Differentiating embryonic neural progenitor cells induce blood–brain barrier properties

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. Keywords: blood-brain barrier, brain microvasculature, endothelial cell, neural progenitor cell, neural stem cell. The blood-brain barrier (BBB) is comprised of a specialized class of endothelium that forms a cellular barrier between the bloodstream and the interstices of the adult brain. By restricting non-specific flux of blood-borne constituents, the BBB plays an important role in maintaining parenchymal homeostasis, and strictly regulates transport of ions, small molecules, proteins, and cells into and out of the brain. The BBB accomplishes these tasks because its unique endothelium is endowed by epithelial-like tight junctions joining adjacent endothelial cells (ECs), lacks fenestrae, and possesses a rich array of molecular transport systems. Although the endothelium is the principle determinant of barrier function, perivascular non-endothelial cells in the local microenvironment have been shown to make significant contributions. Astrocytes (Stewart and Wiley 1981;Risau et al. 1986b;Janzer and Raff 1987), neurons (Tontsch andBauer 1991), and pericytes (Balabanov and Dore-Duffy 1998;Ramsauer et al. 2002) have all been demonstrated to provide cues that result in the unique BBB endothelial phenotype.Although the inductive properties of the aforementioned brain cell types have been confirmed through a multitude of in vivo and in vitro studies, the cell type(s) responsible for early embryonic BBB induction have not been distinguished. The developmental timecourse of embryonic BBB formation differs between species, but it is generally well accepted that the onset of BBB development begins pre-natally and is

Current concepts of blood-brain barrier development

“…Beside the striking phenotype similarities to the Wnt7a/b knock out, a link or epistatic effect of GPCR124 with b-catenin has not been reported so far (Kuhnert et al, 2010). This is further supported by previous publications, showing that NPCs provide BBB-inducing signals to ECs that however, are active during an early phase of barrier differentiation (Weidenfeller et al, 2007). During late embryonic and early postnatal development when neurons, and glial cell types start to differentiate, the quality of BBB inductive cues may change, suggested by the finding that conditioned medium from postnatal ACs have a delayed but longer lasting effect on BBB characteristics in primary brain ECs (Weidenfeller et al, 2007, and own unpublished results).…”

Wnt/β-catenin signaling is required for CNS, but not non-CNS, angiogenesis

“…Reciprocal signals between these two cell populations have been observed in vitro. Endothelial cells signal to neural stem cells regulating their self-renewal and differentiation into neurons (19), whereas neural stem cells have been implicated in regulating the resistance of endothelial tight junctions (20). The dramatic failure of embryonic brain growth that occurred when we blocked Wnt/␤-catenin signaling is likely explained not only by a lack of blood flow due to suppression of angiogenesis but quite possibly also the loss of endothelial signals required to support neural stem cell survival and proliferation.…”

Identification and Dynamic Regulation of Tight Junction Protein Expression in Human Neural Stem Cells

“…Interestingly, in coculture studies of BMVECs and embryonic NPCs, BMVECs increased BBB tightness, while NSCs showed suppressed differentiation [44]. Furthermore, coculture experiments have also demonstrated that NSC proliferation was induced upon removal of brain endothelial cells [45].…”