Sodium-dependent vitamin C transporter 2 (SVCT2) is necessary for the uptake of L-ascorbic acid into Schwann cells.
Ascorbic acid has been shown to be an essential component for in vitro myelination and to improve the clinical and pathological phenotype of a mouse model of Charcot-Marie-tooth disease 1A. The mechanism of ascorbic acid uptake into peripheral nerves, however, has not been addressed so far. Hence, we studied the expression and activity of sodium-dependent vitamin C transporters 1 and 2 (SVCT1 and 2) in the peripheral nervous system. Using immunohistochemistry, immunoblotting, and reverse transcription PCR, we could show that SVCT1 and 2 were differentially expressed in myelinated peripheral nerve fibers and Schwann cell (SC) cultures. SVCT1 was expressed at very low levels confined to the axons, whereas SVCT2 was highly expressed both in the axons and in the SCs. SVCT2 was localized particularly in SC compartments of uncompacted myelin. Uptake assays using (14)C-labeled ascorbic acid showed transport of ascorbic acid into SC cultures. Ascorbic acid transport was dependent on the concentration of sodium, magnesium, and calcium in the extracellular medium. Treatment with the flavonoid phloretin, a known inhibitor of SVCT1 and 2, and specific RNA interference with SVCT2 caused significant reductions in ascorbic acid uptake into SCs. Phloretin-inhibited uptake of ascorbic acid was further shown in freshly dissected, cell-culture-naïve rat sciatic nerves. These results provide evidence for the first time that uptake of ascorbic acid in the peripheral nervous system is crucially dependent on the expression and activity of SVCT2.
Gess
Burkhard
B
Department of Neurology, University of Muenster, Albert-Schweitzer-Strasse 33, Muenster, Germany.
Lohmann
Christina
C
Halfter
Hartmut
H
Young
Peter
P
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D001693:Biological Transport, Active / Q000502:physiology; D002250:Carbon Radioisotopes / Q000378:metabolism; D002478:Cells, Cultured; D045604:Extracellular Fluid / Q000378:metabolism; D015151:Immunoblotting; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D009186:Myelin Sheath / Q000378:metabolism / Q000648:ultrastructure; D009413:Nerve Fibers, Myelinated / Q000378:metabolism / Q000648:ultrastructure; D029363:Organic Anion Transporters, Sodium-Dependent / Q000235:genetics / Q000378:metabolism*; D017933:Peripheral Nervous System / Q000166:cytology / Q000378:metabolism*; D010693:Phloretin / Q000494:pharmacology; D034622:RNA Interference; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012583:Schwann Cells / Q000166:cytology / Q000378:metabolism*; D012584:Sciatic Nerve / Q000378:metabolism; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters / Q000235:genetics / Q000378:metabolism*
D002250:Carbon Radioisotopes; D029363:Organic Anion Transporters, Sodium-Dependent; C555164:Slc23a1 protein, mouse; C555166:Slc23a1 protein, rat; C555165:Slc23a2 protein, mouse; C555167:Slc23a2 protein, rat; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters; D001205:Ascorbic Acid; D010693:Phloretin