Identification of DE-miRNAs
According to the filtering criterion described before, the cutoff value for FC of DE-miRNAs was 1.2. We identified 8 downregulated DE-miRNAs between the control group and the PBC group. When comparing the PSC group to the control, we found 11 altered miRNAs, including 1 upregulated miRNA and 10 downregulated miRNAs. The distributions of DE-miRNA expression between the control group and the PBC or PSC group were intuitively illustrated by volcano maps (Fig. 1a and 1b). Furthermore, the intersection of the candidate DE-miRNAs from the two comparisons was analyzed and visualized by a Venn diagram (Fig. 1c). The shared DE-miRNAs are also listed in Table 1, including miR-122, miR-30e, let-7c, miR-107, miR-503, and miR-192.
Prediction of transcription factors and the target genes of the DE-miRNAs
It is suggested that miRNAs could be affected by transcription factors (TFs) and negatively regulate the expression of targeted genes. Herein, to understand the underlying regulatory network of the identified DE-miRNAs, we first utilized FunRich software to predict the TFs of the 6 DE-miRNAs. The top 10 significant TFs are shown in Fig. 2a, among which EGR1 has the greatest difference and SP1 regulates the most miRNAs (57%).
Additionally, a total of 437 upregulated genes were mapped into 11 downregulated DE-miRNAs. A miRNA-mRNA network was visualized in Cytoscape (Fig. 2b). Information on the targeted genes is also shown in Table 2.
Enrichment analysis of the target mRNAs
To investigate the functions of the DEGs, GO annotation and KEGG pathway analysis were performed utilizing the Cluego plugin of Cytoscape. The results showed that BP terms were significantly enriched in lymphocyte differentiation and activation and immune system-related function (Fig. 3a). The CC terms included side of membrane, secretory granule membrane, anchoring junction, actin cytoskeleton, and MHC class Ⅱ protein complex (Fig. 3b). And the most enriched entries for MF terms were activities associated with GTPase, G protein-coupled purinergic nucleotide receptor, protein tyrosine phosphatase, and immune receptor (Fig. 3c). In addition, the most important pathways of KEGG are shown in Fig. 3d, including those related to inflammation, the immune system, and various infections, which are critical for the pathological development of CLDs.
Construction of the PPI network and identification of hub genes
To distinguish the connections among the 437 target genes, we mapped the PPIs using the logical data originating from the STRING database. 437 nodes and 1442 edges were obtained with an average local clustering coefficient of 0.399. We further used the MCODE plugin to process the network data to identify gene clusters, and the clusters with the top 5 highest scores are shown in Fig. 4a. We also used CytoHubba plugin to rank the nodes by the degree method (Fig. 4b). The top 13 genes are listed in Table 3. Next, to obtain the hub genes, genes in Cluster 1 and Cluster 2 were further filtered by matching the top 13 genes with the highest degree scores (Fig. 4c). Then, we got 8 hub genes: PTPRC, TYROBP, LCP2, RAC2, SYK, TLR2, CD53, and LAPTM5. A PPI network and a miRNA-hub gene regulatory network were also constructed (Fig. 4d-e). Notably, KEGG pathway analysis revealed that the Fc epsilon RI signaling pathway, which was involved with LCP2, RAC2 and SYK, was significantly enriched, suggesting this signaling pathway was important in the development of CLDs (Fig. 4f).
Verification of the identified miRNAs and mRNAs in ANIT-induced cholestasis mice
ANIT, a well-characterized hepatotoxic agent that causes cholestasis by injuring bile duct epithelial cells and hepatocytes, is widely used to emulate human acute intrahepatic cholestasis [14]. To verify the results of the bioinformatics analysis, we then detected the levels of the identified miRNAs in ANIT-induced cholestatic liver injury mice. As shown in Fig. 5a, we observed an enlarged gall bladder and dark bile inside in the ANIT-treated mice, which suggested that the cholestasis model had been established successfully. In addition, serum biochemical detection also confirmed this result (Fig. S2). As expected, the expression of DE-miRNAs was significantly decreased in the ANIT group compared with the control group (Fig. 5b), except miR-503-5p, which did not reach a significant difference despite a downregulation trend in the ANIT group.
