Loubna Akhabir

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 (FEV1) over 5 years and baseline FEV1 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 FEV1 (0.023⩽p⩽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⩽p⩽0.04 in additive genetic models). Conclusion: The results suggest that the IL6_-174G/C SNP is associated with a rapid decline in FEV1 and susceptibility to COPD in smokers.

Genome-wide association studies for discovery of genes involved in asthma

Asthma is the result of a complex interaction between environmental factors and genetic variants that confer susceptibility. Studies of the genetics of asthma have previously been conducted using linkage designs and candidate gene association studies. Recently, the association study design has been extended from specific candidate genes to an unbiased genome‐wide approach: the genome‐wide association study (GWAS). To date, there have been 12 GWAS to look for susceptibility loci for asthma and related traits. The first GWAS for asthma discovered a novel associated locus on chromosome 17q21 encompassing the genes ORMDL3, GSDMB and ZPBP2. None of these genes would have been selected in a candidate association study based on current knowledge of the functions of these genes. Nevertheless, this finding has been consistently replicated in independent populations of European ancestry and also in other ethnic groups. Thus, chromosome 17q21 seems to be a true asthma susceptibility locus. Other genes that were identified in more than one GWAS are IL33, RAD50, IL1RL1 and HLA‐DQB1. Additional novel susceptibility genes identified in a single study include DENND1BI and IL2RB. Discovering the causal mechanism behind these associations is likely to yield great insights into the development of asthma. It is likely that further meta‐analyses of asthma GWAS data from existing international consortia will uncover more novel susceptibility genes and further increase our understanding of this disease.

Functional genetic variation in NFKBIA and susceptibility to childhood asthma, bronchiolitis, and bronchopulmonary dysplasia.

Respiratory diseases are the most frequent chronic illnesses in babies and children. Although a vigorous innate immune system is critical for maintaining lung health, a balanced response is essential to minimize damaging inflammation. We investigated the functional and clinical impact of human genetic variants in the promoter of NFKBIA, which encodes IκBα, the major negative regulator of NF-κB. In this study, we quantified the functional impact of NFKBIA promoter polymorphisms (rs3138053, rs2233406, and rs2233409) on promoter-driven protein expression, allele-specific and total NFKBIA mRNA expression, IκBα protein expression, and TLR responsiveness; mapped innate immune regulatory networks active during respiratory syncytial virus infection, asthma, and bronchopulmonary dysplasia; and genotyped and analyzed independent cohorts of children with respiratory syncytial virus infection, asthma, and bronchopulmonary dysplasia. Genetic variants in the promoter of NFKBIA influenced NFKBIA gene expression, IκBα protein expression, and TLR-mediated inflammatory responses. Using a systems biology approach, we demonstrated that NFKBIA/IκBα is a central hub in transcriptional responses of prevalent childhood lung diseases, including respiratory syncytial virus infection, asthma, and bronchopulmonary dysplasia. Finally, by examining independent pediatric lung disease cohorts, we established that this immunologically relevant genetic variation in the promoter of NFKBIA is associated with differential susceptibility to severe bronchiolitis following infection with respiratory syncytial virus, airway hyperresponsiveness, and severe bronchopulmonary dysplasia. These data highlight the importance of negative innate immune regulators, such as NFKBIA, in pediatric lung disease and begin to unravel common aspects in the genetic predisposition to bronchopulmonary dysplasia, bronchiolitis, and childhood asthma.

Genetics of interleukin 1 receptor-like 1 in immune and inflammatory diseases.

Interleukin 1 receptor-like 1 (IL1RL1) is gaining in recognition due to its involvement in immune/inflammatory disorders. Well-designed animal studies have shown its critical role in experimental allergic inflammation and human in vitro studies have consistently demonstrated its up-regulation in several conditions such as asthma and rheumatoid arthritis. The ligand for IL1RL1 is IL33 which emerged as playing an important role in initiating eosinophilic inflammation and activating other immune cells resulting in an allergic phenotype. An IL1RL1 single nucleotide polymorphism (SNP) was among the most significant results of a genome-wide scan investigating eosinophil counts; in the same study, this SNP associated with asthma in 10 populations. The IL1RL1 gene resides in a region of high linkage disequilibrium containing interleukin 1 receptor genes as well as interleukin 18 receptor and accessory genes. This poses a challenge to researchers interested in deciphering genetic association signals in the region as all of the genes represent interesting candidates for asthma and allergic disease. The IL1RL1 gene and its resulting soluble and receptor proteins have emerged as key regulators of the inflammatory process implicated in a large variety of human pathologies We review the function and expression of the IL1RL1 gene. We also describe the role of IL1RL1 in asthma, allergy, cardiovascular disease, infections, liver disease and kidney disease.

