Anterior pituitary thyrotropes are multifunctional cells

Pituitary multi-hormone cells in mammals and fish: history, origin, and roles

The vertebrate pituitary is a dynamic organ, capable of adapting its hormone secretion to different physiological demands. In this context, endocrinologists have debated for the past 40 years if endocrine cells are mono- or multi-hormonal. Since its establishment, the dominant "one cell, one hormone" model has been continuously challenged. In mammals, the use of advanced multi-staining approaches, sensitive gene expression techniques, and the analysis of tumor tissues have helped to quickly demonstrate the existence of pituitary multi-hormone cells. In fishes however, only recent advances in imaging and transcriptomics have enabled the identification of such cells. In this review, we first describe the history of the discovery of cells producing multiple hormones in mammals and fishes. We discuss the technical limitations that have led to uncertainties and debates. Then, we present the current knowledge and hypotheses regarding their origin and biological role, which provides a comprehensive review of pituitary plasticity.

Thyroid function in children with short stature accompanied by isolated pituitary hypoplasia

PURPOSE

Few studies have focused on thyroid function in children with isolated pituitary hypoplasia (IPH). The purpose of this study was to investigate thyroid function in children with short stature accompanied by IPH and evaluate the values of thyroid function for the diagnosis of IPH.

METHODS

This was a retrospective observational study. A total of 100 children with short stature accompanied by IPH were enrolled. Among them, 68 children presenting with isolated growth hormone deficiency (IGHD) were chosen as the IPH group. Sixty-eight age-matched and sex-matched IGHD children without pituitary abnormalities were chosen as the control group. Clinical, hormonal, and imaging parameters were analyzed. The diagnostic value of thyroid function for IGHD children with IPH was evaluated.

RESULTS

Children in the IPH group had significantly lower height standard deviation score (HSDS), HSDS-target height standard deviation score (THSDS), free thyroxine (FT4), insulin-like growth factor-1 standard deviation score (IGF-1SDS), and pituitary height than the control subjects (p = 0.027, p = 0.033, p < 0.001, p = 0.03, and p < 0.001, respectively). The value of the area under the curve (AUC) was 0.701 (95% CI 0.614-0.788, p < 0.001) when the cut-off value for FT4 was ≤ 16.43 pmol/L and the sensitivity and specificity were 72.1 and 61.8%, respectively. FT4 levels were positively correlated with FT3, GH peak, and IGF-1 SDS levels in all children with short stature accompanied by IPH (p < 0.001, p = 0.009, and p = 0.01, respectively).

CONCLUSION

IGHD children with IPH had lower FT4 levels than IGHD children without pituitary abnormalities. FT4 levels may have diagnostic value for IGHD children with IPH.

Single-cell transcriptomic analysis of adult mouse pituitary reveals sexual dimorphism and physiologic demand-induced cellular plasticity

The anterior pituitary gland drives highly conserved physiologic processes in mammalian species. These hormonally controlled processes are central to somatic growth, pubertal transformation, fertility, lactation, and metabolism. Current cellular models of mammalian anteiror pituitary, largely built on candidate gene based immuno-histochemical and mRNA analyses, suggest that each of the seven hormones synthesized by the pituitary is produced by a specific and exclusive cell lineage. However, emerging evidence suggests more complex relationship between hormone specificity and cell plasticity. Here we have applied massively parallel single-cell RNA sequencing (scRNA-seq), in conjunction with complementary imaging-based single-cell analyses of mRNAs and proteins, to systematically map both cell-type diversity and functional state heterogeneity in adult male and female mouse pituitaries at single-cell resolution and in the context of major physiologic demands. These quantitative single-cell analyses reveal sex-specific cell-type composition under normal pituitary homeostasis, identify an array of cells associated with complex complements of hormone-enrichment, and undercover non-hormone producing interstitial and supporting cell-types. Interestingly, we also identified a Pou1f1-expressing cell population that is characterized by a unique multi-hormone gene expression profile. In response to two well-defined physiologic stresses, dynamic shifts in cellular diversity and transcriptome profiles were observed for major hormone producing and the putative multi-hormone cells. These studies reveal unanticipated cellular complexity and plasticity in adult pituitary, and provide a rich resource for further validating and expanding our molecular understanding of pituitary gene expression programs and hormone production.

Effect of thyroxin on cell morphology and hormone secretion of pituitary grafts in rats

INTRODUCTION

Growth hormone and prolactin secretion is affected by thyroid hormones. To see if this influence is subsidiary to the hyptothalamus, we investigated the effects of thyroxin (T4) on hormone secretion and histology of sellar pituitaries and pituitary grafts detached from the hypothalamus (autografted or allografted under the kidney capsule).

MATERIALS AND METHODS

Male Wistar rats were divided into eight groups: control, thyroidectomised, pituitary autografted, pituitary allografted, and four additional groups that were injected with T4 for two weeks, starting four weeks after surgery. At sacrifice, adenohypophysial hormone blood levels were assessed, and tissue from sellar and grafted pituitaries were investigated by histology and electron microscopy.

RESULTS

Growth hormone and prolactin blood levels, as well as the number of growth hormone immunopositive cells increased in T4-treated groups. Both pituitary auto- and allo-grafts showed lactotroph hyperplasia and displayed spongiform areas containing cells with vesicles in their cytoplasm resembling thyroidectomy cells. This phenomenon was minimized in their respective T4-treated group. Thyroidectomy cells were identified in pituitary grafts, indicating that hypothalamic control was not essential to induce them.

