ACP5-positive macrophages contribute to cerebral oedema and neuroinflammation after traumatic brain injury.

BACKGROUND: Traumatic brain injury (TBI) is a leading cause of death and long-term disability worldwide. Secondary cerebral oedema, driven by neuroinflammation and blood-brain barrier (BBB) disruption, critically determines poor outcomes, yet effective targeted therapies remain absent. This study aimed to identify immune cell subsets associated with post-TBI cerebral oedema and to explore their functional contributions in preclinical models. METHODS: We integrated single-cell transcriptomic datasets from a mouse TBI model (GSE175430) and human intracerebral haemorrhage (ICH) perihaematomal oedema samples (GSE266873) with our previously published temporal bulk RNA-seq profiling data. Through cross-species comparative analysis, Mfuzz clustering, AUCell scoring and gene set enrichment analysis (GSEA), Acp5 was identified as an oedema-associated signature gene, and its macrophage-enriched expression pattern was supported by single-cell profiling and immunofluorescence colocalisation. Using the controlled cortical impact (CCI) model, we validated Acp5 expression dynamics across injury severities. Pharmacological inhibition (AubipyOMe) and genetic knockout of Acp5 were employed to assess brain oedema, neuroinflammation, neurological function and long-term cognitive recovery. RESULTS: A previously unrecognised population of ACP5-positive monocytes/macrophages infiltrated the brain parenchyma within 1-3 days post-injury, coinciding with peak oedema severity and neurological deficits. Inhibiting ACP5 significantly reduced brain water content, BBB leakage and proinflammatory cytokines, while improving sensorimotor function. Mechanistically, ACP5-positive macrophages were associated with CSF2-related JAK/STAT and NF-κB signalling. Genetic Acp5 ablation attenuated acute macrophage infiltration and neuroinflammation, and was associated with improved long-term behavioural outcomes. CONCLUSIONS: ACP5-positive macrophages represent an injury-associated myeloid population that contributes to neuroinflammatory and oedema-related phenotypes after experimental TBI. Pharmacological and genetic findings provide preclinical evidence supporting further investigation of ACP5 and CSF2-related signalling in secondary TBI injury.