Chronic inflammation is a hallmark of IBD, which damages the DNA of epithelial cells from the colon and rectum by producing more free radicals and inflammatory cytokines such as tumor necrosis factor-α (TNF-α) (21). Cytokines, produced through persistent inflammatory responses and signaling pathways, enable cancer-prone cells to avoid apoptosis and progress from dysplasia to CRC (21). In addition, inflammation can induce mutagenesis, and its recurring pattern, paired with epithelial renewal, may exert selection pressure that hastens cancer growth (22).

The pro-inflammatory mediator, TNF-α, regulates cell-to-cell communication in the tumor microenvironment and can potentially induce the metastatic phenotype (23). A meta-analysis study indicates that the TNF-α 308G>A gene polymorphism significantly influences the susceptibility of patients to Crohn's disease and UC (24). Another study found that TNF-α messenger RNA (mRNA) expression is higher in CRC than in normal colorectal tissues. The study also revealed that TNF-α gene expression is higher in stage III and IV neoplasms compared with earlier tumor stages (25). These findings imply that TNF-α may contribute to IBD pathogenesis and its progression to CRC. A recent study revealed that TNF may stimulate the formation of neoplastic lesions at the start of colitis-associated colon cancer (CAC) and decrease them as the disease progresses. TNF deletion in Winnie-Apc^Min/+ mice reduced dysplastic lesions in 5-week-old mice, followed by a faster disease progression at 8 weeks (26). This supports the theory that TNF may be implicated in the progression of IBD to CRC.

Nuclear factor-κB (NF-κB) may contribute to the progression of CRC by regulating the expression of target genes involved in angiogenesis, including COX-2 (27). COX-2, a key player in tumor progression, has been identified as a potential therapeutic target for numerous human and animal cancer types (28). A study found that COX-2 is upregulated along the neoplastic spectrum in UC (29). This may imply that COX-2 is involved in the IBD transition to CRC. In a different study, Gregório et al (28) discovered that COX-2 serves a role in the angiogenesis and inflammatory environment establishment that promotes the growth of melanoma tumors. Another study found that hydroxyeicosatetraenoic acids may increase colonic inflammation and CRC risk in IBD by directly and indirectly inducing COX-2-mediated prostaglandin production (30). A recent study found that Clostridium butyricum inhibited CAC in mice as well as reduced COX-2 levels and phosphorylated NF-κB (31). These data suggest that COX-2 may be implicated in IBD progression to malignancy.

The pro-inflammatory cytokine, IL-6, interacts with soluble or membrane-bound IL-6 receptors (IL-6Rs) to communicate via glycoprotein 130 (gp130) in trans or cis directions (32). IL-6 is a versatile cytokine with wide-ranging effects on the integrated immune response, hematopoiesis and oncogenesis (33,34). Wu et al (35) discovered that miRNA-320 targets IL-6R and reduces carcinogenesis in mice with CAC by decreasing IL-6R expression. Another study also found that patients with active UC, dysplasia and malignancy exhibit significantly higher IL-6 and phosphorylated-signal transducer and activator of transcription 3 (p-STAT3)-positive epithelial cells than the controls (36). These results further affirm the role of inflammatory mediators in IBD progression to cancer.

IL-23, a pro-inflammatory cytokine, has been linked to various health issues, including plaque psoriasis, chronic obstructive pulmonary disease, UC and CRC, and regulates T helper (Th)-17 inflammation (37-40). According to Ljujic et al (41), serum IL-23 levels are markedly higher in patients with CRC than in healthy individuals. These levels are strongly linked to vascular endothelial growth factor (VEGF) upregulation, which suggests that IL-23 may play a role in the development of CRC. Another study by Wu et al (42) found that synbiotic medication can safeguard the intestinal barrier and prevent the occurrence of CAC. The synbiotic could notably block aberrant activation of the intestinal wingless-related integration site (Wnt)/β-catenin signaling pathway, which is highly connected to IL-23 (42).

Chemokines, also known as chemotactic cytokines, are small released proteins that signal via G protein-coupled heptahelical receptors on the cell surface (43). These molecules play a crucial role in the inflammation-related pathophysiology of rheumatoid arthritis, cancer, insulin-resistant diabetes, atherosclerosis, neurological disorders and IBD (44). Mrowicki et al (45) found that IBD may develop more frequently in those with polymorphisms in the C-X-C motif chemokine receptor (CXC)R4/C-X-C motif chemokine ligand (CXCL)12 chemokine axis. Patients with IBD experience inflammation due to the interaction between the G-protein-coupled receptor, CXCR4, and CXCL12, a G-protein natural ligand (46). CXCR4 triggers various processes, including clonogenic growth stimulation, VEGF release induction and intercellular adhesion molecule-1 upregulation in CRC (47). According to data from Ottaiano et al (47), suppressing CXCR4 prevents CRC metastasis. This implies that CXCR4 may be associated with IBD pathogenesis and its progression to CRC metastasis. A systematic study found that patients with CRC who have upregulated CXCR4 expression have a significantly lower overall and disease-free survival (48). Additionally, Cheng et al (49) found that CXCL3 is increased in colon adenocarcinoma (COAD) tissues. CXCL3 is essential for controlling the malignant tendencies of tumor cells (49). Therefore, CXCL3 is involved in the pathogenesis of COAD.

