Mettl3-mediated m6A RNA methylation regulates the fate of bone marrow mesenchymal stem cells and osteoporosis

The m6A reader YTHDF2 protects vascular smooth muscle cells against the osteogenic differentiation through targeting Runx2

Vascular calcification (VC) is an important pathological development progress in chronic kidney disease (CKD) and may increase mortality but lacks effective treatments. N6-methyladenosine (m6A) has been verified to be the most prevalent internal chemical RNA modification in mammalian mRNAs. The M6A-modified mRNA degradation process is mediated by the reader YTHDF2 in an m6A-dependent manner. Nevertheless, the exact role and molecular mechanism of YTHDF2 in VC remain unclear. This study aimed to investigate the potential role of YTHDF2 in the osteogenic differentiation of vascular smooth muscle cells (VSMCs). It was found that YTHDF2 was markedly downregulated in both in vivo and in vitro calcified models. Functionally, YTHDF2 plays a protective role in VC. The overexpression of YTHDF2 inhibited the transdifferentiation of VSMCs from a contractile to an osteogenic phenotype, thus decreasing the expression of mineralization regulatory proteins and calcium deposition. Conversely, YTHDF2 deficiency aggravated this process. At the mechanistic level, YTHDF2 suppressed osteogenic transdifferentiation of VSMCs by regulating the Runt-related transcription factor 2 (Runx2). RNA immunoprecipitation-qPCR (RIP-qPCR) confirmed the binding of YTHDF2 to Runx2, and luciferase reporter assays confirmed the presence of the m6A site in Runx2. In addition, an actinomycin D assay showed that the half-life of Runx2 mRNA was dramatically shortened in VSMCs overexpressing YTHDF2. These results suggest that YTHDF2 directly binds to the m6A modification site of Runx2 to mediate the mRNA degradation that prevents VC by inhibiting the osteogenic development of VSMCs. Therefore, YTHDF2 can be considered a potential therapeutic target for managing VC.

Harnessing engineered exosomes as METTL3 carriers: Enhancing osteogenesis and suppressing lipogenesis in bone marrow mesenchymal stem cells for postmenopausal osteoporosis treatment

Postmenopausal osteoporosis (PMOP), a prevalent skeletal disorder among women post-menopause, has emerged as a pressing global public health concern. Exosomes derived from serum have exhibited encouraging therapeutic potential in addressing PMOP, albeit with underlying mechanisms requiring deeper exploration. To elucidate these mechanisms, we devised a mouse model by surgically inducing ovariectomy and isolated exosomes from serum samples. Subsequently, we employed qRT-PCR, Western blotting, and immunofluorescence analysis to quantify relevant gene and protein expression patterns. To assess the biological effects on treated cells and tissues, we utilized ARS staining, oil red O staining, and micro-CT analysis. Additionally, we examined the METTL3/FOXO1 m6A site interaction and the FOXO1/YTHDF1 complex using dual-luciferase reporter assays and RIP assays. The m6A modification levels of FOXO1 were quantified via MeRIP-PCR. Furthermore, we engineered bone marrow mesenchymal stem cell exosomes by loading abundant METTL3 mRNA and decorating their surfaces with bone-targeting peptides. The successful synthesis and bone-targeting capabilities of these modified exosomes were validated through electron microscopy, in vivo imaging, and immunofluorescence staining. Our findings reveal that METTL3, in collaboration with YTHDF1 within serum-derived exosomes, enhances FOXO1 gene transcription by fostering m6A modification of FOXO1. This, in turn, promotes osteogenic differentiation of bone marrow mesenchymal stem cells while inhibiting lipogenic differentiation. Notably, our engineered exosomes, BT-oe-METTL3-EXO, not only harbor high levels of METTL3 but also demonstrate exceptional bone-targeting efficiency. In vitro studies demonstrated that BT-oe-METTL3-EXO significantly mitigated bone mass loss induced by ovariectomy in mice, bolstered osteogenic differentiation of mouse bone marrow mesenchymal stem cells, and inhibited lipogenic differentiation. Collectively, our research underscores the pivotal regulatory function of serum-derived exosomes in human bone marrow stem cells (hBMSCs) and underscores the promising therapeutic potential of BT-oe-METTL3-EXO for combating postmenopausal osteoporosis.

METTL3: a multifunctional regulator in diseases

N6-methyladenosine (m6A) methylation is the most prevalent and abundant internal modification of mRNAs and is catalyzed by the methyltransferase complex. Methyltransferase-like 3 (METTL3), the best-known m6A methyltransferase, has been confirmed to function as a multifunctional regulator in the reversible epitranscriptome modulation of m6A modification according to follow-up studies. Accumulating evidence in recent years has shown that METTL3 can regulate a variety of functional genes, that aberrant expression of METTL3 is usually associated with many pathological conditions, and that its expression regulatory mechanism is related mainly to its methyltransferase activity or mRNA posttranslational modification. In this review, we discuss the regulatory functions of METTL3 in various diseases, including metabolic diseases, cardiovascular diseases, and cancer. We focus mainly on recent progress in identifying the downstream target genes of METTL3 and its underlying molecular mechanisms and regulators in the above systems. Studies have revealed that the use of METTL3 as a therapeutic target and a new diagnostic biomarker has broad prospects. We hope that this review can serve as a reference for further studies.

Apoptotic vesicles inhibit bone marrow adiposity via wnt/β-catenin signaling

Background

There is currently increasing focus on aging-related diseases. Osteoporosis is a common disease the incidence of which increases with age. In older patients with osteoporosis, bone marrow mesenchymal stem cells (BMMSCs) have a decreased capacity for osteogenesis and an increased capacity for adipogenesis, causing excessive accumulation of adipose tissue in the bone marrow. Therefore, means of reducing bone marrow adiposity may have therapeutic potential for osteoporosis. Apoptotic vesicles (apoVs) participate in a wide range of physiological processes and have been shown to have therapeutic effects in a variety of diseases. The principal objective of this study was to examine the special properties and regulatory mechanisms of BMMSC-derived apoVs in the treatment of bone marrow adiposity.

Results

The results showed that apoVs could decrease bone marrow adiposity in osteoporotic mice and prevent adipogenic differentiation of MSCs by activating the Wnt/β-catenin pathway.

Conclusion

New apoV-based therapies have potential for the treatment of bone marrow adiposity in patients with aging-related osteoporosis and may be further applicable to the treatment of obesity and aging-related diseases.

METTL13 is essential for the survival of acute myeloid leukemia cells by regulating MYC

Recently, some methyltransferase-like (METTL) proteins have been found to play crucial roles in the development of acute myeloid leukemia (AML) through mediating RNA modifications, such as METTL3/14/16 mediated N6-methyladenosine (m6A) and METTL1 mediated N7-methylguanosine (m7G). However, the roles of other METTL proteins in AML progression remain unknown. Here, we examined the expression levels of all METTL members in AML samples and showed that METTL13 was increased in AML and positively correlated with poor prognosis. Moreover, METTL13 deficiency impaired AML cell proliferation capability in vitro, improved the survival of AML cell line xenograft immune-deficient mice, and reduced tumor infiltration in vivo. Mechanistically, MYC was downregulated after METTL13 knockdown and forced expression of MYC rescued the cell proliferation defect in METTL13-deficient AML cells. Our findings uncover the critical role of METTL13 in the survival of AML cells and identify MYC as a potential downstream target of METTL13. This work highlights METTL13 as a promising candidate target for AML therapy.

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.

WTAP/YTHDF1-mediated m6A modification amplifies IFN-γ-induced immunosuppressive properties of human MSCs

INTRODUCTION

The immunosuppressive capacity of mesenchymal stem cells (MSCs) is dependent on the "license" of several pro-inflammatory factors to express immunosuppressive molecular profiles, which determines the therapeutic efficacy of MSCs in immune-mediated inflammatory diseases. Of those, interferon-γ (IFN-γ) is a key inducer for the expression of immunosuppressive molecular profiles; however, the mechanism underlying this effect is unknown.

OBJECTIVES

To elucidate the regulation mechanism and biological functions of N6-methyladenosine (m6A) modification in the immunosuppressive functions by the IFN-γ-licensing MSCs.

METHODS

Epitranscriptomic microarray analysis and MeRIP-qPCR assay were performed to identify the regulatory effect of WTAP in the IFN-γ-licensing MSCs. RIP-qPCR, western blot, qRT-PCR and RNA stability assays were used to determine the regulation of WTAP/m6A/YTHDF1 signaling axis in the expression of immunosuppressive molecules. Further, functional capacity of T cells was tested using flow cytometry, and both DSS-induced colitis mice and CIA mice were constructed to clarify the effect of WTAP and YTHDF1 in MSC-mediated immunosuppression.

RESULTS

We identified that IFN-γ increased the m6A methylation levels of immunosuppressive molecules, while WTAP deficiency abolished the IFN-γ-induced promotion of m6A modification. IFN-γ activated ERK signaling, which induced WTAP phosphorylation. Additionally, the stabilization of WTAP post-transcriptionally increased the mRNA expression of immunosuppressive molecules (IDO1, PD-L1, ICAM1, and VCAM1) in an m6A-YTHDF1-dependent manner; this effect further impacted the immunosuppressive capacity of IFN-γ licensing MSCs on activated T cells. Notably, WTAP/YTHDF1 overexpression enhanced the therapeutic efficacy of IFN-γ licensing MSCs and restructures the ecology of inflammation in both colitis and arthritis models.

