Identification of DEGs
With a threshold of P-value <0.05 and absolute value of |log2FC| > 1, DEGs were identified from dataset. 284 DEGs were screened from the GSE123658 dataset, which consisted of 142 up regulated genes and 142 down regulated genes and only top ten up regulated genes and down regulated genes are listed in Table 2. Volcano plots were used to visualize differential expression of genes between the T1D group and healthy donors group (Fig.1). A heat map showed expression profiling of DEGs in the analysis result (Fig.2).
Gene Ontology (GO) and pathway enrichment analyses of DEGs
To identify the pathways which had the most significant involvement with the genes identified, up regulated and down regulated genes are listed in Table 3 and Table 4. DEGs were submitted into ToppGene for GO and REACTOME pathway enrichment analysis. GO enrichment analysis revealed that in BP terms, the up regulated genes were mainly enriched in cell-cell signaling and reproductive process, whereas down regulated genes were mainly enriched in vesicle fusion and biological adhesion. In CC terms, up regulated genes were mainly enriched in integral component of plasma membrane and supramolecularfiber, whereas down regulated genes were mainly enriched in whole membrane and cell junction. In MF terms, up regulated genes were mainly enriched in signaling receptor activity and structural molecule activity, whereas down regulated genes were mainly enriched in lipid binding and GTPase binding. REACTOME pathway analysis demonstrated that up regulated genes were significantly enriched in signaling by GPCR and muscle contraction, whereas down regulated genes were mainly enriched in innate immune system and cytokine signaling in immune system
PPI network construction and module analysis
Interactions between the identified up and down regulated genes were reported by constructing a PPI network. In total, there were 5017 nodes and 8133 edges in the network (Fig.3). According to node degree, betweenness centrality, stress centrality and closeness centrality levels, the top four hub nodes were: EGFR (degree, 1343; betweenness, 0.514227; stress, 4.35E+08; closeness, 0.441893), GRIN2B (degree, 195; betweenness, 0.008701; stress, 14535992; closeness, 0.282164), POLR2A (degree, 512; betweenness, 0.095104; stress, 2E+08; closeness, 0.3738) and PRKACA (degree, 350; betweenness, 0.104658; stress, 44280174; closeness, 0.378052), and are listed in Table 5. Significant modules were subsequently constructed with 12 nodes and 23 edges for up regulated genes and 5 nodes and 10 edges for down regulated genes, which gained the highest PEWCC1 score (Fig.4). Subsequent functional enrichment analysis revealed that the genes in these modules were mainly enriched in cell-cell signaling and cytokine signaling in immune system.
Prediction of key miRNAs
The regulatory relationships between the target genes and their miRNAs were established using Cytoscape, which showed that the single gene was regulated by multiple miRNAs is shown in Fig.4A. Subsequently, 106 miRNAs (ex, hsa-mir-4257) targeting GRIN2B, 83 miRNAs (ex, hsa-mir-4257) targeting EGFR, 83 miRNAs (ex, hsa-mir-564) targeting EGFR, 190 miRNAs (ex, hsa-mir-4300) targeting TLN1 and 139 miRNAs (ex, hsa-mir-5694) targeting IGF2R were verified in miRNet database are listed in Table 6. Integrating with the result of REACTOME pathway analysis, it was indicated that these key target genes - miRNA network was mainly involved in the signaling by GPCR and innate immune system.
Prediction of key TFs
The regulatory relationships between the target genes and their TFs were established using Cytoscape, which showed that the single gene was regulated by multiple TFs is shown in Fig.4B. Subsequently, 19 TFs (ex, FOXD1) targeting RGS4, 16 TFs (ex, GATA2) targeting EYA1, 15 TFs (ex, STAT3) targeting PRKACA and 14 TFs (ex, TFAP2A) targeting GAB2 were verified in NetworkAnalyst database are listed in Table 6. Integrating with the result of REACTOME pathway analysis, it was indicated that these key target genes - TF network was mainly involved in the signaling by GPCR and innate immune system.
