Extensive research has underscored the pivotal role of METTL3 in modulating the biological functions of ECs implicated in angiogenesis. Kumari et al. (2021) demonstrated that elevated ALKBH5 levels in ECs facilitate sustained angiogenesis post-acute ischemia. ALKBH5 modulates endothelial nitric oxide synthase (eNOS) phosphorylation and sphingosine kinase 1 (SPHK1) expression through METTL3-mediated m⁶A methylation. These findings imply that increased ALKBH5 expression orchestrates EC functions in angiogenesis via the METTL3/SPHK1/eNOS-AKT signaling cascade, underscoring METTL3’s promotive role in angiogenesis. Corroborating this, another study revealed that METTL3 knockdown in ECs hampers angiogenesis (Chamorro-Jorganes et al., 2021). The suppression of METTL3 in ECs results in reduced levels of mature angiogenic microRNAs, such as let-7e-5p and the miR-17-92 cluster, while concurrently upregulating their shared target, thrombospondin 1 (TSP1), thereby impairing the angiogenic capacity of ECs (Chamorro-Jorganes et al., 2021). Conversely, METTL3 overexpression or augmentation of let-7e-5p and miR-18a-5p levels effectively reinstates EC angiogenic functionality. Collectively, these observations suggest that a sustained high level of METTL3 is critical for optimal EC function in angiogenesis, potentially through modulation of the let-7e-5p/miR-17-92-TSP1 axis.

Additionally, maintaining elevated METTL3 levels is vital for addressing angiogenic disorders. Lu et al. (2020) found that Propofol upregulates miR-20b and METTL3 expression during hypoxia/re-oxygenation-induced EC autophagic death, thereby mitigating cellular damage. METTL3 depletion leads to diminished miR-20b expression. Inhibition of miR-20b or METTL3 attenuates Propofol’s protective effect, exacerbating autophagy in ECs by targeting Unc-51-like kinase 1 (ULK1). These results indicate that Propofol confers protection against EC death via the METTL3/miR-20b-ULK1 signaling pathway. Furthermore, Jiang et al. (2021) reported a significant upregulation of METTL3 in endothelial progenitor cells (EPCs) during hypoxia-induced angiogenesis and distraction osteogenesis (DO), enhancing EC proliferation, tube formation, migration, and angiogenic activity. METTL3 upregulation promotes bone regeneration during DO by increasing VEGF and PI3K p110 levels and AKT phosphorylation, thereby facilitating EPC-induced angiogenesis through the PI3K/AKT pathway (Jiang et al., 2021). These insights propose that METTL3 overexpression is a promising therapeutic approach to augment bone regeneration in DO (Figure 1; Table 1).

Retinal neovascularization is a critical feature of various ocular pathologies, such as retinopathy of prematurity, diabetic retinopathy, and retinal vein occlusion (Heath Jeffery and Chen, 2024). The primary etiologies of this aberrant angiogenic response encompass ischemic hypoxia, inflammatory processes, and viral infections within the retina, leading to proteolytic degradation of the basement membrane maintained by ECs (Heath Jeffery and Chen, 2024). The resultant loss of structural support precipitates increased EC migration and proliferation, culminating in angiogenesis and neovascular formations.

Retinal ischemia and hypoxia precipitate in neovascularization, which is closely associated with the upregulation of several angiogenesis-related factors that modulate retinal endothelial cell (REC) proliferation, migration, and angiogenesis, including VEGF, erythropoietin, and angiopoietins (Fevereiro-Martins et al., 2023). Under hypoxic conditions, Yao et al. (2020) identified a significant upregulation of METTL3 expression in both ECs and murine retinas, which subsequently promotes pathological angiogenesis. Mechanistically, the increased expression of METTL3 synergizes with YTHDF1 to enhance the translation of low-density lipoprotein (LDL) receptor-related protein 6 (LRP6) and disheveled 1 (DVL1) via Wnt signaling modulation, thereby promoting heightened EC viability, proliferation, migration, and aberrant tube formation. Conversely, METTL3 ablation in a hypoxia-induced retinopathy model results in reduced avascular regions, diminished pathological neovascular tufts, and inhibition of alkali burn-induced corneal neovascularization (CNV) (Yao et al., 2020). These findings imply that METTL3-mediated regulation of LRP6/DVL1-Wnt signaling under hypoxic stress may be a pivotal mechanism in modulating normal angiogenesis. Consistently, Lin et al. (2023) revealed that both METTL3 expression and m⁶A modification levels are significantly elevated in human retinal microvascular endothelial cells (HRMECs), as well as in retinas and RECs under hypoxic conditions. The elevated METTL3 levels facilitate m⁶A modification on matrix metalloproteinase 2 (MMP2) and TIE2, enhancing their protein expression, which in turn augments endothelial tube formation and migration (Lin et al., 2023). Notably, the knockdown of MMP2 and TIE2 significantly impairs the angiogenic capabilities of HRMECs. Collectively, these findings indicate that METTL3-mediated m⁶A modifications enhance EC angiogenic behaviors by targeting MMP2 and TIE2, underscoring the importance of the METTL3-MMP2 and METTL3-TIE2 axes in retinal angiogenesis and positioning METTL3 as a potential therapeutic target for oxygen-induced retinopathy.