CONCLUSION

Our results showed that m6A modification of IDO1, PD-L1, ICAM1, and VCAM1 mRNA mediated by WTAP-YTHDF1 is involved in the regulation of IFN-γ licensing MSCs immunosuppressive abilities, and shed a light to enhance the clinical therapeutic potential of IFN-γ-licensing MSCs.

Mechanistic insights into stem cell fate regulation via RNA methylation

Stem cells possess an extraordinary ability for self-renewal and differentiation, making them essential for tissue repair, regeneration, and anti-aging. RNA methylation is crucial in regulating stem cell fate by modulating gene expression. This review synthesizes current research on RNA methylation modifications, such as m6A, m7G, m5C, and m1A, and their impact on adult stem cell fate. It provides a comprehensive overview of the molecular machinery involved in RNA methylation, emphasizes the critical roles of these modifications in stem cell biology, reviews the latest advancements in sequencing technologies, and discusses potential crosstalk between RNA methylation and epigenetic mechanisms.

WTAP improves chondrocyte loss and dysfunctions to ameliorate osteoarthritis through mediating the mA methylation and mRNA stability of IL-33

Osteoarthritis (OA) is a multifactorial degenerative disorder entailing cartilage loss and progressive joint failure. m6A RNA methylation could impact multiple disorders, including OA. In this study, m6A methylation regulator WTAP was down-regulated in OA cartilage, accompanied by significantly lower m6A methylation levels in OA tissues. In the DMM-induced mice OA model and IL-1β- or TNF-α-stimulated chondrocytes, WTAP and m6A methylation levels were decreased, but IL-1β, IL-6, and TNF-α cytokine expressions were elevated. In vivo and in vitro, WTAP overexpression increased m6A methylation levels but reduced proinflammatory cytokine contents. Furthermore, WTAP overexpression (OE) increased chondrocyte viability and proliferation, aggrecan and collagen II protein, and decreased cell apoptosis, MMP3, MMP13, and ADAMTS5. WTAP-mediated m6A methylation of IL-33 and impaired IL-33 mRNA stability. IL-33 OE caused no changes to WTAP expression; however, IL-33 OE partially attenuated WTAP OE-induced IL-33 downregulation. IL-33 overexpression inhibited chondrocyte viability and proliferation, decreased aggrecan and collagen II but elevated MMP3, MMP13, and ADAMTS5, and increased cell apoptosis and proinflammatory cytokine contents. More importantly, IL-33 eliminated the effects of WTAP OE on chondrocytes. Therefore, WTAP is down-regulated in OA; WTAP improves chondrocyte proliferation and function, thereby ameliorating OA through mediating m6A methylation of IL-33 and impairing IL-33 mRNA stability.

Arsenic and metabolic diseases: New insights from mesenchymal stem cells

Arsenic is a common toxic metal contaminant in the environment. Humans are exposed to arsenic through drinking water, air, food, and medical treatment. Chronic exposure to arsenic is a well-documented risk factor of type 2 diabetes and a potential risk factor of osteoporosis and obesity. Mesenchymal stem cells (MSCs) are adult stem cells with multiple differentiation potential and immunomodulatory capacity. These cells have shown therapeutic potential in experimental studies of metabolic diseases by differentiating into parenchymal cells of damaged tissues, such as islet-like cells and osteoblasts, and resisting chronic inflammation. Meanwhile, when key functional genes were suppressed in MSCs, experimental animals showed metabolic disease-related changes, such as insulin resistance and obesity. Arsenic exposure inhibits the differentiation capacity of MSCs, leads to changes in the synthesis and secretion of immunomodulatory factors, and induces cellular senescence and apoptosis. Therefore, dysfunction and death of MSCs may be important pathogenesis of arsenic-related metabolic diseases. Future studies on the functional changes of MSCs in arsenic-related metabolic diseases and the role of MSCs in arsenic pathogenesis are worthwhile. In addition, the mechanism of arsenic-induced dysfunction in MSCs needs to be explored in depth.

METTL14 regulates chondrogenesis through the GDF5-RUNX-extracellular matrix gene axis during limb development

m6A RNA methylation is essential for many aspects of mammalian development but its roles in chondrogenesis remain largely unknown. Here, we show that m6A is necessary for chondrogenesis and limb morphogenesis using limb progenitor-specific knockout mice of Mettl14, an essential subunit in the m6A methyltransferase complex. The knockout disrupts cartilage anlagen formation in limb buds with 11 downregulated proteins known to dysregulate chondrogenesis and shorten limb skeletons upon mutation in mice and humans. Further studies show a gene regulatory hierarchy among the 11 proteins. m6A stabilizes the transcript and increases the protein level of GDF5, a BMP family member. This activates the chondrogenic transcription factor genes Runx2 and Runx3, whose mRNAs are also stabilized by m6A. They promote the transcription of six collagen genes and two other chondrogenic genes, Ddrgk1 and Pbxip1. Thus, this study uncovers an m6A-based cascade essential for chondrogenesis during limb skeletal development.

Regulation of protein arginine methyltransferase in osteoporosis: a narrative review

Osteoporosis (OP), a systemic bone disease characterised by increased bone fragility and susceptibility to fracture, is mainly caused by a decline in bone mineral density (BMD) and quality caused by an imbalance between bone formation and resorption. Protein arginine methyltransferases (PRMTs) are epigenetic factors and post-translational modification (PTM) enzymes participating in various biological processes, including mRNA splicing, DNA damage repair, transcriptional regulation, and cell signalling. They act by catalysing the transfer and modification of arginine residues and, thus, have become therapeutic targets for OP. In-depth studies have found that these enzymes also play key roles in bone matrix protein metabolism, skeletal cell proliferation and differentiation, and signal pathway regulation to regulate bone formation, bone resorption balance, or both and jointly maintain bone health and stability. However, the expression changes and mechanisms of action of multiple members of the PRMT family differ in OP. Therefore, this paper discusses the biological functions, mechanisms of action, and influencing factors of PRMTs in OP, which is expected to provide a new understanding of the pathogenesis of OP. Furthermore, we present theoretical support for the development of more precise and effective treatment strategies as well as for further study of the molecular mechanisms of PRMTs.

Metabolite-dependent m6A methylation driven by mechanotransduction-metabolism-epitranscriptomics axis promotes bone development and regeneration

Intramembranous ossification, a major bone development process, begins with the condensation of precursor cells through the timely structural adaption of extracellular matrix (ECM) catering to rapid cellular morphological changes. Inspired by this, we design a highly cell-adaptable hydrogel to recapitulate an ECM-dependent mechanotransduction-metabolism-epitranscriptomics axis in mesenchymal stromal cells (MSCs). This hydrogel significantly enhances the E-cadherin-mediated cell-cell interactions of MSCs and promotes glucose uptake and tricarboxylic acid (TCA) cycle activities. We further show that elevated succinate inhibits fat mass and obesity-associated protein (FTO), a N6-methyladenosine (m6A) demethylase, thereby enhancing methyltransferase-like 3 (METTL3)-driven m6A methylation. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) indicates increased m6A methylation of runt-related transcription 2 (Runx2), a key osteogenic signaling factor, promoting osteogenesis of hydrogel-delivered MSCs and bone regeneration in critical-sized bone defects. Our findings reveal the mechanism underlying the critical impact of adaptable ECM structures on tissue development and provide valuable guidance for the design of ECM-mimetic cell carriers to enhance the therapeutic outcomes of regenerative medicine.

Role of METTL16 in PPARγ methylation and osteogenic differentiation

Osteoporosis, a prevalent bone disease, is characterized by the deterioration of bone tissue microstructure and imbalanced osteogenesis. The regulatory role of PPARγ m6A methylation mediated by METTL16 remains poorly elucidated. This study utilized advanced single-cell RNA sequencing (scRNA-seq) and Bulk RNA-seq techniques to explore how METTL16 influences the osteogenic differentiation of Bone Marrow-Derived Mesenchymal Stem Cells (BMSCs) and its implication in osteoporosis. The research revealed that METTL16 enhances the suppression of osteogenic differentiation in BMSCs, while PPARγ is associated with BMSC ferroptosis. Mechanistically, METTL16 facilitates the m6A modification of PPARγ transcription, thereby promoting ferroptosis in BMSCs and impeding their osteogenic differentiation. The in vivo animal experiments confirmed the pivotal role of the METTL16-PPARγ axis in osteoporosis development in mice. These findings suggest that the regulation of PPARγ m6A methylation by METTL16, leading to ferroptosis, is a critical mechanism impacting BMSC osteogenic differentiation and the pathogenesis of osteoporosis.

