Ohgaki Ryuichi, Ohmori Takahiro, Hara Saori, Nakagomi Saya, Kanai-Azuma Masami, Kaneda-Nakashima Kazuko, Okuda Suguru, Nagamori Shushi, Kanai Yoshikatsu
Department of Bio-system Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.
Center of Experimental Animals, Tokyo Medical and Dental University, Tokyo, Japan.
Mol Cell Biol. 2017 May 16;37(11). doi: 10.1128/MCB.00427-16. Print 2017 Jun 1.
The layers of the epithelial syncytium, i.e., syncytiotrophoblasts, differentiate from chorionic trophoblasts via cell fusion and separate maternal and fetal circulations in hemochorial placentas. L-type amino acid transporter 1 (LAT1) and its covalently linked ancillary subunit 4F2hc are colocalized on both maternal and fetal surfaces of syncytiotrophoblasts, implying their roles in amino acid transfer through the placental barrier. In this study, LAT1 knockout, in addition, revealed a novel role of LAT1 in syncytiotrophoblast development. LAT1 at midgestation was selectively expressed in trophoblastic lineages in the placenta, exclusively as a LAT1-4F2hc heterodimer. In LAT1 homozygous knockout mice, chorionic trophoblasts remained largely mononucleated, and the layers of syncytiotrophoblasts were almost completely absent. The amount of 4F2hc protein, which possesses a fusogenic function in trophoblastic cells, as well as in virus-infected cells, was drastically reduced by LAT1 knockout, with less affecting the mRNA level. Knockdown of LAT1 in trophoblastic BeWo cells also reduced 4F2hc protein and suppressed forskolin-induced cell fusion. These results demonstrate a novel fundamental role of LAT1 to support the protein expression of 4F2hc via a chaperone-like function in chorionic trophoblasts and to promote syncytiotrophoblast formation by contributing to cell fusion in the developing placenta.
上皮合体滋养层，即合体滋养层细胞，通过细胞融合从绒毛膜滋养层细胞分化而来，并在血绒毛膜胎盘中将母体和胎儿循环分开。L型氨基酸转运体1（LAT1）及其共价连接的辅助亚基4F2hc共定位于合体滋养层细胞的母体和胎儿表面，这意味着它们在通过胎盘屏障的氨基酸转运中发挥作用。此外，在本研究中，LAT1基因敲除揭示了LAT1在合体滋养层细胞发育中的新作用。妊娠中期的LAT1在胎盘中的滋养层细胞谱系中选择性表达，仅作为LAT1-4F2hc异二聚体存在。在LAT1纯合基因敲除小鼠中，绒毛膜滋养层细胞大多仍为单核，合体滋养层细胞层几乎完全缺失。在滋养层细胞以及病毒感染细胞中具有融合功能的4F2hc蛋白量因LAT1基因敲除而大幅减少，而对mRNA水平的影响较小。在滋养层BeWo细胞中敲低LAT1也会降低4F2hc蛋白水平并抑制福斯可林诱导的细胞融合。这些结果表明，LAT1通过在绒毛膜滋养层细胞中发挥类似伴侣蛋白的功能来支持4F2hc的蛋白表达，并通过促进发育中的胎盘细胞融合来促进合体滋养层细胞形成，从而发挥了一种新的基本作用。
