Low level of the mtDNA4977 deletion in blood of exceptionally old individuals

Altered lactate/pyruvate ratio may be responsible for aging-associated intestinal barrier dysfunction in male rats

Some evidence points to a link between aging-related increased intestinal permeability and mitochondrial dysfunction in in-vivo models. Several studies have also demonstrated age-related accumulation of the of specific deletion 4834-bp of "common" mitochondrial DNA (mtDNA) in various rat tissues and suggest that this deletion may disrupt mitochondrial metabolism. The present study aimed to investigate possible associations among the mitochondrial DNA (mtDNA) common deletion, mitochondrial function, intestinal permeability, and aging in rats. The study was performed on the intestinal tissue from (24 months) and young (4 months) rats. mtDNA4834 deletion, mtDNA copy number, mitochondrial membrane potential, and ATP, lactate and pyruvate levels were analyzed in tissue samples. Zonulin and intestinal fatty acid-binding protein (I-FABP) levels were also evaluated in serum. Serum zonulin and I-FABP levels were significantly higher in 24-month-old rats than 4-month-old rats (p = 0.04, p = 0.026, respectively). There is not significant difference in mtDNA4834 copy levels was observed between the old and young intestinal tissues (p > 0.05). The intestinal mitochondrial DNA copy number was similar between the two age groups (p > 0.05). No significant difference was observed in ATP levels in the intestinal tissue lysates between old and young rats (p > 0.05). ATP levels in isolated mitochondria from both groups were also similar. Analysis of MMP using JC-10 in intestinal tissue mitochondria showed that mitochondrial membrane potentials (red/green ratios) were similar between the two age groups (p > 0.05). Pyruvate tended to be higher in the 24-month-old rat group and the L/P ratio was found to be approximately threefold lower in the intestinal tissue of the older rats compared to the younger rats (p < 0.002). The tissue lactate/pyruvate ratio (L/P) was three times lower in old rats than in young rats. Additionally, there were significant negative correlations between intestinal permeability parameters and L/P ratios. The intestinal tissues of aged rats are not prone to accumulate mtDNA common deletion, we suggest that this mutation does not explain the age-related increase in intestinal permeability. It seems to be more likely that altered glycolytic capacity could be a link to increased intestinal permeability with age. This observation strengthens assertions that the balance between glycolysis and mitochondrial metabolism may play a critical role in intestinal barrier functions.

Renal mitochondrial toxicity: effects of thymidine analogues and tenofovir disoproxil fumarate in African people with HIV

We investigated the contributions of thymidine analogue and tenofovir disoproxil fumarate (TDF) antiretroviral therapy on renal mitochondrial toxicity in Ghanaian people with HIV (PWH). Similar levels of renal biochemical and mitochondrial dysfunction were seen, and there was no increased risk in PWH who had sequenced from thymidine analogue to TDF. However, mild renal impairment was associated with mitochondrial DNA damage in TDF but not thymidine analogue-treated PWH. These data support the continued use of TDF in resource-limited settings.

DNA methylation QTL analysis identifies new regulators of human longevity

Human longevity is a complex trait influenced by both genetic and environmental factors, whose interaction is mediated by epigenetic mechanisms like DNA methylation. Here, we generated genome-wide whole-blood methylome data from 267 individuals, of which 71 were long-lived (90–104 years), by applying reduced representation bisulfite sequencing. We followed a stringent two-stage analysis procedure using discovery and replication samples to detect differentially methylated sites (DMSs) between young and long-lived study participants. Additionally, we performed a DNA methylation quantitative trait loci analysis to identify DMSs that underlie the longevity phenotype. We combined the DMSs results with gene expression data as an indicator of functional relevance. This approach yielded 21 new candidate genes, the majority of which are involved in neurophysiological processes or cancer. Notably, two candidates (PVRL2, ERCC1) are located on chromosome 19q, in close proximity to the well-known longevity- and Alzheimer’s disease-associated loci APOE and TOMM40. We propose this region as a longevity hub, operating on both a genetic (APOE, TOMM40) and an epigenetic (PVRL2, ERCC1) level. We hypothesize that the heritable methylation and associated gene expression changes reported here are overall advantageous for the LLI and may prevent/postpone age-related diseases and facilitate survival into very old age.

