Introduction: African Americans are one of the populations with the highest asthma burden. Despite having lower bronchodilator response (BDR) than other ethnicities, albuterol is the most widely used drug for asthma treatment among them. BDR and other asthma-related traits are affected by genetics and environmental exposure. Despite DNA methylation (DNAm) capture both factors, its influence on BDR is unknown.
Aims and objectives: To identify DNAm changes associated with BDR.

Methods: African Americans with asthma from the SAGE study (n=221) with DNAm data profiled with the EPIC array (Illumina) were included in the discovery phase. The association between DNAm in whole-blood and BDR was assessed by linear regression models adjusting for age, sex, ancestry, and tissue heterogeneity. Genome-wide significant results (p<9x10-8) were attempted for replication in Latinos from GALA II (n=189). The effect of genetic variation in DNAm was assessed by a methylation quantitative trait loci (meQTL) analysis using a false discovery rate (FDR) of 5%.

Results: Fifteen CpGs were significantly associated with BDR in African Americans (FDR<0.05) even in sensitivity analyses adjusting for socioeconomic factors, clinical parameters, and environmental exposures. The CpGs cg08241295 near FGL2 (p=6.8x10-9) and cg15341340 at DNASE2 (p=7.8x10-8) surpassed the genome-wide significance threshold. The CpG site at DNASE2 replicated with the same effect in Latinos (p=4.9x10-3). In contrast, the effect of the CpG site near FGL2 was specific to African Americans and it was regulated by 100 meQTLs (FDR<0.05).

Conclusion: We revealed novel associations of population-specific and cosmopolitan epigenetic marks with BDR in pediatric asthma.

Introduction: Lung function, a key health indicator in respiratory illnesses, is influenced by numerous environmental exposures and genetic ancestry, which vary by race/ethnicity. Despite this, the role of the DNA methylome on lung function has been investigated primarily in European-descent adults. Here, we aimed to identify DNA methylation loci associated with lung function in Latino youth with asthma and validate previous epigenetic signals from non-Latino populations.

Methods: We performed several epigenome-wide association studies of lung function measurements analyzing whole blood from 247 Puerto Rican and 148 Mexican American youth with asthma. Forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and their pre- and post- albuterol administration ratio were evaluated. The effects of genetic variation on DNA methylation were investigated for the genome-wide significant (p=1.17x10-7) CpG sites identified. Differentially methylated regions and enrichment analyses in previous EWAS associations were also conducted.

Results: Three CpGs were genome-wide significantly associated with lung function in Latinos: cg14441538 near PRKG1-AS1 showed significant association with pre-bronchodilator FVC (p=7.69x10-10), cg00914963 near TBC1D16 was associated with post-bronchodilator FVC (p=5.14x10-8), and cg20515679 near KCNJ6 with post-bronchodilator FEV1/FVC (p=7.21x10-8). DNA methylation at cg00914963 was genetically regulated in Latinos. Additionally, two differentially methylated regions at LY6G5C and AURKC were associated with pre-bronchodilator lung function (adjusted p<0.05) in Puerto Ricans and Mexican Americans. Moreover, some of the epigenetics marks previously associated with lung function in non-Latino populations were replicated. Furthermore, there was significant enrichment (p<0.05) in previous EWAS signals for known lung health-related factors, such as respiratory diseases, smoking, or preterm birth.

Conclusions: We uncovered novel epigenetic markers associated with lung function in Puerto Ricans and Mexican Americans and validated associations previously described in non-Latino populations.