METTL3 obstructs vascular smooth muscle cells osteogenic reprogramming by methylating Runx2 in chronic kidney disease

The reprogrammed osteogenic phenotype of vascular smooth muscle cells (VSMCs) is considered a critical mechanism of vascular calcification (VC) in chronic kidney disease (CKD). Currently, the RNA N6-methyladenosine (m6A) modification is deciphered to be dynamically and reversibly participated in functional regulation of VSMCs. Here, we discover that serum m6A levels in RNA are dramatically reduced as VC progressed in patients with CKD, and this m6A demethylation is mainly due to the downregulation of methyltransferaselike-3 (METTL3). Functionally, METTL3 depletion exacerbates, whereas its overexpression attenuates calcification progression and osteogenic reprogramming. Mechanistically, Runx2, a crucial osteogenic gene, is identified as a key downstream target of METTL3-mediated m6A methylation. METTL3 negatively regulates Runx2 expression through the m6A modification. Overexpression of METTL3 exacerbates Runx2 mRNA degradation, which is orchestrated by the m6A reader YT521-B homology domain family 2 (YTHDF2) through specifically recognizing its m6A sites in the 3'UTR region. Finally, in vivo METTLs inhibitor SAH treatment aggravates VC and osteogenic conversion in aortas of CKD rats, accompanied by Runx2 expression upregulation. These above data reveal an underlying mechanism by which the m6A writer METTL3 regulates Runx2 expression through YTHDF2-mediated mRNA degradation and suggest a potential therapeutic strategy to reverse the osteogenic reprogramming of VSMCs.

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.

An epitranscriptomic program maintains skeletal stem cell quiescence via a METTL3-FEM1B-GLI1 axis

Skeletal stem cells (SSCs) maintain the skeletal system via pluripotency and differentiation capacity. However, it remains largely unknown how these cells precisely regulate their function to maintain skeletal organization. Here, we delineate the RNA m6A modification landscape across skeletal cell populations in the mouse epiphysis. Our findings show that m6A modifications are prevalent in skeletal stem cell and progenitor populations and play critical roles in cell fate determination. Genetic deletion of Mettl3, the core catalytic subunit of the m6A-methyltransferase complex, in murine skeletal stem and progenitors impaired bone development, leading to shortened limbs, disrupted growth plate zonation, and decreased bone mass. Moreover, Mettl3 deficiency induced quiescence exit in SSCs, together with compromised self-renewal capacity and differentiation potential. Mechanistically, Mettl3-mediated m6A modification reduced mRNA stability of the Cul2-RING E3 ligase complex subunit Fem1b, which subsequently stabilizes Gli1 protein, a key transcription factor of Hedgehog pathway for maintaining SSC identity and function. Thus, we present a comprehensive RNA m6A modification landscape of skeletal cell hierarchy and uncover the essential function of epitranscriptomically-regulated proteostasis in maintaining SSCs quiescence and potency.

Fat mass and obesity-associated protein in mesenchymal stem cells inhibits osteoclastogenesis via lnc NORAD/miR-4284 axis in ankylosing spondylitis

BACKGROUND

Ankylosing spondylitis (AS) is recognized as a long-term inflammatory disorder that leads to inflammation in the spine and joints, alongside abnormal bone growth. In previous studies, we reported that mesenchymal stem cells (MSCs) derived from individuals with AS demonstrated a remarkable inhibition in the formation of osteoclasts compared to those obtained from healthy donors. The mechanism through which MSCs from AS patients achieve this inhibition remains unclear.

AIM

To investigate the potential underlying mechanism by which MSCs from individuals with ankylosing spondylitis (AS-MSCs) inhibit osteoclastogenesis.

METHODS

We analysed fat mass and obesity-associated (FTO) protein levels in AS-MSCs and MSCs from healthy donors and investigated the effects and mechanism by which FTO in MSCs inhibits osteoclastogenesis by coculturing and measuring the levels of tartrate-resistant acid phosphatase, nuclear factor of activated T cells 1 and cathepsin K.

RESULTS

We found that FTO, an enzyme responsible for removing methyl groups from RNA, was more abundantly expressed in MSCs from AS patients than in those from healthy donors. Reducing FTO levels was shown to diminish the capacity of MSCs to inhibit osteoclast development. Further experimental results revealed that FTO affects the stability of the long non-coding RNA activated by DNA damage (NORAD) by altering its N6-methyladenosine methylation status. Deactivating NORAD in MSCs significantly increased osteoclast formation by affecting miR-4284, which could regulate the MSC-mediated inhibition of osteoclastogenesis reported in our previous research.

CONCLUSION

This study revealed elevated FTO levels in AS-MSCs and found that FTO regulated the ability of AS-MSCs to inhibit osteoclast formation through the long noncoding RNA NORAD/miR-4284 axis.

METTL3-mediated m6A modification of circSTAT6 modulates miR-188-3p/Beclin1 axis to promote osteogenic differentiation of mesenchymal stem cells

BACKGROUND

The role of N6-methyladenosine (m6A)-modified circRNAs in disease progression is of great significance. However, the specific impact of m6A modification of circSTAT6 on osteoporosis (OP) is still uncertain.

METHODS

The qRT-PCR was employed to assess the levels of METTL3, circSTAT6, miR-188-3p, and Beclin1. To investigate the interaction between miR-188-3p and circSTAT6 or Beclin, a dual-luciferase reporter assay was performed. To evaluate osteogenic differentiation in bone marrow mesenchymal stem cell (BMSC), western blot analysis was conducted to evaluate the protein expression of osteogenic markers, including ALP, OPN, and Runx2. In addition, alizarin red and alkaline phosphatase (ALP) staining assays were employed to assess osteogenesis.

RESULTS

The findings revealed that the downregulation of circSTAT6 was observed in OP. On the other hand, the overexpression of circSTAT6 was found to enhance the osteogenic differentiation of BMSC. In addition, the involvement of METTL3 in mediating m6A methylation of circSTAT6 was identified, which ultimately promoted osteogenesis. Furthermore, circSTAT6 functioned as an miR-188-3p sponge to regulate the expression of Beclin1. Further study revealed that the osteogenic-enhancing effect caused by circSTAT6 overexpression was counteracted by introducing a miR-188-3p mimic. Similarly, the osteogenic-promoting impact of the miR-188-3p inhibitor was reversed by suppressing Beclin1 expression.

CONCLUSIONS

The present study revealed, for the first time, that METTL3-mediated m6A modification of circSTAT6 regulated the miR-188-3p/Beclin1 axis to promote the osteogenic differentiation of BMSC. These findings offer a potential therapeutic target for the treatment of OP.

Review of the role and potential clinical value of m6A methylation modifications in the biological process of osteosarcoma

Osteosarcoma (OS), an aggressive bone tumor, is a substantial threat to the quality of life and survival of affected individuals. Despite recent improvements in OS therapies, the considerable variability and chemotherapy resistance of this cancer necessitate continuous research to discover new treatment targets and biomarkers. Recent epigenetic advances highlight the crucial role of N6-methyladenosine (m6A) methylation in cancer. In OS, m6A methylation has been demonstrated to be a pivotal component in the pathogenesis. This review introduces new findings regarding the association between m6A methylation regulators and OS, and summarizes the potential clinical applications of OS and m6A methylation regulators, including the role of m6A methylation in OS proliferation, growth, apoptosis, and cell migration, invasion, and metastasis; relationship between m6A methylation and OS chemotherapy resistance; and relationship between m6A methylation and OS prognosis. Our review had certain limitations. The interaction between m6A methylation regulators and other oncogenic factors, such as lncRNAs and ncRNAs, is not fully understood. We hope that these potential methods will be translated into clinical applications and effective treatment.

Activated NETosis of bone marrow neutrophils up-regulates macrophage osteoclastogenesis via cGAS-STING/AKT2 pathway to promote osteoporosis

Bone marrow (BM) of postmenopausal osteoporosis has been found highly inflammatory, resulting from dysregulated immune cells induced by both estrogen efficiency and body aging. NETosis of neutrophils has been found aberrantly activated in age-related chronic inflammation, while their role in postmenopausal osteoporosis remains unclear. Here we found NETosis of BM neutrophils of OVX (ovariectomy) mice was significantly activated, and we verified NETs released by neutrophils induced M1 polarization and osteoclastogenesis of RAW264.7 macrophages. Further, we demonstrated effects of NETs on osteoclastogenesis was mediated by cGAS-STING/AKT2 pathway. Finally, we found in vivo NETs-clearance through GSK484 significantly inhibited osteoclastogenesis and attenuated osteoporosis of OVX mice. Our study highlights the role of neutrophil NETosis in activating osteoclastogenesis and bone resorption of postmenopausal osteoporosis, thereby providing novel targets for bone loss treatment.

Cardiovascular Mettl3 Deficiency Causes Congenital Cardiac Defects and Postnatal Lethality in Mice

N6-methyladenosine (m6A) is the most common epigenetic modification of RNA, but whether m6A RNA methylation modulates cardiovascular development or congenital heart diseases (CHDs) has not been determined. The published high-throughput sequencing data suggested that transcripts of genes related to CHDs were prone to m6A modification, while the expression of methyltransferase-like 3 (METTL3)-involved methyltransferase complex was downregulated in mouse embryonic hearts following prenatal alcohol exposure as a critical CHD risk factor, indicating the association of insufficient m6A RNA methylation with CHDs. Using cardiovascular-specific Mettl3 knockout mice (Tagln-Cre; Mettl3flox/flox ), we observed that cardiovascular Mettl3 deficiency resulted in postnatal lethality and profound congenital cardiac defects, including left pulmonary stenosis, ventricular septal defects, and right ventricular hypoplasia. The m6A-specific methylated RNA-immunoprecipitation sequencing identified Sox4, Sox11, and Mef2a, the critical transcription factors involved in the right ventricle and outflow tract development, were the regulatory targets of METTL3-catalyzed m6A RNA methylation. Mettl3 deficiency-caused insufficient m6A RNA methylation downregulated the expression of SOX4, SOX11, and MEF2A in mouse embryonic hearts. In conclusion, cardiovascular Mettl3 deficiency directly led to congenital cardiac defects by downregulating the m6A-dependent expression of Mef2a, Sox4, and Sox11. METTL3-catalyzed m6A RNA methylation may become a potential target for preventing and treating CHDs.

