Glycoprotein hormone subunit alpha 2 (GPHA2): A pituitary stem cell-expressed gene associated with NOTCH2 signaling

NOTCH2 is expressed in pituitary stem cells and is necessary for stem cell maintenance, proliferation, and differentiation. However, the pathways NOTCH2 engages to affect pituitary development remain unclear. In this study, we hypothesized that glycoprotein hormone subunit A2 (GPHA2), a corneal stem cell factor and ligand for the thyroid stimulating hormone receptor (TSHR), is downstream of NOTCH2 signaling. We found Gpha2 is expressed in quiescent pituitary stem cells by RNAscope in situ hybridization and scRNA seq. In Notch2 conditional knockout pituitaries, Gpha2 mRNA is reduced compared with control littermates. We then investigated the possible functions of GPHA2. Pituitaries treated with a GPHA2 peptide do not have a change in proliferation. However, in dissociated adult pituitary cells, GPHA2 increased pCREB expression and this induction was reversed by co-treatment with a TSHR inhibitor. These data suggest GPHA2 is a NOTCH2 related stem cell factor that activates TSHR signaling, potentially impacting pituitary development.

Pituitary adenoma or neuroendocrine tumour: the need for an integrated prognostic classification

In the 2022 fifth edition of the WHO Classification of Endocrine Tumours and of Central Nervous System Tumours, pituitary adenomas are reclassified as neuroendocrine tumours (NETs). This change confers an oncology label to neoplasms that are overwhelmingly benign. A comprehensive clinical classification schema is required to guide prognosis, therapy and outcomes for all patients with pituitary adenomas. Pituitary adenomas and NETs exhibit some morphological and ultrastructural similarities. However, unlike NETs, pituitary adenomas are highly prevalent, yet indolent and rarely become malignant. This Perspective presents the outcomes of an interdisciplinary international workshop that addressed the merit and clinical implications of the classification change of pituitary adenoma to NET. Many non-histological factors provide mechanistic insight and influence the prognosis and treatment of pituitary adenoma. We recommend the development of a comprehensive classification that integrates clinical, genetic, biochemical, radiological, pathological and molecular information for all anterior pituitary neoplasms.

Prenatal Exposure to the Endocrine Disrupting Chemical DEHP Impacts Reproduction-Related Gene Expression in the Pituitary

Phthalates are chemicals used in various common products including plastics and medical devices, leading to widespread contact. Phthalate exposure during embryonic development can cause changes in puberty timing, reduced fertility and genital abnormalities. Previous studies on prenatal exposure to Di-(2-ethylhexyl) phthalate (DEHP) in mice indicated that it disrupts pituitary-gonadal feedback and alters reproductive performance in the offspring, however, the mechanism behind this is unknown. We hypothesize that prenatal exposure to DEHP during a critical period of embryonic development (e15.5 to e18.5) will cause sex-specific disruptions in reproduction-related functions in the pituitary in offspring due to interference with androgen and aryl hydrocarbon receptor (AhR) signaling. In order to discover the direct effects of DEHP on the reproduction-related functions in the pituitary, we performed both in vivo dosing and in vitro pituitary culture experiments. First, we dosed pregnant CD-1 mice with corn oil, the antiandrogen flutamide or DEHP from gestational day 15.5 to 18.5, then collected the pituitaries of the offspring on postnatal day 0. We found that prenatal DEHP exposure caused a significant increase in Fshb specifically in males, and flutamide caused significant increases in both Lhb and Fshb in males. Besides, DEHP exposure significantly increased AhR pathway related gene Cyp1b1 in both males and females. In the in vitro experiment, we took whole pituitaries from e16.5 embryos and cultured them in media containing DEHP, MEHP and/or AhR antagonist for 72hrs. We found that the DEHP metabolite MEHP was actually the chemical that exerted the effects directly at the level of the pituitary. Similar to in vivo experiments, Cyp1a1 and Cyp1b1 mRNA level were increased in pituitaries treated with MEHP in both sexes and the induction could be reduced by co-treatment with AhR antagonist. The mRNA level of Lhb, Fshb and Gnrhr were significantly decreased in both sexes by MEHP and co-treatment with AhR antagonist did not restore mRNA levels. The induction of Cyp1a1/Cyp1b1 gene in both in vivo and in vitro experiments indicates the possible activation of AhR by DEHP/MEHP. The in vitro experiment with AhR antagonist further proved that the induction of Cyp1a1/Cyp1b1 was indeed due to AhR activation directly at the level of the pituitary. The difference between in vivo and in vitro experiments in terms of gonadotropin gene expression indicates multiple mechanisms should be involved in the regulation of gonadotropin gene expression in vivo including androgen-related pathways and possibly AhR-related pathways. In summary, our data suggest that phthalates can directly affect the function of the pituitary in terms of regulation of reproductive- related genes. This indicates that pituitary impacts of phthalates could contribute to reproductive dysfunction observed in exposed mice and humans.

