title: AZT-induced mitochondrial toxicity: an epigenetic paradigm for dysregulation of gene expression through mitochondrial oxidative stress.
abstract: Mitochondrial dysfunction causes oxidative stress and cardiomyopathy. Oxidative stress also is a side effect of dideoxynucleoside antiretrovirals (NRTI) and is observed in NRTI-induced cardiomyopathy. We show here that treatment with the NRTI AZT {1-[(2R,4S,5S)-4-azido-5-(hydroxymethyl)oxolan-2-yl]-5-methylpyrimidine-2,4-dione} modulates cardiac gene expression epigenetically through production of mitochondrially derived reactive oxygen species. Transgenic mice with ubiquitous expression of mitochondrially targeted catalase (MCAT) and C57Bl/6 wild-type mice littermates (WT) were administered AZT (0.22 mg/day po, 35 days), and cardiac DNA and mRNA were isolated. In AZT-treated WT, 95 cardiac genes were differentially expressed compared with vehicle-treated WTs. When MCAT mice were treated with AZT, each of those 95 genes reverted toward the expression of vehicle-treated WTs. In AZT-treated WT hearts, Mthfr [5,10-methylenetetrahydrofolate reductase; a critical enzyme in synthesis of methionine cycle intermediates including S-adenosylmethionine (SAM)], was overexpressed. Steady-state abundance of SAM in cardiac extracts from AZT-treated MCAT mice increased 60% above that of vehicle-treated MCAT. No such change occurred in WT. AZT caused hypermethylation (47%) and hypomethylation (53%) of differentially methylated DNA regions in WT cardiac DNA. AZT-treated MCAT heart DNA exhibited greater hypermethylation (91%) and less hypomethylation (9%) compared with vehicle-treated MCAT controls. The gene encoding protein kinase C-α displayed multifocal epigenetic regulation caused by oxidative stress. Results show that mitochondrially derived oxidative stress in the heart hinders cardiac DNA methylation, alters steady-state abundance of SAM, alters cardiac gene expression, and promotes characteristic pathophysiological changes of cardiomyopathy. This mechanism for NRTI toxicity offers insight into long-term side effects from these commonly used antiviral agents.
authors.affiliation: Department of Pathology, Emory University, Atlanta, Georgia ckoczor@emory.edu.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Koczor
authors.affiliation: Department of Pathology, Emory University, Atlanta, Georgia.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Jiao
authors.affiliation: Department of Pathology, Emory University, Atlanta, Georgia.
authors.forename: Earl
authors.initials: E
authors.lastname: Fields
authors.affiliation: Department of Pathology, Emory University, Atlanta, Georgia.
authors.forename: Rodney
authors.initials: R
authors.lastname: Russ
authors.affiliation: Department of Pathology, Emory University, Atlanta, Georgia.
authors.forename: Tomika
authors.initials: T
authors.lastname: Ludaway
authors.affiliation: Department of Pathology, Emory University, Atlanta, Georgia.
authors.forename: William
authors.initials: W
authors.lastname: Lewis
mesh_terms: D000818:Animals; D002374:Catalase / Q000378:metabolism; D016000:Cluster Analysis; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics; D044127:Epigenesis, Genetic / Q000187:drug effects*; D020869:Gene Expression Profiling; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress / Q000187:drug effects* / Q000235:genetics; D012436:S-Adenosylmethionine / Q000494:pharmacology; D015215:Zidovudine / Q000494:pharmacology*
chemical_list: D015215:Zidovudine; D012436:S-Adenosylmethionine; D002374:Catalase
keywords: AZT; epigenetics; mitochondria; oxidative stress; s-adenosylmethionine