Department of Veterinary and Clinical Diagnostic Sciences, Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada.
Biol Reprod. 2020 Feb 12;102(1):170-184. doi: 10.1093/biolre/ioz157.
Preimplantation equine embryos synthesize and secrete fibrinogen, which is a peculiar finding as fibrinogen synthesis almost exclusively occurs in the liver. This study investigated the hypothesis that conceptus-derived fibrinogen mediates cell adhesion during fixation. On day 21 of pregnancy, five integrin subunits, including ITGA5, ITGB1, ITGAV, and ITGB1, displayed significantly higher transcript abundance than on day 16 of pregnancy. Endometrial epithelial cells adhered to fibrinogen in an integrin-dependent manner in an in vitro cell adhesion assay. Bilaminar trophoblast and allantochorion expressed fibrinogen transcript, indicating that fibrinogen expression persists past fixation. Preimplantation-phase endometrium, conceptuses, and microcotyledonary tissue expressed components of the clotting cascade regulating fibrin homeostasis, leaving open the possibility that fibrinogen is converted to fibrin. Fibrinogen is likely to have functions beyond mediating cell adhesion, such trapping growth factors and triggering signaling cascades, and has remarkable parallels to the expression of fibrinogen by some tumors. The deposition of fibrinogen within tumor stroma is characteristic of breast carcinoma, and tumor-derived fibrinogen has been implicated in the metastatic potential of circulating tumor cells. DNA methylation of the fibrinogen locus in equine conceptuses was examined in comparison to liver and endometrium, and across the full gene cluster, was significantly higher for endometrium than liver and conceptus. DNA methylation of regulatory regions did not differ between liver and conceptus, and was significantly lower than in endometrium. These results, therefore, support the hypothesis of DNA methylation being a regulator of fibrinogen expression in the conceptus.
胚胎植入前的马胚胎合成并分泌纤维蛋白原，这是一个特殊的发现，因为纤维蛋白原的合成几乎只发生在肝脏中。本研究旨在验证以下假说：即胚泡衍生的纤维蛋白原在固定过程中介导细胞黏附。在妊娠第 21 天，五个整合素亚基（包括 ITGA5、ITGB1、ITGAV 和 ITGB1）的转录丰度明显高于妊娠第 16 天。在体外细胞黏附试验中，子宫内膜上皮细胞以整合素依赖的方式黏附于纤维蛋白原。双层滋养层和羊膜绒毛均表达纤维蛋白原转录本，表明纤维蛋白原的表达在固定后仍持续存在。植入前阶段的子宫内膜、胚泡和微胎瓣组织表达调节纤维蛋白稳态的凝血级联反应的成分，这使得纤维蛋白原转化为纤维蛋白的可能性仍然存在。纤维蛋白原可能具有超越介导细胞黏附的功能，例如捕获生长因子和触发信号级联反应，并且与某些肿瘤表达纤维蛋白原具有显著的相似性。纤维蛋白原在肿瘤基质中的沉积是乳腺癌的特征，肿瘤衍生的纤维蛋白原已被牵连到循环肿瘤细胞的转移潜能中。本研究比较了马胚胎、肝脏和子宫内膜中纤维蛋白原基因座的 DNA 甲基化，并对整个基因簇进行了分析，结果显示，子宫内膜的 DNA 甲基化程度明显高于肝脏和胚胎。肝脏和胚胎之间的纤维蛋白原基因座的调控区 DNA 甲基化没有差异，且明显低于子宫内膜。因此，这些结果支持 DNA 甲基化是胚胎中纤维蛋白原表达的调控因子的假说。
