DNA methylation in nasal epithelium, atopy, and atopic asthma in children: a genome-wide study

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1 DNA methylation in nasal epithelium, atopy, and atopic asthma in children: a genome-wide study Erick Forno*, Ting Wang*, Cancan Qi*, Qi Yan, Cheng-Jian Xu, Nadia Boutaoui, Yueh-Ying Han, Daniel E Weeks, Yale Jiang, Franziska Rosser, Judith M Vonk, Sharon Brouwer, Edna Acosta-Perez, Angel Colón-Semidey, María Alvarez, Glorisa Canino, Gerard H Koppelman, Wei Chen, Juan C Celedón Summary Background Epigenetic mechanisms could alter the airway epithelial barrier and ultimately lead to atopic diseases such as asthma. We aimed to identify DNA methylation profiles that are associated with and could accurately classify atopy and atopic asthma in school-aged children. Methods We did a genome-wide study of DNA methylation in nasal epithelium and atopy or atopic asthma in 483 Puerto Rican children aged 9 2 years, recruited using multistage probability sampling. Atopy was defined as at least one positive IgE ( 35 IU/mL) to common aeroallergens, and asthma was defined as a physician s diagnosis plus wheeze in the previous year. Significant (false discovery rate p< 1) methylation signals were correlated with gene expression, and top CpGs were validated by pyrosequencing. We then replicated our top methylation findings in a cohort of 72 predominantly African American children, and in 432 children from a European birth cohort. Next, we tested classification models based on nasal methylation for atopy or atopic asthma in all cohorts. Findings DNA methylation profiles were markedly different between children with (n=312) and without (n=171) atopy in the Puerto Rico discovery cohort, recruited from Feb 12, 214, until May 8, 217. After adjustment for covariates and multiple testing, we found 8664 differentially methylated CpGs by atopy, with false discovery rate-adjusted p values ranging from ¹⁷ to ²² for the top 3 CpGs. These CpGs were in or near genes relevant to epithelial barrier function, including CDHR3 and CDH26, and in other genes related to airway epithelial integrity and immune regulation, such as FBXL7, NTRK1, and SLC9A3. Moreover, 28 of the top 3 CpGs replicated in the same direction in both independent cohorts. Classification models of atopy based on nasal methylation performed well in the Puerto Rico cohort (area under the curve [AUC] and accuracy 85 88%) and in both replication cohorts (AUC 74 92, accuracy 68 82%). The models also performed well for atopic asthma in the Puerto Rico cohort (AUC 95 1, accuracy 88%) and the replication cohorts (AUC 82 88, accuracy 86%). Interpretation We identified specific methylation profiles in airway epithelium that are associated with atopy and atopic asthma in children, and a nasal methylation panel that could classify children by atopy or atopic asthma. Our findings support the feasibility of using the nasal methylome for future clinical applications, such as predicting the development of asthma among wheezing infants. Funding US National Institutes of Health. Copyright 218 Elsevier Ltd. All rights reserved. Introduction Sensitisation to allergens (atopy) is a key component of atopic diseases such as asthma and atopic dermatitis. Over the past few decades, the prevalence of allergic diseases has increased in industrialised nations, probably due to environmental changes. Such changes could alter epi genetic regulation and expression of atopy susceptibility genes, ultimately leading to atopic diseases. 1 A meta-analysis 2 of genome-wide association studies identified 18 genetic loci associated with asthma, but such loci explained only 3 5% of disease risk, emphasising the need to identify non-genetic, environmentally-mediated (ie, epigenetic) causal mechanisms for atopy and asthma. By modulating activating and inhibitory signals, the airway epithelium regulates immune responses to en- vironmental challenges and airway inflammation. 3 Tobacco smoke, allergens, or pollutants could penetrate defective epithelial barriers, interact with dendritic cells, alter immune responses, and cause atopy in children. Several susceptibility genes for asthma are expressed in airway epithelium (eg, CDHR3, PCDH1, 4 and ORMDL3/GSDMB). 5 CDHR3 is a receptor for rhinovirus C (implicated in asthma and severe asthma exacerbations), 6 and bronchial epithelial expression of ORMDL3 contributes to the induction of Alternaria spprelated allergic airway disease in murine models. 7 Similarly, polymorphisms of filaggrin, a filamentassociated protein that binds to keratin in skin epithelium, confer susceptibility to atopic dermatitis. 8 In the USA, asthma affects about 7 million children and 1 12% of adolescents report respiratory or skin allergies. Puerto Ricans are disproportionately affected Lancet Respir Med 218 Published Online December 21, S (18) See Online/Comment S (18)354-6 *Joint first authors Joint senior authors Division of Pulmonary Medicine, Children s Hospital of Pittsburgh of UPMC, Pittsburgh, PA, USA (E Forno MD, T Wang PhD, Q Yan PhD, N Boutaoui PhD, Y-Y Han PhD, Y Jiang, F Rosser MD, W Chen PhD, Prof J C Celedón MD); Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA (E Forno, T Wang, Q Yan, N Boutaoui, Y-Y Han, Y Jiang, F Rosser, W Chen, Prof J C Celedón); Department of Pediatric Pulmonology and Pediatric Allergy, Beatrix Children s Hospital, Groningen, Netherlands (C Qi MsC, C-J Xu PhD, Prof G H Koppelman MD); GRIAC Research Institute (C Qi, C-J Xu, J M Vonk PhD, S Brouwer BSc, Prof G H Koppelman), Department of Epidemiology (J M Vonk), and Department of Pathology and Medical Biology, Experimental Pulmonology and Inflammation Research (S Brouwer), University of Groningen, University Medical Center Groningen, Groningen, Netherlands; Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA (Prof D E Weeks PhD); School of Medicine, Tsinghua University, Beijing, China (Y Jiang); and Behavioral Sciences Research Institute of Puerto Rico (E Acosta-Perez PhD, Prof G Canino PhD) and Department of Pediatrics Published online December 21,

