Proteases and bone remodelling

Structural and functional properties of rBmTI-A: A Kunitz-BPTI serine protease inhibitor with therapeutical potential

Serine proteases are an important group of enzymes present in several organisms such as viruses, bacteria and eukaryotes involved in several physiological and pathological processes such as cancer, neurodegeneration, tissue inflammation and infections. Kunitz-type serine protease inhibitors have been studied as therapeutical targets with positive results in many of these diseases. rBmTI-A (recombinant B. microplus Trypsin Inhibitor A) is a Kunitz-BPTI type inhibitor based on the native protein BmTI-A. BmTI-A was extracted from tick larvae and presented inhibitory activity against trypsin, human plasma kallikrein (HuPK), human neutrophil elastase (HNE) and human plasmin. rBmTI-A presented the same inhibitory activities of the BmTI-A and its thermostability has already been demonstrated. In emphysema induced by porcine pancreatic elastase (PPE) and by cigarette smoke animal models, the treatment using rBmTI-A showed a protective effect against the development of pulmonary emphysema and prevented the increase of inflammatory cells. In chronic allergic animal model, rBmTI-A treatment resulted in attenuated bronchial hyperresponsiveness, inflammation, remodeling. These are important physiological results in emphysema and lung inflammatory animal models with rBmTI-A treatment confirming its therapeutical potential.

KYMASIN UP Natural Product Inhibits Osteoclastogenesis and Improves Osteoblast Activity by Modulating Src and p38 MAPK

The imbalance in osteoblast (OB)-dependent bone formation in favor of osteoclast (OC)-dependent bone resorption is the main cause of loss of tissue mineral mass during bone remodeling leading to osteoporosis conditions. Thus, the suppression of OC activity together with the improvement in the OB activity has been proposed as an effective therapy for maintaining bone mass during aging. We tested the new dietary product, KYMASIN UP containing standardized Withania somnifera, Silybum marianum and Trigonella foenum-graecum herbal extracts or the single extracts in in vitro models mimicking osteoclastogenesis (i.e., RAW 264.7 cells treated with RANKL, receptor activator of nuclear factor kappa-Β ligand) and OB differentiation (i.e., C2C12 myoblasts treated with BMP2, bone morphogenetic protein 2). We found that the dietary product reduces RANKL-dependent TRAP (tartrate-resistant acid phosphatase)-positive cells (i.e., OCs) formation and TRAP activity, and down-regulates osteoclastogenic markers by reducing Src (non-receptor tyrosine kinase) and p38 MAPK (mitogen-activated protein kinase) activation. Withania somnifera appears as the main extract responsible for the anti-osteoclastogenic effect of the product. Moreover, KYMASIN UP maintains a physiological release of the soluble decoy receptor for RANKL, OPG (osteoprotegerin), in osteoporotic conditions and increases calcium mineralization in C2C12-derived OBs. Interestingly, KYMASIN UP induces differentiation in human primary OB-like cells derived from osteoporotic subjects. Based on our results, KYMASIN UP or Withania somnifera-based dietary supplements might be suggested to reverse the age-related functional decline of bone tissue by re-balancing the activity of OBs and OCs, thus improving the quality of life in the elderly and reducing social and health-care costs.

Structure-guided protein engineering of human cathepsin L for efficient collagenolytic activity

Engineering precise substrate specificity of proteases advances the potential to use them in biotechnological and therapeutic applications. Collagen degradation, a physiological process mediated by collagenases, is an integral part of extracellular matrix remodeling and when uncontrolled, implicated in different pathological conditions. Lysosomal cathepsin-K cleaves triple helical collagen fiber, whereas cathepsin-L cannot do so. In this study, we have imparted collagenolytic property to cathepsin-L, by systematically engineering proline-specificity and glycosaminoglycans (GAG)-binding surface in the protease. The proline-specific mutant shows high specificity for prolyl-peptidic substrate but is incapable of cleaving collagen. Engineering a GAG-binding surface on the proline-specific mutant enabled it to degrade type-I collagen in the presence of chondroitin-4-sulfate (C4-S). We also present the crystal structures of proline-specific (1.4 Å) and collagen-specific (1.8 Å) mutants. Finally docking studies with prolyl-peptidic substrate (Ala-Gly-Pro-Arg-Ala) at the active site and a C4-S molecule at the GAG-binding site enable us to identify key structural features responsible for collagenolytic activity of cysteine cathepsins.

Pro-angiogenic and osteogenic composite scaffolds of fibrin, alginate and calcium phosphate for bone tissue engineering

Due to the limitations of bone autografts, we aimed to develop new composite biomaterials with pro-angiogenic and osteogenic properties to be used as scaffolds in bone tissue engineering applications. We used a porous, cross-linked and slowly biodegradable fibrin/alginate scaffold originally developed in our laboratory for wound healing, throughout which deposits of calcium phosphate (CaP) were evenly incorporated using an established biomimetic method. Material characterisation revealed the porous nature and confirmed the deposition of CaP precursor phases throughout the scaffolds. MC3T3-E1 cells adhered to the scaffolds, proliferated, migrated and differentiated down the osteogenic pathway during the culture period. Chick chorioallantoic membrane (CAM) assay results showed that the scaffolds were pro-angiogenic and biocompatible. The work presented here gave useful insights into the potential of these pro-angiogenic and osteogenic scaffolds for bone tissue engineering and merits further research in a pre-clinical model prior to its clinical translation.