Immune cells play a crucial role in both the acute and chronic stages of IBD, as they facilitate the progression of the disease from inflammation to carcinogenesis (50). Immune cells such as macrophages, T cells, regulatory T cells (Tregs), natural killer T (NKT) cells, innate lymphoid cells (ILCs), neutrophils and other T cell subsets play a role in this transitioning process. For instance, obesity-induced IL-6 shifts macrophages toward those that promote tumors and release the chemokine, C-C motif chemokine ligand 20 (CCL20), in the CAC microenvironment (51). As a result, CCL20 facilitates the advancement of CAC by attracting B cells and γδ T cells that express CCR6 by chemotaxis (51). Additionally, IL-6 secretes granulocytic-myeloid-derived suppressor cell (MDSC) exosomal miR-93-5p, promoting monocytic-MDSC differentiation into M2 macrophages via STAT3 signaling, facilitating the transition from colitis to cancer (52). These results demonstrate how macrophages function in CAC.

Moreover, Zhang et al (53) found that patients with UC and high neutrophil infiltration subtype B levels are more likely to acquire CAC. Therefore, neutrophils have been suggested to facilitate the conversion of UC into CAC. Burrello et al (54) found that patients with IBD have invariant NKT (iNKT) cells in their lamina proprias, exposed to mucosa-associated bacteria, causing pro-inflammatory activation and pathogenic actions against the epithelial barrier. Díaz-Basabe et al (55) also revealed that Porphyromonas gingivalis (pathobiont) triggers iNKT cells to upregulate chitinase 3-like-1 protein, limiting cytotoxic functions, promoting immune evasion and accelerating the progression of CRC. These results show that iNKT cells may be involved in the pathogenesis of CRC and IBD.

According to another study, the generation of colorectal IL-22 requires butyrophilin-like protein 2 (BTNL2). BTNL2 stimulates the production of IL-22 via acting on ILC3s, CD4⁺ T cells and γδ T cells. BTNL2 knockout mice have lower colonic carcinogenesis and more severe colitis phenotypes than control mice due to IL-22 production defects (56). This may imply that ILC3s, CD4⁺ T cells and γδ T cells are involved in CAC. Additionally, CD14 has also been found to enhance colon cancer stem cell proliferation, metastasis and carcinogenesis in response to lipopolysaccharide (LPS) stimulation via the toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88) signaling pathway (57). Other studies indicate that RORγt⁺ Treg (58) and Vδ2 T cells (59) are implicated in IBD, CRC and CAC.

In total, 25% of human malignancies are caused by persistent oxidative damage during inflammation (60). During inflammation, inflammatory and epithelial cells produce reactive nitrogen species and reactive oxygen species (ROS) that can harm DNA (60). Studies suggest that oxidative stress and DNA damage may increase the likelihood of IBD advancing to cancer (61,62). In malignancies, nitric oxide (NO) has pro- and antitumor properties. Endogenous NO levels can promote colon cancer, while prolonged exogenous doses can have lethal effects (63). NO is crucial in various CRC signaling pathways, such as extracellular signal-regulated kinase and Wnt/β-catenin, which are linked to the development, spread and resistance to chemotherapy and radiation of CRC (63). One of the three essential enzymes that produce NO from the amino acid, L-arginine, is inducible NO synthase (iNOS) (64). When Helicobacter hepaticus (Hh) infects recombination activating gene 2-deficient (RAG2^−/−) mice, colitis develops and eventually turns into lower colon cancer. NO, a chemical with documented mutagenesis potential, is crucial in this mechanism (65). Wang et al (65) further found that RAG2^−/− mice infected with Hh rapidly produce iNOS and develop DNA double-strand breaks, a unique characteristic of growing crypt epithelial cells. A similar study by Erdman et al (66) found that when Hh infects RAG2^−/− mice, the colon is infiltrated with macrophages and neutrophils. These activities are correlated with the upregulation of iNOS expression and NO generation, as shown by the urine excretion of nitrite. The modifications result in a progressive rise in severe inflammation, hyperplasia, dysplasia and malignancy. Therefore, iNOS and NO may cause IBD to transition to cancer.

