Identification of PCDH1 as a novel susceptibility gene for bronchial hyperresponsiveness

Abstract

Rationale: Asthma is a chronic inflammatory airway disease that affects more than 300 million individuals worldwide. Asthma is caused by interaction of genetic and environmental factors. Bronchial hyperresponsiveness (BHR) is a hallmark of asthma and results from increased sensitivity of the airways to physical or chemical stimulants. BHR and asthma are linked to chromosome 5q31-q33.

Objectives: To identify a gene for BHR on chromosome 5q31-q33.

Methods: In 200 Dutch families with asthma, linkage analysis and fine mapping were performed, and the Protocadherin 1 gene (PCDH1) was identified. PCDH1 was resequenced in 96 subjects from ethnically diverse populations to identify novel sequence variants. Subsequent replication studies were undertaken in seven populations from The Netherlands, the United Kingdom, and the United States, including two general population samples, two family samples, and three case-control samples. PCDH1 mRNA and protein expression was investigated using polymerase chain reaction, Western blotting, and immunohistochemistry.

Measurements and main results: In seven out of eight populations (n = 6,168) from The Netherlands, United Kingdom, and United States, PCHD1 gene variants were significantly associated with BHR (P values, 0.005-0.05) This association was present in both families with asthma and general populations. PCDH1 mRNA and protein were expressed in airway epithelial cells and in macrophages.

Conclusions: PCDH1 is a novel gene for BHR in adults and children. The identification of PCDH1 as a BHR susceptibility gene may suggest that a structural defect in the integrity of the airway epithelium, the first line of defense against inhaled substances, contributes to the development of BHR.

Figures

Figure 1.

Linkage disequilibrium (D′) and association of single nucleotide polymorphisms at chromosome 5q31-q33 and bronchial hyperresponsiveness in the Dutch family study.

Figure 2.

Longitudinal analysis of PCDH1 Ala750Ala in the general Dutch population. Hazard function of developing bronchial hyperresponsiveness (BHR) in the general Dutch population of Vlagtwedde-Vlaardingen over time. PCDH1 CT or TT carriers are at increased risk of becoming hyperresponsive over time compared with PCDH1 Ala750Ala CC homozygotes (P = 0.05).

Figure 3.

mRNA expression of PCDH1 in various tissues and cells. GAPDH = glyceraldehyde 3 phosphate dehydrogenase; PBMC = peripheral blood mononuclear cell.

Figure 4.

Western blot of epithelial cell line 16 HBE, and primary epithelial cell culture of a patient with asthma using a monoclonal and a different polyclonal antibody. Upper lane, PCDH1, lower lane, β-actin. One experiment of n = 4 is shown. Protein expression was identified using two different antibodies, a monoclonal (Abnova, Taiwan) (left panel) and a polyclonal antibody (Eurogentec, Liege, Belgium) (middle panel). The signal of the polyclonal antibody was blocked by preincubation with peptide (right panel).

Figure 5.

Protein expression of PCDH1 in airway epithelial cells and macrophages on (A, B) lung, and (C) airway wall biopsy of patient with asthma. Expression is observed (A, C) at the apical part of airway epithelial cells, and (B) in macrophages.

Figure 5.

Protein expression of PCDH1 in airway epithelial cells and macrophages on (A, B) lung, and (C) airway wall biopsy of patient with asthma. Expression is observed (A, C) at the apical part of airway epithelial cells, and (B) in macrophages.

Figure 5.

Protein expression of PCDH1 in airway epithelial cells and macrophages on (A, B) lung, and (C) airway wall biopsy of patient with asthma. Expression is observed (A, C) at the apical part of airway epithelial cells, and (B) in macrophages.