Unlike other types of cell death, ferroptosis was discovered in 2012, a new type of iron-dependent programmed cell death. Recent studies have shown that the relationship between ferroptosis and cancer is complex and that ferroptosis may represent a new approach to cancer diagnosis and treatment[26]. The sensitivity and specificity of the gastric cancer diagnostic system composed of five ferroptosis-related genes were 88.52% and 93.27%, respectively, and the AUC value of the diagnostic model even reached 0.9450[17]. It shows that the model has high diagnostic efficiency and can be used for clinical diagnosis promotion and application. However, no diagnostic model of ferroptosis-related genes has been reported in CRC.
In this study, we screened the GSE14297 dataset using the GEO database. Further differential analysis and the intersection of ferroptosis genes resulted in 63 ferroptosis-related genes. This indicates that ferroptosis-related genes are involved and regulated in the occurrence of CRC. In vitro and in vivo experiments have shown that SIRT6 can promote ferroptosis and attenuate glycolysis in pancreatic cancer by inhibiting the NF-κB pathway[27]. Similarly, in pancreatic cancer, Zhang et al. demonstrated that TST promotes intracellular iron overload and accumulation of reactive oxygen species through STAT3/GPX4 signaling on the one hand; Overexpression of dialdehyde further reduces the viability of pancreatic cancer cell lines, thereby exerting antitumor effects[28]. In this study, we screened 15 hub gene modules (IL6, PTGS2, NOX4, GPX4, NFE2L2, GPX2, NQO1, SIRT1, GCLC, DUOX2, CAV1, SLC2A1, CD44, PRDX1, and CA9) using MCODE. In the next step, ROC curve analysis was performed, and the results showed that the diagnostic performance of the 15 hub gene modules was very good, whether it was single or combined. The results suggest that ferroptosis-related genes can be used as biomarkers for the early diagnosis of CRC. IL-6 is a ferroptosis inhibitor secreted by immune cells or tumor cells and can promote cancer proliferation and differentiation through the transcription activator 3 pathway[29, 30]. It has been reported that in head and neck squamous cell carcinoma, ferroptosis and growth inhibition induced by xCT knockdown or the ferroptosis inducer elastin can be reversed by IL-6, thereby promoting tumorigenesis and progression[31]. In cervical cancer, the PTGS2 low expression group has stronger immune activity and higher tumor mutation burden, which is considered to be a risk factor for cervical cancer[32]. Xiao et al. demonstrated that NOX4 expression was up-regulated in gastric adenocarcinoma tissue compared with normal gastric mucosal tissue, which can serve as an effective therapeutic target and biomarker for gastric adenocarcinoma[33]. In lung and breast cancer cells, red ginseng polysaccharides exhibit anticancer activity by downregulating GPX4-induced ferroptosis[34]. The in vitro and in vivo models established by Luo et al. confirmed that LINC01564 promotes drug resistance in glioma cells by upregulating NFE2L2 expression and inhibiting ferroptosis[35]. It shows that NFE2L2 is also a risk factor in glioma. Zhu et al. combined bioinformatics and immunohistochemical analysis to confirm that CA9 is highly expressed in tongue cancer tissues, but not in adjacent tissues[36], which is promising as an effective marker for the early diagnosis of tongue cancer. A network pharmacology analysis showed that GSH could regulate the ferroptosis pathway by targeting 15 core targets including CA9 to achieve the purpose of treating oral cancer[37]. However, the roles of the above 15 hub genes in CRC have not been reported yet.
To better understand the biological characteristics of these hub gene modules, we performed GO and KEGG pathway analysis. The results show that the main BPs of these hub gene modules include response to oxidative stress, cellular response to a toxic substance, response to oxygen-containing compound, response to endogenous stimulus, and response to stress. Major CCs include the endomembrane system, cytosol, plasma membrane region, and plasma membrane part. Major MFs include oxidoreductase activity, identity protein binding, antioxidant activity, and peroxidase activity. A large body of evidence indicates that oxidative stress is closely related to the development and progression of CRC. Higher levels of ROS production are shown in chronic diseases of the gastrointestinal tract, such as Crohn's disease, for which oxidative stress is considered a potential cause[38]. Oxidative stress is also a hallmark feature of chronic inflammatory bowel disease such as ulcerative colitis, and if untreated, the disease can progress to colorectal cancer[39]. KEGG pathway analysis showed that the main enrichment pathways of the hub gene module included Metabolic pathways, Pathways in cancer, Ferroptosis, and Glutathione metabolism. It indicates that 15 hub genes play a role in the ferroptosis pathway, and regulate tumor progression by promoting or inhibiting the ferroptosis process. The specific mechanism of action, we will continue to explore in the follow-up research.
As the largest ecosystem in the human body, the role of the gut microbiome has attracted more and more attention. Gut microbes have been reported to induce chronic inflammatory damage and oxidative stress in normal tissues, ultimately leading to the development of intestinal tumors[40, 41]. As previously mentioned, 15 hub gene modules can be involved in CRC progression through oxidative stress. In this process, are there interactions or regulatory mechanisms between hub genes and gut microbes involved in CRC progression? To solve this puzzle, we collected 30 CRC patients and 30 healthy controls for 16S rDNA and metabolome analysis. The results show that the main enrichment pathways of differential metabolites include Neuroactive ligand-receptor interaction, ABC transporters, Aminoacy-tRNA biosynthesis, Cocaine addiction, Central carbon metabolism in cancer, induction Processing, Phenylalanine metabolism and Biosynthesis of amino acids, etc. Analysis based on metaboanalyst5.0 showed that 25 differential metabolites were associated with ferroptosis-related genes.
Studies have confirmed that bile acid metabolism, amino acid metabolism, and short-chain fatty acid metabolism involving gut microbes are also considered to be related to the occurrence and metastasis of CRC[42]. The study of ferroptosis and the above-enriched pathways has been reported in other diseases. For example, in the study of hypertension, Zhang et al. found that EUO-TT drugs may act on proteins related to the neuroactive ligand-receptor interaction pathway to regulate ferroptosis in vascular neuronal cells[43]. In liver cancer, there is evidence that ABCB6 may be involved in regulating cancer progression by regulating ferroptosis. In studies of cocaine addiction, prolonged exposure to psychostimulants, including cocaine, has been found to increase brain iron levels[44]. Therefore, we have reason to speculate that in colorectal cancer, ferroptosis-related genes and gut microbes may jointly participate in cancer progression. Next, we will establish an in vitro animal model to deeply study the molecular mechanism of ferroptosis-related genes and gut microbes jointly participating in CRC progression.