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PubMed1998

Functions of the high mobility group protein, Abf2p, in mitochondrial DNA segregation, recombination and copy number in Saccharomyces cerevisiae.

Previous studies have established that the mitochondrial high mobility group (HMG) protein, Abf2p, of Saccharomyces cerevisiae influences the stability of wild-type (rho+) mitochondrial DNA (mtDNA) and plays an important role in mtDNA organization. Here we report new functions for Abf2p in mtDNA transactions. We find that in homozygous deltaabf2 crosses, the pattern of sorting of mtDNA and mitochondrial matrix protein is altered, and mtDNA recombination is suppressed relative to homozygous ABF2 crosses. Although Abf2p is known to be required for the maintenance of mtDNA in rho+ cells growing on rich dextrose medium, we find that it is not required for the maintenance of mtDNA in p cells grown on the same medium. The content of both rho+ and rho- mtDNAs is increased in cells by 50-150% by moderate (two- to threefold) increases in the ABF2 copy number, suggesting that Abf2p plays a role in mtDNA copy control. Overproduction of Abf2p by > or = 10-fold from an ABF2 gene placed under control of the GAL1 promoter, however, leads to a rapid loss of rho+ mtDNA and a quantitative conversion of rho+ cells to petites within two to four generations after a shift of the culture from glucose to galactose medium. Overexpression of Abf2p in rho- cells also leads to a loss of mtDNA, but at a slower rate than was observed for rho+ cells. The mtDNA instability phenotype is related to the DNA-binding properties of Abf2p because a mutant Abf2p that contains mutations in residues of both HMG box domains known to affect DNA binding in vitro, and that binds poorly to mtDNA in vivo, complements deltaabf2 cells only weakly and greatly lessens the effect of overproduction on mtDNA instability. In vivo binding was assessed by colocalization to mtDNA of fusions between mutant or wild-type Abf2p and green fluorescent protein. These findings are discussed in the context of a model relating mtDNA copy number control and stability to mtDNA recombination.

Binding Sites↗
PubMed2003

Mitochondrial DNA depletion and morphologic changes in adipocytes associated with nucleoside reverse transcriptase inhibitor therapy.

BACKGROUND: Nucleoside analogue reverse transcriptase inhibitor (NRTI) therapy provides sufficient conditions for progressive subcutaneous fat wasting in HIV-infected patients. As NRTI-induced host toxicity is proposed to involve cellular mitochondrial DNA (mtDNA) depletion, determinants of cellular mtDNA copy number and mitochondrial mass in adipocyte samples from NRTI-treated HIV-infected patients and antiretroviral-naive controls were investigated. Adipose tissue morphology was also assessed. METHODS: Subcutaneous fat samples were obtained from NRTI-treated, HIV-infected patients (n = 21), antiretroviral therapy-naive HIV-infected controls (n = 11), and HIV-seronegative controls (n = 6). Non-adipocytes were removed by collagenase digestion. Adipocyte mtDNA copies/cell was measured using a real time PCR-based assay, and adipocyte mitochondrial protein content was also measured. Light and electron microscopy were performed on tissue samples. FINDINGS: Adipocyte mtDNA copies/cell values were similar (P = 0.56) in HIV seronegative and HIV-infected control groups. NRTI treatment was associated with reduced adipocyte mtDNA copies/cell, representing mean mtDNA depletion in NRTI-treated individuals of 77.7% compared with the mean value for the HIV-infected control group (P < 0001). Additionally, significant differences were found in adipocyte mtDNA copies/cell between patients receiving stavudine (n = 12, mean mtDNA depletion 87.1%) and zidovudine (n = 9, mean mtDNA depletion 52.1%) (P < 0.001). Adipocyte mitochondrial mass was increased in the stavudine group only (mean increase 289%, P < 0.01). INTERPRETATION: NRTI therapy is associated with mtDNA depletion and mitochondrial proliferation in adipocytes, consistent with the hypothesis that NRTI-induced mtDNA depletion contributes to the pathogenesis of subcutaneous fat wasting. Morphologic assessment also supports a role for NRTI therapy in inducing adipocyte metabolic dysfunction and cell death.

