Association of the C-285T and A5954G polymorphisms in the DNA repair gene OGG1 with the susceptibility of rheumatoid arthritis

Effects of Human Leukocyte Antigen DRB1 Genetic Polymorphism on Anti-Cyclic Citrullinated Peptide (ANTI-CCP) and Rheumatoid Factor (RF) Expression in Rheumatoid Arthritis (RA) Patients

Rheumatoid arthritis (RA) is a systemic disease characterized by non-infectious inflammation of the joints and surrounding tissues, which can cause severe health problems, affect the patient's daily life, and even cause death. RA can be clinically diagnosed by the occurrence of blood serological markers, rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (anti-CCP). However, about 20% of RA patients exhibit negative results for both markers, which makes RA diagnosis difficult and, therefore, may delay the effective treatment. Previous studies found some evidence that human leukocyte antigen (HLA)-related genes might be the susceptibility genes for RA and their polymorphisms might contribute to varieties of susceptibility and disease severity. This study aimed for the genetic polymorphisms of the RA patient genome and their effects on the RA patient's serological makers, RF and anti-CCP. A total of 4580 patients' electronic medical records from 1992 to 2020 were retrieved from the China Medical University Hospital database. The most representative single-nucleotide polymorphisms (SNPs) were identified through a genome-wide association study (GWAS) followed by enzyme-linked immunosorbent assay (ELISA) validation using the blood from 30 additional RA patients. The results showed significant changes at the position of chromosome 6 with rs9270481 being the most significant locus, which indicated the location of the HLA-DRB1 gene. Further, patients with the CC genotype at this locus were more likely to exhibit negative results for RF and anti-CCP than those with the TT genotype. The C allele was also more likely to be associated with negative results for RF and anti-CCP. The results demonstrated that a genetic polymorphism at rs9270481 affected the expression of RF and anti-CCP in RA patients, which might indicate the necessity to develop a personalized treatment plan for each individual patient based on the genetic profile.

Polymorphisms in DNA Repair Genes and Association with Rheumatoid Arthritis in a Pilot Study on a Central European Population

Rheumatoid arthritis (RA) is a chronic, multifactorial autoimmune disease characterized by chronic arthritis, a tendency to develop joint deformities, and involvement of extra-articular tissues. The risk of malignant neoplasms among patients with RA is the subject of ongoing research due to the autoimmune pathogenesis that underlies RA, the common etiology of rheumatic disease and malignancies, and the use of immunomodulatory therapy, which can alter immune system function and thus increase the risk of malignant neoplasms. This risk can also be increased by impaired DNA repair efficiency in individuals with RA, as reported in our recent study. Impaired DNA repair may reflect the variability in the genes that encode DNA repair proteins. The aim of our study was to evaluate the genetic variation in RA within the genes of the DNA damage repair system through base excision repair (BER), nucleotide excision repair (NER), and the double strand break repair system by homologous recombination (HR) and non-homologous end joining (NHEJ). We genotyped a total of 28 polymorphisms in 19 genes encoding DNA repair-related proteins in 100 age- and sex-matched RA patients and healthy subjects from Central Europe (Poland). Polymorphism genotypes were determined using the Taq-man SNP Genotyping Assay. We found an association between the RA occurrence and rs25487/XRCC1, rs7180135/RAD51, rs1801321/RAD51, rs963917/RAD51B, rs963918/RAD51B, rs2735383/NBS1, rs132774/XRCC6, rs207906/XRCC5, and rs861539/XRCC3 polymorphisms. Our results suggest that polymorphisms of DNA damage repair genes may play a role in RA pathogenesis and may be considered as potential markers of RA.

Inhibition of 8-oxoguanine DNA glycosylase (OGG1) expression suppresses polycystic ovarian syndrome via the NF-κB signaling pathway

