Association of the hOGG1 Ser326Cys polymorphism with sporadic amyotrophic lateral sclerosis

Redox dysregulation as a driver for DNA damage and its relationship to neurodegenerative diseases

Redox homeostasis refers to the balance between the production of reactive oxygen species (ROS) as well as reactive nitrogen species (RNS), and their elimination by antioxidants. It is linked to all important cellular activities and oxidative stress is a result of imbalance between pro-oxidants and antioxidant species. Oxidative stress perturbs many cellular activities, including processes that maintain the integrity of DNA. Nucleic acids are highly reactive and therefore particularly susceptible to damage. The DNA damage response detects and repairs these DNA lesions. Efficient DNA repair processes are therefore essential for maintaining cellular viability, but they decline considerably during aging. DNA damage and deficiencies in DNA repair are increasingly described in age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease. Furthermore, oxidative stress has long been associated with these conditions. Moreover, both redox dysregulation and DNA damage increase significantly during aging, which is the biggest risk factor for neurodegenerative diseases. However, the links between redox dysfunction and DNA damage, and their joint contributions to pathophysiology in these conditions, are only just emerging. This review will discuss these associations and address the increasing evidence for redox dysregulation as an important and major source of DNA damage in neurodegenerative disorders. Understanding these connections may facilitate a better understanding of disease mechanisms, and ultimately lead to the design of better therapeutic strategies based on preventing both redox dysregulation and DNA damage.

Activated or Impaired: An Overview of DNA Repair in Neurodegenerative Diseases

As the population ages, age-related neurodegenerative diseases have become a major challenge in health science. Currently, the pathology of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease, is still not fully understood. Remarkably, emerging evidence indicates a role of genomic DNA damage and repair in various neurodegenerative disorders. Here, we summarized the current understanding of the function of DNA damage repair, especially base excision repair and double strand break repair pathways, in a variety of neurodegenerative diseases. We concluded that exacerbation of DNA lesions is found in almost all types of neurodegenerative diseases, whereas the activities of different DNA repair pathways demonstrate distinct trends, depending on disease type and even brain region. Specifically, key enzymes involved in base excision repair are likely impaired in Alzheimer's disease and amyotrophic lateral sclerosis but activated in Parkinson's disease, while nonhomologous end joining is likely downregulated in most types of neurodegenerative diseases. Hence, impairment of nonhomologous end joining is likely a common etiology for most neurodegenerative diseases, while defects in base excision repair are likely involved in the pathology of Alzheimer's disease and amyotrophic lateral sclerosis but are Parkinson's disease, based on current findings. Although there are still discrepancies and further studies are required to completely elucidate the exact roles of DNA repair in neurodegeneration, the current studies summarized here provide crucial insights into the pathology of neurodegenerative diseases and may reveal novel drug targets for corresponding neurodegenerative diseases.

DNA damage accumulates and responses are engaged in human ALS brain and spinal motor neurons and DNA repair is activatable in iPSC-derived motor neurons with SOD1 mutations

DNA damage is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, relationships between DNA damage accumulation, DNA damage response (DDR), and upper and lower motor neuron vulnerability in human ALS are unclear; furthermore, it is unknown whether epigenetic silencing of DNA repair pathways contributes to ALS pathogenesis. We tested the hypotheses that DNA damage accumulates in ALS motor neurons along with diminished DDR, and that DNA repair genes undergo hypermethylation. Human postmortem CNS tissue was obtained from ALS cases (N = 34) and age-matched controls without neurologic disease (N = 15). Compared to age-matched controls, abasic sites accumulated in genomic DNA of ALS motor cortex and laser capture microdissection-acquired spinal motor neurons but not in motor neuron mitochondrial DNA. By immunohistochemistry, DNA damage accumulated significantly in upper and lower motor neurons in ALS cases as single-stranded DNA and 8-hydroxy-deoxyguanosine (OHdG) compared to age-matched controls. Significant DDR was engaged in ALS motor neurons as evidenced by accumulation of c-Abl, nuclear BRCA1, and ATM activation. DNA damage and DDR were present in motor neurons at pre-attritional stages and throughout the somatodendritic attritional stages of neurodegeneration. Motor neurons with DNA damage were also positive for activated p53 and cleaved caspase-3. Gene-specific promoter DNA methylation pyrosequencing identified the DNA repair genes Ogg1, Apex1, Pnkp and Aptx as hypomethylated in ALS. In human induced-pluripotent stem cell (iPSC)-derived motor neurons with familial ALS SOD1 mutations, DNA repair capacity was similar to isogenic control motor neurons. Our results show that vulnerable neurons in human ALS accumulate DNA damage, and contrary to our hypothesis, strongly activate and mobilize response effectors and DNA repair genes. This DDR in ALS motor neurons involves recruitment of c-Abl and BRCA1 to the nucleus in vivo, and repair of DNA double-strand breaks in human ALS motor neurons with SOD1 mutations in cell culture.