Possible role of the mitochondrial genome in the pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic renal disease in adults and is due to heterozygous germ line variants in either PKD1, PKD2 or rarely other genes. It is characterized by marked intra-familial disease variability suggesting that other genetic and/or environmental factors are involved in determining the lifetime course ADPKD. Recently, research indicates that polycystin-mediated mitochondrial dysfunction and metabolic re-programming contributes to the progression of ADPKD. Although biochemical abnormalities have gained the most interest, variants in the mitochondrial genome could be one of the mechanisms underlying the phenotypic variability in ADPKD. This narrative review aims to evaluate the role of the mitochondrial genome in the pathogenesis of APDKD.

Mitochondrial Common Deletion Level in Blood: New Insight Into the Effects of Age and Body Mass Index

BACKGROUND

Age-related decrease in mitochondrial activity has been reported in several tissues. Reactive Oxygen Species (ROS) produced from defected mitochondria lead to aging and accumulate through time. However, studies about the mitochondrial DNA mutation level in blood are contradictory. Other lifestyle factors may modify the effects of age in post-mitotic tissues such as blood. The BMI represents the sum of the various lifestyle factors.

OBJECTIVE

We proposed that age, obesity and mtDNA deletion are three ROS producing factors, which may interact with each other and induce senescence.

METHODS

In a cross-sectional study, 172 male and female volunteers without known mitochondrial diseases were selected and the presence of common mitochondrial 4977bp deletion (ΔmtDNA4977) evaluated using Nested-PCR.

RESULTS

Our results showed that a high percentage of samples (54.06%) harbor common deletion in blood. Furthermore, both BMI and the ΔmtDNA4977 levels significantly decrease with age. The chronological age, BMI and ΔmtDNA4977 reciprocally affect each other.

CONCLUSION

Our data suggest that age affects purifying selection and BMI, which may influence the relative level of the mtDNA common deletion in blood.

Detection of mitochondrial DNA with 4977 bp deletion in leukocytes of patients with ischemic stroke

BACKGROUND

Coronary artery disease is associated with a common mitochondrial DNA alteration, a 4977 bp deletion (mtDNA4977). The role of mtDNA4977 in ischemic stroke is unknown.

METHODS

Real-time quantitative PCR was performed to quantify total mtDNA and mtDNA4977 in leukocytes in 283 ischemic stroke cases and 135 controls. Ratios of mtDNA4977 to total-mtDNA and total-mtDNA to nuclear-DNA were calculated. Nested PCR and Sanger sequencing were used to confirm undetectable levels of mtDNA4977.

RESULTS

For 191 patients and 74 control subjects in the male group and 92 patients and 61 control subjects in the female group, there were no significant between-group differences in age, cholesterol level, body mass index, stroke severity, or 4977 deletion. After adjusting for confounding factors, there was no correlation between mtDNA4977 amount and infarction risk, recurrent stroke, or stroke severity. However, mtDNA4977 was undetected in 6.94% subjects, and these individuals had a higher prevalence of stroke than those with detectable mtDNA4977 (OR: 0.181, 95% CI 0.041-0.798, p = 0.024). Additionally, mtDNA4977 status had no effect on stroke prognosis, including stroke severity and recurrent stroke.

CONCLUSION

In conclusion, there was no apparent association between mtDNA4977 deletion and cerebral infarction. Undetectable mtDNA4977 may be a marker or risk factor for ischemic stroke.