The association between cystatin C and COPD: a meta-analysis and systematic review

BACKGROUND

In recent years, many studies have discovered that cystatin C (Cys C) may play an important role in respiratory diseases, especially in chronic obstructive pulmonary disease (COPD). However, the findings of these studies were inconsistent. This systematic review and meta-analysis aimed to assess the relationship between serum Cys C and COPD.

METHODS

We conducted a systematic literature search in PubMed, Embase, Web of Science, Wanfang databases, and the China National Knowledge Infrastructure. The standardized mean difference (SMD), Fisher's Z-value and 95% confidence interval (CI) were calculated to investigate the effect sizes. Subgroup analyses were performed on disease status, ethnicity, assay method, and study design. Sensitivity was performed, and publication bias was assessed.

RESULTS

A total of 15 studies, including 4079 COPD patients and 5949 controls, were included in this meta-analysis. The results showed that serum Cys C levels in patients with COPD were significantly higher than those in controls (SMD = 0.99, 95% CI =0.62-1.37, P < 0.001), especially in AECOPD (SMD = 1.59, 95% CI =1.05-2.13, P < 0.001), and there were statistically different among AECOPD and SCOPD (SMD = 0.35, 95% CI =0.10-0.59, P = 0.005). The serum Cys C levels were negatively correlated with FEV1%pre (Z = - 0.45, 95%CI = -0.58--0.32, P = 0.011) and FEV1/FVC (Z = - 0.32, 95%CI = -0.50--0.14, P = 0.006). The serum Cys C levels were independent of ethnicity, assay method, and study design.

CONCLUSION

Serum Cys C levels were associated with COPD and COPD exacerbation, and they were inversely correlated with FEV1%pre and FEV1/FVC.

Cystatin C regulates major histocompatibility complex-II-peptide presentation and extracellular signal-regulated kinase-dependent polarizing cytokine production by bone marrow-derived dendritic cells

Cystatin C is a ubiquitously expressed cysteine protease inhibitor that protects cells from either improper hydrolysis by endogenous proteases or pathogen growth/virulence by exogenous proteases. Although commonly used as a serum biomarker for evaluating renal function, cystatin C is associated with many immunological disorders under various pathophysiological conditions. How cystatin C affects immune cells, especially dendritic cells (DCs), however, is far from clear. In this study, we found that pharmacological treatment with or genetic overexpression of cystatin C in bone marrow-derived DCs (BMDCs) reduced their capacity to stimulate CD4⁺ T-cell proliferation, despite increased antigen uptake. This reduced capacity corresponded with reduced major histocompatibility complex-II presentation owing to diminished levels of the chaperon H2-DM in BMDCs. Instead of promoting proliferation, cystatin C promoted skewing of T cells toward proinflammatory T-helper (Th)1/Th17 differentiation. This was mediated by augmented extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase phosphorylation in BMDCs, leading to secretion of polarizing cytokines, which in turn led to the Th deviation. Collectively, our study explained the cellular and molecular basis of how this protease inhibitor can regulate immune responses, namely by affecting BMDCs and their cytokine pathway. Our results might open up an avenue for the development of therapeutic agents for the treatment of cystatin C-related immunological diseases.

Involvement of cystatin C in immunity and apoptosis

As an abundantly expressed cysteine protease inhibitor widely distributed in the organisms, cystatin C is involved in various physiological processes. Due to its relatively small molecular weight and easy detection, cystatin C is commonly used as a measure for glomerular filtration rate. In pathological conditions, however, growing evidences suggest that cystatin C is associated with various immune responses against either exogenous or endogenous antigens, which ultimately result in inflammatory autoimmune diseases or tumor development if not properly controlled. Thus the fluctuation of cystatin C levels might have more clinical implications than a reflection of kidney functions. Here, we summarize the latest development of studies on the pathophysiological functions of cystatin C, with focus on its immune regulatory roles at both cellular and molecular levels including antigen presentation, secretion of cytokines, synthesis of nitric oxide, as well as apoptosis. Finally, we discuss the clinical implications and therapeutic potentials of what this predominantly expressed protease inhibitor can bring to us.

