Interleukin 33 regulates the autophagy of oxygen-glucose-deprivation/reoxygenation microglia via macrophage polarization.

Abstract

Introduction: Interleukin (IL)-33 is a pleiotropic cytokine in the immune system and inflammatory responses, which is involved in cerebral ischemia/reperfusion (I/R) injury. Evidence indicates that IL-33 plays an essential role in macrophage polarization activation, yet the potential molecular mechanisms remain elusive. This study explored the role of IL-33 in the activation of microglia/macrophage-mediated autophagy for cerebral I/R injury via in vitro experiments.

Material and methods: Primary macrophages were harvested from mouse bone marrow, and microglia were isolated from mouse brains. Lipopolysaccharide (LPS) and interferon γ (IFN-γ) induced polarization toward the M1 phenotype macrophage, and IL-4 induced polarization toward the M2 phenotype macrophage. Oxygen glucose deprivation/reoxygenation (OGD/R) models of primary microglia were established and co-cultured with M1 and M2 macrophages, respectively. The IL-33 knockout microglia OGD/R model and M1/M2 macrophages were co-cultured to explore the effects of IL-33 in the transformation from pro-inflammatory (M1) phenotype to anti-inflammatory (M2) phenotype against inflammation and autophagy. Microglial activation/polarization, autophagy, and inflammation were detected using western blot, immunofluorescence, and ELISA.

Results: Compared with microglia co-cultured with M1 macrophages, microglia co-cultured with M2 macrophages showed significantly higher expression of M2 intracellular markers (STAT6, PPAR-γ, IRF4, CEBP-β, and CD206 (p < 0.05). In contrast, the expression of STAT1 and IRF8 was significantly lower. IL-33 deficiency enhanced the anti-inflammatory phenotype of microglia/M2 macrophages. Furthermore, the expression of IL-10 and transforming growth factor β (TGF-β) was upregulated (p < 0.05), and the expression of IFN-γ was downregulated (p < 0.05) in microglia/M2 macrophages in comparison with microglia/M1 macrophages. Compared with the OGD/R model group, M1 macrophage co-culture increased Beclin-1 and ULK1 expression and reduced P62 expression, and M2 co-culture as well as IL-33 deletion reduced Beclin-1 and ULK1 expression and increased P62 expression levels.

Conclusions: IL-33 deficiency inhibited hypoxia-induced microglia autophagy and promoted macrophage polarization toward the anti-inflammatory phenotype.