Data preprocessing results
In the case of COPD, all samples were clustered based on their expression profiles to detect outliers, we detected four samples in clustered mRNAs of COPD patients and one sample in clustered mRNAs for the normal/smoker as outliers and then removed them from mRNA samples, as well as no outlier has been detected for miRNA samples, finally, the expression matrices for mRNAs and miRNAs contained 26215 mRNAs and 1300 miRNAs for 22 samples. In the case of lung cancer, the outliers were detected after clustering based on expression profiles of mRNAs and miRNAs and the expression matrices were constructed with 28393 mRNAs and 607 miRNAs.
Differential expression and miRNA-mRNA co-expression networks analyses
Regarding COPD dataset, which we retrieved them from GEO database, differentially expressed miRNAs between COPD and healthy tissues contained 173 probes, in which 51 miRNAs were up-regulated and 122 miRNAs were down-regulated. This differentially expression set represents 13% of the total expressed miRNAs. Also, there were 1423 significantly up-regulated and 921 significantly down-regulated mRNAs between COPD and healthy tissues, which this represents 9% of the total expressed mRNAs (Fig. 1a and b).
We performed the differentially expression analysis between normal and cancer tissues as well, in which 76 significantly up-regulated and 125 significantly down-regulated miRNAs which this represents 33.1% of total expressed miRNAs, and There were 1246 significantly up-regulated and 831 significantly down-regulated mRNAs between cancer and normal tissues, that indicates 7.3% of total expressed mRNAs (Fig. 1c and d).
Furthermore, we verified each miRNA-gene pairs with the aid of two target prediction databases (miRBase and targetScan) and set a minimum required Pearson correlation coefficient (PCC) of 5 between gene-target pairs, then, selected those pairs with high probabilities. Finally, we reconstructed correlation matrices between miRNA and mRNA expression matrices for each disease based on the scores (Eq. 1) with adjusted false discovery rate (FDR) p-values. For more information, the properties of two miRNA-mRNA co-expression networks is shown in Table 1 for both COPD and lung cancer networks.
Table 1. Information of COPD and lung cancer miRNA-mRNA co-expression networks
Lung cancer
|
COPD
|
Network Properties
|
0.010983
|
0.004079
|
Density
|
0.5
|
0.5
|
Cluster Coefficient
|
13
|
14
|
Diameter
|
2278
|
2517
|
Total Nodes
|
823
|
913
|
Exclusive Nodes
|
1146
|
1524
|
Total Edges
|
1021
|
1479
|
Exclusive Edges
|
5.183313
|
5.569047
|
Average Path Length
|
Identifying significant nodes from community network of COPD and lung cancer
The analysis results of the community network, is constructed by combining two co-expression networks of both of diseases, are shown in Table 2. The results of network structure analyses illuminated that green nodes (lung cancer) are more effective in terms of degrees and red nodes (COPD) are more important from the point of betweenness in the community network, and so communications in lung cancer are more compact than COPD. This network is demonstrated in Fig. 2. Some nodes in the network are shown by more than one color called pie-nodes, indicating they belong to more than one disease and considering as common nodes.
Heat maps of differential expression analysis for the 50 top mRNAs in COPD case (a) for the 50 top miRNAs in COPD case (b) for the 50 top mRNAs in lung cancer case and (c) for the 50 top miRNAs in lung cancer case (d). Green color indicates down-regulated genes and red color indicates up-regulated genes in the diseases between normal and healthy tissues; hierarchical clustering method is performed based on z-score for log2 fold change with p-value less than 0.05 and FC more than 10; “H” means healthy group which is shown in cyan and “D” means disease group which is shown in magenta for clustering.
Table 2. Topological feature properties of the community network, which is constructed by merging two miRNA-mRNA co-expression networks of COPD and lung cancer.
