IPF is a chronic progressive lung disease that affects 3 million individuals worldwide[13]. Oxidative stress, caused by the imbalance between the oxidants and antioxidants, and immune infiltration are important factors in the occurrence and progression of IPF[14–15]. N-acetylcysteine (NAC), which is a representative of antioxidant, could slow the deterioration of the vital capacity and diffusing capacity of the lung for carbon monoxide (DLCO) in patients with IPF[16]. Furthermore, a study found that NAC supplementation could delay the progression of pulmonary fibrosis by scavenging reactive oxygen species (ROS)[17]. Hence, antioxidant therapy is a crucial treatment option for IPF.
The aim of this study was to identify the hub DEOSRGs of IPF. Firstly, 4 mRNA datasets (GSE10667, GSE32537, GSE110147, and GSE213001) were analyzed, and a total of 238 common DEGs were found in the IPF samples, including 134 common upregulated genes and 104 common downregulated genes. The KEGG analysis results showed that these common DEGs principally involved in ECM-receptor interaction, Protein digestion and absorption, PI3K-Akt signaling pathway and Cell adhesion molecules. Next, we identified 4 hub DEOSRGs (ENC1, EPHA3, FMO1, and GPX8) by the intersection of the common DEGs, oxidative stress related genes from GeneCard database and module genes from WGCNA, and the utilization of the LASSO analysis and SVM-RFE algorithms.
ENC1, a negative regulator of nuclear factor erythroid 2-related factor 2 (Nrf2), is principally produced in the nervous system[18–19]. ENC1 expression was upregulated in endometrial cancer (EC) tissues or EC cell lines, and might be connected with immune infiltration in EC[20]. In addition, ENC1 might contribute to enhancing radio-resistance in breast carcinoma cells by regulating the Hippo/YAP1/TAZ pathway and the expression levels of Gli1, CTGF and FGF1[21]. In this study, we revealed that ENC1 was highly expressed in the lung tissues of IPF patients, and had a diagnostic accuracy value based on GSE24206 and GSE53845 datasets. The AUC was 0.980(95% CI 0.912–1.000) for GSE24206 and 0.944(95% CI 0.844–1.000) for GSE53845.
EPHA3, which belongs to the Eph family of receptor tyrosine kinases, is highly expressed in numerous tumors[22]. For instance, EPHA3, which was dramatically upregulated in the prostate cancer samples, might be involved in the development of prostate cancer[23]. Toyama et al.[24] found that the epidermal growth factor could promote EPHA3 production, and lead to the formation of glioblastoma cell aggregates. Xi et al.[25] revealed that EPHA3 was highly expressed in gastric cancer, and was dramatically related to the Tumor-Node-Metastasis (TNM) stage and poor prognosis of gastric cancer. In our study, we found that the EPHA3 expression level was higher in IPF patients, and had excellent diagnostic efficacy, with an AUC of 0.902(95% CI, 0.676 − 1.000) and 0.969(95% CI 0.903–1.000) for IPF in the GSE24206 and GSE53845 datasets, respectively.
FMO1, a member of the flavin-containing monooxygenases (FMOs) gene family, is a drug-oxygenating enzymes in humans[26]. Gong et al.[27] demonstrated that increased FMO1 expression level was observed in patients with gastric cancer, and typically connected with disease-free-survival (DFS), overall survival (OS), and immune score of gastric cancer. Our study suggested that FMO1 was highly expressed in the lung tissues of IPF patients, and had a high diagnostic value in the two external datasets (GSE24206 and GSE53845).
GPX8, a member of the glutathione peroxidase (GPX) family, can regulate cell proliferation, cell migration, tumorigenesis development, and oxidative stress. Yin et al.[28] revealed that GPX8 was highly expressed in both esophageal squamous cell carcinoma (ESCC) cell lines and tumor tissues, and could promote the proliferation of ESCC cells by regulating the IRE1/JNK pathway. Zhang et al.[29] suggested that GPX8 could promote the migration and invasion of lung cancer cell lines. In addition, a study found that GPX8 knockout could delay the initiation of breast cancer and inhibit its growth rate in mice[30]. However, another study found that GPX8, a regulator of redox homoeostasis, could inhibit the activation of endoplasmic reticulum (ER) stress and cell apoptosis induced by oxidative stress[31]. Our study showed that GPX8 expression level increased in patients with IPF, and that GPX8 might be a diagnostic marker of IPF. Therefore, more experiments are required to confirm the role of GPX8 in IPF.
In our research, “CIBERSORT” package was utilized to explore the level of immune cell infiltration in the lung tissue of IPF patients. Our results indicated that an increased permeability of B cells memory, Plasma cells, T cells CD4 memory activated, T cells regulatory (Tregs), T cells gamma delta, Dendritic cells resting, and Mast cells resting might be connected with the pathogenesis of IPF. Previous research has revealed that innate and adaptive immune mechanisms are strongly connected with the pathogenesis of IPF[32]. Lymphocyte aggregates, which was mainly consisted of T lymphocytes and B lymphocytes, were abundant in the lungs of IPF patients[33]. In the sheep model of bleomycin-induced pulmonary fibrosis, the levels of T-cell and B-cell infiltration were markedly increased[34]. A previous study showed that mast cells were dramatically elevated in the lungs of IPF patients, and positively correlated with the number of fibroblast foci[35]. In vitro, mast cells could promote fibroblast proliferation and activation[35]. Moreover, our study revealed that ENC1, EPHA3, and FMO1 were positively correlated with T cells CD4 memory activated, that GPX8 was positively correlated with Plasma cells. We also found that EPHA3, FMO1, and GPX8 were negatively correlated with Monocytes, and that ENC1 was negatively correlated with Neutrophils.
Our study has several limitations. We identified 4 hub DEOSRGs (ENC1, EPHA3, FMO1, and GPX8) on the basis of the public database, and verified their expression levels in patients with IPF. But further animal and cell experiments are needed to elucidate the roles of ENC1, EPHA3, FMO1, and GPX8 in the pathogenesis of IPF. In addition, clinical trials with larger sample sizes are needed to examine the relationships of ENC1, EPHA3, FMO1, and GPX8 with IPF.
In conclusion, by combining a bioinformatics analysis and two machine learning algorithms, we revealed that ENC1, EPHA3, FMO1, and GPX8 might be considered novel targets for the diagnosis and treatment of IPF.