Paracrinicity: the story of 30 years of cellular pituitary crosstalk

Severe Acquired Hypothyroidism and Van Wyk-Grumbach Syndrome in Two Children

The primary manifestations of chronic hypothyroidism in children include growth arrest, delayed skeletal maturity, and delayed puberty. In 1960, Van Wyk and Grumbach reported three girls with hypothyroidism and a combination of incomplete isosexual precocious puberty (early breast development, menstruation, and absence of pubic hair), galactorrhea, delayed bone age, and pituitary enlargement. All abnormalities regressed after appropriate thyroid hormone replacement therapy. Over the years, an increasing number of reported cases has allowed for a more precise understanding of the clinical, biochemical, and radiological phenotypes of the Van Wyk-Grumbach syndrome (VWGS). These varying clinical manifestations are thought to result from a unique pathophysiological process where the thyroid-stimulating hormone (TSH) is a key element. We describe the cases of two patients (a boy and a girl) with severe autoimmune thyroiditis and VWGS. The clinical, biochemical, and radiological imaging characteristics were similar in both patients and included growth failure, absence of clinical goiter, markedly elevated TSH concentrations >100 mIU/L, undetectable free thyroxine levels, "normal" thyroglobulin levels, high follicle-stimulating hormone (FSH) and prolactin levels, prepubertal levels of luteinizing hormone (LH), delayed bone age, and hyperplasia of the pituitary gland. The two patients displayed differences, especially in the absence of clinical pubertal development, moderate anemia, abnormal renal function, and moderate goiter detected via ultrasonography (in the female patient). Thyroxine replacement therapy reversed the VWGS phenotype and hypothyroidism, with satisfactory growth velocity, strictly normal thyroid function, and normal pituitary size detected via magnetic resonance imaging at the 6-month follow-up visit.

Evaluation of fish pituitary spheroids to study annual endocrine reproductive control

The pituitary gland is a small endocrine gland located below the hypothalamus. This gland releases several important hormones and controls the function of many other endocrine system glands to release hormones. Fish pituitary hormonal cells are controlled by neuroendocrine and sex steroid feedback. To study the complex pituitary function in vivo, we established an in vitro pituitary spheroid assay and evaluated its suitability for monitoring the annual reproductive physiological conditions in Takifugu rubripes, also known as torafugu, is one of the most economically important species distributed in the northwestern part of the Pacific Ocean, in the western part of the East China Sea, and in more northern areas near Hokkaido, Japan. Fish pituitary spheroids can be easily constructed in liquid or solid plates. The culture medium (L-15) made the aggregation faster than MEM (Hank's). A Rho-kinase inhibitor (Y-27632, 10 μM) and/or fish serum (2.5 %) also promoted spheroid formation. Laser confocal microscopy analysis of spheroids cultured with annual serum of both sexes revealed that luteinizing hormone (LH) synthesis has the highest peak in the final maturation stage (3 years old, May) in accordance with the highest serum sex steroid levels; in contrast, follicle stimulating hormone (FSH) synthesis has no correlation with the dose of serum or nutrients. Similarly, 3D cell propagation assays using female serum showed that total pituitary cells displayed the highest proliferation at puberty onset (2 years old, October) before half a year of the spawning season. These results indicate that pituitary spheroids are useful in vitro models for monitoring the reproductive physiological status of fish in vivo and may be applicable to the in vitro screening of environmental chemicals and bioactive compounds affecting reproductive efficiency in aquaculture.

Association between Intracellular Calcium Signaling and Tumor Recurrence in Human Non-Functioning Pituitary Adenomas

Clinically non-functioning pituitary adenomas (CNFPAs) are the second most frequent sellar tumor among studies on community-dwelling adults. They are characterized by the absence of hormonal hypersecretion syndrome, and patients present with compressive symptoms, such as a headache and visual field defects. Immunohistochemically, most CNFPAs are of gonadotrope differentiation, with only a few of them being truly null cell adenomas. Although these tumors express receptors for one or more hypothalamic releasing hormones, to what extent this has an impact on the biological and clinical behavior of these neoplasms remains to be defined. In this research, we evaluated the basal and hypothalamic secretagogue-stimulated intracellular calcium mobilization in 13 CNFPAs, trying to correlate this response to the phenotypic features of the patients. Our results indicate that the recurrence of a CNFPA correlates positively with cellular responsiveness, as measured by spontaneous intracellular calcium activity and the ability to respond to multiple hypothalamic secretagogues. We conclude that this finding may be a useful tool for predicting the clinicopathologic behavior of CNFPAs, by testing the variation of cellular responsiveness to hypothalamic secretagogues.

Single-neuron projectomes of mouse paraventricular hypothalamic nucleus oxytocin neurons reveal mutually exclusive projection patterns

Oxytocin (OXT) plays important roles in autonomic control and behavioral modulation. However, it is unknown how the projection patterns of OXT neurons align with underlying physiological functions. Here, we present the reconstructed single-neuron, whole-brain projectomes of 264 OXT neurons of the mouse paraventricular hypothalamic nucleus (PVH) at submicron resolution. These neurons hierarchically clustered into two groups, with distinct morphological and transcriptional characteristics and mutually exclusive projection patterns. Cluster 1 (177 neurons) axons terminated exclusively in the median eminence (ME) and have few collaterals terminating within hypothalamic regions. By contrast, cluster 2 (87 neurons) sent wide-spread axons to multiple brain regions, but excluding ME. Dendritic arbors of OXT neurons also extended outside of the PVH, suggesting capability to sense signals and modulate target regions. These single-neuron resolution observations reveal distinct OXT subpopulations, provide comprehensive analysis of their morphology, and lay the structural foundation for better understanding the functional heterogeneity of OXT neurons.

Day length regulates gonadotrope proliferation and reproduction via an intra-pituitary pathway in the model vertebrate Oryzias latipes

In seasonally breeding mammals and birds, the production of the hormones that regulate reproduction (gonadotropins) is controlled by a complex pituitary-brain-pituitary pathway. Indeed, the pituitary thyroid-stimulating hormone (TSH) regulates gonadotropin expression in pituitary gonadotropes, via dio2-expressing tanycytes, hypothalamic Kisspeptin, RFamide-related peptide, and gonadotropin-releasing hormone neurons. However, in fish, how seasonal environmental signals influence gonadotropins remains unclear. In addition, the seasonal regulation of gonadotrope (gonadotropin-producing cell) proliferation in the pituitary is, to the best of our knowledge, not elucidated in any vertebrate group. Here, we show that in the vertebrate model Japanese medaka (Oryzias latipes), a long day seasonally breeding fish, photoperiod (daylength) not only regulates hormone production by the gonadotropes but also their proliferation. We also reveal an intra-pituitary pathway that regulates gonadotrope cell number and hormone production. In this pathway, Tsh regulates gonadotropes via folliculostellate cells within the pituitary. This study suggests the existence of an alternative regulatory mechanism of seasonal gonadotropin production in fish.

Revealing Sexual Dimorphism in Prolactin Regulation From Early Postnatal Development to Adulthood in Murine Models

Serum prolactin (PRL) levels exhibit a gradual rise both in male and female rats from birth to adulthood, with females consistently displaying higher levels compared to age-matched males. This pattern has traditionally been attributed to the development and maturation of endocrine and neuroendocrine networks responsible for regulating PRL synthesis and secretion. However, the effect of dopamine (DA), which acts as an inhibitory factor on lactotroph function, also increases from birth to puberty, particularly in females. Nonetheless, the secretion of PRL remains higher in females compared to males. On the other hand, the observed sex differences in serum PRL levels during early postnatal development cannot be attributed to the influence of estradiol (E2). While serum E2 levels gradually increase after birth, only after 45 days of life do the disparities in E2 levels between females and males become evident. These observations collectively suggest that neither the maturation of hypothalamic DA regulation nor the rise in E2 levels can account for the progressive and sustained elevation in serum PRL levels and the observed sexual dimorphism during postnatal development. This review highlights the importance of recent discoveries in animal models that shed light on inhibitory mechanisms in the control of PRL secretion within the pituitary gland itself, that is intrapituitary mechanisms, with a specific emphasis on the role of transforming growth factor β1 and activins in PRL secretion.

