Functional and molecular identification of sodium‐coupled dicarboxylate transporters in rat primary cultured cerebrocortical astrocytes and neurons

Abstract

Na + -coupled carboxylate transporters (NaCs) mediate the uptake of tricarboxylic acid cycle intermediates in mammalian tissues. Of these transporters, NaC3 (formerly known as Na + -coupled dicarboxylate transporter 3, NaDC3/SDCT2) and NaC2 (formerly known as Na + -coupled citrate transporter, NaCT) have been shown to be expressed in brain. There is, however, little information available on the precise distribution and function of both transporters in the CNS. In the present study, we investigated the functional characteristics of Na uptake by unlabeled succinate, N-acetyl-L-aspartate and citrate was 15.9, 155 and 764 lM respectively. In primary cultures of neurons, uptake of citrate was also Na + dependent and saturable with a K t value of 16.2 lM, which was different from that observed in astrocytes, suggesting that different Na + -dependent citrate transport systems are expressed in neurons and astrocytes. RT-PCR and immunocytochemistry revealed that NaC3 and NaC2 are expressed in cerebrocortical astrocytes and neurons respectively. These results are in good agreement with our previous reports on the brain distribution pattern of NaC2 and NaC3 mRNA using in situ hybridization. This is the first report of the differential expression of different NaCs in astrocytes and neurons. These transporters might play important roles in the trafficking of tricarboxylic acid cycle intermediates and related metabolites between glia and neurons.

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

“…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by hNaDC1 located in the apical [14] is unlikely, because NaDC1 has a low affinity for C5 dicarboxylates ( [23] and own unpublished results).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.…”

Mutations in the Na+/Citrate Cotransporter NaCT (SLC13A5) in Pediatric Patients with Epilepsy and Developmental Delay

“…The second therapeutic approach would involve using a second citrate transporter in the brain to bypass the inactive NaCT. The related transporter NaDC3 (SLC13A3) carries citrate and it is expressed in brain (7,8), but it is not known whether mutants found in epilepsy patients had activity. The structural models suggest that the mutations alter substrate binding or helix packing, which would be expected to have severe effects on transport function.…”

“…The NaCT transporter encoded by SLC13A5 is found on the plasma membrane in liver and brain (5,6). NaCT is found in neurons in rats (7) and both astrocytes and neurons in mice (8). NaCT cotransports sodium and citrate from the extracellular fluid into the cells (5).…”

Electrophysiological Characterization of Human and Mouse Sodium-Dependent Citrate Transporters (NaCT/SLC13A5) Reveal Species Differences with Respect to Substrate Sensitivity and Cation Dependence

“…NaCT has been cloned from various species, including humans (Inoue et al, 2002a), rats (Inoue et al, 2002b), and mice . In mammals, NaCT is expressed in the liver (Inoue et al, 2002a,b;Gopal et al, 2007) and in the brain (Inoue et al, 2002a,b;Yodoya et al, 2006) and it transports primarily the tricarboxylate citrate from the circulation into hepatocytes and neurons, where it regulates metabolic processes. The recent crystal structure reported for a bacterial homolog of human NaCT, named VcINDY (Mancusso et al, 2012), provided insight on how proteins of this class of transporters bind their substrates and transport them across the cell membrane (Mulligan et al, 2014).…”