Asthma is the most prevalent chronic respiratory disease in children, disproportionately affecting racially and ethnically minoritized populations in the United States. Puerto Rican and non-Hispanic Black youths, in particular, experience higher rates of emergency department visits due to asthma compared to their non-Hispanic White counterparts. Traditional asthma research has focused primarily on the T helper 2 (T2)-high asthma endotype, characterized by eosinophilic inflammation and elevated levels of interleukin (IL)-4, IL-5, and IL-13. However, T2-low asthma endotypes, including T17-high asthma and paucigranulocytic asthma, remain poorly understood, especially among underserved youth populations. This study aims to bridge this knowledge gap by identifying the molecular mechanisms behind these endotypes to improve diagnostic and therapeutic strategies.
Study Overview and Methodology
Data Sources and Participant Demographics
The investigation derives its data from three prominent studies, leveraging nasal RNA profiles to analyze asthma endotypes in a diverse group of youths. These studies include “Stress and Treatment Response in Puerto Rican and African American Children with Asthma (STAR),” “Epigenetic Variation and Childhood Asthma in Puerto Ricans (EVA-PR),” and “Vitamin D Kids Asthma (VDKA).” Conducted between 2018 and 2022, STAR aimed to evaluate six-week inhaled corticosteroid (ICS) responses among youths from Puerto Rico and Pittsburgh, ranging in age from 8 to 20 years. Eligible participants had physician-diagnosed mild-to-moderate persistent asthma, at least three Puerto Rican or African American grandparents, and no recent corticosteroid use or upper respiratory infections (URIs). Moreover, they contributed demographic and respiratory health data, spirometry, blood testing, and nasal RNA sequencing before receiving ICS treatment.
The EVA-PR study, conducted from 2014 to 2017, focused specifically on Puerto Rican youths aged 9 to 20 years with asthma. Similar to the STAR study, participants underwent spirometry, blood tests, and nasal sampling for gene expression analysis. The third study, VDKA, conducted from 2016 to 2019, was a 48-week randomized trial examining the effects of vitamin D3 supplements in children aged 6 to 16 years with severe asthma. This study also included an ancillary nasal sampling for transcriptomic analysis. Ethical approval was obtained for these three studies, and together, they provided comprehensive data on nasal RNA profiles that facilitated the identification of T2 and T17 asthma endotypes across various populations of children and adolescents.
Ethical Considerations and Data Collection
Participants across the three studies exhibited diverse demographic and clinical characteristics. EVA-PR exclusively included Puerto Rican participants, while STAR and VDKA primarily involved African American or non-Hispanic Black youths. The mean age varied among the groups, with VDKA participants being the youngest at 10.3 years, followed by STAR participants at 14.2 years, and EVA-PR participants at 15.4 years. Overweight or obesity was a common feature, affecting between 45.6% and 65.4% of participants. A significant majority of the participants had Medicaid or medical assistance, with only a minimal proportion—1% to 4%—being uninsured. Across the cohorts, participants’ nasal RNA profiles were crucial for identifying the molecular signatures of different asthma endotypes.
The comprehensive nature of the collected data enabled researchers to conduct an in-depth analysis of asthma among racially and ethnically diverse groups of youths. Ethical approval ensured that the studies met standards for participant safety and consent. The large sample size of 459 participants (with 156 from STAR, 237 from EVA-PR, and 66 from VDKA) added robustness to the findings. By examining nasal RNA profiles, the researchers could identify critical endotypic differences and their distribution among populations traditionally underrepresented in clinical research. This approach provided a foundation for understanding the molecular mechanisms underlying asthma in minority youths, paving the way for more precise and effective treatments.
Identification of Asthma Endotypes
K-means Clustering and Endotype Distribution
The application of K-means clustering to nasal transcriptomic profiles consistently identified three primary asthma endotypes across the cohorts: T2-high (22.7% to 29.1%), T17-high (35.0% to 47.0%), and T2-low/T17-low (30.3% to 37.8%). Patients with T2-high profiles presented elevated levels of total IgE, eosinophils, and allergen sensitization compared to those with T2-low profiles. Interestingly, despite lower IgE levels, 50% to 73.3% of T2-low participants were allergen-specific IgE positive. Such findings affirm the diversity of immune response patterns and reflect the complexity of asthma endotypes, which can vary significantly even within seemingly similar populations.