Adipocytes↗
PubMed1977

The character of protein-nucleic interaction in relation to the mtDNA-membrane complex.

Specific sites that interact with structural proteins of the mitochondrial inner membrane were found in mitochondrial DNA (mtDNA) of rat liver. Analysis of the isolated DNA fragments revealed their capacity to form a complex with membrane proteins in vitro and allowed the detection of a protein with a molecular weight 40,000. The size of the fragments was found to be 12-18 nucleotide pairs with an average molecular weight 10,000 MtDNA sites recognized by membrane protein proved to be quite unique in having a secondary structure, a high content of AT sequences (82%) and oligopyrimidine blocks. It was shown that the light mtDNA strand, rich in adenine, is 60% more active in the binding with membrane mitochondria than the heavy one.

Binding Sites↗
PubMed1996

Expression of the apoptosis-mediator Fas is enhanced by dysfunctional mitochondria.

We applied an antibody against an apoptosis mediator, Fas/APO-1/CD95, to HeLa-derived cells that completely lack mitochondrial DNA (mtDNA) or have mutant mtDNAs. The anti-Fas antibody killed the cells completely lacking mtDNA (EB8), at concentrations as low as 1 ng/ml, but not control cells harboring wild-type mtDNA (Ft2-11). TUNEL (terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end-labeling) and analysis of fragmented DNA indicated that the cell death of EB8 was due to apoptosis. The antibody was cytotoxic to other two cell lines harboring mutant mtDNA with a point mutation or a large-scale deletion. RT-PCR (reverse transcriptase-polymerase chain reaction) showed that the mRNA content of the Fas gene was 2 to 19-fold higher in the cells with deficient mtDNA than in the control cells. In addition, the expressed Fas protein was detected by immunohistochemical staining in the cells without mtDNA but not in the control cells. Incubating the cells containing wild-type mtDNA with the respiratory inhibitors rotenone and antimycin A enhanced the content of mRNA of the Fas gene 2 to 4-fold and sensitized cells to the antibody. Thus, defects in mitochondria caused apoptotic cell death by anti-Fas antibody and enhanced Fas gene expression.

Antimycin A↗
PubMed1995

Codon usage, genetic code and phylogeny of Dictyostelium discoideum mitochondrial DNA as deduced from a 7.3-kb region.

We have sequenced a region (7,376-bp) of the mitochondrial (mt) DNA (54 kb) of the cellular slime mold, Dictyostelium discoideum. From the DNA and amino-acid sequence comparisons with known sequences, genes for ATPase subunit 9 (ATP9), cytochrome b (CYTB), NADH dehydrogenase subunits 1, 3 and 6 (ND1, ND3 and ND6), small subunit rRNA (SSU rRNA) and seven tRNAs (Arg, Asn, Cys, Lys, f-Met, Met and Pro) have been identified. The sequenced region of the mtDNA has a high average A + T-content (70.8%). The A + T-content of protein-genes (73.6%) is considerably higher than that of RNA genes (61.3%). Even with the strong AT-bias, the genetic code employed is most probably the universal one. All seven tRNAs are able to form typical clover leaf structures. The molecular phylogenetic trees of CYTB and SSU rRNA suggest that D. discoideum is closer to green plants than to animals and fungi.

Amino Acid Sequence↗
PubMed2006

Molecular evolution of cytochrome c oxidase in high-performance fish (teleostei: Scombroidei).

