2.1 Identification of DEGs
The study design flow chart is shown in Figure 1. After standardization of the microarray results, DEGs in Psoriasis and IPAH were selected. Compared to the controls, 2294 genes (1192 upregulated and 1102 downregulated genes) in GSE15197 were identified as DEGs in patients with IPAH (Figure 2A). While in the Psoriasis group, there were 2866 DEGs in the GSE30999 dataset, including 1649 upregulated and 1217 downregulated genes (Figure 2B). We take the intersection and obtain 170 communal DEGs (90 upregulated and 80 downregulated genes) between DEGs in GSE15197 and GSE30999 (Figure 2C, D).
2.2 Enrichment analyses of communal DEGs in psoriasis and IPAH
To unearth the potential communal biological roles of Psoriasis and IPAH, the GO enrichment analysis of the overlapping DEGs was conducted (Figure 3A, B). Results were divided into three functional categories, including biological processes (BP), cell component (CC), and molecular function (MF). In the BP group, DEGs were significantly enriched in cardiac right ventricle morphogenesis (GO:0003215), positive regulation of canonical Wnt signaling pathway (GO:0090263), and face morphogenesis (GO:0060325), T cell differentiation (GO:0030217) and signal transduction (GO:0007165). As for CC, DEGs were mainly involved in the dendrite (GO:0030425), cell junction (GO:0030054), postsynaptic membrane (GO:0045211), and extracellular region (GO:0005576), and cytoplasmic vesicle (GO:0031410). In terms of MF, DEGs were mainly enriched in protein transporter activity (GO:0008565), SMAD binding (GO:0046332), ubiquitin-protein ligase activity (GO:0061630), co-receptor binding (GO:0039706), and protein heterodimerization activity (GO:0046982). Meanwhile, according to the pathway enrichment analysis performed by KOBAS 3.0, the overlapping DEGs were particularly enriched in Immune System, Adaptive Immune System, Cytokine Signaling in the Immune system, and Signal Transduction (Figure 3C).
2.3 Protein-protein interaction network construction and module analysis
Based on the STRING database, the PPI network of communal DEGs was constructed and visualized via Cytoscape, consisting of 83 nodes and 104 edges (Figure 4). Three important modules were obtained from the PPI network by the MCODE plugin in Cytoscape, and functional annotation of genes in each module was conducted based on Metascape (Figure 5). The genes in module A mainly enriched in negative regulation of mitotic cell cycle phase transition (GO:1901991) and cellular response to DNA damage stimulus (GO:0006974). As for module B, genes were significantly enriched in Negative regulation of TCF-dependent signaling by WNT ligand antagonists (R-HAS-3772470) and negative regulation of canonical Wnt signaling pathway (GO:0090090). While in terms of module C, genes were mainly involved in PID TCR Pathway (M34).
2.4 Hub gene selection, analysis, and validation
Five algorithms (Betweenness, BottleNeck, DMNC, EcCentricity, Radiality) in the CytoHubba plugin were adopted to identify hub genes in this article, and the top 20 genes were selected by each classification method are listed in Table 1. Subsequently, 6 hub genes (MYO5A, CDT1, ASPM, ACTR2, PTPN11, and SOST) were determined by overlapping the top 20 genes in the above five algorithms (Figure 6).
To reveal the biological role and mechanism of 6 hub genes, function annotation was performed by Metascape and further pathway enrichment analyses were conducted based on KOBAS 3.0 (Figure 7A, B). Similar to the outcome of DEGs enrichment analysis, hub genes were found to be associated with the immune system and immune-related signaling pathways. In addition, a network of hub genes and their co-expression genes was constructed by the GeneMAINA platform (Figure 7C). Six hub genes showed a complex PPI network with co-expression of 89.77%, prediction of 8.97%, and shared protein domains of 1.26%. the functions of the network also emphasized the important role of the immune system. Based on the WoLF PSORT platform, the subcellular localization of proteins encoded by the 6 hub genes was predicted. CDT1 and PTPN11 could exist in the nucleus, MYO5A could exist in the cytosol, ASPM and ACTR2 are located in both cytosol and nucleus and SOST could be in extracellular areas. After that, 10 drug-gene interaction pairs were predicted on the grounds of the DGIdb database, consisting of 3 hub genes (PTPN11, SOST, and ACTR2) and 10 drugs (Figure 7D).
