METTL3: A dual regulator of oral tissue regeneration and malignancy with therapeutic implications for stem cell therapy and chemoresistance

Abstract

The RNA N⁶-methyladenosine (m⁶A) modification, catalyzed by methyltransferase-like 3 (METTL3), is a key epigenetic regulator of oral health and disease. This narrative review positions METTL3 as a dual-function master switch in oral biology. It promotes stem cell-driven regeneration but also drives disease progression. Physiologically, METTL3 enhances the odontogenic/osteogenic differentiation of dental pulp stem cells (DPSCs). It stabilizes key transcripts (e.g., lncSNHG7, GDF6, STC1) via m⁶A modification, activating Wnt/β-catenin signaling to foster dentinogenesis and pulp vitality—key goals in regenerative endodontics. Conversely, METTL3 dysregulation promotes oral diseases. It impairs osteogenesis in periodontal stem cells (BMSCs/PDLSCs) via the IGF2BP1/m⁶A/RUNX2 and PI3K/AKT pathways, worsening bone loss in periodontitis. In oral squamous cell carcinoma (OSCC), METTL3 acts oncogenic. It stabilizes mRNAs like c-Myc, PD-L1, and BMI1 through reader proteins (YTHDF1/IGF2BPs), driving tumor growth, metastasis, and chemoresistance (e.g., to Cisplatin and Anlotinib). Pharmacological inhibition of METTL3 (e.g., with Allocryptopine or Oxymatrine) shows promise by suppressing OSCC progression and rescuing bone formation. We propose METTL3 as a unifying therapeutic target to advance both regenerative dentistry and precision oncology for oral diseases. Targeting METTL3 epitranscriptomics could transform future oral therapies.

Introduction

Oral health is vital for overall well-being, but dental diseases remain a global burden, causing pain, functional impairment, and systemic health issues. ¹ This underscores the urgent need to discover new molecular players in oral disease pathogenesis and treatment.

Epigenetic mechanisms, which regulate gene expression without altering DNA sequence, are increasingly implicated in oral biology. ² A key mechanism is N⁶-methyladenosine (m⁶A), the most abundant RNA modification in eukaryotes. ³ The m⁶A modification is dynamically regulated by writers (methyltransferases like METTL3, METTL14), erasers (demethylases like FTO, ALKBH5), and readers (e.g., YTHDF, IGF2BP proteins). ⁴ Among m⁶A methyltransferases, METTL3 serves as the primary catalytic subunit and has been extensively studied in various biological contexts and a central focus of recent research. ⁵

The m⁶A RNA modification plays a significant role in oral physiology and pathology, particularly in the onset and progression of diseases linked to unhealthy conditions. ⁶ The effectiveness of this modification is primarily reliant on METTL3, the only catalytic subunit involved. Through METTL3, m⁶A RNA modification influences gene expression by regulating splicing, translation, stability, translocation, and higher-order structure. ⁶ In the context of oral health, METTL3 is crucial in the regulation of tooth development, oral inflammation, and the progression of oral squamous cell carcinoma (OSCC). While extensive research has been conducted on METTL3's involvement in tooth and oral health, the essential roles it plays in dental and oral cavity disorders remain inadequately understood; moreover, there are few reviews exploring the therapeutic potential of targeting METTL3.

This narrative review seeks to thoroughly examine the functions of METTL3 in both normal and pathological processes of the oral cavity. We conducted a comprehensive literature search in PubMed, Web of Science, and Google Scholar using keywords including METTL3, m⁶A, oral cancer, periodontitis, and stem cell differentiation. This narrative review was conducted in accordance with the SANRA guidelines. ⁷ It will outline the molecular mechanisms that underlie these alterations, evaluate the therapeutic potential of METTL3 in addressing oral diseases, and provide insights to inform future research directions.

METTL3 in tooth development and stem cell differentiation

Teeth are rigid structures found in the mouths of vertebrates, primarily serving the purpose of assisting in the chewing of food. ⁸ From an anatomical perspective, a tooth generally comprises a crown and one or more roots. The crown is the visible part that extends above the gums, while the roots, which are not visible, secure the tooth within the alveolar bone. ⁸ Therefore, the effective functioning of teeth relies on the complex processes of crown and root development, which involve interactions among various cell types. The crown is covered by enamel derived from epithelial tissue, whereas the roots predominantly consist of dentin that arises from ectomycorrhizal tissue. ⁸ Disruptions in molecular signaling during the maturation of tooth roots can result in abnormalities, such as dysplasia or underdeveloped roots; these issues are frequently linked to congenital conditions and premature wear of teeth.

