Proteinase-activated receptor-2 is required for normal osteoblast and osteoclast differentiation during skeletal growth and repair

Rivaroxaban attenuates neutrophil maturation in the bone marrow niche

Pharmacological inhibition of factor Xa by rivaroxaban has been shown to mediate cardioprotection and is frequently used in patients with, e.g., atrial fibrillation. Rivaroxaban's anti-inflammatory actions are well known, but the underlying mechanisms are still incompletely understood. To date, no study has focused on the effects of rivaroxaban on the bone marrow (BM), despite growing evidence that the BM and its activation are of major importance in the development/progression of cardiovascular disease. Thus, we examined the impact of rivaroxaban on BM composition under homeostatic conditions and in response to a major cardiovascular event. Rivaroxaban treatment of mice for 7 days markedly diminished mature leukocytes in the BM. While apoptosis of BM-derived mature myeloid leukocytes was unaffected, lineage-negative BM cells exhibited a differentiation arrest at the level of granulocyte-monocyte progenitors, specifically affecting neutrophil maturation via downregulation of the transcription factors Spi1 and Csfr1. To assess whether this persists also in situations of increased leukocyte demand, mice were subjected to cardiac ischemia/reperfusion injury (I/R): 7 d pretreatment with rivaroxaban led to reduced cardiac inflammation 72 h after I/R and lowered circulating leukocyte numbers. However, BM myelopoiesis showed a rescue of the leukocyte differentiation arrest, indicating that rivaroxaban's inhibitory effects are restricted to homeostatic conditions and are mainly abolished during emergency hematopoiesis. In translation, ST-elevation MI patients treated with rivaroxaban also exhibited reduced circulating leukocyte numbers. In conclusion, we demonstrate that rivaroxaban attenuates neutrophil maturation in the BM, which may offer a therapeutic option to limit overshooting of the immune response after I/R.

Protease-activated receptor-2 dependent and independent responses of bone cells to prostate cancer cell secretory products

BACKGROUND

Metastatic prostate cancer lesions in the skeleton are frequently characterized by excessive formation of bone. Prostate cancer cells secrete factors, including serine proteases, that are capable of influencing the behavior of surrounding cells. Some of these proteases activate protease-activated receptor-2 (PAR₂ ), which is expressed by osteoblasts (bone-forming cells) and precursors of osteoclasts (bone-resorbing cells). The aim of the current study was to investigate a possible role for PAR₂ in regulating the behavior of bone cells exposed to metastatic prostate cancer cells.

METHODS

The effect of medium conditioned by the PC3, DU145, and MDA-PCa-2b prostate cancer cell lines was investigated in assays of bone cell function using cells isolated from wildtype and PAR₂ -null mice. Osteoclast differentiation was assessed by counting tartrate-resistant acid phosphatase-positive multinucleate cells in bone marrow cultured in osteoclastogenic medium. Osteoblasts were isolated from calvariae of neonatal mice, and BrdU incorporation was used to assess their proliferation. Assays of alkaline phosphatase activity and quantitative PCR analysis of osteoblastic gene expression were used to assess osteoblast differentiation. Responses of osteoblasts to medium conditioned by MDA-PCa-2b cells were analyzed by RNAseq.

RESULTS

Conditioned medium (CM) from all three cell lines inhibited osteoclast differentiation independently of PAR₂ . Media from PC3 and DU145 cells had no effect on assays of osteoblast function. Medium conditioned by MDA-PCa-2b cells stimulated BrdU incorporation in both wildtype and PAR₂ -null osteoblasts but increased alkaline phosphatase activity and Runx2 and Col1a1 expression in wildtype but not PAR₂ -null cells. Functional enrichment analysis of RNAseq data identified enrichment of multiple gene ontology terms associated with lysosomal function in both wildtype and PAR₂ -null cells in response to MDA-PCa-2b-CM. Analysis of individual genes identified osteogenesis-associated genes that were either upregulated by MDA-PCa-2b-CM selectively in wildtype cells or downregulated selectively in PAR₂ -null cells.

