Decreased base excision repair and increased helicase activity in Alzheimer's disease brain

Unraveling the mystery of citrate transporters in Alzheimer's disease: An updated review

A key molecule in cellular metabolism, citrate is essential for lipid biosynthesis, energy production, and epigenetic control. The etiology of Alzheimer's disease (AD), a progressive neurodegenerative illness marked by memory loss and cognitive decline, may be linked to dysregulated citrate transport, according to recent research. Citrate transporters, which help citrate flow both inside and outside of cells, are becoming more and more recognized as possible participants in the molecular processes underlying AD. Citrate synthase (CS), a key enzyme in the tricarboxylic acid (TCA) cycle, supports mitochondrial function and neurotransmitter synthesis, particularly acetylcholine (ACh), essential for cognition. Changes in CS activity affect citrate availability, influencing energy metabolism and neurotransmitter production. Choline, a precursor for ACh, is crucial for neuronal function. Lipid metabolism, oxidative stress reactions, and mitochondrial function can all be affected by aberrant citrate transport, and these changes are linked to dementia. Furthermore, the two main pathogenic characteristics of AD, tau hyperphosphorylation and amyloid-beta (Aβ) aggregation, may be impacted by disturbances in citrate homeostasis. The goal of this review is to clarify the complex function of citrate transporters in AD and provide insight into how they contribute to the development and course of the illness. We aim to provide an in-depth idea of which particular transporters are dysregulated in AD and clarify the functional implications of these dysregulated transporters in brain cells. To reduce neurodegenerative processes and restore metabolic equilibrium, we have also discussed the therapeutic potential of regulating citrate transport. Gaining insight into the relationship between citrate transporters and the pathogenesis of AD may help identify new indicators for early detection and creative targets for treatment. This study offers hope for more potent ways to fight this debilitating illness and is a crucial step in understanding the metabolic foundations of AD.

DNA damage and its links to neuronal aging and degeneration

DNA damage is a major risk factor for the decline of neuronal functions with age and in neurodegenerative diseases. While how DNA damage causes neurodegeneration is still being investigated, innovations over the past decade have provided significant insights into this issue. Breakthroughs in next-generation sequencing methods have begun to reveal the characteristics of neuronal DNA damage hotspots and the causes of DNA damage. Chromosome conformation capture-based approaches have shown that, while DNA damage and the ensuing cellular response alter chromatin topology, chromatin organization at damage sites also affects DNA repair outcomes in neurons. Additionally, neuronal activity results in the formation of programmed DNA breaks, which could burden DNA repair mechanisms and promote neuronal dysfunction. Finally, emerging evidence implicates DNA damage-induced inflammation as an important contributor to the age-related decline in neuronal functions. Together, these discoveries have ushered in a new understanding of the significance of genome maintenance for neuronal function.

Early oxidative stress and DNA damage in Aβ-burdened hippocampal neurons in an Alzheimer's-like transgenic rat model

Oxidative stress is a key contributor to AD pathology. However, the earliest role of pre-plaque neuronal oxidative stress, remains elusive. Using laser microdissected hippocampal neurons extracted from McGill-R-Thy1-APP transgenic rats we found that intraneuronal amyloid beta (iAβ)-burdened neurons had increased expression of genes related to oxidative stress and DNA damage responses including Ercc2, Fancc, Sod2, Gsr, and Idh1. DNA damage was further evidenced by increased neuronal levels of XPD (Ercc2) and γH2AX foci, indicative of DNA double stranded breaks (DSBs), and by increased expression of Ercc6, Rad51, and Fen1, and decreased Sirt6 in hippocampal homogenates. We also found increased expression of synaptic plasticity genes (Grin2b (NR2B), CamkIIα, Bdnf, c-fos, and Homer1A) and increased protein levels of TOP2β. Our findings indicate that early accumulation of iAβ, prior to Aβ plaques, is accompanied by incipient oxidative stress and DSBs that may arise directly from oxidative stress or from maladaptive synaptic plasticity.

Genomic stress and impaired DNA repair in Alzheimer disease

Alzheimer disease (AD) is the most prominent form of dementia and has received considerable attention due to its growing burden on economic, healthcare and basic societal infrastructures. The two major neuropathological hallmarks of AD, i.e., extracellular amyloid beta (Aβ) peptide plaques and intracellular hyperphosphorylated Tau neurofibrillary tangles, have been the focus of much research, with an eye on understanding underlying disease mechanisms and identifying novel therapeutic avenues. One often overlooked aspect of AD is how Aβ and Tau may, through indirect and direct mechanisms, affect genome integrity. Herein, we review evidence that Aβ and Tau abnormalities induce excessive genomic stress and impair genome maintenance mechanisms, events that can promote DNA damage-induced neuronal cell loss and associated brain atrophy.

Novel Techniques for Mapping DNA Damage and Repair in the Brain

DNA damage in the brain is influenced by endogenous processes and metabolism along with exogenous exposures. Accumulation of DNA damage in the brain can contribute to various neurological disorders, including neurodegenerative diseases and neuropsychiatric disorders. Traditional methods for assessing DNA damage in the brain, such as immunohistochemistry and mass spectrometry, have provided valuable insights but are limited by their inability to map specific DNA adducts and regional distributions within the brain or genome. Recent advancements in DNA damage detection methods offer new opportunities to address these limitations and further our understanding of DNA damage and repair in the brain. Here, we review emerging techniques offering more precise and sensitive ways to detect and quantify DNA lesions in the brain or neural cells. We highlight the advancements and applications of these techniques and discuss their potential for determining the role of DNA damage in neurological disease.

DNA repair deficiencies and neurodegeneration

Neurodegenerative diseases are the second most prevalent cause of death in industrialized countries. Alzheimer's Disease is the most widespread and also most acknowledged form of dementia today. Together with Parkinson's Disease they account for over 90 % cases of neurodegenerative disorders caused by proteopathies. Far less known are the neurodegenerative pathologies in DNA repair deficiency syndromes. Such diseases like Cockayne - or Werner Syndrome are described as progeroid syndromes - diseases that cause the premature ageing of the affected persons, and there are clear implications of such diseases in neurologic dysfunction and degeneration. In this review, we aim to draw the attention on commonalities between proteopathy-associated neurodegeneration and neurodegeneration caused by DNA repair defects and discuss how mitochondria are implicated in the development of both disorder classes. Furthermore, we highlight how nematodes are a valuable and indispensable model organism to study conserved neurodegenerative processes in a fast-forward manner.

