Afamin is synthesized by cerebrovascular endothelial cells and mediates α-tocopherol transport across an in vitro model of the blood–brain barrier |
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Authors: | Ingrid Kratzer Eva Bernhart rea Wintersperger Astrid Hammer† Sabine Waltl Ernst Malle Günther Sperk‡ Georg Wietzorrek§ Hans Dieplinger¶ Wolfgang Sattler |
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Institution: | Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria; Institute of Cell Biology, Histology and Embryology, Center of Molecular Medicine, Medical University of Graz, Graz, Austria; Department of Pharmacology, Innsbruck Medical University, Innsbruck, Austria; Division of Molecular and Cellular Pharmacology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria; Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria; Vitateq Biotechnology GmbH, Innsbruck, Austria |
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Abstract: | α-Tocopherol (αTocH), a member of the vitamin E family, is essential for normal neurological function. Despite the importance of αTocH transport into the CNS, transfer mechanisms across the blood–brain barrier (BBB) are not entirely clear. We here investigate whether afamin, a known αTocH-binding protein, contributes to αTocH transport across an in vitro model of the BBB consisting of primary porcine brain capillary endothelial cells (BCEC) and basolaterally cultured astrocytoma cells. Exogenously added afamin had no adverse effects on BCEC viability or barrier function and was transported across BCEC Transwell cultures. Furthermore, αTocH transport across polarized BCEC cultures to astrocytoma cells is facilitated by afamin, though to a lesser extent than by high-density lipoprotein-mediated transport, an essential and in vivo operating αTocH import pathway at the cerebrovasculature. We also demonstrate that porcine BCEC endogenously synthesize afamin. In line with these in vitro findings, afamin was detected by immunohistochemistry in porcine, human postmortem, and mouse brain, where prominent staining was observed almost exclusively in the cerebrovasculature. The demonstration of afamin mRNA expression in isolated brain capillaries suggests that afamin might be a new family member of binding/transport proteins contributing to αTocH homeostasis at the BBB in vivo . |
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Keywords: | astrocytes brain microvascular endothelial cells high-density lipoprotein neurovascular unit vitamin E |
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