Genetic interplay between human longevity and metabolic pathways - a large-scale eQTL study

Human longevity is a complex phenotype influenced by genetic and environmental components. Unraveling the contribution of genetic vs. nongenetic factors to longevity is a challenging task. Here, we conducted a large‐scale RNA‐sequencing‐based expression quantitative trait loci study (eQTL) with subsequent heritability analysis. The investigation was performed on blood samples from 244 individuals from Germany and Denmark, representing various age groups including long‐lived subjects up to the age of 104 years. Our eQTL‐based approach revealed for the first time that human longevity is associated with a depletion of metabolic pathways in a genotype‐dependent and independent manner. Further analyses indicated that 20% of the differentially expressed genes are influenced by genetic variants in cis. The subsequent study of twins showed that the transcriptional activity of a third of the differentially regulated genes is heritable. These findings suggest that longevity‐associated biological processes such as altered metabolism are, to a certain extent, also the driving force of longevity rather than just a consequence of old age.

Tenofovir disoproxil fumarate-associated renal tubular dysfunction: noninvasive assessment of mitochondrial injury

OBJECTIVE

To determine whether tenofovir disoproxil fumarate (TDF)-associated renal tubular dysfunction is associated with evidence of mitochondrial injury in urine.

DESIGN

Single-centre cross-sectional observational study of HIV-positive outpatients.

METHODS

Biochemistry was performed on paired serum and urine samples. Mitochondrial DNA (mtDNA) was studied by real-time PCR and long-range PCR on cellular fractions of urine.

RESULTS

In total, 48 study participants were enrolled of whom half were TDF treated. Mean age was 43 years. 58% had estimated glomerular filtration rate at least 90, with no differences between ART treatment groups. Urinary phosphate wasting was common and independently associated with TDF exposure (P = 0.02). No study participants had low molecular weight proteinuria. Cellular mtDNA content in urine was heavily influenced by the cellularity of the sample. The mtDNA 'common deletion' mutation was detectable significantly more commonly in the urine of TDF exposed study participants compared with unexposed (13/22 TDF study participants (59%), 4/21 TDF (19%), P = 0.01). Common deletion levels were not associated with age, estimated glomerular filtration rate, or urinary phosphate wasting. No mtDNA measures were associated with current or nadir CD4 lymphocyte counts, duration of disease or antiretroviral therapy, or historical exposure to nucleoside analogue reverse transcriptase inhibitors with systemic mitochondrial toxicity.

CONCLUSION

The presence of mtDNA mutations in the context of TDF exposure adds weight to the hypothesis that TDF-associated renal damage is at least in part mitochondrially mediated. The assessment of mtDNA markers in urine may be a feasible noninvasive investigation for TDF-treated patients.

Increased mitochondrial DNA deletions and copy number in transfusion-dependent thalassemia

BACKGROUND

Iron overload is the primary cause of morbidity in transfusion-dependent thalassemia. Increase in iron causes mitochondrial dysfunction under experimental conditions, but the occurrence and significance of mitochondrial damage is not understood in patients with thalassemia.

METHODS

Mitochondrial DNA (mtDNA) to nuclear DNA copy number (Mt/N) and frequency of the common 4977-bp mitochondrial deletion (ΔmtDNA⁴⁹⁷⁷) were quantified using a quantitative PCR assay on whole blood samples from 38 subjects with thalassemia who were receiving regular transfusions.

RESULTS

Compared with healthy controls, Mt/N and ΔmtDNA⁴⁹⁷⁷ frequency were elevated in thalassemia (P = 0.038 and P < 0.001, respectively). ΔmtDNA⁴⁹⁷⁷ was increased in the presence of either liver iron concentration > 15 mg/g dry-weight or splenectomy, with the highest levels observed in subjects who had both risk factors (P = 0.003). Myocardial iron (MRI T2* < 20 ms) was present in 0%, 22%, and 46% of subjects with ΔmtDNA⁴⁹⁷⁷ frequency < 20, 20-40, and > 40/1 × 10⁷ mtDNA, respectively (P = 0.025). Subjects with Mt/N values below the group median had significantly lower Matsuda insulin sensitivity index (5.76 ± 0.53) compared with the high Mt/N group (9.11 ± 0.95, P = 0.008).

CONCLUSION

Individuals with transfusion-dependent thalassemia demonstrate age-related increase in mtDNA damage in leukocytes. These changes are markedly amplified by splenectomy and are associated with extrahepatic iron deposition. Elevated mtDNA damage in blood cells may predict the risk of iron-associated organ damage in thalassemia.

