Taurine Transporter Research Articles

Zinc and zinc chelators modify taurine transport in rat retinal cells.

Zinc regulates Na(+)/Cl(-)-dependent transporters, similar to taurine one, such as those for dopamine, serotonin and norepinephrine. This study examined the ex vivo effect of zinc (ZnSO4), N,N,N,N-tetraquis-(2-piridilmetil)etilendiamino (TPEN) and diethylenetriaminepenta-acetic acid (DTPA), intracellular and extracellular zinc chelators, respectively, on rat retina [(3)H]taurine transport. Isolated cells were incubated in Locke solution with 100 nM of [(3)H]taurine for 25 s. Different concentrations of ZnSO4 (0.5-200 μM) were used. Low concentrations of ZnSO4 (30 and 40 μM) increased the transport, while higher concentrations (100, 150 and 200 μM) decreased it. Various concentrations of TPEN (1-200 μM) were added. Intermediate concentrations of TPEN (10-60 μM) significantly decreased [(3)H]taurine transport. The presence of TPEN, 20 μM, plus ZnSO4 reversed the effect of TPEN alone. Several concentrations of DTPA (1-500 μM) were also investigated. Reduction of transport took place at high concentrations of the chelator (100, 250 and 500 μM). DTPA, 500 μM, plus ZnSO4, did not modify the effect of it. These results indicate that zinc modulates taurine transport in a concentration-dependent manner, directly acting on the transporter or by forming taurine-zinc complexes in cell membranes.

Hyperosmolar stress induces TonEBP activation in human retinal pigmented epithelial cells

AbstractPurpose Macular edema, a frequently encountered complication of diabetic retinopathy (DR), results from alterations of the blood retinal barrier (BRB) and leads to modifications of the retinal pigmented epithelium (RPE) functions. Osmolar changes of the surrounding medium could be responsible for some modifications of the RPE functions leading to a disturbance of the retinal homeostasis.Methods To study the modification and stability of the key hyperosmolar response factor Tonicity Enhancer Binding Protein’s (TonEBP) expression in ARPE‐19 cells, derived from human RPE, were submitted to hyperosmolar stress of increasing concentration and for various times.Results In response to hyperosmolar stimulation of ARPE‐19 cells, a dose‐dependent increase in TonEBP mRNA and protein levels, as well as TonEBP nuclear translocation, were observed. Moreover, the mRNA levels of Aldose Reductase (AR) and Sodium‐dependent Taurine Transporter (TauT), two TonEBP target genes required for increasing the intracellular ionic force, increased in a delayed manner following hyperosmolar stimulation. Additionally, SB203580, a p38 protein kinase inhibitor, but not its inactive analogue SB202474, inhibited TonEBP nuclear translocation in ARPE‐19 cells submitted to hyperosmolar stimulation.Conclusion In ARPE‐19 cells submitted to hyperosmolar stress, TonEBP expression is induced, and its nuclear translocation stimulated through a mechanism involving p38 protein kinase activation. It is likely that TonEBP nuclear translocation mediates the increase of AR and TauT expression induced by hyperosmolar stress and plays a role in RPE cells osmoadaptation.

The anti-epileptic drug substance vigabatrin inhibits taurine transport in intestinal and renal cell culture models

The GABA-mimetic anti-epileptic drug substance vigabatrin is used against infantile spasms. In vitro and in vivo experiments have shown that vigabatrin is transported via the proton coupled amino acid transporter (PAT1) mediating at least parts of the intestinal absorption of the drug. However, such evidence does not preclude the involvement of other transporters. The aim of the present study was, therefore, to investigate if vigabatrin interacts with taurine transport. The uptake of taurine was measured in intestinal human Caco-2 and canine MDCK cell monolayers in the absence or presence of amino acids such as GABA and vigabatrin. Vigabatrin inhibits the uptake of taurine in Caco-2 and MDCK cells to 34±3 and 53±2%, respectively, at a concentration of 30mM. In Caco-2 cells the uptake of vigabatrin under neutral pH conditions is concentration-dependent and saturable with a Km-value of 27mM (logKm is 1.43±0.09). In conclusion, the present study shows that vigabatrin was able to inhibit the uptake of taurine in intestinal and renal cell culture models. Furthermore, uptake of vigabatrin in Caco-2 cells under neutral pH conditions was concentration-dependent and saturable and suggesting that vigabatrin partly was transported via a taurine transporter, which is likely to be TauT.

