Hepatic translation of apolipoprotein A-I mRNA is apparently enhanced in copper-deficient rats

Abstract

Male weanling Sprague-Dawley rats were assigned to Cu-deficient (0.6 mg Cu/kg diet) and Cu-adequate (6.0 mg Cu/kg diet) dietary treatments for 6 weeks. Liver post-mitochondrial cytoplasmic extracts were partitioned by centrifugation into polysomes, monosomes, and ribosomal subunits along a linear sucrose gradient. This gradient was further fractionated. The apolipoprotein (apo) A-I mRNA abundance among individual fractions and in the unfractionated cytoplasmic extract were determined by dot blot analysis. The abundance of cytoplasmic apo A-I mRNA was not different between treatments. However, Cu deficiency significantly shifted a portion of cytoplasmic apo A-I mRNA to the more active and larger size polysome fractions. During translation, an increase in the percentage of larger polysomes is indicative of an accelerated rate of initiation. The present data suggest that an enhanced hepatic apo A-I translation efficiency may have contributed to the observed increases in hepatic apo A-I synthesis and plasma apo A-I level in Cu-deficient rats found in previous studies.