Genetic association analysis of functional impairment in chronic obstructive pulmonary disease

Associations of IL6 polymorphisms with lung function decline and COPD

BACKGROUND

Interleukin-6 (IL6) is a pleiotropic pro-inflammatory and immunomodulatory cytokine which probably plays an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). There is a functional single nucleotide polymorphism (SNP), -174G/C, in the promoter region of IL6. It was hypothesised that IL6 SNPs influence susceptibility for impaired lung function and COPD in smokers.

METHODS

Seven and five SNPs in IL6 were genotyped in two nested case-control samples derived from the Lung Health Study (LHS) based on phenotypes of rate of decline of forced expiratory volume in 1 s (FEV(1)) over 5 years and baseline FEV(1) at the beginning of the LHS. Serum IL6 concentrations were measured for all subjects. A partially overlapping panel of nine IL6 SNPs was genotyped in 389 cases of COPD from the National Emphysema Treatment Trial (NETT) and 420 controls from the Normative Aging Study (NAS).

RESULTS

In the LHS, three IL6 SNPs were associated with decline in FEV(1) (0.023< or =p< or =0.041 in additive models). Among them, the IL6_-174C allele was associated with a rapid decline in lung function. The association was more significant in a genotype-based analysis (p = 0.006). In the NETT-NAS study, IL6_-174G/C and four other IL6 SNPs, all of which are in linkage disequilibrium with IL6_-174G/C, were associated with susceptibility to COPD (0.01< or =p< or =0.04 in additive genetic models).

CONCLUSION

The results suggest that the IL6_-174G/C SNP is associated with a rapid decline in FEV(1) and susceptibility to COPD in smokers.

Mesenchymal cell fate and phenotypes in the pathogenesis of emphysema

Emphysema is characterized by the destruction of alveolar parenchymal tissue and the concordant loss of lung epithelial cells, endothelial cells, and interstitial mesenchymal cells. Key features in the pathobiology of emphysema include inflammation, alveolar epithelial cell injury/apoptosis, and excessive activation of extracellular matrix (ECM) proteases. Mesenchymal cells are versatile connective tissue cells that are critical effectors of wound-repair. The excessive loss of connective tissue and the destruction of alveolar septae in emphysema suggest that the mesenchymal cell reparative response to epithelial injury is impaired. Yet, the mechanisms regulating mesenchymal cell (dys)function in emphysema remain poorly understood. We propose that mesenchymal cell fate, modulated by transforming growth factor beta-1 (TGF-beta1) and the balance of ECM proteases and antiproteases, is a critical determinant of the emphysema phenotype. We examine emphysema in the context of wound-repair responses, with a focus on the regulation of mesenchymal cell fate and phenotype. We discuss the emerging evidence supporting that genetic factors, inflammation and environmental factors, including cigarette smoke itself, collectively impair mesenchymal cell survival and function, thus contributing to the pathogenesis of emphysema.

The human gene map for performance and health-related fitness phenotypes: the 2006-2007 update

This update of the human gene map for physical performance and health-related fitness phenotypes covers the research advances reported in 2006 and 2007. The genes and markers with evidence of association or linkage with a performance or a fitness phenotype in sedentary or active people, in responses to acute exercise, or for training-induced adaptations are positioned on the map of all autosomes and sex chromosomes. Negative studies are reviewed, but a gene or a locus must be supported by at least one positive study before being inserted on the map. A brief discussion on the nature of the evidence and on what to look for in assessing human genetic studies of relevance to fitness and performance is offered in the introduction, followed by a review of all studies published in 2006 and 2007. The findings from these new studies are added to the appropriate tables that are designed to serve as the cumulative summary of all publications with positive genetic associations available to date for a given phenotype and study design. The fitness and performance map now includes 214 autosomal gene entries and quantitative trait loci plus seven others on the X chromosome. Moreover, there are 18 mitochondrial genes that have been shown to influence fitness and performance phenotypes. Thus,the map is growing in complexity. Although the map is exhaustive for currently published accounts of genes and exercise associations and linkages, there are undoubtedly many more gene-exercise interaction effects that have not even been considered thus far. Finally, it should be appreciated that most studies reported to date are based on small sample sizes and cannot therefore provide definitive evidence that DNA sequence variants in a given gene are reliably associated with human variation in fitness and performance traits.

Progression of chronic obstructive pulmonary disease: impact of inflammation, comorbidities and therapeutic intervention

BACKGROUND AND AIM

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality, and through under-diagnosis, is often inappropriately treated. This multicomponent disease involves both airway and systemic inflammation at all stages and may influence the progression of disease and the pathophysiology of comorbidities. This review examines evidence linking inflammation, disease progression and comorbidities in COPD, and the potential role of anti-inflammatory therapies.

METHODS

Systematic searches of Medline and Cochrane Reviews databases from 1976 to March 2008 using the terms: chronic obstructive pulmonary disease, disease progression, inflammation, inflammatory, comorbid condition, comorbidity, treatment, therapy, bronchodilator, inhaled corticosteroid.

