Colorado PROFILES, The Colorado Clinical and Translational Sciences Institute (CCTSI)
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The autophagic pathway and atopic asthma: role of IL-33 and ST2

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Asthma represents a major public health burden characterized as an epidemic that disproportionately affects underrepresented minorities and children. The usual source of the lower airway inflammation characteristic of asthma is a Th2-mediated reaction initiated by common environmental allergens. Multiple independent genome-wide association studies (GWAS) on asthma have identified, as the most consistently associated genes with asthma among diverse ethnic/racial groups. However, the biological role and mechanism of IL-33/ST2 in modulating the innate-adaptive immunity interaction in asthma remains to be defined. Recent evidence suggests that IL-33-activated dendritic cells (DCs) are critical for Th2- mediated allergic airway inflammation. Moreover, autophagy is a core cellular process that contributes to cellular homeostasis with emerging links to the pathogenesis of asthma. Autophagy is involved in the delivery of potential cytoplasmic antigens to the endosome for degradation, processing, activation and presentation by DCs; and its activity is increased in asthmatic airways. We hypothesize that both the IL-33/ST2 and autophagic pathways play a crucial role in asthma and allergic diseases and IL-33/ST2 modulates the innate-adaptive immunity interaction via autophagy in Th2-mediated allergic airway inflammation. We have completed targeted resequencing of ST2 to identify rare variants as well as common variation that is not well tagged by the single nucleotide polymorphisms (SNPs) on the GWAS platforms in populations of African ancestry. We identified a novel and common haplotype that determines serum levels of soluble ST2 (sST2), which is comprised of three promoter variants that potentially alter transcription factor binding. In silico analyses of asthma GWAS databases identify 11 out of 84 selected key autophagic pathway genes for which variants are significantly associated with risk of asthma in African Americans, suggesting variation in this pathway may universally contribute to asthma risk. In the parent R01 grant to this new application, we have nearly completed whole-genome sequencing of >1,000 asthma cases and non-asthmatic controls comprising the 'Consortium on Asthma among African-ancestry Populations in the Americas' (CAAPA). The resulting unique catalog of genetic variation in >1,000 individuals of African ancestry selected for asthma provides a unique opportunity to identify common and rare variants in the IL-33/ST2 and autophagic pathways. Specific aims of this application are: (i) To identify rare and common variants in 84 autophagic pathway genes associated with asthma; and (ii) To test IL-33/ST2-mediated autophagic flux as a critical determinant of dendritic cell homeostasis and the mechanisms by which IL-33/ST2 regulates the innate-adaptive immunity interaction in asthmatic patients and non-asthmatic controls (N=20 each group). Results from these studies will provide insight into the pathogenesis, the genetic underpinnings and ethnic disparities of asthma as well as novel targets for therapy in the clinic.
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