Changes in 20S proteasome activity during ageing of the LOU rat

Muscular functions decline and muscle mass decreases during ageing. In the rat, there is a 27% decrease in muscle protein between 18 and 34 months of age. We examined age-related changes in the proteasome-dependent proteolyti c pathway in rats at 4, 18, 24, 29 and 34 months of age. The three best cha racterised activities of the proteasome (chymotrypsin-like, trypsin-like an d peptidylglutamyl peptide hydrolase) increased to 29 months and then decre ased in the senescent animal. These variations in activity were accompanied by an identical change in the quantity of 20S proteasome measured by Weste rn blot, whereas the S4 subunit of the 19S regulator and the quantity of ub iquitin-linked proteins remained constant. mRNA of subunits C3, C5, C9, and S4 increased in the senescent animal, but ubiquitin mRNA levels were uncha nged. These findings suggest that the 20S proteasome may be partly responsi ble for the muscular atrophy observed during ageing in the rat.