Regulation of FGF2-induced proliferation by inhibitory GPCR in normal pituitary cells

Introduction

Intracellular communication is essential for the maintenance of the anterior pituitary gland plasticity. The aim of this study was to evaluate whether GPCR-Gαi modulates basic fibroblast growth factor (FGF2)-induced proliferative activity in normal pituitary cell populations.

Methods

Anterior pituitary primary cell cultures from Wistar female rats were treated with FGF2 (10ng/mL) or somatostatin analog (SSTa, 100nM) alone or co-incubated with or without the inhibitors of GPCR-Gαi, pertussis toxin (PTX, 500nM), MEK inhibitor (U0126, 100µM) or PI3K inhibitor (LY 294002, 10 μM).

Results

FGF2 increased and SSTa decreased the lactotroph and somatotroph BrdU uptak2e (p<0.05) whereas the FGF2-induced S-phase entry was prevented by SSTa co-incubation in both cell types, with these effects being reverted by PTX, U0126 or LY294002 pre-incubation. The inhibition of lactotroph and somatotroph mitosis was associated with a downregulation of c-Jun expression, a decrease of phosphorylated (p) ERK and pAKT. Furthermore, SSTa was observed to inhibit the S-phase entry induced by FGF2, resulting in a further increase in the number of cells in the G1 phase and a concomitant reduction in the number of cells in the S phases (p< 0.05), effects related to a decrease of cyclin D1 expression and an increase in the expression of the cell cycle inhibitors p27 and p21.

Discussion

In summary, the GPCR-Gαi activated by SSTa blocked the pro-proliferative effect of FGF2 in normal pituitary cells via a MEK-dependent mechanism, which acts as a mediator of both anti and pro-mitogenic signals, that may regulate the principal effectors of the G1 to S-phase transition.

The hidden hedgehog of the pituitary: hedgehog signaling in development, adulthood and disease of the hypothalamic-pituitary axis

Hedgehog signaling plays pivotal roles in embryonic development, adult homeostasis and tumorigenesis. However, its engagement in the pituitary gland has been long underestimated although Hedgehog signaling and pituitary embryogenic development are closely linked. Thus, deregulation of this signaling pathway during pituitary development results in malformation of the gland. Research of the last years further implicates a regulatory role of Hedgehog signaling in the function of the adult pituitary, because its activity is also interlinked with homeostasis, hormone production, and most likely also formation of neoplasms of the gland. The fact that this pathway can be efficiently targeted by validated therapeutic strategies makes it a promising candidate for treating pituitary diseases. We here summarize the current knowledge about the importance of Hedgehog signaling during pituitary development and review recent data that highlight the impact of Hedgehog signaling in the healthy and the diseased adult pituitary gland.

The immune microenviroment in somatotropinomas: from biology to personalized and target therapy

Pituitary tumors are rare neoplasms, with a heterogeneous biological and clinical behavior, due to their clinical course, local invasive growth, resistance to conventional therapies and the risk of disease progression. Recent studies on tumor microenvironment (TME) provided new knowledge on the biology of these neoplasia, that may explain the different phenotypes of these tumors and suggest new biomarkers able to predict the prognosis and the treatment outcome. The identification of molecular markers that act as targets for biological therapies may open new perspectives in the medical treatments of aggressive pituitary tumors.In this paper, we will review data of TME and target therapies in somatotropinomas.

PI(4,5)P2-dependent and -independent roles of PI4P in the control of hormone secretion by pituitary cells

Plasma membrane and organelle membranes are home to seven phosphoinositides, an important class of low-abundance anionic signaling lipids that contribute to cellular functions by recruiting cytoplasmic proteins or interacting with the cytoplasmic domains of membrane proteins. Here, we briefly review the functions of three phosphoinositides, PI4P, PI(4,5)P2, and PI(3,4,5)P3, in cellular signaling and exocytosis, focusing on hormone-producing pituitary cells. PI(4,5)P2, acting as a substrate for phospholipase C, plays a key role in the control of pituitary cell functions, including hormone synthesis and secretion. PI(4,5)P2 also acts as a substrate for class I PI3-kinases, leading to the generation of two intracellular messengers, PI(3,4,5)P3 and PI(3,4)P2, which act through their intracellular effectors, including Akt. PI(4,5)P2 can also influence the release of pituitary hormones acting as an intact lipid to regulate ion channel gating and concomitant calcium signaling, as well as the exocytic pathway. Recent findings also show that PI4P is not only a precursor of PI(4,5)P2, but also a key signaling molecule in many cell types, including pituitary cells, where it controls hormone secretion in a PI(4,5)P2-independent manner.

The Contribution of Cell Imaging to the Study of Anterior Pituitary Function and Its Regulation

Advances in the knowledge of the neuroendocrine system are closely related to the development of cellular imaging and labeling techniques. This synergy ranges from the staining techniques that allowed the first characterizations of the anterior pituitary gland, its relationship with the hypothalamus, and the birth of neuroendocrinology; through the development of fluorescence microscopy applications, specific labeling strategies, transgenic systems, and intracellular calcium sensors that enabled the study of processes and dynamics at the cellular and tissue level; until the advent of super-resolution microscopy, miniscopes, optogenetics, fiber photometry, and other imaging methods that allowed high spatiotemporal resolution and long-term three-dimensional cellular activity recordings in living systems in a conscious and freely moving condition. In this review, we briefly summarize the main contributions of cellular imaging techniques that have allowed relevant advances in the field of neuroendocrinology and paradigm shifts that have improved our understanding of the function of the hypothalamic-pituitary axes. The development of these methods and equipment is the result of the integration of knowledge achieved by the integration of several disciplines and effort to solve scientific questions and problems of high impact on health and society that this system entails.

Differential Diagnosis of the Short IGF-I-Deficient Child with Apparently Normal Growth Hormone Secretion

The current differential diagnosis for a short child with low insulin-like growth factor I (IGF-I) and a normal growth hormone (GH) peak in a GH stimulation test (GHST), after exclusion of acquired causes, includes the following disorders: (1) a decreased spontaneous GH secretion in contrast to a normal stimulated GH peak ("GH neurosecretory dysfunction," GHND) and (2) genetic conditions with a normal GH sensitivity (e.g., pathogenic variants of GH1 or GHSR) and (3) GH insensitivity (GHI). We present a critical appraisal of the concept of GHND and the role of 12- or 24-h GH profiles in the selection of children for GH treatment. The mean 24-h GH concentration in healthy children overlaps with that in those with GH deficiency, indicating that the previously proposed cutoff limit (3.0-3.2 μg/L) is too high. The main advantage of performing a GH profile is that it prevents about 20% of false-positive test results of the GHST, while it also detects a low spontaneous GH secretion in children who would be considered GH sufficient based on a stimulation test. However, due to a considerable burden for patients and the health budget, GH profiles are only used in few centres. Regarding genetic causes, there is good evidence of the existence of Kowarski syndrome (due to GH1 variants) but less on the role of GHSR variants. Several genetic causes of (partial) GHI are known (GHR, STAT5B, STAT3, IGF1, IGFALS defects, and Noonan and 3M syndromes), some responding positively to GH therapy. In the final section, we speculate on hypothetical causes.

CRHR1 mediates the transcriptional expression of pituitary hormones and their receptors under hypoxia

Hypothalamus-pituitary-adrenal (HPA) axis plays critical roles in stress responses under challenging conditions such as hypoxia, via regulating gene expression and integrating activities of hypothalamus-pituitary-targets cells. However, the transcriptional regulatory mechanisms and signaling pathways of hypoxic stress in the pituitary remain to be defined. Here, we report that hypoxia induced dynamic changes in the transcription factors, hormones, and their receptors in the adult rat pituitary. Hypoxia-inducible factors (HIFs), oxidative phosphorylation, and cAMP signaling pathways were all differentially enriched in genes induced by hypoxic stress. In the pituitary gene network, hypoxia activated c-Fos and HIFs with specific pituitary transcription factors (Prop1), targeting the promoters of hormones and their receptors. HIF and its related signaling pathways can be a promising biomarker during acute or constant hypoxia. Hypoxia stimulated the transcription of marker genes for microglia, chemokines, and cytokine receptors of the inflammatory response. Corticotropin-releasing hormone receptor 1 (CRHR1) mediated the transcription of Pomc, Sstr2, and Hif2a, and regulated the function of HPA axis. Together with HIF, c-Fos initiated and modulated dynamic changes in the transcription of hormones and their receptors. The receptors were also implicated in the regulation of functions of target cells in the pituitary network under hypoxic stress. CRHR1 played an integrative role in the hypothalamus-pituitary-target axes. This study provides new evidence for CRHR1 involved changes of hormones, receptors, signaling molecules and pathways in the pituitary induced by hypoxia.