FINDINGS

Increased levels of interleukin-8, tumour necrosis factor-alpha and systemic C-reactive protein correlate with worse disease severity, exacerbation rates and lung function decline. Increased systemic C-reactive protein is also associated with poorer health status and comorbidities (e.g. cardiovascular disease, cancer and skeletal muscle dysfunction). The pivotal role of inflammation in the pathogenesis of COPD and its comorbidities suggests anti-inflammatory therapies will be important in the overall management of COPD. Long-term studies indicate that combination therapies consisting of a long-acting beta-agonist plus an inhaled corticosteroid in one inhaler have the potential to modify disease progression through positive effects on lung function, exacerbations, symptoms and health status. The TOwards a Revolution in COPD Health (TORCH) study is the first to demonstrate that a COPD pharmacotherapy (combination salmeterol plus fluticasone propionate) significantly decreased the rate of lung function decline versus placebo.

CONCLUSION

Better understanding of the specific inflammatory mechanisms underlying COPD disease progression and associated comorbidities will likely lead to more effective management of the disease.

Association between polymorphisms of microsomal epoxide hydrolase and COPD: results from meta-analyses

BACKGROUND AND OBJECTIVE

COPD is a complex polygenic disease in which gene-environment interactions are very important. The gene encoding microsomal epoxide hydrolase (EPHX1) is one of several candidate loci for COPD pathogenesis and is highly polymorphic. Based chi on the polymorphisms of EPHX1 gene (tyrosine/histidine 113, histidine/arginine 139), the population can be classified into four groups of putative EPHX1 phenotypes (fast, normal, slow and very slow). A number of studies have investigated the association between the genotypes and phenotypes of EPHX1 and COPD susceptibility in different populations, with inconsistent results. A systematic review and meta-analysis of the published data was performed to gain a clearer understanding of this association.

METHODS

The MEDLINE database was searched for case-control studies published from 1966 to August 2007. Data were extracted and pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated.

RESULTS

Sixteen eligible studies, comprising 1847 patients with COPD and 2455 controls, were included in the meta-analysis. The pooled result showed that the EPHX1 113 mutant homozygote was significantly associated with an increased risk of COPD (OR 1.59, 95% CI: 1.14-2.21). Subgroup analysis supported the result in the Asian population, but not in the Caucasian population. When the analysis was limited to only the larger-sample-size studies, studies in which controls were in Hardy-Weinberg equilibrium and studies in which controls were smokers/ex-smokers, the pooled results supported the conclusion. The EPHX1 139 heterozygote protected against the development of COPD in the Asian population, but not in the Caucasian population. The other gene types of EPHX1 113 and EPHX1 139 were not associated with an increased risk of COPD. The slow activity phenotype of EPHX1 was associated with an increased risk of COPD. The fast activity phenotype of EPHX1 was a protective factor for developing COPD in the Asian population, but not in the Caucasian population. However, the very slow activity phenotype of EPHX1 was a risk for developing COPD in the Caucasian population, but not in the Asian population.

CONCLUSIONS

The polymorphisms of EPHX1 113 and EPHX1 139 are genetic contributors to COPD susceptibility in Asian populations. The phenotypes of EPHX1 were contributors to overall COPD susceptibility.

Genetic association analysis of COPD candidate genes with bronchodilator responsiveness

Airflow limitation in COPD patients is not fully reversible. However, there may be large variability in bronchodilator responsiveness (BDR) among COPD patients, and familial aggregation of BDR suggests a genetic component. Therefore, we investigated the association between six candidate genes and BDR in subjects with severe COPD. A total of 389 subjects from the National Emphysema Treatment Trial (NETT) were analyzed. Bronchodilator responsiveness to albuterol was expressed in three ways: absolute change in FEV(1), change in FEV(1) as a percent of baseline FEV(1), and change in FEV(1) as a percent of predicted FEV(1). Genotyping was completed for 122 single nucleotide polymorphisms (SNPs) in six candidate genes (EPHX1, SFTPB, TGFB1, SERPINE2, GSTP1, ADRB2). Associations between BDR phenotypes and SNP genotypes were tested using linear regression, adjusting for age, sex, pack-years of smoking, and height. Genes associated with BDR phenotypes in the NETT subjects were assessed for replication in 127 pedigrees from the Boston Early-Onset COPD (EOCOPD) Study. Three SNPs in EPHX1 (p=0.009-0.04), three SNPs in SERPINE2 (p=0.004-0.05) and two SNPs in ADRB2 (0.04-0.05) were significantly associated with BDR phenotypes in NETT subjects. One SNP in EPHX1 (rs1009668, p=0.04) was significantly replicated in EOCOPD subjects. SNPs in SFTPB, TGFB1, and GSTP1 genes were not associated with BDR. In conclusion, a polymorphism of EPHX1 was associated with bronchodilator responsiveness phenotypes in subjects with severe COPD.

