The hCMEC/D3 cell line as a model of the human blood brain barrier

A face-to-face comparison of the BBB cell models hCMEC/D3 and hBMEC for their applicability to adenoviral expression of transporters

The blood-brain barrier (BBB) is a structure mainly formed by brain capillary endothelial cells (BCEC) whose role is to regulate the exchange of compounds between the blood and the brain. In this process efflux and uptake transporters play a key role. Aim of this study was to compare the two previously established cell lines hCMEC/D3 and hBMEC as BBB cell models for the application of an adenoviral system to transiently express OATP2B1 and Pgp. Comparison of hCMEC/D3 and hBMEC mRNA and protein levels of BBB markers showed a unique expression pattern for each cell line. While showing similar expression of the efflux transporter BCRP, transferrin receptor (TFRC) and of the tight junctions proteins Occludin and ZO-1, hCMEC/D3 displayed higher levels of the endothelial marker PECAM1, VE-cadherin, Von Willebrand Factor (VWF) and of the efflux transporter Pgp. Moreover, measuring integrity of the monolayer by determining the Trans-Endothelial Electrical Resistance (TEER), electrical capacitance (CCl), and inulin apparent permeability coefficient (Papp) revealed higher TEER and lower CCl for hBMEC but comparable Papp in the two cell lines. Following adenoviral infection, enhanced OATP2B1 and Pgp expression and functionality could be observed only in hBMEC. Importantly, the adenoviral expression system did not affect expression of BBB markers and permeability in both cell lines. Taken together, our results provide first evidence that hBMEC is an applicable human BBB cell model in which adenoviral infection can be used to transiently express and investigate transporters of interest.

Alzheimer's disease-associated P460L variant of EphA1 dysregulates receptor activity and blood-brain barrier function

INTRODUCTION

Genome-wide association studies link susceptibility to late-onset Alzheimer's disease (LOAD) with EphA1. Sequencing identified a non-synonymous substitution P460L as a LOAD risk variant. Other Ephs regulate vascular permeability and immune cell recruitment. We hypothesized that P460L dysregulates EphA1 receptor activity and impacts neuroinflammation.

METHODS

EphA1/P460L receptor activity was assayed in isogenic Human Embryonic Kidney (HEK) cells. Soluble EphA1/P460L (sEphA1/sP460L) reverse signaling in brain endothelial cells was assessed by T-cell recruitment and barrier function assays.

RESULTS

EphA1 and P460L were expressed in HEK cells, but membrane and soluble P460L were significantly reduced. Ligand engagement induced Y781 phosphorylation of EphA1 but not P460L. sEphA1 primed brain endothelial cells for increased T-cell recruitment; however, sP460L was less effective. sEphA1 decreased the integrity of the brain endothelial barrier, while sP460L had no effect.

DISCUSSION

These findings suggest that P460L alters EphA1-dependent forward and reverse signaling, which may impact blood-brain barrier function in LOAD.

HIGHLIGHTS

EphA1-dependent reverse signaling controls recruitment of T cells by brain endothelial cells. EphA1-dependent reverse signaling remodels brain endothelial cell contacts. LOAD-associated P460L variant of EphA1 shows reduced membrane expression and reduced ligand responses. LOAD-associated P460L variant of EphA1 fails to reverse signal to brain endothelial cells.

Pre-Plated Cell Lines for ADMETox Applications in the Pharmaceutical Industry

Membrane transporters significantly modulate membrane permeability of endobiotics and xenobiotics, such as bile acids and drugs, respectively. Various in vitro methods have been established for both ATP-binding cassette (ABC) transporters to examine cellular efflux and uptake, and for solute carriers (SLC) to examine cellular uptake of substrates. Cell-based systems are the models of choice to test drug-transporter interactions as well as drug-drug interactions for research and regulatory purposes, albeit, for low passive permeability substrates of ABC transporters, vesicular uptake assays are also recommended. Commercially available pre-plated cells (e.g., immortalized or transfected) offer a useful alternative to in-house cell culture. Three main methods are known to manufacture pre-plated cultures: regular culture medium with vacuum seal, cryopreserved delivery, and the solid shipping media technology. The regular culture medium and the solid shipping media technologies provide ready-to-use models for end users. Models expressing a broad selection of transporters are available in pre-plated formats for absorption, distribution, metabolism, excretion, and toxicity (ADMETox) studies. Conversely, the application and utility of pre-plated cultures coupled with personal experiences have not been extensively covered in published research papers or reviews, despite availability and significant use of pre-plated products in the pharmaceutical industry. In this overview, we will briefly describe: 1) in vitro tools commonly used for ADMETox testing; 2) methods employed in manufacturing, shipment and preparation of pre-plated cell lines; 3) cell-membrane barrier models currently available in pre-plated format to reproduce passage restriction of physiological barriers to certain compounds; and 4) recommended pre-plated cell lines overexpressing uptake transporters for ADMETox applications.