Regulation of human dental pulp cell (hDPC) odontogenic differentiation

In vitro studies suggest that the exact mechanisms remain uncertain, yet METTL3 expression has been observed in odontoblasts, hDPCs, dental follicle cells, and the epithelial cells of Hertwig's epithelial root sheath during the formation of tooth roots, where it plays a role in regulating cellular activities. ⁹ Consistently, cell culture experiments show that a reduction in METTL3 levels leads to decreased proliferation and migration of hDPCs, as well as impaired odontogenic differentiation. ⁹ In a similar vein, the inhibition of METTL3 disrupts the translation of nuclear factor I-C, which is crucial for root formation. ⁹ These observations strongly suggest a significant relationship between METTL3-mediated m⁶A RNA modification and stem cell behavior throughout tooth development. The studies by Sheng et al. ⁹ and Luo et al. ¹⁰ provide compelling in vitro evidence for METTL3's role in regulating the cell cycle and odontogenic potential of hDPCs. A key strength lies in the mechanistic dissection linking METTL3 knockdown to specific downstream targets (e.g., NFIC, PLK1). However, these findings are primarily derived from monolayer cell culture systems, which lack the complex three-dimensional microenvironment and cellular crosstalk of the dental pulp. The reliance on overexpression or silencing techniques may also produce non-physiological effects. Future studies utilizing conditional knockout mouse models or 3D organoid cultures would be invaluable to validate these functions in a more biologically relevant context and assess their true therapeutic potential for regenerative endodontics. Further in vitro evidence from Luo et al. ¹⁰ found that undifferentiated hDPCs with enhanced regenerative capabilities exhibit elevated METTL3 expression, while downregulation of METTL3 leads to increased cellular apoptosis and senescence. Mechanistically, the decrease in METTL3 levels interrupts the cell cycle by affecting polo-like kinase 1, an essential regulator of cell division. These results underscore the importance of METTL3 in modulating the hDPC cell cycle and its potential as a target for therapeutic intervention in dental pulp conditions.

Control of osteogenic/odontogenic differentiation in hDPCs

hDPCs exhibit reduced immunogenicity and possess enhanced proliferation rates and cloning capabilities in comparison to mesenchymal stem cells. ¹¹ Furthermore, hDPCs derived from various species can generate regenerative tissue post-implantation in animal models. ¹¹ Additionally, hDPCs are sourced from diverse origins, available in ample quantities, and serve as a convenient resource, highlighting their significant promise in regenerative medicine for addressing numerous human ailments.^11,12 Consequently, they demonstrate strong potential for clinical application. Thus, hDPCs are pivotal in the field of endodontic regeneration. The mechanisms underlying the osteogenic and odontogenic differentiation of hDPCs have been linked to METTL3-mediated m⁶A modifications. According to Yang et al., ¹³ lncSNHG7 undergoes m⁶A modification both prior to and following the mineralization of hDPCs, specifically at site 2081. Notably, after the mineralization process, there is a marked increase in METTL3 expression. The manipulation of lncSNHG7 and METTL3, through either knockdown or overexpression, significantly influences the differentiation pathways of hDPCs, either inhibiting or promoting osteogenic and odontogenic processes. ¹³ Both the m⁶A modification and lncSNHG7 expression are regulated by METTL3, which has also been shown to affect the Wnt/-catenin signaling pathway. These interactions suggest that METTL3 enhances the activation of the Wnt-catenin signaling pathway by regulating the m⁶A modification and expression of lncSNHG7 in hDPCs, thereby supporting their osteogenic and odontogenic differentiation. The work by Yang et al. ¹³ elegantly demonstrates a novel METTL3-lncSNHG7-Wnt/β-catenin regulatory axis in hDPCs. A major strength is the identification of a specific m⁶A site (2081 on lncSNHG7), enhancing the mechanistic depth. However, the functional role of lncSNHG7 itself, independent of m⁶A modification, remains less explored. Furthermore, the clinical translatability of modulating this axis is uncertain, as uncontrolled Wnt/β-catenin signaling is associated with oncogenesis. The safety and efficacy of targeting this pathway for dental regeneration require rigorous investigation in in vivo models before any clinical application can be contemplated.

METTL3 and dentinogenesis potential of hDPCs

The ability of hDPCs to generate dentin forms the essential biological basis for vital pulp therapy (VPT), indicating that enhancing dentinogenesis in hDPCs could be an effective approach to improve the clinical outcomes of VPT. ¹⁴ The differentiation of hDPCs into dentin-forming cells is influenced by the precise spatiotemporal expression of genes associated with differentiation. ¹⁴ According to Pan et al., ¹⁵ the expression of METTL3 increases progressively throughout the dentinogenesis process. Silencing METTL3 negatively affects the differentiation of hDPCs, whereas its overexpression facilitates this process. ¹⁵ Additionally, METTL3's role in m⁶A modification is crucial for regulating the mRNA stability of GDF6 and STC1. Notably, the overexpression of METTL3 has been found to enhance the formation of tertiary dentin in a direct pulp capping model. ¹⁵ These observations imply that METTL3-mediated m⁶A modification plays a significant role in the differentiation of hDPCs by influencing the stability of GDF6 and STC1 mRNA, and its overexpression may have promising implications for VPT through the promotion of tertiary dentin formation in vitro. Pan et al. ¹⁵ present a direct link between METTL3 and a key clinical procedure (VPT), which is a significant strength of their study. The use of a direct pulp capping model in rats provides stronger translational evidence than in vitro studies alone. However, the rodent model may not fully recapitulate human dental pulp biology and inflammatory responses. The long-term stability and quality of METTL3-overexpression-induced tertiary dentin also need evaluation. Crucially, the strategy for safely and controllably upregulating METTL3 specifically in human pulp cells remains a major challenge that must be addressed before this approach can be moved towards clinical trials.

