Differential expression of m6A regulators in Wilms Tumor
We obtained expression data from the TCGA database for a total of 132 samples, including 6 normal tissues and 126 tumor tissues. The results showed significant differences in the expression of almost all m6A regulators between tumor and normal tissues, with the majority of m6A regulators being upregulated in WT tissues (P < 0.001), while ALKBH5 and YTHDC1 were downregulated in WT expression levels (Figure 1.A). In addition, our results showed that TMB in WT patients differed with different clinical characteristics, such as younger age group and diffusely anaplastic Wilms Tumor (DAWT) had higher TMB (Figure 1.B-C).
Univariate COX regression analysis and KM showed that m6A modulators were potential prognostic factors for WT patients, such as RBM15, WTAP and YTHDF2 showed high tumorigenicity (Figure 2.A-C). There was also a significant positive correlation between each m6A modulator (Figure 2.D). In conclusion, m6A regulators showed significant heterogeneity and differential expression in WT tissues compared with normal tissues, and m6A regulators may play a critical role in the development and progression of WT.
m6A modification patterns based on m6A regulators
Based on the expression of 19 m6A regulators, unsupervised cluster analysis was performed and three different m6A modification patterns (clusters 1-3) were identified, with 45 cases in cluster1, 25 cases in cluster2 and 62 cases in cluster3 (Figure 3.A). Survival analysis showed some differences in prognosis between the different modification patterns (Figure 3.B). Further analysis showed differences in regulator expression in the 3 different m6A alteration patterns (Figure 3.C). In addition, we grouped the three different modification patterns into two vehicles for GSVA analysis, and the results showed significant differences in biological behavior between the different modification patterns (Figure 3.D-F).
Immunological characteristics of different m6A modification patterns
The infiltration of 29 immune cells was analyzed by ssGSEA in different m6A modification patterns. The results showed that the immune infiltration was significantly different between the different clusters (Figure 4.A). The results obtained by ESTIMATE algorithm showed that the StromalScore of cluster3 was significantly higher than the other two clusters (Figure 4.B-D). In addition, we analyzed the expression levels of immune checkpoints, immune cell markers and WT metabolites in different clusters31. Among the immune checkpoints, cluster1 had higher expression of CD274 and PDCD1, while cluster3 had higher expression of LAG3; the star molecule in WT metabolites, GPC3, was expressed in the 3 clusters, and cluster2 was higher than the other two groups (Figure 5).
Generation of the m6Ascore model
PCA analysis showed that there were different m6A modification patterns in WT patients (Figure 6). GO enrichment analysis and KEGG pathway analysis of different m6A clusters using the R package "clusterProfiler" showed that DEGs were enriched in biological processes related to tumorigenesis and tumor progression, such as rRNA metabolic processes and cell cycle (Figure 7.A-D).
Univariate Cox regression analysis was used to understand the prognostic value of each DEG, and a total of 284 DEGs with significant effect on prognosis were screened to construct m6Ascore, and the scores were grouped into high and low scores based on the best critical value. The association between m6A modification pattern and m6Ascore was analyzed using analysis of variance, and the results showed that cluster1 had a lower score of m6Ascore (Figure 8.A). The KM method was used to show that the subgroup with low m6Ascore had a worse prognosis (Figure 8.B). We used univariate and multivariate Cox regression analysis including gender, age, tumor type, m6Ascore and tumor stage to confirm that m6Ascore was an independent prognostic factor for WT (Figure 8.C-D). The ROC curve showed that m6Ascore had some diagnostic value (Figure 8.E). We further selected a WT data set of m6A methylation modifications, GSE167054, for differential analysis, and the results showed that m6A modifications differed between normal and WT tissues (Figure 8.F). This validated the reliability of the m6Ascore model to some extent.
To further understand the potential biological mechanisms of m6Ascore, we analyzed the correlation between m6Ascore and some biological processes. m6Ascore was closely associated with the infiltration of immune cells, such as a significant positive correlation with dendritic cells and T cells, and a significant negative correlation with neutrophils (Figure 9.A). However, there was no significant correlation between TMB and m6Ascore (Figure 9.B). In addition, our results showed that patients with low m6Ascore had a higher percentage of death (Figure 9.C). Our results also showed significant differences in the expression of immune checkpoints, immune cell markers, and tumor metabolic markers in high and low m6Ascore groups, such as CCL2, CD8A, CD68, CTLA4, HAVCR2, and PDCD1LG2 were highly expressed in the high m6Ascore group, while two immune checkpoints, CD276 and PDCD1, were highly expressed in the low m6Ascore group (Figure 10). This suggests that m6Ascore may become a new evaluation index in immune-targeted therapy.