DNA damage and repair in neuropsychiatric disorders. What do we know and what are the future perspectives?

Over the past two decades, extensive research has been done to elucidate the molecular etiology and pathophysiology of neuropsychiatric disorders. In majority of them, including Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), bipolar disorder (BD), schizophrenia and major depressive disorder, increased oxidative and nitrosative stress was found. This stress is known to induce oxidative damage to biomolecules, including DNA. Accordingly, increased mitochondrial and nuclear DNA, as well as RNA damage, were observed in patients suffering from these diseases. However, recent findings indicate that the patients are characterised by impaired DNA repair pathways, which may suggest that these DNA lesions could be also a result of their insufficient repair. In the current systematic, critical review, we aim to sum up, using available literature, the knowledge about the involvement of nuclear and mitochondrial DNA damage and repair, as well as about damage to RNA in pathoetiology of neuropsychiatric disorders, i.e., AD, PD, ALS, BD, schizophrenia and major depressive disorder, as well as the usefulness of the discussed factors as being diagnostic markers and targets for new therapies. Moreover, we also underline the new directions to which future studies should head to elucidate these phenomena.

The DNA damage response (DDR) is induced by the C9orf72 repeat expansion in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disease affecting motor neurons. Hexanucleotide (GGGGCC) repeat expansions in a non-coding region of C9orf72 are the major cause of familial ALS and frontotemporal dementia (FTD) worldwide. The C9orf72 repeat expansion undergoes repeat-associated non-ATG (RAN) translation to produce five dipeptide repeat proteins (DRPs), including poly(GR) and poly(PR). Whilst it remains unclear how mutations in C9orf72 lead to neurodegeneration in ALS/FTD, dysfunction to the nucleolus and R loop formation are implicated as pathogenic mechanisms. These events can damage DNA and hence genome integrity. Cells activate the DNA damage response (DDR) with the aim of repairing this damage. However, if the damage cannot be repaired, apoptosis is triggered. In lumbar motor neurons from C9orf72-positive ALS patients, we demonstrate significant up-regulation of markers of the DDR compared to controls: phosphorylated histone 2AX (γ-H2AX), phosphorylated ataxia telangiectasia mutated (p-ATM), cleaved poly (ADP-Ribose) polymerase 1 (PARP-1) and tumour suppressor p53-binding protein (53BP1). Similarly, significant up-regulation of γ-H2AX and p-ATM was detected in neuronal cells expressing poly(GR)100 and poly(PR)100 compared to controls, revealing that DNA damage is triggered by the DRPs. Nucleophosmin (NPM1) is a histone chaperone induced during the DDR, which interacts with APE1 to enhance DNA repair. We also demonstrate that more NPM1 precipitates with APE1 in C9orf72 patients compared to controls. Furthermore, overexpression of NPM1 inhibits apoptosis in cells expressing poly(GR)100 and poly(PR)100. This study therefore demonstrates that DNA damage is activated by the C9orf72 repeat expansion in ALS.

Chronic oxidative damage together with genome repair deficiency in the neurons is a double whammy for neurodegeneration: Is damage response signaling a potential therapeutic target?

A foremost challenge for the neurons, which are among the most oxygenated cells, is the genome damage caused by chronic exposure to endogenous reactive oxygen species (ROS), formed as cellular respiratory byproducts. Strong metabolic activity associated with high transcriptional levels in these long lived post-mitotic cells render them vulnerable to oxidative genome damage, including DNA strand breaks and mutagenic base lesions. There is growing evidence for the accumulation of unrepaired DNA lesions in the central nervous system (CNS) during accelerated aging and progressive neurodegeneration. Several germ line mutations in DNA repair or DNA damage response (DDR) signaling genes are uniquely manifested in the phenotype of neuronal dysfunction and are etiologically linked to many neurodegenerative disorders. Studies in our lab and elsewhere revealed that pro-oxidant metals, ROS and misfolded amyloidogenic proteins not only contribute to genome damage in CNS, but also impede their repair/DDR signaling leading to persistent damage accumulation, a common feature in sporadic neurodegeneration. Here, we have reviewed recent advances in our understanding of the etiological implications of DNA damage vs. repair imbalance, abnormal DDR signaling in triggering neurodegeneration and potential of DDR as a target for the amelioration of neurodegenerative diseases.