Expression of organic osmolyte transporters in cultured rat astrocytes and rat and human cerebral cortex

This study characterizes the expression of the osmolyte transporters betaine/γ-amino-n-butyric acid (GABA) transporter (BGT-1), the taurine transporter (TauT) and the sodium-dependent myo-inositol transporter (SMIT) in various rat brain cells in culture and in rat and human cerebral cortex in situ. Osmolyte transporter expression greatly differed between cultured brain cells with highest mRNA expression levels for SMIT in astrocytes and TauT in neurons. BGT-1 mRNA and protein were expressed in microglia but not in astrocytes and neurons. In rat and human cerebral cortex, SMIT was expressed in astrocytes and TauT was found in neurons. Osmolyte transporter expression was subject to regulation by factors relevant for hepatic encephalopathy (HE). Hypoosmolarity, NH4Cl (0.5–5mmol/l), diazepam (10μmol/l) and TNFα (10ng/ml) time-dependently decreased mRNA expression of SMIT and/or TauT in cultured astrocytes. NH4Cl-induced SMIT/TauT mRNA expression changes were sensitive to inhibitors of glutamine synthetase and NADPH oxidase. In rat cerebral cortex, SMIT mRNA expression decreased after portal vein ligation or ammonium acetate injection probably due to astrocyte swelling in these HE animal models. It is concluded that osmolyte transporters are heterogeneously expressed in brain and are subject to regulation by HE-relevant factors.

Effects of Graded Taurine Levels on Juvenile Cobia

AbstractTaurine, which has multiple important physiological roles in teleost fish and mammals, is an amino acid not found in alternative protein sources not derived from animals. Although taurine is found in fish‐meal‐based feeds, its high water solubility leads to lower taurine levels in reduction‐process‐based feeds, which marine carnivores such as Cobia Rachycentron canadum are adapted to in their natural diets. Graded taurine supplementation (0, 0.5, 1.5, and 5.0%) added to a traditional fish‐meal‐based formulation was examined in two growth trials with Cobia: one initiated with 10‐g individuals and the second initiated with 120‐g individuals. During the first trial, in which growth as weight gain ranged from 123 to 139 g per fish, there was an increase in dietary taurine and a decrease in the feed conversion ratio from 1.04 to 0.99. During the second trial, in which growth ranged from 227 to 313 g gained per fish, there was no significant difference in performance characteristics between dietary treatments. Messenger RNA transcript expression levels for two of the genes involved in taurine synthesis, cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO), as well as the membrane‐bound taurine transporter, TauT, were also measured at the conclusion of the second trial. Increasing dietary taurine in a diet containing 34.5% fish meal did not result in significantly different growth or production characteristics in Cobia, but did result in significantly increased taurine levels in fillet, liver, and plasma.

Role of SLC6A6 in promoting the survival and multidrug resistance of colorectal cancer.

The treatment of colorectal cancer (CRC) might be improved by the identification of a signalling pathway that could be targeted with novel therapeutics. The results of this study indicate that the taurine transporter SLC6A6 is highly expressed in CRC cells compared with normal colonocytes. SLC6A6 knockdown (KD) attenuated cell survival and was accompanied by enhanced drug sensitivity to 5-fluorouracil (5-FU), doxycycline (DOX) and SN-38. Both the population frequency of the side population (SP) cells and their cancer stem cell (CSC)-like properties (such as tumour initiation, differentiation and chemoresistance) were abrogated by SLC6A6-KD. Conversely, SLC6A6 overexpression increased cell survival and the proportion of SP cells, enhancing multidrug resistance (MDR). Additionally, SLC6A6-siRNA treatment enhanced the cytotoxic effects of all 3 drugs, whereas the efficacy of ABCG2-siRNA treatment was limited to its 2 substrate drugs, DOX and SN-38. This study indicates that SLC6A6 plays an important role in the maintenance of CSC characteristics, thus promoting cell survival signalling and chemoresistance. Therefore, SLC6A6 inhibition may be a promising therapeutic strategy for refractory CRC.

Roles of taurine-mediated tonic GABAA receptor activation in the radial migration of neurons in the fetal mouse cerebral cortex.

