GSEA shows that autophagy participates in the progress of AS
We performed GSEA to investigate the biological function of DEGs. As shown in Fig. 1, our results revealed that most of the enriched gene sets were involved in selective autophagy (Fig. 1A, normalized enrichment scores (NES) = 1.372, p.adj = 0.047, FDR = 0.032), programmed cell death (Fig. 1B, NES = 1.481, p.adj = 0.015, FDR = 0.011), neurotrophin signaling pathway (Fig. 1C, NES = 1.406, p.adj = 0.015, FDR = 0.011), oxidative phosphorylation (Fig. 1D, NES = 1.569, p.adj = 0.015, FDR = 0.011), endocytosis (Fig. 1E, NES = 1.375, p.adj = 0.019, FDR = 0.013), and apoptosis (Fig. 1F, NES = 1.427, p.adj = 0.024, FDR = 0.016). These findings indicated autophagy may play an important role in the pathological process of AS.
Identification of DEARGs in GSE25101 and GSE18781 datasets
First, a total of 1592 DEGs were identified via the analysis of the GSE25101 dataset with R software. All genes were presented as volcano plots, of which black green dots represent 761 down-regulated DEGs, red dots represent 831 up-regulated DEGs, and grey dots indicate no significant difference genes (Fig. 2A). Next, a total of 43 DEARGs were obtained between ARGs and DEGs via a Venn tool (Fig. 2B), and the mRNA expression levels of 43 DEARGs in the GSE25101 dataset were presented as a heatmap (Fig. 2C).
We also identified 1311 DEGs via the analysis of the GSE18781 dataset with R software. All genes were presented as volcano plots, of which black green dots represent 417 down-regulated DEGs, red dots represent 894 up-regulated DEGs, and grey dots indicate no significant difference genes (Fig. 2D). Next, a total of 19 DEARGs were obtained between ARGs and DEGs via a Venn tool (Fig. 2E), and the mRNA expression levels of 19 DEARGs in the GSE18781 dataset were presented as a heatmap (Fig. 2F).
PPI network analysis and correlation analysis of DEARGs
First, we identified 10 intersection DEARGs from GSE25101 and GSE18781 datasets by using the Venn tool (Fig. 3A). Then, we used the Cytoscape to visualize the PPI network of the 10 intersection genes. The Fig. 3B exhibited the 10 intersection genes, including BNIP3L, ATG3, PRKCQ, GABARAPL2, TP53, PINK1, NRG1, NPC1, HSP90AB1, and PTEN, these 10 genes were identified as key genes involved in the development and progression of AS. The results also demonstrated that most of these ARGs interacted with each other.
Functional enrichment of DEARGs
As shown in Fig. 4A-B, KEGG enrichment analysis indicated that the DEARGs were mainly associated with mitophagy, autophagy, amyotrophic lateral sclerosis, etc. GO-BP enrichment analysis revealed that the DEARGs were significantly enriched in the process utilizing autophagic mechanism, negative regulation of the catabolic process, macroautophagy, autophagy, etc (Fig. 4C-D).
Assessment of diagnostic effectiveness of potential biomarkers
In the present study, we performed the ROC analysis of 10 intersection DEARGs to assess the diagnostic value of the biomarkers for AS. As shown in Fig. 5A-B, the AUC values of NPC1, PTEN, GABARAPL2, BNIP3L, PRKCQ, TP53, NRG1, HSP90AB1, ATG3, and PINK1 were 0.781, 0.797, 0.744, 0.715, 0.793, 0.758, 0.762, 0.805, 0.809, and 0.713, respectively. As shown in Fig. 5C-D, the AUC values of NPC1, PTEN, GABARAPL2, BNIP3L, PRKCQ, TP53, NRG1, HSP90AB1, ATG3, and PINK1 were 0.648, 0.723, 0.725, 0.675, 0.717, 0.597, 0.525, 0.683, 0.501, and 0.643, respectively. Based on the above results, the AUC of PTEN, GABARAPL2, and PRKCQ is more than 0.7, indicating those genes have the diagnostic ability to distinguish between AS and normal samples.
Validation of PTEN, GABARAPL2, and PRKCQ expression in external independent dataset
As shown in Figs. 6A-B, the expression levels of PTEN and GABARAPL2 genes in the control group were significantly lower than that of the AS group (p < 0.05), while the expression level of PRKCQ gene in the control group was significantly higher than that of the AS group (p < 0.01). Furthermore, one independent microarray datasets (GSE73754) was used for validation. As shown in Fig. 6C, the expression levels of PTEN and GABARAPL2 genes in the control group were significantly lower than that of the AS group (p < 0.01), while the expression level of PRKCQ gene in the control group was significantly higher than that of the AS group (p < 0.001).
Immune cell infiltration analysis
xCell was applied to assess the differences in immune cell infiltrates between the control and AS groups. As presented in Fig. 7A, the score of basophils, CD8 + T cells, CD8 + Tcm, CD8 + Tem, macrophages M2, NK cells, Tgd cells, Th1 cells, and Th2 cells was significantly decreased in the AS group, while the score of neutrophils was significantly increased in the AS group. Besides, correlation analysis showed that GABARAPL2 was negatively correlated with CD4 + T cells, CD8 + T cells, NK cells, pro-B cells, Tgd cells, Th1 cells, and Th2 cells. PRKCQ was positively correlated with CD4 + T cells, CD8 + T cells, NK cells, Tgd cells, Th1 cells, and Th2 cells (Fig. 7B).
We also used MCPCounter to assess the differences in immune cell infiltration between control and AS groups. As shown in Fig. 8A, the score of cytotoxic lymphocytes, NK cells, and monocytic lineage was significantly decreased in the AS group, while the score of neutrophils was significantly increased in the AS group. GABARAPL2 was negatively correlated with T cells, CD8 + T cells, cytotoxic lymphocytes, NK cells, monocytic lineage, and myeloid dendritic cells. PRKCQ was positively correlated with T cells, CD8 + T cells, and cytotoxic lymphocytes (Fig. 8B).