Neutrophil Irg1/itaconate axis protects against experimental colitis by suppressing local inflammation and...

Inflammatory bowel disease (IBD) is a chronic, relapsing disorder characterized by excessive inflammation and often associated with extraintestinal symptoms. Current treatments remain unsatisfactory. Although immune response gene 1 (Irg1) and its product itaconate show promise in alleviating experimental colitis, the underlying mechanisms are unclear. Here, we describe an endogenous, homeostatic pattern that controls both local and systemic inflammatory responses in experimental murine colitis. Our study identifies neutrophils in inflamed colon as the primary Irg1 source. Irg1 deficiency worsens disease severity, as shown by greater weight loss, higher disease activity index, shorter colon length, more severe tissue damage, and more neutrophil infiltration. Depleting neutrophils with Ly6G antibody worsened symptoms in wild-type mice but improved them in knockout mice, highlighting the key role of the Irg1/itaconate axis in neutrophil-mediated protection. Blood analysis showed that Irg1 deficiency increased inflammatory cells and worsened anemia. Bone marrow analysis revealed fewer granulocyte-monocyte progenitors (GMP) and more megakaryocyte-erythroid progenitors (MEP), suggesting a compensatory mechanism. We also found that Irg1 deficiency increased reverse migrated (rM-ed) neutrophils in blood and bone marrow. Exogenous itaconate (4-octyl itaconate, 4-OI) treatment significantly reduced colon inflammation, lowered rM-ed neutrophil levels, and restored hematopoietic homeostasis. RNA sequencing showed that 4-OI mainly acted by blocking NF-κB signaling, inhibiting endocytosis-related genes, and suppressing rM-ed neutrophils-related genes expression. In conclusion, the neutrophil-derived Irg1/itaconate axis plays a key role in mucosal repair and may help maintain hematopoietic balance by regulating rM-ed neutrophils, which suggest that exogenous itaconate derivatives like 4-OI may be effective treatments for IBD.