Metabolism-epigenetic interaction-based bone and dental regeneration: From impacts and mechanisms to treatment potential

Metabolic pathways exhibit fluctuating activities during bone and dental loss and defects, suggesting a regulated metabolic plasticity. Skeletal remodeling is an energy-demanding process related to altered metabolic activities. These metabolic changes are frequently associated with epigenetic modifications, including variations in the expression or activity of enzymes modified through epigenetic mechanisms, which directly or indirectly impact cellular metabolism. Metabolic reprogramming driven by bone and dental conditions alters the epigenetic landscape by modulating the activities of DNA and histone modification enzymes at the metabolite level. Epigenetic mechanisms modulate the expression of metabolic genes, consequently influencing the metabolome. The interplay between epigenetics and metabolomics is crucial in maintaining bone and dental homeostasis by preserving cell proliferation and pluripotency. This review, therefore, aims to examine the effects of metabolic reprogramming in bone and dental-related cells on the regulation of epigenetic modifications, particularly acetylation, methylation, and lactylation. We also discuss the effects of chromatin-modifying enzymes on metabolism and the potential therapeutic benefits of dietary compounds as epigenetic modulators. In this review, we highlight the inconsistencies in current research findings and suggest potential approaches to translate fundamental insights into clinical treatments for bone and tooth diseases.

Methyltransferase-Like 3-Mediated N6-Methyladenosine Modification on RNAs: A Novel Perspective for the Pathogenesis and Treatment of Bone Diseases

Osteoarthritis, osteoporosis, and osteosarcoma are prevalent osseous pathologies associated with the aberrant functionality of chondrocytes, osteoclasts, and osteoblasts, respectively. These conditions frequently exhibit therapeutic resistance and possess a high mortality risk, thus representing substantial health threats. To mitigate these concerns, it is imperative to investigate novel mechanistic insights. Methyltransferase-like 3 (METTL3) is pivotal in these disorders by modulating gene expression via N6-methyladenosine (m6A) modifications on RNA, thereby impacting cellular processes. Although considerable research has elucidated METTL3's involvement in these diseases, a systematic review is essential to summarise these findings and evaluate METTL3's significance. This review endeavours to aggregate and examine contemporary studies to elucidate METTL3's role in bone pathologies and its clinical implications. We propose that METTL3 constitutes a risk gene in these conditions by mediating m6A modifications on both mRNAs and non-coding RNAs, suggesting that METTL3 may serve as a critical diagnostic biomarker and therapeutic target. In conclusion, this review provides an extensive analysis of METTL3 and its correlation with osteoarthritis, osteoporosis, and osteosarcoma, offering valuable perspectives on extant research and serving as a valuable reference for researchers engaged in both basic and translational studies.

A novel PTH1R mutation causes primary failure of eruption via the cAMP-PI3K/AKT pathway

BACKGROUND

Primary failure of eruption (PFE) is a rare disorder characterized by a posterior open bite. While mutations in the parathyroid hormone 1 receptor (PTH1R) gene have been demonstrated to cause PFE, the underlying mechanisms remain largely unknown.

METHODS

Whole exome sequencing was conducted to identify PTH1R variants in a PFE family. MG63 cells that stably expressed the corresponding mutant PTH1R were established using lentiviruses. Next, osteogenesis was assessed by measuring cell alkaline phosphatase activity, conducting alizarin red staining, and evaluating osteoblast-specific gene expression. Then, computational analysis of binding affinity and RNA sequencing were carried out. Lastly, rescue experiments were performed to validate the mechanism underlying the pathogenesis of PFE.

RESULTS

A novel PTH1R missense mutation (c.904G > A, p.E302K) was identified in a Chinese family affected by PFE. Moreover, the E302K mutation inhibited the expression of osteogenic-specific genes and proteins in MG63 cells. Computational analysis revealed the E302K mutation decreased the binding affinity of Gαs to the PTH1R protein. Consistently, cAMP accumulation assays demonstrated that the E302K mutation impaired the intracellular PTH1-34 -induced accumulation of cAMP. Further RNA sequencing analysis and validation experiments revealed that the PI3K-AKT signaling pathway was predominantly down-regulated in response to the E302K mutation. Finally, forskolin partially restored the effects of the E302K mutation on osteogenesis.

CONCLUSIONS

This study indicated that the E302K mutation in PTH1R decreased the binding affinity of PTH1R protein for Gαs, down-regulated the cAMP-PI3K/AKT signaling pathway, and inhibited osteogenesis, eventually leading to PFE. This study not only expands the genotypic spectrum of PTH1R mutations but also elucidates the underlying pathogenic mechanism of PTH1R-associated PFE.

Silencing YTHDF2 Induces Apoptosis of Neuroblastoma Cells In a Cell Line-Dependent Manner via Regulating the Expression of DLK1

Neuroblastoma (NB) is the most common extracranial malignant solid tumor in children. The complications caused by traditional chemoradiotherapy seriously affect the quality of life of patients with NB. In this study, NGP, KCNR, and SH-SY5Y (SY5Y) cell lines were used. Retinoic acid (RA, 5 µM) was used to treat NB cells for 48 h. siRNAs were used to silence the expression of DLK1 or YTHDF2. Cell confluence was analyzed using IncuCyte ZOOM to evaluate cell proliferation of NB cells. RT-qPCR and western blotting were performed to detect the expression of target molecules. Annexin V/PI staining and Caspase-Glo 3/7 assay were performed to detect cell apoptosis. RNA m6A quantification, MeRIP-qPCR, and RIP-qPCR were performed. Results showed that RA treatment decreased the expression of DLK1 and YTHDF2 in NB cells, and low expression of DLK1 was correlated with good prognosis of patients. Knockdown of the expression of DLK1 or YTHDF2 inhibited cell proliferation and induced apoptosis of SY5Y cells, but not NGP and KCNR cells. Furthermore, we found that there are m6A modification sites in DLK1 mRNA, and the expression of m6A modified DLK1 mRNA increased after RA treatment, and YTHDF2 regulates the expression level of DLK1, and the expression of YTHDF2-bound DLK1 mRNA decreased after RA treatment. These suggest that YTHDF2 may regulate the proliferation and apoptosis of NB cells in a cell line-dependent manner by binding to the m6A modification site of DLK1 mRNA to affect its expression, and YTHDF2 and DLK1 are potential therapeutic targets for patients with NB.

Inhibition of Mettl3 by STM2457 and Loss of Macrophage Mettl3 Alleviate Pulmonary Hypertension and Right Heart Remodeling

BACKGROUND

m6A RNA methylation is a critical epigenetic modification involved in the pathogenesis of pulmonary arterial hypertension (PAH). While macrophage-mediated inflammation plays a central role in PAH, the specific contributions of m6A regulators within macrophages are not yet fully understood. This study explores the role of METTL3 in macrophages, with particular emphasis on its contribution to the progression of PAH.

METHODS

SU5416/Hypoxia (SuHx) PAH mouse models were treated daily with STM2457, a selective METTL3 antagonist, or vehicle for 10 days. Additionally, SuHx PAH was induced in Mettl3flox/floxlyz2cre + and Mettl3flox/flox mice using genetic approaches. Pulmonary acceleration time to pulmonary ejection time (PAAT/PAET) and right ventricular free wall (RVFWD) were measured by ultrasound. Hemodynamic parameters, including right ventricular systolic pressure (RVSP), were assessed. Pulmonary vascular and right heart remodeling were evaluated using HE staining, while vascular and right heart fibrosis were assessed by Masson's trichrome staining. The expression of fibrosis-associated genes was quantified by qPCR. Macrophage activation in tissues was determined via CD86 and CD206 immunofluorescence staining, and the expression of inflammatory cytokines and fibrosis-associated genes was quantified by qPCR.

RESULTS

METTL3 expression was significantly upregulated in the lungs and macrophages of PAH models. Treatment with STM2457 reversed the progression of SuHx PAH, as evidenced by a reduction in RVSP, attenuation of pulmonary vascular and right heart remodeling, and decreased fibrosis in both the heart and lungs. Furthermore, the expression of fibrosis-associated genes in the right heart, including Col1a1, Col1a3, and α-SMA, was downregulated following STM2457 treatment and METTL3 depletion in macrophages. Both STM2457 treatment and METTL3 depletion resulted in a significant reduction in the number of CD86+ and CD206+ macrophages, accompanied by a suppression of pro-inflammatory cytokines such as IL-1β and iNOS, alongside an upregulation of anti-inflammatory cytokines, including IL-10 and Arg1.

