Mitochondrial Deletions Research Articles

Correlation analysis between mtDNA 4977-bp deletion and ageing

Mitochondrial DNA 4977-bp deletion (common deletion) has been associated with ageing human tissues and a few studies have demonstrated their presence in breast cancer patients too; however, no previous publication evaluated both topics in the same samples group. First, when analyzing 95 breast cancer patients, we found a higher percentage of cases carrying the deletion in non-tumoral tissue 73.68% (70/95) than in the tumoral counterparts 45.26% (43/95), showing that the 4977-bp deletion is a phenomenon which commonly appear first in the non-tumoral breast tissue rather than tumoral tissue. Secondly, we analyzed and compared the ageing related distribution of the common deletion rates, in a control group of 199 samples (ages ranging from 10 to 80 years), with those found in cancer patients. Significant correlation was observed in control cases, between individual age ranges and rates of deletion (chi2: 23.21 and p < 0.01). In contrast, non-tumoral breast tissue did not show a pattern of correlation, chi2: 0.042 and p: 0.837. However, interestingly, we found that the risk of having deleted mtDNAs was higher for non-tumoral breast samples than for the control group samples, OR: 2.32 [1.22–4.42, 95% CI]; this could be reflecting that other mechanisms are involved in mitochondrial genome deletion increased rate detected in breast cancer cases, than the normal ageing process.

Profiling the Response of Human Hair Follicles to Ultraviolet Radiation

Excessive UVR ranks among the most harmful environmental influences on human skin. However, the direct impact of UVR on human skin appendages remains to be systematically investigated. Organ-cultured human anagen hair follicles in vitro were irradiated, and reduction of hair shaft elongation, premature catagen entry, and reduced hair matrix keratinocyte proliferation were observed upon irradiation with UVB (20/50 mJ cm(-2)). At 20 mJ cm(-2), apoptotic cell death prevailed (casp-3/p53 activation), whereas at 50 mJ cm(-2), necrotic cell death was predominant (lactate dehydrogenase increase). Mitochondrial common deletion and oxidatively damaged genomic DNA (8-OH-dG) was mainly observed at 20 mJ cm(-2). Follicular melanogenesis and ACTH immunoreactivity drastically declined, but alpha-melanocyte-stimulating hormone remained unchanged, whereas transforming growth factor-beta(2) expression shifted from the outer toward the inner root sheath. Both the number of Giemsa+ mast cells and the degree of mast-cell degranulation increased in the connective tissue sheath (CTS), and CD117 immunoreactivity of CTS cells and matrix keratinocytes was upregulated. Thus, UVR differentially modifies hair growth and cycle, promotes cell death, and induces complex regulatory events in human hair follicles in vitro. The leads from this human organ model, which is a living and human tissue interaction system under physiologically relevant in situ conditions, may encourage its use for general investigation of UV-induced effects as well as for testing possible agents for their UV-protective potency.

Mitochondrial bioenergetics and redox state are unaltered in Trypanosoma cruzi isolates with compromised mitochondrial complex I subunit genes

In trypanosomatids the involvement of mitochondrial complex I in NADH oxidation has long been debated. Here, we took advantage of natural Trypanosoma cruzi mutants which present conspicuous deletions in ND4, ND5 and ND7 genes coding for complex I subunits to further investigate its functionality. Mitochondrial bioenergetics of wild type and complex I mutants showed no significant differences in oxygen consumption or respiratory control ratios in the presence of NADH-linked substrates or FADH(2)-generating succinate. No correlation could be established between mitochondrial membrane potentials and ND deletions. Since release of reactive oxygen species occurs at complex I, we measured mitochondrial H(2)O(2) formation induced by different substrates. Significant differences not associated to ND deletions were observed among the parasite isolates, demonstrating that these mutations are not important for the control of oxidant production. Our data support the notion that complex I has a limited function in T. cruzi.

