Blood-Brain Barrier Differentiation

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Science  23 Dec 2011:
Vol. 334, Issue 6063, pp. 1652-1653
DOI: 10.1126/science.1216853

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Endothelial cells lining the microvasculature of the vertebrate central nervous system (CNS) help to form a protective physical barrier that maintains neural homeostasis in the brain. This blood-brain barrier (BBB) blocks uncontrolled transcellular passage of molecules across the microvasculature and also inhibits paracellular diffusion of solutes by a network of intercellular junctional complexes that tightly connect the endothelial cells. However, to meet the high metabolic needs of the CNS tissue, efficient transport of nutrients from the blood into the CNS and rapid efflux of toxic metabolites out of the CNS is ensured by the expression of unique receptors and transporters unique to these endothelial cells. On page 1727 of this issue, Alvarez et al. (1) report that CNS astrocytes secrete the glycoprotein Sonic hedgehog (Shh) to induce and maintain the BBB and also to limit access of the immune system to the CNS during mammalian embryogenesis and adulthood (2).