The regulatory role of melatonin in pituitary thyroid-stimulating hormone synthesis through casein kinase 1α

Introduction: The regulation of thyroid-stimulating hormone (TSH) synthesis involves neurotransmitters, with melatonin being a subject of ongoing debate. TSH transcription, synthesis, and secretion from the pituitary pars distalis (PD) is primarily regulated in a photoperiodic manner by thyrotropin-releasing hormone (TRH). In contrast, in the pituitary pars tuberalis (PT), mRNA transcription and alpha/beta chain synthesis, but not secretion, of a TSHlike product is regulated by melatonin. Conversely, non-photoperiodic melatonin might also affect the secretion of a TSH-like product from the PT. Nevertheless, the impact of exogenous melatonin on the underlying PD-TSH synthesis remains unclear. Casein kinase 1 alpha (CK1 alpha) plays a negative regulatory role in TSH synthesis in the mouse pituitary. Objective: We investigated whether non-photoperiodic melatonin affects PD-TSH synthesis through its interaction with CK1 alpha. Methods: Immunohistochemistry and immunofluorescence staining detected the colocalization of the melatonin receptor MT1 with CK1 alpha and TSH-(3 in the PD. RT-qPCR, western blotting, and ELISA revealed the effect of melatonin on Tshb mRNA, MTNR1A mRNA, Csnk1a1 mRNA, CK1 alpha protein, MT1 protein, and TSH levels. Results: Robust colocalization of the melatonin receptor MT1 with CK1 alpha and TSH-(3 in the PD. Tshb mRNA and CK1 alpha protein expression levels peaked at opposite phases of the 24-h light:dark cycle. Exogenous melatonin administration promoted pituitary TSH synthesis, while concurrently inhibiting CK1 alpha activity. The upregulation of endogenous CK1 alpha activity in primary pituitary cells significantly blunted the melatonin stimulatory impact on Tshb mRNA and TSH levels. Mechanistically, the CK1 alpha agonist pyrvinium abrogated melatonin-induced activation of pPKC and p-CREB expression in vitro. Conclusion: The CK1 alpha/PKC signaling pathway mediates the regulation of melatonin in pituitary TSH synthesis. We demonstrate an important theoretical and experimental basis for understanding the mechanism of endocrine system diseases caused by abnormal TSH synthesis in the pituitary.