The Wnt Inhibitor Apcdd1 Coordinates Vascular Remodeling and Barrier Maturation of Retinal Blood Vessels

Highlights

• Apcdd1 is expressed in retinal endothelium during angiogenesis and barrier formation

• Apcdd1 mutant mice show decreased vessel pruning and precocious barrier maturation

• Apcdd1 overexpression promotes vessel pruning but delays barrier formation

• The Wnt inhibitor Apcdd1 tightly coordinates vascular pruning and barrier maturation

Summary

Coordinating angiogenesis with acquisition of tissue-specific properties in endothelial cells is essential for vascular function. In the retina, endothelial cells form a blood-retina barrier by virtue of tight junctions and low transcytosis. While the canonical Norrin/Fz4/Lrp5/6 pathway is essential for angiogenesis, vascular remodeling, and barrier maturation, how these diverse processes are coordinated remains poorly understood. Here we demonstrate that Apcdd1, a negative regulator of Wnt/β-catenin signaling, is expressed in retinal endothelial cells during angiogenesis and barrier formation. Apcdd1-deficient mice exhibit a transient increase in vessel density at ages P10–P12 due to delayed vessel pruning. Moreover, Apcdd1 mutant endothelial cells precociously form the paracellular component of the barrier. Conversely, mice that overexpress Apcdd1 in retina endothelial cells have reduced vessel density but increased paracellular barrier permeability. Apcdd1 thus serves to precisely modulate Wnt/Norrin signaling activity in the retinal endothelium and coordinate the timing of both vascular pruning and barrier maturation.