Abstract WP278: Metabolic Control of Neuroinflammation: The Role of Irg1/Itaconate in Intracerebral Hemorrhage

Purpose: Secondary brain injury following intracerebral hemorrhage (ICH) is amplified by metabolic reprogramming of resident microglia and infiltrating leukocytes in the peri-hematomal region. We previously identified itaconate—a metabolite generated by immune-responsive gene 1 (Irg1), as a potent immunometabolic regulator that attenuates microglial activation and brain injury after traumatic brain injury (TBI). Here, we tested the hypothesis that the Irg1/itaconate critically modulates metabolic reprogramming–driven inflammatory activation of microglia and brain-infiltrating immune cells, thereby influencing pathological outcomes after ICH. Methods: ICH was induced by collagenase injection in male mice. In Part 1, we examined the effect of itaconate deficiency using myeloid-specific conditional Irg1 knockout mice. In Part 2, we evaluated therapeutic effects of 4-octyl itaconate (4-OI, 20 mg/kg, i.p.), a cell-permeable derivative of itaconate, administered 1-hour post-ICH. Single-cell RNA sequencing (scRNA-seq) and LC-MS/MS metabolomics of brain-infiltrating neutrophils, monocyte-derived macrophages (MDMs), and microglia were analyzed at 12 hours. Flow cytometry, and immunostaining assessed inflammatory phenotypes at 1 and 3 days. Blood–brain barrier (BBB) integrity and brain edema were evaluated at 3 days, and neurobehavioral outcomes up to 14 days post-ICH. Results: Myeloid-specific Irg1 deletion exacerbated hyperglycolysis and proinflammatory activation of neutrophils and MDMs after ICH. Conversely, 4-OI supplementation suppressed proinflammatory gene expression and oxidative pathways (scRNA-seq), reduced hyperglycolysis and mitochondrial dysfunction (LC-MS/MS), and attenuated inflammatory activation in microglia, neutrophils, and MDMs. Treatment with 4-OI significantly reduced BBB leakage and brain edema, and neurological deficits after ICH. Discussion: Our findings establish the Irg1/itaconate axis as a critical regulator of myeloid cell and microglia metabolism and inflammatory activation after ICH. Both genetic and pharmacological interventions demonstrated that itaconate restores metabolic balance, dampens neuroinflammation, and reduces secondary brain injury. Targeting the Irg1/itaconate pathway represents a promising immunometabolic therapeutic strategy for ICH. Further studies are warranted to delineate cell subtype–specific mechanisms of irg1/itaconate, and to optimize the therapeutic potential of itaconate supplementation.