2 (A Colón-Semidey MD, M Alvarez MD), Medical Science Campus, University of Puerto Rico, San Juan, Puerto Rico Correspondence to: Prof Juan C Celedón, Division of Pediatric Pulmonary Medicine, Children s Hospital of Pittsburgh of UPMC, Pittsburgh, PA 15224, USA juan.celedon@chp.edu Research in context Evidence before this study A large meta-analysis of genome-wide association studies identified 18 loci associated with asthma but explaining only 3 5% of disease risk. Given that genes associated with childhood asthma are often expressed in airway epithelium, environmentally-influenced epigenetic regulation of that tissue could play a role in the pathogenesis of atopic asthma. We searched PubMed for articles published in English as of April, 218, using the terms ( DNA methylation OR epigenetic changes ) AND ( atopy OR asthma ) and found previous reports of DNA methylation in blood or white blood cells and asthma, but minimal evidence of a link between airway epithelium DNA methylation and atopy or asthma. Added value of this study To our knowledge, this is the first genome-wide study of the nasal epithelium methylome and atopy, and the first such study of atopic asthma in a large sample of children. We identified 8664 CpG sites that were significantly associated with atopy and atopic asthma in Puerto Rican children; FDR p values ranged from ¹⁷ to ²² for the top 3 CpGs. Several top CpGs were located near genes associated with immune responses or epithelial barrier function, and a high proportion of significant CpGs were associated with changes in gene expression. We replicated 28 of the top 3 CpGs in two independent cohorts from different ethnic backgrounds; combined p values for the three cohorts ranged from ¹⁹ to ⁴⁷. Moreover, we designed a 3-CpG panel that accurately classified children according to atopy (area under the curve for the original cohort and for the replication cohorts) or atopic asthma ( 95 1 in the original cohort, and in the replication cohorts). Our findings were robust to differences in ethnic and racial background, geographic location, and environmental exposures across cohorts. None of the top 3 genes in our study overlapped with the 18 asthma-susceptibility genes identified in a recent genome-wide association study meta-analysis, emphasising the novelty and importance of our results. Moreover, we identified a CpG panel that accurately classifies atopy and atopic asthma across three diverse populations. Implications of all the available evidence DNA methylation profiles in airway epithelium are significantly associated with atopy and atopic asthma, particularly near genes related to epithelial barrier integrity or function and other immune regulatory processes. Epigenetic regulation of the airway epithelium has a key role in the pathogenesis of atopy and asthma, and the nasal methylome could be used to develop much-needed research and clinical tools in future longitudinal studies. Such studies should help identify methylation marks that precede disease development or treatment response, and thus lead to clinical applications for the prediction of atopy or asthma in infants, and therapeutic responses in children with asthma. See Online for appendix 1 by asthma and atopy, 9,1 and are often exposed to environmental agents linked to both DNA methylation and atopic diseases, such as second-hand smoke 1 and air pollution. 11,12 We therefore hypothesised that DNA methylation of airway epithelium is linked to atopy and atopic asthma in Puerto Ricans. To test this hypothesis, we did genome-wide studies of DNA methylation in nasal epithelium (a surrogate marker for bronchial epithelium 13,14 ) and atopy and atopic asthma in Puerto Rican children and adolescents, a high-risk group. We then conducted replication studies for the top methylation signals in two cohorts. 5,15 Moreover, we tested predictive modelling based on nasal methylation to classify children according to whether they had atopy or atopic asthma, as a necessary step to provide proof of concept and show the feasibility of future clinical applications using the nasal methylome. Methods Study design and participants The Epigenetic Variation and Childhood Asthma in Puerto Ricans (EVA-PR) is a case-control study of asthma in participants aged 9 2 years, recruited using a similar approach to that used in a previous study (appendix 1). 16,17 This Article is the first report of several possible future publications of this cohort data. Participants with and without asthma were recruited from households in San Juan, Puerto Rico, using multistage probability sampling. The study was approved by the institutional review boards of the University of Puerto Rico (San Juan, PR) and the University of Pittsburgh (Pittsburgh, PA, USA). Written parental consent and assent were obtained for participants younger than 18 years, and consent was obtained from participants aged 18 years or older. The study protocol included questionnaires on respiratory health, measurement of serum allergen-specific IgE, and nasal samples for DNA and RNA extraction. Atopy was defined as at least one positive IgE ( 35 IU/mL) to five common aeroallergens in Puerto Rico: house dust mite, cockroach, cat dander, dog dander, and mouse urinary protein. Asthma was defined as a physician s diagnosis plus at least one episode of wheeze in the previous year. Procedures DNA and RNA were extracted from nasal specimens collected from the inferior turbinate. To account for potential effects of different cell types, we implemented a protocol in a subset of nasal samples (n=31) to select CD326-positive nasal epithelial cells before DNA and RNA extraction. Whole-genome methylation assays were done with HumanMethylation45 BeadChips (Illumina, San Diego, CA, USA). After quality control (appendix 1), 2 Published online December 21, 218

