Interconnection between circadian clocks and thyroid function

Abstract

Circadian rhythmicity is an approximately 24h cell-autonomous period driven by transcriptiontranslation feedback loops of specific genes, which are referred to as 'circadian clock genes'. In mammals, the central circadian pacemaker, which is located in the hypothalamic suprachiasmatic nucleus, controls peripheral circadian clocks. The circadian system regulates virtually all physiological processes, which are further modulated by changes in external environment, such as light exposure and timing of food intake. Chronic circadian disruption caused by shift work, travel across time zones or irregular sleep-wake cycles has long-term consequences on our health and is an important lifestyle factor that contributes to the risk of obesity, type 2 diabetes mellitus and cancer. Although the hypothalamic-pituitary-thyroid axis is under the control of the circadian clock via the suprachiasmatic nucleus pacemaker, daily TSH secretion profiles are disrupted in some patients with hypothyroidism and hyperthyroidism. Disruption of circadian rhythms has been recognized as a perturbation of the endocrine system and of cell cycle progression. Expression profiles of circadian clock genes are abnormal in well-differentiated thyroid cancer but not in the benign nodules or a healthy thyroid. Therefore, the characterization of the thyroid clock machinery might improve the preoperative diagnosis of thyroid cancer.

The Impact of Shift-Work and Night Shift-Work on Thyroid: A Systematic Review

“…Sleep has been demonstrated to exert an inhibitory influence on TSH production, as confirmed by the increase in hormonal secretion caused by sleep withdrawal [5]. In fact, TSH secretion, which is normally inhibited during sleep, continues to occur during nocturnal sleep deprivation determining higher morning plasma levels of the hormone compared to those found in subjects with a normal night sleep [1].…”

“…The thyroid gland produces hormones, triiodothyronine (T3) and thyroxine (T4), that are essential for body's metabolism, heat production, suitable development and differentiation of cells, and growth [1]. The hypothalamic-pituitary-thyroid (HPT) axis controls the thyroid function, as the T3 and T4 hormones are secreted in response to the pituitary thyroid stimulating hormone (TSH) [2].…”

PER2 inhibits proliferation and stemness of glioma stem cells via the Wnt/β‑catenin signaling pathway

“…Endogenous circadian rhythms are maintained by two feedback loops. Clock circadian regulator (CLOCK) and brain and muscle Arnt-like protein-1 (BMAL1) form heterodimers to rhythmically activate the expression of transcriptional repressor proteins, such as period 1/2/3 and cryptochrome 1/2, which form a complex to inhibit CLOCK and BMAL1 transcriptional activity (9)(10)(11). In some types of cancer and model systems, period circadian clock 2 (PER2) serves as a tumor suppressor gene.…”

Thyroid Cancer and Circadian Clock Disruption

“…Recently a relationship between the circadian clock machinery function and TC has been proposed [ 5 , 6 , 7 , 8 , 9 , 10 ]. During evolution, organisms have developed biological clocks to better adapt to various rhythmic events such as daily and seasonal fluctuations.…”