Medical management of endometriosis: emerging evidence linking inflammation to disease pathophysiology.

Progesterone action normally mediates the balance between anti-inflammatory and proinflammatory processes throughout the female reproductive tract. However, in women with endometriosis, endometrial progesterone resistance, characterized by alterations in progesterone responsive gene and protein expression, is now considered a central element in disease pathophysiology. Recent studies additionally suggest that the peritoneal microenvironment of endometriosis patients exhibits altered physiological characteristics that may further promote inflammation-driven disease development and progression. Within this review, we summarize our current understanding of the pathogenesis of endometriosis with an emphasis on the role that inflammation plays in generating not only the progesterone-resistant eutopic endometrium but also a peritoneal microenvironment that may contribute significantly to disease establishment. Viewing endometriosis from the emerging perspective that a progesterone resistant endometrium and an immunologically compromised peritoneal microenvironment are biologically linked risk factors for disease development provides a novel mechanistic framework to identify new therapeutic targets for appropriate medical management.

Effect of TCDD exposure on CYP1A1 and CYP1B1 expression in explant cultures of human endometrium.

Endometriosis is a debilitating disease estimated to affect 10% of reproductive-age women and characterized by the growth of endometrial tissue outside of the uterus. The present study characterizes a human endometrial explant culture model for studying the direct effects of TCDD exposure by assessing the expression of CYP1A1 and CYP1B1 mRNA (Northern blotting), protein (Western blotting), and activity (7-ethoxyresorufin-O-deethylase; EROD) in explants cultured with and without TCDD. Explants were obtained at laparoscopy or laparotomy from women undergoing surgery for tubal ligation, endometriosis, or pelvic pain unrelated to endometriosis. The explants were cultured with 10 nM estradiol (E(2)) or 1 nM E(2) plus 500 nM progesterone (P(4)) with or without TCDD (first 24 h). The expression of CYP1A1 and CYP1B1 mRNA was greatest with 10 nM TCDD and increased up to 72 h after initial exposure. EROD activity increased up to 120 h. Explants from a secretory phase biopsy became reorganized in culture and formed a new epithelial membrane, while maintaining basic endometrial morphology and viability for up to 120 h. At 24 h, TCDD significantly increased CYP1A1 and CYP1B1 mRNA, and at 72 h, TCDD significantly increased EROD activity and CYP1B1 protein compared to explants cultured without TCDD for similar times. CYP1B1 protein also exhibited substantial constitutive expression that was similar in uncultured biopsies, where CYP1B1 protein was immunolocalized in the cytoplasm of epithelial glands, with only occasional patches of protein in the surface epithelial membrane. In explants cultured with and without TCDD exposure, CYP1B1 protein was localized in the cytoplasm of the new surface epithelial membrane and glands closest to the surface. CYP1A1 protein was not detected in uncultured biopsies or explants. Both younger age (age 30 and under) and proliferative phase were associated with higher TCDD-induced EROD activity in specimens treated with E(2):P(4). No significant endometriosis-related differences were observed for any of the biomarkers, but the detection of disease-specific change was limited by small sample size and variability in tissue-cycle phase. The human endometrial explant culture model will be useful for future studies of the effects of dioxin-like compounds on human endometrium in relationship to cycle phase and hormonal exposure.

Cyclic changes in the matrix metalloproteinase system in the ovary and uterus.

With each estrous or menstrual cycle, extensive alterations occur in the extracellular matrix and connective tissue of the ovary and uterus. In the ovary, these changes occur during follicular development, breakdown of the follicular wall and extrusion of the oocyte, as well as during the formation and regression of the corpus luteum. In the uterus, the endometrium undergoes dramatic connective tissue turnover associated with tissue breakdown and subsequent regrowth during each menstrual cycle. These changes in the ovarian and uterine extracellular architecture are regulated, in part, by the matrix metalloproteinase (MMP) system. This system is comprised of both a proteolytic component, the MMPs, and associated inhibitors, and it is involved in connective tissue remodeling processes throughout the body. The current review highlights the key features of the MMP system and focuses on the changes in the MMPs and the tissue inhibitors of metalloproteinases during the dynamic remodeling that takes place in the ovary and uterus during the estrous and menstrual cycles.