The 13 peptides encoded by vertebrate mitochondrial DNA (mtDNA) are essential subunits of oxidative phosphorylation (OXPHOS) enzymes. These genes normally experience purifying selection and also coevolve with nuclear-encoded subunits of OXPHOS complexes. However, the role of positive selection on mtDNA evolution is still unclear, as most examples of intergenomic coevolution appear to be the result of compensation by nuclear-encoded genes for mildly deleterious mtDNA mutations, and not simultaneous positive selection in both genomes. Organisms that have experienced strong selective pressures to increase aerobic capacity or adapt to changes in thermal environment may be better candidates in which to examine the impact of positively selected changes on mtDNA evolution. The tuna (suborder Scombroidei, family Scombridae) and billfish (suborder Scombroidei, families Xiphiidae and Istiophoridae) are highly aerobic fish with multiple specializations in muscle energetics, including a high mitochondrial content and regional endothermy. We examined the role of positively selected mtDNA substitutions in the production of these unique phenotypes. Focusing on a catalytic subunit of cytochrome c oxidase (COX II), we found that the rate ratio of nonsynonymous (d(N); amino acid changing)-to-synonymous (d(S); silent) substitutions was not increased in lineages leading to the tuna but was significantly increased in the lineage preceding the billfish. Furthermore, there are a number of individual positively selected sites that, when mapped onto the COX crystal structure, appear to interact with other COX subunits and may affect OXPHOS function and regulation in billfish.

Animals↗
PubMed2004

Presence of interaction but not complementation between human mtDNAs carrying different mutations within a tRNA(Leu(UUR)) gene.

This study provided answers to fundamental questions on mammalian mitochondrial genetics: Could respiratory function in mitochondria be maintained by their exchange of genetic contents even when mutations were created within the same genes in different mitochondrial DNA (mtDNA) molecules? Using cell fusion techniques, we created a chance to coexist two types of respiration-deficient syn(-) mitochondria carrying different mtDNA mutations within the same tRNA(Leu(UUR)) gene obtained from patients with mitochondrial diseases. The results showed that two syn(-) mitochondria exchanged their genetic contents, but did not restore respiration defects, suggesting that mitochondrial interaction could not complement the mutations created within the same gene in different mtDNA molecules.

DNA, Mitochondrial↗
PubMed1999

The complete mitochondrial DNA sequences of Nephroselmis olivacea and Pedinomonas minor. Two radically different evolutionary patterns within green algae.

Green plants appear to comprise two sister lineages, Chlorophyta (classes Chlorophyceae, Ulvophyceae, Trebouxiophyceae, and Prasinophyceae) and Streptophyta (Charophyceae and Embryophyta, or land plants). To gain insight into the nature of the ancestral green plant mitochondrial genome, we have sequenced the mitochondrial DNAs (mtDNAs) of Nephroselmis olivacea and Pedinomonas minor. These two green algae are presumptive members of the Prasinophyceae. This class is thought to include descendants of the earliest diverging green algae. We find that Nephroselmis and Pedinomonas mtDNAs differ markedly in size, gene content, and gene organization. Of the green algal mtDNAs sequenced so far, that of Nephroselmis (45,223 bp) is the most ancestral (minimally diverged) and occupies the phylogenetically most basal position within the Chlorophyta. Its repertoire of 69 genes closely resembles that in the mtDNA of Prototheca wickerhamii, a later diverging trebouxiophycean green alga. Three of the Nephroselmis genes (nad10, rpl14, and rnpB) have not been identified in previously sequenced mtDNAs of green algae and land plants. In contrast, the 25,137-bp Pedinomonas mtDNA contains only 22 genes and retains few recognizably ancestral features. In several respects, including gene content and rate of sequence divergence, Pedinomonas mtDNA resembles the reduced mtDNAs of chlamydomonad algae, with which it is robustly affiliated in phylogenetic analyses. Our results confirm the existence of two radically different patterns of mitochondrial genome evolution within the green algae.

Animals↗
PubMed1998

Divergent evolutionary constraints on mitochondrial and nuclear genomes of malaria parasites.

