Calcium-Prolactin Secretion Coupling in Rat Pituitary Lactotrophs Is Controlled by PI4-Kinase Alpha

Postnatal Development and Maintenance of Functional Pituitary Gonadotrophs Is Dependent on PI4-Kinase A

Postnatal development of functional pituitary gonadotrophs is necessary for maturation of the hypothalamic-pituitary-gonadal axis, puberty, and reproduction. Here we examined the role of PI4-kinase A, which catalyzes the biosynthesis of PI4P in mouse reproduction by knocking out this enzyme in cells expressing the gonadotropin-releasing hormone (GnRH) receptor. Knockout (KO) mice were infertile, reflecting underdeveloped gonads and reproductive tracts and lack of puberty. The number and distribution of hypothalamic GnRH neurons and Gnrh1 expression in postnatal KOs were not affected, whereas Kiss1/kisspeptin expression was increased. KO of PI4-kinase A also did not alter embryonic establishment and neonatal development and function of the gonadotroph population. However, during the postnatal period, there was a progressive loss of expression of gonadotroph-specific genes, including Fshb, Lhb, and Gnrhr, accompanied by low gonadotropin synthesis. The postnatal gonadotroph population also progressively declined, reaching approximately one-third of that observed in controls at 3 months of age. In these residual gonadotrophs, GnRH-dependent calcium signaling and calcium-dependent membrane potential changes were lost, but intracellular administration of inositol-14,5-trisphosphate rescued this signaling. These results indicate a key role for PI4-kinase A in the postnatal development and maintenance of a functional gonadotroph population.

Single-cell sequencing identifies differentiation-related markers for molecular classification and recurrence prediction of PitNET

Pituitary neuroendocrine tumor (PitNET) is one of the most common intracranial tumors with variable recurrence rate. Currently, the recurrence prediction is unsatisfying and can be improved by understanding the cellular origins and differentiation status. Here, to comprehensively reveal the origin of PitNET, we perform comparative analysis of single-cell RNA sequencing data from 3 anterior pituitary glands and 21 PitNETs. We identify distinct genes representing major subtypes of well and poorly differentiated PitNETs in each lineage. To further verify the predictive value of differentiation biomarkers, we include an independent cohort of 800 patients with an average follow-up of 7.2 years. In both PIT1 and TPIT lineages, poorly differentiated groups show significantly higher recurrence rates while well-differentiated groups show higher recurrence rates in SF1 lineage. Our findings reveal the possible origin and differentiation status of PitNET based on which new differentiation classification is proposed and verified to predict tumor recurrence.

Is prolactin receptor signaling a target in dopamine-resistant prolactinomas?

The hypothalamic neuroendocrine catecholamine dopamine regulates the lactotroph function, including prolactin (PRL) secretion, proliferation, and apoptosis. The treatment of PRL-secreting tumors, formerly known as prolactinomas, has relied mainly on this physiological characteristic, making dopamine agonists the first therapeutic alternative. Nevertheless, the group of patients that do not respond to this treatment has few therapeutical options. Prolactin is another physiological regulator of lactotroph function, acting as an autocrine/paracrine factor that controls PRL secretion and cellular turnover, inducing apoptosis and decreasing proliferation. Furthermore, the signaling pathways related to these effects, mainly JAK/STAT and PI3K/Akt, and MAPK, have been extensively studied in prolactinomas and other tumors as therapeutic targets. In the present work, the relationship between PRL pathophysiology and prolactinoma development is explored, aiming to comprehend the value of PRL and PRLR-associated pathways as exploratory fields alternative to dopamine-related approaches, which are worth physiological characteristics that might be impaired and can be potentially restored or upregulated to provide more options to the patients.

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

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

Evaluation of autoantibody signatures in pituitary adenoma patients using human proteome arrays

PURPOSE

To identify the specific diagnostic biomarkers related to pituitary adenomas (PAs), we performed serological antibody profiles for three types of PAs, namely Acromegaly, Cushing's and Nonfunctional Pituitary Adenomas (NFPAs), using the human proteome (HuProt) microarray. This is the first study describing the serum autoantibody profile of PAs.

EXPERIMENTAL DESIGN

We performed serological autoantibody profiling of four healthy controls, four Acromegaly, three Cushing's and three NFPAs patient samples to obtain their autoantibody profiles, which were used for studying expression, interaction and altered biological pathways. Further, significant autoantibodies of PAs were compared with data available for glioma, meningioma and AAgAtlas for their specificity.

RESULTS

Autoantibody profile of PAs led to the identification of differentially expressed significant proteins such as AKNAD1 (AT-Hook Transcription Factor [AKNA] Domain Containing 1), NINJ1 (Nerve injury-induced protein 1), L3HYPDH (Trans-3-hydroxy-L-proline dehydratase), RHOG (Rho-related GTP-binding protein) and PTP4A1 (Protein Tyrosine Phosphatase Type IVA 1) in Acromegaly. Protein ABR (Active breakpoint cluster region-related protein), ST6GALNAC6 (ST6 N-acetylgalactosaminide alpha-2, 6-sialyltransferase 6), NOL3 (Nucleolar protein 3), ANXA8 (Annexin A8) and POLR2H (RNA polymerase II, I and III subunit H) showed an antigenic response in Cushing's patient's serum samples. Protein dipeptidyl peptidase 3 (DPP3) and reticulon-4 (RTN4) exhibited a very high antigenic response in NFPA patients. These proteins hold promise as potential autoantibody biomarkers in PAs.