DNA methylation and its influence on the pathogenesis of osteoarthritis: a systematic literature review

in EFORT Open Reviews
Authors:
Thomas Nau Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, UAE
King’s College London Hospital, Dubai, UAE
Ludwig Boltzmann Institute of Traumatology, Vienna, Austria

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https://orcid.org/0000-0003-4654-2991
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Samira Cutts King’s College London Hospital, Dubai, UAE

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Nerissa Naidoo Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, UAE

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Correspondence should be addressed to T Nau: thnau@hotmail.com
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Purpose

  • Evolving evidence demonstrates the role of epigenetics in the pathogenesis of osteoarthritis (OA), whereas in terms of mechanism, DNA methylation has received the highest attention thus far. This systematic review summarizes the current knowledge of DNA methylation and its influence on the pathogenesis of OA.

Methods

  • A protocol in alignment with the PRISMA guidelines was employed to systematically review eight bibliographic databases between 1 January 2015 and 31 January 2021, to identify associations between DNA methylation and articular chondrocytes in OA.

Results

  • We identified 23 gene-specific studies and 28 genome-wide methylation analyses. Gene-specific studies focused on pro-inflammatory markers in OA, demonstrating that DNA hypomethylation in the promoter region results in overexpression and hypermethylation is linked to gene silencing. Others reported on the association between OA risk genes and DNA methylation. Genome-wide methylation studies reported on differentially methylated regions (DMRs) comparing OA and non-OA chondrocytes. DMRs were seen in hip OA and knee OA chondrocytes.

Conclusion

  • The current body of literature demonstrates the potential and crucial role of DNA methylation in the pathogenesis and progression of OA. This knowledge contributes to the understanding of the pathomechanisms behind OA at gene-specific and genome-wide levels. The observed differences in DNA methylation between healthy and diseased tissues indicate the occurrence of changes in DNA methylation. Based on this, future research in this field that explores the characteristics of potentially reversible changes in DNA methylation may lead to opportunities for causative treatment options for OA.

Abstract

Purpose

  • Evolving evidence demonstrates the role of epigenetics in the pathogenesis of osteoarthritis (OA), whereas in terms of mechanism, DNA methylation has received the highest attention thus far. This systematic review summarizes the current knowledge of DNA methylation and its influence on the pathogenesis of OA.

Methods

  • A protocol in alignment with the PRISMA guidelines was employed to systematically review eight bibliographic databases between 1 January 2015 and 31 January 2021, to identify associations between DNA methylation and articular chondrocytes in OA.

Results

  • We identified 23 gene-specific studies and 28 genome-wide methylation analyses. Gene-specific studies focused on pro-inflammatory markers in OA, demonstrating that DNA hypomethylation in the promoter region results in overexpression and hypermethylation is linked to gene silencing. Others reported on the association between OA risk genes and DNA methylation. Genome-wide methylation studies reported on differentially methylated regions (DMRs) comparing OA and non-OA chondrocytes. DMRs were seen in hip OA and knee OA chondrocytes.

Conclusion

  • The current body of literature demonstrates the potential and crucial role of DNA methylation in the pathogenesis and progression of OA. This knowledge contributes to the understanding of the pathomechanisms behind OA at gene-specific and genome-wide levels. The observed differences in DNA methylation between healthy and diseased tissues indicate the occurrence of changes in DNA methylation. Based on this, future research in this field that explores the characteristics of potentially reversible changes in DNA methylation may lead to opportunities for causative treatment options for OA.

Introduction

Osteoarthritis (OA) is the most common joint disease and affects an estimated 10–12% of the adult population worldwide (1). Chronic joint pain, stiffness, reduced range of motion and a variable degree of joint inflammation are the consequences of articular cartilage degeneration, resulting in joint space narrowing, osteophyte formation and subchondral sclerosis (2). Despite the high prevalence and burden of disease, the etiology and pathophysiology of OA are still not fully understood, and so far, no modifying or curative agents have been approved.

OA leads to a progressive loss of articular cartilage, which occurs mainly in load-bearing joints, and thus was long considered a ‘wear and tear’ type of condition over time (3). Other than that, age, obesity and genetic susceptibility were named as the main risk factors.

More recently, a growing number of studies have demonstrated a genetic, genomic and epigenetic role in the pathogenesis of OA (4, 5). Genome-wide association studies are increasingly giving insights into diseases, and significant OA genetic risk loci have been identified. While up to 2017, only 19 OA loci were reported, with the increase in large-scale, well-powered studies and meta-analyses, the number of identified OA genetic risk loci is constantly growing (5).

However, there is an evolving body of evidence that demonstrates the role of epigenetic mechanisms in the pathogenesis of OA. Epigenetics is defined as the study of biological mechanisms that control gene expression without changing the underlying DNA sequence. In general, epigenetic modifications remain as cells divide and can be inherited through generations (6). While epigenetic changes are essential for normal development, aging and health, they can also contribute to diseases and age-related conditions, including OA, usually by abnormal silencing or activation of genes.

These epigenetic mechanisms include changes in DNA methylation, histone modifications and noncoding RNAs, whereas, in relation to OA, DNA methylation certainly has been given the highest attention thus far.

DNA methylation is a chemical process in which a methyl group is added to DNA. This process happens in regions where a cytosine nucleotide is located next to a guanine nucleotide and linked by a phosphate, the so-called CpG sites (7). The process is facilitated by enzymes called DNA methyltransferases. DNA methylation plays an important role in many cellular processes, including embryonic development, preservation of genomic stability, aging and carcinogenesis. In mammals, methylation is found rather sparsely throughout the entire genome, with the exception of CpG islands, which are regions with a high frequency of CpG sites (around 1 kb in length) in promoter and enhancer regions. DNA methylation in promoter and enhancer regions usually results in gene silencing, whereas hypermethylation in the gene body is associated with an increased gene expression. Throughout life, DNA methylation is an important process to ensure cell-specific gene expression, so cells from different tissues have a specific methylation pattern (1). To better understand the role of DNA methylation, sequencing-based DNA methylation profiling has recently been introduced, in order to assess and compare these modifications in a genome-wide fashion (8). Such methylome analyses provide unprecedented opportunities to study individual patterns of healthy and diseased tissue and cells. Methylated DNA can be actively or passively demethylated, which may result in an increased gene expression.

