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 5

Differential effects of eliminating Ctnnb1 and Lrp5 versus Lrp6 on brain versus retina ECs and on retinal artery versus vein/capillary ECs.

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Differential effects of eliminating Ctnnb1 and Lrp5 versus Lrp6 on brain...
(A) P12 Lrp5+/– Lrp6CKO/CKO Tie2-Cre and Lrp5–/– Lrp6CKO/+ Tie2-Cre retinas showing no vascular phenotype with 1 functional copy of Lrp5 and no functional copies of Lrp6 (left) and a nearly complete conversion of retinal ECs from PLVAP–Claudin5+ to PLVAP+Claudin5– with no functional copies of Lrp5 and 1 functional copy of Lrp6 (right). The truncated PLVAP–Claudin5+ vessels emanating from the optic disc in the Lrp5–/– Lrp6CKO/+ Tie2-Cre retina are hyaloid arteries. Scattered foci of sulfo-NHS-biotin leakage are present in the Lrp5–/– Lrp6CKO/+ Tie2-Cre retina (white arrows). Scale bar: 500 μm. (B) P24 Ctnnb1CKO/CKO Pdgfb-CreER retina from a mouse that had received 200 μg 4HT at P17. Efficient conversion of ECs from PLVAP–Claudin5+ to PLVAP+Claudin5– is seen in capillaries and veins, but not in arteries. The boxed region in the upper panel is enlarged in the 2 lower panels. A, artery; V, vein. Scale bar: 1 mm. (C) P70 Ctnnb1CKO/CKO Pdgfb-CreER retina from a mouse that had received 200 μg 4HT at P55. Rare conversions of retinal ECs from PLVAP–Claudin5+ to PLVAP+Claudin5– are seen in capillaries and veins (yellow arrow), but not in arteries (yellow arrow) and correspond to sites of sulfo-NHS-biotin leakage (white arrows). Scale bar: 200 μm.