Ablation of cathepsin k activity in the young mouse causes hypermineralization of long bone and growth plates

Vasorin as an actor of bone turnover?

Bone diseases are increasing with aging populations and it is important to identify clues to develop innovative treatments. Vasn, which encodes vasorin (Vasn), a transmembrane protein involved in the pathophysiology of several organs, is expressed during the development in intramembranous and endochondral ossification zones. Here, we studied the impact of Vasn deletion on the osteoblast and osteoclast dialog through a cell Coculture model. In addition, we explored the bone phenotype of Vasn KO mice, either constitutive or tamoxifen-inducible, or with an osteoclast-specific deletion. First, we show that both osteoblasts and osteoclasts express Vasn. Second, we report that, in both KO mouse models but not in osteoclast-targeted KO mice, Vasn deficiency was associated with an osteopenic bone phenotype, due to an imbalance in favor of osteoclastic resorption. Finally, through the Coculture experiments, we identify a dysregulation of the Wnt/β-catenin pathway together with an increase in RANKL release by osteoblasts, which led to an enhanced osteoclast activity. This study unravels a direct role of Vasn in bone turnover, introducing a new biomarker or potential therapeutic target for bone pathologies.

Embryonic inhibition of colony-stimulating factor 1 receptor induces enlarged cartilaginous zone of the midpalatal suture in postnatal mice

OBJECTIVES

The midpalatal suture acts as the growth centre of the maxilla. Colony-stimulating factor 1 receptor (CSF1R) is essential for osteoclastogenesis. Deletion of CSF1R, and its ligand, results in significant craniofacial phenotypes but has not been studied in detail in the midpalatal suture.

MATERIALS AND METHODS

Pregnant ICR mice were treated with the CSF1R inhibitor PLX5622 at embryo Day 14.5 (E14.5) to E17.5. Pups at E18.5, postnatal Day 3 (P3) and P7 were collected for skeletal and histological staining. Osteoclasts were labelled using TRAP staining. PHH3 and TUNEL were employed to detect cell proliferation and apoptosis. Sox9, Ihh, and Col10a1 and Runx2, Col1a1, and DMP1 were used to detect chondrogenic differentiation and osteogenic differentiation, respectively. CD31, MMP9 and CTSK were utilized to assess vascular invasion and osteoclast secretion enzymes, respectively.

RESULTS

Embryonic inhibition of CSF1R resulted in a depletion of TRAP-positive cells and an enlarged cartilage zone of the midpalatal suture of postnatal mice. Compared to those in the control group, Sox9, Ihh, Col10a1, Runx2 and Col1a1 were upregulated, whereas TUNEL and DMP1 were decreased in this zone. In the trabecular region, Col10a1 was upregulated, while TUNEL, Col1a1 and DMP1 were downregulated. Moreover, the expression of MMP9, CTSK and CD31 was decreased, and invasion into the cartilage zone was delayed.

CONCLUSIONS

Embryonic inhibition of CSF1R led to an abnormally enlarged cartilaginous zone in the midpalatal suture, potentially due to delayed endochondral ossification caused by the depletion of osteoclasts. Additionally, we established a novel model of midpalatal suture dysplasia, offering prospects for future research.

Comparative analysis of two cathepsin L genes in Asiatic hard clam (Meretrix meretrix): Similar in sequence features, different in expression profiles

Cathepsin L is widely found in eukaryotes and prokaryotes, and it plays important roles in innate immunity. In the present study, we cloned two cathepsin L genes (designated as MmCTSL1 and MmCTSL2, respectively) from Asiatic hard clam (Meretrix meretrix). The complete sequence of MmCTSL1 cDNA contained a 5' untranslated region (UTR) of 31 bp, a 3' UTR of 228 bp with a poly (A) tail, and an open reading frame (ORF) of 1005 bp encoding 334 amino acids with predicted molecular weight of 37.5 kDa and theoretical isoelectric point of 5.27, and contained a signal peptide (from M1 to A16), a protease inhibitor I29 family domain (from W27 to F87), and a papain family cysteine protease domain (from L118 to T333). The complete sequence of MmCTSL2 cDNA contained a 5' UTR of 50 bp, a 3' UTR of 162 bp with a poly (A) tail, and an ORF of 996 bp encoding a polypeptide of 331 amino acids with predicted molecular weight of 36.8 kDa and theoretical isoelectric point of 7.07. It contained a signal peptide (from M1 to A16), a protease inhibitor I29 family domain (from W30 to F89), and a papain family cysteine protease domain (from L115 to T330). Real-time quantitative PCR analysis demonstrated that MmCTSL1 and MmCTSL2 were widely expressed in all the tested tissues, including adductor muscle, foot, gill, hemocytes, hepatopancreas and mantle, with the highest mRNA expression level in hepatopancreas and hemocytes, respectively. After Vibrio splendidus challenge, the mRNA expression levels of MmCTSL1 and MmCTSL2 in hemocytes and hepatopancreas were both significantly up-regulated with different expression profiles. In hemocytes, the expression levels of MmCTSL1 and MmCTSL2 reached their respective peaks (3.4-fold and 13.0-fold compared with the control, respectively) at 12 h after bacterial challenge, and MmCTSL2 responds earlier than MmCTSL1. In hepatopancreas, the expression levels of MmCTSL1 and MmCTSL2 reached their respective peaks at 6 h (9.0-fold compared with the control) and 24 h (2.8-fold compared with the control) after bacterial challenge, meaning that MmCTSL1 responds earlier than MmCTSL2. At the same time, whether in hepatopancreas or hemocytes, MmCTSL1 persist for a while after the bacterial challenge peak, while MmCTSL2 would quickly return to the initial level after the bacterial challenge peak. These results indicate that cathepsin L may be involved in the immune process of hard clam against V. splendidus with different potential roles.

