METTL3 promotes IL-1β-induced degeneration of endplate chondrocytes by driving m6A-dependent maturation of miR-126-5p

Reciprocal regulation between m6 A modifications and non-coding RNAs: emerging roles in cancer therapeutic resistance

In recent years, the interplay between N6-methyladenosine (m6A) modifications and non-coding RNAs (ncRNAs) has emerged as a pivotal research area, owing to their crucial involvement in the pathophysiological mechanisms underlying various diseases. A significant hurdle in cancer therapy is therapeutic resistance, which frequently contributes to adverse patient outcomes. Recent investigations have underscored the vital role that interactions between m6A modifications and ncRNAs play in mediating cancer therapeutic resistance via the MAPK, PI3K/Akt/mTOR, Wnt/β-catenin, HIPPO, and NF-κB pathways. This review elucidates how these interactions drive tumor therapeutic resistance by modulating these pathways. By dissecting the regulatory dynamics between m6A and ncRNAs in the context of cancer therapeutic resistance, this review aims to deepen the understanding of m6A-ncRNA interaction in cancer therapeutic resistance and identify potential therapeutic targets to improve cancer treatment efficacy.

RNA Modifications in Osteoarthritis: Epitranscriptomic Insights into Pathogenesis and Therapeutic Targets

Osteoarthritis (OA) is a chronic joint disorder characterized by progressive degeneration of articular cartilage, pain, synovial inflammation, and bone remodeling. Post-transcriptional RNA modifications, known as epitranscriptome, are a group of biochemical alterations in the primary RNA transcript that might influence RNA structure, stability, and function. Different kinds of RNA modifications have been recognized, such as methylation, acetylation, pseudouridylation, and phosphorylation. N6-methyladenosine (m6A), 5-methylcytosine (m5C), N7-methylguanosine (m7G), 2'-O-ribose methylation (2'-O-Me), and pseudouridylation (Ψ) are the most prevalent RNA modifications. Recent studies have shown that disruption in these modifications can interfere with gene expression and protein function. Here, we will review all types of RNA modifications and how they contribute to the onset and progression of OA. To the best of our knowledge, this is the first review comprehensively addressing all epitranscriptomic modifications in OA.

From bone marrow mesenchymal stem cells to diseases: the crucial role of m6A methylation in orthopedics

Elucidating the molecular mechanisms underlying orthopedic diseases is crucial for guiding therapeutic strategies and developing innovative interventions. N6-methyladenosine (m6A)-an epitranscriptomic modification-has emerged as a key regulator of cellular fate and tissue homeostasis. Specifically, m6A plays a pivotal role in several RNA biological processes such as precursor RNA splicing, 3'-end processing, nuclear export, translation, and stability. Recent advancements indicate that m6A methylation regulates stem cell proliferation and osteogenic differentiation by modulating various signaling pathways. Extensive research has shown that abnormalities in m6A methylation contribute significantly to the onset and progression of various orthopedic diseases such as osteoporosis (OP), osteoarthritis (OA), rheumatoid arthritis (RA), and bone tumors. This review aims to summarize the key proteases involved in m6A methylation and their functions. The detailed mechanisms by which m6A methylation regulates osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) through direct and indirect ways are also discussed, with a focus on specific molecular pathways. Finally, this review analyzes the roles and mechanisms of m6A modification in the development and progression of multiple orthopedic diseases, offering a comprehensive understanding of the pathophysiology of these conditions and proposing new directions and molecular targets for innovative treatment strategies.

Regulation of Skeletogenic Pathways by m6A RNA Modification: A Comprehensive Review

In the complex process of skeletal development, the significance of m6A RNA methylation-a predominant form of RNA modification-has not been fully explored. This review discuss how m6A RNA methylation plays an important, though not yet fully understood, role in regulating skeletal formation. It examines how m6A influences key signaling pathways essential for skeletal development and homeostasis, suggesting various possible interactions between m6A methylation and these critical pathways. While the exact mechanisms for many of these interactions remain to be elucidated, m6A RNA methylation is anticipated to be a key emerging regulator in skeletal structure development across vertebrates. Highlighting the need for further research, this overview provides an in-depth look at the potential regulatory interactions of m6A RNA methylation within skeletal system. Uniquely, this review is the most comprehensive compilation of evidence linking components of m6A RNA methylation to signaling pathways involved in skeletogenesis.