CONCLUSIONS

Factors secreted by prostate cancer cells influence bone cell behavior through both PAR₂ -dependent and -independent mechanisms. Both PAR₂ -independent suppression of osteoclast differentiation and PAR₂ -dependent stimulation of osteogenesis are likely to determine the nature of prostate cancer metastases in bone.

Macrophage-Osteoclast Associations: Origin, Polarization, and Subgroups

Cellular associations in the bone microenvironment are involved in modulating the balance between bone remodeling and resorption, which is necessary for maintaining a normal bone morphology. Macrophages and osteoclasts are both vital components of the bone marrow. Macrophages can interact with osteoclasts and regulate bone metabolism by secreting a variety of cytokines, which make a significant contribution to the associations. Although, recent studies have fully explored either macrophages or osteoclasts, indicating the significance of these two types of cells. However, it is of high importance to report the latest discoveries on the relationships between these two myeloid-derived cells in the field of osteoimmunology. Therefore, this paper reviews this topic from three novel aspects of the origin, polarization, and subgroups based on the previous work, to provide a reference for future research and treatment of bone-related diseases.

Protease-activated receptor-2 promotes osteogenesis in skeletal mesenchymal stem cells at the expense of adipogenesis: Involvement of interleukin-6

Bone marrow mesenchymal stem cells (MSCs) give rise to osteoblasts and adipocytes, with an inverse relationship between the two. The MSCs from protease-activated receptor-2 knockout (PAR2 KO) mice have a reduced capacity to generate osteoblasts. Here we describe the observation that PAR2 KO osteoblastic cultures generate more adipocytes than wildtype (WT) cultures. Osteoblasts from PAR2 KO mice expressed lower levels of osteoblastic genes (Runx2, Col1a1 and Bglap), and higher levels of the adipocytic gene Pparg than WT osteoblasts. Bone marrow stromal cells from PAR2 KO mice generated fewer osteoblastic colonies (assessed by staining for alkaline phosphatase activity and mineral deposition) and more adipocytic (Oil Red-O positive) colonies than cultures from WT mice. Similarly, cultures of the bone marrow stromal cell line (Kusa 4b10) in which PAR2 was knocked down (F2rl1 KD), were less osteoblastic and more adipocytic than vector control cells. Putative regulators of PAR2-mediated osteogenesis and suppression of adipogenesis were identified in an RNA-sequencing (RNA-seq) investigation; these include C1qtnf3, Gpr35, Grem1, Snorc and Tcea3, which were more highly expressed, and Cnr1, Enpep, Hmgn5, Il6 and Ramp3 which were expressed at lower levels, in control than in F2rl1 KD cells. Interleukin-6 (IL-6) levels were higher in medium harvested from F2rl1 KD cells than from control cells, and a neutralising anti-IL-6 antibody reduced the number of adipocytes in F2rl1 KD cultures to that of control cultures. Thus, PAR2 appears to be a mediator of the reciprocal relationship between osteogenesis and adipogenesis, with IL-6 having a regulatory role in these PAR2-mediated effects.

Protease Activated Receptors and Arthritis

The catabolic and destructive activity of serine proteases in arthritic joints is well known; however, these enzymes can also signal pain and inflammation in joints. For example, thrombin, trypsin, tryptase, and neutrophil elastase cleave the extracellular N-terminus of a family of G protein-coupled receptors and the remaining tethered ligand sequence then binds to the same receptor to initiate a series of molecular signalling processes. These protease activated receptors (PARs) pervade multiple tissues and cells throughout joints where they have the potential to regulate joint homeostasis. Overall, joint PARs contribute to pain, inflammation, and structural integrity by altering vascular reactivity, nociceptor sensitivity, and tissue remodelling. This review highlights the therapeutic potential of targeting PARs to alleviate the pain and destructive nature of elevated proteases in various arthritic conditions.

