Immunocytochemical localization of prolactin receptors in rat liver cells: I. Dependence on sex and sex steroids

The prolactin receptor long isoform regulates nociceptor sensitization and opioid-induced hyperalgesia selectively in females

Pain is more prevalent in women for reasons that remain unclear. We have identified a mechanism of injury-free nociceptor sensitization and opioid-induced hyperalgesia (OIH) promoted by prolactin (PRL) in females. PRL signals through mutually inhibitory long (PRLR-L) and short (PRLR-S) receptor isoforms, and PRLR-S activation induces neuronal excitability. PRL and PRLR expression were higher in females. CRISPR-mediated editing of PRLR-L promoted nociceptor sensitization and allodynia in naïve, uninjured female mice that depended on circulating PRL. Opioids, but not trauma-induced nerve injury, decreased PRLR-L promoting OIH through activation of PRLR-S in female mice. Deletion of both PRLR-L and PRLR-S (total PRLR) prevented, whereas PRLR-L overexpression rescued established OIH selectively in females. Inhibition of circulating PRL with cabergoline, a dopamine D2 agonist, up-regulated PRLR-L and prevented OIH only in females. The PRLR-L isoform therefore confers protection against PRL-promoted pain in females. Limiting PRL/PRLR-S signaling pharmacologically or with gene therapies targeting the PRLR may be effective for reducing pain in a female-selective manner.

An Emerging Role for Prolactin in Female-Selective Pain

Women experience many pain conditions more frequently when compared with men, but the biological mechanisms underlying sex differences in pain remain poorly understood. In particular, little is known about possible sex differences in peripheral nociceptors, the fundamental building blocks of pain transmission. Emerging evidence reveals that prolactin (PRL) signaling at its cognate prolactin receptor (PRLR) in primary afferents promotes nociceptor sensitization and pain in a female-selective fashion. In this review, we summarize recent progress in understanding the female-selective role of PRL/PRLR in nociceptor sensitization and in pathological pain conditions, including postoperative, inflammatory, neuropathic, and migraine pain, as well as opioid-induced hyperalgesia. The clinical implications of the peripheral PRL/PRLR system for the discovery of new therapies for pain control in women are also discussed.

Stimulation of prolactin receptor induces STAT-5 phosphorylation and cellular invasion in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in humans and is characterized with poor outcome. In this study, we investigated components of prolactin (Prl) system in cell models of GBM and in histological tissue sections obtained from GBM patients. Expression of Prolactin receptor (PrlR) was detected at high levels in U251-MG, at low levels in U87-MG and barely detectable in U373 cell lines and in 66% of brain tumor tissues from 32 GBM patients by immunohistochemical technique. In addition, stimulation of U251-MG and U87-MG cells but not U373 with Prl resulted in increased STAT5 phosphorylation and only in U251-MG cells with increased cellular invasion. Furthermore, STAT5 phosphorylation and cellular invasion induced in Prl stimulated cells were significantly reduced by using a Prl receptor antagonist that consists of Prl with four amino acid replacements. We conclude that Prl receptor is expressed at different levels in the majority of GBM tumors and that blocking of PrlR in U251-MG cells significantly reduce cellular invasion.

Relationships between blood hormonal concentrations and secondary fibre shedding in young cashmere-bearing goats at their first moult

The aim of this study was to evaluate secondary fibre shedding in relation to seasonal hormonal changes in young cashmere-bearing goats reared in southern Italy. We used 14 cashmere-bearing kids, seven males and seven females, of a Scottish breed-population of goats specialized in cashmere production. Monthly, a hair patch of 4 cm2was clipped from both left and right mid sides alternately and cashmere length and its yield were determined. Blood samples were taken every 2 weeks and plasma was assayed for prolactin (PRL), growth hormone (GH), tri-iodothyronine (T3), thyroxine (T4), progesterone and testosterone. With the same frequency, animals were monitored for onset of moult. Our data indicate that in young cashmere goats at their first moult, secondary fibre shedding is a seasonal event that is strictly related to changes in photoperiod and that PRL has a pivotal rôle in regulating this phenomenon. This corresponds with findings in adults. The observation that both thyroid hormones and sex steroids varied seasonally suggests that they are involved in the regulation of the moult cycle, but their precise rôle remains to be elucidated. Our data also indicate that GH seems to be implicated in the control of the moult cycle. The finding that maximal fibre shedding occurred earlier in males than females could be ascribed to differences in GH levels and to the earlier increase in plasma concentration of PRL observed in males.

