Proteinase-activated receptor (PAR)-2 activation impacts bone resorptive properties of human osteoarthritic subchondral bone osteoblasts

Targeting PAR2-mediated inflammation in osteoarthritis: a comprehensive in vitro evaluation of oleocanthal's potential as a functional food intervention for chondrocyte protection and anti-inflammatory effects

BACKGROUND

Osteoarthritis (OA) is a prevalent degenerative joint disease characterized by chronic inflammation and progressive cartilage degradation, ultimately leading to joint dysfunction and disability. Oleocanthal (OC), a bioactive phenolic compound derived from extra virgin olive oil, has garnered significant attention due to its potent anti-inflammatory properties, which are comparable to those of non-steroidal anti-inflammatory drugs (NSAIDs). This study pioneers the investigation into the effects of OC on the Protease-Activated Receptor-2 (PAR-2) mediated inflammatory pathway in OA, aiming to validate its efficacy as a functional food-based therapeutic intervention.

METHODS

To simulate cartilage tissue in vitro, human bone marrow-derived mesenchymal stem cells (BMSCs) were differentiated into chondrocytes. An inflammatory OA-like environment was induced in these chondrocytes using lipopolysaccharide (LPS) to mimic the pathological conditions of OA. The therapeutic effects of OC were evaluated by treating these inflamed chondrocytes with various concentrations of OC. The study focused on assessing key inflammatory markers, catabolic enzymes, and mitochondrial function to elucidate the protective mechanisms of OC. Mitochondrial function, specifically mitochondrial membrane potential (ΔΨm), was assessed using Rhodamine 123 staining, a fluorescent dye that selectively accumulates in active mitochondria. The integrity of ΔΨm serves as an indicator of mitochondrial and bioenergetic function. Additionally, Western blotting was employed to analyze protein expression levels, while real-time polymerase chain reaction (RT-PCR) was used to quantify gene expression of inflammatory cytokines and catabolic enzymes. Flow cytometry was utilized to measure cell viability and apoptosis, providing a comprehensive evaluation of OC's therapeutic effects on chondrocytes.

RESULTS

The results demonstrated that OC significantly downregulated PAR-2 expression in a dose-dependent manner, leading to a substantial reduction in pro-inflammatory cytokines, including TNF-α, IL-1β, and MCP-1. Furthermore, OC attenuated the expression of catabolic markers such as SOX4 and ADAMTS5, which are critically involved in cartilage matrix degradation. Importantly, OC was found to preserve mitochondrial membrane potential (ΔΨm) in chondrocytes subjected to inflammatory stress, as evidenced by Rhodamine 123 staining, indicating a protective effect on cellular bioenergetics. Additionally, OC modulated the Receptor Activator of Nuclear Factor Kappa-Β Ligand (RANKL)/Receptor Activator of Nuclear Factor Kappa-Β (RANK) pathway, suggesting a broader therapeutic action against the multifactorial pathogenesis of OA.

CONCLUSIONS

This study is the first to elucidate the modulatory effects of OC on the PAR-2 mediated inflammatory pathway in OA, revealing its potential as a multifaceted therapeutic agent that not only mitigates inflammation but also protects cartilage integrity. The preservation of mitochondrial function and modulation of the RANKL/RANK pathway further underscores OC's comprehensive therapeutic potential in counteracting the complex pathogenesis of OA. These findings position OC as a promising candidate for integration into nutritional interventions aimed at managing OA. However, further research is warranted to fully explore OC's therapeutic potential across different stages of OA and its long-term effects in musculoskeletal disorders.