The role of base excision repair in pathogenesis of breast cancer in the Polish population

Breast cancer (BC) is leading type of cancer among group of women, which determines almost 23% of invasive cancers. It has been reported repeatedly that the level of oxidative stress is higher for BC in comparison to cancer-free woman. The goal of the present study was to evaluate the role of base excision repair (BER) pathway in the development of BC. One-hundred seventy-one women with confirmed BC and 222 healthy controls were enrolled in presented study. The level of oxidative DNA damage and the kinetic of their repair were analyzed by the modified alkaline comet assay. The efficiency of BER pathway was evaluated by BER assay. The presence of the 326Cys/Cys genotype and 326Cys allele of OGG1 gene and the 324His/His of MUTYH gene are associated with increased risk of BC development. Moreover, correlation between clinical parameter with selected genes has shown increased risk of BC progression. The survival analysis has shown a significant lower DFS for individuals with the 762Ala/Ala genotype compared to 762Val/Vla carriers and the 762Val/Ala genotype in relation to concomitant chemotherapy and radiotherapy. In subgroup of patients with alone chemotherapy and alone radiotherapy, the 762Val/Val genotype was significantly associated with lower overall survival. Furthermore, we also elevated the level of basal and oxidative DNA damage in a group of patients with BC in relation to healthy controls. We also observed the difference in effectiveness of DNA damage repair. The results of present studies suggested the important role of BER pathway in BC development. © 2015 Wiley Periodicals, Inc.

DNA damage in neurodegenerative diseases

Following the observation of increased oxidative DNA damage in nuclear and mitochondrial DNA extracted from post-mortem brain regions of patients affected by neurodegenerative diseases, the last years of the previous century and the first decade of the present one have been largely dedicated to the search of markers of DNA damage in neuronal samples and peripheral tissues of patients in early, intermediate or late stages of neurodegeneration. Those studies allowed to demonstrate that oxidative DNA damage is one of the earliest detectable events in neurodegeneration, but also revealed cytogenetic damage in neurodegenerative conditions, such as for example a tendency towards chromosome 21 malsegregation in Alzheimer's disease. As it happens for many neurodegenerative risk factors the question of whether DNA damage is cause or consequence of the neurodegenerative process is still open, and probably both is true. The research interest in markers of oxidative stress was shifted, in recent years, towards the search of epigenetic biomarkers of neurodegenerative disorders, following the accumulating evidence of a substantial contribution of epigenetic mechanisms to learning, memory processes, behavioural disorders and neurodegeneration. Increasing evidence is however linking DNA damage and repair with epigenetic phenomena, thereby opening the way to a very attractive and timely research topic in neurodegenerative diseases. We will address those issues in the context of Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis, which represent three of the most common neurodegenerative pathologies in humans.

The role of base excision repair in the development of primary open angle glaucoma in the Polish population

Glaucoma is a leading cause of irreversible blindness in developing countries. Previous data have shown that progressive loss of human TM cells may be connected with chronic exposure to oxidative stress. This hypothesis may suggest a role of the base excision repair (BER) pathway of oxidative DNA damage in primary open angle glaucoma (POAG) patients. The aim of our study was to evaluate an association of BER gene polymorphism with a risk of POAG. Moreover, an association of clinical parameters was examined including cup disk ratio (c/d), rim area (RA) and retinal nerve fiber layer (RNFL) with glaucoma progression according to BER gene polymorphisms. Our research included 412 patients with POAG and 454 healthy controls. Gene polymorphisms were analyzed by PCR-RFLP. Heidelberg Retinal Tomography (HRT) clinical parameters were also analyzed. The 399 Arg/Gln genotype of the XRCC1 gene (OR 1.38; 95% CI 1.02-1.89 p = 0.03) was associated with an increased risk of POAG occurrence. It was indicated that the 399 Gln/Gln XRCC1 genotype might increase the risk of POAG progression according to the c/d ratio (OR 1.67; 95% CI 1.07-2.61 P = 0.02) clinical parameter. Moreover, the association of VF factor with 148 Asp/Glu of APE1 genotype distribution and POAG progression (OR 2.25; 95% CI 1.30-3.89) was also found. Additionally, the analysis of the 324 Gln/His MUTYH polymorphism gene distribution in the patient group according to RNFL factor showed that it might decrease the progression of POAG (OR 0.47; 95% CI 0.30-0.82 P = 0.005). We suggest that the 399 Arg/Gln polymorphism of the XRCC1 gene may serve as a predictive risk factor of POAG.

