Role of elongation factor 2 in regulating peptide-chain elongation in the heart

Cardiac muscles of experimentally induced diabetic rats show a progressive decrease in the rate of protein synthesis. The decline in protein synthesis is associated with decreases in both the number and efficiency of cardiac ribosomes. In hearts from 48 h diabetic rats, the decrease in protein synthesis was accounted for solely by a 28% reduction in the ribosome content. In contrast, the inhibition of protein synthesis in hearts from 72 h diabetic rats resulted from a reduction in both the ribosome content (28%) and the translational efficiency (30%). The decreased translational efficiency was not associated with an increase of RNA in ribosomal subunits, indicating the defect resulted from an inhibition of peptide-chain elongation/termination. Diabetes of 72 h duration resulted in a 37% inhibition in the rate of peptide-chain elongation. The decreased rate of peptide-chain elongation was associated with a 66% reduction in the amount of elongation factor 2 (EF-2). Treatment of diabetic rats with insulin for 3 days was sufficient to reverse the effects of 72 h diabetes on protein synthesis, RNA content, and translational efficiency. Also, insulin therapy increased the EF-2 content of diabetic rats to control values. These studies suggest that decreased EF-2 content is a molecular mechanism for the impaired rates of peptide-chain elongation in diabetes.