TET2-mediated 5-hydroxymethylcytosine induces genetic instability and mutagenesis

Glucocorticoid promotes metastasis of colorectal cancer via co-regulation of glucocorticoid receptor and TET2

Glucocorticoids (GCs), commonly used for anti-inflammatory and cancer treatments, have been linked to the promotion of cancer metastasis. Yet, the molecular mechanisms behind this potential remain poorly understood. Clarifying these mechanisms is crucial for a nuanced understanding and potential refinement of GC therapies in the context of cancer treatment. In HEK293T cells, co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation sequencing (ChIP-seq) were used with antibodies of glucocorticoid receptor (GR) and ten-eleven translocation enzymes (TET) family proteins (TET1, TET2, TET3). Drug repositioning was performed through the Connectivity Map database, using common target genes of GR and TET2 in HEK293 and HCT116 cell lines and differentially expressed genes (DEGs) of colorectal cancer (CRC). Cell migration and invasion were tested in CRC cell lines with varying GR expression, that is, HCT116 and HT29 cell lines. Dexamethasone (Dex) treatment resulted in a significant difference in cell migration rates in two CRC cell lines with disparate GR expression levels. Co-IP and ChIP-seq analyses substantiated the interaction between GR and TET family proteins in HEK293T cells. Belinostat, the selected compound, was successfully validated for its potential to counteract the effects of GC-induced invasion in CRC cells in vitro. Transcriptomic analyses of Belinostat-treated HCT116 cells revealed down-regulation of target genes associated with cancer metastasis. This study provides valuable insights into the molecular mechanisms underlying GC-induced metastasis, introducing newly repositioned compounds that could serve as potential adjuvant therapy to GC treatment. Furthermore, it opens avenues for exploring novel drug candidates for CRC treatment.

Loss of tet methyl cytosine dioxygenase 3 (TET3) enhances cardiac fibrosis via modulating the DNA damage repair response

BACKGROUND

Cardiac fibrosis is the hallmark of all forms of chronic heart disease. Activation and proliferation of cardiac fibroblasts are the prime mediators of cardiac fibrosis. Existing studies show that ROS and inflammatory cytokines produced during fibrosis not only signal proliferative stimuli but also contribute to DNA damage. Therefore, as a prerequisite to maintain sustained proliferation in fibroblasts, activation of distinct DNA repair mechanism is essential.

RESULT

In this study, we report that TET3, a DNA demethylating enzyme, which has been shown to be reduced in cardiac fibrosis and to exert antifibrotic effects does so not only through its demethylating activity but also through maintaining genomic integrity by facilitating error-free homologous recombination (HR) repair of DNA damage. Using both in vitro and in vivo models of cardiac fibrosis as well as data from human heart tissue, we demonstrate that the loss of TET3 in cardiac fibroblasts leads to spontaneous DNA damage and in the presence of TGF-β to a shift from HR to the fast but more error-prone non-homologous end joining repair pathway. This shift contributes to increased fibroblast proliferation in a fibrotic environment. In vitro experiments showed TET3's recruitment to H2O2-induced DNA double-strand breaks (DSBs) in mouse cardiac fibroblasts, promoting HR repair. Overexpressing TET3 counteracted TGF-β-induced fibroblast proliferation and restored HR repair efficiency. Extending these findings to human cardiac fibrosis, we confirmed TET3 expression loss in fibrotic hearts and identified a negative correlation between TET3 levels, fibrosis markers, and DNA repair pathway alteration.

CONCLUSION

Collectively, our findings demonstrate TET3's pivotal role in modulating DDR and fibroblast proliferation in cardiac fibrosis and further highlight TET3 as a potential therapeutic target.

Organic Acids Derived from Saliva-amalgamated Betel Quid Filtrate Are Predicted as a Ten-eleven Translocation-2 Inhibitor

