Besides studies revealing the molecular mechanisms underlying the associations of telomere defects and mitochondrial functions, investigations of mitochondrial DNA copy number mtDNAcn and telomere length TL in healthy and disease phenotypes have likewise begun, with the aim of gaining more insights about their relationship in humans.
Material and methods: A total of asymptomatic adult twins, comprising 96 monozygotic MZ and 46 dizygotic DZ twins mean age: Results: We found that twins were similar in their intraclass correlation coefficients irrespective of zygosity, suggesting a possibly more important role of common shared environmental factors compared to non-shared unique environmental and to a smaller degree also individual genetic influences.
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Following bivariate estimates and correction with significant predictors, the independent positive associations were further verified. Conclusions: Our results extend the until now modest number of studies investigating mtDNAcn and TL simultaneously in humans.
Introduction Telomeres are protective heterochromatic structures formed by DNA tandem repeats bound by specialized protein complexes, that cap the end of linear chromosomes and play a key role in maintaining genomic integrity [ 1 ].
Most somatic tissues lack telomerase activity and in the absence of compensatory mechanisms type 1 diabetes low heart rate progressive telomere shortening, leading to loss of chromosomal stability, senescence and apoptosis [ 2 ].
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Telomeres are dynamic structures, showing differences in diverse tissues. Their maintenance and shortening is a complex process which could be influenced by genetics and epigenetic mechanisms [ 34 ]. Several environmental factors might contribute to telomere shortening, including oxidative stress, inflammation or psychiatric conditions [ 5 — 7 ]. Telomere dysfunction and defects in telomere maintenance could contribute to a higher risk of many aging-related diseases [ 8 ], and as some studies found that telomere length TL of leukocytes could predict mortality [ 910 ] and longevity [ 11 ], it was suggested as a potential biomarker of biological aging [ 1213 ], yet the exact relationship between TL and aging is not fully understood [ 14 ].
Material and methods
Mitochondria are fundamental ATP-generating organelles, playing a crucial role in both metabolic homeostasis, cellular differentiation, proliferation and apoptosis [ 16 ]. Each mammalian cell harbours hundreds to thousands of mitochondria in their cytoplasm, and each organelle contains two to ten copies of circular mitochondrial DNA [ 17 ]. With advancing age, more reactive oxygen species ROS are produced by mitochondria, resulting in accumulating mtDNA damage, leading to defects in mitochondrial function, and consequently to cellular dysfunction and senescence, contributing to a wide range of pathologies [ 1819 ].
Because of the close proximity to the main cellular source of ROS, mtDNA could be easily damaged [ 20 ], and it was found that an altered mtDNA sequence could cause several mitochondrial disorders [ 21 ]. Several studies have suggested that alterations of mtDNA copy number could be associated with a number of diseases, such as different types of cancer, cardiomyopathy, diabetes, neurodegeneration, rheumatoid arthritis and infertility [ 22 — 26 ]. Both genetic and environmental factors have been reported to correlate with mtDNA copy number by recent studies [ 27 — 29 ].
Mitochondrial DNA copy number decline has been referred to as a seemingly valid marker of cellular aging, although the literature remains inconsistent [ 30 ].
It has been suggested that co-regulation of TL and mtDNAcn may be important in the pathophysiology of several human diseases, and functional links were proposed, but the relationship is still not completely understood [ 3031 ].
Although population-based studies focusing on the possible co-regulation of mitochondria and telomere length have only recently started and have been limited in number so far, associations were reported both in health and disease [ 3031 ], which could highlight the potential of mtDNAcn and TL as candidate biomarkers.
The aim to identify relevant biomarkers that could help in the early diagnosis of frequent pathologies, such as cancer, cardiovascular disorders or cukorbeteg kismama étrend, has been in the spotlight of recent research [ 32 — 36 ]. Twin studies provide unique opportunities to disentangle genetic and environmental factors that contribute to the variance in a certain phenotype [ 3738 ].
The aim of our study was to investigate the relationship of mtDNA copy number, telomere length and clinical data, besides assessing co-twin similarities of monozygotic MZ and dizygotic DZ twin subjects for their mtDNAcn and TL measures. Material and methods Study subjects and design A total of twin volunteers, comprising 96 monozygotic 48 complete pairs and 46 dizygotic twins 23 complete pairsmembers of the Hungarian Twin Registry [ 39 ], were enrolled and included in the analysis.
The mean age of participants was Medical history was taken, blood pressure and heart rate were measured, and fasting venous blood was drawn for serum glucose, renal function, lipid profile and C-reactive protein CRP measurements.
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An hour after awakening, peripheral blood was drawn, always at the same time for both members of a twin pair. Blood was collected and transferred for molecular biology examinations. The subjects in the selected sample were in generally good health, and none of the subjects had any acute clinical condition or were diagnosed with any type of cancer.
Exclusion criteria included pregnancy or foreseeable lack of compliance with test procedures.
Peripheral blood mononuclear cells PBMCs were extracted applying density gradient centrifugation g for 20 min at 20°Cand the blood samples were layered over the Ficoll-Paque Sigma, St. Louis, USA. Following centrifugation, buffy coat was obtained, and after aspiration washed with PBS. Absolute telomere length and absolute mitochondrial DNA copy number were estimated using quantitative polymerase chain reaction qPCR as previously defined [ 40 ] with minor modifications [ 41 ].
Telomere length was calculated as the number of telomere repeats relative to that of a single-copy gene ALB used as a quantitative control, relative to a reference sample. The primer and probe sequences Table I were previously defined [ 40 — 43 ].
Primer concentrations were nM and cycling conditions were: 10 min at 95°C, followed by type 1 diabetes low heart rate cycles of 95°C for 15 s, 60°C for 1 min. For the standard curve method, 6-point serial-dilution of cloned amplicons with no template control and the same calibrator sample were used in each run to gain comparable data.
The results were evaluated by StepOne Software v2. In each case the correlation coefficient R2 was above 0.
During TL and mtDNAcn measurement, age and twin status of participants were completely blinded for all samples.