The purpose of the present study was to characterize the transport mechanism of basic fibroblast growth factor (bFGF) through the blood-brain barrier (BBB). Following internal carotid artery perfusion, 125I-bFGF was transcytosed through the BBB from blood into brain parenchyma. The binding of 125I-bFGF to the isolated bovine brain capillaries was saturated with a dissociation constant of 40 nM. This binding was significantly inhibited by unlabeled peptide, poly-L-lysine, heparin and glycosaminoglycans with a sulfate residue. RT -PCR analysis revealed mRNA of perlecan, FGF receptors (FGFR1 and FGFR2) in the conditionally immortalized mouse brain capillary endothelial cell lines (TM-BBB). The internalization of 125I-bFGF in TM-BBB was temperature-dependent and concentration-dependent, and showed a dependence on medium osmolarity. This internalization was significantly inhibited by the treatment of heparinase, sodium chlorate and antibody specific to mouse perlecan, a heparan sulfate proteoglycan. These results are consistent with the conclusion, 1) 125I-bFGF is transcytosed through the BBB, 2) internalization of 125I-bFGF into brain capillary endothelial cells is, in part, brought about by an endocytosis mechanism that is triggered by binding to HSPG.