Quantification of the mitochondrial DNA common deletion in presbycusis

This study was conducted to evaluate the association between the mitochondrial DNA (mtDNA) common deletion (CD) level in cochlear tissue and the severity of hearing loss in individuals with presbycusis. Nineteen individuals with presbycusis, ranging from 60 to 87 years of age, who met strict audiometric criteria were compared with four age frequency-matched normal hearing controls ranging from 51 to 76 years of age. Five additional normal hearing individuals, ranging from 9 to 50 years of age, were also studied. A duplex real time polymerase chain reaction assay was used to quantify the mtDNA in archival cochlear tissue samples. Linear regression models were used for comparison of the CD level between groups. The presbycusis group had a mean CD level of 32% with a standard deviation of 14%, and the normal hearing age matched control group had a mean CD level of 12% with a standard deviation of 2%. This difference in CD levels reached statistical significance (P = .011) and remained significant after adjusting for any differences in age between the two groups (age-adjusted P = .007). Furthermore, there was evidence for a significant association between the CD level and the severity of hearing loss based on audiometric thresholds at 8 kHz (r = 0.44, P = .034; age-adjusted partial correlation = 0.55, P = .007). For the first time, to our knowledge, these results demonstrate a relationship between quantitatively measured levels of the CD in human cochlear tissue and the severity of hearing loss in individuals with presbycusis. Laryngoscope, 2009.

Functional consequences of mitochondrial DNA deletions in human skin fibroblasts: increased contractile strength in collagen lattices is due to oxidative stress-induced lysyl oxidase activity

Deletions within the mitochondrial DNA (mtDNA) are thought to contribute to extrinsic skin aging. To study the translation of mtDNA deletions into functional and structural changes in the skin, we seeded human skin fibroblasts into collagen gels to generate dermal equivalents. These cells were either derived from Kearns-Sayre syndrome (KSS) patients, who constitutively carry large amounts of the UV-inducible mitochondrial common deletion, or normal human volunteers. We found that KSS fibroblasts, in comparison with normal human fibroblasts, contracted the gels faster and more strongly, an effect that was dependent on reactive oxygen species. Gene expression and Western blot analysis revealed significant upregulation of lysyl oxidase (LOX) in KSS fibroblasts. Treatment with the specific LOX inhibitor -aminopropionitrile decreased the contraction difference between KSS and normal human fibroblast equivalents. Also, addition of the antioxidant N-tert-butyl--phenylnitrone reduced the contraction difference by inhibiting collagen gel contraction in KSS fibroblasts, and both -aminopropionitrile and N-tert-butyl--phenylnitrone diminished LOX activity. These data suggest a causal relationship between mtDNA deletions, reactive oxygen species production, and increased LOX activity that leads to increased contraction of collagen gels. Accordingly, increased LOX expression was also observed in vivo in photoaged human and mouse skin. Therefore, mtDNA deletions in human fibroblasts may lead to functional and structural alterations of the skin. (Am J Pathol 2009, 175:1019–1029; DOI: 10.2353/ajpath.2009.080832)

Frequency of the mitochondrial DNA 4977bp deletion in oesophageal mucosa during the progression of Barrett’s oesophagus

Purpose The mechanisms of the progression of Barrett’s oesophagus (BO) to oesophageal adenocarcinoma (OA) are poorly understood. The frequency of the 4977bp deletion in mitochondrial DNA (mtDNA) was investigated in specimens ranging from normal oesophageal tissue to OA in order to investigate whether this deletion represents a useful biomarker of disease progression. Methods The presence of the 4977bp deletion was screened by PCR amplification from 70 specimens in total. Results The frequency of specimens with the 4977bp deletion increased in relation to the degree of dysplasia (8.3% in normal squamous epithelium; 15.4% in BO; 40% in low grade dysplasia (LGD); 69.2% in high-grade dysplasia and 90% in para-tumoural tissue). However, the frequency of the deletion reduced sharply in OA specimens (16.7%; p < 0.001). Conclusion The mtDNA 4977bp deletion may be useful as a biomarker to detect the severity of dysplasia but not the presence of OA.