Validation of hub genes
As these 4 genes are remarkably expressed in T1D, we executed a ROC curve analysis to calculate their sensitivity and specificity for the diagnosis of T1D. As shown in Fig. 5A, EGFR, GRIN2B, POLR2A and PRKACA achieved an AUC value of > 0.985, demonstrating that these genes have high sensitivity and specificity for T1D diagnosis. We further used RT-PCR to detect the mRNA expression of the hub gene. The 4 hub genes contain two up regulated genes (EGFR and GRIN2B) and two down regulated gene (POLR2A and PRKACA). The RT-PCR data showed that although the trend of expression patterns of these 4 hub genes were consistent, among these up regulated genes, only EGFR and GRIN2B were significantly up regulated in T1D. In addition, the expression of POLR2A and PRKACA were reduced in T1D (Fig. 5B).
Molecular Docking studies
The docking simulations are conducted in the present study is to identify the active site conformation and major interactions responsible for complex stability with the receptor binding sites. In type 1 diabetes mellitus over expression of genes are identified and their proteins of x-ray crystallographic structure are selected from PDB for docking studies. The drugs containing thiazolidindione ring pioglitazone are most commonly used either alone or in combination with other antidibetic drugs. The docking studies of pioglitazone (as standard) and designed molecules containing the heterocyclic ring of thiazolidinedione have been carried out using Sybyl X 2.1 drug design software. The docking studies were performed to know the biding interaction of pioglitazone standard and designed molecules on identified over expressed genes of protein. The X- RAY crystallographic structure of two proteins from each over expressed genes of EGFR (epidermal growth factor receptor) and its co-crystallised protein of PDB code 2XYJ, 2XYX and GRIN2B (glutamate ionotropic receptor NMDA type of subunit 2B) and its co-crystallised protein of PDB code 5EWL, 6E7V respectively were selected for the docking. The research of designed molecules had been carried out to perceive the potential molecule. A total of 54 molecules were designed and the binding score greater than six are said to be good, few molecules and pioglitazone obtained C-score greater than 7 with one in each of EGFR and GRIN2B over expressed genes of PDB code 2XYJ and 6E7V respectively.The designed molecules The two over expressed gens such as EGFR (epidermal growth factor receptor) and GRIN2B (glutamate ionotropic receptor NMDA type of subunit 2B) and two proteins from each were selected for docking. The compounds obtained with a good binding score with one protein in each over expressed genes out of two are PIO, TSPZP24,TSPZP25, TBPZP5, TSPZP27, TSIO6, TBPZP46, TSPZP23, TBIO34, TSPZ15 and TSPZP24 with binding score of 8.396, 7.6243, 7.3803, 17.3313, 7.2212, 7.20417.2021, 7.1987, 7.0795 and 7.0591 with PDB code of 2XYJ and 6E7V respectively (Fig. 6). Compounds such as TSIO8, TBPZP54, TBPZP49, TBPZP51, TBIO36, TBPZ44, TSPZ18, TSPZ13, TBIO35TSPZ17, TBPZP53, TBPZ45 TBPZP50, TBIO30, TSPZ16, TBIO36, TBPZ40, TBPZ39, TSPZP24 and TSPZP24 TBPZP48 and TSPZ15, TSIO6, TSPZP24, TSPZP26 and TBPZ43, TBPZ42, TSPZ15, TBIO34 with binding score of 6.9341, 6.9257, 6.8768, 6.8488, 6.7296, 6.6452, 6.5682, 6.5625, 6.542, 6.407, 6.4023, 6.3781, 6.3091, 6.254, 6.1603, 6.160, 6.0903, 6.0703, 6.0263 and 6.1225, 5.5282 and 6.4652, 6.3819, 6.3205, 6.208 and 6.5068, 6.3741, 6.256, 5.9959 with PDB code of 2XYJ and 2XYX and 5EWL and 6E7V respectively. The molecules obtained with less binding score with respect to all proteins is TSPZP19 4.7843, TBPZ38 4.6791, TBPZ41 4.5968, TBPZ39 3.9732, TBPZ41 3.7662, TSPZP26 3.6423 and TBPZ41 4.9979, TBIO32 4.9247 and TBPZP48 4.5557, TSPZP21 4.1394 the values are depicted in Table 7. The binding score of the predicted molecules are compared with that of the standard pioglitazone used in type 1 diabetes mellitus, the standard obtained good binding score with all proteins. The molecule TSPZP24 and TSPZP22 has highest binding score its interaction with protein 6E7V and XYJ, and hydrogen bonding and other bonding interactions with amino acids are depicted by 3D (Fig. 7) and 2D (Fig. 8).