Ablation of Cathepsin K Activity in the Young Mouse Causes Hypermineralization of Long Bone and Growth Plates

Abstract

Cathepsin K deficiency in humans causes pycnodysostosis, which is characterized by dwarfism and osteosclerosis. Earlier studies of 10-week-old male cathepsin K-deficient (knockout, KO) mice showed their bones were mechanically more brittle, while histomorphometry showed that both osteoclasts and osteoblasts had impaired activity relative to the wildtype (WT). Here, we report detailed mineral and matrix analyses of the tibia of these animals based on Fourier Transform Infrared (FT-IR) microspectroscopy and imaging. At 10 wks, there was significant hyper-calcification of the calcified cartilage and cortices in the KO. Carbonate content was elevated in the KO calcified cartilage, cortical and cancellous bone areas These data suggest that cathepsin K does not affect mineral deposition but has a significant effect on mineralized tissue remodeling. Since growth plate abnormalities were extensive despite reported low levels of cathepsin K expression in the calcified cartilage, we used a differentiating chick-limb bud mesenchymal cell system that mimics endochondral ossification but does not contain osteoclasts to show that cathepsin K inhibition during initial stages of mineral deposition retards the mineralization process while general inhibition of cathepsins can increase mineralization. These data suggest that the hypercalcification of the cathepsin K-deficient growth plate is due to persistence of calcified cartilage and point to a role of cathepsin K in bone tissue development as well as skeletal remodeling.

Craniosynostosis in pycnodysostosis: Broadening the spectrum of the cranial flat bone abnormalities

“…Despite several studies of this disorder in animal models [Saftig et al, 1998;Gowen et al, 1999;Kiviranta et al, 2005;Li et al, 2006;Boskey et al, 2009], the complete scenario of pycnodysostosis was only recapitulated in the 129Sv inbred strain of cathepsin K À / À mice [Chen et al, 2007]. These authors observed thinner calvarial bones in the mice and speculated that acroosteolysis, spondylolysis, and calvarial thickness could be explained by increased bone resorption due to site-specific variations in cathepsin K action.…”

ADAM17 Controls Endochondral Ossification by Regulating Terminal Differentiation of Chondrocytes

“…Ϫ/Ϫ mice at embryonic day 18.5 (E18.5) were cleaned of soft tissue, embedded in polymethyl methacrylate, and sectioned at a 2-m thickness prior to examination by Fourier transform infrared (FTIR) imaging spectroscopy as detailed elsewhere (36). Three sections from each bone, including the growth plate, primary spongiosa, and a section of long bone, were analyzed for mineral content, crystallinity, and collagen maturity.…”

Impaired fracture healing in macrophage migration inhibitory factor-deficient mice

“…CtsK, which is a cysteine protease that is mainly secreted by osteoclasts, is also produced by chondrocytes and osteoblasts [32,33]. A recent report found that the addition of either a selective inhibitor for CtsK or a broad inhibitor of cathepsin (B/S/L) activity resulted in delayed mineralization in a culture model of mesenchymal stem cells that developed mineral accretion [34]. In addition, Pan et al reported that MIF−/− LDLR−/− mice exhibited suppressed calcification of the aorta compared with LDL−/− mice, possibly due to the reduced elastinolytic and collagenolytic activity of cysteine proteases (e.g., cathepsin S and L) in smooth muscle cells [35].…”