Abstract
The formation and maintenance of blood-brain barrier (BBB) have been ascribed to endothelial cell responses to inductive signal(s) from astrocytes that encircle microvessels in the central nervous system. Here we describe an in vitro BBB model, in which rat fetal cerebral astrocytes are cultivated on one surface of a porous membrane and human umbilical vein endothelial cells on the opposite surface. Electron microscopic examination revealed that astrocytes passed their endfeet through the pores, making contact with endothelial cells. Genes for the representative BBB markers, including γ-glutamyl transpeptidase, transferrin receptor, P-glycoprotein and brain-type glucose transporter, were found to be up-regulated in endothelial cells by contacting astrocytes, but not when the former cells were maintained apart from the latter or when the feeder layer was substituted for by COS cells. Astrocyte induction of close membrane appositions resembling zonulae occludentes between endothelial cells and of an increase in the number of mitochondrion was also noted. Further, an increased barrier activity against inulin was conferred on endothelial cells, when lined with astrocytes, with due polarity. The results thus indicate that, through contact with their feet, astrocytes are capable of transdifferentiating non-neural endothelial cells into the brain-type, endowing them with the BBB properties. The present BBB model would seem useful for studying the drug delivery to the brain.