There is a lack of evidence regarding the use of betel quid (BQ) and its potential contribution to oral cancer. Limited attention has been directed towards investigating the involvement of BQ-derived organic acids in the modulation of metabolic-epigenomic pathways associated with oral cancer initiation and progression. We employed novel protocol for preparing saliva-amalgamated BQ filtrate (SABFI) that mimics the oral cavity environment. SABFI and saliva control were further purified by an in-house developed vertical tube gel electrophoresis tool. The purified SABFI was then subjected to liquid chromatography-high resolution mass spectrometry analysis to identify the presence of organic acids. Profiling of SABFI showed a pool of prominent organic acids such as citric acid. malic acid, fumaric acid, 2-methylcitric acid, 2-hydroxyglutarate, cis-aconitic acid, succinic acid, 2-hydroxyglutaric acid lactone, tartaric acid and β-ketoglutaric acid. SABFI showed anti-proliferative and early apoptosis effects in oral cancer cells. Molecular docking and molecular dynamics simulations predicted that SABFI-derived organic acids as potential inhibitors of the epigenetic demethylase enzyme, Ten-Eleven Translocation-2 (TET2). By binding to the active site of α-ketoglutarate, a known substrate of TET2, these organic acids are likely to act as competitive inhibitors. This study reports a novel approach to study SABFI-derived organic acids that could mimic the chemical composition of BQ in the oral cavity. These SABFI-derived organic acids projected as inhibitors of TET2 and could be explored for their role oral cancer.

Clonal hematopoiesis and bone marrow inflammation

Clonal hematopoiesis (CH) occurs in hematopoietic stem cells with increased risks of progressing to hematologic malignancies. CH mutations are predominantly found in aged populations and correlate with an increased incidence of cardiovascular and other diseases. Increased lines of evidence demonstrate that CH mutations are closely related to the inflammatory bone marrow microenvironment. In this review, we summarize the recent advances in this topic starting from the discovery of CH and its mutations. We focus on the most commonly mutated and well-studied genes in CH and their contributions to the innate immune responses and inflammatory signaling, especially in the hematopoietic cells of bone marrow. We also aimed to discuss the interrelationship between inflammatory bone marrow microenvironment and CH mutations. Finally, we provide our perspectives on the challenges in the field and possible future directions to help understand the pathophysiology of CH.

Enzyme-free targeted DNA demethylation using CRISPR-dCas9-based steric hindrance to identify DNA methylation marks causal to altered gene expression

DNA methylation involves the enzymatic addition of a methyl group primarily to cytosine residues in DNA. This protocol describes how to produce complete and minimally confounded DNA demethylation of specific sites in the genome of cultured cells by clustered regularly interspaced short palindromic repeats (CRISPR)-dCas9 and without the involvement of an epigenetic-modifying enzyme, the purpose of which is the evaluation of the functional (i.e., gene expression or phenotypic) consequences of DNA demethylation of specific sites that have been previously implicated in particular pathological or physiological contexts. This protocol maximizes the ability of the easily reprogrammable CRISPR-dCas9 system to assess the impact of DNA methylation from a causal rather than correlational perspective: alternative protocols for CRISPR-dCas9-based site-specific DNA methylation or demethylation rely on the recruitment of epigenetic enzymes that exhibit additional nonspecific activities at both the targeted site and throughout the genome, confounding conclusions of causality of DNA methylation. Inhibition or loss of DNA methylation is accomplished by three consecutive lentiviral transductions. The first two lentiviruses establish stable expression of dCas9 and a guide RNA, which will physically obstruct either maintenance or de novo DNA methyltransferase activity at the guide RNA target site. A third lentivirus introduces Cre recombinase to delete the dCas9 transgene, which leads to loss of dCas9 from the target site, allowing transcription factors and/or the transcription machinery to interact with the demethylated target site. This protocol requires 3-8 months to complete owing to prolonged cell passaging times, but there is little hands-on time, and no specific skills beyond basic molecular biology techniques are necessary.

The HDAC7-TET2 epigenetic axis is essential during early B lymphocyte development

Correct B cell identity at each stage of cellular differentiation during B lymphocyte development is critically dependent on a tightly controlled epigenomic landscape. We previously identified HDAC7 as an essential regulator of early B cell development and its absence leads to a drastic block at the pro-B to pre-B cell transition. More recently, we demonstrated that HDAC7 loss in pro-B-ALL in infants associates with a worse prognosis. Here we delineate the molecular mechanisms by which HDAC7 modulates early B cell development. We find that HDAC7 deficiency drives global chromatin de-condensation, histone marks deposition and deregulates other epigenetic regulators and mobile elements. Specifically, the absence of HDAC7 induces TET2 expression, which promotes DNA 5-hydroxymethylation and chromatin de-condensation. HDAC7 deficiency also results in the aberrant expression of microRNAs and LINE-1 transposable elements. These findings shed light on the mechanisms by which HDAC7 loss or misregulation may lead to B cell–based hematological malignancies.

