IRE1a Regulates Macrophage Phagocytosis In Immune Thrombocytopenia Through NR1D1 mRNA Decay And Lysosomal Biogenesis

Introduction:Macrophage phagocytosis is crucial for cellular homeostasis and is tightly regulated by stress responses. The ER stress sensor IRE1a, a key unfolded protein response (UPR) regulator, is well-studied, but its role in phagocyte homeostasis remains unknown.Objectives:This study investigates whether IRE1a regulates phagocytosis in macrophages and explores its underlying mechanism, aiming to identify potential therapeutic targets for phagocytosis-related disorders.Methods:We examined IRE1a activation in macrophages during phagocytosis of dextran or platelets. Myeloid-specific IRE1a-knockout mice were used to assess phagocytic function. Mechanistic studies included RIDD analysis to identify IRE1a-dependent mRNA degradation. A mouse model of immune thrombocytopenia (ITP) was employed to evaluate platelet clearance, with pharmacological NR1D1 inhibition (SR8278) tested as a rescue strategy.Results:Phagocytosis specifically activates IRE1a in macrophages, where it maintains phagocytic homeostasis. IRE1a deficiency led to excessive phagocytosis due to uncontrolled lysosomal biogenesis. Mechanistically, IRE1a degrades Nr1d1 mRNA via its RNase activity, suppressing lysosomal expansion. In ITP mice, IRE1a deficiency worsened platelet clearance, while SR8278 treatment rescued this defect. Overall design: Peritoneal macrophages were harvested from 8-week-old male Ern1(fl/fl) and Mac-Ern1(KO) mice three days after they received an intraperitoneal injection of 3% Brewer thioglycolate medium. Following isolation, the cells were co-cultured for two hours with platelets opsonized by the anti-CD42 antibody (R300) in a phagocytosis assay. To investigate transcriptional alterations resulting from these conditions, we then performed bulk RNA sequencing (bulk RNA-seq). The analysis included three biological replicates for each experimental cohort.