SUN-466 Gestational Diabetes Alters Hypothalamic Development, Microglial Activation, and Insulin Signaling in Offspring

Gestational diabetes mellitus (GDM) is characterized by maternal insulin resistance during pregnancy, leading to high blood glucose levels. Offspring of a GDM pregnancy often have high birth weight that continues through life. GDM influence on developing hypothalamic tanycytes may underlie this outcome. Tanycytes line the third ventricle and project into the median eminence (ME). They are a major component of hypothalamic nutrient sensing, particularly of glucose. Tanycytes are also capable of giving rise to hypothalamic neurons that regulate energy homeostasis and are known to proliferate postnatally in response to diet. We hypothesized that GDM would lead to changes in the tanycyte and ME cell populations of offspring. To study this, we utilized a leptin receptor mutant mouse model, Lepr ^+/db, that develops GDM during pregnancy. We looked at three potential mechanisms by which GDM could affect the hypothalamus: tanycyte proliferation, insulin signaling, and microglial activation. First, to examine proliferation, we injected wildtype and Lepr ^+/db dams with BrdU on embryonic days 16.5, 17.5, and 18.5, corresponding with the onset of GDM. Cells immunopositive for BrdU on the day of birth are either minimally proliferating at the time of injection or newly born afterward. We observed significantly fewer positive cells in the α and β1 tanycyte region and in the ME of GDM offspring compared to controls. Fewer cells proliferating in these regions could hinder adaptability to changing metabolic needs. Second, we examined the impact of maternal GDM on insulin signaling in offspring after birth. Brain slices from P9 control and GDM offspring were incubated with vehicle or insulin and immunostained for phospho-AKT (pAKT). While insulin exposure induced pAKT similarly in all offspring, basal pAKT was significantly higher in GDM offspring than controls. pAKT was confined to tanycytes and their projections within the ME. This suggests that GDM offspring have hyperactive insulin signaling when nutrient conditions do not warrant it, particularly in nutrient-sensing tanycytes. Third, we examined microglial activation since GDM causes systemic inflammation in the mothers, and hypothalamic microglia, the brain’s resident immune system, have been shown to play an important role in the development of obesity. We immunostained for Iba-1 in offspring from control and GDM dams on P0 to assess the number and activity state of microglial cells. Compared to offspring of control mothers, offspring born to GDM mothers have more active microglia near α and β1 tanycytes and in the ME. Since microglial activation induced by overnutrition is linked to obesity in adults, a similar mechanism may act on GDM offspring. Taken together, our data suggest that being born to a mother with GDM results in alterations to the tanycyte population and ME, which could play major roles in disordered feeding.

Notch signaling maintains Leydig progenitor cells in the mouse testis

During testis development, fetal Leydig cells increase their population from a pool of progenitor cells rather than from proliferation of a differentiated cell population. However, the mechanism that regulates Leydig stem cell self-renewal and differentiation is unknown. Here, we show that blocking Notch signaling, by inhibiting gamma-secretase activity or deleting the downstream target gene Hairy/Enhancer-of-split 1, results in an increase in Leydig cells in the testis. By contrast, constitutively active Notch signaling in gonadal somatic progenitor cells causes a dramatic Leydig cell loss, associated with an increase in undifferentiated mesenchymal cells. These results indicate that active Notch signaling restricts fetal Leydig cell differentiation by promoting a progenitor cell fate. Germ cell loss and abnormal testis cord formation were observed in both gain- and loss-of-function gonads, suggesting that regulation of the Leydig/interstitial cell population is important for male germ cell survival and testis cord formation.