim of this prospective study was to investigate mitochondrial DNA (mtDNA) copy number in a group of resectable pancreatic cancer (PC) tumor tissues and adjacent normal pancreatic tissues, and to explore the correlation between the mtDNA content in tissues and the clinicopathological parameters and the overall survival.

METHODS

Relative mtDNA copy number was measured by the quantitative PCR-based assay. The tumors specimens (n = 43) originated from the patients with pathologically confirmed pancreatic ductal adenocarcinoma who did not receive any neoadjuvant systemic therapy. The adjacent normal pancreatic tissue samples (n = 31) were obtained from surgical margins.

RESULTS

mtDNA copy number was significantly lower in PC tissue (P < 0.001) compared to adjacent normal pancreatic tissue. Jonckheere-Terpstra trend testing indicated a statistically significant decrease in median mtDNA copy number across the differentiation (adjacent normal pancreatic tissue, low-grade, intermediate-grade, high-grade cancer), P < 0.001. However, the survival analyses failed to show a significant difference in survival between patients with high and low mtDNA copy number.

CONCLUSIONS

To the best of our knowledge, we provided the first evidence that mitochondrial DNA copy number was significantly lower in pancreatic cancer tissue (P < 0.001) compared to adjacent normal pancreatic tissue. Also, we demonstrated that mitochondrial copy number was not a significant marker for predicting prognosis in resectable pancreatic cancer.

Gender-related differences in the association between concomitant amplification of AIB1 and HER2 and clinical outcomes in glioma patients

BACKGROUND

Previous studies demonstrated that AIB1 or HER2 copy number gain (CNG), respectively, were independent predictors for poor prognosis of glioma patients, especially in females. We hypothesize that there are some connections between the two genes and sex-specific characteristics, thus this study aimed to analyze gender-related differences in the prognosis of glioma patients.

METHODS

Using Real-Time Quantitative Reverse Transcription PCR (RT-qPCR) method, we examined AIB1 and HER2 CNG in gliomas samples (n = 114), and inspected the correlation of various genotypes with patients outcomes.

RESULTS

Concomitant AIB1 and HER2 amplification were closely related to shorter survival time and radiotherapy resistance in female gliomas patients (P < 0.01), which also served as an independent risk factor. No significant prognostic value was found with AIB1 and HER2 CNG in male patients. However, linear regression analysis showed a positive relationship between the copy number of AIB1 and HER2 (P < 0.01) in male patients, rather than female patients.

CONCLUSION

In this study, we reveal a gender difference in the prognostic value of concomitant AIB1 and HER2 CNG in glioma patients which were barely noticed before. These observations indicated that genetic alterations synergistic with essential respects of sex determination influence glioma biology and patients outcomes.

Associations of blood mitochondrial DNA copy number with social-demographics and cancer risk: results from the Mano-A-Mano Mexican American Cohort

The relationship between blood mitochondrial DNA (mtDNA) copy number and subsequent cancer risk has been investigated previously. However, such association has never been examined in Mexican Americans. In the current study, we examined association between social-demographic factors and blood mtDNA copy number, as well as longitudinal relationship between cancer and mtDNA copy number, among 10,802 Mexican Americans in the Mano-A-Mano Mexican American Cohort. Overall, mtDNA copy number was statistically significantly higher among participants who developed cancer during the study period than among cancer-free controls (0.17 vs 0.13, P = 0.007). Among cancer-free control participants, mtDNA copy number significantly differed by social-demographic characteristics. However, there was a large degree of heterogeneity in these effects across the mtDNA copy number distribution. In the longitudinal analysis, we observed that higher mtDNA copy number was positively associated with increased risk of all cancer types (adjusted hazard ratio [HR], 1.13; 95% confidence interval [CI], 1.09–1.17). Participants with mtDNA copy number in the fourth (highest) quartile had a higher risk of all cancer (adjusted HR, 2.12; 95% CI, 1.65–2.73) than did participants in the first (lowest) quartile. In summary, our results in Mexican Americans support an association between increased mtDNA copy number and cancer risk. Our results also suggest that mtDNA copy number may be influenced by social and demographic factors.

