Induction of various blood‐brain barrier properties in non‐neural endothelial cells by close apposition to co‐cultured astrocytes

Abstract

Vascular endothelial cells (EC) exhibit organ-to-organ heterogeneity in their functions and morphologies. In particular, brain capillary EC have unique characteristics exemplified by the blood-brain barrier (BBB). The formation and the maintenance of BBB have been ascribed to EC responses to inductive signal(s) or factor(s) from astrocytes that encircle microvessels in the central nervous system. These EC responses were demonstrated in numerous in vivo studies, exemplified by those of Janzer and Raff (Nature 325:253, 1987) and Tout et al. (Neuroscience 55:291, 1993) showing that transplanted astrocytes induced BBB properties in non-neural vascular EC. In this study, we constructed a heterologous co-culture system, in which rat fetal brain astrocytes were cultivated on one surface of a porous membrane and human umbilical vein EC on the opposite surface. Electron microscopic examination revealed that astrocytes passed their endfeet through the pores, making contact with EC. In this system, gamma-glutamyltranspeptidase (gamma-GTP) activity in EC was found to be significantly increased by contacting astrocytes in a density- and time-dependent manner, but not when the astrocyte feeder layer was apart from EC or replaced by COS cells; astrocyte-derived extracellular matrix partially activated gamma-GTP. mRNAs for some of the representative BBB markers, including transferrin receptor, P-glycoprotein, brain-type glucose transporter (GLUT-1), and gamma-GTP were also demonstrated by reverse transcription-polymerase chain reaction to be upregulated in EC co-cultured with astrocytes. Astrocyte inductions of close membrane apposition resembling a zonula occludens and of an increase in the content of mitochondria in EC were also noted in electron micrographs. Furthermore, an increased barrier activity against inulin was conferred on EC when they were lined with astrocytes. The results obtained with this heterologous co-culture system thus indicate that through contact with their feet, astrocytes are capable of transdifferentiating non-neural EC into the brain type, endowing them with the BBB properties.

Astrocytes in the tempest of multiple sclerosis

“…The importance of astrocytes for BBB formation is clearly presented by their ability to induce tight junctions, high mitochondrial content and other intrinsic properties of neural endothelial cells, that build up the BBB, in endothelial cells of non-neural origin [8]. BBBinducing actions of astrocytes are also prominent in heterologous system, where rat astrocytes and human umbilical endothelial cells or immortalized human endothelial cells are co-cultivated, thus implying that BBB-promoting factors made by astrocytes are not species-specific [9,10].…”

Neurotoxicology of the Brain Barrier System: New Implications

“…When co-cultured with endothelial cells in vitro, astrocytes are capable of extending their endfeet to come into contact with endothelia and endow them with BBB properties (71). Interruption of this intimate astrocytic-endothelial cooperation induces negative consequences to the BBB.…”

Differential Replication of Pathogenic and Nonpathogenic Strains of West Nile Virus within Astrocytes

“…In vitro, cocultures of brain endothelial cells and astrocytes establish a tighter barrier than endothelial cells alone, and secretion and activation of matrix metalloproteases (MMPs) by astrocytes result in disruption of the BBB during disease (5,6). Astrocytes also modulate neuronal health and activity through the uptake of excess neurotransmitters and secretion of nutrients (7)(8)(9)(10). Thus, astrocytes serve as a structural and functional bridge between endothelial cells and neurons.…”