Fig 2: Effects of cigarette smoke extract (CSE) treatment on human bronchial epithelial cells (BEAS-2B), cell viability, and the expression of PRDX1 and CBR1. (A) Cell viability of BEAS-2B cells treated with varying concentrations of CSE (0–25%) for 6 h was measured by cell a counting Kit-8 (CCK-8) assay. (B,C) Quantitative real-time reverse transcription-PCR (qRT-PCR) analysis of PRDX1 (B) and CBR1 (C) mRNA levels after 6 h treatment with 5% cigarette smoke extract (CSE), using GAPDH as the internal control. (D,E) Immunofluorescence staining of PRDX1 (D) and CBR1 (E) showing cellular expression and localization. Left: 20× magnification; right: 40× magnification. (F,G) Quantification of single-cell fluorescence intensity from 6–10 randomly selected fields per group. (H,I) Western blot analysis of PRDX1 (H) and CBR1 (I) protein expression after 6 h CSE exposure. (J,K) Quantification of relative protein expression levels of PRDX1 (J) and CBR1 (K), normalized to β-actin. Data are presented as mean ± SEM. Scale bar = 50 μm. * p < 0.05; ** p < 0.01; *** p < 0.001, **** p < 0.0001; ns, not significant vs. control (Ctrl).

Fig 3: Clinical nomogram and drug screening analysis based on the LRG signatures. (A) A nomogram was developed using the expression levels of CBR1 and PRDX1 to evaluate individual risk for the development of COPD. (B) Strong agreement was observed between predicted and actual probabilities in the calibration curve. (C) Decision curve analysis (DCA) highlighted its clinical benefit over various risk thresholds. (D) The nomogram’s receiver operating characteristic (ROC) curve showed an area under the curve (AUC) of 0.926, indicating excellent diagnostic performance. (E) A potential drug–gene interaction network related to CBR1 and PRDX1. In the figure, purple hexagonal nodes represent the key genes (CBR1 and PRDX1), while green elliptical nodes indicate the corresponding transcription factors, miRNAs, or drug molecules. * p < 0.05; ** p < 0.01.

Fig 4: Functional enrichment and immune microenvironment analysis combined with LRG signatures in COPD. (A) Volcano plot of differential pathways identified by gene set variation analysis (GSVA) between the COPD and the control groups. Pathways upregulated in the COPD group are shown in red, while those downregulated are shown in blue. (B) Correlation analysis between CBR1 and PRDX1 and significantly enriched the KEGG pathways. Circle color indicates the direction of the correlation, with red representing positive and blue indicating negative correlations. Circle size reflects the strength of the correlation. (C,D) GSEA results for CBR1 and PRDX1 showing the top five significantly enriched signaling pathways for each gene. (E) Immune cell infiltration differences in the COPD and the control groups. (F) Heatmap of the correlation between gene expression (CBR1 and PRDX1) and immune infiltration, with red indicating positive and blue negative correlations. * p < 0.05; ** p < 0.01; *** p < 0.001; ns, not significant.