γ-Aminobutyric acid (GABA) depolarizes embryonic cerebrocortical neurons and continuous activation of the GABAA receptor (GABAAR) contributes to their tonic depolarization. Although multiple reports have demonstrated a role of GABAAR activation in neocortical development, including in migration, most of these studies have used pharmacological blockers. Herein, we performed in utero electroporation in GABA synthesis-lacking homozygous GAD67-GFP knock-in mice (GAD67GFP/GFP) to label neurons born in the ventricular zone. Three days after electroporation, there were no differences in the distribution of labeled cells between the genotypes. The dose–response properties of labeled cells to GABA were equivalent among genotypes. However, continuous blockade of GABAAR with the GABAAR antagonist SR95531 accelerated radial migration. This effect of GABAAR blockade in GAD67GFP/GFP mice suggested a role for alternative endogenous GABAAR agonists. Thus, we tested the role of taurine, which is derived from maternal blood but is abundant in the fetal brain. The taurine-evoked currents in labeled cells were mediated by GABAAR. Taurine uptake was blocked by a taurine transporter inhibitor, 2-(guanidino)ethanesulfonic acid (GES), and taurine release was blocked by a volume-sensitive anion channel blocker, 4-(2-butyl-6,7-dichlor-2-cyclopentylindan-1-on-5-yl) oxobutyric acid, as examined through high-performance liquid chromatography. GES increased the extracellular taurine concentration and induced an inward shift of the holding current, which was reversed by SR95531. In a taurine-deficient mouse model, the GABAAR-mediated tonic currents were greatly reduced, and radial migration was accelerated. As the tonic currents were equivalent among the genotypes of GAD67-GFP knock-in mice, taurine, rather than GABA, might play a major role as an endogenous agonist of embryonic tonic GABAAR conductance, regulating the radial migration of neurons in the developing neocortex.

Detrimental Effects of Ethanol and Its Metabolite Acetaldehyde, on First Trimester Human Placental Cell Turnover and Function

Fetal alcohol spectrum disorder (FASD) describes developmental issues from high maternal alcohol intake, which commonly results in fetal growth restriction and long term morbidity. We aimed to investigate the effect of alcohol and acetaldehyde, on the first trimester placenta, the period essential for normal fetal organogenesis. Normal invasion and establishment of the placenta during this time are essential for sustaining fetal viability to term. We hypothesise that alcohol (ethanol) and acetaldehyde have detrimental effects on cytotrophoblast invasion, turnover and placental function. Taurine is an important amino acid for neuronal and physiological development, and so, its uptake was assayed in cells and placental explants exposed to alcohol or acetaldehyde. First trimester villous explants and BeWo cells were treated with 0, 10, 20, 40 mM ethanol or 0, 10, 20, 40 µM acetaldehyde. The invasive capacity of SGHPL4, a first trimester extravillous cytotrophoblast cell line, was unaffected by ethanol or acetaldehyde (p>0.05; N = 6). The cells in-cycle were estimated using immunostaining for Ki67. Proliferating trophoblast cells treated with ethanol were decreased in both experiments (explants: 40% at 20 mM and 40 mM, p<0.05, N = 8–9) (cell line: 5% at 20 mM and 40 mM, p<0.05, N = 6). Acetaldehyde also reduced Ki67-positive cells in both experiments (explants at 40 µM p<0.05; N = 6) (cell line at 10 µM and 40 µM; p<0.05; N = 7). Only in the cell line at 20 µM acetaldehyde demonstrated increased apoptosis (p<0.05; N = 6). Alcohol inhibited taurine transport in BeWo cells at 10 mM and 40 mM (p<0.05; N = 6), and in placenta at 40 mM (p<0.05; N = 7). Acetaldehyde did not affect taurine transport in either model (P<0.05; N = 6). Interestingly, system A amino acid transport in placental explants was increased at 10 µM and 40 µM acetaldehyde exposure (p<0.05; N = 6). Our results demonstrate that exposure to both genotoxins may contribute to the pathogenesis of FASD by reducing placental growth. Alcohol also reduces the transport of taurine, which is vital for developmental neurogenesis.

Amino acid residues involved in the substrate specificity of TauT/SLC6A6 for taurine and γ-aminobutyric acid.