Children With Short Stature Display Reduced ACE2 Expression in Peripheral Blood Mononuclear Cells

BACKGROUND

The cause of short stature remains often unknown. The renin-angiotensin system contributes to growth regulation. Several groups reported that angiotensin-converting enzyme 2 (ACE2)-knockout mice weighed less than controls. Our case-control study aimed to investigate if children with short stature had reduced ACE2 expression as compared to controls, and its significance.

MATERIALS AND METHODS

children aged between 2 and 14 years were consecutively recruited in a University Hospital pediatric tertiary care center. Cases were children with short stature defined as height SD ≤ -2 diagnosed with growth hormone deficiency (GHD) or idiopathic short stature (ISS), before any treatment. Exclusion criteria were: acute diseases, kidney disease, endocrine or autoimmune disorders, precocious puberty, genetic syndromes, SGA history. ACE and ACE2 expression were measured in peripheral blood mononuclear cells, angiotensins were measured by ELISA.

RESULTS

Children with short stature displayed significantly lower ACE2 expression, being 0.40 fold induction (0.01-2.27) as compared to controls, and higher ACE/ACE2, with no differences between GHD and ISS. ACE2 expression was significantly and inversely associated with the risk of short stature, OR 0.26 (0.07-0.82), and it had a moderate accuracy to predict it, with an AUC of 0.73 (0.61-0.84). The cutoff of 0.45 fold induction of ACE2 expression was the value best predicting short stature, identifying correctly 70% of the children.

CONCLUSIONS

Our study confirms the association between the reduction of ACE2 expression and growth retardation. Further studies are needed to determine its diagnostic implications.

Relationships Between 24-hour LH and Testosterone Concentrations and With Other Pituitary Hormones in Healthy Older Men

Objective

To investigate the relationship between LH and testosterone (T), which characteristics associate with the strength of this relationship, and their interrelationships with GH, TSH, cortisol, and ACTH.

Design

Hormones were measured in serum samples collected every 10 minutes during 24 hours from 20 healthy men, comprising 10 offspring of long-lived families and 10 control subjects, with a mean (SD) age of 65.6 (5.3) years. We performed cross-correlation analyses to assess the relative strength between 2 timeseries for all possible time shifts.

Results

Mean (95% CI) maximal correlation was 0.21 (0.10-0.31) at lag time of 60 minutes between LH and total T concentrations. Results were comparable for calculated free, bioavailable, or secretion rates of T. Men with strong LH-T cross-correlations had, compared with men with no cross-correlation, lower fat mass (18.5 [14.9-19.7] vs. 22.3 [18.4-29.4] kg), waist circumference (93.6 [5.7] vs. 103.1 [12.0] cm), high-sensitivity C-reactive protein (0.7 [0.4-1.3] vs. 1.8 [0.8-12.3] mg/L), IL-6 (0.8 [0.6-1.0] vs. 1.2 [0.9-3.0] pg/mL), and 24-hour mean LH (4.3 [2.0] vs. 6.1 [1.5] U/L), and stronger LH-T feedforward synchrony (1.5 [0.3] vs. 1.9 [0.2]). Furthermore, T was positively cross-correlated with TSH (0.32 [0.21-0.43]), cortisol (0.26 [0.19-0.33]), and ACTH (0.26 [0.19-0.32]).

Conclusions

LH is followed by T with a delay of 60 minutes in healthy older men. Men with a strong LH-T relationship had more favorable body composition, inflammatory markers, LH levels, and LH-T feedforward synchrony. We observed positive correlations between T and TSH, cortisol, and ACTH.

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.

Differential Regulation of Gonadotropins as Revealed by Transcriptomes of Distinct LH and FSH Cells of Fish Pituitary

From mammals to fish, reproduction is driven by luteinizing hormone (LH) and follicle-stimulating hormone (FSH) temporally secreted from the pituitary gland. Teleost fish are an excellent model for addressing the unique regulation and function of each gonadotropin cell since, unlike mammals, they synthesize and secrete LH and FSH from distinct cells. Only very distant vertebrate classes (such as fish and birds) demonstrate the mono-hormonal strategy, suggesting a potential convergent evolution. Cell-specific transcriptome analysis of double-labeled transgenic tilapia expressing GFP and RFP in LH or FSH cells, respectively, yielded genes specifically enriched in each cell type, revealing differences in hormone regulation, receptor expression, cell signaling, and electrical properties. Each cell type expresses a unique GPCR signature that reveals the direct regulation of metabolic and homeostatic hormones. Comparing these novel transcriptomes to that of rat gonadotrophs revealed conserved genes that might specifically contribute to each gonadotropin activity in mammals, suggesting conserved mechanisms controlling the differential regulation of gonadotropins in vertebrates.

Hyperprolactinemia in a male pituitary androgen receptor knockout mouse is associated with female-like lactotroph development

BACKGROUND

Circulating prolactin concentration in rodents and humans is sexually dimorphic. Oestrogens are a well-characterised stimulator of prolactin release. Circulating prolactin fluctuates throughout the menstrual/oestrous cycle of females in response to oestrogen levels, but remains continually low in males. We have previously identified androgens as an inhibitor of prolactin release through characterisation of males of a mouse line with a conditional pituitary androgen receptor knockout (PARKO) which have an increase in circulating prolactin, but unchanged lactotroph number.

OBJECTIVES

In the present study, we aimed to specify the cell type that androgens act on to repress prolactin release.

MATERIALS AND METHODS

PARKO, lactotroph-specific, Pit1 lineage-specific and neural-specific conditional androgen receptor knockout male mice were investigated using prolactin ELISA, pituitary electron microscopy, immunohistochemistry and qRT-PCR.

RESULTS

Lactotroph-specific, Pit1 lineage-specific and neural-specific conditional AR knockouts did not duplicate the high circulating prolactin seen in the PARKO line. Using electron microscopy to examine ultrastructure, we showed that pituitary androgen receptor knockout male mice develop lactotrophs that resemble those seen in female mice. Castrated PARKO males have significantly reduced circulating prolactin compared to intact males. When expression of selected oestrogen-regulated anterior pituitary genes was examined, there were no differences in expression level between controls and knockouts.

DISCUSSION

The cell type that androgens act on to repress prolactin release is not the lactotroph, cells in the Pit1-lineage, or the dopaminergic neurons in the hypothalamus. PARKO males develop a female-specific lactotroph ultrastructure that this is likely to contribute to the increase in circulating prolactin. Castrated PARKO males have significantly reduced circulating prolactin compared to intact males, which suggests that removal of both circulating oestrogens and androgens reduces the stimulation of pituitary prolactin release.

CONCLUSION

Further investigation is needed into prolactin regulation by changes in androgen-oestrogen balance, which is involved sexual dimorphism of development and diseases including hyperprolactinemia.

MicroRNA-7a2 Regulates Prolactin in Developing Lactotrophs and Prolactinoma Cells

Prolactin production is controlled by a complex and temporally dynamic network of factors. Despite this tightly coordinated system, pathological hyperprolactinemia is a common endocrine disorder that is often not understood, thereby highlighting the need to expand our molecular understanding of lactotroph cell regulation. MicroRNA-7 (miR-7) is the most highly expressed miRNA family in the pituitary gland and the loss of the miR-7 family member, miR-7a2, is sufficient to reduce prolactin gene expression in mice. Here, we used conditional loss-of-function and gain-of-function mouse models to characterize the function of miR-7a2 in lactotroph cells. We found that pituitary miR-7a2 expression undergoes developmental and sex hormone-dependent regulation. Unexpectedly, the loss of mir-7a2 induces a premature increase in prolactin expression and lactotroph abundance during embryonic development, followed by a gradual loss of prolactin into adulthood. On the other hand, lactotroph development is delayed in mice overexpressing miR-7a2. This regulation of lactotroph function by miR-7a2 involves complementary mechanisms in multiple cell populations. In mouse pituitary and rat prolactinoma cells, miR-7a2 represses its target Raf1, which promotes prolactin gene expression. These findings shed light on the complex regulation of prolactin production and may have implications for the physiological and pathological mechanisms underlying hyperprolactinemia.

