Dietary Iron Intake Modulates the Activity of Iron Regulatory Proteins and the Abundance of Ferritin and Mitochondrial Aconitase in Rat Liver , ,

Abstract

Iron regulatory protein 1 (IRP1) and IRP2 are cytoplasmic RNA binding proteins that coordinate cellular iron homeostasis in mammals. We investigated the effect of dietary iron intake on rat liver IRP activity in relation to the abundance of two targets of IRP action, ferritin and mitochondrial aconitase (m-aconitase). Rats were fed diets containing 2, 11, 20, 37 (control), 72 or 107 mg iron/kg diet for 3 wk. RNA binding activity of IRP1 and IRP2 was enhanced one- to twofold in rats fed 11 or 2 mg iron/kg diet compared with control rats. IRP RNA binding activity was inversely correlated to blood hemoglobin levels (r = -0.787; P < 0.0001). Compared with control rats, liver ferritin levels were depressed in rats fed 20 mg iron/kg diet and were undetectable in rats ingesting diets with 11 or 2 mg iron/kg diet. Ferritin concentrations were biphasically related to IRP RNA binding activity with the regulation of IRP occurring before the onset of ferritin accumulation. Iron deficiency caused up to a 50% decline in m-aconitase abundance. IRP RNA binding activity and m-aconitase abundance were inversely correlated (r = -0.751; P < 0.0001). Our results indicate that (1) liver IRP activity is responsive to a range of dietary iron levels, (2) there appears to be a differential effect of IRPs on ferritin and m-aconitase abundance, and (3) activation of IRPs may contribute to the alterations in energy metabolism in iron deficiency through an impairment of m-aconitase synthesis.

Inhibition of Fe-S cluster biosynthesis decreases mitochondrial iron export: Evidence that Yfh1p affects Fe-S cluster synthesis

“…Aconitase activity was measured as described (17). Malate dehydrogenase was measured in isolated mitochondria as described (18), as was succinate dehydrogenase (19).…”

Iron deficiency and iron excess damage mitochondria and mitochondrial DNA in rats

“…First, dietary iron deficiency causes an increase in liver IRP1 activity, which increases transferring receptor synthesis and decreases mitochondrial-aconitase activity (55). The decrease in mitochondrial-aconitase may prevent further mitochondrial release of oxidants by diminishing the supply of reducing equivalents to the electron-transport chain (55).…”

“…The decrease in mitochondrial-aconitase may prevent further mitochondrial release of oxidants by diminishing the supply of reducing equivalents to the electron-transport chain (55). The reduced electron flow may be one way by which the cell protects itself from oxidant stress in iron deficiency (55). How- ever, after 3 weeks of iron deficiency, IRP1 activity is increased, and there is a marked decrease in ferritin synthesis (55), thus decreasing its potential as an antioxidant protein.…”

“…The reduced electron flow may be one way by which the cell protects itself from oxidant stress in iron deficiency (55). How- ever, after 3 weeks of iron deficiency, IRP1 activity is increased, and there is a marked decrease in ferritin synthesis (55), thus decreasing its potential as an antioxidant protein. Up-regulation of transferrin receptor (TFR) first maintains or increases cytosolic iron availability in the face of the initial iron deficiency.…”

Deregulation of iron homeostasis and cold-preservation injury to rat liver stored in University of Wisconsin solution

“…Briefly, an RNA probe was generated by in vitro transcription of a pTZ19-IRE/EcoRI template (containing a human iron-response element [IRE] sequence). The probe subsequently was purified by extraction and labeled with Psoralen-Biotin (BrightStar Psoralen-Biotin nonisotopic labeling kit; #5330-5442, Ambion Inc, Austin, TX), and incubated with liver S100 cytosol fraction (prepared as decribed by Chen et al 22 ). Aliquots were run on a 2% Trevigel 500 (Trevigen Inc, Gaithersburg, MD) gel, and the RNAprotein complex was semiblotted to a positive membrane (Brightstar Plus; Ambion Inc, Austin TX).…”