Cerebral hypoxia/ischemia selectively disrupts tight junctions complexes in stem cell-derived human brain microvascular endothelial cells

Comparative study of expression and activity of glucose transporters between stem cell-derived brain microvascular endothelial cells and hCMEC/D3 cells

Glucose constitutes a major source of energy of mammalian brains. Glucose uptake at the blood-brain barrier (BBB) occurs through a facilitated glucose transport, through glucose transporter 1 (GLUT1), although other isoforms have been described at the BBB. Mutations in GLUT1 are associated with the GLUT1 deficiency syndrome, yet none of the current in vitro models of the human BBB maybe suited for modeling such a disorder. In this study, we investigated the expression of glucose transporters and glucose diffusion across brain microvascular endothelial cells (BMECs) derived from healthy patient-derived induced pluripotent stem cells (iPSCs). We investigated the expression of different glucose transporters at the BBB using immunocytochemistry and flow cytometry and measured glucose uptake and diffusion across BMEC monolayers obtained from two iPSC lines and from hCMEC/D3 cells. BMEC monolayers showed expression of several glucose transporters, in particular GLUT1, GLUT3, and GLUT4. Diffusion of glucose across the monolayers was mediated via a saturable transcellular mechanism and partially inhibited by pharmacological inhibitors. Taken together, our study suggests the presence of several glucose transporters isoforms at the human BBB and demonstrates the feasibility of modeling glucose across the BBB using patient-derived stem cells.

Paving the Way Toward Complex Blood-Brain Barrier Models Using Pluripotent Stem Cells

A tissue with great need to be modeled in vitro is the blood-brain barrier (BBB). The BBB is a tight barrier that covers all blood vessels in the brain and separates the brain microenvironment from the blood system. It consists of three cell types [neurovascular unit (NVU)] that contribute to the unique tightness and selective permeability of the BBB and has been shown to be disrupted in many diseases and brain disorders, such as vascular dementia, stroke, multiple sclerosis, and Alzheimer's disease. Given the progress that pluripotent stem cells (PSCs) have made in the past two decades, it is now possible to produce many cell types from the BBB and even partially recapitulate this complex tissue in vitro. In this review, we summarize the most recent developments in PSC differentiation and modeling of the BBB. We also suggest how patient-specific human-induced PSCs could be used to model BBB dysfunction in the future. Lastly, we provide perspectives on how to improve production of the BBB in vitro, for example by improving pericyte differentiation protocols and by better modeling the NVU in the dish.

Isogenic blood-brain barrier models based on patient-derived stem cells display inter-individual differences in cell maturation and functionality

The blood-brain barrier (BBB) constitutes an important component of the neurovascular unit formed by specialized brain microvascular endothelial cells (BMECs) surrounded by astrocytes, pericytes, and neurons. Recently, isogenic in vitro models of the BBB based on human pluripotent stem cells have been documented, yet the impact of inter-individual variability on the yield and phenotype of such models remains to be documented. In this study, we investigated the impact of inter-individual variability on the yield and phenotype of isogenic models of the BBB, using patient-derived induced pluripotent stem cells (iPSCs). Astrocytes, BMECs, and neurons were differentiated from four asymptomatic patient-derived iPSCs (two males, two females). We differentiated such cells using existing differentiation protocols and quantified expression of cell lineage markers, as well as BBB phenotype, barrier induction, and formation of neurite processes. iPSC-derived BMECs showed barrier properties better than hCMEC/D3 monolayers; however, we noted differences in the expression and activity among iPSC lines. In addition, we noted differences in the differentiation efficiency of these cells into neural stem cells and progenitor cells (as noted by differences in expression of cell lineage markers). Such differences were reflected later in the terminal differentiation, as seen as ability to induce barrier function and to form neurite processes. Although we demonstrated our ability to obtain an isogenic model of the BBB with different patients' iPSCs, we also noted subtle differences in the expression of cell lineage markers and cell maturation processes, suggesting the presence of inter-individual polymorphisms.

In vitro model of cerebral ischemia by using brain microvascular endothelial cells derived from human induced pluripotent stem cells

Brain-derived microvascular endothelial cells (BMECs), which play a central role in blood brain barrier (BBB), can be used for the evaluation of drug transport into the brain. Although human BMEC cell lines have already been reported, they lack original properties such as barrier integrity. Pluripotent stem cells (PSCs) can be used for various applications such as regenerative therapy, drug screening, and pathological study. In the recent study, an induction method of BMECs from PSCs has been established, making it possible to more precisely study the in vitro human BBB function. Here, using induced pluripotent stem (iPS) cell-derived BMECs, we examined the effects of oxygen-glucose deprivation (OGD) and OGD/reoxygenation (OGD/R) on BBB permeability. OGD disrupted the barrier function, and the dysfunction was rapidly restored by re-supply of the oxygen and glucose. Interestingly, TNF-α, which is known to be secreted from astrocytes and microglia in the cerebral ischemia, prevented the restoration of OGD-induced barrier dysfunction in an apoptosis-independent manner. Thus, we could establish the in vitro BBB disease model that mimics the cerebral ischemia by using iPS cell-derived BMECs.

New experimental models of the blood-brain barrier for CNS drug discovery

INTRODUCTION

The blood-brain barrier (BBB) is a dynamic biological interface which actively controls the passage of substances between the blood and the central nervous system (CNS). From a biological and functional standpoint, the BBB plays a crucial role in maintaining brain homeostasis inasmuch that deterioration of BBB functions are prodromal to many CNS disorders. Conversely, the BBB hinders the delivery of drugs targeting the brain to treat a variety of neurological diseases. Area covered: This article reviews recent technological improvements and innovation in the field of BBB modeling including static and dynamic cell-based platforms, microfluidic systems and the use of stem cells and 3D printing technologies. Additionally, the authors laid out a roadmap for the integration of microfluidics and stem cell biology as a holistic approach for the development of novel in vitro BBB platforms. Expert opinion: Development of effective CNS drugs has been hindered by the lack of reliable strategies to mimic the BBB and cerebrovascular impairments in vitro. Technological advancements in BBB modeling have fostered the development of highly integrative and quasi- physiological in vitro platforms to support the process of drug discovery. These advanced in vitro tools are likely to further current understanding of the cerebrovascular modulatory mechanisms.