Taurine Transport Into Fetal Cord Blood Cells: Inhibition by Cyclosporine A

Organic osmolytes increase expression of specific tight junction proteins in skin and alter barrier function in keratinocytes

BACKGROUND

The epidermal barrier is important for water conservation, failure of which is evident in dry-skin conditions. Barrier function is fulfilled by the stratum corneum, tight junctions (TJs, which control extracellular water) and keratinocyte mechanisms, such as organic osmolyte transport, which regulate intracellular water homeostasis. Organic osmolyte transport by keratinocytes is largely unexplored and nothing is known regarding how cellular and extracellular mechanisms of water conservation may interact.

OBJECTIVES

We aimed to characterize osmolyte transporters in skin and keratinocytes, and, using transporter inhibitors, to investigate whether osmolytes can modify TJs. Such modification would suggest a possible link between intracellular and extracellular mechanisms of water regulation in skin.

METHODS

Immunostaining and quantitative polymerase chain reaction of organic osmolyte-treated organ-cultured skin were used to identify changes to organic osmolyte transporters, and TJ protein and gene expression. TJ functional assays were performed on organic osmolyte-treated primary human keratinocytes in culture.

RESULTS

Immunostaining demonstrated the expression of transporters for betaine, taurine and myo-inositol in transporter-specific patterns. Treatment of human skin with either betaine or taurine increased the expression of claudin-1, claudin-4 and occludin. Osmolyte transporter inhibition abolished this response. Betaine and taurine increased TJ function in primary human keratinocytes in vitro.

CONCLUSIONS

Treatment of skin with organic osmolytes modulates TJ structure and function, which could contribute to the epidermal barrier. This emphasizes a role for organic osmolytes beyond the maintenance of intracellular osmolarity. This could be harnessed to enhance topical therapies for diseases characterized by skin barrier dysfunction.

Immunosuppressant therapy in pregnant organ transplant recipients

Transplant recipients are becoming pregnant with increasing frequency, and successful pregnancy outcomes have now been reported for women with all types of solid organ transplants. To prevent rejection of the transplanted organ, these patients are maintained on a life-long immunosuppressive regimen that must also be continued through pregnancy. Controlled human studies of the safety of these drugs have not been conducted, and knowledge regarding the pharmacokinetics of these medications in pregnancy is limited. Significant experience and safety data regarding the use of some of the more common immunosuppressants in pregnancy have, however, been accumulated from large case series and national registries. These observational studies suggest that successful pregnancy outcomes are possible in female organ transplant recipients, although sporadic adverse outcomes have been reported after immunosuppressant use in pregnancy. In this chapter, we will outline the information available regarding the use of immunosuppressive medications in pregnant transplant recipients as well as general concepts regarding fetal exposure to immunosuppressants.

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

Transplacental transfer of taurine, a β-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 β transporter and have compared gene and protein expression for the taurine transporter protein (TAUT) in these two cell types. System β activity in fetal platelets was 15-fold higher compared with fetal T lymphocytes ( P < 0.005), mirroring greater TAUT mRNA expression in platelets than T lymphocytes ( P < 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 β 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.