FVIII at the crossroad of coagulation, bone and immune biology: Emerging evidence of biological activities beyond hemostasis

Hemophilia A is an X-linked hereditary disorder that results from deficient coagulation factor VIII (FVIII) activity, leading to spontaneous bleeding episodes, particularly in joints and muscles. FVIII deficiency has been associated with altered bone remodeling, dysregulated macrophage polarization, and inflammatory processes that are associated with the neoformation of abnormal blood vessels. Treatment based on FVIII replacement can lead to the development of inhibitors that render FVIII concentrate infusion ineffective. In this context, hemophilia has entered a new therapeutic era with the development of new drugs, such as emicizumab, that seek to restore the hemostatic balance by bypassing pathologically acquired antibodies. We discuss the potential extrahemostatic functions of FVIII that may be crucial for defining future therapies in hemophilia.

PAR2 Deficiency Induces Mitochondrial ROS Generation and Dysfunctions, Leading to the Inhibition of Adipocyte Differentiation

Protease-activated receptor 2 (PAR2) is a member of G-protein-coupled receptors and affects ligand-modulated calcium signaling. Although PAR2 signaling promotes obesity and adipose tissue inflammation in high fat- (HF-) fed conditions, its role in adipocyte differentiation under nonobesogenic conditions needs to be elucidated. Here, we used several tissues and primary-cultured adipocytes of mice lacking PAR2 to study its role in the development of adipose tissues. C57BL/6J mice with PAR2 deficiency exhibited a mild lipodystrophy-like phenotype in a chow diet-fed condition. When adipocyte differentiation was examined using primary-cultured preadipocytes, PAR2 deficiency led to a notable decrease in adipocyte differentiation and related protein expression, and PAR2 agonist treatment elevated adipocyte differentiation. Regarding the mechanism, PAR2-deficient preadipocytes exhibited impaired mitochondrial energy consumption. Further studies indicated that calcium-related signaling pathways for mitochondrial biogenesis are disrupted in the adipose tissues of PAR2-deficient mice and PAR2-deficient preadipocytes. Also, a PAR2 antagonist elevated mitochondrial reactive oxygen species and reduced the MitoTracker fluorescent signal in preadipocytes. Our studies revealed that PAR2 is important for the development of adipose tissue under basal conditions through the regulation of mitochondrial biogenesis and adipocyte differentiation.

Mechanisms of Bone Remodeling Disorder in Hemophilia

Hemophilia is caused by a lack of antihemophilic factor(s), for example, factor VIII (FVIII; hemophilia A) and factor IX (FIX; hemophilia B). Low bone mass is widely reported in epidemiological studies of hemophilia, and patients with hemophilia are at an increased risk of fracture. The detailed etiology of bone homeostasis imbalance in hemophilia is unclear. Clinical and experimental studies show that FVIII and FIX are involved in bone remodeling. However, it is likely that antihemophilic factors affect bone biology through thrombin pathways rather than via their own intrinsic properties. In addition, among patients with hemophilia, there are pathophysiological processes in several systems that might contribute to bone loss. This review summarizes studies on the association between hemophilia and bone remodeling, and might shed light on the challenges facing the care and prevention of osteoporosis and fracture in patients with hemophilia.

Bone lesions in systemic mastocytosis: Bone histomorphometry and histopathological mechanisms