Music compensates for altered gene expression in age-related cognitive disorders

Extensive literature has explored the beneficial effects of music in age-related cognitive disorders (ACD), but limited knowledge exists regarding its impact on gene expression. We analyzed transcriptomes of ACD patients and healthy controls, pre-post a music session (n = 60), and main genes/pathways were compared to those dysregulated in mild cognitive impairment (MCI) and Alzheimer's disease (AD) as revealed by a multi-cohort study (n = 1269 MCI/AD and controls). Music was associated with 2.3 times more whole-genome gene expression, particularly on neurodegeneration-related genes, in ACD than in controls. Co-expressed gene-modules and pathways analysis demonstrated that music impacted autophagy, vesicle and endosome organization, biological processes commonly dysregulated in MCI/AD. Notably, the data indicated a strong negative correlation between musically-modified genes/pathways in ACD and those dysregulated in MCI/AD. These findings highlight the compensatory effect of music on genes/biological processes affected in MCI/AD, providing insights into the molecular mechanisms underlying the benefits of music on these disorders.

New Views of the DNA Repair Protein Ataxia-Telangiectasia Mutated in Central Neurons: Contribution in Synaptic Dysfunctions of Neurodevelopmental and Neurodegenerative Diseases

Ataxia-Telangiectasia Mutated (ATM) is a serine/threonine protein kinase principally known to orchestrate DNA repair processes upon DNA double-strand breaks (DSBs). Mutations in the Atm gene lead to Ataxia-Telangiectasia (AT), a recessive disorder characterized by ataxic movements consequent to cerebellar atrophy or dysfunction, along with immune alterations, genomic instability, and predisposition to cancer. AT patients show variable phenotypes ranging from neurologic abnormalities and cognitive impairments to more recently described neuropsychiatric features pointing to symptoms hardly ascribable to the canonical functions of ATM in DNA damage response (DDR). Indeed, evidence suggests that cognitive abilities rely on the proper functioning of DSB machinery and specific synaptic changes in central neurons of ATM-deficient mice unveiled unexpected roles of ATM at the synapse. Thus, in the present review, upon a brief recall of DNA damage responses, we focus our attention on the role of ATM in neuronal physiology and pathology and we discuss recent findings showing structural and functional changes in hippocampal and cortical synapses of AT mouse models. Collectively, a deeper knowledge of ATM-dependent mechanisms in neurons is necessary not only for a better comprehension of AT neurological phenotypes, but also for a higher understanding of the pathological mechanisms in neurodevelopmental and degenerative disorders involving ATM dysfunctions.

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.

DNA Damage Response-Associated Cell Cycle Re-Entry and Neuronal Senescence in Brain Aging and Alzheimer's Disease

Chronological aging is by far the strongest risk factor for age-related dementia and Alzheimer's disease. Senescent cells accumulated in the aging and Alzheimer's disease brains are now recognized as the keys to describing such an association. Cellular senescence is a classic phenomenon characterized by stable cell arrest, which is thought to be applicable only to dividing cells. Emerging evidence indicates that fully differentiated post-mitotic neurons are also capable of becoming senescent, with roles in contributing to both brain aging and disease pathogenesis. The key question that arises is the identity of the upstream triggers and the molecular mechanisms that underly such changes. Here, we highlight the potential role of persistent DNA damage response as the major driver of senescent phenotypes and discuss the current evidence and molecular mechanisms that connect DNA repair infidelity, cell cycle re-entry and terminal fate decision in committing neuronal cell senescence.

Mitochondria - Nucleus communication in neurodegenerative disease. Who talks first, who talks louder?

Mitochondria - nuclear coadaptation has been central to eukaryotic evolution. The dynamic dialogue between the two compartments within the context of multiorganellar interactions is critical for maintaining cellular homeostasis and directing the balance survival-death in case of cellular stress. The conceptualisation of mitochondria - nucleus communication has so far been focused on the communication from the mitochondria under stress to the nucleus and the consequent signalling responses, as well as from the nucleus to mitochondria in the context of DNA damage and repair. During ageing processes this dialogue may be better viewed as an integrated bidirectional 'talk' with feedback loops that expand beyond these two organelles depending on physiological cues. Here we explore the current views on mitochondria - nucleus dialogue and its role in maintaining cellular health with a focus on brain cells and neurodegenerative disease. Thus, we detail the transcriptional responses initiated by mitochondrial dysfunction in order to protect itself and the general cellular homeostasis. Additionally, we are reviewing the knowledge of the stress pathways initiated by DNA damage which affect mitochondria homeostasis and we add the information provided by the study of combined mitochondrial and genotoxic damage. Finally, we reflect on how each organelle may take the lead in this dialogue in an ageing context where both compartments undergo accumulation of stress and damage and where, perhaps, even the communications' mechanisms may suffer interruptions.

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.

The Role of DNA Damage in Neural Plasticity in Physiology and Neurodegeneration

Damage to DNA is generally considered to be a harmful process associated with aging and aging-related disorders such as neurodegenerative diseases that involve the selective death of specific groups of neurons. However, recent studies have provided evidence that DNA damage and its subsequent repair are important processes in the physiology and normal function of neurons. Neurons are unique cells that form new neural connections throughout life by growth and re-organisation in response to various stimuli. This “plasticity” is essential for cognitive processes such as learning and memory as well as brain development, sensorial training, and recovery from brain lesions. Interestingly, recent evidence has suggested that the formation of double strand breaks (DSBs) in DNA, the most toxic form of damage, is a physiological process that modifies gene expression during normal brain activity. Together with subsequent DNA repair, this is thought to underlie neural plasticity and thus control neuronal function. Interestingly, neurodegenerative diseases such as Alzheimer’s disease, amyotrophic lateral sclerosis, frontotemporal dementia, and Huntington’s disease, manifest by a decline in cognitive functions, which are governed by plasticity. This suggests that DNA damage and DNA repair processes that normally function in neural plasticity may contribute to neurodegeneration. In this review, we summarize current understanding about the relationship between DNA damage and neural plasticity in physiological conditions, as well as in the pathophysiology of neurodegenerative diseases.

Evaluation of Utilizing the Distinct Genes as Predictive Biomarkers in Late-Onset Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by a devastating decline in cognitive activities among all types of dementia, and it severely affects the quality of life. Late-onset AD (LOAD) occurs after the age of 65 years and develops sporadically. Although aging comes first along the main risk factors underlying LOAD, disease-causing susceptibility genes have been associated with disease pathogenesis. In our study, we included the genes PARP1 , POLB , HTRA2 , SLC1A2 , HS1BP3 , and DRD3 to be investigated in LOAD patients based on their expression levels. Within this framework, we aimed to determine the possible functions of these genes in the pathophysiology of the disease. We investigated whether the utilization of these genes as biomarkers in the early diagnosis of LOAD may help the treatment scheme to be applied in the clinic. We involved 50 individuals in the study and collected peripheral blood samples from the patients and control groups for molecular genetic analysis. Subsequently, RNA was extracted from the peripheral blood samples, and expression analyzes were performed using qualitative reverse transcription polymerase chain reaction. The results obtained were evaluated by using proper statistical methods. Our results demonstrated that there was no difference between patient and control groups in terms of HTRA2 , DRD3 , HS1BP3 , and POLB genes. The expression levels of the SLC1A2 and PARP1 genes were significantly lower in the patient group compared with the control group. In conclusion, we presume that the PARP1 and SLC1A2 genes can be utilized as molecular biomarkers for LOAD.