TP53, commonly termed the 'guardian of the genome', is an important tumor suppressor gene (67). The TP53-encoded p53 protein acts as a sensor of DNA damage in cells, alerting them when necessary (67). It has long been hypothesized that the primary mechanism by which mutant p53 contributes to carcinogenesis is its decreased capacity to trigger apoptosis, DNA repair and cell cycle arrest in response to carcinogenic stimuli (68). TP53 mutations are prevalent in various malignancies, including lung, breast and colon cancer (67). A systematic review found that patients with IBD-CRC have a higher frequency of TP53 mutations than those with sporadic (S)-CRC (69). In IBD-CRC, TP53 mutations tends to be more significant than KRAS (in terms of frequency and disease pathology), in contrast to S-CRC (69).

Loss of heterozygosity, somatic mutation, decreased expression and enhanced alternative splicing into a dominant negative oncogenic splice variant, Kruppel-like factor 6 (KLF6)-SV1, inactivates the KLF6 tumor suppressor gene in a number of human malignancies (70). A study found that most sporadic and IBD-related CRC cases have inactivated KLF6 due to loss or mutation. At least 55% of tumors have a deleted KLF6 locus and 44% have alterations, with loss and mutation rates comparable to TP53 and KRAS (71). Additionally, gastric cancer has been linked to KLF6 locus-specific deletion (70). Therefore, TP53, KRAS and KLF6 loss or mutation may lead to IBD-CRC.

Epigenetics, including DNA methylation, has been linked to the progression of IBD to cancer. DNA methylation is a crucial epigenetic method that allows cells to regulate gene transcription (72). Certain genes undergo either hypermethylation (increased methylation) or hypomethylation (decreased methylation) in response to DNA methylation. Increased methylation decreases gene expression, while decreased methylation increases gene expression, affecting the function of the genes. In cases of tumor suppressor genes, hypermethylation silences their tumor suppressor action while hypomethylation increases their tumor suppressive roles.

The gene, adenomatous polyposis coli (APC), is a tumor suppressor that regulates the Wnt signaling pathway, and inhibition of APC promotes CRC (73,74). According to Dhir et al (75), Wnt signaling pathway gene methylation is a common early event in IBD and IBD-related neoplasia. It was further found that IBD-associated neoplasia has markedly greater levels of methylation of APC1A, APC2, secreted frizzled-related protein (SFRP)1 and SFRP2 than IBD colitis. Therefore, the transition from IBD colitis to IBD-associated neoplasia is characterized by APC1A, APC2, SFRP1 and SFRP2 methylation (75). Several genes, including Forkhead box protein (FOX)E1 and spectrin repeat-containing nuclear envelope protein 1 (76), fragile histidine triad (77) as well as transcription elongation regulator 1-like gene (78,79), have been linked to the progression of IBD to colon cancer due to methylation changes.

The dynamic and varied microbial community of the human GIT is essential to health, with the gut microbiota fostering the growth and operation of the gut immunological barrier (80). CAC, a type of CRC, is tightly linked to gut microbiota dysbiosis and chronic inflammation (81). Uronis et al (82) showed that CAC development depends on the gut microbiota, and chronic colitis increases the capacity of colorectal tumors to proliferate into advanced stages. Microbial identification by the TLR/MyD88 system is a prerequisite for these activities. In colitis, elevated TLR4 signaling stimulates dual oxidase 2 expression and hydrogen peroxide generation by epithelial cells. The local environment influences the mucosal microbiota, leading to pathogenic characteristics such as elevated ROS levels in the epithelium and a rise in colitis-associated tumors (83). In summary, CAC is caused by ROS in the epithelium, triggered by innate immunological signaling in response to the mucosal microbiota (83). For colon cancer development in chronic colitis, TLR4 signaling is essential (84). Therefore, the interaction of the gut microbiota with TLR signaling may be crucial for therapeutic purposes in treating CAC.