Furthermore, herpes stromal keratitis (HSK) is a potentially vision-impairing condition caused by herpes simplex virus type 1 (HSV-1) infection (Stepp and Menko, 2021). CNV is a clinical manifestation of HSK, leading to irreversible visual impairment and blindness. Although HSV-1 does not encode pro-angiogenic proteins at any infection stage, it induces the production of various growth factors that result in CNV, with VEGF-α playing a predominant role. CNV induced by HSV-1 is significantly influenced by VEGF-α, and some studies suggest that virus-infected ECs are a major source of VEGF-α during early HSV-1 infection (Petti and Lodi, 2019). Therefore, inhibiting VEGF-α in ECs substantially mitigates the progression of HSK. Given the critical role of METTL3 in EC angiogenic properties, the mechanism underlying VEGF-α inhibition in ECs might involve METTL3. Wang et al. (2023) demonstrated that METTL3 is markedly upregulated in HSV-1-infected human umbilical vein endothelial cells (HUVECs), leading to increased m⁶A levels. Mechanistically, METTL3 regulates LRP6 expression through m⁶A-dependent post-transcriptional mRNA modification, enhancing its stability, upregulating VEGF-α expression, and promoting angiogenesis in HSV-1-infected HUVECs. Moreover, METTL3 knockdown or inhibition via STM2457 further reduces m⁶A levels and VEGF-α expression, impairs HUVEC migration and tube formation, and diminishes CNV in vivo following HSV-1 infection. Thus, METTL3 facilitates pathological angiogenesis through canonical Wnt and VEGF signaling pathways both in vitro and in vivo, highlighting METTL3 as a potential pharmacological target for preventing CNV progression in HSK (Figure 1; Table 1).

Bai et al. (2021) observed a marked upregulation of METTL3 in the vasculature of mice and HUVECs subjected to lipopolysaccharide-induced inflammatory insult. This upregulation synergizes with YTHDF1 to enhance the translation of JUN mRNA, thereby elevating JUN expression. Consequently, JUN binds to the promoter of plasminogen activator inhibitor-1 (PAI-1), augmenting PAI-1 expression and promoting fibrin deposition in endotoxin-induced thrombosis. Conversely, EC-specific deletion of METTL3 diminishes PAI-1 plasma levels and facilitates fibrinolysis in endotoxin-induced thrombosis in mice. Thus, METTL3 exacerbates EC-mediated coagulation and thrombosis through the regulation of the JUN-PAI-1 axis, suggesting METTL3 as a promising therapeutic target for endotoxin-induced thrombosis.

Atherosclerosis (AS) is the predominant form of thrombosis (Patti et al., 2023). Human cytomegalovirus (HCMV) infection is a likely etiological factor for AS and restenosis post-vascular transplantation, as it induces inflammatory alterations in the vascular endothelium (Patti et al., 2023). Zhu et al. (2024) revealed that HCMV infection involves METTL3-mediated m⁶A modification in ECs. Specifically, HCMV infection triggers abnormal upregulation of m⁶A modification and R-loops in ECs, while decreasing UCHL1 expression via m⁶A modification-mediated mRNA decay and R-loop-dependent transcriptional termination. UCHL1 deficiency leads to the ubiquitination and degradation of ferredoxin reductase (FDXR), resulting in mitochondrial iron overload and AIM2 inflammasome activation, culminating in endothelial injury. Notably, METTL3 inhibition via the specific inhibitor STM2457 restores UCHL1 expression during HCMV infection, mitigating inflammatory injury in vascular ECs. These findings delineate the METTL3-UCHL1-FDXR axis as a novel mechanism for HCMV-induced endothelial injury, indicating the therapeutic potential of METTL3 suppression in HCMV-induced AS. Moreover, HCMV infection induces apoptosis in vascular ECs, further contributing to AS progression (Zhu et al., 2022). HCMV infection upregulates METTL3 and YTHDF3 expression, with METTL3 methylating mitochondrial calcium uniporter (MCU) mRNA, facilitating YTHDF3 interaction and enhancing MCU translation and expression. In contrast, ALKBH5 negatively regulates MCU mRNA by demethylation. This study highlights that the METTL3/YTHDF3/ALKBH5 axis governs endothelial cell apoptosis by targeting MCU. Collectively, these insights suggest METTL3 suppression as a therapeutic approach for HCMV-induced AS. For instance, Zhu et al. (2022) demonstrated that vitamin D3 protects ECs from HCMV-induced apoptosis by inhibiting both endoplasmic reticulum and mitochondrial apoptosis pathways. Vitamin D3 downregulates METTL3 expression by inactivating the AMPK pathway, thereby reducing m⁶A modification on MCU and preventing cell apoptosis. These findings expand our understanding of virus-induced endothelial damage mechanisms and underscore the therapeutic significance of vitamin D3 in HCMV-induced AS (Figure 1; Table 1).