DISCUSSION AND CONCLUSION

It is intriguing that the pituitary allografted group, even maintaining normal T4 blood levels, developed thyroidectomy cells in their grafts, suggesting that a long- term deficit of vascularization (>4 weeks) prevented T4 from reaching the graft. After 6 weeks, post T4 treatment of two weeks seemed to be the determining factor to minimize thyroidectomy cells in both pituitary autografted + T4 and pituitary allografted + T4 grafts compared to the untreated groups, although more time and/or higher T4 doses may be required to fully restore the euthyroid morphology.

Gonadotrope plasticity at cellular, population and structural levels: A comparison between fishes and mammals

Often referred to as "the master gland", the pituitary is a key organ controlling growth, maturation, and homeostasis in vertebrates. The anterior pituitary, which contains several hormone-producing cell types, is highly plastic and thereby able to adjust the production of the hormones governing these key physiological processes according to the changing needs over the life of the animal. Hypothalamic neuroendocrine control and feedback from peripheral tissues modulate pituitary cell activity, adjusting levels of hormone production and release according to different functional or environmental requirements. However, in some physiological processes (e.g. growth, puberty, or metamorphosis), changes in cell activity may be not sufficient to meet the needs and a general reorganization of cell composition and pituitary structure may occur. Focusing on gonadotropes, this review examines plasticity at the cellular level, which allows precise and rapid control of hormone production and secretion, as well as plasticity at the population and structural levels, which allows more substantial changes in hormone production. Further, we compare current knowledge of the anterior pituitary plasticity in fishes and mammals in order to assess what has been conserved or not throughout evolution, and highlight important remaining questions.

Potential role of cytotoxic T-lymphocyte antigen 2 alpha in secretory activity of endocrine cells in mouse adenohypophysis

The peptide hormones of the adenohypophysis are produced by proteolytic processing of their prohormone precursors. Cathepsin L is known to function as a major proteolytic enzyme involved in the production of the peptide hormones. The structure of the propeptide region of cathepsin L is identical to cytotoxic T-lymphocyte antigen-2 alpha (CTLA-2α) which is also shown to exhibit selective inhibitory activities against cathepsin L. However, the specific cell types synthesizing CTLA-2α in mouse adenohypophysis and its functional implications as relevant in vivo have not been demonstrated. In this study, CTLA-2α expression in the adenohypophysis was evaluated by immunohistochemistry. In both male and female mice, strong immunoreactivity was specifically detected in folliculostellate (FS) cells surrounding endocrine cells which were delineated by CTLA-2α. These findings suggest that the CTLA-2α may be involved in the proteolytic processing and secretion of the hormones in the adenohypophysis through regulation of cathepsin L.

Chain Modeling of Molecular Communications for Body Area Network

Molecular communications provide an attractive opportunity to precisely regulate biological signaling in nano-medicine applications of body area networks. In this paper, we utilize molecular communication tools to interpret how neural signals are generated in response to external stimuli. First, we propose a chain model of molecular communication system by considering three types of biological signaling through different communication media. Second, communication models of hormonal signaling, Ca2+ signaling and neural signaling are developed based on existing knowledge. Third, an amplify-and-forward relaying mechanism is proposed to connect different types of signaling. Simulation results demonstrate that the proposed communication system facilitates the information exchange between the neural system and nano-machines, and suggests that proper adjustment can optimize the communication system performance.

Distribution of Corticotrophin-Releasing Factor Type 1 Receptor-Like Immunoreactivity in the Rat Pituitary

Corticotrophin-releasing factor (CRF) regulates the hypothalamic-pituitary-adrenal axis response to stress through its type 1 receptor (CRF₁ ) in the corticotrophs of the anterior pituitary. Although CRF₁ mRNA expression has been confirmed in the rat pituitary, the distribution pattern of CRF₁ protein in the pituitary has not been reported. Therefore, we generated an antiserum against the amino acid fragment corresponding to the 177-188 sequence of the first extracellular loop of the rat CRF₁ . Using the antiserum, CRF₁ -like immunoreactivity (CRF₁ -LI) was detected in the anterior lobe cells of the rat pituitary where some of them expressed intense signals. CRF₁ -LI also appeared in the intermediate lobe cells and on the fibre-like elements of the posterior lobe of the pituitary. Dual immunofluorescence labelling showed that corticotrophs exhibited the highest percentage of CRF₁ (male: 27.1 ± 3.0%, female: 18.0 ± 3.0%), followed by lactotrophs (male: 6.7 ± 3.0%, female: 12.1 ± 1.3%), gonadotrophs (male: 2.6 ± 1.0%, female: 7.5 ± 0.5%), thyrotrophs (male: 2.9 ± 0.1%, female: 5.3 ± 1.2%) and somatotrophs (male: 1.1 ± 0.3%, female: 1.2 ± 0.5%). The percentage of CRF₁ -LI-positive cells that were corticotrophs was significantly higher in male rats than in female rats, whereas CRF₁ -LI-positive lactotrophs and gonadotrophs were significantly higher in female rats than in male rats. Almost all of the melanotrophs were positive for CRF₁ in the intermediate lobe (98.9 ± 0.2%). CRF₁ -LI and the percentage of CRF₁ -LI in corticotrophs were decreased in the anterior pituitary, and the distribution patterns were altered from a diffuse to punctate one by adrenalectomy; the changes were restored by treatment with dexamethasone (100 μg/kg bw). These results suggest that CRF₁ is involved in the modulation of the functions of the pituitary; moreover, protein expression and the distribution patterns of CRF₁ are regulated by glucocorticoids in the rat anterior pituitary.

