Immunoregulatory roles for exosomes in the gastrointestinal tract

PROJECT ABSTRACT Intestinal homeostasis, which is paramount to maintaining human health and preventing inflammatory bowel diseases (IBDs), relies on the ability of the immune system to react to pathogens while tolerating commensal microbes. Although much has been learned regarding the mechanisms that regulate immunity at this mucosal site, this system is quite complex and many aspects of how the host ensures proper responses remain elusive. Recent work indicates that various cells of the immune system utilize a novel mode of communication that is mediated by small lipid extracellular vesicles (EVs), including exosomes. Following their release from cells, exosomes have been shown to bind target recipient cells and deliver their cargo, including microRNAs (miRNAs), to change cellular functions. Despite decades of knowing that exosomes exist, work in this field has been hampered by a lack of mouse mutants that have impaired exosome production. Moreover, even less is known about the functional roles of exosomes within the gut. Recently, the small GTPases Rab27a/b have been shown to be critical for the release of exosomes, and dysregulated expression of Rab27 is associated with human colitis and colon cancer. Our preliminary data indicate that genetic deletion of Rab27a in CD11c+ macrophages (Macs) and dendritic cells (DCs) leads to inflammation in the gastrointestinal (GI) tract, while injection of dendritic cell exosomes containing miRNAs can rescue this phenotype. We hypothesize that Rab27a-dependent, Ybx1-loaded exosomes produced by Cd11c+ Macs/DCs of the GI tract regulate inflammation during colitis by delivering specific regulatory miRNAs to gut cells. We will carry out the following aims to explore this prediction and gain a deeper understanding about the functional relevance of exosomes in the prevention of intestinal inflammation. Aim 1 will determine functionally relevant CD11c+ exosome producing Mac/DC cell subsets during intestinal inflammation. Aim 2 will determine the role of Ybx1 during colitis, and its contribution to CD11c+ Mac/DC exosome contents. Aim 3 will determine the functional consequences of CD11c+ Mac/DC exosome delivery of specific miRNAs to cells of the GI tract during colitis. This work will lead to groundbreaking insights into the roles played by EVs in the GI tract during human health and disease.