Taurine transporter (TauT/SLC6A6) is an "honorary" γ-aminobutyric acid (GABA) transporter because of its low affinity for GABA. The sequence analysis of TauT implied the role of Gly57, Phe58, Leu306 and Glu406 in the substrate recognition of TauT, and amino acid-substitutions were performed. Immunocytochemistry supported no marked effect of mutations on the expression of TauT. TauT-expressing oocytes showed a reduction in [(3)H]taurine uptake by G57E, F58I, L306Q and E406C, and change in [(3)H]GABA uptake by G57E and E406C, suggesting their significant roles in the function of TauT. G57E lost the activity of [(3)H]taurine and [(3)H]GABA uptake, suggesting that Gly57 is involved in the determination of substrate pocket volume and in the interaction with substrates. E406C exhibited a decrease and an increase in the affinity for taurine and GABA, respectively, suggesting the involvement of Glu406 in the substrate specificity of TauT. The inhibition study supported the role of Glu406 in the substrate specificity since [(3)H]taurine and [(3)H]GABA uptake by E406C was less sensitive to taurine and β-alanine, and more sensitive to GABA and nipecotic acid than was the case with wild type of TauT. F58I had an increased affinity for GABA, suggesting the involvement of Phe58 in the substrate accessibility. The kinetic parameters showed the decreased and increased affinities of L306Q for taurine and GABA, respectively, supporting that substrate recognition of TauT is conformationally regulated by the branched-side chain of Leu306. In conclusion, the present results suggest that these residues play important roles in the transport function and substrate specificity of TauT.

Œil et taurine

La taurine est l’acide aminé le plus abondant dans la rétine. Son rôle, encore mal connu est essentiellement lié à son pouvoir anti-oxydant. Sa concentration tissulaire dépend d’un apport nutritionnel en taurine exogène et du fonctionnement de son transporteur. De plus, une synthèse endogène de taurine participe au maintien de son taux physiologique. D’anciennes études ont montré que la privation nutritionnelle de taurine chez le chat est responsable de dommages rétiniens graves, affectant la couche des photorécepteurs. En découvrant que la toxicité du vigabatrin est liée à une déplétion en taurine, nous avons récemment montré que la taurine participe également à la survie des cellules ganglionnaires rétiniennes dans différents modèles de dégénérescence rétinienne. La taurine pourrait ainsi être impliquée dans la prévention des dégénérescences rétiniennes telles que les rétinopathies et les glaucomes.

Down‐regulation of placental mTOR, insulin/IGF‐I signaling, and nutrient transporters in response to maternal nutrient restriction in the baboon

The mechanisms by which maternal nutrient restriction (MNR) causes reduced fetal growth are poorly understood. We hypothesized that MNR inhibits placental mechanistic target of rapamycin (mTOR) and insulin/IGF-I signaling, down-regulates placental nutrient transporters, and decreases fetal amino acid levels. Pregnant baboons were fed control (ad libitum, n=11) or an MNR diet (70% of controls, n=11) from gestational day (GD) 30. Placenta and umbilical blood were collected at GD 165. Western blot was used to determine the phosphorylation of proteins in the mTOR, insulin/IGF-I, ERK1/2, and GSK-3 signaling pathways in placental homogenates and expression of glucose transporter 1 (GLUT-1), taurine transporter (TAUT), sodium-dependent neutral amino acid transporter (SNAT), and large neutral amino acid transporter (LAT) isoforms in syncytiotrophoblast microvillous membranes (MVMs). MNR reduced fetal weights by 13%, lowered fetal plasma concentrations of essential amino acids, and decreased the phosphorylation of placental S6K, S6 ribosomal protein, 4E-BP1, IRS-1, Akt, ERK-1/2, and GSK-3. MVM protein expression of GLUT-1, TAUT, SNAT-2 and LAT-1/2 was reduced in MNR. This is the first study in primates exploring placental responses to maternal undernutrition. Inhibition of placental mTOR and insulin/IGF-I signaling resulting in down-regulation of placental nutrient transporters may link maternal undernutrition to restricted fetal growth.

