Interrelationship between 3,5,3´-triiodothyronine and the circadian clock in the rodent heart

Abstract

Triiodothyronine (T3) is an important modulator of cardiac metabolism and function, often through modulation of gene expression. The cardiomyocyte circadian clock is a transcriptionally-based molecular mechanism capable of regulating cardiac processes, in part by modulating responsiveness of the heart to extra-cardiac stimuli/stresses in a time-of-day- (TOD) dependent manner. Although TOD-dependent oscillations in circulating levels of T3 (and its intermediates) have been established, whether oscillations in T3 sensitivity in the heart occur is unknown. To investigate the latter possibility, euthyroid male Wistar rats were treated with vehicle or T3 at distinct times of the day, after which induction of known T3 target genes were assessed in the heart (4-h later). The expression of mRNA was assessed by Real-Time qPCR. Here, we report greater T3 induction of transcript levels at the end of the dark phase. Surprisingly, use of cardiomyocyte-specific clock mutant (CCM) mice revealed that TOD-dependent oscillations in T3 sensitivity were independent of this cell autonomous mechanism. Investigation of genes encoding for proteins that affect T3 sensitivity revealed that Dio1, Dio2, and Thrb1 exhibited TOD-dependent variations in the heart, while Thra1 and Thra2 did not. Of these, Dio1 and Thrb1 were increased in the heart at the end of the dark phase. Interestingly, we observed that T3 acutely altered the expression of core clock components (e.g., Bmal1) in the rat heart. To investigate this further, rats were injected with a single dose of T3, after which expression of clock genes were interrogated at 3-h intervals over the subsequent 24h-period. These studies revealed robust effects of T3 on oscillations of both core clock components and clock-controlled genes. In summary, the current study exposed time-of-day-dependent rhythms in cardiac T3 sensitivity, and that T3 alters the circadian clock in the heart.

Repercussions of hypo and hyperthyroidism on the heart circadian clock

“…In the earlier study, a suggestion of direct T3 action on Rora and/or Per2 was raised due to rapid alterations in these genes(Peliciari-Garcia, Previde et al, 2016). T3 exerts its transcriptional actions through interaction with THR, a ligand-regulated transcription factor, which binds to the thyroid-hormone response element (TRE) present in target genes, mainly as a heterodimer with other nuclear receptors (e.g., retinoid X receptor; RXR).…”

“…Candidate gene expression analysis was performed by quantitative RT-PCR, using SYBR GREEN (Invitrogen) as the fluorescent dye, and the 2(-Delta CT) method(Livak & Schmittgen, 2001); the Ct value is the calculated cycle number where the fluorescence signal was emitted significantly above background levels. The primers for Adrb1 , Acot1, Cd36 and Myh7 were designed from rat sequences available in GenBank (Table 1); other primer sequences have been published elsewhere(Young, Razeghi et al, 2001a; Young, Razeghi et al, 2001b; Peliciari-Garcia, Zanquetta et al, 2011; Bargi-Souza, Romano et al, 2013; Peliciari-Garcia, Previde et al, 2016). Efficiency curves were also performed for all investigated candidate genes; the efficiency/slope values obtained were close to the optimal values required for the 2(-Delta CT) analysis(Dussault & Pouliot, 2006).…”

“…Recently, our group has demonstrated that the heart shows a greater transcriptional sensitivity to T3 at the end of the dark phase, with significant alterations of mRNA expression of core clock components; showing therefore, a time-of-day-dependent sensitivity to T3 and modulation of the heart circadian clock(Peliciari-Garcia, Previde et al, 2016). …”

The Circadian Clock Gene Bmal1 Controls Thyroid Hormone-Mediated Spectral Identity and Cone Photoreceptor Function

“…T3 generated by DIO2 contributes to the nuclear pool of T3 and serves as ligand for the thyroid hormone receptors such as TRβ2 (Wu and Koenig, 2000). A number of studies have documented circadian and seasonal dependent oscillations in circulating levels of T3 and intracellular levels of Dio2 and Dio3 (Barrett et al, 2007; Bedolla and Torre, 2011; Ono et al, 2008; Peliciari-Garcia et al, 2016; Watanabe et al, 2007). These observations raise the possibility that T3 availability within the tissues could be under a circadian regulation, however molecular mechanisms underlying this regulation are unknown.…”

Circadian Control of Cardiac Metabolism: Physiologic Roles and Pathologic Implications

“…4,5 In addition, candidate signaling approaches suggest daily oscillations in the heart's sensitivity to extracellular stimuli such as fatty acids, β-adrenergic agonist, and thyroid hormone. [6][7][8][9] The focus of this review is on circadian control of cardiac metabolism, including the mechanisms involved in synchronizing metabolic rhythms, their role in maintaining cardiac function, and the pathological consequences of their disruption/impairment.…”