Somatic gene mutations expose cytoplasmic DNA to co-opt the cGAS-STING-NLRP3 axis in Myelodysplastic syndromes

NLRP3 inflammasome and IFN-stimulated gene (ISG) induction are key biological drivers of ineffective hematopoiesis and inflammation in myelodysplastic syndromes (MDSs). Gene mutations involving mRNA splicing and epigenetic regulatory pathways induce inflammasome activation and myeloid lineage skewing in MDSs through undefined mechanisms. Using immortalized murine hematopoietic stem and progenitor cells harboring these somatic gene mutations and primary MDS BM specimens, we showed accumulation of unresolved R-loops and micronuclei with concurrent activation of the cytosolic sensor cyclic GMP-AMP synthase. Cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) signaling caused ISG induction, NLRP3 inflammasome activation, and maturation of the effector protease caspase-1. Deregulation of RNA polymerase III drove cytosolic R-loop generation, which upon inhibition, extinguished ISG and inflammasome response. Mechanistically, caspase-1 degraded the master erythroid transcription factor, GATA binding protein 1, provoking anemia and myeloid lineage bias that was reversed by cGAS inhibition in vitro and in Tet2^–/– hematopoietic stem and progenitor cell–transplanted mice. Together, these data identified a mechanism by which functionally distinct mutations converged upon the cGAS/STING/NLRP3 axis in MDS, directing ISG induction, pyroptosis, and myeloid lineage skewing.

How Human TET2 Enzyme Catalyzes the Oxidation of Unnatural Cytosine Modifications in Double-Stranded DNA

Methylation of cytosine bases is strongly linked to gene expression, imprinting, aging, and carcinogenesis. The Ten-eleven translocation (TET) family of enzymes, which are Fe(II)/2-oxoglutarate (2OG)-dependent enzymes, employ Fe(IV)=O species to dealkylate the lesioned bases to an unmodified cytosine. Recently, it has been shown that the TET2 enzyme can catalyze promiscuously DNA substrates containing unnatural alkylated cytosine. Such unnatural substrates of TET can be used as direct probes for measuring the TET activity or capturing TET from cellular samples. Herein, we studied the catalytic mechanisms during the oxidation of the unnatural C5-position modifications (5-ethylcytosine (5eC), 5-vinylcytosine (5vC) and 5-ethynylcytosine (5eyC)) and the demethylation of N4-methylated lesions (4-methylcytosine (4mC) and 4,4-dimethylcytosine(4dmC)) of the cytosine base by the TET2 enzyme using molecular dynamics (MD) and combined quantum mechanics and molecular mechanics (QM/MM) computational approaches. The results reveal that the chemical nature of the alkylation of the double-stranded (ds) DNA substrates induces distinct changes in the interactions in the binding site, the second coordination sphere, and long-range correlated motions of the ES complexes. The rate-determining hydrogen atom transfer (HAT) is faster in N4-methyl substituent substrates than in the C5-alkylations. Importantly, the calculations show the preference of hydroxylation over desaturation in both 5eC and 5vC substrates. The studies elucidate the post-hydroxylation rearrangements of the hydroxylated intermediates of 5eyC and 5vC to ketene and 5-formylmethylcytosine (5fmC), respectively, and hydrolysis of hemiaminal intermediate of 4mC to formaldehyde and unmodified cytosine proceed exclusively in aqueous solution outside of the enzyme environment. Overall, the studies show that the chemical nature of the unnatural alkylated cytosine substrates exercises distinct effects on the binding interactions, reaction mechanism, and dynamics of TET2.

D-2-Hydroxyglutarate in Glioma Biology

Isocitrate dehydrogenase (IDH) mutations are common genetic abnormalities in glioma, which result in the accumulation of an "oncometabolite", D-2-hydroxyglutarate (D-2-HG). Abnormally elevated D-2-HG levels result in a distinctive pattern in cancer biology, through competitively inhibiting α-ketoglutarate (α-KG)/Fe(II)-dependent dioxgenases (α-KGDDs). Recent studies have revealed that D-2-HG affects DNA/histone methylation, hypoxia signaling, DNA repair, and redox homeostasis, which impacts the oncogenesis of IDH-mutated cancers. In this review, we will discuss the current understanding of D-2-HG in cancer biology, as well as the emerging opportunities in therapeutics in IDH-mutated glioma.

