Intercellular communication in the anterior pituitary

Single-Cell RNA Sequencing Analysis of Chicken Anterior Pituitary: A Bird's-Eye View on Vertebrate Pituitary

It is well-established that anterior pituitary contains multiple endocrine cell populations, and each of them can secrete one/two hormone(s) to regulate vital physiological processes of vertebrates. However, the gene expression profiles of each pituitary cell population remains poorly characterized in most vertebrate groups. Here we analyzed the transcriptome of each cell population in adult chicken anterior pituitaries using single-cell RNA sequencing technology. The results showed that: (1) four out of five known endocrine cell clusters have been identified and designated as the lactotrophs, thyrotrophs, corticotrophs, and gonadotrophs, respectively. Somatotrophs were not analyzed in the current study. Each cell cluster can express at least one known endocrine hormone, and novel marker genes (e.g., CD24 and HSPB1 in lactotrophs, NPBWR2 and NDRG1 in corticotrophs; DIO2 and SOUL in thyrotrophs, C5H11ORF96 and HPGDS in gonadotrophs) are identified. Interestingly, gonadotrophs were shown to abundantly express five peptide hormones: FSH, LH, GRP, CART and RLN3; (2) four non-endocrine/secretory cell types, including endothelial cells (expressing IGFBP7 and CFD) and folliculo-stellate cells (FS-cells, expressing S100A6 and S100A10), were identified in chicken anterior pituitaries. Among them, FS-cells can express many growth factors, peptides (e.g., WNT5A, HBEGF, Activins, VEGFC, NPY, and BMP4), and progenitor/stem cell-associated genes (e.g., Notch signaling components, CDH1), implying that the FS-cell cluster may act as a paracrine/autocrine signaling center and enrich pituitary progenitor/stem cells; (3) sexually dimorphic expression of many genes were identified in most cell clusters, including gonadotrophs and lactotrophs. Taken together, our data provides a bird's-eye view on the diverse aspects of anterior pituitaries, including cell composition, heterogeneity, cell-to-cell communication, and gene expression profiles, which facilitates our comprehensive understanding of vertebrate pituitary biology.

Transcriptomic analysis of the porcine anterior pituitary gland during the peri-implantation period

The peri-implantation period is controlled by signals originating from hypothalamic-pituitary-ovarian axis, uterus and developing embryos. The transcriptomic activity of the anterior pituitary gland may be important for the control of the peri-implantation period. The aim of this study was to determine the alternations in the transcriptomic profile of porcine anterior pituitary gland during the peri-implantation period (days 15-16 of pregnancy) in comparison with established for the respective days of the oestrous cycle. Analysis using a microarray approach indicated that the 651 genes (fold-change ˂1.2; p ≤ .05) were differentially expressed (DEGs) in the anterior pituitary of pigs during the peri-implantation period when compared to cyclic females. Of these DEGs, 404 were upregulated and 247 downregulated. Analysis of occurred relationships among DEGs revealed that some of them are involved in steroid-response and oestrogen synthesis, FSH secretion, immune response, PPAR signalling pathway and the potential for DNA methylation. In conclusion, the altered transcriptomic profile of the porcine pituitary gland in pigs during the peri-implantation period indicates the role of embryos presence in the creation of transcriptomic activity of the pituitary gland in pigs.

Antibody array strategy for human growth factor secretome profiling of GH-secreting adenomas

PURPOSES

To test if the antibody array strategy could be utilized to simultaneously detect the secretion of multiple growth factors by human pituitary GH-adenomas and to measure octreotide-induced alterations.

METHODS

Specimens of human pituitary adenomas were cultured and incubated with or without octreotide for 24 h. Conditional media were analyzed by human growth factor antibody array and VEGF concentrations were measured by ELISA. Media were also analyzed for GH concentrations. p21 expression levels were examined by Western blot of the specimens lysates.

RESULTS

The antibody arrays successfully identified growth factors secreted by GH-adenomas in vitro. Octreotide treatment induced both elevations and reductions in growth factors secretion. GH response to octreotide was measured, and in this small-sized study resistant and sensitive GH-adenomas presented with no unique secretome pattern of each of the groups. Octreotide-induced VEGF alterations analyzed by the antibody array and by ELISA were not fully matched.

