Cardiac Nuclear Encoded Cytochrome c Oxidase Subunits Are Decreased With Copper Restriction But Not Iron Restriction: Gene Expression, Protein Synthesis and Heat Shock Protein Aspects

Abstract

Hearts from rats fed a copper-deficient (Cu−) diet have decreased levels of nuclear-encoded peptides of cytochrome c oxidase (CCO). Studies were conducted to determine whether iron deficiency would lead to a similar finding, whether mRNA transcripts and the chaperonin heat shock proteins (HSP) 60 and 70 from hearts of Cu− rats were decreased as compared with copper-adequate controls and whether synthesis of mitochondrial and nuclear encoded peptides differed as affected by diet copper. In study 1, weanling rats were assigned to one of three groups ( n = 6 in each group): (1) control copper and iron adequate fed rats; (2) Cu− rats and (3) iron-deficient (Fe−) rats. Western blotting of nonmyofibrillar cardiac proteins revealed that the nuclear encoded peptides of CCO from the Cu− rats were markedly decreased as compared with control and Fe− rats. Mitochondrial encoded subunits did not appear to differ by treatment groups. Iron-deficient rats had similar nuclear encoded peptide levels as those of controls. In study 2, mRNA transcripts from Cu− ( n = 4) and control copper adequate ( n = 4) rats did not appear to differ for subunits II and IV, which correspond to mitochondrial and nuclear encoded subunits, respectively. In study 3, levels of HSP 60 and 70 from hearts of Cu− rats ( n = 3) did not differ from Cu+ rats ( n = 3). In study 4, infusion of 3H-(4,5)-leucine into the hearts of Cu+ and Cu− rats suggested there was no difference in synthesis of the nuclear encoded peptides by copper status and some indication there was enhanced breakdown of the nuclear encoded peptides among the Cu− rats. As expected, more isotope was incorporated into the mitochondria of Cu− rats than Cu+ rats. These results demonstrate an independent effect of copper upon the apparent decrease in the nuclear encoded subunits of CCO, the effect of copper upon the CCO subunits is probably post-transcriptional and that translocation of the nuclear encoded subunits from the ribosomes to the mitochondria via the chaperonin proteins is not a primary defect in explaining these observations in hearts from Cu− rats and synthesis of the nuclear encoded subunits of CCO in not impaired in copper deficiency.