Epigenetics of osteoarticular diseases: recent developments

Longitudinal course of circulating miRNAs in a patient with hypophosphatasia and asfotase alfa treatment: a case report

Hypophosphatasia (HPP) is characterized by low activity of tissue nonspecific alkaline phosphatase (TNSALP). The enzyme replacement therapy asfotase alfa has been approved for childhood-onset forms of HPP. MicroRNAs (miRNAs) have emerged as a novel disease biomarker, with potential application in therapy monitoring. Circulating miRNAs were analyzed at baseline, months 1, 2, 4, and 16 in a 49-yr-old woman with childhood-onset HPP, chronic musculoskeletal pain, and non-traumatic fractures prior to enzyme replacement therapy. Serum RNA was extracted and sequenced using miRNeasy Mini Kit (Qiagen, Germany), RealSeq Biosciences Kit (Santa Cruz, US) together with miND spike-in control kit (TAmiRNA, Austria) and Illumina NovaSeq 6000 SP1 flow cell (San Diego, US). Brief Pain Inventory Severity and Interference scores (BPI-S/BPI-I), fatigue severity scale (FSS), Patient Global Impression of Improvement (PGI-I), Western Ontario and McMaster university hip disability and osteoarthritis outcome score (WOMAC), fibromyalgia impact questionnaire (FIQ), 6-Minute Walking Test (6-MWT), chair-rise-test (CRT), and handgrip dynamometry (HD) were performed at baseline and different timepoints during the therapy. Out of >800 screened, 84 miRNAs were selected based on differences in expression profiles between 24 HPP patients and 24 healthy controls. Six miRNAs showed a clear graphic trend and were up- or downregulated by ≥50% reads per million (rpm). These included hsa-let-7i-5p (+50%), hsa-miR-1-3p (-66.66%), hsa-miR-1294 (+63.63%), hsa-miR-206 (-85.57%), hsa-miR-375-3p (-71.43%), and hsa-miR-624-5p (+69.44%). hsa-miR-1-3p and hsa-miR-206 were identified as muscle-specific miRNAs. hsa-mir-375-3p, which negatively regulates osteogenesis, was significantly downregulated. In terms of patient-reported outcomes, BPI-S, BPI-I, FSS, PGI-I, WOMAC, and FIQ showed a reduction by -58.62%, -68.29%, -33.33%, -75.00%, -63.29%, and -43.02%, respectively. 6-MWT improved by +33.89% and CRT by -44.46%. Mean hand grip strength of the right/left hand measured by HD improved by +12.50% and + 23.53%, respectively. miRNA profile changes during the therapy with asfotase alfa, accompanying improvements in functionality tests and quality of life scores.

Role of Serum Micro-RNA-122-5p Expression as a Circulatory Biomarker in People Having Both Knee Osteoarthritis and Osteoporosis: A Case-Control Study

Background Although knee osteoarthritis (KOA) and osteoporosis (OP) manifest distinct pathophysiologies, they share numerous similarities. These health conditions are commonly found in older individuals, particularly among women. The objective of this study is to explore the expression of micro-RNA (miRNA) 122-5p (miR-122-5p) in people affected by both KOA and OP. The main aim is to identify diagnostic biomarkers and potential therapeutic targets, which could help develop personalized treatment approaches. Methods As part of the study, a total of 268 serum samples were collected from the participants, who were divided into four groups: KOA, OP, KOA and OP, and controls, with 67 subjects per group. The miRNA species-containing total RNA was isolated from the serum samples using an miRNeasy serum/plasma kit by QIAGEN (Hilden, Germany). The expression of miR-122-5p was examined in each group using real-time quantitative polymerase chain reaction. Results Expression of miR-122-5p in all three groups (KOA, OP, and common group of KOA and OP) was significantly upregulated, and the fold change value was much higher in the group having both diseases. Conclusions These results might contribute to the identification of cases at risk, early diagnosis, and development, and might also contribute to the development of therapeutic targets in subjects having both KOA and OP.

