Microglia/macrophages as target to prevent intracerebral hemorrhage in KRAS mutation-induced brain arteriovenous malformations

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Project Summary/Abstract Brain arteriovenous malformation (bAVM) patients have a 50% risk of intracerebral hemorrhage (ICH) which carries a high risk of severe morbidity and mortality. Although a surgical attempt is a conventional treatment for the bAVM, the surgery for critical bAVM is associated with significant complications such as intraoperative hemorrhage or death. Our long-term goal is to identify a preventative strategy for ICH in bAVM patients. The inciting pathophysiology leading to bAVM rupture is unknown. Studies have shown that the presence of a bAVM is highly correlated with local inflammation of intranidal and surrounding brain parenchyma. Immunohistochemistry studies have identified dense concentrations of brain microglia and blood monocyte- derived macrophages (we refer to them as M) surrounding the unruptured human bAVM. Meanwhile, clinical studies found that 62% of human sporadic bAVM patients harbored KRAS mutations in vascular endothelial cells (ECs). Here we found that ECs carrying KRAS mutation (KRAS-EC) induced inflammatory responses toward cultured M that in turn disrupts EC junctions. This suggests that M-mediated inflammation drives bAVM destabilization that may lead to bAVM rupture/ICH. To explore how KRAS-EC alter M phenotype and destabilize bAVM, we established a novel bAVM/ICH mouse model that uses the ECs-specific AAV/BR1 to deliver mutant KRAS (AAV-KRASG12V) into brain ECs (bEC). The KRASG12V/bEC mouse recapitulates human bAVM pathology, including tangled vessels, incomplete mural cell coverage, spontaneous ICH, and neurological deficits (Park 2021 Ann Neurol). In KRASG12V/bEC mouse, we showed that the number of Iba-1+ Mare increased around unruptured bAVM. The mRNA or protein levels for inflammatory cytokines, Proteolytic enzymes, angiogenic mediator, and adhesion molecule are increased in KRASG12V/bEC mice and in KRAS-EC themselves. Furthermore, KRASG12V/bEC mice treated with clodronate liposome (to deplete M) or minocycline reduces early microbleeds. Our preliminary study and existing literature strongly supporting the notion that the activated M- mediated inflammation drives bAVM destabilization that may lead to bAVM rupture/ICH. In this proposal, we will test our hypothesis that KRAS-EC recruit and activate M within bAVM territory and that these activated M in turn exacerbate the (peri)vascular damage causing bAVM rupture/ICH and that inhibition of M can avert/delay this process. In Aim 1, we will determine the mechanism causing Mactivation and BBB disruption in bAVM. In Aim 2, we will evaluate the clinical relevance of M in bAVM rupture and ICH. We expect that the successful completion of this preclinical study will uncover a causative role of Min bAVM rupture and ICH and will provide evidence to test the potential for M modulation in the prevention of bAVM-associated ICH. Our proposal has the potential for broad implications as M are commonly involved in most cerebrovascular diseases.