Osteoporosis is considered the most frequent skeletal manifestation of systemic mastocytosis (SM). We performed a retrospective analysis of sixty patients (37 males and 23 females) who underwent a bone biopsy in the assessment of SM or in the assessment of unexplained bone fragility. Thirty-three had simultaneously a bone marrow biopsy with a Jamshidi's needle; this sample was used for immunohistochemical analysis (tryptase, c-KIT. CD20, VCAM-1). Bone biopsy was realized in 42 cases in the assessment of SM to provide histologic proof of the disease and in 18 cases in the assessment of unexplained bone fragility and surprisingly revealed a SM. An increased bone turnover was observed in patients with SM with elevated eroded surfaces, osteoclast number and bone formation rate. In addition to nodules of mast cells (MC), a high number of MC was directly apposed on the trabeculae, affixed on the osteoblasts or the lining cells. The VCAM-1 adhesion protein recognizing α4β7 and α4β1 integrins may be a candidate to explain this particular adherence. One third of the bone marrow biopsies did not exhibit MC nodules or MC infiltration and led to a false negative diagnosis for SM. SM can be discovered in the assessment of fracture or osteoporosis. Transiliac bone biopsy allows for the diagnosis of the disease more accurately than bone marrow biopsy; it also provides a histomorphometric analysis of bone remodeling.

Nutritional properties and osteogenic activity of enzymatic hydrolysates of proteins from the blue mussel (Mytilus edulis)

Seafood provides a range of health benefits due to its nutritional and bioactive components. The proteins and peptides from Mytilus edulis have good bone growth promoting activities.

Stem cell library screen identified ruxolitinib as regulator of osteoblastic differentiation of human skeletal stem cells

Background

Better understanding of the signaling pathways that regulate human bone marrow stromal stem cell (hBMSC) differentiation into bone-forming osteoblasts is crucial for their clinical use in regenerative medicine. Chemical biology approaches using small molecules targeting specific signaling pathways are increasingly employed to manipulate stem cell differentiation fate.

Methods

We employed alkaline phosphatase activity and staining assays to assess osteoblast differentiation and Alizarin R staining to assess mineralized matrix formation of cultured hBMSCs. Changes in gene expression were assessed using an Agilent microarray platform, and data normalization and bioinformatics were performed using GeneSpring software. For in vivo ectopic bone formation experiments, hMSCs were mixed with hydroxyapatite–tricalcium phosphate granules and implanted subcutaneously into the dorsal surface of 8-week-old female nude mice. Hematoxylin and eosin staining and Sirius Red staining were used to detect bone formation in vivo.

Results

We identified several compounds which inhibited osteoblastic differentiation of hMSCs. In particular, we identified ruxolitinib (INCB018424) (3 μM), an inhibitor of JAK-STAT signaling that inhibited osteoblastic differentiation and matrix mineralization of hMSCs in vitro and reduced ectopic bone formation in vivo. Global gene expression profiling of ruxolitinib-treated cells identified 847 upregulated and 822 downregulated mRNA transcripts, compared to vehicle-treated control cells. Bioinformatic analysis revealed differential regulation of multiple genetic pathways, including TGFβ and insulin signaling, endochondral ossification, and focal adhesion.

Conclusions

We identified ruxolitinib as an important regulator of osteoblast differentiation of hMSCs. It is plausible that inhibition of osteoblast differentiation by ruxolitinib may represent a novel therapeutic strategy for the treatment of pathological conditions caused by accelerated osteoblast differentiation and mineralization.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1068-x) contains supplementary material, which is available to authorized users.

Genetics of pleiotropic effects of dexamethasone

OBJECTIVES

Glucocorticoids such as dexamethasone have pleiotropic effects, including desired antileukemic, anti-inflammatory, or immunosuppressive effects, and undesired metabolic or toxic effects. The most serious adverse effects of dexamethasone among patients with acute lymphoblastic leukemia are osteonecrosis and thrombosis. To identify inherited genomic variation involved in these severe adverse effects, we carried out genome-wide association studies (GWAS) by analyzing 14 pleiotropic glucocorticoid phenotypes in 391 patients with acute lymphoblastic leukemia.

PATIENTS AND METHODS

We used the Projection Onto the Most Interesting Statistical Evidence integrative analysis technique to identify genetic variants associated with pleiotropic dexamethasone phenotypes, stratifying for age, sex, race, and treatment, and compared the results with conventional single-phenotype GWAS. The phenotypes were osteonecrosis, central nervous system toxicity, hyperglycemia, hypokalemia, thrombosis, dexamethasone exposure, BMI, growth trajectory, and levels of cortisol, albumin, and asparaginase antibodies, and changes in cholesterol, triglycerides, and low-density lipoproteins after dexamethasone.

