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Background: The introduction of intraoperative cytology revolutionized neurosurgical procedures in human medicine, providing real‐time diagnostic guidance to surgeons and contributing to improved patient outcomes. In the realm of veterinary medicine, the understanding of pituitary tumors in dogs and cats remains limited due to challenges in obtaining antemortem samples of central nervous system lesions. Objectives: The aim of this study was to describe the cytologic features of pituitary adenomas in 12 dogs that underwent hypophysectomy. Methods: The series included nine melanotroph adenomas and three corticotroph adenomas. Definitive diagnosis was based on histopathology and immunohistochemistry. Results: Cytologically, the adenomas had high numbers of bare nuclei and intact cells that were round to polygonal and situated individually or in small clusters. The intact cells had round to oval, eccentric nuclei with finely stippled chromatin and one to three prominent nucleoli and ample to abundant lightly basophilic to amphophilic, grainy cytoplasm with distinct borders, and variable numbers of discrete vacuoles. Mild‐to‐moderate anisocytosis and anisokaryosis, occasional binucleation, rare and atypical mitotic figures, and nuclear molding were also observed. Conclusions: The results suggest that intraoperative cytology of canine pituitary adenomas holds promise as a valuable diagnostic tool, aiding swift differentiation from other sellar masses before histologic confirmation. Cytologic characterization of pituitary adenomas in dogs is exceptionally rare in the scientific literature, making this study one of the first to offer a comprehensive description of these cytologic features. [ABSTRACT FROM AUTHOR]

Introduction: A recently discovered facet of paraneoplastic adrenocorticotropic hormone (ACTH) deficiency exists in two forms: a paraneoplastic spontaneous isolated ACTH deficiency (IAD) and an immune checkpoint inhibitor (ICI)-related hypophysitis. Autoantibodies against corticotrophs, such as circulating antiproopiomelanocortin (POMC) antibodies are considered disease markers. However, the number of identified cases was limited, implying that the characteristics of these autoantibodies are not fully understood. Methods: We investigate circulating autoimmune autoantibodies in detail through a novel case of IAD that developed as a paraneoplastic autoimmune ACTH deficiency.Results: The patient developed IAD after 25 weeks of ICI therapy for metastasis of large-cell neuroendocrine carcinoma at 69 years of age. Ectopic ACTH expression and infiltration of CD3+, CD4+, CD8+, and CD20+ lymphocytes were observed in the tumor tissues and circulating anti-POMC antibodies were detected specifically in the patient’s serum. Moreover, detailed analyses of immunofluorescence staining using patient serum revealed that the recognition site of the autoantibody was ACTH25-39, which had not been identified in previous cases of paraneoplastic autoimmune ACTH deficiency.Conclusion: This case involved a combination of paraneoplastic spontaneously acquired IAD and ICI-related hypophysitis occupying the middle ground. Moreover, our study reveals new aspects of anti-POMC antibodies in patients with paraneoplastic ACTH deficiency. This report expands our understanding of the immunological landscape and provides new insights for the identification of antibodies associated with paraneoplastic autoimmune ACTH deficiency. [ABSTRACT FROM AUTHOR]

Stress-related illness represents a major burden on health and society. Sex differences in stress-related disorders are well documented, with women having twice the lifetime rate of depression compared to men and most anxiety disorders. Anterior pituitary corticotrophs are central components of the hypothalamic–pituitary–adrenal (HPA) axis, receiving input from hypothalamic neuropeptides corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), while regulating glucocorticoid output from the adrenal cortex. The dynamic control of electrical excitability by CRH/AVP and glucocorticoids is critical for corticotroph function; however, whether corticotrophs contribute to sexually differential responses of the HPA axis, which might underlie differences in stress-related disorders, is very poorly understood. Using perforated patch clamp electrophysiology in corticotrophs from mice expressing green fluorescent protein under the control of the Pomc promoter, we characterized basal and secretagogue-evoked excitability. Both male and female corticotrophs show predominantly single-spike action potentials under basal conditions; however, males predominantly display spikes with smallamplitude (<20 mV) afterhyperpolarizations (B-type), whereas females displayed a mixture of B-type spikes and spikes with a large-amplitude (>25 mV) afterhyperpolarization (A-type). In response to CRH, or CRH/AVP, male cells almost exclusively transition to a predominantly pseudo-plateau bursting, whereas only female B-type cells display bursting in response to CRH±AVP. Treatment of male or female corticotrophs with 1 nM estradiol (E2) for 24–72 h has no effect on the proportion of cells with A- or B-type spikes in either sex. However, E2 results in the cessation of CRH-induced bursting in both male and female corticotrophs, which can be partially reversed by adding a BK current using a dynamic clamp. RNA-seq analysis of purified corticotrophs reveals extensive differential gene expression at the transcriptional level, including more than 71 mRNAs encoding ion channel subunits. Interestingly, there is a two-fold lower level (p < 0.01) of BK channel pore-forming subunit (Kcnma1) expression in females compared to males, which may partially explain the decrease in CRHinduced bursting. This study identified sex differences at the level of the anterior pituitary corticotroph ion channel landscape and control of both spontaneous and CRH-evoked excitability. Determining the mechanisms of sex differences of corticotroph and HPA activity at the cellular level could be an important step for better understanding, diagnosing, and treating stress-related disorders. [ABSTRACT FROM AUTHOR]

The hypothalamic-pituitary-adrenal (HPA) axis plays a critical role in adaptive stress responses and maintaining organism homeostasis. The pituitary corticotroph is the central player in the HPA axis and is regulated by a plethora of hormonal and stress related factors that synergistically interact to activate and temper pro-opiomelanocortin (POMC) transcription, to either increase or decrease adrenocorticotropic hormone (ACTH) production and secretion as needed. Nuclear receptors are a family of highly conserved transcription factors that can also be induced by various physiologic signals, and they mediate their responses via multiple targets to regulate metabolism and homeostasis. In this review, we summarize the modulatory roles of nuclear receptors on pituitary corticotroph cell POMC transcription, describe the unique and complex role these factors play in hypothalamic-pituitary-adrenal axis (HPA) regulation and discuss potential therapeutic targets in disease states.

Abstract Corticotroph macroadenomas are rare but difficult to manage intracranial neoplasms. Mutations in the two Cushing’s disease mutational hotspots USP8 and USP48 are less frequent in corticotroph macroadenomas and invasive tumors. There is evidence that TP53 mutations are not as rare as previously thought in these tumors. The aim of this study was to determine the prevalence of TP53 mutations in corticotroph tumors, with emphasis on macroadenomas, and their possible association with clinical and tumor characteristics. To this end, the entire TP53 coding region was sequenced in 86 functional corticotroph tumors (61 USP8 wild type; 66 macroadenomas) and the clinical characteristics of patients with TP53 mutant tumors were compared with TP53/USP8 wild type and USP8 mutant tumors. We found pathogenic TP53 variants in 9 corticotroph tumors (all macroadenomas and USP8 wild type). TP53 mutant tumors represented 14% of all functional corticotroph macroadenomas and 24% of all invasive tumors, were significantly larger and invasive, and had higher Ki67 indices and Knosp grades compared to wild type tumors. Patients with TP53 mutant tumors had undergone more therapeutic interventions, including radiation and bilateral adrenalectomy. In conclusion, pathogenic TP53 variants are more frequent than expected, representing a relevant amount of functional corticotroph macroadenomas and invasive tumors. TP53 mutations associated with more aggressive tumor features and difficult to manage disease.

