Figure 1.

Endoglin signaling in endothelium.

Notes: Under normal conditions, endoglin promotes transforming growth factor beta-1 signaling via both ALK-1 and ALK-5, which balances endothelial quiescence and proliferation, thereby promoting vascular homeostasis. When endoglin expression is reduced, as in hereditary hemorrhagic telangiectasia 1, signaling via ALK-1 is attenuated, while ALK-5 activity is increased, thereby promoting arrest of endothelial proliferation and impairing vascular homeostasis.

Abbreviation: ALK, activin receptor-like kinase; P, phospho.