Primary sclerosing cholangitis (PSC) is one of the most important IBD-associated extra-intestinal manifestations (EIMs), which is mostly linked with ulcerative cholangitis (UC), and it is estimated that about 75% of PSC patients also have IBD, primarily UC (25). However, the exact molecular relationship between IBD and PSC remains unclear. Recent GWAS studies indicated that several genes, which are mostly implicated in immune responses, are associated with these disorders (26). This strong connection brought us to design a study to explore the molecular relationship of these two conditions using bioinformatics data. According to the DisGeNET and GEO database, we respectively identified 157 and 56 common DEGs between UC and PSC, and only the PTPN2 gene was common between UC and PSC in both the DisGeNET database and microarray datasets. Also, we identified 22 common SNPs between UC and PSC from the DisGeNET database. Based on our functional analysis, the common DEGs were mostly involved in mRNA processing, mRNA splicing processes, RNA bindings, and mRNA binding.
The protein tyrosine phosphatase nonreceptor 2 (PTPN2) gene encodes for the PTPN2 protein, also called T cell tyrosine phosphatase (TCPTP). PTPN2 protein is a member of the protein tyrosine phosphatases (PTP) family, which regulates the functional activity of their targets through the process of tyrosine phosphorylation, resulting in activating or deactivating cell signaling molecules (27). This protein is involved in a variety of cellular substrates, including protein tyrosine kinase targets such as the insulin receptor, the epidermal growth factor receptor (EGFR), Src family kinases, as well as multiple types of Janus kinases (JAK), and signal transducer and activator of transcription (STAT) family members (28, 29). Therefore, PTPN2 plays an important role in cell proliferation, differentiation, growth, mitotic cell cycle, and oncogenic transformation (30). Additionally, PTPN2 dephosphorylates T cell receptor kinases, which modifies immune reactions and cellular responses to inflammation, notable in the intestine (31, 32). Several studies have identified PTPN2 as a susceptibility gene for IBD and variations in this gene have been associated with an increased risk of developing chronic inflammatory and autoimmune diseases, such as celiac disease (33), IBD (including both Crohn's disease and ulcerative colitis) (33, 34), and PSC (35). These genetic variations may affect the expression or function of PTPN2, leading to dysregulated immune responses and increased susceptibility to IBD. For instance, a loss-of-function mutation in the PTPN2 gene in T cells can lead to enhanced expression and differentiation of naive T helper cells into Th1 and Th17 subtypes while simultaneously reducing the expression of T regulatory cells. Indeed, patients with PTPN2 variants exhibited elevated levels of pro-inflammatory cytokines, such as INF-γ, IL17, and IL22 in both their serum and intestinal mucosal layers (36–38).
Two SNPs of PTPN2, namely rs2847297 and SNP rs12968719, have been suggested to be associated with higher risk for PSC (39, 40). Moreover, a significant correlation between intestinal dysbiosis and exacerbated conditions in individuals with IBD has been unveiled regarding the malfunctioning of PTPN2 caused by the SNP rs1893217 (41). Therefore, given the autoimmune inflammatory nature of both UC and PSC, it seems to be reasonable to suggest that the PTPN2 gene, which significantly influences the inflammation process, is involved in the PSC development in patients with UC. Another study investigated the potential association between the presence of SNP rs1893217 in the PTPN2 gene and the occurrence of intestinal dysbiosis in patients with UC and PSC. The findings revealed importance of the gut mucosa-associated microbiome in PSC patients and suggested that the role of PTPN2 rs1893217 as a genetic risk factor for PSC (42). Our analysis demonstrated two SNPs related to PTPN2, including rs62097857 and rs12968719. However, there was no available study regarding the role of these SNPs in UC and/or PSC.
