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Abstract
Co-culture with glial cells and glia-conditioned media can induce blood-brain barrier properties in microvessel endothelial cells and protect against hypoxia-induced blood-brain barrier breakdown. We examined the effect of two types of glia-conditioned media on brain microvessel endothelial cell permeability and tight junction protein expression, and studied potential mechanisms of action. We found that C6-glioma-conditioned media, but not rat astrocyte-conditioned media, protected against an increase in permeability induced by exposure to 1% oxygen for 24 hours. This hypoxic stress caused an increase in the expression of tight junction proteins claudin-1 and actin, particularly in cells treated with C6-conditioned media. We found that C6-conditioned media has a significantly higher level of both basic fibroblast growth factor and vascular endothelial growth factor. Treatment with C6-conditioned media for 1 or 3 days protects against hypoxia-induced permeability increases, and this protective effect may be mediated by signal transduction pathways terminating at the transcription factor NFkappaB.
Highlights
The blood-brain barrier (BBB) is a metabolic and physical barrier separating the microenvironment of the central nervous system (CNS) from the peripheral circulation
We previously demonstrated that 24 hours of hypoxic stress increases the permeability of bovine brain microvessel endothelial cells (BBMEC) monolayers in vitro and increases the expression of the tight junctions (TJ) protein actin (Mark and Davis, 2002)
We examined the effects of normal growth media (MEM/F12), C6-conditioned media (C6CM) and primary rat astrocyte-conditioned media (RA-Conditioned media (CM)) on permeability and expression of TJ proteins under normoxic and hypoxic conditions in BBMEC monolayers
Summary
The blood-brain barrier (BBB) is a metabolic and physical barrier separating the microenvironment of the central nervous system (CNS) from the peripheral circulation. The BBB is located at the level of the cerebral microvessel endothelial cells and characterized by limited paracellular diffusion, reduced fluid-phase endocytosis and the presence of specific transporters for ions, peptides and nutrients (Takakura et al, 1991; Banks, 1999), which allow for strict regulation of CNS homeostasis. Claudin-1 and occludin have been found at the BBB (Huber et al, 2001b; Mark and Davis, 2002). Both of these proteins have multiple transmembrane domains and form homodimeric bridges with adjacent cells, creating a physical blockade to paracellular diffusion (Tsukita and Furuse, 1999). ZO proteins are members of the membrane-associated guanylate kinase (MAGUK) family; they have a conserved guanylate kinase domain, an SH3 domain and multiple PDZ domains (Huber et al, 2001a), suggesting that ZO proteins participate in signal transduction cascades
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