Neutral Amino Acid Transporter ASCT1 Is Preferentially Expressed in l-Ser-Synthetic/Storing Glial Cells in the Mouse Brain with Transient Expression in Developing Capillaries

Abstract

Nonessential amino acid L-Ser plays an essential role in neuronal survival and differentiation, through preferential expression of the L-Ser biosynthetic enzyme 3-phosphoglycerate dehydrogenase (3PGDH), in particular in glial cells but not in neurons. To seek the molecular candidates responsible for glia-borne L-Ser transport, we performed histochemical analyses on amino acid transporter ASCT1, which prefers small neutral amino acids, such as Ala, Ser, Cys, and Thr, and mediates their obligatory exchange. At early developmental stages, neuroepithelial cells constituting the ventricular zone expressed ASCT1 mRNA and protein ubiquitously. Thereafter, ASCT1 expression was gradually downregulated in neuronal populations during the late embryonic and neonatal periods, whereas its high expression was transmitted to radial glial cells and then to astrocytes. High levels of ASCT1 were also detected in the olfactory ensheathing glia. The preferential glial expression of ASCT1 was consistent with that of 3PGDH, and their extensive colocalization was demonstrated at the cellular level. Moreover, high cellular contents of L-Ser were revealed in these glial cells by using a specific antibody to L-Ser. These results strongly suggest that a large amount of L-Ser is synthesized and stored in these glial cells and is released through ASCT1 in exchange for other extracellular substrates. In addition, we observed prominent expression of ASCT1 in capillary endothelial cells of embryonic and neonatal brains. Therefore, ASCT1 appears to be regulated to meet metabolic demands by differentiating and mature neurons through the transport of glia- and blood-borne small neutral amino acids.

Disturbance of cerebellar synaptic maturation in mutant mice lacking BSRPs, a novel brain‐specific receptor‐like protein family

“…Preparation of brain sections, immunofluorescence analysis and immunoelectronmicroscopic observation were carried out as described previously [9]. To examine multiple innervation between climbing fibers (CFs) and Purkinje cells (PCs), triple-fluorescence staining of cerebellar sections was carried out as described previously [8].…”

Glutamate transport by retinal Müller cells in glutamate/aspartate transporter‐knockout mice

“…These include three Na ϩ -dependent, zwitterionic amino acid transporters-ASCT1, ASCT2, and ATB° (Palacin et al, 1998), glutamate-GABA and glutamate-glycine heteroexchangers (Levi et al, 1976;Bonanno et al, 1993Bonanno et al, , 1994, as well as the Na ϩ -independent systems, the cystineglutamate exchanger (Bannai and Tateishi, 1986) and AGT-1 (Matsuo et al, 2002). Because ASCT1 is electroneutral and can transport aspartate and glutamate (Arriza et al, 1993;Shafqat et al, 1993;Zerangue and Kavanaugh, 1996), and is the best-studied zwitterionic amino acid transporter, we examined ASCT1 expression in retinal sections from GLAST Ϫ/Ϫ and wild-type mice using a highly specific antibody (Sakai et al, 2003). ASCT1 was found to be widely distributed in the retina, suggesting that it was expressed by most retinal cells, including Mü ller cells (Fig.…”

Differential expression of endothelial nutrient transporters (MCT1 and GLUT1) in the developing eyes of mice

“…For double immunofluorescence, they were incubated overnight (for sections) or 4 days (for whole mount preparations) with a mixture containing two of a rabbit anti-mouse MCT1 antibody (469-493 amino acids of mouse MCT1; Kaji et al, 2015), guinea pig anti-GLUT1 antibody (460-492 amino acids of mouse GLUT1; Sakai et al, 2003), and rat anti-mouse CD31 antibody (MEC 13.3, 1:900: BD Pharmingen, Tokyo, Japan). The antibodies for MCT1 and GLUT1 were originally produced by an author of this study (M.W.)…”