Association of innate defense proteins BPIFA1 and BPIFB1 with disease severity in COPD

Abstract

Chronic obstructive pulmonary disease (COPD) is characterized by an abnormal inflammatory response in the lungs caused by the inhalation of noxious particles and gases. The airway epithelium has a protective function against these harmful agents by maintaining a physical barrier and by secreting defensive proteins, such as bactericidal/permeability-increasing fold-containing (BPIF) proteins, BPIFA1 and BPIFB1. However, inconsistent data regarding BPIFA1 expression in smokers and COPD patients have been reported to date. Therefore, we investigated the expression of BPIFA1 and BPIFB1 in a large cohort of never-smokers and smokers with and without COPD, both on the messenger RNA (mRNA) level in lung tissue and on the protein level in airway epithelium. Furthermore, we examined the correlation between BPIFA1 and BPIFB1 levels, goblet cell hyperplasia, and lung function measurements. BPIFA1 and BPIFB1 mRNA expressions were significantly increased in stage III–IV COPD patients compared with stage II COPD patients and subjects without COPD. In addition, protein levels in COPD patients were significantly increased in comparison with subjects without COPD. BPIFA1 and BPIFB1 levels were inversely correlated with measurements of airflow limitation and positively correlated with goblet cell hyperplasia. In addition, by the use of immunofluorescence double staining, we demonstrated the expression of BPIFB1 in goblet cells. In conclusion, we show that BPIFA1 and BPIFB1 levels are elevated in COPD patients and correlate with disease severity.

Keywords:

• BPIFA1
• BPIFB1
• COPD

Supplementary materials

Figure S1 Correlation of BPIFA1 and BPIFB1 mRNA levels with different lung function parameters.

Notes: Spearman correlation analysis of BPIFA1 and BPIFB1 mRNA levels with post-bronchodilator values of FEV₁ (A, B), and the ratio of FEV₁ to FVC (FEV₁/FVC) (C, D), D_LCO (E, F), and the ratio of D_LCO to alveolar volume (K_CO) (G, H). R²= determination coefficient.

Abbreviations: BPIF protein, bactericidal/permeability-increasing fold-containing protein; D_LCO, diffusing capacity of the lung for carbon monoxide; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; K_CO, the ratio of D_LCO to alveolar volume.

Figure S2 Correlation of BPIFA1 and BPIFB1 protein levels with parameters of lung diffusion capacity.

Notes: Spearman correlation analysis of BPIFA1 and BPIFB1 protein levels with D_LCO (A, C) and K_CO (B, D). R²= determination coefficient.

Abbreviations: BPIF protein, bactericidal/permeability-increasing fold-containing protein; D_LCO, diffusing capacity of the lung for carbon monoxide; K_CO, the ratio of D_LCO to alveolar volume.

Table S1 General linear model for BPIFA1 mRNA expression

Table S2 General linear model for BPIFB1 mRNA expression

Table S3 General linear model for BPIFA1 protein expression

Table S4 General linear model for BPIFB1 protein expression

Acknowledgments

The authors would like to thank Greet Barbier, Indra De Borle, Katleen De Saedeleer, Anouck Goethals, Marie-Rose Mouton, and Ann Neesen from the Laboratory for Translational Research in Obstructive Pulmonary Diseases, Department of Respiratory Medicine (Ghent University Hospital, Ghent, Belgium), for their excellent technical assistance. They would also like to thank Prof Wim Janssens and Dr Stijn Verleden (Department of Pneumology, Leuven, Belgium) for providing the explant lungs of patients with severe COPD. The BPIFA1 and BPIFB1 antibodies were produced and validated using funding from the Wellcome Trust (076491/Z/05/Z). This research was supported by the Concerted Research Action of the Ghent University (BOF/GOA, 01G01009), by the Fund for Scientific Research in Flanders (FWO Vlaanderen, G.0195.09 and G.0194.10), and by the Interuniversity Attraction Poles program (IUAP, P7/30).

Author contributions

KRB, GGB, CDB, and LJMS conceived the project and designed the experiments; KRB, LJMS, FMV, and EGDS conducted the experiments; KRB, GGB, FMV, LJMS, BMV, and EGDS contributed to the data analysis and interpretation; LJMS and EGDS wrote the manuscript; and all authors contributed toward data analysis, drafting and revising the paper and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.