Developmental control of cathepsin B expression in bovine fetal muscles

Expression of lysosomal cysteine proteinases was studied during fetal calf muscle development. The peptide cleaving activities of cathepsins B and L decreased strongly from 80 to 250 days of fetal age. This decrease in cathepsin activities occurred similarly in three muscles exhibiting different metabolic and contractile properties in adult animals. Cathepsin B from adult or fetal muscle revealed similar enzymatic properties, but presented a five- to sixfold lower concentration in adult muscle as indicated by active-site titration with L-3-carboxy-trans-2,3-epoxypropionyl-leucylamido-(4-guani din o)butane. During fetal growth, decreases in muscle cathepsin B specific activity and active enzyme concentration were associated with a parallel drop of cathepsin B mRNA levels. Bovine cathepsin B is encoded by two different transcripts resulting from alternative polyadenylation [Mordier, S. B., Béchet, D. M., Roux, M. P., Obled, A., and Ferrara, M. (1995) Eur. J. Biochem. 229, 35-44]. As revealed by ribonuclease protection assays, the two mRNAs encoding cathepsin B declined similarly during fetal muscle growth. This study indicates that lysosomal proteinases in skeletal muscle are under developmental control. The decrease of muscle cathepsins during fetal development appears sufficient to account for the low levels of these enzymes in adult muscles. In fetuses, high activities of lysosomal cysteine proteinases might be important for remodeling muscles during early development.