This systematic review aims to summarize the current knowledge of DNA methylation and its influence on the pathogenesis of OA. The epigenetic regulation of gene expression in articular cartilage, in the healthy and degenerated state, will be discussed in detail. Finally, we will present novel diagnostic and therapeutic approaches that may consequently be developed.

Methods

This review was conducted using a protocol in alignment with the PRISMA guidelines (9). Eight bibliographic databases (MEDLINE (Ovid), Embase, Web of Science, Scopus, PubMed, CINAHL (EBSCOhost), Cochrane Central and Google Scholar) were searched between 1 January 2015 and 31 December 2023, to ensure the focus remained on new insights gained in DNA methylation and OA. No language restrictions were placed on the search. The search strategy combined the following MeSH terms related to exposure and outcomes: ((osteoarthritis or degenerative joint disease or inflammatory disease or joint disorder) and (epigenetic or epigenetic mechanisms or epigenome or DNA Methylation) and (gene expression or genomics or genomic)). No restrictions were placed on participant/subject type (humans/animals). Following the elimination of duplicate articles, potentially relevant citations were identified.

Study selection and inclusion criteria

Published studies were eligible to be included if they described an association between epigenetic markers, gene-specific or genome-wide DNA methylation, of articular chondrocytes and OA. Two independent reviewers screened the retrieved titles and abstracts and selected eligible studies. In case of disagreement, a third reviewer was consulted. Full texts were selected from studies that satisfied all selection criteria. Subsequently, the selected studies were divided into two groups: ‘gene-specific’ and ‘genome-wide’.

Data extraction

Data extraction was performed by two independent researchers using a standardized data collection form, in which the following items were recorded: study design, study population/cell source, sample size, site of collection, type of epigenetic markers used and tool used for DNA methylation analysis.

Risk-of-bias assessment and methodological quality (Supplementary Table 3)

The potential risk of bias in this systematic review was minimized, as we had two independent assessors who employed rigorous selection criteria to include the relevant studies. We employed the ROBINS-E tool for non-randomized observational studies to critically appraise the quality of the included studies and to account for any potential bias (10).

Results

A flow diagram is presented in Fig. 1. We identified 23 trials as ‘gene-specific’ and 28 trials as ‘genome-wide’ analyses. A chronological overview covering the 7-year observation period for both types of studies is shown in Supplementary Tables 1 and 2 (see section on Supplementary materials given at the end of the article).

Figure 1
Figure 1

PRISMA systematic review flow diagram of study selection (adapted from 9).