RESULTS

The integrative analysis identified more pleiotropic single nucleotide polymorphism variants (P=1.46×10(-215), and these variants were more likely to be in gene-regulatory regions (P=1.22×10(-6)) than traditional single-phenotype GWAS. The integrative analysis yielded genomic variants (rs2243057 and rs6453253) in F2RL1, a receptor that functions in hemostasis, thrombosis, and inflammation, which were associated with pleiotropic effects, including osteonecrosis and thrombosis, and were in regulatory gene regions.

CONCLUSION

The integrative pleiotropic analysis identified risk variants for osteonecrosis and thrombosis not identified by single-phenotype analysis that may have importance for patients with underlying sensitivity to multiple dexamethasone adverse effects.

Serine proteinases in the turnover of the cartilage extracellular matrix in the joint: implications for therapeutics

Cartilage destruction is a key characteristic of arthritic disease, a process now widely established to be mediated by metzincins such as MMPs. Despite showing promise in preclinical trials during the 1990s, MMP inhibitors for the blockade of extracellular matrix turnover in the treatment of cancer and arthritis failed clinically, primarily due to poor selectivity for target MMPs. In recent years, roles for serine proteinases in the proteolytic cascades leading to cartilage destruction have become increasingly apparent, renewing interest in the potential for new therapeutic strategies that utilize pharmacological inhibitors against this class of proteinases. Herein, we describe key serine proteinases with likely importance in arthritic disease and highlight recent advances in this field. LINKED ARTICLES: This article is part of a themed section on Translating the Matrix. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.1/issuetoc.

Rheumatic Disease: Protease-Activated Receptor-2 in Synovial Joint Pathobiology

Protease-activated receptor-2 (PAR2) is one member of a small family of transmembrane, G-protein-coupled receptors. These receptors are activated via cleavage of their N terminus by serine proteases (e.g., tryptase), unveiling an N terminus tethered ligand which binds to the second extracellular loop of the receptor. Increasing evidence has emerged identifying key pathophysiological roles for PAR2 in both rheumatoid arthritis (RA) and osteoarthritis (OA). Importantly, this includes both pro-inflammatory and destructive roles. For example, in murine models of RA, the associated synovitis, cartilage degradation, and subsequent bone erosion are all significantly reduced in the absence of PAR2. Similarly, in experimental models of OA, PAR2 disruption confers protection against cartilage degradation, subchondral bone osteosclerosis, and osteophyte formation. This review focuses on the role of PAR2 in rheumatic disease and its potential as an important therapeutic target for treating pain and joint degradation.

Membrane-anchored Serine Protease Matriptase Is a Trigger of Pulmonary Fibrogenesis

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a devastating disease that remains refractory to current therapies.

OBJECTIVES

To characterize the expression and activity of the membrane-anchored serine protease matriptase in IPF in humans and unravel its potential role in human and experimental pulmonary fibrogenesis.

METHODS

Matriptase expression was assessed in tissue specimens from patients with IPF versus control subjects using quantitative reverse transcriptase-polymerase chain reaction, immunohistochemistry, and Western blotting, while matriptase activity was monitored by fluorogenic substrate cleavage. Matriptase-induced fibroproliferative responses and the receptor involved were characterized in human primary pulmonary fibroblasts by Western blot, viability, and migration assays. In the murine model of bleomycin-induced pulmonary fibrosis, the consequences of matriptase depletion, either by using the pharmacological inhibitor camostat mesilate (CM), or by genetic down-regulation using matriptase hypomorphic mice, were characterized by quantification of secreted collagen and immunostainings.

