Localisation of novel forms of glutamate transporters and the cystine-glutamate antiporter in the choroid plexus: Implications for CSF glutamate homeostasis

Abstract

The choroid plexus is a structure within each ventricle of the brain that is composed of fenestrated vessels surrounded by secretory epithelial cells. The epithelial cells are linked by tight junctions to create a permeability barrier. The epithelial cells are derived from neuroectoderm, and are thus defined by some authors as a subtype of macroglia. Glutamate is a tightly regulated substance in the CSF, as it is in the rest of the brain. In the brain macroglia express multiple sodium dependent and independent glutamate transporters and are the main regulators of extracellular glutamate. However, the identities of the transporters in the choroid plexus and their localisations have remained poorly defined. In this study we examined the expression and distribution of multiple splice variants of classical sodium-dependent glutamate transporters, as well as the cystine-glutamate antiporter, and the PDZ protein NHERF1, (which acts as a molecular anchor for proteins such as the glutamate transporter GLAST). We identified three forms of sodium-dependent transporters (GLAST1a, GLAST1c and GLT1b) that are expressed at the apical surface of the epithelial cells, a location that matches the distribution of NHERF1 and the cystine-glutamate antiporter. We propose that this coincident localisation of GLAST1a/GLAST1c/GLT1b and the cystine-glutamate antiporter would permit the cyclical trafficking of glutamate and thus optimise the accumulation of cystine for the formation of glutathione in the choroid plexus.

Choroid plexus LAT2 and SNAT3 as partners in CSF amino acid homeostasis maintenance

“…In agreement with an earlier study by Lee et al [39], also Glu transporter EAAT1/GLAST (Slc1a3) mRNA was detected in our study. Recently another glutamate transporter, EAAT3 (Slc1a1), was suggested to be the main Glu transporter in CP based on immunofluorescence and transport studies made in rat [23].…”

Transporter-mediated L-glutamate elimination from cerebrospinal fluid: possible involvement of excitatory amino acid transporters expressed in ependymal cells and choroid plexus epithelial cells

“…Our in vitro transport studies imply that EAATs are involved in the uptake of L-Glu into CPE and ependymal cells from the CSF via carrier-mediated mechanisms. EAAT1, EAAT3, and xCT have been reported to be expressed in ependymal cells although their localization on ependymal cells has not been fully evaluated [ 22 , 19 ]. From our immunohistochemical study using rat brain sections (Figure 1 A-C), we found that EAAT1 was strongly expressed in ependymal cells relative to CPE cells, and localized on the apical membrane (i.e.…”

“…Mannitol, D-[1- 14 C] ([ 14 C]D-mannitol, 55 mCi/mmol) and butanol, n [1- 14 C] ([ 14 C] n -butanol, 2 mCi/mmol) were purchased from American Radiolabeled Chemicals (St. Louis, MO, USA). Rabbit anti-EAAT1 antibodies [ 27 ], which recognize EAAT1 and three kinds of splice variants (GLAST1a, GLAST1b, and GLAST1c [ 22 ]), and rabbit anti-EAAT2 antibodies [ 28 ], which recognize EAAT2 and do not bind to other splice variants (GLT-1b, exon 9-skipped GLT-1b, and GLT-1c [ 22 ]), were kindly gifted from Dr. M. Watanabe, Hokkaido University, Sapporo, Japan. All other chemicals were commercial products of analytical grade.…”

GLAST But Not Least—Distribution, Function, Genetics and Epigenetics of l-Glutamate Transport in Brain—Focus on GLAST/EAAT1

“…GLAST was found to be present and probably functional at the mammalian neuromuscular junction [45], in the choroid plexus [46] and in other tissues, for example in pancreas [47] and in the heart muscle cells where it may have an important function [48]. GLT and possibly other EAATs exist in testes [49,50] and EAAT5 is present in many peripheral tissues [42,51].…”