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.
