Taurine transporter in fetal T lymphocytes and platelets: differential expression and functional activity

Abstract

Transplacental transfer of taurine, a ␤-amino acid essential for fetal and neonatal development, constitutes the primary source of taurine for the fetus. Placental transport of taurine is compromised in pregnancies complicated by intrauterine growth restriction, resulting in a reduced concentration of taurine in cord plasma. This could impact on fetal cellular metabolism as taurine represents the most abundant intracellular amino acid in many fetal cell types. In the present study, we have used pure isolates of fetal platelets and T lymphocytes from cord blood of placentas, from normal, term pregnancies, as fetal cell types to examine the cellular uptake mechanisms for taurine by the system ␤ transporter and have compared gene and protein expression for the taurine transporter protein (TAUT) in these two cell types. System ␤ activity in fetal platelets was 15-fold higher compared with fetal T lymphocytes (P Ͻ 0.005), mirroring greater TAUT mRNA expression in platelets than T lymphocytes (P Ͻ 0.005). Cell-specific differences in TAUT protein moieties were detected with a doublet of 75 and 80 kDa in fetal platelets compared with 114 and 120 kDa in fetal T lymphocytes, with relatively higher expression in platelets. We conclude that greater system ␤ activity in fetal platelets compared with T lymphocytes is the result of relatively greater TAUT mRNA and protein expression. This study represents the first characterization of amino acid transporters in fetal T lymphocytes. cord blood cells; amino acid; taurine transporter protein; system ␤ TAURINE (2-aminoethanesulfonic acid) is the most abundant free amino acid in several tissues, including the placenta and the cellular components of blood (9,21,38,41,46). It is a ␤-amino acid with the sulfonic acid group attached to the ␤-carbon atom and is not incorporated into proteins (14). The physiological functions of taurine are diverse, including bile and xenobiotic conjugation, regulation of neuronal excitability, membrane protection, antioxidation, detoxification, and osmoregulation (22,24,31). The nutritional requirements for taurine are met both by dietary sources and biosynthesis from cysteine and methionine (53). However, in the human fetus and the neonate, taurine is an essential amino acid, as biosynthetic capacity is almost negligible (51) due to the lack of cysteine sulfonic acid decarboxylase, which catalyses the rate-limiting step in taurine synthesis (4). Transplacental transfer of taurine from maternal blood therefore constitutes the primary source of fetal taurine.Taurine is transported across cell membranes, including those of the syncytiotrophoblast, the transporting epithelium of human placenta, by the system ␤-amino acid transport system which is specific for taurine and other ␤-amino acids such as ␤-alanine and hypotaurine (29,32,36). System ␤ is a highaffinity, low-capacity transport system that is Na ϩ -and Cl Ϫ -dependent (10) with a 2:1:1 Na ϩ :Cl Ϫ :taurine stoichiometry (39, 48). System ␤ activity has been demonstrated in many cell types and its ca...

Taurine transporter gene expression in peripheral mononuclear blood cells of type 2 diabetic patients

“…These results are in line with previous data that described TauT gene expression in foetal peripheral lymphocytes and platelets (Iruloh et al 2007). Indeed, here we show that TauT expression: (1) is not sexual dimorphic, and (2) in normal subjects is inversely related with fasting plasma glucose (r = -0.36; P \ 0.05) and positively associated with Hba1c (r = 0.34; P \ 0.05).…”

Amino-acid transporters in T-cell activation and differentiation

“…15 T cells express various numbers of the system BETA family, including GAT-1, 9, 16, 17 GAT-2, 17 BGT1 18 and TAUT. 19 Other AA transporters have also been reported in T cells, such as ASCT2, 10 LAT1 20 and Cat-1. 21 …”

Isolation of Plasma Membrane Vesicles from Mouse Placenta at Term and Measurement of System A and System β Amino Acid Transporter Activity

“…Interestingly, several TAUT species were detected in mouse placental vesicles, similar, in part, to the banding pattern observed in human placental MVM. This may reflect the existence of differentially glycosylated TAUT variants in the plasma membrane of syncytiotrophoblast layer II [45]. The trend towards a less intense TAUT signal in mouse placental vesicles compared to human placental MVM would accord with the lower system β activity measured in mouse vesicles.…”