CIRCADIAN PATTERNS OF RORa AND REV-ERB EXPRESSION ARE MODIFIED IN THE HIPPOCAMPUS OF VITAMIN A-DEFICIENT RATS

GOLINI RS; NAVIGATORE FONZO LS; RANDAZZO G; DELGADO SM; ANZULOVICH AC

Congreso; XXXII Reunión Anual de la Soc. de Biología de Cuyo; 2014

In mammals, the circadian clock mechanism involves two interlocking transcriptional-translational feedback loops. BMAL1/CLOCK heterodimer activates the expression of clock and clock-controlled genes while the PER-CRY complex represses it. The REV-ERB/ROR orphan nuclear receptors regulate the Bmal1 circadian expression contributing to the robustness of the clock mechanism. Some evidence points out retinoids as regulators of clock genes activity through retinoid receptors (RARs and RXRs). Previously, we have demonstrated vitamin A deficiency modifies daily rhythms of clock genes expression in the hippocampus, under 12h-light:12h-dark conditions; however, to date, no study on clock endogenous (free running) circadian rhythms in that cerebral area has been found. Thus, our objectives were: first, to investigate whether RORa and REV-ERB also displays a circadian expression pattern in the rat hippocampus and second, to evaluate the effect of a vitamin A-depleted diet on those temporal patterns. Twenty one-day old Holtzman rats received a diet containing 4000 IU of vitamin A/Kg diet (Control group), or the same diet devoided of vitamin A (Vitamin A-deficient, VAD, group), during 3 months. In order to study endogenous circadian rhythms, rats were maintained under constant darkness conditions along 10 days before the experiment. RORa and REV-ERB mRNA levels were determined by RT-PCR and RARα, RXRß and BMAL1 proteins by immunoblotting, in hippocampus samples isolated every 4 h during a 24h period. Regulatory regions of RORa and REV-ERB genes were scanned for clock- and retinoic acid-responsive sites. E-box, RXRE, RARE and RORE sites were found. RORa and REV-ERB expression displays an endogenously-generated circadian rhythm in the rat hippocampus, which was modified in the VAD group; probably, as a consequence of alterations in the circadian patterns of BMAL1 and/or retinoic acid receptors proteins.