The Complex Mechanisms by Which Neurons Die Following DNA Damage in Neurodegenerative Diseases

Human cells are exposed to numerous exogenous and endogenous insults every day. Unlike other molecules, DNA cannot be replaced by resynthesis, hence damage to DNA can have major consequences for the cell. The DNA damage response contains overlapping signalling networks that repair DNA and hence maintain genomic integrity, and aberrant DNA damage responses are increasingly described in neurodegenerative diseases. Furthermore, DNA repair declines during aging, which is the biggest risk factor for these conditions. If unrepaired, the accumulation of DNA damage results in death to eliminate cells with defective genomes. This is particularly important for postmitotic neurons because they have a limited capacity to proliferate, thus they must be maintained for life. Neuronal death is thus an important process in neurodegenerative disorders. In addition, the inability of neurons to divide renders them susceptible to senescence or re-entry to the cell cycle. The field of cell death has expanded significantly in recent years, and many new mechanisms have been described in various cell types, including neurons. Several of these mechanisms are linked to DNA damage. In this review, we provide an overview of the cell death pathways induced by DNA damage that are relevant to neurons and discuss the possible involvement of these mechanisms in neurodegenerative conditions.

Sleep deficiency as a driver of cellular stress and damage in neurological disorders

Neurological disorders encompass an extremely broad range of conditions, including those that present early in development and those that progress slowly or manifest with advanced age. Although these disorders have distinct underlying etiologies, the activation of shared pathways, e.g., integrated stress response (ISR) and the development of shared phenotypes (sleep deficits) may offer clues toward understanding some of the mechanistic underpinnings of neurologic dysfunction. While it is incontrovertibly complex, the relationship between sleep and persistent stress in the brain has broad implications in understanding neurological disorders from development to degeneration. The convergent nature of the ISR could be a common thread linking genetically distinct neurological disorders through the dysregulation of a core cellular homeostasis pathway.

Extra Virgin Olive Oil consumption from Mild Cognitive Impairment patients attenuates oxidative and nitrative stress reflecting on the reduction of the PARP levels and DNA damage

Oxidative/nitrative stress that results from the unbalance of the overproduction/clearance of reactive oxygen/nitrogen species (ROS/NOS), originated from a variety of endo- and/or exo-genous sources, can have detrimental effects on DNA and is involved in Alzheimer's disease (AD) pathology. An excellent marker of oxidative DNA lesions is 8-hydroxy-2'-deoxyguanosine (8-OHdG) while of nitrative stress the enzyme NOS2 (Nitric oxide synthase 2). Under massive oxidative stress, poly(ADP-ribose)polymerase 1 (PARP-1) enzyme activity, responsible for restoration of DNA damage, is augmented, DNA repair enzymes are recruited, and cell survival/or death is ensued through PARP-1 activation, which is correlated positively with neurodegenerative diseases. In this biochemical study the levels of PARP-1, 8-oxo-dG, and NOS2, Aβ1-42, and p-tau in their sera determined using Enzyme-Linked Immunosorbent Assay (ELISA). Patients diagnosed with Mild Cognitive Impairment participated in MICOIL clinical trial, were daily administered with 50 ml Extra Virgin Olive Oil (EVOO) for one year. All MCI patients' biomarkers that had consumed EVOO were tantamount to those of healthy participants, contrary to MCI patients who were not administered. EVOO administration in MCI patients resulted in the restoration of DNA damage and of the well-established "hallmarks" AD biomarkers, thanks probably to its antioxidant properties exhibiting a therapeutic potentiality against AD. Molecular docking simulations of the EVOO constituents on the crystal structure of PARP-1 and NOS-2 target enzymes were also employed, to study in silico the ability of the compounds to bind to these enzymes and explain the observed in vitro activity. In silico analysis has proved the binding of EVOO constituents on PARP-1and NOS-2 enzymes and their interaction with crucial amino acids of the active sites. CLINICAL TRIAL REGISTRATION: https://clinicaltrials.gov/ct2/show/NCT03362996. MICOIL GOV IDENTIFIER: NCT03362996.

Insights into the Pathogenesis of Neurodegenerative Diseases: Focus on Mitochondrial Dysfunction and Oxidative Stress

As the population ages, the incidence of neurodegenerative diseases is increasing. Due to intensive research, important steps in the elucidation of pathogenetic cascades have been made and significantly implicated mitochondrial dysfunction and oxidative stress. However, the available treatment in Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis is mainly symptomatic, providing minor benefits and, at most, slowing down the progression of the disease. Although in preclinical setting, drugs targeting mitochondrial dysfunction and oxidative stress yielded encouraging results, clinical trials failed or had inconclusive results. It is likely that by the time of clinical diagnosis, the pathogenetic cascades are full-blown and significant numbers of neurons have already degenerated, making it impossible for mitochondria-targeted or antioxidant molecules to stop or reverse the process. Until further research will provide more efficient molecules, a healthy lifestyle, with plenty of dietary antioxidants and avoidance of exogenous oxidants may postpone the onset of neurodegeneration, while familial cases may benefit from genetic testing and aggressive therapy started in the preclinical stage.

Theoretical study of the dissociative photodetachment dynamics of the hydrated superoxide anion cluster

The dissociative photodetachment of the hydrated superoxide anion cluster, O2-·H2O + hν → O2 + H2O + e-, is theoretically investigated using path-integral and ring-polymer molecular dynamics simulation methods, which can account for nuclear quantum effects. Full-dimensional potential energy surfaces for the anionic and lowest two neutral states (triplet and singlet spin states) are constructed based on extensive density-functional theory calculations. The calculated photoelectron spectrum agrees well with the experimental spectra measured for different photodetachment laser wavelengths. The calculated photoelectron-photofragment kinetic energy correlation spectrum also agrees well with previous experimental measurements. The dissociation mechanisms, including available energy partitioning and the importance of nuclear quantum effects in photodetachment, are discussed in detail.

DNA Damage-Induced Neurodegeneration in Accelerated Ageing and Alzheimer's Disease

DNA repair ensures genomic stability to achieve healthy ageing, including cognitive maintenance. Mutations on genes encoding key DNA repair proteins can lead to diseases with accelerated ageing phenotypes. Some of these diseases are xeroderma pigmentosum group A (XPA, caused by mutation of XPA), Cockayne syndrome group A and group B (CSA, CSB, and are caused by mutations of CSA and CSB, respectively), ataxia-telangiectasia (A-T, caused by mutation of ATM), and Werner syndrome (WS, with most cases caused by mutations in WRN). Except for WS, a common trait of the aforementioned progerias is neurodegeneration. Evidence from studies using animal models and patient tissues suggests that the associated DNA repair deficiencies lead to depletion of cellular nicotinamide adenine dinucleotide (NAD⁺), resulting in impaired mitophagy, accumulation of damaged mitochondria, metabolic derailment, energy deprivation, and finally leading to neuronal dysfunction and loss. Intriguingly, these features are also observed in Alzheimer’s disease (AD), the most common type of dementia affecting more than 50 million individuals worldwide. Further studies on the mechanisms of the DNA repair deficient premature ageing diseases will help to unveil the mystery of ageing and may provide novel therapeutic strategies for AD.

