The Study On The Effect Of PR Promoter Acetylation To Labor Onset That Before And After The Parturition

There are a lot theories about labor onset, but the the cellular and molecularmechanisms that how uterine smooth muscle cells enhance their contractility gradually tolaunch the labor from a quiescent condition is still unclear. The status of uterine smoothmuscle cells are controlled by various hormones, and the progesterone is the most importantone which inhibit the calcium transport protein and the secretion of oxytocin, promoting theexpression of β-adrenergic receptor to maintain the quiescent condition of smooth musclecells(SMCs).The labor onset of most non-primates that always accompanied by the decline ofplasmic progesterone is different from the delivery of human being that the level of plasmicestrogen and progesterone was elevated together. Other researches find RU486, anantagonist of progesterone receptor, can induce uterine contraction and end the pregnancyat any time during the gestation. which suggest that withdrawl of progesterone may play animportant role in the delivery of human being. All the evidences imply that the “functionalprogesterone withdrawl” may play a key role in the labor onset, even though the level ofplasmic progesterone doesn’t go down.Current studies peculate the mechanisms of “functional progesterone withdrawl” mayinclude the progesterone inactivation induced by environmental change of uterine SMCs,transformation of progesterone receptor(PR) subtypes, the transcriptional activity change ofPR induced by coactivators and retroinhibition of NFκB. Among them, the hypothesis ofPR subtypes transformation which lead to a sensitivity alteration of uterine SMCs toprogesterone is supported by experimental evidences.Human PR gene cantains8exons, locates in11q22-23, and the length is more than90kb. PRA and PRB are two subtypes of PR, and the former one lacks164amino acidsfrom N-terminal which contain a AF3transcriptional activation domain than the latter one.PRB has a transcriptional activation which can be inhibited by PRA. In the other hand, PRB can induce the uterine SMCs relaxation but can be antagonized by PRA. A plenty ofevidences show that PRB expression is elevated related to PRA, which result in analteration of their proportion can change the sensitivity of uterine SMCs to progesterone.All of that imply the alteration of PR subtypes has a significance for labor onset. Someepigenetic studies on PR reveal that both of DNA methylation and histone acetylation caninfluence the expression of PRA and PRB dramatically. To be specific, DNA methylationand histone acetylation can silence PR gene and down-regulate PR protein, and the DNAdemethylation and histone deacetylation will active PR gene and up-regulate PR protein.We can speculate logically that epigenetic modification of PR gene whicn alter theexpressions of PRA and PRB and even their proportion may play an important role in themechanism of “functional progesterone withdrawl”.Our research target the uterine smooth muscle tissue to detect the alteration of PRAand PRB expression through immunohistochemistry, western blot, Realtime PCR and todetect the histone acetylation level of PR promoter region through chromatinimmunoprecipitation(ChIP). And the methylation level and acetylation level of promoterregions of PRA and PRB had also been detected after SMCs was incubated with the histoneacetylase inhibitor (trichostatinA, TSA) or H3K4methylase inhibitor (5’-deoxy-5’-methylthioadenosine, MTA) before and after parturition. All above was to observe whetherthe acetylation level of PR promoter region changes after the labor onset, whether acetylatemodification of PR promoter region influences PRB expression and whether acetylatemodification of PR promoter region correlates with mechanism of labor onset induced by“functional progesterone withdrawl”. Eventually, we turned to provide the precaution ofpremature labor and postmature birth with new theoretical basis.The detection of ChIP shows that H3, H4acetylation and H3K4trimethylation of PRApromoter region was elevated in the parturient uterine SMCs compared with non-parturient,but PRB’s has no obvious change. Accordingly, we speculate that the elevation of PRA inparturient uterine SMCs was caused by the H3, H4acetylation and H3K4trimethylation.Then the non-parturient uterine SMCs were purified, cultured and incubated with TSA andMTA. We found TSA would elevated the PRA mRNA expression obviously and that MTAplayed a opposite role. ChIP results showed that TSA and MTA could affected H3, H4acetylation and H3K4trimethylation of PRA promoter region signally and then afftected the ratio of PRA/PRB, which implied the H3, H4acetylation and H3K4trimethylation ofuterine SMCs changed PRA/PRB ratio in virtue of the adjustment of PRA expression.Our results show PRA and PRB expressed on the nuclei of both parturient andnon-parturient uterine SMCs. A significant differences existed in PRA expression beforeand after the labor onset, but not in PRB expression, and the PRA/PRB ratio changedobviously at last. All above illustrate that the elevations of PRA expression and PRA/PRBratio may related to the labor onset.