Alteration of Cartilage Lysosomal Enzyme Activities during Development. (acid hydrolases/cartilage development/cartilage growth/hypophysectomy)

Abstract

Cartilage cathepsin D, cathepsin B and acid phosphatase activities decreased with maturation of Sprague-Dawley rats. Although this phenomenon may largely be due to an age-dependent decrease in cell concentration at young ages (1-8 weeks), in older (8-25 weeks) rats there appeared to be a decrease in enzyme activity per cell.' The dimunition in cartilage cathepsin D activity coincided with an apparent decrease in its concentration. In addition, the inverse correlation between rat age and cartilage lysosomal enzyme activities was, at least in part, tissue specific as the pattern of liver lysosomal enzyme activities was quite different from that noted with cartilage. Interestingly, hypophysectomy greatly diminished age-related modulations in lysosomal enzyme activities suggesting that one or more pituitary hormones may be involved in the mechanism of this age-dependent phenomenon. In addition, cartilage grow;h rate appeared to be correlated with the level of cartilage lysosomal enzyme activities, indicating that these enzymes may be related to the biochemical mechanism of cartilage growth and development.Lysosomes contain many degradative enzymes which function optimally at acidic pH. Although these enzymes were first thought to be involved in cell autolysis, it is becoming increasingly apparent that they may play vital roles in the biochemical mechanism of many normal and pathological processes (1, 2).Developmental changes in lysosomal enzymes have been examined primarily .in liver (3, 4) and cardiac (5) tissues. Cartilage lysosomal enzymes have been highly studied with regard to certain pathological disorders such as osteoarthritis (6). However, age-related perturbations of cartilage lysosomal enzymes have not been well characterized. Examination of cartilage lysosomal enzyme changes with age could lead to important insights regarding the mechanism of cartilage growth, development and pathology.Recently, we found that a nonspecific cartilage acid protease activity was age-dependent (7). The primary purpose of the present investigation was to characterize developmental changes of specific lysosomal enzymes in rat cartilage. Our results show that cartilage (but not liver) cathepsin D, acid phosphatase, and cathepsin B activities decrease with age. In addition, these alterations in enzyme activities were significantly depressed in hypophysectomized rats suggesting that one or more pituitary hormones may be involved in the mechanism of these age-related metabolic changes.