Methyltransferase-like 3-mediated N6-methyladenosine modification of miR-7212-5p drives osteoblast differentiation and fracture healing

Recent advances in the reciprocal regulation of m6A modification with non-coding RNAs and its therapeutic application in acute myeloid leukemia

N6-methyladenosine (m6A) is one of the most common modifications of RNA in eukaryotic cells and is involved in mRNA metabolism, including stability, translation, maturation, splicing, and export. m6A also participates in the modification of multiple types of non-coding RNAs, such as microRNAs, long non-coding RNAs, and circular RNAs, thereby affecting their metabolism and functions. Increasing evidence has revealed that m6A regulators, such as writers, erasers, and readers, perform m6A-dependent modification of ncRNAs, thus affecting cancer progression. Moreover, ncRNAs modulate m6A regulators to affect cancer development and progression. In this review, we summarize recent advances in understanding m6A modification and ncRNAs and provide insights into the interaction between m6A modification and ncRNAs in cancer. We also discuss the potential clinical applications of the mechanisms underlying the interplay between m6A modifications and ncRNAs in acute myeloid leukemia (AML). Therefore, clarifying the mutual regulation between m6A modifications and ncRNAs is of great significance to identify novel therapeutic targets for AML and has great clinical application prospects.

METTL3-mediated pre-miR-665/DLX3 m6A methylation facilitates the committed differentiation of stem cells from apical papilla

Methyltransferase-like 3 (METTL3) is a crucial element of N6-methyladenosine (m6A) modifications and has been extensively studied for its involvement in diverse biological and pathological processes. In this study, we explored how METTL3 affects the differentiation of stem cells from the apical papilla (SCAPs) into odonto/osteoblastic lineages through gain- and loss-of-function experiments. The m6A modification levels were assessed using m6A dot blot and activity quantification experiments. In addition, we employed Me-RIP microarray experiments to identify specific targets modified by METTL3. Furthermore, we elucidated the molecular mechanism underlying METTL3 function through dual-luciferase reporter gene experiments and rescue experiments. Our findings indicated that METTL3+/- mice exhibited significant root dysplasia and increased bone loss. The m6A level and odonto/osteoblastic differentiation capacity were affected by the overexpression or inhibition of METTL3. This effect was attributed to the acceleration of pre-miR-665 degradation by METTL3-mediated m6A methylation in cooperation with the "reader" protein YTHDF2. Additionally, the targeting of distal-less homeobox 3 (DLX3) by miR-665 and the potential direct regulation of DLX3 expression by METTL3, mediated by the "reader" protein YTHDF1, were demonstrated. Overall, the METTL3/pre-miR-665/DLX3 pathway might provide a new target for SCAP-based tooth root/maxillofacial bone tissue regeneration.

Unraveling IGFBP3-mediated m6A modification in fracture healing

BACKGROUND

This study investigates the role of IGFBP3-mediated m6A modification in regulating the miR-23a-3p/SMAD5 axis and its impact on fracture healing, aiming to provide insights into potential therapeutic targets.

METHODS

Utilizing fracture-related datasets, we identified m6A modification-related mRNA and predicted miR-23a-3p as a regulator of SMAD5. We established a mouse fracture healing model and conducted experiments, including Micro-CT, RT-qPCR, Alizarin Red staining, and Alkaline phosphatase (ALP) staining, to assess gene expression and osteogenic differentiation.

RESULTS

IGFBP3 emerged as a crucial player in fracture healing, stabilizing miR-23a-3p through m6A modification, leading to SMAD5 downregulation. This, in turn, inhibited osteogenic differentiation and delayed fracture healing. Inhibition of IGFBP3 partially reversed through SMAD5 inhibition, restoring osteogenic differentiation and fracture healing in vivo.

CONCLUSION

The IGFBP3/miR-23a-3p/SMAD5 axis plays a pivotal role in fracture healing, highlighting the relevance of m6A modification. IGFBP3's role in stabilizing miR-23a-3p expression through m6A modification offers a potential therapeutic target for enhancing fracture healing outcomes.

METTL3 promotes osteoblast ribosome biogenesis and alleviates periodontitis

BACKGROUND

Periodontitis is a highly prevalent oral disease characterized by bacterium-induced periodontal inflammation and alveolar bone destruction. Osteoblast function is impaired in periodontitis with a global proteome change. METTL3 is the pivotal methyltransferase of N6-methyladenosine (m6A) that is recently proved to exert a crucial role in osteoblast differentiation. This study aims to investigate the role of METTL3 in osteoblast ribosome biogenesis in periodontitis progression.

RESULTS

METTL3 was knocked down in osteoblasts, and the downregulated genes were enriched in ribosome and translation. METTL3 knockdown inhibited ribosome biogenesis and oxidative phosphorylation in LPS-stimulated osteoblasts, whereas METTL3 overexpression facilitated ribosomal and mitochondrial function. Mechanistically, METTL3 mediated osteoblast biological behaviors by activating Wnt/β-catenin/c-Myc signaling. METTL3 depletion enhanced the mRNA expression and stability of Dkk3 and Sostdc1 via YTHDF2. In periodontitis mice, METTL3 inhibitor SAH promoted alveolar bone loss and local inflammatory status, which were partially rescued by Wnt/β-catenin pathway activator CHIR-99021 HCl.

CONCLUSIONS

METTL3 promoted ribosome biogenesis and oxidative phosphorylation by activating Wnt/β-catenin/c-Myc signaling in LPS-treated osteoblasts and alleviated the inflammatory alveolar bone destruction in periodontitis mice.

