Identification of DEGs
The DEGs in the GSE4290, GSE7696, GSE13276, GSE29796 and TCGA datasets were identified by GEO2R. Add up to 1756 DEGs were recognized in the GSE4290, add up to 938 DEGs were identified in the GSE7696, add up to 546 DEGs were recognized in the GSE13276, add up to 3873 DEGs were recognized in the GSE29796, and add up to 2283 DEGs were recognized in TCGA(GBM). Through visual hierarchical clustering analysis, the volcano map of these DEGs is clearly shown (Figure 1A), where the scarlet and blue dots respectively represent upregulated and downregulated genes. Then, the Venn plot of the co-expression genes containing overlapping DEGs in the GSE4290, GSE7696, GSE13276, GSE29796 and TCGA datasets were constructed (Figure 1B, C). These 54 upregulated DEGs and 22 downregulated DEGs were plotted in Table 2. Add up to 54 overlapping upregulated genes were acquired as core genes for further analysis.
GO and KEGG Enrichment Analyses
We conducted GO and KEGG enrichment analysis of 54 upregulated DEGs and 22 downregulated DEGs to systematically understand the biological role of these DEGs. Figure 2 respectively lists the top enriched GO terms and Figure 3A lists the top 30 KEGG pathways.
GO BP displayed that 54 upregulated DEGs were obviously enriched in the lectin pathway of extracellular matrix organization, extracellular structure organization, cell-substrate adhesion and urogenital system development. GO CC analysis shown that, the most enriched terms were collagen-containing extracellular matrix, basement membrane, endoplasmic reticulum lumen and complex of collagen trimers. The top four significantly enriched MF terms included extracellular matrix structural constituent, extracellular matrix structural constituent conferring tensile strength, platelet-derived growth factor binding and collagen binding (Figure 2A).
GO BP displayed that 22 downregulated DEGs were obviously enriched in the protein localization to axon, regulation of SNARE complex assembly, response to magnesium ion and SNARE complex assembly. GO CC analysis shown that, the top obviously enriched terms were main axon, juxtaparanode region of axon, voltage-gated potassium channel complex and potassium channel complex. The top four significantly enriched MF terms included structural constituent of myelin sheath, magnesium ion binding, nucleoside monophosphate kinase activity and phosphotransferase activity (Figure 2B).
In addition, the four obvious enrichment pathways of these 54 upregulated DEGs attracted our attention were ECM-receptor interaction, Focal adhesion, Pathways in cancer, and the p53 signaling pathway (Figure 3A). Pathway diagram shows one of the top enrichment pathways, ECM-receptor interaction (Figure 3B).
Module screening from the PPI network
The PPI pairs in 54 upregulated DEGs were determined by using the STRING. The Cytoscape identified the top 10 central genes for connectivity of the degree score (Table 3). Cytoscape identifies the most tightly connected modules (Figure 4B). KEGG analysis revealed that the 10 hub genes were significantly enriched in the pathways of ECM-receptor interaction, Focal adhesion, Amoebiasis, Protein digestion and absorption, Bladder cancer, Pathways in cancer, mTOR signaling pathway, Shigellosis and the p53 signaling pathway (Figure 4C).
Validation of mRNA Expression in GBM.
The results of GEPIA database displayed that the mRNA expression levels of 10 genes in GBM tissues were expressively higher than that in non-malignant cerebral cortex specimens (P<0.01) (Figure 5A). Notably, the protein levels of CD44, COL1A1, COL1A2, COL3A1, FN1, POSTN, TIMP1 and VEGFA were not voiced in normal cerebral cortex tissues, nevertheless, moderately and highly expressed of these genes were took stock of GBM tissues (Figure 5B). As a whole, the consequences of this study manifested that the hub genes were overexpressed at both transcriptional and translational expression levels in GBM patients.
Changes in Hub gene frequency and prognostic value in GBM.
The CBioPortal database was used to assess the frequency of genetic changes in these selected central genes from GBM. Approximately 43.45% of GBM clinical patients displayed vital changes in these central genes (Figure 6A). The mRNA alteration was the noticeably vital factors for the altered hub genes in 36 patients (24.83%) of GBM. The consequences showed that the percentage variation in the mRNA expression of LOX, IGFBP3, CD44, TIMP1, FN1, VEGFA, POSTN, COL1A1, COL1A2 and COL3A1 in GBM were 2.8, 18, 3, 4, 3, 8, 5, 10, 16 and 5%, separately (Figure 6B).