Targeted exon capture and sequencing in sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive degeneration of motor neurons, ultimately leading to paralysis and death. Approximately 10% of ALS cases are familial, with the remaining 90% of cases being sporadic. Genetic studies in familial cases of ALS have been extremely informative in determining the causative mutations behind ALS, especially as the same mutations identified in familial ALS can also cause sporadic disease. However, the cause of ALS in approximately 30% of familial cases and in the majority of sporadic cases remains unknown. Sporadic ALS cases represent an underutilized resource for genetic information about ALS; therefore, we undertook a targeted sequencing approach of 169 known and candidate ALS disease genes in 242 sporadic ALS cases and 129 matched controls to try to identify novel variants linked to ALS. We found a significant enrichment in novel and rare variants in cases versus controls, indicating that we are likely identifying disease associated mutations. This study highlights the utility of next generation sequencing techniques combined with functional studies and rare variant analysis tools to provide insight into the genetic etiology of a heterogeneous sporadic disease.

Amyotrophic lateral sclerosis (ALS), also known as Charcot disease or Lou Gehrig's disease, is one of the most common neuromuscular diseases worldwide. This disease is characterized by a progressive degeneration of motor neurons, leading to patient death within a few years after onset. Despite the fact that most ALS cases are sporadic, most of the ALS genetic studies have focused on familial forms, leading to the genetic determination of cause for 70% of cases of familial ALS but for only 10% of sporadic ALS cases. This, coupled with the dearth of families available for study, suggests that researchers should begin tapping into the relatively untouched reservoir of available sporadic samples to identify novel genetic causes of sporadic ALS. Here we take advantage of high-throughput target sequencing techniques to test four different hypotheses about the genetic causes of ALS in sporadic ALS and uncover new candidate genes and pathways implicated in ALS.

ALS and oxidative stress: the neurovascular scenario

Oxidative stress and angiogenic factors have been placed as the prime focus of scientific investigations after an establishment of link between vascular endothelial growth factor promoter (VEGF), hypoxia, and amyotrophic lateral sclerosis (ALS) pathogenesis. Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter and mutant superoxide dismutase 1 (SOD1) which are characterised by atrophy and muscle weakness resulted in phenotype resembling human ALS in mice. This results in lower motor neurodegeneration thus establishing an important link between motor neuron degeneration, vasculature, and angiogenic molecules. In this review, we have presented human, animal, and in vitro studies which suggest that molecules like VEGF have a therapeutic, diagnostic, and prognostic potential in ALS. Involvement of vascular growth factors and hypoxia response elements also highlights the converging role of oxidative stress and neurovascular network for understanding and treatment of various neurodegenerative disorders like ALS.

Base excision repair in physiology and pathology of the central nervous system

Relatively low levels of antioxidant enzymes and high oxygen metabolism result in formation of numerous oxidized DNA lesions in the tissues of the central nervous system. Accumulation of damage in the DNA, due to continuous genotoxic stress, has been linked to both aging and the development of various neurodegenerative disorders. Different DNA repair pathways have evolved to successfully act on damaged DNA and prevent genomic instability. The predominant and essential DNA repair pathway for the removal of small DNA base lesions is base excision repair (BER). In this review we will discuss the current knowledge on the involvement of BER proteins in the maintenance of genetic stability in different brain regions and how changes in the levels of these proteins contribute to aging and the onset of neurodegenerative disorders.

