It is well-established that the initiation of MG critically hinges on the activation of autoreactive T cells (57). Consequently, the miRNAs exhibiting abnormal expression and responsibility for T cell proliferation and activation may represent a pivotal link in MG pathogenesis. Certain miRNAs have been identified to be involved in the regulation of T cells in MG. Cron et al. (58) discovered that miR-150 could target MYB, a proto-oncogene, thus affecting the survival of CD4⁺ and CD8⁺T cells, which may contribute to the maintenance of an immunologically activated state. Research showed that miR-20b would inhibit T cell proliferation and activation by suppressing the NFAT signaling pathway through downregulating NFAT5 and CAMTA1 (33). Moreover, decreased miR-522-3p can lead to the overexpression of CD25, CD69, IL-2, and IL-10 by targeting SLC31A1, consequently promoting the activation and proliferation of Jurkat cells, a T cell leukemia line (31). Dysregulation of key immune cell populations, including Tregs, Th17, and Th1, exerts a significant influence on MG pathogenesis. Studies have reported that the expression of Tregs is associated with disease severity, with observations of decreased Foxp3, a Treg-related cytokine, in peripheral blood mononuclear cells (PBMCs) of MG patients (39). In an AIRE knockout mouse model, reduced Tregs and increased Th17 cells in the thymus rendered the mice more susceptible to experimental autoimmune myasthenia gravis (EAMG) (42), mirroring the pathogenesis of LOMG and TAMG (15). Villegas et al. (46) noted that an imbalance between Tregs and Th17 cells is associated with chronic thymic inflammatory conditions in AChR-MG.

The lapses in Treg function result in the loss of their inhibitory effect on excessive inflammatory responses, leading to uncontrolled inflammatory cell activity in MG (25). This unchecked immune activity gives rise to chronic inflammation and thymic hyperplasia, further disrupting immune tolerance mechanisms. Recent research outcomes have unveiled a miR-146b-TRAF6-NF-κB-Foxp3 pathway, which plays a crucial role in suppressing Treg proliferation and its inhibitory function (49, 59). Intriguingly, Yan et al. (60) proposed that overexpressed miR-146a may contribute to the pathogenesis of MG by promoting TRAF6 expression, which could further disrupt Treg function. miR-125a-5p was confirmed to negatively regulate Foxp3, consequently inhibiting the generation of Treg with a great possibility (37). Additionally, there is a positive correlation between the reduced miR-126 and Foxp3 mRNA in MG, providing strong evidence for the downregulation of Treg activity (50). In summary, differentially expressed miRNAs in MG have been observed to inhibit Treg proliferation and weaken their inhibitory function. Consequently, these miRNA-mediated changes impair immunological tolerance mechanisms and play an important role in the pathogenesis of MG.

Compelling scholarly evidence has demonstrated that the activation of Th17 and Th1 cells, when losing the control of Tregs, can lead to the release of pro-inflammatory cytokines such as INF-γ and IL-17 (61), which may build the bridge between some dysregulated miRNAs and MG. For instance, Wang et al. (62) revealed that miR-145 could serve as a regulator that promotes T cell proliferation and differentiation into Th17 cells, by targeting CD28 and NFATc1. Similarly, Cron et al. (34) reported a reduction of the miR-29 family within thymic tissues of MG, potentially in connection with an increase of IFN-β. Among these, miR-29a/b1, part of a miR-29a genomic cluster, could possibly facilitate the flourishing of Th17 cells. Besides, miR-19b-5p in TAMG has been shown to post-transcriptionally inhibit thymic stromal lymphopoietin (TSLP), thereby regulating Th17 cells and their related cytokines (44). It’s reasonable to speculate that these abnormally expressed miRNAs may function as regulators, promoting the release of Th17-related cytokines (IL-6, TGF-β, IL-17, IL-1β, and IL-23) and the proliferation of Th17 cells. On the grounds of research by Cheng et al. (45), with the target of MAPK1, miR-320a may influence the Th1-associated cytokines, like IL-2, and IFN-γ, by adjusting COX-2 through the regulation of ERK/NF-κB pathways. In addition, several miRNAs contribute to the pathogenesis of MG by influencing both Th1 and Th17 responses concurrently. Liu et al. (63) reported that miR-15a could affect the CXCL10 gene by regulating Th1- and Th17-related cytokines to generate immune responses. In conclusion, the dysregulation of miRNAs can disrupt Treg function, promote the proliferation of Th1 and Th17 cells, and result in the overexpression of pro-inflammatory cytokines, thus modulating the pathogenesis of MG.

