Highly differential expression of SN1, a bidirectional glutamine transporter, in astroglia and endothelium in the developing rat brain

Abstract

The transmitters glutamate and GABA also subserve trophic action and are required for normal development of the brain. They are formed from glutamine, which may be synthesized in glia or extracted from the blood. In the adult, the glutamine transporter SN1 is expressed in the astroglia. SN1 works in both directions, depending on the concentration gradients of its substrates and cotransported ions, and is thought to regulate extracellular glutamine and to supply the neurons with the transmitter precursor. In this article, we have quantified the expression and studied the localization of SN1 at different developmental stages. SN1 is expressed in astroglia throughout the CNS from embryonic stages through adulthood. No indication of SN1 staining in neuronal elements has been obtained at any stage. Quantitative immunoblotting of whole brain extracts demonstrates increasing expression of SN1 from P0, reaching a peak at P14, twice the adult level. A moderate and slower rise and fall of the expression levels of SN1 occurs in the cerebellum. Strong transient SN1-like staining is also found in Bergmann glia and vascular endothelium in the first postnatal weeks. Strong intracellular staining in the same time period suggests a high rate of SN1 synthesis in the early postnatal period. This coincides with the increasing levels of glutamate and GABA in the CNS and with the time course of synaptogenesis. This study suggests that the expression of SN1 is highly regulated, correlating with the demand for glutamine during the critical period of development.

Glutamatergic and GABAergic Neurotransmitter Cycling and Energy Metabolism in Rat Cerebral Cortex during Postnatal Development

“…Glial and neuronal glutamine transporters (SN1 and SN2, respectively) are present at birth and peak at P14 (Boulland et al, 2003). The uptake of neuronally released glutamate and GABA by astroglia is also functional by this time (Vitellaro-Zuccarello et al, 2003).…”

Induction and Targeting of the Glutamine Transporter SN1 to the Basolateral Membranes of Cortical Kidney Tubule Cells during Chronic Metabolic Acidosis Suggest a Role in pH Regulation

“…Antibodies against SN1 and PAG previously have been characterized extensively and were used as described (12)(13)(14). Other antibodies were obtained commercially for aquaporin-1 (AQP1; Alpha-Diagnostics, San Antonio, TX), AQP2 (Santa Cruz Biotechnology, Santa Cruz, CA), Calbindin (Abcam, Cambridge, UK), and Tamm-Horsfall glycoprotein (Chemicon International, Temecula, CA), URO-8 (Bioquote Limited, North Yorkshire, UK) or as a gift for phosphate-independent glutaminase (PIG; Dr. Huseby, University of Tromsø, Norway).…”

“…PAG protein Western blots with quantification was performed with ECL plus as described (13,14). Immunoperoxidase and immunofluorescence staining was carried out with the biotin-streptavidin-peroxidase/DAB system and immunofluorescence-coupled secondary antibodies, respectively.…”

Neuron–Astrocyte Interactions, Pyruvate Carboxylation and the Pentose Phosphate Pathway in the Neonatal Rat Brain

“…The number of glutamine transporters on astrocytes (SN1) on postnatal day seven (P7) is similar to adult levels but increases over the next 7 days and peaks on P14 with twice the number found on adult astrocytes, paralleling the synaptogenetic spurt period [14,15]. Neuronal glutamine transporters are also present on postnatal day 7 [16], setting the stage for transport of glutamine from astrocytes to neurons and the subsequent utilisation of glutamine for glutamate synthesis.…”