GlycoRNA control of immune homeostasis

About This Grant

PROJECT SUMMARY Biopolymers of life fall into four broad categories: proteins, nucleic acids, lipids, and carbohydrates, also called glycans. Hybrid forms of these biopolymers are common, as is the case with glycoproteins and glycolipids on the cell surface. Nearly 80% of secreted or cell surface proteins are glycosylated; some contain up to 50% by mass carbohydrates. Recently, we discovered a new hybrid macromolecule, glycosylated RNA, expressed broadly across many cell and tissue types and is made up of N-glycans modifying small noncoding RNAs. Interestingly, these glycoRNAs are mainly found on the cell surface. While the observation that glycosylation can occur on RNA is transformative, a key question arising from this discovery is what the functional significance of RNA glycosylation is. Nucleic acid sensing is a critical immune surveillance program that monitors for invading pathogens. Innate immune sensors monitor the endosomes and the cytosol for foreign nucleic acids, with TLR3, 7, 8, and 9 sensing nucleic acids that end up in the endosome—these nucleic acids can come from pathogens and dead cells during efferocytosis. Because cells exist in a homeostatic state with glycoRNAs that can access the spaces where TLR sensors are deployed, we hypothesize that glycosylation of mammalian small RNAs prevents immune sensing of glycoRNAs. We plan to test our hypothesis through the innovative approaches proposed in three specific aims. In Aims 1 and 2, we will characterize the features of glycans that enable the “shielding” of glycoRNAs from the endosomal TLR sensing machinery and the mechanism involved. In Aim 3, we will define how pathogenetic bacteria remodel the features of cell surface glycoRNAs and connect this to the functional role of glycoRNAs during the infection of mammalian cells. Altogether, we anticipate that the results generated by this proposal will address a fundamental knowledge gap by establishing the first direct function of glycosylated RNA in the context of immune surveillance and cellular homeostasis.