Inflammatory Mediators Enhance The Induction Of PTGS2 By Bradykinin Peptides In The Amnion And Its Implication In Parturition

Preterm delivery refers to delivery before 37 weeks of gestation.Preterm delivery is not only the primary cause of perinatal death,but also led to the long-term complications which seriously endangered the neonatal health and quality of life.Prostaglandin E2(PGE2)is one of the most pivotal factors in initiating preterm delivery,which was synthesized by prostaglandin endoperoxide synthase 2(PTGS2),the key rate limiting enzyme for PGE2.Therefore,up-regulation of amnion PTGS2 is very important for the initiation of labor and preterm delivery.Bradykinin(BK)is a type of small molecular polypeptide,which participates in important coagulation,inflammation and immune response in plasma and tissue.Research has found that BK is locally involved in the initiation of labor in decidua and myometrium,but as an important tissue involved in the initiation of labor,whether amnion contains bradykinin peptides and their receptors haven’t not been reported previously.In this study,we aimed to clarify the role and mechanism of bradykinin system in amnion tissue.In this study,we measured the abundance of bradykinin peptides,type 1(BDKRB1)and type 2(BDKRB2)bradykinin receptors m RNA between amnion tissue in-labor and the one not in-labor by real-time PCR and ELISA.We employed immunohistochemical staining and cellular immunofluorescence staining to determine the cellular position of BDKRB1 and BDKRB2.Human amnion fibroblasts were cultured in vitro to test the effects of BK and DABK on the expression of PTGS2 expression and PGE2 secretion of human amnion fibroblasts and the mechanism involved.We studied the enhancing effect of LPS and SAA1 on the expression of PTGS2 and the release of PGE2 promoted by BK and DABK.The results are as follows:1.Bradykinin peptides exist in the amnion tissue.Bradykinin receptors BDKRB1 and BDKRB2 are expressed in the amnion tissue,mainly in amnion fibroblasts.2.The bradykinin peptides abundance and their receptors BDKRB1 and BDKRB2 m RNA abundance were significantly higher in full-term and preterm inlabor amnion tissues than in full-term and preterm not in-labor tissues.3.In vitro experiments showed that BK and DABK improved the expression of PTGS2 in both m RNA and protein level and the release of PGE2 in amnion fibroblasts significantly by binding to BDKRB2 and BDKRB1 respectively.4.Both BK and DABK activated ERK1/2,p38 and JNK phosphorylation.BK and DABK up-regulated the expression of PTGS2 in amnion fibroblasts by activating ERK1/2/MAPK pathway and p38/MAPK phosphorylation,while JNK/MAPK pathway is not involved in the up-regulation of PTGS2 expression.5.LPS and SAA1 significantly induced the m RNA and protein expression of BDKRB1 and BDKRB2 in amnion fibroblasts.LPS and SAA1 enhanced the role of BK and DABK in promoting PTGS2 expression and PGE2 synthesis in amnion fibroblasts.In conclusion,we demonstrate for the first time the existence of bradykinin system in amnion membrane.As the main active ingredients in the bradykinin system,BK and DABK,bind to bradykinin receptors BDKRB2 and BDKRB1 respectively,induced PTGS2 m RNA and protein expression and promoted the release of PGE2 in amnion fibroblasts by activating ERK1/2/MAPK and p38/MAPK phosphorylation.LPS and SAA1 upregulated the expression of BDKRB1 and BDKRB2 and enhanced BK and DABK induced PTGS2 expression and PGE2 secretion in amnion fibroblasts.Our findings reveal that bradykinin system may involve in the initiation of labor in amnion tissue by inducing the expression of PTGS2 and PGE2 secretion which can be enhanced in inflammation condition.We believe the work provides a therapeutic target for the prevention and treatment of preterm birth.