Genetic variation among malaria parasites has important consequences with regard to drug resistance, pathogenicity, immunity, transmission, and speciation. In this regard, malaria parasites have been shown to display a high degree of inter- and intra-species genetic divergence. The nuclear genomes of Plasmodium falciparum, Plasmodium yoelii, and Plasmodium gallinaceum are vastly divergent yet share a similar codon usage and total A/T content of approximately 82%. This is in contrast to other primate-specific species including P. vivax which have an A/T content of approximately 67%. To assess the effects of this evolutionary divergence on the conservation of gene content, organization, and codon usage in the mitochondrial DNA (mtDNA) of malaria parasites, we have cloned and sequenced the mitochondrial genome of Plasmodium vivax, and compared it with the mtDNAs of P. falciparum, P. yoelii, and P. gallinaceum. The P. vivax mitochondrial genome was found to be 5990 base pairs in length, and displayed a gene organization identical to that of P. falciparum, P. yoelii, and P. gallinaceum. Furthermore, there was a remarkable 90% conservation of sequence identity between the mitochondrial genomes of all four species. As an example of intra-species conservation, comparison of mtDNAs from two independently cloned P. falciparum isolates, Malay Camp and C10, revealed only a single nucleotide substitution. A/T content of the P. vivax mitochondrial genome was found to be identical to other species of Plasmodium, hence, we have postulated that the mitochondrial genomes of malaria parasites were refractory to the evolutionary shifts in nucleotide content seen among the nuclear genomes of malaria parasites. Among different Plasmodium species, the second position of mitochondrial codons were found to be the least prone to substitutions and displayed a significant bias in pyrimidines. These aspects of mitochondrial codon usage were distinct from the nuclear genome and may reflect functional aspects of decoding by the mitochondrial translational system.

Amino Acid Sequence↗
PubMed2006

Defective oxidative phosphorylation in thyroid oncocytic carcinoma is associated with pathogenic mitochondrial DNA mutations affecting complexes I and III.

Oncocytic tumors are characterized by cells with an aberrant accumulation of mitochondria. To assess mitochondrial function in neoplastic oncocytic cells, we studied the thyroid oncocytic cell line XTC.UC1 and compared it with other thyroid non-oncocytic cell lines. Only XTC.UC1 cells were unable to survive in galactose, a condition forcing cells to rely solely on mitochondria for energy production. The rate of respiration and mitochondrial ATP synthesis driven by complex I substrates was severely reduced in XTC.UC1 cells. Furthermore, the enzymatic activity of complexes I and III was dramatically decreased in these cells compared with controls, in conjunction with a strongly enhanced production of reactive oxygen species. Osteosarcoma-derived transmitochondrial cell hybrids (cybrids) carrying XTC.UC1 mitochondrial DNA (mtDNA) were generated to discriminate whether the energetic failure depended on mitochondrial or nuclear DNA mutations. In galactose medium, XTC.UC1 cybrid clones showed reduced viability and ATP content, similarly to the parental XTC.UC1, clearly pointing to the existence of mtDNA alterations. Sequencing of XTC.UC1 mtDNA identified a frameshift mutation in ND1 and a nonconservative substitution in cytochrome b, two mutations with a clear pathogenic potential. In conclusion, this is the first demonstration that mitochondrial dysfunction of XTC.UC1 is due to a combined complex I/III defect associated with mtDNA mutations, as proven by the transfer of the defective energetic phenotype with the mitochondrial genome into the cybrids.

Adenoma, Oxyphilic↗
PubMed2005

Oxidative damage and mitochondrial DNA mutations with endometriosis.

Endometriosis, a frequently encountered disease in gynecology, is a considerable threat to the physical, psychological, and social integrity of women. Moreover, up to 50% of infertile patients have this disease. The etiology and pathogenesis of this important disease are poorly understood; it is defined as an ectopic location for endometrium-like glandular epithelium and stroma outside of the uterine cavity. It still remains an open question as to what extent the peritoneal environment influences the establishment and/or progression of endometriosis. As a result of such stress, a sterile, inflammatory reaction with the secretion of growth factors, cytokines, and chemokines is generated, which is especially deleterious to successful reproduction. Significantly higher amounts of oxidative damage were detected in endometriotic lesions than in controlled normal endometrium, including mitochondrial DNA (mtDNA) rearrangement, 8-OH-deoxyguanosine (8-OH-dG), and lipoperoxide contents. There were approximately sixfold increases in 8-OH-dG and lipoperoxides in chocolate cysts compared with normal endometrial tissues. A novel 5,335-bp deletion of mtDNA was identified in endometriotic tissue. According to these results, we propose that oxidative stress and mtDNA mutations might be anticipated in the initiation or progression of endometriosis. Only by understanding the mechanisms involved in the pathogenesis of endometriosis can we develop a basis for new diagnostic and therapeutic approaches.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2004