Pycnodysostosis: a case report and literature review concerning oral and maxillofacial complications and their management

OBJECTIVE

There is a lack of knowledge regarding pycnodysostosis (PYCD), which is commonly misdiagnosed as other, similar malformations. This study aims to report a patient with PYCD and conjointly present a comprehensive literature review regarding oral complications after oral surgery procedures.

STUDY DESIGN

This study aims to report a noteworthy case of a 40-year-old woman with PYCD who suffered from a midface defect after iatrogenic fracture during extraction of the upper right molars. A comprehensive electronic search was carried out in January 2020 for detection and analysis of the most commonly encountered dentoalveolar PYCD-related complications. The study was granted an exemption from the local institutional review board.

RESULTS

The electronic search yielded 35 articles reporting 41 PYCD cases with 62 various reported dentoalveolar complications. The survey reported a prevalence of osteomyelitis (n = 39) followed by pathologic fracture (n = 17), iatrogenic fracture (n = 5), and oronasal communication (n = 1).

CONCLUSIONS

This study advocates handling patients with PYCD with care through the use of extensive clinical and radiographic examinations, giving priority to any conservative treatment modalities, atraumatic surgical procedures, prophylactic antibiotic prescriptions, and a regular follow-up schedule to tackle any anticipated complications.

Fumitremorgin C Attenuates Osteoclast Formation and Function via Suppressing RANKL-Induced Signaling Pathways

Excessive bone resorption conducted by osteoclasts is considered as the main cause of osteoclast-related bone diseases such as osteoporosis. Therefore, the suppression of excessive osteoclast formation and function is one of the strategies to treat osteoclast-related bone diseases. Fumitremorgin C (Fum) is a mycotoxin extracted from Aspergillus fumigatus. It has been shown to have extensive pharmacological properties, but its role in the treatment of osteoclast-related bone diseases remains unclear. In this study, we aim to find out whether Fum can inhibit the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation and function. The results showed that Fum could significantly attenuate osteoclast formation and function at concentrations from 2.5 to 10 µM. The protein expression of bone resorption factors such as NFATc1, cathepsin K, V-ATPase-d2, and c-Fos was suppressed with the treatment of Fum at a concentration of 10 µM. In addition, Fum was also shown to suppress the activity of NF-κB, intracellular reactive oxygen species level, and MAPK pathway. Taken together, the present study showed that Fum could attenuate the formation and function of osteoclast via suppressing RANKL-induced signaling pathways, suggesting that Fum might be a potential novel drug in the treatment of osteoclast-related bone diseases.

AP-1 and Mitf interact with NFATc1 to stimulate cathepsin K promoter activity in osteoclast precursors

Cathepsin K (CTSK) is a secreted protease that plays an essential role in osteoclastic bone resorption and osteoporotic bone loss. We have previously shown that activator protein 1 (AP-1) stimulates CTSK promoter activity and that proximal nuclear factor of activated T cells cytoplasmic 1 (NFATc1)-binding sites play a major role in the stimulation of CTSK gene expression by receptor activator of NFκB ligand (RANKL). In the present study, we have extended these observations and further dissected the effects of transcription factors involved in the regulation of CTSK gene expression. Our aim was to investigate the cooperative interplay among transcription factors AP-1, microphthalmia-associated transcription factor (Mitf), and NFATc1, and the consequent regulatory effects on CTSK transcription. Experiments were carried out in RAW 264.7 cells, which can be readily differentiated to osteoclasts upon RANKL stimulation. Our data show that AP-1, Mitf, and NFATc1 are capable of independently stimulating CTSK promoter activity. A combination of any two factors further enhances CTSK promoter activity, with the combination of AP-1 (c-fos/c-jun) and NFATc1 inducing the largest increase. We further identify a synergistic effect when all three factors cooperate intimately at the proximal promoter region, yielding maximal transcriptional upregulation of the CTSK promoter. RANKL induces temporal localization of AP-1 and NFATc1 to the CTSK promoter. These results suggest that the interaction of multiple transcription factors mediate a maximal response to RANKL-induced CTSK gene expression.