CONCLUSIONS

This study suggests that the broad proteomic strategy of antibody arrays may be utilized to study the growth factors secretion pattern of GH-adenomas and its regulation by somatostatin analogs or other compounds.

Anatomical and functional gonadotrope networks in the teleost pituitary

Mammalian pituitaries exhibit a high degree of intercellular coordination; this enables them to mount large-scale coordinated responses to various physiological stimuli. This type of communication has not been adequately demonstrated in teleost pituitaries, which exhibit direct hypothalamic innervation and expression of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in distinct cell types. We found that in two fish species, namely tilapia and zebrafish, LH cells exhibit close cell-cell contacts and form a continuous network throughout the gland. FSH cells were more loosely distributed but maintained some degree of cell-cell contact by virtue of cytoplasmic processes. These anatomical differences also manifest themselves at the functional level as evidenced by the effect of gap-junction uncouplers on gonadotropin release. These substances abolished the LH response to gonadotropin-releasing hormone stimulation but did not affect the FSH response to the same stimuli. Dye transfer between neighboring LH cells provides further evidence for functional coupling. The two gonadotropins were also found to be differently packaged within their corresponding cell types. Our findings highlight the evolutionary origin of pituitary cell networks and demonstrate how the different levels of cell-cell coordination within the LH and FSH cell populations are reflected in their distinct secretion patterns.

Pituitary adenoma nitroproteomics: current status and perspectives

Oxidative stress is extensively associated with tumorigenesis. A series of studies on stable tyrosine nitration as a marker of oxidative damage were performed in human pituitary and adenoma. This paper reviews published research on the mass spectrometry characteristics of nitropeptides and nitroproteomics of pituitary controls and adenomas. The methodology used for nitroproteomics, the current status of human pituitary nitroproteomics studies, and the future perspectives are reviewed. Enrichment of those low-abundance endogenous nitroproteins from human tissues or body fluid samples is the first important step for nitroproteomics studies. Mass spectrometry is the essential approach to determine the amino acid sequence and locate the nitrotyrosine sites. Bioinformatics analyses, including protein domain and motif analyses, are needed to locate the nitrotyrosine site within the corresponding protein domains/motifs. Systems biology techniques, including pathway analysis, are necessary to discover signaling pathway networks involving nitroproteins from the systematically global point of view. Future quantitative nitroproteomics will discover pituitary adenoma-specific nitroprotein(s). Structural biology techniques such as X-ray crystallography analysis will solidly clarify the effects of tyrosine nitration on structure and functions of a protein. Those studies will eventually address the mechanisms and biological functions of tyrosine nitration in pituitary tumorigenesis and will discover nitroprotein biomarkers for pituitary adenomas and targets for drug design for pituitary adenoma therapy.

Secondary amenorrhea in a woman with spinocerebellar degeneration treated with thyrotropin-releasing hormone: a case report and in vitro analysis

Introduction

While thyrotropin-releasing hormone is known to be a prolactin-release stimulating factor, thyrotropin-releasing hormone-tartrate and its derivative, taltirelin hydrate, are used for the treatment of spinocerebellar degeneration, a degenerative disease characterized mainly by motor ataxia. We report the case of a patient being treated with a thyrotropin-releasing hormone preparation for spinocerebellar degeneration who developed amenorrhea after a dose increase. Her hormonal background was analyzed and the effect of prolonged exposure to thyrotropin-releasing hormone on pituitary prolactin-producing cells was examined in vitro.

Case presentation

Our patient was a 36-year-old Japanese woman who experienced worsening of gait disturbance at around 23 years of age, and was subsequently diagnosed as having spinocerebellar degeneration. She had been treated with thyrotropin-releasing hormone-tartrate for four years. Taltirelin hydrate was added to the treatment seven months prior to her presentation, followed by an improvement in gait disturbance. Around the same period, she started lactating and subsequently developed amenorrhea three months later. Taltirelin hydrate was discontinued and she was referred to our hospital. She was found to have normal sex hormone levels. A thyrotropin-releasing hormone provocation test showed a normal response of thyroid-stimulating hormone level and an over-response of prolactin at 30 minutes (142.7 ng/mL). Resumption of menstruation was noted three months after dose reduction of thyrotropin-releasing hormone. In our in vitro study, following long-term exposure to thyrotropin-releasing hormone, cells from the rat pituitary prolactin-producing cell line GH3 exhibited an increased basal prolactin promoter activity but showed a marked decrease in responsiveness to thyrotropin-releasing hormone.