N6-Methyladenosine in Cell-Fate Determination of BMSCs: From Mechanism to Applications

The methylation of adenosine base at the nitrogen-6 position is referred to as "N6-methyladenosine (m6A)" and is one of the most prevalent epigenetic modifications in eukaryotic mRNA and noncoding RNA (ncRNA). Various m6A complex components known as "writers," "erasers," and "readers" are involved in the function of m6A. Numerous studies have demonstrated that m6A plays a crucial role in facilitating communication between different cell types, hence influencing the progression of diverse physiological and pathological phenomena. In recent years, a multitude of functions and molecular pathways linked to m6A have been identified in the osteogenic, adipogenic, and chondrogenic differentiation of bone mesenchymal stem cells (BMSCs). Nevertheless, a comprehensive summary of these findings has yet to be provided. In this review, we primarily examined the m6A alteration of transcripts associated with transcription factors (TFs), as well as other crucial genes and pathways that are involved in the differentiation of BMSCs. Meanwhile, the mutual interactive network between m6A modification, miRNAs, and lncRNAs was intensively elucidated. In the last section, given the beneficial effect of m6A modification in osteogenesis and chondrogenesis of BMSCs, we expounded upon the potential utility of m6A-related therapeutic interventions in the identification and management of human musculoskeletal disorders manifesting bone and cartilage destruction, such as osteoporosis, osteomyelitis, osteoarthritis, and bone defect.

Novel insights into the METTL3-METTL14 complex in musculoskeletal diseases

N6-methyladenosine (m⁶A) modification, catalyzed by methyltransferase complexes (MTCs), plays many roles in multifaceted biological activities. As the most important subunit of MTCs, the METTL3-METTL14 complex is reported to be the initial factor that catalyzes the methylation of adenosines. Recently, accumulating evidence has indicated that the METTL3-METTL14 complex plays a key role in musculoskeletal diseases in an m⁶A-dependent or -independent manner. Although the functions of m⁶A modifications in a variety of musculoskeletal diseases have been widely recognized, the critical role of the METTL3-METTL14 complex in certain musculoskeletal disorders, such as osteoporosis, osteoarthritis, rheumatoid arthritis and osteosarcoma, has not been systematically revealed. In the current review, the structure, mechanisms and functions of the METTL3-METTL14 complex and the mechanisms and functions of its downstream pathways in the aforementioned musculoskeletal diseases are categorized and summarized.

Reversal of Epigenetic Peroxisome Proliferator-Activated Receptor-γ Suppression by Diacerein Alleviates Oxidative Stress and Osteoarthritis in Mice

Aims: The pathogenesis of osteoarthritis (OA) is characterized by oxidative stress (OS) and sustained inflammation that are substantially associated with epigenetic DNA methylation alterations of osteogenic gene expression. Diacerein as an anthraquinone anti-OA drug exhibits multiple chondroprotective properties, but less clarified pharmacological actions. Since anthraquinone contain an epigenetic modulating property, in this study we investigate whether the anti-OA functions of diacerein involve DNA methylation modulation and antioxidant signaling. Results: The OA mice incurred by destabilization of medial meniscus exhibited marked suppression of peroxisome proliferator-activated receptor-gamma (PPARγ), a chondroprotective transcription factor with anti-inflammation and OS-balancing properties, aberrant upregulations of DNA methyltransferase (DNMT)1/3a, and PPARγ promoter hypermethylation in knee joint cartilage. Diacerein treatment mitigated the cartilage damage and significantly inhibited the DNMT1/3a upregulation, the PPARγ promoter hypermethylation, and the PPARγ loss, and it effectively corrected the adverse expression of antioxidant enzymes and inflammatory cytokines. In cultured chondrocytes, diacerein reduced the interleukin-1β-induced PPARγ suppression and the abnormal expression of its downstream antioxidant enzymes in a gain of DNMT and PPARγ inhibition-sensitive manner, and in PPARγ knockout mice, the anti-OA effects of diacerein were significantly reduced. Innovation: Our work reveals a novel anti-OA pharmacological property of diacerein and identifies the aberrant DNMT elevation and the resultant PPARγ suppression as an important epigenetic pathway that mediates diacerein's anti-OA activities. Conclusion: DNA methylation aberration and the resultant PPARγ suppression contribute significantly to epigenetic OA pathogenesis, and targeting PPARγ suppression via DNA demethylation is an important component of diacerein's anti-OA functions. Antioxid. Redox Signal. 37, 40-53.