Mitochondrial DNA Copy Number Variation as a Potential Predictor of Renal Cell Carcinoma

Background

Peripheral blood mitochondrial DNA (mtDNA) copy number alteration has been suggested as a risk factor for several types of cancer. The aim of the present study was to assess the role of peripheral blood mtDNA copy number variation as a noninvasive biomarker in the prediction and early detection of renal cell carcinoma (RCC) in a cohort of Egyptian patients.

Methods

Quantitative real-time polymerase chain reaction (qPCR) was used to measure peripheral blood mtDNA copy numbers in 57 patients with newly diagnosed, early-stage localized RCC and 60 age- and sex-matched healthy individuals as a control group.

Results

Median mtDNA copy number was significantly higher in RCC cases than in controls (166 vs. 91, p<0.001). Increased mtDNA copy number was associated with an 18-fold increased risk of RCC (95% confidence interval: 5.065-63.9). On receiver operating characteristic curve analysis, it was found that mtDNA could distinguish between RCC patients and healthy controls, with 86% sensitivity, 80% specificity, 80.3% positive predictive value and 85.7% negative predictive value at a cutoff value of 108.5.

Conclusions

Our results showed that increased peripheral blood mtDNA copy number was associated with increased risk of RCC. Therefore, RCC might be considered as part of a range of potential tumors in cases with elevated blood mtDNA copy number.

Global DNA hypomethylation in leukocytes associated with glioma risk

Global DNA hypomethylation in leukocytes has been associated with increased risk for a variety of cancers. However, the role of leukocyte global DNA hypomethylation in glioma development, if any, is largely unknown. To define this role, we performed a case-control study with 390 glioma patients and 390 controls with no known cancer. Levels of 5-methylcytosine (5-mC%), a marker for global DNA methylation, were measured in leukocyte DNA. Overall, median levels of 5-mC% were significantly lower in glioma cases than in controls (3.45 vs 3.82, P=0.001). Levels of 5-mC% differed significantly by age and sex among controls and by tumor subtype and grade among glioma cases. In multivariate analysis, lower levels of 5-mC% were associated with a 1.31-fold increased risk of glioma (odds ratio = 1.31, 95% confidence interval = 1.10-1.41). A significant dose-response trend was observed in quartile analysis (P=0.001). In an analysis further stratified by clinical characteristics at baseline, the association between lower levels of 5-mC% and glioma risk was evident only among younger participants (age <52 years), women, and those with aggressive tumor characteristics, such as glioblastoma subtype, high tumor grade (grade III or IV), and absence of IDH1 mutation. Our findings indicate that global DNA hypomethylation in leukocytes may contribute to the development of glioma and that the association is affected by age, sex, and tumor aggressiveness.

Altered mitochondrial DNA copy number contributes to human cancer risk: evidence from an updated meta-analysis

Accumulating epidemiological evidence indicates that the quantitative changes in human mitochondrial DNA (mtDNA) copy number could affect the genetic susceptibility of malignancies in a tumor-specific manner, but the results are still elusive. To provide a more precise estimation on the association between mtDNA copy number and risk of diverse malignancies, a meta-analysis was conducted by calculating the pooled odds ratios (OR) and the 95% confidence intervals (95% CI). A total of 36 case-control studies involving 11,847 cases and 15,438 controls were finally included in the meta-analysis. Overall analysis of all studies suggested no significant association between mtDNA content and cancer risk (OR = 1.044, 95% CI = 0.866–1.260, P = 0.651). Subgroup analyses by cancer types showed an obvious positive association between mtDNA content and lymphoma and breast cancer (OR = 1.645, 95% CI = 1.117–2.421, P = 0.012; OR = 1.721, 95% CI = 1.130–2.622, P = 0.011, respectively), and a negative association for hepatic carcinoma. Stratified analyses by other confounding factors also found increased cancer risk in people with drinking addiction. Further analysis using studies of quartiles found that populations with the highest mtDNA content may be under more obvious risk of melanoma and that Western populations were more susceptible than Asians.