It has been reported that oxidative stress and chronic inflammation may be involved in the pathogenesis of polycystic ovary syndrome (PCOS). 8-oxoguanine DNA glycosylase (OGG1) is the main glycosylase that catalyzes the excision of DNA oxidation products. In this study, we investigated the role and potential mechanisms of OGG1 in the development of PCOS. We first analyzed OGG1 levels in serum and follicular fluid (FF) of PCOS patients, and significantly elevated OGG1 levels were noted in PCOS patients. We similarly observed a significant upregulation of OGG1 expression levels in ovarian tissue of the dehydroepiandrosterone (DHEA)-induced PCOS rat model. In addition, increased apoptosis and increased production of reactive oxygen species (ROS) were observed after the addition of OGG1-specific inhibitor (TH5487) in human granulosa-like tumor cell line (KGN) cells following a concentration gradient, along with a significant decrease in mRNA levels of inflammatory factors such as CXCL2, IL-6, MCP1, IL-1β, and IL-18. Significant decreases in protein phosphorylation levels of P65 and IκBα were also observed in cells. In addition, we found a significant positive correlation between OGG1 and IL-6 expression levels in human and DHEA-induced PCOS rat models. In conclusion, our results suggest that OGG1 might be involved in the pathogenesis of PCOS by regulating the secretion of IL-6 through NF-κB signaling pathway, and there might be a balance between the inhibition of oxidative stress and the promotion of chronic inflammation by OGG1 on KGN cells.

Base Excision Repair in the Immune System: Small DNA Lesions With Big Consequences

The integrity of the genome is under constant threat of environmental and endogenous agents that cause DNA damage. Endogenous damage is particularly pervasive, occurring at an estimated rate of 10,000–30,000 per cell/per day, and mostly involves chemical DNA base lesions caused by oxidation, depurination, alkylation, and deamination. The base excision repair (BER) pathway is primary responsible for removing and repairing these small base lesions that would otherwise lead to mutations or DNA breaks during replication. Next to preventing DNA mutations and damage, the BER pathway is also involved in mutagenic processes in B cells during immunoglobulin (Ig) class switch recombination (CSR) and somatic hypermutation (SHM), which are instigated by uracil (U) lesions derived from activation-induced cytidine deaminase (AID) activity. BER is required for the processing of AID-induced lesions into DNA double strand breaks (DSB) that are required for CSR, and is of pivotal importance for determining the mutagenic outcome of uracil lesions during SHM. Although uracils are generally efficiently repaired by error-free BER, this process is surprisingly error-prone at the Ig loci in proliferating B cells. Breakdown of this high-fidelity process outside of the Ig loci has been linked to mutations observed in B-cell tumors and DNA breaks and chromosomal translocations in activated B cells. Next to its role in preventing cancer, BER has also been implicated in immune tolerance. Several defects in BER components have been associated with autoimmune diseases, and animal models have shown that BER defects can cause autoimmunity in a B-cell intrinsic and extrinsic fashion. In this review we discuss the contribution of BER to genomic integrity in the context of immune receptor diversification, cancer and autoimmune diseases.

Dual Inhibitors of 8-Oxoguanine Surveillance by OGG1 and NUDT1

Oxidative damage in DNA is one of the primary sources of mutations in the cell. The activities of repair enzymes 8-oxoguanine DNA glycosylase (OGG1) and human MutT Homologue 1 (NUDT1 or MTH1), which work together to ameliorate this damage, are closely linked to mutagenesis, genotoxicity, cancer, and inflammation. Here we have undertaken the development of small-molecule dual inhibitors of the two enzymes as tools to test the relationships between these pathways and disease. The compounds preserve key structural elements of known inhibitors of the two enzymes, and they were synthesized and assayed with recently developed luminescence assays of the enzymes. Further structural refinement of initial lead molecules yielded compound 5 (SU0383) with IC50(NUDT1) = 0.034 μM and IC50(OGG1) = 0.49 μM. The compound SU0383 displayed low toxicity in two human cell lines at 10 μM. Experiments confirm the ability of SU0383 to increase sensitivity of tumor cells to oxidative stress. Dual inhibitors of these two enzymes are expected to be useful in testing multiple hypotheses regarding the roles of 8-oxo-dG in multiple disease states.

Oxidized base 8-oxoguanine, a product of DNA repair processes, contributes to dendritic cell activation