RNA polymerase II pre-initiation complex development within repressive heterochromatin in drosophila enforces the transcription of piRNA clusters, tiny RNA source loci, in animal gonads (98). Primary piRNAs are found in distinct genomic regions known as piRNA clusters, and they appear to have originated from lengthy, single-stranded precursors (99). Zucchini is essential in defining the 5′ and 3′ ends of piRNAs in this evolutionarily conserved piRNA biogenesis process (100). Pre-piRNAs are released by aubergine or argonaute (Ago)3-mediated cleavages, which require time-consuming removal by the Nibbler exoribonuclease in the 3′-to-5′ direction, while cleavages caused by Zucchini accurately determine the exact locations of mature piRNA 3′ ends (101). The action of the MOV10L1 RNA helicase facilitates the unwinding and redirection of the single-stranded piRNA precursor transcripts towards the endonuclease responsible for the initial cleavage step in piRNA processing (102). The 5′ end of silkworm PIWI (SIWI)-bound piRNAs is strongly biased toward uridine, and adenine is abundant at position 10 in piRNAs linked to Ago3 (BmAgo3) (103). In contrast to BmAgo3, which binds sense piRNAs, SIWI preferentially binds antisense piRNAs (103). Perinuclear Yb bodies, the sites of piRNA synthesis, are where piRNA maturation and connection with PIWI occur (104). Trimmer and Hua-Enhancer 1 (Hen1) mature pre-piRNAs regardless of the endonucleolytic process (105). Trimmer binds to Papi/Tdrkh and is abundant in the mitochondrial fraction (106). Hen1 is the enzyme that introduces the 2′-O-methyl modification to the 3′ ends of piRNAs (107). Trimmer and Papi/Tdrkh depletion additively inhibit trimming, leading to the buildup of 35-40 nucleotide (nt) pre-piRNAs that are unstable and prone to destruction (106) (Fig. 2).

Most snoRNAs in vertebrates are encoded in the introns of genes that code for proteins and are released through the exonucleolytic cleavage of linearized intron lariats (108). The spliceosome or an RNase III-like activity releases intron-encoded and polycistronic snoRNAs from primary transcripts as pre-snoRNAs (109). Via exonucleolytic activities, pre-snoRNA leader and trailer sequences are eliminated (109). A debranching activity in the spliceosomal pathway then linearizes the resultant intron lariat (109). The nucleolus, which concentrates rRNA modification guide RNAs known as snoRNAs, is where posttranscriptional modifications of rRNA occur. However, small Cajal body-specific RNAs, which guide modifications for spliceosomal small nuclear RNAs (snRNAs), accumulate in the Cajal body (110). Posttranscriptional modification of rRNAs, specifically 2′-O-methylation (Nm) and pseudouridylation, is the canonical function of box C/D snoRNA (SNORD) and box H/ACA snoRNA (SNORA), respectively (111) (Fig. 3).

miRNAs, derived from sequences of DNA, are transcribed into primary miRNAs and transformed into precursors and mature miRNAs (112). Drosha, a nuclease belonging to the RNase III family, catalyzes the initial cleavage of primary miRNA transcripts (pri-miRNAs) found in the nucleus (113). RNase III domains A and B of Drosha form an intramolecular dimer and cleave the 3′ and 5′ strands of the stem, respectively. This mechanism is identical to that of human dicer (114). Post-transcriptional processing transforms each miRNA into a duplex of two strands (115). During miRNA strand selection, one of two strands is loaded into an Ago protein to create the miRNA-induced silence complex (miRISC), and the other strand of the complex collapses after being removed (115). Human RNA-induced silencing complexes, including the Ago subfamily proteins Ago1-4, are where siRNAs and miRNAs are integrated (116). miRNA must form a miRISC with an Ago protein for active function, which binds to specific mRNA through complementarity sequences (117). miRNAs often cause translational repression and mRNA degradation by interacting with the 3′ untranslated region (UTR) of target mRNAs but also engage with the 5′ UTR, coding sequence and gene promoters (112) (Fig. 4).

tsRNAs are produced from mature tRNA and tRNA precursors when tRNAs are cleaved explicitly by angiogenin (ANG) and dicer in specific tissues or cells or under certain circumstances such as hypoxia and stress (118). tRNA halves (tiRNA) and fragments produced from tRNA (tRFs) are the two subtypes of tsRNAs (119). tRFs-1, 2, 3, 5 and i-tRF, which consist of 3′ and 5′ tiRNA, are the five types of tRFs based on the incision loci (119). 5′-tRNA and 3′-tRNA halves are the two different forms of tRNA halves (120). The 31-40 nt-long tRNA halves are created when mature tRNAs undergo specific cleavage in their anticodon loops (120).

Within eukaryotic cells, m6A is the most common co-transcriptional modification in RNAs. The m6A methyltransferases, or 'writers', such as methyltransferase-like (METTL)3/14/16, RNA-binding motif protein 15 (RBM15)/15B, zinc finger CCCH domain-containing protein 13, VIRMA, CBLL1, Wilms' tumor 1-associating protein (WTAP) and KIAA1429, modify the m6A modification. The demethylases, or 'erasers', such as fat mass and obesity-associated protein (FTO) and alkylation protein AlkB homolog 5 (ALKBH5), remove it. The proteins known as 'readers' that bind to m6A include YTH domain family (YTHDF)1/2/3, YTH domain containing 1 (YTHDC1)/2, insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1)/2/3, and heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1) (121).