Mitochondrial DNA 4977-bp deletion correlated with reactive oxygen species production and manganese superoxide dismutase expression in gastric tumor cells

Background Mitochondrial DNA 4977-bp deletion (ΔmtDNA4977) was reported in many human neoplasia. However, its biological significance remains to be evaluated and the molecular mechanism needs to be investigated. In this study, we analyzed the frequency of ΔmtDNA4977 in gastric cancer (GC) cell lines and tissues, as well as reactive oxygen species (ROS) contents and manganese superoxide dismutase (MnSOD) expression levels in GC cell lines to explore its biological significance and molecular mechanism. Methods Semi-quantitative PCR and real-time PCR were used to detect the incidence of ΔmtDNA4977 in 13 GC cell lines and 272 human gastric tissues (108 GC specimens and the respective adjacent normal tissues, and 56 normal gastric mucosa from non-cancer patients). We further identified intracellular ROS production by flow cytometry and MnSOD expression by semi-quantitative reverse transcription-PCR (RT-PCR) and Western blotting. Statistical analyses were carried out using the Logistic regression analysis and Kaplan-Meier method. Results Based on our earlier study, we optimized the PCR amplification condition by reducing the cycle number. In this study, we systematically documented the high incidence of ΔmtDNA4977 in GC cell lines (10/13, 76.9%), GC tissues (86/108, 79.6%), matched normal tissues (73/108, 67.6%), and normal gastric mucosa of non-cancer patients (29/56, 51.8%). A significantly higher incidence of mutated ΔmtDNA4977 was observed in GC tissues with respect to the adjacent normal tissues (79.6% vs 67.6%, P=0.045), and they were both higher than that in normal controls (P &lt;0.05). Most importantly, we linked the ΔmtDNA4977 mutations with the expression level of MnSOD and ROS contents. The cell lines containing lower expression level of MnSOD was found to have generally higher frequent ΔmtDNA4977 and more ROS. Conclusion The decreased anti-oxidative ability, which leads to increased ROS contents, is correlated with the mtDNA damage during gastric carcinogenesis. Chin Med J 2009;122(4):431–436

The mitochondrial theory of aging: Insight from transgenic and knockout mouse models

A substantial body of evidence has accumulated over the past 35 years in support of a role for oxidative damage to the mitochondrial respiratory chain and mitochondrial DNA in the determination of mammalian lifespan. The goal of this review is to provide a concise summary of recent studies using transgenic and knockout mouse models with altered expression of mitochondrial antioxidant enzymes (MnSOD ( Sod2Tg and Sod2 +/− ), thioredoxin 2 ( Trx2 +/− ), mitochondrial targeted catalase (mCAT) and mutant mice models that have been genetically manipulated to increase mitochondrial deletions or mutations ( Polγ D257A/D257A mutant mice) to examine the role of mitochondrial oxidative stress in aging. The majority of studies using these strategies do not support a clear role for mitochondrial oxidative stress or a vicious cycle of oxidative damage in the determination of lifespan in mice and furthermore do not support the free radical theory of aging. However, several key questions remain to be addressed and clearly more studies are required to fully understand the role of mitochondria in age-related disease and aging.

Madelung′s disease with myopathy

Madelung′s disease with myopathy

Mechanisms of formation and accumulation of mitochondrial DNA deletions in aging neurons

Age-dependent accumulation of partially deleted mitochondrial DNA (DeltamtDNA) has been suggested to contribute to aging and the development of age-associated diseases including Parkinson's disease. However, the molecular mechanisms underlying the generation and accumulation of DeltamtDNA have not been addressed in vivo. In this study, we have developed a mouse model expressing an inducible mitochondria-targeted restriction endonuclease (PstI). Using this system, we could trigger mtDNA double-strand breaks (DSBs) in adult neurons. We found that this transient event leads to the generation of a family of DeltamtDNA with features that closely resemble naturally-occurring mtDNA deletions. The formation of these deleted species is likely to be mediated by yet uncharacterized DNA repairing machineries that participate in homologous recombination and non-homologous end-joining. Furthermore, we obtained in vivo evidence that DeltamtDNAs with larger deletions accumulate faster than those with smaller deletions, implying a replicative advantage of smaller mtDNAs. These findings identify DSB, DNA repair systems and replicative advantage as likely mechanisms underlying the generation and age-associated accumulation of DeltamtDNA in mammalian neurons.