Oxidative genome damage and its repair: implications in aging and neurodegenerative diseases

Reactive oxygen species (ROS), generated endogenously during respiration or exogenously by genotoxic agents, induce oxidized bases and single-strand breaks (SSBs) in DNA that are repaired via the base excision/SSB repair (BER/SSBR) pathway in both the nucleus and mitochondria. Tightly regulated BER/SSBR with multiple sub-pathways is highly complex, and is linked to the replication and transcription. The repair-initiating DNA glycosylases (DGs) or AP-endonuclease (APE1) control the sub-pathway by stably interacting with downstream proteins usually via their common interacting domain (CID). A nonconserved CID with disordered structure usually located at one of the termini includes the sequences for covalent modifications and/or organelle targeting. While the DGs are individually dispensable, the SSBR-initiating APE1 and polynucleotide kinase 3' phosphatase (PNKP) are essential. BER/SSBR of mammalian nuclear and mitochondrial genomes share the same early enzymes. Accumulation of oxidative damage in nuclear and mitochondrial genomes has been implicated in aging and various neurological disorders. While defects in BER/SSBR proteins have been linked to hereditary neurodegenerative diseases, our recent studies implicated transition metal-induced inhibition of NEIL family DGs in sporadic diseases. This review focuses on the recent advances in repair of oxidatively damages in mammalian genomes and their linkage to aging and neurological disorders.

Polymorphisms of DNA repair pathway genes and cigarette smoking in relation to susceptibility to large artery atherosclerotic stroke among ethnic Chinese in Taiwan

AIM

Cigarette-smoking induced oxidative DNA damage to endothelial cells has been reported to play an etiological role in atherosclerosis development. Individual vulnerability to oxidative stress through smoking exposure and the ability to repair DNA damage, which plays a critical role in modifying the risk susceptibility of large artery atherosclerotic (LAA) stroke, is hypothesized. Thus, we examined the effect of genetic polymorphisms of DNA repair pathway genes and cigarette smoking in relation to risk susceptibility of LAA stroke.

METHODS

We enrolled 116 LAA stroke patients and 315 healthy controls from the Armed Forces Taoyuan General Hospital, Taoyuan, Taiwan. Genotyping of polymorphisms of the OGG1 (Ser326Cys), XRCC1 (Arg399Gln), ERCC2 (Lys751Gln), and ERCC5 (Asp1104His) genes was performed and used to evaluate LAA stroke susceptibility.

RESULTS

Of those non-synonymous polymorphisms, the ERCC2 Lys751Gln variant was found to be associated with LAA stroke risk (OR: 1.69, 95%CI: 1.02-2.86), and this association was more pronounced in smokers, manifesting a 2.73-fold increased risk of LAA stroke (p=0.027). A joint effect on risk elevation of LAA stroke was seen in those patients with OGG1 and ERCC2 polymorphisms (OR: 2.75, 95%CI: 1.26-6.00). Moreover, among smokers carrying the OGG1 Ser326Cys polymorphism, there was a tendency toward an increased risk of LAA stroke in those patients who had a greater number of high-risk genotypes of XRCC1, ERCC2, and ERCC5 polymorphisms (p(trend)=0.010).

CONCLUSION

The susceptible polymorphisms of DNA repair pathway genes may have a modifying effect on the elevated risk of LAA stroke in smokers among ethnic Chinese in Taiwan.

Oxidized base damage and single-strand break repair in mammalian genomes: role of disordered regions and posttranslational modifications in early enzymes

Oxidative genome damage induced by reactive oxygen species includes oxidized bases, abasic (AP) sites, and single-strand breaks, all of which are repaired via the evolutionarily conserved base excision repair/single-strand break repair (BER/SSBR) pathway. BER/SSBR in mammalian cells is complex, with preferred and backup sub-pathways, and is linked to genome replication and transcription. The early BER/SSBR enzymes, namely, DNA glycosylases (DGs) and the end-processing proteins such as abasic endonuclease 1 (APE1), form complexes with downstream repair (and other noncanonical) proteins via pairwise interactions. Furthermore, a unique feature of mammalian early BER/SSBR enzymes is the presence of a disordered terminal extension that is absent in their Escherichia coli prototypes. These nonconserved segments usually contain organelle-targeting signals, common interaction interfaces, and sites of posttranslational modifications that may be involved in regulating their repair function including lesion scanning. Finally, the linkage of BER/SSBR deficiency to cancer, aging, and human neurodegenerative diseases, and therapeutic targeting of BER/SSBR are discussed.

