Drastic induction of MMP-7 by cortisol in the human amnion: implications for membrane rupture at parturition

Paradoxical Induction of ALOX15/15B by Cortisol in Human Amnion Fibroblasts: Implications for Inflammatory Responses of the Fetal Membranes at Parturition

Inflammation of the fetal membranes is an indispensable event of parturition, with increasing prostaglandin E2 (PGE2) synthesis as one of the ultimate products that prime labor onset. In addition to PGE2, the fetal membranes also boast a large capacity for cortisol regeneration. It is intriguing how increased PGE2 synthesis is achieved in the presence of increasing amounts of classical anti-inflammatory glucocorticoids in the fetal membranes at parturition. 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) synthesized by lipoxygenase 15/15B (ALOX15/15B) has been shown to enhance inflammation-induced PGE2 synthesis in amnion fibroblasts. Here, we examined whether glucocorticoids could induce ALOX15/15B expression and 15(S)-HETE production to promote PGE2 synthesis in amnion fibroblasts at parturition. We found that cortisol and 15(S)-HETE abundance increased parallelly in the amnion at parturition. Cortisol induced ALOX15/15B expression and 15(S)-HETE production paradoxically in amnion fibroblasts. Mechanism study revealed that this paradoxical induction was mediated by p300-mediated histone acetylation and interaction of glucocorticoid receptor with transcription factors CREB and STAT3. Conclusively, cortisol regenerated in the fetal membranes can paradoxically induce ALOX15/15B expression and 15(S)-HETE production in human amnion fibroblasts, which may further assist in the induction of PGE2 synthesis in the inflammatory responses of the fetal membranes for parturition.

ER-phagy Is Involved in the Degradation of Collagen I by IL-1β in Human Amnion in Parturition

The process of parturition is associated with inflammation within the uterine tissues, and IL-1β is a key proinflammatory cytokine involved. Autophagy is emerging as an important pathway to remove redundant cellular components. However, it is not known whether IL-1β employs the autophagy pathway to degrade collagen, thereby participating in membrane rupture at parturition. In this study, we investigated this issue in human amnion. Results showed that IL-1β levels were significantly increased in human amnion obtained from deliveries with spontaneous labor and membrane rupture, which was accompanied by decreased abundance of COL1A1 and COL1A2 protein but not their mRNA, the two components of collagen I. Consistently, IL-1β treatment of cultured primary human amnion fibroblasts reduced COL1A1 and COL1A2 protein but not their mRNA abundance along with increased abundance of autophagy activation markers, including the microtubule-associated protein L chain 3β II/I ratio and autophagy-related 7 (ATG7) in the cells. The reduction in COL1A1 and COL1A2 protein abundance induced by IL-1β could be blocked by the lysosome inhibitor chloroquine or small interfering RNA-mediated knockdown of ATG7 or ER-phagy receptor FAM134C, suggesting that FAM134C-mediated ER-phagy was involved in IL-1β-induced reduction in COL1A1 and COL1A2 protein in amnion fibroblasts. Consistently, levels of L chain 3β II/I ratio, ATG7, and FAM134C were significantly increased in human amnion obtained from deliveries with spontaneous labor and membrane rupture. Conclusively, increased IL-1β abundance in human amnion may stimulate ER-phagy-mediated COL1A1 and COL1A2 protein degradation in amnion fibroblasts, thereby participating in membrane rupture at parturition.

Cortisol Stimulates Local Progesterone Withdrawal Through Induction of AKR1C1 in Human Amnion Fibroblasts at Parturition

Fetal membrane activation is seen as being one of the crucial triggering components of human parturition. Increased prostaglandin E2 (PGE2) production, a common mediator of labor onset in virtually all species, is recognized as one of the landmark events of membrane activation. Fetal membranes are also equipped with a high capacity of cortisol regeneration by 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1), and the cortisol regenerated potently induces PGE2 synthesis, an effect normally suppressed by progesterone during gestation. There is no precipitous decline of progesterone synthesis in human parturition. It is intriguing how this suppression is lifted in parturition. Here, we investigated this issue by using human amnion tissue and primary amnion fibroblasts which synthesize the most PGE2 in the fetal membranes. Results showed that the expression of 11β-HSD1 and aldo-keto reductase family 1 member C1 (AKR1C1), a progesterone-inactivating enzyme, increased in parallel in human amnion tissue with gestational age toward the end of gestation and at parturition. Cortisol induced AKR1C1 expression via the transcription factor CCAAT enhancer binding protein δ (C/EBPδ) in amnion fibroblasts. Inhibition of AKR1C1 not only blocked progesterone catabolism induced by cortisol, but also enhanced the suppression of cortisol-induced cyclooxygenase-2 (COX-2) expression by progesterone in amnion fibroblasts. In conclusion, our results indicate that cortisol regenerated in the fetal membranes triggers local progesterone withdrawal through enhancement of AKR1C1-mediated progesterone catabolism in amnion fibroblasts, so that the suppression of progesterone on the induction of COX-2 expression and PGE2 synthesis by cortisol can be lifted for parturition.