Bone-specific poly(ethylene sodium phosphate)-bearing biodegradable nanoparticles

Chemotherapy is the most reliable treatment for osteoporosis and osseous metastases. To facilitate better drug delivery for bone treatments, a novel preparation of polymeric nanoparticles with high affinity to bone has been prepared. Two-step synthesis of cholesteryl-functionalized poly(ethylene sodium phosphate) (Ch-PEP_n·Na) was performed via ring-opening polymerization of cyclic phosphoesters and the demethylation. The molecular weight of Ch-PEP_n·Na could be well controlled by changing the ratio of cholesterol and cyclic phosphoesters. Because Ch-PEP_n·Na exhibits an amphiphilic nature in aqueous media, Ch-PEP_n·Na-bearing nanoparticles (PEP_n·Na NPs) were prepared by a solvent evaporation technique. The size of the nanoparticles investigated in the current study is approximately 100nm, which was determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to the presence of highly water-soluble polymer chains, dispersion of PEP_n·Na NPs in aqueous media was stable for at least 1 week. Hemolytic activity of PEP_n·Na NPs was found to be low and PEP_n·Na NPs did not disintegrate mammalian cell membranes. Additionally, cytotoxicity of PEP_n·Na NPs was not observed at concentrations below 100μg/mL. The adsorption of PEP_n·Na NPs on hydroxyapatite (HAp) microparticles was studied in comparison with poly(ethylene glycol) nanoparticles (PEG NPs). Both PEP_n·Na NPs and PEG NPs adsorbed well onto HAp microparticles in distilled water with binding equilibrium constants (K_HAp) for PEP_n·Na NPs and PEG NPs of 3.6×10⁶ and 7.9×10⁶, respectively. In contrast, only PEP_n·Na NPs adsorbed onto HAp microparticles in a saline phosphate buffer. Moreover, the adsorption of PEP_n·Na NPs onto HAp microparticles occurred even in the presence of 1.2mM calcium ions or low-pH media. The affinity of the nanoparticles to bovine bone slices was also studied, with the result that large quantities of adsorbed PEP_n·Na NPs were observed on the slices by scanning electron microscope.

RANK-RANKL signalling in cancer

Oncogenic events combined with a favourable environment are the two main factors in the oncological process. The tumour microenvironment is composed of a complex, interconnected network of protagonists, including soluble factors such as cytokines, extracellular matrix components, interacting with fibroblasts, endothelial cells, immune cells and various specific cell types depending on the location of the cancer cells (e.g. pulmonary epithelium, osteoblasts). This diversity defines specific "niches" (e.g. vascular, immune, bone niches) involved in tumour growth and the metastatic process. These actors communicate together by direct intercellular communications and/or in an autocrine/paracrine/endocrine manner involving cytokines and growth factors. Among these glycoproteins, RANKL (receptor activator nuclear factor-κB ligand) and its receptor RANK (receptor activator nuclear factor), members of the TNF and TNFR superfamilies, have stimulated the interest of the scientific community. RANK is frequently expressed by cancer cells in contrast with RANKL which is frequently detected in the tumour microenvironment and together they participate in every step in cancer development. Their activities are markedly regulated by osteoprotegerin (OPG, a soluble decoy receptor) and its ligands, and by LGR4, a membrane receptor able to bind RANKL. The aim of the present review is to provide an overview of the functional implication of the RANK/RANKL system in cancer development, and to underline the most recent clinical studies.

Over-expression of cathepsin B in hepatocellular carcinomas predicts poor prognosis of HCC patients

Background

Several studies have found that Cathepsin B (CTSB) is up-regulated in many tumor types and facilitates tumor progression. However, the role of CTSB in hepatocellular carcinoma (HCC) progression remains unclear. This study was aimed at investigating the expression and role of CTSB in HCC in a large set of samples and cell lines (MHCC-97H and MHCC-97 L), and evaluating the clinical and prognostic significance of CTSB protein in patients with HCC.

Methods

The expression of CTSB was examined in HCC tissue and cell lines by Western-blotting, Real-time PCR, and immunohistochemical staining. Wound healing assay and invasion assay were used to verify the effect of CTSB on the migration and invasion ability of HCC cell lines. Tumor formation assay in nude mice was used to analyze the effect of CTSB on the tumorigenicity of HCC cell lines.

Results

The status of CTSB protein in carcinoma tissues is much higher than that in paracarcinoma tissues. The overall survival of the patients with high CTSB expression was significantly shorter than the low CTSB expression group. High CTSB expression was significantly correlated with advanced clinical staging, histological grade, and tumor recurrence. In vitro and in vivo experiments demonstrated that over-expression of CTSB in MHCC-97 L cells promoted cell invasion and tumor progression ability. Down-regulation of CTSB in MHCC-97H showed the opposite effects. These phenotypic changes caused by CTSB knockdown or over-expression correlated with expression of the matrix metallopeptidase MMP-9. Moreover, multivariate analysis suggested that CTSB expression might be an independent prognostic indicator for the survival of HCC patients after curative surgery.

Conclusions

CTSB might be involved in the development and progression of HCC as an oncogene, and thereby may be a valuable prognostic marker for HCC patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-016-0503-9) contains supplementary material, which is available to authorized users.