In vitro embryo production efficiency in cattle and its association with oocyte adenosine triphosphate content, quantity of mitochondrial DNA, and mitochondrial DNA haplogroup.

Mitochondria have a broad range of functions that affect reproduction, and structural as well as quantitative variation in mtDNA has been associated with gamete quality and reproductive success. To investigate the mitochondria effect on in vitro embryo production, we collected oocytes by ultrasound-guided follicular aspiration from donor cows known to differ in the developmental capacity, measured by the blastocyst formation rate, of their oocytes. To evaluate the potential effects of mtDNA and mitochondrial function on oocyte quality, the donor cows' mtDNA control region was sequenced and, after pairwise comparisons of polymorphisms, animals were grouped into two major haplogroups. The number of mtDNA molecules per oocyte was quantified by real-time PCR, and the adenosine triphosphate (ATP) content was measured in each oocyte to identify variations between haplogroups. Overall, ATP stocks in oocytes of the two haplogroups differed significantly (P < 0.05; means +/- SEM) both at the germinal vesicle and metaphase II stages (2.8 +/- 0.06 pmol vs. 2.6 +/- 0.07 pmol and 2.9 +/- 0.1 pmol vs. 2.3 +/- 0.06 pmol, respectively). The proportion of development to blastocyst was significantly different between haplogroups (22.3 +/- 2.1 % vs. 36.7 +/- 2.9 %). The number of mtDNA molecules per oocyte was highly variable (377 327 +/- 14 104, ranging from 2.0 x 10(3) to 1.2 x 10(6)) but not significantly different between the two haplogroups; significant differences were observed between animals without any apparent relationship to blastocyst production. These data suggest that mitochondria and mtDNA haplogroup affect the developmental capacity of bovine oocytes in vitro.

Adenosine Triphosphate↗
PubMed1998

Smoking-associated mitochondrial DNA mutations and lipid peroxidation in human lung tissues.

To investigate the effect of cigarette smoking on mitochondrial DNA (mtDNA) mutation and lipid peroxidation in lung tissues, 152 samples from lung resections were collected. A novel deletion of 4,839 bp of mtDNA was found in 80 (52.6%) of the 152 lung samples. The breakpoints of the 4,839-bp mtDNA deletion were flanked by a nine-nucleotide direct repeat (5'-CATACACAA-3'). The frequency of occurrence and the proportion of the 4,839-bp mtDNA deletion in the lung increased significantly with the smoking index in terms of pack-years (P < 0.05). The incidence and proportion of the 4,839-bp mtDNA deletion in the lung tissues of current smokers were significantly higher than in those of nonsmokers (P < 0.05). In addition, we found that the content of lipid peroxides in the lung tissues of the smokers was significantly higher than in that of nonsmokers, and increased with the smoking index. The average malondialdehyde level in the lung tissues was 12.81 +/- 4.99 micromol/g for subjects with a smoking index of more than 50 pack-yr, and was 5.39 +/- 0.48 micromol/g for nonsmokers (P < 0.05). Multiple regression analysis showed that the smoking index, tissue lipid-peroxide content, and FEV1/FVC ratio were correlated with the proportion of the 4,839-bp mtDNA deletion in the lung. These results suggest that cigarette smoke plays an important role in the increase in mtDNA mutation and lipid peroxidation in the lung tissues of smokers.

Adult↗
PubMed2002

Base composition at mtDNA boundaries suggests a DNA triple helix model for human mitochondrial DNA large-scale rearrangements.

