DNA repair after oxidative stress: current challenges (original) (raw)
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Formation and repair of oxidative damage in the mitochondrial DNA
Mitochondrion, 2014
The mitochondrial DNA (mtDNA) encodes for only 13 polypeptides, components of 4 of the 5 oxidative phosphorylation complexes. But despite this apparently small numeric contribution, all 13 subunits are essential for the proper functioning of the oxidative phosphorylation circuit. Thus, accumulation of lesions, mutations and deletions/insertions in the mtDNA could have severe functional consequences, including mitochondrial diseases, aging and age-related diseases. The DNA is a chemically unstable molecule, which can be easily oxidized, alkylated, deaminated and suffer other types of chemical modifications, throughout evolution the organisms that survived were those who developed efficient DNA repair processes. In the last two decades, it has become clear that mitochondria have DNA repair pathways, which operate, at least for some types of lesions, as efficiently as the nuclear DNA repair pathways. The mtDNA is localized in a particularly oxidizing environment, making it prone to accumulate oxidatively generated DNA modifications (ODMs). In this article, we: i) review the major types of ODMs formed in mtDNA and the known repair pathways that remove them; ii) discuss the possible involvement of other repair pathways, just recently characterized in mitochondria, in the repair of these modifications; and iii) address the role of DNA repair in mitochondrial function and a possible cross-talk with other pathways that may potentially participate in mitochondrial genomic stability, such as mitochondrial dynamics and nuclear-mitochondrial signaling. Oxidative stress and ODMs have been increasingly implicated in disease and aging, and thus we discuss how variations in DNA repair efficiency may contribute to the etiology of such conditions or even modulate their clinical outcomes.
Role of mitochondrial dysfunction in the pathophysiology of DNA repair disorders
2018
DNA is constantly being damaged, either by endogenous or exogenous genotoxins. In that regard, DNA repair activities are essential for maintaining genomic stability and to life itself. Mutations in genes encoding DNA repair proteins cause severe human syndromes, but DNA repair defects have also been linked to several other diseases, notably to cancer and normal aging. Recently, new evidence has emerged indicating that some DNA repair diseases display mitochondrial and metabolic dysfunction through mechanisms that are yet being uncovered. These results suggest that mitochondria play an import role in the DNA damage response pathways and that damage accumulation may lead to mitochondrial dysfunction via metabolic imbalance and mitophagy impairment. Here we review the recent findings linking mitochondrial impairment and cell death to DNA damage accumulation in the context of DNA repair defects. In addition, the general involvement of DNA damage in cellular dysfunction suggests that these phenomena may be also involved in other human pathologies in which mitochondrial dysfunction and metabolic disruption play causative roles.
Effect of Oxidative Stress on DNA Repairing Genes
Selected Topics in DNA Repair, 2011
Oxidative DNA damage has been thought to contribute to the general decline in cellular functions that are associated with a variety of diseases including Alzheimer disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease, atherosclerosis, ischemia/reperfusion neuronal injuries, degenerative disease of the human temporomandibular-joint, cataract formation, macular degeneration, degenerative retinal damage, rheumatoid arthritis , multiple sclerosis , muscular dystrophy, diabetes mellitus, human cancers as well as the aging process itself. Oxidative stress occurs when the production of the reactive oxygen species (ROS) exceeds natural antioxidant defence mechanisms. There are several sources that form the ROS. Most of ROS come from the endogenous sources as by-products of normal and essential m e t a b o l i c r e a c t i o n s , s u c h a s e n e r g y g e n e r a t i on from mitochondria or the detoxification reactions involving the liver cytochrome P-450 enzyme system. There are also exogenous ROS sources including exposure to cigarette smoke, environmental pollutants such as emission from automobiles and industries, consumption of alcohol in excess, asbestos, exposure to ionizing radiation, and bacterial, fungal or viral infections. ROS cause damage to biomolecules such as lipid, proteins and DNA by attaching. ROS may directly attack DNA, either the sugar, phosphate or purine and pyrimidine bases. On the other hand, oxidative damage may be indirect by rising of intracellular Ca +2 ions. Free radical-mediated reactions can cause structural alterations in DNA (e.g., nicking, base-pair mutations, rearrangement, deletions insertions and sequence amplification). Degradation of the bases will produce numerous products, including 8-OH-Gua, hydroxymethylurea, urea, thymine glycol; thymine and adenine ring opened and saturated products. Most oxidized bases in DNA are repaired by base excision repair (BER). BER consists of four main steps. The first step involves the removal of the oxidised base by a specific DNA glycosylase, yielding an apurinic/apyrimidinic (AP) site. In the second step, an AP endonuclease removes the deoxyribose phosphate group from the AP site generating a single nucleotide gap. A DNA polymerase, thought to be predominantly DNA polymerase b, fills this gap. Finally, a DNA ligase, probably DNA ligase III, seals the stand break and completes the repair process. This chapter mainly deals with: (i) formation of ROS in physiological and pathological conditions, (ii) ROS-mediated DNA damage, leading to cellular pathology and ultimately to cell death (iii) Oxidative DNA damage repair systems, (iv) The molecular mechanism of ROS-mediated diseases such as cancer, cardiovascular disease, neurodegenerative diseases, inflammatory disease, ischemia-reperfusion injury and aging.