RATIONALE
Current guidelines do not sufficiently capture the heterogenous nature of asthma leading to suboptimal management and treatment strategies. A more comprehensive classification of asthma into biologically meaningful subgroups is needed. Given its position on the central biological dogma, as the ‘ome closest to phenotype, reflecting genetics, environment and their interactions, metabolomics represents a novel and compelling approach to accurately identifying asthma endotypes; i.e. subtypes defined by their functional or pathobiological mechanisms, with the potential for clinical translation.
METHODS
We performed plasma metabolomic profiling of 1155 asthmatic children from the Genetics of Asthma in Costa Rica Study (GACRS) across four profiling platforms covering a broad range of the metabolome. We generated patient similarity networks for each platform that connected asthmatics via edges representing patient-to-patient similarity in their metabolomic profiles (controlling for age, sex and body mass index). We then fused the four platform-specific networks using Similarity Network Fusion and performed spectral clustering on the resulting fused similarity network to identify metabo-endotypes. We explored phenotypic and clinical differences across the metabo-endotypes using ANOVA and chi-square tests. For validation we recapitulated the endotypes in an independent population of asthmatic children (CAMP, n=911) to determine whether the same between-endotype differences were observed. Finally, we identified metabolomic and genomic drivers of validated metabo-endotype membership, meta-analyzing findings from GACRS and CAMP.
RESULTS
We identified five metabo-endotypes in GACRS and observed significant differences across metabo-endotypes in asthma-relevant phenotypes pre-bronchodilator (p-ANOVA=8.3x10-5) and post-bronchodilator (p-ANOVA=1.8x10-5) FEV1/FVC ratio; use of inhaled (p-ANOVA=5.0x10-13) and oral (p-ANOVA=0.007) steroids, and airway hyperresponsiveness to methacholine (AHR PC20<16.8, p-ANOVA=8.4x10-7)p-ANOVA=8.4x10-7). Furthermore, there was a significant difference in eosinophil count (p-ANOVA=0.009). The recapitulated metabo-endotypes in CAMP displayed significant differences (p<0.05) in many of the same phenotypes. (Table 1). The “most-severe” asthma endotype was defined by the lowest FEV1/FVC ratio, and the highest prevalence of AHR and oral steroid usage. It was characterized by higher levels of glycerolipids and lysophospholipids, as well as lower levels of nucleotides relative to the other endotypes. These findings suggest dysregulation of pulmonary surfactant homeostasis in the “most-severe” endotype and were supported by the genetic analysis, which found that members of this endotype were more likely to carry variants in key pulmonary surfactant regulation genes such as BACH3 (meta-analyzed p=5.2x10-4) and BMP3 (meta-analyzed p=8.5x10-4).
CONCLUSIONS
These findings demonstrate that clinically meaningful endotypes can be derived and validated using metabolomic data, and that interrogating the drivers of these metabo-endotypes can help understand their pathophysiology and identify therapeutic targets.

Asthma disparities by race and ethnicity in the U.S. may be influenced by differences in asthma drug response: African American and Puerto Rican children have lower drug response to bronchodilators, the most commonly used asthma rescue therapy. In this talk, we will present results from whole genome sequencing association analyses for bronchodilator response (BDR) among 6385 minority children from the Asthma Translational Genomics Collaboration (ATGC) that is part of the NHLBI’s TOPMed program. Genome-wide association analyses for BDR were conducted with TOPMed Freeze 8 data for each cohort and racial/ethnic group using linear mixed models, while adjusting for sex, age, BMI and four principal components. Racial/ethnic-specific and overall meta-analyses were performed using METASOFT under a fixed-effects model. Among common variants (MAF>0.01), the top association in 4562 African American children was nearest IZUMO3, in 1154 Puerto Rican children was nearest DNAH5, and in 669 Mexican children was nearest ZNF311. Across all racial-ethnic groups, the top variant was nearest SFXN4. We previously developed the app Reducing Associations by Linking Genes And omics Results (REALGAR) that provides insights helpful for prioritizing and designing functional validation studies for genetic associations using publicly available omics data. Using REALGAR, we found that 1) SFXN4 had decreased expression (q=3.8e-4) in whole blood of 318 people with severe asthma versus 87 healthy controls (GSE69683), 2) ZNF311 had increased expression (q=5.3e-7) and 3) DNAH5 and decreased expression (q=5.5e-25) in airway smooth muscle exposed to 100nM budesonide for 18hr (SRP098649). Thus, cell-specific omics suggests potential disease mechanisms of BDR associations and are useful to prioritize associated genes and facilitate the design of validation experiments.