Immunomodulatory role of decidual prolactin on the human fetal membranes and placenta.

The close interaction between fetal and maternal cells during pregnancy requires multiple immune-endocrine mechanisms to provide the fetus with a tolerogenic environment and protection against any infectious challenge. The fetal membranes and placenta create a hyperprolactinemic milieu in which prolactin (PRL) synthesized by the maternal decidua is transported through the amnion-chorion and accumulated into the amniotic cavity, where the fetus is bedded in high concentrations during pregnancy. PRL is a pleiotropic immune-neuroendocrine hormone with multiple immunomodulatory functions mainly related to reproduction. However, the biological role of PRL at the maternal-fetal interface has yet to be fully elucidated. In this review, we have summarized the current information on the multiple effects of PRL, focusing on its immunological effects and biological significance for the immune privilege of the maternal-fetal interface.

Prolactin and its receptor as therapeutic targets in glioblastoma multiforme.

Although prolactin (PRL) and its receptor (PRLR) have been detected in glioblastoma multiforme (GBM), their role in its pathogenesis remains unclear. Our aim was to explore their contribution in GBM pathogenesis. We detected PRL and PRLR in all GBM cell lines tested. PRLR activation or overexpression using plasmid transfection increased proliferation, viability, clonogenicity, chemoresistance and matrix metalloproteinase activity in GBM cells, while PRLR antagonist ∆1-9-G129R-hPRL reduced their proliferation, viability, chemoresistance and migration. Meta-analysis of transcriptomic data indicated that PRLR was expressed in all grade II-III glioma (GII-III) and GBM samples. PRL was upregulated in GBM biopsies when compared to GII-III. While in the general population tumour PRL/PRLR expression did not correlate with patient survival, biological sex-stratified analyses revealed that male patients with PRL+/PRLRHIGH GBM performed worse than PRL+/PRLRLOW GBM. In contrast, all male PRL+/PRLRHIGH GII-III patients were alive whereas only 30% of PRL+/PRLRLOW GII-III patients survived after 100 months. Our study suggests that PRLR may be involved in GBM pathogenesis and could constitute a therapeutic target for its treatment. Our findings also support the notion that sexual dimorphism should be taken into account to improve the care of GBM patients.

JAK2/STAT5 Pathway Mediates Prolactin-Induced Apoptosis of Lactotropes.

Prolactinomas are increasingly viewed as a "problem of signal transduction." Consequently, the identification of factors and signaling pathways that control lactotrope cell turnover is needed in order to encourage new therapeutic developments. We have previously shown that prolactin (PRL) acts as a proapoptotic and antiproliferative factor on lactotropes, maintaining anterior pituitary cell homeostasis, which contrasts with the classical antiapoptotic and/or proliferative actions exerted by PRL in most other target tissues. We aimed to investigate the PRLR-triggered signaling pathways mediating these nonclassical effects of PRL in the pituitary. Our results suggest that (i) the PRLR/Jak2/STAT5 pathway is constitutively active in GH3 cells and contributes to PRL-induced apoptosis by increasing the Bax/Bcl-2 ratio, (ii) PRL inhibits ERK1/2 and Akt phosphorylation, thereby contributing to its proapoptotic effect, and (iii) the PI3K/Akt pathway participates in the PRL-mediated control of lactotrope proliferation. We hypothesize that the alteration of PRL actions in lactotrope homeostasis due to the dysregulation of any of the mechanisms of actions described above may contribute to the pathogenesis of prolactinomas.

Alpha2-adrenoceptor agonists trigger prolactin signaling in breast cancer cells.