RNA N6-methyladenosine modification in arthritis: New insights into pathogenesis

The commonest type of eukaryotic RNA modification, N6-methyladenosine (m6A), has drawn increased scrutiny in the context of pathological functioning as well as relevance in determination of RNA stability, splicing, transportation, localization, and translation efficiency. The m6A modification plays an important role in several types of arthritis, especially osteoarthritis and rheumatoid arthritis. Recent studies have reported that m6A modification regulates arthritis pathology in cells, such as chondrocytes and synoviocytes via immune responses and inflammatory responses through functional proteins classified as writers, erasers, and readers. The aim of this review was to highlight recent advances relevant to m6A modification in the context of arthritis pathogenesis and detail underlying molecular mechanisms, regulatory functions, clinical applications, and future perspectives of m6A in arthritis with the aim of providing a foundation for future research directions.

Role of macrophage in intervertebral disc degeneration

Intervertebral disc degeneration is a degenerative disease where inflammation and immune responses play significant roles. Macrophages, as key immune cells, critically regulate inflammation through polarization into different phenotypes. In recent years, the role of macrophages in inflammation-related degenerative diseases, such as intervertebral disc degeneration, has been increasingly recognized. Macrophages construct the inflammatory microenvironment of the intervertebral disc and are involved in regulating intervertebral disc cell activities, extracellular matrix metabolism, intervertebral disc vascularization, and innervation, profoundly influencing the progression of disc degeneration. To gain a deeper understanding of the inflammatory microenvironment of intervertebral disc degeneration, this review will summarize the role of macrophages in the pathological process of intervertebral disc degeneration, analyze the regulatory mechanisms involving macrophages, and review therapeutic strategies targeting macrophage modulation for the treatment of intervertebral disc degeneration. These insights will be valuable for the treatment and research directions of intervertebral disc degeneration.

METTL14 is Involved in TNF-α-Induced Inflammation in Colorectal Epithelial Cells via Autophagy Modulation

Ulcerative colitis (UC) is a chronic and relapsing inflammatory bowel disease (IBD) characterized by colorectal inflammation. The N6-methyladenosine (m6A) modification of RNA regulates gene expression through the modulation of RNA metabolism, thus influencing various physiological and pathological processes. The aim of this study was to investigate the biological function of m6A methyltransferase METTL14 in colorectal epithelial cell inflammation. Bioinformatics analysis indicated that METTL14 expression was decreased in UC and was associated with disease severity and immune infiltration. We also noted a downregulation of METTL14 expression and a decrease in the total m6A RNA levels in TNF-α-stimulated Caco-2 cells. Moreover, METTL14 knockdown promoted inflammation and inhibited autophagy in TNF-α-stimulated Caco-2 cells, as indicated by the upregulation of NF-κB signaling and pro-inflammatory cytokine expression as well as LC3B protein downregulation. Treatment with the autophagy activator Torin-1 ameliorated the pro-inflammatory effects of METTL14 silencing. Furthermore, METTL14 knockdown significantly reduced the expression of ATG5. ATG5 overexpression could nullify the pro-inflammatory effect of METTL14 knockdown in TNF-α-stimulated Caco-2 cells. Mechanistically, METTL14 knockdown promoted ATG5 mRNA degradation, and luciferase analysis identified ATG5 as a target of m6A modification by METTL14. Taken together, silencing METTL14 promoted inflammation in Caco-2 cells via the downregulation of ATG5. Our findings revealed the importance of the m6A modification in colonic inflammation and autophagy, indicating that targeting METTL14 might be a potential therapeutic strategy for anti-inflammatory treatment in UC.

Transcriptome-wide RNA m6A methylation profiles in an endemic osteoarthropathy, Kashin-Beck disease

Kashin-Beck disease (KBD) is a chronic degenerative, disabling disease of the bones and joints and its exact aetiology and pathogenesis remain uncertain. This study is to investigate the role of m6A modification in the pathogenesis of KBD. Combined analysis of m6A MeRIP-Seq and RNA-Seq were used to analyse human peripheral blood samples from three KBD patients and three normal controls (NC). Bioinformatic methods were used to analyse m6A-modified differential genes and RT-qPCR was performed to validate the mRNA expression of several KBD-related genes. The results indicated that the total of 16,811 genes were modified by m6A in KBD group, of which 4882 genes were differential genes. A large number of differential genes were associated with regulation of transcription, signal transduction and protein binding. KEGG analysis showed that m6A-enriched genes participated the pathways of Vitamin B6 metabolism, endocytosis and Rap 1 signalling pathway. There was a positive association between m6A abundance and levels of gene expression, that there were 6 hypermethylated and upregulated genes (hyper-up), 23 hypomethylated and downregulated genes (hypo-down) in KBD group compared with NC. In addition, the mRNA expression of levels of MMP8, IL32 and GPX1 were verified and the protein-protein interaction networks of these key factors were constructed. Our study showed that m6A modifications may play a vital role in modulating gene expression, which represents a new clue to reveal the pathogenesis of KBD.