Analysis of exonic elastin variants in severe, early-onset chronic obstructive pulmonary disease

The destruction of elastic fibers has been implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Emphysema has been described in autosomal dominant cutis laxa, which can be caused by mutations in the elastin gene. Previously, a rare functional mutation in the terminal exon of elastin was found in a case of severe, early-onset COPD. To test the hypothesis that other similar elastin mutations may predispose to COPD, we screened 90 probands from the Boston Early-Onset COPD Study and 90 smoking control subjects from the Normative Aging Study for mutations in elastin exons using high-resolution DNA melt analysis followed by resequencing. Rare nonsynonymous single-nucleotide polymorphisms (SNPs) seen only in cases were examined for segregation with airflow obstruction within pedigrees. Common nonsynonymous SNPs were tested for association with COPD in a family-based analysis of 949 subjects from the Boston Early-Onset COPD Study, and in a case-control analysis in 389 COPD cases from the National Emphysema Treatment Trial and 472 control subjects from the Normative Aging Study. Of 28 elastin variants found, 3 were nonsynonymous SNPs found only in cases. The previously described Gly773Asp mutation was found in another proband. The other two SNPs did not clearly segregate with COPD within families. Two common nonsynonymous SNPs did not demonstrate significant associations in either a family-based or case-control analysis. Exonic SNPs in the elastin gene do not appear to be common risk factors for severe COPD.

Genetic associations with hypoxemia and pulmonary arterial pressure in COPD

BACKGROUND

Hypoxemia, hypercarbia, and pulmonary arterial hypertension are known complications of advanced COPD. We sought to identify genetic polymorphisms associated with these traits in a population of patients with severe COPD from the National Emphysema Treatment Trial (NETT).

METHODS

In 389 participants from the NETT Genetics Ancillary Study, single-nucleotide polymorphisms (SNPs) were genotyped in five candidate genes previously associated with COPD susceptibility (EPHX1, SERPINE2, SFTPB, TGFB1, and GSTP1). Linear regression models were used to test for associations among these SNPs and three quantitative COPD-related traits (Pao(2), Paco(2), and pulmonary artery systolic pressure). Genes associated with hypoxemia were tested for replication in probands from the Boston Early-Onset COPD Study.

RESULTS

In the NETT Genetics Ancillary Study population, SNPs in microsomal epoxide hydrolase (EPHX1) [p = 0.01 to 0.04] and serpin peptidase inhibitor, clade E, member 2 (SERPINE2) [p = 0.04 to 0.008] were associated with hypoxemia. One SNP within surfactant protein B (SFTPB) was associated with pulmonary artery systolic pressure (p = 0.01). In probands from the Boston Early-Onset COPD Study, SNPs in EPHX1 and in SERPINE2 were associated with the requirement for supplemental oxygen.

CONCLUSIONS

In participants with severe COPD, SNPs in EPHX1 and SERPINE2 were associated with hypoxemia in two separate study populations, and SNPs from SFTPB were associated with pulmonary artery pressure in the NETT participants.

Glutathione S-transferase and microsomal epoxide hydrolase gene polymorphisms and risk of chronic obstructive pulmonary disease in Slovak population

AIM

To determine the risk of chronic obstructive pulmonary disease (COPD) associated with polymorphisms in the glutathione S-transferase (GST) M1, GST T1, and microsomal epoxide hydrolase (EPHX1) genes in a cohort of Slovak population.

METHODS

Two hundred and seventeen patients with the diagnosis of COPD and 160 control subjects were enrolled in the study. Blood samples were collected from all subjects and the DNA from peripheral blood lymphocytes was used for subsequent genotyping assays, using polymerase chain reaction and restriction fragment-length polymorphism methods.

RESULTS

In an unadjusted model, an increased risk for COPD was observed in subjects with EPHX1 His113-His113 genotype (odds ratio [OR], 2.32; 95% confidence interval [CI], 1.20-4.69; P=0.008), compared with the carriers of the Tyr113 allele. However, after the adjustments for age, sex, and smoking status, the risk was not significant (adjusted OR, 1.79; 95% CI, 0.91-3.53; P=0.093). In a combined analysis of gene polymorphisms, the genotype combination EPHX1 His113-His113/GSTM1 null significantly increased the risk of COPD in both, unadjusted (OR, 5.08; 95% CI, 1.70-20.43; P=0.001) and adjusted model (OR, 4.87; 95% CI, 1.57-15.13; P=0.006).

CONCLUSION

Although none of the tested gene polymorphisms was significantly related to an increased risk of COPD alone, our results suggest that the homozygous exon 3 mutant variant of EPHX1 gene in the combination with GSTM1 null genotype is a significant predictor of increased susceptibility to COPD in the Slovak population. The findings of the present study emphasize the importance of detoxifying and antioxidant pathways in the pathogenesis of COPD.

National Emphysema Treatment Trial state of the art: genetics of emphysema

Although a hereditary contribution to emphysema has been long suspected, severe alpha1-antitrypsin deficiency remains the only conclusively proven genetic risk factor for chronic obstructive pulmonary disease (COPD). Recently, genome-wide linkage analysis has led to the identification of two promising candidate genes for COPD: TGFB1 and SERPINE2. Like multiple other COPD candidate gene associations, even these positionally identified genes have not been universally replicated across all studies. Differences in phenotype definition may contribute to nonreplication in genetic studies of heterogeneous disorders such as COPD. The use of precisely measured phenotypes, including emphysema quantification on high-resolution chest computed tomography scans, has aided in the discovery of additional genes for clinically relevant COPD-related traits. The use of computed tomography scans to assess emphysema and airway disease as well as newer genetic technologies, including gene expression microarrays and genome-wide association studies, has great potential to detect novel genes affecting COPD susceptibility, severity, and response to treatment.