Functional morphology of pituitary -thyroid and -adrenocortical axes in middle-aged male rats treated with Vitex agnus castus essential oil

We previously reported that Vitex agnus-castus L. essential oil (VACEO), when administered to middle-aged males, exerts a bone-protective effect, induces silencing of locomotor activities and decreases pituitary prolactin immunopositivity. To further assess the putative endocrine effects of VACEO, we examined the pituitary-thyroid and -adrenocortical axes in our model. Sixteen-month-old Wistar rats were subcutaneously administered 60mg/kg of VACEO dissolved in sterile olive oil, while the control group received the same amount of vehicle alone for three weeks. Pituitaries, thyroids and adrenals were analyzed by qualitative and quantitative histological approaches. Concentration of thyroid stimulating hormone (TSH), total thyroxine and triiodothyronine (TH), adrenocorticotrophic hormone (ACTH), corticosterone in serum and in adrenal tissue were measured. In VACEO-treated rats, the relative volume density of pituitary thyrotrophs increased (p<0.001), while intensity of cytoplasmic TSHβ immunostaining decreased (p<0.001), consistent with elevated TSH in serum (p<0.01). The thyroid tissue was characterized by a micro-follicular structure, increased relative volume of follicular epithelium (p<0.05), decreased volume of luminal colloid (p<0.001) and increased basolateral expression of sodium-iodide symporter-immunopositivity (p<0.05). Serum TH also increased (p<0.01). The relative volume density of pituitary corticotrophs decreased (p<0.05), compatible with decline in circulating ACTH (p<0.05). Neither tissue nor serum corticosterone levels were affected by VACEO treatment. In conclusion, the observed changes in TSH and ACTH strongly indicate central endocrine effects of prolonged VACEO treatment. In this respect, production of ACTH decreased without impact on corticosterone production. Increase in serum concentration of both TH and TSH are not compatible with a negative feedback loop and suggest a major change in set-point regulation of the hypothalamic-pituitary-thyroid axis.

Corticotropin-releasing hormone: Mediator of vertebrate life stage transitions?

Hormones, particularly thyroid hormones and corticosteroids, play critical roles in vertebrate life stage transitions such as amphibian metamorphosis, hatching in precocial birds, and smoltification in salmonids. Since they synergistically regulate several metabolic and developmental processes that accompany vertebrate life stage transitions, the existence of extensive cross-communication between the adrenal/interrenal and thyroidal axes is not surprising. Synergies of corticosteroids and thyroid hormones are based on effects at the level of tissue hormone sensitivity and gene regulation. In addition, in representative nonmammalian vertebrates, corticotropin-releasing hormone (CRH) stimulates hypophyseal thyrotropin secretion, and thus functions as a common regulator of both the adrenal/interrenal and thyroidal axes to release corticosteroids and thyroid hormones. The dual function of CRH has been speculated to control or affect the timing of vertebrate life history transitions across taxa. After a brief overview of recent insights in the molecular mechanisms behind the synergic actions of thyroid hormones and corticosteroids during life stage transitions, this review examines the evidence for a possible role of CRH in controlling vertebrate life stage transitions.

Single-Cell Phenotypic Characterization of Human Pituitary GHomas and Non-Functioning Adenomas Based on Hormone Content and Calcium Responses to Hypothalamic Releasing Hormones

Human pituitary tumors are generally benign adenomas causing considerable morbidity due to excess hormone secretion, hypopituitarism, and other tumor mass effects. Pituitary tumors are highly heterogeneous and difficult to type, often containing mixed cell phenotypes. We have used calcium imaging followed by multiple immunocytochemistry to type growth hormone secreting (GHomas) and non-functioning pituitary adenomas (NFPAs). Individual cells were typed for stored hormones and calcium responses to classic hypothalamic releasing hormones (HRHs). We found that GHomas contained growth hormone cells either lacking responses to HRHs or responding to all four HRHs. However, most GHoma cells were polyhormonal cells responsive to both thyrotropin-releasing hormone (TRH) and GH-releasing hormone. NFPAs were also highly heterogeneous. Some of them contained ACTH cells lacking responses to HRHs or polyhormonal gonadotropes responsive to LHRH and TRH. However, most NFPAs were made of cells storing no hormone and responded only to TRH. These results may provide new insights on the ontogeny of GHomas and NFPAs.

Morphological and functional changes in pituitary-thyroid axis following prolonged exposure of female rats to constant light

Light regulates numerous physiological functions and synchronizes them with the environment, in part by adjusting secretion of different hormones. We hypothesized that constant light (CL) would disturb pituitary-thyroid axis. Our aim was to determine morphological and functional changes in this endocrine system in such extreme conditions and, based on the obtained results, to propose the underlying mechanism(s). Starting from the thirtieth postnatal day, female Wistar rats were exposed to CL (600 lx) for the following 95 days. The controls were maintained under the regular laboratory lighting conditions. After decapitation, pituitaries and thyroids were prepared for further histomorphometric, immunohistochemical, and immunofluorescence examinations. Concentration of thyroid stimulating hormone (TSH), total T4 and T3 (TH) were determined. Thyroid tissue of light-treated rats was characterized by microfollicular structure. We detected no change in total thyroid volume, localization and accumulation of thyroglobulin, thyroid peroxidase, and sodium-iodide symporter in the follicular epithelium of CL rats. The volume of follicular epithelium and activation index were increased, while volume of the colloid and serum levels of TH decreased. In the pituitary, the relative intensity of TSH β-immunofluorescence signal within the cytoplasm of thyrotrophs increased, but their average cell volume and the relative volume density decreased. Serum TSH was unaltered. We conclude that exposure of female rats to CL induced alterations in pituitary-thyroid axis. Thyroid tissue was characterized by microfollicular structure. Serum TH levels were reduced without accompanying increase in serum TSH. We hypothesize that increased secretion and clearance of TH together with unchanged or even decreased hormonal synthesis, resulted in decreased serum TH levels in CL group. We assume this decrease consequently led to increased synthesis and/or accumulation of pituitary TSH. However, decreased average TSH cell volume and relative volume density, together with unchanged serum TSH, point to additional, negative regulation of thyrotrophs.