The essential roles of m6A modification in osteogenesis and common bone diseases

N6-methyladenosine (m6A) is the most prevalent modification in the eukaryotic transcriptome and has a wide range of functions in coding and noncoding RNAs. It affects the fate of the modified RNA, including its stability, splicing, and translation, and plays an important role in post-transcriptional regulation. Bones play a key role in supporting and protecting muscles and other organs, facilitating the movement of the organism, ensuring blood production, etc. Bone diseases such as osteoarthritis, osteoporosis, and bone tumors are serious public health problems. The processes of bone development and osteogenic differentiation require the precise regulation of gene expression through epigenetic mechanisms including histone, DNA, and RNA modifications. As a reversible dynamic epigenetic mark, m6A modifications affect nearly every important biological process, cellular component, and molecular function, including skeletal development and homeostasis. In recent years, studies have shown that m6A modification is involved in osteogenesis and bone-related diseases. In this review, we summarized the proteins involved in RNA m6A modification and the latest progress in elucidating the regulatory role of m6A modification in bone formation and stem cell directional differentiation. We also discussed the pathological roles and potential molecular mechanisms of m6A modification in bone-related diseases like osteoporosis and osteosarcoma and suggested potential areas for new strategies that could be used to prevent or treat bone defects and bone diseases.

RNA N6-methyladenosine demethylase FTO inhibits glucocorticoid-induced osteoblast differentiation and function in bone marrow mesenchymal stem cells

Excess glucocorticoids (GCs) have been reported as key factors that impair osteoblast (OB) differentiation and function. However, the role of RNA N6-methyladenosine (m6 A) in this process has not yet been elucidated. In this study, we report that both the mRNA and protein expression of fat mass and obesity-associated gene (FTO), a key m6 A demethylase, were dose-dependently downregulated during OB differentiation by dexamethasone (DEX) in bone marrow mesenchymal stem cells (BMSCs), and FTO was gradually increased during OB differentiation. Meanwhile, FTO knockdown suppressed OB differentiation and mineralization, whereas overexpression of wide-type FTO, but not mutant FTO (mutated m6 A demethylase active site), reversed DEX-induced osteogenesis impairment. Interfering with FTO inhibited proliferation and the expression of Ki67 and Pcna in BMSCs during OB differentiation, whereas forced expression of wide-type FTO improved DEX-induced inhibition of BMSCs proliferation. Moreover, FTO knockdown reduced the mRNA stability of the OB marker genes Alpl and Col1a1, and FTO-modulated OB differentiation via YTHDF1 and YTHDF2. In conclusion, our results suggest that FTO inhibits the GCs-induced OB differentiation and function of BMSCs.

Circulating MiRNA-21-enriched extracellular vesicles promote bone remodeling in traumatic brain injury patients

Fracture combined with traumatic brain injury (TBI) is one of the most common and serious types of compound trauma in the clinic and is characterized by dysfunction of cellular communication in injured organs. Our prior studies found that TBI was capable of enhancing fracture healing in a paracrine manner. Exosomes (Exos), as small extracellular vesicles, are important paracrine vehicles for noncell therapy. However, whether circulating Exos derived from TBI patients (TBI-Exos) regulate the prohealing effects of fractures remains unclear. Thus, the present study aimed to explore the biological effects of TBI-Exos on fracture healing and reveal the potential molecular mechanism. TBI-Exos were isolated by ultracentrifugation, and the enriched miR-21-5 p was identified by qRT‒PCR analysis. The beneficial effects of TBI-Exos on osteoblastic differentiation and bone remodeling were determined by a series of in vitro assays. Bioinformatics analyses were conducted to identify the potential downstream mechanisms of the regulatory effect of TBI-Exos on osteoblasts. Furthermore, the role of the potential signaling pathway of TBI-Exos in mediating the osteoblastic activity of osteoblasts was assessed. Subsequently, a murine fracture model was established, and the effect of TBI-Exos on bone modeling was demonstrated in vivo. TBI-Exos can be internalized by osteoblasts, and in vitro, suppression of SMAD7 promoted osteogenic differentiation, whereas knockdown of miR-21-5 p in TBI-Exos strongly inhibited this bone-beneficial effect. Similarly, our results confirmed that preinjection of TBI-Exos led to enhanced bone formation, whereas knockdown of exosomal miR-21-5 p substantially impaired this bone-beneficial effect in vivo.

The promotive role of USP1 inhibition in coordinating osteogenic differentiation and fracture healing during nonunion

BACKGROUND

Nonunion is a failure of fracture healing and a major complication after fractures. Ubiquitin-specific protease 1 (USP1) is a deubiquitinase that involved in cell differentiation and cell response to DNA damage. Herein we investigated the expression, function and mechanism of USP1 in nonunion.

METHODS AND RESULTS

Clinical samples were used to detect the USP1 expression in nonunion. ML323 was selected to inhibit USP1 expression throughout the study. Rat models and mouse embryonic osteoblasts cells (MC3T3-E1) were used to investigate the effects of USP1 inhibition on fracture healing and osteogenesis in vivo and in vitro, respectively. Histological changes were examined by micro-computerized tomography (Micro-CT), hematoxylin & eosin (H&E) staining and Masson staining. Alkaline phosphatase (ALP) activity detection and alizarin red staining were used for osteogenic differentiation observation. The expression of related factors was detected by quantitative real-time PCR, western blot or immunohistochemistry (IHC). It was shown that USP1 was highly expressed in nonunion patients and nonunion rats. USP1 inhibition by ML323 promoted fracture healing in nonunion rats and facilitated the expression of osteogenesis-related factors and the signaling of PI3K/Akt pathway. In addition, USP1 inhibition accelerated osteogenic differentiation and promoting PI3K/Akt signaling in MC3T3-E1 cells.