An overview of DNA repair in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND), is an adult onset neurodegenerative disorder characterised by the degeneration of cortical and spinal cord motor neurons, resulting in progressive muscular weakness and death. Increasing evidence supports mitochondrial dysfunction and oxidative DNA damage in ALS motor neurons. Several DNA repair enzymes are activated following DNA damage to restore genome integrity, and impairments in DNA repair capabilities could contribute to motor neuron degeneration. After a brief description of the evidence of DNA damage in ALS, this paper focuses on the available data on DNA repair activity in ALS neuronal tissue and disease animal models. Moreover, biochemical and genetic data on DNA repair in ALS are discussed in light of similar findings in other neurodegenerative diseases.

Oxidative genome damage and its repair in neurodegenerative diseases: function of transition metals as a double-edged sword

The neurons in the central nervous system (CNS) with high O2 consumption and prolonged life span are chronically exposed to high levels of reactive oxygen species (ROS). Accumulation of ROS-induced genome damage in the form of oxidized bases and single-strand breaks (SSBs) as well as their defective or reduced repair in the brain has been implicated in the etiology of various neurological disorders including Alzheimer's/Parkinson's diseases (AD/PD). Although inactivating mutations in some DNA repair genes have been linked to hereditary neurodegenerative diseases, the underlying mechanisms of repair deficiencies for the sporadic diseases is not understood. The ROS-induced DNA damage is predominantly repaired via the highly conserved and regulated base excision/SSB repair (BER/SSBR) pathway. We recently made an interesting discovery that the transition metals iron and copper, which accumulate excessively in the brains of AD, PD, and other neurodegenerative diseases, act as a 'double-edged sword' by inducing genotoxic ROS and inhibiting DNA damage repair at the same time. These metals inhibit the base excision activity of NEIL family DNA glycosylases by oxidizing them, changing their structure, and inhibiting their binding to downstream repair proteins. Metal chelators and reducing agents partially reverse the inhibition, while curcumin with both chelating and reducing activities reverses the inhibition nearly completely. In this review, we have discussed the possible etiological linkage of BER/SSBR defects to neurodegenerative diseases and the therapeutic potential of metal chelators in restoring DNA repair capacity.

Alteration of protein folding and degradation in motor neuron diseases: Implications and protective functions of small heat shock proteins

Motor neuron diseases (MNDs) are neurodegenerative disorders that specifically affect the survival and function of upper and/or lower motor neurons. Since motor neurons are responsible for the control of voluntary muscular movement, MNDs are characterized by muscle spasticity, weakness and atrophy. Different susceptibility genes associated with an increased risk to develop MNDs have been reported and several mutated genes have been linked to hereditary forms of MNDs. However, most cases of MNDs occur in sporadic forms and very little is known on their causes. Interestingly, several molecular mechanisms seem to participate in the progression of both the inherited and sporadic forms of MNDs. These include cytoskeleton organization, mitochondrial functions, DNA repair and RNA synthesis/processing, vesicle trafficking, endolysosomal trafficking and fusion, as well as protein folding and protein degradation. In particular, accumulation of aggregate-prone proteins is a hallmark of MNDs, suggesting that the protein quality control system (molecular chaperones and the degradative systems: ubiquitin-proteasome-system and autophagy) are saturated or not sufficient to allow the clearance of these altered proteins. In this review we mainly focus on the MNDs associated with disturbances in protein folding and protein degradation and on the potential implication of a specific class of molecular chaperones, the small heat shock proteins (sHSPs/HSPBs), in motor neuron function and survival. How boosting of specific HSPBs may be a potential useful therapeutic approach in MNDs and how mutations in specific HSPBs can directly cause motor neuron degeneration is discussed.

DNA damage and repair in endometrial cancer in correlation with the hOGG1 and RAD51 genes polymorphism

The cellular reaction to the DNA-damaging agents may modulate individual's cancer susceptibility. This reaction is mainly determined by the efficacy of DNA repair, which in turn, may be influenced by the variability of DNA repair genes, expressed by their polymorphism. The hOGG1 gene encodes a glycosylase of base excision repair and RAD51 specifies a key protein in homologues recombination repair. Both proteins can be involved in the repair of DNA lesions, which are known to contribute to endometrial cancer. In the present work we determined the extent of basal DNA damage and the efficacy of removal of DNA damage induced by hydrogen peroxide and N-methyl-N'-nitro N-nitrosoguanidyne (MNNG) in peripheral blood lymphocytes of 30 endometrial cancer patients and 30 individuals without cancer. The results from DNA damage and repair study were correlated with the genotypes of two common polymorphisms of the hOGG1 and RAD51 genes: a G>C transversion at 1245 position of the hOGG1 gene producing a Ser → Cys substitution at the codon 326 (the Ser326Cys polymorphism) and a G>C substitution at 135 position of the RAD51 gene (the 135G>C polymorphism). DNA damage and repair were evaluated by alkaline single cell gel electrophoresis and genotypes were determined by restriction fragment length polymorphism PCR. We observed a strong association between endometrial cancer and the C/C genotype of the 135G>C polymorphism of the RAD51 gene. Moreover, there was a strong correlation between that genotype and endometrial cancer occurrence in subjects with a high level of basal DNA damage. We did not observe any correlation between the Ser326Cys polymorphism of the hOGG1 gene and endometrial cancer. Our result suggest that the 135G>C polymorphism of the RAD51 gene may be linked to endometrial cancer and can be considered as an additional marker of this disease.

