Pathogenesis of frequent asthma exacerbators

ABSTRACT Asthma is one of the most common non-communicable illness among children in the United States. This disease is comprised of multiple pathobiological subgroups, also known as endotypes, which have distinct pathologies and differential responses to treatment. Clinical evidence has identified an endotype of asthma comprised of individuals who are frequently (≥2 times per 12 months) hospitalized for an asthma exacerbation. While there have been previous studies examining the clinical characteristics of the frequent exacerbator (FE) endotype, the heterogeneity of the populations studied makes findings difficult to generalize to pediatric populations. Additionally, there have been no studies examining the underlying biological differences which may be responsible for recurrent exacerbations. To answer these questions, we have leveraged the Ohio Pediatric Asthma Repository (OPAR), the first statewide repository of patients admitted for an asthma exacerbation at any of the 6 major pediatric medical centers. In addition to clinical and epidemiologic data, biosamples (nasal epithelial cells, blood, etc) are stored in our laboratory at Cincinnati Children’s Hospital, allowing us a unique opportunity to explore the biologic underpinnings of the FE endotype. In our first study, we performed RNA- sequencing (RNA-seq) of upper airway epithelial cells and found: (a) FEs are a biologically distinct endotype of pediatric asthma; (b) the transcriptome of FEs is characterized by an increase in expression of gene modules enriched for nervous system processes; (c) non-FEs (nFEs) show an increase in gene modules enriched for allergic immunity as has been described previously in asthma; and (d) increased expression of modules enriched for nervous system processes in individuals with >2 annual exacerbations, regardless of whether it was the 2nd or the 7th. We also have preliminary data showing differences in methylation patterns between FEs and nFEs indicative of epigenetic changes coupled with our transcriptomic results. Together, our findings and existing literature suggest a durable molecular shift in the airways which predisposes an individual for frequent asthma exacerbations. Therefore, we hypothesize the unique transcriptional divergence exhibited in the airways of FEs is a durable change characterized by cell-specific epigenetic and gene expression changes. We propose to test this hypothesis by: (i) collecting samples from FEs during an exacerbation and a period of normal lung function to assess gene expression durability (Aim 1), and (iii) generate single cell RNA-seq and ATAC- seq datasets to determine cell-specific patterns of expression and gene regulatory networks associated with frequent asthma exacerbations (Aim 2). Our studies will further define the molecular etiology of this important pediatric asthma endotype and provide putative targets for therapeutic intervention.