CONCLUSIONS

USP1 inhibition plays a promotive role in coordinating osteogenic differentiation and fracture healing during nonunion. PI3K/Akt may be the downstream pathway of USP1.

The effects of epigenetic modifications on bone remodeling in age-related osteoporosis

PURPOSE

As the population ages, there is an increased risk of fracture and morbidity diseases associated with aging, such as age-related osteoporosis and other bone diseases linked to aging skeletons.

RESULTS

Several bone-related cells, including multipotent bone mesenchymal stem cells, osteoblasts that form bone tissue, and osteoclasts that break it down, are in symbiotic relationships throughout life. Growing evidence indicates that epigenetic modifications of cells caused by aging contribute to compromised bone remodeling and lead to osteoporosis. A number of epigenetic mechanisms are at play, including DNA/RNA modifications, histone modifications, microRNAs (miRNAs), and long noncoding RNAs (lncRNAs), as well as chromatin remodeling.

CONCLUSION

In this review, we summarized the epigenetic modifications of different bone-related cells during the development and progression of osteoporosis associated with aging. Additionally, we described a compensatory recovery mechanism under epigenetic regulation that may lead to new strategies for regulating bone remodeling in age-related osteoporosis.

METTL3 Regulates Osteoclast Biological Behaviors via iNOS/NO-Mediated Mitochondrial Dysfunction in Inflammatory Conditions

Excessive differentiation of osteoclasts contributes to the disruption of bone homeostasis in inflammatory bone diseases. Methyltransferase-like 3 (METTL3), the core methyltransferase that installs an N6-methyladenosine (m⁶A) modification on RNA, has been reported to participate in bone pathophysiology. However, whether METTL3-mediated m⁶A affects osteoclast differentiation in inflammatory conditions remains unelucidated. In this study, we observed that the total m⁶A content and METTL3 expression decreased during LPS-induced osteoclastogenesis. After knocking down METTL3, we found reduced levels of the number of osteoclasts, osteoclast-related gene expression and bone resorption area. A METTL3 deficiency increased osteoclast apoptosis and pro-apoptotic protein expression. RNA sequencing analysis showed that differentially expressed genes in METTL3-deficient cells were mainly associated with the mitochondrial function. The expression of the mitochondrial function-related genes, ATP production and mitochondrial membrane potential decreased after METTL3 knockdown. Moreover, the most obviously upregulated gene in RNA-Seq was Nos2, which encoded the iNOS protein to induce nitric oxide (NO) synthesis. METTL3 knockdown increased the levels of Nos2 mRNA, iNOS protein and NO content. NOS inhibitor L-NAME rescued the inhibited mitochondrial function and osteoclast formation while suppressing osteoclast apoptosis in METTL3-silenced cells. Mechanistically, a METTL3 deficiency promoted the stability and expression of Nos2 mRNA, and similar results were observed after m⁶A-binding protein YTHDF1 knockdown. Further in vivo evidence revealed that METTL3 knockdown attenuated the inflammatory osteolysis of the murine calvaria and suppressed osteoclast formation. In conclusion, these data suggested that METTL3 knockdown exacerbated iNOS/NO-mediated mitochondrial dysfunction by promoting a Nos2 mRNA stability in a YTHDF1-dependent manner and further inhibited osteoclast differentiation and increased osteoclast apoptosis in inflammatory conditions.

Prognostic and therapeutic potential of microRNAs for fracture healing processes and non-union fractures: A systematic review

BACKGROUND

Approximately 10% of all bone fractures result in delayed fracture healing or non-union; thus, the identification of biomarkers and prognostic factors is of great clinical interest. MicroRNAs (miRNAs) are known to be involved in the regulation of the bone healing process and may serve as functional markers for fracture healing.

AIMS AND METHODS

This systematic review aimed to identify common miRNAs involved in fracture healing or non-union fractures using a qualitative approach. A systematic literature search was performed with the keywords 'miRNA and fracture healing' and 'miRNA and non-union fracture'. Any original article investigating miRNAs in fracture healing or non-union fractures was screened. Eventually, 82 studies were included in the qualitative analysis for 'miRNA and fracture healing', while 19 were selected for the 'miRNA and fracture non-union' category.

RESULTS AND CONCLUSIONS

Out of 151 miRNAs, miR-21, miR-140 and miR-214 were the most investigated miRNAs in fracture healing in general. miR-31-5p, miR-221 and miR-451-5p were identified to be regulated specifically in non-union fractures. Large heterogeneity was detected between studies investigating the role of miRNAs in fracture healing or non-union in terms of patient population, sample types and models used. Nonetheless, our approach identified some miRNAs with the potential to serve as biomarkers for non-union fractures, including miR-31-5p, miR-221 and miR-451-5p. We provide a discussion of involved pathways and suggest on alignment of future research in the field.

Bioinformatics identification and experimental validation of m6A-related diagnostic biomarkers in the subtype classification of blood monocytes from postmenopausal osteoporosis patients

BACKGROUND

Postmenopausal osteoporosis (PMOP) is a common bone disorder. Existing study has confirmed the role of exosome in regulating RNA N6-methyladenosine (m6A) methylation as therapies in osteoporosis. However, it still stays unclear on the roles of m6A modulators derived from serum exosome in PMOP. A comprehensive evaluation on the roles of m6A modulators in the diagnostic biomarkers and subtype identification of PMOP on the basis of GSE56815 and GSE2208 datasets was carried out to investigate the molecular mechanisms of m6A modulators in PMOP.

