Characterization of folate uptake by choroid plexus epithelial cells in a rat primary culture model.
Reduced derivatives of folic acid (folates) play a critical role in the development, function and repair of the CNS. However, the molecular systems regulating folate uptake and homeostasis in the central nervous system remain incompletely defined. Choroid plexus epithelial cells express high levels of folate receptor alpha (FRalpha) suggesting that the choroid plays an important role in CNS folate trafficking and maintenance of CSF folate levels. We have characterized 5-methyltetrahydrofolate (5-MTHF) uptake and metabolism by primary rat choroid plexus epithelial cells in vitro. Two distinct processes are apparent; one that is FRalpha dependent and one that is independent of the receptor. FRalpha binds 5-MTHF with high affinity and facilitates efficient uptake of 5-MTHF at low extracellular folate concentrations; a lower affinity FRalpha independent system accounts for increased folate uptake at higher concentrations. Cellular metabolism of 5-MTHF depends on the route of folate entry into the cell. 5-MTHF taken up via a non-FRalpha -mediated process is rapidly metabolized to folylpolyglutamates, whereas 5-MTHF that accumulates via FRalpha remains non-metabolized, supporting the hypothesis that FRalpha may be part of a pathway for transcellular movement of the vitamin. The proton-coupled folate transporter, proton-coupled folate transporter (PCFT), mRNA was also shown to be expressed in choroid plexus epithelial cells. This is consistent with the role we have proposed for proton-coupled folate transporter in FRalpha-mediated transport as the mechanism of export of folates from the endocytic compartment containing FRalpha.
Wollack
Jan B
JB
Department of Pediatrics, Cancer Institute of New Jersey, Robert Wood Johnson Medical School, New Brunswick, New Jersey, USA.
Makori
Benedette
B
Ahlawat
Stuti
S
Koneru
Rajeth
R
Picinich
Sonia C
SC
Smith
Angela
A
Goldman
I David
ID
Qiu
Andong
A
Cole
Peter D
PD
Glod
John
J
Kamen
Barton
B
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002831:Choroid Plexus / Q000166:cytology*; D004706:Endodeoxyribonucleases / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D013763:Tetrahydrofolates / Q000493:pharmacokinetics; D022161:Transport Vesicles / Q000378:metabolism; D014316:Tritium; D014803:Vitamin B Complex / Q000493:pharmacokinetics*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D013763:Tetrahydrofolates; D014316:Tritium; D014803:Vitamin B Complex; D005492:Folic Acid; D004706:Endodeoxyribonucleases; C078472:mENase protein, Coprinus cinereus; C005984:5-methyltetrahydrofolate