Stress-related illness represents a major burden on health and society. Sex differences in stress-related disorders are well documented, with women having twice the lifetime rate of depression compared to men and most anxiety disorders. Anterior pituitary corticotrophs are central components of the hypothalamic–pituitary–adrenal (HPA) axis, receiving input from hypothalamic neuropeptides corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), while regulating glucocorticoid output from the adrenal cortex. The dynamic control of electrical excitability by CRH/AVP and glucocorticoids is critical for corticotroph function; however, whether corticotrophs contribute to sexually differential responses of the HPA axis, which might underlie differences in stress-related disorders, is very poorly understood. Using perforated patch clamp electrophysiology in corticotrophs from mice expressing green fluorescent protein under the control of the Pomc promoter, we characterized basal and secretagogue-evoked excitability. Both male and female corticotrophs show predominantly single-spike action potentials under basal conditions; however, males predominantly display spikes with small-amplitude (25 mV) afterhyperpolarization (A-type). In response to CRH, or CRH/AVP, male cells almost exclusively transition to a predominantly pseudo-plateau bursting, whereas only female B-type cells display bursting in response to CRH±AVP. Treatment of male or female corticotrophs with 1 nM estradiol (E2) for 24–72 h has no effect on the proportion of cells with A- or B-type spikes in either sex. However, E2 results in the cessation of CRH-induced bursting in both male and female corticotrophs, which can be partially reversed by adding a BK current using a dynamic clamp. RNA-seq analysis of purified corticotrophs reveals extensive differential gene expression at the transcriptional level, including more than 71 mRNAs encoding ion channel subunits. Interestingly, there is a two-fold lower level (p < 0.01) of BK channel pore-forming subunit (Kcnma1) expression in females compared to males, which may partially explain the decrease in CRH-induced bursting. This study identified sex differences at the level of the anterior pituitary corticotroph ion channel landscape and control of both spontaneous and CRH-evoked excitability. Determining the mechanisms of sex differences of corticotroph and HPA activity at the cellular level could be an important step for better understanding, diagnosing, and treating stress-related disorders.

Generation of a variety of organs and tissues from human pluripotent stem cells (hPSCs) has been attempted in vitro. We here present a simple and efficient method for induction of hypothalamic and pituitary tissues from hPSCs. On provision of exogenous agents important for early hypothalamus-pituitary organogenesis, including bone morphogenetic protein 4 and activators of sonic hedgehog, in three-dimensional culture, hPSCs spontaneously form spherical organoids with two distinct tissues, hypothalamus and adenohypophysis. The pituitary tissues derived from hPSCs not only secrete adenocorticotropic hormone, but also retain both positive and negative feedback mechanisms, recapitulating mature endocrine organs in vivo. Furthermore, the results of ectopic transplantation with mouse models of hypopituitarism suggest that these hypothalamus-pituitary organoids have potential as engraftment organs. In addition to their use in transplantation for patients with hypopituitarism they will allow establishment of disease models in vitro and enable research impossible in humans. Hypothalamus-pituitary organoids promise to be a powerful tool in regenerative medicine, drug discovery, and basic research into pituitary development. [ABSTRACT FROM AUTHOR]

Simple Summary: Cushing's disease is caused by autonomous adrenocorticotropic hormone (ACTH) produced by corticotroph pituitary neuroendocrine tumors, leading to cortisol over-production in the adrenal glands. Cushing's disease presents with a variety of clinical features, ranging from overt to subtle, which are caused by hormonal activities. To treat the disease adequately, the molecular and genetic causes of Cushing's disease need to be understood. This review discusses recent advances in molecular insights and targeted therapy for Cushing's disease. Cushing's disease is caused by autonomous secretion of adrenocorticotropic hormone (ACTH) from corticotroph pituitary neuroendocrine tumors. As a result, excess cortisol production leads to the overt manifestation of the clinical features of Cushing's syndrome. Severe complications have been reported in patients with Cushing's disease, including hypertension, menstrual disorders, hyperglycemia, osteoporosis, atherosclerosis, infections, and mental disorders. Cushing's disease presents with a variety of clinical features, ranging from overt to subtle. In this review, we explain recent advances in molecular insights and targeted therapy for Cushing's disease. The pathophysiological characteristics of hormone production and pituitary tumor cells are also explained. Therapies to treat the tumor growth in the pituitary gland and the autonomous hypersecretion of ACTH are discussed. Drugs that target corticotroph pituitary neuroendocrine tumors have been effective, including cabergoline, a dopamine receptor type 2 agonist, and pasireotide, a multi-receptor-targeted somatostatin analog. Some of the drugs that target adrenal hormones have shown potential therapeutic benefits. Advances in potential novel therapies for Cushing's disease are also introduced. [ABSTRACT FROM AUTHOR]

Corticotroph macroadenomas are rare but difficult to manage intracranial neoplasms. Mutations in the two Cushing's disease mutational hotspots USP8 and USP48 are less frequent in corticotroph macroadenomas and invasive tumors. There is evidence that TP53 mutations are not as rare as previously thought in these tumors. The aim of this study was to determine the prevalence of TP53 mutations in corticotroph tumors, with emphasis on macroadenomas, and their possible association with clinical and tumor characteristics. To this end, the entire TP53 coding region was sequenced in 86 functional corticotroph tumors (61 USP8 wild type; 66 macroadenomas) and the clinical characteristics of patients with TP53 mutant tumors were compared with TP53/USP8 wild type and USP8 mutant tumors. We found pathogenic TP53 variants in 9 corticotroph tumors (all macroadenomas and USP8 wild type). TP53 mutant tumors represented 14% of all functional corticotroph macroadenomas and 24% of all invasive tumors, were significantly larger and invasive, and had higher Ki67 indices and Knosp grades compared to wild type tumors. Patients with TP53 mutant tumors had undergone more therapeutic interventions, including radiation and bilateral adrenalectomy. In conclusion, pathogenic TP53 variants are more frequent than expected, representing a relevant amount of functional corticotroph macroadenomas and invasive tumors. TP53 mutations associated with more aggressive tumor features and difficult to manage disease. [ABSTRACT FROM AUTHOR]