Differing Effects of Parathyroid Hormone, Alendronate, and Odanacatib on Bone Formation and on the Mineralization Process in Intracortical and Endocortical Bone of Ovariectomized Rabbits

Bone is formed by deposition of a collagen-containing matrix (osteoid) that hardens over time as mineral crystals accrue and are modified; this continues until bone remodeling renews that site. Pharmacological agents for osteoporosis differ in their effects on bone remodeling, and we hypothesized that they may differently modify bone mineral accrual. We, therefore, assessed newly formed bone in mature ovariectomized rabbits treated with the anti-resorptive bisphosphonate alendronate (ALN-100µ g/kg/2×/week), the anabolic parathyroid hormone (PTH (1-34)-15µ g/kg/5×/week), or the experimental anti-resorptive odanacatib (ODN 7.5 µM/day), which suppresses bone resorption without suppressing bone formation. Treatments were administered for 10 months commencing 6 months after ovariectomy (OVX). Strength testing, histomorphometry, and synchrotron Fourier-transform infrared microspectroscopy were used to measure bone strength, bone formation, and mineral accrual, respectively, in newly formed endocortical and intracortical bone. In Sham and OVX endocortical and intracortical bone, three modifications occurred as the bone matrix aged: mineral accrual (increase in mineral:matrix ratio), carbonate substitution (increase in carbonate:mineral ratio), and collagen molecular compaction (decrease in amide I:II ratio). ALN suppressed bone formation but mineral accrued normally at those sites where bone formation occurred. PTH stimulated bone formation on endocortical, periosteal, and intracortical bone surfaces, but mineral accrual and carbonate substitution were suppressed, particularly in intracortical bone. ODN treatment did not suppress bone formation, but newly deposited endocortical bone matured more slowly with ODN, and ODN-treated intracortical bone had less carbonate substitution than controls. In conclusion, these agents differ in their effects on the bone matrix. While ALN suppresses bone formation, it does not modify bone mineral accrual in endocortical or intracortical bone. While ODN does not suppress bone formation, it slows matrix maturation. PTH stimulates modelling-based bone formation not only on endocortical and trabecular surfaces, but may also do so in intracortical bone; at this site, new bone deposited contains less mineral than normal.

Effectiveness of elcatonin for alleviating pain and inhibiting bone resorption in patients with osteoporotic vertebral fractures

Elderly patients with osteoporotic vertebral fractures often experience severe pain that reduces their quality of life (QOL). Calcitonin, a bone resorption inhibitor, has been reported to alleviate pain in such patients; however, few clinical studies have demonstrated this effect. The objective of this study was to compare changes in pain scores, activities of daily living (ADL), QOL, bone resorption, bone mineral density (BMD), and fracture healing among patients with new vertebral fractures who received different treatment modalities. We conducted an open-label, multicenter, randomized, parallel control group study comprising 107 female patients ≥55 years old with acute back pain from vertebral fracture. All subjects received either intramuscular injections of elcatonin, a derivative of calcitonin, or an oral nonsteroidal antiinflammatory drug (NSAID) combined with an active vitamin D₃ (VD3) analogue for 6 months. The pain was assessed using a visual analogue scale, and ADL and QOL were assessed using questionnaires. BMD was measured using dual-energy X-ray absorptiometry. A two-tailed significance level of 5% was used. The elcatonin IM group had significantly higher QOL score at 2 weeks and later, and significantly lower VAS and ADL scores than those in the NSAID + VD3 group at 1 month and later. The elcatonin IM group had significantly reduced TRACP-5b levels compared with those in the NSAID + VD3 group at 3 months and later and significantly higher percent changes in BMD than the NSAID + VD3 group. These results suggest that elcatonin significantly alleviated pain, inhibited bone resorption, and improved ADL, QOL, and BMD compared with NSAID + VD3.

Cathepsin K Inhibitors for Osteoporosis: Biology, Potential Clinical Utility, and Lessons Learned

Cathepsin K is a cysteine protease member of the cathepsin lysosomal protease family. Although cathepsin K is highly expressed in osteoclasts, lower levels of cathepsin K are also found in a variety of other tissues. Secretion of cathepsin K from the osteoclast into the sealed osteoclast-bone cell interface results in efficient degradation of type I collagen. The absence of cathepsin K activity in humans results in pycnodysostosis, characterized by increased bone mineral density and fractures. Pharmacologic cathepsin K inhibition leads to continuous increases in bone mineral density for ≤5 years of treatment and improves bone strength at the spine and hip. Compared with other antiresorptive agents, cathepsin K inhibition is nearly equally efficacious for reducing biochemical markers of bone resorption but comparatively less active for reducing bone formation markers. Despite multiple efforts to develop cathepsin K inhibitors, potential concerns related to off-target effects of the inhibitors against other cathepsins and cathepsin K inhibition at nonbone sites, including skin and perhaps cardiovascular and cerebrovascular sites, prolonged the regulatory approval process. A large multinational randomized, double-blind phase III study of odanacatib in postmenopausal women with osteoporosis was recently completed. Although that study demonstrated clinically relevant reductions in fractures at multiple sites, odanacatib was ultimately withdrawn from the regulatory approval process after it was found to be associated with an increased risk of cerebrovascular accidents. Nonetheless, the underlying biology and clinical effects of cathepsin K inhibition remain of considerable interest and could guide future therapeutic approaches for osteoporosis.

