TY - JOUR
T1 - Regulation of Reduced Folate Carrier (RFC) by Vitamin D Receptor at the Blood-Brain Barrier
AU - Alam, Camille
AU - Hoque, Md Tozammel
AU - Finnell, Richard H.
AU - Goldman, I. David
AU - Bendayan, Reina
N1 - Funding Information:
We thank Dr. Robert Steinfeld (University Medical Center Göttingen, Göttingen, Germany) and Dr. Bogdan Wlodarczyk (Baylor College of Medicine, Texas, USA) for their insights on this work. We also thank Theodora Bruun, Marc Li, and Adrian Turner for their technical assistance. This research was supported by an operating grant from the Natural Sciences and Engineering Research Council of Canada (NSERC) awarded to Dr. Reina Bendayan. Camille Alam is a recipient of an Ontario Graduate Scholarship, Centre for Pharmaceutical Oncology Scholarship, and Pfizer Canada Graduate Fellowship. Dr. Richard Finnell was supported by NIH grants R01HD081216 and R01HD083809. Dr. I. David Goldman was supported by a National Cancer Institute grant CA082621.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/11/6
Y1 - 2017/11/6
N2 - Folates are essential for brain development and function. Folate transport in mammalian tissues is mediated by three major folate transport systems, i.e., reduced folate carrier (RFC), proton-coupled folate transporter (PCFT), and folate receptor alpha (FRα), known to be regulated by ligand-activated nuclear receptors, such as vitamin D receptor (VDR). Folate uptake at the choroid plexus, which requires the actions of both FRα and PCFT, is critical to cerebral folate delivery. Inactivating FRα or PCFT mutations cause severe cerebral folate deficiency resulting in early childhood neurodegeneration. The objective of this study was to investigate the role of RFC in folate uptake at the level of the blood-brain barrier (BBB) and its potential regulation by VDR. We detected robust expression of RFC in different in vitro BBB model systems, particularly in immortalized cultures of human cerebral microvascular endothelial cells (hCMEC/D3) and isolated mouse brain capillaries. [3H]-methotrexate uptake by hCMEC/D3 cells at pH 7.4 was inhibited by PT523 and pemetrexed, antifolates with high affinity for RFC. We also showed that activation of VDR through calcitriol (1,25-dihydroxyvitamin D3) exposure up-regulates RFC mRNA and protein expression as well as function in hCMEC/D3 cells and isolated mouse brain capillaries. We further demonstrated that RFC expression could be down-regulated by VDR-targeting siRNA, further confirming the role of VDR in the direct regulation of this folate transporter. Together, these data suggest that augmenting RFC functional expression could constitute a novel strategy for enhancing brain folate delivery for the treatment of neurometabolic disorders caused by loss of FRα or PCFT function.
AB - Folates are essential for brain development and function. Folate transport in mammalian tissues is mediated by three major folate transport systems, i.e., reduced folate carrier (RFC), proton-coupled folate transporter (PCFT), and folate receptor alpha (FRα), known to be regulated by ligand-activated nuclear receptors, such as vitamin D receptor (VDR). Folate uptake at the choroid plexus, which requires the actions of both FRα and PCFT, is critical to cerebral folate delivery. Inactivating FRα or PCFT mutations cause severe cerebral folate deficiency resulting in early childhood neurodegeneration. The objective of this study was to investigate the role of RFC in folate uptake at the level of the blood-brain barrier (BBB) and its potential regulation by VDR. We detected robust expression of RFC in different in vitro BBB model systems, particularly in immortalized cultures of human cerebral microvascular endothelial cells (hCMEC/D3) and isolated mouse brain capillaries. [3H]-methotrexate uptake by hCMEC/D3 cells at pH 7.4 was inhibited by PT523 and pemetrexed, antifolates with high affinity for RFC. We also showed that activation of VDR through calcitriol (1,25-dihydroxyvitamin D3) exposure up-regulates RFC mRNA and protein expression as well as function in hCMEC/D3 cells and isolated mouse brain capillaries. We further demonstrated that RFC expression could be down-regulated by VDR-targeting siRNA, further confirming the role of VDR in the direct regulation of this folate transporter. Together, these data suggest that augmenting RFC functional expression could constitute a novel strategy for enhancing brain folate delivery for the treatment of neurometabolic disorders caused by loss of FRα or PCFT function.
KW - Vitamin D receptor
KW - blood-brain barrier
KW - brain folate transport
KW - reduced folate carrier
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U2 - 10.1021/acs.molpharmaceut.7b00572
DO - 10.1021/acs.molpharmaceut.7b00572
M3 - Article
C2 - 28885847
AN - SCOPUS:85033360078
SN - 1543-8384
VL - 14
SP - 3848
EP - 3858
JO - Molecular Pharmaceutics
JF - Molecular Pharmaceutics
IS - 11
ER -