Congenital taurine deficiency in mice is associated with reduced sensitivity to nociceptive chemical stimulation

The amino acid taurine is required for development and functioning of the central and peripheral nervous system where it exerts osmoregulatory, neuromodulatory and anti-apoptotic actions. It is subject to cellular import by the taurine transporter slc6a6. Absence of the transporter and consequently, absence of taurine leads to several neurologic deficits and sensory losses. In a slc6a6 knock-out mouse model, consequences of congenital taurine deficiency were assessed in nociceptive sensory processes. The formalin assay, hot plate assay, and summated generator potentials in response to local nociceptive stimulation with gaseous CO2 were applied. Reduced responsiveness of slc6a6(−/−) mice to nociceptive stimulation was observed in particular to chemical nociceptive stimuli. Scl6a6 knock-out mice spent significantly less time licking the formalin injected paw and displayed smaller amplitudes of the nociceptive nasal mucosa potentials than wild-type mice (p=0.002 and 0.01 respectively). In contrast, withdrawal latencies on a hot plate did not significantly differ, suggesting that intracellular taurine deficits lead in particular to a hyposensitivity of nociceptive sensory neurons sensitive to noxious chemical stimulation. As hereditary absence of taurine affects biological processes of anatomical structure development, the altered nociceptive responses likely reflect consequences of compromised peripheral nervous system development.

Evolutionary history of the GABA transporter (GAT) group revealed by marine invertebrate GAT-1.

The GABA transporter (GAT) group is one of the major subgroups in the solute career 6 (SLC6) family of transmembrane proteins. The GAT group, which has been well studied in mammals, has 6 known members, i.e., a taurine transporter (TAUT), four GABA transporters (GAT-1, -2, -3, - 4), and a creatine transporter (CT1), which have important roles in maintaining physiological homeostasis. However, the GAT group has not been extensively investigated in invertebrates; only TAUT has been reported in marine invertebrates such as bivalves and krills, and GAT-1 has been reported in several insect species and nematodes. Thus, it is unknown how transporters in the GAT group arose during the course of animal evolution. In this study, we cloned GAT-1 cDNAs from the deep-sea mussel, Bathymodiolus septemdierum, and the Antarctic krill, Euphausia superba, whose TAUT cDNA has already been cloned. To understand the evolutionary history of the GAT group, we conducted phylogenetic and synteny analyses on the GAT group transporters of vertebrates and invertebrates. Our findings suggest that transporters of the GAT group evolved through the following processes. First, GAT-1 and CT1 arose by tandem duplication of an ancestral transporter gene before the divergence of Deuterostomia and Protostomia; next, the TAUT gene arose and GAT-3 was formed by the tandem duplication of the TAUT gene; and finally, GAT-2 and GAT-4 evolved from a GAT-3 gene by chromosomal duplication in the ancestral vertebrates. Based on synteny and phylogenetic evidence, the present naming of the GAT group members does not accurately reflect the evolutionary relationships.

Novel strategy for a high-yielding mAb-producing CHO strain (overexpression of non-coding RNA enhanced proliferation and improved mAb yield)

Background Innovation in mAb production is driven by strategies to increase yield. A host cell line constructed to overexpress TAUT (taurine transporter) produced a higher proportion of high-mAb-titer strains [1]. From these we selected a single TAUT/mAb strain that remained viable for as long as 1 month. Its improved viability is attributed to improved metabolic properties. It was also more productive (>100 pg/cell/day) and yielded more mAb (up to 8.1 g/L/31 days) than the parent cell line [2]. These results suggested that this host cell engineering strategy has great potential for the improvement of mAb-producing CHO cells.

Proteomic and Transcriptomic Analyses of “CandidatusPelagibacter ubique” Describe the First PII-Independent Response to Nitrogen Limitation in a Free-Living Alphaproteobacterium

