BST2 expression at astrocyte borders promotes microglial recruitment via the C3/C3aR signaling

Following central nervous system injury, astrocytes form borders that were traditionally regarded as physical barriers. Emerging evidence demonstrates their capacity to regulate inflammation and repair; however, the specific characteristics of these border astrocytes and their interactions with immune cells remain insufficiently characterized. Using single-cell sequencing and spatial transcriptomics, we identified astrocytes expressing the interferon-inducible protein bone marrow stromal cell antigen 2 (BST2) enriched at injury boundaries that promote microglial recruitment via C3/C3aR signaling. Astrocyte-specific Bst2 knockout reduced astrocyte-microglia interactions and attenuated border formation, correlating with early neurological improvement after stroke. Mechanistically, BST2 enhanced C3 expression through protein kinase C-βII (PKCβII) phosphorylation. Moreover, treatment with a BST2 monoclonal antibody diminished astrocyte-microglia interactions and improved neurological function. Together, these findings highlight the pivotal role of astrocyte-microglia interactions in lesion border formation and suggest that BST2 may represent a therapeutic target to modulate these interactions and reduce early brain injury after stroke.