The incidence of sexually dimorphic gene expression varies greatly between tissues in the rat

The sexually dimorphic expression of genes across 26 somatic rat tissues was using Affymetrix RAE-230 genechips. We considered probesets to be sexually dimorphically expressed (SDE) if they were measurably expressed above background in at least one sex, there was at least a two-fold difference in expression (dimorphism) between the sexes, and the differences were statistically significant after correcting for false discovery. 14.5% of expressed probesets were SDE in at least one tissue, with higher expression nearly twice as prevalent in males compared to females. Most were SDE in a single tissue. Surprisingly, nearly half of the probesets that were (SDE) in multiple tissues were oppositely sex biased in different tissues, and most SDE probesets were also expressed without sex bias in other tissues. Two genes were widely SDE: Xist (female-only) and Eif2s3y (male-only). The frequency of SDE probesets varied widely between tissues, and was highest in the duodenum (6.2%), whilst less than 0.05% in over half of the surveyed tissues. The occurrence of SDE probesets was not strongly correlated between tissues. Within individual tissues, however, relational networks of SDE genes were identified. In the liver, networks relating to differential metabolism between the sexes were seen. The estrogen receptor was implicated in differential gene expression in the duodenum. To conclude, sexually dimorphic gene expression is common, but highly tissue-dependent. Sexually dimorphic gene expression may provide insights into mechanisms underlying phenotypic sex differences. Online data are provided as a resource for further analyses (GEO reference GSE63362).

Prolactin promotes normal liver growth, survival, and regeneration in rodents: effects on hepatic IL-6, suppressor of cytokine signaling-3, and angiogenesis

Prolactin (PRL) is a potent liver mitogen and proangiogenic hormone. Here, we used hyperprolactinemic rats and PRL receptor-null mice (PRLR−/−) to study the effect of PRL on liver growth and angiogenesis before and after partial hepatectomy (PH). Liver-to-body weight ratio (LBW), hepatocyte and sinusoidal endothelial cell (SEC) proliferation, and hepatic expression of VEGF were measured before and after PH in hyperprolactinemic rats, generated by placing two anterior pituitary glands (AP) under the kidney capsule. Also, LBW and hepatic expression of IL-6, as well as suppressor of cytokine signaling-3 (SOCS-3), were evaluated in wild-type and PRLR−/−mice before and after PH. Hyperprolactinemia increased the LBW, the proliferation of hepatocytes and SECs, and VEGF hepatic expression. Also, liver regeneration was increased in AP-grafted rats and was accompanied by elevated hepatocyte and SEC proliferation, and VEGF expression compared with nongrafted controls. Lowering circulating PRL levels with CB-154, an inhibitor of AP PRL secretion, prevented AP-induced stimulation of liver growth. Relative to wild-type animals, PRLR−/−mice had smaller livers, and soon after PH, they displayed an approximately twofold increased mortality and elevated and reduced hepatic IL-6 and SOCS-3 expression, respectively. However, liver regeneration was improved in surviving PRLR−/−mice. PRL stimulates normal liver growth, promotes survival, and regulates liver regeneration by mechanisms that may include hepatic downregulation of IL-6 and upregulation of SOCS-3, increased hepatocyte proliferation, and angiogenesis. PRL contributes to physiological liver growth and has potential clinical utility for ensuring survival and regulating liver mass in diseases, injuries, or surgery of the liver.

Prolactin and male fertility: the long and short feedback regulation

In the last 20 years, a pituitary-hypothalamus tissue culture system with intact neural and portal connections has been developed in our lab and used to understand the feedback mechanisms that regulate the secretions of adenohypophyseal hormones and fertility of male rats. In the last decade, several in vivo rat models have also been developed in our lab with a view to substantiate the in vitro findings, in order to delineate the role of pituitary hormones in the regulation of fertility of male rats. These studies have relied on both surgical and pharmacological interventions to modulate the secretions of gonadotropins and testosterone. The interrelationship between the circadian release of reproductive hormones has also been ascertained in normal men. Our studies suggest that testosterone regulates the secretion of prolactin through a long feedback mechanism, which appears to have been conserved from rats to humans. These studies have filled in a major lacuna pertaining to the role of prolactin in male reproductive physiology by demonstrating the interdependence between testosterone and prolactin. Systemic levels of prolactin play a deterministic role in the mechanism of chromatin condensation during spermiogenesis.