Cells co-expressing luteinising hormone and thyroid-stimulating hormone are present in the ovine pituitary pars distalis but not the pars tuberalis: implications for the control of endogenous circannual rhythms of prolactin

BACKGROUND/AIMS

A mammalian circannual pacemaker responsible for regulating the seasonal pattern of prolactin has been recently described in sheep. This pacemaker resides within the pars tuberalis, an area of the pituitary gland that densely expresses melatonin receptors. However, the chemical identity of the cell type which acts as the pacemaker remains elusive. Mathematical-modelling approaches have established that this cell must be responsive to the static melatonin signal as well as prolactin negative feedback. Considering that in sheep the gonadotroph is the only cell in the pars tuberalis which expresses the prolactin receptor, and that in other photoperiodic species the thyrotroph is the only cell expressing the melatonin receptor in this tissue, a cell type which expresses both proteins would fulfil the theoretical criteria of a circannual pacemaker.

METHODS

Pituitary glands were obtained from female sheep under short days (breeding season) and long days (non-breeding season) and double immunofluorescent staining was conducted to determine the prevalence of bi-hormonal cells in the pars distalis and pars tuberalis using specific antibodies to luteinising hormone-β and thyroid-stimulating hormone-β.

RESULTS

The results reveal that whilst such a bihormonal cell is clearly present in the pars distalis and constitute 4% of the gonadotroph population in this region, the same cell type is completely absent from the pars tuberalis even though LH gonadotrophs are abundantly expressed.

CONCLUSIONS

Based on these findings, together with existing data, we are able to propose an alternative model where the gonadotroph itself is controlled indirectly by neighbouring melatonin responsive cells, allowing it to act as a pacemaker.

Anterior pituitary cell networks

Both endocrine and non-endocrine cells of the pituitary gland are organized into structural and functional networks which are formed during embryonic development but which may be modified throughout life. Structural mapping of the various endocrine cell types has highlighted the existence of distinct network motifs and relationships with the vasculature which may relate to temporal differences in their output. Functional characterization of the network activity of growth hormone and prolactin cells has revealed a role for cell organization in gene regulation, the plasticity of pituitary hormone output and remarkably the ability to memorize altered demand. As such, the description of these endocrine cell networks alters the concept of the pituitary from a gland which simply responds to external regulation to that of an oscillator which may memorize information and constantly adapt its coordinated networks' responses to the flow of hypothalamic inputs.

Characterization of Xenobiotic-Induced Hepatocellular Enzyme Induction in Rats

During routine safety evaluation of RO2910, a non-nucleoside reverse transcriptase inhibitor for HIV infection, histopathology findings concurrent with robust hepatocellular induction occurred in multiple organs, including a unique, albeit related, finding in the pituitary gland. For fourteen days, male and female rats were administered, by oral gavage vehicle, 100, 300, or 1000 mg/kg/day of RO2910. Treated groups had elevated serum thyroid-stimulating hormone and decreased total thyroxine, and hypertrophy in the liver, thyroid gland, and pituitary pars distalis. These were considered consequences of hepatocellular induction and often were dose dependent and more pronounced in males than in females. Hepatocellular centrilobular hypertrophy corresponded with increased expression of cytochrome P450s 2B1/2, 3A1, and 3A2 and UGT 2B1. Bilateral thyroid follicular cell hypertrophy occurred concurrent to increased mitotic activity and sometimes colloid depletion, which were attributed to changes in thyroid hormone levels. Males had hypertrophy of thyroid-stimulating hormone–producing cells (thyrotrophs) in the pituitary pars distalis. All findings were consistent with the well-established adaptive physiologic response of rodents to xenobiotic-induced hepatocellular microsomal enzyme induction. Although the effects on the pituitary gland following hepatic enzyme induction-mediated hypothyroidism have not been reported previously, other models of stress and thyroid depletion leading to pituitary stimulation support such a shared pathogenesis.

The role of the hGH locus control region in somatotrope restriction of hGH-N gene expression

Expression of mammalian GH is normally restricted to somatotropes and somatolactotropes (somatotrope lineages) in the anterior pituitary. The basis for this restriction remains incompletely understood. Recent studies indicate that deoxyribonuclease I hypersensitive site I (HSI) of the hGH locus control region, located at -14.5 kb relative to the hGH-N promoter, acts as a potent long-range enhancer of hGH-N transcription. Here we report that HSI is also critical to somatotrope-restriction of hGH-N expression. Loss of HSI activity, either by direct inactivation of HSI or by interference with HSI-dependent downstream events, results in a relaxation of hGH-N cell-type specification with expansion of hGH-N expression to the full spectrum of Pit-1 positive pituitary cell types. These findings expand the defined roles for HSI of the hGH locus control region to include somatotrope lineage restriction as well as transcriptional enhancement of hGH-N gene expression.