3 CpG probes remained. Methylation β values were calculated as a percentage: M β= M + U + α where M values and U values represent methylated and unmethylated signal intensities, respectively, and α is an arbitrary offset to stabilise β values where fluorescent intensities are low. β values were then transformed to M values as: M=log 2 β 1 β M values were used in all downstream analyses. RNA- Seq was done with the Illumina NextSeq 5 platform (Illumina; San Diego, CA, USA), paired-end reads at 75 cycles, and 8M reads/sample; reads were aligned to reference human genome (hg19) and transcripts per kilobase million were used as proxy for gene expression level. After quality control, genes were retained; our analysis focused on genes within less than 1 kbp with significant CpGs (false discovery rate [FDR] p< 1) from the methylation analysis, to include cis-regulatory elements. For both genome-wide methylation and RNA-Seq, known batch effects (eg, plates) were removed using an empirical Bayes framework, and sva was used to estimate latent factors that capture unknown data heterogeneity. Association analysis We did an epigenome-wide association study using multivariable logistic regression with the general model: Atopy or atopic asthma=cpg M + age + sex + latent factors + A + B where A is the top five principal components from genotypic data and (for the analysis of atopy only) B is asthma status. Adjustment for multiple testing was done with the FDR; significance was defined as FDR-corrected p values less than 1. We analysed differentially methylated regions using Python tool comb-p, with a seed p value of 1 and a maximum extendable distance of 3 bp. The regression output included the effect size and p value for each CpG. For ease of interpretation, tables show the difference in mean β between participants with atopy and those without atopy, expressed as a percentage: Methylation Δ (%) = mean β atopy mean β no atopy To evaluate whether significant methylation signals were associated with gene expression, we did a trascriptomewide association study (following a similar model but using log 2 -scaled transcripts per kilobase million instead of M values) and then did an expression quantitative trait DNA methylation (eqtm) analysis of significant CpGs and genes in and within less than 1 kbp from those CpGs. We then did a mediation analysis to evaluate whether any proportion of the association between methylation and atopy was mediated by differences in gene expression. In this mediation analysis, we assessed the contributions of the direct pathway between methylation and atopy and the indirect (or mediated) pathway through changes in gene expression (appendix 1). Finally, we did an ingenuity pathway analysis including all genes with FDR p value less than 1 in the transcriptome-wide association study, epigenome-wide association study, and eqtm analysis. Classification models To investigate whether genome-wide methylation data could be used to classify atopy, we used three classic machine learning models to select the best performing panel for each method and their optimal probability cutoffs (appendix 1). For each method, we trained the model with 1111 potential households 145 screened households 72 eligible households 66 with missing contact data 325 not eligible 18 could not be reached 121 residents moved away 24 out of age range 638 people (1 per household) invited to participate 543 participants 483 in methylation analysis 236 asthma 247 no asthma 82 not interviewed (recruitment goal reached) 95 refused to participate 6 not included in analysis 4 missing data for atopy or covariates 2 with no or inadequate methylation data Figure 1: Study flow of participants in the EVA-PR case-control study EVA-PR=Epigenetic Variation and Childhood Asthma in Puerto Ricans. Published online December 21,

4 the top 5 CpGs from the epigenome-wide association study on all samples, and sorted all CpGs according to variable importance, defined as each CpG s contribution to the model (appendix 1). We then sequentially selected the top ten to 1 CpGs to train and test the models and to optimise the parameters (appendix 1). The performance of different methods using different numbers of features was compared based on the testing area under the receiver operating characteristic curve (AUC), with the largest average AUC among ten cross-validations indicating the best performance. On this basis, we selected a 3-CpG panel and evaluated its diagnostic test performance (appendix 1). To further compare the performance of the CpG panel, we used two negative controls: a model using 3 randomly selected CpGs; and a model using only demographic or questionn aire variables (age, sex, household income, parental history of asthma, tobacco smoke exposure in early life, obesity, and allergic rhinitis). Validation and external replications We internally validated top CpGs using pyrosequencing in a random subsample from the Puerto Ricon cohort of Puerto Rico (discovery cohort; n=483) Yang and colleagues (n=72) 5 PIAMA (n=432) 18 Atopy No atopy Atopic asthma Non-atopic controls (no atopy or asthma) Atopic asthma Non-atopic controls (no atopy or asthma) Atopy No atopy Participants, n/n (%) 312/483 (65%) 171/483 (35%) 169/273 (62%) 14/273 (38%) 36 (5%) 36 (5%) 27 (48%) 225 (52%) Age, years 15 (3) 15 (3) 15 (3) 16 (3) 11 1 ( 8) 1 9 ( 9) 16 4 ( 2) 16 3 ( 2) Sex Male 