Single-Cell Analysis of Brain Arteriovenous Malformations Reveals Pro-Angiogenic Myeloid Programs

Background/Objectives: Brain arteriovenous malformations (bAVMs) are complex cerebrovascular lesions that carry a substantial risk of intracranial hemorrhage, yet the biological mechanisms underlying vascular remodeling remain incompletely understood. As increasing evidence suggests that inflammatory processes contribute to vascular remodeling and bAVM progression, this study aimed to characterize the cellular composition of the immune microenvironment in human bAVMs at single-cell resolution and to identify immune cell populations associated with transcriptional programs related to angiogenesis and extracellular matrix remodeling. Methods: Publicly accessible single-cell RNA sequencing data from five human bAVM samples and five control brain specimens were analyzed. After quality control and data integration, immune cell types were annotated based on canonical marker gene expression. To assess biological processes relevant to vascular remodeling, the expression of predefined gene sets associated with angiogenesis and extracellular matrix remodeling, derived from the Molecular Signatures Database (MSigDB), was quantified across cell populations using rank-based gene set scoring (UCell). Differences between bAVM and control samples were evaluated at the sample level using the Wilcoxon rank-sum test. For each immune cell type, mean UCell scores were calculated per biological sample and compared between groups. To account for multiple comparisons across cell types, p-values were adjusted using the Benjamini-Hochberg procedure. Results: After quality control, 46,360 immune cells were analyzed. Compared with control tissue, bAVMs showed numerically higher proportions of lymphoid (activated T cells and CD8 T cells) and myeloid populations (M1-like macrophages, monocytes, and dendritic cells). Angiogenesis-related transcriptional activity was highest in myeloid cells and significantly increased in bAVMs, particularly in M1-like macrophages (UCell score 0.22 vs. 0.13), dendritic cells (0.16 vs. 0.10) and monocytes (0.20 vs. 0.15), whereas proliferating CD8 T cells showed a lower score (0.04 vs. 0.05; adjusted p = 0.040 for all four). Extracellular matrix-related programs showed a similar but weaker and non-significant pattern in myeloid populations (e.g., monocytes, dendritic cells, microglia-like cells; adjusted p = 0.09). Conclusions: Our findings identify myeloid cells, particularly M1-like macrophages, monocytes and dendritic cells, as important immune populations associated with angiogenesis in bAVMs. These findings highlight a potential role of immune-driven vascular remodeling in the pathophysiology of bAVMs.