Reassessment of Pioglitazone for Alzheimer's Disease

Alzheimer's disease is a quintessential 'unmet medical need', accounting for ∼65% of progressive cognitive impairment among the elderly, and 700,000 deaths in the United States in 2020. In 2019, the cost of caring for Alzheimer's sufferers was $244B, not including the emotional and physical toll on caregivers. In spite of this dismal reality, no treatments are available that reduce the risk of developing AD or that offer prolonged mitiagation of its most devestating symptoms. This review summarizes key aspects of the biology and genetics of Alzheimer's disease, and we describe how pioglitazone improves many of the patholophysiological determinants of AD. We also summarize the results of pre-clinical experiments, longitudinal observational studies, and clinical trials. The results of animal testing suggest that pioglitazone can be corrective as well as protective, and that its efficacy is enhanced in a time- and dose-dependent manner, but the dose-effect relations are not monotonic or sigmoid. Longitudinal cohort studies suggests that it delays the onset of dementia in individuals with pre-existing type 2 diabetes mellitus, which small scale, unblinded pilot studies seem to confirm. However, the results of placebo-controlled, blinded clinical trials have not borne this out, and we discuss possible explanations for these discrepancies.

Crosstalk between Different DNA Repair Pathways Contributes to Neurodegenerative Diseases

Simple Summary

Constant exposure to endogenous and environmental factors induces oxidative stress and DNA damage. Rare brain disorders caused by defects in DNA repair and DNA damage response (DDR) signaling establish that failure to process DNA damage may lead to neurodegeneration. In this review, we present mechanisms that link DDR with neurodegeneration in these disorders and discuss their relevance for common age-related neurodegenerative diseases (NDDs). Moreover, we highlight recent insight into the crosstalk between the DDR and other cellular processes known to be disturbed during NDDs.

Abstract

Genomic integrity is maintained by DNA repair and the DNA damage response (DDR). Defects in certain DNA repair genes give rise to many rare progressive neurodegenerative diseases (NDDs), such as ocular motor ataxia, Huntington disease (HD), and spinocerebellar ataxias (SCA). Dysregulation or dysfunction of DDR is also proposed to contribute to more common NDDs, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Amyotrophic Lateral Sclerosis (ALS). Here, we present mechanisms that link DDR with neurodegeneration in rare NDDs caused by defects in the DDR and discuss the relevance for more common age-related neurodegenerative diseases. Moreover, we highlight recent insight into the crosstalk between the DDR and other cellular processes known to be disturbed during NDDs. We compare the strengths and limitations of established model systems to model human NDDs, ranging from C. elegans and mouse models towards advanced stem cell-based 3D models.

[Effectiveness of the DNA double-strand breaks repair system in lymphocytes of patients with cognitive impairments and healthy volunteers]

The individual differences in the efficiency of DNA DSB repair were estimated by the level of residual γH2AX foci after γ-irradiation at a dose of 2 Gy, in lymphocytes of patients with amnestic mild cognitive impairment (AMCI) and Alzheimer's disease (AD) and of healthy volunteers. Lymphocytes were isolated from the peripheral blood of the examined patients and were frozen in a medium for freezing cells. Before the study, the lymphocytes were thawed, suspended in RPMI 1640 culture medium supplemented with 10% inactivated fetal bovine serum, and half of the cells were γ-irradiated at 4°C from a 60Co source on a GUT-200M facility at a dose of 2 Gy (a dose rate of 0.75 Gy/min). Control and irradiated lymphocytes were cultured for 24 h, collected, fixed, and stored until the study of the number of spontaneous and residual foci of γH2AX using fluorescent microscopy after staining with fluorescent labeled antibodies. In lymphocytes of patients with AMCI and AD a higher number of residual γH2AX foci in lymphocytes and the higher number of lymphocytes with foci were found compared with healthy volunteers. This indicates a decrease in the ability to repair DNA DSB in these patients. Indicators of cellular immunity and the concentration of TNF-α in the blood serum in the group of examined patients were normal. In the group of patients with the cognitive impairments (AMCI+AD), a correlation was found between the number of residual foci of γH2AX and the number of CD3+CD4+ lymphocytes and the concentration of proinflammatory cytokine TNF-α in the blood serum. This suggests the development of stronger neuroinflammation in patients with reduced ability to repair DNA DSB in this pathology.

Evaluation of GammaH2AX in Buccal Cells as a Molecular Biomarker of DNA Damage in Alzheimer's Disease in the AIBL Study of Ageing

In response to double-stranded breaks (DSBs) in chromosomal DNA, H2AX (a member of histone H2A family) becomes phosphorylated to form γH2AX. Although increased levels of γH2AX have been reported in the neuronal nuclei of Alzheimer's disease (AD) patients, the understanding of γH2AX responses in buccal nuclei of individuals with mild cognitive impairment (MCI) and AD remain unexplored. In the current study, endogenous γH2AX was measured in buccal cell nuclei from MCI (n = 18) or AD (n = 16) patients and in healthy controls (n = 17) using laser scanning cytometry (LSC). The γH2AX level was significantly elevated in nuclei of the AD group compared to the MCI and control group, and there was a concomitant increase in P-trend for γH2AX from the control group through MCI to the AD group. Receiver-operating characteristic curves were carried out for different γH2AX parameters; γH2AX in nuclei resulted in the greatest area under the curve value of 0.7794 (p = 0.0062) with 75% sensitivity and 70% specificity for the identification of AD patients from control. In addition, nuclear circularity (a measure of irregular nuclear shape) was significantly higher in the buccal cell nuclei from the AD group compared with the MCI and control groups. Additionally, there was a positive correlation between the nuclear circularity and γH2AX signals. The results indicated that increased DNA damage is associated with AD.

Mitochondrial and Nuclear DNA Oxidative Damage in Physiological and Pathological Aging

Mitochondria play an important role in numerous processes, including energy generation, regulating ion homeostasis, and cell signaling. Mitochondria are also the main source of reactive oxygen species (ROS). Due to the oxidative environment within mitochondria, the macromolecules therein, for example, mtDNA, proteins, and lipids are more susceptible to sustaining damage. During aging, mitochondrial functions decline, partly as a result of an accumulation of mtDNA mutations, decreased mtDNA copy number and protein expression, and a reduction in oxidative capacity. The aim of this study was to summarize the knowledge on DNA oxidative damage in aging and age-related neurodegenerative diseases. It has been hypothesized that various ROS may play an important role not only in physiological senescence but also in the development of neurodegenerative diseases, for example, Alzheimer's disease and Parkinson's disease. Thus, mitochondria seem to be a potential target of novel treatments for neurodegenerative diseases.