Different mechanisms have been proposed to account for mitochondrial DNA (mtDNA) instability based on the presence of short homologous sequences (direct repeats, DR) at the potential boundaries of mtDNA rearrangements. Among them, slippage-mispairing of the replication complex during the asymmetric replication cycle of the mammalian mitochondrial DNA has been proposed to account for the preferential localization of deletions. This mechanism involves a transfer of the replication complex from the first neo-synthesized heavy (H) strand of the DR1, to the DR2, thus bypassing the intervening sequence and producing a deleted molecule. Nevertheless, the nature of the bonds between the DNA strands remains unknown as the forward sequence of DR2, beyond the replication complex, stays double-stranded. Here, we have analyzed the base composition of the DR at the boundaries of mtDNA deletions and duplications and found a skewed pyrimidine content of about 75% in the light-strand DNA template. This suggests the possible building of a DNA triple helix between the G-rich neo-synthesized DR1 and the base-paired homologous G.C-rich DR2. In vitro experiments with the purified human DNA polymerase gamma subunits enabled us to show that the third DNA strand may be used as a primer for DNA replication, using a template with the direct repeat forming a hairpin, with which the primer could initiate DNA replication. These data suggest a novel molecular basis for mitochondrial DNA rearrangements through the distributive nature of the DNA polymerase gamma, at the level of the direct repeats. A general model accounting for large-scale mitochondrial DNA deletion and duplication is proposed. These experiments extend to a DNA polymerase from an eucaryote source the use of a DNA triple helix strand as a primer, like other DNA polymerases from phage and bacterial origins.

Base Composition↗
PubMed2004

Endogenously oxidized mitochondrial DNA induces in vivo and in vitro inflammatory responses.

We report that mitochondrial DNA (mtDNA) is inflammatogenic in vitro and in vivo as a result of the presence of unmethylated CpG sequences and its oxidative status. Purified human and murine mtDNAs induced arthritis when injected intra-articularly (i.a.) in mice. Importantly, oligodeoxynucleotide that contained a single oxidatively damaged base also induced arthritis when injected i.a. in mice. In contrast, neither human nor murine nuclear DNA induced inflammation. mtDNA-induced arthritis was neither B cell- nor T cell-dependent but was mediated by monocytes/macrophages. mtDNA-induced nuclear factor-kappaB stimulation resulted in the production of tumor necrosis factor alpha, a potent, arthritogenic factor. Finally, extracellular mtDNA was detected in the synovial fluids of rheumatoid arthritis patients but not of control subjects. We conclude that endogenous mtDNA displays inflammatogenic properties as a result of its content of unmethylated CpG motifs and oxidatively damaged adducts.

Animals↗
PubMed1998

AZT decreases rat myocardial cytochrome oxidase activity and increases beta-myosin heavy chain content.

AZT, a widely-utilized drug for the treatment of HIV infection, inhibits the polymerase responsible for mitochondrial DNA replication (mtDNA). The aim of this study was to assess myocardial alterations caused by this action. Ventricular muscle from rats treated for > or = 35 days with 1 mg/ml of AZT in their drinking water was analysed for cytochrome oxidase activity and the content of mRNAs for the nuclear-encoded cytochrome oxidase (COX) subunit VIc and the mitochondrial-encoded COX subunit III. In addition contractile protein expression was assessed by examining mRNA levels for alpha- and beta-myosin heavy chains (MHC). Changes in MHC mRNA levels were correlated with changes in alpha- and beta-MHC proteins and changes in myofibrillar ATPase activity. Results show that AZT caused a reduction in COX activity, COX subunit III mRNA, and mtDNA levels. There was no decrease in the COX subunit VIc mRNA. MHC expression was altered such that the relative content of beta-MHC protein and mRNA were increased. Accumulation of beta-MHC was reflected in the reduction of myofibrillar ATPase activity at pCa values of 5.875 and 6.125. These data demonstrate that AZT induces a reorganization of cardiac gene expression indicative of changes in cardiac contractile properties. The observed decreases in mtDNA levels along with mRNA for a mitochondrial-encoded protein and COX activity is consistent with the postulated mechanism whereby AZT induces a myopathy by diminishing mtDNA replication.