Pathological progression of osteoarthritis: a perspective on subchondral bone

Osteoarthritis (OA) is a degenerative bone disease associated with aging. The rising global aging population has led to a surge in OA cases, thereby imposing a significant socioeconomic burden. Researchers have been keenly investigating the mechanisms underlying OA. Previous studies have suggested that the disease starts with synovial inflammation and hyperplasia, advancing toward cartilage degradation. Ultimately, subchondral-bone collapse, sclerosis, and osteophyte formation occur. This progression is deemed as "top to bottom." However, recent research is challenging this perspective by indicating that initial changes occur in subchondral bone, precipitating cartilage breakdown. In this review, we elucidate the epidemiology of OA and present an in-depth overview of the subchondral bone's physiological state, functions, and the varied pathological shifts during OA progression. We also introduce the role of multifunctional signal pathways (including osteoprotegerin (OPG)/receptor activator of nuclear factor-kappa B ligand (RANKL)/receptor activator of nuclear factor-kappa B (RANK), and chemokine (CXC motif) ligand 12 (CXCL12)/CXC motif chemokine receptor 4 (CXCR4)) in the pathology of subchondral bone and their role in the "bottom-up" progression of OA. Using vivid pattern maps and clinical images, this review highlights the crucial role of subchondral bone in driving OA progression, illuminating its interplay with the condition.

Protease-activated receptor type 2 activation downregulates osteogenesis in periodontal ligament stem cells

Protease-activated receptor-2 (PAR2) is associated with the pathogenesis of many chronic diseases with inflammatory characteristics, including periodontitis. This study aimed to evaluate how the activation of PAR2 can affect the osteogenic activity of human periodontal ligament stem cells (PDLSCs) in vitro. PDLSCs collected from three subjects were treated in osteogenic medium for 2, 7, 14, and 21 days with trypsin (0.1 U/mL), PAR2 specific agonist peptide (SLIGRL-NH2) (100 nM), and PAR2 antagonist peptide (FSLLRY-NH2) (100 nM). Gene (RT-qPCR) expression and protein expression (ELISA) of osteogenic factors, bone metabolism, and inflammatory cytokines, cell proliferation, alkaline phosphatase (ALP) activity, alizarin red S staining, and supernatant concentration were assessed. Statistical analysis of the results with a significance level of 5% was performed. Activation of PAR2 led to decreases in cell proliferation and calcium deposition (p < 0.05), calcium concentration (p < 0.05), and ALP activity (p < 0.05). Additionally, PAR2 activation increased gene and protein expression of receptor activator of nuclear factor kappa-Β ligand (RANKL) (p < 0.05) and significantly decreased the gene and protein expression of osteoprotegerin (p <0. 05). Considering the findings, the present study demonstrated PAR2 activation was able to decrease cell proliferation, decreased osteogenic activity of PDLSCs, and upregulated conditions for bone resorption. PAR2 may be considered a promising target in periodontal regenerative procedures.

Synovial tissue-derived extracellular vesicles induce chondrocyte inflammation and degradation via NF-κB signalling pathway: An in vitro study

Osteoarthritis (OA) is a whole‐joint disease characterized by synovial inflammation and cartilage degeneration. However, the relationship between synovial inflammation and cartilage degeneration remains unclear. The modified Hulth's method was adopted to establish a knee OA (KOA) rabbit model. Synovial tissue was collected after 8 weeks, and synovial tissue‐derived extracellular vesicles (ST‐EVs) were extracted by filtration combined with size exclusion chromatography (SECF), followed by identification through transmission electron microscopy (TEM), nanoparticle tracer analysis (NTA) and Western blot (WB). The collagenase digestion method was used to extract normal rabbit chondrocytes, which were then treated with the SF‐EVs to observe the effect and mechanism of SF‐EVs on chondrocytes. The morphology, particle size and labelled protein marker detection confirmed that SECF successfully extract ST‐EVs. The ST‐EVs in the KOA state significantly inhibited chondrocyte proliferation and promoted chondrocytes apoptosis. Moreover, the ST‐EVs also promoted the expression of pro‐inflammatory cytokines (IL‐1β, IL‐6, TNF‐α and COX‐2) and cartilage degradation‐related enzymes (MMP13, MMP9 and ADAMTS5) in the chondrocytes. Mechanistically, the ST‐EVs significantly promoted the activation of NF‐κB signalling pathway in chondrocytes. Inhibition the activation of the NF‐κB signalling pathway significantly rescued the expression of inflammatory cytokines and cartilage degradation‐related enzymes in the ST‐EVs–induced chondrocytes. In conclusion, the ST‐EVs promote chondrocytes inflammation and degradation by activating the NF‐κB signalling pathway, providing novel insights into the occurrence and development of OA.

