17q21 Variants Disturb Mucosal Host Defense in Childhood Asthma

Abstract

Rationale: The strongest genetic risk factor for childhood-onset asthma, the 17q21 locus, is associated with increased viral susceptibility and disease-promoting processes.Objectives: To identify biological targets underlying the escalated viral susceptibility associated with the clinical phenotype mediated by the 17q21 locus.Methods: Genome-wide transcriptome analysis of nasal brush samples from 261 children (78 healthy, 79 with wheezing at preschool age, 104 asthmatic) within the ALLIANCE (All-Age-Asthma) cohort, with a median age of 10.0 (range, 1.0-20.0) years, was conducted to explore the impact of their 17q21 genotype (SNP rs72163891). Concurrently, nasal secretions from the same patients and visits were collected, and high-sensitivity mesoscale technology was employed to measure IFN protein levels.Measurements and Main Results: This study revealed that the 17q21 risk allele induces a genotype- and asthma/wheeze phenotype-dependent enhancement of mucosal GSDMB expression as the only relevant 17q21-encoded gene in children with preschool wheeze. Increased GSDMB expression correlated with the activation of a type-1 proinflammatory, cell-lytic immune, and natural killer signature, encompassing key genes linked to an IFN type-2-signature (IFNG, CXCL9, CXCL10, KLRC1, CD8A, GZMA). Conversely, there was a reduction in IFN type 1 and type 3 expression signatures at the mRNA and protein levels.Conclusions: This study demonstrates a novel disease-driving mechanism induced by the 17q21 risk allele. Increased mucosal GSDMB expression is associated with a cell-lytic immune response coupled with compromised airway immunocompetence. These findings suggest that GSDMB-related airway cell death and perturbations in the mucosal IFN signature account for the increased vulnerability of 17q21 risk allele carriers to respiratory viral infections during early life, opening new options for future biological interventions.The All-Age-Asthma (ALLIANCE) cohort is registered at www.clinicaltrials.gov (pediatric arm, NCT02496468).

Keywords: ALLIANCE; asthma; nasal transcriptome; preschool wheeze.

Figure 1.

Transcriptional changes in nasal brushings of wheezing children with and without the 17q21 risk allele. (A) Volcano plot of differentially expressed genes in wheezing children carrying the 17q21 homozygous risk allele compared with those with a wild-type allele. Red squares indicate significant upregulation, and blue squares indicate significant downregulation. (B) Heat map of genes with increased abundance in wheezing children carrying the 17q21 homozygous risk allele (right column) compared with those with a wild-type allele (left column). Expression in heterozygous children is shown in the middle column (1.5-fold change threshold; P ⩽ 0.05; false discovery rate ⩽ 5%; moderated t test). Red boxes indicate more abundant genes, white boxes intermediately abundant genes, and blue boxes less abundant genes. Corresponding gene symbols are listed on the right side of the panel and the Ward’s clustering tree on the left side of the heat map.

Figure 2.

Transcriptional changes associated with GSDMB expression intensity in wheezing and asthmatic children. A simplified scheme is shown illustrating the differentially expressed genes associated with the intensity of GSDMB expression in wheezing and asthmatic children, focusing on the top scoring hits with a change threshold of 4.5-fold. (A) Venn diagram showing the cut set of GSDMB expression intensity–dependent (GSDMB-high vs. GSDMB-low) upregulated genes from wheezing (left) and asthmatic (right) children. (B) Heat map of GSDMB expression–associated upregulated hits in wheezing and asthmatic children from the cut set of A. Heat maps show averaged intensities of healthy, wheezing, or asthmatic children categorized into GSDMB-low (lower 20%), moderate, and GSDMB-high (upper 20%) expression intensity. To gain insight into the most prominent functional changes, the display is reduced to the top scoring hits at the 4.5-fold change threshold (P ⩽ 0.05; false discovery rate ⩽ 5%; moderated t test).

Figure 3.

Gene expression intensity for genes involved in type 1, 2, 3, and regulatory immunity in nasal nasal brushings of children in relation to GSDMB expression, asthma, IgE, and fractional exhaled nitric oxide (Fe_NO) class. Heat maps show average intensities of genes prototypical for types 1, 2, 3, and regulatory immunity in healthy, wheezing, and asthmatic children categorized into (A) low (lower 20%), moderate, and high GSDMB (upper 20%) expression intensity; (B) healthy, wheezing, and asthmatic children with low IgE and asthmatic children with high IgE levels; and (C) wheezing and asthmatic children with low and moderate Fe_NO and asthmatic children with high Fe_NO. Statistical significance is marked with an asterisk (1.5-fold change threshold; P ⩽ 0.05; false discovery rate ⩽ 5%; moderated t test): (A) GSDMB-high versus GSDMB-low, (B) asthma IgE-high versus asthma IgE-low, and (C) asthma Fe_NO-high versus asthma Fe_NO-low.

Figure 4.

Gene expression intensity for IFN-related genes in nasal brush samples of children in relation to GSDMB expression and 17q21 genotype. Heat maps show average intensities of IFN-related genes in healthy, wheezing, and asthmatic children who were categorized into (A) low (lower 20%), moderate, and high GSDMB (upper 20%) expression intensity; (B) healthy, wheezing, and asthmatic children carrying wild-type, heterozygous (+/−), or homozygous (−/−) 17q21 polymorphisms. Statistical significances in gene expression analysis is marked with an asterisk (1.5-fold change threshold; P ⩽ 0.05; false discovery rate ⩽ 5%; moderated t test): (A) GSDMB-high versus GSDMB-low and (B) heterozygous versus wild-type and homozygous versus wild-type of the corresponding disease entity. Protein levels of (C) IFN-λ3 and (D) IFN-γ measured by mesoscale multiplex ELISA are depicted in relation to GSDMB expression (low/moderate/high) and tested using Mann-Whitney U tests. *P ⩽ 0.05. Protein levels of (E) IFN-λ3 and (F) IFN-γ measured by mesoscale multiplex ELISA technique are depicted in relation to mutational status (wt = wild-type; mut = mutant) and tested using Mann-Whitney U tests.