Expression of plurihormonal mRNAs in somatotrophic adenomas detected using a nonisotopic in situ hybridization method: comparison with lactotrophic adenomas

Pathogenesis, clinical features, and treatment of plurihormonal pituitary adenoma

Plurihormonal pituitary adenoma (PPA) is a type of pituitary tumor capable of producing two or more hormones and usually presents as an aggressive, large adenoma. As yet, its pathogenesis remains unclear. This is the first study to systematically summarize the underlying pathogenesis of PPA. The pathogenesis is related to plurihormonal primordial stem cells, co-transcription factors, hormone co-expression, differential gene expression, and cell transdifferentiation. We conducted a literature review of PPA and analyzed its clinical characteristics. We found that the average age of patients with PPA was approximately 40 years, and most showed only one clinical symptom. The most common manifestation was acromegaly. Currently, PPA is treated with surgical resection. However, recent studies suggest that immunotherapy may be a potentially effective treatment.

Immunohistochemical Analyses of Mammalian Target of Rapamycin (mTOR) Expression in Pituitary Neuroendocrine Tumors (PitNETs): mTOR as a Therapeutic Target for Functional PitNETs

Current therapeutic modalities for pituitary neuroendocrine tumors (PitNETs) include medication, surgery, and radiotherapy. Some patients have tumors that are refractory to current modalities. Therefore, novel treatment options are needed for patients with intractable diseases. Consequently, we examined the pathological data of PitNETs to study medical therapies. We retrospectively studied 120 patients with histologically diagnosed PitNETs. We used the data for the histopathological examination of hormones, such as growth hormone (GH), prolactin (PRL), adrenocorticotropic hormone, thyroid stimulating hormone, luteinizing hormone, follicle-stimulating hormone, and α-subunit, together with the immunohistochemical studies of the phospho-mammalian target of rapamycin (mTOR), cytokeratin (CAM5.2), somatostatin receptor (SSTR) type 2 and 5, Pit-1 (POU1F1/GHF-1), steroidogenic factor-1 (SF-1), and Tpit. GH-, PRL-, and SSTR5-immunopositive PitNETs had significantly higher percentage of mTOR-positivity, compared with GH-, PRL-, and SSTR5-immunonegative Pit NETs. Our results show that activation of the AKT/phosphatidylinositol-3-kinase pathway, including mTOR activation, might be related the development of PitNETs, especially GH- and PRL-producing PitNETs. Thus, mTOR is a potential target for treating functional PitNETs.

Mucin 1 and poly I:C activates dendritic cells and effectively eradicates pituitary tumors as a prophylactic vaccine

Pituitary tumors are the most common type of cancer within the central nervous system. In the present study, the expression levels of mucin 1 (Muc1) were examined in invasive and non‑invasive pituitary tumor samples, and the results of immunohistochemical staining and Western blot analysis demonstrated marked positive expression of Muc1. In addition, Muc1 + polyinosinic:polycytidylic acid (poly I:C) was found to stimulate the expression levels of the surface molecules cluster of differentiation (CD)40, CD83 and CD80, and HLA‑DRm and decreased the expression of CD14 in the dendritic cells, determined using fluorescence‑activated cell sorting. The secretions of interleukin (IL)‑6, tumor necrosis factor‑α and IL‑1β cytokines were also significantly induced, in a dose‑dependent manner. In in vivo experiments, a higher percentage of CD3+CD4+ T lymphocytes was detected, and the levels of interferon‑γ and IL‑2 in the splenocytes were also upregulated. Furthermore, the combination treatment of Muc1 with poly I:C increased anti‑Muc1 IgM and anti‑Muc1 IgG titers, and altered the balance of IgG2a and IgG1, all of which increased the T helper (Th)1 polarized immune response. Thus, the tumor antigen, Muc1, with poly I:C may produce potent protective effects, which polarize immune responses towards Th1, and elicit antitumor immunity to inhibit the progression of pituitary tumors.

