Endothelial Rbpj deletion normalizes Notch4-induced brain arteriovenous malformation in mice

Upregulation of Notch signaling is associated with brain arteriovenous malformation (bAVM), a disease that lacks pharmacological treatments. Tetracycline (tet)-regulatable endothelial expression of constitutively active Notch4 (Notch4*(tetEC)) from birth induced bAVMs in 100% of mice by P16. To test whether targeting downstream signaling, while sustaining the causal Notch4*(tetEC) expression, induces AVM normalization, we deleted Rbpj, a mediator of Notch signaling, in endothelium from P16, by combining tet-repressible Notch4*(tetEC) with tamoxifen-inducible Rbpj deletion. Established pathologies, including AV connection diameter, AV shunting, vessel tortuosity, intracerebral hemorrhage, tissue hypoxia, life expectancy, and arterial marker expression were improved, compared with Notch4*(tetEC) mice without Rbpj deletion. Similarly, Rbpj deletion from P21 induced advanced bAVM regression. After complete AVM normalization induced by repression of Notch4*(tetEC), virtually no bAVM relapsed, despite Notch4*(tetEC) re-expression in adults. Thus, inhibition of endothelial Rbpj halted Notch4*(tetEC) bAVM progression, normalized bAVM abnormalities, and restored microcirculation, providing proof of concept for targeting a downstream mediator to treat AVM pathologies despite a sustained causal molecular lesion.