Effect of heme oxygenase-1 polymorphisms on lung function and gene expression.

BackgroundOxidative stress induced by smoking is considered to be important in the pathogenesis of Chronic Obstructive Pulmonary Disease (COPD). Heme oxygenase-1 (HMOX1) is an essential enzyme in heme catabolism that is induced by oxidative stress and may play a protective role as an antioxidant in the lung. We determined whether HMOX1 polymorphisms were associated with lung function in COPD patients and whether the variants had functional effects.MethodsWe genotyped five single nucleotide polymorphisms (SNPs) in the HMOX1 gene in Caucasians who had the fastest (n = 278) and the slowest (n = 304) decline of FEV1 % predicted, selected from smokers in the NHLBI Lung Health Study. These SNPs were also studied in Caucasians with the lowest (n = 535) or the highest (n = 533) baseline lung function. Reporter genes were constructed containing three HMOX1 promoter polymorphisms and the effect of these polymorphisms on H2O2 and hemin-stimulated gene expression was determined. The effect of the HMOX1 rs2071749 SNP on gene expression in alveolar macrophages was investigated.ResultsWe found a nominal association (p = 0.015) between one intronic HMOX1 SNP (rs2071749) and lung function decline but this did not survive correction for multiple comparisons. This SNP was in perfect linkage disequilibrium with rs3761439, located in the promoter of HMOX1. We tested rs3761439 and two other putatively functional polymorphisms (rs2071746 and the (GT)n polymorphism) in reporter gene assays but no significant effects on gene expression were found. There was also no effect of rs2071749 on HMOX1 gene expression in alveolar macrophages.ConclusionsWe found no association of the five HMOX1 tag SNPs with lung function decline and no evidence that the three promoter polymorphisms affected the regulation of the HMOX1 gene.

NFE2L2 pathway polymorphisms and lung function decline in chronic obstructive pulmonary disease

An oxidant-antioxidant imbalance in the lung contributes to the development of chronic obstructive pulmonary disease (COPD) that is caused by a complex interaction of genetic and environmental risk factors. Nuclear erythroid 2-related factor 2 (NFE2L2 or NRF2) is a critical molecule in the lungs defense mechanism against oxidants. We investigated whether polymorphisms in the NFE2L2 pathway affected the rate of decline of lung function in smokers from the Lung Health Study (LHS)(n = 547) and in a replication set, the Vlagtwedde-Vlaardingen cohort (n = 533). We selected polymorphisms in NFE2L2 in genes that positively or negatively regulate NFE2L2 transcriptional activity and in genes that are regulated by NFE2L2. Polymorphisms in 11 genes were significantly associated with rate of lung function decline in the LHS. One of these polymorphisms, rs11085735 in the KEAP1 gene, was previously shown to be associated with the level of lung function in the Vlagtwedde-Vlaardingen cohort but not with decline of lung function. Of the 23 associated polymorphisms in the LHS, only rs634534 in the FOSL1 gene showed a significant association in the Vlagtwedde-Vlaardingen cohort with rate of lung function decline, but the direction of the association was not consistent with that in the LHS. In summary, despite finding several nominally significant polymorphisms in the LHS, none of these associations were replicated in the Vlagtwedde-Vlaardingen cohort, indicating lack of effect of polymorphisms in the NFE2L2 pathway on the rate of decline of lung function.

Genetic association between human chitinases and lung function in COPD

Two primary chitinases have been identified in humans—acid mammalian chitinase (AMCase) and chitotriosidase (CHIT1). Mammalian chitinases have been observed to affect the host’s immune response. The aim of this study was to test for association between genetic variation in the chitinases and phenotypes related to chronic obstructive pulmonary disease (COPD). Polymorphisms in the chitinase genes were selected based on previous associations with respiratory diseases. Polymorphisms that were associated with lung function level or rate of decline in the Lung Health Study (LHS) cohort were analyzed for association with COPD affection status in four other COPD case–control populations. Chitinase activity and protein levels were also related to genotypes. In the caucasian LHS population, the baseline forced expiratory volume in one second (FEV1) was significantly different between the AA and GG genotypic groups of the AMCase rs3818822 polymorphism. Subjects with the GG genotype had higher AMCase protein and chitinase activity compared with AA homozygotes. For CHIT1 rs2494303, a significant association was observed between rate of decline in FEV1 and the different genotypes. In the African American LHS population, CHIT1 rs2494303 and AMCase G339T genotypes were associated with rate of decline in FEV1. Although a significant effect of chitinase gene alleles was found on lung function level and decline in the LHS, we were unable to replicate the associations with COPD affection status in the other COPD study groups.

