Transport characteristics of <i>N</i>‐acetyl‐<scp>l</scp>‐aspartate in rat astrocytes: involvement of sodium‐coupled high‐affinity carboxylate transporter NaC3/NaDC3‐mediated transport system

Fujita, Takuya; Katsukawa, Hiromi; Yodoya, Etsuo; Wada, Mayuko; Shimada, Ayumi; Okada, Naoki; Yamamoto, Akira; Ganapathy, Vadivel

doi:10.1111/j.1471-4159.2005.03067.x

Cited by 44 publications

(43 citation statements)

References 37 publications

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“…A reabsorption of these compounds by hNaDC1 located in the apical [14] is unlikely, because NaDC1 has a low affinity for C5 dicarboxylates ( [23] and own unpublished results). NaDC3 is not only localized in the basolateral membrane of human and rat kidneys [24] but also in rat astrocytes [25,26] where it mediates αKG-inhibitable transport of [ 14 C]N-acetyl-L-aspartate, a compound with a dicarboxylic acid like structure. It needs to be established which role hNaDC3 plays in the brain of affected patients.…”

Section: Discussionmentioning

confidence: 99%

Organic anion transporters OAT1 and OAT4 mediate the high affinity transport of glutarate derivatives accumulating in patients with glutaric acidurias

Hagos

Krick

Braulke

et al. 2008

Pflugers Arch - Eur J Physiol

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Glutaric acidurias are rare inherited neurodegenerative disorders accompanied by accumulation of the metabolites glutarate (GA) and 3-hydroxyglutarate (3OHGA), glutaconate, L-, or D-2-hydroxyglutarate (L-2OHGA, in all body fluids. Oocytes expressing the human (h) sodium-dicarboxylate cotransporter (NaDC3) showed sodium-dependent inward currents mediated by GA, 3OHGA, L-, and D-2OHGA. The organic anion transporters (OATs) were examined as additional transporters for GA derivatives. The uptake of [ 3 H]p-aminohippurate in hOAT1-transfected human embryonic kidney (HEK293) cells was inhibited by GA, 3OHGA, D-, or L-2OHGA in a concentration-dependent manner. None of these compounds affected the hOAT3-mediated uptake of [ 3 H]estrone sulfate (ES). In hOAT4-expressing cells and oocytes, ES uptake was strongly increased by intracellular GA derivatives. The data provide a model for the concerted action of OAT1 and NaDC3 mediating the basolateral uptake, and OAT4 mediating apical secretion of GA derivatives from proximal tubule cells and therefore contribute to the renal clearance of these compounds.

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Section: Discussionmentioning

confidence: 99%

Organic anion transporters OAT1 and OAT4 mediate the high affinity transport of glutarate derivatives accumulating in patients with glutaric acidurias

Hagos

Krick

Braulke

et al. 2008

Pflugers Arch - Eur J Physiol

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“…In addition to this route of NAA clearance, extracellular NAA can arise through efflux from neurons along the steep intraneuronal to extracellular concentration gradient, or through the enzymatic release of NAA from NAAG by the action of glutamate carboxypeptidase II on the surface of astrocytes (Berger et al, 1999;Blakely et al, 1988;Cassidy and Neale, 1993b;Slusher et al, 1992). Extracellular NAA has been shown to be preferentially taken up by astrocytes as opposed to neurons (Sager et al, 1999b) via the dicarboxylate transporter NaDC3, (Fujita et al, 2005;Ganapathy and Fujita, 2006;George et al, 2004;Huang et al, 2000), and NAA appears in urine at low micromolar concentrations, indicating that there is continuous efflux from the brain (Kelley and Stamas, 1992;Kvittingen et al, 1986;Miyake et al, 1982). Normal serum NAA levels are very low, and this may be due to glomerular filtration in the kidneys (Hagenfeldt et al, 1987).…”

Section: Naa Transporters and Clearancementioning

confidence: 99%

“…However, other results have failed to show significant ASPA activity in O2A cells in culture (Madhavarao et al, 2002), and immunohistochemical studies have shown a complete lack of ASPA expression in astrocytes in the brain . Considering the facts that astrocytes form a significant portion of the blood-brain barrier, and that NAA is normally found in the urine (Hagenfeldt et al, 1987;Kvittingen et al, 1986), and that astrocytes express a sodium-dependent transporter for the uptake of extracellular NAA (Fujita et al, 2005), it seems likely that these glial cells take up extracellular NAA and excrete it to the circulation. In this regard it is interesting to note that we have observed NAAimmunoreactivity in a sub-population of brain endothelia ( Figure 5).…”

Section: Naa Transporters and Clearancementioning

confidence: 99%

“…Neuronal NAA must then be transferred to oligodendrocytes at their point of contact; the inner plasma membrane of the myelin sheath. It seems likely that specific dicarboxylate transport proteins or exchangers in both neurons and oligodendrocytes are involved in this process (Fujita et al, 2005). After axonal-glial transfer of NAA to oligodendrocytes, it provides acetate units for fatty acid and steroid synthesis in the cytosol via the actions of ASPA and cytoplasmic acetyl CoA synthetase (ACS1).…”

Section: Integrating Various Naa Functions In the Cnsmentioning

confidence: 99%

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N-Acetylaspartate in the CNS: From neurodiagnostics to neurobiology

