Modulation of Progesterone Receptor Isoform Expression in Pregnant Human Myometrium

Abstract

Background. Regulation of myometrial progesterone receptor (PR) expression is an unresolved issue central to understanding the mechanism of functional progesterone withdrawal and initiation of labor in women. Objectives. To determine whether pregnant human myometrium undergoes culture-induced changes in PR isoform expression ex situ and, further, to determine if conditions approaching the in vivo environment stabilise PR isoform expression in culture. Methods. Term nonlaboring human myometrial tissues were cultured under specific conditions: serum supplementation, steroids, stretch, cAMP, PMA, PGF2α, NF-κB inhibitors, or TSA. Following 48 h culture, PR-T, PR-A, and PR-B mRNA levels were determined using qRT-PCR. PR-A/PR-B ratios were calculated. Results. PR-T and PR-A expression and the PR-A/PR-B ratio significantly increased in culture. Steroids prevented the culture-induced increase in PR-T and PR-A expression. Stretch blocked the effects of steroids on PR-T and PR-A expression. PMA further increased the PR-A/PR-B ratio, while TSA blocked culture-induced increases of PR-A expression and the PR-A/PR-B ratio. Conclusion. Human myometrial tissue in culture undergoes changes in PR gene expression consistent with transition toward a laboring phenotype. TSA maintained the nonlaboring PR isoform expression pattern. This suggests that preserving histone and/or nonhistone protein acetylation is critical for maintaining the progesterone dependent quiescent phenotype of human myometrium in culture.

Methods and Model Systems Used to Study Pregnant Human Uterine Smooth Muscle

“…Furthermore, it has been shown that the onset of labor is associated with increased abundance of PR-A mRNA, and an increase in the PR-A/PR-B expression ratio in term human myometrium [82]. The observation that PR-A mRNA abundance and the PR-A/PR-B expression ratio significantly increased during in vitro incubation is therefore once again consistent with the non-laboring tissue pieces transitioning to a labor-like state as a consequence of in vitro conditions [88]. Performing in vitro experiments using myometrium that is in a state of flux is not ideal, and raises the possibility that the relevant literature may contain findings reported for 'non-laboring' tissue that were in fact obtained with myometrium that was actively transitioning, or had already transitioned to, a laboring phenotype.…”

“…In light of these findings, Ilicic et al [88] further examined whether myometrial tissue pieces undergo culture-induced changes in PGR isoform expression that are consistent with transition to a pro-contractile, labor-like phenotype. It was revealed that progesterone receptor A (PR-A) mRNA abundance increased after just 1 h culture, whereas progesterone receptor B (PR-B) mRNA abundance remained constant [88]. The net effect was a statistically significant increase in the PR-A/PR-B expression ratio after just 6 h of in vitro incubation [88].…”

“…It was revealed that progesterone receptor A (PR-A) mRNA abundance increased after just 1 h culture, whereas progesterone receptor B (PR-B) mRNA abundance remained constant [88]. The net effect was a statistically significant increase in the PR-A/PR-B expression ratio after just 6 h of in vitro incubation [88]. This was consistent with previous reports that PR-A protein abundance increased during labor, while levels of PR-B were not altered by labor status [89].…”

“…Performing in vitro experiments using myometrium that is in a state of flux is not ideal, and raises the possibility that the relevant literature may contain findings reported for 'non-laboring' tissue that were in fact obtained with myometrium that was actively transitioning, or had already transitioned to, a laboring phenotype. To address this, the authors sought to identify culture conditions that could be implemented to maintain a non-laboring state, whereby ex vivo myometrial tissue pieces retained high OXTR mRNA expression, low ESR1, PTGS2 and PR-A mRNA expression, as well as a low PR-A/PR-B expression ratio (<1; a PR-B dominant state), thereby providing a more appropriate in vitro model for conducting studies into myometrial biology [81,88]. Adding progesterone to culture media prevented the culture-induced increase in ESR1, but failed to prevent culture-induced increases in PTGS2 [81].…”

Progesterone through Progesterone Receptor B Isoform Promotes Rodent Embryonic Oligodendrogenesis

“…In the brain and the spinal cord, they present a different expression pattern, regulation, and function [31][32][33][34][35]. Generally, given that the PR-B is a more potent transcription activator than the PR-A, the former is the positive regulator of the genomic effects of progesterone, whereas PR-A is mainly a transcriptional repressor [36][37][38].…”