Microglial Lcn2 knockout enhances chronic intracerebral hemorrhage recovery by restoring myelin and reducing inflammation

<b>Rationale:</b> Damage to white matter and myelin poses a significant challenge to neurological recovery in the chronic phase of intracerebral hemorrhage (ICH). The repair of myelin damage post-ICH largely depends on the activation and differentiation of oligodendrocyte precursor cells (OPCs) into oligodendrocytes, a process that is significantly influenced by the inflammatory microenvironment. Lipocalin-2 (Lcn2) regulate phenotypic transformation of microglia and thus modulates inflammation. However, the exact role of Lcn2 in facilitating myelin recovery during the chronic phase of ICH remains to be fully understood. <b>Methods:</b> To create the ICH model, autologous blood from male C57BL/6 and Lcn2^fl/flCx3cr1^Cre mice was utilized. Behavioral tests were conducted to evaluate neurological recovery. The differentiation of OPCs and extent of myelin recovery were assessed using OPC and myelin markers. A multi-factor inflammatory chip was employed to investigate potential molecular regulatory mechanisms. Additionally, the Lcn2 inhibitor ZINC-94/89 was administered to explore its potential in targeting Lcn2 for enhancing myelin recovery during the chronic phase of ICH. <b>Results:</b> Knocking out Lcn2 in microglia significantly improved behavioral performance in chronic ICH mice, reduced inflammatory response, and enhanced myelin recovery. Both <i>in vivo</i> and <i>in vitro</i> experiments confirmed that Lcn2 knockout promoted microglia transformation to the M2 phenotype and enhanced OPCs differentiation. Mechanistically, Lcn2 knockout might affect Gdf-1 secretion in BV2 cells by modulating the JAK/STAT signaling pathway. Treatment with JAK inhibitors decreased Gdf-1 expression in BV2 cells, inhibiting OPCs migration and differentiation. Additionally, phosphorylation of Stat3 at Thr705 plays a critical role in enhancing Gdf-1 transcription and translation. Administration of the Lcn2 inhibitor ZINC-94/89 significantly improved behavioral performance, reduced inflammatory response, and promoted myelin recovery in chronic ICH mice. <b>Conclusions:</b> Lcn2 is crucial for myelin recovery in the chronic phase of ICH by modulating microglial phenotypes, thereby enhancing the migration and differentiation of OPCs. Administering an Lcn2 inhibitor early on could serve as a novel and effective strategy to boost recovery during this phase.