Thrombin receptor deficiency leads to a high bone mass phenotype by decreasing the RANKL/OPG ratio

Thrombin and its receptor (TR) are, respectively, expressed in osteoclasts and osteoblasts. However, their physiological roles on bone metabolism have not been fully elucidated. Here we investigated the bone microarchitecture by micro-computed tomography (μCT) and demonstrated increased trabecular and cortical bone mass in femurs of TR KO mice compared to WT littermates. Trabecular thickness and connectivity were significantly enhanced. The physiological role of TR on both inorganic and organic phases of bone is illustrated by a significant increase in BMD and a decrease in urinary deoxypyridinoline (DPD) crosslink concentration in TR KO mice. Moreover, TR KO cortical bone expanded and had a higher polar moment of inertia (J), implying stronger bone. Bone histomorphometry illustrated unaltered osteoblast and osteoclast number and surface in femoral metaphyses, indicating that thrombin/TR regulates osteoblasts and osteoclasts at functional levels. Serum analysis showed a decrease in RANKL and an increase in osteoprotegerin (OPG) levels and reflected a reduced RANKL/OPG ratio in the TR KO group. In vitro experiments using MC3T3 pre-osteoblasts demonstrated a TR-dependent stimulatory effect of thrombin on the RANKL/OPG ratio. This effect was blocked by TR antagonist and p42/p44-ERK inhibitor. In addition, thrombin also intensified p42/p44-ERK expression and phosphorylation. In conclusion, the thrombin/TR system maintains normal bone remodeling by activating RANKL and limiting OPG synthesis by osteoblasts through the p42/44-ERK signaling pathway. Consequently, TR deficiency inhibits osteoclastogenesis, resulting in a high bone mass phenotype.

Bone-targeted acid-sensitive doxorubicin conjugate micelles as potential osteosarcoma therapeutics

Osteosarcoma is a malignancy of the bone that primarily affects adolescents. Current treatments retain mortality rates, which are higher than average cancer mortality rates for the adolescent age group. We designed a micellar delivery system with the aim to increase drug accumulation in the tumor and potentially reduce side effects associated with chemotherapy. The design features are the use of the hydrophilic D-aspartic acid octapeptide as both the effective targeting agent as well as the hydrophilic micelle corona. Micelle stabilization was accomplished by binding of model drug (doxorubicin) via an acid-sensitive hydrazone bond and incorporating one to four 11-aminoundecanoic acid (AUA) moieties to manipulate the hydrophobic/hydrophilic ratio. Four micelle-forming unimers have been synthesized and their self-assembly into micelles was evaluated. Size of the micelles could be modified by changing the architecture of the unimers from linear to branched. The stability of the micelles increased with increasing content of AUA moieties. Adsorption of all micelles to hydroxyapatite occurred rapidly. Doxorubicin release occurred at pH 5.5, whereas no release was detected at pH 7.4. Cytotoxicity toward human osteosarcoma Saos-2 cells correlated with drug release data.

Cathepsin B: multiple roles in cancer

Proteases, including intracellular proteases, play roles at many different stages of malignant progression. Our focus here is cathepsin B, a lysosomal cysteine cathepsin. High levels of cathepsin B are found in a wide variety of human cancers, levels that often induce secretion and association of cathepsin B with the tumor cell membrane. In experimental models, such as transgenic models of murine pancreatic and mammary carcinomas, causal roles for cathepsin B have been demonstrated in initiation, growth/tumor cell proliferation, angiogenesis, invasion, and metastasis. Tumor growth in transgenic models is promoted by cathepsin B in tumor-associated cells, for example, tumor-associated macrophages, as well as in tumor cells. In transgenic models, the absence of cathepsin B has been associated with enhanced apoptosis, yet cathepsin B also has been shown to contribute to apoptosis. Cathepsin B is part of a proteolytic pathway identified in xenograft models of human glioma; targeting only cathepsin B in these tumors is less effective than targeting cathepsin B in combination with other proteases or protease receptors. Understanding the mechanisms responsible for increased expression of cathepsin B in tumors and association of cathepsin B with tumor cell membranes is needed to determine whether targeting cathepsin B could be of therapeutic benefit.

Cathepsin K is present in invasive oral tongue squamous cell carcinoma in vivo and in vitro

Objectives

Cathepsin K, a lysosomal cysteine protease, is expressed in the tumor microenvironment (TME) of skin carcinoma, but nothing is known about cathepsin K in oral tongue squamous cell carcinoma (OTSCC). Our aim was to describe the expression of cathepsin K in invasive OTSCC in vitro and in a series of clinical cancer specimens.

Materials and Methods

OTSCC invasion in vitro was studied using invasive HSC-3 tongue carcinoma cells in 3D organotypic models. In total, 121 mobile tongue OTSCCs and 10 lymph node metastases were analyzed for cathepsin K expression. The association between cathepsin K expression and clinicopathological factors was evaluated.

Results

Cysteine protease inhibitor E64 and cathepsin K silencing significantly (p<0.0001) reduced HSC-3 cell invasion in the 3D models. Cathepsin K was expressed in a majority of carcinoma and metastatic cells, but the expression pattern in carcinoma cells did not correlate with clinical parameters. Instead, the weak expression of cathepsin K in the invasive TME front correlated with increased overall recurrence (p<0.05), and in early-stage tumors this pattern predicted both cancer recurrence and cancer-specific mortality (p<0.05 and p<0.005, respectively).

