Abstract
Direct communication between arteries and veins without intervening capillary beds is the primary pathology of arteriovenous malformations (AVMs). Although Notch signaling is implicated in embryonic arteriovenous (AV) differentiation, its function in the adult mammalian vasculature has not been established due to the embryonic lethality that often occurs in both gain- and loss-of-function mutants. We expressed a constitutively active
Notch4
,
int3
, in the adult mouse endothelium by using the tetracycline-repressible system to suppress
int3
during embryogenesis.
int3
caused profound blood vessel enlargement and AV shunting, which are hallmarks of AVM, and led to lethality within weeks of its expression. Vessel enlargement, a manifestation of AVM, occurred in an apparently tissue-specific fashion; the liver, uterus, and skin were affected.
int3
-mediated vascular defects were accompanied by arterialization, including ectopic venous expression of
ephrinB2
, increased smooth muscle cells, and up-regulation of endogenous Notch signaling. Remarkably, the defective vessels and illness were reversed upon repression of
int3
expression. Finally, endothelial expression of a constitutively active
Notch1
induced similar hepatic vascular lesions. Our results provide gain-of-function evidence that Notch signaling in the adult endothelium is sufficient to render arterial characteristics and lead to AVMs.