N6-methyladenosine-driven miR-143/145-KLF4 circuit orchestrates the phenotypic switch of pulmonary artery smooth muscle cells

Pulmonary hypertension (PH) is characterized by vascular remodeling predominantly driven by a phenotypic switching in pulmonary artery smooth muscle cells (PASMCs). However, the underlying mechanisms for this phenotypic alteration remain incompletely understood. Here, we identified that RNA methyltransferase METTL3 is significantly elevated in the lungs of hypoxic PH (HPH) mice and rats, as well as in the pulmonary arteries (PAs) of HPH rats. Targeted deletion of Mettl3 in smooth muscle cells exacerbated hemodynamic consequences of hypoxia-induced PH and accelerated pulmonary vascular remodeling in vivo. Additionally, the absence of METTL3 markedly induced phenotypic switching in PASMCs in vitro. Mechanistically, METTL3 depletion attenuated m6A modification and hindered the processing of pri-miR-143/145, leading to a downregulation of miR-143-3p and miR-145-5p. Inhibition of hnRNPA2B1, an m6A mediator involved in miRNA maturation, similarly resulted in a significant reduction of miR-143-3p and miR-145-5p. We demonstrated that miR-145-5p targets Krüppel-like factor 4 (KLF4) and miR-143-3p targets fascin actin-bundling protein 1 (FSCN1) in PASMCs. The decrease of miR-145-5p subsequently induced an upregulation of KLF4, which in turn suppressed miR-143/145 transcription, establishing a positive feedback circuit between KLF4 and miR-143/145. This regulatory circuit facilitates the persistent suppression of contractile marker genes, thereby sustaining PASMC phenotypic switch. Collectively, hypoxia-induced upregulation of METTL3, along with m6A mediated regulation of miR-143/145, might serve as a protective mechanism against phenotypic switch of PASMCs. Our results highlight a potential therapeutic strategy targeting m6A modified miR-143/145-KLF4 loop in the treatment of PH.

Decoding the role of m6A Regulators in identifying and characterizing molecular subtypes of rosacea

Rosacea is a common skin disease that predominantly affects individuals aged between 30 and 50 years. While the exact cause of the disease remains unclear, various factors have been shown to trigger or exacerbate its symptoms. N6-methyladenosine (m6A) modification is one of the most abundant epigenetic methylation modification in messenger RNA (mRNA) and non-coding RNA (ncRNA), plays a crucial role in RNA splicing, export, stability, and translation. In this study, we aimed to characterize m6A genes in rosacea, identify molecular subtypes based on m6A gene expression, characterize the immune features among subtypes, explore key molecules based on co-expression analysis, and identify potential targets and drugs. To achieve our objectives, we first compared the expression pattern and immune regulation of m6A genes between healthy and diseased groups. Then, we performed clustering to stratify disease samples into different subtypes and analyzed immune regulation and functional enrichment among the subtypes. Then, we conducted differential analysis between subtypes and applied weighted gene co-expression network analysis (WGCNA) in three subtypes. We found hub differential expression analysis (DEG) genes and their potential drug based on the WGCNA results and the drug-gene interaction database (DGIdb). Finally, in vivo and in vitro studies showed significant differences in m6A methyltransferase METTL3 levels in rosacea mice and control mice, as well as in the skin of rosacea patients and healthy people, while reducing METTL3 significantly inhibited the inflammatory response of human fibroblasts (HDFs) stimulated by LL37, suggesting that METTL3 may be associated with changes in overall m6A levels in rosacea. Taken together, our findings provide valuable insights into therapeutic targets and drug predictions for rosacea.