METTL3 methylates pri-miRNAs to designate them for DGCR8 recognition and processing (122). HNRNPA2/B1 detects m6A pri-miRNA alteration by METTL3 or METTL14, promoting the DGCR8-pri-miRNA interaction and accelerating miRNA production (10). To perform cellular m6A deposition on mammalian nuclear RNAs, METTL3 and METTL14 form a heterodimeric complex (123,124). METTL3/14 is situated in the nucleus and is localized to nuclear speckles. The splicing regulator, WTAP, is required for this specific nuclear localization pattern (124). A study found that suppressing RBM15 and RBM15B or METTL3 is a significant barrier to XIST-mediated gene silencing (125). METTL16 has been identified as the cause of m6A deposition in certain transcripts (126). ZC3H13 (127), KIAA1429 (128), Hakai (129) and ZCCHC4 (130) are other methyltransferases that cause m6A alterations.

Two m6A demethylases, FTO and ALKBH5, have been identified, which play a crucial role in various aspects of mRNA biology, including processing, export, metabolism and stability (131). The catalytic domain of ALKBH5 has been demonstrated to demethylate single-stranded DNA and single-stranded RNA through catalytic experiments (132), while FTO catalyzes Fe(II) and 2-oxoglutarate-dependent modifications of nucleic acids, notably the demethylation of m6A in mRNA (133). YTHDC1, a crucial m6A nuclear reader, is vital for managing mRNA splicing, export and stability (134). HNRNPA2B1, similar to m6A writer METTL3, directly binds a set of nuclear transcripts, causing alternative splicing effects (135).

The effects of m6A are considered to be mediated through a complex network of interactions between various m6A sites and three diverse cytoplasmic YTHDF m6A-binding proteins, DF1, DF2 and DF3 (136). Other cytoplasmic readers include IGF2BP1, IGF2BP2, IGF2BP3 and eukaryotic initiation factor 3 (eIF3). IGF2BP1, IGF2BP2 and IGF2BP3 are RNA-binding proteins that contribute to development and disease by regulating the stability of mRNA and the translation of essential modulators of cell division and metabolism (137). Additionally, over the past 3 years, research has significantly enhanced the comprehension of the role of eIF3 in mRNA translation (130). A study has shown that the m6A alteration of D-3-phosphoglycerate dehydrogenase mRNA, mediated by METTL3, improves its interaction with eIF3i, thereby accelerating its translational rate (138), implying that eIF3 may be involved in mRNA translation.

Nm is a well-known RNA modification found in non-coding RNAs that has been detected at various internal locations of mRNA. Extensive Nm at internal locations of mRNA enhances mRNA stability (139). RNA Nm, a common feature in non-coding RNAs such as rRNA, tRNA and snRNA, is found at the 5′ cap of most mRNAs in higher eukaryotes (140). However, rRNA is one vitally important RNA that Nm drastically changes (141). The miRNA methyltransferase, Hen1, adds a methyl group to the most 3′ nucleotide of miRNAs (142). In plants, 3′-end uridylation and 3′-to-5′ exonuclease-mediated degradation of small RNAs are prevented by Hen1 (143). These results show the stabilizing effect of Nm on small RNAs via Hen1. Drosophila piRNAs also contain 2′-O-methylation at the 3′ ends. Drosophila piRNA loses its Nm when piRNA methyltransferase, the Drosophila homolog of Arabidopsis Hen1, is lost (144). These results suggest that piRNAs may undergo Nm. In eukaryotes, fibrillarin, a conserved methyltransferase unit of a ribonucleoprotein complex directed by C/D box snoRNAs, places most Nm modifications (145). It has been shown that activation-induced cytidine deaminase-related snoRNA, aSNORD1C, interacts with 2′-O-methyltransferase fibrillarin to promote Nm (146).

m5C, a widespread RNA modification, is essential for regulating RNA fate and gene expression (147). m5C related enzymes, such as m5C methyltransferases [NOP2/sun (NSUN), DNA methyltransferase (DNMT) and TRDMT family members], demethylases [ten-eleven translocation (TET) family and ALKBH1] and binding proteins [YTHDF2, ALYREF and Y-box binding protein (YBX1)], dynamically regulate it (148,149). NSUN2 is an RNA methyltransferase that introduces m5C in nuclear-encoded tRNAs, mRNAs and miRNAs and has been associated with cell proliferation and differentiation. Pathogenic variations of mammalian NSUN2 have been connected to neurodevelopmental disorders (150). The nuclear-cytoplasmic shuttling of ALYREF, RNA-binding affinity and related mRNA export are all modulated by NSUN2 (151). YBX1 is essential for transcriptional control and RNA stabilization (152). TET2 facilitates the conversion of m5C to 5-hydroxymethylcytosine on tRNA and regulates the stability or processing of specific tRNA fragment classes (153).

m3C is widely distributed at position C32 of eukaryotic tRNAThr and tRNASer species (154). m3C, despite being less common, is frequently found in tRNAs, rRNAs and mRNAs (155). METTL6 in humans is a m3C methyltransferase that works with tRNAs, such as tRNASer (UGA) (155). In mouse stem cells, deletion of Mettl6 causes alterations in RNA levels and ribosome occupancy in addition to decreased pluripotency (156). METTL8 has been proven to cause m3C in mRNA (157).