Increase in sex-dependent expression of prolactin receptors after intrahepatic transplantation of H27 rat hepatoma cells

Immunohistochemical study revealed overexpression of prolactin receptors in central and peripheral cells of intrahepatic grafts from H27 rat hepatoma without changes in compartmentalization compared to hepatocytes of intact animals. Experiments with gonadectomized animals showed that the hormonal regulation of prolactin receptors in both types of tumor cells does not differ from that in normal liver cells (positive estrogen-dependent regulation and negative androgen-dependent regulation).

Overexpression of prolactin receptors during intrahepatic transplantation of RS1 rat cholangiocellular carcinoma cells

Immunohistochemical study showed that expression of prolactin receptors in intrahepatically transplanted cells of RS1 cholangiocellular carcinoma 2-fold exceeds that in cholangiocytes of intact rats. The number of prolactin receptors significantly increased in tumor cell nuclei of male and female animals. The RS1 transplant induced overexpression of prolactin receptors in hepatocytes and increased their number in nuclei of these cells.

Expression of prolactin receptors in rat reproductive tissues during periovulatory prolactin imbalance

Indirect immunoperoxidase technique in combination with cytophotometry showed that prolactin imbalance in the periovulatory period is characterized by considerable changes in the expression of prolactin receptors in uterine glands and endometrial stroma (but not in the myometrium) and in the pituitary gland and hypothalamus, while receptor compartmentalization pattern remains unchanged.

Increased expression of growth hormone and prolactin receptors in hepatocellular carcinomas

The liver is an essential target tissue for growth hormone (GH) and prolactin (PRL). The aim of this study was to determine the in situ expression of growth hormone receptor (GHR) and prolactin receptor (PRLR) in hepatocellular carcinomas and to compare the results with normal liver. For this purpose, in situ hybridization (ISH) and immunohistochemical techniques were performed and several tests were conducted to validate the results. By radioactive ISH, all the hepatocellular carcinomas studied showed labeling for GHR and PRLR mRNAs. Relative expression levels, determined by computer-assisted microdensity, were higher in hepatocellular carcinomas than in normal liver. Immunohistochemistry led us to confirm the constant expression of both receptor proteins in hepatocellular carcinomas and normal liver and to demonstrate their localization not only in the cytoplasm but also in the nucleus. These results confirm that the liver is a major GH and PRL target tissue and suggest that in hepatocellular carcinomas the proliferative effects of these hormones may be increased by a higher expression of their receptors.

Prolactin receptor messenger ribonucleic acid in normal and neoplastic human pituitary tissues

We examined the specific cell types in normal human pituitaries that expressed PRL receptor (PRL-R) messenger ribonucleic acid (mRNA) by combined in situ hybridization and immunohistochemistry. The distribution of PRL-R mRNA in 28 pituitary adenomas was examined by in situ hybridization and reverse transcription-PCR in 12 cases of adenomas. In another set of experiments, 34 PRL adenomas from men, women, and bromocriptine-treated patients were analyzed for PRL-R by in situ hybridization. In the normal pituitary, PRL- and LH-producing cells had significantly more mean grain counts per cell and higher percentages of cells positive for PRL-R than GH and TSH cells. PRL-R mRNA was present in all groups of adenomas by in situ hybridization and reverse transcription-PCR. PRL adenomas had a significantly higher density of labeling compared to other adenoma types. Although there was no difference in the levels of PRL-R mRNA in PRL adenomas from men and premenopausal and postmenopausal women, patients treated with bromocriptine before pituitary surgery had significantly lower levels of PRL-R compared to all other groups. These results indicate that in the normal pituitary, PRL and LH cells have the highest level of PRL-R mRNA, whereas PRL adenomas have significantly higher levels of PRL-R mRNA than other types of adenomas, and bromocriptine treatment decreases the levels of PRL-R mRNA in PRL adenomas.