Abstract
The canonical Wnt/β-catenin signaling pathway is crucial for blood-brain barrier (BBB) formation in brain endothelial cells. Although glucose transporter 1, claudin-3, and plasmalemma vesicular-associated protein have been identified as Wnt/β-catenin targets in brain endothelial cells, further downstream targets relevant to BBB formation and function are incompletely explored. By Affymetrix expression analysis, we show that the cytochrome P450 enzyme Cyp1b1 was significantly decreased in β-catenin-deficient mouse endothelial cells, whereas its close homolog Cyp1a1 was upregulated in an aryl hydrocarbon receptor-dependent manner, hence indicating that β-catenin is indispensable for Cyp1b1 but not for Cyp1a1 expression. Functionally, Cyp1b1 could generate retinoic acid from retinol leading to cell-autonomous induction of the barrier-related ATP-binding cassette transporter P-glycoprotein. Cyp1b1 could also generate 20-hydroxyeicosatetraenoic acid from arachidonic acid, decreasing endothelial barrier function in vitro In mice in vivo pharmacological inhibition of Cyp1b1 increased BBB permeability for small molecular tracers, and Cyp1b1 was downregulated in glioma vessels in which BBB function is lost. Hence, we propose Cyp1b1 as a target of β-catenin indirectly influencing BBB properties via its metabolic activity, and as a potential target for modulating barrier function in endothelial cells. Significance statement: Wnt/β-catenin signaling is crucial for blood-brain barrier (BBB) development and maintenance; however, its role in regulating metabolic characteristics of endothelial cells is unclear. We provide evidence that β-catenin influences endothelial metabolism by transcriptionally regulating the cytochrome P450 enzyme Cyp1b1 Furthermore, expression of its close homolog Cyp1a1 was inhibited by β-catenin. Functionally, Cyp1b1 generated retinoic acid as well as 20-hydroxyeicosatetraenoic acid that regulated P-glycoprotein and junction proteins, respectively, thereby modulating BBB properties. Inhibition of Cyp1b1 in vivo increased BBB permeability being in line with its downregulation in glioma endothelia, potentially implicating Cyp1b1 in other brain pathologies. In conclusion, Wnt/β-catenin signaling regulates endothelial metabolic barrier function through Cyp1b1 transcription.