Altered Expression of Aggrecan, FAM20B, B3GALT6, and EXTL2 in Patients with Osteoarthritis and Kashin-Beck Disease

OBJECTIVE

The objective of this study was to investigate the expression of enzymes involved in synthesis and modification of chondroitin sulfate (CS) in knee cartilage tissue of patients with osteoarthritis (OA) and Kashin-Beck disease (KBD).

METHODS

The knee articular cartilage samples were obtained from 18 age- and gender-matched donors with 6 each in KBD, OA, and control groups. Hematoxylin and eosin (HE) staining, toluidine blue (TB) staining, and immunohistochemical (IHC) staining were performed to estimate the expression level and localization of aggrecan, along with FAM20B, GalT-II, and EXTL2, which are associated with CS synthesis and modification. Rank-based analyses of variance test was used for the multiple comparisons of discrepancy in the positive staining rate among the 3 groups.

RESULTS

In HE and TB staining results, damaged morphology, decreased chondrocyte numbers and proteoglycans were observed in OA and KBD groups compared with the control group. In line with these trends, the positive staining rates of aggrecan were lower in KBD and OA groups than in the control group. Meanwhile, the positive staining rates of CS chain modifying enzymes FAM20B, GalT-II, and EXTL2 decreased in OA and KBD groups.

CONCLUSIONS

In conclusion, it was demonstrated that altered expression of CS chain modifying enzymes in OA and KBD groups influenced the synthesis procession of CS and could contribute to the damage of cartilage. Further investigation of these enzymes can provide new theoretical and experimental targets for OA and KBD pathogenesis studies.

Epigenetics of ankylosing spondylitis: Recent developments

Ankylosing spondylitis (AS) is a chronic inflammatory autoimmune disease which mainly affects the spine, sacroiliac joint and peripheral joints. To date, the exact causes and pathogenesis of AS still remain unknown. It is considered that the pathogenesis of AS is associated with genetic, infection, environment, immunity and other factors. Among them, the role of genetic factors in the pathogenesis of AS has been studied most deeply. However, over the past few years, the function of environmental predisposition and epigenetic modification in the pathogenesis of AS has received extensive attention. This paper summarizes the recent progress in the epigenetics of AS, including abnormal epigenetic modifications at AS-associated genomic loci, such as DNA methylation, histone modification, microRNA, and so on. In summary, the findings of this review attempt to explain the role of epigenetic modification in the occurrence and development of AS. Nevertheless, there are still unknown and complicated aspects worth exploring to deepen our understanding of the pathogenesis of AS.

5-Aza-2-deoxycytidine inhibits osteolysis induced by titanium particles by regulating RANKL/OPG ratio

Periprosthetic osteolysis (PIO) caused by wear particles is the main cause of implant failure, which is regulated by nuclear factor κ B receptor activator ligand (RANKL)/osteoprotegerin (OPG) system. At present, there is a lack of effective drugs to prevent or treat PIO. Previous studies have confirmed that DNA methylation is closely related to postmenopausal osteoporosis and can affect the expression of OPG and RANKL. However, the relationship between DNA methylation and PIO is not clear. In this study, we investigated the inhibitory effect of 5-Aza-2-deoxycytidine (AzadC) on osteolysis induced by titanium particles in a mouse model. This inhibition mechanism is achieved by changing the ratio of RANKL/OPG in the osteolysis model. In conclusion, there is a relationship between DNA methylation and PIO. AzadC has a certain inhibitory effect on osteolysis induced by titanium particles. Regulating DNA methylation may be a new way to treat PIO. Our findings lay a foundation for epigenetic understanding and intervention of osteolysis.