Mitochondrial DNA 4977-base pair common deletion in blood leukocytes and melanoma risk

The 4977-base pair common deletion DmtDNA4977 is the most frequently observed mitochondrial DNA mutation in human tissues. Because mitochondrial DNA mutations are mainly caused by reactive oxygen species (ROS), and given that oxidative stress plays an important role in melanoma carcinogenesis, the investigation of DmtDNA4977 may be particularly relevant to the development of melanoma. In this study, we compared DmtDNA4977 levels in blood leukocytes from 206 melanoma patients and 219 healthy controls. Overall, melanoma cases had significantly higher levels of DmtDNA4977 than healthy controls (median: 0.60 vs 0.20, P = 0.008). The difference was evident among individuals who were older than 47 yrs, women, and had pigmentation risk factors (e.g., blond or red hair, blue eye, fair skin, light, or none tanning ability after prolonged sun exposure, and freckling in the sun as a child). The difference was also evident among those who had at least one lifetime sunburn with blistering and had no reported use of a sunlamp. Interestingly, among controls, DmtDNA4977 levels differed by phenotypic index and reported use of a sunlamp. In the risk assessment, increased levels of DmtDNA4977 were associated with a 1.23-fold increased risk of melanoma (odds ratio (OR): 1.23, 95% confidence interval (90% CI): 1.01, 1.50). A significant dose-response relationship was observed in quartile analysis (P = 0.001). In summary, our study suggests that high levels of DmtDNA4977 in blood leukocytes are associated with increased risk of melanoma and that association is affected by both pigmentation and personal history of sun exposure.

Lack of association between increased mitochondrial DNA4977 deletion and ATP levels of sputum cells from chronic obstructive pulmonary disease patients versus healthy smokers

In this study we looked at smokers with and without chronic obstructive pulmonary disease (COPD) patients in order to evaluate the incidence of 4977 base pair (bp) mtDNA (mtDNA⁴⁹⁷⁷) deletion and mtDNA copy number in sputum cells and in peripheral blood leukocytes (PBLs) in relation to mitochondrial function and oxidative stress status. Twenty-five COPD patients who were current smokers, 22 smokers and 23 healthy nonsmokers (for only PBLs studies) participated in this study. The 4977-bp deletion was detected in all examined samples within 40 cyles of PCR amplification, using a quantitative real time PCR. The frequency of the mtDNA⁴⁹⁷⁷ was significantly higher in the sputum cells of patients with COPD compared to smokers without COPD (p < 0.0001). This difference was not observed in PBLs. Levels of cellular oxidative stress were significantly higher in the sputum cells of subjects with COPD than in the smoker group. However, mtDNA copy number, mitochondrial membrane potential (ΔΨm) and cellular ATP levels in PBLs and sputum cells were not significantly different between the studied groups. The Pearson analysis revealed no correlations between the accumulation of mtDNA⁴⁹⁷⁷, and intracellular ATP content and ΔΨm values of the sputum cells, although there was a positive correlation between the increase in the percentage of deleted mtDNA⁴⁹⁷⁷ and the levels of cellular oxidative stress in COPD patients (r = 0.80, p < 0.0001). Our studies may suggest that the accumulation of mtDNA⁴⁹⁷⁷ in the sputum cells of smokers with COPD does not seem to have an important impact on mitochondrial dysfunction in relation to ATP production and ΔΨm when compared to those of healthy smokers.

Age-related decrease in mtDNA content as a consequence of mtDNA 4977 bp deletion

As one of the most frequent somatic mutations accumulated during aging in human mitochondrial DNA, the 4977 bp deletion has intrigued scientific interest in recent years. Although many studies have shown a significant increase in the amount of 4977 bp deletion, the findings with respect to an age-dependent escalate of ΔmtDNA4977 bp in blood are still disputatious. Therefore, we investigated the presence of common deletion and mtDNA deletion level in whole blood samples of 100 old individuals (60-90 years). We detected the accumulation of common deletion in 46 old individuals. Consequently, there was statistically significant difference between the aged and young individuals in mitochondrial content (p = 0.01) and deletion levels ranged from 2% to 17% of the total mtDNA (mean: 10% ± 0.02%). We conclude that common deletion has decreased the mtDNA content; however, it is not clearly detectable in the blood as one of the fast replicating tissues comparing with tissues with low mitotic activity.

