CNS resident macrophages exhibit region-specific states and immunogenic responses during Rbpj-deficient brain arteriovenous malformation.

Microglia are heterogeneous macrophage cells that serve as the central nervous system's resident immune cells. During neuro-related diseases, CNS resident macrophages change their molecular, cellular, and functional properties-that collectively define "states"-in response to specific neural perturbations. Neurovascular diseases elicit state changes, by promoting increased vascular permeability among microvessels and thus altering blood-brain barrier integrity. Here, we used a mouse model of brain arteriovenous malformation (bAVM)-mediated by endothelial loss of Recombination signal binding protein for immunoglobulin kappa J region (Rbpj)-to investigate changes to brain resident macrophage states during neurovascular disease pathogenesis. We found increased area of Ionized calcium-binding adapter molecule 1 (Iba1) expression in Rbpj-deficient bAVM tissue, as well as Iba1 + cell hypertrophy, increased cell number, and hyperproliferation within areas of increased Iba1 + density. Hypertrophic cells had increased cell body areas and decreased process length, suggesting a transition in surveillance state. Gene expression data revealed region-specific molecular changes to Iba + cells, suggestive of altered metabolic activity. CNS resident macrophages isolated from cortical and cerebellar regions showed profiles consistent with cytokine-associated immunogenic responses and an immunovigilant pathogen-recognition response, respectively. Thus, our findings demonstrate region-specific changes to CNS resident macrophages during Rbpj-deficient bAVM.