Worm Breeder's Gazette 9(3): 120

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Age-Dependent Decline in Protease Activities in C. elegans

G.J. Sarkis, J.M. Hawdon and L.A. Jacobson

The accumulation of altered or damaged enzymes in aging organisms, 
first observed in Turbatrix aceti by Gershon & Gershon, has also been 
found to occur in mammals. It has been suggested that this 
accumulation may result from an age-dependent decline in the ability 
of cells to degrade these abnormal proteins. Sharma et al. [1979] and 
Prasanna & Lane [1979] reported an age-dependent decline in turnover 
rates in T. aceti, both for specific enzymes and for global protein. 
The measurement of protein turnover is fraught with technical 
difficulties and we know very little about the enzymatic mechanisms 
involved. One simple hypothesis to explain declining rates of turnover 
in older animals is that the amount of cellular protease activity also 
declines with age, leading to a decreased capacity for intracellular 
proteolysis. We have found that the activities of several lysosomal 
proteases decline markedly in aging C. vity 
of the major aspartyl protease cathepsin D declines about 10-fold from 
its peak at 4 days of age (growth at 25 C; mean lifespan about 12 days)
to a minimum at about 10-11 days. Both the total activity per animal 
and the specific activity (per unit protein) decline. Immunoblot 
analysis using anti-cathepsin D antibody shows that this activity loss 
is accompanied by a parallel loss of cathepsin D measured as antigen. 
Using enzymatic assays after isoelectric focusing of crude extracts, 
we have also measured the age-dependence of the thiol cathepsins Ce1 
and Ce2 (see Sarkis et al ., this issue) which hydrolyze Z-phe-arg-
aminomethylcoumarin. From day 3 to day 11, the specific activity of 
cathepsin Ce2 declines about 8-fold, whereas that of cathepsin Ce1 
declines about 2.5-fold. These experiments also revealed a previously 
undetected enzyme which hydrolyzes the same substrate, but has a 
different isoelectric point from those of Ce1 and Ce2. On the basis of 
IEF analysis of purified lysosomes, this new enzyme is nonlysosomal. 
Its specific activity is essentially independent of the age of the 
animals. The age-dependent decrease in lysosomal protease activities 
is quite different from the strong (as much as 100-fold) increase in 
lysosomal glycosidase and phosphatase activities (Bolanowski et al., 
1983). We think it possible that the decrease in protease levels is 
causally related to the increase in other lysosomal enzyme levels, 
since the cad-l mutant which is deficient in cathepsin D has 
abnormally elevated levels of  -hexosaminidase and  -glucosidase at 
all ages. It would not be surprising if lysosomal glycosidases were at 
risk for proteolysis while cohabiting with proteases. The age-
dependent declines in lysosomal protease activities are at least 
consistent with the possibility that there is a simple enzymatic basis 
for decreasing protein turnover capacity in aging animals. We 
emphasize, however, that there is still no direct evidence that these 
Iysosomal enzymes are principally responsible for intracellular 
protein turnover.