Breast cancer is the most frequent malignancy among women worldwide. We have described the expression of α2-adrenoceptors in breast cancer cell lines, associated with increased cell proliferation and tumor growth. A mitogenic autocrine/paracrine loop of prolactin (Prl) has been described in breast cancer cells. We hypothesized that the α2-adrenergic enhancement of proliferation could be mediated, at least in part, by this Prl loop. In both T47D and MCF-7 cell lines, the incubation with the α2-adrenergic agonist dexmedetomidine significantly increased Prl release into the culture medium (measured by the Nb2 bioassay), this effect being reversed by the α2-adrenergic antagonist rauwolscine. No change in Prl receptors (PrlR) was observed by RT-qPCR in these cell lines. In IBH-6 cells a decrease in Prl secretion was observed at the lower dexmedetomidine concentration. The signaling pathways involved in ovine Prl (oPrl) and dexmedetomidine action were also assessed. Both compounds significantly activated STAT5 and ERK in all three cell lines. In T47D and MCF-7 cell lines also AKT was activated by both Prl and dexmedetomidine. We therefore describe the STAT5 phosphorylation by an α2-adrenergic agonist, dexmedetomidine. In T47D cells, the α2-adrenergic stimulation of cell proliferation is probably mediated, at least in part, by the Prl autocrine/paracrine loop, because this effect is abrogated by the specific PrlR antagonist Δ1-9-G129R-hPrl. The implication of Prl loop describes a novel mechanism of action of this GPCR.

Prolactin protects retinal pigment epithelium by inhibiting sirtuin 2-dependent cell death.

The identification of pathways necessary for retinal pigment epithelium (RPE) function is fundamental to uncover therapies for blindness. Prolactin (PRL) receptors are expressed in the retina, but nothing is known about the role of PRL in RPE. Using the adult RPE 19 (ARPE-19) human cell line and mouse RPE, we identified the presence of PRL receptors and demonstrated that PRL is necessary for RPE cell survival via anti-apoptotic and antioxidant actions. PRL promotes the antioxidant capacity of ARPE-19 cells by reducing glutathione. It also blocks the hydrogen peroxide-induced increase in deacetylase sirtuin 2 (SIRT2) expression, which inhibits the TRPM2-mediated intracellular Ca(2+) rise associated with reduced survival under oxidant conditions. RPE from PRL receptor-null (prlr(-/-)) mice showed increased levels of oxidative stress, Sirt2 expression and apoptosis, effects that were exacerbated in animals with advancing age. These observations identify PRL as a regulator of RPE homeostasis.

Prolactin induces apoptosis of lactotropes in female rodents.

Anterior pituitary cell turnover occurring during female sexual cycle is a poorly understood process that involves complex regulation of cell proliferation and apoptosis by multiple hormones. In rats, the prolactin (PRL) surge that occurs at proestrus coincides with the highest apoptotic rate. Since anterior pituitary cells express the prolactin receptor (PRLR), we aimed to address the actual role of PRL in the regulation of pituitary cell turnover in cycling females. We showed that acute hyperprolactinemia induced in ovariectomized rats using PRL injection or dopamine antagonist treatment rapidly increased apoptosis and decreased proliferation specifically of PRL producing cells (lactotropes), suggesting a direct regulation of these cell responses by PRL. To demonstrate that apoptosis naturally occurring at proestrus was regulated by transient elevation of endogenous PRL levels, we used PRLR-deficient female mice (PRLRKO) in which PRL signaling is totally abolished. According to our hypothesis, no increase in lactotrope apoptotic rate was observed at proestrus, which likely contributes to pituitary tumorigenesis observed in these animals. To decipher the molecular mechanisms underlying PRL effects, we explored the isoform-specific pattern of PRLR expression in cycling wild type females. This analysis revealed dramatic changes of long versus short PRLR ratio during the estrous cycle, which is particularly relevant since these isoforms exhibit distinct signaling properties. This pattern was markedly altered in a model of chronic PRLR signaling blockade involving transgenic mice expressing a pure PRLR antagonist (TGΔ1-9-G129R-hPRL), providing evidence that PRL regulates the expression of its own receptor in an isoform-specific manner. Taken together, these results demonstrate that i) the PRL surge occurring during proestrus is a major proapoptotic signal for lactotropes, and ii) partial or total deficiencies in PRLR signaling in the anterior pituitary may result in pituitary hyperplasia and eventual prolactinoma development, as observed in TGΔ1-9-G129R-hPRL and PRLRKO mice, respectively.