Genetic variation and gene expression in antioxidant related enzymes and risk of COPD: a systematic review

BACKGROUND

Observational epidemiological studies of dietary antioxidant intake, serum antioxidant concentration and lung outcomes suggest that lower levels of antioxidant defences are associated with decreased lung function. Another approach to understanding the role of oxidant/antioxidant imbalance in the risk of chronic obstructive pulmonary disease (COPD) is to investigate the role of genetic variation in antioxidant enzymes, and indeed family based studies suggest a heritable component to lung disease. Many studies of the genes encoding antioxidant enzymes have considered COPD or COPD related outcomes, and a systematic review is needed to summarise the evidence to date, and to provide insights for further research.

METHODS

Genetic association studies of antioxidant enzymes and COPD/COPD related traits, and comparative gene expression studies with disease or smoking as the exposure were systematically identified and reviewed. Antioxidant enzymes considered included enzymes involved in glutathione metabolism, in the thioredoxin system, superoxide dismutases (SOD) and catalase.

RESULTS

A total of 29 genetic association and 15 comparative gene expression studies met the inclusion criteria. The strongest and most consistent effects were in the genes GCL, GSTM1, GSTP1 and SOD3. This review also highlights the lack of studies for genes of interest, particularly GSR, GGT and those related to TXN. There were limited opportunities to evaluate the contribution of a gene to disease risk through synthesis of results from different study designs, as the majority of studies considered either association of sequence variants with disease or effect of disease on gene expression.

CONCLUSION

Network driven approaches that consider potential interaction between and among genes, smoke exposure and antioxidant intake are needed to fully characterise the role of oxidant/antioxidant balance in pathogenesis.

Polymorphic variation in surfactant protein B is associated with COPD exacerbations

Exacerbations of chronic obstructive pulmonary disease (COPD) reduce quality of life and increase mortality. Genetic variation might explain the substantial variability seen in exacerbation frequency among COPD subjects with similar lung function. Polymorphisms in five candidate genes, previously associated with COPD susceptibility, were analysed in order to determine whether they demonstrated association with COPD exacerbations. A total of 88 single nucleotide polymorphisms (SNPs) in the genes microsomal epoxide hydrolase (EPHX1), transforming growth factor, beta-1 (TGFB1), serpin peptidase inhibitor, clade E (nexin, plasminogen activator inhibitor type 1), member 2 (SERPINE2), glutathione S-transferase pi (GSTP1) and surfactant protein B (SFTPB) were genotyped in 389 non-Hispanic white participants in the National Emphysema Treatment Trial. Exacerbations were defined as COPD-related emergency room visits or hospitalisations using the Centers for Medicare and Medicaid Services claims data. One or more exacerbations were experienced by 216 (56%) subjects during the study period. An SFTPB promoter polymorphism, rs3024791, was associated with COPD exacerbations. Logistic regression models, analysing a binary outcome of presence or absence of exacerbations, confirmed the association of rs3024791 with COPD exacerbations. Negative binomial regression models demonstrated association of multiple SFTPB SNPs (rs2118177, rs2304566, rs1130866 and rs3024791) with exacerbation rates. Polymorphisms in EPHX1, GSTP1, TGFB1 and SERPINE2 did not demonstrate association with COPD exacerbations. In conclusion, genetic variation in surfactant protein B is associated with chronic obstructive pulmonary disease susceptibility and exacerbation frequency.

Exacerbations in chronic obstructive pulmonary disease: do they contribute to disease progression?

The impact of chronic obstructive pulmonary disease (COPD) exacerbations on decline in FEV(1) has been a controversial topic for decades. We will review some of the key studies in this area and discuss potential contributors to inconsistent results of these studies. Dissecting the heterogeneous COPD syndrome into meaningful subtypes and assessing the genetic and environmental influences on COPD-related phenotypes such as exacerbation frequency could clarify the impact of exacerbations on the natural history of COPD.

Variability in small airway epithelial gene expression among normal smokers

BACKGROUND

Despite overwhelming data that cigarette smoking causes COPD, only a minority of long-term smokers are affected, strongly suggesting that genetic factors modify susceptibility to this disease. We hypothesized that individual variations exist in the response to cigarette smoking, with variability among smokers in expression levels of protective/susceptibility genes.

METHODS

Affymetrix arrays and quantitative polymerase chain reaction were used to assess the variability of gene expression in the small airway epithelium obtained by fiberoptic bronchoscopy of 18 normal nonsmokers, 18 normal smokers, and 18 smokers with COPD.

RESULTS

We identified 201 probe sets representing 152 smoking-responsive genes that were significantly up-regulated or down-regulated, and assessed the coefficient of variation in expression levels among the study population. Variation was a reproducible property of each gene as assessed by different microarray probe sets and real-time polymerase chain reaction, and was observed in both normal smokers and smokers with COPD. Greater individual variability was found in smokers with COPD than in normal smokers. The majority of these highly variable smoking-responsive genes were in the functional categories of signal transduction, xenobiotic degradation, metabolism, transport, oxidant related, and transcription. A similar pattern of the same highly variable genes was observed in an independent data set.

CONCLUSIONS

We propose that genetic diversity is likely within this subset of genes, with highly variable individual-to-individual responses of the small airway epithelium to smoking, and that this subset of genes represents putative candidates for assessment of susceptibility/protection from disease in future gene-based epidemiologic studies of smokers' risk for COPD.

