Unal R, Ahmed B A, Jeffus B C, Harney J T, Lyle C S, Wu Y-K, Chambers T C, Reece E A, Kilic F
Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
J Neurochem. 2007 May;101(4):937-48. doi: 10.1111/j.1471-4159.2007.04469.x. Epub 2007 Mar 12.
Serotonin [5-hydroxytryptamine (5HT)] is a vasoconstrictor that also acts as a developmental signal early in embryogenesis. The 5HT transporter (SERT) on the membranes of the placental trophoblast cells controls 5HT levels in the maternal bloodstream to maintain stable transplacental blood flow and simultaneously provide 5HT to the embryo. The 5HT uptake rate of placental SERT is important for both the mother and the developing embryo. The impact of glucose on the placental SERT system during diabetic pregnancy is not known. The present in vitro study investigated this important issue in human placental choriocarcinoma (JAR) cells that were cultured for 24-96 h in a medium containing either 5.5 (physiologic concentration) or 25 mmol/L D-glucose (diabetic-like concentration). The 5HT uptake rates of the cultured cells were not altered at exogenous D-glucose concentrations in the range of 5.5-15 mmol/L, but were decreased significantly at a diabetic-like concentration (>or=25 mmol/L). To understand better the role of glucose on the placental 5HT system, we first characterized SERT in JAR cells at different cell-cycle phases and then determined the expression levels of SERT on the plasma membrane and in the intracellular pools of JAR cells at the late-S and G2 phases, where the uptake rates were decreased 73% under diabetic-like glucose concentrations. Finally, the importance of self-association of SERT molecules was examined. In JAR cells co-expressing Flag- and myc-tagged SERT, myc-antibody precipitated 70% of Flag-SERT, indicating that a large percentage of SERT proteins exist as oligomers in situ. Under diabetic conditions, myc-antibody no longer precipitated Flag-SERT, suggesting a disruption in the aggregation of SERT molecules. Therefore, we propose that under uncontrolled diabetic conditions, glucose down-regulates 5HT uptake rates of placental SERT by interfering with its functional expression in a cell-cycle-dependent manner.
血清素[5-羟色胺（5HT）]是一种血管收缩剂，在胚胎发育早期也作为一种发育信号。胎盘滋养层细胞膜上的5HT转运体（SERT）控制母体血液中的5HT水平，以维持稳定的胎盘血流，同时为胚胎提供5HT。胎盘SERT的5HT摄取率对母亲和发育中的胚胎都很重要。糖尿病妊娠期间葡萄糖对胎盘SERT系统的影响尚不清楚。本体外研究在人胎盘绒毛膜癌细胞（JAR）中探讨了这一重要问题，这些细胞在含有5.5（生理浓度）或25 mmol/L D-葡萄糖（糖尿病样浓度）的培养基中培养24-96小时。在5.5-15 mmol/L范围内的外源性D-葡萄糖浓度下，培养细胞的5HT摄取率没有改变，但在糖尿病样浓度（≥25 mmol/L）下显著降低。为了更好地理解葡萄糖在胎盘5HT系统中的作用，我们首先在不同细胞周期阶段对JAR细胞中的SERT进行了表征，然后确定了SERT在S期后期和G2期JAR细胞的质膜和细胞内池中的表达水平，在糖尿病样葡萄糖浓度下，摄取率降低了73%。最后，研究了SERT分子自我结合的重要性。在共表达Flag和myc标签的SERT的JAR细胞中，myc抗体沉淀了70%的Flag-SERT，表明很大比例的SERT蛋白以寡聚体形式原位存在。在糖尿病条件下，myc抗体不再沉淀Flag-SERT，表明SERT分子的聚集受到破坏。因此，我们提出，在糖尿病控制不佳的情况下，葡萄糖通过以细胞周期依赖性方式干扰其功能表达来下调胎盘SERT的5HT摄取率。