In summary, the evidence indicates that m⁶A RNA modification mediated by METTL3 is vital for the proper development and maturation of dental stem cells. While current research has primarily concentrated on hDPCs, it is important to note that tooth development also requires interactions with various other cell types, such as odontoblasts, dental follicle cells, and epithelial cells. Therefore, further investigations are necessary to clarify the role of METTL3 in the odontogenic differentiation process involving these additional cell types.

METTL3 in oral inflammatory pathogenesis

Oral inflammation is a complex condition that impacts not only the mouth but also has broader implications for overall health. The modification of RNA by m⁶A and the associated regulatory enzymes play a crucial role in the inflammatory process. These elements influence the expression of genes linked to various inflammatory disorders, including oral ulcers, pulpitis, periodontitis, and peri-implantitis. ¹⁶

Role in oral ulcers

Oral ulcers are among the most prevalent inflammatory conditions affecting the oral mucosa, significantly impacting patients’ well-being. An analysis focusing on m⁶A single nucleotide polymorphisms (SNPs) related to oral ulcers unveiled a total of 7490 m⁶A-SNPs connected to this condition. ¹⁷ Subsequent functional validation and comparative gene analysis revealed that 11 of these SNPs have a correlation with oral ulcers. Notably, the SNP rs11266744 appears to influence the expression of the local gene CCRL2, thereby contributing to the development of oral ulcers. ¹⁷ In conclusion, this study, through genome-wide association analyses, indicates that m⁶A modifications may play a role in the pathogenesis of oral ulcers, with CCRL2 identified as a potential target gene. ¹⁷ Nonetheless, additional extensive research is required to elucidate the specific roles and mechanisms of each m⁶A regulator. Specifically, investigation into the role of METTL3 in oral ulcers reveals significant insights into the underlying mechanisms that contribute to this condition.

Involvement in pulpitis

Pulpitis, an inflammatory disease of the dental pulp, is closely related to epigenetic modifications. ¹⁸ Bioinformatics analysis on data from pulpitis microarrays by Xu et al. ¹⁹ found significant differences in the m⁶A modification-related genes ALKBH5, METTL14, METTL3, METTL16, RBM15B, and YTHDF1. And their interaction relationships and hub genes are determined. The hub m⁶A regulator targets are enriched in immune cell differentiation, glutamatergic synapse, ephrin receptor binding, and osteoclast differentiation in pulpitis. ¹⁹ The expression of METTL14 and METTL3 is decreased, which may play a key role in pulpitis. ¹⁹ These findings provide valuable resources to guide the mechanistic and therapeutic analysis of the role of key m⁶A modulators in pulpitis.

METTL3 dysregulation in periodontitis

Periodontitis is a chronic inflammation that associated with the accumulation of dental plaque occurs in periodontal tissue and has a high incidence rate. ¹⁶ Its common pathogenic features include the progressive destruction of the tooth-supporting apparatus, such as the periodontal ligament and alveolar bone. ¹⁶ Both environmental and genetic factors contribute to the development of periodontitis, leading to tooth loss and reduced life quality. ¹⁶ Human genetic association studies have revealed a link between m⁶A and periodontitis. For instance, Lin et al. ²⁰ analyzed clinical genomic data and identified that m⁶A-related SNPs may affect m⁶A methylation in multiple periodontitis SNPs. They identified 1938 m⁶A SNPs, of which 104 seem to be associated with periodontitis, and predicted that the leading SNP rs2723183 could regulate the expression of local gene IL-37 in periodontitis. ²⁰

