Disease relevance of Ctsk

• Impaired osteoclastic bone resorption in Ctsk-/- mice results in activation of osteoblastic cells to produce increased amounts of other proteolytic enzymes and RANKL in vivo [1].
• Overexpression of cathepsin K during silica-induced lung fibrosis and control by TGF-beta [2].
• Impaired osteoclastic bone resorption leads to osteopetrosis in cathepsin-K-deficient mice [3].
• Pycnodysostosis is a rare inherited osteochondrodysplasia that is caused by mutations of the cathepsin-K gene, characterized by osteosclerosis, short stature, and acroosteolysis of the distal phalanges [3].
• RESULTS: At the age of 7 months, UTU17 mice exhibited clear signs of synovitis, with strong immunostaining for cathepsin K in the synovial lining and the stroma, while control knee joints appeared normal [4].

High impact information on Ctsk

• Cathepsin K, a cysteine protease gene that is highly expressed in osteoclasts, localized to the pycnodysostosis region [5].
• These findings suggest that cathepsin K is a major protease in bone resorption, providing a possible rationale for the treatment of disorders such as osteoporosis and certain forms of arthritis [5].
• Transient transfection experiments revealed that overexpression of JDP2 leads to activation of both tartrate-resistant acid phosphatase (TRAP) and cathepsin K gene promoters in RAW264.7 cells [6].
• The typical multilayered appearance of extracellularly stored thyroglobulin was retained in cathepsin K(-/-) mice only [7].
• Messenger RNA levels of IL-17, IL-12, and cathepsin K in the synovial tissue were suppressed, as were IL-6 and IL-12 protein production [8].

Chemical compound and disease context of Ctsk

• Cathepsin K-specific inhibition using peptidyl vinyl sulfones as selective cysteine protease inactivators reduced bone resorption by 80% in a dose-dependent manner at sub-micromolar concentrations [9].
• The identification of cathepsin K in resorption pits and the inhibition of bone resorption and intracellular cathepsin K activity by selective vinyl sulfone inhibitors indicate the critical role of the protease in osteoclastic bone resorption [9].
• Although none of the compounds in the proline series that was tested proved to be submicromolar in the in vitro bone resorption assay, two Cat K inhibitors in the 3-substituted pyrrolidine series, 24 and 25 were relatively potent in that assay [10].
• Using SB-357114, we evaluated the effect of inhibition of cathepsin K on bone resorption in vivo using a nonhuman primate model of postmenopausal bone loss in which the active form of cathepsin K is identical to the human orthologue [11].

Biological context of Ctsk

• Some features of the phenotype of Ctsk knockout mice, however, suggest the presence of mechanisms by which Ctsk-deficient mice compensate for the lack of cathepsin K [1].
• To study these mechanisms in detail, we generated Ctsk-deficient (Ctsk-/-) mice and analyzed them at the age of 2, 7, and 12 months using peripheral quantitative computed tomography, histomorphometry, resorption marker measurements, osteoclast and osteoblast differentiation cultures, and gene expression analyses [1].
• This places Ctsk approximately 4.5 kb downstream of Arnt on mouse chromosome 3 at locus 47.9 [12].
• Detailed sequence analysis of 1.7 kb of Ctsk promoter revealed several putative binding sites for transcription factors and two stretches of 280-320 bp which were > 70% homologous with the human cathepsin K promoter [12].
• The sizes of the coding exons 2-7 as well as the pattern of intron sizes are conserved between the human and mouse cathepsin K genes [12].

Anatomical context of Ctsk

• The number of osteoclasts in trabecular bone was significantly increased in Ctsk-/- mice compared to controls, as was the number of osteoclast precursors in bone marrow [1].
• Pulmonary macrophages and fibroblasts were identified as Cat K overproducing cells in the lung of silicotic mice [2].
• Cathepsin-K-deficient mice survive and are fertile, but display an osteopetrotic phenotype with excessive trabeculation of the bone-marrow space [3].
• Cathepsin-K-deficient osteoclasts manifested a modified ultrastructural appearance: their resorptive surface was poorly defined with a broad demineralized matrix fringe containing undigested fine collagen fibrils; their ruffled borders lacked crystal-like inclusions, and they were devoid of collagen-fibril-containing cytoplasmic vacuoles [3].
• In areas of cartilage degeneration, both chondrocytes and cells of hypertrophic synovia were positive for cathepsin K [4].

