Identification of co-expressed DEGs
Figure 1 shows the flow chart of this study. In the combined CAVD dataset, a total of 209 DEGs were obtained, including 142 upregulated genes and 67 downregulated genes. The volcano plot and heatmap of CAVD DEGs are shown in Figs. 2A, B. A total of 434 DEGs were found in the ASCVD dataset, among which 322 genes were upregulated and 112 genes were downregulated. Figures 2C, D are the heatmap and volcano plots of ASCVD DEGs, respectively. The intersection of DEGs was obtained by Venn diagram (Fig. 2E), and a total of 56 differential genes were obtained. After excluding genes with opposite expression trends in the two disease datasets, a total of 55 co-expressed DEGs were used for the next analysis.
Functional enrichment analyses of co-DEGs
To clarify the function of these co-DEGs, we performed GO functional analysis and KEGG pathway analysis on these DEGs. GO analysis results showed that the DEGs were mainly enriched in Serine-type peptidase activity, serine hydrolase activity, Serine-type endopeptidase activity, Chemokine receptor binding, and Cytokine activity (Fig. 3A). KEGG pathway analysis showed that the pathway was primarily enriched in the Cytokine- Cytokine receptor interaction, Viral protein interaction with cytokine and cytokine receptor, and Chemokine signaling pathway (Fig. 3B). These results suggest that cytokines and chemokines play a role in CAVD and ASCVD.
Establishment of PPI network and preliminary screening of hub genes
PPI network analysis of co-DEGs was performed using the STRING database, and then we use CYTOSCAPE software to visualize the PPI network. As shown in Fig. 4A, the network includes 43 nodes and 404 interaction pairs. Through the MCODE plug-in of Cytoscape, we got three gene modules and these modules included a total of 23 differential genes and 130 interaction pairs (Fig. 4B, C, D). Using the CYTOHUBBA plug-in, the top 20 hub genes were calculated by selecting six of the algorithms (Table 1), after intersecting the hub genes obtained by the six algorithms, a total of 15 hub genes were obtained (Fig. 4E). Finally, after taking the intersection of the above genes with the MCODE module genes again, 14 hub genes were identified (Fig. 4F). They are "CCR1", "TREM1", "CCR5", "CCR2", "CCL4", "TLR2", "MMP9", "CCL5", "TYROBP", "LY86", "LCP2", "FCER1G", " LAPTM5", "CTSS". Pathway and process enrichment analysis of these 14 key genes using the METASCAPE website revealed that these key genes were mainly associated with leukocyte migration, myeloid leukocyte migration, myeloid leukocyte activation, positive regulation of cytokine production, Neutrophil degranulation (Fig. 4G). Most of these processes are associated with inflammatory and immune responses.
Table 1
The top 20 hub genes rank of six algorithms in cytoHubba.