Moffett

Ross

Arun

et al. 2007

Progress in Neurobiology

1,230

1,126

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The brain is unique among organs in many respects, including its mechanisms of lipid synthesis and energy production. The nervous system-specific metabolite N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A in neurons, appears to be a key link in these distinct biochemical features of CNS metabolism. During early postnatal CNS development, the expression of lipogenic enzymes in oligodendrocytes, including the NAA-degrading enzyme aspartoacylase (ASPA), is increased along with increased NAA production in neurons. NAA is transported from neurons to the cytoplasm of oligodendrocytes, where ASPA cleaves the acetate moiety for use in fatty acid and steroid synthesis. The fatty acids and steroids produced then go on to be used as building blocks for myelin lipid synthesis. Mutations in the gene for ASPA result in the fatal leukodystrophy Canavan disease, for which there is currently no effective treatment. Once postnatal myelination is completed, NAA may continue to be involved in myelin lipid turnover in adults, but it also appears to adopt other roles, including a bioenergetic role in neuronal mitochondria. NAA and ATP metabolism appear to be linked indirectly, whereby acetylation of aspartate may facilitate its removal from neuronal mitochondria, thus favoring conversion of glutamate to alpha ketoglutarate which can enter the tricarboxylic acid cycle for energy production. In its role as a mechanism for enhancing mitochondrial energy production from glutamate, NAA is in a key position to act as a magnetic resonance spectroscopy marker for neuronal health, viability and number. Evidence suggests that NAA is a direct precursor for the enzymatic synthesis of the neuron specific dipeptide N-acetylaspartylglutamate, the most concentrated neuropeptide in the human brain. Other proposed roles for NAA include neuronal osmoregulation and axon-glial signaling. We propose that NAA may also be involved in brain nitrogen balance. Further research will be required to more fully understand the biochemical functions served by NAA in CNS development and activity, and additional functions are likely to be discovered.

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“…Therefore, to test our hypothesis that the NAAGS gene encodes NAAG synthetase, we initially expressed NAAGS (variant v1) in primary astrocytes, which are known to express the NAA transporter NaDC3 (39). Transfected cells were incubated for 4 h with [ 14 C]glutamate (in the absence or presence of unlabeled 10 mM NAA in the culture medium).…”

Section: Naag Synthesis In Naags-expressing Cells-no In Vitromentioning

confidence: 99%

Molecular Characterization of N-Acetylaspartylglutamate Synthetase

Becker

Lodder

Gieselmann

et al. 2010

Journal of Biological Chemistry

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The dipeptide N-acetylaspartyl-glutamate (NAAG) is an abundant neuropeptide in the mammalian brain. Despite this fact, its physiological role is poorly understood. NAAG is synthesized by a NAAG synthetase catalyzing the ATP-dependent condensation of N-acetylaspartate and glutamate. In vitro NAAG synthetase activity has not been described, and the enzyme has not been purified. Using a bioinformatics approach we identified a putative dipeptide synthetase specifically expressed in the nervous system. Expression of the gene, which we named NAAGS (for NAAG synthetase) was sufficient to induce NAAG synthesis in primary astrocytes or CHO-K1 and HEK-293T cells when they coexpressed the NAA transporter NaDC3. Furthermore, coexpression of NAAGS and the recently identified N-acetylaspartate (NAA) synthase, Nat8l, in CHO-K1 or HEK-293T cells was sufficient to enable these cells to synthesize NAAG. Identity of the reaction product of NAAGS was confirmed by HPLC and electrospray ionization tandem mass spectrometry (ESI-MS). High expression levels of NAAGS were restricted to the brain, spinal cord, and testis. Taken together our results strongly suggest that the identified gene encodes a NAAG synthetase. Its identification will enable further studies to examine the role of this abundant neuropeptide in the vertebrate nervous system. N-acetylaspartylglutamate (NAAG)3 is an abundant neuropeptide in the central nervous system of mammals, present in high micromolar to low millimolar concentrations (for review see Refs. 1-3). It was first identified in rabbit and horse brain tissue by Curatolo et al. (4) and in bovine brain by Miyamoto et al. (5). NAAG is present in all regions of the central nervous system of mammals, though the highest concentrations are found in the spinal cord and stem brain (6). Despite its abundance throughout the mammalian nervous system, its physiological role is not fully understood.Because NAAG synthesis in sensory ganglia was not blocked by translation inhibitors, it was assumed that NAAG is not derived from a post-translational process, but is synthesized by a neuron specific NAAG synthetase, catalyzing the condensation of N-acetylaspartate (NAA) and glutamate (Ref. 7; see Fig. 1). After its calcium-dependent release from synaptic terminals, NAAG can be degraded by glutamate carboxypeptidase II (N-acetylated-␣-linked-acidic dipeptidase; GCP-II) or GCP-III, membrane-bound enzymes mainly expressed by astrocytes (for review see Ref. 8). The released NAA is then taken up by glial cells via the high-affinity, sodium-dependent dicarboxylate (NaDC3) transporter (9). In oligodendrocytes, NAA can then be hydrolyzed to aspartate and acetate by aspartoacylase II (8). The released acetate may be used for lipid synthesis by myelinating oligodendrocytes (10,11). To what extent NAA is taken up by astrocytes in vivo and its metabolic fate in these cells is not clear. Deficiency in aspartoacylase II leads to accumulation of NAA, but also NAAG (11), and causes a rare leukodystrophy, Canavan disease (12, 13).Studies on...

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Transport characteristics of N‐acetyl‐l‐aspartate in rat astrocytes: involvement of sodium‐coupled high‐affinity carboxylate transporter NaC3/NaDC3‐mediated transport system

Cited by 44 publications

References 37 publications

Organic anion transporters OAT1 and OAT4 mediate the high affinity transport of glutarate derivatives accumulating in patients with glutaric acidurias

Organic anion transporters OAT1 and OAT4 mediate the high affinity transport of glutarate derivatives accumulating in patients with glutaric acidurias

N-Acetylaspartate in the CNS: From neurodiagnostics to neurobiology

Molecular Characterization of N-Acetylaspartylglutamate Synthetase

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