Temporal patterns of lipoperoxidation and antioxidant enzymes are modified in the hippocampus of vitamin A‐deficient rats

Abstract

Animals can adapt their behavior to predictable temporal fluctuations in the environment through both, memory-and-learning processes and an endogenous time-keeping mechanism. Hippocampus plays a key role in memory and learning and is especially susceptible to oxidative stress. In compensation, antioxidant enzymes activity, such as Catalase (CAT) and Glutathione peroxidase (GPx), has been detected in this brain region. Daily rhythms of antioxidant enzymes activitiy, as well as of glutathione and lipid peroxides levels, have been described in brain. Here, we investigate day/night variations in lipoperoxidation, CAT and GPx expression and activity, as well as the temporal fluctuations of two key components of the endogenous clock, BMAL1 and PER1, in the rat hippocampus and evaluate to which extent vitamin A deficiency may affect their amplitude or phase. Holtzman male rats from control, vitamin A-deficient and vitamin A-refed groups were sacrificed throughout a 24-h period. Daily levels of clock proteins, lipoperoxidation, CAT and GPx mRNA, protein, and activity, were determined in the rat hippocampus obtained every 4 or 5 h. Gene expression of RARα and RXRβ was also quantified in the hippocampus of the three groups of rats. Our results show significant daily variations of BMAL1 and PER1 protein expression. Rhythmic lipoperoxidation, CAT, and GPx, expression and activity, were also observed in the rat hippocampus. Vitamin A deficiency reduced RXRβ mRNA level, as well as the amplitude of BMAL1 and PER1 daily oscillation, phase-shifted the daily peak of lipoperoxidation, and had a differential effect on the oscillating CAT and GPx mRNA, protein, and activity. Learning how vitamin A deficiency affects the circadian gene expression in the hippocampus may have an impact on the neurobiology, nutritional and chronobiology fields, emphasizing for the first time the importance of nutritional factors, such as dietary micronutrients, in the regulation of circadian parameters in this brain memory-and-learning-related region.

Circadian Synchronization of Cognitive Functions

“…Maximal RC3 expression occurs at the end of the night preceding BDNF mRNA peak, as in the cellular events which occurs for postsynaptic activation [ 38 ]. As expected, BDNF and RC3 rhythms are in phase with the circadian clock, BMAL1 and Per1, protein levels as well as with the maximal antioxidant enzyme activity shown by Fonzo and colleagues [ 39 ]. In turn, the nocturnal peaks of catalase (CAT) and glutathione peroxidase (GPx) activity seen in the rat hippocampus would be in phase with the best time for performing learning and memory tests, as shown in young rats by Winocur and Hasher [ 27 , 39 ].…”

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

“…Even though, previously, some studies show 24 hours variations in the antioxidant enzymes expression and activity in the mammals' brain, 21,22,39 all of them were done in animals maintained under light:dark (LD) conditions; thereafter, none of them was able to report circadian, endogenously driven, rhythms in the hippocampus. Particularly, previous studies from our and Sewerynek's labs demonstrated that, under LD conditions, levels of CAT and GPx expression and activity vary throughout a 24-hour period in the rat and chicken hippocampus, respectively.…”

“…Particularly, previous studies from our and Sewerynek's labs demonstrated that, under LD conditions, levels of CAT and GPx expression and activity vary throughout a 24-hour period in the rat and chicken hippocampus, respectively. 20,22 Such observations led us to question whether those daily oscillations were generated endogenously, in that memory-and-learning-related area. Thus, we continued analysing CAT and GPx mRNA levels and activity in the hippocampus of animals maintained under constant darkness (DD) conditions.…”

“…22 We wondered whether these expression patterns could be synchronized endogenously. For that, hippocampus samples were obtained every 4 hours during a 24-hour period from control rats maintained under constant darkness (DD)…”

“…18 A role for CREB as transcriptional regulator of antioxidant superoxide dismutase gene expression has been described by Bedogni et al 19 Daily rhythms of CAT, superoxide dismutase, GPx, and glutathione reductase expression and activity have been demonstrated by us, and others, in different brain areas of animals maintained under a conditioned light:dark schedule. [20][21][22] These variations in the day/ night activity of the antioxidant defense system suggest that genes that encode them could be under the endogenous control of the biological clock.…”