The Importance of Leptin to Reproduction

A healthy nutritional state is required for all aspects of reproduction and is signaled by the adipokine leptin. Leptin acts in a relatively narrow concentration range: too much or too little will compromise fertility. The leptin signal timing is important to prepubertal development in both sexes. In the brain, leptin acts on ventral premammillary neurons which signal kisspeptin (Kiss1) neurons to stimulate gonadotropin releasing hormone (GnRH) neurons. Suppression of Kiss1 neurons occurs when agouti-related peptide neurons are activated by reduced leptin, because leptin normally suppresses these orexigenic neurons. In the pituitary, leptin stimulates production of GnRH receptors (GnRHRs) and follicle-stimulating hormone at midcycle, by activating pathways that derepress actions of the messenger ribonucleic acid translational regulatory protein Musashi. In females, rising estrogen stimulates a rise in serum leptin, which peaks at midcycle, synchronizing with nocturnal luteinizing hormone pulses. The normal range of serum leptin levels (10-20 ng/mL) along with gonadotropins and growth factors promote ovarian granulosa and theca cell functions and oocyte maturation. In males, the prepubertal rise in leptin promotes testicular development. However, a decline in leptin levels in prepubertal boys reflects inhibition of leptin secretion by rising androgens. In adult males, leptin levels are 10% to 50% of those in females, and high leptin inhibits testicular function. The obesity epidemic has elucidated leptin resistance pathways, with too much leptin in either sex leading to infertility. Under conditions of balanced nutrition, however, the secretion of leptin is timed and regulated within a narrow level range that optimizes its trophic effects.

Pituitary Remodeling Throughout Life: Are Resident Stem Cells Involved?

The pituitary gland has the primordial ability to dynamically adapt its cell composition to changing hormonal needs of the organism throughout life. During the first weeks after birth, an impressive growth and maturation phase is occurring in the gland during which the distinct hormonal cell populations expand. During pubertal growth and development, growth hormone (GH) levels need to peak which requires an adaptive enterprise in the GH-producing somatotrope population. At aging, pituitary function wanes which is associated with organismal decay including the somatopause in which GH levels drop. In addition to these key time points of life, the pituitary's endocrine cell landscape plastically adapts during specific (patho-)physiological conditions such as lactation (need for PRL) and stress (engagement of ACTH). Particular resilience is witnessed after physical injury in the (murine) gland, culminating in regeneration of destroyed cell populations. In many other tissues, adaptive and regenerative processes involve the local stem cells. Over the last 15 years, evidence has accumulated that the pituitary gland houses a resident stem cell compartment. Recent studies propose their involvement in at least some of the cell remodeling processes that occur in the postnatal pituitary but support is still fragmentary and not unequivocal. Many questions remain unsolved such as whether the stem cells are key players in the vivid neonatal growth phase and whether the decline in pituitary function at old age is associated with decreased stem cell fitness. Furthermore, the underlying molecular mechanisms of pituitary plasticity, in particular the stem cell-linked ones, are still largely unknown. Pituitary research heavily relies on transgenic in vivo mouse models. While having proven their value, answers to pituitary stem cell-focused questions may more diligently come from a novel powerful in vitro research model, termed organoids, which grow from pituitary stem cells and recapitulate stem cell phenotype and activation status. In this review, we describe pituitary plasticity conditions and summarize what is known on the involvement and phenotype of pituitary stem cells during these pituitary remodeling events.

Functional Pituitary Networks in Vertebrates

The pituitary is a master endocrine gland that developed early in vertebrate evolution and therefore exists in all modern vertebrate classes. The last decade has transformed our view of this key organ. Traditionally, the pituitary has been viewed as a randomly organized collection of cells that respond to hypothalamic stimuli by secreting their content. However, recent studies have established that pituitary cells are organized in tightly wired large-scale networks that communicate with each other in both homo and heterotypic manners, allowing the gland to quickly adapt to changing physiological demands. These networks functionally decode and integrate the hypothalamic and systemic stimuli and serve to optimize the pituitary output into the generation of physiologically meaningful hormone pulses. The development of 3D imaging methods and transgenic models have allowed us to expand the research of functional pituitary networks into several vertebrate classes. Here we review the establishment of pituitary cell networks throughout vertebrate evolution and highlight the main perspectives and future directions needed to decipher the way by which pituitary networks serve to generate hormone pulses in vertebrates.

Natriuretic Peptide Expression and Function in GH3 Somatolactotropes and Feline Somatotrope Pituitary Tumours

Patients harbouring mutations in genes encoding C-type natriuretic peptide (CNP; NPPC) or its receptor guanylyl cyclase B (GC-B, NPR2) suffer from severe growth phenotypes; loss-of-function mutations cause achondroplasia, whereas gain-of-function mutations cause skeletal overgrowth. Although most of the effects of CNP/GC-B on growth are mediated directly on bone, evidence suggests the natriuretic peptides may also affect anterior pituitary control of growth. Our previous studies described the expression of NPPC and NPR2 in a range of human pituitary tumours, normal human pituitary, and normal fetal human pituitary. However, the natriuretic peptide system in somatotropes has not been extensively explored. Here, we examine the expression and function of the CNP/GC-B system in rat GH3 somatolactotrope cell line and pituitary tumours from a cohort of feline hypersomatotropism (HST; acromegaly) patients. Using multiplex RT-qPCR, all three natriuretic peptides and their receptors were detected in GH3 cells. The expression of Nppc was significantly enhanced following treatment with either 100 nM TRH or 10 µM forskolin, yet only Npr1 expression was sensitive to forskolin stimulation; the effects of forskolin and TRH on Nppc expression were PKA- and MAPK-dependent, respectively. CNP stimulation of GH3 somatolactotropes significantly inhibited Esr1, Insr and Lepr expression, but dramatically enhanced cFos expression at the same time point. Oestrogen treatment significantly enhanced expression of Nppa, Nppc, Npr1, and Npr2 in GH3 somatolactotropes, but inhibited CNP-stimulated cGMP accumulation. Finally, transcripts for all three natriuretic peptides and receptors were expressed in feline pituitary tumours from patients with HST. NPPC expression was negatively correlated with pituitary tumour volume and SSTR5 expression, but positively correlated with D2R and GHR expression. Collectively, these data provide mechanisms that control expression and function of CNP in somatolactotrope cells, and identify putative transcriptional targets for CNP action in somatotropes.

The Hypothalamic-Pituitary-Adrenal Axis: Development, Programming Actions of Hormones, and Maternal-Fetal Interactions

The hypothalamic-pituitary-adrenal axis is a complex system of neuroendocrine pathways and feedback loops that function to maintain physiological homeostasis. Abnormal development of the hypothalamic-pituitary-adrenal (HPA) axis can further result in long-term alterations in neuropeptide and neurotransmitter synthesis in the central nervous system, as well as glucocorticoid hormone synthesis in the periphery. Together, these changes can potentially lead to a disruption in neuroendocrine, behavioral, autonomic, and metabolic functions in adulthood. In this review, we will discuss the regulation of the HPA axis and its development. We will also examine the maternal-fetal hypothalamic-pituitary-adrenal axis and disruption of the normal fetal environment which becomes a major risk factor for many neurodevelopmental pathologies in adulthood, such as major depressive disorder, anxiety, schizophrenia, and others.

