Reconstitution of the blood-retinal barrier and blood-brain barrier, and its application for drug delivery study

Blood-brain (BBB) and inner blood-retinal barriers (iBRB) are formed by tight-junction of the brain and retinal capillary endothelial cells, respectively. These barriers are known to restrict the entry of substances from circulating blood to the brain and retina. For the development of new drug targeting system and tissue regeneration of these barrier organs, it would be very important subject to reconstitute barrier organs using in vitro immortalized cell line. Conditionally immortalized brain and retinal capillary endothelial cell lines were established from a transgenic rat (Tg rat) and rnouse (Tg mouse) harboring temperature-sensitive a simian virus 40 (ts SV 40) large T-antigen. These cell lines have temperature-sensitive cell growth due to the expression of is SV 40 large T-antigen and endothelialmarkers. These cell lines have expression of in vivo influx and efflux transporters such as P-glycoprotein, GLUT 1 and MCT 1, demonstrating that these in vitro models would reflect the in vivo conditions. Gene expression of GLUT 1 and enzyme activities of γ-glutamyl transpeptidase and alkaline phosphatase were significantly induced by the co-culture between rat conditionally immortalized brain endothelial cell line (TR-BBB) and conditionally immortalized astrocyte cell line (TR-AST). Our in vitro model system could be very useful tool to clarify the barrier functions, including transporter genes and tight junction proteins and their regulation system.