Transforming growth factor-beta activation in the lung: focus on fibrosis and reactive oxygen species

Transforming growth factor-betas (TGF-beta) regulate a wide variety of cellular functions in normal development and are involved in both tissue homeostasis and disease pathogenesis. The regulation of the TGF-beta family of growth factors is unique because they are targeted to the extracellular matrix in a biologically inactive form. The release from pericellular matrices and the activation of TGF-beta are important mechanisms in several pathophysiologic conditions. Reactive oxygen species (ROS) can activate TGF-beta either directly or indirectly via the activation of proteases. In addition, TGF-beta itself induces ROS production as part of its signal-transduction pathway. The lung is a unique organ, because its structures act as boundaries between gaseous and aqueous phases, allowing the utilization of inhaled oxygen. However, this renders pulmonary tissues vulnerable to the toxic effects of inhaled air. The oxidant pathways are especially relevant in the lung, where TGF-beta is known to have a role in tissue repair and connective tissue turnover. In pulmonary fibrosis, TGF-beta activation is considered as a hallmark of disease progression. More recently, the oxidative effects of cigarette smoking have been found to activate TGF-beta in chronic obstructive pulmonary disease (COPD), a disease consisting of emphysema, airway fibrosis, and focal lung fibrosis.

Frontiers in emphysema research

Chronic obstructive pulmonary disease (COPD) is a complex inflammatory disease with a myriad of pulmonary and nonpulmonary disease manifestations. COPD is a heterogeneous disease consisting of emphysematous destruction, airway inflammation, remodeling, and obstruction. Once conceptualized as a unidimensional disease isolated to the lung, it is now recognized to have significant systemic manifestations, such as osteoporosis, cardiovascular disease, and skeletal muscle wasting. As the clinical phenotypic expressions of COPD become more precisely characterized, so does the pathogenesis of this disease. Great strides are now being made in our understanding of genetic susceptibility, airway inflammation, the immune response to cigarette smoke, and inflammatory biomarkers. This review will discuss the most recent progress on selected topics in COPD pathogenesis, inflammation, and genetics. With time, we hope to expand our current understanding to predict who will develop disease and who will not, and why some patients develop particular disease phenotypes. In addition, we hope to clarify the inflammatory mechanisms involved in order to develop novel therapies and identify disease biomarkers that will lead to better tools for monitoring disease activity. Finally, we hope to develop treatments aimed at lung regeneration and repair, to reverse lung damage that has already occurred. We are optimistic that novel therapies like gene therapy and advanced antiinflammatory agents will be in our future. Judging by the progress made in the last decade, these tools may soon become a reality.

The association of transforming growth factor beta 1 gene polymorphisms with the emphysema phenotype of COPD in Japanese

OBJECTIVE

The transforming growth factor beta-1 gene (TGFB1) is one of the most promising candidate genes for chronic obstructive pulmonary disease (COPD). Several case-control studies have been performed and generated inconsistent results. The possible reasons for these discrepancies include the diversity of ethnic populations and the heterogeneity of COPD, including emphysema and airway disease. We designed this study to investigate the association of single nucleotide polymorphisms (SNPs) of TGFB1 with the emphysema phenotype in the Japanese population.

METHODS

Eight SNPs in TGFB1 (rs2241712, rs1982072, and rs1800469 in the promoter region; rs1982073 in exon 1; rs2241716 and rs4803455 in intron 2; rs6957 and rs2241718 in the 3' region) were genotyped by allelic discrimination assays in 70 COPD patients with emphysema phenotype and 99 healthy smokers. The emphysema phenotype was identified by high-resolution computed tomography imaging using Goddard's method.

RESULTS

The frequency of one significant haplotype structured by the eight SNPs was significantly higher in the emphysema group (10%) than in the healthy smokers (4%, p=0.02). In the emphysema group, the predicted value of forced expiratory volume in 1 second after bronchodilator administration was significantly associated with the minor alleles of the two SNPs (rs1800469 and rs1982073, p=0.007 and 0.032, respectively), however, the low attenuation area and carbon monoxide diffusing capacity were not associated with the SNPs. In addition, the rs1800469T and rs1982073C alleles were significantly more prevalent in patients with severe and very severe airflow limitation than in those with mild and moderate airflow limitation (p=0.007 and 0.041, respectively).

CONCLUSIONS

One significant haplotype of TGFB1 is associated with the emphysema phenotype in the Japanese population. Two TGFB1 SNPs (rs1800469 and rs1982073) are associated with the severity of COPD in patients with emphysema phenotype.