N6-methyladenosine (m6A) methyltransferase WTAP-mediated miR-92b-5p accelerates osteoarthritis progression

The study was design to investigate the functional roles of Wilms tumor 1-associated protein (WTAP), an enzyme catalyzes m6A modification, in the pathogenesis of osteoarthritis (OA) and further elucidate its possible regulatory mechanism. Herein, we discovered that WTAP was outstandingly upregulated in chondrocyte stimulated with Lipopolysaccharide (LPS) and cartilage tissue of patients with OA. Functional studies have demonstrated that WTAP knockdown enhances proliferation ability, suppresses apoptosis, and reduces extracellular matrix (ECM) degradation in an LPS-induced OA chondrocyte injury model and ameliorates cartilage damage in a destabilizing the medial meniscus (DMM)-induced OA mice model. Conversely, overexpression of WTAP contributes to the opposite effects. Mechanistically, our data has demonstrated that m6A modification mediated by WTAP promotes the maturation of pri-miR-92b to miR-92b-5p, thereby enhancing the targeted inhibitory function of miR-92b-5p on TIMP4. Furthermore, we have discovered that WTAP can directly facilitate the degradation of TIMP4 mRNAs in a YTHDF2-dependent manner. In a nutshell, our findings suggested that WTAP knockdown alleviated OA progression by modulating the miR-92b-5p/TIMP4 axis in an m6A-dependent manner. Our study disclosed that WTAP-mediated m6A modification displayed a crucial role in OA development and suggested that targeting WTAP could be a promising preventive and therapeutic target for patients with OA. Video Abstract.

Diagnostic value and immune infiltration characterization of YTHDF2 as a critical m6A regulator in osteoarthritic synovitis

BACKGROUND

N6-methyladenosine (m6A) is a universal RNA modification pattern regulated by multiple m6A regulators. In osteoarthritis (OA), m6A regulators influence disease progression by regulating cartilage degradation. However, the function of m6A regulators in synovial tissue remains unclear. In this work, we investigated the biological significance of m6A regulators in osteoarthritic synovitis.

METHODS

Datasets were acquired from Gene Expression Omnibus. Differential analysis of merged data identified the differentially expressed m6A regulators. Machine learning models were used to evaluate genetic importance. To predict disease risk, a nomogram was constructed based on above m6A regulators. Cluster analysis divided the OA sample into different subgroups. Immune infiltration revealed the immune m6A regulators, which were validated using clinical samples. Eventually, a competing endogenous RNA (ceRNA) network was constructed.

RESULTS

We acquired five differentially expressed m6A regulators and a random forest model. The nomogram accurately predicted disease risk. We identified 122 differentially expressed genes between two m6A subgroups. The analysis of immune infiltration showed that YTHDF2 was an immune-related m6A regulator closely related with macrophages. In clinical samples, the protein and mRNA contents of YTHDF2 were consistent with the results of bioinformatic analysis. The ceRNA network based on YTHDF2 revealed 75 lncRNA nodes and 19 miRNA nodes.

CONCLUSION

YTHDF2 has a high diagnostic value in the synovitis of OA and significantly influences the immune status of patients. Hence, YTHDF2, a critical m6A regulator, may provide a biomarker for diagnosis and immune therapy of osteoarthritic synovitis.

RNA-binding proteins in degenerative joint diseases: A systematic review

RNA-binding proteins (RBPs), which are conserved proteins comprising multiple intermediate sequences, can interact with proteins, messenger RNA (mRNA) of coding genes, and non-coding RNAs to perform different biological functions, such as the regulation of mRNA stability, selective polyadenylation, and the management of non-coding microRNA (miRNA) synthesis to affect downstream targets. This article will highlight the functions of RBPs, in degenerative joint diseases (intervertebral disc degeneration [IVDD] and osteoarthritis [OA]). It will reviews the latest advancements on the regulatory mechanism of RBPs in degenerative joint diseases, in order to understand the pathophysiology, early diagnosis and treatment of OA and IVDD from a new perspective.

METTL3 contributes to slow transit constipation by regulating miR-30b-5p/PIK3R2/Akt/mTOR signaling cascade through DGCR8

BACKGROUND

N6-methyladenosine (m6A) is the most prevalent methylation modification of eukaryotic RNA, and methyltransferase-like 3 (METTL3) plays a vital role in multiple cell functions. This study aimed to investigate the role of m6A methylase METTL3 in slow transit constipation (STC).

MATERIAL AND METHOD

The expression of METTL3 and DGCR8 was measured in STC tissues and glutamic acid-induced interstitial cells of Cajal (ICCs). The effects of METTL3, miR-30b-5p, and DGCR8 on the biological characteristics of ICCs were investigated on the basis of loss-of-function analyses. Luciferase reporter assay was used to identify the direct binding sites of miR-30b-5p with PIK3R2.