Conclusions

Cathepsin K is expressed in OTSCC tissue in both carcinoma and TME cells. Although the diminished activity and expression in aggressive tongue HSC-3 cells reduced 3D invasion in vitro, the amount of cathepsin K in carcinoma cells was not associated with the outcome of cancer patients. Instead, cathepsin K in the invasive TME front seems to have a protective role in the complex progression of tongue cancer.

Osteoprotegerin: multiple partners for multiple functions

Osteoprotegerin (OPG) is an essential secreted protein in bone turnover due to its role as a decoy receptor for the Receptor Activator of Nuclear Factor-kB ligand (RANKL) in the osteoclasts, thus inhibiting their differentiation. However, there are additional ligands of OPG that confer various biological functions. OPG can promote cell survival, cell proliferation and facilitates migration by binding TNF-related apoptosis inducing ligand (TRAIL), glycosaminoglycans or proteoglycans. A large number of in vitro, pre-clinical and clinical studies provide evidences of OPG involvement in vascular, bone, immune and tumor biology. This review describes an overview of the different OPG ligands regulating its biological functions.

Immunohistochemical expression of MMP-9 and VEGF in squamous cell carcinoma of the tongue

Squamous cell carcinomas (SCCs) account for approximately 95% of all oral malignant neoplasms and for about 38% of all malignant head and neck tumors, especially affecting the tongue and lips. The aim of this study was to evaluate the immunohistochemical expression of MMP-9 and VEGF in oral SCC according to the occurrence of metastasis. Eighteen cases of tongue SCC without metastases and 17 cases of tongue SCC with metastases were subjected to immunohistochemical methods. High immunohistochemical expression of MMP-9 and VEGF by neoplastic cells and stroma was observed in tongue SCCs at the invasion front. Metastatic tumors tended to express higher levels of MMP-9 and VEGF than non-metastatic tumors, but the difference was not significant (P > 0.05). Spearman's correlation test showed no significant correlation between VEGF-immunopositive vessels and metastasis (P > 0.05). The present results demonstrate the importance of the expression of MMP-9 and VEGF for the development of SCC of the tongue. However, no significant association was observed between the overexpression of MMP-9 or VEGF and the presence of metastases.

Breast tumor-associated osteoblast-derived CXCL5 increases cancer progression by ERK/MSK1/Elk-1/snail signaling pathway

The skeleton is the most common metastatic site for breast cancer, with bone metastasis causing pain as well as risk of pathological fractures. Interaction between tumors and the bone microenvironment creates a vicious cycle that accelerates both bone destruction and cancer progression. This study is the first to analyze the soluble factors secreted by breast tumor-associated osteoblasts (TAOBs), which are responsible for promoting cancer progression. The addition of CXCL5 (chemokine (C-X-C motif) ligand 5), present in large amounts in TAOB-condition medium (TAOB-CM), mimicked the inductive effect of TAOB-CM on breast cancer epithelial-mesenchymal transition, migration and invasion. In contrast, inhibition of CXCL5 in OBs decreased TAOB-mediated cancer progression. Inducement of MCF-7 and MDA-MB-231 cancer progression by TAOB-derived CXCL5 is associated with increased Raf/MEK/ERK activation, and mitogen- and stress-activated protein kinase 1 (MSK1) and Elk-1 phosphorylation, as well as Snail upregulation. Activation of Elk-1 facilitates recruitment of phosphorylated MSK1, which in turn enhances histone H3 acetylation and phosphorylation (serine 10) of Snail promoter, resulting in Snail enhancement and E-cadherin downregulation. Moreover, mice treated with anti-CXCL5 antibodies showed decreased metastasis of 4T1 breast cancer cells. Our study suggests that inhibition of CXCL5-mediated ERK/Snail signaling is an attractive therapeutic target for treating metastases in breast cancer patients.

Targeting polymer therapeutics to bone

An aging population in the developing world has led to an increase in musculoskeletal diseases such as osteoporosis and bone metastases. Left untreated many bone diseases cause debilitating pain and in the case of cancer, death. Many potential drugs are effective in treating diseases but result in side effects preventing their efficacy in the clinic. Bone, however, provides a unique environment of inorganic solids, which can be exploited in order to effectively target drugs to diseased tissue. By integration of bone targeting moieties to drug-carrying water-soluble polymers, the payload to diseased area can be increased while side effects decreased. The realization of clinically relevant bone targeted polymer therapeutics depends on (1) understanding bone targeting moiety interactions, (2) development of controlled drug delivery systems, as well as (3) understanding drug interactions. The latter makes it possible to develop bone targeted synergistic drug delivery systems.