MEASUREMENTS AND MAIN RESULTS

Matriptase expression and activity were up-regulated in IPF and bleomycin-induced pulmonary fibrosis. In cultured human pulmonary fibroblasts, matriptase expression was significantly induced by transforming growth factor-β. Furthermore, matriptase elicited signaling via protease-activated receptor-2 (PAR-2), and promoted fibroblast activation, proliferation, and migration. In the experimental bleomycin model, matriptase depletion, by the pharmacological inhibitor CM or by genetic down-regulation, diminished lung injury, collagen production, and transforming growth factor-β expression and signaling.

CONCLUSIONS

These results implicate increased matriptase expression and activity in the pathogenesis of pulmonary fibrosis in human IPF and in an experimental mouse model. Overall, targeting matriptase, or treatment by CM, which is already in clinical use for other diseases, may represent potential therapies for IPF.

Bone Metastasis from Renal Cell Carcinoma

About one-third of patients with advanced renal cell carcinoma (RCC) have bone metastasis that are often osteolytic and cause substantial morbidity, such as pain, pathologic fracture, spinal cord compression and hypercalcemia. The presence of bone metastasis in RCC is also associated with poor prognosis. Bone-targeted treatment using bisphosphonate and denosumab can reduce skeletal complications in RCC, but does not cure the disease or improve survival. Elucidating the molecular mechanisms of tumor-induced changes in the bone microenvironment is needed to develop effective treatment. The “vicious cycle” hypothesis has been used to describe how tumor cells interact with the bone microenvironment to drive bone destruction and tumor growth. Tumor cells secrete factors like parathyroid hormone-related peptide, transforming growth factor-β and vascular endothelial growth factor, which stimulate osteoblasts and increase the production of the receptor activator of nuclear factor κB ligand (RANKL). In turn, the overexpression of RANKL leads to increased osteoclast formation, activation and survival, thereby enhancing bone resorption. This review presents a general survey on bone metastasis in RCC by natural history, interaction among the immune system, bone and tumor, molecular mechanisms, bone turnover markers, therapies and healthcare burden.

Pharmacological Targeting of Protease-Activated Receptor 2 Affords Protection from Bleomycin-Induced Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is the most devastating diffuse fibrosing lung disease that remains refractory to therapy. Despite increasing evidence that protease-activated receptor 2 (PAR-2) contributes to fibrosis, its importance in pulmonary fibrosis is under debate. We addressed whether PAR-2 deficiency persistently reduces bleomycin-induced pulmonary fibrosis or merely delays disease progression and whether pharmacological PAR-2 inhibition limits experimental pulmonary fibrosis. Bleomycin was instilled intranasally into wild-type or PAR-2-deficient mice in the presence/absence of a specific PAR-2 antagonist (P2pal-18S). Pulmonary fibrosis was consistently reduced in PAR-2-deficient mice throughout the fibrotic phase, as evident from reduced Ashcroft scores (29%) and hydroxyproline levels (26%) at d 28. Moreover, P2pal-18S inhibited PAR-2-induced profibrotic responses in both murine and primary human pulmonary fibroblasts (p < 0.05). Once daily treatment with P2pal-18S reduced the severity and extent of fibrotic lesions in lungs of bleomycin-treated wild-type mice but did not further reduce fibrosis in PAR-2-deficient mice. Importantly, P2pal-18S treatment starting even 7 d after the onset of fibrosis limits pulmonary fibrosis as effectively as when treatment was started together with bleomycin instillation. Overall, PAR-2 contributes to the progression of pulmonary fibrosis, and targeting PAR-2 may be a promising therapeutic strategy for treating pulmonary fibrosis.

Depletion of protease-activated receptor 2 but not protease-activated receptor 1 may confer protection against osteoarthritis in mice through extracartilaginous mechanisms

OBJECTIVE

To explore the involvement of protease-activated receptor 1 (PAR-1) and PAR-2 in the pathologic processes of osteoarthritis (OA) and to identify the cells/tissues primarily affected by ablation of PAR-1 or PAR-2 in mice.