Valproic Acid Impacts the Growth of Growth Plate Chondrocytes

A range of bone abnormalities including short stature have been reported to be associated with the use of antiepileptic drugs (AEDs) in children. Exactly how AEDs impact skeletal growth, however, is not clear. In the present study, rat growth plate chondrocytes were cultured to study the effects of AEDs, including valproic acid (VPA), oxcarbazepine (OXA), levetiracetam (LEV), lamotrigine (LTG), and topiramate (TPM) on the skeletal growth. VPA markedly reduced the number of chondrocytes by apoptosiswhile other AEDs had no effect. The apoptosis associated noncleaved and cleaved caspase 3, and caspases were increased by exposure to VPA, which up-regulated cyclooxygenase 2 (COX-2) mRNA and protein levels likely through histone acetylation. The COX-2 inhibitor NS-398 attenuated the effects of VPA up-regulating COX-2 expression and decreased VPA-induced caspase 3 expression. The use of VPA in children should be closely monitored or replaced, where appropriate, by AEDs which do not apparently affect the growth plate chondrocytes.

Jumonji domain containing-3 (JMJD3) inhibition attenuates IL-1β-induced chondrocytes damage in vitro and protects osteoarthritis cartilage in vivo

OBJECTIVES

This study aimed to explore the effects and relative mechanism of JMJD3 on knee osteoarthritis (OA).

METHODS

In this study, we first analyzed the expression of JMJD3 in OA cartilage using western blot and immunohistochemistry. In an in vitro study, the effects of GSK-J4, JMJD3 inhibitor, on ATDC-5 chondrocytes were evaluated by CCK-8 assay. Real-time PCR and western blot were used to examine the inhibitory effect of GSK-J4 on the inflammation and ECM degradation of chondrocytes. NF-κB p65 phosphorylation and nuclear translocation were measured by western blot and immunofluorescence. In the animal study, twenty mice were randomized into four experimental groups: sham group, DMM-induced OA + DMSO group, OA + low-dose GSK-J4 group, and OA + high-dose GSK-J4 group. After the treatment, hematoxylin-eosin and safranin O/fast green staining were used to evaluate cartilage degradation of knee joint, with OARSI scores for quantitative assessment of cartilage damage.

RESULTS

Our results revealed that JMJD3 was overexpressed in OA cartilage and GSK-J4 could suppress the IL-1β-induced production of pro-inflammatory cytokines and catabolic enzymes, including IL-6, IL-8, MMP-9 and ADAMTS-5. Consistent with these findings, GSK-J4 could inhibit IL-1β-induced degradation of collagen II and aggrecan. Mechanistically, GSK-J4 dramatically suppressed IL-1β-stimulated NF-κB signal pathway activation. In vivo, GSK-J4 prevented cartilage damage in mouse DMM-induced OA model.

CONCLUSIONS

This study elucidates the important role of JMJD3 in cartilage degeneration in OA, and our results indicate that JDJM3 may become a novel therapeutic target in OA therapy.

[Correlation between histone methylation level and pathological development of osteoarthritis]

Osteoarthritis is the most common degenerative cartilage disease. A large number of studies have shown the close association between epigenetics and osteoarthritis. Histone methylation is a type of epigenetic modification, and the link between histone methylation and osteoarthritis has also been revealed. In this article, we summarize the correlation between methylation levels of different histones and osteoarthritis in an attempt to explore the changes and regulation mechanisms of histone methylation in osteoarthritis. It has been shown that there are possible relations between the methylation levels of different amino acids on histone H3 and the pathological development of osteoarthritis; specifically, the rise of methylation level at the lysine 4 would aggravate the pathological development of osteoarthritis, while the the pattern of lysine 9 and 27 would be the opposite. These results indicate the possible existence of a complex network of histone methylation modifications. And the specific regulation of histone methylation levels in different positions may delay or prevent the occurrence and development of osteoarthritis.

