Susceptibility to chronic mucus hypersecretion, a genome wide association study

Background: Chronic mucus hypersecretion (CMH) is associated with an increased frequency of respiratory infections, excess lung function decline, and increased hospitalisation and mortality rates in the general population. It is associated with smoking, but it is unknown why only a minority of smokers develops CMH. A plausible explanation for this phenomenon is a predisposing genetic constitution. Therefore, we performed a genome wide association (GWA) study of CMH in Caucasian populations.Methods: GWA analysis was performed in the NELSON-study using the Illumina 610 array, followed by replication and metaanalysis in 11 additional cohorts. In total 2,704 subjects with, and 7,624 subjects without CMH were included, all current or former heavy smokers (&gt;= 20 pack-years). Additional studies were performed to test the functional relevance of the most significant single nucleotide polymorphism (SNP).Results: A strong association with CMH, consistent across all cohorts, was observed with rs6577641 (p = 4.25610(-6), OR = 1.17), located in intron 9 of the special AT-rich sequence-binding protein 1 locus (SATB1) on chromosome 3. The risk allele (G) was associated with higher mRNA expression of SATB1 (4.3610 29) in lung tissue. Presence of CMH was associated with increased SATB1 mRNA expression in bronchial biopsies from COPD patients. SATB1 expression was induced during differentiation of primary human bronchial epithelial cells in culture.Conclusions: Our findings, that SNP rs6577641 is associated with CMH in multiple cohorts and is a cis-eQTL for SATB1, together with our additional observation that SATB1 expression increases during epithelial differentiation provide suggestive evidence that SATB1 is a gene that affects CMH.</p

Susceptibility to chronic mucus hypersecretion, a genome wide association study

Background: Chronic mucus hypersecretion (CMH) is associated with an increased frequency of respiratory infections, excess lung function decline, and increased hospitalisation and mortality rates in the general population. It is associated with smoking, but it is unknown why only a minority of smokers develops CMH. A plausible explanation for this phenomenon is a predisposing genetic constitution. Therefore, we performed a genome wide association (GWA) study of CMH in Caucasian populations. Methods: GWA analysis was performed in the NELSON-study using the Illumina 610 array, followed by replication and meta-analysis in 11 additional cohorts. In total 2,704 subjects with, and 7,624 subjects without CMH were included, all current or former heavy smokers (≥20 pack-years). Additional studies were performed to test the functional relevance of the most significant single nucleotide polymorphism (SNP). Results: A strong association with CMH, consistent across all cohorts, was observed with rs6577641 (p = 4.25x10-6, OR = 1.17), located in intron 9 of the special AT-rich sequence-binding protein 1 locus (SATB1) on chromosome 3. The risk allele (G) was associated with higher mRNA expression of SATB1 (4.3x10 -9) in lung tissue. Presence of CMH was associated with increased SATB1 mRNA expression in bronchial biopsies from COPD patients. SATB1 expression was induced during differentiation of primary human bronchial epithelial cells in culture. Conclusions: Our findings, that SNP rs6577641 is associated with CMH in multiple cohorts and is a cis-eQTL for SATB1, together with our additional observation that SATB1 expression increases during epithelial differentiation provide suggestive evidence that SATB1 is a gene that affects CMH

A pro-inflammatory role for the Frizzled-8 receptor in chronic bronchitis

Rationale We have previously shown increased expression of the Frizzled-8 receptor of the Wingless/integrase-1 (WNT) signalling pathway in COPD. Here, we investigated if the Frizzled-8 receptor has a functional role in airway inflammation associated with chronic bronchitis. Methods Acute cigarette-smoke-induced airway inflammation was studied in wild-type and Frizzled-8-deficient mice. Genetic association studies and lung expression quantitative trait loci (eQTL) analyses for Frizzled-8 were performed to evaluate polymorphisms in FZD8 and their relationship to tissue expression in chronic bronchitis. Primary human lung fibroblasts and primary human airway epithelial cells were used for in vitro studies. Results Cigarette-smoke-exposure induced airway inflammation in wild-type mice, which was prevented in Frizzled-8-deficient mice, suggesting a crucial role for Frizzled-8 in airway inflammation. Furthermore, we found a significant genetic association (p=0.009) between single nucleotide polymorphism (SNP) rs663700 in the FZD8 region and chronic mucus hypersecretion, a characteristic of chronic bronchitis, in a large cohort of smoking individuals. We found SNP rs663700 to be a cis-eQTL regulating Frizzled-8 expression in lung tissue. Functional data link mesenchymal Frizzled-8 expression to inflammation as its expression in COPD-derived lung fibroblasts was regulated by pro-inflammatory cytokines in a genotype-dependent manner. Moreover, Frizzled-8 regulates inflammatory cytokine secretion from human lung fibroblasts, which in turn promoted MUC5AC expression by differentiated human airway epithelium. Conclusions These findings indicate an important pro-inflammatory role for Frizzled-8 and suggest that its expression is related to chronic bronchitis. Furthermore, our findings indicate an unexpected role for fibroblasts in regulating airway inflammation in COPD

