Pro-repair macrophages driven by CGRP rescue white matter integrity following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) triggers a dynamic immune response involving macrophages, However, the functional heterogeneity of these cells and the mechanisms through which they promote repair remain unclear. Although the neuropeptide CGRP has been shown to modulate macrophage phenotypes in other pathological contexts, its role in ICH recovery and white matter repair remains unexplored. Single-cell RNA sequencing (scRNA-seq) of CD45 + cells from ICH mice (GSE167593 and GSE230414 datasets) identified macrophage subsets. Flow cytometry, diffusion tensor imaging (DTI), behavioral assays, and immunofluorescence validated macrophage dynamics and white matter (WM) integrity. Bone marrow and skull analyses traced macrophage origins. The role of calcitonin gene-related peptide (CGRP) was tested via intraperitoneal administration in ICH mice, with outcomes assessed through transcriptomics, ultrastructural imaging, and functional recovery. scRNA-seq revealed sustained accumulation of THBS1 + macrophages post-ICH, correlating with WM repair and neurological recovery. These macrophages exhibited pro-repair and remyelination gene signatures (e.g., Arg1, Tgm2). Bone marrow-derived myeloid cells, particularly skull-resident populations, served as the primary source of THBS1 + macrophages. CGRP, elevated in meninges and bone marrow post-ICH, drove macrophage polarization toward THBS + phenotypes. CGRP administration expanded THBS1-positive macrophages in the bone marrow and brain, improving WM integrity (reduced radial diffusivity, higher fractional anisotropy) and sensorimotor function. Ultrastructural analysis confirmed enhanced myelin regeneration (lower g-ratio) in CGRP-treated mice. This study identifies a neuroimmune axis wherein CGRP promotes bone marrow-derived THBS1 + macrophages to facilitate WM repair and functional recovery after ICH. Targeting CGRP-macrophage signaling offers a therapeutic strategy to enhance recovery in hemorrhagic brain injury.