RESULTS

The results showed that the METTL3, DGCR8, miR-30b-5p, and the methylation level of m6A were significantly increased in STC tissues and glutamic acid-induced ICCs. Silencing of METTL3 and miR-30b-5p inhibited apoptosis, autophagy, and pyroptosis of glutamic acid-induced ICCs. Moreover, overexpression of miR-30b-5p reversed the cytoprotection of METTL3 knockdown in glutamic acid-induced ICCs. Besides, DGCR8 knockdown could facilitate cell growth and decrease apoptotic glutamic acid-induced ICCs. Mechanically, we illustrated that METTL3 in glutamic acid-induced ICCs significantly accelerated the maturation of pri-miR-30b-5p by m6A methylation modification, resulting in the reduction of PIK3R2, which results in the inhibition of PI3K/Akt/mTOR pathway and ultimately leads to the cell death of STC.

CONCLUSIONS

Collectively, these data demonstrated that METTL3 promoted the apoptosis, autophagy, and pyroptosis of glutamic acid-induced ICCs by interacting with the DGCR8 and successively modulating the miR-30b-5p/PIK3R2 axis in an m6A-dependent manner, and METTL3 may be a potential therapeutic target for STC.

Methyltransferase-like 3 facilitates lung cancer progression by accelerating m6A methylation-mediated primary miR-663 processing and impeding SOCS6 expression

OBJECTIVE

Lung cancer (LC) remains a threatening health issue worldwide. Methyltransferase-like protein 3 (METTL3) is imperative in carcinogenesis via m6A modification of microRNAs (miRNAs). This study estimated the effect of METTL3 in LC by regulating m6A methylation-mediated pri-miR-663 processing.

METHODS

miR-663 expression in 4 LC cell lines and normal HBE cells was determined using RT-qPCR. A549 and PC9 LC cells selected for in vitro studies were transfected with miR-663 mimics or inhibitor. Cell viability, migration, invasion, proliferation, and apoptosis were detected by CCK-8, Transwell, EdU, and flow cytometry assays. The downstream target genes and binding sites of miR-663 were predicted via Starbase database and validated by dual-luciferase assay. LC cells were delivered with oe-METTL3/sh-METTL3. Crosslinking between METTL3 and DGCR8 was verified by co-immunoprecipitation. Levels of m6A, miR-663, and pri-miR-663 were measured by m6A dot blot assay and RT-qPCR. m6A modification of pri-miR-663 was verified by Me-RIP assay. Finally, the effects of METTL3 in vivo were ascertained by tumor xenograft in nude mice.

RESULTS

miR-663 was upregulated in LC cells, and miR-663 overexpression promoted cell proliferation, migration, invasion, and inhibited apoptosis, but miR-663 knockdown exerted the opposite effects. miR-663 repressed SOCS6 expression. SOCS6 overexpression annulled the promotion of miR-663 on LC cell growth. METTL3 bound to DGCR8, and METTL3 silencing elevated the levels of pri-miR-663 and m6A methylation-modified pri-miR-663, and suppressed miR-663 maturation and miR-663 expression. METTL3 facilitated tumor growth in mice through the miR-663/SOCS6 axis.

CONCLUSION

METTL3 promotes LC progression by accelerating m6A methylation-mediated pri-miR-663 processing and repressing SOCS6.

Extracellular vesicles derived from human umbilical cord mesenchymal stem cells alleviate osteoarthritis of the knee in mice model by interacting with METTL3 to reduce m6A of NLRP3 in macrophage

BACKGROUND

Osteoarthritis (OA) is a prevalent degenerative joint disease that not only significantly impairs the quality of life of middle-aged and elderly individuals but also imposes a significant financial burden on patients and society. Due to their significant biological properties, extracellular vesicles (EVs) have steadily received great attention in OA treatment. This study aimed to investigate the influence of EVs on chondrocyte proliferation, migration, and apoptosis and their protective efficacy against OA in mice.

METHODS

The protective impact of EVs derived from human umbilical cord mesenchymal stem cells (hucMSCs-EVs) on OA in mice was investigated by establishing a mouse OA model by surgically destabilizing the medial meniscus (DMM). Human chondrocytes were isolated from the cartilage of patients undergoing total knee arthroplasty (TKA) and cultured with THP-1 cells to mimic the in vivo inflammatory environment. Levels of inflammatory factors were then determined in different groups, and the impacts of EVs on chondrocyte proliferation, migration, apoptosis, and cartilage extracellular matrix (ECM) metabolism were explored. N6-methyladenosine (m6A) level of mRNA and methyltransferase-like 3 (METTL3) protein expression in the cells was also measured in addition to microRNA analysis to elucidate the molecular mechanism of exosomal therapy.

