Ca2+ Channels in Anterior Pituitary Somatotrophs: A Therapeutic Perspective

Transcriptomic Classification of Pituitary Neuroendocrine Tumors Causing Acromegaly

Acromegaly results from growth hormone hypersecretion, predominantly caused by a somatotroph pituitary neuroendocrine tumor (PitNET). Acromegaly-causing tumors are histologically diverse. Our aim was to determine transcriptomic profiles of various somatotroph PitNETs and to evaluate clinical implication of differential gene expression. A total of 48 tumors were subjected to RNA sequencing, while expression of selected genes was assessed in 134 tumors with qRT-PCR. Whole-transcriptome analysis revealed three transcriptomic groups of somatotroph PitNETs. They differ in expression of numerous genes including those involved in growth hormone secretion and known prognostic genes. Transcriptomic subgroups can be distinguished by determining the expression of marker genes. Analysis of the entire cohort of patients confirmed differences between molecular subtypes of tumors. Transcriptomic group 1 includes ~20% of acromegaly patients with GNAS mutations-negative, mainly densely granulated tumors that co-express GIPR and NR5A1 (SF-1). SF-1 expression was verified with immunohistochemistry. Transcriptomic group 2 tumors are the most common (46%) and include mainly GNAS-mutated, densely granulated somatotroph and mixed PitNETs. They have a smaller size and express favorable prognosis-related genes. Transcriptomic group 3 includes predominantly sparsely granulated somatotroph PitNETs with low GNAS mutations frequency causing ~35% of acromegaly. Ghrelin signaling is implicated in their pathogenesis. They have an unfavorable gene expression profile and higher invasive growth rate.

Mel1b and Mel1c melatonin receptors mediate green light-induced secretion of growth hormone in chick adenohypophysis cells via the AC/PKA and ERK1/2 signalling pathways

A previous study showed that melatonin (MEL) membrane receptors 1b (Mel1b) and Mel1c promoted the secretion of growth hormone (GH) in chick adenohypophysis cells under monochromatic green light. However, the intracellular signalling pathways of these two receptors are unclear. Therefore, cultured adenohypophysis cells derived from chickens exposed to monochromatic green light were treated with MEL, Mel1b- and Mel1c-specific blockers, protein kinase A (PKA) inhibitors and adenylate cyclase (AC), or AC activator in vitro to explore the signal transduction mechanism that promote the secretion of GH. The results showed that Mel1b and Mel1c participate in MEL-mediated green light-induced secretion of GH in chick adenohypophysis cells. However, MEL increased cyclic adenosine monophosphate (cAMP) levels, and p-PKA protein levels were blocked by a Mel1b-specific antagonist but not a Mel1c-specific antagonist, which indicated that Mel1b affected the secretion of GH via the AC/cAMP/PKA signalling pathway. Moreover, Mel1b and Mel1c both activated ERK1/2 to regulate the secretion of GH. In addition, intracellular and extracellular Ca²⁺ channels were also involved in secretion of GH in chick adenohypophysis cells. These results demonstrate that the MEL mediated green light-induced secretion of GH in chick adenohypophysis via the Mel1b/AC/PKA/ERK1/2, Mel1c/ERK1/2, and intracellular and extracellular Ca2⁺ channel signalling pathways.

Regulation of GH and GH Signaling by Nutrients

Growth hormone (GH) and insulin-like growth factor-1 (IGF-I) are pleiotropic hormones with important roles in lifespan. They promote growth, anabolic actions, and body maintenance, and in conditions of energy deprivation, favor catabolic feedback mechanisms switching from carbohydrate oxidation to lipolysis, with the aim to preserve protein storages and survival. IGF-I/insulin signaling was also the first one identified in the regulation of lifespan in relation to the nutrient-sensing. Indeed, nutrients are crucial modifiers of the GH/IGF-I axis, and these hormones also regulate the complex orchestration of utilization of nutrients in cell and tissues. The aim of this review is to summarize current knowledge on the reciprocal feedback among the GH/IGF-I axis, macro and micronutrients, and dietary regimens, including caloric restriction. Expanding the depth of information on this topic could open perspectives in nutrition management, prevention, and treatment of GH/IGF-I deficiency or excess during life.

Genetic and Epigenetic Characterization of Growth Hormone-Secreting Pituitary Tumors

Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characterized; apart from mutations in the stimulatory Gα protein (Gα_s encoded by GNAS) causing activated cAMP synthesis, pathogenic variants are rarely found in growth hormone-secreting pituitary tumors (somatotropinomas). The purpose of the current work was to clarify how genetic and epigenetic alterations contribute to the development of somatotropinomas by conducting an integrated copy number alteration, whole-genome and bisulfite sequencing, and transcriptome analysis of 21 tumors. Somatic mutation burden was low, but somatotropinomas formed two subtypes associated with distinct aneuploidy rates and unique transcription profiles. Tumors with recurrent chromosome aneuploidy (CA) were GNAS mutation negative (Gsp^- ). The chromosome stable (CS) -group contained Gsp⁺ somatotropinomas and two totally aneuploidy-free Gsp^- tumors. Genes related to the mitotic G₁-S-checkpoint transition were differentially expressed in CA- and CS-tumors, indicating difference in mitotic progression. Also, pituitary tumor transforming gene 1 (PTTG1), a regulator of sister chromatid segregation, showed abundant expression in CA-tumors. Moreover, somatotropinomas displayed distinct Gsp genotype-specific methylation profiles and expression quantitative methylation (eQTM) analysis revealed that inhibitory Gα (Gα_i) signaling is activated in Gsp⁺ tumors. These findings suggest that aneuploidy through modulated driver pathways may be a causative mechanism for tumorigenesis in Gsp^- somatotropinomas, whereas Gsp⁺ tumors with constitutively activated cAMP synthesis seem to be characterized by DNA methylation activated Gα_i signaling. IMPLICATIONS: These findings provide valuable new information about subtype-specific pituitary tumorigenesis and may help to elucidate the mechanisms of aneuploidy also in other tumor types.