Combined non-isotopic in situ hybridisation and indirect immunohistochemical analysis of hormone production in the rat pituitary gland

An understanding of the intracellular relation between hormonal expression (storage) and gene expression (production) is essential for elucidating the functional status of the individual cells in endocrine tissue such as the pituitary gland. To this end, mRNA expression was visualised by using a combined in situ hybridisation and immunohistochemistry method in routinely processed, formalin fixed, paraffin wax embedded rat pituitaries. mRNA was detected by non-isotopic in situ hybridisation (alkaline phosphatase antialkaline phosphatase method, with nitroblue tetrazolium and 5-bromo-4-chloro-3-indolylphosphate as substrates). Sections were then stained by using the immunoperoxidase method to demonstrate pituitary hormone expression. The specificity of the combined staining method was confirmed by staining adjacent sections separately. The antigenicity of rat growth hormone and prolactin was adequately preserved following hybridisation. In conclusion, this method is specific, easy to use and permits the determination of the functional status of individual cells.

Pathology of pituitary tumors

Pituitary adenomas are benign neoplasms originating in adenohypophysial cells. They represent the most common neoplasm of the sellar region, comprising approximately 15% of all primary intracranial tumors. Depending on the studies of unselected adult autopsy material, their frequency as an incidental finding varies between 5% and 20%. The first part of this article summarizes the immunohistochemistry of nontumorous human adenohypophysis. In the second part, the classification of pituitary tumors is discussed, followed by the immunohistochemical and electron microscopic findings of pituitary adenomas and pituitary carcinomas.

Ontogeny of plurihormonal cells in the anterior pituitary of the mouse, as studied by means of hormone mRNA detection in single cells

The expression of mRNA of growth hormone (GH), prolactin (PRL), pro-opiomelanocortin (POMC) and the common glycoprotein hormone alpha-subunit (alphaGSU) was studied by means of single cell reverse transcriptase-polymerase chain reaction in male mouse pituitary cells at key time points of fetal and postnatal development: embryonic day 16 (E16); postnatal day 1 (P1) and young-adult age (P38). At E16, the hormone mRNAs examined were detectable, although only in 44% of total cells. Most of the hormone-positive cells expressed only one of the tested hormone mRNAs (monohormonal) but 14% of them contained more than one hormone mRNA (plurihormonal cells). Combinations of GH mRNA with PRL mRNA, of alphaGSU mRNA with GH and/or PRL mRNA and of POMC mRNA with GH and/or PRL mRNA or alphaGSU mRNA were found. As expected, the proportion of hormone-positive cells rose as the mouse aged. The proportions of plurihormonal cells followed a developmental pattern independent of that of monohormonal cells and characteristic for each hormone mRNA examined. Cells coexpressing POMC mRNA with GH or PRL mRNA significantly rose in proportion between E16 and P1, while the proportion of cells coexpressing GH and PRL mRNA markedly increased between P1 and P38. The occurrence of cells displaying combined expression of alphaGSU mRNA with GH and/or PRL mRNA did not significantly change during development. Remarkably, the population of cells expressing PRL mRNA only, was larger at E16 than at P1 and expanded again thereafter. In conclusion, the normal mouse pituitary develops a cell population that is capable of expressing multiple hormone mRNAs, thereby combining typical phenotypes of different cell lineages. These plurihormonal cells are already present during embryonic life. This population is of potential physiological relevance because development-related factors appear to determine which hormone mRNAs are preferentially coexpressed. Coexpression of multiple hormone mRNAs may represent a mechanism to respond to temporally increased endocrine demands. The data also suggest that the control of combined hormone expression is different from that of single hormone expression, raising questions about the current view on pituitary cell lineage specifications.

Cytochemical and molecular biological aspects of the pituitary and pituitary adenomas--cell differentiation and transcription factors

The anterior pituitary is composed of several cell types, each responsible for the production of specific hormones. Each hormone secreting cells is defined by the activation of its respective hormone genes in a temporally and spatially regulated manner. Recent development in cytochemistry and molecular biology have provided various aspects of human pituitary adenomas, i.e., functional differentiation and classification. The molecular factors that determine hormone production have now been identified as transcription factors. Many novel transcription factors that play a role in anterior pituitary development are implicated. In this review, we focus on the transcriptional factors roles on functional differentiation of the pituitary cells and adenomas and the contribution of cytochemistry and recent development in molecular biological techniques.

