Hypothyroidism alters the rhythmicity of the central clock, body temperature and metabolism: evidence of Bmal1 transcriptional regulation by T3

• Published in: The Journal of physiology Vol. 602; no. 19; pp. 4865 - 4887
• Main Authors: Emrich, Felipe, Gomes, Bruno Henrique, Selvatici‐Tolentino, Letícia, Lopes, Roberta Araújo, Secio‐Silva, Ayla, Carvalho‐Moreira, João Pedro, Bittencourt‐Silva, Paloma Graziele, Guarnieri, Leonardo de Oliveira, Silva, Ana Bárbara de Paula, Drummond, Lucas Rios, da Silva, Glauber Santos Ferreira, Szawka, Raphael Escorsim, Moraes, Márcio Flávio Dutra, Coimbra, Cândido Celso, Peliciari‐Garcia, Rodrigo Antonio, Bargi‐Souza, Paula
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.10.2024
• Subjects: Activity patterns; Animals; ARNTL Transcription Factors - genetics; ARNTL Transcription Factors - metabolism; BMAL1 protein; Body temperature; Body Temperature - physiology; Circadian Clocks - genetics; Circadian Clocks - physiology; Circadian rhythm; Circadian Rhythm - physiology; Circadian rhythms; Clock gene; clock genes; Gene expression; Gene Expression Regulation; Gene regulation; Hypothalamus (anterior); Hypothyroidism; Hypothyroidism - genetics; Hypothyroidism - metabolism; Hypothyroidism - physiopathology; Innervation; Locomotor activity; Male; Metabolic syndrome; Metabolism; Mice; Mice, Inbred C57BL; Oxygen consumption; Pituitary (anterior); Preoptic area; Preoptic area (medial); Respiratory quotient; Suprachiasmatic nucleus; Suprachiasmatic Nucleus - metabolism; Suprachiasmatic Nucleus - physiology; thermoregulation; Thyroid diseases; Thyroid gland; Thyroid hormones; Triiodothyronine; clock genes; hypothyroidism; thyroid hormones; locomotor activity; metabolism; suprachiasmatic nucleus; thermoregulation
• ISSN: 0022-3751; 1469-7793; 1469-7793
• DOI: 10.1113/JP286449

In mammals, the central circadian oscillator is located in the suprachiasmatic nucleus (SCN). Hypothalamus–pituitary–thyroid axis components exhibit circadian oscillation, regulated by both central clock innervation and intrinsic circadian clocks in the anterior pituitary and thyroid glands. Thyroid disorders alter the rhythmicity of peripheral clocks in a tissue‐dependent response; however, whether these effects are influenced by alterations in the master clock remains unknown. This study aimed to characterize the effects of hypothyroidism on the rhythmicity of SCN, body temperature (BT) and metabolism, and the possible mechanisms involved in this signalling. C57BL/6J adult male mice were divided into Control and Hypothyroid groups. Profiles of spontaneous locomotor activity (SLA), BT, oxygen consumption (V̇O2${{\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}}$) and respiratory quotient (RQ) were determined under free‐running conditions. Clock gene expression, and neuronal activity of the SCN and medial preoptic nucleus (MPOM) area were investigated in light–dark (LD) conditions. Triiodothyronine (T3) transcriptional regulation of Bmal1 promoter activity was evaluated in GH3‐transfected cells. Hypothyroidism delayed the rhythmicity of SLA and BT, and altered the expression of core clock components in the SCN. The activity of SCN neurons and their outputs were also affected, as evidenced by the loss of circadian rhythmicity in V̇O2${{\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}}$ and RQ and alterations in the neuronal activity pattern of MPOM. In GH3 cells, T3 increased Bmal1 promoter activity in a time‐dependent manner. Thyroid hormone may act as a temporal cue for the central circadian clock, and the uncoupling of central and peripheral clocks might contribute to a wide range of metabolic and thermoregulatory impairments observed in hypothyroidism. Key points Hypothyroidism alters clock gene expression in the suprachiasmatic nucleus (SCN). Thyroid hypofunction alters the phase of spontaneous locomotor activity and body temperature rhythms. Thyroid hormone deficiency alters the daily pattern of SCN and medial preoptic nucleus neuronal activities. Hypothyroidism alterations are extended to daily oscillations of oxygen consumption and metabolism, which might contribute to the development of metabolic syndrome. Triiodothyronine increases Bmal1 promoter activity acting as temporal cue for the central circadian clock. figure legend This study aimed to characterize the effects of hypothyroidism in central clock rhythmicity, daily regulation of body temperature and metabolism, and the mechanisms triggered by triiodothyronine (T3) to modulate the circadian clock machinery. C57BL/6J adult male mice were divided into Control and Hypothyroid groups. The daily profiles of spontaneous locomotor activity (SLA), body temperature (BT), oxygen consumption (V̇O2${{\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}}$) and respiratory quotient (RQ) were evaluated under light–dark (LD) and constant dark (DD) conditions. Then, the animals were killed every 4 h over 24 h under deep anaesthesia and the tissues were freshly collected. Gene expression analysis of the suprachiasmatic nucleus (SCN) and the pituitary gland was performed by RT‐qPCR. Some of the animals were perfused with 4% PFA, and the fixed brains were used to evaluate neuronal activity of SCN and the medial preoptic nucleus (MPOM) by immunohistochemistry of c‐Fos. Hypothyroidism delayed the rhythmicity of SLA and BT and disrupted the expression of core clock components in the SCN. The activity of SCN and its outputs were affected, as evidenced by the loss of circadian rhythmicity in V̇O2${{\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}}$ and RQ, and alterations in MPOM neuronal activity. In silico analysis of regulatory and promoter regions of Bmal1 pointed to putative thyroid hormone response element (TRE). GH3 cells were transfected with the pBmal1:luc promoter and treated with triiodothyronine (T3). T3 increased Bmal1 promoter activity in a time‐dependent manner. In summary, our findings reveal a novel role of thyroid hormones contributing to the fine‐tuned synchronization of the central circadian clock machinery.