Fibroblast senescence

Fibroblast senescence

A common sequence motif associated with recombination hot spots and genome instability in humans

In humans, most meiotic crossover events are clustered into short regions of the genome known as recombination hot spots. We have previously identified DNA motifs that are enriched in hot spots, particularly the 7-mer CCTCCCT. Here we use the increased hot-spot resolution afforded by the Phase 2 HapMap and novel search methods to identify an extended family of motifs based around the degenerate 13-mer CCNCCNTNNCCNC, which is critical in recruiting crossover events to at least 40% of all human hot spots and which operates on diverse genetic backgrounds in both sexes. Furthermore, these motifs are found in hypervariable minisatellites and are clustered in the breakpoint regions of both disease-causing nonallelic homologous recombination hot spots and common mitochondrial deletion hot spots, implicating the motif as a driver of genome instability.

Mitochondrial DNA single deletion in a patient with postural tremor

Mitochondrial DNA single deletion in a patient with postural tremor

Cholestasis: Current Issues and Plan for the Future

Cholestasis: Current Issues and Plan for the Future

Technical report: Laser microdissection of cochlear structures from celloidin embedded human temporal bone tissues and detection of the mitochondrial DNA common deletion using real time PCR

Laser microdissection (LMD) has been used to isolate groups of cells and single cells from numerous tissues. In this study, we describe a technique for isolating cochlear structures and individual spiral ganglion cells from archival celloidin embedded human temporal bone sections. The specimens isolated are suitable for quantifying the mitochondrial DNA (mtDNA) common deletion (CD) within these tissues using a real time polymerase chain reaction (PCR) assay. The results presented in this manuscript demonstrate the feasibility of using this LMD technique to study the accumulation of mtDNA deletions in diseases of the ear. To our knowledge, this approach to analyzing archival human temporal bone tissues has not been previously reported.

Sunbed Use Induces the Photoaging-Associated Mitochondrial Common Deletion

Sunbeds have become very popular and, as a result, health effects of their use are of growing concern. In this regard, exposure to ultraviolet radiation from sunbeds may cause premature skin aging. Evidence for this assumption, however, has thus far been elusive. In this study, we assessed whether sunbed use induced the generation of a large-scale mitochondrial DNA mutation in human skin, the so-called Common Deletion, which is well known to be photoaging-associated. Fifty-nine individuals who voluntarily started to use sunbeds were observed over 3 months. Punch biopsies were taken from neck and buttock skin before the first and after their last sunbed visit. The Common Deletion content was determined by quantitative real-time PCR. Multiple linear regression analysis was performed for statistical analysis. Volunteers without previous sunbed use showed a 2.56-fold increase (95% CI: 0.97-6.78) of the Common Deletion in neck and a 3.58-fold increase (95% CI: 1.44-8.89) of the Common Deletion in buttock skin samples after sunbed use. Participants with previous sunbed use showed no increase. This study indicates that sunbed use may contribute to mtDNA deletion-associated skin photoaging.

The 4977 bp deletion of mitochondrial DNA in human skeletal muscle, heart and different areas of the brain: A useful biomarker or more?