It is critical to comprehend the role of piRNAs, a novel class of sncRNAs linked to several disorders in the last 10 years (176). A recent study indicates that piRNAs are not only found in the mammalian germline but are also expressed differently in different human tissues, and are linked to several diseases, including neurological, cardiovascular and urinary tract disorders (177). The roles of piRNAs in IBD are limited. However, piRNAs have been found to play certain roles in other diseases. For instance, putative piRNAs have been found in the mammalian brain, and they may have a similar role to piRNAs in the testes in silencing retrotransposons, which are vital contributors to the genomic variability in the brain that underlies adaptation, stress response and brain disease (178). It is documented that, in leukemia, has-piR-011186 upregulation accelerates cell cycle progression and reduces apoptosis (179). Ding et al (180) revealed that piR-823 activates Wnt signaling and induces cancer cell stemness in luminal subtype breast cancer cells by upregulating DNMT expression and encouraging DNA methylation of the APC gene. These are only a few of the numerous roles of piRNAs in other diseases; therefore, more studies focusing on IBD should be explored for therapeutic relevance.

Patients with IBD have a significantly higher isolation of Aeromonas species than patients without the illness. Downregulating cytoplasmic tRNA, small nuclear RNA and snoRNA is one of the ways Aeromonas veronii damages IECs (181), implying that these small RNAs may play a role in the pathogenesis of IBD. Although piRNA, tsRNA and snoRNA have been linked to other diseases such as Lewy body diseases (182), atrial fibrillation (183) and endometrial cancer (184), respectively, more research is needed to understand their pathogenesis in IBD.

Maintaining the integrity of the intestinal mucosal barrier is essential for defending the epithelium of the intestine from pathogens and retaining commensal bacteria, which helps prevent colitis (185). Occludins, claudins and zonula occludens (ZO) are tight junction proteins crucial for maintaining the integrity of the epithelial barrier (186). However, research has demonstrated that specific miRNAs harm the intestinal barrier, contributing to the pathophysiology of IBD. In this context, it has been discovered that miR-124 causes intestinal inflammation by blocking the aryl hydrocarbon receptor (AHR), which in turn affects the generation of cytokines that promote inflammation and advance the pathology of Crohn's disease (187). Guz et al (188) indicated that increased miRNA expression is associated with inflammation mediated by IBD and is inversely correlated with expression of the E-cadherin 1 (CDH1) gene, which suggests the function of epithelial-to-mesenchymal transition (EMT) in the development of IBD. E-cadherin is a crucial barrier in the colon that maintains organ balance and inhibits the growth of colon tumors (189). Consequently, increased miRNA expression and a reduction in CDH1 may facilitate the transition to EMT. Similarly, miR301A is expressed at higher levels in IECs from patients with IBD who are actively ill, and CDH1 expression is downregulated by human IECs expressing transgenic miR301A (190). In other studies, lncRNAs have been found to either sequester miRNAs or inhibit them, contributing to the progression of IBD by disrupting the intestinal barrier. For instance, H19 lncRNA is a precursor for miR-675, which plays a crucial role in regulating the function of the intestinal epithelial barrier. Upregulation of H19 increases miR-675 cellular abundance, destabilizing and suppressing mRNAs encoding E-cadherin and ZO-1, ultimately causing membrane barrier malfunction (191). Additionally, lncRNA FBXL19 antisense RNA 1 diminishes the targeting of miR-339-3p to RAS homologous protein B and exacerbates intestinal epithelial barrier impairment in dextran sodium sulfate (DSS)-induced colitis in mice (192). Other lncRNA, including colon cancer-associated transcript-1, can damage the intestinal barrier by downregulating miR-185-3p (193).

