Transmembrane (TM) proteins localized at the plasma membrane, such as transporters and receptors, play important roles in regulating the selective permeability of the blood-brain barrier (BBB). The purpose of the present study was to clarify the differences in the expression levels of TM proteins in the plasma membrane between two established human BBB model cell lines, hCMEC/D3 and HBMEC/ciβ, in order to assist researchers in selecting the most appropriate cell line for particular purposes. We first confirmed that plasma membranes could be enriched sufficiently for a quantitative proteomics study by using the Plasma Membrane Protein Extraction Kit provided by BioVision with a modified protocol. This method was applied to hCMEC/D3 and HBMEC/ciβ cells, and fractions were used for untargeted quantitative proteomics based on sequential window acquisition of all theoretical fragment-ion spectra. In the plasma membrane fractions, 345 TM proteins were quantified, among which 135 showed significant expression differences between the two cell lines. In hCMEC/D3 cells, amino acid transporters SNAT1, SNAT2, SNAT5, ASCT1, CAT1, and LAT1; adenosine 5'-triphosphate-binding cassette transporters P-gp and MRP4; and GLUT1 were more highly expressed. The transferrin receptor expression was also 4.56-fold greater in hCMEC/D3 cells. In contrast, HBMEC/ciβ cells expressed greater levels of IgG transporter neonatal Fc receptor, as well as tight-junction proteins PECAM1, JAM1, JAM3, and ESAM. Our results suggest that hCMEC/D3 cells have greater efflux transport, amino acid transport, and transferrin receptor-mediated uptake activities, whereas HBMEC/ciβ cells have greater IgG-transport activity and tight-junction integrity.
Keywords: blood−brain barrier; human brain capillary endothelial cells; plasma membrane enrichment; quantitative proteomics; receptor; tight-junction protein; transporter.