Cathepsin K-Cre causes unexpected germline deletion of genes in mice

Osteoclasts are terminally differentiated cells that attach to bone and secrete proteases to degrade the bone matrix. The primary protease responsible for the degradation of the organic component of the bone matrix is Cathepsin K, which was largely thought to be unique to osteoclasts. Given its apparent selective expression in osteoclasts, the Cathepsin K promoter has been engineered to drive the expression of Cre recombinase in mice and has been the most relevant tool for generating osteoclast-specific gene loss. In an effort to understand the role of the ARF tumor suppressor in osteoclasts, we crossed Arf ^fl/fl mice to Ctsk^Cre/+ mice, which unexpectedly resulted in the germline loss of Arf. We subsequently confirmed Cre activity in gametes by generating Ctsk^Cre/+; Rosa⁺ mice. These results raise significant concerns regarding in vivo bone phenotypes created using Ctsk^Cre/+ mice and warrant further investigation into the role of Cathepsin K in gametes as well as alternative tools for studying osteoclast-specific gene loss in vivo.

Molecular pathways involved in crosstalk between cancer cells, osteoblasts and osteoclasts in the invasion of bone by oral squamous cell carcinoma

AIMS

This study investigates whether matrix metalloproteinases (MMPs), specifically MMP-2 and MMP-9, interacting with other molecules important in osteoblast differentiation and osteoclastogenesis, could play important roles in the invasion of bone by oral squamous cell carcinoma (OSCC).

METHODS

Supernatant (conditioned medium, CM) was collected from OSCC cell lines (SCC15 and SCC25), and from cultured osteoblasts (hFOB cell line and a primary culture, OB), and used for indirect co-culture: OSCC cells were treated with CM from osteoblasts and vice versa. Zymogenic activities of MMP-2 and -9, and protein quantities of all molecules studied, were detected by gelatine zymography and Western blotting, respectively. Real-time polymerase chain reaction (PCR) analysed mRNA of these molecules. Targeted molecules were examined by immunohistochemistry in tissue sections of bone-invasive OSCCs.

RESULTS

Zymogenic activities of both MMPs were increased in OSCC cells following culture with CM from hFOB: Twist1 protein expression was increased while Runx2 did not alter. The RANKL/OPG ratio, zymogen and protein expression of MMP-9 were increased in hFOB cells cultured with CM from OSCC lines, while zymogen expression of MMP-2 was decreased. Real-time PCR showed generally similar changes in expression of these molecules. All targeted molecules were expressed in invading malignant keratinocytes, and all but OPG were expressed in osteoclasts of clinical samples.

CONCLUSIONS

Crosstalk between different cell types appears to exist in the invasion of bone by OSCC. Understanding and ultimately interfering with the molecules involved may provide therapeutic approaches to inhibit such bone invasion.

Cathepsins D and L reduce the toxicity of advanced glycation end products

Advanced glycation end product-modified proteins are known for accumulating during aging and in several pathological conditions such as diabetes, renal failure, and neurodegenerative disorders. There is little information about the intracellular fate of endocytosed advanced glycation end products (AGEs) and their influence on proteolytic systems. However, it is known that the lysosomal system is impaired during aging. Therefore, undegraded material may accumulate and play a considerable role in the development of diverse diseases. To investigate if AGEs can be degraded and to test whether they accumulate because of impaired lysosomal proteases we studied the effects of advanced glycation end products on the endosomal-lysosomal system. Five different types of AGEs were generated by bovine serum albumin incubation with glyoxal, methylglyoxal, glucose, fructose, and ribose. The first experiments revealed the uptake of AGEs by the macrophage cell line RAW 264.7. Further investigations demonstrated an increase in cathepsin D and L activity and an increase in mature cathepsins D and L. Increased activities were accompanied by the presence of more lysosomes, measured by staining with LysoTracker blue. To specify the roles of cathepsins D and L we used knockout cells to test the roles of both cathepsins on the toxicity of advanced glycation end products. In summary we conclude that both cathepsins are required for a reduction in advanced glycation end product-induced cytotoxicity.

Molecular alterations associated with osteosarcoma development

Osteosarcoma is the most frequent malignant primary bone tumor characterized by a high potency to form lung metastases which is the main cause of death. Unfortunately, the conventional chemotherapy is not fully effective on osteosarcoma metastases. The progression of a primary tumor to metastasis requires multiple processes, which are neovascularization, proliferation, invasion, survival in the bloodstream, apoptosis resistance, arrest at a distant organ, and outgrowth in secondary sites. Consequently, recent studies have revealed new insights into the molecular mechanisms of metastasis development. The understanding of the mechanism of molecular alterations can provide the identification of novel therapeutic targets and/or prognostic markers for osteosarcoma treatment to improve the clinical outcome.

Proteoglycans and osteolysis

Osteolysis is a complex mechanism resulting from an exacerbated activity of osteoclasts associated or not with a dysregulation of osteoblast metabolism leading to bone loss. This bone defect is not compensated by bone apposition or by apposition of bone matrix with poor mechanical quality. Osteolytic process is regulated by mechanical constraints, by polypeptides including cytokines and hormones, and by extracellular matrix components such as proteoglycans (PGs) and glycosaminoglycans (GAGs). Several studies revealed that GAGs may influence osteoclastogenesis, but data are very controversial: some studies showed a repressive effect of GAGs on osteoclastic differentiation, whereas others described a stimulatory effect. The controversy also affects osteoblasts which appear sometimes inhibited by polysaccharides and sometimes stimulated by these compounds. Furthermore, long-term treatment with heparin leads to the development of osteoporosis fueling the controversy. After a brief description of the principal osteoclastogenesis assays, the present chapter summarizes the main data published on the effect of PGs/GAGs on bone cells and their functional incidence on osteolysis.