Conclusions

Physicians should be aware of hyperprolactinemia-associated side effects in patients receiving thyrotropin-releasing hormone treatment. Long-term treatment with a thyrotropin-releasing hormone preparation might cause a large amount of prolactin to accumulate in prolactin-producing cells and be released in response to exogenous thyrotropin-releasing hormone stimulation.

Sexual dimorphism in the effect of concomitant progesterone administration on changes caused by long-term estrogen treatment in pituitary hormone immunoreactivities of rats

BACKGROUND

Since in clinical practice long-term estrogen (E) treatment is frequently applied, our aim was to study the effect of concomitant progesterone (P) administration on changes caused by long-term estrogen treatment in the secretion of LH, FSH, PRL and GH.

MATERIAL/METHODS

Diethylstilbestrol (DES), P or both in silastic capsules were implanted under the skin of prepubertal Sprague-Dawley male and female rats. Animals survived for two or five months. We have also studied whether the changed hormone secretion caused by DES can return to normal level 1 or 2 months after removing DES capsule.

RESULTS

1.) The males more rapidly responded than females with decreasing basal LH release upon treatments. The basal FSH release was decreased only in males. The effect of DES persisted in males; however, in females basal LH and FSH levels were upregulated after removal of DES capsule. 2.) The basal GH levels were low in each group. The body weight and length were depressed by DES in both genders and P little blunted this effect. The body weight and length in males remained low after removal of DES capsule, in females it was nearly similar to intact rats. 3.) There was no sexual dimorphism in the effect of steroids on PRL secretion. In both genders DES extremely enhanced the PRL levels, P prevented the effect of DES. PRL levels returned to intact value after removal of DES influence. 4.) Removal of DES capsule reversed the changes in the immunohistochemical appearance of hormone immunoreactivities.

CONCLUSIONS

There was sexual dimorphism in the change of basal gonadotropic hormone and GH secretion but not of PRL upon DES and DES+P treatments. P was basically protective and this role may be mediated by P receptors locally in the pituitary gland.

Prolonged oestrogen treatment does not correlate with a sustained increase in anterior pituitary mitotic index in ovariectomized Wistar rats

Oestrogen is a powerful mitogen that is believed to exert a continuous, dose-dependent trophic stimulus at the anterior pituitary. This persistent mitotic effect contrasts with corticosterone and testosterone, changes in the levels of which induce only transient, self-limiting fluctuations in pituitary mitotic activity. To further define the putative long-term trophic effects of oestrogen, we have accurately analysed the effects of 7 and 28 days oestrogen treatment on anterior pituitary mitotic activity in ovariectomized 10-week-old Wistar rats using both bromodeoxyuridine (BrdU) and timed colchicine-induced mitotic arrest. An oestrogen dose-dependent increase in mitotic index was seen 7 days after the start of treatment as expected, representing an acceleration in gross mitotic activity from 1.7%/day in ovariectomized animals in the absence of any oestrogen replacement to 3.7%/day in the presence of a pharmacological dose of oestrogen (50 mcg/rat per day: approximately 230 mcg/kg per day). Despite continued exposure to high-dose oestrogen and persistence of the increase in pituitary wet weight, the increase in mitotic index was unexpectedly not sustained. After 28 days of high-dose oestrogen treatment, anterior pituitary mitotic index and BrdU-labelling index were not significantly different from baseline. Although a powerful pituitary mitogen in the short term, responsible, presumably, for increased trophic variability in oestrus cycling females, these data indicate that in keeping with other trophic stimuli to the pituitary and in contrast to a much established dogma, the mitotic response to longer-term high-dose oestrogen exposure is transient and is not the driver of persistent pituitary growth, at least in female Wistar rats.

