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Biological mechanisms underlying the clinical effects of RU 486: modulation of cultured endometrial stromal cell
1Department of Obstetrics and Gynecology, New York University Medical Center, New York 10016, USA.
Abstract:
During in vitro decidualization of human endometrial stromal cells (HESCs), medroxyprogesterone acetate (MPA) inhibits expression of the potent extracellular matrix (ECM)-degrading protease stromelysin-1 (MMP-3), but enhances PRL expression. Consistent with its priming role in vivo, estradiol (E2) augments these effects. In the current study, immunoblot analysis revealed that coincubation with 10(-6) M RU 486 blocked the inhibition in HESC-secreted MMP-3 levels (50,000 mol wt) evoked by 10(-8) M E2 + 10(-7) M MPA. Although MPA can act as a glucocorticoid, the HESCs were refractory to 10(-7) M dexamethasone added alone or with E2. Because E2 elevates progesterone but not glucocorticoid receptor levels, MPA and RU 486 control MMP-3 expression as a progestin and antiprogestin, respectively. To study RU 486 involvement in steroid withdrawal leading to menstruation, HESCs were decidualized during 10 days incubation with E2 + MPA, and parallel cultures were kept in E2 + MPA or withdrawn to either control or RU 486-containing medium. Compared with E2 + MPA-suppressed HESCs, increases in levels of secreted MMP-3 (2.0-fold), and its 2.1-kilobase messenger RNA (10-fold) were observed in HESCs after 4 days of withdrawal to control medium, with much greater increases seen in RU 486-containing medium (10-fold protein, 100-fold messenger RNA). Previously, we showed that RU 486 up-regulated E2 + MPA-inhibited plasminogen activator expression in the cultured HESCs. Extrapolation of these in vitro observations to endometrial events following RU 486 administration suggests that coordinate enhancement of MMP-3 and plasminogen activator expression promotes proteolysis of the stromal/decidual ECM, which leads to endometrial sloughing. Moreover, destabilization of endometrial microvessels resulting from degradation of their surrounding ECM is consistent with the heavy menstrual bleeding stemming from RU 486 administration. However, in contrast to the marked RU 486-initiated reversal of MMP-3 expression, RU 486 did not significantly reverse E2 + MPA-enhanced PRL secretion by the cultured HESCs. Interestingly, decidual PRL, unlike decidual MMP-3, does not appear to play a role in menstruation. Interleukin-1 beta counteracted E2 + MPA-mediated inhibition of secreted MMP-3 levels, implying that leukocyte/trophoblast-derived cytokines can modulate steroid-regulated MMP-3 expression by stromal/decidual cells during menstruation and pregnancy.
Insights
Medroxyprogesterone acetate (MPA) and estradiol (E2) regulate human endometrial stromal cell (HESC) extracellular matrix (ECM) degradation. RU 486, an antiprogestin, promotes MMP-3 expression, potentially causing endometrial sloughing and menstrual bleeding.
Area of Science:
- Reproductive Endocrinology
- Cell Biology
- Molecular Biology
Background:
- During in vitro decidualization, human endometrial stromal cells (HESCs) express specific proteins under steroid hormone influence.
- Medroxyprogesterone acetate (MPA) inhibits stromelysin-1 (MMP-3) but enhances prolactin (PRL) expression, effects augmented by estradiol (E2).
- The role of antiprogestins like RU 486 in modulating these steroid-regulated pathways is crucial for understanding menstruation.
Purpose of the Study:
- To investigate the role of RU 486 in controlling MMP-3 expression in HESCs during in vitro decidualization.
- To determine if RU 486 influences steroid withdrawal-induced changes in MMP-3 and PRL expression.
- To explore the implications of these findings for RU 486-induced endometrial events, including menstruation.
Main Methods:
- Immunoblot analysis was used to quantify protein levels of MMP-3 in HESCs.
- Messenger RNA (mRNA) levels for MMP-3 were assessed using specific assays.
- HESCs were cultured under various steroid treatments (E2, MPA, RU 486, dexamethasone) and withdrawal conditions.
Main Results:
- RU 486 blocked the inhibition of MMP-3 secretion by E2 + MPA.
- Withdrawal from E2 + MPA led to increased MMP-3 protein and mRNA levels, with significantly greater increases observed with RU 486.
- RU 486 reversed E2 + MPA-inhibited MMP-3 expression but did not significantly affect E2 + MPA-enhanced PRL secretion.
Conclusions:
- MPA and RU 486 act as a progestin and antiprogestin, respectively, in controlling MMP-3 expression in HESCs.
- RU 486-induced enhancement of MMP-3 and plasminogen activator expression likely promotes ECM proteolysis, leading to endometrial sloughing and bleeding.
- Decidual PRL does not appear to play a significant role in menstruation, unlike MMP-3.