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The role of beta-catenin signaling in regulating barrier vs. non-barrier gene expression programs in circumventricular organ and ocular vasculatures

ABSTRACT: The mammalian brain, spinal cord, and retina are supplied by capillaries that do not permit free diffusion of molecules between serum and parenchyma, a property that defines the blood-brain and blood-retina barriers. Exceptions to this pattern are found in the circumventricular organs (CVOs), a set of small midline brain structures that are supplied by high permeability capillaries. In the eye and brain, high permeability capillaries are also present in the choriocapillaris, which supplies the retinal pigment epithelium and photoreceptors, and the ciliary body and choroid plexus, the sources of aqueous humor and cerebrospinal fluid, respectively. We show here that endothelial cells in these vascular systems exhibit a low level of beta-catenin signaling. By elevating beta-catenin signaling in endothelial cells, these vasculatures can be partially converted to a barrier state. In one CVO, the area postrema, high permeability is maintained, in part, by local production of Wnt inhibitory factor-1.

ORGANISM(S): Mus musculus

PROVIDER: GSE122117 | GEO | 2019/03/26

REPOSITORIES: GEO

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Project description:Rationale. The microvasculature of the central nervous system includes the blood-brain barrier (BBB), which regulates the permeability to nutrients and restricts the passage of toxic agents and inflammatory cells. Canonical Wnt/b-catenin signaling is responsible for the early phases of brain vascularization and blood-brain barrier differentiation. However, this signal declines after birth and other signaling pathways able to maintain barrier integrity at postnatal stage are still unknown. Objective. Sox17 constitutes a major downstream target of Wnt/b-catenin in endothelial cells and regulates arterial differentiation. In the present paper, we asked whether Sox17 may act downstream of Wnt/b-catenin in inducing BBB differentiation and maintenance. Methods and Results. Using reporter mice and nuclear staining of Sox17 and b-catenin, we report that while b-catenin signaling declines after birth, Sox17 activation increases and remains high in the adult. Endothelial-specific inactivation of Sox17 leads to increase of permeability of the brain microcirculation. The severity of this effect depends on the degree of BBB maturation: it is strong in the embryo, and progressively declines after birth. In search of Sox17 mechanism of action, RNA-Seq analysis of gene expression of brain endothelial cells has identified members of the Wnt/b-catenin signaling pathway as downstream targets of Sox17. Consistently, we found that Sox17 is a positive inducer of Wnt/b-catenin signaling and it acts in concert with this pathway to induce and maintain BBB properties. In vivo, inhibition of the b-catenin destruction complex or expression of a degradation-resistant b-catenin mutant, prevent the increase in permeability and retina vascular malformations observed in the absence of Sox17. Conclusions. Our data highlight a novel role for Sox17 in the induction and maintenance of the BBB and they underline the strict reciprocal tuning of this transcription factor and Wnt/b-catenin pathway. Modulation of Sox17 activity may be relevant to control BBB permeability in pathological conditions.

Project description:Bacterial meningitis is a deadly disease most commonly caused by Streptococcus pneumoniae that leads to severe neurological sequelae including cerebral edema, seizures, stroke, and mortality when untreated. Meningitis is initiated by the transfer of S. pneumoniae from hematogenous source into the brain across the blood-brain barrier (BBB); the mechanisms however are still poorly understood. Current treatment strategies include adjuvant dexamethasone therapy for cerebral edema, the prime reason for neurological complications and mortality, which is followed up by antibiotics. The success of corticosteroids is however inconclusive, necessitating the development of new therapies for controlling cerebral edema. We have previously shown a general activation of hypoxia inducible factor (HIF-1α) in bacterial infections, we therefore hypothesized that HIF-1α, via induction of vascular endothelial growth factor (VEGF) is critically involved in the transmigration of pathogens across the BBB. In human and murine meningitis brain samples, HIF-1 activation was observed by immunohistochemistry. HIF-1α/VEGF expression and permeability was therefore analyzed in vitro in infected brain endothelial cells (ECs). Localization of S. pneumoniae in brain ECs from mouse/human sources was visualized in vitro and in vivo by confocal, super-resolution, and electron microscopy. S. pneumoniae infection in brain ECs resulted in upregulation of HIF-1α/VEGF by Western blotting and qRT-PCR that was associated with increased paracellular permeability, which was supported by bacterial localization at cell-cell junctions. RNA sequencing of brain microvessels from hematogenously infected mice with increased permeability and S. pneumoniae deposition in the brain showed upregulation of genes in HIF-1α/VEGF pathway. Inhibition of HIF-1α with echinomycin, siRNA in bEnd5 cells and by using primary brain ECs from HIF-1α KO mice revealed a reduced endothelial permeability and transmigration of S. pneumoniae. We thus demonstrate a critical role for HIF-1α/VEGF in transmigration of S. pneumoniae across the BBB and propose targeting this pathway to prevent BBB dysfunction in infections.

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The role of beta-catenin signaling in regulating barrier vs. non-barrier gene expression programs in circumventricular organ and ocular vasculatures

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