Histopathological analyses of silent pituitary somatotroph adenomas using immunohistochemistry, in situ hybridization and confocal laser scanning microscopic observation

To characterize the morphological and functional aspects of silent somatotroph adenomas with paradoxical responses of GH in TRH or GnRH provocation tests, which are considered to be a useful strategy for endocrinological identification of silent somatotroph adenomas, we examined three silent somatotroph adenomas histopathologically. The adenomas were investigated by immunohistochemistry, including the highly sensitive catalyzed signal amplification system, the non-radioisotopic in situ hybridization method, and confocal laser scanning microscopy. GH production and GH-immunopositive secretory granules in the adenoma cells were demonstrated histopathologically, and the adenomas were interpreted as being densely granulated somatotroph adenomas. Endocrinological identification of silent somatotroph adenomas in combination with paradoxical responses of GH in TRH or GnRH provocation tests may elucidate the increasing number of silent somatotroph adenomas that have been regarded as mammotroph or clinically inactive adenomas. One should be aware of the differences between the previously reported silent somatotroph adenomas, most of which are sparsely granulated somatotroph adenomas, a somatotroph adenomas with paradoxical and the silent somatotroph adenomas, most of which are sparsely granulated somatotroph adenomas, and the silent somatotroph adenomas with paradoxical responses of GH in TRH or GnRH provocation tests, which are densely granulated somatotroph adenomas.

Identification of a silent pituitary somatotropic adenoma based on a paradoxic response of growth hormone on a thyrotropin-releasing hormone or gonadotropin-releasing hormone provocation test

Preoperative endocrinologic identification and surgical removal of a silent somatotropic adenoma among patients with either amenorrhea or galactorrhea, or both, are beneficial for the restoration of menstruation and ovulation. Paradoxic rises of serum growth hormone in either a thyrotropin-releasing hormone or a gonadotropin-releasing hormone provocation test and high serum growth hormone levels were noted in the 3 patients with a silent somatotropic adenoma.

Target cells of gamma3-melanocyte-stimulating hormone detected through intracellular Ca2+ responses in immature rat pituitary constitute a fraction of all main pituitary cell types, but mostly express multiple hormone phenotypes at the messenger ribonucleic acid level. Refractoriness to melanocortin-3 receptor blockade in the lacto-somatotroph lineage

Gamma3-MSH has recently been shown to be a biologically active peptide in the rat anterior pituitary. It induces a sustained rise in intracellular free calcium levels ([Ca2+]i) in a relatively small population of immature pituitary cells. The present study was intended to identify the target cells of this peptide and to discern the signal-transducing melanocortin (MC) receptor. In dispersed pituitary cells from 14-day-old rats, increasing doses of gamma3-MSH (0.1, 1, and 10 nM) evoked a sustained oscillating [Ca2+]i rise in an increasing number of cells (up to 14.5%). Within the responsive cells, 53% showed GH immunoreactivity (-ir), 12% showed PRL-ir, 2% showed TSHbeta-ir, 5% showed LHbeta-ir, and 10% showed ACTH-ir, whereas 18% did not express any hormone-ir to a detectable level. As assessed by single cell RT-PCR for the presence of pituitary hormone messenger RNA (mRNA), 26% of the gamma3-MSH-responsive cells contained only GH mRNA, 5% contained only PRL mRNA, and 4% contained only TSHbeta mRNA. Twenty-two percent contained mRNA of GH, PRL, and TSHbeta in various dual or triple combinations. About 24% of the gamma3-MSH-responsive cells expressed POMC mRNA, mostly together with other mRNAs, i.e. with GH mRNA and/or PRL mRNA or with mRNA of GH, PRL, and TSHbeta. Eighteen percent of the responsive cells expressed LHbeta, all of them together with mRNA of GH, PRL, and TSHbeta in various combinations. The absence of hormone mRNA was found in less than 1% of the responsive cells. In cells chosen at random (representative of the total pituitary cell population), the proportion of cells expressing two or multiple hormone mRNAs was twice as low as that in the gamma3-MSH-responsive population, whereas the proportion of cells expressing a single hormone mRNA was twice as high (about two thirds of all cells). Moreover, unlike in the gamma3-MSH-responsive cell population, randomly chosen cells were found that coexpressed POMC mRNA with LHbeta mRNA. The effect of gamma3-MSH on [Ca2+]i was blocked by the MC-3 receptor antagonist SHU9119 (used up to a 1000-fold excess) in 46% or less of the responsive cells. SHU9119 failed to block the [Ca2+]i response to gamma3-MSH in PRL-, GH-, and TSHbeta-ir cells, but it did block the response in most ACTH-ir cells and in cells expressing no hormone to a detectable level. Single cell RT-PCR revealed that expression of MC-3 receptor mRNA was detected in only 16% of gamma3-MSH-responsive cells. The present data suggest that the target cells of gamma3-MSH in terms of [Ca2+]i responses in the immature rat pituitary constitute subpopulations of all main pituitary cell types, including nonhormonal (or low expression hormonal) cells. However, in contrast to the total pituitary cell population, most of these cells display multilineage gene activation at the mRNA level, i.e. express mRNA of GH, PRL, TSHbeta, POMC, and LHbeta in dual, triple, or quadruple combinations. Although gamma3-MSH may act through the MC-3 receptor in a portion of these cells, most of these cells (mainly in the lacto-somatotroph lineage) may transduce the signal through another receptor or through an MC-3 receptor with unconventional binding characteristics.

