Modeling the blood–brain barrier using stem cell sources

Abstract

The blood–brain barrier (BBB) is a selective endothelial interface that controls trafficking between the bloodstream and brain interstitial space. During development, the BBB arises as a result of complex multicellular interactions between immature endothelial cells and neural progenitors, neurons, radial glia, and pericytes. As the brain develops, astrocytes and pericytes further contribute to BBB induction and maintenance of the BBB phenotype. Because BBB development, maintenance, and disease states are difficult and time-consuming to study in vivo, researchers often utilize in vitro models for simplified analyses and higher throughput. The in vitro format also provides a platform for screening brain-penetrating therapeutics. However, BBB models derived from adult tissue, especially human sources, have been hampered by limited cell availability and model fidelity. Furthermore, BBB endothelium is very difficult if not impossible to isolate from embryonic animal or human brain, restricting capabilities to model BBB development in vitro. In an effort to address some of these shortcomings, advances in stem cell research have recently been leveraged for improving our understanding of BBB development and function. Stem cells, which are defined by their capacity to expand by self-renewal, can be coaxed to form various somatic cell types and could in principle be very attractive for BBB modeling applications. In this review, we will describe how neural progenitor cells (NPCs), the in vitro precursors to neurons, astrocytes, and oligodendrocytes, can be used to study BBB induction. Next, we will detail how these same NPCs can be differentiated to more mature populations of neurons and astrocytes and profile their use in co-culture modeling of the adult BBB. Finally, we will describe our recent efforts in differentiating human pluripotent stem cells (hPSCs) to endothelial cells with robust BBB characteristics and detail how these cells could ultimately be used to study BBB development and maintenance, to model neurological disease, and to screen neuropharmaceuticals.

In Vitro Models of CNS Barriers

“…A promising new development from the Shusta group is an in vitro BBB model derived from human pluripotent stem cells (hPSCs), involving initial codifferentiation of endothelial and neural cells, then purifi cation and further maturation of the endothelial cells to develop a full BBB-like phenotype (Lippmann et al 2012(Lippmann et al , 2013 ). It will be interesting to see how well this model replicates the in vivo behaviour in further characterization studies and applications, and whether it proves suitable for screening BBB permeation of a range of drug chemistries, including those subject to transfer by carrier-mediated mechanisms, and nanocarriers and engineered peptides and proteins, candidates for RMT.…”

Probing the biomechanical contribution of the endothelium to lymphocyte migration: diapedesis by the path of least resistance

“…This result suggests that alterations in junctional barrier properties can modify the route of leukocyte transmigration. As further confirmation for the role of 'junctional tightness' itself in the above results, we took advantage of an established agent-independent means of progressively reducing primary rat brain MVEC barrier strength through extended culture passaging (Lippmann et al, 2013). We found that by culturing rat brain MVECs for .4 passages, we could promote a substantial decrease in electrical resistance to ,26 Vcm 2 , which was coupled with a shift towards a majority of diapedesis occurring by the paracellular route (Fig.…”

In vitro porcine blood–brain barrier model for permeability studies: pCEL-X software pKaFLUX method for aqueous boundary layer correction and detailed data analysis

“…However, to be an effective screening assay an in vitro BBB model needs to be robust, reproducible, and with highly restrictive tight junctions to mimic the in vivo condition. A number of in vitro BBB models have been developed, including several recently reported (Bernas et al, 2010;Sano et al, 2010;Hatherell et al, 2011;Lippmann et al, 2013;Xue et al, 2013), but most of the cell line models and many of the primary cultures show low transendothelial electrical resistance (TEER), indicating a leaky cell monolayer. A few models do show high TEER and are in principle suitable for permeability assays (Franke et al, 1999 (Culot et al, 2008;Vandenhaute et al, 2012).…”