Retinoic acid receptors move in time with the clock in the hippocampus. Effect of a vitamin-A-deficient diet

Abstract

An endogenous time-keeping mechanism controls circadian biological rhythms in mammals. Previously, we showed that the vitamin A deficiency modifies clock BMAL1 and PER1 as well as BDNF and Neurogranin daily rhythmicity in the rat hippocampus, when animals are maintained under 12h-light:12h-dark conditions. Retinoic acid nuclear receptors, RARs and RXRs, have been detected in the same brain area. Our objectives were 1) to analyze whether RARα, RARβ and RXRβ exhibit a circadian variation in the rat hippocampus, 2) to investigate the effect of a vitamin A-deficient diet on the circadian expression of BMAL1, PER1 and retinoic acid receptors (RARs and RXRβ) genes. Holtzman male rats from control and vitamin A-deficient groups were maintained under 12h-light:12h-dark or 12h-dark:12h-dark during the last week of treatment. RARα, RARβ, RXRβ, BMAL1 and PER1 transcript and protein levels were determined in hippocampus samples isolated every 4h in a 24h period. Regulatory regions of RARs and RXRβ genes were scanned for clock-responsive sites while BMAL1 and PER1 promoters were analyzed for RAREs and RXREs. E-box and RORE sites were found on regulatory regions of retinoid receptors genes, which display an endogenously-controlled circadian expression in the rat hippocampus. Those temporal profiles were modified when animals were fed with a vitamin A-deficient diet. Similarly, the nutritional vitamin A deficiency phase shifted BMAL1 and abolished PER1 circadian expression at both, mRNA and protein levels. Our data suggests that the vitamin A deficiency may affect the circadian expression in the hippocampus by modifying the rhythmic profiles of retinoic acid receptors.

Daily rhythms of catalase and glutathione peroxidase expression and activity are endogenously driven in the hippocampus and are modified by a vitamin A-free diet

“…Instead, and consistently with our and others' work, changes in the circadian expression of RARs, observed in the hippocampus of animals fed a vitamin A-free diet, might lead to alterations in the circadian expression of BMAL1 and PER1 and, consequently, to changes in their target genes oscillation. Thus, and additionally to circadian rhythms of RARα, RARβ, and RXRβ previously reported 41 here, we also observed RXRγ expression displays a circadian profile in the rat hippocampus, peaking at the beginning of the subjective day (Figs. 4A-B and Table 3).…”

“…CREB1 transcript levels are maximal at the beginning of the subjective night period in the control rats, preceding BMAL1 and PER1 mRNA peaks (acrophases at CT 15:30 ± 01:15 and CT 17:55 ± 00:21, respectively) observed in our previous work. 41 In this study, we found two CRE sites on the BMAL1 regulatory intronic region and three CREs on the PER1 promoter. This would also support a role for CREB1 as transcriptional regulator of the clock as it was demonstrated by Lee.…”

“…The circadian expression of clock components, BMAL1 and PER1, as well as RA receptors, RARα, RARβ, and RXRβ, has been assessed in the same brain area, in the DD paradigm. 41 Interestingly, the bioinformatic analysis revealed us the presence of several clock-responsive, E-box, elements in the regulatory regions of CAT and GPx genes, suggesting they could be controlled by the endogenous clock. Indeed, and consequently with our previous work, 41 we found maximal CAT and GPx mRNA expression is in phase with the clock transcriptional activator BMAL1 protein (acrophase at CT 04:31 ± 01:12) and in antiphase with the clock repressor PER1 protein (acrophase at CT: 22:44 ± 00:40).…”

“…41 Interestingly, the bioinformatic analysis revealed us the presence of several clock-responsive, E-box, elements in the regulatory regions of CAT and GPx genes, suggesting they could be controlled by the endogenous clock. Indeed, and consequently with our previous work, 41 we found maximal CAT and GPx mRNA expression is in phase with the clock transcriptional activator BMAL1 protein (acrophase at CT 04:31 ± 01:12) and in antiphase with the clock repressor PER1 protein (acrophase at CT: 22:44 ± 00:40). The last finding is consistent with observations made by Hirayama et al, 42 who showed an oscillating pattern of CAT expression and activity, in antiphase with the expression of other components of the clock negative circuit, PER2 and Cry1, in Z3 zebrafish embryonic cell line.…”

Direct inhibition of retinoic acid catabolism by fluoxetine

“…On the other hand, RA has previously been shown to act as a ''Zeitgeber molecule'' in entraining endogenous biorhythms (Sherman et al 2012;Navigatore-Fonzo et al 2013), which are often found to be deregulated in depressed subjects (Bedrosian and Nelson 2013;Partonen 2012) and affected by fluoxetine treatment (Uz et al 2005;Sprouse et al 2006).…”