H and L ferritin subunit mRNA expression differs in brains of control and iron-deficient rats

The mRNA expression of ferritin subunits has not been studied thoroughly in the brain regions of iron-deficient rats. Sprague-Dawley rats (n = 26; 21 d old) were randomly assigned to an iron-deficient (3.5 mg Fe/kg diet) or a control diet (35 mg Fe/kg diet) for 6 wk. Ferritin protein and mRNA contents were quantified and the cellular expression of ferritin subunits in brain was determined. H and L ferritin had the same mRNA locations in nearly all brain regions. Both ferritin subunit mRNAs had heterogeneous distributions and there was a regional effect across brain regions. Iron deficiency did not affect the amount of ferritin mRNA in most brain regions, suggesting the post-transcriptional regulation of messengers by iron status. H ferritin protein was predominant in neurons and oligodendrocytes, whereas L ferritin protein and iron predominated in microglia cells and astrocytes as well as in oligodendrocytes and neurons. Ferritin mRNA was detectable only in neurons. Iron deficiency did not induce new types of cells containing either ferritin protein or mRNA. The fact that ferritin protein was found in four types of cells whereas mRNA was found in only one type of cell suggests that the site of ferritin synthesis is different from protein location in the brain. All of these data suggest that regulation of ferritin subunits is cellular and/or regional specific.