The 4F2hc/LAT1 complex transports L-DOPA across the blood-brain barrier.
L-DOPA is transported across the blood-brain barrier (BBB) by an amino acid transporter, system L. Recently, it has been demonstrated that system L consists of two subunits, 4F2hc and either LAT1 or LAT2. 4F2hc/LAT1 and 4F2hc/LAT2 show different transport characteristics, while their distribution in the brain has not been determined. To clarify whether 4F2hc/LAT1 participates in L-DOPA transport across the BBB, we first examined the expression of 4F2hc/LAT1 in the mouse brain capillary endothelial cell line, MBEC4, as an in vitro BBB model. Northern hybridization and immunoblotting revealed that both 4F2hc and LAT1 are expressed and form a heterodimer in MBEC4 cells. To confirm whether 4F2hc/LAT1 acts as system L to transport L-DOPA, we characterized L-DOPA uptake into the cells. The uptake process was time-dependent, temperature-sensitive, and Na(+)-independent. Neutral amino acids with bulky side chains and a bicyclic amino acid, 2-aminobicyclo-[2, 2,1]-heptane-2-carboxylic acid (BCH), inhibited L-DOPA uptake into MBEC4 cells to a great extent, while an acidic amino acid, basic amino acids, and glycine had no effect. Other neutral amino acids, such as alanine, asparagine, glutamine, serine, and threonine inhibited L-DOPA uptake by 40-70% at most. These characteristics are more compatible with those of 4F2hc/LAT1, rather than those of 4F2hc/LAT2. Finally, immunohistochemistry with anti-LAT1 antibody demonstrated that LAT1 is predominantly expressed in the microvessels of the central nervous system. This is the first report showing that the 4F2hc/LAT1 complex participates in L-DOPA transport across the BBB.
Kageyama
T
T
Department of Neurology, Graduate School of Medicine, Kyoto University, 54 Shogoin-Kawaharacho, Sakyo-ku, 606-8507, Kyoto, Japan.
Nakamura
M
M
Matsuo
A
A
Yamasaki
Y
Y
Takakura
Y
Y
Hashida
M
M
Kanai
Y
Y
Naito
M
M
Tsuruo
T
T
Minato
N
N
Shimohama
S
S
D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism*; D002196:Capillaries / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004730:Endothelium, Vascular / Q000378:metabolism*; D005260:Female; D027261:Fusion Regulatory Protein-1; D007980:Levodopa / Q000097:blood / Q000378:metabolism*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000378:metabolism
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D015703:Antigens, CD; D002352:Carrier Proteins; D027261:Fusion Regulatory Protein-1; D021122:Protein Subunits; D011994:Recombinant Proteins; D007980:Levodopa