C/EBPδ drives key endocrine signals in the human amnion at parturition

Amnion-derived prostaglandin E2 (PGE2) and cortisol are key to labor onset. Identification of a common transcription factor driving the expression of both cyclooxygenase-2 (COX-2) and 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1), the key enzymes in their production, may hold the key to the treatment of pre-term labor. Here, we have found that the CCAAT enhancer binding protein δ (C/EBPδ) is such a transcription factor which underlies the feed-forward induction of COX-2 and 11β-HSD1 expression by their own products PGE2 and cortisol in human amnion fibroblasts so that their production would be ensured in the amnion for the onset of labor. Moreover, the abundance of C/EBPδ in the amnion increases along with COX-2 and 11β-HSD1 at term and further increases at parturition. Knockout of C/EBPδ in mice delays the onset of labor further supporting the concept. In conclusion, C/EBPδ pathway may be speculated to serve as a potential pharmaceutical target in the amnion for treatment of pre-term labor.

Collagen at the maternal-fetal interface in human pregnancy

The survival and development of a semi-allogenic fetus during pregnancy require special immune tolerance microenvironment at the maternal fetal interface. During the establishment of a successful pregnancy, the endometrium undergoes a series of changes, and the extracellular matrix (ECM) breaks down and remodels. Collagen is one of the most abundant ECM. Emerging evidence has shown that collagen and its fragment are expressed at the maternal fetal interface. The regulation of expression of collagen is quite complex, and this process involves a multitude of factors. Collagen exerts a critical role during the successful pregnancy. In addition, the abnormal expressions of collagen and its fragments are associated with certain pathological states associated with pregnancy, including recurrent miscarriage, diabetes mellitus with pregnancy, preeclampsia and so on. In this review, the expression and potential roles of collagen under conditions of physiological and pathological pregnancy are systematically discussed.

Cortisol Regeneration in the Fetal Membranes, A Coincidental or Requisite Event in Human Parturition?

The fetal membranes are equipped with high capacity of cortisol regeneration through the reductase activity of 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1). The expression of 11β-HSD1 in the fetal membranes is under the feedforward induction by cortisol, which is potentiated by proinflammatory cytokines. As a result, the abundance of 11β-HSD1 increases with gestational age and furthermore at parturition with an escalation of cortisol concentration in the fetal membranes. Accumulated cortisol takes parts in a number of crucial events pertinent to the onset of labor in the fetal membranes, including extracellular matrix (ECM) remodeling and stimulation of prostaglandin output. Cortisol remodels the ECM through multiple approaches including induction of collagen I, III, and IV degradation, as well as inhibition of their cross-linking. These effects of cortisol are executed through activation of the autophagy, proteasome, and matrix metalloprotease 7 pathways, as well as inhibition of the expression of cross-linking enzyme lysyl oxidase in mesenchymal cells of the membranes. With regard to prostaglandin output, cortisol not only increases prostaglandin E2 and F2α syntheses through induction of their synthesizing enzymes such as cytosolic phospholipase A2, cyclooxygenase 2, and carbonyl reductase 1 in the amnion, but also decreases their degradation through inhibition of their metabolizing enzyme 15-hydroxyprostaglandin dehydrogenase in the chorion. Taking all together, data accumulated so far denote that the feedforward cortisol regeneration by 11β-HSD1 in the fetal membranes is a requisite event in the onset of parturition, and the effects of cortisol on prostaglandin synthesis and ECM remodeling may be enhanced by proinflammatory cytokines in chorioamnionitis.