CONCLUSION

STM2457 treatment and METTL3 depletion in macrophages effectively reversed SuHx PAH by modulating macrophage inflammatory responses and alleviating pulmonary vascular and right heart remodeling, as well as fibrosis. These findings underscore the role of METTL3 in PAH pathogenesis by regulating macrophage function and inflammation.

Landscape analysis of m6A modification reveals the dysfunction of bone metabolism in osteoporosis mice

Osteoporosis (OP) is a prevalent chronic bone metabolic disorder that affects the elderly population, leading to an increased susceptibility to bone fragility. Despite extensive research on the onset and progression of OP, the precise mechanisms underlying this condition remain elusive. The m6A modification, a prevalent form of chemical RNA modification, primarily regulates posttranscriptional processes, including RNA stability, splicing, and translation. Numerous studies have underscored the crucial functions of m6A regulators in OP. This study aimed to explore the relationship between OP and RNA m6A methylation, investigating its underlying mechanisms through comprehensive bioinformatic analysis and experimental validation. The mRNA sequencing (mRNA-seq) and methylated RNA immunoprecipitation sequencing (MeRIP-seq) were performed on control mice as well as ovariectomized mice to discover differentially expressed genes (DEGs) and m6A regulators in OP. The results revealed dysregulation of a majority of bone metabolism-related genes and m6A regulators in ovariectomized mice, indicating a closely linked relationship between them. Our research findings indicated that m6A modification is essential in regulating OP, offering potential insights for prevention and treatment.

Role of the m6A demethylase ALKBH5 in gastrointestinal tract cancer (Review)

N6‑methyladenosine (m6A) is one of the most universal, abundant and conserved types of internal post‑transcriptional modifications in eukaryotic RNA, and is involved in nuclear RNA export, RNA splicing, mRNA stability, gene expression, microRNA biogenesis and long non‑coding RNA metabolism. AlkB homologue 5 (ALKBH5) acts as a m6A demethylase to regulate a wide variety of biological processes closely associated with tumour progression, tumour metastasis, tumour immunity and tumour drug resistance. ALKBH5 serves a crucial role in human digestive system tumours, mainly through post‑transcriptional regulation of m6A modification. The present review discusses progress in the study of the m6A demethylase ALKBH5 in gastrointestinal tract cancer, summarizes the potential molecular mechanisms of ALKBH5 dysregulation in gastrointestinal tract cancer, and discusses the significance of ALKBH5‑targeted therapy, which may provide novel ideas for future clinical prognosis prediction, biomarker identification and precise treatment.

Oestrogen suppresses the adipogenesis of fibro/adipogenic progenitors through reactivating the METTL3-ESR1-mediated loop in post-menopausal females

BACKGROUND

Post-menopausal women experience more severe muscular fatty infiltration, though the mechanisms remain unclear. The decline in estrogen levels is considered as a critical physiological alteration during post-menopause. Fibro/adipogenic progenitors (FAPs) are identified as major contributors to muscular fatty infiltration. This study aimed to investigate the detailed mechanism underlying the excessive muscular fatty infiltration in postmenopausal females.

METHODS

Supraspinatus muscle samples were collected from female patients with or without menopause, and from mice with or without ovariectomy (OVX), to evaluate muscular fatty infiltration and isolated FAPs. The expressions of (estrogen receptor 1) ESR1, methyltransferase-like 3 (METTL3), and adipogenesis ability in FAPs from post-menopausal women and OVX mice were investigated. RNA sequencing (RNA-Seq) was performed to explore the gene expression profiles and potential mechanisms in FAPs from Pdgfrα-CreERT2; Esr1 knockout (Esr1 KO) mice and Esr1 flox/flox (Esr1 f/f) mice. The interplay of the METTL3-ESR1 mediated loop and its role in regulating adipogenesis in FAPs were investigated using dual luciferase reporter assays, chromatin immunoprecipitation (ChIP), and protein and RNA stability assays. The effects of estrogen supplementation on muscular fatty infiltration and locomotor function in OVX mice were evaluated by immunofluorescent staining and functional analysis.

RESULTS

Decreased expression of ESR1/METTL3 and increased adipogenesis ability in FAPs was found in post-menopausal female. METTL3-mediated m6A methylation promoted ESR1 mRNA stability at the post-transcriptional level in FAPs. METTL3-mediated m6A modification promoted ESR1 expression by stabilizing ESR1 mRNA, while ESR1 acted as a transcription factor that enhanced METTL3 transcription in turn. ESR1 also suppressed the transcription of the adipogenic transcription factor peroxisome proliferator-activated receptor gamma (PPARγ), thereby inhibiting adipogenesis in FAPs. Reactivation of the METTL3-ESR1 mediated loop by estrogen alleviated excessive adipogenesis in FAPs from post-menopausal women, and it also reduced muscular fatty infiltration, and improved locomotor function in OVX mice.

CONCLUSION

Excessive muscular fatty infiltration in post-menopausal women arose from the disruption of the METTL3-ESR1 mediated loop of FAPs due to estrogen deficiency. Reactivation of the METTL3-ESR1 mediated loop by estrogen may serve as a novel intervention to inhibit excessive adipogenesis of post-menopausal female FAPs, thereby ameliorating muscular fatty infiltration and improving locomotor function in post-menopausal females.

KEY POINTS

Oestrogen insufficiency disrupted the METTL3ESR1 loop in post-menopausal FAPs, causing excessive muscular fatty infiltration. METTL3-mediated m6A modification stabilized ESR1 mRNA and enhanced ESR1 expression, while increased ESR1 further promoted METTL3 transcription. ESR1 inhibited the transcription of adipogenic factor PPARγ, ameliorating adipogenesis in FAPs. Reactivating the METTL3ESR1 loop via oestrogen in FAPs reduced muscular fatty infiltration and improved locomotor function.

MAM-STAT3-Driven Mitochondrial Ca+2 Upregulation Contributes to Immunosenescence in Type A Mandibuloacral Dysplasia Patients

Individuals with homozygous laminA/C p.R527C mutations manifest a severe form of Mandibuloacral dysplasia-(MAD) and exhibit overlapping progeroid symptoms, for which the underlying molecular pathology remains unknown. Herein, it is shown that MAD patients achieved inflammaging with different pro-inflammatory cytokines compared to progeria-(HGPS) patient. Characterization of MAD iPSC-derived Mesenchymal stem cells (MAD-iMSC) uncovers deregulated mitochondrial Ca+2 as the primary cause of inflammaging, mediated through inflammasome formation rather than the cGAS-STING pathway. Moreover, MAD-iMSCs extracellular vesicles (EVs) can also upregulate mitochondrial Ca+2 in healthy cells. This deregulated Ca+2 homeostasis is indirectly mediated by mitochondrial calcium mediator, signal transducer, and activator of transcription-3 (STAT3), situated on the mitochondrial associated membrane (MAM). Inflammaging is mitigated by various FDA-approved MAM-STAT3 upstream inhibitors, such as (Tocilizumab) or by correcting R527C mutation with CRISPR/CAS9. These results provide new insights into MAD disease and propose targeting defective mitochondrial Ca+2 homeostasis as a promising therapy for reversing immunosenescence.

Melatonin antagonizes bone loss induced by mechanical unloading via IGF2BP1-dependent m6A regulation

Disuse bone loss is prone to occur in individuals who lack mechanical stimulation due to prolonged spaceflight or extended bed rest, rendering them susceptible to fractures and placing an enormous burden on social care; nevertheless, the underlying molecular mechanisms of bone loss caused by mechanical unloading have not been fully elucidated. Numerous studies have focused on the epigenetic regulation of disuse bone loss; yet limited research has been conducted on the impact of RNA modification bone formation in response to mechanical unloading conditions. In this study, we discovered that m6A reader IGF2BP1 was downregulated in both osteoblasts treated with 2D clinostat and bone tissue in HLU mice. Supplementing IGF2BP1 could promote osteoblast proliferation and partially alleviate the adverse effects of mechanical unloading on bone formation. Mechanistically, IGF2BP1 inhibited the degradation of Lef1 mRNA by directly binding to its mRNA and recognizing the m6A modification. Furthermore, LEF1 promoted osteoblast proliferation by upregulating c-Myc and Cyclin D1 expression, as well as participated in mediating IGF2BP1-induced osteoblast activity under mechanical unloading. Notably, Melatonin (MT) might participate in the regulation of the IGF2BP1/LEF1 axis, thereby regulating the proliferation of osteoblasts and bone formation. Collectively, this study revealed a new insight into the regulation of the MT/IGF2BP1/LEF1 pathway in the process of unloading-induced bone loss, which could potentially contribute to establishing therapeutic strategies for disuse osteoporosis.

