The Expression And Function Of C-type Natriuretic Peptide And Its Receptor NPR-B In Mouse Uterus During Early Pregnancy

Embryo implantation and decidualization are crucial during early pregnancy.C-type natriuretic peptide(CNP)belongs to the natriuretic peptide family and exerts its biological effects predominantly through autocrine or paracrine fashion.Many studies have shown that CNP and its specific receptor natriuretic peptide receptor B(NPR-B)are highly expressed in human gonads,placenta and embryonic tissues,and play an important role in reproductive processes,such as oocyte maturation and spermatogenesis.Although CNP expression in mouse uterus has been reported,the regulation and function of CNP during embryo implantation and decidualization are still unclear.We examined the expression and localization of Cnp and its receptors in the uterus of early pregnancy,delayed and activated implantation,hormone treatment using in situ hybridization.Cnp was expressed in endometrial epithelial and glandular epithelium from days 1 to 4 of pregnancy.The strongest expression was detected on day 5,mainly in the subluminal stromal cells around the implantating blastocyst.On days 6 to 8,Cnp was expressed in the primary decidual area and the embryo.Compared to delayed implantation,Cnp was mainly detected in the subluminal stromal cells surrounding implanting blastocysts when delayed implantation was terminated by estrogen.Uterine Cnp was significantly induced by estrogen in a time-dependent manner.The estrogen stimulation of Cnp expression was abolished in ERα knockout mice,suggesting that estrogen regulates Cnp expression mainly though ERα.Under in vitro decidualization,there was a 10 folds increase of Cnp expression.Dtprp expression was upregulated by exogenous CNP,and CNP siRNA also increased Dtprp expression.Cnp expression was up-regulated 8 folds in mouse stromal cell by norepinephrine in a concentration dependent manner.Cnp was also induced about 5 folds by the treatment of 25 ?M epinephrine.Cnp was significantiy upregulated by 9 ?M corticosterone,which was abrogated by RU486,suggesting that corticosterone stimulates Cnp expression through its receptor.In both ovariectomy and adrenalectomy mouse model,corticosterone treatment could stimulate Cnp mRNA expression in a time-and concentration-dependent manner.Based on our prediction,there were many Egr2 binding sites in Cnp promoter.The expression of Cnp was upregulated after mouse stromal cells were treated with Egr2 siRNA,indicating that Egr2 is a negative regulator of Cnp.In conclusion,Cnp may play a role during decidualization and is regulated by different hormones.