Lung development and adult lung diseases

Adult respiratory diseases are caused by many factors, including genetic-environmental interaction. Genetic abnormalities can impact early fetal lung development, postnatal lung maturation, as well as adult lung injury and repair. Studies suggest that abnormally developed lung structure and function may contribute as a susceptibility factor for several adult lung diseases. This review focuses on the relationship between lung development and pathogenesis of several lung diseases including COPD, cystic fibrosis (CF), and asthma. COPD with emphysema has been considered to be an accelerated involutional disease of aging smokers. However, since only a proportion (approximately 15%) of smokers get COPD with emphysema, clearly genetic susceptibility must play a significant part in determining both the age of onset and the rapidity of decline in lung function. In mice, interference with key genes either by null mutation, hypomorphism, or gain or loss of function results in phenotypes comprising either neonatal lethal respiratory distress if the structural effect is severe, or reduced alveolarization and/or early onset emphysema if the effect is milder. Reported susceptibility candidate genes are therefore discussed in some detail, including elastin, lysyl oxidase, fibrillin, the transforming growth factor-beta-Smad3 pathway, as well as extracellular matrix proteases. In the case of CF, the Cftr gene has been shown to regulate fetal lung epithelial cell differentiation and maturation. Subtle abnormalities of lung structure and function are found in clinically asymptomatic CF infants. Finally, airway remodeling due to chronic inflammation is important in infants who later acquire asthma.

IL10 polymorphisms are associated with airflow obstruction in severe alpha1-antitrypsin deficiency

Severe alpha(1)-antitrypsin (AAT) deficiency is a proven genetic risk factor for chronic obstructive pulmonary disease (COPD), especially in individuals who smoke. There is marked variability in the development of lung disease in individuals homozygous (PI ZZ) for this autosomal recessive condition, suggesting that modifier genes could be important. We hypothesized that genetic determinants of obstructive lung disease may be modifiers of airflow obstruction in individuals with severe AAT deficiency. To identify modifier genes, we performed family-based association analyses for 10 genes previously associated with asthma and/or COPD, including IL10, TNF, GSTP1, NOS1, NOS3, SERPINA3, SERPINE2, SFTPB, TGFB1, and EPHX1. All analyses were performed in a cohort of 378 PI ZZ individuals from 167 families. Quantitative spirometric phenotypes included forced expiratory volume in one second (FEV(1)) and the ratio of FEV(1)/forced vital capacity (FVC). A qualitative phenotype of moderate-to-severe COPD was defined for individuals with FEV(1) </= 50 percent predicted. Six of 11 single-nucleotide polymorphisms (SNPs) in IL10 (P = 0.0005-0.05) and 3 of 5 SNPs in TNF (P = 0.01-0.05) were associated with FEV(1) and/or FEV(1)/FVC. IL10 SNPs also demonstrated association with the qualitative COPD phenotype. When phenotypes of individuals with a physician's diagnosis of asthma were excluded, IL10 SNPs remained significantly associated, suggesting that the association with airflow obstruction was independent of an association with asthma. Haplotype analysis of IL10 SNPs suggested the strongest association with IL10 promoter SNPs. IL10 is likely an important modifier gene for the development of COPD in individuals with severe AAT deficiency.

Xenobiotic metabolizing enzyme gene polymorphisms predict response to lung volume reduction surgery

BACKGROUND

In the National Emphysema Treatment Trial (NETT), marked variability in response to lung volume reduction surgery (LVRS) was observed. We sought to identify genetic differences which may explain some of this variability.

METHODS

In 203 subjects from the NETT Genetics Ancillary Study, four outcome measures were used to define response to LVRS at six months: modified BODE index, post-bronchodilator FEV1, maximum work achieved on a cardiopulmonary exercise test, and University of California, San Diego shortness of breath questionnaire. Sixty-four single nucleotide polymorphisms (SNPs) were genotyped in five genes previously shown to be associated with chronic obstructive pulmonary disease susceptibility, exercise capacity, or emphysema distribution.

RESULTS

A SNP upstream from glutathione S-transferase pi (GSTP1; p = 0.003) and a coding SNP in microsomal epoxide hydrolase (EPHX1; p = 0.02) were each associated with change in BODE score. These effects appeared to be strongest in patients in the non-upper lobe predominant, low exercise subgroup. A promoter SNP in EPHX1 was associated with change in BODE score (p = 0.008), with the strongest effects in patients with upper lobe predominant emphysema and low exercise capacity. One additional SNP in GSTP1 and three additional SNPs in EPHX1 were associated (p < 0.05) with additional LVRS outcomes. None of these SNP effects were seen in 166 patients randomized to medical therapy.

CONCLUSION

Genetic variants in GSTP1 and EPHX1, two genes encoding xenobiotic metabolizing enzymes, were predictive of response to LVRS. These polymorphisms may identify patients most likely to benefit from LVRS.

Protection against inhaled oxidants through scavenging of oxidized lipids by macrophage receptors MARCO and SR-AI/II

Alveolar macrophages (AMs) express the class A scavenger receptors (SRAs) macrophage receptor with collagenous structure (MARCO) and scavenger receptor AI/II (SRA-I/II), which recognize oxidized lipids and provide innate defense against inhaled pathogens and particles. Increased MARCO expression in lungs of ozone-resistant mice suggested an additional role protecting against inhaled oxidants. After ozone exposure, MARCO-/- mice showed greater lung injury than did MARCO+/+ mice. Ozone is known to generate oxidized, proinflammatory lipids in lung lining fluid, such as 5beta,6beta-epoxycholesterol (beta-epoxide) and 1-palmitoyl-2-(9'-oxo-nonanoyl)-glycerophosphocholine (PON-GPC). Intratracheal instillation of either lipid caused substantial neutrophil influx in MARCO-/- mice, but had no effect in MARCO+/+ mice. Normal AMs showed greater uptake in vitro of beta-epoxide compared with MARCO-/- AMs, consistent with SRA function in binding oxidized lipids. SR-AI/II-/- mice showed similar enhanced acute lung inflammation after beta-epoxide or another inhaled oxidant (aerosolized leachate of residual oil fly ash). In contrast, subacute ozone exposure did not enhance inflammation in SR-AI/II-/- versus SR-AI/II+/+ mice, reflecting increased AM expression of MARCO. These data identify what we believe to be a novel function for AM SRAs in decreasing pulmonary inflammation after oxidant inhalation by scavenging proinflammatory oxidized lipids from lung lining fluids.