Modulatory effects of proteoglycans on proteinase activities

Proteoglycans (PGs), composed of a core protein and one or more covalently attached sulfated glycosaminoglycan (GAG) chains, interact with a wide range of bioactive molecules, such as growth factors and chemokines, to regulate cell behaviors in normal and pathological processes. Additionally, PGs, through their compositional diversity, play a broad variety of roles as modulators of proteinase activities. Interactions of proteinases with other molecules on the plasma membrane anchor and activate them at a specific location on the cell surface. These interactions with macromolecules other than their own protein substrates or inhibitors result in changes in their activity and/or may have important biological effects. Thus, GAG chains induce conformational changes upon their binding to peptides or proteins. This behavior may be related to the ability of GAGs to act as modulators for some proteins (1) by acting as crucial structural elements by the control of proteinase activities, (2) by increasing the protein stability, (3) by permitting some binding to occur, exposing binding regions on the target protein, or (4) by acting as coreceptors for some inhibitors, playing important roles for the acceleration of proteinase inhibition. Understanding the modulatory effects exerted by PGs on proteinase activities is expected to lead to new insights in the understanding of some molecular systems present in pathological states, providing new targets for drug therapy.

Differential gene expression from microarray analysis distinguishes woven and lamellar bone formation in the rat ulna following mechanical loading

Formation of woven and lamellar bone in the adult skeleton can be induced through mechanical loading. Although much is known about the morphological appearance and structural properties of the newly formed bone, the molecular responses to loading are still not well understood. The objective of our study was to use a microarray to distinguish the molecular responses between woven and lamellar bone formation induced through mechanical loading. Rat forelimb loading was completed in a single bout to induce the formation of woven bone (WBF loading) or lamellar bone (LBF loading). A set of normal (non-loaded) rats were used as controls. Microarrays were performed at three timepoints after loading: 1 hr, 1 day and 3 days. Confirmation of microarray results was done for a select group of genes using quantitative real-time PCR (qRT-PCR). The micorarray identified numerous genes and pathways that were differentially regulated for woven, but not lamellar bone formation. Few changes in gene expression were evident comparing lamellar bone formation to normal controls. A total of 395 genes were differentially expressed between formation of woven and lamellar bone 1 hr after loading, while 5883 and 5974 genes were differentially expressed on days 1 and 3, respectively. Results suggest that not only are the levels of expression different for each type of bone formation, but that distinct pathways are activated only for woven bone formation. A strong early inflammatory response preceded an increase in angiogenic and osteogenic gene expression for woven bone formation. Furthermore, at later timepoints there was evidence of bone resorption after WBF loading. In summary, the vast coverage of the microarray offers a comprehensive characterization of the early differences in expression between woven and lamellar bone formation.

Lung tumor-associated osteoblast-derived bone morphogenetic protein-2 increased epithelial-to-mesenchymal transition of cancer by Runx2/Snail signaling pathway

Bone is a frequent target of lung cancer metastasis and is associated with significant morbidity and a dismal prognosis. Interaction between cancer cells and the bone microenvironment causes a vicious cycle of tumor progression and bone destruction. This study analyzed the soluble factors secreted by lung tumor-associated osteoblast (TAOB), which are responsible for increasing cancer progression. The addition of bone morphogenetic protein-2 (BMP-2), present in large amounts in TAOB conditioned medium (TAOB-CM) and lung cancer patient sera, mimicked the inductive effect of TAOB-CM on lung cancer migration, invasion, and epithelial-to-mesenchymal transition. In contrast, inhibition of BMP by noggin decreases the inductive properties of TAOB-CM and lung cancer patient sera on cancer progression. Induction of lung cancer migration by BMP-2 is associated with increased ERK and p38 activation and the up-regulation of Runx2 and Snail. Blocking ERK and p38 by a specific inhibitor significantly decreases cancer cell migration by inhibiting Runx2 up-regulation and subsequently attenuating the expression of Snail. Enhancement of Runx2 facilitates Rux2 to recruit p300, which in turn enhances histone acetylation, increases Snail expression, and decreases E-cadherin. Furthermore, inhibiting Runx2 by siRNA also suppresses BMP-2-induced Snail up-regulation and cell migration. Our findings provide novel evidence that inhibition of BMP-2 or BMP-2-mediated MAPK/Runx2/Snail signaling is an attractive therapeutic target for osteolytic bone metastases in lung cancer patients.