Oxidized purine nucleotides, genome instability and neurodegeneration

Oxidative DNA damage can be the consequence of endogenous metabolic processes and exogenous insults and several DNA repair enzymes provide protection against the toxic effects of oxidized DNA bases. Here we review the increasing knowledge on the relationship between an oxidized dNTPs pool and genome instability. The review also describes some important progress toward understanding the role of oxidative DNA damage and its repair in neurodegenerative diseases. In particular the hMTH1 hydrolase destroys oxidized nucleic acid precursors to prevent their harmful incorporation into DNA and RNA. Based on results obtained in our transgenic mouse overexpressing hMTH1 in the brain we discussed the mechanisms by which this hydrolase protects against neurodegeneration in Huntington disease models.

Role of transition metals in the pathogenesis of amyotrophic lateral sclerosis

ALS (amyotrophic lateral sclerosis) is a devastating progressive neurodegenerative disorder resulting in selective degeneration of motor neurons in brain and spinal cord and muscle atrophy. In approx. 2% of all cases, the disease is caused by a mutation in the Cu,Zn-superoxide dismutase (SOD1) gene. The transition metals zinc and copper regulate SOD1 protein stability and activity, and disbalance of the homoeostasis of these metals has therefore been implicated in the pathogenesis of ALS. Recent data strengthen the hypothesis that these transition metals are excellent potential targets to develop an effective therapy for ALS.

Base excision repair, aging and health span

DNA damage and mutagenesis are suggested to contribute to aging through their ability to mediate cellular dysfunction. The base excision repair (BER) pathway ameliorates a large number of DNA lesions that arise spontaneously. Many of these lesions are reported to increase with age. Oxidized guanine, repaired largely via base excision repair, is particularly well studied and shown to increase with age. Spontaneous mutant frequencies also increase with age which suggests that mutagenesis may contribute to aging. It is widely accepted that genetic instability contributes to age-related occurrences of cancer and potentially other age-related pathologies. BER activity decreases with age in multiple tissues. The specific BER protein that appears to limit activity varies among tissues. DNA polymerase-beta is reduced in brain from aged mice and rats while AP endonuclease is reduced in spermatogenic cells obtained from old mice. The differences in proteins that appear to limit BER activity among tissues may represent true tissue-specific differences in activity or may be due to differences in techniques, environmental conditions or other unidentified differences among the experimental approaches. Much remains to be addressed concerning the potential role of BER in aging and age-related health span.

DNA damage and repair: relevance to mechanisms of neurodegeneration

DNA damage is a form of cell stress and injury that has been implicated in the pathogenesis of many neurologic disorders, including amyotrophic lateral sclerosis, Alzheimer disease, Down syndrome, Parkinson disease, cerebral ischemia, and head trauma. However, most data reveal only associations, and the role for DNA damage in direct mechanisms of neurodegeneration is vague with respect to being a definitive upstream cause of neuron cell death, rather than a consequence of the degeneration. Although neurons seem inclined to develop DNA damage during oxidative stress, most of the existing work on DNA damage and repair mechanisms has been done in the context of cancer biology using cycling nonneuronal cells but not nondividing (i.e. postmitotic) neurons. Nevertheless, the identification of mutations in genes that encode proteins that function in DNA repair and DNA damage response in human hereditary DNA repair deficiency syndromes and ataxic disorders is establishing a mechanistic precedent that clearly links DNA damage and DNA repair abnormalities with progressive neurodegeneration. This review summarizes DNA damage and repair mechanisms and their potential relevance to the evolution of degeneration in postmitotic neurons.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.