Progesterone exposure prevents matrix metalloproteinase-3 (MMP-3) stimulation by interleukin-1alpha in human endometrial stromal cells.

Suppression of endometrial matrix metalloproteinases (MMPs) is necessary to maintain tissue stability during the invasive events of implantation and placental development. Several laboratories have shown that inflammatory cytokines, including interleukin-lalpha (IL-1alpha), can oppose progesterone suppression of MMPs in the human endometrium. Furthermore, we have recently demonstrated colocalization of epithelial cell IL-1alpha and MMP-7 expression at sites of ectopic pregnancy. The current study extends these findings, revealing a previously unrecognized interrelationship between progesterone and IL-1alpha in regulation of MMP-3. Although IL-1alpha is a potent stimulator of MMP-3 in proliferative phase endometrium in organ culture, we demonstrate that progesterone exposure in vivo reduces IL-1alpha stimulation of MMP-3 in secretory phase tissue. This loss of sensitivity to IL-1alpha was duplicated in isolated stromal cells treated with progesterone in vitro, and IL-1alpha stimulation of MMP-3 returned in a dose-dependent manner with progesterone withdrawal. The antiprogestin, onapristone, partially blocked the ability of progesterone to prevent stimulation of MMP-3 by IL-1alpha. These data suggest a novel mechanism by which progesterone may preserve tissue integrity during the establishment and maintenance of pregnancy by limiting stimulation of MMPs by inflammatory cytokines such as IL-1a.

Retinoic acid synthesis and expression of cellular retinol-binding protein and cellular retinoic acid-binding protein type II are concurrent with decidualization of rat uterine stromal cells.

Decidualization of stromal cells at the site of embryo implantation in the rat uterus is accompanied by expression of cellular retinol-binding protein and cellular retinoic acid-binding protein [CRABP(II)], whose presence has been shown to correlate with gain of ability to synthesize retinoic acid in other cells. Here we examined whether decidual cells also acquired the ability to synthesize retinoic acid, which would have important implications for understanding the implantation process. Decidual cells were isolated from the uterus on day 8 of pregnancy and cultured. When provided with retinol, they indeed synthesized and released retinoic acid to the medium. To follow acquisition of this ability more closely, artificial induction of decidualization was exploited. Ovariectomized rats were placed on a hormonal regimen that allows decidualization to occur in vivo, with oil stimulation, or in vitro, if cells are isolated on day 5 of the regimen and then cultured. Decidualization in vivo reproduced the expression of cellular retinol-binding protein and CRABP(II) seen during pregnancy. Stromal cells isolated on regimen day 2 synthesized little retinoic acid and expressed little alkaline phosphatase, a marker of decidualization. Stromal cells isolated on regimen day 5 had elevated levels of alkaline phosphatase, increasing during the 3 days of culture examined. The ability of the stromal cells to synthesize retinoic acid showed the same pattern: a substantially elevated production from that previously observed, on day 2, with production increasing significantly over the next 2 culture days. Thus, expression of CRABP(II) was correlated with gain of ability to synthesize retinoic acid. Retinoid signaling may be an important part of the process of embryo implantation.

Paracrine regulation of matrix metalloproteinase expression in the normal human endometrium.

Endometrial expression of matrix metalloproteinase (MMP)-3, MMP-7 and MMP-11 occurs during menstrual breakdown and subsequent estrogen-mediated growth, but not during the secretory phase. These enzymes are suppressed by progesterone treatment. Paracrine factors, including transforming growth factor-beta (TGF-beta) and retinoic acid, are also critical for MMP regulation in the endometrium. In contrast, inflammatory cytokines such as interleukin-1alpha may block or interfere with steroid-mediated MMP regulation at ectopic sites of growth. Using in vitro models, our laboratory has investigated the complex interactions between progesterone and locally produced cytokines that may affect MMP expression during the development of endometriosis. Our results indicate that targeting the regulation of MMPs may represent an appropriate therapeutic strategy for the treatment of endometriosis. Copyrightz1999S. KargerAG,Basel

The potential role of environmental toxins in the pathophysiology of endometriosis.