Direct and Indirect Effects of Sex Steroids on Gonadotrope Cell Plasticity in the Teleost Fish Pituitary

The pituitary gland controls many important physiological processes in vertebrates, including growth, homeostasis, and reproduction. As in mammals, the teleost pituitary exhibits a high degree of plasticity. This plasticity permits changes in hormone production and secretion necessary to meet the fluctuating demands over the life of an animal. Pituitary plasticity is achieved at both cellular and population levels. At the cellular level, hormone synthesis and release can be regulated via changes in cell composition to modulate both sensitivity and response to different signals. At the cell population level, the number of cells producing a given hormone can change due to proliferation, differentiation of progenitor cells, or transdifferentiation of specific cell types. Gonadotropes, which play an important role in the control of reproduction, have been intensively investigated during the last decades and found to display plasticity. To ensure appropriate endocrine function, gonadotropes rely on external and internal signals integrated at the brain level or by the gonadotropes themselves. One important group of internal signals is the sex steroids, produced mainly by the gonadal steroidogenic cells. Sex steroids have been shown to exert complex effects on the teleost pituitary, with differential effects depending on the species investigated, physiological status or sex of the animal, and dose or method of administration. This review summarizes current knowledge of the effects of sex steroids (androgens and estrogens) on gonadotrope cell plasticity in teleost anterior pituitary, discriminating direct from indirect effects.

Interrelationships Between Pituitary Hormones as Assessed From 24-hour Serum Concentrations in Healthy Older Subjects

CONTEXT

Hormones of the hypothalamic-pituitary-target gland axes are mostly investigated separately, whereas the interplay between hormones might be as important as each separate hormonal axis.

OBJECTIVE

Our aim is to determine the interrelationships between GH, TSH, ACTH, and cortisol in healthy older individuals.

DESIGN

We made use of 24-hour hormone serum concentrations assessed with intervals of 10 minutes from 38 healthy older individuals with a mean age (SD) of 65.1 (5.1) years from the Leiden Longevity Study. Cross-correlation analyses were performed to assess the relative strength between 2 24-hour hormone serum concentration series for all possible time shifts. Cross-approximate entropy was used to assess pattern synchronicity between 2 24-hour hormone serum concentration series.

RESULTS

Within an interlinked hormonal axis, ACTH and cortisol were positively correlated with a mean (95% confidence interval) correlation coefficient of 0.78 (0.74-0.81) with cortisol following ACTH concentrations with a delay of 10 minutes. Between different hormonal axes, we observed a negative correlation coefficient between cortisol and TSH of -0.30 (-0.36 to -0.25) with TSH following cortisol concentrations with a delay of 170 minutes. Furthermore, a positive mean (95% confidence interval) correlation coefficient of 0.29 (0.22-0.37) was found between TSH and GH concentrations without any delay. Moreover, cross-approximate entropy analyses showed that GH and cortisol exhibit synchronous serum concentration patterns.

CONCLUSIONS

This study demonstrates that interrelations between hormones from interlinked as well as different hypothalamic-pituitary-target gland axes are observed in healthy older individuals. More research is needed to determine the biological meaning and clinical consequences of these observations.

Pituitary Hyperplasia, Hormonal Changes and Prolactinoma Development in Males Exposed to Estrogens-An Insight From Translational Studies

Estrogen signaling plays an important role in pituitary development and function. In sensitive rat or mice strains of both sexes, estrogen treatments promote lactotropic cell proliferation and induce the formation of pituitary adenomas (dominantly prolactin or growth-hormone-secreting ones). In male patients receiving estrogen, treatment does not necessarily result in pituitary hyperplasia, hyperprolactinemia or adenoma development. In this review, we comprehensively analyze the mechanisms of estrogen action upon their application in male animal models comparing it with available data in human subjects. Sex-specific molecular targets of estrogen action in lactotropic (PRL) cells are highlighted in the context of their proliferative and secretory activity. In addition, putative effects of estradiol on the cellular/tumor microenvironment and the contribution of postnatal pituitary progenitor/stem cells and transdifferentiation processes to prolactinoma development have been analyzed. Finally, estrogen-induced morphological and hormone-secreting changes in pituitary thyrotropic (TSH) and adrenocorticotropic (ACTH) cells are discussed, as well as the putative role of the thyroid and/or glucocorticoid hormones in prolactinoma development, based on the current scarce literature.

Development of the Pituitary Gland

The development of the anterior pituitary gland occurs in distinct sequential developmental steps, leading to the formation of a complex organ containing five different cell types secreting six different hormones. During this process, the temporal and spatial expression of a cascade of signaling molecules and transcription factors plays a crucial role in organ commitment, cell proliferation, patterning, and terminal differentiation. The morphogenesis of the gland and the emergence of distinct cell types from a common primordium are governed by complex regulatory networks involving transcription factors and signaling molecules that may be either intrinsic to the developing pituitary or extrinsic, originating from the ventral diencephalon, the oral ectoderm, and the surrounding mesenchyme. Endocrine cells of the pituitary gland are organized into structural and functional networks that contribute to the coordinated response of endocrine cells to stimuli; these cellular networks are formed during embryonic development and are maintained or may be modified in adulthood, contributing to the plasticity of the gland. Abnormalities in any of the steps of pituitary development may lead to congenital hypopituitarism that includes a spectrum of disorders from isolated to combined hormone deficiencies including syndromic disorders such as septo-optic dysplasia. Over the past decade, the acceleration of next-generation sequencing has allowed for rapid analysis of the patient genome to identify novel mutations and novel candidate genes associated with hypothalmo-pituitary development. Subsequent functional analysis using patient fibroblast cells, and the generation of stem cells derived from patient cells, is fast replacing the need for animal models while providing a more physiologically relevant characterization of novel mutations. Furthermore, CRISPR-Cas9 as the method for gene editing is replacing previous laborious and time-consuming gene editing methods that were commonly used, thus yielding knockout cell lines in a fraction of the time. © 2020 American Physiological Society. Compr Physiol 10:389-413, 2020.

IGSF1 Deficiency Results in Human and Murine Somatotrope Neurosecretory Hyperfunction

CONTEXT

The X-linked immunoglobulin superfamily, member 1 (IGSF1), gene is highly expressed in the hypothalamus and in pituitary cells of the POU1F1 lineage. Human loss-of-function mutations in IGSF1 cause central hypothyroidism, hypoprolactinemia, and macroorchidism. Additionally, most affected adults exhibit higher than average IGF-1 levels and anecdotal reports describe acromegaloid features in older subjects. However, somatotrope function has not yet been formally evaluated in this condition.

OBJECTIVE

We aimed to evaluate the role of IGSF1 in human and murine somatotrope function.

PATIENTS, DESIGN, AND SETTING

We evaluated 21 adult males harboring hemizygous IGSF1 loss-of-function mutations for features of GH excess, in an academic clinical setting.

MAIN OUTCOME MEASURES

We compared biochemical and tissue markers of GH excess in patients and controls, including 24-hour GH profile studies in 7 patients. Parallel studies were undertaken in male Igsf1-deficient mice and wild-type littermates.

RESULTS

IGSF1-deficient adult male patients demonstrated acromegaloid facial features with increased head circumference as well as increased finger soft-tissue thickness. Median serum IGF-1 concentrations were elevated, and 24-hour GH profile studies confirmed 2- to 3-fold increased median basal, pulsatile, and total GH secretion. Male Igsf1-deficient mice also demonstrated features of GH excess with increased lean mass, organ size, and skeletal dimensions and elevated mean circulating IGF-1 and pituitary GH levels.

CONCLUSIONS

We demonstrate somatotrope neurosecretory hyperfunction in IGSF1-deficient humans and mice. These observations define a hitherto uncharacterized role for IGSF1 in somatotropes and indicate that patients with IGSF1 mutations should be evaluated for long-term consequences of increased GH exposure.

The Microenvironment of Pituitary Tumors-Biological and Therapeutic Implications

The tumor microenvironment (TME) includes resident and infiltrative non-tumor cells, as well as blood and lymph vessels, extracellular matrix molecules, and numerous soluble factors, such as cytokines and chemokines. While the TME is now considered to be a prognostic tool and a therapeutic target for many cancers, little is known about its composition in pituitary tumors. This review summarizes our current knowledge of the TME within pituitary tumors and the strong interest in TME as a therapeutic target. While we cover the importance of angiogenesis and immune infiltrating cells, we also address the role of the elusive folliculostellate cells, the emerging literature on pituitary tumor-associated fibroblasts, and the contribution of extracellular matrix components in these tumors. The cases of human pituitary tumors treated with TME-targeting therapies are reviewed and emerging concepts of vascular normalization and combined therapies are presented. Together, this snapshot overview of the current literature pinpoints not only the underestimated role of TME components in pituitary tumor biology, but also the major promise it may offer for both prognosis and targeted therapeutics.