The cartilage extracellular matrix as a transient developmental scaffold for growth plate maturation

The cartilage growth plate is a specialized developmental tissue containing characteristic zonal arrangements of chondrocytes. The proliferative and differentiative states of chondrocytes are tightly regulated at all stages including the initial limb bud and rudiment cartilage stages of development, the establishment of the primary and secondary ossification centers, development of the growth plates and laying down of bone. A multitude of spatio-temporal signals, including transcription factors, growth factors, morphogens and hormones, control chondrocyte maturation and terminal chondrocyte differentiation/hypertrophy, cell death/differentiation, calcification and vascular invasion of the growth plate and bone formation during morphogenetic transition of the growth plate. This involves hierarchical, integrated signaling from growth and factors, transcription factors, mechanosensory cues and proteases in the extracellular matrix to regulate these developmental processes to facilitate progressive changes in the growth plate culminating in bone formation and endochondral ossification. This review provides an overview of selected components which have particularly important roles in growth plate biology including collagens, proteoglycans, glycosaminoglycans, growth factors, proteases and enzymes.

Glycoprotein130 (Gp130)/interleukin-6 (IL-6) signalling in osteoclasts promotes bone formation in periosteal and trabecular bone

Interleukin-6 (IL-6) and interleukin-11 (IL-11) receptors (IL-6R and IL-11R, respectively) are both expressed in osteoclasts and transduce signal via the glycoprotein130 (gp130) co-receptor, but the physiological role of this pathway is unclear. To determine the critical roles of gp130 signalling in the osteoclast, we generated mice using cathepsin K Cre (CtskCre) to disrupt gp130 signalling in osteoclasts. Bone marrow macrophages from CtskCre.gp130(f/f) mice generated more osteoclasts in vitro than cells from CtskCre.gp130(w/w) mice; these osteoclasts were also larger and had more nuclei than controls. While no increase in osteoclast numbers was observed in vivo, osteoclasts on trabecular bone surfaces of CtskCre.gp130(f/f) mice were more spread out than in control mice, but had no functional defect detectable by serum CTX1 levels or trabecular bone cartilage remnants. However, trabecular osteoblast number and mineralising surfaces were significantly lower in male CtskCre.gp130(f/f) mice compared to controls, and this was associated with a significantly lower trabecular bone volume at 12 weeks of age. Furthermore, CtskCre.gp130(f/f) mice exhibited greatly suppressed periosteal bone formation at this age, indicated by significant reductions in both double-labelled surface and mineral apposition rate. By 26 weeks of age, CtskCre.gp130(f/f) mice exhibited narrower femora, with lower periosteal and endocortical perimeters than CtskCre.gp130(w/w) controls. Since IL-6 and IL-11R global knockout mice exhibited a similar reduction in femoral width, we also assessed periosteal bone formation in those strains, and found bone forming surfaces were also reduced in male IL-6 null mice. These data suggest that IL-6/gp130 signalling in the osteoclast is not essential for normal bone resorption in vivo, but maintains both trabecular and periosteal bone formation in male mice by promoting osteoblast activity through the stimulation of osteoclast-derived "coupling factors" and "osteotransmitters", respectively.

The mineral dissolution function of osteoclasts is dispensable for hypertrophic cartilage degradation during long bone development and growth

During long bone development and post-natal growth, the cartilaginous model of the skeleton is progressively replaced by bone, a process known as endochondral ossification. In the primary spongiosa, osteoclasts degrade the mineralized cartilage produced by hypertrophic chondrocytes to generate cartilage trabeculae that osteoblasts embed in bone matrix. This leads to the formation of the trabecular bone network of the secondary spongiosa that will undergo continuous remodeling. Osteoclasts are specialized in mineralized tissue degradation, with the combined ability to solubilize hydroxyapatite and to degrade extracellular matrix proteins. We reported previously that osteoclasts lacking Dock5 could not degrade bone due to abnormal podosome organization and absence of sealing zone formation. Consequently, adult Dock5(-/-) mice have increased trabecular bone mass. We used Dock5(-/-) mice to further investigate the different functions of osteoclast during endochondral bone formation. We show that long bones are overall morphologically normal in developing and growing Dock5(-/-) mice. We demonstrate that Dock5(-/-) mice also have normal hypertrophic cartilage and cartilage trabecular network. Conversely, trabecular bone volume increased progressively in the secondary spongiosa of Dock5(-/-) growing mice as compared to Dock5(+/+) animals, even though their osteoclast numbers were the same. In vitro, we show that Dock5(-/-) osteoclasts do present acidic compartments at the ventral plasma membrane and produce normal amounts of active MMP9, TRAP and CtsK for matrix protein degradation but they are unable to solubilize minerals. These observations reveal that contrarily to bone resorption, the ability of osteoclasts to dissolve minerals is dispensable for the degradation of mineralized hypertrophic cartilage during endochondral bone formation.