Chronic stress results in long-term dynamic changes at multiple levels of the hypothalamic-pituitary-adrenal (HPA) axis resulting in stress axis dysregulation with long-term impacts on human and animal health. However, the underlying mechanisms and dynamics of altered of HPA axis function, in particular at the level of pituitary corticotrophs, during a period of chronic stress and in the weeks after its cessation (defined as "recovery") are very poorly understood. Here, we address the fundamental question of how a period of chronic stress results in altered anterior pituitary corticotroph function and whether this persists in recovery, as well as the transcriptomic changes underlying this. We demonstrate that, in mice, spontaneous and corticotrophin-releasing hormone-stimulated electrical excitability of corticotrophs, essential for ACTH secretion, is suppressed for weeks to months of recovery following a period of chronic stress. Surprisingly, there are only modest changes in the corticotroph transcriptome during the period of stress, but major alterations occur in recovery. Importantly, although transcriptional changes for a large proportion of mRNAs follow the time course suppression of corticotroph excitability, many other genes display highly dynamic transcriptional changes with distinct time courses throughout recovery. Taken together, this suggests that chronic stress results in complex dynamic transcriptional and functional changes in corticotroph physiology, which are highly dynamic for weeks following cessation of chronic stress. These insights provide a fundamental new framework to further understand underlying molecular mechanisms as well approaches to both diagnosis and treatment of stress-related dysfunction of the HPA axis., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society.)

Nonsurgical medical treatments are often performed for Cushing's disease due to high recurrence rates. However, current medical treatment that targets corticotroph adenomas are limited. To develop a treatment that specifically targets corticotrophs in Cushing's disease, it is necessary to identify corticotroph lineage–specific proteins, which are involved in the Cushing's tumor phenotype. We have previously reported that the expression of E2F transcription factor 1 (E2F1), one of the cell cycle regulatory proteins, was increased in corticotrophs in Cushing's disease model mice and was involved in the regulation of POMC gene expression. Phosphorylation of Ser337 of E2F1 (pS337-E2F1) facilitates its binding to the POMC promoter, which was suggested to contribute to elevated POMC expression in corticotrophs. Here, we report that E2F1 expression is specific to the corticotroph lineage in normal human pituitaries and that the E2F1 protein is localized in the cytosol in normal corticotrophs. We show that pS337-E2F1 is localized in the nucleus specifically in Cushing's tumors, while it is localized in the perinuclear cytoplasm in the normal pituitary. This observation demonstrates that pS337 is a marker for Cushing's tumors and suggests that phosphorylation of E2F1 may be a target for developing a novel pharmacological treatment for tumorigenesis and hormone dysregulation of Cushing's disease. [ABSTRACT FROM AUTHOR]

Once temozolomide has failed, there is no recommended treatment option for pituitary carcinomas and aggressive pituitary tumors. Immune-checkpoint inhibitors (ICIs) represent the most recent therapeutic avenue, having raised hope with the publication of the first successful case in 2018. Here, we present an overview of immunotherapy in pituitary carcinomas and aggressive pituitary tumors, starting with the rationale for using ICIs and the implications of tumor-infiltrating lymphocytes in anterior pituitary tumors, followed by a systematic review of all published cases, analyzing both treatment response and potential predictors of response and finishing with research and clinical perspectives. Seven corticotroph and four lactotroph tumors have been so far treated with ICIs. Corticotroph tumors showed radiological partial response in 57% of cases, followed by stable disease in 29% of cases, which was accompanied by bio chemical partial or complete response in 83% of cases. Half of lactotroph tumors showed radiological complete or partial response, accompanied by biochemical complete response in 33% of the cases. In the case of a dissociate response, continuation of immunotherapy combined with local treatment represents a good option. At this time, a high tumor mutational burden appears to be the most promising predictive marker of response. MMR deficiency does not guarantee a response. Negative PD-L1 staining should not preclude ICIs administration. Therefore, ICIs are a promising option after temozolomide failure. This review highlights key clinical aspects that can already be implemented into practice and also discusses tumor biology concepts and perspectives expected to improve immunotherapy outcomes. [ABSTRACT FROM AUTHOR]

Corticotroph cells give rise to aggressive and rare pituitary neoplasms comprising ACTH-producing adenomas resulting in Cushing disease (CD), clinically silent ACTH adenomas (SCA), Crooke cell adenomas (CCA) and ACTH-producing carcinomas (CA). The molecular pathogenesis of these tumors is still poorly understood. To better understand the genomic landscape of all the lesions of the corticotroph lineage, we sequenced the whole exome of three SCA, one CCA, four ACTH-secreting PA causing CD, one corticotrophinoma occurring in a CD patient who developed Nelson syndrome after adrenalectomy and one patient with an ACTH-producing CA. The ACTH-producing CA was the lesion with the highest number of single nucleotide variants (SNV) in genes such as USP8, TP53, AURKA, EGFR, HSD3B1 and CDKN1A. The USP8 variant was found only in the ACTH-CA and in the corticotrophinoma occurring in a patient with Nelson syndrome. In CCA, SNV in TP53, EGFR, HSD3B1 and CDKN1A SNV were present. HSD3B1 and CDKN1A SNVs were present in all three SCA, whereas in two of these tumors SNV in TP53, AURKA and EGFR were found. None of the analyzed tumors showed SNV in USP48, BRAF, BRG1 or CABLES1. The amplification of 17q12 was found in all tumors, except for the ACTH-producing carcinoma. The four clinically functioning ACTH adenomas and the ACTH-CA shared the amplification of 10q11.22 and showed more copy-number variation (CNV) gains and single-nucleotide variations than the nonfunctioning tumors. [ABSTRACT FROM AUTHOR]

Clinically silent double pituitary adenomas consisting of corticotroph and somatotroph cells are an exceedingly rare clinical finding. In this report, we present the case of a 28-year-old man with a 1-year history of recurrent headaches. Imaging revealed a 2.1 (anterior-posterior) × 2.2 (transverse) × 1.3 (craniocaudal) cm pituitary adenoma invading into the left cavernous sinus and encasing the left internal carotid artery. Endoscopic transnasal resection was performed without complications. Immunohistochemical staining revealed a double adenoma consisting of distinct sparsely granulated somatotroph and densely granulated corticotroph cells that were positive for growth hormone and adrenocorticotropic hormone, respectively. Ki-67 index labeling revealed a level of 6% within the corticotroph adenoma. No increase in serum growth hormone or adrenocorticotropic hormone was found, indicating a clinically silent double adenoma. While transsphenoidal surgery remains a first-line approach for silent adenomas presenting with mass effects, increased rates of proliferative markers, such as the Ki-67 index, provide useful insight into the clinical course of such tumors. Determining the Ki-67 index of silent pituitary adenomas could be valuable in predicting recurrence after initial surgical resection and identifying tumors that are at an increased risk of needing additional therapeutic interventions or more frequent surveillance imaging.