By contrast, certain miRNAs have been shown to attenuate IEC injury or IBD, implying that miRNAs may play a dual role in IEC or IBD pathogenesis. miR-200b has been demonstrated to reduce tight junction damage and inhibit intestinal epithelial IL-8 release in vitro (194). Moreover, miR31, which is elevated in colon tissues from patients with UC or Crohn's disease, decreases the inflammatory reaction in the colon epithelium of mice by suppressing the production of signaling proteins (gp130) and receptors for inflammatory cytokines (IL7R and IL17RA) (195). In UC mice, miR-495 targets STAT3 and inhibits the Janus tyrosine kinase/STAT3 signaling pathway to improve intestinal mucosal barrier function (196). Research indicates that specific lncRNAs can bind to miRNAs, potentially preventing intestinal damage in IBD. For instance, PlncRNA1 (an lncRNA) binds to miR-34c, and PlncRNA1 upregulation appears to shield the intestinal epithelial barrier from damage. Nevertheless, upregulation of miR-34c counteracts the protective effects of PlncRNA1 on intestinal epithelial barrier function (197). This may suggest that PlncRNA1 binds to low expression of miR-34c to prevent damage to the intestinal barrier. Notably, the upregulation of miR-34c has been found to significantly alter the integrity and increase the permeability of the blood-tumor barrier (198). This further confirms the role of PlncRNA1 in binding to low miR-34c levels to prevent barrier damage.

Evidence supporting the regulatory function of miRNAs in the pathogenic pathways of several conditions encompassing IBD has been mounting in recent years, and based on these discoveries, miRNAs appear to be novel prospects for IBD treatment (199). miRNA, which functions as a post-transcriptional moderator of mRNA by binding to complementary regions inside mRNAs, participates in the intricate interplay between tumors and the immune system (200). Therefore, miRNAs are emerging as critical regulators of innate and adaptive immune responses, and aberrant immune system expression and function have been related to a number of human diseases, including inflammatory disorders such as IBD and cancer (201).

It has been documented that miR-132 and 223 inhibit FOXO3a to increase pro-inflammatory cytokine expression, making them essential mediators in the pathogenesis of IBD (202). Additionally, miR-124a can suppress AHR, disrupting intestinal inflammation and the intestinal barrier (203). One potential mechanism underlying inflammatory cell trafficking during colonic inflammation is the targeting of CXCL12β by the miR-141 pathway. Therefore, using miRNA precursors to inhibit colonic CXCL12β expression and prevent colonic immune cell recruitment is a potential strategy that could be useful for treating Crohn's disease (204). It has been shown that LPS-induced M1 macrophage polarization changes to M2 macrophage polarization by miR-98-5p knockdown, which reduces inflammation by upregulating tribbles homolog 1 (205), implying that miR-98-5p expression may control M1 macrophages to cause IBD. lncRNA has been demonstrated to modulate specific miRNAs, resulting in the stimulation of immune responses. For instance, Qiao et al (206) discovered that inhibiting lncRNA ANRIL can prevent UC by regulating the miR-323b-5p/TLR4/MyD88/NF-κB pathway, implying that the activation of lncRNA ANRIL may lead to the development of UC by regulating the miR-323b-5p/TLR4/MyD88/NF-κB pathway. The transcription-related factor, NF-κB, is a key modulator of inflammatory reactions and controls several facets of innate and adaptive immune responses (207).

The expression of nucleotide-binding oligomerization domain 2 and IL-12/IL-23p40 is inhibited by miR-10a, which also reduces inflammation in the inflammatory mucosa of patients with IBD and suppresses the Th1/Th17 cell immunological response (208). Another study has shown that miR-144/451 inhibits dendritic cell (DC) activation and improves DSS-induced colitis in mice by aiming specifically at the 3′ UTR of interferon-regulatory factor 5 (209). It is also documented that miR-19b reduces the inflammatory response by decreasing the levels of suppressor of cytokine signaling 3, which modulates chemokine synthesis in IECs, thus preventing Crohn's disease pathogenesis (210). Additionally, miR-29a has been shown to suppress DSS-induced colitis. Real-time PCR assays have shown that miR-29 in CD11c⁺ DCs suppress the synthesis of transforming growth factor-β (TGF-β), IL-23 subunits and IL-6 in DSS-treated mice (211). The regulation of miRNAs by lncRNA is crucial for reducing immune responses. For instance, Wang et al (212) discovered that increasing the expression of lncRNA maternally expressed 3 (MEG3) can reduce colonic ulceration in UC rats by upregulating IL-10 expression through miR-98-5p sponging. Additionally, overexpression of lncRNA MEG3 in UC rat colons reduces oxidative stress, inflammation, apoptosis and pyroptosis (212). These results suggest that miRNAs may have dual roles in IBD immunological response regulation.