Targeting DNA Repair Pathways in Hematological Malignancies

DNA repair plays an essential role in protecting cells that are repeatedly exposed to endogenous or exogenous insults that can induce varying degrees of DNA damage. Any defect in DNA repair mechanisms results in multiple genomic changes that ultimately may result in mutation, tumor growth, and/or cell apoptosis. Furthermore, impaired repair mechanisms can also lead to genomic instability, which can initiate tumorigenesis and development of hematological malignancy. This review discusses recent findings and highlights the importance of DNA repair components and the impact of their aberrations on hematological malignancies.

A chromatin perspective on metabolic and genotoxic impacts on hematopoietic stem and progenitor cells

Fate determination in self-renewal and differentiation of hematopoietic stem and progenitor cells (HSCs and HPCs) is ultimately controlled by gene expression, which is profoundly influenced by the global and local chromatin state. Cellular metabolism directly influences the chromatin state through the dynamic regulation of the enzymatic activities that modify DNA and histones, but also generates genotoxic metabolites that can damage DNA and thus pose threat to the genome integrity. On the other hand, mechanisms modulating the chromatin state impact metabolism by regulating the expression and activities of key metabolic enzymes. Moreover, through regulating either DNA damage response directly or expression of genes involved in this process, chromatin modulators play active and crucial roles in guarding the genome integrity, breaching of which results in defective HSPC function. Therefore, HSPC function is regulated by the dynamic and two-way interactions between metabolism and chromatin. Here, we review recent advances that provide a chromatin perspective on the major impacts the metabolic and genotoxic factors can have on HSPC function and fate determination.

Direct observation and analysis of TET-mediated oxidation processes in a DNA origami nanochip

DNA methylation and demethylation play a key role in the epigenetic regulation of gene expression; however, a series of oxidation reactions of 5-methyl cytosine (5mC) mediated by ten-eleven translocation (TET) enzymes driving demethylation process are yet to be uncovered. To elucidate the relationship between the oxidative processes and structural factors of DNA, we analysed the behavior of TET-mediated 5mC-oxidation by incorporating structural stress onto a substrate double-stranded DNA (dsDNA) using a DNA origami nanochip. The reactions and behaviors of TET enzymes were systematically monitored by biochemical analysis and single-molecule observation using atomic force microscopy (AFM). A reformative frame-like DNA origami was established to allow the incorporation of dsDNAs as 5mC-containing substrates in parallel orientations. We tested the potential effect of dsDNAs present in the tense and relaxed states within a DNA nanochip on TET oxidation. Based on enzyme binding and the detection of oxidation reactions within the DNA nanochip, it was revealed that TET preferred a relaxed substrate regardless of the modification types of 5-oxidated-methyl cytosine. Strikingly, when a multi-5mCG sites model was deployed to further characterize substrate preferences of TET, TET preferred the fully methylated site over the hemi-methylated site. This analytical modality also permits the direct observations of dynamic movements of TET such as sliding and interstrand transfer by high-speed AFM. In addition, the thymine DNA glycosylase-mediated base excision repair process was characterized in the DNA nanochip. Thus, we have convincingly established the system's ability to physically regulate enzymatic reactions, which could prove useful for the observation and characterization of coordinated DNA demethylation processes at the nanoscale.

TET2 is involved in DNA hydroxymethylation, cell proliferation and inflammatory response in keratinocytes

DNA methylation and hydroxymethylation are the most common epigenetic modifications associated with the cell cycle and the inflammatory response. The present study aimed to investigate the role of 5-hydroxymethyl-cytosine (5-hmC) and ten-eleven translocation-2 (TET2) in keratinocytes. Following TET2 knockdown, dot blot analysis was performed to assess the levels of 5-hmC in keratinocytes, using HaCaT cells. Subsequently, the viability and cell cycle of HaCaT cells were assessed by MTT, Cell Counting Kit-8 assay and flow cytometric assays. Cyclin-dependent kinase inhibitor 2A and proinflammatory cytokine protein and mRNA expression levels were also detected. The present results suggested that TET2 may play an important role in regulating cellular proliferation by mediating DNA hydroxymethylation in HaCaT cells. In addition, TET2 knockdown decreased the production of proinflammatory cytokines, including lipocalin 2, S100 calcium binding protein A7, matrix metallopeptidase 9, C-X-C motif chemokine ligand 1, interferon regulatory factor 7 and interleukin-7 receptor. The present study suggested that TET2 regulated cell viability, apoptosis and the expression of inflammatory mediators in keratinocytes. Collectively, the results indicated that TET2 knockdown may relieve inflammatory responses in the skin.

