Mural norrin/β-catenin signaling regulates Lama2 expression to promote neurovascular unit assembly

Neurovascular unit (NVU) assembly and barrier maturation rely on vascular basement membrane (vBM) composition. Laminins, a major vBM component, are critical for these processes, yet which signaling pathway(s) regulate their expression remains unknown. Here we show that mural cells have active Norrin/{beta}-catenin signaling during central nervous system development. Bulk RNA sequencing and validation using P10 and P14 wild-type versus Apcdd1-/- retinas reveal that Lama2 (Laminin-2 chain) mRNA and protein levels are increased in mutant vasculature undergoing higher Norrin/{beta}-catenin signaling. Mural cells are the main source of Lama2, and {beta}-catenin activation induces Lama2 expression in mural cells in vitro. Markers of mature astrocytes including Aquaporin-4 (a water channel in astrocyte endfeet) and Integrin-6 (a laminin receptor) are upregulated in Apcdd1-/- retinas following higher Lama2 vBM deposition. Thus, the Norrin/{beta}-catenin pathway regulates Lama2 expression in mural cells to promote NVU assembly and neurovascular barrier maturation. SUMMARYBiswas et al., demonstrate that Norrin/{beta}-catenin signaling is active in CNS mural cells and regulates Lama2 deposition in the vascular basement membrane, promoting neurovascular unit assembly and blood-CNS barrier maturation.