Multichrome encoding-based multiplexed, spatially resolved imaging reveals single-cell RNA epigenetic modifications heterogeneity

Understanding the heterogeneity of epigenetic modifications within single cells is pivotal for unraveling the nature of the complexity of gene expression and cellular function. In this study, we have developed a strategy based on multichrome encoding and "AND" Boolean logic recognition for multiplexed, spatially resolved imaging of single-cell RNA epigenetic modifications, termed as PRoximity Exchange-assisted Encoding of Multichrome (PREEM). Through the implementation of this strategy, we can now map the expression and nuclear distribution of multiple site-specific RNA N6-methyladenosine (m6A) modifications at the single-molecule resolution level in single-cells, and reveal the previously unknown heterogeneity. Notably, we demonstrate how these patterns change after treatment with various drugs. Moreover, cyclic imaging with tailed DNA self-assembly further suggest the scalability and adaptability of PREEM's design. As an innovative epigenetic modification imaging tool, PREEM not only broadens the horizons of single-cell epigenetics research, enabling joint analysis of multiple targets beyond the limitations of imaging channels, but also reveals cell-to-cell variability, thereby enhancing our capacity to explore cellular functions.

METTL14 Promotes the Osteogenic Differentiation of Human Bone Marrow Stromal Cells via m6A-Dependent Stabilization of USP7 mRNA

Osteoporosis (OP) is a common clinical bone disease that can cause a high incidence of non-stress fractures and is one of the main degenerative diseases that endangers the health and life of middle-aged and older women. The mechanism underlying the abnormal differentiation and function of human bone marrow stem cells (hBMSCs) remains to be elucidated. Cell proliferation and differentiation were determined using 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay, alkaline phosphatase (ALP) staining, and Alizarin Red Staining. The interaction between insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) and ubiquitin-specific protease 7 (USP7) was predicted and validated using bioinformatics approaches, luciferase assays, RNA immunoprecipitation (RIP), and immunoprecipitation (IP). Actinomycin D treatment was used to test the stability of mRNA in the various groups. Methyltransferase-like 14 (METTL14) expression was increased in osteogenic differentiation medium-induced hBSMCs and was associated with enhanced osteogenic differentiation. METTL14 regulated the expression USP7 by modulating its N6-methyladenosine (m6A) level. IGF2BP2 exerted an m6A-dependent effect on USP7 mRNA stability and USP7 increased sirtuin 1 (SIRT1) expression in hBMSCs by enhancing SIRT1 deubiquitination. METTL14 stimulated the osteogenic differentiation of hBMSCs through the m6A-IGF2BP2-USP7 pathway and promoted hBMSCs osteogenic development via SIRT1-Bmi1 signaling. METTL14 stimulated the osteogenic differentiation of hBMSCs by stabilizing USP7 mRNA in an m6A-dependent manner. USP7 was also stabilized by IGF2BP2 and it regulated downstream SIRT1-Bmi1 signaling.

The Role of mRNA Modifications in Bone Diseases

As a type of epigenetic modifications, mRNA modifications regulate the metabolism of mRNAs, thereby influencing gene expression. Previous studies have indicated that dysregulation of mRNA modifications is closely associated with the occurrence and progression of bone diseases (BDs). In this study, we first introduced the dynamic regulatory processes of five major mRNA modifications and their effects on the nucleus export, stability, and translation of mRNAs. We then summarized the mechanisms of mRNA modifications involved in the development of osteoporosis, osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, fractures, osteomyelitis, and osteosarcoma. Finally, we reviewed therapeutic strategies for BDs based on the above mechanisms, focusing on regulating osteoblast and osteoclast differentiation, inhibiting cellular senescence and injury, and alleviating inflammation. This review identified mRNA modifications as potential targets for treating BDs and proposes perspectives on the diversity, targetability, and safety of mRNA-modifying therapies.

METTL3 promotes immature dental pulp stem cells-induced angiogenesis by regulating ETS1 mRNA stability in an m6A-HuR-dependent manner

Angiogenesis serves as the determinate element of pulp regeneration. Dental pulp stem cell (DPSC) implantation can promote the regeneration of dental pulp tissue. Herein, the role of m6A methyltransferase methyltransferase-like 3 (METTL3) in regulating DPSCs-induced angiogenesis during pulp regeneration therapy was investigated. Cell DPSC viability, HUVEC migration, and angiogenesis ability were analyzed by CCK-8 assay, wound healing, Transwell assay, and tube formation assay. The global and EST1 mRNA m6A levels were detected by m6A dot blot and Me-RIP. The interactions between E26 transformation-specific proto-oncogene 1(ETS1), human antigen R(HuR), and METTL3 were analyzed by RIP assay. The relationship between METTL3 and the m6A site of ETS1 was performed by dual-luciferase reporter assay. ETS1 mRNA stability was examined with actinomycin D. Herein, our results revealed that human immature DPSCs (hIDPSCs) showed stronger ability to induce angiogenesis than human mature DPSCs (hMDPSCs), which might be related to ETS1 upregulation. ETS1 knockdown inhibited DPSCs-induced angiogenesis. Our mechanistic experiments demonstrated that METTL3 increased ETS1 mRNA stability and expression level on DPSCs in an m6A-HuR-dependent manner. ETS1 upregulation abolished sh-METTL3's inhibition on DPSCs-induced angiogenesis. METTL3 upregulation promoted DPSCs-induced angiogenesis by enhancing ETS1 mRNA stability in an m6A-HuR-dependent manner. This study reveals a new mechanism by which m6A methylation regulates angiogenesis in DPSCs, providing new insights for stem cell-based tissue engineering.

Epigenetic Mechanisms in Osteoporosis: Exploring the Power of m6A RNA Modification

Osteoporosis, recognised as a metabolic disorder, has emerged as a significant burden on global health. Although available treatments have made considerable advancements, they remain inadequately addressed. In recent years, the role of epigenetic mechanisms in skeletal disorders has garnered substantial attention, particularly concerning m6A RNA modification. m6A is the most prevalent dynamic and reversible modification in eukaryotes, mediating various metabolic processes of mRNAs, including splicing, structural conversion, translation, translocation and degradation and serves as a crucial component of epigenetic modification. Research has increasingly validated that m6A plays a vital role in the proliferation, differentiation, migration, invasion,and repair of bone marrow mesenchymal stem cells (BMSCs), osteoblasts and osteoclasts, all of which impact the whole process of osteoporosis pathogenesis. Continuous efforts have been made to target m6A regulators and natural products derived from traditional medicine, which exhibit multiple biological activities such as anti-inflammatory and anticancer effects, have emerged as a valuable resources for m6A drug discovery. This paper elaborates on m6A methylation and its regulatory role in osteoporosis, emphasising its implications for diagnosis and treatment, thereby providing theoretical references.

N6-Methyladenosine Regulates Cilia Elongation in Cancer Cells by Modulating HDAC6 Expression

Primary cilia are microtubule-based organelles that function as cellular antennae to address multiple metabolic and extracellular cues. The past decade has seen significant advances in understanding the pro-tumorigenic role of N6-methyladenosine (m6A) modification in tumorigenesis. Nevertheless, whether m6A modification modulates the cilia dynamics during cancer progression remains unclear. Here, the results show that m6A methyltransferase METTL3 regulates cilia length in cancer cells via HDAC6-dependent deacetylation of axonemal α-tubulin, thereby controlling cancer development. Mechanically, METTL3 positively regulates the translation of HDAC6 in an m6A-dependent manner, while m6A methylation of A3678 in the coding sequence (CDS) of HDAC6 ameliorates its translation efficiency via facilitating the binding with YTHDF3. The upregulation of HDAC6 induced by METTL3 over-expression is capable of inhibiting cilia elongation and acetylation of α-tubulin, thereby shortening cilia length and accelerating the progression of cervical cancer both in vitro and in vivo. Collectively, depletion of METTL3-mediated m6A modification leads to abnormally elongated cilia via suppressing HDAC6-dependent deacetylation of axonemal α-tubulin, ultimately attenuating cell growth and cervical cancer development.

Bioinformatics analysis and validation of RNA methylation-related genes in osteogenic and adipogenic differentiation of rat bone marrow mesenchymal stem cells

BACKGROUND

The regulatory mechanisms of RNA methylation during the processes of osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) have yet to be fully understood. The objective of our study was to analyze and validate the contribution of RNA methylation regulators to the mechanisms underlying the osteogenic and adipogenic differentiation of rat BMSCs.

METHODS

We downloaded the GSE186026 from the Gene Expression Omnibus (GEO). Differentially expressed genes (DEGs) were screened using the DESeq2 package in R software (version 3.6.3). A total of 50 RNA methylation genes obtained from literature review and summary were intersected with the previous DEGs to obtain RNA methylation genes, which have different expressions (RM-DEGs). Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were utilized to reveal the functional enrichment. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to validate RM-DEGs. Protein-protein interaction network (PPI) analysis and visual analysis were performed using STRING and Cytoscape. RM-DEGs regulatory network was constructed to analyze the top 10 hub genes. The relationship between RM-DEGs, some enriched GO and pathways was also been analyzed. The miRNAs and RM-DEGs regulatory networks were established by using miRWalk and TargetScan.