Pituitary somatotroph adenoma producing growth hormone (GH)-releasing hormone (GHRH) with an elevated plasma GHRH concentration: a model case for autocrine and paracrine regulation of GH secretion by GHRH

An acromegalic patient with a pituitary somatotroph adenoma associated with an extremely elevated plasma GHRH concentration is presented. The preoperatively high concentration of plasma GHRH returned to the normal level after successful removal of the adenoma. GHRH production and GHRH gene expression were confirmed in the adenoma by studies including immunohistochemistry and in situ hybridization. Expression of GHRH receptor messenger ribonucleic acid was verified by in situ hybridization. Immunohistochemical double staining for GH and GHRH revealed their colocalization in single adenoma cells. These findings confirmed the autocrine or paracrine regulation of GH production by endogenous GHRH from the adenoma cells. GHRH synthesis in the pituitary gland has recently been demonstrated, however, there have been no previous reports of a GHRH-producing pituitary somatotroph adenoma associated with an elevated plasma GHRH concentration. The existence of this GHRH-producing adenoma suggests a possible role of locally generated GHRH in the progression of somatotroph adenomas, i.e. the monoclonally established somatotroph adenomas develop further under the influence of locally produced GHRH. The demonstration of GHRH production by this somatotroph adenoma is of importance in clarifying the autocrine or paracrine regulation of GH production and the progression of human somatotroph adenomas.

The multihormonal character of pituitary adenomas: immuno-electron microscopic studies

This study investigates the multihormonal character of pituitary adenomas at the ultrastructural level. The growth hormone (GH)- and prolactin (PRL)-secreting adenomas under study consisted of many moderately or densely granulated cells and a few sparsely or slightly granulated cells. The GH-secreting adenomas showed well-developed cytoplasmic organelles and many large (250 nm or more) or medium-sized (200 nm) secretory granules, as well as a few small (70-150 nm) secretory granules. The PRL-secreting hormones exhibited poorly or slightly developed cyto-plasmic organelles and several small secretory granules. Morphologically and antigenically, these sparsely or slightly granulated cells were similar to those of clinically non-functioning (CN-F) adenomas, which appeared identical to cells expressing little or slight immunoreaction to pituitary hormones at the light microscopic level. As well as those of CN-F adenomas, the small secretory granules of both densely and sparsely granulated cells expressed little or only slight antigenicity of various hormones. Con-comitantly showing slight or moderate antigenicity of hormones biochemically unrelated to GH or PRL, the medium-sized or large secretory granules larger than 140 or 160 nm significantly exhibited intense PRL or GH antigenicity, respectively (Fisher's exact test; P < 0.05 or 0.01). Their GH or PRL antigenicity increased as they grew larger. Showing intermediate cells between sparsely and densely granulated cells, two CN-F adenomas, however, appeared to develop into growth hormone-secreting adenomas. This study led us to conclude that pituitary adenomas may originate from sparsely granulated cells with slight biochemically unrelated hormones, and that their hormonality may be selectively activated singly or multiply in the course of their development.