B cells, integral players in the pathogenesis of MG, participate in the formation of ectopic GCs, receive signals from antigen-presenting cells (APCs), and contribute to the production of autoimmune antibodies (38). Many dysregulated miRNAs can modulate chemokines and specific signaling pathways to promote the maturation of autoreactive B cells and the development of GCs.

miR-155, found to be elevated in B cells, engaged in the immune response through the BAFF-R/TRAF3/NIK/NF-κB p65 pathway, mediating the survival of activated B cells and increasing the production of AChR antibodies by regulating co-stimulatory molecules (48). The binding of BAFF to BAFF-R is necessary for B cell maturation and survival (43). And miR-155 can promote the expression of BAFF-R and TRAF3 to facilitate the phosphorylation of NIK, thus helping the NF-κB to translocate into the nuclear of B cells (48). At the same time, miR-155 can also modulate the co-stimulatory molecules, such as CD40, CD80, and CD86, to enhance the production of antibodies by B cells. Two independent studies mentioned an elevation of miR-146a in AchR-specific B cells and they also reported that miR-146a could affect B cell immunity (64, 65). Notably, one of these studies proposed that miR-146a may facilitate the activation of B cells and the production of antibodies by modulating the TLR4 and NF-κB pathways (64). In a study by Bortone et al. (66), the downregulated miR-146a showed a noteworthy negative correlation with IRAK1, c-REL, ICOS, and FAS in the follicular hyperplastic thymus of EOMG. The genes targeted by miR-146a appear to collectively contribute to the activation of B cells and the formation of GCs. Firstly, the downregulation of miR-146a allows IRAK1 to induce excessive inflammation and disrupt immune tolerance through the TLR signaling pathway. Secondly, the deficiency of miR-146a can enhance the activation of c-REL, thereby promoting the proliferation and differentiation of B cells and amplifying GCs formation. Furthermore, reduced miR-146a may fail to effectively restrict the aggregation of follicular helper T cells (Tfhs) and the proliferation of B cells in GCs by targeting ICOS. Lastly, miR-146a can downregulate FAS expression, promoting lymphoproliferation and GCs formation. Wang et al. (67) found that miR-181a may influence the levels of inflammatory cytokines, such as TNF-α, IL-4, and IL-6, affecting B cell proliferation by regulating TRIM9.

Additionally, miR-548k, reduced in the thymus of MG, can target CXCL13 (40), which plays a role in directing B cells and facilitating GCs formation. miR-452-5p and miR-139-5p were associated with the promotion of RGS13 expression, leading to B cell proliferation and GCs expansion (54). miR-150-5p has shown a positive correlation with CD19⁺ and CD27⁺ B cells, suggesting its involvement in B cell differentiation, memory B cell formation, and further possible immune responses, including B cell activation and antibody production (30). Additionally, the abnormally expressed miR-126 and miR-21 in PBMCs were proved to upregulate the expression of IL-6, thus promoting the proliferation and differentiation of B cells, consequently facilitating the production of antibodies (50). let-7c was reported to target IL-10, probably participating in MG pathogenesis by stimulating B cells (68). Besides, the reduced miR-7 in thymus was reported to upregulate the expression of CCL21, thus helping the formation of GCs (69).

AChR-Ab is the most prevalent antibody in MG, accounting for approximately 85% of cases (70). AChR-MG can be further classified according to clinical features. Interestingly, there are some differences in thymus pathology among EOMG, LOMG and TAMG. EOMG refers to individuals under the age of 50, characterized by hyperplastic thymus pathology. In contrast, LOMG manifests in individuals over the age of 50, commonly associated with thymic atrophy. TAMG, on the other hand, represents a paraneoplastic syndrome of thymoma (4). A few of studies (54, 55, 58, 64, 66, 69, 71) revealed some differentially expressed miRNAs, such as miR-139-5p, miR-452-5p, miR-612, miR-3654, miR-365, miR-150, miR-20b, miR-192, miR-7, miR-125a-5p, and miR-146a, in the AChR antibody-positive EOMG (AChR-EOMG) patients. A decrease in miR-15b expression was observed in the serum of both early-onset and late-onset AChR-MG (71), which aligns with findings from an animal model of EAMG in mice injected with Torpedo AChR (72). In addition, in patients with AChR antibody-positive LOMG (AChR-LOMG), miR-122, miR-140-3p, miR-185, miR-885-5p, miR-106b-3p, miR-223-5p, miR-140-5p, miR-19b-3p, miR-30e-5p, and miR-150-5p were found to express abnormally (29, 32, 71). These findings suggest a nuanced expression profile of dysregulated miRNAs between EOMG and LOMG. Many miRNAs were reported to express aberrantly in TAMG, including miR-125a-5p, miR-19b-5p, miR-20b and miR-522-3p (25, 33, 50, 58). Additionally, a study by Shi et al. (72) indicated a decrease in miR-15b expression in TAMG, EOMG, and LOMG patients.