RESULTS

As part of our research, we detected varying levels of expression for m6A regulators Mettl3 and Rbm15, as well as m7G regulators Mettl1 and Wdr4, in relation to osteogenic differentiation, along with m6A regulator Fmr1 in adipogenic differentiation. The protein-protein interaction (PPI) networks were constructed for 49 differentially expressed genes (DEGs) related to RNA methylation during the process of osteogenic differentiation, and 13 DEGs for adipogenic differentiation. Moreover, top10 hub genes were calculated. In osteogenic differentiation, Mettl3 regulated the Wnt pathway and Hippo pathway by regulating Smad3, Rbm15 regulated the Notch pathway by Notch1, Mettl1 regulated the PI3K-Akt pathway by Gnb4. In adipogenic differentiation, Fmr1 regulated the PI3K-Akt pathway by Egfr. M6A methylation sites of Smad3, Notch1 and Gnb4 were predicted, and the results showed that all three genes were possibly methylated by m6A, and more than 9 sites per gene were possibly methylated. Finally, we constructed the regulatory networks of Mettl3, Rbm15, Mettl1, and Wdr4 and 109 miRNAs in osteogenic differentiation, Fmr1 and 118 miRNAs in adipogenic differentiation.

CONCLUSIONS

Mettl3(m6A), Rbm15(m6A), Wdr4 and Mettl1(m7G) were differentially expressed in osteogenic differentiation, while Fmr1(m6A) was differentially expressed in adipogenic differentiation. These findings offered potential candidates for further research on the involvement of RNA methylation in the osteogenic and adipogenic differentiation of BMSCs.

Mettl3-Mediated m6A Modification is Essential for Visual Function and Retinal Photoreceptor Survival

Purpose

N6-methyladenosine (m6A) modification, one of the most common epigenetic modifications in eukaryotic mRNA, has been shown to play a role in the development and function of the mammalian nervous system by regulating the biological fate of mRNA. METTL3, the catalytically active component of the m6A methyltransferase complex, has been shown to be essential in development of in the retina. However, its role in the mature retina remains elusive. In this study we aim to investigate the in vivo function of Mettl3 in the photoreceptor cells using a conditional knockout allele of Mettl3.

Methods

Deletion of Mettl3 in rod cells led to progressive retinal degeneration, including progressive retinal thinning, impaired visual function, shortened photoreceptor outer segments (OS), and reduced expression of disk membrane proteins. Similarly, Mettl3 deficiency in cone cells led to the gradual degeneration of cone opsins. Additionally, Mettl3 knockout significantly decreased the expression of the METTL14 subunit and overall m6A methylation levels in the retina.

Results

Multi-omics analyses revealed that Mettl3 deletion led to the downregulation of mRNA and protein levels of 10 key target genes in rod cells, ultimately resulting in the progressive death of photoreceptors. Mettl3 controls expression of its target genes by regulating their m6A modification, ultimately leading to rod cell death.

Conclusions

These findings highlight critical roles of METTL3 in maintaining retinal photoreceptor function and further elucidate the mechanisms of m6A modification in photoreceptors.

Qianggu Decoction Alleviated Osteoporosis by Promoting Osteogenesis of BMSCs through Mettl3-Mediated m6A Methylation

Osteoporosis development is linked to abnormal bone marrow mesenchymal stem cells (BMSCs) differentiation. N6-methyladenosine (m6A), a prevalent mRNA modification, is known to influence BMSCs' osteogenic capacity. Qianggu decoction (QGD), a traditional Chinese medicine for osteoporosis, has unknown effects on BMSCs differentiation. This study investigates QGD's impact on BMSCs and its potential to ameliorate osteoporosis through m6A regulation. Using Sprague-Dawley (SD) rats with ovariectomy-induced osteoporosis, it is evaluated QGD's antiosteoporotic effects through micro-CT, histology, Western blotting, and osteoblastogenesis markers. QGD is found to enhance bone tissue growth and upregulate osteogenic markers Runx2, OPN, and OCN. It also promoted BMSCs osteogenic differentiation, as shown by increased calcium nodules and ALP activity. QGD treatment significantly increased m6A RNA levels and Mettl3 expression in BMSCs. Silencing Mettl3 with siRNA negated QGD's osteogenic effects. Collectively, QGD may improve BMSCs differentiation and mitigate osteoporosis, potentially through Mettl3-mediated m6A modification.

RNA modifications: emerging players in the regulation of reproduction and development

The intricate world of RNA modifications, collectively termed the epitranscriptome, covers over 170 identified modifications and impacts RNA metabolism and, consequently, almost all biological processes. In this review, we focus on the regulatory roles and biological functions of a panel of dominant RNA modifications (including m 6A, m 5C, Ψ, ac 4C, m 1A, and m 7G) on three RNA types-mRNA, tRNA, and rRNA-in mammalian development, particularly in the context of reproduction as well as embryonic development. We discuss in detail how those modifications, along with their regulatory proteins, affect RNA processing, structure, localization, stability, and translation efficiency. We also highlight the associations among dysfunctions in RNA modification-related proteins, abnormal modification deposition and various diseases, emphasizing the roles of RNA modifications in critical developmental processes such as stem cell self-renewal and cell fate transition. Elucidating the molecular mechanisms by which RNA modifications influence diverse developmental processes holds promise for developing innovative strategies to manage developmental disorders. Finally, we outline several unexplored areas in the field of RNA modification that warrant further investigation.

KMT2A regulates the autophagy-GATA4 axis through METTL3-mediated m6A modification of ATG4a to promote NPCs senescence and IVDD progression

Intervertebral disc degeneration (IVDD), a disease associated with ageing, is characterised by a notable increase in senescent nucleus pulposus cells (NPCs) as IVDD progresses. However, the specific mechanisms that regulate the senescence of NPCs remain unknown. In this study, we observed impaired autophagy in IVDD-NPCs, which contributed to the upregulation of NPCs senescence and the senescence-associated secretory phenotype (SASP). The dysregulated SASP disrupted NPCs viability and initiated extracellular matrix degradation. Conversely, the restoration of autophagy reversed the senescence phenotype by inhibiting GATA binding protein 4 (GATA4). Moreover, we made the novel observation that a cross-talk between histone H3 lysine 4 trimethylation (H3K4me3) modification and N6-methyladenosine(m6A)-methylated modification regulates autophagy in IVDD-NPCs. Mechanistically, lysine methyltransferase 2A (KMT2A) promoted the expression of methyltransferase-like 3 (METTL3) through H3K4me3 modification, whereas METTL3-mediated m6A modification reduced the expression of autophagy-associated 4a (ATG4a) by attenuating its RNA stability, leading to autophagy damage in NPCs. Silencing KMT2A and METTL3 enhanced autophagic flux and suppressed SASP expression in IVDD-NPCs. Therefore, targeting the H3K4me3-regulated METTL3/ATG4a/GATA4 axis may represent a promising new therapeutic strategy for IVDD.

A two-pronged approach to inhibit ferroptosis of MSCs caused by the iron overload in postmenopausal osteoporosis and promote osseointegration of titanium implant

Postmenopausal osteoporosis (PMOP) is a prevalent condition among elderly women. After menopause, women exhibit decreased iron excretion, which is prone to osteoporosis. To design a specific titanium implant for PMOP, we first analyze miRNAs and DNA characteristics of postmenopausal patients with and without osteoporosis. The results indicate that iron overload disrupts iron homeostasis in the pathogenesis of PMOP. Further experiments confirm that iron overload can cause lipid peroxidation and ferroptosis of MSCs, thus breaking bone homeostasis. Based on the findings above, we have designed a novel Ti implant coated with nanospheres of caffeic acid (CA) and deferoxamine (DFO). CA can bind on the Ti surface through the two adjacent phenolic hydroxyls and polymerize into polycaffeic acid (PCA) dimer, as well as the PCA nanospheres with the repetitive 1,4-benzodioxan units. DFO was grafted with PCA through borate ester bonds. The experimental results showed that modified Ti can inhibit the ferroptosis of MSCs in the pathological environment of PMOP and promote osseointegration in two main ways. Firstly, DFO was released under high oxidative stress, chelating with excess iron and decreasing the labile iron pool in MSCs. Meanwhile, CA and DFO activated the KEAP1/NRF2/HMOX1 pathway in MSCs and reduced the level of intracellular lipid peroxidation. So, the ferroptosis of MSCs is inhibited by promoting the SLC7A11/GSH/GPX4 pathway. Furthermore, the remained CA coating on the Ti surface could reduce the extracellular oxidative stress and glutathione level. This study offers a novel inspiration for the specific design of Ti implants in the treatment of PMOP.

The miR-665/SOST Axis Regulates the Phenotypes of Bone Marrow Mesenchymal Stem Cells and Osteoporotic Symptoms in Female Mice

Osteoporosis is a common degenerative skeletal disease among older people, especially postmenopausal women. Bone marrow mesenchymal stem cells (BMSCs), the progenitors of osteoblasts, are essential to the pathophysiology of osteoporosis. Herein, targeting miRNAs with differential expression in dysfunctional BMSCs was accomplished by bioinformatics analysis based on public databases. Target mRNAs were predicted and applied for signaling pathway and function enrichment annotations. In vitro and in vivo effects of selected miRNA on BMSC proliferation and osteogenesis were investigated, the putative binding between selected miRNA and predicted target mRNA was verified, and the co-effects of the miRNA/mRNA axis on BMSCs were determined. miRNA 665 (miR-665) was down-regulated in osteoporotic BMSCs compared with normal BMSCs and elevated in BMSCs experiencing osteogenic differentiation. In BMSCs, miR-665 overexpression promoted cell proliferation and osteogenic differentiation. miR-665 targeted the Wnt signaling inhibitor sclerostin (SOST) and inhibited SOST mRNA and protein expression. SOST overexpression inhibited BMSC cell proliferation and osteogenic differentiation. When co-transduced to BMSCs, SOST knockdown significantly reversed the effects of miR-665 on BMSCs. In ovariectomy (OVX)-induced osteoporosis model mice, OVX remarkably decreased bone mass, whereas miR-665 overexpression partially improved OVX-induced bone mass loss. miR-665 was down-regulated in osteoporotic BMSCs and up-regulated in osteogenically differentiated BMSCs. In conclusion, the miR-665/SOST axis modulates BMSC proliferation, osteogenic differentiation, and OVX-induced osteoporosis in mice, possibly through Wnt signaling.