Cell Type- and Sex-Dependent Transcriptome Profiles of Rat Anterior Pituitary Cells

Understanding the physiology and pathology of an organ composed of a variety of cell populations depends critically on genome-wide information on each cell type. Here, we report single-cell transcriptome profiling of over 6,800 freshly dispersed anterior pituitary cells from postpubertal male and female rats. Six pituitary-specific cell types were identified based on known marker genes and characterized: folliculostellate cells and hormone-producing corticotrophs, gonadotrophs, thyrotrophs, somatotrophs, and lactotrophs. Also identified were endothelial and blood cells from the pituitary capillary network. The expression of numerous developmental and neuroendocrine marker genes in both folliculostellate and hormone-producing cells supports that they have a common origin. For several genes, the validity of transcriptome analysis was confirmed by qRT-PCR and single cell immunocytochemistry. Folliculostellate cells exhibit impressive transcriptome diversity, indicating their major roles in production of endogenous ligands and detoxification enzymes, and organization of extracellular matrix. Transcriptome profiles of hormone-producing cells also indicate contributions toward those functions, while also clearly demonstrating their endocrine function. This survey highlights many novel genetic markers contributing to pituitary cell type identity, sexual dimorphism, and function, and points to relationships between hormone-producing and folliculostellate cells.

Regulation and Function of C-Type Natriuretic Peptide (CNP) in Gonadotrope-Derived Cell Lines

C-type natriuretic peptide (CNP) is the most conserved member of the mammalian natriuretic peptide family, and is implicated in the endocrine regulation of growth, metabolism and reproduction. CNP is expressed throughout the body, but is particularly abundant in the central nervous system and anterior pituitary gland. Pituitary gonadotropes are regulated by pulsatile release of gonadotropin releasing hormone (GnRH) from the hypothalamus, to control reproductive function. GnRH and CNP reciprocally regulate their respective signalling pathways in αT3-1 gonadotrope cells, but effects of pulsatile GnRH stimulation on CNP expression has not been explored. Here, we examine the sensitivity of the natriuretic peptide system in LβT2 and αT3-1 gonadotrope cell lines to continuous and pulsatile GnRH stimulation, and investigate putative CNP target genes in gonadotropes. Multiplex RT-qPCR assays confirmed that primary mouse pituitary tissue express Nppc,Npr2 (encoding CNP and guanylyl cyclase B (GC-B), respectively) and Furin (a CNP processing enzyme), but failed to express transcripts for Nppa or Nppb (encoding ANP and BNP, respectively). Pulsatile, but not continuous, GnRH stimulation of LβT2 cells caused significant increases in Nppc and Npr2 expression within 4 h, but failed to alter natriuretic peptide gene expression in αT3-1 cells. CNP enhanced expression of cJun, Egr1, Nr5a1 and Nr0b1, within 8 h in LβT2 cells, but inhibited Nr5a1 expression in αT3-1 cells. Collectively, these data show the gonadotrope natriuretic peptide system is sensitive to pulsatile GnRH signalling, and gonadotrope transcription factors are putative CNP-target genes. Such findings represent additional mechanisms by which CNP may regulate reproductive function.

Distinct Expression Patterns of Osteopontin and Dentin Matrix Protein 1 Genes in Pituitary Gonadotrophs

Cell-matrix interactions play important roles in pituitary development, physiology, and pathogenesis. In other tissues, a family of non-collagenous proteins, termed SIBLINGs, are known to contribute to cell-matrix interactions. Anterior pituitary gland expresses two SIBLING genes, Dmp1 (dentin matrix protein-1) and Spp1 (secreted phosphoprotein-1) encoding DMP1 and osteopontin proteins, respectively, but their expression pattern and roles in pituitary functions have not been clarified. Here we provide novel evidence supporting the conclusion that Spp1/osteopontin, like Dmp1/DMP1, are expressed in gonadotrophs in a sex- and age-specific manner. Other anterior pituitary cell types do not express these genes. In contrast to Dmp1, Spp1 expression is higher in males; in females, the expression reaches the peak during the diestrus phase of estrous cycle. In further contrast to Dmp1 and marker genes for gonadotrophs, the expression of Spp1 is not regulated by gonadotropin-releasing hormone in vivo and in vitro. However, Spp1 expression increases progressively after pituitary cell dispersion in both female and male cultures. We may speculate that gonadotrophs signal to other pituitary cell types about changes in the structure of pituitary cell-matrix network by osteopontin, a function consistent with the role of this secretory protein in postnatal tissue remodeling, extracellular matrix reorganization after injury, and tumorigenesis.

Sex-specific changes in postnatal GH and PRL secretion in somatotrope LEPR-null mice

The developing pituitary is a rapidly changing environment that is constantly meeting the physiological demands of the growing organism. During early postnatal development, the anterior pituitary is refining patterns of anterior hormone secretion in response to numerous genetic factors. Our laboratory previously developed a somatotrope leptin receptor (LEPR) deletion mouse model that had decreased lean body mass, disrupted metabolism, decreased GH stores and was GH deficient as an adult. To understand how deletion of LEPR in somatotropes altered GH, we turned our attention to postnatal development. The current study examines GH, PRL, TSH, ACTH, LH and FSH secretion during postnatal days 4, 5, 8, 10 and 15 and compares age and sex differences. The LEPR mutants have dysregulation of GH (P < 0.03) and a reduced developmental prolactin peak in males (P < 0.04) and females (P < 0.002). There were no differences in weight between groups, and the postnatal leptin surge appeared to be normal. Percentages of immunolabeled GH cells were reduced in mutants compared with controls in all age groups by 35-61% in males and 41-44% in females. In addition, we measured pituitary expression of pituitary transcription factors, POU1F1 and PROP1. POU1F1 was reduced in mutant females at PND 10 (P < 0.009) and PND 15 (P < 0.02) but increased in males at PND 10 (P < 0.01). PROP1 was unchanged in female mutants but showed developmental increases at PND 5 (P < 0.02) and PND 15 (P < 0.01). These studies show that the dysfunction caused by LEPR deletion in somatotropes begins as early as neonatal development and involves developing GH and prolactin cells (somatolactotropes).

Role of MAPK/MNK1 signaling in virus replication

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Viruses are known to exploit cellular signaling pathways.

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MAPK is a major cell signaling pathway activated by diverse group of viruses.

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MNK1 regulates both cap-dependent and IRES-mediated mRNA translation.

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This review discuss the role of MAPK, particularly the role of MNK1 in virus replication.

Viruses are obligate intracellular parasites; they heavily depend on the host cell machinery to effectively replicate and produce new progeny virus particles. Following viral infection, diverse cell signaling pathways are initiated by the cells, with the major goal of establishing an antiviral state. However, viruses have been shown to exploit cellular signaling pathways for their own effective replication. Genome-wide siRNA screens have also identified numerous host factors that either support (proviral) or inhibit (antiviral) virus replication. Some of the host factors might be dispensable for the host but may be critical for virus replication; therefore such cellular factors may serve as targets for development of antiviral therapeutics. Mitogen activated protein kinase (MAPK) is a major cell signaling pathway that is known to be activated by diverse group of viruses. MAPK interacting kinase 1 (MNK1) has been shown to regulate both cap-dependent and internal ribosomal entry sites (IRES)-mediated mRNA translation. In this review we have discuss the role of MAPK in virus replication, particularly the role of MNK1 in replication and translation of viral genome.