Several dysregulated miRNAs in AChR-MG, compared with ocular myasthenia gravis (OMG), have more severe abnormalities in generalized myasthenia gravis (GMG), some of which are correlated with quantitative myasthenia gravis scores (QMGs) or myasthenia gravis composite scores (MGCs), reflecting the severity of MG and further serving as potential biomarkers for disease surveillance with great possibility. Research findings indicated that both OMG and GMG patients showed elevated miR-150-5p, miR-21-5p, and miR-30e-5p, which had a positive correlation with MGCs and significantly more overexpressed in GMG than in OMG (29, 32). Conversely, the lower expressed miR-181a, miR-106a-5p, and miR-20b in MG, had a negative relationship between QMGs, with GMG displaying notably reduced levels compared to OMG (73–75). Additionally, several studies (51, 76) on curative effect indicated a parallel between the reduction of AChR-Ab titers and the improvement of symptoms. A fast decrease of AChR-Ab titers more than 50% also made a clinical sense (23). Interestingly, some studies showed that miR-126, and miR-145 were negatively correlated with AChR-Ab titer (50, 62), while miR-21 was positively related to AChR-Ab titer (50). We therefore speculate that specific ncRNAs may also be useful for efficacy detection.

MiR-150-5p, miR-30e-5p, and miR-146a levels in the serum of AChR-MG patients have shown promising responses to various treatments like thymectomy and immunosuppression, indicating a correlation between their levels and clinical improvement (26, 30, 32, 35, 52, 58, 66). These miRNAs could potentially serve as biomarkers for monitoring therapeutic efficacy and reflecting the disease severity. Furthermore, research by Zhang et al. (65) suggested that silencing miR-146a could reduce the expression of CD40, CD80, and CD86 on the surface of B cells, inhibit B cell differentiation, and consequently reduce the production of anti-AChR antibodies. By comparing the level of miR-146a and the expression of c-REL in the thymus of MG in corticosteroid-naïve patients and corticosteroid-treated patients, Bortone et al. (66) reported that after corticosteroid treatment, the immune response of c-REL, which was originally active in GCs and infiltrating B cells of untreated patients, was strongly inhibited, highlighting the miR-146a/c-REL axis as a potential therapeutic target for immunosuppressants. These discoveries suggests that miR-146a could serve as both a therapeutic target and a monitoring indicator for treatment efficacy. Moreover, Wang et al. (48) demonstrated that silencing miR-155 could inhibit the production of anti-T-AChR antibodies, making miR-155 another potential treatment target. Sengupta et al. (54) proposed that miR-139-5p and miR-452-5p might be considered for MG treatment, especially for EOMG, as their mimics inhibit B cell chemotaxis and GCs formation. Additionally, Cavalcante et al. reported that AChR-MG with abnormally expressed miRNAs such as miR-323b-3p, miR-409-3p, miR-485-3p, miR-181d-5p, and miR-340-3p are not sensitive to immunosuppressants (47), suggesting the presence of these miRNAs may result in poor treatment. In other words, these miRNAs may be used to forecast clinical response.

In essence, miRNAs exhibit subtle variations in expression across MG subgroups. Certain miRNAs with abnormal expression levels have the potential to facilitate disease monitoring, aid in targeted therapy, and assess treatment efficacy. Firstly, several miRNAs tend to normalize after appropriate treatment. Secondly, certain miRNAs may be implicated in antibody production, making them potential targets for MG treatment. Lastly, the presence of specific miRNAs may indicate the response to treatment. These miRNAs hold promise as specific biomarkers reflecting disease severity or treatment responses and may serve as novel targets for MG therapy. Consequently, there arises the prospect of precision therapy and personalized monitoring for individuals with MG.