Environmental contaminants that are known to disrupt steroid action can influence the development of reproductive diseases. Our group has focused on whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin) can disrupt steroid regulation of endometrial matrix metalloproteinase (MMP) expression. The MMPs regulate extracellular matrix turnover in normal tissues, but the inappropriate expression of these enzymes is associated with numerous disease states that involve invasive processes. We have previously shown that secretion of MMPs by human endometrium is critical for establishment of ectopic lesions in a nude mouse model of experimental endometriosis. In this report, we show that TCDD exposure promotes establishment of experimental endometriosis by interfering with the ability of progesterone to suppress endometrial MMP expression. Copyrightz1999S. KargerAG,Basel

Progesterone and transforming growth factor-beta coordinately regulate suppression of endometrial matrix metalloproteinases in a model of experimental endometriosis.

Endometriosis is a benign, though aggressive, disease of the female reproductive tract that consists of endometrial stromal and epithelial cells growing at an extrauterine site. Although it is widely accepted that the majority of cases of endometriosis result from the ectopic implantation of refluxed menstrual tissue, the precise mechanisms by which this disease becomes established are not well understood. Matrix metalloproteinases (MMPs), enzymes which are important for extracellular matrix turnover, have recently been implicated in the development of endometriosis. MMPs appear to be overexpressed in endometriotic lesions, but expression levels decrease following successful medical therapy. Intriguingly, although transforming growth factor-beta (TGF-beta) mediates progesterone suppression of specific endometrial MMPs, this growth factor is overexpressed in women with endometriosis. In the current study, we used an established experimental model of endometriosis to explore MMP regulation by TGF-beta. Our findings indicate that blocking the action of TGF-beta opposes progesterone-mediated suppression of MMPs and blocks the ability of this steroid to prevent experimental endometriosis. However, we also show that the action of TGF-beta does not lead to a sustained suppression of MMPs as observed following progesterone treatment. Taken together, our data suggest that in the absence of a normal progesterone response, common in ectopic lesions of endometriosis, sensitivity to TGF-beta may be altered, resulting in a failure to regulate MMPs.

Synthesis of retinoic acid by rat ovarian cells that express cellular retinoic acid-binding protein-II.

The induction of pseudopregnancy by the injection of eCG in rats results in the appearance of cellular retinoic acid-binding protein type II (CRABP[II]) in the granulosa cells of the ovary and the lining epithelium of the uterus within 48 h. This expression pattern is also seen in the normal mature female rat, in which CRABP(II) is expressed in the uterine epithelium during estrus (but not diestrus) and in the granulosa and luteal cells of the ovary. We have previously demonstrated that the uterine epithelial cells from the pseudopregnant rat have gained the ability to synthesize retinoic acid from retinol, in correlation with the induced expression of CRABP(II). If this is true for other sites of CRABP(II) expression, then local production of retinoic acid is intimately connected with various stages of reproduction in the female. Here we report that granulosa cells from the ovary of the eCG-treated immature rat and luteal cells from the ovary of the eCG/hCG-treated immature rat (both of which express CRABP[II]) synthesized markedly higher amounts of retinoic acid when cultured, compared to granulosa cells cultured from the ovary of the prepubertal rat treated with control vehicle. Culturing the granulosa cells from either control or eCG-treated animals had no effect on the expression of CRABP(II) cells. These data are consistent with our hypothesis that CRABP(II) expression is associated with retinoic acid synthesis and strengthen the case that local generation of retinoic acid plays an important role in reproduction.

Suppression of matrix metalloproteinases inhibits establishment of ectopic lesions by human endometrium in nude mice.

Matrix metalloproteinases of the stromelysin family are expressed in the human endometrium as a consequence of cellular events during the menstrual cycle that require extracellular matrix remodeling. We have recently documented the presence of these enzymes in lesions of endometriosis, a benign disease that presents as persistent ectopic sites of endometrial tissue, usually within the peritoneal cavity. Endometriosis can develop after retrograde menstruation of endometrial tissue fragments, and establishment of ectopic sites within the peritoneal cavity requires breakdown of extracellular matrix. To examine whether matrix metalloproteinases might contribute to the steroid-dependent epidemiology and cellular pathophysiology of endometriosis, we have developed an experimental model of endometriosis using athymic nude mice as recipients of human endometrial tissue. Our results demonstrate that estrogen treatment of human endometrial tissue in organ culture maintains secretion of matrix metalloproteinases, and promotes establishment of ectopic peritoneal lesions when injected into recipient animals. In contrast, suppressing metalloproteinase secretion in vitro with progesterone treatment, or blocking enzyme activity with a natural inhibitor of metalloproteinases, inhibits the formation of ectopic lesions in this experimental model.