Regulation of reproduction via tight control of gonadotropin hormone levels

Mammalian reproduction is controlled by the hypothalamic-pituitary-gonadal axis. GnRH from the hypothalamus regulates synthesis and secretion of gonadotropins, LH and FSH, which then control steroidogenesis and gametogenesis. In females, serum LH and FSH levels exhibit rhythmic changes throughout the menstrual or estrous cycle that are correlated with pulse frequency of GnRH. Lack of gonadotropins leads to infertility or amenorrhea. Dysfunctions in the tightly controlled ratio due to levels slightly outside the normal range occur in a larger number of women and are correlated with polycystic ovaries and premature ovarian failure. Since the etiology of these disorders is largely unknown, studies in cell and mouse models may provide novel candidates for investigations in human population. Hence, understanding the mechanisms whereby GnRH regulates gonadotropin hormone levels will provide insight into the physiology and pathophysiology of the reproductive system. This review discusses recent advances in our understanding of GnRH regulation of gonadotropin synthesis.

Gonadotropin regulation by pulsatile GnRH: Signaling and gene expression

The precise orchestration of hormonal regulation at all levels of the hypothalamic-pituitary-gonadal axis is essential for normal reproductive function and fertility. The pulsatile secretion of hypothalamic gonadotropin-releasing hormone (GnRH) stimulates the synthesis and release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by pituitary gonadotropes. GnRH acts by binding to its high affinity seven-transmembrane receptor (GnRHR) on the cell surface of anterior pituitary gonadotropes. Different signaling cascades and transcriptional mechanisms are activated, depending on the variation in GnRH pulse frequency, to stimulate the synthesis and release of FSH and LH. While changes in GnRH pulse frequency may explain some of the differential regulation of FSH and LH, other factors, such as activin, inhibin and sex steroids, also contribute to gonadotropin production. In this review, we focus on the transcriptional regulation of the gonadotropin subunit genes and the signaling pathways activated by pulsatile GnRH.

Neurotransmitter receptors as signaling platforms in anterior pituitary cells

The functions of anterior pituitary cells are controlled by two major groups of hypothalamic and intrapituitary ligands: one exclusively acts on G protein-coupled receptors and the other activates both G protein-coupled receptors and ligand-gated receptor channels. The second group of ligands operates as neurotransmitters in neuronal cells and their receptors are termed as neurotransmitter receptors. Most information about pituitary neurotransmitter receptors was obtained from secretory studies, RT-PCR analyses of mRNA expression and immunohistochemical and biochemical analyses, all of which were performed using a mixed population of pituitary cells. However, recent electrophysiological and imaging experiments have characterized γ-aminobutyric acid-, acetylcholine-, and ATP-activated receptors and channels in single pituitary cell types, expanding this picture and revealing surprising differences in their expression between subtypes of secretory cells and between native and immortalized pituitary cells. The main focus of this review is on the electrophysiological and pharmacological properties of these receptors and their roles in calcium signaling and calcium-controlled hormone secretion.

Anterior Pituitary Transcriptome Suggests Differences in ACTH Release in Tame and Aggressive Foxes

Domesticated species exhibit a suite of behavioral, endocrinological, and morphological changes referred to as "domestication syndrome." These changes may include a reduction in reactivity of the hypothalamic-pituitary-adrenal (HPA) axis and specifically reduced adrenocorticotropic hormone release from the anterior pituitary. To investigate the biological mechanisms targeted during domestication, we investigated gene expression in the pituitaries of experimentally domesticated foxes (Vulpes vulpes). RNA was sequenced from the anterior pituitary of six foxes selectively bred for tameness ("tame foxes") and six foxes selectively bred for aggression ("aggressive foxes"). Expression, splicing, and network differences identified between the two lines indicated the importance of genes related to regulation of exocytosis, specifically mediated by cAMP, organization of pseudopodia, and cell motility. These findings provide new insights into biological mechanisms that may have been targeted when these lines of foxes were selected for behavior and suggest new directions for research into HPA axis regulation and the biological underpinnings of domestication.

Autocrine IL-6 mediates pituitary tumor senescence

Cellular senescence is a stable proliferative arrest state. Pituitary adenomas are frequent and mostly benign, but the mechanism for this remains unknown. IL-6 is involved in pituitary tumor progression and is produced by the tumoral cells. In a cell autonomous fashion, IL-6 participates in oncogene-induced senescence in transduced human melanocytes. Here we prove that autocrine IL-6 participates in pituitary tumor senescence. Endogenous IL-6 inhibition in somatotroph MtT/S shRNA stable clones results in decreased SA-β-gal activity and p16INK4a but increased pRb, proliferation and invasion. Nude mice injected with IL-6 silenced clones develop tumors contrary to MtT/S wild type that do not, demonstrating that clones that escape senescence are capable of becoming tumorigenic. When endogenous IL-6 is silenced, cell cultures derived from positive SA-β-gal human tumor samples decrease the expression of the senescence marker. Our results establish that IL-6 contributes to maintain senescence by its autocrine action, providing a natural model of IL-6 mediated benign adenoma senescence.

Neuroimmune Interactions: From the Brain to the Immune System and Vice Versa

Because of the compartmentalization of disciplines that shaped the academic landscape of biology and biomedical sciences in the past, physiological systems have long been studied in isolation from each other. This has particularly been the case for the immune system. As a consequence of its ties with pathology and microbiology, immunology as a discipline has largely grown independently of physiology. Accordingly, it has taken a long time for immunologists to accept the concept that the immune system is not self-regulated but functions in close association with the nervous system. These associations are present at different levels of organization. At the local level, there is clear evidence for the production and use of immune factors by the central nervous system and for the production and use of neuroendocrine mediators by the immune system. Short-range interactions between immune cells and peripheral nerve endings innervating immune organs allow the immune system to recruit local neuronal elements for fine tuning of the immune response. Reciprocally, immune cells and mediators play a regulatory role in the nervous system and participate in the elimination and plasticity of synapses during development as well as in synaptic plasticity at adulthood. At the whole organism level, long-range interactions between immune cells and the central nervous system allow the immune system to engage the rest of the body in the fight against infection from pathogenic microorganisms and permit the nervous system to regulate immune functioning. Alterations in communication pathways between the immune system and the nervous system can account for many pathological conditions that were initially attributed to strict organ dysfunction. This applies in particular to psychiatric disorders and several immune-mediated diseases. This review will show how our understanding of this balance between long-range and short-range interactions between the immune system and the central nervous system has evolved over time, since the first demonstrations of immune influences on brain functions. The necessary complementarity of these two modes of communication will then be discussed. Finally, a few examples will illustrate how dysfunction in these communication pathways results in what was formerly considered in psychiatry and immunology to be strict organ pathologies.

Extracellular Vesicles Secreted by Atherogenic Macrophages Transfer MicroRNA to Inhibit Cell Migration

OBJECTIVE

During inflammation, macrophages secrete vesicles carrying RNA, protein, and lipids as a form of extracellular communication. In the vessel wall, extracellular vesicles (EVs) have been shown to be transferred between vascular cells during atherosclerosis; however, the role of macrophage-derived EVs in atherogenesis is not known. Here, we hypothesize that atherogenic macrophages secrete microRNAs (miRNAs) in EVs to mediate cell-cell communication and promote proinflammatory and proatherogenic phenotypes in recipient cells.

APPROACH AND RESULTS

We isolated EVs from mouse and human macrophages treated with an atherogenic stimulus (oxidized low-density lipoprotein) and characterized the EV miRNA expression profile. We confirmed the enrichment of miR-146a, miR-128, miR-185, miR-365, and miR-503 in atherogenic EVs compared with controls and demonstrate that these EVs are taken up and transfer exogenous miRNA to naive recipient macrophages. Bioinformatic pathway analysis suggests that atherogenic EV miRNAs are predicted to target genes involved in cell migration and adhesion pathways, and indeed delivery of EVs to naive macrophages reduced macrophage migration both in vitro and in vivo. Inhibition of miR-146a, the most enriched miRNA in atherogenic EVs, reduced the inhibitory effect of EVs on macrophage migratory capacity. EV-mediated delivery of miR-146a repressed the expression of target genes IGF2BP1 (insulin-like growth factor 2 mRNA-binding protein 1) and HuR (human antigen R or ELAV-like RNA-binding protein 1) in recipient cells, and knockdown of IGF2BP1 and HuR using short interfering RNA greatly reduced macrophage migration, highlighting the importance of these EV-miRNA targets in regulating macrophage motility.

CONCLUSIONS

EV-derived miRNAs from atherogenic macrophages, in particular miR-146a, may accelerate the development of atherosclerosis by decreasing cell migration and promoting macrophage entrapment in the vessel wall.