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.

A Metalloproteinase Induces an Inflammatory Response in Preadipocytes with the Activation of COX Signalling Pathways and Participation of Endogenous Phospholipases A2

Matrix metalloproteinases (MMPs) are proteolytic enzymes that have been associated with the pathogenesis of inflammatory diseases and obesity. Adipose tissue in turn is an active endocrine organ capable of secreting a range of proinflammatory mediators with autocrine and paracrine properties, which contribute to the inflammation of adipose tissue and adjacent tissues. However, the potential inflammatory effects of MMPs in adipose tissue cells are still unknown. This study investigates the effects of BmooMPα-I, a single-domain snake venom metalloproteinase (SVMP), in activating an inflammatory response by 3T3-L1 preadipocytes in culture, focusing on prostaglandins (PGs), cytokines, and adipocytokines biosynthesis and mechanisms involved in prostaglandin E2 (PGE2) release. The results show that BmooMPα-I induced the release of PGE2, prostaglandin I2 (PGI2), monocyte chemoattractant protein-1 (MCP-1), and adiponectin by preadipocytes. BmooMPα-I-induced PGE2 biosynthesis was dependent on group-IIA-secreted phospholipase A2 (sPLA2-IIA), cytosolic phospholipase A2-α (cPLA2-α), and cyclooxygenase (COX)-1 and -2 pathways. Moreover, BmooMPα-I upregulated COX-2 protein expression but not microsomal prostaglandin E synthase-1 (mPGES-1) expression. In addition, we demonstrate that the enzymatic activity of BmooMPα-I is essential for the activation of prostanoid synthesis pathways in preadipocytes. These data highlight preadipocytes as important targets for metalloproteinases and provide new insights into the contribution of these enzymes to the inflammation of adipose tissue and tissues adjacent to it.

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.

Association of PAR-2 Gene Polymorphisms with the Inflammatory Response and Susceptibility to Knee Osteoarthritis in the Chinese Han Population

OBJECTIVE

To investigate the relationship between single nucleotide polymorphisms (SNPs) of protease-activated receptor 2 (PAR-2) and the susceptibility to knee osteoarthritis (KOA) and synovial expression of inflammatory factors in the Chinese Han population.

METHODS

Three hundred fifty KOA patients (KOA group) and 345 healthy volunteers (control group) were recruited for the study. Five milliliters of venous blood was taken from each subject to detect the PAR-2 rs1529505, rs631465, and rs2242991 locus genotypes. The expression of PAR-2 mRNA in the synovial tissue and the levels of matrix metalloproteinase (MMP-1), MMP-9, interleukin (IL)-6, and IL-1β in the joint effusion were detected in 205 KOA patients who had undergone joint replacement surgery.

RESULTS

The PAR-2 rs1529505 T allele and the rs2242991 G allele carriers had a higher risk of KOA (p < 0.001). The severity of KOA in patients with the PAR-2 rs1529505 and rs2242991 mutations were higher than in the wild-type controls (p < 0.05). The expression levels of the PAR-2 mRNA in wild types, heterozygotes, and homozygotes of the rs1529505 and rs2242991 loci increased in turn (p < 0.001). The levels of MMP-1, MMP-9, IL-6, and IL-1β in the synovial fluid of the PAR-2 rs1529505 and rs2242991 locus mutants were distinctly higher than those with the wild-type alleles (p < 0.01). There was no correlation between the rs631465 SNP and susceptibility to KOA, severity of KOA, nor levels of PAR-2 mRNA, MMP-1, MMP-9, IL-6, and IL-1β.

CONCLUSIONS

The PAR-2 SNPs rs1529505 and rs2242991 are associated with the susceptibility to KOA. KOA is more severe in patients harboring the T and G alleles of these two SNPs, respectively. The levels of inflammatory factors in synovial tissue and blood are higher than those in wild-type patients.