Purpose: To estimate the prevalence of USP8, USP48, and BRAF mutations in patients with Cushing's disease (CD) from the Indian subcontinent, and determine their genotype-phenotype correlation. Methods: We prospectively recruited 46 patients with CD who underwent surgery between September 2015 and July 2019 at our institute. Fresh frozen tumour tissue was obtained in all patients. Using Sanger sequencing, the presence of somatic USP8 mutations was documented and the frequency of USP48 and BRAF mutations in USP8 wild-type corticotroph adenomas was determined. Clinical, hormonal, and surgical data were then compared between USP8-, USP48- and BRAF-variant carriers and patients with wild-type tumours. Results: Signature USP8 mutations were detected in 17 (37%) patients. Of the 29 USP8 wild-type adenomas, 4 (13.8%) harboured USP48 mutations, one of them being a splice-site mutation that has previously not been described. BRAF mutations were not found in any of the 29 patients. Corticotroph adenomas with USP8 mutations had a higher incidence of Crooke's hyaline change than wild-type tumours (70.6 vs. 37.9%, p = 0.032). Adenomas with USP48 mutations had a higher rate of cavernous sinus invasion than their wild-type counterparts (50 vs. 4%, p = 0.042). No other significant phenotypic difference could be established between mutant and wild-type tumours. Conclusions: The prevalence of USP8 mutations in our series of patients with CD was 37%. The prevalence of USP48 mutations in USP8 wild-type adenomas was 13.8%, including a novel splice-site mutation. BRAF mutations were not found in any USP8 wild-type tumour. USP8-mutants showed significantly more Crooke's hyaline change and USP48-mutants were more likely to demonstrate cavernous sinus invasion. [ABSTRACT FROM AUTHOR]

Corticotroph adenomas/pituitary neuroendocrine tumors (PitNETs) are associated with significant morbidity and mortality. Predictors of tumor behavior have not shown high prognostic accuracy. For somatotroph adenomas/PitNETs, E-cadherin expression correlates strongly with prognosis. E-cadherin expression has not been investigated in other PitNETs. A retrospective chart review of adults with corticotroph adenomas/PitNETs was conducted to assess correlation between E-cadherin expression and tumor characteristics. In addition, gene expression microarray was performed in subset of tumors (n = 16). Seventy-seven patients were identified; 71% were female, with median age of cohort 45.2 years. Seventy-five percent had macroadenomas, of which 22% were hormonally active. Ninety-five percent of microadenomas were hormonally active. Adrenocorticotropic hormone granulation pattern by IHC identified 63% as densely granulated (DG) and 34% as sparsely granulated (SG). All microadenomas were DG (p < .001); 50% of macroadenomas were DG associated with increased tumor invasion compared to SG. E-cadherin IHC was positive in 80%, diminished in 17%, and absent in 20% and did not correlate with corticotroph PitNETs subtype, size, or prognosis. In contrast to the distinct transcriptomes of corticotroph PitNETs and normal pituitaries, a comparison of clinically active and silent corticotroph PitNETs demonstrated similar molecular signatures indicating their common origin, but with unique differences related to their secretory status., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Association of Neuropathologists, Inc. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Corticotroph cells give rise to aggressive and rare pituitary neoplasms comprising ACTH-producing adenomas resulting in Cushing disease (CD), clinically silent ACTH adenomas (SCA), Crooke cell adenomas (CCA) and ACTH-producing carcinomas (CA). The molecular pathogenesis of these tumors is still poorly understood. To better understand the genomic landscape of all the lesions of the corticotroph lineage, we sequenced the whole exome of three SCA, one CCA, four ACTH-secreting PA causing CD, one corticotrophinoma occurring in a CD patient who developed Nelson syndrome after adrenalectomy and one patient with an ACTH-producing CA. The ACTH-producing CA was the lesion with the highest number of single nucleotide variants (SNV) in genes such as USP8, TP53, AURKA, EGFR, HSD3B1 and CDKN1A. The USP8 variant was found only in the ACTH-CA and in the corticotrophinoma occurring in a patient with Nelson syndrome. In CCA, SNV in TP53, EGFR, HSD3B1 and CDKN1A SNV were present. HSD3B1 and CDKN1A SNVs were present in all three SCA, whereas in two of these tumors SNV in TP53, AURKA and EGFR were found. None of the analyzed tumors showed SNV in USP48, BRAF, BRG1 or CABLES1. The amplification of 17q12 was found in all tumors, except for the ACTH-producing carcinoma. The four clinically functioning ACTH adenomas and the ACTH-CA shared the amplification of 10q11.22 and showed more copy-number variation (CNV) gains and single-nucleotide variations than the nonfunctioning tumors.

Retinoic acid (RA), an active metabolite of Vitamin A, and bone morphogenetic protein 4 (BMP-4) pathways control the transcription of pro-opiomelanocortin (Pomc), the precursor of ACTH. We describe a novel mechanism by which RA and BMP-4 ac t together in the context of pituitary corticotroph tumoral cells to regulate Pomc transcription. BMP-4 and RA exert a potentiated inhibition on Pomc gene expression. This potentiation of the inhibitory action on Pomc transcription was blocked by the inhibitory SMADs of the BMP-4 pathway (SMAD6 and SMAD7), a negative regulator of BMP-4 signaling (TOB1) and a blocker of RA pathway (COUP-TFI). AtT-20 corticotrophinoma cells express RA receptors (RARB, RXRA and RXRG) which associate with factors of BMP-4 (SM AD4 and SMAD1) signaling cascade in transcriptional complexes that block Pomc transcription. COUP-TFI and TOB1 disrupt these complexes. Deletions and mutations of the Pomc promoter and a specific DNA-binding assay show that the complexes bind to the RARE site in the Pomc promoter. The enhanced inhibitory interaction between RA and BMP-4 pathways occurs also in another relevant corticotroph gene promoter, the corticotropin-releasing hormone receptor 1 (Crh-r1). The understanding of the molecules that participate in the c ontrol of corticotroph gene expression contribute to define more precise targets for the treatment of corticotrophinomas. [ABSTRACT FROM AUTHOR]

An 11-year-old castrated male Chihuahua dog was presented with complaints of polyuria, polydipsia, abdominal enlargement, and alopecia. Hyperadrenocorticism was diagnosed on the basis of clinical signs, blood tests, adrenocorticotropin-stimulation test results, and an elevated serum adrenocorticotropin concentration. Contrast-enhanced magnetic resonance imaging showed that the pituitary gland was enlarged, compatible with a pituitary macroadenoma. Pituitary-dependent hyperadrenocorticism was suspected, and transsphenoidal hypophysectomy was thus performed for complete resection of the tumor. After surgery, the serum adrenocorticotropin concentration normalized and the hyperadrenocorticism resolved. Histological and immunocytochemical analyses revealed a benign tumor composed of mature neuronal cells and glial cells, suggestive of a ganglioglioma with immunolabeling for adrenocorticotropin. Careful analysis of the resected tumor revealed no pituitary adenoma tissue. The clinical and histopathologic findings indicated that the ganglioglioma was directly responsible for the hyperadrenocorticism. This is the first case of hyperadrenocorticism caused by a ganglioglioma in a dog. [ABSTRACT FROM AUTHOR]

