Exploration of key ferroptosis-related genes and immune infiltration in Crohn's disease using bioinformatics

Crohn's disease (CD) is a type of inflammatory bowel disease (IBD) that manifests mainly as chronic inflammation in different parts of the gastrointestinal tract, and its incidence has come to be increasing in recent years. Ferroptosis, a novel type of programmed cell death, it seems the role of ferroptosis-related biomarkers in CD has not been mentioned. Thus, the role of ferroptosis in CD and its relationship with immune infiltration were explored in this study. The CD dataset was downloaded from the Gene Expression Omnibus database. The validated ferroptosis genes (FRGs) were retrieved from the public FerrDb database. The gene expression matrix of the CD dataset was analyzed with the "limma" package in R language to obtain differentially expressed genes (DEGs) between diseased and healthy samples. Then, intersecting genes between DEGs and FRGs were identified as differentially expressed ferroptosis-associated genes (DE-FRGs). Protein-protein interaction (PPI) network analysis and visualization were carried out with STRING and Cytoscape, and key CD ferroptosis-related genes (CD-FRGs) were identified along with their Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways using the clusterProfiler package. Immune cell infiltration was analyzed with CIBERSORT. The correlation between key CD-FRGs and immune-infiltrated cells in CD was studied by Spearman's correlation method. A total of 37 DE-FRGs and 6 key CD-FRGs (CAV1, CD44, HIF1A, IFNG, TIMP1 and TLR4) were identified. GO and KEGG functional analysis indicated these genes enrichment in programmed cell death and apoptotic process, HIF-1 signaling pathway and IBD. Infiltration matrix analysis of immune cells showed abundant T cells CD4 memory activated, M1 macrophages, M2 macrophages, Mast cells activated and Neutrophils in CD intestinal tissues. The 6 key CD-FRGs were correlated with immune-infiltrated cells in CD based on correlation analysis. Taken together, immune cells with abnormal infiltration can be implicated in CD due to ferroptosis. This study identified 6 key CD-FRGs that may be key biomarkers of ferroptosis in CD; they include CAV1, CD44, HIF1A, IFNG, TIMP1 and TLR4. These findings suggest that the immune response is critical in CD caused by ferroptosis through the interaction between key CD-FRGs and immune infiltrating cells.