Delta-like protein 1 in the pituitary-adipose axis in the adult male mouse

With the aim of studying delta-like protein 1 (DLK1) with respect to the relationship between adipocyte leptin and adenohypophyseal hormones, we carried out an immunohistochemical study analysing the presence of receptors for these hormones in the pituitary and adipose cells of male wild-type (WT) mice (Dlk1^+/+ ) compared to knockout (KO) mice (Dlk1^-/- ). The mRNA expression of these molecules was also determined using the reverse transcriptase-polymerase chain reaction. The results obtained showed that, in WT adipose cells, all of the adenohypophyseal hormone receptors were present, with a higher mRNA expression for growth hormone (GH) receptor and thyroid-stimulating hormone (TSH) receptor. Of the total cells in the anterior pituitary lobe, 17.09±0.9% were leptin receptor (LEPR) immunoreactive (-IR), mainly in GH-IR and prolactin (PRL)-IR cells (41.5±3.8%; 13.5±1.7%, respectively). In Dlk1^-/- mice, adipocyte cells showed a significant increase in the TSH receptor mRNA expression level. Moreover, the percentage of LEPR-IR GH cells showed a statistically significant increase compared to controls, from 41.5±3.8% to 53.1±4.0%. By contrast, only 3.0±0.6% of LEP-IR anterior pituitary cells were detected in Dlk1 KO mice, as opposed to 6.8±1.1% observed in WT mice. The results suggest that relationships exist between adipocytes and pituitary GH, PRL and TSH cells, in addition to an influence with respect to the synthesis and release of pituitary leptin, particularly in PRL cells.

Notch Signaling and Maintenance of SOX2 Expression in Rat Anterior Pituitary Cells

After publication of reports describing the presence of stem/progenitor cells among non-hormone-producing cells in the pituitary, the mechanism responsible for proliferation and differentiation generated considerable interest. Several studies have suggested that Notch signaling is involved. In the present study, we examined the histochemical relationship between Notch signaling molecules and the transcription factor SOX2 in rat pituitary. Combined in situ hybridization and immunohistochemistry showed that Notch2 mRNA and SOX2 were co-expressed at embryonic day 14.5 in most cells in the adenohypophyseal primordium. In adult rat pituitary, double immunohistochemistry showed that SOX2 and either Notch2 or the Notch signaling target HES1 were co-localized within cells with large oval nuclei in both the marginal cell layer and cell aggregates in the main part of the anterior lobe, which are believed to be stem cell niches. Furthermore, when the Notch signaling inhibitor DAPT was added to a primary culture of adult rat anterior pituitary cells, the proportion of SOX2-expressing cells within Notch2-positive cells was approximately 30% lower. These findings suggest that Notch signaling has a role in maintaining the stemness of precursor cells in the adult rat pituitary gland.

Mechanisms regulating angiogenesis underlie seasonal control of pituitary function

Seasonal changes in mammalian physiology, such as those affecting reproduction, hibernation, and metabolism, are controlled by pituitary hormones released in response to annual environmental changes. In temperate zones, the primary environmental cue driving seasonal reproductive cycles is the change in day length (i.e., photoperiod), encoded by the pattern of melatonin secretion from the pineal gland. However, although reproduction relies on hypothalamic gonadotrophin-releasing hormone output, and most cells producing reproductive hormones are in the pars distalis (PD) of the pituitary, melatonin receptors are localized in the pars tuberalis (PT), a physically and functionally separate part of the gland. How melatonin in the PT controls the PD is not understood. Here we show that melatonin time-dependently acts on its receptors in the PT to alter splicing of vascular endothelial growth factor (VEGF). Outside the breeding season (BS), angiogenic VEGF-A stimulates vessel growth in the infundibulum, aiding vascular communication among the PT, PD, and brain. This also acts on VEGF receptor 2 (VEGFR2) expressed in PD prolactin-producing cells known to impair gonadotrophin secretion. In contrast, in the BS, melatonin releases antiangiogenic VEGF-A_xxxb from the PT, inhibiting infundibular angiogenesis and diminishing lactotroph (LT) VEGFR2 expression, lifting reproductive axis repression in response to shorter day lengths. The time-dependent, melatonin-induced differential expression of VEGF-A isoforms culminates in alterations in gonadotroph function opposite to those of LTs, with up-regulation and down-regulation of gonadotrophin gene expression during the breeding and nonbreeding seasons, respectively. These results provide a mechanism by which melatonin can control pituitary function in a seasonal manner.

Information Transfer via Gonadotropin-Releasing Hormone Receptors to ERK and NFAT: Sensing GnRH and Sensing Dynamics

Information theoretic approaches can be used to quantify information transfer via cell signaling networks. In this study, we do so for gonadotropin-releasing hormone (GnRH) activation of extracellular signal-regulated kinase (ERK) and nuclear factor of activated T cells (NFAT) in large numbers of individual fixed LβT2 and HeLa cells. Information transfer, measured by mutual information between GnRH and ERK or NFAT, was <1 bit (despite 3-bit system inputs). It was increased by sensing both ERK and NFAT, but the increase was <50%. In live cells, information transfer via GnRH receptors to NFAT was also <1 bit and was increased by consideration of response trajectory, but the increase was <10%. GnRH secretion is pulsatile, so we explored information gained by sensing a second pulse, developing a model of GnRH signaling to NFAT with variability introduced by allowing effectors to fluctuate. Simulations revealed that when cell–cell variability reflects rapidly fluctuating effector levels, additional information is gained by sensing two GnRH pulses, but where it is due to slowly fluctuating effectors, responses in one pulse are predictive of those in another, so little information is gained from sensing both. Wet laboratory experiments revealed that the latter scenario holds true for GnRH signaling; within the timescale of our experiments (1 to 2 hours), cell–cell variability in the NFAT pathway remains relatively constant, so trajectories are reproducible from pulse to pulse. Accordingly, joint sensing, sensing of response trajectories, and sensing of repeated pulses can all increase information transfer via GnRH receptors, but in each case the increase is small.

VanWyk-Grumbach syndrome in a male pediatric patient: A rare case report and literature review

Primary hypothyroidism usually leads to retardation of linear growth and delay or even arrest of puberty in juvenile patients. In rare cases, pediatric patients with hypothyroidism may present with signs of VanWyk-Grumbach's syndrome (VWGS), which includes juvenile hypothyroidism, delayed bone age and pseudoprecocious puberty. The present study reported on a rare case of VWGS and other complications, including obesity, short stature, hepatomegaly and pituitary hyperplasia. In addition, a comprehensive literature review was performed to illustrate the treatment and outcome of VWGS in pediatric patients. The present study contributed to the current knowledge regarding the diagnosis and treatment of VWGS in pediatric patients.

Functional Role of Gonadotrope Plasticity and Network Organization

Gonadotrope cells of the anterior pituitary are characterized by their ability to mount a cyclical pattern of gonadotropin secretion to regulate gonadal function and fertility. Recent in vitro and in vivo evidence suggests that gonadotropes exhibit dramatic remodeling of the actin cytoskeleton following gonadotropin-releasing hormone (GnRH) exposure. GnRH engagement of actin is critical for gonadotrope function on multiple levels. First, GnRH-induced cell movements lead to spatial repositioning of the in vivo gonadotrope network toward vascular endothelium, presumably to access the bloodstream for effective hormone release. Interestingly, these plasticity changes can be modified depending on the physiological status of the organism. Additionally, GnRH-induced actin assembly appears to be fundamental to gonadotrope signaling at the level of extracellular signal-regulated kinase (ERK) activation, which is a well-known regulator of luteinizing hormone (LH) β-subunit synthesis. Last, GnRH-induced cell membrane projections are capable of concentrating LHβ-containing vesicles and disruption of the actin cytoskeleton reduces LH secretion. Taken together, gonadotrope network positioning and LH synthesis and secretion are linked to GnRH engagement of the actin cytoskeleton. In this review, we will cover the dynamics and organization of the in vivo gonadotrope cell network and the mechanisms of GnRH-induced actin-remodeling events important in ERK activation and subsequently hormone secretion.