Abstract
INTRODUCTION: Neonatal hypoxic-ischemic (HI) brain injury is a major cause of mortality and long-term neurological disability, yet effective neuroprotective strategies remain limited. Microglia are central mediators of injury and repair, with arginase 1 (ARG1) marking anti-inflammatory, reparative states. However, the functional roles of ARG1+ microglia in tissue remodeling after HI are poorly understood. METHODS: Neonatal mice (P10) underwent HI using the Vannucci procedure. ARG1 activity was inhibited pharmacologically using N-omega-hydroxy-nor-L-arginine (nor-NOHA). ARG1 expression, microglial morphology, efferocytosis, tissue scar, and injury volume were assessed via immunohistochemistry, Western blotting, and arginase activity assays at 1 and 5 days post-injury. RESULTS: ARG1+ microglia rapidly engaged apoptotic neurons, exhibiting phagocytic activity confirmed by CD68 expression. Nor-NOHA treatment reduced ARG1 enzymatic activity, impaired microglial process extension, attenuated efferocytosis, and increased injury volume. ARG1+ microglia persisted in the glial scar and colocalized with collagen I alpha-1 (Col1a1), suggesting a role in extracellular matrix (ECM) deposition. Inhibition of ARG1 decreased Col1a1 expression, highlighting its contribution to tissue remodeling. CONCLUSIONS: ARG1+ microglia are pivotal in neonatal HI, mediating early efferocytosis and later ECM remodeling, thereby limiting injury and shaping scar architecture. Pharmacological blockade of ARG1 exacerbates injury, underscoring its reparative function. These findings establish ARG1 as a critical regulator of microglial-mediated neuroprotection and tissue repair, providing a potential therapeutic target for neonatal HI brain injury.