ABSTRACTNitrogen is one of the major nutrients limiting microbial productivity in the ocean, and as a result, most marine microorganisms have evolved systems for responding to nitrogen stress. The highly abundant alphaproteobacterium “Candidatus Pelagibacter ubique,” a cultured member of the order Pelagibacterales (SAR11), lacks the canonical GlnB, GlnD, GlnK, and NtrB/NtrC genes for regulating nitrogen assimilation, raising questions about how these organisms respond to nitrogen limitation. A survey of 266 Alphaproteobacteria genomes found these five regulatory genes nearly universally conserved, absent only in intracellular parasites and members of the order Pelagibacterales, including “Ca. Pelagibacter ubique.” Global differences in mRNA and protein expression between nitrogen-limited and nitrogen-replete cultures were measured to identify nitrogen stress responses in “Ca. Pelagibacter ubique” strain HTCC1062. Transporters for ammonium (AmtB), taurine (TauA), amino acids (YhdW), and opines (OccT) were all elevated in nitrogen-limited cells, indicating that they devote increased resources to the assimilation of nitrogenous organic compounds. Enzymes for assimilating amine into glutamine (GlnA), glutamate (GltBD), and glycine (AspC) were similarly upregulated. Differential regulation of the transcriptional regulator NtrX in the two-component signaling system NtrY/NtrX was also observed, implicating it in control of the nitrogen starvation response. Comparisons of the transcriptome and proteome supported previous observations of uncoupling between transcription and translation in nutrient-deprived “Ca. Pelagibacter ubique” cells. Overall, these data reveal a streamlined, PII-independent response to nitrogen stress in “Ca. Pelagibacter ubique,” and likely other Pelagibacterales, and show that they respond to nitrogen stress by allocating more resources to the assimilation of nitrogen-rich organic compounds.

Comparative analysis of amino acid metabolism and transport in CHO variants with different levels of productivity

Chinese hamster ovary (CHO) cells are widely used for the production of biopharmaceuticals; however, our understanding of several physiological elements that contribute to productivity is limited. One of these is amino acid transport and how its limitation and/or regulation might affect productivity. To further our understanding, we have examined the expression of 40 mammalian amino acid transporter genes during batch cultures of three CHO cell lines: a non-producer and two antibody-producing cell lines with different levels of productivity. In parallel, extracellular and intracellular levels of amino acids were quantified. The aim was to identify differences in gene regulation between cell lines and within culture. Our results show that three transporters associated with transport of taurine and β-alanine, acidic amino acids and branched chain amino acids, are highly upregulated in both antibody-producing cell lines but not in the non-producer. Additionally, genes associated with the transport of amino acids related to the glutathione pathway (alanine, cysteine, cystine, glycine, glutamate) were found to be highly upregulated during the stationary phase of cell culture, correlating well with literature data on the importance of the pathway. Our analysis highlights potential markers for cell line selection and targets for process optimization.

β-Alanine and l-histidine transport across the inner blood-retinal barrier: Potential involvement in l-carnosine supply

The supply of l-carnosine, a bioactive dipeptide of β-alanine and l-histidine, to the retina across the blood-retinal barrier (BRB) was studied. The in vivo and in vitro studies revealed low uptake activities for [3H]Gly-Sar, a representative dipeptide, suggesting that l-carnosine transport plays only a minor role at the BRB. The in vivo study using rats showed approximately 18- and 23-fold greater retinal uptake indexes (RUI) for [3H]β-alanine and [3H]l-histidine compared with that of a paracellular marker, respectively. The RUI of [3H]β-alanine was taurine- and γ-aminobutyric acid-sensitive, and the in vitro uptake by TR-iBRB2 cells showed time- concentration- and temperature-dependent [3H]β-alanine uptake, suggesting that a carrier-mediated process was involved in β-alanine transport across the inner BRB. [3H]β-Alanine uptake was inhibited by taurine and β-guanidinopropionic acid, suggesting that taurine transporter (TAUT/SLC6A6) is responsible for the influx transport of β-alanine across the inner BRB. Regarding l-histidine, the l-leucine-sensitive RUI of [3H]l-histidine was identified, and the in vitro [3H]l-histidine uptake by TR-iBRB2 cells suggested that a carrier-mediated process was involved in l-histidine transport across the inner BRB. The inhibition profile suggested that L-type amino acid transporter (LAT1/SLC7A5) is responsible for the influx transport of l-histidine across the inner BRB. These results show that the influx transports of β-alanine and l-histidine across the inner BRB is carried out by TAUT and LAT1, respectively, suggesting that the retinal l-carnosine is supplied by enzymatic synthesis from two kinds of amino acids transported across the inner BRB.