172 (55%) 78 (46%) 13 (61%) 43 (41%) 19 (53%) 17 (47%) 115 (56%) 98 (44%) Female 14 (45%) 93 (54%) 66 (39%)* 61 (59%) 17 (47%) 19 (53%) 92 (44%) 127 (56%) Asthma 169 (54%)* 67 (39%) 169 (1%)* 36 (1%)* 27 (13%)* 6 (3%) Total IgE, IU/mL 49 (27 816)* Number of positive allergen-specific IgEs 43 (22 93) 386 (214 86)* 42 (21 78) 366 ( ) 29 ( ) 14 (55 14) 2 (1 3)* 2 (1 3)* n/a 2 (1 3)* 2 (1 55) Data are n (%), mean (SD), or median (IQR), unless otherwise stated. In EVA-PR, all participants were Hispanic or Latino. In Yang and colleagues study, 5 ten (14%) were Hispanic or Latino, 66 (92%) were African American, five (7%) were non-hispanic white, and three (4%) were unknown or other ethnicity; data do not add up to 1% because participants could report more than one race or ethnicity. In the PIAMA study, (97%) were non-hispanic white, and 13 (3%) were unknown or other ethnicity. n/a=not available in public dataset. EVA-PR=Epigenetic Variation and Childhood Asthma in Puerto Ricans. PIAMA=Prevention and Incidence of Asthma and Mite Allergy. *p< 5 for atopy vs no atopy, or asthma vs no asthma within each cohort. Table 1: Characteristics of study participants in the discovery and replication cohorts 3 25 EWAS of atopy in nasal epithelium EWAS of atopy, nasal, FDR p value cutoff 1 Non-significant 3834 hypermethylated CpGs hypomethylated CpGs 2 15 log 1 (p) 15 log1(fdr) Chromosome Effect size Figure 2: Epigenome-wide association study of atopy in nasal epithelium Left panel shows the Manhattan plot, with log 1 (p value) on the y axis and chromosome position on the x-axis; the red line indicates FDR p< 1. Right panel shows the volcano plot, with log 1 (FDR p value) on the y-axis and effect size on the x-axis. Hypermethylated CpGs (ie, more methylation in participants with atopy than in those with no atopy) are shown in red, hypomethylated CpGs in blue, and non-significant CpGs (FDR p> 1) in black. FDR=false discovery rate. EWAS=epigenome-wide association study. 4 Published online December 21, 218

5 4 participants with atopic asthma and 4 non-atopic, non-asthmatic controls. We also did external replication in two independent cohorts: a public dataset (GSE6525) from a case-control study of atopic asthma and nasal epithelial DNA methylation in 72 predominantly African American children; 5 and data from year-old participants in the Prevention and Incidence of Asthma and Mite Allergy (PIAMA) cohort of Dutch children born in Full details of all our methods are provided in appendix 1. Data sharing statement Appendix 1 contains the table with the summary estimates (effect estimates and p values) for the top 1 CpG sites from the analysis in Puerto Rico. Appendix 2 contains the table with all 8664 significant CpG sites (FDR p< 1). Further data are available upon request by contacting the corresponding author. Role of the funding source The study funder had no role in study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the paper for publication. The corresponding author had full access to all of the study data and takes responsibility for the integrity of the data and the accuracy of the data analysis and takes responsibility for the final decision to submit for publication. See Online for appendix 2 Puerto Rican (discovery) cohort CpG Gene Chromosome Position Methylation (%)* p value FDR p value Methylation (%)* Yang and colleagues PIAMA 18 Combined study 5 p value p value Methylation (%)* 1 cg METTL % ²⁸ ²² 22 4% ¹² 7 4% ¹⁸ ⁴⁷ 2 cg GJA % ²⁶ ²¹ 15 4% ¹⁰ 4 4% ¹⁴ ⁴⁰ 3 cg24772 NTRK % ²⁵ ²¹ 8 % ⁷ 3 8% ¹³ ³⁷ 4 cg PDE6A % ²⁵ ²¹ 12 7% ⁷ 8 1% ⁹ ³² 5 cg FBXL % ²⁵ ²¹ 23 3% ¹⁰ 6 9% ¹² ³⁷ 6 cg SPP % ²⁵ ²¹ 2 4% ⁹ 5 2% ⁷ ³² 7 cg CDHR % ²⁵ ²¹ 23 6% ¹³ 7 6% ¹⁴ ⁴³ 8 cg SUCNR % 3 1 ²⁵ ²¹ 2 8% ⁸ 11 7% ¹¹ ³⁵ 9 cg PCSK % ²⁵ ²¹ 16 % ¹¹ 5 3% ¹⁷ ⁴³ 1 cg LINC % ²⁴ ¹⁹ 25 9% ¹¹ 5 8% ⁷ ³² 11 cg PLEC % ²³ ¹⁹ 21 2% ⁸ 5 9% ¹⁰ ³³ 12 cg PCSK % ²³ ¹⁹ 9 % ⁶ 6 % ⁹ ²⁹ 13 cg94726 NCF % ²³ ¹⁹ 14 4% ⁵ 7 2% ⁴ ²³ 14 cg ANKRD % ²³ ¹⁹ 7 1% ⁴ 4 6% ⁹ ²⁷ 15 cg TEX36 AS % ²² ¹⁸ 6 5% ⁴ 2 4% ⁴ ²² 16 cg C22orf % ²² ¹⁸ 16 3% ¹⁰ 4 2% ⁹ ³³ 17 cg LRRFIP % ²² ¹⁸ 7 6% ⁴ 2 6% ⁷ ²⁵ 18 cg BANF % ²² ¹⁸ 15 2% ⁷ 4 2% ¹¹ ³¹ 19 cg CES4A % ²² ¹⁸ 12 % ⁸ 1 6% ²³ 2 cg ADCK % ²² ¹⁸ 9 1% ⁷ 5 6% ⁷ ²⁷ 21 cg46211 GRK % ²² ¹⁸ 13 6% ⁴ 3 2% ⁴ ²¹ 22 cg EFNA % ²² ¹⁸ 11 1% ⁹ 4 7% ¹⁴ ³⁵ 23 cg SLC9A % ²² ¹⁸ 4% % ⁶ ²¹ 24 cg CDH % ²² ¹⁸ 1 1% ⁴ 2 1% ¹⁹ 25 cg CAPN % ²¹ ¹⁸ 9 7% ⁶ 4 % ¹¹ ²⁹ 26 cg TSHR % ²¹ ¹⁷ 17 1% ⁷ 3 4% ⁶ ²⁷ 27 cg ZPLD % ²¹ ¹⁷ 17 3% ⁹ 4 % ⁷ ²⁹ 28 cg18321 NUP % ²¹ ¹⁷ 15 2% ⁶ 4 3% ⁶ ²⁴ 29 cg MAP3K % ²¹ ¹⁷ 3 9% ⁵ 3 8% ⁴ ²² 3 cg PRKD % ²⁰ ¹⁷ 7 1% % ⁶ ²⁰ Discovery cohort analysis adjusted for age, sex, asthma status, methylation latent factors, and genotypic principal components. Analysis of participants in Yang and colleagues study 5 adjusted for age, sex, and latent factors. PIAMA 18 replication adjusted for age, sex, asthma status, batch, and study centre. CpG position is from hg19 reference genome. A list of the top 1 significant CpGs in the Puerto Rico cohort is found in appendix 1, which also contains Bonferroni-corrected p values for those CpGs. All significant CpGs in Puerto Rico are found in appendix 2. EWAS=epigenome-wide association study. PIAMA=Prevention and Incidence of Asthma and Mite Allergy. *Methylation shows the difference between the mean methylation β in participants with atopy and those without atopy; 23 8% means that the mean β for participants with atopy was 238 lower than for participants without atopy. Fisher combined p value. Table 2: Top 3 results for epigenome-wide association study of atopy p value Published online December 21,