Deletion of a 4977-bp Fragment in the Mitochondrial Genome Is Associated with Mitochondrial Disease Severity

Large deletions in mitochondrial DNA (mtDNA) may be involved in the pathogenesis of mitochondrial disease. In this study, we investigated the relationship between a 4,977-bp deletion in the mitochondrial genome (ΔmtDNA⁴⁹⁷⁷) and the severity of clinical symptoms in patients with mitochondrial disease lacking known point mutations. A total of 160 patients with mitochondrial disease and 101 healthy controls were recruited for this study. The copy numbers of ΔmtDNA⁴⁹⁷⁷ and wild-type mtDNA were determined by real-time quantitative PCR and analyzed using Spearman’s bivariate correlation analysis, t-tests, or one-way ANOVA. The overall ΔmtDNA⁴⁹⁷⁷ copy number per cell and the proportion of mtDNA⁴⁹⁷⁷ relative to the total wild-type mtDNA, increased with patient age and symptom severity. Surprisingly, the total mtDNA copy number decreased with increasing symptom severity. Our analyses revealed that increases in the proportion and total copy number of ΔmtDNA⁴⁹⁷⁷ in the blood may be associated with disease severity in patients with mitochondrial dysfunction.

A mitochondrial haplogroup is associated with decreased longevity in a historic new world population

Interest in mitochondrial influences on extended longevity has been mounting, as evidenced by a growing literature. Such work has demonstrated that some haplogroups are associated with increased longevity and that such associations are population specific. Most previous work, however, suffers from the methodological shortcoming that long-lived individuals are compared with "controls" who are born decades after the aged individuals. The only true controls of the elderly are people who were born in the same time period but who did not have extended longevity. Here we present results of a study in which we are able to test whether longevity is independent of haplogroup type, controlling for time period, by using mtDNA genealogies. Since mtDNA does not recombine, we know the mtDNA haplogroup of the maternal ancestors of our living participants. Thus, we can compare the haplogroup of people with and without extended longevity who were born during the same time period. Our sample is an admixed New World population that has haplogroups of Amerindian, European, and African origin. We show that women who belong to Amerindian, European, and African haplogroups do not differ in their mean longevity. Therefore, to the extent that ethnicity was tied in this population to mtDNA make-up, such ethnicity did not impact longevity. In support of previous suggestions that the link between mtDNA haplogroups and longevity is specific to the population being studied, we found an association between haplogroup C and decreased longevity. Interestingly, the lifetime reproductive success and the number of grandchildren produced via a daughter of women with haplogroup C are not reduced. Our diachronic approach to the mtDNA and longevity link allowed us to determine that the same haplogroup is associated with decreased longevity during different time periods and allowed us to compare the haplogroup of short- and long-lived individuals born during the same time period. By controlling for time period, we minimized the effect of different cultural and ecological environments on differential longevity. With our diachronic approach, we investigated the mtDNA and longevity link with a biocultural perspective.

The somatic common deletion in mitochondrial DNA is decreased in schizophrenia

Large deletions in mitochondrial DNA (mtDNA) can occur during or result from oxidative stress leading to a vicious cycle that increases reactive oxygen species (ROS) damage and decreases mitochondrial function, thereby causing further oxidative stress. The objective of this study was to determine if disease specific brain differences of the somatic mtDNA common deletion (4977 bp) could be observed in major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ) compared to a control group. The accumulation of the mtDNA common deletion was measured using a quantitative assay across 10 brain regions (anterior cingulate cortex, amygdala, caudate nucleus, dorsolateral prefrontal cortex, hippocampus, nucleus accumbens, orbitofrontal cortex, putamen, substantia nigra, and thalamus). The correlation with age of the mtDNA deletion was highly significant across brain regions as previously shown. A significant decrease in the global accumulation of common deletion in subjects with SZ compared to MDD, BD, and controls was observed after correcting for age, pH, PMI, and gender. The decreases in SZ were largest in dopaminergic regions. One potential side effect of antipsychotic drugs on mitochondria is the impairment of mitochondria function, which might explain these findings. The decreased global brain mtDNA common deletion levels suggests that mitochondrial function is impaired and might be part of an overall mitochondria dysfunction signature in subjects with schizophrenia.

