Circadian expression of clock proteins and brain-derived neurotrophic factor is modified in the hippocampus of vitamin A deficient rats

NAVIGATORE FONZO LS; GOLINI RS; PONCE IT; DELGADO SM; GIMÉNEZ MS; ANZULOVICH AC

Washington, DC (USA)

Congreso; Neuroscience 2008; 2008

Society for Neuroscience

A role for vitamin A has been established in phenomena related to higher cognitive function in the adult mouse and rat brain. On the other hand, some evidence points out retinoids as regulators of clock genes activity through retinoid nuclear receptors (RARs and RXRs). RARá and RXRâ nuclear receptors have been detected in the hippocampus of rat. The brain-derived neurotrophic factor (BDNF), a molecular marker of synaptic plasticity related to learning and memory, contains fourteen clock responsive, E-box, sites in its gene promoter region. The objectives of this study were to investigate whether BDNF display a circadian expression pattern in the rat hippocampus, and evaluate to which extent vitamin A deficiency could modify the rhythmic expression (mRNA and protein) of Bmal1, Per1 and BDNF. Holtzman rats were weaned at 21 days of age and immediately assigned randomly to either the experimental diet, devoid of vitamin A (vitamin A-deficient group or the same diet with 4000 IU of vitamin A per Kg of diet (control group) during 3 months. Hippocampus samples were taken every 5 hours from control and vitamin A-deficient rats. Total RNA was extracted using the Trizol reagent and following manufacturer’s instructions. Transcript levels of Bmal1, Per1 and BDNF were determined by RT-PCR and normalized to â-actin as endogenous control. Relative quantification by Real-time PCR was performed to measure the mRNA levels of RARá and RXRâ using SYBR Green I dye. Protein levels were determined by immunoblotting and normalized to actin levels. We found mRNA levels of BDNF display a daily rhythmicity in the hippocampus of control rats. RXRâ mRNA levels were significantly lower in the vitamin A-deficient rats compared to controls. Daily rhythms of mRNA and protein expression of Bmal1, Per1 and BDNF were phase shifted in the vitamin A-deficient group. Thus, vitamin A deficiency modifies the circadian expression of clock (BMAL1 and PER1) and putative clock-controlled genes (BDNF) probably by reducing the availability of retinoid nuclear receptors such as RXRâ. Above observations raise the possibility that nutritional factors might be essential to maintain the circadian expression of clock (Bmal1 and Per1) and clock-controlled, learning-related (BDNF) genes in the hippocampus.