Citation: EFORT Open Reviews 10, 2; 10.1530/EOR-22-0088

Gene-specific studies

The earlier studies (2015–2017) focused mostly on the expression of inflammatory markers that are known to be involved in OA. Takahashi and coworkers (11) demonstrated the role of DNA methylation in the expression of IL8 in human chondrocytes. The IL8 expression in OA chondrocytes was 37 times higher than in non-OA controls. Three CpG sites in the promoter region of IL8 were significantly demethylated in OA patients. They also found that in vitro methylation decreased IL8 promoter activity. Papathanasiou et al. (12) studied DNA methylation on sclerostin (SOST) in OA chondrocytes. SOST expression was upregulated in OA with the CpG region of the SOST promoter being hypomethylated. 5-AzadC treatment of normal chondrocytes led to hypomethylation and SOST upregulation. Bomer et al. (13) reported on the influence of DNA methylation on the deiodinase iodothyronine type 2 (DIO2) gene, which is known to be a susceptibility gene in human OA. The gene product plays a role in thyroid hormone conversion, T4 to T3, which signals hypertrophy of growth plate chondrocytes and the stepwise mineralization and bone formation. Hypertrophic chondrocytes in OA show similar signals, and thus, it is believed that age and disease may result in reactivation of these genes involved in endochondral ossification, leading to cartilage loss and mineralization. In their study, an in vitro chondrogenesis model was used to explore the epigenetic control of DIO2. OA chondrocytes showed an upregulated DIO2 expression compared to healthy cartilage, with several CpG dinucleotides to be differentially methylated and a positive correlation between methylation and DIO2 expression. Interestingly, this was mainly seen in carriers of the risk allele. The in vitro chondrogenesis of mesenchymal stem cells with DIO2 overexpression resulted in a reduced expression of cartilage proteins (COL2A1 and ACAN) and an increased expression of OA markers (MMP13, RUNX2 and ADAMTS5). In contrast, inhibiting DIO2 resulted in prolonged healthy cartilage homeostasis. The authors concluded that the combination of genetic predisposition and loss of epigenetic silencing of DIO2 may lead to increased risk of OA. Zhang et al. (14) studied the role of transcription factor NFAT1 in regulating gene expression in chondrocytes of aged mice. NFAT1 was significantly reduced after 12 months of age, which was associated with a decreased expression of chondrocyte markers and decreased proteoglycan staining. Forced NFAT1 expression was able to reverse these changes in chondrocytes of aged mice. de Andrés et al. (15) studied the methylation of the nuclear factor-kB enhancer region of the inducible nitric oxide synthase (iNOS) and its role in OA induction. In vitro demethylation of the NF-kB enhancer region resulted in iNOS overexpression. This led to an altered cell cycle regulation and a pathogenic phenotype of daughter cells. In contrast, hypermethylation of the enhancer region was able to reduce these pro-inflammatory changes and may be a target for therapy in OA. Takahashi et al. (16) demonstrated the influence of the methylation status of the RUNX2 promoter on RUNX2-driven MMP13 expression in OA chondrocytes. OA chondrocytes showed a significant correlation between MMP13 levels and RUNX2 expression, independent of the MMP13 promoter methylation status. RUNX2 promoter methylation was negatively correlated with RUNX2 expression. Deep-layer chondrocytes in comparison with superficial chondrocytes showed an increased RUNX2 expression. They concluded that RUNX2 transcription is regulated by the methylation status of its promoter region and, by this, influences the expression of MMP13, which is a major contributor to cartilage degradation in OA. Li et al. (17) reviewed the MMP13 regulatory network and its role in early OA. They mentioned that DNA hypomethylation in the promoter region results in an increased expression and this may be a possible direct target for therapy in early stages of OA. During the more recent years (2018–2021), we saw an increasing study focus on the genetic/epigenetic interplay, analyzing OA risk loci and DNA methylation. Rice et al. (18) reported a new methylation-dependent RUNX2 regulatory region associated with OA risk. Based on previously observed correlations between a certain genotype and a differentially methylated region (DMR) close to the RUNX2 and SUPT3H gene, a detailed characterization of the DMR and its regulatory effect on RUNX2 was done using joint tissues of OA patients. The OA-associated single nucleotide polymorphism (SNP) rs10948172 showed a strong correlation with methylation, and two intergenic SNPs within the DMR had genetic and epigenetic effects on the activity of the region. They concluded that the modulation of methylation of the regulatory region and its impact on the expression of the targeted RUNX2 gene represent an important OA signal. Becerra et al. (19) studied DNA methylation and its effects on PHLPP1 promoter activity in chondrocytes. PHLPP1 is an important enzyme for chondrocyte function, and altered levels are seen in OA. DNA methylation resulted in a low expression of PHLPP1 and demethylation of the promoter region led to overexpression. In 2019, Papathanasiou et al. (20) reported on the regulation of miR-140-5p and miR-146a in OA via DNA methylation. Hypermethylation in miR-140 and miR-146a regulatory regions led to downregulation in OA chondrocytes and synoviocytes, whereas induced demethylation resulted in upregulation of miR-140 and miR-146a. MiR-140 and MiR-146a are known to play a vital role in cartilage homeostasis and are downregulated in OA. In 2020, Zhang et al. (21) presented an investigation of methylation levels of the miR34a gene in chondrocytes of OA patients and healthy subjects. They identified an interplay between small nuclear RNA host gene 9 (SNHG9) and miR34a, which is a regulator of apoptosis in OA. SNHG9 was downregulated in OA, but its induced overexpression in OA chondrocytes led to downregulation of miR-34a via DNA hypermethylation, resulting in decreased apoptosis of chondrocytes, a mechanism interpreted as a potential target for treating OA. In 2021, Zhang et al. (22) reported on the epigenetic manifestations of TNF and the pathogenesis of OA. Compared to healthy controls, OA chondrocytes showed overexpression of TNF with DNA hypomethylation in its promoter region. Increasing the DNA methylation in the promoter region resulted in suppression of TNF. Kehayova et al. (23) studied the interplay between the OA-associated SNP rs11583641 and the COLGALT2 expression, which encodes an enzyme for glycosylation of collagen. This genotype correlated with DNA methylation in the enhancer, and targeted methylation and demethylation led to altered COLGALT2 expression. Rice et al. (24) demonstrated the genetic and epigenetic mechanisms in TGFB1 expression in OA chondrocytes. The OA risk SNP rs75621460 is located in the TGFB1 enhancer region and influenced TGFB1 expression by DNA methylation within the enhancer region. Lv et al. (25) studied the regulatory mechanisms of the protective factor Gsk3b and the pro-inflammatory factor Nr4a3 in posttraumatic OA (PTOA). Gsk3B was downregulated in PTOA chondrocytes. In a mouse model, the authors showed that Gsk3b alleviated the PTOA changes by recruiting DNMT1 to the Nr4a3 promoter region to promote methylation and consequent inhibition of Nr4a3 expression (25). Papageorgiou et al. (26) reported on the downregulation of the anti-aging factor SIRT1 expression in human OA chondrocytes. DNA hypermethylation of the promoter region was found in OA, and treatment with 5-AzadC resulted in demethylation and SIRT1 upregulation. Zhang et al. (27) demonstrated the effect of the chemical triclocarban (TCC) on zebrafish cartilage and human chondrocytes. TCC caused OA in the zebrafish anal fin and suppressed type II collagen in chondrocytes. TCC stimulated the expression of DNMT1, which led to hypermethylation of the type II collagen-coding gene. Kehayova et al. (28) showed that COLGALT2, which encodes an enzyme that leads to glycosylation of collagen, is a target of the OA risk locus rs1046934 in human chondrocytes. The effect was mediated by DNA methylation changes within the COLGALT2 enhancer region and increased gene expression. The same group reported a similar effect for the OA risk locus rs11583641. In another study, Kehayova et al. (29) demonstrated that DNA methylation and gene expression have opposing effects between chondrocytes and synovium. The OA risk locus rs11583641 was associated with DNA methylation and COLGALT2 expression, but unlike in chondrocytes, these changes led to a decreased expression of COLGALT2.