Global analysis of gene expression in the estrogen induced pituitary tumor of the F344 rat

The F344 rat rapidly forms large prolactinomas in response to chronic estrogen treatment. To identify genes expressed in the course of this estrogen induced pituitary tumor growth, we performed microarray analysis on the F344 rat pituitary after chronic estrogen treatment and on untreated controls. At a significance level set to minimize type I error, some 72 genes were found to be differentially expressed between estrogen treated and untreated. Of those genes, 70 have not been reported previously as being affected by estrogen in the F344 rat pituitary. Since many other investigators have studied the effect of estrogen on specific gene expression in rat pituitary, we also examined the mRNA expression of the 36 genes that have been previously reported as having their expression affected by estrogen in the rat pituitary. Of these, 13 were found to have their expression affected by estrogen treatment in the same direction as had been reported by others.

Tumor necrosis factor-alpha activates the human prolactin gene promoter via nuclear factor-kappaB signaling

Pituitary function has been shown to be regulated by an increasing number of intrapituitary factors, including cytokines. Here we show that the important cytokine TNF-alpha activates prolactin gene transcription in pituitary GH3 cells stably expressing luciferase under control of 5 kb of the human prolactin promoter. Similar regulation of the endogenous rat prolactin gene by TNF-alpha in GH3 cells was confirmed using real-time PCR. Luminescence microscopy revealed heterogeneous dynamic response patterns of promoter activity in individual cells. In GH3 cells treated with TNF-alpha, Western blot analysis showed rapid inhibitory protein kappaB (IkappaBalpha) degradation and phosphorylation of p65. Confocal microscopy of cells expressing fluorescence-labeled p65 and IkappaBalpha fusion proteins showed transient cytoplasmic-nuclear translocation and subsequent oscillations in p65 localization and confirmed IkappaBalpha degradation. This was associated with increased nuclear factor kappaB (NF-kappaB)-mediated transcription from an NF-kappaB-responsive luciferase reporter construct. Disruption of NF-kappaB signaling by expression of dominant-negative variants of IkappaB kinases or truncated IkappaBalpha abolished TNF-alpha activation of the prolactin promoter, suggesting that this effect was mediated by NF-kappaB. TNF-alpha signaling was found to interact with other endocrine signals to regulate prolactin gene expression and is likely to be a major paracrine modulator of lactotroph function.

Autocrine regulation of prolactin secretion by endothelins throughout the estrous cycle

We have previously found that the ovarian steroid background determines the efficiency of the endothelin-mediated autocrine feedback regulation of prolactin (PRL) secretion. In this study, we investigated the role of endogenous endothelins in regulating PRL secretion during the estrous cycle. Adult female rats representing different stages of the 4-d cycle were sacrificed by decapitation, and the anterior pituitary cells were enzymatically dispersed using collagenase and hyaluronidase. PRL secretion of individual lactotrophs was measured in a PRL-specific reverse hemolytic plaque assay, and the influence of endogenous endothelins on PRL secretion was assessed by applying the selective ET(A) receptor antagonist peptide, BQ123. Blocking the endothelin-mediated autocrine feedback resulted in an increase in PRL secretion when cells were obtained at proestrus, estrus, and diestrus-1, whereas PRL secretion was decreased at diestrus-2 by ET(A) receptor blockade. These observations suggest that endogenous endothelins are predominantly inhibitory during proestrus, estrus, and diestrus-1, whereas at diestrus-2 their influence on PRL secretion is stimulatory. Whereas the bell-shaped concentration-response curves with BQ123 at proestrus and diestrus-1 may indicate a transition state in which endogenous endothelins can be both stimulatory and inhibitory, at estrus the influence of endogenous endothelins is unequivocally inhibitory in nature. We propose that intensification of the endogenous endothelin- mediated negative feedback at estrus may play a role in restraining PRL secretion following the estradiol- induced proestrous PRL surge.