Genetic determinants of emphysema distribution in the national emphysema treatment trial

RATIONALE

Computed tomography (CT) scanning of the lung may reduce phenotypic heterogeneity in defining subjects with chronic obstructive pulmonary disease (COPD), and allow identification of genetic determinants of emphysema severity and distribution.

OBJECTIVES

We sought to identify genes associated with CT scan distribution of emphysema in individuals without alpha1-antitrypsin deficiency but with severe COPD.

METHODS

We evaluated baseline CT densitometry phenotypes in 282 individuals with emphysema enrolled in the Genetics Ancillary Study of the National Emphysema Treatment Trial, and used regression models to identify genetic variants associated with emphysema distribution.

MEASUREMENTS AND MAIN RESULTS

Emphysema distribution was assessed by two methods--assessment by radiologists and by computerized density mask quantitation, using a threshold of -950 Hounsfield units. A total of 77 polymorphisms in 20 candidate genes were analyzed for association with distribution of emphysema. GSTP1, EPHX1, and MMP1 polymorphisms were associated with the densitometric, apical-predominant distribution of emphysema (p value range = 0.001-0.050). When an apical-predominant phenotype was defined by the radiologist scoring method, GSTP1 and EPHX1 single-nucleotide polymorphisms were found to be significantly associated. In a case-control analysis of COPD susceptibility limited to cases with densitometric upper-lobe-predominant cases, the EPHX1 His139Arg single-nucleotide polymorphism was associated with COPD (p = 0.005).

CONCLUSIONS

Apical and basal emphysematous destruction appears to be influenced by different genes. Polymorphisms in the xenobiotic enzymes, GSTP1 and EPHX1, are associated with apical-predominant emphysema. Altered detoxification of cigarette smoke metabolites may contribute to emphysema distribution, and these findings may lead to further insight into genetic determinants of emphysema.

Current thinking on genetics of chronic obstructive pulmonary disease

PURPOSE OF REVIEW

There is growing evidence that genetics plays a role in the development of chronic obstructive pulmonary disease. This review deals with the most recent findings, new methods to detect genetic susceptibility that may be helpful in this field, and how the environment may act on the genetic code of susceptible individuals and chronic obstructive pulmonary disease sufferers.

RECENT FINDINGS

Candidate gene association studies have identified genes that may have roles in the pathogenesis of chronic obstructive pulmonary disease. Not all studies that have found associations between genes and chronic obstructive pulmonary disease phenotypes have been replicated, however. The realization of this challenge in itself is a major step forward and, coupled with exciting new methods to identify susceptibility genes, may provide the impetus to move the field beyond the notion that alpha-1 antitrypsin is the only proven cause of the disease.

SUMMARY

Candidate gene studies need to be interpreted with caution because of their lack of reproducibility. Genome-wide association studies may offer the best approach to identifying susceptibility genes in chronic obstructive pulmonary disease. Epigenetics needs to be considered in concert with genetic findings.

Pulmonary emphysema: when more is less

Pulmonary emphysema results from the loss of intricate alveolar architecture and progressive simplification of small and highly effective gas-exchanging units into large, inefficient cyst-like spaces. Because of the loss of alveolar gas-exchanging units and the capillary bed within them, blood oxygen levels eventually fall and pressures within the pulmonary circulation rise. Recent insights from genetically manipulated mouse models have refined our understanding of the molecular events that prevent or promote the development of pulmonary emphysema. Capitalizing on an improved molecular understanding of emphysema with improved therapeutics has the potential to enhance both the survival and quality of life of patients with this common lung disease.

Glutathione S-transferase genotypes modify lung function decline in the general population: SAPALDIA cohort study

Background

Understanding the environmental and genetic risk factors of accelerated lung function decline in the general population is a first step in a prevention strategy against the worldwide increasing respiratory pathology of chronic obstructive pulmonary disease (COPD). Deficiency in antioxidative and detoxifying Glutathione S-transferase (GST) gene has been associated with poorer lung function in children, smokers and patients with respiratory diseases. In the present study, we assessed whether low activity variants in GST genes are also associated with accelerated lung function decline in the general adult population.

Methods

We examined with multiple regression analysis the association of polymorphisms in GSTM1, GSTT1 and GSTP1 genes with annual decline in FEV1, FVC, and FEF_25–75 during 11 years of follow-up in 4686 subjects of the prospective SAPALDIA cohort representative of the Swiss general population. Effect modification by smoking, gender, bronchial hyperresponisveness and age was studied.

