Poster Sessions CP10: Blood–Brain Barrier. Expression of vitamin C transporter SVCT2 in hypothalamic glial cells. An immunohistochemical and kinetic analysis

Abstract

Kinetic analysis of vitamin C uptake has demonstrated that specialized cells take up ascorbic acid (AA), the reduced form of vitamin C, through sodium‐AA cotransporters. Recently, two different isoforms of sodium‐vitamin C cotransporters (SVCT 1, 2) that mediate high affinity Na+‐dependent l‐ascorbic acid have been cloned. SVCT2 was detected mainly in choroid plexus cells and neurons, however, there are no evidences of SVCT2 expression in glial cells. High concentrations of vitamin C has been demonstrated in brain hypothalamic area. The hypothalamic glial cells, known as alpha and beta tanycytes, are specialized ependymal cells that bridge the cerebrospinal fluid and the portal blood of the median eminence. Our hypothesis postulates that tanycytes take up reduced vitamin C from the portal blood and cerebrospinal fluid generating an high concentration of this vitamin in brain hypothalamic area. In situ immunohistochemical analyses demonstrated that SVCT2 transporter is selectively expressed in apical region of tanycytes. A newly developed primary culture of mouse hypothalamic tanycytes was used to confirm the expression and function of SVCT2 isoform in these cells. Reduced vitamin C uptake was temperature and sodium dependent. Kinetic analysis showed an apparent Km of 20 μm and a Vmax of 45 pmol/min per million cells for the transport of ascorbic acid. The expression of SVCT2 was confirmed by immunoblots and RT–PCR. Tanycytes may perform a neuroprotective role concentrating the vitamin C in the hypothalamic area.Acknowledgements: Supported by Grands FONDECYT 1010843 and DIUC‐GIA 201.034.006‐1.4 from Concepción University.