6 2 156 hypomethylated CpGs and 815 upregulated genes 1773 hypomethylated CpGs and 1199 non-significant genes 59 hypomethylated CpGs and 474 downregulated genes non-significant CpGs and 298 upregulated genes non-significant CpGs and 447 downregulated genes 986 hypermethylated CpGs and 528 upregulated genes 1536 hypermethylated CpGs and 98 non-significant genes 779 hypermethylated CpGs and 514 downregulated genes Non-significant Gene expression, sign(effect) ( log1 [FDR p value]) DNA methylation, sign(effect) ( log1 [FDR p value]) 1 Figure 3: Integration of epigenome-wide and transcriptome-wide association study results for atopy Figure shows the log1(fdr p value) for DNA methylation (epigenome-wide association study) on the x-axis, and for gene expression (transcriptome-wide association study) on the y-axis; positive values indicate hypermethylation or over-expression, and negative values indicate hypomethylation or under-expression. Pairs where both epigenome-wide and transcriptome-wide results are non-significant (FDR p> 1) are shown in the middle quadrant. Significantly hypermethylated CpGs with underexpressed corresponding genes are shown in the right lower quadrant (779 CpGs, 514 genes); hypomethylated and overexpressed genes are shown in the left upper quadrant (156 CpGs, 815 genes). FDR=false discovery rate. Results From Feb 12, 214, until May 8, 217, 638 of 72 households with at least one eligible child were invited to participate, and 543 (85%) children (one per household) agreed to participate. There were no significant differences in age or sex between eligible children who did and did not participate. A total of 53 participants had complete data for atopy, atopic asthma, and all covariates; 483 had data for nasal genome-wide methylation and 456 had data for nasal RNA-Seq (figure 1; appendix 1). The main characteristics of study participants are shown in table 1. Atopic participants had higher mean total IgE (79 IU/mL vs 11 IU/mL) and were more likely to have asthma (169 [57%] vs 67 [39%]) than were those without atopy, without significant differences in age or sex. DNA methylation profiles were remarkably different between participants with and without atopy (figure 2). After adjustment for covariates and multiple testing, we 6 found 8664 differentially methylated CpGs by atopy (FDR p< 1): 3834 with higher methylation in atopic participants and 483 with lower methylation in atopic participants. Table 2 shows the top 3 differentially methylated CpGs, with FDR-adjusted p values ranging from ¹⁷ to ²². Similarly, we found differentially methylated regions associated with those top genes (appendix 1). These CpGs and differentially methylated regions were in or near biologically plausible genes for atopy, such as FBXL7 (FDR p=8 5 1 ²¹), NTRK1 (FDR p=8 5 1 ²¹), CDHR3 (FDR p=8 5 1 ²¹), CDH26 (FDR p=5 8 1 ¹⁸), CAPN14 (FDR p=9 5 1 ¹⁸), GRK5 (FDR p=5 2 1 ¹⁸), and SLC9A3 (FDR p=5 6 1 ¹⁸). There was no residual clustering by sex, batch group, or processing protocol (ie, whole nasal sample vs CD326positive epithelial cells; appendix 1). Moreover, we obtained similar results in analyses restricted to the 31 cell-sorted samples despite small sample size (appendix 1) or after removing samples from 12 participants using nasal steroids (data not shown). There was substantial overlap between differential meth ylation and expression (figure 3), including 779 hyper methylated CpGs corresponding to 514 down regulated genes, and 156 hypomethylated CpGs corresponding to 815 upregulated genes. Among genes at or near our top results from the epigenomewide association study, 13 (43%) of 3 showed differential expression by atopy, including SLC9A3, PCSK6, CDH26, FBXL7, and NTRK1 (appendix 1). The eqtm analysis revealed 157 CpG gene expression pairs, including 11 (37%) of the top 3 results from the epigenome-wide association study (appendix 1). On the basis of these findings, we did a mediation analysis for each top 3 CpG gene pair to evaluate direct pathways (between methylation and atopy) and indirect or mediated pathways through changes in gene expression; we found significant mediation for 12 (4%) of 3 genes (appendix 1), including CDH26, PCSK6, PRKD1, SLC9A3, and MAP3K14. Results from the pathway analysis of the 724 genes that were significant in the epigenome-wide and transcriptome-wide association studies and eqtm analyses are shown in appendix 1 and figure 4. The top 2 enriched pathways were related to immune regulation (T-helper-1 [Th1] and T-helper-2 [Th2] pathways, antigen presentation, regulatory T cell and NK cell signalling pathways, among others), as well as gap junction signalling and the ErbB or epidermal growth factor receptor pathway. The results of the analysis of atopic asthma are shown in appendix 1. DNA methylation profiles markedly differed between children with atopic asthma and those without atopy or asthma; FDR-adjusted p values for the top 3 CpGs in atopic asthma ranged from ¹³ to ¹⁶ (appendix 1). There was substantial overlap between the results for atopy and those for atopic asthma (appendix 1), and the top epigenome-wide association study results for atopic asthma were similar to our results for atopy. Published online December 21, 218