The hypothalamic–pituitary–adrenal (HPA) axis plays a critical role in adaptive stress responses and maintaining organism homeostasis. The pituitary corticotroph is the central player in the HPA axis and is regulated by a plethora of hormonal and stress related factors that synergistically interact to activate and temper pro-opiomelanocortin (POMC) transcription, to either increase or decrease adrenocorticotropic hormone (ACTH) production and secretion as needed. Nuclear receptors are a family of highly conserved transcription factors that can also be induced by various physiologic signals, and they mediate their responses via multiple targets to regulate metabolism and homeostasis. In this review, we summarize the modulatory roles of nuclear receptors on pituitary corticotroph cell POMC transcription, describe the unique and complex role these factors play in hypothalamic–pituitary–adrenal axis (HPA) regulation and discuss potential therapeutic targets in disease states.

Introduction: A recently discovered facet of paraneoplastic adrenocorticotropic hormone (ACTH) deficiency exists in two forms: a paraneoplastic spontaneous isolated ACTH deficiency (IAD) and an immune checkpoint inhibitor (ICI)-related hypophysitis. Autoantibodies against corticotrophs, such as circulating anti-proopiomelanocortin (POMC) antibodies are considered disease markers. However, the number of identified cases was limited, implying that the characteristics of these autoantibodies are not fully understood., Methods: We investigate circulating autoimmune autoantibodies in detail through a novel case of IAD that developed as a paraneoplastic autoimmune ACTH deficiency., Results: The patient developed IAD after 25 weeks of ICI therapy for metastasis of large-cell neuroendocrine carcinoma at 69 years of age. Ectopic ACTH expression and infiltration of CD3+, CD4+, CD8+, and CD20+ lymphocytes were observed in the tumor tissues and circulating anti-POMC antibodies were detected specifically in the patient's serum. Moreover, detailed analyses of immunofluorescence staining using patient serum revealed that the recognition site of the autoantibody was ACTH 25-39 , which had not been identified in previous cases of paraneoplastic autoimmune ACTH deficiency., Conclusion: This case involved a combination of paraneoplastic spontaneously acquired IAD and ICI-related hypophysitis occupying the middle ground. Moreover, our study reveals new aspects of anti-POMC antibodies in patients with paraneoplastic ACTH deficiency. This report expands our understanding of the immunological landscape and provides new insights for the identification of antibodies associated with paraneoplastic autoimmune ACTH deficiency., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2023 Urai, Watanabe, Bando, Motomura, Yamamoto, Tachihara, Kanzawa, Fukuoka, Iguchi and Ogawa.)

The production and secretion of adrenocorticotropin, a proopiomelanocortin (POMC)-derived hormone, by corticotrophs in the anterior pituitary, is regulated by corticotrophin-releasing hormone (CRH) and glucocorticoids. We have previously demonstrated that adrenalectomy induces α-tubulin N-acetyltransferase 1 (ATAT1) expression and α-tubulin acetylation in corticotrophs. However, the regulatory mechanism of ATAT1 expression and the function of acetylated microtubules in corticotrophs are unclear. Here, we analyze the effect of CRH or dexamethasone on Atat1 expression in the mouse corticotroph AtT20 cell line. The expression of Atat1 was increased by CRH and decreased by dexamethasone in AtT20 cells. We examined the effect of Atat1 knockdown on the expression of POMC-associated genes and the dexamethasone-induced nuclear translocation of glucocorticoid receptor (GR) by real-time polymerase chain reaction and Western blot analysis, respectively. Atat1 knockdown resulted in a significant increase in the expression of ACTH-producing genes and decreased the dexamethasone-induced nuclear translocation of GR accompanied with a reduction in α-tubulin acetylation. Atat1 overexpression resulted in a significant increase in α-tubulin acetylation and the dexamethasone-induced nuclear translocation of GR. These results suggest that the acetylated microtubules function as the rail-line for the transportation of GR into the nucleus. We conclude that ATAT1 finely tunes the cellular responses of corticotrophs to hormonal stimulation through an intracellular feedback circuit. [ABSTRACT FROM AUTHOR]

Purpose: IgG4-related disease is a systemic inflammatory disease characterized by infiltration of IgG4-positive plasma cells into multiple organs, including the pituitary gland. Autoimmunity is thought to be involved in the pathogenesis of IgG4-related disease. The diagnosis of IgG4-related hypophysitis (IgG4-RH) is difficult because its clinical features, such as pituitary swelling and hypopituitarism, are similar to those of other pituitary diseases, including lymphocytic hypophysitis and sellar/suprasellar tumors. The presence and significance of anti-pituitary antibodies (APA) in IgG4-RH is unclear. Methods: In this case-control study, we used single indirect immunofluorescence on human pituitary substrates to assess the prevalence of serum APA in 17 patients with IgG4-RH, 8 control patients with other pituitary diseases (lymphocytic infundibulo-neurohypophysitis, 3; craniopharyngioma, 2; germinoma, 3), and 9 healthy subjects. We further analyzed the endocrine cells targeted by the antibodies using double indirect immunofluorescence. Results: APA were found in 5 of 17 patients with IgG4-RH (29%), and in none of the pituitary controls or healthy subjects. The endocrine cells targeted by the antibodies in the 5 IgG4-RH cases were exclusively corticotrophs. Antibodies were of the IgG1 subclass, rather than IgG4, in all 5 cases, suggesting that IgG4 is not directly involved in the pathogenesis. Finally, antibodies recognized pro-opiomelanocortin in 2 of the cases. Conclusions: Our study suggests that autoimmunity is involved in the pathogenesis of IgG4-RH and that corticotrophs are the main antigenic target, highlighting a possible new diagnostic marker for this condition. [ABSTRACT FROM AUTHOR]

After temozolomide failure, no evidence-based treatment option is currently available for aggressive pituitary tumors (APTs) and pituitary carcinomas (PCs). Moreover, once temozolomide has failed, the survival of these patients is very poor. The use of immune-checkpoint inhibitors (ICIs) has been so far reported in a large cohort, a small phase 2 clinical trial, and in another five isolated cases (24 cases in total). Here, we review the available evidence on the efficacy and potential predictors of response to ICIs in PCs and APTs, namely the histological type (corticotroph versus lactotroph), the tumor type (PC versus APT), the presence of uncontrolled endogenous hypercortisolism, the type of protocol (combined ICIs versus monotherapy), programmed death-ligand 1 (PD-L1) expression, CD8+ cell infiltration, tumor mutational burden (TMB), microsatellite instability (MSI), and mismatch repair (MMR) status. We also discuss key clinical aspects that can already be implemented in the everyday practice and identify future research needs. [ABSTRACT FROM AUTHOR]