Rank
|
MCC
|
MNC
|
EPC
|
Closeness
|
Betweenness
|
Stress
|
1
|
CCR1
|
TYROBP
|
TLR2
|
TYROBP
|
MMP9
|
MMP9
|
2
|
TREM1
|
TLR2
|
TYROBP
|
MMP9
|
TYROBP
|
TYROBP
|
3
|
CCR5
|
MMP9
|
CCR1
|
TLR2
|
TLR2
|
CORO1A
|
4
|
CCR2
|
CCR1
|
CCR5
|
CCR1
|
CORO1A
|
TLR2
|
5
|
CCL4
|
CCR5
|
CCR2
|
CCR5
|
CTSS
|
LCP2
|
6
|
TLR2
|
LCP2
|
MMP9
|
CCR2
|
LCP2
|
CCR5
|
7
|
MMP9
|
CCR2
|
LY86
|
TREM1
|
CCL5
|
PLA2G7
|
7
|
CCL5
|
CCL5
|
TREM1
|
LCP2
|
PLA2G7
|
CCR2
|
9
|
IL1RN
|
TREM1
|
CCL4
|
CCL5
|
CCR5
|
CTSS
|
10
|
TYROBP
|
LY86
|
CCL5
|
LY86
|
CCR1
|
CCR1
|
11
|
LY86
|
CCL4
|
LCP2
|
CCL4
|
CCR2
|
CCL5
|
12
|
LCP2
|
FCER1G
|
FCER1G
|
CTSS
|
SPP1
|
CCL4
|
13
|
FCER1G
|
MNDA
|
MNDA
|
FCER1G
|
TREM1
|
TREM1
|
14
|
CD300A
|
IL1RN
|
IL1RN
|
MNDA
|
CCL4
|
SPP1
|
15
|
MNDA
|
CTSS
|
GZMA
|
IL1RN
|
CD3D
|
CD52
|
16
|
LAPTM5
|
SPP1
|
CD52
|
SPP1
|
LY86
|
LAPTM5
|
17
|
CXCL16
|
CD52
|
LAPTM5
|
CD52
|
CD52
|
LY86
|
18
|
CTSS
|
LAPTM5
|
CTSS
|
GZMA
|
LAPTM5
|
CD3D
|
19
|
CD52
|
GZMA
|
CD300A
|
LAPTM5
|
GZMA
|
IL1RN
|
20
|
GZMA
|
CD300A
|
CXCL16
|
CORO1A
|
FCER1G
|
FCER1G
|
Immune infiltration analysis
Since the hub genes screened above are involved in immune regulation, we performed immune cell infiltration analysis hoping to find similarities in immune regulation between CAVD and ASCVD. Figure 5A and Fig. 6A respectively show the percentage of immune cells in CAVD and ASCVD. Observation of Fig. 5B and Fig. 6B revealed that the expression of Macrophages M0, Macrophages M2, and T cells gamma delta was higher in the lesioned group than in the control group in both CAVD and ASCVD datasets. Figure 5C and Fig. 6C show the correlation between 22 immune cells in CAVD and ASCVD, respectively. In conclusion, we found certain similarities in the regulation of immune cells in CAVD and ASCVD, which may provide a novel idea for the future treatment of both diseases.
Validation and screening of hub genes
In order to further verify the expression level of these hub genes and do further screening, we chose two other datasets to validate their expressions. Figure 7 and Fig. 8 respectively show the expression levels of hub genes in CAVD and ASCVD datasets. The results showed that in the CAVD dataset, the expression levels of "CCR1", "TREM1", "MMP9", "CCL5", "TYROBP", "LY86", and "LAPTM5" were significantly higher in calcified aortic valves compared with normal aortic valve tissue. In ASCVD dataset, the expression levels of "CCR1", "TREM1", "CCR5", "CCR2", "TLR2", "MMP9", "CCL5", "TYROBP", "LY86", "LCP2", "FCER1G", "LAPTM5", "CTSS" were significantly increased in atherosclerotic lesions compared with normal vascular tissues. After intersecting the genes with elevated expression in both datasets, we finally identified 7 hub genes. Functional analysis was performed again for these genes. GO analysis showed that these genes were mainly enriched in phosphatidylinositol phospholipase C activity, phospholipase C activity, Phosphoric diester hydrolase activity, Phospholipase activity, and Lipase activity (Fig. 9A). KEGG analysis showed that these genes were enriched in Viral protein interaction with cytokine and cytokine receptors, TNF signaling pathway, Chemokine signaling pathway, Lipid and atherosclerosis, and Human cytomegalovirus infection (Fig. 9B). The results of enrichment analysis of these hub genes showed that lipids and inflammation disorders were common mechanisms in the two diseases.
Validation of diagnostic value of hub genes
To verify the diagnostic value of the seven hub genes obtained from the above analysis, we constructed ROC curves and calculated the corresponding AUC for the expression levels of these genes in CAVD and ASCVD datasets, respectively, as shown in Fig. 10 and Fig. 11. Our results suggest that the hub genes screened in this study have a high diagnostic value in both CAVD and ASCVD.