IBD is a group of chronic non-specific diseases with an unknown cause. IBD affects at least 6.8 million people worldwide, and its inflammatory response involves the intestines but causes systemic inflammatory reactions(13).AS development is closely associated with chronic inflammation according to recent observations (14). The risk of developing atherosclerotic cardiovascular disease in IBD patients has been reported to be significantly higher than in healthy adults(15). In addition, clinical evidence indicates that the risk of acute coronary syndrome significantly increases in IBD patients(16). The immune response, inflammatory reaction, endothelial dysfunction, and changes in intestinal flora are possible mechanisms for the development of AS in IBD patients. However, there seems to be little research on the pathogenesis of AS in IBD patients at the genetic level.
Our study results suggest that the CDEGs were enriched in KEGG pathways such as “Tuberculosis”, “Lipid and Atherosclerosis”, “Osteoclast Differentiation”, “Platelet Activation”, “FcεRI Signaling Pathway”, “B Cell Receptor Signaling Pathway”, and “Asthma”. Tuberculosis is related to immune response and is known to be associated with elevated serum IgG levels. Asthma is associated with elevated IgE levels. The development of B cells relies on the potency of the signaling of the B cell receptor. B cell differentiation is driven by B cell receptor signaling throughout all stages of B cell development and is associated with B cell autoreactivity upon recognition of self-antigens(17). Previous studies have reported that increased genetic risk for autoimmunity is associated with enhanced B cell receptor signaling(18, 19). Takahiro et al. demonstrated that CD40L/B Tg mice spontaneously develop colitis at 8–15 weeks of age, suggesting that the pathogenesis of IBD may be primarily established by a B cell-triggered mechanism(20). Strong BCR signaling in transitional B cells leads to the development of follicular (FO) B cells, which support Th1 responses and the production of pro-inflammatory cytokines(21). Moreover, upon the stimulation of Tfh cells, FO B cells transform into the germinal center(GC) B cells which are involved in the creation of GC(22). GC B cell proliferation and affinity maturation lead to increased production of IgG and IgE(23). It has been demonstrated in several studies that FO B cells contribute to the promotion of AS primarily through the production of IgG and activation of Th1 cells(24). The FcεRI signaling pathway is related to the development of AS and regulates allergic reactions(25). Activated mast cells through IgE antigen complex cross-linking FcεRI can release and secrete histamine, chemokines, platelet-activating factor, lipid mediators, and proteoglycans, causing inflammation(26). The analysis of immune infiltration also indicated that AS has a greater proportion of memory B cells and mast cells that are activated..
Through the PPI network and machine learning, we screened 3 hub genes (LCP2, MMP9, NCF2) with high diagnostic values and obtained reliable validation in external datasets. Lymphocyte cytosolic protein (LCP2) is capable of regulating T cell receptor signaling in stimulated T lymphocytes and is intimately associated with the progression of IBD(27). Although bioinformatics studies have reported that LCP2 expression is closely related to AS, there is still a lack of experimental research to prove this association(28–30). One possible explanation is that LCP2 is a target gene of STAT1. Upon activation by IFN-γ, STAT1 translocates to the nucleus and interacts with the enhancers of LCP2 and TNFAIP2.EP300 collaborates with p-STAT1 to enhance H3K27ac levels on the enhancer, leading to the transcription of LCP2 and TNFAIP2 and ultimately facilitating the progression of chronic inflammation (31). The intestinal barrier is remodeled by a significant group of enzymes called matrix metalloproteinases (MMPs) that can break down extracellular matrix (ECM) and basement membrane components(32). In the intestines of IBD patients, bacteria or their products trigger the epithelial layer to release large amounts of chemokine (CXCCL8) to mediate neutrophil migration and produce large amounts of MMP9(33). S Arihiro et al. reported that MMP9 was highly expressed in activated fibroblasts and vascular smooth muscle cells in IBD patients and participated in biological processes such as angiogenesis, remodeling, and inflammation(34). In the MMP-9 transgenic (Tg) rabbits model, increased sensitivity to cholesterol diet-induced AS was observed, and vascular wall calcification was more likely to occur compared to the wild type(35). Neutrophil cytoplasmic factor 2 (NCF2) is a subunit of NADPH oxidase that produces superoxide as a major source of reactive oxygen species (ROS)(36, 37). Missense mutations in NCF2 have been reported to be closely related to the development of IBD, and potential destructive mistranslation mutations in NCF2 are associated with reduced neutrophil ROS production and reduced bacterial killing(38). In CD patients with low ROS production, co-enhancement of hypoxia-inducible factor 1, TNF, NF-κB, and TNF signaling was observed, and glucose energy utilization was more dependent on fatty acid metabolism because of glucose energy utilization disorder, leading to AS development(39). Consistent with our nomogram results, NCF2 acts as a protective factor. Notably, univariate regression analysis indicated that an increase in the expression of NCF2 was a risk factor for AS. We speculate that NCF2 may be secondarily elevated after the illness. Furthermore, ssGSEA analysis of hub genes in the IBD dataset revealed that hub genes were significantly positively correlated with “APOPTOSIS”, “IL2_STAT5_SIGNALING”, “IL6_JAK_STAT3_SIGNALING”, “HYPOXIA”, “INFLAMMATORY_RESPONSE”. The immune infiltration analysis revealed that hub genes were significantly positively correlated with MO macrophages, γ-δT cells, regulatory T cells, and activated mast cells, supporting the reliability of the aforementioned views.
In summary, we believe that IBD patients have high sensitivity and that the B cell receptor signaling pathway is up-regulated. Reducing the production of excessive B cells promotes the differentiation of B cells into FO B cells, mediating Th1 responses and the production of pro-inflammatory cytokines, which is related to the development of AS. Furthermore, the B cell receptor signaling pathway is also closely related to the secretion of IgG and IgE. IgG and IgE activate the FcεRI signaling pathway; subsequently, activated mast cells release and secrete histamine, chemokines, platelet-activating factor, lipid mediators, and proteoglycans, causing inflammation and leading to the development of AS. LCP2, MMP9, and NCF2 may play a central role in the aforementioned mechanisms.
Furthermore, we performed a co-clustering analysis to identify two subtypes of AS. Subtype B exhibited a significantly greater expression of hub genes compared to subtype A.Subtype B exhibited a significantly greater percentage of activated mast cells, γ-δT cells, and M0 macrophages compared to subtype A.. Most immune checkpoint genes were also highly expressed in subtype B, suggesting that subtype B patients have a higher correlation with immune infiltration and are more likely to benefit from immunotherapy. This finding provides direction for future precision medicine treatment.
Limitation
The co-expressed differential genes obtained in our study are derived from the intersection of two diseases. Although the reliability of the analysis results has been validated in external datasets, it should be verified by differential genes in patients with IBD complicated by AS. The diversity of sample types can cause bias, but we standardized the samples to minimize errors. Additionally, while this study lacks validation of AS hub gene expression levels through clinical specimens or animal models, the high expression of hub genes has been validated in multiple datasets, ensuring the reliability of the analysis results to the greatest extent.