Localisation and activity of cathepsins K and B in equine osteoclasts

• Published in: Research in veterinary science 2002-04, Vol.72 (2), p.95-103
• Main Authors: Gray, A.W., Davies, M.E., Jeffcott, L.B.
• Format: Article
• Language: English
• Subjects: Animals; Antibody Specificity; Bone and Bones - cytology; Bone Resorption; Cartilage, Articular - cytology; Cathepsin B - analysis; Cathepsin B - immunology; Cathepsin B - metabolism; Cathepsin K; Cathepsins - analysis; Cathepsins - immunology; Cathepsins - metabolism; Cells, Cultured; Chondrocytes - enzymology; Endothelium, Vascular - cytology; Endothelium, Vascular - enzymology; Fetus; Gene Expression; Horses; Immunohistochemistry; Osteoclasts - enzymology; Staining and Labeling
• ISSN: 0034-5288; 1532-2661
• DOI: 10.1053/rvsc.2001.0522

Cathepsin K and cathepsin B were immunolocalised in equine osteoclasts (OC s) present in ex vivo cartilage/subchondral bone samples. Samples were obtained post mortem from the lateral trochlear ridge (LTR) of six horses and ponies aged between 303 days gestation to 8 months. Strong expression of cathepsin K was detected in OC s, particularly those located at the osteochondral junction, apparently involved in the resorption of calcified cartilage. Cathepsin K expression was also detected in hypertrophic chondrocytes and in the endothelial cells of some blood vessels penetrating the hypertrophic zone of cartilage. By contrast, cathepsin B was either absent or present at very low levels in OC s. Osteoclast-like cells (OCL s) were generated in vitro from bone marrow (BM), obtained from the femurs of one horse and two ponies. High levels of cathepsin K activity but only very low levels of cathepsin B activity were demonstrated inOCL s using fluorogenic substrates for these enzymes. The cathepsin K activity could be blocked by the general cysteine proteinase inhibitor, E-64, but not by the cathepsin B inhibitor, CA-074Me. The cathepsin B activity was completely blocked by both CA-074Me and E-64. Taken together, these results suggest that cathepsin K is more important than cathepsin B in the osteoclastic resorption of bone and calcified cartilage of developing equine long bones. Given the apparent importance of cathepsin K in equine endochondral ossification further investigation into the possibility that abnormal expression of this enzyme is involved in the pathogenesis of equine developmental orthopaedic disease is warranted.