Endothelial oncogenic KRAS mutation drives the dynamics of microglia and macrophages in brain arteriovenous malformation.

Mutation of KRAS in endothelial cells (KRAS-ECs) leads to intracerebral hemorrhage (ICH) in brain arteriovenous malformation (bAVM), resulting in severe disabilities or even death. However, it is unclear what causes this hemorrhagic conversion of bAVMs. Here, using a locally established, clinically relevant sporadic bAVM mouse model, created by overexpressing mutant KRAS (KRASG12V) in brain ECs, we demonstrate that KRAS-ECs act as trigger for activation of microglia (MG) and infiltration of macrophages (Mϕ). Using a 3-dimensional immunostaining approach with cleared human and mouse bAVM tissues, we demonstrate an abundance of MG/Mϕ around the bAVM nidus. The presence of MG/Mϕ was correlated to the blood-brain barrier leakage in bAVM areas. Time-lapsed intravital imaging in Cx3cr1-gfp;Ccr2-rfp reporter mice demonstrated the dynamic activation of MG and infiltration of Mϕ toward mutant KRASG12V-modified dysplastic vessels. Importantly, a time-course analysis showed that these activated MG and infiltrated Mϕ are present around the bAVMs prior to hemorrhagic conversion, and controlled depletion of MG/Mϕ reduced ICH incidence in bAVMs. Inhibition of MG/Mϕ with long-term minocycline treatment attenuated the incidence of ICHs around bAVMs. Our study indicates that MG/Mϕ are involved in destabilization of KRASG12V-induced bAVM, leading to hemorrhagic conversion/ICH. Thus, modulation of MG/Mϕ may reduce ICH risk in patients with bAVM.