METHODS

We carried out a series of bioinformatics analyses including difference analysis to identify significant m6A modulators, m6A model construction of random forest, support vector machine and nomogram, m6A subtype consensus clustering, GO and KEGG enrichment analysis of differentially expressed genes (DEGs) between different m6A patterns, principal component analysis, and single sample gene set enrichment analysis (ssGSEA) for evaluation of immune cell infiltration, experimental validation of significant m6A modulators by real-time quantitative polymerase chain reaction (RT-qPCR), etc.

RESULTS

In the current study, we authenticated 7 significant m6A modulators via difference analysis between normal and PMOP patients from GSE56815 and GSE2208 datasets. In order to predict the risk of PMOP, we adopted random forest model to identify 7 diagnostic m6A modulators, including FTO, FMR1, YTHDC2, HNRNPC, RBM15, RBM15B and WTAP. Then we selected the 7 diagnostic m6A modulators to construct a nomogram model, which could provide benefit with patients according to our subsequent decision curve analysis. We classified PMOP patients into 2 m6A subtypes (clusterA and clusterB) on the basis of the significant m6A modulators via a consensus clustering approach. In addition, principal component analysis was utilized to evaluate the m6A score of each sample for quantification of the m6A subgroups. The m6A scores of patients in clusterB were higher than those of patients in clusterA. Moreover, we observed that the patients in clusterA had close correlation with immature B cell and gamma delta T cell immunity while clusterB was linked to monocyte, neutrophil, CD56dim natural killer cell, and regulatory T cell immunity, which has close connection with osteoclast differentiation. Notably, m6A modulators detected by RT-qPCR showed generally consistent expression levels with the bioinformatics results.

CONCLUSION

In general, m6A modulators exert integral function in the pathological process of PMOP. Our study of m6A patterns may provide diagnostic biomarkers and immunotherapeutic strategies for future PMOP treatment.

Potential genetic therapies based on m6A methylation for skin regeneration: Wound healing and scars/keloids

Skin wound healing is a complex and multistage process, where any abnormalities at any stage can result in the accumulation of non-functional fibrotic tissue, leading to the formation of skin scars. Epigenetic modifications play a crucial role in regulating gene expression, inhibiting cell fate determination, and responding to environmental stimuli. m6A methylation is the most common post-transcriptional modification of eukaryotic mRNAs and long non-coding RNAs. However, it remains unclear how RNA methylation controls cell fate in different physiological environments. This review aims to discuss the current understanding of the regulatory pathways of RNA methylation in skin wound healing and their therapeutic implications with a focus on the specific mechanisms involved.

The RANK/RANKL/OPG system and tumor bone metastasis: Potential mechanisms and therapeutic strategies

With the markedly increased diagnosis and incidence of cancer in the population, tumor bone metastasis has become a frequent event in tumor patients. Healthy bone integrity is maintained by a delicate balance between bone formation and bone resorption. Unfortunately, many tumors, such as prostate and breast, often metastasize to the bone, and the alterations to the bone homeostasis can particularly favor tumor homing and consequent osteolytic or osteoblastic lesions. Receptor activator of NF-κB ligand (RANKL), its receptor RANK, and osteoprotegerin (OPG) are involved in the regulation of the activation, differentiation, and survival of osteoclasts, which play critical roles in bone metastasis formation. High rates of osteoclastic bone resorption significantly increase fracture risk, cause severe bone pain, and contribute to homing tumor cells in bone and bone marrow. Consequently, suppression of the RANK/RANKL/OPG system and osteoclastic activity can not only ameliorate bone resorption but may also prevent tumor bone metastases. This review summarizes the important role of the RANK/RANKL/OPG system and osteoclasts in bone homeostasis and its effect on tumor bone metastasis and discusses therapeutic strategies based on RANKL inhibition.

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.

Non-coding RNA and n6-methyladenosine modification play crucial roles in neuropathic pain

After peripheral nerve injury, pain signals are transmitted from primary sensory neurons in the dorsal root ganglion (DRG) to the central nervous system. Epigenetic modification affects neuropathic pain through alterations in the gene expression in pain-related areas and glial cell activation. Recent studies have shown that non-coding RNA and n6-methyladenosine (m6A) methylation modification play pivotal regulatory roles in the occurrence and maintenance of neuropathic pain. Dysregulation of the RNA m6A level via dynamic changes in methyltransferase and demethylase after central or peripheral nerve injury commonly regulates pain-associated genes, contributing to the induction and maintenance of neuropathic pain. The dynamic process has significant implications for the development and maintenance of neuropathic pain. However, the underlying mechanisms by which non-coding RNA and m6A RNA modification regulate neuropathic pain are not well-characterized. This article elucidates the multiple mechanisms of non-coding RNA and m6A methylation in the context of neuropathic pain, and summarizes its potential functions as well as recent advances.

MicroRNA-loaded biomaterials for osteogenesis

The large incidence of bone defects in clinical practice increases not only the demand for advanced bone transplantation techniques but also the development of bone substitute materials. A variety of emerging bone tissue engineering materials with osteogenic induction ability are promising strategies for the design of bone substitutes. MicroRNAs (miRNAs) are a class of non-coding RNAs that regulate intracellular protein expression by targeting the non-coding region of mRNA3′-UTR to play an important role in osteogenic differentiation. Several miRNA preparations have been used to promote the osteogenic differentiation of stem cells. Therefore, multiple functional bone tissue engineering materials using miRNA as an osteogenic factor have been developed and confirmed to have critical efficacy in promoting bone repair. In this review, osteogenic intracellular signaling pathways mediated by miRNAs are introduced in detail to provide a clear understanding for future clinical treatment. We summarized the biomaterials loaded with exogenous cells engineered by miRNAs and biomaterials directly carrying miRNAs acting on endogenous stem cells and discussed their advantages and disadvantages, providing a feasible method for promoting bone regeneration. Finally, we summarized the current research deficiencies and future research directions of the miRNA-functionalized scaffold. This review provides a summary of a variety of advanced miRNA delivery system design strategies that enhance bone regeneration.