Genome-wide studies

Rushton et al. (30) presented a study linking the OA susceptibility loci, known at that time, with genome-wide methylation to see if the known OA susceptibility loci actually regulate gene expression by DNA methylation. Sixteen gene loci were assessed and combined with genome-wide methylation data from cartilage of 99 patients, 80 of them with OA and 19 without OA. Four loci were initially identified that correlated with methylation. Looking in detail, it was seen that methylation levels in these areas were lower in non-OA patients, but there was no difference between knee and hip OA patients. The same group reported another genome-wide methylation study in which two clusters of hip OA patients, defined by different methylation patterns of inflammatory genes and the consequent effects on gene expression, were evaluated (31). One of the OA clusters showed promoter hypomethylation and increased expression of inflammatory markers IL1A and TNF. By that, they could identify a subgroup of hip OA patients that is epigenetically and transcriptomically characterized by an inflammatory phenotype. den Hollander et al. (32) were the first to report on combined genetic, epigenomic and transcriptomic data to better understand joint-independent DNA methylation changes during OA progression. They could identify cartilage-specific genes, primarily active during development, involved in OA progression, using gene expression data and DNA methylation data in healthy and diseased tissues. Aref-Eshghi et al. (33) performed a genome-wide DNA methylation study of hip and knee cartilage with and without OA. The comparison between hip and knee OA revealed 67 DMRs. The combined OA patients compared to healthy controls showed 103 DMRs. The clustering of the identified genes revealed clusters that are enriched in skeletal morphogenesis and development. Bonin et al. (34) analyzed OA cartilage and healthy cartilage from the same knee joints. More than 1000 DMRs were detected in the OA cartilage. Gene expression evaluation showed that hypermethylated DMRs with decreased expression were more common than hypomethylated DMRs with an increased expression. Induced demethylation resulted in an increased expression of the hypermethylated genes in damaged chondrocytes. Zhang et al. (35) studied cartilage from three regions of tibial plateau of OA patients, representing early-, mid- and late-stage OA. No significant differences in methylation were found between early-stage and mid-stage OA, while 519 DMRs were identified between early-stage and late-stage OA cartilage. The same group (36) presented a study reporting on the DNA methylation changes in subchondral bone of three different regions of the tibial plateau, representing the same different stages of OA. DMRs were detected in the mid-stage and late-stage OA. The authors compared the findings in subchondral bone with the site-matched cartilage and found that DNA methylation changes occur earlier in subchondral bone, but methylation appeared to be one key mechanism in the crosstalk between subchondral bone and cartilage. Jeffries et al. (37) performed a study of subchondral bone underlying eroded and intact cartilage within the same joint. Around 7300 DMRs were found in subchondral bone, and around 1400 DMRs were seen in eroded cartilage. Alvarez-Garcia et al. (1) compared the methylome of normal and OA knee articular cartilage. A total of 929 DMRs were identified, within a total of 500 genes. Further analysis revealed that six transcription factors were hypermethylated and downregulated in OA cartilage, which may be an important step in OA pathogenesis. Interestingly, these changes could be reversed by 5-AzadC treatment. Steinberg et al. (38) did a genome-wide analysis comparing healthy and OA chondrocytes regarding DNA methylation, gene expression and proteomics. They identified 49 differentially regulated genes in at least two omics levels. AQP1, COL1A1 and CLEC3B were significantly differentially regulated in all three omics levels and were consistently seen as molecular players in OA progression. Song et al. (39) reported on a genome-wide bioinformatics analysis of DNA methylation and gene expression in OA. Datasets of DNA methylation and gene expression from Gene Expression Omnibus were used and compared to the methylation and gene expression profiles of OA cartilage. The results showed that the majority of DMRs were upregulated and hypomethylated in OA, affecting mostly inflammatory, immune and gene expression regulation-associated pathways. A cross-analysis revealed 30 genes that simultaneously showed differential expression and methylation in OA.

The more recent studies focused on the genetic/epigenetic interplay, demonstrating the epigenetic regulation of OA risk loci. Rice et al. (40) performed a genome-wide methylation analysis, together with genotype and RNA sequencing data in cartilage of OA patients. Forty-two OA risk loci were investigated, and in 10 of these, 24 CpGs were detected, in which methylation correlated with the genotype. The same group (41) identified four new OA methylation quantitative trait loci (mQTLs) by doing a screen of novel OA risk loci followed by methylation and gene expression analysis. The most significant mQTLs where methylation correlated with OA risk genotype were found within the PLEC and neighboring GRINA gene. These genes also showed differential expression between OA hip and non-OA hip cartilage. Li et al. (42) reported on a methylation and gene expression analysis in order to identify methylation-based biomarkers for OA. Datasets from Gene Expression Omnibus were used to evaluate differentially expressed genes (DEGs) and DMRs from patients with OA and controls. DEGs with functions in inflammatory responses, immune responses, regulation of apoptosis, TNF signaling pathway and osteoclast differentiation were identified. Twenty-six genes revealed differential expression and methylation in OA samples, whereas ADAMTS9, FKBP5 and PFKBF3 were named as potential methylation-based biomarkers for OA. Li et al. (43) studied the relationship between osteoporosis (OP) and OA based on DNA methylation. Methylation levels of cancellous bone of OA, OP and combined OA/OP were compared to normal controls. The level of genome-wide methylation was lower in combined OA/OP compared to OA and OP, but it was the highest in the control group. Lin et al. (44) presented a study on methylation of enhancer DNA in OA. Based on a dataset of 108 samples from patients with hip and knee OA as well as hip tissues from healthy individuals, around 16,800 DMRs were seen, and around 8100 of them were found in enhancer regions. In hip OA, 2426 DMRs were identified between males and females (84.5% hypomethylated in females) and enriched in hip OA phenotypes. In knee OA, 280 DMRs were seen that were enriched in OA. In addition, differentially methylated enhancer regions between knee OA and hip OA were detected. Barter et al. (45) evaluated DNA methylation changes during chondrogenesis of mesenchymal stem cells. Significant hypomethylation was seen during chondrogenic differentiation at many key cartilage gene loci. They compared the methylation profile with healthy and diseased articular cartilage, and chondrocyte-specific regions of hypomethylation were seen overlapping with DMRs in OA. These identified DNA methylation levels associated with chondrocyte phenotype are thought to be helpful for cartilage tissue regeneration purposes and to provide a better understanding of methylation changes seen in OA. Yi et al. (46) reported on DMRs and DEGs between OA and non-OA chondrocytes using two different datasets. In total, 2170 DMRs and 1986 DEGs were identified, and functional analysis revealed that 17 transcription factors were differentially expressed, giving further insights into the role of DNA methylation as a transcription regulator. Singh et al. (47) conducted a study on mouse OA chondrocytes, analyzing DNA methylation and DNA hydroxymethylation 4 and 8 weeks after injury. The structural progression of OA was accompanied by DNA methylation changes over time associated with recapitulation of developmental processes. Izda et al. (48) compared the genome-wide DNA methylation pattern in mouse chondrocytes after injury with that of old animals. Aging and PTOA showed similar DNA methylation changes in terms of magnitude and direction, indicating that aging may predispose cartilage to OA development via epigenetic poising. Kreitmaier et al. (49) performed a genome-wide association study (GWAS) in human knee cartilage comparing intact and degraded chondrocytes. They found replication methylation markers and developed a methylation model of cartilage degeneration. The authors introduced a genome-wide mQTL map of articular cartilage and identified 18 OA grade-specific mQTLs. Sarkar et al. (50) studied the role of the transcription factor STAT3, which is highly active in fetal and OA chondrocytes. DNA methylation profiling was used to see the relation between DNA methylation and age. STAT3 decreased DNA methylation and led to an immature phenotype in a subset of cells, which was interpreted as an intrinsic repair attempt. Deletion of STAT3 in chondrocytes resulted in OA progression in an OA mouse model.