Exogenous taurine attenuates mitochondrial oxidative stress and endoplasmic reticulum stress in rat cardiomyocytes

Taurine, a conditionally essential amino acid, plays a critical role in cardiovascular function. Here we examined the effect of taurine on mitochondria and endoplasmic reticulum in rat cardiomyocytes during glucose deprivation (GD). Data showed that cell viability, intracellular taurine contents, and taurine transporter expression were decreased during GD. In contrast, an increase in reactive oxygen species and intracellular Ca(2+) contents was observed. GD also caused disrupted mitochondrial membrane potential, apoptotic cell death, and dissociation of unfolded protein response (UPR)-relative proteins in cardiomyocytes. Signal transduction analysis showed that Bcl-2 family protein balance was disturbed, caspase-12 was activated and UPR-relative protein levels were up-regulated. Moreover, pre-treatment with 80 mM exogenous taurine attenuated GD effect in cardiomyocytes. Our results suggest that taurine have beneficial effects on inhibiting mitochondria-dependent cell apoptosis and UPR-associated cell apoptosis and might have clinical implications on acute myocardial infarction in future.

Cooverexpression of alanine aminotransferase 1 in Chinese hamster ovary cells overexpressing taurine transporter further stimulates metabolism and enhances product yield

Innovation in monoclonal antibody (mAb) production continues to be driven by cell engineering strategies to increase yield and improve product quality. In a previous study, to investigate the effectiveness of transporter overexpression strategies, we prepared a taurine transporter-overexpressing host cell line (DXB11/TAUT) that produced a higher proportion of high-mAb-titer strains than did the parent host cell line. In the current study, we selected a single DXB11/TAUT/mAb1 strain that remained viable for longer (up to 1 month) under common fed-batch culture conditions, and the improvement in viability could be attributed to its improved metabolic properties. It was also more productive (up to >100 pg/cell/day) and yielded more mAb1 (up to 8.1 g/L/31 days) than the parent cell line, and the mAb1 it produced was of comparable quality. These results suggested that this host cell engineering strategy has unique potential for the improvement of mAb-producing Chinese hamster ovary (CHO) cells; for example, it may be appropriate for high cell density perfusion culture. TAUT-overexpressing cell lines rapidly accumulated the byproduct alanine, and our challenge in the present study was to apply a strategy for modulating cell metabolism to utilize this byproduct to achieve a high mAb yield in a shorter culture period. To accomplish this, we genetically modified the DXB11/TAUT/mAb1 strain to cooverexpress alanine aminotransferase 1 (ALT1). The resulting DXB11/TAUT/mAb1/ALT1 cooverexpressing strain gave a higher mAb yield in a shorter culture period (5.9 g/L/14 days). It is usually difficult to drive the overexpression of two functional genes while balancing competing goals. However, forced cooverexpression of TAUT and ALT1 in our DXB11/TAUT/mAb1/ALT1 strain resulted in a higher proliferation than the DXB11/TAUT/mAb1 strain, with an ideal balance between cell viability and productivity. Therefore, we have demonstrated a strategy capable of achieving an optimum balance among the goals of cell viability, productivity, and proliferative capacity.

Taurine transport in human placental trophoblast is important for regulation of cell differentiation and survival.

The outer epithelial cell layer of human placenta, the syncytiotrophoblast, is a specialised terminally differentiated multinucleate tissue. It is generated and renewed from underlying cytotrophoblast cells that undergo proliferation, differentiation and fusion with syncytiotrophoblast. Acquisition of fresh cellular components is thought to be balanced by apoptosis and shedding of aged nuclei. This process of trophoblast cell turnover maintains a functional syncytiotrophoblast, capable of sufficient nutrient transfer from mother to foetus. Foetal growth restriction (FGR) is a pregnancy complication associated with aberrant trophoblast turnover and reduced activity of certain amino acid transporters, including the taurine transporter (TauT). Taurine is the most abundant amino acid in human placenta implying an important physiological role within this tissue. Unlike other amino acids, taurine is not incorporated into proteins and in non-placental cell types represents an important osmolyte involved in cell volume regulation, and is also cytoprotective. Here, we investigated the role of taurine in trophoblast turnover using RNA interference to deplete primary human trophoblast cells of TauT and reduce intracellular taurine content. Trophoblast differentiation was compromised in TauT-deficient cells, and susceptibility of these cells to an inflammatory cytokine that is elevated in FGR was increased, evidenced by elevated levels of apoptosis. These data suggest an important role for taurine in trophoblast turnover and cytoprotection.