Human bone marrow-derived mesenchymal stem cells display enhanced clonogenicity but impaired differentiation with hypoxic preconditioning

Stem cells are promising candidate cells for regenerative applications because they possess high proliferative capacity and the potential to differentiate into other cell types. Mesenchymal stem cells (MSCs) are easily sourced but do not retain their proliferative and multilineage differentiative capabilities after prolonged ex vivo propagation. We investigated the use of hypoxia as a preconditioning agent and in differentiating cultures to enhance MSC function. Culture in 5% ambient O(2) consistently enhanced clonogenic potential of primary MSCs from all donors tested. We determined that enhanced clonogenicity was attributable to increased proliferation, increased vascular endothelial growth factor secretion, and increased matrix turnover. Hypoxia did not impact the incidence of cell death. Application of hypoxia to osteogenic cultures resulted in enhanced total mineral deposition, although this effect was detected only in MSCs preconditioned in normoxic conditions. Osteogenesis-associated genes were upregulated in hypoxia, and alkaline phosphatase activity was enhanced. Adipogenic differentiation was inhibited by exposure to hypoxia during differentiation. Chondrogenesis in three-dimensional pellet cultures was inhibited by preconditioning with hypoxia. However, in cultures expanded under normoxia, hypoxia applied during subsequent pellet culture enhanced chondrogenesis. Whereas hypoxic preconditioning appears to be an excellent way to expand a highly clonogenic progenitor pool, our findings suggest that it may blunt the differentiation potential of MSCs, compromising their utility for regenerative tissue engineering. Exposure to hypoxia during differentiation (post-normoxic expansion), however, appears to result in a greater quantity of functional osteoblasts and chondrocytes and ultimately a larger quantity of high-quality differentiated tissue.

ADAM17 controls endochondral ossification by regulating terminal differentiation of chondrocytes

Endochondral ossification is a highly regulated process that relies on properly orchestrated cell-cell interactions in the developing growth plate. This study is focused on understanding the role of a crucial regulator of cell-cell interactions, the membrane-anchored metalloproteinase ADAM17, in endochondral ossification. ADAM17 releases growth factors, cytokines, and other membrane proteins from cells and is essential for epidermal growth factor receptor (EGFR) signaling and for processing tumor necrosis factor alpha. Here, we report that mice lacking ADAM17 in chondrocytes (A17ΔCh) have a significantly expanded zone of hypertrophic chondrocytes in the growth plate and retarded growth of long bones. This abnormality is caused by an accumulation of the most terminally differentiated type of chondrocytes that produces a calcified matrix. Inactivation of ADAM17 in osteoclasts or endothelial cells does not affect the zone of hypertrophic chondrocytes, suggesting that the main role of ADAM17 in the growth plate is in chondrocytes. This notion is further supported by in vitro experiments showing enhanced hypertrophic differentiation of primary chondrocytes lacking Adam17. The enlarged zone of hypertrophic chondrocytes in A17ΔCh mice resembles that described in mice with mutant EGFR signaling or lack of its ligand transforming growth factor α (TGFα), suggesting that ADAM17 regulates terminal differentiation of chondrocytes during endochondral ossification by activating the TGFα/EGFR signaling axis.

ADAM17 controls endochondral ossification by regulating terminal differentiation of chondrocytes

Endochondral ossification is a highly regulated process that relies on properly orchestrated cell-cell interactions in the developing growth plate. This study is focused on understanding the role of a crucial regulator of cell-cell interactions, the membrane-anchored metalloproteinase ADAM17, in endochondral ossification. ADAM17 releases growth factors, cytokines, and other membrane proteins from cells and is essential for epidermal growth factor receptor (EGFR) signaling and for processing tumor necrosis factor alpha. Here, we report that mice lacking ADAM17 in chondrocytes (A17ΔCh) have a significantly expanded zone of hypertrophic chondrocytes in the growth plate and retarded growth of long bones. This abnormality is caused by an accumulation of the most terminally differentiated type of chondrocytes that produces a calcified matrix. Inactivation of ADAM17 in osteoclasts or endothelial cells does not affect the zone of hypertrophic chondrocytes, suggesting that the main role of ADAM17 in the growth plate is in chondrocytes. This notion is further supported by in vitro experiments showing enhanced hypertrophic differentiation of primary chondrocytes lacking Adam17. The enlarged zone of hypertrophic chondrocytes in A17ΔCh mice resembles that described in mice with mutant EGFR signaling or lack of its ligand transforming growth factor α (TGFα), suggesting that ADAM17 regulates terminal differentiation of chondrocytes during endochondral ossification by activating the TGFα/EGFR signaling axis.

