IRF5 regulates microglial myelin clearance and cholesterol metabolism after demyelination
Interferon regulatory factor 5 (IRF5), a transcription factor highly involved in innate immunity that drives microglia/macrophage towards a pro-inflammatory state, has been associated to multiple sclerosis susceptibility but its role in MS pathogenesis is unknown. Here we analysed the role of IRF5 in multiple sclerosis animal models. Irf5-/- mice showed exacerbated damage in the chronic phase of experimental autoimmune encephalomyelitis (EAE) mice, despite an initial delay in its onset, as well as after lysolecithin injection into the spinal cord. Transcriptomic and lipidomic analysis evidence a role of this transcription factor in myelin metabolism and cholesterol homeostasis. Indeed, Irf5-/- mice showed an aberrant accumulation of myelin debris and lipidic structures, such as CE-containing lipid droplets and cholesterol crystals, suggesting that myelin-derived lipids are not properly processed. Cholesterol crystal accumulation leads to an aberrant inflammatory response, which block oligodendrocyte migration into the core of demyelinated lesion and remyelination. Pharmacologically facilitating cholesterol transport reduces lipid droplet accumulation and ameliorates EAE exacerbated damage in Irf5-/- mice. These results reveal for the first time the role of Irf5, a transcription factor necessary to orchestrate the immune responses, in phagocytes lipid metabolism which could be pivotal in regenerative responses such as remyelination.