The role of RNA modifications in macrophages

Abstract

RNA modifications and effector RNA binding proteins regulate gene expression in most biological processes. Amongst RNA modifications are N6-methyladenosine (m6A), which results from methylation of adenosine residues by the METTL3-METTL14 methyltransferase complex, and RNA 5-hydroxymethylcytosine (5hmC), which arises from oxidation of 5-methylcytosine by the Ten-Eleven Translocation (TET) enzymes. While m6A is established as a versatile regulator of RNA metabolism in various biological contexts, the functions of RNA 5hmC are unknown. Despite some evidence linking RNA modifications to immunity, their implications in macrophage development and functions are unclear. Since macrophages are central effectors of the innate immune response and are heavily involved in chronic inflammation, understanding the molecular pathways behind macrophage-mediated responses is critical to developing new treatments for inflammatory disorders. In this thesis, I present novel insights into m6A- and 5hmC-mediated gene expression regulation in macrophages. I found that m6A and 5hmC occur together in transcripts with key roles in macrophage biology and that METTL3 and TET enzymes are involved in macrophage differentiation. I also identified specific transcripts regulated by these enzymes in a cellular-context-dependent manner. Furthermore, I discovered that METTL3 regulates inflammasome activation, a critical event that triggers the innate immune response. I demonstrate that METTL3 depletion protects mice from septic shock-induced death and attenuates NLRP3 hyperactivation in primary cells isolated from patients suffering from an NLRP3 inflammasome-driven autoinflammatory disease. Mechanistically, I found that METTL3-mediated m6A methylation promotes NLRP3 translation. This thesis extends current knowledge on RNA modifications in macrophages and the immune response and establishes RNA modification regulatory proteins as potential targets for therapeutic intervention in inflammatory diseases.