In the next step, we constructed PPI network for common DEGs that 5 genes were involved in the top module, including PABPC1, SNRPA1, NOP56, NHP2L1, and HNRNPA2B1 which all have an almost common duty in genome expression, and RNA modification. The PABPC1 gene (Poly (A) binding protein cytoplasmic 1), located within chromosome region 8q22.2–23, acts as an RNA binding protein through attaching to the poly(A) tail on mRNA to facilitate the processes of pre-mRNA splicing and maintain the mRNA stability (43). Importantly, PABPC1 was found to participate in an inhibitory translational complex to suppress the overexpression of pro-inflammatory mediators in activated macrophages (44). On the other hand, PABPC1 overexpression has also been linked to cancer progression (45, 46) and mediating cell stress responses (47). The SNRPA1 gene encodes a protein named small nuclear ribonucleoprotein polypeptide A', which plays a critical role as a constituent of the U2 small nuclear ribonucleoprotein (snRNP). This complex identifies the branch-point site in the initial stages of pre-mRNA splicing (48, 49). Additionally, SNRPA1 has been found to inhibit the formation of R-loops, thereby supporting DNA repair processes (48). Previous research has demonstrated that SNRPA1 functions as a component of the spliceosome and is involved in reprogramming of pluripotent stem cells (50). In a study, SNRPA1 was identified as a remarkable factor in inactivating p53, a tumor suppressor gene, in colorectal cancer (51). The NOP56 gene plays a pivotal role in processing ribosomal RNA (rRNA) precursors. Reduced expression of NOP56 can impede rRNA biosynthesis, thereby compromising the overall efficiency of rRNA synthesis (52). Reducing NOP56 expression significantly decreases the growth rate of lung, pancreatic, and colorectal cancer cells harboring KRAS mutations (53).
The NHP2L1 gene plays crucial roles in telomere maintenance and ribosome biogenesis, both of which are essential for cell viability and proper cellular function (54). Indeed, protein NHP2L1 was discovered to interact with the U4 RNA, hence, is involved in spliceosome assembly, splicing, and gene expression (55). Dysfunction or mutations in the NHP2L1 gene can lead to telomere shortening, genomic instability, and impaired protein synthesis, potentially contributing to the development of various diseases, including cancer and genetic disorders (56). The HNRNPA2B1 gene encodes a critical RNA-binding protein, heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1). This protein plays a key role in "reading" RNA methylation modifications and actively participates in downstream processes such as RNA translation and degradation (57). As a result, HNRNPA2B1 plays a multifaceted role in various cellular processes, such as telomere function, RNA biology, splicing, correct localization of transcripts, and loading of exosomes (58). A recent study demonstrated that HNRNPA2B1 exacerbates inflammation by enhancing M1 macrophage polarization, which is mediated by regulating mRNA stability (59). Another investigation showed the role of the HNRNPA2B1 gene in N6-Methyladenosine (m6A) modification of mRNAs, contributing to IBD pathophysiology (60). Despite the lack of research in examining these 5 genes in both UC and PSC, the biological function of these genes, alongside our findings, suggests the potential role of these genes in the UC and PSC relationship.
In further analysis, we identified the 94 potential miRNAs involved in regulating the genes of the top cluster and 200 circRNAs related to the potential miRNAs. We constructed the ceRNA network by the identified mRNAs, miRNAs, and circRNAs and detected 30 RNA molecules with the highest score in this network. Of 94 identified miRNAs, 38 miRNAs were found to be associated with 590 lncRNAs.