Associations of Ctsk with chemical compounds

• Epoxy succinate peptide derivatives, CLIK-066, 088, 112, 121, 148, 181, 185 and 187, are typical specific inhibitors for cathepsin L. Aldehyde derivatives CLIK-060 and CLIK-164 showed specific inhibition against cathepsin S and cathepsin K, respectively [13].
• RAW.CLM-1 cells fail to multinucleate and do not up-regulate calcitonin receptor, but they express tartrate-resistant acid phosphatase, cathepsin K, and beta(3) integrin, suggesting that osteoclastogenesis is blocked at a late-intermediate stage [14].
• The sequence of cathepsin K expression was linked to osteoclast differentiation in vivo and in vitro by a tartrate-resistant acid phosphatase-anticathepsin K dual immunostaining technique [15].
• In vitro, recombinant cathepsin K liberated thyroxine from thyroglobulin by limited proteolysis at neutral pH [16].
• Calvarial Osteoclasts Express a Higher Level of Tartrate-Resistant Acid Phosphatase than Long Bone Osteoclasts and Activation Does not Depend on Cathepsin K or L Activity [17].
• These studies suggest that cathepsin K interaction with type I collagen is required for 1) the release of cryptic Arg-Gly-Asp motifs during the initial attachment of osteoclasts and 2) termination of resorption via the creation of autocrine signals originating from type I collagen degradation [18].

Regulatory relationships of Ctsk

• Impaired bone resorption in cathepsin K-deficient mice is partially compensated for by enhanced osteoclastogenesis and increased expression of other proteases via an increased RANKL/OPG ratio [1].
• These results suggest that the RANKL-induced cathepsin K gene expression is cooperatively regulated by the combination of the transcription factors and p38 MAP kinase in a gradual manner [19].
• The results show that IFN-gamma down-regulates mRNA levels of cathepsin K in a time- and dose-dependent manner [20].
• Therefore, it is suggested that cystatin C regulates the degradation of bone matrix by cathepsin K, both extracellularly and intracellularly [21].

Other interactions of Ctsk

• Synthesis and secretion of CAL were up-regulated by 1alpha,25-(OH)2D3, but neither those of CAK, dominant relative to CAL, nor CAB, barely detectable, levels changed in the experiments [22].
• CONCLUSION: Altogether, these data suggest that while Cat K may contribute to control lung fibrosis, TGF-beta appears to limit its overexpression in response to silica particles [2].
• Z-Gly-Pro-Arg-MbetaNA is efficiently hydrolyzed by cathepsin K but only poorly by cathepsins L, S, and B. On the contrary, the intracellular hydrolysis of the cathepsin B-specific substrate, Z-Arg-Arg-MbetaNA, was prevented by both types of inhibitors [9].
• RESULTS: The analyses of the cathepsin-deficient bone explants showed that, in addition to cathepsin K, calvarial osteoclasts use other cysteine proteinases to degrade bone matrix [23].
• In vitro modified low density lipoprotein (LDL) uptake assays, using bone marrow derived macrophages preincubated with caveolae and scavenger receptor inhibitors, confirmed the importance of caveolins and CD36 in increasing modified LDL uptake in the absence of cathepsin K [24].

Analytical, diagnostic and therapeutic context of Ctsk

• Cat expression (Cat K, S, L and B) was quantified in lung tissue and isolated pulmonary cells by quantitative RT-PCR [2].
• Confocal microscopy analysis did not reveal an accumulation of cathepsin K containing vesicles opposing the ruffled border and the resorption lacuna [9].
• Distribution of cathepsin K in the knee joints was studied by immunohistochemistry [4].
• To determine whether the expression of cathepsin K mRNA during mouse embryogenesis was more widespread, cryostat sections of early (day 11-13) and late (day 15-17) mouse fetuses were analyzed by in situ hybridization [25].
• Northern blot analysis of RNAs from a number of mouse tissues revealed that cathepsin K mRNA is selectively expressed in osteoclast [15].

References