After the verification of the DE-miRNAs, we continued to analyze the expression of the hub genes in the ANIT-treated mice. Consistently, ANIT-induced cholestasis significantly stimulated the liver expression of the hub genes (Fig. 5c). Taken together, these findings implied that the miRNA-mRNA regulatory network (except miR-503-5p) may participate in the ANIT-induced cholestatic liver injury.
Verification of the identified miRNAs and mRNAs in BDL-induced cholestasis mice
The BDL mouse model is a classic animal model to induce extrahepatic cholestasis. Therefore, we utilized gene expression data from GSE166867 to verify the level of the identified DE-miRNAs between BDL mice and sham operation mice. As shown in Fig. 6a, 5 forementioned DE-miRNAs except miR-503 were detected in this dataset. The expression of miR-30e and miR-107 was significantly decreased 21 days after BDL (21 d BDL) compared to the sham group, which was consistent with our previous results. In contrast, the expression of the other 3 miRNAs remained constant between the two groups, indicating that they were not involved in the BDL-induced cholestatic liver injury.
We next analyzed the alteration of the hub genes. As shown in Fig.6b-i, compared to the sham group, the 8 hub genes were remarkably increased in the 21d BDL group, which was consistent with our previous results. Changes could occur in the gene signature during disease progression. To better master the role of the DEGs in the dynamic development of cholestatic liver injury, we analyzed the changes of hub genes early after BDL. Results showed that BDL dramatically enhanced most hub genes levels both 3 days and 7 days after BDL (3 d BDL and 7 d BDL) compared to the sham group. Notably, among the 8 hub genes, except TLR2, the 7d and 21d BDL groups exhibited a significant upregulation trend compared to the 3d BDL group. Although this trend weakened from 7 days to 21 days after BDL, we still found that most genes continued to increase in the process of cholestatic liver injury. These findings suggested that these hub genes were continuously activated throughout the process of cholestasis, playing an important role in the cholestasis-mediated liver injury.
Analysis of the DE-mRNAs and UDCA response
Recently, UDCA dominates the drug therapy of cholestasis. However, nearly half of PBC patients face the dilemma that they do not fully respond to UDCA. Thus, we were curious about whether these identified DE-mRNAs were associated with UDCA response.
Dataset GSE79850, which contained the first liver biopsies from 9 PBC patients requiring liver transplantation (high-risk group) and 7 PBC patients whose condition was greatly controlled by UDCA therapy (low-risk group), was chosen to compare levels of the identified hub genes between the two groups (Fig. 7a-d). Interestingly, we found that the level of SYK in the high-risk group was more than twice as high as that in the low-risk group (79.59±11.48 vs 31.18±3.55, P= 0.003), which implied that SYK may play an important role in the response to UDCA.
Analysis of the DEGs in the blood of patients with CLDs
According to the result of functional analysis, DEGs were enriched in the pathway associated with hematopoietic cells, which prompted us to speculate whether levels of the DE-miRNAs and DE-mRNAs in peripheral blood of patients with CLDs were changed. The GSE119600 dataset was selected for further analysis. As a result, 5 hub genes (PTPRC, RAC2, SYK, TLR2, and LAPTM5) were detected in the blood samples (Fig. 8a-e). Most hub genes remarkably increased in the PSC or PBC group when compared to the control group, except PTPRC, which remained constant among the 3 groups. After that, to investigate the efficacy of these altered genes as potential biomarkers of CLDs, we performed ROC curve analysis. As shown in Fig. 8f-i, the AUC values of the 4 DE-mRNAs were all greater than 0.6 when used to diagnose both PSC and PBC, especially SYK and LAPTM5, which were greater than 0.7. These results indicated that SYK and LAPTM5 in the blood had potential as diagnostic markers in CLDs.