Mechanistic insights from in vitro models indicate that METTL3-mediated RNA m⁶A modification influences the fate of stem cells, providing novel insights into the pathogenesis of periodontitis. For instance, studies on bone marrow-derived stromal cells (BMSCs) in culture suggest the disequilibrium between the osteogenic or adipogenic differentiation of BMSCs is a major pathological feature of maxillofacial bone defects in periodontal diseases, and such differentiation can be modulated by METTL3. ²¹ Specifically, Zhou et al. ²² reported, based on cell line experiments, that METTL3 upregulation facilitates the osteogenic differentiation of BMSCs, while METTL3 downregulation suppresses it. Studies have confirmed that the mRNA of runt-related transcription factor 2 (RUNX2), which is encoded by a bone formation-related gene, is a target of m⁶A-mediated methylation and catalyzed by METTL3 at its 3′-untranslated region (3′-UTR). ²² Moreover, IGF2BP1 recognizes the m⁶A binding site on RUNX2 mRNA, enhancing its stability. ²² These findings are instrumental in revealing the novel roles of METTL3 in the osteogenic differentiation of BMSCs by modulating the IGF2BP1/m⁶A/RUNX2 signaling axis, suggesting a potential target for curing the maxillofacial bone defects. Similarly, experiments using human periodontal ligament stem cells (PDLSCs) isolated from patients show that the upregulation of METTL3 expression increases the content of m⁶A, which further promotes the proliferation capacity and osteogenic differentiation ability of PDLSCs. ²³ In contrast, the activity and osteogenic differentiation ability of PDLSCs are decreased after silencing METTL3. ²³ Therefore,METTL3-mediated m⁶A modification promotes the osteogenic differentiation of PDLSCs, offers a novel understanding of the mechanisms underlying osteogenic differentiation, and implies a possible method for accelerating bone formation. In line with this study, Zhang et al. ²⁴ reported that upregulation of METTL3 facilitates the osteogenic differentiation of PDLSCs by enhancing the stability and expression of long non-coding RNA 4114 (lncRNA4114); METTL3 downregulation results in an inhibitory effect. ²⁴ This study provides novel insights into the role of the METTL3-mediated m⁶A-lncRNA mechanism, which perpetuates the differentiation of PDLSCs and is a novel approach for ameliorating the osteogenic dysfunction of patients with periodontitis. ²⁴ To mimic the inflammatory environment in vitro, studies have treated PDLSCs with lipopolysaccharides (LPS). Under these experimental conditions, METTL3 knockdown reduces proinflammatory cytokines, osteogenic markers, ALP activity, and mineralized nodules in both environments. ²⁵ Bioinformatics analysis suggests a link between METTL3 and the PI3K/Akt pathway. ²⁵ METTL3 knockdown inhibits the PI3K/Akt signaling pathway. ²⁵ In conclusion, METTL3 knockdown might inhibit osteogenesis in PDLSCs through the inactivation of the PI3K/Akt signaling pathway. Concomitant findings might shed novel light on the roles and potential mechanisms of METTL3 in the LPS-stimulated inflammatory microenvironments of PDLSCs. Furthermore, the FOXO1 transcription factor belongs to the Fox family and is generally expressed at low levels in clinical samples from patients with periodontitis. Wang et al. ²⁶ provided evidence that FOXO1 promotes osteogenic differentiation in PDLSCs, which activates the PI3K/AKT signaling pathway by transcriptionally activating METTL3. In summary, FOXO1 affects osteogenic differentiation of PDLSCs by regulating METTL3 modification of the PI3K/AKT pathway.

As a highly prevalent microbiome-driven chronic inflammatory disease, periodontitis can progressively destroy the periodontium manifested in clinical attachment loss, bone resorption, and eventually tooth loss. ²⁷ In addition to serving as a bridge between the cementum and the alveolar bone, the periodontal ligament helps provide resistance to excessive occlusal loads, delivering nutrients to the alveolar bone and cementum and facilitating repair after mild damage. ²⁸ METTL3 knockdown exerts detrimental effects on the biological behaviors of periodontal ligament cells, affecting cell proliferation, migration, and osteogenesis. ²⁹ Furthermore, METTL3 upregulation occurs in hDPCs exposed to LPS. ³⁰ Silencing METTL3 elevates the expression of myeloid differentiation primary response 88 (MyD88), a splice variant of MyD88 that inhibits inflammatory cytokine production; this finding suggests that low levels of METTL3 are crucial for suppressing the LPS-induced inflammatory response in hDPCs by regulating the alternative splicing of MyD88 during dental pulp inflammation. ³⁰ Therefore, METTL3 overexpression is responsible for an inflammatory response to periodontitis in cell types involved in tooth formation (Figure 1).

Figure 1.

METTL3 induces oral inflammation. Targets, mechanisms, functions, and outcomes related to METTL3 in oral inflammation (periodontitis and peri-implantitis) are summarized. Extensive METTL3 expression contributes to the differentiation and inflammation response of BMSC, PDLSC, and HDCP. N⁶-methyladenosine (m⁶A). Methyltransferase-like 3 (METTL3). Insulin-like growth factor 2 mRNA-binding proteins (IGF2BP). Bone marrow-derived stromal cell (BMSC). Runt-related transcription factor 2 (RUNX2). Periodontal ligament stem cell (PDLSC). Long non-coding RNA 4114 (lncRNA4114). Myeloid differentiation primary response 88S (MyD88S). Human dental pulp cell (hDPC). Lipopolysaccharide (LPS). Fibroblast growth factor receptor 2 (FGFR2).