Cellular retinoic acid-binding protein(II) presence in rat uterine epithelial cells correlates with their synthesis of retinoic acid.

Vitamin A (retinol) and retinoic acid are necessary for the maintenance of the female reproductive system of higher animals. Our previous work has demonstrated cell specific expression of cellular retinoic acid-binding protein (CRABP) and cellular retinoic-acid binding protein(II) [CRABP(II)] in the uterus of the rat. CRABP(II) expression was shown to be induced in the uterine surface epithelial cells by treatment of prepubertal rats with pregnant mare serum gonadotropin (PMSG). Here we report that, after PMSG treatment, collected uteri had markedly higher levels of retinoic acid than did the uteri of prepubertal rats treated with the control vehicle. Smooth muscle, stromal, and epithelial cells were then cultured from uteri from such animals and provided with retinol or with the retinol/retinol-binding protein complex. Retinoic acid production, analyzed by high-performance liquid chromatography, was observed for the epithelial cells from the uteri of prepubertal animals treated with PMSG, cells previously shown to express CRABP(II) and confirmed here to continue to express it in culture. Little or no retinoic acid was produced by cultured epithelial cells from the prepubertal uteri [shown previously to be negative for CRABP(II)] or by smooth muscle and stromal cells taken from uteri of prepubertal or PMSG-treated rats (shown previously to express CRABP). Retinoic acid production by uterine epithelial cells [and CRABP(II) expression] was also observed if the prepubertal rat was treated with estrogen before cell collection. At no time did cells expressing CRABP exhibit significant retinoic acid synthesis. Thus, this system revealed an important difference in retinoid metabolism between cells expressing CRABP and CRABP(II) and suggests CRABP(II) may participate in retinoic acid production and/or secretion.

Does disruption of immune and endocrine systems by environmental toxins contribute to development of endometriosis?

The proper function of the normal human endometrium relies on well organized cell-cell interactions regulated locally by cytokines and growth factors under the direction of steroid hormones. The onset and progression of the disease processes of endometriosis may result from disruptions of this well balanced cellular equilibrium. Evidence continues to accumulate indicating that environmental toxins, whether naturally occurring or man-made, may directly (hormone disruptor) or indirectly (immune toxin) affect the response of the endometrium to steroids, resulting in various pathological states including endometriosis.

Regulation and localization of cellular retinol-binding protein, retinol-binding protein, cellular retinoic acid-binding protein (CRABP), and CRABP II in the uterus of the pseudopregnant rat.

Three members of the superfamily of small intracellular carrier proteins for lipophilic compounds are cellular retinol-binding protein (CRBP), cellular retinoic acid-binding protein (CRABP), and cellular retinoic acid-binding protein II (CRABP II). Retinol-binding protein (RBP) is a secreted protein that binds and solubilizes vitamin A for transport. Here we report the coordinate regulation of RBP, CRBP, retinol, and CRABP II in the uterus of the pseudopregnant rat. In the proliferative stage of the uterus, which was induced by PMSG, the messenger RNA (mRNA) and protein levels of RBP and CRBP as well as retinol levels significantly decreased. This pattern of regulation was duplicated by estrogen treatment of prepubertal rats. In addition, CRBP and RBP were found to be colocalized to the stromal cells of the rat uterus by immunohistochemistry and [35S]methionine-labeled affinity chromatography, respectively, and were not detected in other cell populations. CRABP II mRNA and protein expression were up-regulated in the proliferative phase of the uterus brought about by PMSG injection or, alternatively, by estrogen treatment of prepubertal rats. CRABP II was localized to the surface epithelium, but was not seen elsewhere, including glandular epithelium. Immunolocalization of CRABP showed staining of the smooth muscle and stromal cells of the uterus. The appearance of CRABP in the stroma of the uterus also correlated with PMSG injection as well as estrogen treatment. Although estrogen induced the appearance of both binding proteins, CRABP mRNA levels peaked between 4-24 h postestrogen treatment, whereas CRABP II mRNA levels continued to rise 48 h postestrogen treatment. These data demonstrate an important role for vitamin A and retinoid-binding proteins in rat uterine physiology.