Animals↗
PubMed2004

Effect of nucleoside reverse transcriptase inhibitors on mitochondrial DNA synthesis in rats and humans.

Nucleoside reverse transcriptase inhibitors (NRTIs) have been hypothesized to inhibit mitochondrial DNA polymerase gamma, resulting in decreased mtDNA synthesis and mitochondrial insufficiency in HIV-1-infected patients. mtDNA synthesis was measured directly using a stable isotope mass spectrometric method following NRTI treatment in rodents. 3'-Azido-3'-deoxythymidine (AZT) was added to water (1 mg/mL) and administered ad libitum to female Sprague-Dawley rats for 1-8 weeks (n = 4 or 5 animals/timepoint). Neither body weight nor food intake was affected by AZT intake. Untreated controls and AZT-treated rats were given 4% H2O as drinking water for 2 weeks. AZT (approximately 100 mg/kg/d) produced a significant (P < 0.05) decrease in cardiac and hindlimb muscle mtDNA fractional synthesis compared with control groups (from 13.8 +/- 4.2% to 7.0 +/- 4.8% and from 7.6 +/- 1.8% to 4.5 +/- 0.4%, respectively) after 4 weeks. Cytochrome c oxidase content in hindlimb muscle was also decreased by 50% compared with controls after 4 weeks of AZT treatment (P < 0.07) and a calculated index of absolute mitochondrial biogenesis rate was significantly reduced by week 2 of AZT (P < 0.05) in hindlimb muscle. In preliminary studies, platelet mtDNA enrichments were compared to monocyte nDNA enrichments (used as a marker of a fully turned over tissue) in healthy human subjects. Fractional synthesis of mtDNA in platelets reached 98 +/- 3% after 5 weeks of H2O labeling. It is concluded that NRTIs decrease mtDNA synthesis and oxidative enzyme content and thus mitochondrial biogenesis in rodents and that the effects of NRTIs on mitochondrial biogenesis in tissues of HIV-1- infected humans can in principle be measured using this approach.

Animals↗
PubMed2002

Low mitochondrial respiratory chain content correlates with tumor aggressiveness in renal cell carcinoma.

A mechanism decreasing oxidative metabolism during normal cell division and growth is expected to direct substrates toward biosyntheses rather than toward complete oxidation to CO(2). Hence, any event decreasing oxidative phosphorylations (OXPHOS) could provide a proliferating advantage to a transformed or tumor cell in an oxidative tissue. To test this hypothesis, we studied mitochondrial enzymes, DNA and OXPHOS protein content in three types of renal tumors from 25 patients. Renal cell carcinomas (RCCs) of clear cell type (CCRCCs) originate from the proximal tubule and are most aggressive. Chromophilic RCCs, from similar proximal origin, are less aggressive. The benign renal oncocytomas originate from collecting duct cells. Mitochondrial enzyme and DNA contents in all tumor types or grades differed significantly from normal tissue. Mitochondrial impairment increased from the less aggressive to the most aggressive RCCs, and correlated with a considerably decreased content of OXPHOS complexes (complexes II, III, and IV of the respiratory chain, and ATPase/ATP synthase) rather than to the mitochondrial content (citrate synthase and mitochondrial (mt)DNA). In benign oncocytoma, some mitochondrial parameters (mtDNA, citrate synthase, and complex IV) were increased 4- to 7-fold, and some were slightly increased by a factor of 2 (complex V) or close to normal (complexes II and III). A low content of complex V protein was found in all CCRCC and chromophilic tumors studied. However F(1)-ATPase activity was not consistently decreased and its impairment was associated with increased aggressiveness in CCRCCs. Immunodetection of free F(1)-sector of complex V demonstrated a disturbed assembly/stability of complex V in several CCRCC and chromophilic tumors. All results are in agreement with the hypothesis that a decreased OXPHOS capacity favors faster growth or increased invasiveness.

Base Sequence↗