Contribution to peri-implantitis

Infections surrounding an oral implant or destruction of the surrounding bone induce immune and inflammatory responses in the oral cavity; these changes are analogous to those of periodontitis and are called peri-implantitis. The RNA m⁶A methylation levels are substantially increased in the gingival tissue samples of patients with peri-implantitis. In addition, METTL3 expression at the RNA and protein levels is significantly greater in comparison with the healthy controls. ³¹ Furthermore, METTL3 mediates m⁶A modification on the fibroblast growth factor receptor 2 (FGFR2) transcripts. It functions by regulating the FGFR2 signaling pathway in an m⁶A-dependent manner, associated with bone and fibroblast growth. ³¹ These findings suggest that altering METTL3 expression elevates m⁶A RNA methylation levels in patients with peri-implantitis through the FGFR2 signaling pathway (Figure 1).

While beyond the primary scope of this review, it is noteworthy that METTL3-mediated m⁶A modification also plays a role in the pathogenesis of salivary gland disorders. For instance, a recent study by Truffinet et al. ³² demonstrated that METTL3 expression is altered in the salivary glands of patients with Sjögren's syndrome, an autoimmune disorder characterized by dry mouth, and contributes to the inflammatory dysregulation therein. This underscores the broad influence of epitranscriptomic mechanisms across oral tissues. However, this review deliberately focuses on METTL3's functions in tooth development, pulpitis, periodontitis, peri-implantitis, and OSCC to provide a detailed and cohesive analysis of these interconnected areas.

METTL3 in oral squamous cell carcinoma: pathogenesis and therapy

The tumor grade and stage classifications are valuable for predicting the prognosis of patients with cancer; however, pathologists may supplement this information with the status of other histological features to facilitate individualized patient management to improve clinical outcomes. OSCC, which accounts for over 90% of all cases of oral malignancies, can be further sub-classified according to the location of the tumor, its etiology, and the expected prognosis. Historically, the degree of differentiation is a prognostic indicator; it correlates significantly with survival outcomes. METTL3 is found to be present in both the peripheral and central cells of the OSCC tumor islands. ³³ The percentage of METTL3 positive cells and H-score are highest in OSCC, followed by oral epithelial dysplasia (OED) and normal oral mucosa, respectively. Interestingly, the H-score is greater in high-grade OED when compared with low-grade OED. ³³ Collectively, these findings suggest that METTL3 expression in OED and OSCC is more outstanding than in normal oral mucosa, suggesting possible roles of METTL3 for OED and OSCC pathogenesis, as well as may be an indicator for OED progression to OSCC.

Mechanisms driving OSCC pathogenesis

Clinical evidence from human tissue samples shows an abnormally upregulated level of METTL3 in OSCC tissues, which correlates with short overall survival. ³⁴ Subsequent in vitro experiments in OSCC cell lines confirm that this high METTL3 expression promotes cell proliferation. Besides, the upregulated level of METTL3 usually indicates a more severe clinical feature in patients with OSCC. ³⁵ Functional studies using genetic knockdown in cultured OSCC cells demonstrate that deletion of METTL3 decreases m⁶A levels and p38 expression in OSCC cells, weakening the stem-like ability of tumorigenicity and colony formation. ³⁵ This mechanistic insight is strengthened by rescue experiments, where overexpression of p38 reverses the effects of METTL3 deletion. ³⁵ In line with this study, Zhao et al. ³⁶ revealed that METTL3 expression is elevated in tissue samples from patients with OSCC and that the high expression levels are associated with an unfavorable prognosis. Moreover, they observed in vitro that the deletion of METTL3 in OSCC cells impairs proliferation, invasion, and migration capacities. This was further validated in vivo, as METTL3 deletion also inhibits tumor growth in xenograft mouse models. ³⁶ Mechanistically, METTL3 facilitates m⁶A RNA modification by targeting the 3′-UTR of the c-Myc transcript, thereby bolstering its stability; this heightened stability is facilitated by YTHDF1, promoting OSCC tumorigenesis. ³⁶ Therefore, METTL3 contributes to OSCC tumorigenesis.

Consistent results are reported by Xu et al., ³⁷ who demonstrated that METTL3 expression is significantly enhanced in OSCC tissues compared to the levels in the adjacent control tissues, and its expression levels are positively correlated with the T stage, lymphatic metastasis, and overall prognosis. Silencing METTL3 reduces the proliferation, invasion, and migration abilities of OSCC cells by targeting solute carrier family 7-member 11 (SLC7A11) mRNA. ³⁷ Biochemical assays and in vitro analyses showed that METTL3 knockdown impairs the physical interaction between SLC7A11 mRNA and IGF2BP2 at the binding site, accelerating the degradation of SLC7A11 mRNA. ³⁷ These findings collectively support the idea that METTL3 downregulation decreases SLC7A11 mRNA stability in an IGF2BP2-dependent manner. Furthermore, treatment with triptolide, a component of a Chinese medicinal herb, suppresses OSCC cell malignancy by inhibiting the METTL3-mediated change in SLC7A11 expression, highlighting its potential as a targeted anti-OSCC drug. ³⁷ In addition, other studies identified a positive correlation between METTL3 overexpression and poor prognosis of OSCC. ³⁸ Moreover, inhibiting METTL3 further impairs the invasion, migration, and proliferation of OSCC cells and attenuates CD8⁺ T-cell activation. ³⁸ These effects are attributed to the METTL3-mediated m⁶A modification on protein arginine methyltransferase 5 (PRMT5) and programmed death-ligand 1 (PD-L1). ³⁸ These findings suggest that METTL3 amplifies the proliferation and metastasis of OSCC by modulating the m⁶A modification levels of PRMT5 and PD-L1. Thus, targeting METTL3 is a prospective therapeutic strategy for patients with OSCC.

