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Functional interactors of genomewide association study genes are differentially expressed in severe chronic obstructive pulmonary disease lung tissue

ABSTRACT: Multiple gene expression studies have been performed in lung or airway tissues from subjects with chronic obstructive pulmonary disease (COPD). However, in comparison to genome-wide association studies (GWAS), there has been poor replication across these studies. We sought to perform gene expression profiling on a large sample of severe COPD cases and control smokers and use network methods to identify interacting genes and pathways. We collected surgically-resected lung tissue samples from subjects with severe COPD and controls with normal lung function; all subjects were former smokers. Gene expression profiling on homogenized lung tissue was performed using Illumina HumanHT-12 BeadChips. Protein and RNA binding studies, RNA-interference, a murine smoking model, and expression quantitative trait locus analyses were used to identify genes and proteins that may interact with three known COPD GWAS genes: IREB2, HHIP and FAM13A. Weighted Gene Co-Expression Network Analysis (WGCNA) was used to define co-expressed gene modules. Comparing 111 COPD cases and 40 control smokers, 214 genes were differentially expressed; none of these genes were at significant GWAS loci. However, the top differentially expressed gene was HMGB1, which interacts with AGER, a gene implicated through COPD GWAS. The genes differentially expressed in lung tissue showed strong enrichment for putative interactors of IREB2 and HHIP, with less support for FAM13A, based on the gene sets from the in vitro, in vivo, and in silico studies. In the WGCNA, the module most highly associated for COPD was enriched for B-cell pathways, which shared seventeen genes with the results of the Hhip+/- mouse smoking model. As in other common diseases, genes at COPD GWAS loci were not differentially expressed with COPD status; however, using a combination of network methods, experimental studies of interaction and careful phenotype definition, we found differential expression of putative interactors of these genes, and we replicated previous human and mouse microarray results involving B cell pathways.

ORGANISM(S): Homo sapiens

PROVIDER: GSE76925 | GEO | 2017/03/29

SECONDARY ACCESSION(S): PRJNA308946

REPOSITORIES: GEO

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Project description:Background: The identification of causal variants responsible for disease associations from genome-wide association studies (GWAS) facilitates functional understanding of the disease mechanisms implicated by GWAS. One of the earliest GWAS associations to COPD spans an intragenic region within FAM13A, but the causal variants at this loci have not yet been identified. Massively parallel reporter assays (MPRA) can be used to prioritize functional regulatory variants in a high-throughput manner. Methods: We used an integrated approach using fine-mapping in over 10,000 subjects from COPD GWAS studies, two MPRA experiments, traditional reporter assays, chromatin conformation capture, and CRISPR-based gene editing to characterize COPD-associated regulatory variants in FAM13A in human bronchial epithelial cell lines. Results: Conditional genetic association and fine mapping analyses identified two independent COPD association signals in FAM13A. MPRA identified 45 common functional regulatory variants, and six COPD-associated putative functional variants were prioritized for further functional investigation. Three variants demonstrated significant activity in traditional reporter assays, and one variant, rs2013701, was selected for further testing in the endogenous genomic context based on a direction of effect consistent with postulated mechanisms of FAM13A-mediated COPD susceptibility. CRISPR-based genome editing for this variant confirmed allele-specific effects on FAM13A expression and altered rates of cellular proliferation, providing multiple levels of functional characterization for this COPD-associated variant. Conclusions: Comprehensive screening for regulatory variants near FAM13A identified the presence of extensive functional regulatory variation within a 250kb window of FAM13A in HBECs. Focused functional evaluation of the COPD-associated functional variants in LD with the two independent association signals in this region prioritized the common variant rs2013701, for which multiple parallel lines of functional evidence confirm allelic effects on FAM13A regulation.

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Functional interactors of genomewide association study genes are differentially expressed in severe chronic obstructive pulmonary disease lung tissue

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