Rebourcet R, Deborde S, De Ceuninck F, Willeput J, Ferré F
INSERM U.361, Maternité Baudelocque, Paris, France.
Biol Reprod. 1996 Nov;55(5):1119-25. doi: 10.1095/biolreprod55.5.1119.
The primary function of the placenta is to ensure an optimal environment for fetal growth and development. In normal pregnancy, placental vascular tone regulation assures fetus well-being and normal development by maintaining adequate blood flow so as to ensure materno-fetal exchanges. In human placenta, synthesis of insulin-like growth factor (IGF)-II and specific binding sites have been previously characterized in the trophoblast; in contrast, no studies have dealt with this subject in the fetoplacental vascular system, particularly in stem villi vessels. We thus investigated whether membranes of the muscular layer of stem villi vessels contained 125I-IGF-II binding sites. Two complementary approaches were used: 125I-IGF-II binding and affinity cross-linking studies. 125I-IGF-II labeled, in a saturable and noncooperative manner, a single class of high-affinity binding sites characterized by a Kd of 1.24 +/- 0.26 nM (n = 6), a maximum binding capacity (Bmax) of 3.02 +/- 0.45 pmol/mg protein, and a Hill coefficient of 1.00 +/- 0.15. Competitors for 125I-IGF-II binding to membranes were in the order of potency IGF-II > IGF-I. Insulin was not a competitor. Affinity cross-linking of membranes with 125I-IGF-II, followed by SDS-PAGE and autoradiography, revealed two labeled bands: a protein complex of 250 kDa, which corresponds to the type II IGF receptor, and another of 135 kDa, corresponding to the type I IGF receptor. Only IGF-II could displace 125I-IGF-II binding from the major 250-kDa band, while 125I-IGF-II bound to the minor 135-kDa band was displaced by either IGF-I, IGF-II, or insulin. In conclusion, high levels of specific binding sites for 125I-IGF-II are present in the muscular layer of stem villi vessels, which are considered placenta resistance vessels. The involvement of both type I and type II IGF receptors in the growth-promoting action of IGF-II remains to be determined in the fetoplacental vascular system.
胎盘的主要功能是确保为胎儿生长发育提供最佳环境。在正常妊娠中，胎盘血管张力调节通过维持充足的血流来保证胎儿的健康和正常发育，从而确保母胎之间的物质交换。在人胎盘中，胰岛素样生长因子（IGF）-II的合成及特异性结合位点先前已在滋养层细胞中得到表征；相比之下，尚无研究涉及胎儿-胎盘血管系统，尤其是干绒毛血管中的这一主题。因此，我们研究了干绒毛血管肌层的细胞膜是否含有125I-IGF-II结合位点。我们采用了两种互补的方法：125I-IGF-II结合实验和亲和交联研究。125I-IGF-II以可饱和且非协同的方式标记了一类单一的高亲和力结合位点，其解离常数（Kd）为1.24±0.26 nM（n = 6），最大结合容量（Bmax）为3.02±0.45 pmol/mg蛋白质，希尔系数为1.00±0.15。与125I-IGF-II竞争结合细胞膜的物质的效力顺序为IGF-II > IGF-I。胰岛素不是竞争者。用125I-IGF-II对细胞膜进行亲和交联，随后进行SDS-PAGE和放射自显影，结果显示有两条标记带：一条250 kDa的蛋白质复合物，对应于II型IGF受体；另一条135 kDa的带，对应于I型IGF受体。只有IGF-II能够从主要的250 kDa条带中取代125I-IGF-II的结合，而与次要的135 kDa条带结合的125I-IGF-II可被IGF-I、IGF-II或胰岛素取代。总之，在被视为胎盘阻力血管的干绒毛血管肌层中存在高水平的125I-IGF-II特异性结合位点。在胎儿-胎盘血管系统中，I型和II型IGF受体在IGF-II促生长作用中的参与情况仍有待确定。