Persistently elevated METTL3 levels in patients with OSCC are strongly associated with an unfavorable prognosis. ³⁹ Suppression of METTL3 in OSCC cells diminishes cell proliferation, self-renewal, migration, and invasion, halting tumor expansion and metastasis. ³⁹ The mechanism of METTL3 works in tandem with the m⁶A reader IGF2BP1 to facilitate the translation of the polycomb complex protein BMI1 mRNA in OSCC. ³⁹ In summary, these findings suggest that METTL3 promotes the proliferation and metastasis of OSCC through m⁶A-mediated methylation on BMI1. Therefore, the METTL3-IGF2BP1-BMI1 axis may be a target for diagnosis or treatment in patients with OSCC. Furthermore, the rich amount of METTL3 expression in OSCC cells enhances the m⁶A modification on pri-miR-99a-5p and thereby facilitates miR-99a-5p maturation that targets ZBTB7A, contributing to OSCC recurrence and prognosis. ⁴⁰ Moreover, the knockdown of METTL3 inhibits OSCC metastasis and suppresses OSCC progression by downregulating miR-99a-5p. ⁴⁰ Taken together, these findings suggest that METTL3 promotes miR-99a-5p maturation in an m⁶A-dependent manner, which further targets ZBTB7A to accelerate the metastasis and progression of OSCC, implying that METTL3 is a potential therapeutic target for OSCC (Figure 2).

Figure 2.

METTL3 promotes the occurrence and progression of OSCC. Targets, mechanisms, functions, and outcomes related to METTL3 in OSCC are summarized. METTL3 facilitates the proliferation, invasion, and migration of OSCC cells; these changes are mediated predominantly through targeting oncogenes. Methyltransferase-like 3 (METTL3). Oral squamous cell carcinoma (OSCC). YT521-B homology domain family proteins (YTHDF). Insulin-like growth factor 2 mRNA-binding proteins (IGF2BP). Solute carrier family 7-member 11 (SLC7A11). Protein arginine methyltransferase 5 (PRMT5). Programmed death-ligand 1 (PD-L1).

These studies conducted to date collectively suggest that elevated METTL3 levels contribute to the proliferation, invasion, and migration of OSCC cells, predominantly by targeting oncogenes. The collective evidence from multiple groups^33–40 robustly establishes METTL3 as an oncogenic driver in OSCC through diverse mechanisms (e.g., stabilizing c-Myc, PD-L1, BMI1). A consistent strength across these studies is the correlation of high METTL3 expression with poor clinical prognosis, underscoring its clinical relevance. However, a significant limitation is the predominant reliance on established cell lines and xenograft models, which may not mimic the tumor microenvironment and immune context of human OSCC accurately. The oncogenic effects of METTL3 appear to be highly context-dependent, targeting a wide array of mRNAs. This pleiotropy poses a challenge for therapeutic targeting, as global inhibition of METTL3 could disrupt its vital physiological functions. Future research should prioritize the identification of critical, context-specific METTL3 targets that drive OSCC progression, which could be targeted with greater precision and reduced off-tumor effects.

Promoting therapy resistance

Chemotherapy improves overall survival in patients with OSCC. However, some patients suffer therapeutic resistance, which leads to poor prognosis. Qiao et al. ⁴¹ found that CEBPA-DT overexpression significantly enhances Cisplatin resistance by activating the METTL3/METTL14/BHLHB9 axis. Moreover, CEBPA-DT overexpression inhibits the activity of IL-17 signaling, resulting in the homeostasis breakdown of immune infiltration and cytokine release. ⁴¹ Additionally, Arecoline exposure aberrantly elevates METTL3 and drives the pathological progression of OSCC. Wang et al. ⁴² found that hypoxia-inducible factor 1-alpha (HIF-1α) stimulates METTL3 expression at the transcriptional level and METTL3-MYC-HIF-1 forms a positive autoregulation loop in arecoline-transformed OSCC cells. METTL3 depletion profoundly reduces cell proliferation, cell migration, oncogenicity, and Cisplatin resistance of Arecoline-exposed OSCC cells. ⁴² Collectively, METTL3 facilitates tumorigenesis and Cisplatin resistance of OSCC, highlighting the potential therapeutic targets in OSCC chemoresistance.