METHODS

OA was induced in the joints of wild-type (WT), PAR-1(+/+) , PAR-1(-/-) , and PAR-2(-/-) mice by destabilization of the medial meniscus (DMM), and scores of histologic features (cartilage aggrecan loss and erosion, subchondral bone sclerosis, osteophytes, and synovitis) were compared at 1, 4, and 8 weeks post-DMM. The effects of PAR ablation on cartilage degradation and chondrocyte metalloproteinase expression/activity were studied in cultures of mouse femoral head tissue with or without interleukin-1α (IL-1α). At 1 week post-DMM, synovial expression of cytokines and metalloproteinase genes was measured by reverse transcription-polymerase chain reaction, and populations of inflammatory cells were quantified by flow cytometry.

RESULTS

Deletion of PAR-2, but not that of PAR-1, in mice significantly delayed the progression of cartilage damage and inhibited subchondral bone sclerosis following DMM. There was no inhibitory effect of PAR-1 or PAR-2 ablation on IL-1α-induced cartilage degradation or chondrocyte metalloproteinase expression/activation. A low but significant level of synovitis persisted in mice subjected to DMM compared to that in control mice subjected to sham surgery, but no differences between the genotypes were seen 4 or 8 weeks post-DMM. One week after DMM, increased synovial expression of proinflammatory cytokines and metalloproteinase genes, along with increased levels of CD4+ T cells, inflammatory monocytes, and activated macrophages, were seen in all genotypes. However, there was a significant reduction in the percentage of activated macrophages in PAR-2(-/-) mice compared to PAR-1(-/-) and WT mice.

CONCLUSION

Deletion of PAR-2, but not that of PAR-1, results in a significant decrease in DMM-induced cartilage damage. The chondroprotection in PAR-2(-/-) mice appears to occur indirectly through modulation of extracartilaginous events such as subchondral bone remodeling and synovial macrophage activation, rather than through alteration of chondrocyte catabolic responses.

Regulatory Tweak/Fn14 signaling pathway as a potent target for controlling bone loss

Metabolic bone diseases, such as rheumatoid arthritis (RA) and osteoporosis, are characterized as imbalance between bone formation and bone resorption, leading to bone microarchitecture damage and bone mineral density loss. Bone loss is huge threat for older people's health, which imposes a heavy financial burden on patients and their families. However, the effectiveness of bone loss treatment in clinical practice is limited. With the understanding of the molecular and cellular regulators and mediators of bone remodelling, we know that some signaling pathways and inflammatory cytokines play important roles in the development of RA and osteoporosis. The increasing evidence showed that tumor necrosis factor (TNF)-like weak inducer of apoptosis (Tweak)/fibroblast growth factor-inducible 14 (Fn14) signalling controls a variety of cellular activities in biological processes, such as proliferation, differentiation, and apoptosis and has diverse biological functions in pathological mechanisms like inflammation that are associated with the process of bone metabolism. Recent studies suggest that the interactions between Tweak/Fn14 play critical roles in osteoblast and osteoclast differentiation and apoptosis, especially in those rheumatoid arthritis patients. These findings suggest that interventions targeting Tweak/Fn14 signaling pathway to regulate osteoblast-osteoclast coupling according to its biological effects, which results in promoting osteoblast formation and inhibiting osteoclast resorption, may be a promising approach for bone loss prevention and treatment in the near future.

