Consequences of mast cell activation and complement dysregulation in eosinophilic esophagitis

About This Grant

PROJECT SUMMARY Eosinophilic esophagitis (EoE) is a chronic, food-induced allergic inflammatory disease that has an increasing prevalence, estimated to affect 450,000 individuals in the USA with a healthcare burden of 1.4 billion dollars/year. It is now recognized as the most common reason for chronic dysphagia in young adults. EoE histopathology involves epithelial alterations, including hyperplasia and decreased barrier integrity, as well as lamina propria fibrosis. Despite eosinophils being pathognomonic to EoE diagnosis, recent clinical trials with eosinophil- depleting antibodies showed that eosinophils are not the primary causal cell. Mast cells (MC) associate more closely than eosinophils with important disease symptoms and histologic and endoscopic changes, are significantly increased in EoE, and produce IL-13, an essential driver of EoE. A novel machine learning protocol that we developed (MC-AI) showed significant MC activation in EoE epithelium and lamina propria. However, the mechanisms of MC activation and contribution to disease pathology, including epithelial dysfunction and fibrosis, are unclear. These data highlight a potential clinical need for MC-targeted EoE therapies and the related search for mechanisms of MC activation. Our preliminary data show that the gene encoding the receptor for the anaphylatoxin/ MC activator C3a, C3AR1, is overexpressed in the esophagus of patients with EoE. C3AR1 expression correlates strongly with expression of MC-specific genes and is enriched in MCs by single-cell RNA sequencing (scRNAseq). Additionally, C3aR protein levels on MCs are proportional to esophageal MC levels and activation status. C3a is generated when complement component 3 (C3) protein is cleaved into the bioactive fragments C3a and C3b. Esophageal C3a is increased in patients with EoE compared to control subjects and present in the epithelium and lamina propria, the locations where we and others have identified MCs in EoE. In the lamina propria, fibroblasts are key producers of C3, and C3 expression is increased in fibroblasts in patients with EoE compared to control individuals. Notably, C3 is the most upregulated esophageal gene in an animal model of EoE compared to controls. These and the additional observations described below give rise to our central hypothesis that mediators released by C3a-activated mast cells (MCs) contribute to epithelial dysfunction and fibrosis in eosinophilic esophagitis (EoE). We will test this hypothesis through a combination of in vitro and in vivo models. To achieve this, I will learn skills in murine models, RNA sequencing/bioinformatics, statistics, and advanced flow cytometry. Completion of these research and career development goals will successfully transition me into an independent physician-scientist with a translational laboratory that combines clinical and basic laboratory research to study the role of mast cells in EGID, with an initial focus on EoE.