7 log(b-h p value) Calcium-induced T-lymphocyte apoptosis CD28 signalling in T-helper cells icos-icosl signalling in T-helper cells Th1 pathway Type 1 diabetes signalling Cdc42 signalling OX4 signalling pathway Th1 and Th2 activation pathway Th2 pathway Antigen presentation pathway Natural killer cell signalling RAR activation CTLA4 signalling in cytotoxic T-lymphocytes HER2 signalling in breast cancer Osteoarthritis pathway Renin angiotensin signalling Role of NFAT in regulation of the immune response Neuropathic pain signalling in dorsal horn neurons Gap junction signalling ErbB signalling Enrichment ratios log(p value) Ratio Calcium-induced T-lymphocyte apoptosis Type 1 diabetes signalling Role of NFAT in regulation of the immune response OX4 signalling pathway Th1 pathway Gap junction signalling Cdc42 signalling icos-icosl signalling in T-helper cells Th2 pathway Th1 and Th2 activation pathway CTLA4 signalling in cytotoxic T-lymphocytes Natural killer cell signalling Neuropathic pain signalling in dorsal horn neurons CD28 signalling in T-helper cells Renin angiotensin signalling HER2 signalling in breast cancer RAR activation Figure 4: Pathway analysis of nasal epigenomics and atopy Top panel shows the top 2 enriched canonical pathways for our analyses of atopy. Bottom panel shows the overlap between these top 2 pathways. Only connections between pathways with at least five genes in common are shown. Pathway analysis performed including all genes that were significant (FDR p< 1) in the epigenomewide association study, transcriptome-wide association study, and expression quantitative trait DNA methylation analyses (n=724 genes). Further details are provided in appendix 1. FDR=false discovery rate. Published online December 21,

8 1 Puerto Rico Yang and colleagues PIAMA 8 Sensitivity 6 4 AUC 2 GBM 934 GLMNET 928 RF Specificity GLMNET Atopy No atopy Test positive 249 Test negative 45 Sensitivity Specificity 87 PPV 92 NPV 76 Accuracy Specificity Atopy Sensitivity 67 No atopy 1 35 Specificity 97 AUC GBM 923 GLMNET 915 RF 99 PPV 96 NPV 75 Accuracy Specificity Atopy Sensitivity 58 No atopy Specificity 87 AUC GBM 734 GLMNET 792 RF 738 PPV 8 NPV 69 Accuracy 73 Figure 5: DNA methylation panel and classification of atopy in study cohorts ROC curves are shown for each cohort using three different statistical approaches, with classification tables shown for atopy in the GLMNET model. Results shown are from using the same 3-CpG panel, coefficients, and probability cutoffs trained from the Puerto Rico cohort data, then applied to both independent cohorts. Accuracy refers to the sum of true positives and true negatives, divided by the total number. ROC=receiver operating characteristic. GBM=gradient boosting machine. GLMNET=Lasso and elastic-net regularised generalised linear model. RF=random forest. PPV=positive predictive value. NPV=negative predictive value. Pyrosequencing of 15 top CpGs (nine for atopy, six for atopic asthma) showed strong correlation with microarray results (appendix 1; correlation coefficients from 84 to 96, p values from ²² to ⁴²). Furthermore, methylation of all CpGs measured by pyrosequencing was significantly associated with atopy in the same direction as the microarray epigenome-wide association study (appendix 1). Results from the replication analysis of our epigenomewide association study of atopy are shown in table 2. Using data from Yang and colleagues, 5 28 of 3 CpGs replicated in the same direction with p less than 1. Likewise, in PIAMA, 29 of 3 CpGs replicated in the same direction with p less than 1. Fisher combined p values across the three cohorts ranged from ¹⁹ to ⁴⁷ (table 2). Additionally, we replicated most of the top results reported by Yang and colleagues (appendix 1). On the basis of our analysis using three models to determine the best predictive CpGs, optimal number of markers, and probability cutoffs (appendix 1), we selected a 3-CpG panel (appendix 1). Results from applying this panel to classify participants by atopy are shown in figure 5. Depending on the model, in the Puerto Rico cohort the AUC ranged from 93 to 94; accuracy was 85 88%, sensitivity 85 87, specificity 85 89, positive predictive value 91 94, and negative predictive value Similar results were obtained after applying the same panel and model to data from Yang and colleagues for atopic asthma (AUC 91 92, accuracy 81 82%, sensitivity 67 92, specificity 75 97, positive predictive value 77 96, and negative predictive value 74 9). In PIAMA, we obtained AUCs ranging from 74 to 79, accuracy 68 73%, sensitivity 51 62, specificity 74 87, positive predictive value 69 8, and negative predictive value for atopy. By contrast, our negative control models yielded AUCs of (for a panel of 3 randomly selected CpGs) and (for the model including only demographic and questionnaire data) among Puerto Rican children in EVA-PR (appendix 1). Next, we applied the same CpG panel to classify atopic asthma (appendix 1). In Puerto Rico, the panel yielded AUCs of 95 1 and accuracy of 88%. In PIAMA, the analysis of atopic asthma yielded AUCs of and accuracy of 86%. Because Yang and colleagues compared patients with atopic asthma with non-atopic controls, the analysis of atopy and atopic asthma yielded the same results as that of atopy versus no atopy. Discussion Nasal epithelium is a non-invasive surrogate marker for bronchial epithelium in children. 13,14 We showed that epigenomic profiles in nasal epithelium are significantly associated with atopy or atopic asthma in three cohorts of children and adolescents. Moreover, many top DNA methylation signals were associated with expression of their corresponding genes and, in several instances, the association between methylation and atopy was mediated by gene expression. Importantly, the 3-CpG panel we selected accurately identified atopy or atopic asthma. To our knowledge, this is the first genome-wide study of DNA methylation and atopy, and the largest such study of atopic asthma. Our results strongly suggest a key role for a dysfunctional airway epithelium in atopy and asthma. 8 Published online December 21, 218

