Differential axial localization along the mouse brain vascular tree of luminal sodium-dependent glutamine transporters Snat1 and Snat3

Abstract

A specialized brain vasculature is key for establishing and maintaining brain interstitial fluid homeostasis, which for most amino acids (AAs) are B10% plasma levels. Indeed, regulation of AA homeostasis seems critical for normal central nervous system functions, and disturbances in brain levels have both direct and indirect roles in several neuropathologies. One mechanism contributing to the plasma to brain AA gradients involves polarized expression of solute carrier (SLC) family transporters on blood-brain barrier (BBB) endothelial cells. Of particular interest is the localization of sodium-dependent transporters that can actively move substrates against their concentration gradient. In this study, the in vivo endothelial membrane localization of the sodium-dependent glutamine transporters Snat3 (Slc38a3) and Snat1 (Slc38a1) was investigated in the mouse brain microvasculature using immunofluorescent colocalization with cellular markers. In addition, luminal membrane expression was probed by in vivo biotinylation. A portion of both Snat3 and Snat1 vascular expressions was localized on luminal membranes. Importantly, Snat1 expression was restricted to larger cortical microvessels, whereas Snat3 was additionally expressed on BBB capillary membranes. This differential expression of system A (Snat1) versus system N (Snat3) transporters suggests distinct roles for Snats in the cerebral vasculature and is consistent with Snat3 involvement in net transendothelial BBB AA transport.

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

“…2d, m) and anti-SNAT1 (Fig. 2g, p) antibodies [30][31][32][33][34]. The fact that we localized only these three amino acid transporters may be considered as a limitation in view of the larger number of transporters detected at the mRNA level, but since protein localization studies are per se prone to artefacts (cross-reactivity etc.…”

Loss of function mutation of the Slc38a3 glutamine transporter reveals its critical role for amino acid metabolism in the liver, brain, and kidney

“…SNAT3 is highly abundant in liver, kidney, and brain, and expression has also been reported for adipose tissue, pancreas, skeletal muscle, and eye. In kidney, SNAT3 is mainly localized to the proximal tubule, in liver to both perivenous and periportal hepatocytes, and in brain mostly in astrocytes and endothelial cells of the blood-brain-barrier [17][18][19][20][21]. In the brain, SNAT3 and SNAT5…”

Brain interstitial fluid glutamine homeostasis is controlled by blood–brain barrier SLC7A5/LAT1 amino acid transporter

“…23 Due to abundant expression and endothelium membrane localization LAT1 and SNAT3 may perform central roles in the BBB modulated control of brain ISF homeostasis for Gln and other AAs. 2,23 A central aim of the current study was to accurately measure the ISF AA concentrations. Hippocampal ISF AT2 (SLC6A15, sodium amino acid symporter), y þ LAT1 and y þ LAT2 (SLC7A7 and SLC7A6, antiporters of neutral amino acids and sodium against cationic amino acids), SNAT1, SNAT2 and SNAT7 (SCL38A1, SLC38A2 and SLC38A7, sodium amino acid symporters), SNAT3 and SNAT5 (SCL38A3 and SLC38A5, sodium amino acid symporters and proton antiporters) and LAT1 and LAT2 (SLC7A5 and SLC7A8 sodium-independent amino acid antiporters).…”

“…The data are based on in vivo and in vitro studies. 2,3,[12][13][14][15][16][17][18][19][20][21][22][23]24 AA content was quantified and AA regulation investigated by in vivo microdialysis in freely moving mice.…”

“…Furthermore, the endothelium exhibits a polarized (luminal vs. abluminal) distribution of proteins including transporters. [1][2][3] The BBB endothelium in association with pericytes (within a common basement membrane), astrocytic endfeet (with an associated parenchymal basement membrane), and neurons form ''the neurovascular unit''. 1 All amino acids (AAs), whose diverse metabolic and regulatory functions include serving as neurotransmitters and neurotransmitter precursors, are tightly controlled in the central nervous system (CNS).…”