A growing body of evidence suggests that elevated levels of reactive oxygen species (ROS) in the airways caused by exposure to gas phase pollutants or particulate matter are able to activate dendritic cells (DCs); however, the exact mechanisms are still unclear. When present in excess, ROS can modify macromolecules including DNA. One of the most abundant DNA base lesions is 7,8-dihydro-8-oxoguanine (8-oxoG), which is repaired by the 8-oxoguanine DNA glycosylase 1 (OGG1)-initiated base excision repair (BER) (OGG1-BER) pathway. Studies have also demonstrated that in addition to its role in repairing oxidized purines, OGG1 has guanine nucleotide exchange factor activity when bound to 8-oxoG. In the present study, we tested the hypothesis that exposure to 8-oxoG, the specific product of OGG1-BER, induces functional changes of DCs. Supporting our hypothesis, transcriptome analysis revealed that in mouse lungs, out of 95 genes associated with DCs' function, 22 or 42 were significantly upregulated after a single or multiple intranasal 8-oxoG challenges, respectively. In a murine model of allergic airway inflammation, significantly increased serum levels of ovalbumin (OVA)-specific IgE antibodies were detected in mice sensitized via nasal challenges with OVA+8-oxoG compared to those challenged with OVA alone. Furthermore, exposure of primary human monocyte-derived DCs (moDC) to 8-oxoG base resulted in significantly enhanced expression of cell surface molecules (CD40, CD86, CD83, HLA-DQ) and augmented the secretion of pro-inflammatory mediators IL-6, TNF and IL-8, whereas it did not considerably influence the production of the anti-inflammatory cytokine IL-10. The stimulatory effects of 8-oxoG on human moDCs were abolished upon siRNA-mediated OGG1 depletion. Collectively, these data suggest that OGG1-BER-generated 8-oxoG base-driven cell signaling activates DCs, which may contribute to initiation of both the innate and adaptive immune responses under conditions of oxidative stress.

Potent and Selective Inhibitors of 8-Oxoguanine DNA Glycosylase

The activity of DNA repair enzyme 8-oxoguanine DNA glycosylase (OGG1), which excises oxidized base 8-oxoguanine (8-OG) from DNA, is closely linked to mutagenesis, genotoxicity, cancer, and inflammation. To test the roles of OGG1-mediated repair in these pathways, we have undertaken the development of noncovalent small-molecule inhibitors of the enzyme. Screening of a PubChem-annotated library using a recently developed fluorogenic 8-OG excision assay resulted in multiple validated hit structures, including selected lead hit tetrahydroquinoline 1 (IC50 = 1.7 μM). Optimization of the tetrahydroquinoline scaffold over five regions of the structure ultimately yielded amidobiphenyl compound 41 (SU0268; IC50 = 0.059 μM). SU0268 was confirmed by surface plasmon resonance studies to bind the enzyme both in the absence and in the presence of DNA. The compound SU0268 was shown to be selective for inhibiting OGG1 over multiple repair enzymes, including other base excision repair enzymes, and displayed no toxicity in two human cell lines at 10 μM. Finally, experiments confirm the ability of SU0268 to inhibit OGG1 in HeLa cells, resulting in an increase in accumulation of 8-OG in DNA. The results suggest the compound SU0268 as a potentially useful tool in studies of the role of OGG1 in multiple disease-related pathways.

In Vitro Fluorogenic Real-Time Assay of the Repair of Oxidative DNA Damage

The repair of oxidative damage to DNA is essential to avoid mutations that lead to cancer. Oxidized DNA bases, such as 8-oxoguanine, are a main source of these mutations, and the enzyme 8-oxoguanine glycosylase 1 (OGG1) is the chief human enzyme that excises 8-oxoguanine from DNA. The activity of OGG1 has been linked to human inflammation responses and to cancer, and researchers are beginning to search for inhibitors of the enzyme. However, measuring the activity of the enzyme typically requires laborious gel-based measurements of radiolabeled DNAs. Here we report the design and properties of fluorogenic probes that directly report on the activity of OGG1 (and its bacterial homologue Fpg) in real time as the oxidized base is excised. The probes are short, modified DNA oligomers containing fluorescent DNA bases and are designed to utilize 8-oxoguanine itself as a fluorescence quencher. Screening of combinations of fluorophores and 8-oxoguanine revealed two fluorophores, pyrene and tCo, that are strongly quenched by the damaged base. We tested 42 potential probes containing these fluorophores: the optimum probe, OGR1, yields a 60-fold light-up signal in vitro with OGG1 and Fpg. It can report on oxidative repair activity in mammalian cell lysate and with bacterial cells overexpressing a repair enzyme. Such probes might prove useful in quantifying enzyme activity and performing competitive inhibition assays.

Effect of MPG gene rs2858056 polymorphism, copy number variation, and level of serum MPG protein on the risk for rheumatoid arthritis

OBJECTIVE

This study examined the role of SNP rs2858056 of the MPG gene on the incidence and severity of rheumatoid arthritis (RA).

