Reports from the Bailly- and Guignabert laboratories add to a more complicated picture of BMP9 as a vascular quiescence factor, whereby they demonstrated that knockout of BMP9 or inhibition of BMP9 with neutralizing antibodies protected from PAH development in rodent models possibly due to reduced levels of Endothelin-1, a potent vasoconstrictor and contributor to vascular remodeling in PAH [30]. Here, GDF2 is linked to pulmonary arterial hypertension.