Anlotinib has effective antitumor effects in OSCC, which targets FGFR3, inhibits tumor cell proliferation, and promotes apoptosis by inactivating the FGFR3/AKT/mTOR signaling pathway. ⁴³ Importantly, METTL3 and FGFR3 levels are tightly correlated with the Anlotinib efficacy in OSCC. Chen et al. ⁴⁴ demonstrated that METTL3 knockdown promotes Anlotinib sensitivity of OSCC cells by inhibiting the FGFR3 expression through m⁶A methylation on FGFR3 and then decreasing the FGFR3 mRNA stability. This work reveals that METTL3-mediated FGFR3 m⁶A modification plays a critical function in OSCC Anlotinib sensitivity.

Therefore, developing novel strategies to target METTL3 may be a potential way to treat patients with OSCC, particularly those with Cisplatin and Anlotinib treatment.

Targeting METTL3 for OSCC treatment

Allocryptopine, a natural compound extracted from Macleaya cordata, has been shown to inhibit the proliferation, migration, and invasion of OSCC cells in preclinical studies. ⁴⁵ At a mechanistic level, Allocryptopine upregulates E-cadherin expression and downregulates N-cadherin and Vimentin expression in in these cellular models. ⁴⁵ Furthermore, experimental evidence indicates that Allocryptopine decreases METTL3 expression and inhibits m⁶A modification of PTCH1. ⁴⁵ Collectively, these preclinical findings suggest that Allocryptopine suppresses the proliferation and epithelial-mesenchymal transition of OSCC cells partially through modulating the Hedgehog signaling pathway, thereby attenuating carcinogenic behaviors in vitro. However, its clinical efficacy and safety for OSCC treatment remain entirely unexplored and require rigorous future investigation.

Similarly, Oxymatrine has demonstrated antitumor activity in preclinical models of OSCC, where it inhibits proliferation and migration while promoting apoptosis of OSCC cells. ⁴⁶ Luo et al. ⁴⁶ proposed a mechanism whereby Oxymatrine inhibits the m⁶A modification of CXCR4 mRNA and promotes its degradation by downregulating METTL3 expression, thereby contributing to the inhibition of OSCC progression in their experimental system. Therefore, the preclinical antitumor effect of Oxymatrine appears to be mediated, at least in part, by downregulating METTL3. It is crucial to emphasize that these promising results are derived from cell-based and animal studies, and the translation of Oxymatrine into a clinical therapy for OSCC patients faces significant challenges that have not yet been addressed.

Discussion and future perspectives

This review consolidates critical evidence establishing METTL3-mediated m⁶A RNA modification as a pivotal epigenetic regulator governing both physiological homeostasis and pathological processes in the oral cavity. Unlike previous reviews that have often focused solely on the oncogenic role of METTL3 in OSCC, ⁴⁷ this work provides a comprehensive synthesis that integrates its dual functions in stem cell-driven regeneration and inflammatory pathogenesis, offering a more holistic view of this protein in oral biology. Under physiological conditions, METTL3 orchestrates tooth development by directing the odontogenic/osteogenic differentiation of hDPCs and dentinogenesis through precise m⁶A-dependent modulation of key targets (e.g., lncSNHG7, GDF6, STC1) and signaling pathways (e.g., Wnt/β-catenin). Crucially, however, this regulatory equilibrium undergoes profound dysregulation in disease states. In oral inflammatory pathologies, METTL3 exhibits context-dependent duality: it suppresses LPS-induced inflammation in pulpitis by modulating MyD88 alternative splicing, yet conversely exacerbates bone destruction in periodontitis and peri-implantitis via dysregulation of RUNX2, PI3K/AKT, and FGFR2 pathways. Most notably, in OSCC, METTL3 functions as an oncogenic amplifier, stabilizing critical oncogenes (c-Myc, PD-L1, BMI1, SLC7A11) through reader proteins (YTHDF1, IGF2BPs)—thereby fueling tumor proliferation, invasion, metastasis, and therapy resistance.

These mechanistic insights translate directly to clinical applications. Elevated METTL3 expression correlates robustly with OSCC aggressiveness, lymph node metastasis, and poor survival outcomes, positioning it as a promising noninvasive diagnostic and prognostic biomarker. Parallelly, METTL3-associated SNPs (e.g., rs2723183 near IL37) offer potential for genetic risk stratification in periodontitis. Therapeutically, pharmacological inhibition of METTL3 (e.g., via Allocryptopine or Oxymatrine) effectively attenuates OSCC progression by disrupting oncogene stability, while strategic modulation of its activity could rescue osteogenic differentiation in periodontal stem cells, opening avenues for regenerative dentistry.

