Department of Chemistry, University College London, London WC1H 0AJ, UK.
Institute of the Physics and Living Systems, University College London, London WC1H 0AJ, UK.
Cells. 2020 Dec 14;9(12):2685. doi: 10.3390/cells9122685.
Within the brain, endothelial cells lining the blood vessels meticulously coordinate the transport of nutrients, energy metabolites and other macromolecules essential in maintaining an appropriate activity of the brain. While small molecules are pumped across specialised molecular transporters, large macromolecular cargos are shuttled from one side to the other through membrane-bound carriers formed by endocytosis on one side, trafficked to the other side and released by exocytosis. Such a process is collectively known as transcytosis. The brain endothelium is recognised to possess an intricate vesicular endosomal network that mediates the transcellular transport of cargos from blood-to-brain and brain-to-blood. However, mounting evidence suggests that brain endothelial cells (BECs) employ a more direct route via tubular carriers for a fast and efficient transport from the blood to the brain. Here, we compile the mechanism of transcytosis in BECs, in which we highlight intracellular trafficking mediated by tubulation, and emphasise the possible role in transcytosis of the Bin/Amphiphysin/Rvs (BAR) proteins and glycocalyx (GC)-a layer of sugars covering BECs, in transcytosis. Both BAR proteins and the GC are intrinsically associated with cell membranes and involved in the modulation and shaping of these membranes. Hence, we aim to summarise the machinery involved in transcytosis in BECs and highlight an uncovered role of BAR proteins and the GC at the brain endothelium.
在大脑中，血管内皮细胞精心协调着营养物质、能量代谢物和其他维持大脑适当活动所必需的大分子的运输。虽然小分子可以通过专门的分子转运体泵出，但大分子货物则通过内吞作用在一侧形成的膜结合载体从一侧穿梭到另一侧，并通过胞吐作用释放。这种过程统称为转胞吞作用。已知脑内皮细胞（BEC）具有复杂的囊泡内体网络，介导从血液到大脑和从大脑到血液的细胞间货物运输。然而，越来越多的证据表明，脑内皮细胞（BEC）通过管状载体来实现从血液到大脑的快速而有效的运输，而不是通过这种复杂的囊泡内体网络。在这里，我们总结了 BEC 中转胞吞作用的机制，其中我们强调了管腔化介导的细胞内运输，并强调了 Bin/Amphiphysin/Rvs（BAR）蛋白和糖萼（GC）在转胞吞作用中的可能作用，GC 是覆盖 BEC 的一层糖。BAR 蛋白和 GC 都与细胞膜内在相关，并参与这些细胞膜的调节和塑造。因此，我们旨在总结 BEC 中转胞吞作用所涉及的机制，并强调 BAR 蛋白和 GC 在脑内皮细胞中的未被发现的作用。