Interaction between N6-methyladenosine and autophagy in the regulation of bone and tissue degeneration

Bone and tissue degeneration are the most common skeletal disorders that seriously affect people’s quality of life. N6-methyladenosine (m6A) is one of the most common RNA modifications in eukaryotic cells, affecting the alternative splicing, translation, stability and degradation of mRNA. Interestingly, increasing number of evidences have indicated that m6A modification could modulate the expression of autophagy-related (ATG) genes and promote autophagy in the cells. Autophagy is an important process regulating intracellular turnover and is evolutionarily conserved in eukaryotes. Abnormal autophagy results in a variety of diseases, including cardiomyopathy, degenerative disorders, and inflammation. Thus, the interaction between m6A modification and autophagy plays a prominent role in the onset and progression of bone and tissue degeneration. In this review, we summarize the current knowledge related to the effect of m6A modification on autophagy, and introduce the role of the crosstalk between m6A modification and autophagy in bone and tissue degeneration. An in-depth knowledge of the above crosstalk may help to improve our understanding of their effects on bone and tissue degeneration and provide novel insights for the future therapeutics.

Exosomal PD-L1 induces osteogenic differentiation and promotes fracture healing by acting as an immunosuppressant

A moderate inflammatory response at the early stages of fracture healing is necessary for callus formation. Over-active and continuous inflammation, however, impairs fracture healing and leads to excessive tissue damage. Adequate fracture healing could be promoted through suppression of local over-active immune cells in the fracture site. In the present study, we achieved an enriched concentration of PD-L1 from exosomes (Exos) of a genetically engineered Human Umbilical Vein Endothelial Cell (HUVECs), and demonstrated that exosomes overexpressing PD-L1 specifically bind to PD-1 on the T cell surface, suppressing the activation of T cells. Furthermore, exosomal PD-L1 induced Mesenchymal Stem Cells (MSCs) towards osteogenic differentiation when pre-cultured with T cells. Moreover, embedding of Exos into an injectable hydrogel allowed Exos delivery to the surrounding microenvironment in a time-released manner. Additionally, exosomal PD-L1, embedded in a hydrogel, markedly promoted callus formation and fracture healing in a murine model at the early over-active inflammation phase. Importantly, our results suggested that activation of T cells in the peripheral lymphatic tissues was inhibited after local administration of PD-L1-enriched Exos to the fracture sites, while T cells in distant immune organs such as the spleen were not affected. In summary, this study provides the first example of using PD-L1-enriched Exos for bone fracture repair, and highlights the potential of Hydrogel@Exos systems for bone fracture therapy through immune inhibitory effects.

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.

The m6A demethylase FTO promotes the osteogenesis of mesenchymal stem cells by downregulating PPARG

N⁶-methyladenosine (m⁶A) is the most abundant posttranscriptional methylation modification that occurs in mRNA and modulates the fine-tuning of various biological processes in mammalian development and human diseases. In this study we investigated the role of m⁶A modification in the osteogenesis of mesenchymal stem cells (MSCs), and the possible mechanisms by which m⁶A modification regulated the processes of osteoporosis and bone necrosis. We performed systematic analysis of the differential gene signatures in patients with osteoporosis and bone necrosis and conducted m⁶A-RNA immunoprecipitation (m⁶A-RIP) sequencing to identify the potential regulatory genes involved in osteogenesis. We showed that fat mass and obesity (FTO), a primary m⁶A demethylase, was significantly downregulated in patients with osteoporosis and osteonecrosis. During the differentiation of human MSCs into osteoblasts, FTO was markedly upregulated. Both depletion of FTO and application of the FTO inhibitor FB23 or FB23-2 impaired osteogenic differentiation of human MSCs. Knockout of FTO in mice resulted in decreased bone mineral density and impaired bone formation. PPARG, a biomarker for osteoporosis, was identified as a critical downstream target of FTO. We further revealed that FTO mediated m⁶A demethylation in the 3'UTR of PPARG mRNA, and reduced PPARG mRNA stability in an YTHDF1-dependent manner. Overexpression of PPARG alleviated FTO-mediated osteogenic differentiation of MSCs, whereas knockdown of PPARG promoted FTO-induced expression of the osteoblast biomarkers ALPL and OPN during osteogenic differentiation. Taken together, this study demonstrates the functional significance of the FTO-PPARG axis in promoting the osteogenesis of human MSCs and sheds light on the role of m⁶A modification in mediating osteoporosis and osteonecrosis.

METTL3-m6 A methylase regulates the osteogenic potential of bone marrow mesenchymal stem cells in osteoporotic rats via the Wnt signalling pathway

OBJECTIVES

Bone marrow mesenchymal stem cells (BMSCs) hold a high osteogenic differentiation potential, but the mechanisms that control the osteogenic ability of BMSCs from osteoporosis (OP-BMSCs) need further research. The purpose of this experiment is to discuss the osteogenic effect of Mettl3 on OP-BMSCs and explore new therapeutic target that can enhance the bone formation ability of OP-BMSCs.

