Canonical WNT signaling components in vascular development and barrier formation
Yulian Zhou, … , Makoto M. Taketo, Jeremy Nathans
Yulian Zhou, … , Makoto M. Taketo, Jeremy Nathans
Published August 1, 2014
Citation Information: J Clin Invest. 2014;124(9):3825-3846. https://doi.org/10.1172/JCI76431.
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Research Article Vascular biology

Canonical WNT signaling components in vascular development and barrier formation

Abstract

Canonical WNT signaling is required for proper vascularization of the CNS during embryonic development. Here, we used mice with targeted mutations in genes encoding canonical WNT pathway members to evaluate the exact contribution of these components in CNS vascular development and in specification of the blood-brain barrier (BBB) and blood-retina barrier (BRB). We determined that vasculature in various CNS regions is differentially sensitive to perturbations in canonical WNT signaling. The closely related WNT signaling coreceptors LDL receptor–related protein 5 (LRP5) and LRP6 had redundant functions in brain vascular development and barrier maintenance; however, loss of LRP5 alone dramatically altered development of the retinal vasculature. The BBB in the cerebellum and pons/interpeduncular nuclei was highly sensitive to decrements in canonical WNT signaling, and WNT signaling was required to maintain plasticity of barrier properties in mature CNS vasculature. Brain and retinal vascular defects resulting from ablation of Norrin/Frizzled4 signaling were ameliorated by stabilizing β-catenin, while inhibition of β-catenin–dependent transcription recapitulated the vascular development and barrier defects associated with loss of receptor, coreceptor, or ligand, indicating that Norrin/Frizzled4 signaling acts predominantly through β-catenin–dependent transcriptional regulation. Together, these data strongly support a model in which identical or nearly identical canonical WNT signaling mechanisms mediate neural tube and retinal vascularization and maintain the BBB and BRB.

Authors

Yulian Zhou, Yanshu Wang, Max Tischfield, John Williams, Philip M. Smallwood, Amir Rattner, Makoto M. Taketo, Jeremy Nathans

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Figure 6

Vascular growth and BRB defects in retinas with different combinations of loss-of-function mutations in canonical WNT signaling components.

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Vascular growth and BRB defects in retinas with different combinations o...
(A) PLVAP expression in capillary and vein ECs in Fz4+/– but not Fz4+/+ retinas. Scale bar: 200 μm. (B) Mosaic recombination in Fz4CKO/+ Ctnnb1CKO/+ Tie2-Cre retinas: recombined territory (upper two-thirds) with enhanced PLVAP and reduced Claudin5 in veins and capillaries and reduced vascular density, and unrecombined territory (arrows) with PLVAP–Claudin5+ ECs and normal vascular density. Scale bar: 500 μm. (C) More severe vascular defects in Fz4CKO/– Ctnnb1CKO/+ Tie2-Cre (right 4 panels) compared with Fz4CKO/– Tie2-Cre retinas (left 2 panels). Scale bar: 500 μm. (D) Representative flat-mount retina from an adult Ndp+/– female. Rare PLVAP+Claudin5– ECs (arrows) are associated with sulfo-NHS-biotin leakage. Boxed regions in low-magnification panels are enlarged to the right. Scale bar: 500 μm. (E) Compared with Ndp+/– retinas (e.g., D), approximately 50% of adult Fz4+/– Ndp+/– retinas show more extensive conversion of ECs from to a PLVAP+Claudin5– state. The HprttdT reporter and the Ndp+ allele are on the same X chromosome, and the Ndp– allele is on the unmarked X chromosome. tdTomato shows the pattern of X chromosome mosaicism. Retina 3318 shows few PLVAP+Claudin5– ECs. Retina 3329a shows multiple territories with a high density of PLVAP+Claudin5– ECs. Boxed regions marked a (low density of Ndp+ cells) and b (high density of Ndp+ cells) are enlarged at right. Scale bars: 1 mm (left panels); 200 μm (right panels).