title: Diverse Functions of Retinoic Acid in Brain Vascular Development.
abstract: As neural structures grow in size and increase metabolic demand, the CNS vasculature undergoes extensive growth, remodeling, and maturation. Signals from neural tissue act on endothelial cells to stimulate blood vessel ingression, vessel patterning, and acquisition of mature brain vascular traits, most notably the blood-brain barrier. Using mouse genetic and in vitro approaches, we identified retinoic acid (RA) as an important regulator of brain vascular development via non-cell-autonomous and cell-autonomous regulation of endothelial WNT signaling. Our analysis of globally RA-deficient embryos (Rdh10 mutants) points to an important, non-cell-autonomous function for RA in the development of the vasculature in the neocortex. We demonstrate that Rdh10 mutants have severe defects in cerebrovascular development and that this phenotype correlates with near absence of endothelial WNT signaling, specifically in the cerebrovasculature, and substantially elevated expression of WNT inhibitors in the neocortex. We show that RA can suppress the expression of WNT inhibitors in neocortical progenitors. Analysis of vasculature in non-neocortical brain regions suggested that RA may have a separate, cell-autonomous function in brain endothelial cells to inhibit WNT signaling. Using both gain and loss of RA signaling approaches, we show that RA signaling in brain endothelial cells can inhibit WNT-β-catenin transcriptional activity and that this is required to moderate the expression of WNT target Sox17. From this, a model emerges in which RA acts upstream of the WNT pathway via non-cell-autonomous and cell-autonomous mechanisms to ensure the formation of an adequate and stable brain vascular plexus.
  
  
  
  Work presented here provides novel insight into important yet little understood aspects of brain vascular development, implicating for the first time a factor upstream of endothelial WNT signaling. We show that RA is permissive for cerebrovascular growth via suppression of WNT inhibitor expression in the neocortex. RA also functions cell-autonomously in brain endothelial cells to modulate WNT signaling and its downstream target, Sox17. The significance of this is although endothelial WNT signaling is required for neurovascular development, too much endothelial WNT signaling, as well as overexpression of its target Sox17, are detrimental. Therefore, RA may act as a "brake" on endothelial WNT signaling and Sox17 to ensure normal brain vascular development.
authors.affiliation: Department of Pediatrics, Section of Developmental Biology, University of Colorado, School of Medicine-Anschutz Medical Campus Aurora, Colorado 80045.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bonney
authors.affiliation: Department of Neurology, University of California, San Francisco, California 94158.
authors.forename: Susan
authors.initials: S
authors.lastname: Harrison-Uy
authors.affiliation: Department of Pediatrics, Section of Developmental Biology, University of Colorado, School of Medicine-Anschutz Medical Campus Aurora, Colorado 80045.
authors.forename: Swati
authors.initials: S
authors.lastname: Mishra
authors.affiliation: Department of Pediatrics, Section of Developmental Biology, University of Colorado, School of Medicine-Anschutz Medical Campus Aurora, Colorado 80045.
authors.forename: Amber M
authors.identifier: 0000-0003-4955-8104
authors.initials: AM
authors.lastname: MacPherson
authors.affiliation: Department of Neurology, University of California, San Francisco, California 94158.
authors.forename: Youngshik
authors.identifier: 0000-0002-2132-4771
authors.initials: Y
authors.lastname: Choe
authors.affiliation: Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School Boston, Massachusetts 02215, and.
authors.forename: Dan
authors.initials: D
authors.lastname: Li
authors.affiliation: Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School Boston, Massachusetts 02215, and.
authors.forename: Shou-Ching
authors.initials: SC
authors.lastname: Jaminet
authors.affiliation: Institute of Ophthalmology-Cell Biology, University College London, London EC1V 9EL, United Kingdom.
authors.forename: Marcus
authors.identifier: 0000-0002-6962-5485
authors.initials: M
authors.lastname: Fruttiger
authors.affiliation: Department of Neurology, University of California, San Francisco, California 94158.
authors.forename: Samuel J
authors.identifier: 0000-0001-8599-1613
authors.initials: SJ
authors.lastname: Pleasure
authors.affiliation: Department of Pediatrics, Section of Developmental Biology, University of Colorado, School of Medicine-Anschutz Medical Campus Aurora, Colorado 80045, julie.siegenthaler@ucdenver.edu.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Siegenthaler
mesh_terms: D000367:Age Factors; D000429:Alcohol Oxidoreductases / Q000172:deficiency / Q000235:genetics; D000818:Animals; D001921:Brain / Q000166:cytology* / Q000196:embryology; D002454:Cell Differentiation; D002478:Cells, Cultured; D002552:Cerebral Ventricles / Q000166:cytology* / Q000196:embryology; D004622:Embryo, Mammalian; D042783:Endothelial Cells / Q000378:metabolism; D036342:Ephrins / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D000072482:Retinoic Acid Receptor alpha / Q000235:genetics / Q000378:metabolism*; D014212:Tretinoin / Q000378:metabolism* / Q000494:pharmacology; D060449:Wnt Signaling Pathway / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: C495267:CTNNB1 protein, mouse; D036342:Ephrins; D009419:Nerve Tissue Proteins; C000607072:Rara protein, mouse; D000072482:Retinoic Acid Receptor alpha; D051176:beta Catenin; D014212:Tretinoin; D000429:Alcohol Oxidoreductases; C113992:trans-retinol dehydrogenase; D001616:beta-Galactosidase
keywords: VEGF; WNT; brain vascular development; cerebrovasculature; endothelial cell; retinoic acid