Nevertheless, the exact extent
of P-gp/caveolin-1 co-localization is only revealed on #AZD0156 cell line randurls[1|1|,|CHEM1|]# the merged images, which were obtained by superimposing the two fluorescent signals (Fig 2d and Fig 2h, yellow fluorescence). P-gp and caveolin-1 most frequently co-localized in the luminal compartment of the endothelial cells, although elsewhere, the fluorescent signals do not appear to overlap completely, and co-localization was detectable only at the boundary between the luminal and abluminal endothelial cell compartments. Figure 2 Immune co-labeling of P-gp/caveolin-1 in capillary endothelial cells. (×40 ×2 zoom). (a, e) Nuclear staining. (b, f) P-gp labeling appears concentrated in the luminal compartment of the endothelial cells. (c, g) Caveolin-1 stains the entire endothelial cytoplasm with fine puncta in the luminal compartment and larger, intensely immunoreactive puncta in the abluminal compartment. (d, h) The merged images show P-gp and caveolin-1 co-expression (yellowish fluorescence). the two
proteins co-localize either in the luminal endothelial compartment (d, arrow) or at the border of LY2835219 research buy the luminal/abluminal compartments (h, arrow). Discussion A large number of studies have analyzed P-gp substrates, expression and activities in brain tumors. Cultures of cerebral endothelial cells, isolated brain microvessels, and the P-gp knockout mouse have been used to study the functions of P-gp. In the specific field of the human BBB, our study contributes to the knowledge of cellular localization and molecular interactions of P-gp in brain tumor tissue in situ. The results shown here indicate that P-gp is mainly expressed in the endothelial cells lining and surrounding small vessels, in which the transporter appears concentrated within the luminal cellular compartment. LRP, MRP, GST-π and Topo II are not expressed in the capillary vessels and are partly expressed in the interstitium. In order to identify the exact location of P-gp in the capillary vessels, immunostaining
for S-100 protein was simultaneously performed. S-100 is expressed in glial and Schwann cells but is not expressed in capillary endothelial cells and basement membrane. Our results confirm that P-gp is located in the end-feet of glial cells. There were two pieces of evidence about to support this. One, S-100 was observed in capillary vessels, and the localization of S-100 was similar to that of P-gp. Two, the localization of S-100 was consistent with P-gp localization in the interstitial tissue. In the intracranial region, most of the glial cells are astrocytes, and P-gp is located in the end-feet of the astrocytes. These data confirm an effective role of endothelial P-gp as a “”gatekeeper”" in the BBB that limits the influx of drugs in the brain and indicate the pericytes as a possible second line of defense at BBB sites.