Discussion

In this systematic review, we have collected the relevant studies between 2015 and 2023, exploring the role of DNA methylation as an epigenetic mechanism in the pathogenesis and progression of OA. The research interest in this field has grown over the past years, and with the techniques in genetic and epigenetic analysis becoming more cost-effective and easily available, it is expected that the scientific research effort in this direction will continue to grow.

Among the known epigenetic mechanisms that may contribute to the pathogenesis of OA, DNA methylation is the most widely studied so far. DNA methylation is the most stable epigenetic modification and, importantly, is passed down to daughter cells, preserving specific changes in future generations. The role of DNA methylation in biological processes and health-related conditions is often linked to the early 1970s, but the discovery of modified cytosine dates back to 1948, when it was identified during a paper chromatography analysis of calf thymus (51). However, its involvement in gene expression and regulation and cell differentiation was only later revealed in the 1980s (51). Techniques for DNA methylation analysis have since undergone substantial development from providing basic measurements to more comparative quantification methods, such as bisulfite sequencing and methylation-sensitive restriction enzymes in combination with polymerase chain reaction, immunoprecipitation, microarray technology and next-generation sequencing (52). In the case of OA, genome-wide profiling of DNA methylation of the affected cartilage has established specific methylation patient strata profiles, confirming that abnormal transcription is primarily responsible for the development of OA (46, 53). Moreover, according to a recent review on the present status of DNA methylation studies related to OA pathogenesis, bisulfite sequencing, in isolation or in combination with pyrosequencing or restriction enzyme-based methods, has emerged as the most common strategies and revealed a correlation between methylation and gene repression regarding OA pathogenesis (2).

In this review, we have separated the publications into gene-specific DNA methylation studies and genome-wide DNA methylation studies in order to give a better overview of this already very diverse body of literature. We have also limited our literature search to studies using cartilage tissue only, being aware that other tissues, such as bone, synovium and even whole blood may be of interest as well (54). Twenty-three gene-specific DNA methylation studies were identified during the observation period for this review. Prior to that, methylation analyses already reported alterations in genes belonging to the MMP family as well as in the obesity- and inflammation-linked leptin genes (54). Apart from the observed altered methylation pattern affecting inflammatory markers, more recently, there has been a focus on the interaction of OA risk genes and DNA methylation changes. Interestingly, certain DNA methylation changes in association with OA risk loci lead to a reactivation of genes responsible for endochondral ossification during development and bone growth. These are important findings and may help identify possible targets for future therapy, as it has also been shown that reversing the changed DNA methylation pattern can result in a correction of the OA pathological gene expression at a cellular level. As important as the gained knowledge of gene-specific studies in the field is, there has been an increasing effort on genome-wide DNA methylation studies over recent years. This is a consequence of constantly improving sequencing techniques, but also from a clinical perspective, genome-wide studies may give a much better overall picture to understand the pathogenesis of OA. During the observation period, we collected 28 genome-wide DNA methylation studies. A common finding is the association of DMRs with known OA risk loci, demonstrating the genetic/epigenetic interplay. In addition, most of the studies are comparing OA chondrocytes with healthy chondrocytes, where differences in DNA methylation and consequent gene expression patterns are observed. DMRs are also seen in diseased compared to non-affected cartilage regions within one knee joint. In addition, deep-layer chondrocytes demonstrate a different methylation pattern compared to superficial-layer chondrocytes. Despite the important findings, the interpretation of these findings appears difficult. As Peffers et al. (55) mentioned in their review paper in 2017, the methylation changes seem to appear later in OA progression. Thus, the following question remains: are DNA methylation changes the causes or consequences of cartilage degeneration? However, these constantly seen changes in DNA methylation between OA-affected and healthy chondrocytes provide a strong body of knowledge in this field. Based on this, further research strategies may include longitudinal studies, in which the DNA methylation status of chondrocytes of the same subject at different time points are analyzed, and thus, may be able to demonstrate the characteristics of DNA methylation changes in a much better way. We believe that if future efforts can demonstrate a causal relationship between DNA methylation changes and the time points at which these changes occur – such as after an injury – it may open new pathways for reversing these changes and enable genuine causal treatment for OA before structural changes take place. Technically, under in vivo conditions, repeated biopsies of the same joint would be needed at different time points, which will raise considerable ethical concerns if planned in humans. Several animal models have been used to study OA development and progress, including mice, rats, rabbits, dogs, sheep, goats and horses (56). Housman et al. (56) introduced a nonhuman primate model to study the DNA methylation patterns in baboon cartilage with and without knee OA. The rationale to use this nonhuman primate model is based on the fact that, compared to other animals, the primate DNA methylome is similar to the human methylome, which allows the usage of DNA methylation assays that are specifically designed for humans.

In conclusion, DNA methylation is, so far, the most broadly studied epigenetic mechanism in the development and progress of OA. The current body of literature demonstrates the differences in the methylation pattern between diseased and healthy chondrocytes, indicating the possible role in the pathogenesis of OA. These differences in DNA methylation are observed at gene-specific and genome-wide levels. This knowledge provides a strong basis for future studies, in which the characteristics of the changes in DNA methylation can be explored in a detailed and individual manner, which may further help better understand the pathogenesis of OA and develop curative treatment strategies.

Supplementary materials

This is linked to the online version of the paper at https://doi.org/10.1530/EOR-22-0088.

ICMJE Statement of Interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the work.

Funding Statement

This work did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.