Insulin/IGF-1R, SIRT1, and FOXOs Pathways-An Intriguing Interaction Platform for Bone and Osteosarcoma

Aging is a substantial risk factor for the development of osteoarthritis (OA) and, probably, an essential substrate for the development of neoplastic disease of the bone, such as osteosarcoma, which is the most common malignant mesenchymal primary bone tumor. Genetic studies have established that the insulin/insulin-like growth factor 1 (IGF-1)/phosphatidylinositol-3 kinase (PI3K)/AKT (Protein Kinase B) signal transduction pathway is involved across species, including nematodes, fruit flies, and mammals. SIRT1, a phylogenetically-conserved family of deacetylases, seems to play pleiotropic effects in epithelial malignancies of the liver and interact with the IGF-1/PI3K/AKT signal transduction pathway. Some of the most critical processes in degenerative conditions may indeed include the insulin/IGF1R and SIRT1 signaling pathways as well as some specific transcription factors. The Forkhead box O (FOXO) transcription factors (FOXOs) control diverse cellular functions, such as metabolism, longevity, and cell death. FOXOs play a critical role in the IGF-1/PI3K/AKT signal transduction pathway. FOXOs can indeed be modulated to reduce age-related diseases. FOXOs have advantageous inhibitory effects on fibroblast and myofibroblast activation, which are accompanied by a subsequent excessive production of extracellular matrix. FOXOs can block or decrease the fibrosis levels in numerous organs. Previously, we observed a correlation between nuclear FOXO3 and high caspase-8 expression, which induces cellular apoptosis in response to harmful external stimuli. In this perspective, we emphasize the current advances and interactions involving the insulin/IGF1R, SIRT1, and FOXOs pathways in the bone and osteosarcoma for a better understanding of the mechanisms potentially underpinning tissue degeneration and tumorigenesis.

The Potential Role of miRNAs as New Biomarkers for Osteoporosis

Osteoporosis is the most common metabolic bone disorder affecting up to 40% of postmenopausal women, characterized by a reduction in bone mass and strength leading to bone fragility and fractures. Despite the available tools for diagnosis and stratification of a fracture risk, bone loss occurs insidiously and osteoporosis is often diagnosed after the first fracture has occurred, with important health-related outcomes. Therefore, the need of markers that could efficiently diagnose bone fragility and osteoporosis is still necessary. Over the past few years, novel studies have focused on miRNAs, small noncoding RNAs that are differentially expressed in many pathological conditions, making them attractive biomarkers. To date, the role of miRNAs in bone disorders remains in great part unclear. In particular, limited and partly conflicting information is available concerning their use as potential biomarkers for osteoporosis, due to differences in patient selection, type of samples, and analytical methods. Despite these limits, concordant information about some specific miRNAs is now arising, making likely their use as additional tools to stratify the risk of osteoporosis and possibly fractures. In this review, we summarize the most relevant studies concerning circulating miRNAs differentially expressed in osteoporotic patients along with their function in bone cells and bone turnover.

Quantitative genetics of circulating Hyaluronic Acid (HA) and its correlation with hand osteoarthritis and obesity-related phenotypes in a community-based sample

BACKGROUND

One of the potential molecular biomarkers of osteoarthritis (OA) is hyaluronic acid (HA). HA levels may be related to the severity and progression of OA. However, little is known about the contribution of major risk factors for osteoarthritis, e.g. obesity-related phenotypes and genetics to HA variation.

AIM

To clarify the quantitative effect of these factors on HA.

SUBJECTS AND METHODS

An ethnically homogeneous sample of 911 apparently healthy European-derived individuals, assessed for radiographic hand osteoarthritis (RHOA), HA, leptin, adiponectin, and several anthropometrical measures of obesity-related phenotypes was studied. Model-based quantitative genetic analysis was used to reveal genetic and shared environmental factors affecting the variation of the study's phenotypes.

RESULTS

The HA levels significantly correlated with the age, RHOA, adiponectin, obesity-related phenotypes, and the waist-to-hip ratio. The putative genetic effects contributed significantly to the variation of HA (66.2 ± 9.3%) and they were also significant factors in the variations of all the other studied phenotypes, with the heritability estimate ranging between 0.122 ± 4.4% (WHR) and 45.7 ± 2.2% (joint space narrowing).

CONCLUSIONS

This is the first study to report heritability estimates of HA variation and its correlation with obesity-related phenotypes, ADP and RHOA. However, the nature of genetic effects on HA and its correlation with other study phenotypes require further clarification.

