Localisation and activity of cathepsins K and B in equine osteoclasts.
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 in OCL 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.
Gray
A W
AW
Equine Orthopaedic Research Group, University of Cambridge, Department of Clinical Veterinary Medicine, Madingley Road, Cambridge, UK.
Davies
M E
ME
Jeffcott
L B
LB
D000818:Animals; D000918:Antibody Specificity; D001862:Bone Resorption; D001842:Bone and Bones / Q000166:cytology; D002358:Cartilage, Articular / Q000166:cytology; D002401:Cathepsin B / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D056657:Cathepsin K; D002403:Cathepsins / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000201:enzymology; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology; D005333:Fetus; D015870:Gene Expression; D006736:Horses; D007150:Immunohistochemistry; D010010:Osteoclasts / Q000201:enzymology*; D013194:Staining and Labeling
D002403:Cathepsins; D002401:Cathepsin B; D056657:Cathepsin K