Microtubules play an important role in the intracellular transport of secretory granules in endocrine cells and in mitosis and the maintenance of cell morphology and are composed of heterodimers of α- and β-tubulin. α-Tubulin N-acetyltransferase 1 (ATAT1), which acetylates the lysine residue at position 40 of α-tubulin, functions not only in stabilizing microtubule structures and forming the primary cilium assembly but also in vesicular trafficking in neurons. However, the localization of ATAT1 and the role of α-tubulin acetylation in endocrine cells in the pituitary are still poorly understood. Corticotrophs in the anterior lobe of the pituitary produce and secrete adrenocorticotropin (ACTH). Although removal of the adrenal gland, a target organ of ACTH, is reported to promote the synthesis and secretion of ACTH in corticotrophs and to induce structural alterations in their organelles, uncertainty remains as to whether the acetylation of α-tubulin is involved in such intracellular events of corticotrophs. We investigate the expression and localization of ATAT1 and the acetylation of α-tubulin in the pituitary of normal and adrenalectomized rats. We find that ATAT1 is localized to the Golgi apparatus of endocrine cells in the anterior lobe of normal pituitary and that the expression levels of ATAT1 and acetylation levels of α-tubulin increase following adrenalectomy. These results agree with the hypothesis that the acetylation of α-tubulin by ATAT1 regulates the intracellular transport of secretory granules in corticotrophs. [ABSTRACT FROM AUTHOR]

In the article, the author discusses the possible effects of glucocorticoid receptor (GR) variants in corticotroph tumorigenesis, particularly on adrenocorticotropin synthesis and corticotroph tumor growth. Topics include the effects of dexamethasone treatment on cell viability and how the variants affect GR transcriptional activity and gene expression.

Generation of a variety of organs and tissues from human pluripotent stem cells (hPSCs) has been attempted in vitro . We here present a simple and efficient method for induction of hypothalamic and pituitary tissues from hPSCs. On provision of exogenous agents important for early hypothalamus-pituitary organogenesis, including bone morphogenetic protein 4 and activators of sonic hedgehog, in three-dimensional culture, hPSCs spontaneously form spherical organoids with two distinct tissues, hypothalamus and adenohypophysis. The pituitary tissues derived from hPSCs not only secrete adenocorticotropic hormone, but also retain both positive and negative feedback mechanisms, recapitulating mature endocrine organs in vivo . Furthermore, the results of ectopic transplantation with mouse models of hypopituitarism suggest that these hypothalamus-pituitary organoids have potential as engraftment organs. In addition to their use in transplantation for patients with hypopituitarism they will allow establishment of disease models in vitro and enable research impossible in humans. Hypothalamus-pituitary organoids promise to be a powerful tool in regenerative medicine, drug discovery, and basic research into pituitary development., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Kano, Sasaki, Miwata and Suga.)

The activity of the hypothalamic-pituitary-adrenal (HPA) axis is characterised by complex dynamics spanning several timescales. This ranges from slow circadian rhythms in blood hormone concentration to faster ultradian pulses of hormone secretion and even more rapid oscillations in electrical and calcium activity in neuroendocrine cells of the hypothalamus and pituitary gland. Here, we focus on the system's oscillations on the short timescale. We highlight some of the mathematical modelling and experimental work that has been carried out to characterise the mechanisms regulating this highly dynamic mode of neuroendocrine signalling and discuss some future directions that may be explored to enhance understanding of HPA function., Competing Interests: Nothing declared., (© 2022 The Author(s).)

The hypothalamic-pituitary-adrenocortical (HPA) responses to bacterial infection are mediated, in part, by the actions of lipopolysaccharide (LPS) on pituitary folliculostellate (FS) cells that release pro-inflammatory cytokines [e.g. interleukin (IL)-6] and thereby facilitate adrenocorticotrophic hormone (ACTH) release from neighbouring corticotrophs. In the present study, two murine pituitary cell lines [TtT/GF (FS cells) and AtT20 D16:16 (corticotrophs)], alone and in co-culture, and an in vivo model of endotoxaemia were used to examine the potential role of nuclear factor-kappa B (NF-κB) in mediating LPS-induced ACTH secretion. Both cell lines expressed mRNAs for the key components of the LPS signalling system. LPS stimulated IL-6 release from TtT/GF cells via a glucocorticoid-sensitive, NF-κB-dependent mechanism; it also activated NF-κB in AtT20 cells, as did corticotrophin-releasing hormone (CRH). IL-6 potentiated (but LPS reduced) the stimulatory effects of CRH on ACTH release from AtT20 cells, whereas blockade of NF-κB (SC-514) increased the ACTH release induced by CRH in the presence or absence of LPS. In co-cultures, CRH and LPS acted synergistically to induce release of both IL-6 and ACTH. However, although SC-514 suppressed the release of IL-6 evoked by CRH and LPS, it potentiated the concomitant increase in ACTH release. In vivo both immunological (LPS) and psychological (restraint) stress increased intrapituitary NF-κB, whereas an NF-κB inhibitor (PHA781535E) attenuated the LPS-induced release of ACTH and abolished the HPA response to restraint stress. The results obtained in the present study support the premise that NF-κB plays an important role in mediating LPS signalling in the anterior pituitary gland, particularly in relation to IL-6 and ACTH secretion, and provide novel evidence that NF-κB blockade in vivo compromises stress-induced ACTH release. [ABSTRACT FROM AUTHOR]

Summary: An 11-month-old neutered female weimaraner was humanely destroyed 6days after an acute onset of neurological signs. At necropsy examination the pituitary gland was replaced by a large neoplastic mass that compressed and infiltrated the overlying hypothalamus. Small nodules were detected in the spleen, kidneys and stomach. Adrenal, thyroid and parathyroid glands were normal in size. The primary pituitary mass, visceral nodules and microscopical metastases detected within the ventricles and leptomeninges of the brain comprised polygonal, chromophobic neoplastic cells, which labelled strongly for adrenocorticotrophic hormone (ACTH) on immunohistochemical examination. These findings, in the absence of clinical or pathological evidence of pituitary-dependent hyperadrenocorticism, support a diagnosis of endocrinologically-inactive (‘silent’) pituitary corticotroph (ACTH-containing) carcinoma. [Copyright &y& Elsevier]