Fourier transform infrared spectroscopic imaging parameters describing acid phosphate substitution in biologic hydroxyapatite

Acid phosphate substitution into mineralized tissues is an important determinant of their mechanical properties and their response to treatment. This study identifies and validates Fourier transform infrared spectroscopic imaging (FTIRI) spectral parameters that provide information on the acid phosphate (HPO4) substitution into hydroxyapatite in developing mineralized tissues. Curve fitting and Fourier self-deconvolution were used to identify subband positions in model compounds (with and without HPO4). The intensity of subbands at 1127 and 1110 cm(-1) correlated with the acid phosphate content in these models. Peak height ratios of these subbands to the ν3 vibration at 1096 cm(-1) found in stoichiometric apatite were evaluated in the model compounds and mixtures thereof. FTIRI spectra of bones and teeth at different developmental ages were analyzed using these spectral parameters. Factor analysis (a chemometric technique) was also conducted on the tissue samples and resulted in factor loadings with spectral features corresponding to the HPO4 vibrations described above. Images of both factor correlation coefficients and the peak height ratios 1127/1096 and 1112/1096 cm(-1) demonstrated higher acid phosphate content in younger vs. more mature regions in the same specimen. Maps of the distribution of acid phosphate content will be useful for characterizing the extent of new bone formation, the areas of potential decreased strength, and the effects of therapies such as those used in metabolic bone diseases (osteoporosis, chronic kidney disease) on mineral composition. Because of the wider range of values obtained with the 1127/1096 cm(-1) parameter compared to the 1110/1096 cm(-1) parameter and the smaller scatter in the slope, it is suggested that this ratio should be the parameter of choice.

Lactating Ctcgrp nulls lose twice the normal bone mineral content due to fewer osteoblasts and more osteoclasts, whereas bone mass is fully restored after weaning in association with up-regulation of Wnt signaling and other novel genes

The maternal skeleton resorbs during lactation to provide calcium to milk and the lost mineral content is restored after weaning. The changes are particularly marked in Ctcgrp null mice, which lose 50% of spine mineral content during lactation but restore it fully. The known calciotropic hormones are not required for skeletal recovery to occur; therefore, unknown factors that stimulate bone formation may be responsible. We hypothesized that the genes responsible for regulating postweaning bone formation are differentially regulated in bone or marrow, and this regulation may be more marked in Ctcgrp null mice. We confirmed that Ctcgrp null mice had twice as many osteoclasts and 30-40% fewer osteoblasts as compared with wild-type mice during lactation but no deficit in osteoblast numbers after weaning. Genome-wide microarray analyses on tibial RNA showed differential expression of 729 genes in wild-type mice at day 7 after weaning vs prepregnancy, whereas the same comparison in Ctcgrp null mice revealed only 283 genes. Down-regulation of Wnt family inhibitors, Sost and Dkk1, and inhibition of Mef2c, a sclerostin stimulator, were observed. Ctsk, a gene expressed during osteoclast differentiation, and Igfbp2, which stimulates bone resorption, were inhibited. Differential regulation of genes involved in energy use was compatible with a net increase in bone formation. The most marked changes occurred in genes not previously associated with bone metabolism. In conclusion, the postlactation skeleton shows dynamic activity with more than 700 genes differentially expressed. Some of these genes are likely to promote bone formation during postweaning by stimulating the proliferation and activity of osteoblasts, inhibiting osteoclasts, and increasing energy use.

A novel mutation (R122Q) in the cathepsin K gene in a Chinese child with Pyknodysostosis

BACKGROUND

Pyknodysostosis (OMIM 265800) is a rare, autosomal recessive sclerosing skeletal dysplasia as a consequence of the diminished capacity of osteoclasts to degrade organic bone matrix. Pyknodysostosis is caused by mutation in the cathepsin K (CTSK) gene. Up to date, 34 different CTSK mutations have been identified in patients with Pyknodysostosis; however, only one mutation was previously identified in a Chinese patient. The objective of this study was to characterize the clinical manifestations and features of Pyknodysostosis and identify the mutation of the causative gene in a Chinese family with Pyknodysostosis.

METHODS

We investigated a non-consanguineous Chinese family in which an 11-year-old child was affected with Pyknodysostosis. Altogether, 203 persons, including the affected individual, his parents and 200 healthy donors, were recruited and genomic DNA was extracted. All 8 exons of the CTSK gene, including the exon-intron boundaries, were amplified and sequenced directly.

RESULTS

The proband displayed a novel homozygous missense mutation c.365G>A in exon 4 of the CTSK gene. This mutation leads to the substitution of the arginine at position 122 by glutamine (R122Q) in cathepsin K. The parents were heterozygous for this gene mutation, and the mutation was not found in the 200 unrelated controls.

CONCLUSION

Our study suggests that the novel missense mutation c.365G>A (R122Q) in exon 4 of CTSK gene was responsible for Pyknodysostosis in the Chinese family.