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    Takahashi A , de Andrés MC , Hashimoto K , et al. Epigenetic regulation of interleukin-8, an inflammatory chemokine, in osteoarthritis. Osteoarthritis Cartilage 2015 23 A191A192. (https://doi.org/10.1016/j.joca.2015.02.975)

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  • 12

    Papathanasiou I , Kostopoulou F , Malizos KN , et al. DNA methylation regulates sclerostin (SOST) expression in osteoarthritic chondrocytes by bone morphogenetic protein 2 (BMP-2) induced changes in Smads binding affinity to the CpG region of SOST promoter. Arthritis Res Ther 2015 17 160210. (http://dx.doi.org/10.1186/s13075-015-0674-6)

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  • 13

    Bomer N , den Hollander W , Ramos YFM , et al. Underlying molecular mechanisms of DIO2 susceptibility in symptomatic osteoarthritis. Ann Rheum Dis 2015 74 15711579. (https://doi.org/10.1136/annrheumdis-2013-204739)

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  • 14

    Zhang M , Lu Q , Egan B , et al. Epigenetically mediated spontaneous reduction of NFAT1 expression causes imbalanced metabolic activities of articular chondrocytes in aged mice. Osteoarthritis Cartilage 2016 24 12741283. (https://doi.org/10.1016/j.joca.2016.02.003)

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  • 15

    de Andrés MC , Takahashi A & Oreffo ROC . Demethylation of an NF-κB enhancer element orchestrates iNOS induction in osteoarthritis and is associated with altered chondrocyte cell cycle. Osteoarthritis Cartilage 2016 24 19511960. (https://doi.org/10.1016/j.joca.2016.06.002)

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  • 16

    Takahashi A , de Andrés MC , Hashimoto K , et al. DNA methylation of the RUNX2 P1 promoter mediates MMP13 transcription in chondrocytes. Sci Rep 2017 7 7771. (https://doi.org/10.1038/s41598-017-08418-8)

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  • 17

    Li H , Wang D , Yuan Y , et al. New insights on the MMP-13 regulatory network in the pathogenesis of early osteoarthritis. Arthritis Res Ther 2017 19 248. (https://doi.org/10.1186/s13075-017-1454-2)

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  • 18

    Rice SJ , Aubourg G , Sorial AK , et al. Identification of a novel, methylation-dependent, RUNX2 regulatory region associated with osteoarthritis risk. Hum Mol Genet 2018 27 34643474. (https://doi.org/10.1093/hmg/ddy257)

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  • 19

    Castillejo Becerra CM , Mattson AM , Molstad DHH , et al. DNA methylation and FoxO3a regulate PHLPP1 expression in chondrocytes. J Cell Biochem 2018 119 74707478. (https://doi.org/10.1002/jcb.27056)

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  • 20

    Papathanasiou I , Trachana V , Mourmoura E , et al. DNA methylation regulates miR-140-5p and miR-146a expression in osteoarthritis. Life Sci 2019 228 274284. (https://doi.org/10.1016/j.lfs.2019.05.018)

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  • 21

    Zhang H , Li J , Shao W , et al. LncRNA SNHG9 is downregulated in osteoarthritis and inhibits chondrocyte apoptosis by downregulating miR-34a through methylation. BMC Musculoskelet Disord 2020 21 511. (https://doi.org/10.1186/s12891-020-03497-7)

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  • 22

    Zhang Q , Ouyang Z , Song X , et al. Epigenetic modifications of tumor necrosis factor-alpha in joint cartilage tissue from osteoarthritis patients - CONSORT. Medicine 2021 100 e27868. (https://journals.lww.com/10.1097/MD.0000000000027868)

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  • 23

    Kehayova YS , Watson E , Wilkinson JM , et al. Genetic and epigenetic interplay within a COLGALT2 enhancer associated with osteoarthritis. Arthritis Rheumatol 2021 73 18561865. (https://doi.org/10.1002/art.41738)

    • PubMed
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    • Export Citation
  • 24

    Rice SJ , Roberts JB , Tselepi M , et al. Genetic and epigenetic fine-tuning of TGFB1 expression within the human osteoarthritic joint. Arthritis Rheumatol 2021 73 18661877. (https://doi.org/10.1002/art.41736)

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  • 25

    Lv Z , Sun D , Li X , et al. GSK3B overexpression alleviates posttraumatic osteoarthritis in mice by promoting DNMT1-mediated hypermethylation of NR4A3 promoter. Dis Markers 2022 2022 4185489. (https://doi.org/10.1155/2022/4185489)

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  • 26

    Papageorgiou AA , Litsaki M , Mourmoura E , et al. DNA methylation regulates Sirtuin 1 expression in osteoarthritic chondrocytes. Adv Med Sci 2023 68 101110. (https://doi.org/10.1016/j.advms.2023.02.002)

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  • 27

    Zhang Y , He L , Yang Y , et al. Triclocarban triggers osteoarthritis via DNMT1-mediated epigenetic modification and suppression of COL2A in cartilage tissues. J Hazard Mater 2023 447 130747. (https://doi.org/10.1016/j.jhazmat.2023.130747)

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  • 28

    Kehayova YS , Wilkinson JM , Rice SJ , et al. Mediation of the same epigenetic and transcriptional effect by independent osteoarthritis risk–conferring alleles on a shared target gene, COLGALT2. Arthritis Rheumatol 2023 75 910922. (https://doi.org/10.1002/art.42427)

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    • Export Citation
  • 29

    Kehayova YS , Wilkinson JM , Rice SJ , et al. Osteoarthritis genetic risk acting on the galactosyltransferase gene COLGALT2 has opposing functional effects in articulating joint tissues. Arthritis Res Ther 2023 25 83. (https://doi.org/10.1186/s13075-023-03066-y)

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  • 30

    Rushton MD , Reynard LN , Young DA , et al. Methylation quantitative trait locus analysis of osteoarthritis links epigenetics with genetic risk. Hum Mol Genet 2015 24 74327444. (https://doi.org/10.1093/hmg/ddv433)

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  • 31

    Rushton MD , Young DA , Loughlin J , et al. Differential DNA methylation and expression of inflammatory and zinc transporter genes defines subgroups of osteoarthritic hip patients. Ann Rheum Dis 2015 74 17781782. (https://doi.org/10.1136/annrheumdis-2014-206752)

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  • 32

    den Hollander W , Ramos YFM , Bomer N , et al. Transcriptional associations of osteoarthritis-mediated loss of epigenetic control in articular cartilage. Arthritis Rheumatol 2015 67 21082116. (https://doi.org/10.1002/art.39162)

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  • 33

    Aref-Eshghi E , Zhang Y , Liu M , et al. Genome-wide DNA methylation study of hip and knee cartilage reveals embryonic organ and skeletal system morphogenesis as major pathways involved in osteoarthritis. BMC Musculoskelet Disord 2015 16 287. (http://dx.doi.org/10.1186/s12891-015-0745-5)