Contributions of DNA Damage to Alzheimer's Disease

Alzheimer’s disease (AD) is the most common type of neurodegenerative disease. Its typical pathology consists of extracellular amyloid-β (Aβ) plaques and intracellular tau neurofibrillary tangles. Mutations in the APP, PSEN1, and PSEN2 genes increase Aβ production and aggregation, and thus cause early onset or familial AD. Even with this strong genetic evidence, recent studies support AD to result from complex etiological alterations. Among them, aging is the strongest risk factor for the vast majority of AD cases: Sporadic late onset AD (LOAD). Accumulation of DNA damage is a well-established aging factor. In this regard, a large amount of evidence reveals DNA damage as a critical pathological cause of AD. Clinically, DNA damage is accumulated in brains of AD patients. Genetically, defects in DNA damage repair resulted from mutations in the BRAC1 and other DNA damage repair genes occur in AD brain and facilitate the pathogenesis. Abnormalities in DNA damage repair can be used as diagnostic biomarkers for AD. In this review, we discuss the association, the causative potential, and the biomarker values of DNA damage in AD pathogenesis.

Autophagy as a Cellular Stress Response Mechanism in the Nervous System

Cells of an organism face with various types of insults during their lifetime. Exposure to toxins, metabolic problems, ischaemia/reperfusion, physical trauma, genetic diseases, neurodegenerative diseases are among the conditions that trigger cellular stress responses. In this context, autophagy is one of the mechanisms that supports cell survival under stressful conditions. Autophagic vesicle engulfs the cargo and transports it to lysosome for degradation and turnover. As such, autophagy eliminates abnormal proteins, clears damaged organelles, limits oxidative stress and helps to improve metabolic balance. Nervous system cells and particularly postmitotic neurons are highly sensitive to a spectrum of insults, and autophagy emerges as one of the key stress response mechanism, ensuring health and survival of these vulnerable cell types. In this review, we will overview mechanisms through which cells cope with stress, and how these stress responses regulate autophagy, with a special focus on the nervous system.

Mitochondrial dysfunction in Alzheimer's disease: Role in pathogenesis and novel therapeutic opportunities

Dysfunction of cell bioenergetics is a common feature of neurodegenerative diseases, the most common of which is Alzheimer's disease (AD). Disrupted energy utilization implicates mitochondria at its nexus. This review summarizes some of the evidence that points to faulty mitochondrial function in AD and highlights past and current therapeutic development efforts. Classical neuropathological hallmarks of disease (β-amyloid and τ) and sporadic AD risk genes (APOE) may trigger mitochondrial disturbance, yet mitochondrial dysfunction may incite pathology. Preclinical and clinical efforts have overwhelmingly centred on the amyloid pathway, but clinical trials have yet to reveal clear-cut benefits. AD therapies aimed at mitochondrial dysfunction are few and concentrate on reversing oxidative stress and cell death pathways. Novel research efforts aimed at boosting mitochondrial and bioenergetic function offer an alternative treatment strategy. Enhancing cell bioenergetics in preclinical models may yield widespread favourable effects that could benefit persons with AD. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Investigation of base excision repair gene variants in late-onset Alzheimer's disease

Base excision repair (BER) defects and concomitant oxidative DNA damage accumulation play a role in the etiology and progression of late-onset Alzheimer’s disease (LOAD). However, it is not known whether genetic variant(s) of specific BER genes contribute to reduced BER activity in LOAD patients and whether they are associated with risk, development and/or progression of LOAD. Therefore, we performed targeted next generation sequencing for three BER genes, uracil glycosylase (UNG), endonuclease VIII-like DNA glycosylase 1 (NEIL1) and polymerase β (POLβ) including promoter, exonic and intronic regions in peripheral blood samples and postmortem brain tissues (temporal cortex, TC and cerebellum, CE) from LOAD patients, high-pathology control and cognitively normal age-matched controls. In addition, the known LOAD risk factor, APOE was included in this study to test whether any BER gene variants associate with APOE variants, particularly APOE ε4. We show that UNG carry five significant variants (rs1610925, rs2268406, rs80001089, rs1018782 and rs1018783) in blood samples of Turkish LOAD patients compared to age-matched controls and one of them (UNG rs80001089) is also significant in TC from Brazilian LOAD patients (p<0.05). The significant variants present only in CE and TC from LOAD are UNG rs2569987 and POLβ rs1012381950, respectively. There is also significant epistatic relationship (p = 0.0410) between UNG rs80001089 and NEIL1 rs7182283 in TC from LOAD subjects. Our results suggest that significant BER gene variants may be associated with the risk of LOAD in non-APOE ε4 carriers. On the other hand, there are no significant UNG, NEIL1 and POLβ variants that could affect their protein level and function, suggesting that there may be other factors such as post-transcriptional or–translational modifications responsible for the reduced activities and protein levels of these genes in LOAD pathogenesis. Further studies with increased sample size are needed to confirm the relationship between BER variants and LOAD risk.

The Role of Mitochondrial Dysfunction in the Progression of Alzheimer's Disease

The current molecular understanding of Alzheimer's disease (AD) has still not resulted in successful interventions. Mitochondrial dysfunction of the AD brain is currently emerging as a hallmark of this disease. One mitochondrial function often affected in AD is oxidative phosphorylation responsible for ATP production, but also for production of reactive oxygen species (ROS) and for the de novo synthesis of pyrimidines. This paper reviews the role of mitochondrial produced ROS and pyrimidines in the aetiology of AD and their proposed role in oxidative degeneration of macromolecules, synthesis of essential phospholipids and maintenance of mitochondrial viability in the AD brain.

Biothiols and oxidative stress markers and polymorphisms of TOMM40 and APOC1 genes in Alzheimer's disease patients

Alzheimer’s disease (AD) is a progressive disease, with frequently observed improper biothiols turnover, homocysteine (Hcy) and glutathione (GSH). GSH protects cells from oxidative stress and may be determined by 8-oxo-2’-deoxyguanosine (8-oxo2dG) level and its repair enzyme 8-oxoguanine DNA glycosylase (OGG1). The presence of unfavorable alleles, e.g., in APOE cluster, TOMM40 or APOC1 is known to facilitate the dementia onset under oxidative stress.

The aim of the study was to analyze rs1052452, rs2075650 TOMM40 polymorphisms, rs4420638 APOC1, and their correlation with Hcy, GSH, 8-oxo2dG, OGG1 levels in plasma of AD patients and controls.

We recruited 230 individuals: 88 AD, 80 controls without (UC), 62 controls with (RC) positive family history of AD. The TOMM40 genotype was determined by HRM and capillary electrophoresis, while APOC1 by HRM. The concentrations of OGG1, 8-oxo2dG were determined by ELISA, whereas Hcy, GSH by HPLC/EC.

