THE ROLE OF IRON REGULATORY PROTEINS IRP1 AND IRP2 IN MODULATING ANTI-INFLAMMATORY PROCESSES IN MACROPHAGES

Iron is an essential element in many cellular processes including immune responses. Its homeostasis is regulated by Iron Regulatory Proteins 1 and 2 (IRP1 and IRP2), which are both activated, when cellular iron is low. In macrophages, inflammatory conditions elicit an increase in IRP1 activity, whereas IRP2 protein is degraded. However, the interplay between IRPs and inflammation is poorly understood.

Upon inflammatory stimulus, macrophages adopt a spectrum of activation states, ranging from pro-inflammatory (M1-like) to anti-inflammatory (M2-like) phenotypes. M2-like macrophages often referred to as "alternatively activated" play essential roles in wound healing, tissue remodelling, and the resolution of inflammation. M2 polarization is typically induced by signals such as interleukin-4 (IL-4), which lead to a distinct gene expression profile that includes markers such as CD206 (mannose receptor), Arginase-1, and IL-10.

Our previous work demonstrated opposing effects of IRP1 and IRP2 deletion on inflammation progression in a murine model of bacterial orchitis. Based on our findings, we hypothesized that IRP1 or IRP2 deletions differentially affect macrophage inflammatory responses. Specifically, we propose that IRP1-deficient macrophages (Irp1-/-) tend to polarize toward an anti-inflammatory M2-like phenotype.

To investigate this, we exposed bone marrow-derived macrophages (BMDMs) from Irp1-/- and Irp2-/- mice to IL-4. First, we examined differences in morphology and polarization markers between genotypes upon IL-4 treatment. Iron homeostasis was assessed by analysing ferritin subunit composition and its iron content. Additionally, anti-inflammatory pathways such as cytokine production were evaluated. Phagocytosis activity was also tested.

Our results demonstrated differences in morphology and polarization markers between genotypes upon IL-4 stimulus.

These results suggest that IRP1 and IRP2 are involved in M2-like activation state, potentially extending their roles beyond iron regulation. Future research will focus on deciphering the mechanisms linking IRPs to metabolic pathways, including glycolysis and oxidative processes, and identifying their mRNA targets during macrophage polarization.