Results

The associations of GST genotypes with FEV1, FVC, and FEF_25–75 were comparable in direction, but most consistent for FEV1. GSTT1 homozygous gene deletion alone or in combination with GSTM1 homozygous gene deletion was associated with excess decline in FEV1 in men, but not women, irrespective of smoking status. The additional mean annual decline in FEV1 in men with GSTT1 and concurrent GSTM1 gene deletion was -8.3 ml/yr (95% confidence interval: -12.6 to -3.9) relative to men without these gene deletions. The GSTT1 effect on the FEV1 decline comparable to the observed difference in FEV1 decline between never and persistent smoking men. Effect modification by gender was statistically significant.

Conclusion

Our results suggest that genetic GSTT1 deficiency is a prevalent and strong determinant of accelerated lung function decline in the male general population.

Genetics of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a complex disease with multifactorial background, based on the interaction of environmental and genetic factors. Environmental factors are clearly related to the development of the disease. However, family and twin studies suggested genetics factors to be one of the important determinants for the development of COPD. Different approaches have been used to identify genes of interest. Genomewide linkage analysis found areas of interest on different chromosomes, with some genes located in this regions being identified and replicated as susceptibility genes. Numerous of candidate genes that could be linked to disease pathogenesis have been implicated in COPD genetics. However, the candidate gene approach is often limited by inconsistent results in other study populations. Recently, a combination of different methods is used giving more evidence for some candidate genes, including TGFbeta-1, Surfactant, SERPINE2 and microsomal epoxide hydrolase. In the future ongoing exact phenotype definition, combination of several approaches, genome-wide association studies and animal model genetics will lead to new insights into the genetics of COPD, with epigenetic factors needs to be further investigated and considered in concert with genetic findings.

Elastin protein levels are a vital modifier affecting normal lung development and susceptibility to emphysema

Cigarette smoking is the strongest risk factor for emphysema. However, sensitivity to cigarette smoke-induced emphysema is highly variable, and numerous genetic and environmental factors are thought to mitigate lung response to injury. We report that the quantity of functional elastin in the lung is an important modifier of both lung development and response to injury. In mice with low levels of elastin, lung development is adversely affected, and mice manifest with congenital emphysema. Animals with intermediate elastin levels exhibit normal alveolar structure but develop worse emphysema than normal mice following cigarette smoke exposure. Mechanical testing demonstrates that lungs with low levels of elastin experience greater tissue strains for any given tissue stress compared with wild-type lungs, implying that force-mediated propagation of lung injury through alveolar wall failure may worsen the emphysema after an initial enzymatic insult. Our findings suggest that quantitative deficiencies in elastin predispose to smoke-induce emphysema in animal models and suggest that humans with altered levels of functional elastin could have relatively normal lung function while being more susceptible to smoke-induced lung injury.

The stumbling block in lung repair of emphysema: elastic fiber assembly

The mechanical properties of the lung are largely determined by the connective tissue networks laid down during development. The macromolecules most important for lung mechanics and structural integrity are collagen, elastin, and proteoglycans. Members of the fibrillar collagen gene family provide the structural framework of the various lung compartments and elastic fibers provide elastic recoil. Elastin is also an important architectural component that influences lung development, predominantly during the alveolar stage. Previous studies have conclusively shown that elastin degradation is a key step in the pathogenesis of chronic obstructive pulmonary disease. Exacerbating the disease process is the inability of lung cells to repair damaged elastic fibers, which leads to permanently compromised lung function and ongoing degenerative disease. Elastic fibers are among the most difficult matrix structures to repair because of their size, molecular complexity, and the requirement for numerous helper proteins to facilitate fiber assembly. Recent studies of elastin assembly combined with new insight into the functional role of elastic fiber proteins obtained from gene inactivation studies and linkage of human disease to elastin mutations provide new insight into the molecular and cellular complexities of elastin homeostasis.

The genetics of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease caused by the interaction of genetic susceptibility and environmental influences. There is increasing evidence that genes link to disease pathogenesis and heterogeneity by causing variation in protease anti-protease systems, defence against oxidative stress and inflammation. The main methods of genomic research for complex disease traits are described, together with the genes implicated in COPD thus far, their roles in disease causation and the future for this area of investigation.

Gene–environment interactions in the development of chronic obstructive pulmonary disease

PURPOSE OF REVIEW

Genetic factors influence the variable development of chronic obstructive pulmonary disease in response to smoking and are likely to vary between populations. Recent studies have begun to shed some light on these gene-environment interactions.

RECENT FINDINGS

A variety of approaches has been used to identify novel susceptibility genes for chronic obstructive pulmonary disease. These studies have provided evidence for the possible role of many inflammatory mediators and their receptors, proteases, antiproteases, and antioxidant and xenobiotic genes in chronic obstructive pulmonary disease pathophysiology. However, ethnic differences and subtle phenotype differences often make replication of these studies difficult.

SUMMARY

The completion of the Human Genome Project, the HapMap project, technological advances in single-nucleotide-polymorphism genotyping and the potential of genome-wide association analysis will allow the identification of susceptibility genes for chronic obstructive pulmonary disease. The challenge is to understand the influence of multiple genetic factors and multiple environmental factors as well as gene-gene and gene-environment interactions. Careful clinical characterization of phenotypes for chronic obstructive pulmonary disease is essential and this will include comparison of biomarkers of distinct pathologies including radiological assessment to separate the components of pulmonary emphysema and small-airway disease.