The pituitary of non-pregnant and pregnant viscachas (Lagostomus maximus maximus): a comparative study by immunohistochemistry and morphometric analysis

The neuroendocrine hypothalamic-pituitary axis undergoes morphological and biochemical changes throughout gestation. In viscacha, pregnancy lasts approximately 154 days, and three stages can be described: early, mid- and late pregnancy. The aim of this work was to study the pituitary LH-gonadotrophs, FSH-gonadotrophs, somatotrophs, corticotrophs and thyrotrophs of non-pregnant and pregnant adult viscachas by immunohistochemistry and morphometric analysis. Immunopositive percentage area (%IA), cell percentage in the pars distalis (%PDC), number of cells per reference area (n°cell/RA), and major cellular (MCD) and nuclear (ND) diameters were analyzed. The different cell populations showed a well-defined morphology, immunolabeling patterns and regionalization in the pars distalis (PD). In the early pregnancy of animals the morphometric analysis demonstrated that %IA, %PDC and n°cell/RA increased in the FSH-gonadotrophs and decreased in the somatotrophs in relation to non-pregnant animals. In mid-pregnancy, there was an increase in %IA, %PDC, and n°cell/RA of LH-gonadotrophs, FSH-gonadotrophs, somatotrophs, and thyrotrophs. The MCD of LH-gonadotrophs and FSH-gonadotrophs increased. In late pregnancy, the %IA, %PDC and n°cell/RA of LH-gonadotrophs, FSH-gonadotrophs, somatotrophs and corticotrophs decreased whereas the values of the thyrotrophs remained constant. The MCD of LH-gonadotrophs, FSH-gonadotrophs and corticotrophs decreased. No significant changes were observed in the ND of the studied cell types. In conclusion, this work provides evidence for histological and morphometric changes in the different cell types of the pituitary PD in viscachas during pregnancy, probably according to the requirements of this physiological stage.

Corticotropin-releasing hormone receptor expression and functional signaling in murine gonadotrope-like cells

Corticotropin-releasing hormone (CRH) is a key regulator of the mammalian stress response, mediating a wide variety of stress-associated behaviors including stress-induced inhibition of reproductive function. To investigate the potential direct action of CRH on pituitary gonadotrope function, we examined CRH receptor expression and second messenger signaling in alpha T3-1 cells, a murine gonadotrope-like cell line. Reverse transcriptase PCR (RT-PCR) studies demonstrated that alpha T3-1 cells express mRNA for the two CRH receptor subtypes, CRHR1 and CRHR2, with CRHR2alpha as the predominant CRHR2 isoform. Stimulation of the cells with CRH or urocortin (UCN) resulted in rapid, transient increases in the intracellular levels of cAMP that were completely blocked by the addition of alpha-helical CRH 9-41 or astressin, non-selective CRH receptor antagonists. Stimulation of the cells with CRHR2-specific ligands, urocortin 2 (UCN2) or urocortin 3 (UCN3), resulted in rapid increases in intracellular cAMP levels to 50-60% of the levels observed with UCN. Treatment with a selective CRHR2 antagonist, antisauvagine, completely blocked UCN3-mediated increases in cAMP and significantly reduced, but did not completely block UCN-mediated increases in cAMP, demonstrating that both CRHR1 and CRHR2 are functionally active in these gonadotrope-like cells. Finally, UCN treatment significantly increased the transcriptional activity of the glycoprotein hormone alpha-subunit promoter as assessed by alpha-luciferase transfection assays. Together, these results demonstrate the functional signaling of CRH receptors in alpha T3-1 cells, suggesting that CRH may also modulate pituitary gonadotrope function in vivo.

Novel expression of type 1 corticotropin-releasing hormone receptor in multiple endocrine cell types in the murine anterior pituitary

The CRH family of ligands signals via two distinct receptors, CRH-R1 and CRH-R2. Previous studies localized CRH-R1 and CRH-R2 to a subset of anterior pituitary corticotropes and gonadotropes, respectively. However, numerous studies have indicated that stress and CRH activity can alter the secretion of multiple anterior pituitary hormones, suggesting a broader expression of the CRH receptors in pituitary. To examine this hypothesis, the in vivo expression of CRH-R1 and CRH-R2 mRNA was further characterized in adult mouse pituitary. Quantitative RT-PCR analysis demonstrated that CRH-R1 mRNA is greater than 100-fold more abundant than CRH-R2 mRNA in male and female mouse pituitaries. Dual in situ hybridization analysis identified cell-specific CRH-R1 expression in the anterior pituitary. At least half of the CRH-R1-positive cells expressed proopiomelanocortin-mRNA (50% in females; 70% in males). In females, a significant percentage of the cells expressing CRH-R1 also expressed transcript for prolactin (40%), LHbeta (10%), or TSH (3%), all novel sites of CRH-R1 expression. Similarly in males, a percentage of CRH-R1-positive cells expressed prolactin (12%), LHbeta (13%), and TSH (5%). RT-PCR studies with immortalized murine anterior pituitary cell lines showed CRH-R1 and/or CRH-R2 expression in corticotropes (AtT-20 cells), gonadotropes (alphaT3-1 and LbetaT2 cells), and thyrotropes (alphaTSH cells). Whereas CRH-R1 expression in corticotropes is well established, the presence of CRH-R1 mRNA in a subset of lactotropes, gonadotropes, and thyrotropes establishes these cell types as novel sites of murine CRH-R1 expression and highlights the pituitary as an important site of interaction between the hypothalamus-pituitary-adrenal and multiple endocrine axes.