Cushing’s disease is caused by an ACTH-producing pituitary tumor, and accounts for 10–15% of pituitary tumors. The majority of corticotroph tumors are microadenomas (<10 mm), and accurate histologic identification of these tumors can be challenging because of their small size and the presence of nests of normal corticotroph cells in the anterior pituitary. Retinoic acid has been shown to inhibit ACTH production and induce apoptosis in corticotroph tumor cells. The expression of the orphan nuclear receptor COUP-TFI antagonizes retinoic acid signaling and has been shown to be expressed in normal corticotroph cells, but absent in corticotroph tumor cell lines. We analyzed 34 corticotroph tumor specimens by immunohistochemistry using a goat polyclonal IgG antibody with epitope mapping to the N-terminus of human COUP-TFI. Segments of normal pituitary in each of the 34 specimens demonstrate COUP-TFI immunoreactivity in normal corticotroph cells. Twenty-nine of 34 ACTH producing tumors were immunonegative for COUP-TFI. All of the tumors measuring less than 5 mm by preoperative MRI were COUP-TFI immunonegative. Two tumors, measuring 9 and 11 mm, showed consistent (>90%) expression of COUP-TFI, and three adenomas (5, 11, and 18 mm) showed heterogenous (20–80%) expression of COUP-TFI. Immunohistochemistry of COUP-TFI may be a useful adjuvant diagnostic tool in distinguishing corticotroph microadenomas from nests of normal corticotroph cells in the anterior pituitary. Furthermore, this study identifies two unique corticotroph tumor populations which differ in their expression of COUP-TFI, the presence of which occurs more frequently in macroadenomas. [ABSTRACT FROM AUTHOR]

Kisspeptin neurones in the arcuate nucleus play a pivotal role in the regulation of hypothalamic gonadotrophin-releasing hormone (GnRH) secretion in higher primates. To examine whether kisspeptin also influences the function of the primate pituitary directly, two experiments were performed in adult male rhesus monkeys. First, the distribution of kisspeptin-containing cells in the pituitary was described using fluorescence immunohistochemistry. Second, the secretion of non-gonadotrophin adenohypophysial hormones [growth hormone (GH), prolactin and thyroid-stimulating hormone (TSH)] and cortisol in response to i.v. kisspeptin administration was examined. Eight animals were deeply anaesthetised and transcardially perfused with 4% paraformaldehyde. Fluorescence immunohistochemistry was performed on 25-μm thick free-floating pituitary sections to localise immunopositive kisspeptin cells and to examine their relationship with immunostaining for luteinising hormone (LH), follicle-stimulating hormone, GH, prolactin, α-melanocyte-stimulating hormone (MSH), adrenocorticotrophic hormone (ACTH) and GnRH. Kisspeptin cells were found in the intermediate lobe of all animals and, in four monkeys, this neuropeptide was also observed in cells scattered in the periphery of the anterior lobe. Kisspeptin colocalised with α-MSH-immunopositive cells in the intermediate lobe and, in 50% of the monkeys, with ACTH-immuunopositive cells in the periphery of the adenohypophysis. There was no evidence for colocalisation of kisspeptin with gonadotrophs, somatotrophs or lactotrophs. Beaded kisspeptin axons were observed in the neural lobe. In addition, assay of plasma samples that had been collected for a previous study documenting kisspeptin-10-induced LH release in male monkeys revealed that kisspeptin administration failed to influence circulating concentrations of GH, prolactin, TSH and cortisol. Release of all four of these non-gonadotrophic hormones, however, was stimulated markedly by NMDA, which is considered to act centrally. Although the morphological findings obtained in the present study are consistent with the notion that kisspeptin may act directly at the level of the pituitary, the nature of such an action remains to be defined. [ABSTRACT FROM AUTHOR]

Pituitary melanotroph and corticotroph cells produce and secrete peptides from the multifunctional precursor protein proopiomelanocortin (POMC). Stimulation of the secretory activity of both cell types involves production of cyclic 3′5′-adenosine monophosphate (cAMP) and increases in the concentration of intracellular Ca2+. The increase in secretory activity is accompanied by enhanced expression of the POMC gene. Surprisingly, the POMC promoter lacks both cAMP-responsive elements and Ca2+-responsive elements through which the cAMP and Ca2+ signals could, in a relatively direct way, act on POMC gene expression. It is thus apparent that other, more indirect, mechanisms have evolved to utilize cAMP and Ca2+ signaling cascades to regulate POMC expression. This review gives an overview of the complex pathways and events that lead to the regulation of POMC gene expression in corticotrophs and melanotrophs. Another major site for POMC production is in hypothalamic neurons of the arcuate nucleus. In these neurons expression of the POMC gene relies on enhancer regions and responsive elements that differ from those utilized in the pituitary gland. In this review some attention will be given to progress made in unraveling the regulatory strategies acting on POMC expression in hypothalamic neurons. It is clear that the complexities of the promoter/enhancer structure of the POMC gene contribute to the versatility of this gene in participating in complex adaptation processes. [ABSTRACT FROM AUTHOR]

Large conductance calcium-activated potassium (BK) channels are very prominently expressed in adrenal chromaffin and many anterior pituitary cells, where they shape intrinsic excitability complexly. Stress- and sex-steroids regulate alternative splicing of Slo-α, the pore-forming subunit of BK channels, and chronic behavioural stress has been shown to alter Slo splicing in tree shrew adrenals. In the present study, we focus on mice, measuring the effects of chronic behavioural stress on total mRNA expression of the Slo-α gene, two key BK channel β subunit genes (β2 and β4), and the ‘STREX’ splice variant of Slo-α. As a chronic stressor, males of the relatively aggressive SJL strain were housed with a different unfamiliar SJL male every 24 h for 19 days. This ‘social-instability’ paradigm stressed all individuals, as demonstrated by reduced weight gain and elevated corticosterone levels. Five quantitative reverse transcriptase-polymerase chain assays were performed in parallel, including β-actin, each calibrated against a dilution series of its corresponding cDNA template. Stress-related changes in BK expression were larger in mice tested at 6 weeks than 9 weeks. In younger animals, Slo-α mRNA levels were elevated 44% and 116% in the adrenal medulla and pituitary, respectively, compared to individually-housed controls. β2 and β4 mRNAs were elevated 162% and 194% in the pituitary, but slightly reduced in the adrenals of stressed animals. In the pituitary, dominance scores of stressed animals correlated negatively with α and β subunit expression, with more subordinate individuals exhibiting levels that were three- to four-fold higher than controls or dominant individuals. STREX variant representation was lower in the subordinate subset. Thus, the combination of subunits responding to stress differs markedly between adrenal and pituitary glands. These data suggest that early stress will differentially affect neuroendocrine cell excitability, and call for detailed analysis of functional consequences. [ABSTRACT FROM AUTHOR]

