The sodium leak channel NALCN encodes the major background sodium ion conductance in murine anterior pituitary cells

The pituitary gland, the so-called master gland produces and secretes a variety of hormones essential for regulating growth and development, metabolic homeostasis, reproduction, and the stress response. The interplay between the brain and peripheral feedback signals controls hormone secretion from pituitary cells by regulating the properties of ion channels, and in turn, cell excitability. Endocrine anterior pituitary cells fire spontaneous action potentials to regulate their intracellular calcium level and eventually hormone secretion. However, the molecular identity of the non-selective cationic leak channel involved in maintaining the resting membrane potential at the firing threshold remained unknown. Here, we show that the sodium leak channel NALCN, known to modulate neuronal excitability, also regulates excitability in murine anterior pituitary cells. Using viral transduction combined with electrophysiology and calcium imaging we show that NALCN encodes the major Na+ leak conductance which tunes the resting membrane potential close to firing threshold to sustain the intrinsically-regulated firing in endocrine pituitary cells. Genetic interruption of NALCN channel activity, hyperpolarised the membrane potential drastically and stopped the firing activity, and consequently abolished the cytosolic calcium oscillations. Moreover, we found that NALCN conductance forms a very small fraction of the total cell conductance yet has a profound impact on modulating pituitary cell excitability. Taken together, our results demonstrate that, NALCN is a crucial regulator of pituitary cell excitability and supports spontaneous firing activity to consequently regulate hormonal secretion. Our results suggest that receptor-mediated and potentially circadian changes in NALCN conductance can powerfully affect the pituitary activity and hormone secretion.

Pathogenesis of Anti–PIT-1 Antibody Syndrome: PIT-1 Presentation by HLA Class I on Anterior Pituitary Cells

Context Anti–pituitary-specific transcriptional factor-1 (anti–PIT-1) antibody syndrome is characterized by acquired and specific deficiencies in growth hormone, prolactin, and thyroid-stimulating hormone. Although PIT-1–reactive cytotoxic T lymphocytes (CTLs) have been speculated to recognize anterior pituitary cells and to cause the injury in the pathogenesis of the syndrome, it remains unclear whether endogenous PIT-1 protein is processed through the proteolytic pathway and presented as an antigen on anterior pituitary cells. Objective To examine how PIT-1 protein is processed and whether its epitope is presented by major histocompatibility complex (MHC)/HLA class I on anterior pituitary cells. Materials and Methods Immunofluorescence staining and proximity ligation assay (PLA) were performed using anti–PIT-1 antibody and patients’ sera on PIT-1–expressing cell line GH3 cells and human induced pluripotent stem cell (iPSC)-derived pituitary tissues. Results PIT-1 was colocalized with MHC class I molecules, calnexin, and GM130 in the cytosol. PLA results showed that PIT-1 epitope was presented by MHC/HLA class I molecules on the cell surface of GH3 cells and iPSC-derived pituitary cells. The number of PIT-1/HLA complexes on the cell surface of pituitary cells in the patient was comparable with that in the control subject. Conclusions Our data indicate that PIT-1 protein is processed in the antigen presentation pathway and that its epitopes are presented by in MHC/HLA class I on anterior pituitary cells, supporting the hypothesis that PIT-1–reactive CTLs caused the cell-specific damage. It is also suggested that number of epitope presentation was not associated with the pathogenesis of anti–PIT-1 antibody syndrome.