RESULTS

The results indicated that hucMSCs-EVs slowed OA progression, decreased osteophyte production, increased COL2A1 and Aggrecan expression, and inhibited ADAMTS5 and MMP13 overexpression in the knee joint of mice via decreasing pro-inflammatory factor secretion. The in vitro cell line analysis revealed that EVs enhanced chondrocyte proliferation and migration while inhibiting apoptosis. METTL3 is responsible for these protective effects. Further investigations revealed that EVs decreased the m6A level of NLRP3 mRNA following miR-1208 targeted binding to METTL3, resulting in decreased inflammatory factor release and preventing OA progression.

CONCLUSION

This study concluded that hucMSCs-EVs inhibited the secretion of pro-inflammatory factors and the degradation of cartilage ECM after lowering the m6A level of NLRP3 mRNA with miR-1208 targeting combined with METTL3, thereby alleviating OA progression in mice and providing a novel therapy for clinical OA treatment.

Novel insights into the interaction between N6-methyladenosine methylation and noncoding RNAs in musculoskeletal disorders

BACKGROUND

Musculoskeletal disorder (MSD) are a class of inflammatory and degener-ative diseases, but the precise molecular mechanisms are still poorly understood. Noncoding RNA (ncRNA) N6-methyladenosine (m6A) modification plays an essential role in the pathophysiological process of MSD. This review summarized the interaction be-tween m6A RNA methylation and ncRNAs in the molecular regulatory mechanism of MSD. It provides a new perspective for the pathophysiological mechanism and ncRNA m6A targeted therapy of MSD.

METHODS

A comprehensive search of databases was conducted with musculoskeletal disorders, noncoding RNA, N6-methyladenosine, intervertebral disc degeneration, oste-oporosis, osteosarcoma, osteoarthritis, skeletal muscle, bone, and cartilage as the key-words. Then, summarized all the relevant articles.

RESULTS

Intervertebral disc degeneration (IDD), osteoporosis (OP), osteosarcoma (OS), and osteoarthritis (OA) are common MSDs that affect muscle, bone, cartilage, and joint, leading to limited movement, pain, and disability. However, the precise pathogenesis remains unclear, and no effective treatment and drug is available at present. Numerous studies confirmed that the mutual regulation between m6A and ncRNAs (i.e., microRNAs, long ncRNAs, and circular RNAs) was found in MSD, m6A modification can regulate ncRNAs, and ncRNAs can also target m6A regulators. ncRNA m6A modification plays an essential role in the pathophysiological process of MSDs by regulating the homeostasis of skeletal muscle, bone, and cartilage.

CONCLUSION

m6A interacts with ncRNAs to regulate multiple biological processes and plays important roles in IDD, OP, OS, and OA. These studies provide new insights into the pathophysiological mechanism of MSD and targeting m6A-modified ncRNAs may be a promising therapy approach.

The crucial mechanism and therapeutic implication of RNA methylation in bone pathophysiology

Methylation is the most common posttranscriptional modification in cellular RNAs, which has been reported to modulate the alteration of RNA structure for initiating relevant functions such as nuclear translocation and RNA degradation. Recent studies found that RNA methylation especially N6-methyladenosine (m⁶A) regulates the dynamic balance of bone matrix and forms a complicated network in bone metabolism. The modulation disorder of RNA methylation contributes to several pathological bone diseases including osteoporosis (OP), osteoarthritis (OA), rheumatoid arthritis (RA), and so on. In the review, we will discuss advanced technologies for detecting RNA methylation, summarize RNA methylation-related biological impacts on regulating bone homeostasis and pathological bone diseases. In addition, we focus on the promising roles of RNA methylation in early diagnosis and therapeutic implications for bone-related diseases. Then, we aim to establish a theoretical basis for further investigation in this meaningful field.

Mechanism of METTL3-mediated m6A modification in depression-induced cognitive deficits

Depressive disorder (DD) is associated with N6-methyladenosine (m6A) hypermethylation. This study sought to explore the molecular mechanism of Methyltransferase-like 3 (METTL3) in cognitive deficits of chronic unpredictable mild stress (CUMS)-treated rats and provide novel targets for DD treatment. A DD rat model was established via CUMS treatment. Cognitive deficits were assessed via body weighing and behavioral tests. METTL3, microRNA (miR)-221-3p, pri-miR-221, GRB2-associated binding protein 1 (Gab1) expressions in hippocampal tissues were detected via RT-qPCR and Western blotting. m6A, DiGeorge syndrome critical region gene 8 (DGCR8)-bound pri-miR-221 and pri-miR-221 m6A levels were measured. The binding relationship between miR-221-3p and Gab1 was testified by dual-luciferase and RNA pull-down assays. Rescue experiments were designed to confirm the role of miR-221-3p and Gab1. METTL3 was highly expressed in CUMS rats, and silencing METTL3 attenuated cognitive deficits of CUMS rats. METTL3-mediated m6A modification facilitated processing and maturation of pri-miR-221 via DGCR8 to upregulate miR-221-3p. miR-221-3p targeted Gab1. miR-221-3p overexpression or Gab1 downregulation reversed the role of silencing METTL3 in CUMS rats. Overall, METTL3-mediated m6A modification facilitated processing and maturation of pri-miR-221 to upregulate miR-221-3p and then inhibit Gab1, thereby aggravating cognitive deficits of CUMS rats.