Risk factors for chronic mucus hypersecretion in individuals with and without COPD: influence of smoking and job exposure on CMH

BACKGROUND: Chronic mucus hypersecretion (CMH) is highly prevalent in smokers and associated with an accelerated lung function decline and chronic obstructive pulmonary disease (COPD). Several risk factors contribute to CMH and to COPD. It is, however, unknown if risk factors for CMH are similar in persons with and without COPD.\n\nMETHODS: 1479 persons with and 8529 without COPD, participating in the general population-based LifeLines cohort, completed questionnaires and underwent spirometry. Occupational exposure was assessed using the ALOHA+ job exposure matrix. Analyses were performed using multiple logistic regression models.\n\nRESULTS: In COPD, a significantly higher risk for CMH was associated with higher pack-years smoking (per 10 pack-years) (OR=1.28; 1.12 to 1.46) and environmental tobacco smoke (ETS) (OR=2.06; 1.33 to 3.19). In non-COPD; male gender (OR=1.91; 1.51 to 2.41), higher Body Mass Index (OR=1.04; 1.01 to 1.06), higher pack-years smoking (OR=1.28; 1.14 to 1.44), current smoking (OR=1.50; 1.04 to 2.18), low and high exposure to mineral dust (OR=1.39; 1.04 to 1.87 and OR=1.60; 1.02 to 2.52), high exposure to gases & fumes (OR=2.19; 1.49 to 3.22). Significant interactions were found between COPD and exposure to gases & fumes (p=0.018) and aromatic solvents (p=0.038).\n\nCONCLUSIONS: A higher risk for CMH was associated with higher pack-years smoking regardless of COPD status. However, a higher risk for CMH was associated with high occupational exposure to gases & fumes in individuals without COPD only

Novel genes for airway wall thickness identified with combined genome-wide association and expression analyses

Rationale: Airway wall thickness (AWT) is affected by both environmental and genetic factors and is strongly associated with airflow limitation in smaller airways. Objectives: To investigate the genetic component of AWT. Methods: AWT was measured on low-dose computed tomography scans in male heavy smokers participating in a lung cancer screening study (n = 2,640). Genome-wide association studies on AWT were performed under an additive model using linear regression (adjusted for pack-years, lung volume), followed by metaanalysis. An independent cohort was used for validation of the most strongly associated single-nucleotide polymorphisms (SNPs). The functional relevance of significant SNPs was evaluated. Measurements and Main Results: Three significant loci on chromosomes 2q (rs734556; P = 6.2 × 10-7) and 10q (rs10794108, P = 8.6 × 10-8; rs7078439, P = 2.3 × 10-7) were associated with AWTand confirmed in the metaanalysis in cohorts with comparable lung function: P values = 4.6 × 10-8, 7.4 × 10-8, and 7.5 × 10-8, respectively. SNP rs734556 was associated with decreased lung tissue expression of SERPINE2, a susceptibility gene for emphysema. Two nominally significant SNPs showed effects with similar direction: rs10251504 in MAGI2 (P = 5.8 × 10-7) and rs4796712 in NT5C3B (P = 3.1 × 10-6). Higher MAGI2 expression in bronchial biopsies of patients with chronic obstructive pulmonary disease was significantly associated with fewer inflammatory cells. The presence of the NT5C3B risk allele was associated with higher lung tissue expression (P = 1.09 × 10-41). Conclusions: Genetic variants contribute to AWT. Among others, the identified genes are also involved in emphysema, airway obstruction, and bronchial inflammation

Dissecting the genetics of chronic mucus hypersecretion in smokers with and without COPD

Smoking is a notorious risk factor for chronic mucus hypersecretion (CMH). CMH frequently occurs in chronic obstructive pulmonary disease (COPD). The question arises whether the same single-nucleotide polymorphisms (SNPs) are related to CMH in smokers with and without COPD. We performed two genome-wide association studies of CMH under an additive genetic model in male heavy smokers (≥20 pack-years) with COPD (n=849, 39.9% CMH) and without COPD (n=1348, 25.4% CMH), followed by replication and meta-analysis in comparable populations, and assessment of the functional relevance of significantly associated SNPs. Genome-wide association analysis of CMH in COPD and non-COPD subjects yielded no genome-wide significance after replication. In COPD, our top SNP (rs10461985, p=5.43×10-5) was located in the GDNF-AS1 gene that is functionally associated with the GDNF gene. Expression of GDNF in bronchial biopsies of COPD patients was significantly associated with CMH (p=0.007). In non-COPD subjects, four SNPs had a p-value <10-5 in the meta-analysis, including a SNP (rs4863687) in the MAML3 gene, the T-allele showing modest association with CMH (p=7.57×10-6, OR 1.48) and with significantly increased MAML3 expression in lung tissue (p=2.59×10-12). Our data suggest the potential for differential genetic backgrounds of CMH in individuals with and without COPD