Genome-wide DNA methylation analysis of articular chondrocytes identifies TRAF1, CTGF, and CX3CL1 genes as hypomethylated in osteoarthritis

The aim of this study is to identify osteoarthritis (OA)-associated differentially methylated genes in human articular chondrocytes from patients with OA. DNA methylation profiling of articular chondrocytes from OA patients, rheumatoid arthritis (RA) patients, and controls was performed, and candidate genes were chosen for validation of gene demethylation status. The mRNA expression levels of candidate genes in chondrocytes were detected by real-time quantitative PCR. Chondrocytes from OA and RA group were treated with 5-Aza-2-deoxycytidine (5-Aza), and then the mRNA expression levels were detected. Forty-five genes with significant methylation differences between OA and control group were identified. Tumor necrosis factor receptor-associated factor 1 (TRAF1), connective tissue growth factor (CTGF), and chemokine (C-X3-C motif) ligand 1(CX3CL1) genes were hypomethylated in chondrocytes of OA and RA patients, which verified by bisulfite sequencing analysis. The mRNA expression level of TRAF1 and CTGF was significantly increased in OA and RA group (p < 0.05), while the expression level of CX3CL1 was only increased in OA group (p < 0.05). For the chondrocytes from OA and RA treated with 5-Aza, the mRNA expression level of TRAF1 and CTGF was highly increased (p < 0.05). It is the first time to show that TRAF1, CTGF, and CX3CL1 genes were hypomethylated in OA chondrocytes and have a consistent correlation with mRNA expression, which suggests that epigenetic changes in the methylation status of TRAF1, CTGF, and CX3CL1 contribute to the pathology of OA.

MicroRNAs in bone diseases

MicroRNAs are small, noncoding single-stranded RNAs that have emerged as important posttranscriptional regulators of gene expression, with an essential role in vertebrate development and different biological processes. This review highlights the recent advances in the function of miRNAs and their roles in bone remodeling and bone diseases. MicroRNAs (miRNAs) are a class of small (∼22 nt), noncoding single-stranded RNAs that have emerged as important posttranscriptional regulators of gene expression. They are essential for vertebrate development and play critical roles in different biological processes related to cell differentiation, activity, metabolism, and apoptosis. A rising number of experimental reports now indicate that miRNAs contribute to every step of osteogenesis and bone homeostasis, from embryonic skeletal development to maintenance of adult bone tissue, by regulating the growth, differentiation, and activity of different cell systems inside and outside the skeleton. Importantly, emerging information from animal studies suggests that targeting miRNAs might become an attractive and new therapeutic approach for osteoporosis or other skeletal diseases, even though there are still major concerns related to potential off target effects and the need of efficient delivery methods in vivo. Moreover, besides their recognized effects at the cellular level, evidence is also gathering that miRNAs are excreted and can circulate in the blood or other body fluids with potential paracrine or endocrine functions. Thus, they could represent suitable candidates for becoming sensitive disease biomarkers in different pathologic conditions, including skeletal disorders. Despite these promising perspectives more work remains to be done until miRNAs can serve as robust therapeutic targets or established diagnostic tools for precision medicine in skeletal disorders.

How to interpret epigenetic association studies: a guide for clinicians

Epigenetic mechanisms are able to alter gene expression, without altering DNA sequence, in a stable manner through cell divisions. They include, among others, the methylation of DNA cytosines and microRNAs and allow the cells to adapt to changing environmental conditions. In recent years, epigenetic association studies are providing new insights into the pathogenesis of complex disorders including prevalent skeletal disorders. Unlike the genome, the epigenome is cell and tissue specific and may change with age and a number of acquired factors. This poses particular difficulties for the design and interpretation of epigenetic studies, particularly those exploring the association of genome-wide epigenetic marks with disease phenotypes. In this report, we propose a framework to help in the critical appraisal of epigenetic association studies. In line with previous suggestions, we focus on the questions critical to appraise the validity of the study, to interpret the results and to assess the generalizability and relevance of the information.