Photoacoustic FTIR spectroscopic study of undisturbed human cortical bone

Chemical pretreatment has been the prevailing sample preparation procedure for infrared (IR) spectroscopic studies on bone. However, experiments have indicated that chemical pretreatment can potentially affect the interactions between the components. Typically the IR techniques have involved transmission experiments. Here we report experimental studies using photoacoustic Fourier transform infrared spectroscopy (PA-FTIR). As a nondestructive technique, PA-FTIR can detect absorbance spectrum from a sample at controllable sampling depth and with little or no sample preparation. Additionally, the coupling inert gas, helium, which is utilized in the PA-FTIR system, can inhibit bacteria growth of bone by displacing oxygen. Therefore, we used this technique to study the undisturbed human cortical bone. It is found that photoacoustic mode (linear-scan, LS-PA-FTIR) can obtain basically similar spectra of bone as compared to the traditional transmission mode, but it seems more sensitive to amide III and ν(2) carbonate bands. The ν(3) phosphate band is indicative of detailed mineral structure and symmetry of native bone. The PA-FTIR depth profiling experiments on human cortical bone also indicate the influence of water on OH band and the cutting effects on amide I and mineral bands. Our results indicate that phosphate ion geometry appears less symmetric in its undisturbed state as detected by the PA-FTIR as compared to higher symmetry observed using transmission techniques on disturbed samples. Moreover, the PA-FTIR spectra indicate a band at 1747 cm(-1) possibly resulting from CO stretching of lipids, cholesterol esters, and triglycerides from the arteries. Comparison of the spectra in transverse and longitudinal cross-sections demonstrates that, the surface area of the longitudinal section bone appears to have more organic matrix exposed and with higher mineral stoichiometry.

Proteases involved in cartilage matrix degradation in osteoarthritis

Osteoarthritis is a common joint disease for which there are currently no disease-modifying drugs available. Degradation of the cartilage extracellular matrix is a central feature of the disease and is widely thought to be mediated by proteinases that degrade structural components of the matrix, primarily aggrecan and collagen. Studies on transgenic mice have confirmed the central role of Adamalysin with Thrombospondin Motifs 5 (ADAMTS-5) in aggrecan degradation, and the collagenolytic matrix metalloproteinase MMP-13 in collagen degradation. This review discusses recent advances in current understanding of the mechanisms regulating expression of these key enzymes, as well as reviewing the roles of other proteinases in cartilage destruction. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Impaired fracture healing in macrophage migration inhibitory factor-deficient mice

This study investigated the role of macrophage migration inhibitory factor (MIF) in fracture repair using MIF gene-deficient mice (MIF KO). Fracture healing was delayed in MIF KO, and this was mainly due to the delay in the mineralization of osteoid within the fracture callus.

INTRODUCTION

We previously reported that the expression of macrophage migration inhibitory factor (MIF) was up-regulated during the fracture healing process in rats. However, its role in the pathophysiology of this process remained unclear. The aim of the present study was to clarify the role of MIF in the fracture healing process using MIF gene-deficient mice (MIF KO).

METHODS

Bone repair in wild-type mice (WT) and MIF KO (n = 70, respectively) was investigated using a tibia fracture model. Radiographic, biomechanical, histological, bone histomorphometric, and molecular analyses were performed.

RESULTS

Post-fracture biomechanical testing showed that maximum load and stiffness were significantly lower in MIF KO than in WT on day 42. However, similar levels were observed between the two groups on day 84. Bone histomorphometric analysis revealed significantly higher osteoid volume, a lower mineral apposition rate, and smaller numbers of osteoclasts in the MIF KO callus compared to the WT callus. The messenger ribonucleic acid expressions of matrix metalloproteinase (MMP)-2, membranous type 1-MMP, cathepsin K, and tissue nonspecific alkaline phosphatase were found to be significantly suppressed in the MIF KO callus.

CONCLUSION

The results of the present study suggest that delayed fracture healing in MIF KO was mainly attributable to a delay in osteoid mineralization.

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

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia caused by the absence of active cathepsin K, which is a lysosomal cysteine protease that plays a role in degrading the organic matrix of bones, acting in bone resorption and bone remodeling. The disease is primarily characterized by osteosclerosis, bone fragility, short stature, acro-osteolysis, and delayed closure of the cranial sutures. A differing feature, cranial synostosis, has occasionally been described in this disorder. We reviewed six unrelated patients with pycnodysostosis (mean age of 10 years and 4 months) in order to evaluate the presence of craniosynostosis. In addition to the typical findings of the condition, they all presented premature fusion of the coronal suture. Although none of them showed signs of cranial hypertension, one patient had had the craniosynostosis surgically corrected previously. These data suggest that the cranial sutures in pycnodysostosis can display contradictory features: wide cranial sutures, which are commonly described, and craniosynostosis. The clinical impact of this latter finding still remains to be elucidated. Further studies are necessary to address more precisely the role of cathepsin K in suture patency.