MATERIALS AND METHODS

The bilateral ovariectomy (OVX) method was used to establish the SD rat OP model. Dot blots were used to reveal the different methylation levels of BMSCs and OP-BMSCs. Lentiviral-mediated overexpression of Mettl3 was applied in OP-BMSCs. QPCR and WB detected the molecular changes of osteogenic-related factors and Wnt signalling pathway in vitro experiment. The staining of calcium nodules and alkaline phosphatase detected the osteogenic ability of OP-BMSCs. Micro-CT and histological examination evaluated the osteogenesis of Mettl3 in OP rats in vivo.

RESULTS

The OP rat model was successfully established by OVX. Methylation levels and osteogenic potential of OP-BMSCs were decreased in OP-BMSCs. In vitro experiment, overexpression of Mettl3 could upregulate the osteogenic-related factors and activate the Wnt signalling pathway in OP-BMSCs. However, osteogenesis of OP-BMSCs was weakened by treatment with the canonical Wnt inhibitor Dickkopf-1. Micro-CT showed that the Mettl3(+) group had an increased amount of new bone formation at 8 weeks. Moreover, the results of histological staining were the same as the micro-CT results.

CONCLUSIONS

Taken together, the methylation levels and osteogenic potential of OP-BMSCs were decreased in OP-BMSCs. In vitro and in vivo studies, overexpression of Mettl3 could partially rescue the decreased bone formation ability of OP-BMSCs by the canonical Wnt signalling pathway. Therefore, Mettl3 may be a key targeted gene for bone generation and therapy of bone defects in OP patients.

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.

The roles of N6-methyladenosine methylation in the regulation of bone development, bone remodeling and osteoporosis

N⁶-methyladenosine (m⁶A), a novel epitranscriptomic RNA modification, plays crucial roles in a variety of biological processes and diseases. Recently, there are growing evidence supporting that m⁶A methylation is essential for bone development and homeostasis through the regulation of key genes by regulating RNA stability, localization, turnover and translation efficiency. In this review, we summarized our current understanding of the functional roles of m⁶A methylation and its related regulators in bone development and bone remodeling. These findings will offer new directions and insights on the further investigations of m⁶A methylation in bone biology. Moreover, we also discussed important advances of m⁶A methylation related regulators as potential therapeutic targets, which allows for novel therapeutic strategies on the medications of bone-related diseases including osteoporosis.

Emerging role of m6A modification in osteogenesis of stem cells

The differentiation of stem cells into osteoblasts is a key link in the treatment of bone defects and other orthopedic diseases. N6-methyladenosine (m6A) modification, an important post-transcriptional modification, is a methylation that occurs at the N6 site of RNA adenylate. The modification plays a regulatory role in the growth and development of biological individuals, the directional differentiation of stem cells and the occurrence of diseases. It is involved in various processes of the fate decision of stem cells. And it regulates the development and constant renewal of bone and keeps bone homeostasis by controlling and maintaining the balance between osteogenesis and adipogenesis. Meanwhile, it also affects the progress of orthopedic-associated diseases such as degenerative osteoporosis and bone tumor. In this review, we mainly summarize the new findings of three key molecules including Writers, Erasers and Readers which regulate m6A modification, and the emerging role of m6A modification in determining the fate and directed differentiation potential of stem cells, especially highlight the regulatory mechanism of osteogenic differentiation, the balance between osteogenesis and adipogenesis and the occurrence and development of bone-related diseases. It may provide some important ideas about finding new strategies to recover from bone defect and degenerative bone disease.

Stimulation of Let-7 Maturation by Metformin Improved the Response to Tyrosine Kinase Inhibitor Therapy in an m6A Dependent Manner

The molecular mechanism of the tyrosine kinase inhibitor (TKI) resistant lung adenocarcinoma is currently unclear, and the role of methylated adenosine at the N6 position in the resistance of cancer stem cells (CSCs) therapy is unknown. This study identified a novel and effective strategy to enhance TKIs therapy response. We first confirmed the sensitization of Metformin enforcing on Osimertinib treatment and revealed the mature miRNAs signatures of the Osimertinib resistant H1975 and HCC827 cells. Let-7b expression was stimulated when adding Metformin and then increasing the therapy sensitivity by decreasing the stem cell groups expanding. Methyltransferase-like 3 (METTL3) increased the pri-Let-7b, decreased both the pre-Let-7b and mature Let-7b, attenuating the Let-7b controlling of stem cell renewal. The addition of Metformin increased the bindings of DNA methyltransferase-3a/b (DNMT3a/b) to the METTL3 promoter. With the help of the readers of NKAP and HNRNPA2B1, the cluster mediated m6A formation on pri-Let-7b processing increased the mature Let-7b, the key player in suppressing Notch signaling and re-captivating Osimertinib treatment. We revealed that the maturation processing signaling stimulated the methylation regulation of the miRNAs, and may determine the stemness control of the therapy resistance. Our findings may open up future drug development, targeting this pathway for lung cancer patients.

m6A Methylation Regulates Osteoblastic Differentiation and Bone Remodeling

Osteoporosis is a prevalent bone disease of the aging population, which is characterized by a decrease in bone mass because of the imbalance of bone metabolism. Although the prevention and treatment of osteoporosis have been explored by different researchers, the mechanisms underlying osteoporosis are not clear exactly. N6 methyladenosine (m6A) is a methylated adenosine nucleotide, which functions through its interaction with the proteins called “writers,” “readers” and “erasers.” The epigenetic regulation of m6A has been demonstrated to affect mRNA processing, nuclear export, translation, and splicing. At the cellular level, m6A modification has been known to affect cell proliferation, differentiation, and apoptosis of bone-related cells, such as bone marrow mesenchymal stem cells (BMSC), osteoblasts, and osteoclasts by regulating the expression of ALP, Runx2, Osterix, VEGF, and other related genes. Furthermore, PTH/Pth1r, PI3K‐Akt, Wnt/β‐Catenin, and other signaling pathways, which play important roles in the regulation of bone homeostasis, are also regulated by m6A. Thus, m6A modification may provide a new approach for osteoporosis treatment. The key roles of m6A modification in the regulation of bone health and osteoporosis are reviewed here in this article.

