Cathepsin expression during skeletal development

Cysteine proteinases, cathepsins B, H, K, L and S, have been implicated in several proteolytic processes during development, growth, remodeling and ag ing, as well as in a variety of pathological processes. For systematic anal ysis of cathepsin gene expression we have produced cDNA clones for mouse an d human cysteine cathepsins. Northern analysis of a panel of total RNAs iso lated from 16-19 different human and mouse tissues revealed the presence of mRNAs for cathepsin B, H, K, L and S in most tissues, but each with a dist inct profile. Of the different cathepsin mRNAs, those for cathepsin K were clearly the highest in bone and cartilage. However, relatively high mRNA le vels for the other cathepsins were also present in these tissues. To better understand the roles of different cathepsins during endochondral ossificat ion in mouse long bones, cathepsin mRNAs were localized by in situ hybridiz ation. Cathepsin K mRNAs were predominantly seen in multinucleated chondroc lastic and osteoclastic cells at the osteochondral junction and on the surf ace of bone spicules. The other cathepsin mRNAs were also seen in osteoclas ts, and in hypertrophic and proliferating chondrocytes. These observations were confirmed by immunohistochemistry and suggest that all cysteine cathep sins are involved in matrix degradation during endochondral ossification. ( C) 1999 Elsevier Science B.V. All rights reserved.