Kaplan‑Meier diagrams were used to contradistinguish DSS and progression free survival (PFS) in GBM patients with or without changes in the mRNA expression levels of central genes. As uncovered in Figure 6C, GBM sufferers with changed central gene expression represented notably worse DSS compared to those with unchanged central gene expression (P=0.0117). Similarly, GBM sufferers with changed hub gene expression showed observably poor PFS (P=0.0251) confronted with those with unchanged central gene expression (Figure 6D).
Survival Curve of Hub Genes
Corresponding AUCs for these hub genes were also obtained, including CD44 (AUC=0.981), COL1A1 (AUC=0.970), COL1A2 (AUC=0.993), COL3A1 (AUC=0.996), FN1 (AUC=0.997), IGFBP3 (AUC=0.972), LOX (AUC=0.975), POSTN (AUC =0.961), TIMP1 (AUC=0.981), VEGFA (AUC=0.924) (all p < 0.0001) (Figure 7). From the above results, it can be concluded that these variables have high accuracy in predicting the outcomes of non-tumor patients and GBM patients.
Survival Analysis and Cox Regression Analysis in GBM
OS and DFS analyses of the central genes were farther conducted by GEPIA database. As shown in Figure 8A, high expressions of TIMP1, FN1, LOX, and POSTN in GBM patients were significantly correlated with worse OS. Adverse DFS were also significantly scanned in GBM patients with elevated TIMP1, FN1, LOX, and POSTN expression levels (Figure 8B). The results of Log-rank P test showed that only the OS and DFS of TIMP1, FN1, LOX and POSTN had statistical significance simultaneously.
Furthermore, univariate cox regression analysis revealed that FN1 was remarkably correlated with the OS (HR 1.66401, 95% CI=1.54102,1.79681, p<0.0001), LOX was remarkably correlated with the OS (HR 1.66184, 95% CI=1.55921,1.77123, p<0.0001), POSTN was observably correlated with the OS (HR 1.37421, 95% CI=1.32001,1.43063, p<0.0001) and TIMP1 was observably correlated with the OS (HR 1.56064, 95% CI=1.48016,1.64549, p<0.0001). Moreover, multivariate cox regression analysis revealed that TIMP1 was isolated risk factor for OS (HR 1.44208, 95% CI=1.16537,1.7845, p= 0.00076). The results are summarized in Figure 8C.
Immune Infiltration Analysis of GBM
The degree of immune cell infiltration in tumor tissue is an isolated prognostic factor for different tumor survival. Therefore, we focused on analyzing the association between TIMP1 expression and infiltrating immune cells in GBM. TIMER2.0 was revealed that the expression of TIMP1 remarkably associated with the infiltration of CD4+ T cell (Rho=0.335, P=6.28e−05), B cell (Rho=0.408, P=7.63e−07), T cell regulatory (Tregs) (Rho=0.514, P=1.29e−10), Neutrophils (Rho=0.312, P=2.10e−04), Cancer associated fibroblast (Rho=0.653, P=5.46e−18), Macrophage M1 (Rho=0.492, P=1.04e−09) and Myeloid dendritic cell (Rho=0.338, P=5.40e−05) in GBM. By comparison, it negatively correlated with cancer purity (Rho=−0.41, P=5.81e−07) (Figure 9A).
To further explore the connection with GBM and the level of immune cell infiltration, we used TIMER2.0 to evaluate the connection with TIMP1 expression of various immune cells and immune marker genes in GBM. As the results revealed that, the expression level of TIMP1 was remarkably positively associated with most immune cell markers in GBM. Whereas, the result displayed that TAM marker (CCL2), Macrophage M1 marker (PTGS2), Macrophage M2 markers (CD163, VSIG4, MS4A4A), Neutrophil marker (ITGAM), Treg marker (TGFB1) were observably positively associated with TIMP1 expression level in GBM (Table 4). This suggests that TIMP1 plays a dynamic role in the glioma immune microenvironment. Finally, higher Tregs infiltration was related with worse prognosis for TIMP1 in GBM (Figure 9B, HR=2.05, P=0.0395). Equally, higher Cancer associated fibroblast and Mast cell infiltration also associated with poor outcome in GBM (Figure 9C, D, HR=1.81, P=0.0497, HR=1.98, P=0.0341).