BPIFB4 rs4339026 A > G polymorphism impacts COPD susceptibility in the Kashi population, China

Abstract

The etiology of chronic obstructive pulmonary disease (COPD) is multifaceted. This study aims to explore the association between the bactericidal/permeability-increasing bold-containing family B member 4 (BPIFB4) rs4339026 A > G (NC_000,020.11: g.33083793 A > G) polymorphism and COPD susceptibility in Kashi population, and investigate the potential role of BPIFB4 in COPD. A total of 541 unrelated COPD patients and 534 healthy controls were enrolled from the First People's Hospital and Kashi village. The association between rs4339026 A > G polymorphism and COPD risk were assessed by multivariable logistic regression. BPIFB4 expression and associated pathways were analyzed through bioinformatics approaches using human peripheral blood and bronchoalveolar lavage fluid (BALF) datasets from the GEO database (GSE13896 and GSE42057). Experimental validation was performed in a cigarette smoke (CS)-induced COPD mouse model. BPIFB4 rs4339026 G/G genotype was associated with significantly increased COPD risk across all genetic models: genotype model [adjusted odds ratios (aOR) = 2.52, corresponding 95% confidence interval (95% CI): 1.34-4.71], recessive model (aOR = 2.32, 95% CI: 1.25-4.31), dominant model (aOR = 1.39, 95% CI: 1.07-1.81), allele model (aOR = 1.42, 95% CI: 1.13-1.77), and additive model (aOR = 1.40, 95% CI: 1.12-1.75). Stratified analysis based on smoking status revealed that BPIFB4 rs4339026 G/G genotype was also associated with an increased risk of COPD, regardless of smoking status. However, the risk was more pronounced in smokers compared to non-smokers, as evidenced by the dominant model (aOR = 2.52, 95% CI: 1.23-5.15), additive model (aOR = 2.61, 95% CI: 1.37-4.97), and allele model (aOR = 2.68, 95% CI: 1.41-5.08). In non-smokers, the association remained significant, with the genotype model (aOR = 1.99, 95% CI: 1.03-3.85), additive model (aOR = 1.28, 95% CI: 1.01-1.62), and allele model (aOR = 1.29, 95% CI: 1.01-1.64). The bioinformatics analysis demonstrated a decrease in BPIFB4 expression in peripheral blood and BALF of COPD patients, with pathway enrichment analysis implicating PI3K/AKT signaling. Consistently, COPD mice exhibited significant BPIFB4 downregulation (P < 0.0001), accompanied by upregulation of PI3K, p-PI3K, and p-AKT was upregulated (P < 0.001 vs. controls). We confirmed that BPIFB4 rs4339026 A > G increased the risk of COPD. BPIFB4 might contribute to COPD pathogenesis through the PI3K/AKT pathway.

Keywords: BPIFB4; COPD; Gene polymorphisms; Susceptibility; rs4339026 A > G.

Fig. 1

Analysis of genotypes of BPIFB4 rs4339026 A > G. (a) Case-control study of BPIFB4 rs4339026 A > G. 541 COPD patients in case group, and 533 healthy people in control group. The call rate for rs4339026 of BPIFB4 was 99.91% (1,074/1,075). ^a Logistic regression: Corrected for sex, age, BMI, smoking status, FEV₁% and FEV₁/FVC. *P < 0.05, **P < 0.01. (b) Stratified analysis of smokers in the case–control study. ^b Logistic regression: Corrected for sex, age, BMI, FEV₁% and FEV₁/FVC. *P < 0.05, **P < 0.01. (c) Stratified analysis of non-smokers in the case–control study. ^b Logistic regression: Corrected for sex, age, BMI, FEV₁% and FEV₁/FVC. *P < 0.05, **P < 0.01. OR Odds Ratio, 95%CI 95% confidence interval, NA Not Available.

Fig. 2

Results of bioinformatics analysis for BPIFB4. (a) BPIFB4 expression in human peripheral blood. (b) BPIFB4 expression in human BALF. The horizontal axis represented different groups, and the vertical axis represented BPIFB4 expression. The upper left corner represented the statistical test method used to assess significance. *P < 0.05, **P < 0.01. (c) Venn diagram of overlapping proteins associated with both BPIFB4 and COPD. (d) PPI network of overlapping proteins. Circles represented nodes (proteins), and straight lines indicated protein-protein interactions. The size of each node was positively correlated with its degree (the more connections a node had, the higher its degree and the larger its size). The node color was also positively correlated with its degree (the redder the node, the greater its degree; the greener the node, the smaller its degree). (e, f) BPIFB4 participated in key pathways and functional classification in COPD. CC represented cell component, MF represented molecular function, BP represented biological process.

Fig. 3

Expression of BPIFB4 and key proteins in the PI3K/AKT pathway in COPD mice. (a) Illustration for COPD mouse models. (b, c) Western blot analysis of BPIFB4 (n = 10/group), PI3K, p-PI3K, AKT1, and p-AKT1 (n = 3/group) in the lung tissues of COPD mice and controls. (d) BPIFB4 mRNA expression assessed by RT-qPCR (n = 10/group). (e, f) Statistical significance: ns represented not significant, ***P < 0.001, and ****P < 0.0001, versus controls.