Up-to-date on the evidence linking miRNA-related epitranscriptomic modifications and disease settings. Can these modifications affect cross-kingdom regulation?

The field of epitranscriptomics is rapidly developing. Several modifications (e.g. methylations) have been identified for different RNA types. Current evidence shows that chemical RNA modifications can influence the whole molecule's secondary structure, translatability, functionality, stability, and degradation, and some are dynamically and reversibly modulated. miRNAs, in particular, are not only post-transcriptional modulators of gene expression but are themselves submitted to regulatory mechanisms. Understanding how these modifications are regulated and the resulting pathological consequences when dysregulation occurs is essential for the development of new therapeutic targets. In humans and other mammals, dietary components have been shown to affect miRNA expression and may also induce chemical modifications in miRNAs. The identification of chemical modifications in miRNAs (endogenous and exogenous) that can impact host gene expression opens up an alternative way to select new specific therapeutic targets.Hence, the aim of this review is to briefly address how RNA epitranscriptomic modifications can affect miRNA biogenesis and to summarize the existing evidence showing the connection between the (de)regulation of these processes and disease settings. In addition, we hypothesize on the potential effect certain chemical modifications could have on the potential cross-kingdom journey of dietary plant miRNAs.

Transcriptome-wide m6A methylome during osteogenic differentiation of human adipose-derived stem cells

Objectives

Adipose-derived stem cells are frequently used for bone regeneration both in vitro and in vivo. N⁶-methyladenosine (m⁶A) is the most abundant post-transcriptional modification on eukaryotic RNAs and plays multifaceted roles in development and diseases. However, the regulatory mechanisms of m⁶A in osteogenic differentiation of human adipose-derived stem cells (hASCs) remain elusive. The present study aimed to build the transcriptome-wide m⁶A methylome during the osteogenic differentiation of hASCs.

Materials and methods

hASCs were harvested after being cultured in a basic or osteogenic medium for 7 days, and the osteogenic differentiation was validated by alkaline phosphatase (ALP) and Alizarin Red S staining, ALP activity assay, and qRT-PCR analysis of ALP, RUNX2, BGLAP, SPP1, SP7, and COL1A1 genes. The m⁶A level was colorimetrically measured, and the expression of m⁶A regulators was confirmed by qRT-PCR and western blot. Moreover, m⁶A MeRIP-seq and RNA-seq were performed to build the transcriptome and m⁶A methylome. Furthermore, bioinformatic analyses including volcano plots, Venn plots, clustering analysis, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, gene sets enrichment analysis, and protein-protein interaction analysis were conducted.

Results

In total, 1145 differentially methylated peaks, 2261 differentially expressed genes, and 671 differentially methylated and expressed genes (DMEGs) were identified. GO and KEGG pathway analyses conducted for these DMEGs revealed extensive and osteogenic biological functions. The “PI3K-Akt signaling pathway”; “MAPK signaling pathway”; “parathyroid hormone synthesis, secretion, and action”; and “p53 signaling pathway” were significantly enriched, and the DMEGs in these pathways were identified as m⁶A-specific key genes. A protein-protein interaction network based on DMEGs was built, and VEGFA, CD44, MMP2, HGF, and SPARC were speculated as the hub DMEGs.

Conclusions

The total m⁶A level was reduced with osteogenic differentiation of hASCs. The transcriptome-wide m⁶A methylome built in the present study indicated quite a few signaling pathways, and hub genes were influenced by m⁶A modification. Future studies based on these epigenetic clues could promote understanding of the mechanisms of osteogenic differentiation of hASCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02508-1.

The crosstalk between m6A RNA methylation and other epigenetic regulators: a novel perspective in epigenetic remodeling

Epigenetic regulation involves a range of sophisticated processes which contribute to heritable alterations in gene expression without altering DNA sequence. Regulatory events predominantly include DNA methylation, chromatin remodeling, histone modifications, non-coding RNAs (ncRNAs), and RNA modification. As the most prevalent RNA modification in eukaryotic cells, N⁶-methyladenosine (m⁶A) RNA methylation actively participates in the modulation of RNA metabolism. Notably, accumulating evidence has revealed complicated interrelations occurring between m⁶A and other well-known epigenetic modifications. Their crosstalk conspicuously triggers epigenetic remodeling, further yielding profound impacts on a variety of physiological and pathological processes, especially tumorigenesis. Herein, we provide an up-to-date review of this emerging hot area of biological research, summarizing the interplay between m⁶A RNA methylation and other epigenetic regulators, and highlighting their underlying functions in epigenetic reprogramming.

Regulatory Role of the RNA N6-Methyladenosine Modification in Immunoregulatory Cells and Immune-Related Bone Homeostasis Associated With Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease for which the etiology has not been fully elucidated. Previous studies have shown that the development of RA has genetic and epigenetic components. As one of the most highly abundant RNA modifications, the N⁶-methyladenosine (m⁶A) modification is necessary for the biogenesis and functioning of RNA, and modification aberrancies are associated with various diseases. However, the specific functions of m⁶A in the cellular processes of RA remain unclear. Recent studies have revealed the relationship between m⁶A modification and immune cells associated with RA. Therefore, in this review, we focused on discussing the functions of m⁶A modification in the regulation of immune cells and immune-related bone homeostasis associated with RA. In addition, to gain a better understanding of the progress in this field of study and provide the proper direction and suggestions for further study, clinical application studies of m⁶A modification were also summarized.