Matriptase and MET are prominently expressed at the site of bone metastasis in renal cell carcinoma: immunohistochemical analysis

High MET expression in renal cell carcinoma (RCC) and MET activation in bone metastases are reportedly important in progression of several cancers. To find new treatment targets in bone metastasis, we immunohistochemically analyzed expression levels of MET and matriptase (specific cellular activator of hepatocyte growth factor). We obtained nephrectomy specimens from 17 RCC patients with metastasis, and bone metastases specimens from 7 RCC patients who underwent metastasectomies, and who were treated at our hospital between 2008 and 2012. We tested the samples with anti-human MET polyclonal antibody and anti-human matriptase polyclonal antibody, and compared postoperative overall survival (OS) rates between positive and negative groups. High MET expression was seen at primary sites in 8/17 (47 %) nephrectomy specimens, and 6/7 (86 %) bone specimens. Matriptase was expressed in 6/17 (35 %) nephrectomy specimens, and all 7 (100 %) bone specimens. Interestingly, matriptase was strongly expressed in osteoclasts of 5/7 bone specimens. Postoperative OS rate was significantly higher in the MET⁻ group than the MET⁺ group. The high MET and matriptase expression seen in RCC cells in bone metastasis accompanied by matriptase expression in osteoclasts indicates their importance in bone metastasis.

Protease-activated receptors expression in gingiva in periodontal health and disease

OBJECTIVE

Protease-activated receptors (PARs) are a unique class of receptors which are implicated in mediating inflammation, pain and other functions. The aim of this study was to elucidate the role of PARs in the pathogenesis of chronic periodontitis by differential expression analysis of PARs in the gingival tissues of chronic periodontitis patients compared with those of healthy control individuals.

DESIGN

Gingival tissue specimens were collected from chronic periodontitis patients (n=20) and control individuals (n=20). The expression of PAR-1, -2, -3 and -4 was determined in these tissues by immunohistochemistry and differential expression between the two groups was investigated by quantitative real-time reverse transcription-polymerase chain reaction analysis.

RESULTS

PAR-1, -2, -3 and -4 were expressed in all gingival tissues. A significant overexpression of PAR-3 was detected in chronic periodontitis-affected tissues compared to healthy gingival tissues. However, expression of PAR-2 was decreased in periodontal lesions.

CONCLUSIONS

Our study shows that PAR-1, -2, -3 and -4 are expressed in both healthy and inflamed gingival tissues. Furthermore, PAR-2 and PAR-3 may contribute to the inflammatory responses associated with chronic periodontitis.

Evaluation of antibodies directed against human protease-activated receptor-2

Protease-activated receptor 2 (PAR2) is a G protein-coupled receptor activated by intramolecular docking of a tethered ligand that is released by the actions of proteases, mainly of the serine protease family. Here, we evaluate four commercially available anti-PAR2 antibodies, SAM11, C17, N19 and H99, demonstrating marked differences in the ability of these reagents to detect the target receptor in Western blot, immunocytochemical and flow cytometry applications. In Western blot analysis, we evaluated antibody reactivity against both ectopic and endogenous receptors. Against material from transfected cells, we show that SAM11 and N19, and to a lesser extent C17, but not H99, are able to detect ectopic PAR2. Interestingly, these Western blot analyses indicate that N19 and C17 detect conformations of ectopic PAR2 distinct to those recognised by SAM11. Significantly, our data also indicate that Western blot signal detected by SAM11 and C17, and much of the signal detected by N19, against cells endogenously expressing PAR2 is non-specific. Despite confounding non-specific signals, we were able to discern N19 reactivity against endogenous PAR2 as a broad smear that we also observed in ectopically expressing human and mouse cells and that is sensitive to loss of N-glycosylation. In immunocytochemistry analysis, each antibody is able to detect ectopic PAR2 although it appears that H99 detects only a subset of the ectopically expressed receptor. In addition, SAM11 and N19 are able to detect both ectopic and endogenous cell surface PAR2 by flow cytometry. In summary: (1) each antibody can detect ectopic PAR2 by immunocytochemical analysis with SAM11 and N19 suitable for cell surface detection of both ectopic and endogenous receptor by flow cytometry; (2) in Western blot analysis, N19, SAM11 and C17 can detect ectopically expressed PAR2, with only N19 able to detect the endogenous receptor by this technique and (3) in each of these approaches, appropriate controls are essential to ensure that non-specific reactivity is identified.