MuSK antibodies are present in approximately 1-10% of MG cases, predominantly affecting young women under the age of 40 (77). Although research on MuSK-Ab-positive MG (MuSK-MG) has not been as extensive as that on AChR-MG, several studies have reported differentially expressed miRNAs in this subgroup. Sabre et al. (36) observed a significant decrease in miR-210-3p and miR-324-3p levels in the serum of MuSK-MG. Punga et al. (78) identified differential expression of let-7a-5p, let-7f-5p, miR-151a-3p, and miR-423-5p in the serum of MuSK-MG compared to healthy controls. An investigation of PBMCs in MuSK-MG revealed 5 overexpressed and 96 under expressed miRNAs, with marked decreases observed in miR-340-5p, miR-106b-5p, miR-27a-3p, and miR-15a-3p (79). Moreover, an animal study identified 13 abnormally expressed miRNAs in the omohyoid muscle of MuSK-Ab-positive EAMG mice, particularly highlighting the elevation of miR-1933-3p and miR-1930-5p (80). Additionally, in a therapeutic study, the serum level of miR-151a-3p in MuSK-MG patients decreased after treatment (81), indicating a possibility for miR-151a-3p as potential therapeutic target and monitor for treatment efficacy in MuSK-MG.

Unlike AChR and MuSK antibodies, Lrp4 and agrin antibodies are rare in MG, resulting in limited research on these subgroups. Although some miRNAs have been identified as potential regulators of Lrp4 or agrin (82–88), the precise relationship between miRNAs and these two antibodies remains undiscovered (89).

Just like miRNAs, dysregulated lncRNAs can also influence pro-inflammatory cytokines and associated signaling pathways, promoting the proliferation of CD4+ T cells and B cells, inhibiting the proliferation of Treg cells, and activating Th17 and Th1 cells to disrupt immune homeostasis in MG.

In the study by Xu et al. (98), GAS5 was found to decrease in CD4⁺T cells and directly negatively regulate the expression of miR-23a. Furthermore, overexpressed GAS5 was shown to disrupt the balance between Th17 and Treg cells, restraining Th17 differentiation by sponging miR-23a. Another related study (103) indicated that the upregulation of GAS5 was associated with increased levels of IL-10, coinciding with an improvement in MG symptoms. Two studies by Hu et al. (94, 102) demonstrated that XLOC_003810 was elevated in thymic CD4⁺T cells in MG. In one study, overexpression of XLOC_003810 in TAMG disrupted the balance between Treg and Th17 by favoring Th17 differentiation and increasing Th17-associated markers such as RORγt, IL-6, and IL-17, while reducing Treg-related markers like Foxp3, TGF-β1, and IL-10. Another study emphasized that XLOC_003810 promoted the expression of CD4⁺T cells and their inflammatory cytokines, such as IFN-γ, TNF-α, and IL-1β, highlighting its significant role in MG pathogenesis, especially in TAMG. Luo et al. (100) found lower levels of IFNG-AS1 in PBMCs of MG, which were negatively correlated with HLA-DOB and HLA-DRB1. They also demonstrated that increased IFNG-AS1 could suppress the proliferation of Th1 cells and promote the expansion of Treg cells, along with some of their transcription factors. IFNG-AS1 was considered to downregulate CD40L and T-bet in CD4⁺T cells of MG, partly dependent on HLA-DRB1, implying the involvement of IFNG-AS1 in CD4⁺ T-related immune responses. HCG18, an upregulated ceRNA in PBMCs, sponging miR-145-5p to modulate CD28, was proved to inhibit apoptosis and enhance the proliferation of Jurkat cells (99). Moreover, OIP5-AS1 was also verified to have a similar effect on Jurkat cells in another study (105), which can be achieved through regulating IL-7 by sponging miR-181c-5p. Additionally, Wang et al. (101) demonstrated that the upregulated SNHG16 can serve as a ceRNA, competitively binding with let-7c-5p in PBMCs of MG. This action not only facilitates Jurkat cell proliferation and inhibits their apoptosis but also influences the level of IL-10, potentially further promoting the activation of B cells.