9 Our enrichment analysis revealed that the methylation signals linked to atopy or atopic asthma are in pathways related to gap junction signalling and immune regulation, including antigen presentation and Th1/Th2 signalling. Indeed, several genes identified in this study are implicated in epithelial barrier processes and immune regulation, including CDH26, a cadherin family protein that is involved in allergic responses, modulates CD4-positive T cells and interleukin 2 production, 19 and regulates airway epithelial cell structure and polarity. 2 CDHR3, in the same family, has been strongly implicated in interactions between rhinovirus infection and asthma exacerbations, and in bronchiolitis. 21,22 GJA4 expression in bronchiolar epithelium is markedly decreased in murine asthma. 23 CAPN14, a susceptibility locus for eosinophilic oesophagitis, is induced by interleukin 13, and together they alter epithelial function and repair MTRNL (meteorin-like), part of our classification panel and a cytokine present in mucosal barrier and skin, is over-expressed in atopic dermatitis. 27 Our findings suggest that DNA methylation may alter airway epithelial integrity and function, leading to antigen penetration of the epithelial barrier, antigen presentation to dendritic cells, altered Th1/Th2 immune responses, and ultimately atopy or atopic asthma. Other genes present in both our top CpGs and the classification panel are involved in atopy, lung disease, or inflammation. We found decreased methylation (and increased expression) of NTRK1 in atopy. NTRK1 has been linked to circulating nerve growth factor in children with asthma, with epistasis between both genes; 28 NTRK1 is induced by interleukin 13, enhances allergic inflammation, and is increased in eosinophilic oesophagitis. 29 SLC9A3 codes for an Na + /H + exchanger and has been linked to decreased lung function in cystic fibrosis; 3,31 to our knowledge, our study is the first report to link SLC9A3 to atopy or asthma. Among genes significant at multiple levels (eg, epigenome-wide association study, eqtm, and mediation analyses), PCSK6 was among the top findings from Yang and colleagues; we also found decreased methylation of PCSK6 in atopy, and further report a corresponding increase in gene expression. PCSK6 activates NF-κB, interleukin 1, and interleukin 6, 32 and might have a paracrine role in activating matrix metalloproteases. 33 We also found hypomethylation (and upregulation) of FBXL7 in atopic participants; FBXL7 expression has been associated with decreased inhaled corticosteroid response in asthma, 34 and FBXL7 has been implicated in aspirininduced urticaria and angio-oedema. 35 GRK5 (also hypomethylated and upregulated among atopic children in our study) might mediate β2-adrenergic receptor desensitisation, 36 and PRKD1 polymorphisms could interact with cleaning products in adult-onset asthma. 37 Finally, among genes that were not among the most significant by p values but included in the classification panel, DUOX1 mediates inflammation, mucous cell metaplasia, and airway remodelling in asthma, 38 interleukin 4 signalling can activate IRS2 leading to M2 polarisation of lung macrophages, which has been linked to poor lung function in atopic asthma, 39 and LRP1 modulates dendritic cell responses and attenuates dustmite-induced eosinophilic airway inflammation. 4 Our methylation results are biologically relevant. Beyond plausibility from existing literature, our transcriptome-wide association study and eqtm analyses examined whether methylation is associated with gene expression, and our mediation analysis further evaluated whether the methylation atopy relationship is explained by transcriptomic differences. Several CpG gene pairs showed significant mediation, including SLC9A3, CDH26, PCSK6, and MAP3K14; others, like FBXL7 or NTRK1, showed little or non-significant mediation, suggesting that the link between methylation and atopy occurs through other mechanisms. Moreover, we replicated more than 93% of our top results from the epigenome-wide association study in two cohorts. Of note, two of our top genes (METTL1 and PCSK6) were also among the genes reported by Yang et al, 5 as were two genes in our CpG classification panel. We also provide the first replication of the top results in that study, which linked the nasal methylome to atopic asthma but had limited statistical power and lacked external replication. With regard to the clinical significance of our findings, predictors of asthma or atopy in early life are needed in paediatrics, because only about 41% of children who report any wheeze by age 3 years will go on to have true asthma by age 6 years, while the remaining 59% of young children with early wheeze will report no wheeze at age 6 years. 41 Using data from four clinical parameters and peripheral blood eosinophil count, Castro-Rodriguez and colleagues 41 developed the Asthma Predictive Index to help differentiate young children with transient wheeze from those who go on to develop asthma. However, this index has limited predictive accuracy: for asthma at age 11 years, the stringent version of the index had a sensitivity of 15%, a positive predictive value of 42%, and a negative predictive value of 86%. At present, neither parents nor physicians know with certainty whether an infant with wheeze will go on to develop atopy or asthma at school age. Such knowledge could help guide treatment or reduce anxiety in the child s family. Our study is cross-sectional, and thus we cannot determine whether specific methylation marks preceded or were a consequence of atopy or atopic asthma. Moreover, we were unable to examine non-atopic asthma because of scarce or no data on this outcome. However, our findings demonstrate the feasibility of using the nasal methylome to develop clinical tools in future longitudinal studies, as highlighted by the ability of the 3-CpG panel to identify atopic participants in three studies despite racial and ethnic differences; our cohort included Puerto Ricans with about 24% African ancestry, 42 the study by Yang predominantly (92%) included African Americans, and PIAMA included mostly (97%) western Europeans. Published online December 21,