Transforming growth factor beta mediates the progesterone suppression of an epithelial metalloproteinase by adjacent stroma in the human endometrium.

Unlike most normal adult tissues, cyclic growth and tissue remodeling occur within the uterine endometrium throughout the reproductive years. The matrix metalloproteinases (MMPs), a family of structurally related enzymes that degrade specific components of the extracellular matrix are thought to be the physiologically relevant mediators of extracellular matrix composition and turnover. Our laboratory has identified MMPs of the stromelysin family in the cycling human endometrium, implicating these enzymes in mediating the extensive remodeling that occurs in this tissue. While the stromelysins are expressed in vivo during proliferation-associated remodeling and menstruation-associated endometrial breakdown, none of the stromelysins are expressed during the progesterone-dominated secretory phase of the cycle. Our in vitro studies of isolated cell types have confirmed progesterone suppression of stromal MMPs, but a stromal-derived paracrine factor was found necessary for suppression of the epithelial-specific MMP matrilysin. In this report, we demonstrate that transforming growth factor beta (TGF-beta) is produced by endometrial stroma in response to progesterone and can suppress expression of epithelial matrilysin independent of progesterone. Additionally, we find that an antibody directed against the mammalian isoforms of TGF-beta abolishes progesterone suppression of matrilysin in stromal-epithelial cocultures, implicating TGF-beta as the principal mediator of matrilysin suppression in the human endometrium.

Stromal-epithelial interaction mediates steroidal regulation of metalloproteinase expression in human endometrium.

The hallmark of the menstrual cycle is extensive steroid-dependent tissue turnover. Estrogen mediates endometrial cell growth and structural remodeling, whereas progesterone suppresses estrogen-dependent proliferation and promotes cellular differentiation. In nonfertile cycles, tissue degradation and menstruation occur as a consequence of steroidal deprivation as the ovarian corpus luteum fails. Stromal-epithelial interactions are recognized as a necessary component in mediating steroid-induced endometrial turnover. Specific mRNAs for metalloproteinases of the stromelysin family are expressed during endometrial growth and menstrual breakdown but are absent in the progestin-dominated secretory phase. This expression pattern suggests involvement of stromelysins in remodeling the extracellular matrix of the endometrium during tissue growth and breakdown and implicates progesterone in the suppression of these enzymes. We examined the regulation of endometrial stromelysins in explant cultures and found no acute effect of estradiol on their expression, whereas progesterone was a potent inhibitor of stromelysin expression. Progesterone also suppressed stromelysin expression in cultures of isolated stromal cells, but epithelial cells were progesterone insensitive. Coculture of recombined stromal and epithelial cells restored steroidal suppression of the epithelial-specific metalloproteinase. Our data confirm that progesterone inhibits endometrial stromelysins and further demonstrate the necessity for a stromal-derived factor(s) as a mediator of steroid suppression of an epithelial metalloproteinase.

Patterns of matrix metalloproteinase expression in cycling endometrium imply differential functions and regulation by steroid hormones.

Matrix metalloproteinases are a highly regulated family of enzymes, that together can degrade most components of the extracellular matrix. These proteins are active in normal and pathological processes involving tissue remodeling; however, their sites of synthesis and specific roles are poorly understood. Using in situ hybridization, we determined cellular distributions of matrix metalloproteinases and tissue inhibitor of metalloproteinase-1, an inhibitor of matrix metalloproteinases, in endometrium during the reproductive cycle. The mRNAs for all the metalloproteinases were detected in menstrual endometrium, but with different tissue distributions. The mRNA for matrilysin was localized to epithelium, while the others were detected in stromal cells. Only the transcripts for the 72-kD gelatinase and tissue inhibitor of metalloproteinases-1 were detected throughout the cycle. Transcripts for stromelysin-2 and the 92-kD gelatinase were only detected in late secretory and menstrual endometrium, while those for matrilysin, the 72-kD gelatinase, and stromelysin-3 were also consistently detected in proliferative endometrium. These data indicate that matrix metalloproteinases are expressed in cell-type, tissue, and reproductive cycle-specific patterns, consistent with regulation by steroid hormones, and with specific roles in the complex tissue growth and remodeling processes occurring in the endometrium during the reproductive cycle.