A growing body of evidence indicated the essential role of ncRNAs and ceRNA networks in various biological processes, including cell proliferation and growth, apoptosis, immune response, and tissue homeostasis. Therefore, dysregulation of them could contribute to the development of human diseases (61, 62). Regarding UC, the first miRNA profiling study was conducted in 2008 on colonic tissues of IBD patients. These workers identified eleven miRNAs, which showed differential expression compared to the controls. Among them, 3 and 8 miRNAs were significantly downregulated and upregulated, respectively (63). Furthermore, Xu S. et al. showed that the circRNA- and miRNA-associated ceRNA network plays a crucial role in various aspects of UC, including the regulation of inflammatory response, immune response, cell proliferation, apoptosis, and progress to tumor formation. This network's involvement in these processes suggests its significance in the pathogenesis and progression of UC (64). According to the findings of a study by Ouyang et al., circ_0001187 could exacerbate TNF-α-induced inflammation injury in human normal colorectal mucosa cells through affecting the MYD88 pathway via its interaction with miR-1236-3p (65). As we identified hsa-miR-23b-3p as a hub node in our study, Fasseu et al. found this miRNA as a differentially expressed miRNAs in human CD colonic tissue (66). Also, hsa-miR-149-3p which is among 30 hub nodes in the present study, showed a significant decrease in both active and inactive CD patients compared to the healthy controls in Wu et al.’s study (67). Povero et al. conducted a study using whole miRNA-sequencing analysis and identified more than 100 different miRNAs in extracellular vesicles derived from patients with PSC. Among these miRNAs, eleven were found to be differentially expressed in extracellular vesicles from PSC patients. The top five down-regulated miRNAs were miR-7113-5p, miR-4715-5p, miR-221-5p, miR-4444, and miR-150-3p. Conversely, the top upregulated miRNAs included miR-3183, miR-192-5p, miR-122-5p, miR-4465, miR-4784, and miR-4645-3p (68). These differentially expressed miRNAs may provide valuable insights into the molecular mechanisms underlying PSC and potentially serve as diagnostic or therapeutic targets in the future. Nevertheless, none of these miRNAs have been identified as a hub node in our study, which might bring the idea that different miRNAs are involved in connecting PSC to UC. The ongoing research has expanded our knowledge of miRNA and circRNA diversity and their functional significance in various biological processes and diseases. The continuous exploration of miRNAs and circRNAs is crucial for gaining a comprehensive understanding of their regulatory roles and potential therapeutic applications.
We further identified the co-expression network between the hub genes consisting of 3 main subnetworks linked together by several genes. The CUL3 and DHX15 genes were found to be associated with all 3 main subnetworks; these associations were stronger for the DHX15 gene. DHX15 is a gene that encodes a putative ATP-dependent RNA helicase, which is reported to play a role in pre-mRNA splicing (22). DHX15 belongs to the RNA helicase family and is involved in numerous biological processes. Moreover, the CUL3 gene is responsible for coding the cullin-3 protein. Cullin-3 is a vital component of an E3 ubiquitin ligase complex that functions through the tagging of excess and defective proteins with ubiquitin molecules, making them recognizable for proteasomes, which leads to their degradation. Additionally, this system regulates the levels of proteins involved in critical cellular processes, including the timing of cell division and growth (23, 24).
According to our findings, several drugs, including CHEMBL585964, CHEMBL592588, Ditolylguanidine, and CHEMBL589711were found to interact with “PABPC1” gene, one of our top cluster genes. Ditolylguanidine is a nonselective sigma receptor agonist which binds to both sigma1 and sigma2 receptors with equal affinity (69). In a study, Johannessen et al. focused on exploring how σ-receptors modulate the voltage-gated sodium channel (Nav1.5) in the heart. Ditolylguanidine as a sigma1-2 receptor ligand reversibly inhibited Nav1.5 channels to multiple degrees in human embryonic kidney 293 (HEK-293) cells and COS-7 cells (70). Despite the novel finding of this study regarding the potential of the Ditolylguanidine to be utilized in context of regulating PABPC1 gene, according to the literature, no study has been conducted in this area. Also, there is no available evidence regarding other detected drugs in our analysis.
Besides the top cluster genes, we extracted possible gene-drug reactions for PTPN2 as the only common DEG between the DisGeNET and microarray datasets and identified 8 potential interacting drugs with this gene. Between these drugs, Cloxyquin is a specific activator of the two-pore domain potassium channel TRESK [TWIK-related spinal cord K + channel (also known as K2P18.1)], which is linked to typical migraine occurrence and neuronal excitability control (71). In fact, TRESK functions to maintain membrane potential in various cells. In this regard, a recent study revealed the pivotal role of physiological TRESK function in the differentiation of T-cells toward regulatory subtypes, thus presenting a novel pharmacological target with potential implications for the treatment of autoimmune disorders. Also, TRESK is a crucial mediator in translating the signal from the T-cell receptor during the selection process of thymus-derived regulatory T-cells (Treg), ultimately influencing Treg development and function (72). Hence, the activation of this channel by the compound Cloxyquin demonstrates promise as an initial candidate for the development of a novel class of immunomodulatory agents.
At last, our study was constrained by the absence of experimental data to validate these findings and the limited availability of datasets. Although additional verification is needed, our research offers significant insights into potential genes that might play a role in the molecular connection between UC and PSC. This could facilitate the development of diagnostic tools and treatment targets for these conditions.