Gonzalez I M, Ackerman W E, Vandre D D, Robinson J M
Department of Physiology and Cell Biology, Ohio State University, Columbus, OH, USA.
Department of Obstetrics and Gynecology, Ohio State University, Columbus, OH, USA.
Placenta. 2014 Jul;35(7):442-9. doi: 10.1016/j.placenta.2014.04.015. Epub 2014 May 9.
Protein production and secretion are essential to syncytiotrophoblast function and are associated with cytotrophoblast cell fusion and differentiation. Syncytiotrophoblast hormone secretion is a crucial determinant of maternal-fetal health, and can be misregulated in pathological pregnancies. Although, polarized secretion is a key component of placental function, the mechanisms underlying this process are poorly understood.
While the octameric exocyst complex is classically regarded as a master regulator of secretion in various mammalian systems, its expression in the placenta remained unexplored. We hypothesized that the syncytiotrophoblast would express all exocyst complex components and effector proteins requisite for vesicle-mediated secretion more abundantly than cytotrophoblasts in tissue specimens.
A two-tiered immunobiological approach was utilized to characterize exocyst and ancillary proteins in normal, term human placentas. Exocyst protein expression and localization was documented in tissue homogenates via immunoblotting and immunofluorescence labeling of placental sections.
The eight exocyst proteins, EXOC1, 2, 3, 4, 5, 6, 7, and 8, were found in the human placenta. In addition, RAB11, an important exocyst complex modulator, was also expressed. Exocyst and Rab protein expression appeared to be regulated during trophoblast differentiation, as the syncytiotrophoblast expressed these proteins with little, if any, expression in cytotrophoblast cells. Additionally, exocyst proteins were localized at or near the syncytiotrophoblast apical membrane, the major site of placental secretion.
DISCUSSION/CONCLUSION: Our findings highlight exocyst protein expression as novel indicators of trophoblast differentiation. The exocyst's regulated localization within the syncytiotrophoblast in conjunction with its well known functions suggests a possible role in placental polarized secretion.
蛋白质的产生和分泌对于合体滋养层细胞的功能至关重要，并且与细胞滋养层细胞的融合和分化相关。合体滋养层激素分泌是母婴健康的关键决定因素，在病理性妊娠中可能会出现分泌失调。尽管极化分泌是胎盘功能的一个关键组成部分，但该过程背后的机制仍知之甚少。
虽然八聚体外排复合体在各种哺乳动物系统中通常被视为分泌的主要调节因子，但其在胎盘中的表达尚未得到研究。我们假设在组织标本中，合体滋养层比细胞滋养层更丰富地表达囊泡介导分泌所需的所有外排复合体成分和效应蛋白。
采用两级免疫生物学方法对正常足月人胎盘的外排复合体和辅助蛋白进行表征。通过胎盘组织匀浆的免疫印迹和胎盘切片的免疫荧光标记记录外排复合体蛋白的表达和定位。
在人胎盘中发现了八种外排复合体蛋白，即EXOC1、2、3、4、5、6、7和8。此外，还表达了一种重要的外排复合体调节剂RAB11。外排复合体和Rab蛋白的表达似乎在滋养层细胞分化过程中受到调节，因为合体滋养层表达这些蛋白，而细胞滋养层细胞中几乎没有表达。此外，外排复合体蛋白定位于合体滋养层顶膜或其附近，这是胎盘分泌的主要部位。
讨论/结论：我们的研究结果突出了外排复合体蛋白表达作为滋养层细胞分化的新指标。外排复合体在合体滋养层内的定位受调控，结合其已知功能，提示其在胎盘极化分泌中可能发挥作用。
