The SERPINE2 gene is associated with chronic obstructive pulmonary disease

Abstract

Chronic obstructive pulmonary disease (COPD) is a complex human disease likely influenced by multiple genes, cigarette smoking, and gene-by-smoking interactions, but only severe alpha 1-antitrypsin deficiency is a proven genetic risk factor for COPD. Prior linkage analyses in the Boston Early-Onset COPD Study have demonstrated significant linkage to a key intermediate phenotype of COPD on chromosome 2q. We integrated results from murine lung development and human COPD gene-expression microarray studies with human COPD linkage results on chromosome 2q to prioritize candidate-gene selection, thus identifying SERPINE2 as a positional candidate susceptibility gene for COPD. Immunohistochemistry demonstrated expression of serpine2 protein in mouse and human adult lung tissue. In family-based association testing of 127 severe, early-onset COPD pedigrees from the Boston Early-Onset COPD Study, we observed significant association with COPD phenotypes and 18 single-nucleotide polymorphisms (SNPs) in the SERPINE2 gene. Association of five of these SNPs with COPD was replicated in a case-control analysis, with cases from the National Emphysema Treatment Trial and controls from the Normative Aging Study. Family-based and case-control haplotype analyses supported similar regions of association within the SERPINE2 gene. When significantly associated SNPs in these haplotypic regions were included as covariates in linkage models, LOD score attenuation was observed most markedly in a smokers-only linkage model (LOD 4.41, attenuated to 1.74). After the integration of murine and human microarray data to inform candidate-gene selection, we observed significant family-based association and independent replication of association in a case-control study, suggesting that SERPINE2 is a COPD-susceptibility gene and is likely influenced by gene-by-smoking interaction.

Figure 1

Gene expression during normal murine lung development. We assessed the expression of genes within the chromosome 2–linked locus, using a microarray data set of normal mouse lung development. Shown are the expression profiles for 25 probe sets, representing 23 mouse orthologues for human genes present within the locus. Signal intensities were determined using MAS 4.0. Most genes were expressed at low levels in the lung (signal intensity <4,000); seven genes were expressed at a signal intensity >4,000. Three of these genes were expressed at a signal intensity >15,000 during at least one time point, including RPL37A (a ribosomal protein), ITM2C (an integral membrane protein highly expressed in brain), and SERPINE2. E = embryonic day; P = postnatal day; AD = adult.

Figure 2

SERPINE2 localization in normal adult mouse lung. Immunohistochemistry for SERPINE2 in the normal adult mouse lung was performed using a rabbit polyclonal antibody (PN1). Staining was evident in small airway (AW)–conducting epithelium (EPI) and in the vascular (V) adventitia in an extracellular matrix-associated (ECM) pattern. No staining was observed for control IgG.

Figure 3

SERPINE2 localization in human lung. SERPINE2 immunostaining was observed in normal (A), emphysematous (C), and asthmatic (D) human lung. Staining was evident in small airway epithelial cells (EPI) and in the vascular adventitia extracellular matrix (ECM). No staining was observed for control IgG (B).

Figure 4

Simulated P values for sliding-window haplotype analysis of SNPs in the NETT cases and NAS controls. Graphs of the 6-, 4-, and 2-SNP sliding window–simulated P values (Y-axis) against the midpoint SNP of each sliding window (X-axis), demonstrate the most significant global simulated P value for 2-SNP sliding-window haplotypes in the regions including SNPs rs7579646-rs840088 (P=.02), rs840088-rs7562213 (P=.01), rs7562213-rs920251 (P=.01), rs920251-rs1371029 (P=.02), rs7581619-rs3795877 (P=.02), rs3795877-rs1866153 (P=.04), rs1866153-rs6747096 (P=.004), rs6747096-rs3795879 (P=.02), rs3795879-ss49785624 (P=.02), ss49785624-rs6715768 (P=.02), and rs6715768-rs6738983 (P=.02).