Base Excision Repair and Lesion-Dependent Subpathways for Repair of Oxidative DNA Damage
Antioxidants & Redox Signaling, 2011
Nuclear and mitochondrial genomes are under continuous assault by a combination of environmentally and endogenously derived reactive oxygen species, inducing the formation and accumulation of mutagenic, toxic, and=or genome-destabilizing DNA lesions. Failure to resolve these lesions through one or more DNA-repair processes is associated with genome instability, mitochondrial dysfunction, neurodegeneration, inflammation, aging, and cancer, emphasizing the importance of characterizing the pathways and proteins involved in the repair of oxidative DNA damage. This review focuses on the repair of oxidative damage-induced lesions in nuclear and mitochondrial DNA mediated by the base excision repair (BER) pathway in mammalian cells. We discuss the multiple BER subpathways that are initiated by one of 11 different DNA glycosylases of three subtypes: (a) bifunctional with an associated b-lyase activity; (b) monofunctional; and (c) bifunctional with an associated b,dlyase activity. These three subtypes of DNA glycosylases all initiate BER but yield different chemical intermediates and hence different BER complexes to complete repair. Additionally, we briefly summarize alternate repair events mediated by BER proteins and the role of BER in the repair of mitochondrial DNA damage induced by ROS. Finally, we discuss the relation of BER and oxidative DNA damage in the onset of human disease. Antioxid. Redox
Free Radical Biology and Medicine, 2002
The lesions induced by reactive oxygen species in both nuclear and mitochondrial genomes include altered bases, abasic (AP) sites, and single-strand breaks, all repaired primarily via the base excision repair (BER) pathway. Although the basic BER process (consisting of five sequential steps) could be reconstituted in vitro with only four enzymes, it is now evident that repair of oxidative damage, at least in mammalian cell nuclei, is more complex, and involves a number of additional proteins, including transcription-and replication-associated factors. These proteins may be required in sequential repair steps in concert with other cellular changes, starting with nuclear targeting of the early repair enzymes in response to oxidative stress, facilitation of lesion recognition, and access by chromatin unfolding via histone acetylation, and formation of metastable complexes of repair enzymes and other accessory proteins. Distinct, specific subclasses of protein complexes may be formed for repair of oxidative lesions in the nucleus in transcribed vs. nontranscribed sequences in chromatin, in quiescent vs. cycling cells, and in nascent vs. parental DNA strands in replicating cells. Characterizing the proteins for each repair subpathway, their signaling-dependent modifications and interactions in the nuclear as well as mitochondrial repair complexes, will be a major focus of future research in oxidative damage repair.
Oxidative DNA damage: mechanisms, mutation, and disease
The FASEB Journal, 2003
Oxidative DNA damage is an inevitable consequence of cellular metabolism, with a propensity for increased levels following toxic insult. Although more than 20 base lesions have been identified, only a fraction of these have received appreciable study, most notably 8-oxo-2deoxyguanosine. This lesion has been the focus of intense research interest and been ascribed much importance, largely to the detriment of other lesions. The present work reviews the basis for the biological significance of oxidative DNA damage, drawing attention to the multiplicity of proteins with repair activities along with a number of poorly considered effects of damage. Given the plethora of (often contradictory) reports describing pathological conditions in which levels of oxidative DNA damage have been measured, this review critically addresses the extent to which the in vitro significance of such damage has relevance for the pathogenesis of disease. It is suggested that some shortcomings associated with biomarkers, along with gaps in our knowledge, may be responsible for the failure to produce consistent and definitive results when applied to understanding the role of DNA damage in disease, highlighting the need for further studies.
Oxidative DNA damage repair in mammalian cells: A new perspective
Dna Repair, 2007
Oxidatively induced DNA lesions have been implicated in the etiology of many diseases (including cancer) and in aging. Repair of oxidatively damaged bases in all organisms occurs primarily via the DNA base excision repair (BER) pathway, initiated with their excision by DNA glycosylases. Only two mammalian DNA glycosylases, OGG1 and NTH1 of E. coli Nth family, were previously characterized, which excise majority of the oxidatively damaged base lesions. We recently discovered and characterized two human orthologs of E. coli Nei, the prototype of the second family of oxidized base-specific glycosylases and named them NEIL (Nei-like)-1 and 2. NEILs are distinct from NTH1 and OGG1 in structural features and reaction mechanism but act on many of the same substrates. Nth-type DNA glycosylases after base excision, cleave the DNA strand at the resulting AP-site to produce a 3′-αβ unsaturated aldehyde whereas Nei-type enzymes produce 3′-phosphate terminus. E. coli APEs efficiently remove both types of termini in addition to cleaving AP sites to generate 3′-OH, the primer terminus for subsequent DNA repair synthesis. In contrast, the mammalian APE, APE1, which has an essential role in NTH1/OGG1-initiated BER, has negligible 3′-phosphatase activity and is dispensable for NEIL-initiated BER. Polynucleotide kinase (PNK), present in mammalian cells but not in E. coli, removes the 3′ phosphate, and is involved in NEILinitiated BER. NEILs show a unique preference for excising lesions from a DNA bubble, while most DNA glycosylases, including OGG1 and NTH1, are active only with duplex DNA. The dichotomy in the preference of NEILs and NTH1/OGG1 for bubble versus duplex DNA substrates suggests that NEILs function preferentially in repair of base lesions during replication and/or transcription and hence play a unique role in maintaining the functional integrity of mammalian genomes.