Javam M, Audette M C, Iqbal M, Bloise E, Gibb W, Matthews S G
Department of Physiology, University of Toronto, Toronto, Canada.
Dept Ob-Gyn, University of Ottawa, Ottawa, Canada; Dept Cellular & Molecular Medicine, University of Ottawa, Ottawa, Canada.
Placenta. 2014 May;35(5):324-30. doi: 10.1016/j.placenta.2014.02.010. Epub 2014 Mar 18.
The placenta contains efflux transporters, including P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), that limit the passage of xenobiotics, certain hormones and nutrients from the maternal to the fetal circulation. The expression of these transporters changes with gestational age, yet the mechanisms involved remain unknown. However, the changes in P-gp and BCRP transporter expression coincide with those of oxygen tension in the placenta, and oxygen tension has been shown to modulate P-gp and BCRP expression in other tissues. The objective of this study was to investigate the effects of oxygen tension on P-gp and BCRP expression in the term human placenta.
Following equilibration in culture (96 h), term placental explants (n = 7) were cultured in 3% or 20% oxygen for 24 and 48 h. Culture medium was collected every 24 h to measure lactate dehydrogenase (LDH; explant viability) and human chorionic gonadotropin (hCG; syncytiotrophoblast function). P-gp (encoded by ABCB1) and BCRP (encoded by ABCG2) protein and mRNA, as well as VEGFA mRNA were measured using western blot and qRT-PCR. P-gp localization was determined using immunofluorescence.
Oxygen tension had a significant effect on P-gp expression, with ABCB1/P-gp mRNA and protein levels increased in the hypoxic condition (3% O2) after 48 h (p < 0.05). VEGFA mRNA was elevated by hypoxia at both 24 and 48 h (p < 0.05). In contrast, placental ABCG2/BCRP mRNA and protein expression were stable with changes in oxygen tension. We identified profound differences in the glycosylation of P-gp between cultured and non-cultured placental tissue, with cultured explants expressing deglycosylated P-gp.
These findings demonstrate that, at term, the expression of placental P-gp, is regulated by oxygen tension. This suggests that changes in oxygenation of the placenta in the third trimester may alter levels of placental P-gp, and in doing so alter fetal exposure to P-gp substrates, including xenobiotics and certain hormones.
胎盘含有外排转运蛋白，包括P-糖蛋白（P-gp）和乳腺癌耐药蛋白（BCRP），这些转运蛋白会限制外源性物质、某些激素和营养物质从母体循环进入胎儿循环。这些转运蛋白的表达会随着胎龄而变化，但其涉及的机制仍不清楚。然而，P-gp和BCRP转运蛋白表达的变化与胎盘中氧张力的变化一致，并且已经表明氧张力可调节其他组织中P-gp和BCRP的表达。本研究的目的是调查氧张力对足月人胎盘中P-gp和BCRP表达的影响。
在培养中平衡96小时后，将足月胎盘外植体（n = 7）在3%或20%氧气中培养24小时和48小时。每24小时收集培养基以测量乳酸脱氢酶（LDH；外植体活力）和人绒毛膜促性腺激素（hCG；合体滋养层功能）。使用蛋白质印迹法和qRT-PCR测量P-gp（由ABCB1编码）和BCRP（由ABCG2编码）的蛋白质和mRNA，以及VEGFA mRNA。使用免疫荧光法确定P-gp的定位。
氧张力对P-gp表达有显著影响，48小时后低氧条件（3% O2）下ABCB1/P-gp mRNA和蛋白质水平升高（p < 0.05）。缺氧在24小时和48小时均使VEGFA mRNA升高（p < 0.05）。相比之下，胎盘ABCG2/BCRP mRNA和蛋白质表达随氧张力变化而稳定。我们发现培养的胎盘组织和未培养的胎盘组织中P-gp的糖基化存在显著差异，培养的外植体表达去糖基化的P-gp。
这些发现表明，足月时胎盘P-gp的表达受氧张力调节。这表明妊娠晚期胎盘氧合的变化可能会改变胎盘P-gp的水平，进而改变胎儿对P-gp底物（包括外源性物质和某些激素）的暴露。