We showed that over 60% of AD patients had increased Hcy levels (p<0.01 vs. UC, p<0.001 vs. RC), while GSH (p<0.01 vs. UC), 8-oxo2dG (p<0.01 vs. UC, p<0.001 vs. RC) were reduced. Minor variants: rs10524523-L, rs4420638-G, rs2075650-G were significantly overrepresented in AD. For rs4420638-G, rs2075650-G variants, the association remained significant in APOE E4 non-carriers. The misbalance of analyzed biothiols, and 8-oxo2dG, OGG1 were more pronounced in carriers of major variants: rs10524523-S/VL, rs4420638-A, rs2075650-A.

We showed, for the first time, that APOC1 and TOMM40 rs2075650 polymorphisms may be independent risk factors of developing AD, whose major variants are accompanied by disruption of biothiols metabolism and inefficient removal of DNA oxidation.

Role of Estrogen and Other Sex Hormones in Brain Aging. Neuroprotection and DNA Repair

Aging is an inevitable biological process characterized by a progressive decline in physiological function and increased susceptibility to disease. The detrimental effects of aging are observed in all tissues, the brain being the most important one due to its main role in the homeostasis of the organism. As our knowledge about the underlying mechanisms of brain aging increases, potential approaches to preserve brain function rise significantly. Accumulating evidence suggests that loss of genomic maintenance may contribute to aging, especially in the central nervous system (CNS) owing to its low DNA repair capacity. Sex hormones, particularly estrogens, possess potent antioxidant properties and play important roles in maintaining normal reproductive and non-reproductive functions. They exert neuroprotective actions and their loss during aging and natural or surgical menopause is associated with mitochondrial dysfunction, neuroinflammation, synaptic decline, cognitive impairment and increased risk of age-related disorders. Moreover, loss of sex hormones has been suggested to promote an accelerated aging phenotype eventually leading to the development of brain hypometabolism, a feature often observed in menopausal women and prodromal Alzheimer's disease (AD). Although data on the relation between sex hormones and DNA repair mechanisms in the brain is still limited, various investigations have linked sex hormone levels with different DNA repair enzymes. Here, we review estrogen anti-aging and neuroprotective mechanisms, which are currently an area of intense study, together with the effect they may have on the DNA repair capacity in the brain.

Role of Estrogen and Other Sex Hormones in Brain Aging. Neuroprotection and DNA Repair

Aging is an inevitable biological process characterized by a progressive decline in physiological function and increased susceptibility to disease. The detrimental effects of aging are observed in all tissues, the brain being the most important one due to its main role in the homeostasis of the organism. As our knowledge about the underlying mechanisms of brain aging increases, potential approaches to preserve brain function rise significantly. Accumulating evidence suggests that loss of genomic maintenance may contribute to aging, especially in the central nervous system (CNS) owing to its low DNA repair capacity. Sex hormones, particularly estrogens, possess potent antioxidant properties and play important roles in maintaining normal reproductive and non-reproductive functions. They exert neuroprotective actions and their loss during aging and natural or surgical menopause is associated with mitochondrial dysfunction, neuroinflammation, synaptic decline, cognitive impairment and increased risk of age-related disorders. Moreover, loss of sex hormones has been suggested to promote an accelerated aging phenotype eventually leading to the development of brain hypometabolism, a feature often observed in menopausal women and prodromal Alzheimer's disease (AD). Although data on the relation between sex hormones and DNA repair mechanisms in the brain is still limited, various investigations have linked sex hormone levels with different DNA repair enzymes. Here, we review estrogen anti-aging and neuroprotective mechanisms, which are currently an area of intense study, together with the effect they may have on the DNA repair capacity in the brain.

Associations between DNA Damage, DNA Base Excision Repair Gene Variability and Alzheimer's Disease Risk

BACKGROUND

Increased oxidative damage to DNA is one of the pathways involved in Alzheimer's disease (AD). Insufficient base excision repair (BER) is in part responsible for increased oxidative DNA damage. The aim of the present study was to assess the effect of polymorphic variants of BER-involved genes and the peripheral markers of DNA damage and repair in patients with AD.

MATERIAL AND METHODS

Comet assays and TaqMan probes were used to assess DNA damage, BER efxFB01;ciency and polymorphic variants of 12 BER genes in blood samples from 105 AD patients and 130 controls. The DNA repair efficacy (DRE) was calculated according to a specific equation.

RESULTS

The levels of endogenous and oxidative DNA damages were higher in AD patients than controls. The polymorphic variants of XRCC1 c.580C>T XRCC1 c.1196A>G and OGG1 c.977C>G are associated with increased DNA damage in AD.

CONCLUSION

Our results show that oxidative stress and disturbances in DRE are particularly responsible for the elevated DNA lesions in AD. The results suggest that oxidative stress and disruption in DNA repair may contribute to increased DNA damage in AD patients and risk of this disease. In addition, disturbances in DRE may be associated with polymorphisms of OGG1 and XRCC1.

Genome instability in Alzheimer disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Autosomal dominant, familial AD (fAD) is very rare and caused by mutations in amyloid precursor protein (APP), presenilin-1 (PSEN-1), and presenilin-2 (PSEN-2) genes. The pathogenesis of sporadic AD (sAD) is more complex and variants of several genes are associated with an increased lifetime risk of AD. Nuclear and mitochondrial DNA integrity is pivotal during neuronal development, maintenance and function. DNA damage and alterations in cellular DNA repair capacity have been implicated in the aging process and in age-associated neurodegenerative diseases, including AD. These findings are supported by research using animal models of AD and in DNA repair deficient animal models. In recent years, novel mechanisms linking DNA damage to neuronal dysfunction have been identified and have led to the development of noninvasive treatment strategies. Further investigations into the molecular mechanisms connecting DNA damage to AD pathology may help to develop novel treatment strategies for this debilitating disease. Here we provide an overview of the role of genome instability and DNA repair deficiency in AD pathology and discuss research strategies that include genome instability as a component.

Defective mitochondrial respiration, altered dNTP pools and reduced AP endonuclease 1 activity in peripheral blood mononuclear cells of Alzheimer's disease patients

AIMS

Accurate biomarkers for early diagnosis of Alzheimer's disease (AD) are badly needed. Recent reports suggest that dysfunctional mitochondria and DNA damage are associated with AD development. In this report, we measured various cellular parameters, related to mitochondrial bioenergetics and DNA damage, in peripheral blood mononuclear cells (PBMCs) of AD and control participants, for biomarker discovery.

METHODS

PBMCs were isolated from 53 patients with AD of mild to moderate degree and 30 age-matched healthy controls. Tests were performed on the PBMCs from as many of these participants as possible. We measured glycolysis and mitochondrial respiration fluxes using the Seahorse Bioscience flux analyzer, mitochondrial ROS production using flow cytometry, dNTP levels by way of a DNA polymerization assay, DNA strand breaks using the Fluorometric detection of Alkaline DNA Unwinding (FADU) assay, and APE1 incision activity (in cell lysates) on a DNA substrate containing an AP site (to estimate DNA repair efficiency).

RESULTS

In the PBMCs of AD patients, we found reduced basal mitochondrial oxygen consumption, reduced proton leak, higher dATP level, and lower AP endonuclease 1 activity, depending on adjustments for gender and/or age.