Thymic stromal lymphopoietin (TSLP) secretion from human nasal epithelium is a function of TSLP genotype

Recent candidate gene and genome-wide association studies have identified “protective” associations between the single-nucleotide polymorphism (SNP) rs1837253 in the TSLP gene and risk for allergy, asthma, and airway hyperresponsiveness. The absence of linkage disequilibrium of rs1837253 with other SNPs in the region suggests it is likely a causal polymorphism for these associations, having functional consequences. We hypothesized that rs1837253 genotype would influence TSLP secretion from mucosal surfaces. We therefore evaluated the secretion of TSLP protein from primary nasal epithelial cells (NECs) of atopic and nonatopic individuals and its association with rs1837253 genotype. We found that although atopic sensitization does not affect the secretion of TSLP from NECs, there was decreased TSLP secretion in NECs obtained from heterozygous (CT; 1.8-fold) and homozygous minor allele (TT; 2.5-fold) individuals, as compared with NECs from homozygous major allele individuals (CC; P<0.05), after double-stranded RNA (dsRNA) stimulation (50 μg ml−1). Our novel results show that rs1837253 polymorphism may be directly involved in the regulation of TSLP secretion. This may help explain the protective association of this genetic variant with asthma and related traits. Identifying functional consequences of SNPs in genes with previously reported clinical associations is critical in understanding and targeting allergic inflammation.

Genome-wide association study and meta-analysis in multiple populations identifies new loci for peanut allergy and establishes C11orf30/EMSY as a genetic risk factor for food allergy

Background: Peanut allergy (PA) is a complex disease with both environmental and genetic risk factors. Previously, PA loci were identified in filaggrin (FLG) and HLA in candidate gene studies, and loci in HLA were identified in a genome‐wide association study and meta‐analysis. Objective: We sought to investigate genetic susceptibility to PA. Methods: Eight hundred fifty cases and 926 hyper‐control subjects and more than 7.8 million genotyped and imputed single nucleotide polymorphisms (SNPs) were analyzed in a genome‐wide association study to identify susceptibility variants for PA in the Canadian population. A meta‐analysis of 2 phenotypes (PA and food allergy) was conducted by using 7 studies from the Canadian, American (n=2), Australian, German, and Dutch (n=2) populations. Results: An SNP near integrin &agr;6 (ITGA6) reached genome‐wide significance with PA (P=1.80×10−8), whereas SNPs associated with Src kinase–associated phosphoprotein 1 (SKAP1), matrix metallopeptidase 12 (MMP12)/MMP13, catenin &agr;3 (CTNNA3), rho GTPase–activating protein 24 (ARHGAP24), angiopoietin 4 (ANGPT4), chromosome 11 open reading frame (C11orf30/EMSY), and exocyst complex component 4 (EXOC4) reached a threshold suggestive of association (P≤1.49×10−6). In the meta‐analysis of PA, loci in or near ITGA6, ANGPT4, MMP12/MMP13, C11orf30, and EXOC4 were significant (P≤1.49×10−6). When a phenotype of any food allergy was used for meta‐analysis, the C11orf30 locus reached genome‐wide significance (P=7.50×10−11), whereas SNPs associated with ITGA6, ANGPT4, MMP12/MMP13, and EXOC4 and additional C11orf30 SNPs were suggestive (P≤1.49×10−6). Functional annotation indicated that SKAP1 regulates expression of CBX1, which colocalizes with the EMSY protein coded by C11orf30. Conclusion: This study identifies multiple novel loci as risk factors for PA and food allergy and establishes C11orf30 as a risk locus for both PA and food allergy. Multiple genes (C11orf30/EMSY, SKAP1, and CTNNA3) identified by this study are involved in epigenetic regulation of gene expression.

Canadian genome-wide association study and meta-analysis confirm HLA as a risk factor for peanut allergy independent of asthma

_To the Editor:_ Previously, we identified the HLA region as a risk factor forpeanut allergy (PA); this observation is supported further by 2 independent genome-wide association studies (GWASs). The HLA class II genes (including HLA-DR, HLA-DQ, and HLADP) encode molecules involved in presentation of extracellular antigens, such as peanut allergens, to T lymphocytes, which in turn mediates B-cell antibody production.We used the Canadian Peanut Allergy Registry (CanPAR) and the Busselton Health Study to conduct the largest GWAS for PA to date. Here we report analysis of the HLA region and a meta-analysis with data from 6 additional studies, which confirms and narrows the region of interest to HLA-DQB1 and establishes independence from asthma loci. [...]