1760
|
total nodes
|
2670
|
total edges
|
27
|
diameter
|
0.0149
|
graph density
|
0.5
|
graph clustering coefficient
|
5.183313
|
graph average path length
|
We extracted four miRNAs from the community network: hsa-miR-484, hsa-miR-107, hsa-miR-326, and hsa-miR-1293 as common nodes between COPD and lung cancer. In Table 3, these miRNAs are shown along with their targets and related log FC values in order to study regulatory effects of these miRNAs on their targets in each disease. Significant changes in FC values of miRNAs may indicate the effectiveness of them in regulation of genes in a disease biologically. We selected two miRNAs among these common miRNAs based on log FC value changes between COPD and lung cancer: hsa-miR-326 is up-regulated and hsa-miR-1293 is down-regulated in both of diseases. Also, 8 common mRNAs between COPD and lung cancer are identified and extracted from community network: FHL1, FAT2, TMEM125, SLC2A1, ALOX5AP, LDB2, TNNC1, and FOLR1. For a better recognition of the biological processes of these genes in both of diseases, we performed the functional enrichment analysis using Gene Ontology (GO) for each mRNA by Fisher exact test with p-value less than 0.05. These common genes along with their co-expressed miRNAs, extracted from community network, in each disease, biological processes, and p-values are shown in Table 4. The p-values, which we obtained them through the statistical enrichment test can highlight the significance of each biological process as well.
The community network that is constructed by merging the co-expression network of COPD genes (red nodes) with the co-expression network of lung cancer genes (green nodes). All nodes (miRNAs and mRNAs) are depicted as circles for detecting the common nodes, which are represented as the pie-nodes between two loaded networks. Indeed, these pie-nodes represent the coexistence between the two co-expression networks of COPD and lung cancer.
Table 3. Extracted common miRNAs from the community network as well as their targets along with their log FCs in each disease.
miRNA
|
Target genes in
COPD
|
Target genes in
Lung cancer
|
log FC in
COPD
|
log FC in
Lung cancer
|
hsa-miR-484
|
CIRBP
CFD
COG2
GNS
ZFYVE1
|
PRX
GPX3
|
0.37
|
0.44
|
hsa-miR-107
|
SLC15A4
LMAN2L
|
GNS
TUBB
TMPRSS4
|
-0.55
|
-0.5
|
hsa-miR-326
|
EBF1
CLUH
TGFB1
CLU
|
RRAD
PNCK
SLC2A1
RHCG
|
0.35
|
2.6
|
hsa-miR-1293
|
SH3KBP1
DNAJC5
|
ATOH8
AQP4
RTKN2
|
-0.3
|
-4.3
|
Furthermore, we extracted the most significant miRNAs of each network called exclusive miRNAs that targeted the most significant common mRNAs (FAT2, ALOX5AP, and LDB2) based on p-values and their biological processes of enrichment analysis between COPD and lung cancer. In other words, there exists at least one miRNA in each disease that can target common mRNAs between the two diseases.
Enrichment analysis results for significant common miRNAs and their targets
Functional enrichment analysis by MiEAA revealed that hsa-miR-326 was enriched for several pathways, including non-small cell lung cancer, EGF EGFR signaling pathway, pathways in cancer, and epithelial to mesenchymal transition. As well as enrichment analysis results for hsa-miR-326 target genes (using GO) highlighted that TGFB1 was enriched for regulation of apoptotic process, regulation of cell proliferation and execution phase of apoptosis. In addition, hsa-miR-1293 as one of the common miRNAs was enriched for two significant pathways: regulation of translation and translation factor activity. Moreover, the functional enrichment analysis for hsa-miR1293 target genes revealed that ATOH8 was enriched for DNA binding, regulation of transcription by RNA polymerase II and transcription by RNA polymerase II in lung cancer. Also, RTKN2 as the other target of hsa-miR-1293 was enriched for mitotic nuclear division, mitotic cytokinesis, septin ring organization, and membrane fission. Based on enrichment analysis results, no significant pathways were detected for the other target genes of hsa-miR-326 and hsa-miR-1293 in both of diseases. Sub network of two significant miRNAs with their target genes in both COPD and lung cancer is depicted in Fig. 3.