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  • 34

    Bonin CA , Lewallen EA , Baheti S , et al. Identification of differentially methylated regions in new genes associated with knee osteoarthritis. Gene 2016 576 312318. (https://doi.org/10.1016/j.gene.2015.10.037)

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  • 35

    Zhang Y , Fukui N , Yahata M , et al. Genome-wide DNA methylation profile implicates potential cartilage regeneration at the late stage of knee osteoarthritis. Osteoarthritis Cartilage 2016 24 835843. (http://dx.doi.org/10.1016/j.joca.2015.12.013)

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  • 36

    Zhang Y , Fukui N , Yahata M , et al. Identification of DNA methylation changes associated with disease progression in subchondral bone with site-matched cartilage in knee osteoarthritis. Sci Rep 2016 6 34460. (https://doi.org/10.1038/srep34460)

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  • 37

    Jeffries MA , Donica M , Baker LW , et al. Genome-wide DNA methylation study identifies significant epigenomic changes in osteoarthritic subchondral bone and similarity to overlying cartilage. Arthritis Rheumatol 2016 68 14031414. (https://doi.org/10.1002/art.39555)

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  • 38

    Steinberg J , Ritchie GRS , Roumeliotis TI , et al. Integrative epigenomics, transcriptomics and proteomics of patient chondrocytes reveal genes and pathways involved in osteoarthritis. Sci Rep 2017 7 8935. (http://dx.doi.org/10.1038/s41598-017-09335-6)

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  • 39

    Song D , Qi W , Lv M , et al. Combined bioinformatics analysis reveals gene expression and DNA methylation patterns in osteoarthritis. Mol Med Rep 2018 17 80698078. (https://doi.org/10.3892/mmr.2018.8874)

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    • Export Citation
  • 40

    Rice SJ , Cheung K , Reynard LN , et al. Discovery and analysis of methylation quantitative trait loci (mQTLs) mapping to novel osteoarthritis genetic risk signals. Osteoarthritis Cartilage 2019 27 15451556. (https://doi.org/10.1016/j.joca.2019.05.017)

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  • 41

    Rice SJ , Tselepi M , Sorial AK , et al. Prioritization of PLEC and GRINA as osteoarthritis risk genes through the identification and characterization of novel methylation quantitative trait loci. Arthritis Rheumatol 2019 71 12851296. (https://doi.org/10.1002/art.40849)

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Supplementary Materials

 

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  • Figure 1

    PRISMA systematic review flow diagram of study selection (adapted from 9).

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    Alvarez-Garcia O , Fisch KM , Wineinger NE , et al. Increased DNA methylation and reduced expression of transcription factors in human osteoarthritis cartilage. Arthritis Rheumatol 2016 68 18761886. (https://doi.org/10.1002/art.39643)

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    Zhang M , Egan B & Wang J . Epigenetic mechanisms underlying the aberrant catabolic and anabolic activities of osteoarthritic chondrocytes. Int J Biochem Cell Biol 2015 67 101109. (https://doi.org/10.1016/j.biocel.2015.04.019)

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    Reynard LN & Barter MJ . Osteoarthritis year in review 2019: genetics, genomics and epigenetics. Osteoarthritis Cartilage 2020 28 275284. (https://doi.org/10.1016/j.joca.2019.11.010)

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    Higgins JPT , Morgan RL , Rooney AA , et al. A tool to assess risk of bias in non-randomized follow-up studies of exposure effects (ROBINS-E). Environ Int 2024 186 108602. (https://doi.org/10.1016/j.envint.2024.108602)

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  • 11

    Takahashi A , de Andrés MC , Hashimoto K , et al. Epigenetic regulation of interleukin-8, an inflammatory chemokine, in osteoarthritis. Osteoarthritis Cartilage 2015 23 A191A192. (https://doi.org/10.1016/j.joca.2015.02.975)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    Papathanasiou I , Kostopoulou F , Malizos KN , et al. DNA methylation regulates sclerostin (SOST) expression in osteoarthritic chondrocytes by bone morphogenetic protein 2 (BMP-2) induced changes in Smads binding affinity to the CpG region of SOST promoter. Arthritis Res Ther 2015 17 160210. (http://dx.doi.org/10.1186/s13075-015-0674-6)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13

    Bomer N , den Hollander W , Ramos YFM , et al. Underlying molecular mechanisms of DIO2 susceptibility in symptomatic osteoarthritis. Ann Rheum Dis 2015 74 15711579. (https://doi.org/10.1136/annrheumdis-2013-204739)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Zhang M , Lu Q , Egan B , et al. Epigenetically mediated spontaneous reduction of NFAT1 expression causes imbalanced metabolic activities of articular chondrocytes in aged mice. Osteoarthritis Cartilage 2016 24 12741283. (https://doi.org/10.1016/j.joca.2016.02.003)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 15

    de Andrés MC , Takahashi A & Oreffo ROC . Demethylation of an NF-κB enhancer element orchestrates iNOS induction in osteoarthritis and is associated with altered chondrocyte cell cycle. Osteoarthritis Cartilage 2016 24 19511960. (https://doi.org/10.1016/j.joca.2016.06.002)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Takahashi A , de Andrés MC , Hashimoto K , et al. DNA methylation of the RUNX2 P1 promoter mediates MMP13 transcription in chondrocytes. Sci Rep 2017 7 7771. (https://doi.org/10.1038/s41598-017-08418-8)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Li H , Wang D , Yuan Y , et al. New insights on the MMP-13 regulatory network in the pathogenesis of early osteoarthritis. Arthritis Res Ther 2017 19 248. (https://doi.org/10.1186/s13075-017-1454-2)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18

    Rice SJ , Aubourg G , Sorial AK , et al. Identification of a novel, methylation-dependent, RUNX2 regulatory region associated with osteoarthritis risk. Hum Mol Genet 2018 27 34643474. (https://doi.org/10.1093/hmg/ddy257)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19

    Castillejo Becerra CM , Mattson AM , Molstad DHH , et al. DNA methylation and FoxO3a regulate PHLPP1 expression in chondrocytes. J Cell Biochem 2018 119 74707478. (https://doi.org/10.1002/jcb.27056)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20