Differential effects of the early and late intrauterine environment on corticotrophic cell development

The developing embryo and fetus respond to a range of intrauterine stressors, but the effect of chronic intrauterine stress on the programmed development of pituitary corticotrophs has not been investigated. We have used a pregnant sheep model in which the embryonic environment at conception has been surgically perturbed by uterine carunclectomy. This procedure results in the development of fetuses that either are placentally restricted and chronically hypoxemic or that demonstrate compensatory placental growth and maintain normoxemia throughout late gestation. We found that uterine carunclectomy resulted in the emergence of a population of non-corticotrophin-releasing hormone (non-CRH) target cells that secreted high amounts of adrenocorticotrophic hormone (ACTH) in the fetal pituitary. This change in corticotroph development was independent of late-gestation hypoxemia. However, chronic hypoxemia during late gestation (in either carunclectomized or non-carunclectomized uterine environments) resulted in a reduction in the proportion of ACTH stored in CRH-target. Thus, the early and late intrauterine environments differentially program the development of specific corticotrophic cell types in the fetal pituitary. These patterns of altered corticotroph development are important given the central roles of the hypothalamo-pituitary-adrenal axis in the fetal adaptive response to intrauterine stress and in the early programming of adult disease.

Folliculostellate cell network: a route for long-distance communication in the anterior pituitary

All higher life forms critically depend on hormones being rhythmically released by the anterior pituitary. The proper functioning of this master gland is dynamically controlled by a complex set of regulatory mechanisms that ultimately determine the fine tuning of the excitable endocrine cells, all of them heterogeneously distributed throughout the gland. Here, we provide evidence for an intrapituitary communication system by which information is transferred via the network of nonendocrine folliculostellate (FS) cells. Local electrical stimulation of FS cells in acute pituitary slices triggered cytosolic calcium waves, which propagated to other FS cells by signaling through gap junctions. Calcium wave initiation was because of the membrane excitability of FS cells, hitherto classified as silent cells. FS cell coupling could relay information between opposite regions of the gland. Because FS cells respond to central and peripheral stimuli and dialogue with endocrine cells, the form of large-scale intrapituitary communication described here may provide an efficient mechanism that orchestrates anterior pituitary functioning in response to physiological needs.

Leptin and the pituitary

Although leptin was originally viewed as an antiobesity hormone, it is now evident that it may have more pleiotropic actions. Experiments in rodents have shown that leptin activates the sympathetic nervous system, is involved in regulation of blood pressure, hematopoiesis, immune function, angiogenesis and brain, bone and pituitary development. Some biological effects expected based on observations in rodents, have so far not been seen in humans. Thus due to species differences in the role of leptin it is difficult to translate the data from rodents to human physiology. Hypothalamus is the primary brain site targeted by circulating leptin, secreted by fat cells. Leptin receptor has homology to members of class I cytokine receptor family, which may imply similarities in molecular events engaged by cytokines and leptin. In view of its cytokine-like properties it is likely that leptin produced and secreted outside of fat tissue i.e. in other tissues (CNS, pituitary, ovary, placenta, etc), is a paracrine regulator. Leptin receptor isoforms, long-signaling and short-nonsignaling, have been recently localized in human pituitaries. This opens the possibility of a direct action of leptin on the pituitary. However this appears to be quite complex and is species dependent. Leptin can be synthesized by normal and tumorous pituitary cells. Leptin protein expression in pituitary adenomas is decreased compared to that in normal pituitaries. Colocalization studies with leptin and anterior pituitary cells showed that 70% of ACTH cells are positive for leptin, 21% of GH cells, 29% of LH cells, 33% of FSH cells, 32% of TSH cells, 64% folliculo-stellate cells whereas very few PRL cells were positive (3%). Leptin is stored in secretory granules and secretory cells retain leptin in granules until stimulated. This follows a different secretory pathway than in adipocytes where upon synthesis leptin is immediately released. Question to be raised is does the pituitary contribute to the body leptin pool or is its action predominantly paracrine/autocrine? Clinically based evidence from studies performed in patients harboring different functional pituitary tumors causing a state of hormonal hypersecretion (acromegaly, prolactinomas, Cushing's disease) or hypopituitarism (due to non-functioning pituitary adenomas), are in favor of a paracrine/autocrine role of the pituitary leptin. Most of the studies have shown that the link between leptin, body composition and hormones of the pituitary is indirect. Thus changes in levels of circulating leptin are most likely due to changes in the metabolic and hormonal milieu during the chronic course of the disease or chronic treatment. Furthermore, circadian rhythm of leptin, its pulsatility and gender difference are preserved in hypopituitarism as well as in patients with functional pituitary adenomas implying that intact hypothalamic-pituitary function is not essential for leptin's circadian rhythm.