Growth factor and protease expression during different phases of healing after rabbit deep flexor tendon repair

The purpose of the study was to contribute to the mapping of molecular events during flexor tendon healing, in particular the growth factors insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF) and nerve growth factor (NGF), matrix metalloproteinases (MMP-3 and MMP-13) and their inhibitors (tissue inhibitors of metalloproteinases, TIMP-1 and TIMP-3, and the protease cathepsin K. In a rabbit model of flexor tendon injury, the mRNA expression for the growth factors, MMPs and TIMPs were measured in tendon and tendon sheath tissue at several time points (3, 6, 21, and 42 days) representing different phases of the healing process. We found that MMP-13 remained increased during the study period, whereas MMP-3 returned to normal levels within the first week after injury. TIMP-3 was down-regulated in the tendon sheaths. Cathepsin K was up-regulated in tendons and sheaths after injury. NGF was present in both tendons and sheaths, but unaltered. IGF-1 exhibited a late increase in the tendons, while VEGF was down-regulated at the later time points. In conclusion, we have demonstrated the presence of NGF in flexor tendons. MMP-13 expression appears to play a more protracted role in flexor tendon healing than MMP-3. The relatively low levels of endogenous IGF-1 and VEGF mRNA following injury support their potential beneficial role as exogenous modulators to optimize tendon healing and strength without increasing adhesion formation.

Impaired turnover of autophagolysosomes in cathepsin L deficiency

Some of the phenotypes of mice deficient for the lysosomal cysteine endopeptidase cathepsin L (Ctsl) are characterized by large dysmorphic vesicles in the cytoplasm. Specifically, the heart (dilative cardiomyopathy), the thyroid (impaired thyroglobulin processing) and keratinocytes (periodic hair loss and epidermal hyperproliferation) are affected. We hypothesized that the formation of aberrant vesicles is owing to defects in macroautophagy. Therefore, primary mouse embryonic fibroblasts (MEF), which were derived from Ctsl(-/-) animals crossed with mice transgenic for the autophagy marker GFP-LC3, were investigated. Ctsl(-/-) MEF show increased number and size of vesicular structures belonging to the 'acidic' cellular compartment and are also characterized by GFP-LC3. Induction of autophagy by nutrient starvation or rapamycin treatment showed no significant impairment of the initiation of autophagy, the formation of autophagosomes or autophagosome-lysosome fusion in Ctsl(-/-) MEF, but co-localization of GFP-LC3 and Lamp1 revealed unusually large autophagolysosomes filled with Lamp1. Furthermore, the soluble lysosomal enzyme cathepsin D was elevated in Ctsl(-/-) MEF. Thus, degradation of autophagolysosomal content is impaired in the absence of Ctsl. This could slow the turnover of autophagolysosomes and result in accumulation of the dysmorphic and 'acidic' vesicles that were previously described in the context of the pathological phenotypes of Ctsl(-/-) mice.

Effect of stress on mRNA expression of H+-ATPase in osteoclasts

This study was designed to investigate the effect of various strengths and action times of flow stress on mRNA expression of H+-ATPase in osteoclasts. Osteoclasts were obtained through a classical mechanical-anatomical technique. They were identified by their morphology, tartrate-resistant acid phosphatase (TRAP) staining, and by a test of their ability to form resorption lacunae. Osteoclasts were mechanically loaded by flow stress using a cell-loading system. The stress-loading experiments were divided into various strength groups and action time groups. The morphological changes of osteoclasts after application of loading stress were analyzed using an image analysis system and Image-Pro Plus software. Expression of H+-ATPase mRNA in osteoclasts was detected by real-time fluorescent quantitative polymerase chain reaction. The existence of significant differences between experimental groups was analyzed using SPSS 12.0 software. The cytoplasm of osteoclasts with positive TRAP staining appeared with a characteristic claret-red color. Cells were able to form resorption pits in the surface of dentine slices. Morphological changes of osteoclasts with applied stress assumed an early increasing tendency before reaching a peak value and following a decreasing tendency. A significant difference of H+-ATPase mRNA expression of osteoclasts was seen between any two groups (P < 0.05). H+-ATPase mRNA expression in osteoclasts had a tendency to first increase with increasing stress and was observed to then decrease in one action time group. In this present study, a close relationship between the stress and mRNA expression of H+-ATPase in osteoclasts was observed.

Safety concern between autologous fat graft, mesenchymal stem cell and osteosarcoma recurrence

BACKGROUND

Osteosarcoma is the most common malignant primary bone tumour in young adult treated by neo adjuvant chemotherapy, surgical tumor removal and adjuvant multidrug chemotherapy. For correction of soft tissue defect consecutive to surgery and/or tumor treatment, autologous fat graft has been proposed in plastic and reconstructive surgery.

PRINCIPAL FINDINGS

We report here a case of a late local recurrence of osteosarcoma which occurred 13 years after the initial pathology and 18 months after a lipofilling procedure. Because such recurrence was highly unexpected, we investigated the possible relationship of tumor growth with fat injections and with mesenchymal stem/stromal cell like cells which are largely found in fatty tissue. Results obtained in osteosarcoma pre-clinical models show that fat grafts or progenitor cells promoted tumor growth.

SIGNIFICANCE

These observations and results raise the question of whether autologous fat grafting is a safe reconstructive procedure in a known post neoplasic context.