Increased Expression of Ryanodine Receptors and the Iron Transporter DMT1 in Hippocampal Neurons by Brain Derived Neurotrophic Factor (BDNF), NMDA or Spatial Memory Training

Abstract

Ryanodine receptors (RyR) mediate skeletal and cardiac muscle contraction and amplify via CICR postsynaptic calcium signals generated by activity-dependent calcium influx through NMDA receptors (NMDAR) in hippocampal glutamatergic synapses. We have recently shown that reactive oxygen species (ROS) and iron, which as shown here promotes ROS generation in neurons, stimulate RyR-mediated calcium release when added to primary hippocampal neurons. Here, we report that 5 min incubation of hippocampal cells in primary culture with NMDA (50 μM), induced RyR-mediated calcium signals that were inhibited by pre-incubation with the iron chelator desferroxamine. Incubation with NMDA also enhanced >2-fold the expression (measured 24 h later) of the iron transporter DMT1 (IRE form), while incubation with BDNF (50 ng/ml) increased >5-fold RyR expression. Additionally, we investigated if spatial memory training of male rats in a Morris water maze affected RyR and DMT1 expression. The hippocampus was dissected 6 h after the last behavioral task (5d, 2d rest, 1d platform free) and samples from tissue were prepared for Western blot and RT-PCR experiments. We found that spatial memory training increased the mRNA and protein expression of DMT1, RyR2 and RyR3. Our results confirm enhanced RyR2 expression following spatial memory training and correlate for the first time enhanced in vivo expression of the iron transporter DMT1 and RyR3 with spatial memory acquisition/consolidation. We propose that iron-induced ROS production stimulates the emergence of RyR-mediated intracellular calcium signals that promote RyR and DMT1 expression during the spatial memory task.FONDECYT (PostDoc) 3070035, CEMC-FONDAP 15010006, Millennium P05-001F, FONDECYT 1060177.