Unraveling the landscape of m6A RNA methylation in wound healing and scars

Wound healing is a complex process involving sequential stages of hemostasis, inflammation, proliferation, and remodeling. Multiple cell types and factors, including underlying conditions like diabetes and bacterial colonization, can influence healing outcomes and scar formation. N6-methyladenosine (m6A), a predominant RNA modification, plays crucial roles in gene expression regulation, impacting various biological processes and diseases. m6A regulates embryonic skin morphogenesis, wound repair, and pathophysiological processes like inflammation and angiogenesis. Recent studies have highlighted the role of m6A in wound healing, scar formation, and tissue remodeling. Additionally, m6A presents a unique expression pattern in pathological wounds and scars, potentially influencing wound healing and scar formation through modulating gene expression and cellular signaling, thereby serving as potential biomarkers or therapeutic targets. Targeting m6A modifications are potential strategies to enhance wound healing and reduce scar formation. This review aims to explore the roles and mechanisms of m6A RNA methylation in wound healing and scars, and discuss current challenges and perspectives. Continued research in this field will provide significant value for optimal wound repair and scar treatment.

Structure of METTL3-METTL14 with an m6A nucleotide reveals insights into m6A conversion and sensing

The nuclear METTL3-METTL14 transfers a methyl group from SAM to convert the N 6 of adenosine (A) in RNA to m6A and in ssDNA to 6mA. m6A marks are prevalent in eukaryotic mRNAs and lncRNAs and modulate their stability and fate in a context-dependent manner. The cytoplasmic METTL3 can act as a m6A reader. However, the precise mechanism during m6A writing, reading, or sensing is unclear. Here, we present a ~2.5 Å structure of the methyltransferase core of human METTL3-METTL14 in complex with the reaction product mimic, N 6 -methyladenosine monophosphate (m6A), representing a state post-catalysis but before the release of m6A. m6A occupies an evolutionarily conserved RNA-binding pocket ~16 Å away from the SAM pocket that also frequently mutates in cancer. We propose a two-step model of swiveling of target A upon conversion to m6A and sensing its methylation status by this pocket, enabling it to actuate enzymes' switch from writer to an m6A-sensor. Cancer-associated mutations show impaired RNA binding dynamics, de-stacking, and defective m6A writing and sensing.

Single-cell sequencing reveals that specnuezhenide protects against osteoporosis via activation of METTL3 in LEPR+ BMSCs

BACKGROUND

Osteoporosis (OP) has garnered significant attention due to its substantial morbidity and mortality rates, imposing considerable health burdens on societies worldwide. However, the molecular mechanisms underlying osteoporosis pathogenesis remain largely elusive, and the available therapeutic interventions are limited. Therefore, there is an urgent need for innovative strategies in the treatment of osteoporosis.

PURPOSE

The primary objective of this study was to elucidate the molecular mechanisms underlying osteoporosis pathogenesis using single-cell RNA sequencing (scRNA-seq), thereby proposing novel therapeutic agents.

METHODS

The mice osteoporosis model was established through bilateral ovariectomy. Micro-computed tomography (μCT) and hematoxylin and eosin (H&E) staining were employed to assess the pathogenesis of osteoporosis. scRNA-seq was utilized to identify and analyze distinct molecular mechanisms and sub-clusters. Gradient dilution analysis was used to obtain specific sub-clusters, which were further validated by immunofluorescence staining and flow cytometry analysis. Molecular docking and cellular thermal shift assay (CETSA) were applied for screening potential agents in the TCMSPs database. Alkaline phosphatase (ALP) activity and alizarin red S (ARS) staining were performed to evaluate the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Osteogenic organoids analysis was employed to assess the proliferation and sphere-forming ability of BMSCs. Quantitative real-time PCR (qRT-PCR) and western blot analysis were conducted to investigate signaling pathways. Wound healing assay and tube formation analysis were employed to evaluate the angiogenesis of endothelial cells.

RESULTS

The scRNA-seq analysis revealed the crucial role of LEPR+ BMSCs in the pathogenesis of osteoporosis, which was confirmed by immunofluorescence staining of the epiphysis. Subsequently, the LEPR+ BMSCs were obtained by gradient dilution analysis and identified by immunofluorescence staining and flow cytometry. Accordingly, specnuezhenide (Spe) was screened and identified as a potential compound targeting METTL3 from the TCMSPs database. Spe promoted bone formation as evidenced by μ-CT, and H&E analysis. Additionally, Spe enhanced the osteogenic capacity of LEPR+ BMSCs through ALP and ARS assay. Notably, METTL3 pharmacological inhibitors S-Adenosylhomocysteine (SAH) attenuated the aforementioned osteo-protective effects of Spe. Particularly, Spe enhanced the LEPR+ BMSCs-dependent angiogenesis through the secretion of SLIT3, which was abolished by SAH in LEPR+ BMSCs.

CONCLUSION

Collectively, these findings suggest that Spe could enhance the osteogenic potential of LEPR+ BMSCs and promote LEPR+ BMSCs-dependent angiogenesis by activating METTL3 in LEPR+ BMSCs, indicating its potential as an ideal therapeutic agent for clinical treatment of osteoporosis.

ALKBH5 regulates etoposide-induced cellular senescence and osteogenic differentiation in osteoporosis through mediating the m6A modification of VDAC3

Osteoporosis, a common bone disease in older individuals, involves the progression influenced by N6-methyladenosine (m6A) modification. This study aimed to elucidate the effects of VDAC3 m6A modification on human bone mesenchymal stromal cell (BMSC) senescence and osteogenic differentiation. BMSCs were treated with etoposide to induce senescence. Senescence was assessed by β-galactosidase staining and quantitative real-time PCR (qPCR), and osteogenic differentiation was evaluated using Western blot, alkaline phosphatase, and alizarin red S staining. VDAC3 and ALKBH5 expression were quantified by qPCR, and their interaction was assessed by RNA immunoprecipitation (RIP) and luciferase reporter assay. m6A methylation was analyzed using the Me-RIP assay. VDAC3 expression was significantly decreased in etoposide-treated BMSCs (1.00 ± 0.13 vs. 0.26 ± 0.06). VDAC3 overexpression reduced etoposide-induced senescence and promoted osteogenic differentiation. ALKBH5 overexpression inhibited VDAC3 m6A modification (1.00 ± 0.095 vs. 0.233 ± 0.177) and its stability. ALKBH5 knockdown decreased etoposide-induced senescence and promoted osteogenic differentiation, effects that were reversed by VDAC3 knockdown. YTHDF1 was identified as the m6A methylation reader, and its overexpression inhibited VDAC3 stability. We demonstrated that ALKBH5 inhibited osteogenic differentiation of etoposide-induced senescent cells through the inhibition of VDAC3 m6A modification, and YTHDF1 acted as the m6A methylation reader. These findings provide a novel theoretical basis for the treatment of osteoporosis.

Inhibition of Mettl3 ameliorates osteoblastic senescence by mitigating m6A modifications on Slc1a5 via Igf2bp2-dependent mechanisms

Age-related osteoporosis is characterized by a marked decrease in the number of osteoblasts, which has been partly attributed to the senescence of cells of the osteoblastic lineage. Epigenetic studies have provided new insights into the mechanisms of current osteoporosis treatments and bone repair pathophysiology. N6-methyladenosine (m6A) is a novel transcript modification that plays a major role in cellular senescence and is essential for skeletal development and internal environmental stability. Bioinformatics analysis revealed that the expression of the m6A reading protein Igf2bp2 was significantly higher in osteoporosis patients. However, the role of Igf2bp2 in osteoblast senescence has not been elucidated. In this study, we found that Igf2bp2 levels are increased in ageing osteoblasts induced by multiple repetition and H2O2. Increasing Igf2bp2 expression promotes osteoblast senescence by increasing the stability of Slc1a5 mRNA and inhibiting cell cycle progression. Additionally, Mettl3 was identified as Slc1a5 m6A-methylated protein with increased m6A modification. The knockdown of Mettl3 in osteoblasts inhibits the reduction of senescence, whereas the overexpression of Mettl3 promotes the senescence of osteoblasts. We found that administering Cpd-564, a specific inhibitor of Mettl3, induced increased bone mass and decreased bone marrow fat accumulation in aged rats. Notably, in an OVX rat model, Igf2bp2 small interfering RNA delivery also induced an increase in bone mass and decreased fat accumulation in the bone marrow. In conclusion, our study demonstrated that the Mettl3/Igf2bp2-Slc1a5 axis plays a key role in the promotion of osteoblast senescence and age-related bone loss.