However, the translational path of targeting METTL3 is fraught with significant challenges that must be rigorously addressed. Firstly, as a ubiquitous writer enzyme responsible for a fundamental RNA modification, systemic inhibition of METTL3 raises substantial concerns about on-target, off-tumor toxicity. METTL3 is indispensable for normal development, stem cell maintenance, and immune cell function. Pan-inhibition could therefore disrupt vital physiological processes in non-target tissues, leading to unforeseen adverse effects. Secondly, achieving tissue-specific or cell-type-specific targeting remains a formidable hurdle. Current preclinical inhibitors, such as STM2457, are broad-acting. The development of innovative delivery systems—for example, nanoparticle-based carriers functionalized with ligands for oral tissue-specific receptors (e.g., integrins or epidermal growth factor receptor prevalent in OSCC)—is crucial to concentrate therapeutic effects at the desired site while minimizing systemic exposure. Until these challenges of specificity and delivery are overcome, the clinical application of METTL3 inhibition will remain limited.

Notwithstanding these hurdles, METTL3 research holds significant promise for integration into existing clinical paradigms. In regenerative dentistry, METTL3 agonists could be co-applied with current pulp capping agents (e.g., calcium hydroxide or mineral trioxide aggregate) or incorporated into bioactive scaffolds to enhance the osteogenic/odontogenic differentiation of resident stem cells, thereby improving the outcomes of vital pulp therapy and periodontal regeneration. In oral oncology, METTL3 inhibitors are not envisioned as standalone treatments but as potential adjuvants to conventional chemotherapy (e.g., Cisplatin) or immunotherapy. By targeting the epitranscriptomic drivers of chemoresistance and immune evasion (e.g., PD-L1), METTL3 inhibition could resensitize tumors to existing standard-of-care therapies, offering a novel combinatorial strategy to overcome treatment failure in OSCC.

Despite these advances, significant knowledge gaps persist. First, the cell-type-specific functions of METTL3 in odontoblasts, dental follicle cells, and epithelial cells remain largely unexplored. Second, the mechanistic basis for its paradoxical roles in pulpitis (anti-inflammatory) versus periodontitis (pro-inflammatory) requires resolution. Third, METTL3's relationship with clinical variables, such as age, sex, HPV status, and dynamic chemoresistance evolution in OSCC, demands systematic investigation. Translational barriers further arise from the absence of tissue-specific METTL3 modulators and potential off-target effects of current inhibitors. To address these challenges, future research must prioritize the development and application of next-generation experimental strategies: (1) Spatially Resolved Epitranscriptomics: Employing single-cell and spatial m⁶A sequencing technologies (e.g., scm⁶A-seq, MERFISH) on human oral tissues will be crucial to map the METTL3-m⁶A landscape across diverse cell lineages within the periodontal niche, pulp chamber, and tumor microenvironment, thereby elucidating cell-type-specific functions; (2) Advanced Genetic Models: Generating cell-type-specific and inducible METTL3 knockout mouse models (e.g., using Cre-loxP systems under dental pulp- or keratinocyte-specific promoters) is essential to dissect its causal roles in tooth development, inflammation, and OSCC pathogenesis in a physiologically relevant context, moving beyond cell lines; (3) Precision Epitranscriptomic Editing: Utilizing CRISPR-based tools (e.g., dCas13-mediated m⁶A editing or CRISPRoff/on) to site-specifically manipulate m⁶A modifications on individual target transcripts (e.g., RUNX2, c-MYC) will allow researchers to move from correlation to causation, definitively linking specific m⁶A sites to functional outcomes; (4) Translational Delivery Platforms: Investing in the design of tissue-specific nanoparticle delivery systems (e.g., functionalized with ligands for oral epithelium-specific receptors) for METTL3 modulators could overcome the critical hurdle of on-target, off-tumor toxicity, paving the way for therapeutic application. Bridging mechanistic depth with clinical innovation through these strategies will be essential to harness METTL3 as a cornerstone of next-generation oral diagnostics and therapies, ultimately transforming molecular insights into tangible improvements in patient care.

This review, while comprehensive, has several limitations that should be acknowledged. First, our focus on METTL3 in tooth development, inflammation, and OSCC necessitated the exclusion of other oral diseases and tissues where METTL3 is also active, such as salivary gland disorders (e.g., Sjögren's syndrome). ³² Second, the translational potential of many findings discussed herein is primarily supported by in vitro and preclinical animal studies; the direct clinical evidence linking METTL3 to patient outcomes in dentistry remains sparse and correlative. Finally, the precise mechanistic switch that dictates whether METTL3 exerts pro-regenerative or pro-pathological effects is still not fully understood, highlighting a critical gap in our fundamental knowledge that future research must address.

In conclusion, METTL3 serves as a critical dual-function regulator in oral health and disease, governing key processes in tissue regeneration, inflammation, and oncogenesis. Its context-dependent roles make it a compelling but challenging therapeutic target. Pharmacological modulation of METTL3 activity holds promise for enhancing regenerative dentistry outcomes and overcoming therapy resistance in oral cancer. However, realizing this potential requires overcoming significant translational challenges, particularly achieving tissue-specific targeting and mitigating off-target effects. Future research focused on elucidating cell-specific mechanisms and developing precise-intervention strategies will be crucial to leverage METTL3 biology for improving patient care.