Effects of mifepristone and progesterone on collagen synthesis in the human uterine cervix

Signaling Pathways Regulating Human Cervical Ripening in Preterm and Term Delivery

At the end of gestation, the cervical tissue changes profoundly. As a result of these changes, the uterine cervix becomes soft and vulnerable to dilation. The process occurring in the cervical tissue can be described as cervical ripening. The ripening is a process derivative of enzymatic breakdown and inflammatory response. Therefore, it is apparent that cervical remodeling is a derivative of the reactions mediated by multiple factors such as hormones, prostaglandins, nitric oxide, and inflammatory cytokines. However, despite the research carried out over the years, the cellular pathways responsible for regulating this process are still poorly understood. A comprehensive understanding of the entire process of cervical ripening seems crucial in the context of labor induction. Greater knowledge could provide us with the means to help women who suffer from dysfunctional labor. The overall objective of this review is to present the current understanding of cervical ripening in terms of molecular regulation and cell signaling.

Immunobiology of Cervix Ripening

The cervix is the essential gatekeeper for birth. Incomplete cervix remodeling contributes to problems with delivery at or post-term while preterm birth is a major factor in perinatal morbidity and mortality in newborns. Lack of cervix biopsies from women during the period preceding term or preterm birth have led to use of rodent models to advanced understanding of the mechanism for prepartum cervix remodeling. The critical transition from a soft cervix to a compliant prepartum lower uterine segment has only recently been recognized to occur in various mammalian species when progesterone in circulation is at or near the peak of pregnancy in preparation for birth. In rodents, characterization of ripening resembles an inflammatory process with a temporal coincidence of decreased density of cell nuclei, decline in cross-linked extracellular collagen, and increased presence of macrophages in the cervix. Although a role for inflammation in parturition and cervix remodeling is not a new concept, a comprehensive examination of literature in this review reveals that many conclusions are drawn from comparisons before and after ripening has occurred, not during the process. The present review focuses on essential phenotypes and functions of resident myeloid and possibly other immune cells to bridge the gap with evidence that specific biomarkers may assess the progress of ripening both at term and with preterm birth. Moreover, use of endpoints to determine the effectiveness of various therapeutic approaches to forestall remodeling and reduce risks for preterm birth, or facilitate ripening to promote parturition will improve the postpartum well-being of mothers and newborns.

Distinct reorganization of collagen architecture in lipopolysaccharide-mediated premature cervical remodeling

Previous work has identified divergent mechanisms by which cervical remodeling is achieved in preterm birth (PTB) induced by hormone withdrawal (mifepristone) or lipopolysaccharide (LPS). Our current study aims to document how collagen architecture is modified to achieve premature cervical remodeling in mice treated with LPS as a model of infection-induced inflammation. Cervices were collected on gestation day (d) 15 from mice with premature cervical ripening induced by LPS and compared to d15 and d18 controls as well as a hormone withdrawal PTB model. Second harmonic generation (SHG) and electron microscopy were utilized for visualization of collagen morphology and ultrastructure. LPS-mediated premature cervical ripening is characterized by unique structural changes in collagen fiber morphology. LPS treatment increased the interfibrillar spacing of collagen fibrils. A preferential disruption of collagen fiber architecture in the subepithelial region compared to midstroma region was evidenced by increased pores lacking collagen signal in SHG images in the LPS-treated mice. Coinciding with this alteration, the infiltration of neutrophils was concentrated in the subepithelial stromal region as compared to midstromal region implicating the potential role of immune cells to extracellular matrix reorganization in inflammation-induced preterm cervical ripening. The current study demonstrates a preferential disorganization of collagen interfibrillar spacing and collagen fiber structure in LPS-mediated ripening.

Contributions to the dynamics of cervix remodeling prior to term and preterm birth

Major clinical challenges for obstetricians and neonatologists result from early cervix remodeling and preterm birth. Complications related to cervix remodeling or delivery account for significant morbidity in newborns and peripartum mothers. Understanding morphology and structure of the cervix in pregnant women is limited mostly to the period soon before and after birth. However, evidence in rodent models supports a working hypothesis that a convergence of factors promotes a physiological inflammatory process that degrades the extracellular collagen matrix and enhances biomechanical distensibility of the cervix well before the uterus develops the contractile capabilities for labor. Contributing factors to this remodeling process include innervation, mechanical stretch, hypoxia, and proinflammatory mediators. Importantly, the softening and shift to ripening occurs while progesterone is near peak concentrations in circulation across species. Since progesterone is required to maintain pregnancy, the premise of this review is that loss of responsiveness to progesterone constitutes a common final mechanism for remodeling the mammalian cervix in preparation for birth at term. Various inputs are suggested to promote signaling between stromal cells and resident macrophages to drive proinflammatory processes that advance the soft cervix into ripening. With infection, pathophysiological processes may prematurely drive components of this remodeling mechanism and lead to preterm birth. Identification of critical molecules and pathways from studies in various rodent models hold promise for novel endpoints to assess risk and provide innovative approaches to treat preterm birth or promote the progress of ripening at term.

Progestin-Containing Contraceptives Alter Expression of Host Defense-Related Genes of the Endometrium and Cervix

Epidemiological studies indicate that progestin-containing contraceptives increase susceptibility to HIV, although the underlying mechanisms involving the upper female reproductive tract are undefined. To determine the effects of depot medroxyprogesterone acetate (DMPA) and the levonorgestrel intrauterine system (LNG-IUS) on gene expression and physiology of human endometrial and cervical transformation zone (TZ), microarray analyses were performed on whole tissue biopsies. In endometrium, activated pathways included leukocyte chemotaxis, attachment, and inflammation in DMPA and LNG-IUS users, and individual genes included pattern recognition receptors, complement components, and other immune mediators. In cervical TZ, progestin treatment altered expression of tissue remodeling and viability but not immune function genes. Together, these results indicate that progestins influence expression of immune-related genes in endometrium relevant to local recruitment of HIV target cells with potential to increase susceptibility and underscore the importance of the upper reproductive tract when assessing the safety of contraceptive products.

Effects of estrogen and progesterone on urinary bladder in female rabbit: evaluation by quantitative morphometric analysis

OBJECTIVES

To investigate possible effects of estrogen and/or progesterone on the histologic characteristics of female rabbit urinary bladders, we carried out quantitative morphometric analysis of the rabbit bladders.

METHODS

Mature female rabbits were treated by ovariectomy with and without successive estrogen and/or progesterone administration. Area densities of the connective tissue (CT) and smooth muscle (SM) cells, the area of single SM cells, and the thickness of the bladder wall were determined by computer-assisted quantitative morphometric analysis.

RESULTS

Six weeks after each treatment, ovariectomy alone resulted in a decrease in CT density of the bladder. Successive estrogen treatment increased the bladder wet weight and SM cell density within the bladder wall. Progesterone treatment reduced CT degradation in ovariectomized rabbits. Sex steroids did not significantly influence the area of each SM cell. There was no significant difference in histologic characteristics between the rabbits treated by estrogen alone and those treated by combination (estrogen and progesterone) therapy.

CONCLUSIONS

Ovariectomy and successive hormonal replacement therapy resulted in morphologic changes within the rabbit urinary bladder. Cotreatment with progesterone did not significantly change the morphologic findings produced by estrogen treatment alone.