It has been suggested that deletions of mitochondrial DNA (mtDNA) are important players with regard to the ageing process. Since the early 1990s, the 4977 bp deletion has been studied in various tissues, especially in postmitotic tissues with high energy demand. Unfortunately, some of these studies included less than 10 subjects, so the aim of our study was to quantify reliably the deletion amount in nine different regions of human brain, heart and skeletal muscle in a cohort of 92 individuals. The basal ganglia contain the highest deletion amounts with values up to 2.93% and differences in deletion levels between early adolescence and older ages were up to three orders of magnitude. Values in frontal lobe were on average an order of magnitude lower, but lowest in cerebellar tissue where the amount was on average only 5 × 10 −3 of the basal ganglia. The deletion started to accumulate in iliopsoas muscle early in the fourth decade of life with values between 0.00019% and 0.0035% and was highest in a 102-year-old woman with 0.14%. In comparison to skeletal muscle, the overall abundance in heart muscle of the left ventricle was only one-third. The best linear logarithmic correlation between amount of the deletion and age was found in substantia nigra with r = 0.87 ( p < 0.0005) followed by anterior wall of the left ventricle ( r = 0.82; p < 0.0005). With regard to mitochondrial DNA damage, we propose to use the 4977 bp deletion as an ideal biomarker to discriminate between physiological ageing and accelerated ageing. The biological meaning of mitochondrial deletions in the process of ageing is under discussion, but there is experimental evidence that large-scale deletions impair the oxidative phosphorylation in single cells and sensitize these cells to undergo apoptosis.

Novel mitochondrial tRNALeu(CUN) transition and D4Z4 partial deletion in a patient with a facioscapulohumeral phenotype

Point mutations in mtDNA-encoded tRNA genes frequently cause isolated myopathies but rarely cause the facioscapulohumeral phenotype.We report on a patient affected with chronic progressive weakness of facioscapulohumeral/peroneal muscles whose muscle biopsy showed a mitochondrial myopathy. mtDNA direct sequencing and RFLP analysis revealed a heteroplasmic transition T12313C which disrupts a conserved site in the TΨC stem of the tRNALeu(CUN) gene and fulfills the accepted criteria of pathogenicity.A partial deletion of the nuclear DNA D4Z4 region with residual repeat sizes of 25kb was also found in the patient and in her mother.This is the first reported case of mitochondrial myopathy/facioscapulohumeral muscular dystrophy (FSHD) “double trouble”.

Mitochondrial Genome Deletion Aids in the Identification of False- and True-Negative Prostate Needle Core Biopsy Specimens

We report the usefulness of a 3.4-kb mitochondrial genome deletion (3.4 mtdelta) for molecular definition of benign, malignant, and proximal to malignant (PTM) prostate needle biopsy specimens. The 3.4 mtdelta was identified through long-extension polymerase chain reaction (PCR) analysis of frozen prostate cancer samples. A quantitative PCR assay was developed to measure the levels of the 3.4 mtdelta in clinical samples. For normalization, amplifications of a nuclear target and total mitochondrial DNA were included. Cycle threshold data from these targets were used to calculate a score for each biopsy sample. In a pilot study of 38 benign, 29 malignant, and 41 PTM biopsy specimens, the difference between benign and malignant core biopsy specimens was well differentiated (P & .0001), with PTM indistinguishable from malignant samples (P = .833). Results of a larger study were identical. In comparison with histopathologic examination for benign and malignant samples, the sensitivity and specificity were 80% and 71%, respectively, and the area under a receiver operating characteristic (ROC) curve was 0.83 for the deletion. In a blinded external validation study, the sensitivity and specificity were 83% and 79%, and the area under the ROC curve was 0.87. The 3.4 mtdelta may be useful in defining malignant, benign, and PTM prostate tissues.

DELAYED DIAGNOSIS OF KEARNS-SAYRE SYNDROME IN A 38-YEAR-OLD MALE PATIENT: A CASE REPORT

Kearns-Sayre syndrome is a rare disorder caused by mitochondrial deoxyribonucleic acid deletion. It is characterized by a triad of progressive external ophthalmoplegia, initial symptoms that develop before the age of 20 years, and pigmentary retinopathy. Multisystem involvement is frequently associated with those features. Ragged red fibers can be identified during histopathologic examination and confirmed by electron microscopy. In this article, the case of a 38-year-old man with Kearns-Sayre syndrome in whom diagnosis was delayed despite abundant clinical evidence is presented. A brief review of clinical and laboratory findings in patients with that disorder is also provided.