Differentiating embryonic neural progenitor cells induce blood–brain barrier properties

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Abstract
The blood–brain barrier (BBB) is a multifunctional endothelial interface separating the bloodstream from the brain interior. Although the mature BBB is well characterized, the embryonic development of this complex system remains poorly understood. Embryonic neural progenitor cells (NPC) are a potential inductive cell type populating the developing brain, and their ability to influence BBB properties was therefore examined. When puromycin‐purified brain microvascular endothelial cells (BMEC) were co‐cultured with embryonic NPC in a two‐compartment Transwell system, the BMEC exhibited enhanced barrier properties in the form of increased transendothelial electrical resistance (TEER) and decreased permeability to the small molecule tracer, sodium fluorescein. These changes required the presence of NPC in the early stages of differentiation and were accompanied by alterations in the fidelity of BMEC tight junctions as indicated by occludin, claudin 5, and zonula occluden‐1 redistribution at cell–cell borders. In contrast to the findings with NPC, post‐natal astrocytes elicited a delayed, but longer duration response in BMEC TEER. BMEC co‐culture also suppressed neuronal differentiation of NPC indicating a reciprocal signaling between the two cell populations. This study demonstrates that NPC–BMEC interactions are prevalent and for the first time demonstrates that NPC are capable of inducing BBB properties.