METHODS

This cohort study enrolled 365 RA patients and 375 age- and gender-matched healthy controls, all of whom had Han Chinese ethnicity and were from Taiwan. Gene polymorphism of the SNP rs2858056 of MPG was determined from genomic DNA. Allelic frequencies and genotypes were compared among cases and controls. Quantitation of rs2858056 copy number variation (CNV) was determined. Serum samples from RA patients and controls were analyzed to determine serum levels of MPG. The relationship between rs2858056 polymorphism and clinical manifestations of RA was evaluated.

RESULTS

Our results indicated a statistically significant difference in genotype frequency distributions at rs2858056 for RA patients and controls (p = 0.05) and a significant difference in allelic frequency in patients and controls (p = 0.04). Furthermore, there was a significantly greater level of serum MPG protein in patients than controls (p < 0.001). However, the cases and controls had no significant differences in MPG CNV (p = 0.12). We also did not detect any association of the MPG rs2858056 with rheumatoid factor (RF), extraarticular involvement, or bone erosion in the RA patients.

CONCLUSION

Our study suggests that RA is associated with a polymorphism in the MPG gene (rs2858056) and increased serum level of the MPG protein.

Might there be a link between intron 3 VNTR polymorphism in the XRCC4 DNA repair gene and the etiopathogenesis of rheumatoid arthritis?

DNA repair genes are involved in several diseases such as cancers and autoimmune diseases. Previous studies indicated that a DNA repair system was involved in the development of rheumatoid arthritis (RA). In this study, we aimed to examine whether four polymorphisms in the DNA repair genes (xeroderma pigmentosum complementation group D [XPD], X-ray repair cross-complementing group 1 [XRCC1], and X-ray repair cross-complementing group 4 [XRCC4]) were associated with RA. Sixty-five patients with RA and 70 healthy controls (HCs) were examined for XPD (A-751G), XRCC1 (A399G), and XRCC4 (intron 3 VNTR and G-1394T) polymorphisms. All polymorphisms were genotyped by PCR and/or PCR-RFLP. The association between the polymorphisms and RA was analyzed using the chi-square test and de Finetti program. The intron 3 VNTR polymorphism in the XRCC4 gene showed an association with RA patients. The DI genotype was found lower in RA patients (χ(2)=8.227; p=0.0021), while the II genotype was higher in RA patients (χ(2)=5.285; p=0.010). There were deviations from the Hardy-Weinberg Equilibrium (HWE) in both intron 3 VNTR and G-1394T polymorphisms in the XRCC4 gene and in the polymorphism in the XRCC1 gene, and the observed genotype counts deviated from those expected according to the HWE (p=0.027, 0.004, and 0.002, respectively); however, there was no deviation in the other gene polymorphisms. There is no statistical difference between the RA patients and HCs for XPD (A-751G), XRCC1 (A399G), and XRCC4 (G-1394T) gene polymorphisms (p>0.05). Although XPD (A-751G), XRCC1 (A399G), and XRCC4 (G-1394T) gene polymorphisms have been extensively investigated in different clinical pictures, this is the first study to evaluate the role of these polymorphisms in the genetic etiopathogenesis of RA in Turkish patients. In conclusion, we suggested that the intron 3 VNTR polymorphism in the XRCC4 gene may be associated with the etiopathogenesis of RA as a marker of immune aging.

Association between XRCC3 Thr241Met SNP and systemic lupus erythematosus in Han Chinese patients in Taiwan, and a meta-analysis of healthy populations

BACKGROUND

X-ray repair cross-complementing group 3 (XRCC3) plays a crucial role in mammalian DNA repair processes. The polymorphism of XRCC3, rs861539 (Thr > Met at codon 241), is common in populations worldwide. This study analyzed the relationship between this functional single nucleotide polymorphism and systemic lupus erythematosus (SLE) in the Han Chinese population in Taiwan (HC-TW).

METHODS

Genotyping was performed using polymerase chain reaction restriction fragment length polymorphism on 163 SLE patients and 191 healthy participants in the control group.

RESULTS

The data showed that the genotype frequency at codon 241 did not differ significantly between the SLE patients and the healthy participants in the control group; however, the allele frequency analysis indicated a significant difference between these groups. In addition, we used the genotype and allele frequencies of 191 healthy HC-TW participants for comparison with HapMap populations. The results indicated a significant difference of XRCC3 Thr241Met allele and genotype frequencies between the HC-TW population and HapMap populations, except for the other Han Chinese populations. A prior study showed that Thr241 > Met substitution in XRCC3 protein was positive as damaging and functional consequences as well.

CONCLUSION

This is the first study to demonstrate the difference of XRCC3 Thr241 > Met variant between the HC-TW population and HapMap population.