Galectin-1 and -9 in angiogenesis: a sweet couple

The growth of new blood vessels out of the pre-existing vasculature, i.e., angiogenesis, is executed by endothelial cells that normally form the inner lining of blood vessels. During angiogenesis, these cells exert different activities which require interactions with other cells and with the extracellular environment. It has become evident that this frequently involves galectins since the members of this protein family facilitate interactions between cells and/or glycoproteins via carbohydrate binding. In addition, they can regulate intracellular processes like signaling and splicing via non-carbohydrate interactions. We have previously reported on the role of galectin-1 and -9 in endothelial cell function. Here, we review the current knowledge of these two galectins in endothelial cell biology and angiogenesis. In addition, we describe the contribution of both galectins to other processes that involve the endothelium, including inflammation and coagulation. Finally, we discuss the challenges for future research in order to better understand how this "sweet" couple exerts its multifunctional activities within the vasculature.