CONCLUSIONS

This study reveals impaired mitochondrial respiration, altered dNTP pools and reduced DNA repair activity in PBMCs of AD patients, thus suggesting that these biochemical activities may be useful as biomarkers for AD.

p53-dependent SIRT6 expression protects Aβ42-induced DNA damage

Alzheimer's disease (AD) is the most common type of dementia and age-related neurodegenerative disease. Elucidating the cellular changes that occur during ageing is an important step towards understanding the pathogenesis and progression of neurodegenerative disorders. SIRT6 is a member of the mammalian sirtuin family of anti-aging genes. However, the relationship between SIRT6 and AD has not yet been elucidated. Here, we report that SIRT6 protein expression levels are reduced in the brains of both the 5XFAD AD mouse model and AD patients. Aβ42, a major component of senile plaques, decreases SIRT6 expression, and Aβ42-induced DNA damage is prevented by the overexpression of SIRT6 in HT22 mouse hippocampal neurons. Also, there is a strong negative correlation between Aβ42-induced DNA damage and p53 levels, a protein involved in DNA repair and apoptosis. In addition, upregulation of p53 protein by Nutlin-3 prevents SIRT6 reduction and DNA damage induced by Aβ42. Taken together, this study reveals that p53-dependent SIRT6 expression protects cells from Aβ42-induced DNA damage, making SIRT6 a promising new therapeutic target for the treatment of AD.

Methylation analysis of DNA repair genes in Alzheimer's disease

There is substantial evidence of impaired DNA repair activities in Alzheimer's disease (AD) neurons and peripheral tissues, inducing some investigators to speculate that this could partially result from promoter hypermethylation of DNA repair genes, resulting in gene silencing in those tissues. In the present study a screening cohort composed by late-onset AD (LOAD) patients and healthy matched controls was evaluated with a commercially available DNA methylation array for the assessment of the methylation levels of a panel of 22 genes involved in major DNA repair pathways in blood DNA. We then applied a cost-effective PCR based methylation-sensitive high-resolution melting (MS-HRM) technique, in order to evaluate the promoter methylation levels of the following DNA repair genes: OGG1, PARP1, MRE11A, BRCA1, MLH1, and MGMT. The analysis was performed in blood DNA from 56 LOAD patients and 55 matched controls, including the samples previously assessed with the DNA methylation array as validating samples. Both approaches revealed that all the investigated genes were largely hypomethylated in LOAD and control blood DNA, and no difference between groups was observed. Collectively, present data do not support an increased promoter methylation of some of the major DNA repair genes in blood DNA of AD patients.

Variants of Base Excision Repair Genes MUTYH , PARP1 and XRCC1 in Alzheimer's Disease Risk

BACKGROUND

Many clinical studies have shown that oxidative stress pathways and the efficiency of the oxidative DNA damage base excision repair (BER) system are associated with the pathogenesis of Alzheimer's disease (AD). Reduced BER efficiency may result from polymorphisms of BER-related genes. In the present study, we examine whether single nucleotide polymorphisms (SNPs) of BER genes are associated with increased risk of AD.

METHODS

SNP genotyping was carried out on DNA isolated from peripheral blood mononuclear cells obtained from 120 patients with AD and 110 healthy volunteers. Samples were genotyped for the presence of BER-related SNPs, i.e. XRCC1-rs1799782, rs25487; MUTYH-rs3219489, and PARP1-rs1136410.

RESULTS

We found a positive association between AD risk and the presence of G/A genotype variant of the XRCC1 rs25487 polymorphism [odds ratio (OR) = 3.762, 95% CI: 1.793-7.891]. The presence of the A/A genotype of this polymorphism reduced the risk of AD (OR = 0.485, 95% CI: 0.271-0.870). In cases of the PARP1 gene rs1136410 polymorphism, we observed that the T/C variant increases (OR = 4.159, 95% CI: 1.978-8.745) while the T/T variant reduces risk (OR = 0.240, 95% CI: 0.114-0.556) of AD.

CONCLUSIONS

We conclude that BER gene polymorphisms may play an important role in the etiology of AD. Diagnosing the presence or absence of particular genetic variants may be an important marker of AD. Further research on a larger population is needed. There is also a need to examine polymorphisms of other BER in the context of AD risk.

The Response to Oxidative DNA Damage in Neurons: Mechanisms and Disease

There is a growing body of evidence indicating that the mechanisms that control genome stability are of key importance in the development and function of the nervous system. The major threat for neurons is oxidative DNA damage, which is repaired by the base excision repair (BER) pathway. Functional mutations of enzymes that are involved in the processing of single-strand breaks (SSB) that are generated during BER have been causally associated with syndromes that present important neurological alterations and cognitive decline. In this review, the plasticity of BER during neurogenesis and the importance of an efficient BER for correct brain function will be specifically addressed paying particular attention to the brain region and neuron-selectivity in SSB repair-associated neurological syndromes and age-related neurodegenerative diseases.

The role of DNA base excision repair in brain homeostasis and disease

Chemical modification and spontaneous loss of nucleotide bases from DNA are estimated to occur at the rate of thousands per human cell per day. DNA base excision repair (BER) is a critical mechanism for repairing such lesions in nuclear and mitochondrial DNA. Defective expression or function of proteins required for BER or proteins that regulate BER have been consistently associated with neurological dysfunction and disease in humans. Recent studies suggest that DNA lesions in the nuclear and mitochondrial compartments and the cellular response to those lesions have a profound effect on cellular energy homeostasis, mitochondrial function and cellular bioenergetics, with especially strong influence on neurological function. Further studies in this area could lead to novel approaches to prevent and treat human neurodegenerative disease.

Genome instability biomarkers and blood micronutrient risk profiles associated with mild cognitive impairment and Alzheimer's disease

Successful maintenance of metabolic systems relating to accurate DNA replication and repair is critical for optimal lifelong human health. Should this homeostatic balance become impaired, genomic instability events can arise, compromising the integrity of the genome, which may result in gene expression and human disease. Both genome instability and micronutrient imbalance have been identified and implicated in diseases associated with accelerated ageing which potentially leads to an increased risk for the future development of clinically defined neurodegenerative disorders. Cognitive decline leading to the clinical diagnosis of mild cognitive impairment (MCI) has been shown to predict an increased risk in later life of developing Alzheimer's disease (AD). Knowledge on the impact of dietary factors in relation to MCI and AD risk is improving but incomplete; in particular the role of nutrient combinations (i.e. nutriomes) has not been thoroughly investigated. Currently, there is a need for preventative strategies as well as the identification of robust and reproducible diagnostic biomarkers that will allow identification of those individuals with increased risk for neurodegenerative diseases. Growing evidence suggests cells originating from different somatic tissues derived from individuals that have been clinically diagnosed with neurodegenerative disorders exhibit elevated frequencies of DNA damage compared to tissues of cognitively normal individuals which could be due to malnutrition. The objective of this review is to discuss current evidence and identify knowledge gaps relating to genome instability biomarkers and blood micronutrient profiles from human studies of MCI and AD that may be specific to and contribute to the increased risk of these diseases. This is a vital step in order to create research strategies for the future development of diagnostics that are indicative of dementia risk and to inform preventative therapies.

