Constitutively active endothelial Notch4 causes lung arteriovenous shunts in mice

Abstract

Lung arteriovenous (AV) shunts or malformations cause significant morbidity and mortality in several distinct clinical syndromes. For most patients with lung AV shunts, there is still no optimal treatment. The underlying molecular and cellular etiology for lung AV shunts remains elusive, and currently described animal models have insufficiently addressed this problem. Using a tetracycline-repressible system, we expressed constitutively active Notch4 (Notch4*) specifically in the endothelium of adult mice. More than 90% of mice developed lung hemorrhages and respiratory insufficiency and died by 6-7 wk after gene expression began. Vascular casting and fluorescent microsphere analysis showed evidence of lung AV shunts in affected mice. Cessation of Notch4* expression reversed these pathophysiological effects. Assessment of the vascular morphology revealed enlarged, tortuous vessels in the lungs that resembled arteriovenous malformations. By using whole lung organ culture, we demonstrated the effects of constitutively active Notch4 on the lung vasculature to be a primary lung phenomenon. Together, our results indicate the importance of Notch signaling in maintaining the lung vasculature and offer a new, reliable model with which to study the pathobiology of lung arteriovenous shunts and malformations.

ALK1 Signaling Inhibits Angiogenesis by Cooperating with the Notch Pathway

“…Both Notch loss- and gain-of function mutations cause AVMs (Gale et al, 2004; Krebs et al, 2004, 2010; Murphy et al, 2009, 2012), but interestingly, the phenotype of the Acvrl1 knockout mice is more reminiscent of Notch gain-of-function mutants (Park et al, 2009). In addition, inducible overexpression of active Notch in transgenic mice has been shown to induce AVMs, which were resolved following arrest of transgene expression (Miniati et al, 2010). Furthermore, human brain AVMs showed increased Notch and Notch ligand expression, suggesting that once AVMs are established, they exhibit increased Notch activation.…”

Deletion of Rbpj from postnatal endothelium leads to abnormal arteriovenous shunting in mice

“…Adult endothelial Rbpj deletion leads to enlarged, tortuous vessels in mature vascular beds associated with the gastrointestinal tract, uterus and skin. Similarly, activation of the Notch4* mutation from birth results in brain AV shunts (Murphy et al, 2008), whereas Notch4* activation post-weaning leads to AV shunts in the gastrointestinal tract, uterus, skin and lung (Carlson et al, 2005;Miniati et al, 2010) but not in the brain (Carlson et al, 2005). Our results suggest that Rbpj is required in postnatal endothelium during two distinct temporal windows, but selectively in organs such as the brain.…”

“…Activation of Notch1 in ECs results in dorsal aortae fusing with developing cardinal veins in the mouse embryo (Krebs et al, 2010). In postnatal mouse endothelium, expression of a constitutively active Notch4 mutation leads to and sustains features of AVMs, including AV shunts and tortuous vessels, in brain, liver, uterus and lung (Carlson et al, 2005;Miniati et al, 2010;Murphy et al, 2008Murphy et al, , 2012. Vessels from these mice show increased Efnb2 expression at the expense of Ephb4, suggesting that mutant venous ECs acquire arterial gene expression (Carlson et al, 2005;Murphy et al, 2008).…”

Constitutively active Notch4 receptor elicits brain arteriovenous malformations through enlargement of capillary-like vessels

“…ECs results in spontaneous AVMs in mice (15)(16)(17)21). Although this work has facilitated new research directions regarding the Notch pathway in AVMs, how aberrant Notch signaling leads to AVM remains unknown.…”