Hirano, M. et al. DNA single-strand break repair is impaired in aprataxin-related ataxia. Ann. Neurol. 61, 162-174

Department of Neurology, Radioisotope Research Center, Nara Medical University, Nara, Japan.
Annals of Neurology (Impact Factor: 9.98). 02/2007; 61(2):162-74. DOI: 10.1002/ana.21078
Source: PubMed


Early-onset ataxia with ocular motor apraxia and hypoalbuminemia (EAOH)/ataxia with oculomotor apraxia type 1 (AOA1) is an autosomal recessive form of cerebellar ataxia. The causative protein for EAOH/AOA1, aprataxin (APTX), interacts with X-ray repair cross-complementing 1 (XRCC1), a scaffold DNA repair protein for single-strand breaks (SSBs). The goal of this study was to prove the functional involvement of APTX in SSB repair (SSBR).
We visualized the SSBR process with a recently developed laser irradiation system that allows real-time observation of SSBR proteins and with a local ultraviolet-irradiation system using a XPA-UVDE cell line that repairs DNA lesions exclusively via SSBR. APTX was knocked down using small interference RNA in the cells. Oxidative stress-induced DNA damage and cell death were assessed in EAOH fibroblasts and cerebellum.
Our systems showed the XRCC1-dependent recruitment of APTX to SSBs. SSBR was impaired in APTX-knocked-down cells. Oxidative stress in EAOH fibroblasts readily induced SSBs and cell death, which were blocked by antioxidants. Accumulated oxidative DNA damage was confirmed in EAOH cerebellum.
This study provides the first direct evidence for the functional involvement of APTX in SSBR and in vivo DNA damage in EAOH/AOA1, and suggests a benefit of antioxidant treatment.

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    • "The characteristic shared by all these disorders is a high level of spontaneously occurring chromosome abnormalities as well as the hypersensitivity to chromosome aberrations induced by genotoxic agents. In addition, there are other disorders caused by mutations in genes involved in DNA SSB repair, such as ataxiaoculomotor apraxia, in which cells from patients are hypersensitive to genotoxic agents inducing SSB [16] [25]. All these disorders are autosomal recessive and the hypersensitivity to genotoxic agents is demonstrated in cells originating from homozygous subjects; however, an increased hypersensitivity has also been detected in cells from heterozygous subjects [26]. "
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    • "Cells from AOA1 patients are also not particularly susceptible to genotoxic agents, including methyl methane sulphonate (MMS) and hydrogen peroxide (Clements et al., 2004; El-Khamisy et al., 2009). Indeed, the main function of aprataxin may not reside in the nucleus, as APTX knockout mice do not exhibit a clear defect in SSBR and aprataxin does not appear to re-localize to nuclear DNA lesions after exposure to a range of DNA damaging agents (Hirano et al., 2007). These observations led us to hypothesize that AOA1 may stem from mitochondrial dysfunction, rather than nuclear repair defect. "
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    ABSTRACT: Oxidative DNA damage has been attributed to increased cancer incidence and premature aging phenotypes. Reactive oxygen species (ROS) are unavoidable byproducts of oxidative phosphorylation and are the major contributors of endogenous oxidative damage. To prevent the negative effects of ROS, cells have developed DNA repair mechanisms designed to specifically combat endogenous DNA modifications. The base excision repair (BER) pathway is primarily responsible for the repair of small non-helix distorting lesions and DNA single strand breaks. This repair pathway is found in all organisms, and in mammalian cells, consists of three related sub-pathways: short patch (SP-BER), long patch (LP-BER) and single strand break repair (SSBR). While much is known about nuclear BER, comparatively little is known about this pathway in the mitochondria, particularly the LP-BER and SSBR sub-pathways. There are a number of proteins that have recently been found to be involved in mitochondrial BER, including Cockayne syndrome proteins A and B (CSA and CSB), aprataxin (APTX), tryosyl-DNA phosphodiesterase 1 (TDP1), flap endonuclease 1 (FEN-1) and exonuclease G (EXOG). These significant advances in mitochondrial DNA repair may open new avenues in the management and treatment of a number of neurological disorders associated with mitochondrial dysfunction, and will be reviewed in further detail herein.
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    • "Environmental and Molecular Mutagenesis 52:623^635 (2011) 2005; Hirano et al., 2007]. Xrcc1 2/2 cells were recently shown to have a slightly reduced rate of repair of uracil in DNA, but not repair of AP sites [Akbari et al., 2010]. "
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