ILC3 Syndecan-4 in the Regulation of Intestinal Health and Inflammation

PROJECT SUMMARY Inflammatory bowel disease (IBD) arises when gut microbes elicit inappropriate immune responses in the intestine, leading to chronic inflammation and tissue damage. As cases rise worldwide, it is important to identify the pathways that restrain these responses and promote mucosal healing. Critically, group 3 innate lymphoid cells (ILC3s) are a recently identified cell type which is enriched in the healthy intestine and becomes dysregulated during IBD, colon cancer and other chronic inflammatory disorders. Further, mouse models have revealed fundamental roles for ILC3s in controlling immune tolerance, immunity, and inflammation in the intestine. Despite these advances, the mechanisms by which ILC3s sense and respond to the intricate milieu of signals present in the intestinal mucosa to coordinate intestinal health, impact inflammation, or promote tissue healing remains unclear and represents an important area of future investigation. In new preliminary data, I have unexpectedly determined that ILC3s are uniquely enriched in expression of a cell surface heparan sulfate proteoglycan receptor, syndecan-4, a pathway linked to wound healing, cell migration/adhesion, and control of growth factor signaling. Further, I identified a cellular and molecular mechanism regulating syndecan-4 on ILC3s and discovered that syndecan-4 becomes dysregulated in experimental mouse models of intestinal inflammation or human IBD. Finally, mice lacking ILC3-specific syndecan-4 show greater tissue damage and susceptibility to intestinal inflammation. This provokes a novel hypothesis that syndecan-4 is a critical pathway impacting ILC3 biology, host-microbiota homeostasis, and tissue repair during intestinal health and inflammation. The fundamental focus of this research proposal is to test this hypothesis and define the regulation and functional significance of ILC3-specific syndecan-4 by employing novel mouse models, innovative technical approaches, and translational studies. It is expected that the results from the two aims of this proposal will reveal crucial signaling mechanisms for inflammatory responses in the intestine that may have therapeutic potential for the treatment of IBD.