Clinical variability among the endotypes was notable across the different cohorts. The STAR study highlighted that individuals with T2-high endotypes were more prone to allergic rhinitis, higher household incomes, and increased rates of asthma-related emergency visits, pointing towards socioeconomic factors influencing asthma severity and management. The T17-high participants, typically younger, underscored a potential age-related predisposition to this endotype. Obesity emerged as an essential factor in differentiating endotype profiles, being linked to T2-low endotypes in both STAR and EVA-PR studies but associated with T2-high profiles in the VDKA study. These insights into clinical and demographic correlations play a vital role in tailoring asthma management strategies based on endotype prevalence and patient characteristics.
Clinical Findings and Biomarker Analysis
Clinical findings underscored that lung function measures did not show significant differences between the various endotypes, suggesting that endotypic distinctions may be more reflective of immunological and molecular parameters rather than respiratory function alone. STAR cohort biomarker analysis provided valuable cutoff points for identifying T2-high profiles: total IgE (≥417.5 IU/mL), eosinophils (≥210.4 cells/μL), and FeNO (≥32.5 parts per billion). Creating a decision tree model incorporating these biomarkers enhanced predictive accuracy, showcasing the potential of multi-biomarker approaches in asthma diagnostics.
These clinical and biomarker findings reveal the intricate interplay between immune responses and asthma characteristics among racially and ethnically minoritized youths. They suggest that while single biomarkers alone may not suffice to accurately predict T2-high asthma, combined biomarker integration offers a viable strategy for improved diagnosis. Notably, the exclusion of participants with recent corticosteroid use minimized potential confounding factors, ensuring the robustness and reliability of the findings. Such precision informs therapeutic decisions, enabling more targeted and effective asthma management in diverse populations.
Molecular Mechanisms and Gene Expression
Differential Gene Expression Analysis
The differential gene expression analysis unveiled a total of 3,516 genes associated with T2-high profiles, with a significant emphasis on IL-13 signaling pathways. This extensive gene network underscores the central role of IL-13 in mediating eosinophilic inflammation and allergic responses typical of T2-high asthma. The identification of such genes not only deepens our understanding of T2-high asthma mechanics but also highlights potential targets for novel therapeutic interventions aimed at modulating these pathways.
In contrast, the analysis revealed 2,494 genes correlated with T17-high profiles, emphasizing cytokine and interferon-γ pathways. Key genes identified, including FPR1, TREM1, and IL23A, provided critical insights into the molecular mechanisms of T17-high asthma, suggesting a distinctive immune response profile dominated by neutrophilic and T#7-driven inflammation. These findings elucidate the molecular dichotomy between T2 and T17-high endotypes and point to divergent pathogenic pathways necessitating tailored clinical approaches.
Clinical Implications and Future Directions
This investigation draws from three significant studies, using nasal RNA profiles to examine asthma endotypes in diverse youth populations. The studies include “Stress and Treatment Response in Puerto Rican and African American Children with Asthma (STAR),” “Epigenetic Variation and Childhood Asthma in Puerto Ricans (EVA-PR),” and “Vitamin D Kids Asthma (VDKA).” Conducted between 2018 and 2022, STAR aimed to evaluate six-week inhaled corticosteroid (ICS) responses among youths from Puerto Rico and Pittsburgh, ages 8 to 20 years. Eligible participants had mild-to-moderate persistent asthma diagnosed by a physician, at least three Puerto Rican or African American grandparents, and no recent corticosteroid use or respiratory infections. They provided demographic and respiratory health data, spirometry, blood samples, and nasal RNA sequencing before ICS treatment.
The EVA-PR study (2014-2017) focused on Puerto Rican youths aged 9 to 20 years with asthma, performing similar tests as STAR. VDKA (2016-2019), a 48-week trial, examined the impact of vitamin D3 supplements in children aged 6 to 16 with severe asthma, including nasal sampling for gene expression analysis. These studies gained ethical approval and offered comprehensive nasal RNA data, helping identify T2 and T17 asthma endotypes in different child and adolescent populations.