Use of prolactin receptor antagonist to better understand prolactin regulation of pituitary homeostasis.

The anterior pituitary is permanently regulated by processes of apoptosis and proliferation in order to maintain tissue homeostasis. Several factors have been implicated in this regulation and lately, prolactin (PRL) has been included into that list. However, since PRL is secreted by anterior pituitary lactotropes, the actual outcome of its autocrine/paracrine actions on pituitary cells has remained difficult to assess. The availability of the pure PRL receptor antagonist Del1-9-G129R-hPRL has been helpful to circumvent this problem. While PRL has been traditionally associated with increased cell proliferation, recent studies revealed that this hormone actually induces apoptosis and decreases proliferation of anterior pituitary cells, by mechanisms involving the PRL receptor. The aim of this short review is to overview our current understanding of the regulation of pituitary homeostasis by PRL. Moreover, studies involving Del1-9-G129R-hPRL have helped anticipate to what extent future treatments involving PRL receptor inhibitors may interfere with processes regulated by PRL at the central level.

Prolactin receptor antagonism in mouse anterior pituitary: effects on cell turnover and prolactin receptor expression.

Since anterior pituitary expresses prolactin receptors, prolactin secreted by lactotropes could exert autocrine or paracrine actions on anterior pituitary cells. In fact, it has been observed that prolactin inhibits its own expression by lactotropes. Our hypothesis is that prolactin participates in the control of anterior pituitary cell turnover. In the present study, we explored the action of prolactin on proliferation and apoptosis of anterior pituitary cells and its effect on the expression of the prolactin receptor. To determine the activity of endogenous prolactin, we evaluated the effect of the competitive prolactin receptor antagonist Δ1-9-G129R-hPRL in vivo, using transgenic mice that constitutively and systemically express this antagonist. The weight of the pituitary gland and the anterior pituitary proliferation index, determined by BrdU incorporation, were higher in transgenic mice expressing the antagonist than in wild-type littermates. In addition, blockade of prolactin receptor in vitro by Δ1-9-G129R-hPRL increased proliferation and inhibited apoptosis of somatolactotrope GH3 cells and of primary cultures of male rat anterior pituitary cells, including lactotropes. These results suggest that prolactin acts as an autocrine/paracrine antiproliferative and proapoptotic factor in the anterior pituitary gland. In addition, anterior pituitary expression of the long isoform of the prolactin receptor, measured by real-time PCR, increased about 10-fold in transgenic mice expressing the prolactin receptor antagonist, whereas only a modest increase in the S3 short-isoform expression was observed. These results suggest that endogenous prolactin may regulate its own biological actions in the anterior pituitary by inhibiting the expression of the long isoform of the prolactin receptor. In conclusion, our observations suggest that prolactin is involved in the maintenance of physiological cell renewal in the anterior pituitary. Alterations in this physiological role of prolactin could contribute to pituitary tumor development.

Elevated serum bioactive prolactin concentrations in patients with systemic lupus erythematosus are associated with disease activity as disclosed by homologous receptor bioassays.

OBJECTIVE: To assess the bioactivity of circulating prolactin (PRL) in serum samples from patients with systemic lupus erythematosus (SLE) using 2 novel homologous in vitro bioassays, and to correlate PRL bioactivity with lupus activity. METHODS: Serum samples from 98 SLE patients with and without disease activity were tested for immunoreactive and bioactive concentrations of PRL. RESULTS: Patients with active disease exhibited higher bioactive serum PRL levels in homologous bioassays (p

Application of new homologous in vitro bioassays for human lactogens to assess the actual bioactivity of human prolactin isoforms in hyperprolactinaemic patients.

