The ageing heart: influence of cellular and tissue ageing on total content and distribution of the variants of elongation factor-2

The involvement of elongation factor-2 (EEF-2), a key-protein of peptide-chain elongation, in the slowing down of protein synthesis during cardiac ageing was addressed. EEF-2 was measured in rat heart extracts and isolated rat cardiomyocytes (CM) from newborn and adult rats using sodium-dodecylsulphate polyacrylamide gel electrophoresis after specific labeling with [32P]ADP-ribosylation or immunoblot. The age-dependent proportional content of several eucaryotic elongation factor-2 (eEF-2) subtypes in rat CM and rat heart extracts was compared using one-dimensional isoelectric focusing. EEF-2 was considerably reduced in the hearts of adult compared to neonatal rats (P<0.01). EEF-2 was also significantly decreased in isolated CM from adult versus newborn rats and during prolonged cultivation of neonatal CM. Cellular ageing was combined with reduced protein synthesis. During adolescence the eEF-2 variants shifted to acidic subtypes. Young adult and old rats revealed similar amounts and subtype distribution of cardiac eEF-2. Only the more acidic eEF-2 variants appeared to contain phosphorylated eEF-2. We concluded that total cardiac eEF-2 and its subtype pattern might play an important role in developmental and age-related proteomic changes.