mtDNA depletion myopathy: elucidation of the tissue specificity in the mitochondrial thymidine kinase (TK2) deficiency

Saada, Ann; Shaag, Avraham; Elpeleg, Orly

doi:10.1016/s1096-7192(03)00063-5

Cited by 92 publications

(64 citation statements)

References 20 publications

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“…Data supporting this latter scenario are available from both human genetic diseases and from the genetically engineered mouse studies. Reduced mitochondrial TK2 activity reduces mtDNA abundance in selected tissues (10,39,44,45). It may be possible that mtDNA mutation rates are increased in parallel.…”

Section: Discussionmentioning

confidence: 99%

Thymidine kinase and mtDNA depletion in human cardiomyopathy: epigenetic and translational evidence for energy starvation

Koczor

Torres

Fields

et al. 2013

Physiological Genomics

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Koczor CA, Torres RA, Fields EJ, Boyd A, He S, Patel N, Lee EK, Samarel AM, Lewis W. Thymidine kinase and mtDNA depletion in human cardiomyopathy: epigenetic and translational evidence for energy starvation. Physiol Genomics 45: 590 -596, 2013. First published May 21, 2013 doi:10.1152/physiolgenomics.00014.2013.-This study addresses how depletion of human cardiac left ventricle (LV) mitochondrial DNA (mtDNA) and epigenetic nuclear DNA methylation promote cardiac dysfunction in human dilated cardiomyopathy (DCM) through regulation of pyrimidine nucleotide kinases. Samples of DCM LV and right ventricle (n ϭ 18) were obtained fresh at heart transplant surgery. Parallel samples from nonfailing (NF) controls (n ϭ 12) were from donor hearts found unsuitable for clinical use. We analyzed abundance of mtDNA and nuclear DNA (nDNA) using qPCR. LV mtDNA was depleted in DCM (50%, P Ͻ 0.05 each) compared with NF. No detectable change in RV mtDNA abundance occurred. DNA methylation and gene expression were determined using microarray analysis (GEO accession number: GSE43435). Fifty-seven gene promoters exhibited DNA hypermethylation or hypomethylation in DCM LVs. Among those, cytosolic thymidine kinase 1 (TK1) was hypermethylated. Expression arrays revealed decreased abundance of the TK1 mRNA transcript with no change in transcripts for other relevant thymidine metabolism enzymes. Quantitative immunoblots confirmed decreased TK1 polypeptide steady state abundance. TK1 activity remained unchanged in DCM samples while mitochondrial thymidine kinase (TK2) activity was significantly reduced. Compensatory TK activity was found in cardiac myocytes in the DCM LV. Diminished TK2 activity is mechanistically important to reduced mtDNA abundance and identified in DCM LV samples here. Epigenetic and genetic changes result in changes in mtDNA and in nucleotide substrates for mtDNA replication and underpin energy starvation in DCM.

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Section: Discussionmentioning

confidence: 99%

Thymidine kinase and mtDNA depletion in human cardiomyopathy: epigenetic and translational evidence for energy starvation

Koczor

Torres

Fields

et al. 2013

Physiological Genomics

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“…Strong support for this hypothesis of mitochondrial DNA depletion comes from a human inherited disease of severe muscle myopathy with mitochondrial DNA depletion caused by a partial deficiency of thymidine kinase 2 [30,31]. This disease is usually lethal in childhood.…”

Section: Discussionmentioning

confidence: 99%

3′-Azido-3′-deoxythymidine (AZT) inhibits thymidine phosphorylation in isolated rat liver mitochondria: A possible mechanism of AZT hepatotoxicity

Lynx

Bentley

McKee

2006

Biochemical Pharmacology

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Abstract3′-Azido-3′-deoxythymidine (AZT) is a staple of highly active antiretroviral therapy (HAART). Prior to HAART, long-term use of high-dosage AZT caused myopathy, cardiomyopathy, and hepatotoxicity, associated with mitochondrial DNA depletion. As a component of HARRT, AZT causes cytopenias and lipodystrophy. AZT-5′-triphosphate (AZTTP) is a known inhibitor of the mitochondrial polymerase γ and has been targeted as the source of the mitochondrial DNA depletion. However, in previous work from this laboratory with isolated rat heart mitochondria, AZT phosphorylation beyond AZT-5′-monophosphate (AZTMP) was not detected. Rather, AZT was shown to be a more potent inhibitor of thymidine phosphorylation (50% inhibitory concentration (IC 50 ) of 7.0 ± 1.0 μM) than AZTTP is of polymerase γ (IC 50 of >100 μM), suggesting that depletion of mitochondrial stores of TTP may limit replication. This work has investigated whether an identical mechanism might account for the hepatotoxicity seen with long-term use of AZT. Isolated rat liver mitochondria were incubated with labeled thymidine or AZT, and the rate and extent of phosphorylation were determined by HPLC analysis of acid-soluble extracts of the incubated mitochondria. The results showed that in the phosphorylation of thymidine to TMP, liver mitochondria exhibit a higher V max and K m than heart mitochondria, but otherwise heart and liver mitochondria display similar kinetics. AZT is phosphorylated to AZTMP, but no further phosphorylated forms were detected. In addition, AZT inhibited the production of TTP, with an IC 50 of 14.4 ± 2.6 μM AZT. This is higher, but comparable to, the results seen in isolated rat heart mitochondria. KeywordsAZT; Liver mitochondria; Thymidine; Mitochondrial toxicity; Thymidine kinase 2; Reverse transcriptase inhibitors Abbreviations AIDS, acquired immunodeficiency syndrome; AZT, 3′-azido-3′-deoxythymidine; AZTDP, 3′-azido-3′-deoxythymidine-5′-diphosphate; AZTMP, 3′-azido-3′-deoxythymidine-5′-monophosphate; AZTTP, 3′-azido-3′-deoxythymidine-5′-triphosphate; HAART, highly active antiretroviral therapy; HIV, human immunodeficiency virus; IC 50 , 50% inhibitory concentration; S.E.M., standard error of mean