To ensure the reliability and accuracy of the bioinformatics analysis results, GSE41662 and GSE113439 were used to verify the expression of hub genes in Psoriasis and IPAH samples by independent testing analysis respectively. Compared with non-lesional skin tissue, the expression of 6 hub genes in lesional skin tissue was significantly higher. In IPAH lung tissue, MYO5A, ASPM, ACTR2, and PTPN11 were significantly upregulated compared to in normal lung tissue, However, SOST was not seemed to change significantly and CDT1 shows a downregulated trend (Figure 8).
2.5 Construction of the TF-mRNA-miRNA regulatory network
Based on the Mirwalk database, a total of 80 miRNAs were found with the condition that predicted miRNA could be verified by other databases or experiments. 5 TFs that could regulate the expression of hub genes were predicted on the grounds of the TRRUST database. After the prediction of TFs and miRNAs, the TF-mRNA-miRNA regulatory network was constructed and visualized using Cytoscape software (Figure 9).
2.6 Evaluation of immune cell infiltration
On the ground of the CIBERSORT algorithm, we analyzed the immune infiltration of 22 immune cell subgroups difference in IPAH samples and control samples (Figure 10A). The violin chart shows that compared with the normal control sample, there are more CD8 T cells, and activated Mast cells in the IPAH samples, but fewer T regulatory cells, resting mast cells, and neutrophils. As for psoriasis (Figure 11A), there are more CD4 memory-activated T cells, T follicular helper cells, T gamma delta cells, M1 macrophages, resting dendritic cells, activated dendritic cells, and neutrophils in lesional tissue compared to non-lesional tissue, but fewer plasma cells, CD8 T cells, CD4 naïve T cells, resting NK cells, activated NK cells, M2 macrophages and resting mast cells. The analysis outcome of Immune Cell Infiltration seems to exist overlap in terms of mast cells between IPAH and psoriasis.
2.7 Correlation analysis of hub genes and infiltrating immune cells
Correlation heatmap of the 22 types of immune cells revealed that resting Mast cells had a significant positive correlation with activated dendritic cells and resting NK cells and had a significant negative correlation with activated T regulatory cells in IPAH (Figure 10B). As for psoriasis (Figure 11B), resting mast cells had a significant positive correlation with M0 macrophages and activated mast cells, and had a significant negative correlation with resting dendritic cells, CD4 naïve T cells, B memory cells, T follicular helper cells, M1 macrophages, and T gamma delta cells.
In terms of IPAH (Figure 10C), Correlation analysis showed that SOST was positively correlated with mast cells activated; CDT1 was negatively correlated with plasma cells and resting dendritic cells; PTPN11 was negatively correlated with M1 macrophages and B memory cells; ASPM was negatively correlated with resting dendritic cells, but was positively correlated with CD4 naïve T cells; MYO5A was negatively correlated with resting dendritic cells, but was positively correlated with T follicular helper cells; ACTR2 was negatively correlated with resting dendritic cells and B memory cells, but was positively correlated with resting CD4 memory T cells and M0 macrophages. As for psoriasis (Figure 11C), SOST, MYO5A, CDT1, and ASPM were negatively correlated with plasma cells, resting dendritic cells, resting NK cells, and CD4 naive T cells, but were positively correlated with naïve B cells, M0 macrophages, B memory cells, T regulatory cells, and T gamma delta cells, resting T memory cells. Besides, MYO5A was also negatively correlated with CD8 T cells and positively correlated with T follicular helper cells and eosinophils; CDT1 was also positively correlated with monocytes and eosinophils; ASPM was also negatively correlated with CD8 T cells; ACTR2 was negatively correlated with M1 macrophages, resting dendritic cells and CD4 naïve T cells, but was positively correlated with monocytes, B memory cells, B naïve cells, M0 macrophages, activated CD4 memory T cells and T gamma delta cells; PTPN11 was negatively correlated with activated mast cells, resting dendritic cells, CD8 T cells and plasma cells, but was positively correlated with M0 macrophages and T regulatory cells.