Folate deficiency is not associated with increased mitochondrial genomic instability: results from dietary intake and lymphocytic mtDNA 4977-bp deletion in healthy young women in Italy

The mitochondrial DNA (mtDNA) 4977-bp deletion is a biomarker of mitochondrial genomic instability. It is frequently detected in a number of sporadic diseases, and it accumulates in many tissues during aging. Folic acid plays an important role in the maintenance of genomic stability in mammals. The aim of the present cross-sectional study was to characterise the levels of the mtDNA deletion in the lymphocytes of healthy young women, taking into account folate intake, red blood cell (RBC) folate levels and the distribution of the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism. Folate intake was estimated by a food frequency questionnaire. Determination of the MTHFR C677T polymorphism and of the mtDNA deletion was performed by real-time polymerase chain reaction analysis. A total of 476 women were enrolled. Low levels of deletion were found (mean ΔCt = 1.24). After multivariate analysis, results did not show any significant relationship between age, smoking habits, pregnancy status, nutritional status, inadequate folate intake, folate deficiency, use of folic acid supplements, MTHFR C677T polymorphism and mtDNA 4977-bp deletions. The lack of association between inadequate folate intake, folate deficiency and mitochondrial genomic instability was confirmed also considering reference values of folate based on DNA damage prevention. Our results indicate that mtDNA 4977-bp deletions are maintained at low levels in lymphocytes of young healthy women despite the wide range of variation of folate intakes and folate status. Future studies, carefully designed to address limits and methodological issues related to variation of this biomarker as an effect of different dietary patterns and of folate status, could provide further insight on the specific mechanisms that are acting in lymphocytes of healthy subjects under observed folate intake.

Mitochondrial DNA 4977 bp deletion is a common phenomenon in hair and increases with age

Mitochondrial DNA (mtDNA) is believed to be particularly susceptible to oxidative damage during aging, resulting in mtDNA point mutations, duplications, and deletions. Although mtDNA deletions have been reported in various human tissues, e.g., the brain, heart, and skeletal muscle, little is known about the occurrence in hair. Therefore, we screened for the presence of mtDNA 13162 bp, 10422 bp, 7663 bp, 7436 bp, 4989 bp, and 4977 bp deletions in 90 hair samples from subjects aged 5 days to 91 years by using polymerase chain reaction (PCR) and investigated the deletion load by TaqMan probe-based real-time PCR. We detected the mtDNA 4977 bp deletion in hair samples, but none of the other deletions that were screened for. The proportion of mtDNA 4977 deletion carriers was 98.3% (89/90) and the deletion loads increased from 0 to 1.436 ± 0.2086% of the total mtDNA with an exponential increase with age (r = 0.677, p < 0.05). These results suggest that mtDNA 4977 bp deletion is a common phenomenon in hair and increases with age. These findings expand our understanding of the tissue-specific distribution of mtDNA deletions.

Tissue-specific implications of mitochondrial alterations in aging

Aging is a multifactorial process during which physiological alterations occur in all tissues. A decline in mitochondrial function plays an important role in the process of aging and in aging-associated diseases. The mitochondrial genome encodes 13 essential subunits of protein complexes belonging to the oxidative phosphorylation system, while most of the mitochondria-related genes are encoded by the nuclear genome. Coordination between the nucleus and mitochondria is crucial for the regulation of mitochondrial biogenesis and function. In this review, we will discuss aging-related mitochondrial dysfunction in various tissues and its implication in aging-related diseases and the aging process.