Altering chromatin methylation patterns and the transcriptional network involved in regulation of hematopoietic stem cell fate

Hematopoietic stem cells (HSCs) are quiescent cells with self-renewal capacity and potential multilineage development. Various molecular regulatory mechanisms such as epigenetic modifications and transcription factor (TF) networks play crucial roles in establishing a balance between self-renewal and differentiation of HSCs. Histone/DNA methylations are important epigenetic modifications involved in transcriptional regulation of specific lineage HSCs via controlling chromatin structure and accessibility of DNA. Also, TFs contribute to either facilitation or inhibition of gene expression through binding to enhancer or promoter regions of DNA. As a result, epigenetic factors and TFs regulate the activation or repression of HSCs genes, playing a central role in normal hematopoiesis. Given the importance of histone/DNA methylation and TFs in gene expression regulation, their aberrations, including changes in HSCs-related methylation of histone/DNA and TFs (e.g., CCAAT-enhancer-binding protein α, phosphatase and tensin homolog deleted on the chromosome 10, Runt-related transcription factor 1, signal transducers and activators of transcription, and RAS family proteins) could disrupt HSCs fate. Herewith, we summarize how dysregulations in the expression of genes related to self-renewal, proliferation, and differentiation of HSCs caused by changes in epigenetic modifications and transcriptional networks lead to clonal expansion and leukemic transformation.

Mitochondria in the signaling pathways that control longevity and health span

Genetic and pharmacological intervention studies have identified evolutionarily conserved and functionally interconnected networks of cellular energy homeostasis, nutrient-sensing, and genome damage response signaling pathways, as prominent regulators of longevity and health span in various species. Mitochondria are the primary sites of ATP production and are key players in several other important cellular processes. Mitochondrial dysfunction diminishes tissue and organ functional performance and is a commonly considered feature of the aging process. Here we review the evidence that through reciprocal and multilevel functional interactions, mitochondria are implicated in the lifespan modulation function of these pathways, which altogether constitute a highly dynamic and complex system that controls the aging process. An important characteristic of these pathways is their extensive crosstalk and apparent malleability to modification by non-invasive pharmacological, dietary, and lifestyle interventions, with promising effects on lifespan and health span in animal models and potentially also in humans.

Benzene metabolites trigger pyroptosis and contribute to haematotoxicity via TET2 directly regulating the Aim2/Casp1 pathway

Background

Long term low-dose benzene exposure leads to the inhibition of haematopoiesis. However, the underlying mechanisms remained poorly defined, especially mediated by early effector molecules.

Methods

Here, we first found in mRNA microarray that pyroptotic classic genes (Casp1, 4, 5, and IL1β) were up-regulated and represented dose-dependent differential expression in controls, low-dose benzene-exposed and chronic benzene-poisoned workers, and the expression of Casp1 and IL1β were confirmed in low-dose benzene-exposed workers and was accompanied with elevated potent proinflammatory IL1β. In vitro studies showed that benzene metabolites induced AHH-1 cell pyroptosis through activating Aim2/Casp1 pathway with the increased expression of GSDMD. Meanwhile, TET2 overexpression was elevated in vivo and in vitro and it was positively correlated with IL1β. Further, we verified that pyroptosis caused by 1,4-BQ could be ameliorated in vitro by RNAi or pretreatment with Dimethyloxalylglycine (DMOG), the inhibitor of TET2.

Findings

Exposure to benzene can trigger pyroptosis via TET2 directly regulating the Aim2/Casp1 signaling pathway to cause haematotoxicity.

Interpretation

Benzene metabolites induced pyroptotic cell death through activation of the Aim2/Casp1 pathway which can be regulated by Tet2 overexpression. Tet2 may be a potential risk factor and is implicated in the development of benzene-related diseases.

Fund

National Natural Science Foundation of China; the Support Project of High–level Teachers in Beijing Municipal Universities in the Period of 13th Five–year Plan; Beijing Natural Science Foundation Program and Scientific Research Key Program of Beijing Municipal Commission of Education.

