Performing a hepatic timing signal: glucocorticoids induce gper1a and gper1b expression and repress gclock1a and gbmal1a in the liver of goldfish

Abstract

Glucocorticoids have been recently proposed as input signals of circadian system, although the underlying molecular mechanism remains unclear. This work investigates the role of glucocorticoids as modulators of clock genes expression in the liver of goldfish. In fish maintained under a 12L:12D photoperiod, an intraperitoneal injection at Zeitgeber Time 2 of a glucocorticoid analog, dexamethasone (1 μg/g body weight) induced per1 genes while decreased gbmal1a and gclock1a expression in the liver at 8 h post-injection. A 4-h in vitro exposure of goldfish liver to cortisol (0.1-10 μM) also induced gper1 genes in a concentration-dependent manner. Similarly, the exposure of the goldfish cultured liver to dexamethasone produced a concentration-dependent induction of gper1 genes. Moreover, this glucocorticoid analog led to a decrease in gbmal1a and gclock1a transcripts, while the other clock genes analyzed were unaffected. The induction of gper1a and gper1b by dexamethasone in vitro was observed at short times (2 h), whereas the reductions of gbmal1a and gclock1a transcripts needed longer exposure times (8 h) to the glucocorticoid to be significant. Additionally, a 2-h exposure to dexamethasone in the liver culture was enough to extend the induction of per genes for more than 12 h. Present results indicate that gper1 genes are targets for glucocorticoids in the regulation of goldfish hepatic oscillator, as previously reported in mammals, suggesting a conserved role of glucocorticoids in the functional organization of the peripheral circadian system in vertebrates. The repression of clock1a and bmal1a is not so well established, and suggests that other clock genes could be glucocorticoid targets in the goldfish liver.

Interplay between the endocrine and circadian systems in fishes

“…The finding that per genes in the hypothalamus and foregut are upregulated 3 h after an intracerebroventricular orexin injection indicates that this peptide may act as an input to these oscillators and regulate their daily functioning in goldfish (Nisembaum et al 2014a). Moreover, in situ hybridisation studies in this teleost have revealed that some of the brain regions that exhibit day/night differences in per1b expression (Sánchez-Bretaño et al 2015c) also possess orexin receptors (Facciolo et al 2012). In this sense, recent data in mammals have suggested that the REV-ERBs may be involved in the repression of orexinergic gene expression (Feillet et al 2015, Amador et al 2016.…”

“…The candidate function of melatonin as an input to the central circadian oscillator is supported by the observed coexpression of melatonin receptors with clock and per1b genes in some encephalic areas in rainbow trout (Mazurais et al 2000) and goldfish (Sánchez-Bretaño et al 2015c).…”

“…Recently, high day-night variations in per1b mRNA levels were observed in some diencephalic nuclei of goldfish (Carassius auratus), but no changes were observed in the telencephalon (Sánchez-Bretaño et al 2015c). Similarly, some brain structures of zebrafish lack some of the core clock genes, even if such areas are photosensitive (Moore & Whitmore 2014).…”

“…Such a master clock has not yet been clearly identified in fishes although the pineal gland plays a key role in its circadian system (Cahill 2002, Noche et al 2011, Idda et al 2012, Moore & Whitmore 2014, Sánchez-Bretaño et al 2015c. Furthermore, the peripheral and central oscillators in fishes appear to be in phase or even more advanced in the peripheral tissues (Cermakian et al 2000, Sánchez-Bretaño et al 2015c, suggesting that these pacemakers may be independently synchronised.…”

“…Such a master clock has not yet been clearly identified in fishes although the pineal gland plays a key role in its circadian system (Cahill 2002, Noche et al 2011, Idda et al 2012, Moore & Whitmore 2014, Sánchez-Bretaño et al 2015c. Furthermore, the peripheral and central oscillators in fishes appear to be in phase or even more advanced in the peripheral tissues (Cermakian et al 2000, Sánchez-Bretaño et al 2015c, suggesting that these pacemakers may be independently synchronised. In some fish species, the locomotor activity patterns are also flexible and dependent on food availability (goldfish; Aranda et al 2001, Feliciano et al 2011 or metamorphosis (Senegalese sole, Solea senegalensis; Blanco-Vives et al 2012).…”