    Papathanasiou I , Trachana V , Mourmoura E , et al. DNA methylation regulates miR-140-5p and miR-146a expression in osteoarthritis. Life Sci 2019 228 274284. (https://doi.org/10.1016/j.lfs.2019.05.018)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Zhang H , Li J , Shao W , et al. LncRNA SNHG9 is downregulated in osteoarthritis and inhibits chondrocyte apoptosis by downregulating miR-34a through methylation. BMC Musculoskelet Disord 2020 21 511. (https://doi.org/10.1186/s12891-020-03497-7)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 22

    Zhang Q , Ouyang Z , Song X , et al. Epigenetic modifications of tumor necrosis factor-alpha in joint cartilage tissue from osteoarthritis patients - CONSORT. Medicine 2021 100 e27868. (https://journals.lww.com/10.1097/MD.0000000000027868)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23

    Kehayova YS , Watson E , Wilkinson JM , et al. Genetic and epigenetic interplay within a COLGALT2 enhancer associated with osteoarthritis. Arthritis Rheumatol 2021 73 18561865. (https://doi.org/10.1002/art.41738)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 24

    Rice SJ , Roberts JB , Tselepi M , et al. Genetic and epigenetic fine-tuning of TGFB1 expression within the human osteoarthritic joint. Arthritis Rheumatol 2021 73 18661877. (https://doi.org/10.1002/art.41736)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25

    Lv Z , Sun D , Li X , et al. GSK3B overexpression alleviates posttraumatic osteoarthritis in mice by promoting DNMT1-mediated hypermethylation of NR4A3 promoter. Dis Markers 2022 2022 4185489. (https://doi.org/10.1155/2022/4185489)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 26

    Papageorgiou AA , Litsaki M , Mourmoura E , et al. DNA methylation regulates Sirtuin 1 expression in osteoarthritic chondrocytes. Adv Med Sci 2023 68 101110. (https://doi.org/10.1016/j.advms.2023.02.002)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27

    Zhang Y , He L , Yang Y , et al. Triclocarban triggers osteoarthritis via DNMT1-mediated epigenetic modification and suppression of COL2A in cartilage tissues. J Hazard Mater 2023 447 130747. (https://doi.org/10.1016/j.jhazmat.2023.130747)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28

    Kehayova YS , Wilkinson JM , Rice SJ , et al. Mediation of the same epigenetic and transcriptional effect by independent osteoarthritis risk–conferring alleles on a shared target gene, COLGALT2. Arthritis Rheumatol 2023 75 910922. (https://doi.org/10.1002/art.42427)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29

    Kehayova YS , Wilkinson JM , Rice SJ , et al. Osteoarthritis genetic risk acting on the galactosyltransferase gene COLGALT2 has opposing functional effects in articulating joint tissues. Arthritis Res Ther 2023 25 83. (https://doi.org/10.1186/s13075-023-03066-y)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 30

    Rushton MD , Reynard LN , Young DA , et al. Methylation quantitative trait locus analysis of osteoarthritis links epigenetics with genetic risk. Hum Mol Genet 2015 24 74327444. (https://doi.org/10.1093/hmg/ddv433)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 31

    Rushton MD , Young DA , Loughlin J , et al. Differential DNA methylation and expression of inflammatory and zinc transporter genes defines subgroups of osteoarthritic hip patients. Ann Rheum Dis 2015 74 17781782. (https://doi.org/10.1136/annrheumdis-2014-206752)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 32

    den Hollander W , Ramos YFM , Bomer N , et al. Transcriptional associations of osteoarthritis-mediated loss of epigenetic control in articular cartilage. Arthritis Rheumatol 2015 67 21082116. (https://doi.org/10.1002/art.39162)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 33

    Aref-Eshghi E , Zhang Y , Liu M , et al. Genome-wide DNA methylation study of hip and knee cartilage reveals embryonic organ and skeletal system morphogenesis as major pathways involved in osteoarthritis. BMC Musculoskelet Disord 2015 16 287. (http://dx.doi.org/10.1186/s12891-015-0745-5)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 34

    Bonin CA , Lewallen EA , Baheti S , et al. Identification of differentially methylated regions in new genes associated with knee osteoarthritis. Gene 2016 576 312318. (https://doi.org/10.1016/j.gene.2015.10.037)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 35

    Zhang Y , Fukui N , Yahata M , et al. Genome-wide DNA methylation profile implicates potential cartilage regeneration at the late stage of knee osteoarthritis. Osteoarthritis Cartilage 2016 24 835843. (http://dx.doi.org/10.1016/j.joca.2015.12.013)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 36

    Zhang Y , Fukui N , Yahata M , et al. Identification of DNA methylation changes associated with disease progression in subchondral bone with site-matched cartilage in knee osteoarthritis. Sci Rep 2016 6 34460. (https://doi.org/10.1038/srep34460)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 37

    Jeffries MA , Donica M , Baker LW , et al. Genome-wide DNA methylation study identifies significant epigenomic changes in osteoarthritic subchondral bone and similarity to overlying cartilage. Arthritis Rheumatol 2016 68 14031414. (https://doi.org/10.1002/art.39555)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 38

    Steinberg J , Ritchie GRS , Roumeliotis TI , et al. Integrative epigenomics, transcriptomics and proteomics of patient chondrocytes reveal genes and pathways involved in osteoarthritis. Sci Rep 2017 7 8935. (http://dx.doi.org/10.1038/s41598-017-09335-6)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 39

    Song D , Qi W , Lv M , et al. Combined bioinformatics analysis reveals gene expression and DNA methylation patterns in osteoarthritis. Mol Med Rep 2018 17 80698078. (https://doi.org/10.3892/mmr.2018.8874)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 40

    Rice SJ , Cheung K , Reynard LN , et al. Discovery and analysis of methylation quantitative trait loci (mQTLs) mapping to novel osteoarthritis genetic risk signals. Osteoarthritis Cartilage 2019 27 15451556. (https://doi.org/10.1016/j.joca.2019.05.017)

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 41

    Rice SJ , Tselepi M , Sorial AK , et al. Prioritization of PLEC and GRINA as osteoarthritis risk genes through the identification and characterization of novel methylation quantitative trait loci. Arthritis Rheumatol 2019 71 12851296. (https://doi.org/10.1002/art.40849)

    • PubMed
    • Search Google Scholar
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