The blood-tumor barrier (BTB) poses a significant challenge to therapeutic efficacy by restricting drug penetration; thus, enhancing BTB permeability is crucial for glioma treatment (Ponmozhi et al., 2023). Tight junctions, constituted by tight-junction-associated proteins (TJPs), are pivotal targets for modulating BTB permeability (Scalise et al., 2021). Zhang et al. (2022) demonstrated that METTL3-driven m⁶A modification is instrumental in regulating BTB permeability. Specifically, glioma microvascular ECs exhibit aberrant upregulation of METTL3 and IGF2BP3, which augments the stability of CPEB2 mRNA via m⁶A methylation. CPEB2 subsequently interacts with and stabilizes SRSF5 mRNA, which facilitates the SRSF5-mediated alternative splicing of ETS1. Consequently, the METTL3/IGF2BP3- CPEB2-SRSF5-ETS1 pathway upregulates TJPs, including zonula occludens-1 (ZO-1), occludin, and claudin-5, thereby reducing BTB permeability. In vivo silencing of METTL3 or CPEB2 in glioblastoma xenograft models results in diminished expression of ZO-1, occludin, and claudin-5, leading to increased BTB permeability and enhanced glioma-targeted chemotherapeutic efficacy. Thus, METTL3 is a key regulator of BTB permeability, offering insights into glioma treatment strategies targeting METTL3 (Figure 1; Table 1).

In summary, sustaining elevated levels of METTL3 under physiological conditions is critical for EC function in angiogenesis; whereas under stress response conditions, METTL3 exacerbates pathological features. Therefore, we propose that METTL3 serves as a potential diagnostic biomarker and therapeutic target for EC dysfunction-related vascular disorders.

The phenotypic transition of VSMCs has been linked to METTL3 activity. Lin et al. (2020) demonstrated that hypoxic conditions markedly enhance METTL3 expression in VSMCs. Elevated METTL3 levels facilitate VSMC proliferation and generation while suppressing the expression of a-SMA, sm22α, calponin, and smooth muscle myosin heavy chain. Furthermore, METTL3 overexpression induces the differentiation of adipose-derived stem cells into VSMCs and augments the secretion of angiogenesis-promoting factors, including VEGF, HGF, TGF-β, FGF, and SDF-1, collectively enhancing VSMC-driven angiogenesis (Figure 2; Table 1).

While VSMC proliferation is essential for maintaining vascular architecture, pathological conditions result in both excessive and insufficient VSMC proliferation, adversely affecting the organism. METTL3 significantly influences VSMC proliferation, contributing to neointima formation post-vascular injury. Luo et al. (2023) found that METTL3 modulates VSMC autophagy to promote neointima formation by decreasing p-mTOR and cyclin-dependent kinase 1 (p-CDK1/CDC2) levels, thereby inhibiting VSMC proliferation through autophagosome formation. Similarly, Fang et al. (2023) indicated that METTL3 downregulation during VSMC proliferation and neointima formation suppresses VSMC phenotypic switching by activating autophagosome formation. METTL3 enhances autophagosome formation by upregulating autophagy-related genes ATG5 and ATG7. Knockdown of ATG5 or ATG7 substantially reverses METTL3’s regulatory impact on human aortic smooth muscle cells (HASMCs) phenotypic switching. METTL3 knockdown promotes, while its overexpression suppresses, HASMC proliferation by arresting cells at the G2/M checkpoint and deactivating CDC2 phosphorylation (p-CDC2). Notably, aberrant VSMC proliferation and autophagosome formation contribute to neointima formation, a primary cause of poor outcomes post-stenting or coronary artery bypass grafting, regulated by METTL3. Additionally, METTL3 knockdown enhances HASMC migration and synthetic phenotype, whereas its overexpression inhibits these processes. Overexpression of METTL3 reduces MMP2, MMP7, and MMP9 protein levels while increasing tissue inhibitor of metalloproteinase 3 expression in HASMCs. These findings suggest that METTL3 impedes VSMC phenotypic switching by positively regulating ATG5 and ATG7-mediated autophagosome formation. Thus, mitigating neointima formation necessitates preventing abnormal VSMC proliferation and autophagosome formation by targeting METTL3, thereby improving long-term outcomes following stenting or coronary artery bypass grafting (Figure 2; Table 1).

