Expression And Regulation Of Amiloride Binding Protein 1 In Mouse Uterus During Early Pregnancy

Embryo implantation requires a precise synchronism between the receptive uterus and activated blastocyst. Embryo implantation is followed by decidualization, when stromal cells go through proliferation and differentiation. Histamine and polyamines play key roles in pregnancy. Uterine-derived histamine interacts with embryonic H2 receptors in a paracrine fashion to initiate the process of implantation; the balance of polyamines is important for cell proliferation and differentiation. Amiloride binding protein 1 (Abp1), an amine oxidase involved in the metabolism of histamine and putrescine, is important in the regulation of amine levels. In situ hybridization, real-time PCR and western blot was preformed to detect the expression of Abp1 in mouse uterus during early pregnancy. We also used pseudopregnancy, delayed implantation and activation, artificial decidualization and hormonal treatment models to study the regulation of Abp1 in uterus. In cultured uterine stromal cells, we examined the regulation of steroid hormones and induced decidualization on Abp1 expression. Using promoter assay, the effects of Cebpb and cAMP on Abp1 was also investigated.On day 5 of pregnancy, a high level of Abp1 mRNA signal was found in the subluminal stroma immediately surrounding the implanting blastocyst. From days 6 to 8, Abp1 was highly expressed in the primary decidua and increased during decidualization. There was no detectable Abp1 mRNA signal in the uterus from days 1 to 5 of pseudopregnancy or under delayed implantation. After delayed implantation was terminated by estrogen treatment, Abp1 expression was observed in the subluminal stroma cells surrounding the implanting blastocyst. Under artificial decidualization, no Abp1 mRNA signal was detected in the control horn, but the expression was strongly seen in the decidualized cells. Induction of decidualization in vitro confirmed the up-regulation of Abp1 expression during decidualization. cAMP treatment also elevated the level of Abp1. The endometrial stromal cells cultured in vitro was also used to determine whether steroid hormones could regulate Abp1 expression. In the cultured stromal cells, Abp1 expression was significantly stimulated by progesterone. Estrogen attenuated the up-regulated effect of progesterone. RU486 treatment before progesterone reversed the up-regulation of Abp1 by progesterone. These results showed that Abp1 is a downstream target of PR. With promoter assay, transcriptional factors CCAAT/enhancer binding proteinβ(Cebpb) binding sites were found in the promoter region of mouse Abp1 gene. Dual-luciferase activity assay confirmed the regulation of Cebpb on Abp1 expression. Abp1 promoter activity was significantly induced in primary uterine stromal cells by Cebpb. Site-directed mutagenesis of the Cebpb binding sites in Abp1 promoter abolished the upregulation of Abp1 promoter activity. Our results showed that the expression of Abp1 was dependent on the presence of active blastocyst and increased during the process of decidualization. Abp1 expression was under the regulation of progesterone, cAMP and Cebpb. In conclusion, our data suggested that Abp1 may play a key role during implantation and decidualization.