Asthma is a common disease, affecting more than 300 million people worldwide. Though well controlled in most, some experience disease that is refractory to standard treatments such as corticosteroids. Recent efforts focused on understanding these severe asthma (SA) patients suggests ontological heterogeneity. Previous work from the Severe Asthma Research Program (SARP) cohort linked epithelial gene signature to clinical phenotype. We revisited this data set and identified 3 novel groups of asthmatics, one of which housing the majority of SA cases and having the worst lung function and greatest exacerbation history. Using principal drivers of variance in the data set, we found that expression of the interleukin 18 receptor (IL18R1) along with 18 other genes was able identify at-risk asthmatics. IL18R1 has been previously linked to asthma in genome-wide association studies. Its ligand, interleukin-18 (IL-18), may be a cofactor for both Th1 and Th2 inflammation. High IL-18 levels have been detected in serum and sputum of asthmatics including in those with fatal asthma. Importantly, IL-18 and IL18R1 regulate epithelial barrier function in other inflammatory conditions. We have confirmed an increase in IL18R1 at the protein level in SA patients compared to healthy controls (HC) using lung biopsies from very severe asthma cases. These SA patients also harbor increased numbers IL-18+ cells, the cognate ligand for IL18R1. Downstream targets of IL18 stimulation, including the active phosphorylated forms of JNK1 and c-Jun, show increase in SA airway epithelium. SA patients also show disorganization of adherens junctions, suggesting breakdown in epithelial barrier integrity. Based on this background and our preliminary data, we hypothesize that IL-18 pathway activation, via elevated IL18R1 expression in bronchial epithelium, promotes dysregulated barrier function that contributes to SA pathobiology by increasing immune cell access to foreign antigens. We propose 2 aims to address this:
Aim 1. We will interrogate pre-existing tissue banks for quantitative analysis of IL18R1 and compare that with levels of its ligand in tissue and fluids from these patients. These data will be corroborated with activity of associated signaling pathways and tight/adherens junction integrity.
Aim 2. We will us primary human airway epithelial cells, obtained bronchoscopically from HCs and asthmatic patients to mechanistically confirm and expand upon the results from Aim 1. This will include validation of ex vivo results as well as quantification of barrier function. These data will identify a novel role for IL18 in severe asthma pathogenesis and open up new avenues for treatment of this difficult and costly disease. The activities of the project will provide the PI with valuable experience in obtaining, culturing and manipulating primary human airway epithelial cells and lay the foundation for future in vivo work by integrating study in computational biology and immunology.
Severe asthma is disease with tremendous impact on patient quality of life and significant cost of treatment. We have used machine learning to identify the IL-18 pathway as a potential driver of this disease which may one day be targeted for novel treatments. Thus, we propose confirmation of these findings using an extensive ex vivo tissue collection as well as mechanistic validation using primary human airway epithelial cells to lay groundwork for future in vivo study.
