Crohn's disease has a multifactorial etiology, involving various factors such as genetic family history, the microbiome, and environmental factors. Currently, there is limited research on the association between Crohn's disease and metabolism. Literature reviews indicate that the human host's intestinal microbiota, particularly bacteria and archaea, play a significant role in human metabolism (Fan and Pedersen 2021). There are some studies reporting a close correlation between changes in the gut microbiota and autoimmune responses (De Luca and Shoenfeld 2019). Dysbiosis of the gut microbiome has been observed in many studies on autoimmune diseases (López et al. 2016). Crohn's disease, being an autoimmune disorder, is intricately linked to the gut microbiota. Therefore, we conducted an in-depth investigation into the metabolic processes associated with Crohn's disease. CD and normal samples were collected from the GEO database. Through GSVA and WGCNA analysis, we identified hub genes. Subsequently, we conducted immune infiltration and functional enrichment analysis on these genes. After screening using machine learning methods, we finally obtained four feature genes and established a predictive model for Crohn's disease. GO and KEGG results indicate that hub genes are associated with extracellular matrix structural constituent, focal adhesion, and ECM-receptor interaction. Crohn's disease is a chronic inflammation. Long-term stimulation of the intestine leads to the release of a large number of inflammatory mediators, which stimulate the activation of fibroblasts and aggregation at the injured site.
Some reports has shown that ACTN1 is associated with the effectiveness of anti-tumor necrosis factor (TNF) therapy, where higher expression of ACTN1 is correlated with better treatment outcomes (Iacucci et al. 2023). Matrix metalloproteinases (MMPs) constitute a family of zinc-dependent extracellular matrix remodeling endopeptidases (Cabral-Pacheco et al. 2020), capable of collectively degrading all components of the extracellular matrix at neutral pH (Ravi et al. 2007). Early studies have found upregulation of MMPs (MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, MMP-12, and MT1-MMP-1) in various colitis animal models and IBD patients (Baugh et al. 1999). MMPs levels are directly associated with disease activity (von Lampe et al. 2000). MMP-2 is expressed in the normal colon, mainly in epithelial cells and the lamina propria. In IBD patients, MMP-2 is highly upregulated and localized to fibroblasts/myofibroblasts around the epithelium and crypts, mononuclear cells (macrophages and lymphocytes), epithelial cells, and vascular endothelial cells (Kirkegaard et al. 2004). MMP-2 is typically involved in regulating physiological processes such as barrier and mucosal defense (Baugh et al. 1999). Studies have shown a significant increase in MMP2 expression in CD, which may contribute to impaired intestinal barrier function by increasing FITC glucose translocation, thus exacerbating the disease (Brazil et al. 2013). THY1 initially considered a thymocyte marker, has diverse biological functions, including tumor suppression, regulation of adipogenesis, cell-cell and cell-matrix adhesion, cell migration, cell differentiation, and T cell activation. Research has reported its upregulation in active Crohn's disease (Arijs et al. 2011), which may be linked to the pathogenesis of CD. Currently, there are few reports on ZCCHC24. Some literature associates it with smoking (Markunas et al. 2021) and alternative splicing (Cieply et al. 2016). There is no report on ZCCHC24 in Crohn's disease, so further exploration is needed to determine whether ZCCHC24 is a potential target gene in CD.
Crohn's disease is an autoimmune disorder, and its pathogenesis is closely related to innate immunity. Innate immune responses constitute the first line of defense against diseases in humans, involving various cells such as immune cells (neutrophils, monocytes, macrophages, and dendritic cells) and non-immune cells (epithelial cells, endothelial cells, and mesenchymal cells) (Brazil et al. 2013). In the context of IBD, neutrophils are the first immune cells to infiltrate the intestinal mucosa, and as long as active inflammation, these white blood cells persist throughout the entire IBD process. Neutrophils contribute to the onset and progression of IBD through various mechanisms, including compromised epithelial barrier function, tissue damage caused by oxidative stress and protein hydrolysis, and the sustained presence of inflammation through the release of various inflammatory mediators (de Souza and Fiocchi 2016).
In comparison to normal tissue, dendritic cells in the intestinal mucosa of CD are in an activated state (Hart et al. 2005), consistent with the results of our immune infiltration analysis. Our four feature genes are positively correlated with the activation of neutrophils and dendritic cells. It is speculated that these four feature genes may participate in the innate immunity of CD by regulating neutrophils or dendritic cells, contributing to the onset and development of CD. The products secreted by immune cells, such as cytokines and chemokines, play a significant role in initiating, mediating, and sustaining inflammation and tissue damage (Neurath 2014b). In Crohn's disease, dendritic cells produce IL-12 and IL-6, mediating immune responses (Neurath 2014a). Elevated levels of IL-8 have been observed in patients with inflammatory bowel disease (Mahida et al. 1992), consistent with our research findings. The results of GSEA enrichment analysis in this study indicate that characteristic genes are associated with pathways regulating chemokines and cytokines.
Crohn's disease is not only characterized by complex pathological mechanisms but also imposes long-term challenges for patients. One-third of patients require multiple surgeries, and approximately 14% of severe cases, especially those with rectal involvement, may require permanent ostomy, leading to various serious complications (Cosnes et al. 2012). With the development of tumor necrosis factor inhibitors, the treatment landscape of CD has evolved beyond conventional approaches. Although these drugs exhibit long-term efficacy, some patients do not respond to them or cannot sustain the treatment. Therefore, through bioinformatic analysis, we have identified metabolism-related feature genes and conducted molecular docking analysis to clarify the interaction targets of drugs and characteristic genes, providing new avenues for clinical treatment.