Extracellular Vesicles Derived From Stem Cells in Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is the leading cause of low back pain related to degradation of cartilaginous tissues, mainly resulting from oxidative stress, cell apoptosis, and extracellular matrix degradation. Extracellular vesicles (EVs) exist in all bodily fluids and can be produced by all types of cells. Stem cell-derived EVs (SC-EVs), which are the main paracrine components of stem cells, have gained significant attention in the field of regenerative medicine. Over the past years, accumulating evidence indicates the therapeutic and diagnostic potentials of EVs in IVDD. The main mechanisms involve the induction of regenerative phenotypes, apoptosis alleviation, and immune modulation. In addition, the efficiency of SC-EVs can be enhanced by choosing appropriate donor cells and cell phenotypes, optimizing cell culture conditions, or engineering EVs to deliver drugs and targeting molecules. Given the importance and novelty of SC-EVs, we give an overview of SC-EVs and discuss the roles of SC-EVs in IVDD.

METTL3-mediated m6A modification of ATG7 regulates autophagy-GATA4 axis to promote cellular senescence and osteoarthritis progression

OBJECTIVE

The aim of the study was to investigate the role and regulatory mechanisms of fibroblast-like synoviocytes (FLSs) and their senescence in the progression of osteoarthritis (OA).

METHODS

Synovial tissues from normal patients and patients with OA were collected. Synovium FLS senescence was analysed by immunofluorescence and western blotting. The role of methyltransferase-like 3 (METTL3) in autophagy regulation was explored using N6-methyladenosine (m6A)-methylated RNA and RNA immunoprecipitation assays. Mice subjected to destabilisation of the medial meniscus (DMM) surgery were intra-articularly injected with or without pAAV9 loaded with small interfering RNA (siRNA) targeting METTL3. Histological analysis was performed to determine cartilage damage.

RESULTS

Senescent FLSs were markedly increased with the progression of OA in patients and mouse models. We determined that impaired autophagy occurred in OA-FLS, resulting in the upregulation of senescence-associated secretory phenotype (SASP). Re-establishment of autophagy reversed the senescent phenotype by suppressing GATA4. Further, we observed for the first time that excessive m6A modification negatively regulated autophagy in OA-FLS. Mechanistically, METTL3-mediated m6A modification decreased the expression of autophagy-related 7, an E-1 enzyme crucial for the formation of autophagosomes, by attenuating its RNA stability. Silencing METTL3 enhanced autophagic flux and inhibited SASP expression in OA-FLS. Intra-articular injection of synovium-targeted METTL3 siRNA suppressed cellular senescence propagation in joints and ameliorated DMM-induced cartilage destruction.

CONCLUSIONS

Our study revealed the important role of FLS senescence in OA progression. Targeted METTL3 inhibition could alleviate the senescence of FLS and limit OA development in experimental animal models, providing a potential strategy for OA therapy.

Novel Insights Into the Multifaceted Functions of RNA n6-Methyladenosine Modification in Degenerative Musculoskeletal Diseases

N6-methyladenosine (m6A) is an important modification of eukaryotic mRNA. Since the first discovery of the corresponding demethylase and the subsequent identification of m6A as a dynamic modification, the function and mechanism of m6A in mammalian gene regulation have been extensively investigated. "Writer", "eraser" and "reader" proteins are key proteins involved in the dynamic regulation of m6A modifications, through the anchoring, removal, and interpretation of m6A modifications, respectively. Remarkably, such dynamic modifications can regulate the progression of many diseases by affecting RNA splicing, translation, export and degradation. Emerging evidence has identified the relationship between m6A modifications and degenerative musculoskeletal diseases, such as osteoarthritis, osteoporosis, sarcopenia and degenerative spinal disorders. Here, we have comprehensively summarized the evidence of the pathogenesis of m6A modifications in degenerative musculoskeletal diseases. Moreover, the potential molecular mechanisms, regulatory functions and clinical implications of m6A modifications are thoroughly discussed. Our review may provide potential prospects for addressing key issues in further studies.