Abstract: Corticotropin-releasing factor (CRF) is a major regulatory peptide in the hypothalamic-pituitary-adrenal (HPA) axis under stress conditions. In response to stress, CRF, produced in the hypothalamic paraventricular nucleus, releases adrenocorticotropic hormone (ACTH) from the anterior pituitary (AP). ACTH in turn stimulates the release of glucocorticoid from the adrenal glands. Glucocorticoid then inhibits hypothalamic production of CRF and pituitary production of ACTH. Mice lacking a functional gene for CRF (CRF KO) showed severe impairment of the HPA axis, indicating that CRF is required for its regulation. We applied oligonucleotide microarray analysis to the AP of CRF KO to identify gene expression induced by CRF. Twenty-four genes showed less than 60% expression in CRF KO compared with normal mice. Real-time PCR analysis revealed that p21-activated kinase 3 (Pak3), prohormone convertase type 1 (PC1), and CRF-binding protein (BP) mRNA expression levels were increased by CRF in AP cells. Both Pak3 and PC1 were also increased by dexamethasone in AP cells, while CRF-BP mRNA levels were reduced. Therefore, both Pak3 and PC1 mRNA levels would be regulated by both CRF and glucocorticoids. Pak3 knockdown inhibited CRF-induced cell viability in AtT-20 cells, suggesting the important role of Pak3 in the proliferation of corticotrophs. [Copyright &y& Elsevier]

Abstract: Cushing''s disease caused by pituitary corticotroph adenoma in dogs is usually treated by medical treatment, and the efficacy of this treatment has been reported. However, controversy remains as to whether reduced negative feedback through the inhibition of cortisol secretion, similar to Nelson''s syndrome, may appear as an adverse effect. The purpose of this study was to investigate the effect of reduced negative feedback through the inhibition of cortisol secretion by daily trilostane administration on the pituitary–adrenal axis in clinically normal dogs. Dogs were administered 5mg/kg trilostane twice a day every day for 8 weeks (n =8) or 16 weeks (n =3). After the initiation of trilostane administration, plasma adrenocorticotropic hormone (ACTH) concentrations were increased remarkably. As assessed by magnetic resonance imaging (MRI) during administration, the pituitary became enlarged. After trilostane administration, the cytoplasmic areas of the pituitary corticotrophs were increased and the ratio of pituitary corticotrophs to all cells in the anterior lobe was greater in the trilostane-treated dogs than that in untreated animals. In addition, histological examinations revealed bilateral adrenal cortical hyperplasia. Using real-time PCR quantification, the expression of proopiomelanocortin (POMC) mRNA in the pituitary and ACTH receptor (ACTH-R) mRNA in the adrenal gland was greater in the dogs treated with trilostane than in untreated dogs. These results indicate that reduced negative feedback induced hyperfunction of the pituitary corticotrophs and pituitary enlargement in healthy dogs. These changes suggest that the inhibition of cortisol secretion by trilostane may increase the risk for accelerating the growth of corticotroph adenomas in dogs with Cushing''s disease. [Copyright &y& Elsevier]

Myostatin (MSTN), known as growth and differentiation factor 8 (GDF-8), is a member of the transforming growth factor β (TGF-β) superfamily that negatively regulates skeletal muscle mass. Myostatin binds with high affinity to the receptor serine threonine kinase activin receptor type IIB (ActRIIB). Activins that also belong to the TGF-β superfamily, stimulate follicle-stimulating hormone production in gonadotrophs and suppress growth hormone and adrenocorticotropic hormone production in somatotrophs and corticotrophs, respectively. The aim of the present paper was therefore to clarify the endocrine action of MSTN in adenohypophysis. The present study details the expression and cellular localization of MSTN and ActRIIB in porcine anterior pituitary gland. The mRNA of MSTN and ActRIIB was consistently expressed in RT-PCR. Immunohistochemistry of MSTN and specific hormones showed that MSTN localized in thyrotrophs and gonadotrophs, in which most of the MSTN immunoreactive cells were identified as thyrotrophs. The immunostaining of ActRIIB was restricted to corticotrophs. These results indicate that MSTN was mainly produced in thyrotrophs and its receptor, ActRIIB, was restrictively contained in corticotrophs. Interestingly, thyrotrophs immunoreactive for MSTN were frequently close to corticotrophs immunoreactive for ActRIIB. The present study suggests that MSTN from thyrotrophs may regulate corticotroph function as a paracrine mediator among the porcine anterior pituitary cells. [ABSTRACT FROM AUTHOR]

In the anterior pituitary gland, c-Fos expression is evoked by various stimuli. However, whether c-Fos expression is directly related to the stimulation of anterior pituitary cells by hypothalamic secretagogues is unclear. To confirm whether the reception of hormone-releasing stimuli evokes c-Fos expression in anterior pituitary cells, we have examined c-Fos expression of anterior pituitary glands in rats administered with synthetic corticotrophin-releasing hormone (CRH) intravenously or subjected to restraint stress. Single intravenous administration of CRH increases the number of c-Fos-expressing cells, and this number does not change even if the dose is increased. Double-immunostaining has revealed that most of the c-Fos-expressing cells contain adrenocorticotrophic hormone (ACTH); corticotrophs that do not express c-Fos in response to CRH have also been found. However, restraint stress evokes c-Fos expression in most of the corticotrophs and in a partial population of lactotrophs. These results suggest that c-Fos expression increases in corticotrophs stimulated by ACTH secretagogues, including CRH. Furthermore, we have found restricted numbers of corticotrophs expressing c-Fos in response to CRH. Although the mechanism underlying the different responses to CRH is not apparent, c-Fos is probably a useful immunohistochemical marker for corticotrophs stimulated by ACTH secretagogues. [ABSTRACT FROM AUTHOR]

Abstract: The corticotropin-releasing factor (CRF) family of peptides generally exerts its biological actions by binding to two major subtypes of CRF receptors: CRF receptor type 1 (CRF1 receptor) and CRF receptor type 2 (CRF2 receptor). In this study, we investigated the mechanism by which three ligands altered phosphorylation of CREB and ERK 1/2, using AtT-20 cells (expressing CRF1 receptor) and A7r5 cells (expressing CRF2 receptor). Incubation with 100nM of CRF, urocortin 1 (UCN 1), or UCN 2 increased CREB phosphorylation. The protein kinase A pathway was involved in the CRF- or UCN-mediated increase in CREB phosphorylation in both cell lines. Bisindolylmaleimide partially inhibited the CRF-mediated increase in CREB phosphorylation, but only in AtT-20 cells, suggesting that the protein kinase C pathway is involved in regulation of CREB phosphorylation via CRF1 receptor but not CRF2 receptor. CRF increased ERK phosphorylation in AtT-20 cells, whereas the UCNs decreased it in A7r5 cells. Bisindolylmaleimide partially inhibited the UCN-mediated decrease in ERK phosphorylation in A7r5 cells, suggesting that the protein kinase C pathway is partially involved in CRF2 receptor signal transduction. In AtT-20 cells, the mitogen-activated protein kinase kinase pathway regulated ERK phosphorylation following CRF1 receptor activation. These findings suggest differential regulation of CREB and ERK 1/2 phosphorylation through CRF receptors. [Copyright &y& Elsevier]