Molecular Pathology of the Pituitary Adenomas

Molecular techniques have been applied to the study of pituitary adenomas by many investigators. We have used nonisotopic in situ hybridization (ISH) to analyze pituitary adenomas in our laboratory. These studies have provided insight into mRNA production by various adenomas, and have contributed toward our new proposed clinical and cytofunctional classification of pituitary adenomas.

Simultaneous ultrastructural identification of growth hormone and its messenger ribonucleic acid using combined immunohistochemistry and non-radioisotopic in situ hybridization: a technical note

The present electron microscopical study is concerned with the simultaneous visualization of messenger ribonucleic acid (mRNA) and its encoded protein in the same specimen. Pre-embedding electron microscopical in situ hybridization (EM-ISH) on rat pituitary gland tissue localized growth hormone mRNA in the polysomes of the rough endoplasmic reticulum, and subsequent postembedding immunolabelling using protein A-colloidal gold particles identified growth hormone mainly in the secretory granules. We believe that our report provides the first simultaneous ultrastructural identification of mRNA and its encoded protein using combined pre-embedding EM-ISH and immunohistochemistry. In this method, the signals for mRNA were localized specifically as highly electron dense products on the polysomes of the endoplasmic reticulum, and those for its encoded protein were recognized as gold particles both in the cisternae of the reticulum and in the secretory granules. Our ultrastructural double labelling method for mRNA and protein may provide a tool to find important clues for elucidating the intracellular correlation of mRNA translation and secretion of translated protein, because of its high resolution, good morphological preservation, and the specific localization of the reaction products.

Clinical and cytofunctional classification of pituitary adenomas: proposal of a new classification

Recent methodological advances in immunohistochemistry, ultrastructural techniques, hormonal assays, resolution imaging and molecular biology techniques have provided new insights into the pathology, function and cytogenesis of pituitary adenomas. Pituitary adenomas have been classified historically on the basis of tinctorial affinities, followed by the basis of ultrastructure and immunohistochemistry. The current development of technologies necessitate the new classification of pituitary adenomas which integrates these numerous parameters as well as the clinical manifestations. For this purpose, we suggest a new clinico-cytofunctional classification of pituitary adenomas, which is based on these clinical manifestations and integrates the information on biology, imaging function and ultrastructure. This classification which corresponds to current advances will not only provide pertinent clinical data but facilitate better understanding of the biology and nature of these complexed lesions.

A case of pituitary somatotroph adenoma with concomitant secretion of growth hormone, prolactin, and adrenocorticotropic hormone--an adenoma derived from primordial stem cell, studied by immunohistochemistry, in situ hybridization, and cell culture

Somatotroph adenomas often secrete prolactin (PRL) besides growth hormone (GH) and are sometimes immunostained for other anterior pituitary hormones or their subunits, such as thyroid-stimulating hormone (TSH) beta-subunit and glycoprotein hormone alpha-subunit (alpha SU). However, somatotroph adenomas showing hypersecretion of adrenocorticotropic hormone (ACTH) are extremely rare. There have been, to our knowledge, only five published reports on somatotroph adenomas accompanied by excessive ACTH secretion. Here we report a case of intracavernously invading somatotroph macro-adenoma with high serum GH, PRL, and ACTH levels. We examined the case using immunohistochemistry (IHC), in situ hybridization (ISH), and cell culture, and confirmed GH, PRL, and ACTH, as well as alpha SU, production, and the expression of Pit-1 protein by the adenoma, which is known as a transcriptional factor for GH, PRL, and TSH, not for ACTH. Therefore, the presence of unknown transcriptional factor other than Pit-1, common to GH, PRL, and ACTH, may be speculated to be expressed in this adenoma. In our previous study, we had found plurihormonal mRNA expression, especially for ACTH, the beta-subunit of follicle-stimulating hormone and luteinizing hormone in some somatotroph adenomas, using non-radio-isotopic ISH, and suggested that these adenomas might be derived from plurihormonal primordial stem cells. Our present case is significant from the viewpoint of histogenesis of pituitary adenomas, because it further supports the cell origin of somatotroph adenomas from plurihormonal primordial stem cells, and moreover it suggests the presence of unknown transcriptional factor other than Pit-1, common to GH, PRL, and ACTH.