Reck enables cerebrovascular development by promoting canonical Wnt signaling

Abstract

The cerebral vasculature provides the massive blood supply that the brain needs to grow and survive. By acquiring distinctive cellular and molecular characteristics it becomes the blood-brain barrier (BBB), a selectively permeable and protective interface between the brain and the peripheral circulation that maintains the extracellular milieu permissive for neuronal activity. Accordingly, there is great interest in uncovering the mechanisms that modulate the formation and differentiation of the brain vasculature. By performing a forward genetic screen in zebrafish we isolated no food for thought (nft y72 ), a recessive late-lethal mutant that lacks most of the intracerebral central arteries (CtAs), but not other brain blood vessels. We found that the cerebral vascularization deficit of nft y72 mutants is caused by an inactivating lesion in reversion-inducing cysteine-rich protein with Kazal motifs [reck; also known as suppressor of tumorigenicity 15 protein (ST15)], which encodes a membrane-anchored tumor suppressor glycoprotein. Our findings highlight Reck as a novel and pivotal modulator of the canonical Wnt signaling pathway that acts in endothelial cells to enable intracerebral vascularization and proper expression of molecular markers associated with BBB formation. Additional studies with cultured endothelial cells suggest that, in other contexts, Reck impacts vascular biology via the vascular endothelial growth factor (VEGF) cascade. Together, our findings have broad implications for both vascular and cancer biology.

Reck and Gpr124 Are Essential Receptor Cofactors for Wnt7a/Wnt7b-Specific Signaling in Mammalian CNS Angiogenesis and Blood-Brain Barrier Regulation

“…In mice, Reck plays an essential role in embryonic and placental vascular remodeling, and these activities have been ascribed to its function as an MMP inhibitor, with at least one site of action in pericytes (Oh et al, 2001; Chandana et al, 2010; de Almeida et al, 2015). In zebrafish, loss-of-function Gpr124 and Reck mutations have very similar phenotypes, with each gene playing an essential role in the development of dorsal root ganglia and intracerebral vascularization (Prendergast et al, 2012; Vanhollebeke et al, 2015; Ulrich et al, 2016). In cell culture, Gpr124 and Reck strongly enhance Frizzled- and Lrp5/6-dependent canonical Wnt signaling by Wnt7a and Wnt7b, but not by any of the other 17 mammalian Wnts or by Norrin, and in mice the Gpr124 knockout phenotype can be rescued by experimentally activating canonical Wnt signaling (Zhou and Nathans, 2014; Posokhova et al, 2015; Vanhollebeke et al, 2015).…”

Gradual Suppression of Transcytosis Governs Functional Blood-Retinal Barrier Formation

“…Whether canonical Wnt signaling also regulates the gradual suppression of transcytosis is not clear. On one hand, recent studies demonstrated canonical Wnt signaling is essential in the tip cells of nascent sprouts (Ulrich et al, 2016; Vanhollebeke et al, 2015) yet these nascent, distal vessels display bulk transcytosis and lack Mfsd2a during BRB development. But on the other hand, microarray analysis on retinas from canonical Wnt signaling deficient mice showed that Mfsd2a is downregulated (Chen et al, 2012).…”

TSPAN12 Is a Norrin Co-receptor that Amplifies Frizzled4 Ligand Selectivity and Signaling

“…However, biochemical evidence for this concept is largely lacking. TSPAN12 (tetraspanin family) and GPR124 (adhesion GPCR family) have distinct structures and characteristics, e.g., GPR124 appears to function together with another membrane molecule, RECK (Ulrich et al, 2016; Vanhollebeke et al, 2015). Available crystal structures of NDP in complex with the extracellular domain of FZD4 show that a NDP head-to-tail dimer contacts two FZD4 molecules (Chang et al, 2015; Shen et al, 2015).…”