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“…In contrast, NRTI-sparing regimens caused no functional changes. The cellular processes of NRTI mitochondrial import and phosphorylation [16][17][18][19][20][21][22][23][24][25] received increasing interest and awareness as playing a role in the regulation of mtDNA replication. 17 The DNC TG here offered an approach to evaluate NRTI toxicity in vivo and linked NRTI toxicity to mitochondrial import and nucleotide homeostasis.…”

Section: Discussionmentioning

confidence: 99%

Transgenic expression of the deoxynucleotide carrier causes mitochondrial damage that is enhanced by NRTIs for AIDS

Lewis

Haase

Miller

et al. 2005

Laboratory Investigation

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Nucleoside reverse transcriptase inhibitors (NRTIs) are antiretrovirals for AIDS with limiting mitochondrial side effects. The mitochondrial deoxynucleotide carrier (DNC) transports phosphorylated nucleosides for mitochondrial DNA replication and can transport phosphorylated NRTIs into mitochondria. Transgenic mice (TG) that exclusively overexpress DNC in the heart tested DNC's role in mitochondrial dysfunction from NRTIs. Two TG lines were created that overexpressed the human DNC gene in murine myocardium. Cardiac and mitochondrial structure and function were examined by magnetic resonance imaging, echocardiography, electrocardiography, transmission electron microscopy, and plasma lactate. Antiretroviral combinations (HAART) that contained NRTIs (stavudine (2 0 , 3 0 -didehydro-2 0 , 3 0 -deoxythymidine or d4T)/lamivudine/indinavir; or zidovudine (3 0 azido-3 0 -deoxythymidine or AZT)/lamivudine/indinavir; 35 days) were administered to simulate AIDS therapy. In parallel, a HAART combination without NRTIs (nevirapine/efavirenz/indinavir; 35 days) served as an NRTI-sparing, control regimen. Untreated DNC TGs exhibited normal cardiac function but abnormal mitochondrial ultrastructure. HAART that contained NRTIs caused cardiomyopathy in TGs with increased left ventricle mass and volume, heart rate variability, and worse mitochondrial ultrastructural defects. In contrast, treatment with an NRTI-sparing HAART regimen caused no cardiac changes. Data suggest the DNC is integral to mitochondrial homeostasis in vivo and may relate mechanistically to mitochondrial dysfunction in patients treated with HAART regimens that contain NRTIs. Keywords: deoxynucleotide; NRTI; AIDS; antiretroviral; mitochondrial import; DNC; cardiac; HIV The inner mitochondrial membrane contains transport proteins to move molecules into and out of the matrix. Members of the mitochondrial carrier family of proteins contain three conserved tandemrepeated sequences (B100 residues with two hydrophobic transmembrane a-helices and a hydrophilic segment thought to be an extramembranous loop 1 ). One of these proteins functions as a deoxynucleotide carrier (DNC) to import phosphorylated precursors of mitochondrial (mt-) DNA synthesis and has been characterized. 1-3 Toxicity to mitochondria from antiretroviral nucleoside reverse transcriptase inhibitors (NRTI) is an established side effect of AIDS therapy that limits effective treatment (reviewed in Lewis et al 4 ). Alternative combinations that are NRTI-sparing may be effective if toxicity is a significant clinical problem (reviewed in Joly et al 5 ).Since DNC provides a route for mitochondrial uptake of NRTIs including zidovudine (3 0 azido-3 0 -deoxythymidine or AZT) and stavudine (2 0 , 3 0 -didehydro-2 0 , 3 0 -deoxythymidine or d4T), its role in mitochondrial NRTI import and toxicity was addressed in vivo using transgenic mice (TG) and HAART treatment. One HAART regimen included NRTIs (with either an AZT or D4T 'backbone'). A second NRTI-sparing regimen was administered in parallel as a control.DNC ov...

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mtDNA depletion myopathy: elucidation of the tissue specificity in the mitochondrial thymidine kinase (TK2) deficiency

Cited by 92 publications

References 20 publications

Thymidine kinase and mtDNA depletion in human cardiomyopathy: epigenetic and translational evidence for energy starvation

Thymidine kinase and mtDNA depletion in human cardiomyopathy: epigenetic and translational evidence for energy starvation

3′-Azido-3′-deoxythymidine (AZT) inhibits thymidine phosphorylation in isolated rat liver mitochondria: A possible mechanism of AZT hepatotoxicity

Transgenic expression of the deoxynucleotide carrier causes mitochondrial damage that is enhanced by NRTIs for AIDS

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