Differentiation and mineralization of murine mesenchymal C3H10T1/2 cells in micromass culture

The murine mesenchymal cell line, C3H10T1/2 in micromass culture undergoes chondrogenic differentiation with the addition of BMP-2. This study compares the use of BMP-2 vs. insulin, transferrin, and sodium selenite (ITS) to create a chondrogenic micromass cell culture system that models cartilage calcification in the presence of 4mM inorganic phosphate. BMP-2 treated cultures showed more intense alcian blue staining for proteoglycans than ITS treated cultures at early time points. Both ITS and BMP-2 treated cultures showed similar mineral deposition in cultures treated with 4mM phosphate via von Kossa staining, however FTIR spectroscopy of cultures showed different matrix properties. ITS treated cultures produced matrix that more closely resembled mouse calcified cartilage by FTIR analysis. (45)Ca uptake curves showed delayed onset of mineralization in cultures treated with BMP-2, however they had an increased rate of mineralization (initial slope of (45)Ca uptake curve) when compared to the cultures treated with ITS. Immunohistochemistry showed the presence of both collagens type I and type II in BMP-2 and ITS treated control (1mM inorganic phosphate) and mineralizing cultures. BMP-2 treated mineralizing cultures displayed more intense staining for collagen type II than all other cultures. Collagen type X staining was detected at Day 9 only in mineralizing cultures treated with ITS. Western blotting of Day 9 cultures confirmed the presence of collagen type X in the mineralizing ITS cultures, and also showed very small amounts of collagen type X in BMP-2 treated cultures and control ITS cultures. By Day 16 all cultures stained positive for collagen type X. These data suggest that BMP-2 induces a more chondrogenic phenotype, while ITS treatment favors maturation and hypertrophy of the chondrocytes in the murine micromass cultures.

Potential role of cathepsin K in the pathophysiology of mucopolysaccharidoses

Cathepsin K, a papain-like cysteine protease, is highly expressed in osteoclasts and plays a critical role in bone resorption. Dysfunction of the enzyme leads to various skeletal abnormalities. The recent knowledge that the collagenolytic activity of cathepsin K depends on interactions with bone and cartilage-resident glycosaminoglycans (GAGs) may shed some light on diseases such as mucopolysaccharidoses (MPSs). MPSs are a group of lysosomal storage diseases characterized by the accumulation of GAGs in tissues including bone. Typical pathological features of these diseases include skeletal abnormalities such as dysostosis multiplex, short stature, and multiple irregularities in bone development. We describe how further investigation of the cathepsin K/GAG complexes could provide valuable insights into the bone pathology associated with MPS diseases. In this review, we discuss the inhibition of osteoclast function through altered activity of cathepsin K by GAGs and offer insight into a mechanism for the bone pathology seen in MPS patients.

Identification of NFAT binding sites that mediate stimulation of cathepsin K promoter activity by RANK ligand

The receptor activator of NFkappaB ligand (RANKL) is a critical mediator of osteoclastogenesis and regulates cathepsin K (CTSK) expression, which is essential for normal bone resorption. RANKL acts, in part, via the Ca(2+)/calmodulin/calcineurin signaling pathway, which in turn, activates NFATc1 (nuclear factor of activated T-cells) and downstream gene expression. We investigated the signals and promoter elements that regulate CTSK gene expression in RAW 264.7 cells, which can be differentiated to osteoclasts by RANKL. Disrupting Ca(2+) signaling, by blocking Ca(2+) channels, thus inhibiting calcineurin or chelation of intracellular Ca(2+), prevented the stimulation of CTSK expression by RANKL. Both RANKL treatment and overexpression of NFATc1 dramatically enhanced CTSK promoter activity, but not in an identical manner. NFATc1 regulates CTSK promoter activity, but the motifs have not been explicitly identified. We found that as few as 238 bp of the CTSK promoter were sufficient to elicit a marked response to both RANKL and NFATc1, truncations of the CTSK promoter illustrated differences in regional responsiveness. Transfection analysis of CTSK promoter-luciferase plasmids revealed that NFATc1 binding sites at 85, 289 and 345 bp upstream of the transcriptional start site mediated responses to RANKL and NFATc1. Deletion of a 4-bp core element from the site at -85 bp dramatically reduced the response of the CTSK promoter to both RANKL and NFATc1, whereas a similar deletion at -345 bp decreased NFATc1- but not RANKL-mediated responses. Mutation of the site at -289 bp did not affect NFAT-mediated stimulation of CTSK on its own, but did decrease responsiveness in combination with either or both of the other two deletions. Electrophoretic mobility shift assays demonstrated NFATc1 binding to oligonucleotides containing the -85-bp and -345-bp sites, while chromatin immunoprecipitation assays demonstrated enhanced in situ binding by NFATc1 to two analogous sites in the mouse CTSK promoter in response to RANKL treatment. Therefore, proximal NFAT binding sites play a significant role in the NFATc1-mediated stimulation of CTSK gene expression by RANKL.