METTL3 Intensifies the Progress of Oral Squamous Cell Carcinoma via Modulating the m6A Amount of PRMT5 and PD-L1

N6-Methyladenosine (m6A) modification is one of the commonest chemical modifications in eukaryotic mRNAs, which has essential effects on mRNA translation, splicing, and stability. Currently, there is a rising concern on the regulatory role of m6A in tumorigenesis. As a known component in the m6A methyltransferase complex, METTL3 (methyltransferase-like 3) plays an essential role in m6A methylation. Till now, the functions of METTL3 in oral squamous cell carcinoma (OSCC) and its relative mechanism remain to be explored. In this research, through the GEPIA database, we found that high METTL3 expression has a correlation with poor prognosis of squamous cell carcinoma of head and neck. qRT-PCR displayed that METTL3 was highly expressed in OSCC cells. Functionally, METTL3 knockdown reduced the invasion, migration, and proliferation competence of OSCC cells and attenuated the activation of CD8+ T cells. In contrast, METTL3 overexpression resulted in opposite results. GEPIA, UALCAN, and SRAMP databases, PCR, western blot, and m6A RNA methylation assay confirmed the m6A modification of PRMT5 and PD-L1 mediated by METTL3. In conclusion, our results displayed that METTL3 intensified the metastasis and proliferation of OSCC by modulating the m6A amounts of PRMT5 and PD-L1, suggesting that METTL3 may be a therapeutic target for OSCC patients.

METTL3 involves the progression of osteoarthritis probably by affecting ECM degradation and regulating the inflammatory response

We aimed to identify RNA N6-methyladenosine methylation associated genes in osteoarthritis (OA), and to explore possible regulatory mechanisms of these RNA methylation associated genes. Bioinformatics analyses, including differential expression analysis, functional enrichment analysis, verification analysis, and box plot analysis, were conducted based on different datasets from OA and non-OA patients. Gene expression at mRNA and protein levels was determined by quantitative reverse transcription PCR, western blot and immunofluorescence. Interleukin 1β (IL-1β)-treated SW1353 cells was used as cell model. Lentiviral vector was used for over-expression METTL3 in vitro. CCK-8 assay kit was used to determine cell viability and inflammatory cytokines (IL-1α, IL-6, IL-8, IL-10 and TNF-α) was detected using ELISA kits. Bioinformatics analysis showed that METTL3 expression was decreased in OA group, which was confirmed in clinical samples. Expression of METTL3 was also reduced in IL-1β-treated cells. Levels of inflammatory cytokines were obviously reduced in the METTL3 overexpression group, while IL-1β treatment reversed such decrease caused by METTL3 overexpression (p < 0.05). Both METTL3 overexpression and IL-1β treatment promoted expression of p65 protein and p-ERK (p < 0.01). Additionally, increased expression of MMP1 and MMP3, and decreased expression of MMP13, TIMP-1, and TIMP-2 at both mRNA and protein levels were observed in the METTL3 overexpression group when compared with the control group (p < 0.01). Expression of m6A methylation gene METTL3 was reduced in OA. METTL3 is involved in OA probably by regulating the inflammatory response. METTL3 overexpression may affect extracellular matrix degradation in OA by adjusting the balance between TIMPs and MMPs.

RNA N6-methyladenosine modification, spermatogenesis, and human male infertility

RNA N6-methyladenosine (m6A) modification is one of the main forms of posttranscriptional modification, and its dysregulation is involved in a series of pathological processes. RNA m6A regulators, which mediate dynamic RNA m6A modification, are expressed in almost all types of testicular cells, including spermatogenetic cells and somatic cells. Cumulative studies have found that knockout of RNA m6A regulators in the testis leads to abnormal metabolism of the target mRNAs, which eventually causes spermatogenetic disorders and infertility. To date, a role for dysregulated RNA m6A modification in human male infertility remains elusive; however, dysregulated expression of RNA m6A regulators in abnormal human semen samples, including oligospermia, asthenozoospermia and azoospermia, has been found. Therefore, we speculate that abnormal RNA m6A methylation may be an important mechanism of male infertility. In this review, we summarize the recent findings regarding the spatiotemporal expression of RNA m6A regulators in the testes, mechanisms of RNA m6A modification in spermatogenesis and the relation between dysregulated RNA m6A regulators and human male infertility. In addition, we also discuss future directions in studying the molecular mechanism of male infertility and exploring their clinical applications from the viewpoint of RNA m6A modification.