Expanded nonhuman primate tregs exhibit a unique gene expression signature and potently downregulate alloimmune responses

We have established two complementary strategies for purifying naturally occurring regulatory T cells (Tregs) from rhesus macaques in quantities that would be sufficient for use as an in vivo cellular therapeutic. The first strategy identified Tregs based on their being CD4+/CD25(bright). The second incorporated CD127, and purified Tregs based on their expression of CD4 and CD25 and their low expression of CD127. Using these purification strategies, we were able to purify as many as 1x10(6) Tregs from 120 cc of peripheral blood. Cultures of these cells with anti-CD3, anti-CD28 and IL-2 over 21 days yielded as much as a 450-fold expansion, ultimately producing as many as 4.7x10(8) Tregs. Expanded Treg cultures potently inhibited alloimmune proliferation as measured by a carboxyfluorescein succinimidyl ester- mixed lymphocyte reaction (CFSE-MLR) assay even at a 1:100 ratio with responder T cells. Furthermore, both responder-specific and third-party Tregs downregulated alloproliferation similarly. Both freshly isolated and cultured Tregs had gene expression signatures distinguishable from concurrently isolated bulk CD4+ T-cell populations, as measured by singleplex reverse transcriptase-polymerase chain reaction (RT-PCR) and gene array. Moreover, an overlapping yet distinct gene expression signature seen in freshly isolated compared to expanded Tregs identifies a subset of Treg genes likely to be functionally significant.

Functional and morphological changes in the adenohypophysis of dogs with induced primary hypothyroidism: loss of TSH hypersecretion, hypersomatotropism, hypoprolactinemia, and pituitary enlargement with transdifferentiation

From case studies in humans it is known that primary hypothyroidism (PH) may be associated with morphological and functional changes of the pituitary. There is no insight into the time scale of these changes. In this study, seven beagle dogs were followed up for 3 years after the induction of primary hypothyroidism. Three of these dogs were followed up for another 1.5 years while receiving l-thyroxine. Adenohypophyseal function was investigated at 2-month intervals with the combined intravenous injection of CRH, GHRH, GnRH, and TRH, and measurement of the plasma concentrations of ACTH, GH, LH, PRL, and TSH. In addition, after 2 years of hypothyroidism a single TRH-stimulation test and a somatostatin test were performed, with measurements of the same pituitary hormones. Every 6 months the pituitary gland was visualized by computed tomography (CT). Induction of PH led to high plasma TSH concentrations for a few months, where after concentrations gradually declined to values no longer significantly different from pre-PH values. A blunted response to stimulation of TSH release preceded this decline. Basal plasma GH concentrations increased during PH and there was a paradoxical hyperresponsiveness to TRH stimulation. Basal GH concentrations remained elevated and returned only to low values during l-thyroxine treatment. Basal PRL concentrations decreased significantly during PH and normalized after several months of l-thyroxine treatment. The pituitary gland became enlarged in all dogs. Histomorphology and immunohistochemical studies in 4 dogs, after 3 years of PH, revealed thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and decreased numbers of mammotrophs. Several cells stained for both GH and TSH. In conclusion, with time PH led to a loss of the TSH response to low T4 concentrations, hypersecretion of GH, and hyposecretion of PRL. The enlarged pituitaries were characterized by thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and double-staining cells, which are indicative of transdifferentiation.

Rapid changes in anterior pituitary cell phenotypes in male and female mice after acute cold stress

The anterior pituitary (AP) is made of five different cell types. The relative abundance and phenotype of AP cells may change in different physiological situations as an expression of pituitary plasticity. Here, we analyze in detail the phenotype of mouse corticotropes and the effects of acute cold stress on AP cell populations. The hormone content and the expression of hypothalamic-releasing hormone (HRH) receptors in all the five AP cell types were studied in the male and female mice at rest and after a 30-min cold stress. Expression of HRH receptors was evidenced by imaging the single-cell cytosolic Ca(2+) responses in fura-2-loaded cells. Hormone contents were studied by multiple, simultaneous immunofluorescence of all the five hormones. Corticotropes displayed a striking sexual dimorphism, even in the resting condition. Male corticotropes showed the orthodox phenotype. They were monohormonal, storing only ACTH, and monoreceptorial, responding only to CRH. In contrast, female corticotropes were made of about equal parts of orthodox cells and multifunctional cells, which co-stored additional AP hormones and expressed additional HRH receptors. Cold stress did not modify the number of ACTH containing cells, but, according to immunostaining, it increased the relative abundance of other AP cell types at the expense of the pool of cells storing no hormones. Cold stress also modified the response to CRH and other HRHs. Most of these phenotypical changes presented a strong sexual dimorphism. These results indicate that pituitary plasticity is even larger than previously thought.

Hypothalamic input is required for development of normal numbers of thyrotrophs and gonadotrophs, but not other anterior pituitary cells in late gestation sheep

To evaluate the hypothalamic contribution to the development of anterior pituitary (AP) cells we surgically disconnected the hypothalamus from the pituitary (hypothalamo-pituitary disconnection, HPD) in fetal sheep and collected pituitaries 31 days later. Pituitaries (n = 6 per group) were obtained from fetal sheep (term = 147 +/- 3 days) at 110 days (unoperated group) of gestation and at 141 days from animals that had undergone HPD or sham surgery at 110 days. Cells were identified by labelling pituitary sections with antisera against the six AP hormones. Additionally, we investigated the colocalization of glycoprotein hormones. The proportions of somatotrophs and corticotrophs were unchanged by age or HPD. Lactotrophs increased 80% over time, but the proportion was unaffected by HPD. Thyrotrophs, which were unaffected by age, increased 70% following HPD. Gonadotrophs increased with gestational age (LH+ cells 55%; FSH+ cells 19-fold), but this was severely attenuated by HPD. We investigated the possible existence of a reciprocal effect of HPD on multipotential glycoprotein-expressing cells. Co-expression of LH and TSH was extremely rare (< 1%) and unchanged over the last month of gestation or HPD. The increase of gonadotrophs expressing FSH only or LH and FSH was attenuated by HPD. Therefore, the proportions of somatotrophs, lactotrophs and corticotrophs are regulated independently of hypothalamic input in the late gestation fetal pituitary. In marked contrast, the determination of the thyrotroph and gonadotroph lineages over the same time period is subject to complex mechanisms involving hypothalamic factors, which inhibit differentiation and/or proliferation of thyrotrophs, but stimulate gonadotrophs down the FSH lineage. Development of a distinct population of gonadotrophs, expressing only LH, appears to be subject to alternative mechanisms.

