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Iron‐dependent Regulation of Cytoglobin in Neuro 2A Cells

Iron deficiency (ID) is estimated to affect one‐third of the world's population. As an essential micronutrient, iron is required for DNA synthesis, cellular proliferation, and oxygen transport. Iron is potentially toxic through its ability to promote the generation of ROS, thus cellular iron is tightly controlled. A family of iron‐regulated cytosolic RNA binding proteins known as iron regulatory proteins (IRP) play a central role in maintaining cellular iron homeostasis by repressing translation of ferritin and stabilizing transferrin receptor (Tfrc) mRNA under iron deficient conditions. Independent of iron status, reactive oxygen species (ROS) can also increase IRP1 RNA binding activity indicating the convergence of iron and O2 sensing through IRP. Hypoxia is associated with increased generation of ROS and oxidative stress. Like other members of the globin family of proteins, cytoglobin (Cygb) contains a heme prosthetic group that coordinates O2 binding. Cygb gene expression is rapidly induced with hypoxia and is postulated to play a role in O2 storage under these conditions. Cygb is ubiquitously expressed but appears to be enriched in neurons. The aim of the current study was to examine the iron‐ and O2‐dependent regulation of Cygb mRNA expression in Neuro 2A cells. Cells were treated with 100 μM desferrioxamine (DFO) or 1% hypoxia for 18 hours. Following treatments, total RNA was extracted and reverse‐transcribed. Quantitative real‐time PCR was used to examine mRNA expression of Cygb, Hif1α, and Tfrc. To confirm cytosolic iron depletion, IRP RNA binding activity was also determined. Following treatment, IRP1 binding increased ~2‐fold in response to DFO though with 1% hypoxia IRP1 binding decreased. DFO treatment increased Cygb and Tfrc expression by >2‐fold with no change in Hif1a expression. In contrast to iron chelation, hypoxia reduced Cygb expression by ~50% whereas the expression of Tfrc and Hif1a mRNA unchanged. These results demonstrate that iron and O2 status may regulate Cygb independently and suggests different mechanisms for the control of Cygb expression. Current studies are focused on examining the potential mechanisms of regulation of Cygb under iron‐depleted and/or hypoxic conditions and will provide additional insight into the coordination of iron and O2 signaling in cells.