BACKGROUND: Prolactin (PRL) plays a central role in mammary gland development and lactation. Due to its molecular heterogeneity, measurement of PRL immunoreactivity does not necessarily reflect its intrinsic bioactivity. For many years the Nb2 rat lymphoma cell bioassay has been the only reference bioassay for human lactogens. This bioassay, however, does not always correlate with the clinical features found in some patients exhibiting normal or elevated immunoreactive serum PRL concentrations. OBJECTIVES: (1) To determine the concentrations of bioactive PRL in serum samples from individuals with normoprolactinaemia or with different forms of hyperprolactinaemia using two recently described homologous in vitro bioassays (i.e. a transcriptional bioassay in HEK-293 cells and a proliferation assay in Ba/F3 cells); and (2) to compare these results with those generated by the classical Nb2 cell bioassay. DESIGN: Cross-sectional study. SETTING: An institutional biomedical research laboratory. PARTICIPANTS: Ten patients with symptomatic hyperprolactinaemia due to prolactinoma, 11 patients with asymptomatic hyperprolactinaemia and macroprolactinaemia, and nine normal women. MAIN OUTCOME MEASURES: Measurement of immunoreactive and bioactive concentrations of serum PRL. RESULTS: Samples from normal women and patients with tumoral hyperprolactinaemia due to prolactinoma exhibited similar within-group concentration values of bioactive and immunoreactive serum PRL when tested by the three bioassays and the immunoradiometric assay employed. By contrast, measurement of bioactive PRL in samples from patients with macroprolactinaemia revealed that macroprolactin was poorly active in the homologous receptor bioassays, while it was more active in the Nb2 bioassay. CONCLUSIONS: The reduced bioactivity of PRL in patients with macroprolactinaemia may further explain the absence of clinical features of hyperprolactinaemia in these individuals. In addition, our findings indicate that species-specificity and sensitivity of the bioassays are determinant factors in the measurement of the intrinsic biological activity of circulating PRL.

Human macroprolactin displays low biological activity via its homologous receptor in a new sensitive bioassay.

CONTEXT: Macroprolactinemia is a frequent finding in hyperprolactinemic individuals, usually without clinical impact. Data on biological activity of macroprolactin (bbPRL) are controversial and mostly based on a heterologous rat Nb2 cell bioassay. Biological activity of bbPRL observed in vitro but not in vivo may be due to its high molecular weight, preventing its passage through capillary barrier. Alternatively, bbPRL bioactivity may differ depending on the prolactin (PRL) receptor (PRLR) species specificity. OBJECTIVE: The objective of the study was to characterize the bioactivity of bbPRL in a homologous bioassay: Ba/F-3 cells stably expressing the human PRLR. DESIGN/SETTING/PATIENTS: Chromatography-purified bbPRL from macroprolactinemic individuals (group I, n = 18) and monomeric PRL from hyperprolactinemic patients without macroprolactinemia (group II, n = 5) were tested in Nb2 and Ba/F-LLP bioassays. Both groups were followed up at the neuroendocrinology outpatients' clinic. MAIN OUTCOME MEASURE: Biological activity of bbPRL presented in the two bioassays was measured. RESULTS: In group I, no patient had hypogonadism. Mean ratio bioactivity to immunoactivity of bbPRL in the Nb2 assay was 0.69. There was no dose-response in 15 of the 18 samples tested in Ba/F-LLP assay. In group II, three patients had galactorrhea and all five had hypogonadism. Mean ratio bioactivity to immunoactivity of monomeric PRL samples was 1.35 in Nb2 and 0.91 in Ba/F-LLP assay. CONCLUSION: Whereas both bioassays achieve similar results with respect to monomeric PRL activity, our results indicate that the activity displayed by bbPRL toward the rat receptor may be inappropriate because it is not observed in the human PRLR-mediated assay, consistent with the apparent absence of bioactivity in vivo.