Effect of nutrient restriction on the somatotropes and substance P-immunoreactive cells in the pituitary of the female ovine fetus

The maternal environment affects fetal development and may influence the physiology of the adult. Fetal growth hormone (GH) is increased by maternal undernutrition but the mechanisms responsible are unknown. This study determined the effect of maternal undernutrition on the development of fetal pituitary somatotropes in the female. Ewes were grouped randomly into control (fed 100% of requirements) or nutrient restricted (fed 50%) from Days 28 to 78 of gestation. At Day 78, the ewes were killed and fetuses collected (Day 78 NR (nutrient restricted): n=6; Day 78C (control): n=6). Remaining ewes were realimented to 100% of nutritional requirements and were killed at Day 135 (Day 135 NR (nutrient restricted): n=6; Day 135 C (control): n=6). Somatotropes were visualized immunocytochemically and the size, mean density, total percentage and proportion colocalized with substance P were determined for each group. Nutrient restriction increased (p<0.01) the density of pituitary cells in Day 78 fetuses but this difference was no longer apparent by Day 135 after realimentation. The density and proportion of somatotropes were not different between treatment groups at Day 78 but were significantly (p<0.05) lower in the nutrient restricted Day 135 fetuses as compared to the Day 135 control animals. Somatotropes from restricted fetuses were significantly (p<0.001) larger at Day 78. Nutrient restriction increased the density (p<0.001) and percentage (p<0.05) of substance P-immunoreactive cells Day 135 fetuses. Similarly, the proportion of somatotropes that expressed substance P was significantly (p<0.05) increased by nutrient restriction in the Day 135 fetuses. Although nearly two thirds of substance P-immunoreactive cells co-expressed GH, there was no significant effect of treatment on this co-expression. Additional studies are required to determine if other components of the neuroendocrine GH axis are affected by this nutritional insult, if the alterations that we have observed, particularly in the tachykinin system, persist into adulthood and, importantly, what are the long-term consequences of an altered GH axis.

Cells of the anterior pituitary

The anterior pituitary is made up of a number of cell types that are essential for such physiological processes as growth, development, homeostasis, metabolism, and reproduction. These include the hormonal cells corticotropes, thyrotropes, gonadotropes, somatotropes, lactotropes and a small population of mammosomatotropes, together with a non-hormonal cell type called the folliculo-stellate cells. The anterior pituitary hormonal cells are highly differentiated and are committed very early on during embryonic development. Their development is tightly regulated by both extrinsic signals as well as by endogenous gene expression. Many transcription factors that shape the development and functions of the anterior pituitary cells have been identified. Even after differentiation, pituitary cells continue to undergo mitosis and this process could be augmented under certain conditions in adulthood. Some anterior pituitary cells are multifunctional and exhibit mixed phenotypes. Pituitary tumors, which are mostly monoclonal in nature, are rather common. The molecular pathogenesis of pituitary tumorigenesis involves complex and diverse mechanisms. Aberrant intra- and extra-pituitary factors are involved. Mutations of some genes specific to pituitary tumors also play a role.

Triiodothyronine expands the lactotroph and maintains the lactosomatotroph population, whereas thyrotrophin-releasing hormone augments thyrotroph abundance in aggregate cell cultures of postnatal rat pituitary gland

In the present study, we used a three-dimensional pituitary cell culture system from early postnatal rats to examine the in vitro developmental potential of triiodothyronine (T3) and thyrotrophin-releasing hormone (TRH). Cell types were identified at the hormone mRNA level by single-cell reverse transcription-polymerase chain reaction and any change in abundance was further examined by immunofluorescence staining of the corresponding hormone protein. In aggregates from 14-day-old rats, long-term (12-16 days) treatment with T3 (0.5 nM) increased the abundance of cells expressing prolactin mRNA (PRLmRNA cells) by 2.5-fold and lowered that of nonhormonal cells and thyroid-stimulating hormone beta (TSHbeta)mRNA cells. The abundance of growth hormone (GH)mRNA cells decreased during culture compared to that in the freshly dispersed pituitary gland and T3 did not significantly affect this cell population. Cells coexpressing PRL mRNA and GH mRNA virtually disappeared during culture but reappeared in the presence of T3. T3 increased the abundance of PRL-immunoreactive (ir) cells in aggregates from 14-day-old rats, as well as in aggregates from newborn and 1-week-old rats. As estimated by bromodeoxyuridine (BrdU) labelling, a 3-day treatment with T3 enhanced the number of PRL-ir cells that had incorporated BrdU, but did not yet expand the total population of PRL-ir cells. Long-term treatment with TRH (100 nM) did not affect the proportion of PRLmRNA or GHmRNA cells, but consistently increased the proportional number of TSHbeta(mRNA) and TSHbeta-ir cells. The present data confirm the findings obtained in recent in vivo loss of function genetic studies suggesting that T3 plays a prominent role in postnatal expansion of the lactotroph population and that TRH is important for thyrotroph development. The data suggest that the effect of T3 is brought about by a direct action on the pituitary gland through a cell proliferation mechanism. T3 also appears to support the lactosomatotroph population. In view of the established theory that lactotrophs develop from GH-expressing progenitor cells and that this is a post mitotic event, we propose that T3 is mitogenic for GHmRNA cells that lack GH-ir material and that transdifferentiate into PRL-ir cells, but that a pathway of PRL cell development from mitotic nonhormonal cell progenitors may also be involved.

