Mutant KRAS in brain endothelial cells promotes vascular inflammation and impairs vascular integrity in brain arteriovenous malformation

Somatic KRAS (KRAS^G12V) mutation in endothelial cells (EC) induces brain arteriovenous malformation (bAVM) that could lead to vascular instability and ultimately bleeding. However, the causes of bAVM instability remain unclear. Here we demonstrate that KRAS^G12V expressing cultured ECs (KRAS-G12V-EC) have increased expression of pro-inflammatory mediators and reduced expression of blood-brain-barrier (BBB) junction constituents. The conditioned medium from KRAS-G12V-EC can activate BV2-microglia (BV2-MG) and conditioned media from this primed BV2-MG can compromise the expression of EC-junction constituents when added to wild-type ECs. In an in vitro BBB model, KRAS-G12V-EC form a dysfunctional EC barrier that is further disrupted, leading to lower transendothelial electrical resistance and increased FITC-dextran leakage when blood-derived macrophages (Mφ) are included. KRAS-G12V-EC potently stimulates BV2-MG chemotaxis. In vitro BBB leakage and BV2-MG chemotaxis were inhibited by treatment with the anti-inflammatory drug minocycline in the KRAS-G12V-EC. In our bAVM mouse model that uses AAV-BR1-KRAS^G12V injection to produce EC expression of KRAS^G12V in the brain, minocycline injection reduced production of inflammatory cytokines by bAVM nidus, reduced leakage of BSA-647, and restored VE-cadherin expression on malformed vessels. Our findings suggest that KRAS-G12V-EC can activate local MG/Mφ that causes vascular inflammation and instability of malformed vessels in bAVM.