The role of serpins and LRP1 in the esophageal epithelium during eosinophilic esophagitis

PROJECT SUMMRAY Eosinophilic esophagitis (EoE) is a chronic allergic disease of the esophagus, partly mediated by type 2 immunity and epithelial dysfunction. Patients with EoE suffer from dysphagia, pain, and the lowest quality of life among children with chronic, pediatric conditions. The epithelium is the first line of defense against potential threats, providing a physical barrier between the host and the external environment. The site where the barrier breach occurs may be a location where normally harmless antigens encounter immune cells and potentially lead to production of danger signals, priming a break in immune tolerance and initiation of allergic responses. Understanding the physiologic factors that preserve/restore esophageal homeostasis will facilitate our long-term goal of developing improved therapies with long-lasting effects and a cure for EoE. The sharp edge between intact barrier versus barrier breach is orchestrated by proteases and protease inhibitors. We demonstrated that losing an epithelial protease inhibitor or altering proteolytic activity provide a paramount signal in the development of EoE. Delivery of the serine protease inhibitor A1AT reversed EoE phenotypes (e.g., barrier function, type 2 mediator production) in vitro and in an EoE mouse model. We have now revealed another variable in the protease-inhibitor equation; the low-density lipoprotein receptor– related protein 1 (LRP1). LRP1 is a scavenger receptor that mediates endocytosis and elimination of ligands, including serine protease inhibitors (serpins) in complex with proteases. Interaction of a serpin with a protease, exposes encrypt motifs in the serpin’s sequence that interact with LRP1 and serve as LRP1 agonists. Following the binding of a serpin-protease complex to LRP1, LRP1 initiates signaling pathways that terminate inflammatory responses and promote epithelial homeostasis. We demonstrated that LRP1 agonists potently reverse EoE disease in vitro and in vivo. In addition, we showed that an intracellular truncated LRP1 fragment appears exclusively in EoE biopsies. The function of the truncated LRP1 fragment in EoE biopsies is unknown. We hypothesize that excessive LRP1 processing during EoE promotes transcriptional changes that propagate EoE. In this study, we will explore the mechanism of action by which serpins and synthetic LRP1 agonists promote inflammatory resolution in vitro and in vivo. We developed an experimental platform to investigate the function of full-length serpins, serpin-derived peptides with LRP1 binding motifs, and small molecule inhibitors that inhibit proteolytic activity but lack LRP1 binding motifs. Our unique experimental framework enables us to test serpin functions that are independent of protease inhibition. We will elucidate the downstream functional consequences of LRP1 processing in esophageal epithelial cells and investigate the enzymes responsible for LRP1 processing. Successful completion of this study will provide fundamental insights into LRP1-serpin-protease crosstalk and facilitate developing drugs to achieve inflammatory resolution and epithelial homeostasis in individuals with EoE.