The impact of base excision DNA repair in age-related neurodegenerative diseases

The aging process and several age-related neurodegenerative disorders have been linked to elevated levels of DNA damage induced by ROS and deficiency in DNA repair mechanisms. DNA damage induced by ROS is a byproduct of cellular respiration and accumulation of damage over time, is a fundamental aspect of a main theory of aging. Mitochondria have a pivotal role in generating cellular oxidative stress, and mitochondrial dysfunction has been associated with several diseases. DNA base excision repair is considered the major pathway for repair of oxidized bases in DNA both in the nuclei and in mitochondria, and in neurons this mechanism is particularly important because non-diving cells have limited back-up DNA repair mechanisms. An association between elevated oxidative stress and a decrease in BER is strongly related to the aging process and has special relevance in age-related neurodegenerative diseases. Here, we review the role of DNA repair in aging, focusing on the implications of the DNA base excision repair pathways and how alterations in expression of these DNA repair proteins are related to the aging process and to age-related neurodegenerative diseases.

Gliotoxicity of the cyanotoxin, β-methyl-amino-L-alanine (BMAA)

The amino acid variant β-methyl-amino-L-alanine (BMAA) has long been associated with the increased incidence and progression of the amyotrophic lateral sclerosis/Parkinsonism dementia complex (ALS/PDC). Previous studies have indicated that BMAA damages neurons via excitotoxic mechanisms. We have challenged rat olfactory ensheathing cells (OECs) with exogenous BMAA and found it to be cytotoxic. BMAA also induces a significant increase in Ca2+ influx, enhanced production of reactive oxygen species (ROS), and disrupts mitochondrial activity in OECs. This is the first study investigating BMAA toxicity using pure glial cells. These findings align BMAA with the three proposed mechanisms of degeneration in ALS, those being non-cell autonomous death, excitotoxicity and mitochondrial dysfunction.

Do we age because we have mitochondria?

The process of aging remains a great riddle. Production of reactive oxygen species (ROS) by mitochondria is an inevitable by-product of respiration, which has led to a hypothesis proposing the oxidative impairment of mitochondrial components (e.g., mtDNA, proteins, lipids) that initiates a vicious cycle of dysfunctional respiratory complexes producing more ROS, which again impairs function. This does not exclude other processes acting in parallel or targets for ROS action in other organelles than mitochondria. Given that aging is defined as the process leading to death, the role of mitochondria-based impairments in those organ systems responsible for human death (e.g., the cardiovascular system, cerebral dysfunction, and cancer) is described within the context of "garbage" accumulation and increasing insulin resistance, type 2 diabetes, and glycation of proteins. Mitochondrial mass, fusion, and fission are important factors in coping with impaired function. Both biogenesis of mitochondria and their degradation are important regulatory mechanisms stimulated by physical exercise and contribute to healthy aging. The hypothesis of mitochondria-related aging should be revised to account for the limitations of the degradative capacity of the lysosomal system. The processes involved in mitochondria-based impairments are very similar across a large range of organisms. Therefore, studies on model organisms from yeast, fungi, nematodes, flies to vertebrates, and from cells to organisms also add considerably to the understanding of human aging.

Nicotinamide treatment reduces the levels of oxidative stress, apoptosis, and PARP-1 activity in Aβ(1-42)-induced rat model of Alzheimer's disease

The underlying mechanisms of Alzheimer's Disease (AD) are still unclear. It is suggested that poly(ADP-ribose) polymerase-1 (PARP-1) overactivation can cause neuroinflammation and cell death. In this study we searched the effects of nicotinamide (NA), endogenous PARP-1 inhibitor, on oxidative stress, apoptosis, and the regulation of PARP-1 and nuclear factor kappa B (NF-κB) in amyloid beta peptide (1-42) (Aβ(1-42))-induced neurodegeneration. Sprague-Dawley rats were divided into four groups as control, Aβ(1-42), Aβ(1-42) + NA(100 and 500 mg/kg). All groups were stereotaxically injected bilaterally into the hippocampus with Aβ(1-42) or saline. After surgery NA administrations were made intraperitoneally (ip) for 7 days. In order to investigate the effects of Aβ(1-42) and NA, protein carbonyls, lipid peroxidation, reactive oxygen species (ROS) production, glutathione (GSH) levels, activities of antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), mitochondrial function, mRNA and protein levels of PARP-1, NF-κB, p53, Bax, and Bcl-2 were measured in specific brain regions such as cortex and hippocampus. Aβ(1-42) treatment only increased the oxidative stress parameters and caused decline in antioxidant enzyme activities, mitochondrial function, and GSH levels. Also, overexpression of PARP-1, NF-κB, p53, Bax, and the decreased levels of Bcl-2 were observed in Aβ(1-42)-treated group. NA treatments against Aβ(1-42)-upregulated Bcl-2 and downregulated PARP-1, NF-κB, p53, and Bax levels. NA treatments also decreased the oxidative stress parameters and elevated antioxidant enzyme activities, GSH levels, and mitochondrial function against Aβ(1-42) treatment. These data suggest that NA may have a therapeutic potential in neurodegenerative processes due to the decreased levels of oxidative stress, apoptosis, and PARP-1 activity.

DNA-repair in mild cognitive impairment and Alzheimer's disease

While the pathogenesis of the sporadic form of Alzheimer disease (late onset Alzheimer disease, LOAD) is not fully understood, it seems to be clear that a combination of genetic and environmental factors are involved and influence the course of the disease. Among these factors, elevated levels of oxidative stress have been recognized and individual differences in the capacity to deal with DNA damage caused by its effects have been the subject of numerous studies. This review summarizes the research on DNA repair proteins and genes in the context of LOAD pathogenesis and its possible prodromal stage, mild cognitive impairment (MCI). The current status of the research in this field is discussed with respect to methodological issues which might have compromised the outcome of some studies and future directions of investigation on this subject are depicted.

The role of DNA repair in brain related disease pathology

Oxidative DNA damage is implicated in brain aging, neurodegeneration and neurological diseases. Damage can be created by normal cellular metabolism, which accumulates with age, or by acute cellular stress conditions which create bursts of oxidative damage. Brain cells have a particularly high basal level of metabolic activity and use distinct oxidative damage repair mechanisms to remove oxidative damage from DNA and dNTP pools. Accumulation of this damage in the background of a functional DNA repair response is associated with normal aging, but defective repair in brain cells can contribute to neurological dysfunction. Emerging research strongly associates three common neurodegenerative conditions, Alzheimer's, Parkinson's and stroke, with defects in the ability to repair chronic or acute oxidative damage in neurons. This review explores the current knowledge of the role of oxidative damage repair in preserving brain function and highlights the emerging models and methods being used to advance our knowledge of the pathology of neurodegenerative disease.