Up-regulation of the human prolactin receptor in the endometrium

Unveiling the Pathogenesis of Adenomyosis through Animal Models

Background: Adenomyosis is a common gynecological disorder traditionally viewed as “elusive”. Several excellent review papers have been published fairly recently on its pathogenesis, and several theories have been proposed. However, the falsifiability, explanatory power, and predictivity of these theories are often overlooked. Since adenomyosis can occur spontaneously in rodents and many other species, the animal models may help us unveil the pathogenesis of adenomyosis. This review critically tallies experimentally induced models published so far, with a particular focus on their relevance to epidemiological findings, their possible mechanisms of action, and their explanatory and predictive power. Methods: PubMed was exhaustively searched using the phrase “adenomyosis and animal model”, “adenomyosis and experimental model”, “adenomyosis and mouse”, and “adenomyosis and rat”, and the resultant papers were retrieved, carefully read, and the resultant information distilled. All the retrieved papers were then reviewed in a narrative manner. Results: Among all published animal models of adenomyosis, the mouse model of adenomyosis induced by endometrial–myometrial interface disruption (EMID) seems to satisfy the requirements of falsifiability and has the predictive capability and also Hill’s causality criteria. Other theories only partially satisfy Hill’s criteria of causality. In particular, animal models of adenomyosis induced by hyperestrogenism, hyperprolactinemia, or long-term exposure to progestogens without much epidemiological documentation and adenomyosis is usually not the exclusive uterine pathology consequent to those induction procedures. Regardless, uterine disruption appears to be a necessary but not sufficient condition for causing adenomyosis. Conclusions: EMID is, however, unlikely the sole cause for adenomyosis. Future studies, including animal studies, are warranted to understand how and why in utero and/or prenatal exposure to elevated levels of estrogen or estrogenic compounds increases the risk of developing adenomyosis in adulthood, to elucidate whether prolactin plays any role in its pathogenesis, and to identify sufficient condition(s) that cause adenomyosis.

Prolactin receptor in human endometriotic tissues

BACKGROUND

Augmented serum prolactin (PRL) levels have been implicated as a cause for infertility in patients with endometriosis. However, it has not been established whether this lactogenic hormone or its receptor (PRLR) have specific effects on the development of human endometriosis. In the present study we assessed PRLR expression in human endometriotic and normal tissue.

METHODS

Fourteen patients with laparoscopically proven endometriosis were recruited and the negative or positive expression of the PRLR in normal endometrial and endometriotic tissues obtained during the mid-late proliferative phase of the menstrual cycle was evaluated by RT-PCR. Evaluation of serum prolactin, and peritoneal fluid estradiol content were carried out by specific radioimmunoassays (RIA).

RESULTS

In endometriotic tissue samples the corresponding 1048 bp PRLR transcript was negative in 12/14 of the samples (86%) and positive in two samples (14%). The opposite was seen in normal tissue, since PRLR expression was positive in 11/14 samples (79%) and negative in the remaining three samples (21%). There was an association between serum prolactin concentrations and PRLR expression in normal tissue but not in endometriotic tissue.

CONCLUSIONS

The PRLR is expressed in normal endometrium, while cells of the endometriotic tissues did not express the PRLR, at least during the mid-late proliferative phase of the menstrual cycle. The absence of the PRLR in the endometriotic tissues could not be correlated with the serum prolactin levels. These results suggest the existence of differential regulation of PRLR expression between normal and endometriotic tissue.

Expression of prolactin and its receptor in the baboon uterus during the menstrual cycle and pregnancy

PRL is known to be a major secretory product of the human decidua. However, the physiological role of decidual PRL during the menstrual cycle and pregnancy has not been fully defined, primarily due to the lack of an appropriate nonhuman primate model for in vivo studies. Therefore, this initial study examined the expression of PRL and its receptor in the baboon uterus during the cycle and pregnancy. PRL and PRL receptor messenger ribonucleic acid expression were detected by semiquantitative RT-PCR, and protein was localized by immunocytochemistry. PRL was shown to be expressed in myometrial smooth muscle during the follicular phase by both RT-PCR and immunocytochemistry. Expression of PRL messenger ribonucleic acid and protein was first observed in the epithelial cells of the deep basal glands during the late luteal phase. With the onset of pregnancy, PRL expression increased steadily and was evident primarily in the decidual tissue. In contrast to PRL, its receptor was expressed at constant levels in both the myometrium and endometrium during the cycle. An increase in receptor expression was evident in both the decidua and placenta throughout pregnancy. In summary, these results demonstrate that the baboon uterus is a site of both PRL production and action during the cycle and pregnancy. These studies establish the baboon as a nonhuman primate model to investigate the potential roles of PRL in implantation and maintenance of pregnancy.

Localization and temporal expression of prolactin receptor in human endometrium

Extrapituitary PRL is synthesized by the decidualized endometrial stromal cells from the mid to late secretory phase in the nonpregnant cycle and throughout pregnancy. The function of PRL in the uterus is unknown, but the temporal expression indicates a role in implantation and placentation. PRL is a powerful immunoregulatory agent, and thus, a role in modulating endometrial leukocytes may be envisaged. To investigate the site of action of PRL, immunohistochemistry was conducted to localize the PRL receptor (PRL-R). In addition, ribonucleic acid was extracted and reverse transcriptase-PCR for PRL-R was conducted. PRL-R protein was immunolocalized to the glandular epithelium and a subset of stromal cells from the mid to late secretory phase of the menstrual cycle and in early decidua. PRL-R transcripts were also detected from the late secretory phase and first trimester decidua. These findings indicate that the receptor is expressed in a temporal pattern similar to that of PRL. PRL-R expression in the glandular epithelium is consistent with a role in regulating glandular activity. Furthermore, immunoreactivity for PRL-R in a subset of stromal cells may be evidence for paracrine interactions between decidualized cells or an immunoregulatory role for PRL.

Prolactin stimulates mitogen-activated protein kinase in human leiomyoma cells

The effects of prolactin (PRL) on proliferation of cultured human uterine leiomyoma-derived smooth muscle cells (SMC) and its mechanism of action were investigated. PRL stimulated DNA synthesis and the expression of PRL receptor was identified by ribonuclease protection assay. Moreover, the regulation of mitogen-activated protein (MAP) kinase by PRL in leiomyoma-derived SMC was investigated. PRL stimulated MAP kinase activity, as detected by 32P incorporation into MAP-2, in a dose-dependent manner. PRL also rapidly stimulated MAP kinase phosphorylation as detected by in vivo phosphorylation using 32P labeling and phosphotyrosine immunoblotting. These results suggest that PRL stimulates the proliferation of human leiomyoma cells via the MAP kinase cascade.