Reversible EMT and MET mediate amnion remodeling during pregnancy and labor

The amnion is remodeled during pregnancy to protect the growing fetus it contains, and it is particularly dynamic just before and during labor. By combining ultrastructural, immunohistochemical, and Western blotting analyses, we found that human and mouse amnion membranes during labor were subject to epithelial-to-mesenchymal transition (EMT), mediated, in part, by the p38 mitogen-activated protein kinase (MAPK) pathway responding to oxidative stress. Primary human amnion epithelial cell cultures established from amnion membranes from nonlaboring, cesarean section deliveries exhibited EMT after exposure to oxidative stress, and the pregnancy maintenance hormone progesterone (P4) reversed this process. Oxidative stress or transforming growth factor-β (TGF-β) stimulated EMT in a manner that depended on TGF-β-activated kinase 1 binding protein 1 (TAB1) and p38 MAPK. P4 stimulated the reverse transition, MET, in primary human amnion mesenchymal cells (AMCs) through progesterone receptor membrane component 2 (PGRMC2) and c-MYC. Our results indicate that amnion membrane cells dynamically transition between epithelial and mesenchymal states to maintain amnion integrity and repair membrane damage, as well as in response to inflammation and mechanical damage to protect the fetus until parturition. An irreversible EMT and the accumulation of AMCs characterize the amnion membranes at parturition.

Involvement of STAT3 in the synergistic induction of 11β-HSD1 by SAA1 and cortisol in human amnion fibroblasts

PROBLEM

Cortisol, which is regenerated from biologically inactive cortisone by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in human fetal membranes, may play an important role in human parturition. Recently, we have demonstrated that human fetal membranes are capable of de novo synthesis of serum amyloid A1 (SAA1), an acute-phase protein of inflammation, and SAA1 may be engaged in multiple actions associated with human parturition. It remains to be determined whether SAA1 can interact with cortisol in the regulation of 11β-HSD1 in the fetal membranes.

METHOD OF STUDY

In the current study, we examined the regulation of 11β-HSD1 expression by SAA1, and the interaction between SAA1 and cortisol in the regulation of 11β-HSD1 expression in primary human amnion fibroblasts and amnion tissue.

RESULTS

Either SAA1 or cortisol induced 11β-HSD1 expression in a concentration-dependent manner. Combination of SAA1 and cortisol synergistically enhanced 11β-HSD1 expression. Mechanism studies revealed that SAA1 and cortisol induced the phosphorylation of the transcription factor STAT3 in a sequential order with the induction by SAA1 preceding the induction by cortisol. Furthermore, the induction of 11β-HSD1 expression by either SAA1 or cortisol or combination of SAA1 and cortisol was blocked by STAT3 inhibition with its antagonist S3I-201 or siRNA-mediated knockdown.

CONCLUSION

This study has demonstrated that SAA1 and cortisol can reinforce each other in the induction of 11β-HSD1 expression through sequential phosphorylation of STAT3. The synergistic enhancement of 11β-HSD1 expression by SAA1 and cortisol may lead to excessive cortisol accumulation in the fetal membranes at parturition.

Involvement of serum amyloid A1 in the rupture of fetal membranes through induction of collagen I degradation

The de novo synthesis of serum amyloid A1 (SAA1) is augmented in human fetal membranes at parturition. However, its role in parturition remains largely unknown. Here, we investigated whether SAA1 was involved in the rupture of fetal membranes, a crucial event in parturition accompanied with extensive degradation of collagens. Results showed that SAA1 decreased both intracellular and extracellular COL1A1 and COL1A2 abundance, the two subunits of collagen I, without affecting their mRNA levels in human amnion fibroblasts. These reductions were completely blocked only with inhibition of both matrix metalloproteases (MMPs) and autophagy. Consistently, SAA1 increased MMP-2/9 abundance and the markers for autophagic activation including autophagy related (ATG) 7 (ATG7) and the microtubule-associated protein light chain 3 β (LC3B) II/I ratio with the formation of LC3 punctas and autophagic vacuoles in the fibroblasts. Moreover, the autophagic degradation of COL1A1/COL1A2 and activation of MMP-2/9 by SAA1 were blocked by inhibitors for the toll-like receptors 2/4 (TLR2/4) or NF-κB. Finally, reciprocal corresponding changes of SAA1 and collagen I were observed in the amnion following spontaneous rupture of membranes (ROM) at parturition. Conclusively, SAA1 may participate in membrane rupture at parturition by degradating collagen I via both autophagic and MMP pathways. These effects of SAA1 appear to be mediated by the TLR2/4 receptors and the NF-κB pathway.