Introduction: Pituitary hormone secretion fluctuates over 24h, reflecting a possible role for of the intrinsic circadian clock in these oscillations. Both Hypo and Hyperthyroidism alter the pituitary hormone synthesis/secretion, however, the interaction between thyroid hormones and circadian clock in pituitary is unknown. Objectives: The goal of this study was to characterize whether T3 modulates the circadian clock expression in anterior pituitary cells. Methods: Male rats were divided in euthyroid, hypothyroid and hyperthyroid and euthanized every 3h, across 24h; afterwards, the pituitaries were excised and total RNA was extracted and evaluated for gene expression. One and Two-way ANOVA and cosinor analysis were applied to evaluate the time-of-day-dependent differential expression for each gene/group and their interactions. In addition, the T3 transcriptional regulation of clock genes promoters was evaluated in GH3 cells transfected with mouse Bmal1 or Nr1d1 promoters by Luciferase assay. Results: The hyperthyroidism increased the expression of all core clock components and the mesors of Bmal1 and Nr1d1 were increased compared to euthyroid animals. In hypothyroid rats, the circadian pattern of Bmal1 and Per2 expression was lost, while the mesor of Nr1d1 was reduced. In silico analysis pointed out the putative existence of thyroid hormone responsive elements in promoter or regulatory regions of Bmal1 and Nr1d1 genes. The in vitro analysis showed that T3 rapidly increases the activity of both Bmal1 and Nr1d1 promoters. Conclusion: Our data indicate a role of T3 in the modulation of clock gene expression in pituitary cells, which could be related to the altered pituitary hormone secretion observed in hypo and hyperthyroid conditions.
TRIIODOTHYRONINE INCREASES THE CIRCADIAN CLOCK EXPRESSION IN RAT ANTERIOR PITUITARY BY TRANSCRIPTIONAL MECHANISMS
Michela Zamboni;Donato Civitareale;
2021
Abstract
Introduction: Pituitary hormone secretion fluctuates over 24h, reflecting a possible role for of the intrinsic circadian clock in these oscillations. Both Hypo and Hyperthyroidism alter the pituitary hormone synthesis/secretion, however, the interaction between thyroid hormones and circadian clock in pituitary is unknown. Objectives: The goal of this study was to characterize whether T3 modulates the circadian clock expression in anterior pituitary cells. Methods: Male rats were divided in euthyroid, hypothyroid and hyperthyroid and euthanized every 3h, across 24h; afterwards, the pituitaries were excised and total RNA was extracted and evaluated for gene expression. One and Two-way ANOVA and cosinor analysis were applied to evaluate the time-of-day-dependent differential expression for each gene/group and their interactions. In addition, the T3 transcriptional regulation of clock genes promoters was evaluated in GH3 cells transfected with mouse Bmal1 or Nr1d1 promoters by Luciferase assay. Results: The hyperthyroidism increased the expression of all core clock components and the mesors of Bmal1 and Nr1d1 were increased compared to euthyroid animals. In hypothyroid rats, the circadian pattern of Bmal1 and Per2 expression was lost, while the mesor of Nr1d1 was reduced. In silico analysis pointed out the putative existence of thyroid hormone responsive elements in promoter or regulatory regions of Bmal1 and Nr1d1 genes. The in vitro analysis showed that T3 rapidly increases the activity of both Bmal1 and Nr1d1 promoters. Conclusion: Our data indicate a role of T3 in the modulation of clock gene expression in pituitary cells, which could be related to the altered pituitary hormone secretion observed in hypo and hyperthyroid conditions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
