Novel vascular roles of human endoglin in pathophysiology

Endoglin, alias CD105, is a human membrane glycoprotein highly expressed in vascular endothelial cells. It is involved in angiogenesis and angiogenesis-related diseases, including the rare vascular pathology known as hereditary hemorrhagic telangiectasia type 1. Although endoglin acts as an accessory receptor for members of the transforming growth factor-β family, in recent years, emerging evidence has shown a novel functional role for this protein beyond the transforming growth factor-β system. In fact, endoglin has been found to be an integrin counterreceptor involved in endothelial cell adhesion processes during pathological inflammatory conditions and primary hemostasis. Furthermore, a circulating form of endoglin, also named as soluble endoglin, whose levels are abnormally increased in different pathological conditions, such as preeclampsia, seems to act as an antagonist of membrane-bound endoglin and as a competitor of the fibrinogen-integrin interaction in platelet-dependent thrombus formation. These studies suggest that membrane-bound endoglin and circulating endoglin are important components involved in vascular homeostasis and hemostasis.