Functional enrichment analysis results for target genes of exclusive miRNAs
The functional enrichment analysis revealed that FAT2 as one of the common target genes of exclusive miRNAs is significantly enriched for several biological processes, including anatomical structure morphogenesis and embryo development. In addition, LDB2 (the other common gene) is enriched for multicellular organism development and transcription by RNA polymerase II as the biological processes. Also, functional enrichment analysis results for ALOX5AP as common gene revealed multiple biological processes including, enriched for carboxylic acid biosynthetic process, cellular response to chemical stimulus and response to toxic substance. Moreover, we investigated the exclusive miRNAs for each disease that dysregulated FAT2, LDB2, and ALOX5AP as the common genes between two diseases. For FAT2, hsa-miR-574-3p in COPD and hsa-miR-592 were up-regulated in both of diseases with log FC = 0.87 and 0.7, respectively. Hsa-miR-142-5p up-regulated LDB2 in COPD with log FC = 0.61 and hsa-miR-135b and hsa-miR-421 up-regulated LDB2 in lung cancer with log FC = 2 and 1.38, respectively as well.
Subnetworks of common miRNAs between COPD and lung cancer along with their target genes in each disease (a) and common mRNAs between COPD and lung cancer with exclusive miRNAs in each disease (b). In each sub network, the genes related to COPD are specified in a green group and the genes in association with lung cancer are located in a red group. Also, for better recognition, all miRNAs are showed by diamonds and all mRNAs are showed by circles as nodes within the both of networks, and the up-regulation is indicated by green color and the down-regulation is indicated by yellow color, in which greater size of nodes means the higher FC values. These sub networks are plotted using Cytoscape.
Comparison of log FC values for the exclusive miRNAs between COPD and lung cancer showed a significant difference between the two diseases. Moreover, hsa-miR-574-3p and hsa-miR-28-5p as detected as exclusive miRNAs in COPD for ALOX5AP, were up-regulated with log FC = 0.78 and 0.76, respectively. As well as hsa-miR-31, hsa-miR-335, hsa-miR-474, and hsa-miR-106b were down-regulated in lung cancer with log FC = 4.2, 0.35, 1.2, and 0.7, respectively. Log FC values comparison for the exclusive miRNAs that targeted ALOX5AP in lung cancer illuminated that hsa-miR-31 was significantly down-regulated than the others. Fig. 4b shows a sub network of exclusive miRNAs that target FAT2, ALOX5AP, and LDB2 as common genes of COPD and lung cancer.
Construction of drug-target networks for candidate genes
After identifying common and exclusive miRNAs from the community network, we investigated the potential drug targets for target genes of common and exclusive miRNAs in COPD and lung cancer. Among all target genes of exclusive miRNAs (hsa-miR-326 and hsa-miR-1293), TGFB1 and CLU in lung cancer and SLCA1in COPD were selected as candidate genes based on the interactions which we extracted from the DGIdb. Moreover, no drug-target interactions were detected for other target genes of common miRNAs between COPD and lung cancer (Fig. 3a) in DGIdb. Also, we inspected the potential drug targets for all of common genes (Table 4) through DGIdb, and found five drug-target interactions for ALOX5AP and five drug-target interactions for FOLR1. Moreover, for other common genes between COPD and lung cancer, there were no interactions in DGIdb. Also, we inspected the potential drug targets for all of common genes (Table 4) through DGIdb, and found five drug-target interactions for ALOX5AP and five drug-target interactions for FOLR1. Moreover, there were no potential drug-target in DGIdb for the other common genes as shown in Table 4 between COPD and lung cancer. The drug-target interaction networks of candidate genes (TGFB1, CLU, and SLCA1) in each disease and common genes (ALOX5AP and FOLR1) between COPD and lung cancer are illustrated in Fig. 4a and b, respectively. The number of genes, interactions, and targets in drug-target networks were 2, 10, 10 and as well as 3, 53, 48 for common and candidate genes respectively.
Candidate drug-target networks for common genes between COPD and lung cancer (a) and for candidate target genes of common miRNAs (hsa-miR-326 and hsa-miR-1293) (b). Furthermore, all genes in the networks are depicted by red ellipses and candidate drugs are shown as blue diamonds, the drug-target interactions are detected through DGIdb and are designed by Cytoscape.
Table 4. Common genes that are extracted from the community network and exclusive miRNAs in each disease with the most important biological processes and p-values.