Functional expression and localization of P‐glycoprotein at the blood brain barrier
- 22 May 2002
- journal article
- review article
- Published by Wiley in Microscopy Research and Technique
- Vol. 57 (5), 365-380
- https://doi.org/10.1002/jemt.10090
Abstract
Until recently, the blood‐brain barrier was viewed as a static lipid membrane barrier. Physical attributes of the cerebral endothelial cells such as the presence of tight junctions, paucity of vesicles or caveolae, and high electrical resistance were believed to be the primary components that provide the membrane selectivity of the blood‐brain barrier to a variety of circulating compounds from the periphery. However, results from molecular biology, immunocytochemistry, biochemistry, and transport studies show that the cerebral endothelial cells possess an asymmetrical array of metabolic enzymes (i.e., alkaline phosphatase, cytochrome P450 enzymes, glutathione transferases) and energy‐dependent efflux transport proteins (i.e., P‐glycoprotein and Multidrug‐resistance proteins) that are instrumental to the barrier function. P‐glycoprotein, a membrane‐associated, energy‐dependent, efflux transporter, is expressed in brain parenchyma (i.e., astrocytes and microglia) as well as in blood‐brain and blood‐cerebrospinal fluid barriers. Its function along the blood‐brain barrier is believed to prevent the accumulation of potentially harmful compounds in the brain by actively removing them from the brain into the peripheral circulation. This is a brief review on the expression and activity of P‐glycoprotein at the blood‐brain barrier, which reports on the localization of the protein in rat brain capillaries in situ as well as in a well‐characterized in vitro model of the blood‐brain barrier, an immortalized rat brain endothelial cell line, the RBE4. Immunocytochemical analysis employing various P‐glycoprotein monoclonal antibodies, demonstrated the presence of the protein along the plasma membrane, in plasmalemmal vesicles and nuclear envelope of rat cerebral endothelial cells, both in situ and in vitro. Western blot analysis revealed a single band with a molecular weight of 170–180 kDa, a size previously reported for P‐glycoprotein, in RBE4 cells. In addition, results from functional studies show that the accumulation of the P‐glycoprotein substrate digoxin by RBE4 monolayer cells is significantly enhanced in the presence of standard P‐glycoprotein inhibitors (verapamil, cyclosporin A, PSC 833), protease inhibitors (saquinavir, ritonavir, indinavir), and the metabolic inhibitor, sodium azide. These results demonstrate the functional expression of P‐glycoprotein in the immortalized rat brain endothelial cell line, RBE4. Novel in situ and in vitro intracellular locations of P‐glycoprotein in cerebral endothelial cells have been identified suggesting that this transporter may play a significant role in the subcellular distribution of substrates in the brain. Microsc. Res. Tech. 57:365–380, 2002.Keywords
This publication has 102 references indexed in Scilit:
- Cerebral and pial microvessels: differential expression of γ-glutamyl transpeptidase and alkaline phosphataseBrain Structure and Function, 1999
- Brain Microvascular and Astrocyte Localization of P‐GlycoproteinJournal of Neurochemistry, 1997
- The P-glycoprotein multidrug transporterGeneral Pharmacology: The Vascular System, 1996
- Comparisons of P‐glycoprotein expression in isolated rat brain microvessels and in primary cultures of endothelial cells derived from microvasculature of rat brain, epididymal fat pad and from aortaFEBS Letters, 1995
- Absence of the mdr1a P-Glycoprotein in mice affects tissue distribution and pharmacokinetics of dexamethasone, digoxin, and cyclosporin A.JCI Insight, 1995
- Potential mechanisms of the age-related changes in the blood-brain barrierNeurobiology of Aging, 1994
- Differential modulation of P-glycoprotein transport by protein kinase inhibitionBiochemistry, 1993
- Choline Uptake by Cerebral Capillary Endothelial Cells in CultureJournal of Neurochemistry, 1990
- Multidrug Resistance: Molecular Biology Clinical RelevanceJNCI Journal of the National Cancer Institute, 1989
- A comparative study on the uptake and subsequent decarboxylation of monoamine precursors in cerebral microvesselsActa Physiologica Scandinavica, 1979