TET2 Function in Hematopoietic Malignancies, Immune Regulation, and DNA Repair

Over the last decade, investigation of Ten-Eleven Translocation 2 (TET2) gene function and TET2 mutation have become of increasing interest in the field of hematology. This heightened interest was sparked by the seminal discoveries that (1) TET2 mutation is associated with development of hematological malignancies and that (2) the TET family of proteins is critical in promoting DNA demethylation and immune homeostasis. Since then, additional studies have begun to unravel the question “Does TET2 have additional biological functions in the regulation of hematopoiesis?” Here, we present a mini-review focused on the current understanding of TET2 in hematopoiesis, hematological malignancies, and immune regulation. Importantly, we highlight the critical function that TET2 facilitates in maintaining the stability of the genome. Based on our review of the literature, we provide a new hypothesis that loss of TET2 may lead to dysregulation of the DNA repair response, augment genome instability, and subsequently sensitize myeloid leukemia cells to PARP inhibitor treatment.

DNA Modifications: Naturally More Error Prone?

Epigenetic DNA modifications are essential for normal cell function in vertebrates, but they can also be hotspots of mutagenesis. Methylcytosine in particular has long been known to be less stable than other nucleotides and spontaneously deaminates to thymine. Beyond this well-established phenomenon, however, the influence of epigenetic marks on mutagenesis has recently become an active field of investigation. In this review, we summarize current knowledge of the interactions between different DNA modifications and other mutagenic processes. External mutagens, such as UV light or smoking carcinogens, affect modified cytosines differently from unmodified ones, and modified cytosine can in some cases be protective rather than mutagenic. Notably, cell-intrinsic processes, such as DNA replication, also appear to influence the mutagenesis of modified cytosines. Altogether, evidence is accumulating to show that epigenetic changes have a profound influence on tissue-specific mutation accumulation.

Consequences of mutant TET2 on clonality and subclonal hierarchy

Somatic mutations in TET2 are common in myelodysplastic syndromes (MDS), myeloproliferative, and overlap syndromes. TET2 mutant (TET2^MT) clones are also found in asymptomatic elderly individuals, a condition referred to as clonal hematopoiesis of indeterminate potential (CHIP). In various entities of TET2^MT neoplasia, we examined the phenotype in relation to the strata of TET2 hits within the clonal hierarchy. Using deep sequencing, 1781 mutations were found in 1205 of 4930 patients; 40% of mutant cases were biallelic. Hierarchical analysis revealed that of TET2^MT cases >40% were ancestral, e.g., representing 8% of MDS. Higher (earlier) TET2 lesion rank within the clonal hierarchy (greater clonal burden) was associated with impaired survival. Moreover, MDS driven by ancestral TET2^MT is likely derived from TET2^MT CHIP with a penetrance of ~1%. Following ancestral TET2 mutations, individual disease course is determined by secondary hits. Using multidimensional analyses, we demonstrate how hits following the TET2 founder defect induces phenotypic shifts toward dysplasia, myeloproliferation, or progression to AML. In summary, TET2^MT CHIP-derived MDS is a subclass of MDS that is distinct from de novo disease.

The Ageing Brain: Effects on DNA Repair and DNA Methylation in Mice

Base excision repair (BER) may become less effective with ageing resulting in accumulation of DNA lesions, genome instability and altered gene expression that contribute to age-related degenerative diseases. The brain is particularly vulnerable to the accumulation of DNA lesions; hence, proper functioning of DNA repair mechanisms is important for neuronal survival. Although the mechanism of age-related decline in DNA repair capacity is unknown, growing evidence suggests that epigenetic events (e.g., DNA methylation) contribute to the ageing process and may be functionally important through the regulation of the expression of DNA repair genes. We hypothesize that epigenetic mechanisms are involved in mediating the age-related decline in BER in the brain. Brains from male mice were isolated at 3-32 months of age. Pyrosequencing analyses revealed significantly increased Ogg1 methylation with ageing, which correlated inversely with Ogg1 expression. The reduced Ogg1 expression correlated with enhanced expression of methyl-CpG binding protein 2 and ten-eleven translocation enzyme 2. A significant inverse correlation between Neil1 methylation at CpG-site2 and expression was also observed. BER activity was significantly reduced and associated with increased 8-oxo-7,8-dihydro-2'-deoxyguanosine levels. These data indicate that Ogg1 and Neil1 expression can be epigenetically regulated, which may mediate the effects of ageing on DNA repair in the brain.