A16057 Tonicity responses by TonEBP and SMIT in human primary term cytotrophoblasts

Abstract

Objectives: Previously, we and others have demonstrated that in pregnancy enhanced intake of salt (NaCl) lowers maternal blood pressure and improves pregnancy outcome; the reasons why are unknown. It has been shown in non-renal tissues such as the skin interstitium, that in response to high salt, macrophages upregulate tonicity-responsive enhancer binding protein (TonEBP), which regulates transcription of sodium-myo-inositol cotransporter (SMIT). We hypothesised that human primary term cytotrophoblasts (CTBs) are able to respond to salt in a similar manner. Methods: CTBs were incubated with 3 different salt concentrations (110, 140 and 170 mM NaCl) for 6 or 24 hours. mRNA expression of TonEBP and SMIT were measured by RT-PCR and normalised to the geometric mean of the reference genes Cyclophilin A, HPRT1 and YWHAZ. Results: After 6 h incubation with high salt (170 mM NaCl), TonEBP and SMIT mRNA levels were upregulated (p < 0.05) compared to 110 mM NaCl. After 24 h incubation with high salt, TonEBP mRNA was no longer upregulated in CTBs. However, SMIT mRNA levels stayed upregulated also after 24 h incubation with high salt (p < 0.05). Conclusion: The results of this study indicate that TonEBP regulates transcription of SMIT in human primary term cytotrophoblasts and that this regulation can be enhanced following treatment with NaCl. The TonEBP response enables cells to survive hypertonic conditions via the accumulation of organic osmolytes. The results of the CTBs confirm our results in three human trophoblast cell lines (HTR8/SVneo, JEG3, BeWo).