Reduced Placental Taurine Transporter (TauT) Activity in Pregnancies Complicated by Pre-eclampsia and Maternal Obesity - Advances in Experimental Medicine and Biology - page 79

Abbreviations
TauT Taurine transporter
STB Syncytiotrophoblast
MVM Microvillous membrane
BM Basal membrane
PE Pre-eclampsia
FGR Fetal growth restriction
BMI Body mass index
NPY Neuropeptide Y
PKC Protein kinase C
PMA Phorbol12-myristate-13-acetate
QPCR Quantitative polymerase chain reaction
9.1 Introduction
Taurine is a vital nutrient for fetal well-being and animal studies demonstrate a key
role for this amino acid in promoting the development of fetal brain, heart, kidney,
pancreas, retina, and skeletal muscle (Sturman 1988 ; Han et al. 2000 ; Heller-Stilb
et al. 2002 ). In human pregnancy taurine is conditionally essential, as the fetus and
placenta lack the enzyme required for taurine synthesis (Gaull et al. 1972 ) , and the
fetal demand for taurine must be met by placental transfer from maternal blood.
Nutrients are transported across the human placenta via the syncytiotrophoblast
(STB), a highly specialised multinucleate epithelium with a microvillous plasma
membrane (MVM) in direct contact with maternal blood and a basal membrane
(BM) in close apposition to the fetal capillary. Taurine is transported into STB by
the Na + -dependent amino acid transporter TauT, which is expressed on the MVM
(Roos et al. 2004 ). TauT accumulates taurine in the cell (STB concentration 10 mM,
maternal and fetal plasma 60 and 120 mM, respectively) such that taurine is the most
abundant free amino acid in STB (Philipps et al. 1978 ). This high intracellular tau-
rine provides a driving force for taurine efflux to the fetus, thought to occur through
taurine-permeable anion channels (Shennan and McNeillie 1995 ; Vallejos and
Riquelme 2007 ) .
Studies of fetal growth restriction (FGR) suggest that taurine is important for
human fetal growth and development. Idiopathic FGR is a condition in which
the fetus fails to achieve its growth potential in the absence of genetic or envi-
ronmental abnormalities and the growth-restricted fetus is at increased risk of
neonatal mortality and morbidity (McCormick 1985 ) and development of meta-
bolic and cardiovascular disease in later life (Calkins and Devaskar 2011 ; Barker
1999 ). Plasma taurine concentration is lower in FGR compared to the normally
grown fetus (Economides et al. 1989 ; Cetin et al. 1990 ) and this is associated
with a significantly lower TauT activity in the STB MVM compared to normal
pregnancy (Norberg et al. 1998 ) .