miRNAs have been found to inhibit immunological checkpoints in CRC and enhance T cell-mediated anticancer responses. For instance, Roshani Asl et al (283) found that miR-124 can suppress PD-L1 expression in CRC cells, which may improve the T cell-mediated anticancer response. In addition, miR-124 significantly reverses cancer characteristics (proliferation, stemness, migration and invasion) in CRC cells by reducing STAT3 signaling activity and altering its downstream targets, indicating its potential tumor-suppressive effect. Additionally, exosomal miR-124 from bone marrow mesenchymal stromal cells (BMMSCs) enhances the PD-1 blocking therapy response and inhibits tumor growth in ovarian cancer immunotherapy (284). The study suggests a potential therapeutic method for enhancing immune checkpoint blockade therapy using exosomes from BMMSCs carrying miR-124 (284). Another study by Jin et al (285) found that polydatin modulates the miR-382/PD-L1 axis to suppress CRC cell growth and induce apoptosis. The study confirmed that miR-382 directly targets PD-L1 and that polydatin could inhibit PD-L1 expression by increasing miR-382. These results demonstrate the role of miRNAs in immune checkpoints in CRC preclinical studies.

In a clinical study, Jiang et al (286) discovered that miR-140-3p, a tumor suppressor in CRC, directly targets PD-L1 and inactivates the PI3K/AKT pathway, suggesting it is a potential target for CRC diagnosis and treatment. Overexpression of miR-140-3p inhibits proliferation, migration and invasion while inducing apoptosis in CRC cells. A different study by Chen et al (287) found that dexmedetomidine (DEX) partially increases miR-140-3p levels in RLE-6TN (alveolar epithelial) cells, which helps suppress PD-L1 expression. DEX also inactivates the JNK/Bnip3 pathway, which reduces inflammation and alveolar type II cell damage. Additionally, Chen et al (288) found that the expression of miR-93-5p decreases in CRC tissues while PD-L1 increases. The expression level of miR-93-5p was higher in patients with PD-L1-negative CRC than those with PD-L1-positive CRC. Furthermore, the study found that miR-93-5p targets PD-L1 to downregulate MMP1, MMP2 and MMP9, thereby inhibiting motility, invasion and immune evasion of CRC cells. An increase in miR-93-5p may lead to a decrease in PD-L1. In patients with breast cancer, miR-93-5p has been found to inhibit cell proliferation, migration and invasion as well as cell cycle progression (289). The study further found that miR-93-5p targets PD-L1/Cyclin D1 in breast cancer to control carcinogenesis and tumor immunity.

Multiple miRNAs have been demonstrated to target PD-L1 to prevent tumorigenesis (290-292). Nevertheless, non-coding RNAs such as LINC00460 (293) have been found to act as molecular sponges for miR-186-3p, promoting PD-L1 expression and facilitating tumorigenesis in CRC. Similarly, circular_0000052 (294) has been found to bind to miR-382-3p, thereby increasing PD-L1 expression and enhancing cell aggression in head and neck squamous cell carcinoma. Small RNAs such as piRNA, tsRNA and snoRNA may require further investigation to understand their role in other tumor immune checkpoints in CRC.

Immune checkpoint inhibitors (ICIs) can improve survival but may also cause immune-related adverse events (irAEs), such as irAE-colitis, which hinders the progression of immune checkpoint treatment (295,296). Blocking TNF-α and modifying the gut flora are useful approaches to combat this (296). A study by Grover et al (297) revealed that patients with pre-existing colitis receiving an ICI for a solid tumor developed enterocolitis. Anti-TNF medication was administered to a few patients. As a result, ICI therapy was stopped in all patients. The study suggests that ICIs may be effective in treating patients with cancer and IBD or microscopic colitis; however, patients should be continuously monitored for possible flare-ups of enterocolitis, and patients with pre-existing colitis should utilize the immune checkpoint combination with caution. Notably, Abu-Sbeih et al (298) also found that patients with preexisting IBD are more likely to experience severe gastrointestinal side effects when receiving ICIs. Thus, small RNAs that show increased expression upon anti-TNF treatment may be combined with ICIs to enhance outcomes in immunotherapy for IBD. For instance, co-administration of surrogate anti-CTLA-4 and anti-PD-1 monoclonal antibodies to mice improves transplantable cancer models but worsens autoimmune colitis (299). Notably, colitis is improved and antitumor activity is increased in mice treated concurrently with therapeutically accessible TNF inhibitors and combination CTLA-4 and PD-1 immunotherapy (299). Although this study did not investigate the role of miRNA, there is an inverse correlation between TNFα and miR-374a-5p (300). Increased expression of miR-374a-5p modulates macrophage-induced inflammation by inhibiting proinflammatory mediators and reducing the capacity of monocytes to migrate and activate T cells (300). Therefore, miRNAs that block TNF may be feasible in combination treatment with CTLA-4 and PD-1 inhibitors. Although particular miRNA regulation in IBD immunotherapy is limited, further studies are needed to explore their roles in IBD immunotherapy. Additionally, investigations on ICIs using other small RNAs should be conducted.