10 Furthermore, PIAMA participants were not selected for atopy or asthma and thus had lower total IgE (table 1), which probably explains the somewhat smaller effect sizes in PIAMA, though a small contribution of European ancestry effects is also possible. Of note, the same CpG panel was able to reliably classify atopic asthma, with accuracy of 88% in Puerto Rico, 82% in the data from Yang and colleagues, and 86% in PIAMA. Although the positive predictive value in PIAMA was lower at 42, this finding is expected from an unselected birth cohort with about 1% prevalence of the outcome (atopic asthma). These very promising results are far superior to predictive models using genetic variants, and also in clear contrast to those of our so-called negative control analyses, in which panels composed of either 3 random CpGs (AUC about 57 63) or demographic and questionnaire data (AUC of about 65 69) performed markedly worse than our selected CpG panel. Although nasal transcriptomics offers an alternative approach for asthma or atopy classification, DNA is more stable than RNA, and methylation marks offer a more direct assessment of environmental exposures. Moreover, preliminary (nonreplicated) findings from a small study in adults suggest that a panel of 9 genes (considerably larger than our 3-CpG panel) might be needed for asthma diagnosis using transcriptomics. 43 Our results suggest that nasal methylation patterns can reliably classify atopy or atopic asthma in children differing in age, race, ethnicity, and degree of atopy. Furthermore, novel genes in our predictive panel (eg, MAP2K6, EPHA4, ACOX2, BBOX1, or AXIN2) are worthy of further study. Our findings were robust to nasal sample collection and processing protocols. Indeed, our results were unchanged when excluding CD326-positive sorted samples, and were consistent when analysing only the CD326-positive subset. Notably, the study by Yang and colleagues used histology and gene expression to ensure high proportion of ciliated epithelial cells, and PIAMA included whole nasal samples collected using a protocol similar to ours. Of interest, none of our top results overlapped with the 14 CpGs reported in a recent epigenome-wide association study of asthma in whole blood (appendix 1), 15 further highlighting the novelty of our findings in airway epithelium and the crucial importance of tissue specificity in epigenomic studies. In summary, we have identified novel and biologically plausible methylation markers of atopy and atopic asthma in nasal epithelium, which are located in or near genes related to immune regulation and airway epithelial integrity. Most of these genes were not identified in genome-wide association study, and thus our results support a key role of epigenetic changes in the nasal epithelium in the causality of atopy and atopic asthma in children. Moreover, we report a nasal methylation profile that accurately classifies participants according to atopy or atopic asthma, thus supporting future longitudinal studies to develop predictive nasal methylation panels. Such panels could be used for early prediction of asthma, identifying early-life environmental risk factors for asthma, and assessing response to asthma therapies in children. Contributors EF, TW, CQ, GC, GHK, WC, and JCC contributed to the design of the study, and GHK and JCC obtained funding for the study. NB, YY-H, JMV, SB, EA-P, AC-S, MA, and GC contributed to participant recruitment, study procedures, and laboratory procedures. EF, TW, CQ, QY, C-JX, DEW, FR, and YJ contributed to the data analysis. All coauthors contributed to results interpretation. EF, TW, CQ, GHK, WC, and JCC contributed to the initial manuscript draft. All coauthors revised the manuscript draft for important intellectual content, and approved the final version for submission. Declaration of interests GHK has received grants from Lung Foundation of the Netherlands, during the conduct of the study; and grants from TEVA the Netherlands, GSK, Vertex, Ubbo Emmius Foundation, and TETRI foundation, outside of the submitted work. JCC has received research materials from GSK and Merck (inhaled steroids) and Pharmavite (vitamin D and placebo capsules) to provide medications free of cost to participants in NIH-funded studies, unrelated to the current work. The other authors declare no competing interests. Acknowledgments We thank all the participating children and families. This study was supported by grants HL79966, HL117191, and MD11764 (principal investigator: JCC) from the National Heart, Lung, and Blood Institute of the US National Institutes of Health (NIH). EF s contribution was supported by NIH grant HL JCC s contribution was additionally supported by the Heinz Endowments. Research operations at the University of Puerto Rico were additionally supported by grant U54MD7587 from the National Institute on Minority Health and Health Disparities and the National Institute of Allergy and Infectious Diseases of the US NIH. PIAMA was supported by the Netherlands Organization for Health Research and Development, the Netherlands Organization for Scientific Research, the Netherlands Lung Foundation (with methylation studies supported by AF ), the Netherlands Ministry of Spatial Planning, Housing, and the Environment, and the Netherlands Ministry of Health, Welfare, and Sport. CQ is supported by a grant from the China Scholarship Council. References 1 Davidson EJ, Yang IV. Role of epigenetics in the development of childhood asthma. Curr Opin Allergy Clin Immunol 218; 18: Demenais F, Margaritte-Jeannin P, Barnes KC, et al. Multiancestry association study identifies new asthma risk loci that colocalize with immune-cell enhancer marks. 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