System β and System A amino acid transporters in the feline endotheliochorial placenta

Champion, E. E.; Mann, Sarah; Glazier, Jocelyn D.; Jones, Carolyn J.P.; Rawlings, John M.; Sibley, Colin P.; Greenwood, Susan

doi:10.1152/ajpregu.00530.2003

Cited by 18 publications

(12 citation statements)

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“…The pellet was suspended in 200 l PBS containing 1% protease inhibitor cocktail and homogenized with a Dounce homogenizer on ice. JAr cell (a choriocarcinoma cell line) lysate and MVM isolates were included as positive controls for TAUT (13,40). Protein concentration was determined using Bio-Rad dye reagent.…”

Section: Methodsmentioning

confidence: 99%

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

Iruloh

D'Souza²,

Speake³

et al. 2007

American Journal of Physiology-Cell Physiology

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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...

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Section: Methodsmentioning

confidence: 99%

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

Iruloh

D'Souza²,

Speake³

et al. 2007

American Journal of Physiology-Cell Physiology

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“…System A is sensitive to N-methylated amino acids (Johnson and Smith, 1988) such as α-(methylamino)isobutyric acid (MeAIB). This non-metabolised amino acid analogue has a specific affinity for the System A transporter (Christensen et al, 1965) and has been used extensively to study this transport system in the placenta (Champion et al, 2004;Jansson et al, 2003;Johnson and Smith, 1988;Mahendran et al, 1993;Moe et al, 1994).…”

Section: Transporter Mechanisms and Characteristicsmentioning

confidence: 99%

“…Using custom synthesised SNAT isoform-specific antibodies, we have used immunohistochemistry to confirm localisation of each SNAT isoform to the syncytiotrophoblast in both first trimester and term placental samples (Champion et al, 2004;Desforges et al, 2006Desforges et al, , 2009. This pattern of localization allows for the possibility that each isoform of system A has the potential to transport amino acids from maternal blood in the intervillous space into the placenta.…”

Section: Molecular Characterisation and Expression In Human Placentamentioning

confidence: 99%

Placental nutrient supply and fetal growth

Desforges¹,

Sibley²

2010

Int. J. Dev. Biol.

147

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This review considers mechanisms by which transfer across the placenta takes place and how the capacity of the placenta to supply nutrients relates to fetal growth and vice versa. Blood flow through both uterine and umbilical circulations of the placenta, the structural properties of the placental exchange barrier and its related diffusional permeability, and the expression and activity of a wide range of transporter proteins in the syncytiotrophoblast, the transporting epithelium of the placenta, all need to be taken into account in considering placental supply capacity. We discuss the evidence that each of these factors affects, and is affected by, fetal growth rate and consider the regulatory mechanisms involved, with a particular focus on data that has emerged from study of the system A amino acid transporter. We consider that future work will build on the considerable foundation of knowledge regarding placental transfer mechanisms, as well as the other aspects of placental structure and function, to develop new diagnostic and therapeutic strategies for pregnancy complications, such as fetal growth restriction or overgrowth.

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“…Protein was extracted from first-trimester (7-13 wk; n ϭ 8) and term placental villous tissue homogenates (38 -40 wk; n ϭ 8) as described previously (6). Total liver homogenate (Sigma Aldrich, Dorset, UK) was used as the positive control tissue for SNAT4, and BeWo choriocarcinoma cell homogenate was used as the negative control because these cells do not express Slc38a4 (25,36).…”

Section: Protein Expressionmentioning

confidence: 99%

“…PAGE was performed using 3% stacking gels and 7% resolving gels. The proteins were then electrotransferred onto nitrocellulose membrane, and antibody probing was performed as described previously (6). A rabbit anti-SNAT4 affinity-purified polyclonal antibody was used (1:100 dilution; 2 g/ml).…”

Section: Protein Expressionmentioning

confidence: 99%

SNAT4 isoform of system A amino acid transporter is expressed in human placenta

Desforges¹,

Lacey²,

Glazier³

et al. 2006

American Journal of Physiology-Cell Physiology

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. SNAT4 isoform of system A amino acid transporter is expressed in human placenta. Am J Physiol Cell Physiol 290: C305-C312, 2006. First published September 7, 2005 doi:10.1152/ajpcell.00258.2005.-The system A amino acid transporter is encoded by three members of the Slc38 gene family, giving rise to three subtypes: Na ϩ -coupled neutral amino acid transporter (SNAT)1, SNAT2, and SNAT4. SNAT2 is expressed ubiquitously in mammalian tissues; SNAT1 is predominantly expressed in heart, brain, and placenta; and SNAT4 is reported to be expressed solely by the liver. In the placenta, system A has an essential role in the supply of neutral amino acids needed for fetal growth. In the present study, we examined expression and localization of SNAT1, SNAT2, and SNAT4 in human placenta during gestation. Real-time quantitative PCR was used to examine steady-state levels of system A subtype mRNA in early (6 -10 wk) and late (10 -13 wk) first-trimester and full-term (38 -40 wk) placentas. We detected mRNA for all three isoforms from early gestation onward. There were no differences in SNAT1 and SNAT2 mRNA expression with gestation. However, SNAT4 mRNA expression was significantly higher early in the first trimester compared with the full-term placenta (P Ͻ 0.01). We next investigated SNAT4 protein expression in human placenta. In contrast to the observation for gene expression, Western blot analysis revealed that SNAT4 protein expression was significantly higher at term compared with the first trimester (P Ͻ 0.05). Immunohistochemistry and Western blot analysis showed that SNAT4 is localized to the microvillous and basal plasma membranes of the syncytiotrophoblast, suggesting a role for this isoform of system A in amino acid transport across the placenta. This study therefore provides the first evidence of SNAT4 mRNA and protein expression in the human placenta, both at the first trimester and at full term. SNAT1; SNAT2; gestational expression; syncytiotrophoblast SYSTEM A IS A UBIQUITOUS Na ϩ -dependent transporter that actively transports small, zwitterionic, neutral amino acids with short, unbranched side chains such as alanine, serine, and glutamine (24). It has a unique ability to transport N-methylated amino acids such as ␣-(methylamino)isobutyric acid (MeAIB) (7). This nonmetabolized amino acid analog has been used extensively to study system A in the placenta (21,27,37).Recent data show that system A is encoded by three different members of the SLC38 gene family (Slc38a1, Slc38a2, and Slc38a4), giving rise to the three subtypes of this Na ϩ -coupled neutral amino acid transporter (SNAT): SNAT1, SNAT2, and SNAT4 (previously referred to as ATA1, ATA2, and ATA3, respectively) (31). SNAT1 was the first isoform to be cloned from rat brain and initially was designated GlnT because of its preference for glutamine as a substrate (49). Cloning of the human homolog as well as SNAT2 and SNAT4 followed (18,19,44,45,50,51). These previous studies showed the three isoforms to be highly homologous: amino acid sequences for SNAT1 and S...

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System β and System A amino acid transporters in the feline endotheliochorial placenta

Abstract: . System ␤ and System A amino acid transporters in the feline endotheliochorial placenta.

Cited by 18 publications

References 50 publications

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

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

Placental nutrient supply and fetal growth

SNAT4 isoform of system A amino acid transporter is expressed in human placenta

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