Novel Insights Into the Role of N6-Methyladenosine RNA Modification in Bone Pathophysiology

Thus far, there are more than known 150 modifications to RNA, in which common internal modifications of mRNA include N6-methyladenosine (m6A), N1-methyladenosine, and 5-methylcytosine. Among them, m6A RNA modification is one of the highest abundance modifications in eukaryotes, regulating mechanisms controlling gene expression at the post-transcription level. As an invertible and dynamic epigenetic marker, m6A base modification influences almost all vital biological processes, cellular components, and molecular functions. Once the m6A modification process is abnormal, a series of diseases-including cancer, neurological diseases, and growth disorders-will be caused. Besides, several base modification activities also have been created by noncoding RNAs (ncRNAs), for instance, microRNAs, and circular RNAs, long ncRNAs, which were dynamically regulated during bone and cartilage pathophysiology processes. Therefore, it has now been clear that dynamic modification on coding RNAs and ncRNAs represents a completely new way to modulate genetic information. In this review, we highlight up-to-date progress and applications of m6A RNA modification in bone and cartilage pathophysiology, and we discuss the pathological roles and underlying molecular mechanism of m6A modifications in osteoarthritis and osteoporosis and osteosarcoma pathogenesis.

Inhibition of exosomal miR-24-3p in diabetes restores angiogenesis and facilitates wound repair via targeting PIK3R3

Diabetic foot ulcer (DFU) is one of the common ailments of elderly people suffering from diabetes. Exosomes containing various active regulators have been found to play a significant role in apoptosis, cell proliferation and other biological processes. However, the effect and the underlying mechanism of action of diabetes patients derived from circulating exosomes (Dia-Exos) on DFU remain unclear. Herein, we aim to explore the potential regulatory role of Dia-Exos. First, we attempted to demonstrate the harmful effect of Dia-Exos both in vivo and in vitro. miRNA-24-3p (miR-24-3p) was found enriched with Dia-Exos. Hence, inhibition of this miRNA could partially reverse the negative effect of Dia-Exos, thus, in ture, accelerates wound repair. Luciferase assay further verified the binding of miR-24-3p to the 3'-UTR of phosphatidylinositol 3-kinase regulatory subunit gamma (PIK3R3) mRNA and the PIK3R3 expression enhanced human umbilical vein endothelial cells functionality in vitro. Hence, the findings of this study reveal the regulatory role of Dia-Exos in the process of wound healing and provide experimental evidence for the therapeutic effects of knocking down miR-24-3p in DFU treatment.

Novel insights into the interplay between m6A modification and noncoding RNAs in cancer

N6-methyladenosine (m⁶A) is one of the most common RNA modifications in eukaryotes, mainly in messenger RNA (mRNA). Increasing evidence shows that m⁶A methylation modification acts an essential role in various physiological and pathological bioprocesses. Noncoding RNAs (ncRNAs), including miRNAs, lncRNAs and circRNAs, are known to participate in regulating cell differentiation, angiogenesis, immune response, inflammatory response and carcinogenesis. m⁶A regulators, such as METTL3, ALKBH5 and IGF2BP1 have been reported to execute a m⁶A-dependent modification of ncRNAs involved in carcinogenesis. Meanwhile, ncRNAs can target or modulate m⁶A regulators to influence cancer development. In this review, we provide an insight into the interplay between m⁶A modification and ncRNAs in cancer.

MicroRNA-21-3p accelerates diabetic wound healing in mice by downregulating SPRY1

A variety of novel drugs and advanced therapeutic strategies have been developed for diabetic foot ulcers (DFUs); however, the clinical outcomes are unsatisfactory and the underlying mechanisms of DFU remain elusive. MicroRNAs (miRNA) regulate the pathological processes of many diseases. Fibroblasts are involved in each stage of wound healing, and the functions of fibroblasts may be regulated by miRNAs. In the present study, we found that the levels of miRNA-21-3p (miR-21-3p) were decreased in patients with diabetes as compared with those in the healthy control. Similarly, the level of miRNA-21-3p was decreased in fibroblasts that were stimulated with D-glucose as compared with that in the control fibroblasts. Furthermore, enhanced function was found in fibroblasts followed by the miR-21-3p agonist treatment, and a rapid wound healing process was achieved in the miR-21-3p agonist-treated mice. MiR-21-3p directly targeted protein sprout homolog 1 (SPRY1), and the miR-21-3p-regulated reduction in SPRY1 enhanced the function of fibroblasts and accelerated wound healing in vivo. These findings suggest that miR-21-3p may treat DFU by reducing SPRY1.

Methyltransferase-like 3-mediated N6-methyladenosine modification of miR-7212-5p drives osteoblast differentiation and fracture healing

N6-methyladenosine (m6A) modification has been reported in various diseases and implicated in increasing numbers of biological processes. However, previous studies have not focused on the role of m6A modification in fracture healing. Here, we demonstrated that m6A modifications are decreased during fracture healing and that methyltransferase-like 3 (METTL3) is the main factor involved in the abnormal changes in m6A modifications. Down-regulation of METTL3 promotes osteogenic processes both in vitro and in vivo, and this effect is recapitulated by the suppression of miR-7212-5p maturation. Further studies have shown that miR-7212-5p inhibits osteoblast differentiation in MC3T3-E1 cells by targeting FGFR3. The present study demonstrated an important role of the METTL3/miR-7212-5p/FGFR3 axis and provided new insights on m6A modification in fracture healing.