Changes in expression of hypothalamic releasing hormone receptors in individual rat anterior pituitary cells during maturation, puberty and senescence

Anterior pituitary (AP) is formed by five different cell types, each one producing a different AP hormone whose secretion is regulated by a specific hypothalamic-releasing hormone (HRH). On the other hand, a significant number of AP cells express multiple HRH receptors (multiresponsive cells). Plastic changes in expression of HRH receptors in individual AP cells are involved in critical endocrine events. Here we have characterized the changes in functional responses to CRH, LHRH, TRH, and GHRH in individual AP cells throughout the whole life span of the rat. To this end, calcium responses to the HRHs were followed by single-cell imaging in freshly dispersed AP cells prepared from rats of different ages (0-540 postnatal days). Three different cell pools were identified: 1) monoresponsive cells, holding a single class of HRH receptor; 2) multiresponsive cells; and 3) nonresponsive cells. The relative abundance of each pool changed with age. Nonresponsive cells were abundant at birth, multiresponsive cells were abundant at puberty, and monoresponsive cells dominated at senescence. The relative abundance of each HRH receptor changed largely with age but not gender. In addition, the contribution of monoresponsive and multiresponsive cells to responses to each HRH changed very much with age. Thus, the anterior pituitary shows large changes in cell populations typed by functional responses to HRHs during maturation, puberty, and senescence.

Colocalization of GH, TSH and prolactin, but not ACTH, with betaLH-immunoreactivity: evidence for pluripotential cells in the ovine pituitary

Increasing evidence suggests that multihormonal cells in the pituitary gland may be more commonplace than previously thought. This has forced us to reconsider our classical view of cell populations in the pituitary gland. Studies so far have focused almost exclusively on the rat, and there is a dearth of information on other species. Our first objective was to determine whether a subpopulation of gonadotropes also express somatotropin in the ewe, as reported in the rat. In addition, we sought to determine whether gonadotropes express any of the other known pituitary hormones. Finally, we investigated whether the stage of the estrous cycle influenced the occurrence of these pluripotential gonadotropes. We found that a small population of betaLH-immunoreactive cells also expresses immunoreactive GH, prolactin and TSH. No gonadotropes colocalized with ACTH. Significantly (P<0.001) more gonadotropes expressed GH during the luteal (10.7+/-0.4%) than the late follicular (5.4+/-0.3%) phase but there was no difference between the luteal and follicular phases in the proportion of gonadotropes expressing prolactin (follicular: 5.7+/-0.7%; luteal: 5.5+/-0.6%) or TSH (follicular: 3.1+/-0.7%; luteal: 4.2+/-0.5%). Similarly, there was a significant (P<0.05) difference in the proportion of GH-immunoreactive cells expressing betaLH immunoreactivity in the luteal (5.9+/-0.3%) and follicular (3.4+/-0.5%) phases but no difference in the proportion of prolactin- (follicular: 2.2+/-0.7%; luteal: 2.0+/-0.8%) or TSH-immunoreactive cells (follicular: 9.6+/-3.7%; luteal: 10.8+/-2.9%) expressing betaLH. The specific function of these multihormonal gonadotropes in sheep remains to be determined.

Inter-relationships between the secretory dynamics of thyrotrophin-releasing hormone, thyrotrophin and prolactin in periovulatory mares: effect of hypothyroidism

We used our nonsurgical technique for collecting pituitary venous blood to relate the dynamics of thyrotrophin-releasing hormone (TRH) secretion to the secretion patterns of both prolactin and thyrotrophin in periovulatory mares, either euthyroid (n = 5) or made hypothyroid by treatment with propyl-thiouracil (n = 5). Pituitary venous blood was collected continuously and divided into 1-min aliquots for 4 h. To test the effect of dopamine on the relationship between secretion patterns, sulpiride, a selective D2 receptor antagonist, was given i.m. after 2 h of sampling. Thorough testing of the model and blood collection procedure revealed no sites of TRH loss. Hypothyroidism increased the mean secretion rates of TRH (P = 0.04) and thyrotrophin (P < 0.0001) but not prolactin. Sulpiride increased prolactin secretion rates in hypothyroid (P < 0.0001) and control (P = 0.007) mares, but did not alter TRH or thyrotrophin secretion rates. In both groups of mares, all three hormones were secreted episodically but not rhythmically. In both groups, the secretion pattern of TRH was almost always significantly related to that of thyrotrophin, as assessed by cross correlation and cross approximate entropy (ApEn) analysis. However, the degree of linear correlation was weak, with only 14% (hypothyroid) or 8% (controls) of the variation in thyrotrophin secretion rates attributable to TRH. Prolactin and TRH secretion patterns before sulpiride were coupled on cross ApEn analysis in both groups, and the minute-to-minute secretion rates of the two hormones were correlated in four hypothyroid and three euthyroid mares. Overall, the small, but significant, degree of association between TRH and prolactin was similar to that between TRH and thyrotrophin. In hypothyroid mares, sulpiride increased (P = 0.02) the synchrony between TRH and prolactin patterns. We conclude that in horses: (i) little TRH degradation occurs during passage through the pituitary or in blood after 1 h at 37 degrees C; (ii) TRH is not the major factor controlling minute-to-minute fluctuations in either thyrotrophin or prolactin; and (iii) reducing two strongly inhibitory inputs (i.e. dopamine and thyroid hormones) may magnify the stimulatory effect of TRH on prolactin secretion.