Wnt signaling in angiogenesis.

Although progress has been made in understanding the role of growth factors and their receptors in angiogenesis, little is known about how the Wnt family of growth factors function in the vasculature. Wnts are multifunctional factors that act through the frizzled receptors to regulate proliferation, apoptosis, branching morphogenesis, inductive processes, and cell polarity. All of these processes must occur as developing vascular structures are formed and maintained. Recent evidence has linked the Wnt/Frizzled signaling pathway to proper vascular growth in murine and human retina. Here we review the literature describing the angiogenic functions for Wnt signaling and focus on a newly discovered angiogenic factor, Norrin, which acts through the Wnt receptor, Frizzled4.