Moreover, the phenotypic shift of VSMCs from a differentiated to a dedifferentiated state is pivotal in AS pathogenesis (Zhai et al., 2022). Vascular calcification stands as a clinical hallmark of AS. Han et al. (2021) elucidated that METTL3 expression is markedly elevated in VSMCs during vascular calcification instigated by oxidized LDL, acting as a target for miR-33a-5p. Similarly, Zhao et al. (2022) established that METTL3 is a crucial agent in catalyzing a global increase in m⁶A methylation in response to carotid artery injury and diverse VSMC phenotype transitions. Elevated METTL3 expression induces a global rise in m⁶A modifications, thereby augmenting VSMC proliferation and migration while suppressing contractile gene expression. Conversely, Mettl3 ablation mitigates this phenotypic transition in VSMCs, evidenced by reduced m⁶A levels, diminished proliferation, migration, neointimal hyperplasia, and upregulated contractile gene expression (Zhao et al., 2022). Mechanistically, Mettl3 silencing enhances PI3K mRNA decay, thereby deactivating the PI3K/AKT signaling pathway to inhibit VSMC phenotypic switching. Collectively, these results underscore the significance of METTL3-mediated m⁶A in VSMC phenotypic modulation, proposing METTL3 as a therapeutic target for AS and restenosis (Figure 2; Table 1).

The phenotypic transition of HASMCs similarly contributes to TAD, characterized by dedifferentiated VSMCs (Chakraborty et al., 2023). Yang et al. (2023) discovered that METTL3 expression is significantly elevated in HASMCs, fostering extensive HASMC proliferation by repressing α-SMA, sm22α, calponin, and NOTCH1. Mechanistically, METTL3 enhances m⁶A modification on NOTCH1 mRNA and facilitates NOTCH1 mRNA degradation via collaboration with YTHDF2, thereby inducing HASMC phenotypic alteration. METTL3 knockdown exhibits contrary effects. These findings indicate that METTL3 orchestrates HASMC phenotypic changes by upregulating m⁶A modifications on NOTCH1 and suppressing NOTCH1 expression, consequently driving TAD development. In summary, elevated METTL3 levels promote VSMC formation and angiogenesis, playing a critical role in TAD (Figure 2; Table 1).

AAA, or abdominal aortic aneurysm, is characterized by a localized abnormal dilation of blood vessels, often resulting from the thinning of arterial walls due to vascular injury (Li et al., 2023). Key histopathological features of AAA include chronic inflammation of the vascular wall, apoptosis of smooth muscle cells (SMCs), and remodeling of the extracellular matrix (ECM) (Li et al., 2023). SMCs are the predominant cell type in the middle layer of the aortic wall (Zhong et al., 2020). An imbalance between SMC proliferation and apoptosis is pivotal in the remodeling of the aortic wall and the progression of AAA (Chakraborty et al., 2023). In the context of angiotensin II (Ang II)-induced AAA, there is an observed increase in necroptosis and inflammatory cytokines within vascular SMCs (Ji et al., 2023). Additionally, levels of m6A modification and the expression of METTL3 and METTL14 are heightened in the aortic wall tissues affected by AAA, indicating a significant association with Ang II-induced aneurysm formation (Ji et al., 2023). Ji et al. (2023) demonstrated that the METTL3-METTL14 complex interacts with rip3 mRNA and SMAD2/3 through YTHDF3 in the vascular SMCs of Ang II-induced AAA. Ang II activation stimulates SMAD2/3 in the abdominal aortic wall SMCs, which subsequently enhances the m6A modification of rip3 mRNA mediated by the METTL3-METTL14 complex. This process increases the binding of YTHDF3 to rip3 mRNA, raising the protein levels of rip3 and thereby promoting SMC necroptosis, inflammatory responses, and contributing to the pathological development of AAA (Ji et al., 2023). Inhibition of METTL3/METTL14 has been shown to reduce SMC necroptosis, the inflammatory response, and the progression of AAA (Ji et al., 2023). Furthermore, Li et al. (2022) found that elevated METTL3 levels facilitate the maturation of primary microRNA-34a into miR-34a by targeting DGCR8 during apolipoprotein-induced AAA formation both in vitro and in vivo. The upregulation of miR-34a significantly inhibits sirtuin 1 expression, worsening the condition of AAA (Li et al., 2022). These findings underscore the crucial role of METTL3 in the development of AAA, suggesting it as a potential target for novel therapeutic interventions and as a diagnostic biomarker for this disease (Figure 2; Table 1).