[Research progress on protease-activated receptor 2 in pathogenesis of osteoarthritis]

Objective

To review the research progress on protease-activated receptor 2 (PAR-2) in the pathogenesis of osteoarthritis (OA).

Methods

The relevant literature about the mechanism of PAR-2 in the occurrence and development of OA in recent years was extensively reviewed and comprehensively analyzed.

Results

Abnormal activation of PAR-2 plays an important role in responses to occurrence and development of OA. Through regulating production and releasing of a variety of cytokines (such as inflammatory factors, metabolic factors, pain factors, etc.), the PAR-2 can involve in pathophysiological progression of OA articular cartilage, subchondral bone, and synovial membrane, as well as occurrence and transmission of pain.

Conclusion

PAR-2 participation in the development of OA has been confirmed. However, since PAR-2 is complicated and widespread, it is necessary to study the specific role of PAR-2 and the interaction between various signal pathways in the progression of OA, and to elucidate the potential pathophysiological mechanisms of PAR-2 participating in the process of OA, in the hope of exploring the new targets for the effective control of OA.

The Role of Proteinase-Activated Receptors 1 and 2 in the Regulation of Periodontal Tissue Metabolism and Disease

Proteinase-activated receptors 1 (PAR1) and 2 (PAR2) are the most highly expressed members of the PAR family in the periodontium. These receptors regulate periodontal inflammatory and repair processes through their activation by endogenous and bacterial enzymes. PAR1 is expressed by the periodontal cells such as human gingival fibroblasts, gingival epithelial cells, periodontal ligament cells, osteoblasts, and monocytic cells and can be activated by thrombin, matrix metalloproteinase 1 (MMP-1), MMP-13, fibrin, and gingipains from Porphyromonas gingivalis. PAR2 is expressed by neutrophils, osteoblasts, oral epithelial cells, and human gingival fibroblasts, and its possible activators in the periodontium are gingipains, neutrophil proteinase 3, and mast cell tryptase. The mechanisms through which PARs can respond to periodontal enzymes and result in appropriate immune responses have until recently been poorly understood. This review discusses recent findings that are beginning to identify a cardinal role for PAR1 and PAR2 on periodontal tissue metabolism.

Downregulation of Proteinase-Activated Receptor-2, Interleukin-17, and Other Proinflammatory Genes by Subantimicrobial Doxycycline Dose in a Rat Periodontitis Model

BACKGROUND

Subantimicrobial dose doxycycline (SDD) has been used as an adjunct in periodontal treatment because of its matrix metalloproteinase inhibition properties. Although the benefits of SDD therapy, such as improvement in the parameters of periodontal probing depth and clinical attachment level, have been proven in multiple clinical studies, the comprehension of other biologic mechanisms of action on periodontitis remains poorly investigated. Therefore, this animal-model study evaluated the effects of SDD monotherapy on the expressions of the following key proinflammatory genes: proteinase-activated receptor-2 (PAR2), tumor necrosis factor (TNF)-α, interleukin (IL)-17, and IL-1β.

METHODS

Male Wistar rats were assigned randomly to the following: 1) control group: no ligature-induced periodontitis and no treatment; 2) ligature group: ligature-induced periodontitis and placebo treatment; and 3) ligature + doxycycline group: ligature-induced periodontitis and SDD treatment. After the experimental time, animals were sacrificed, and reverse transcription-polymerase chain reaction was performed to analyze the mRNA expression of IL-1β, IL-17, TNF-α, and PAR2 in gingival tissue samples. Histologic analyses were performed on the furcation region and mesial gingiva of mandibular first molars to measure periodontal bone loss and collagen content.

RESULTS

SDD administration significantly downregulated PAR2, IL-17, TNF-α, and IL-1β mRNA expressions (P <0.05). In addition, SDD treatment was accompanied by lower rates of alveolar bone loss (P <0.05) and maintenance of the amount of gingival collagen fibers.

CONCLUSION

These findings reveal new perspectives regarding SDD efficacy because it can be partially related to proinflammatory gene expression modulation, even considering PAR2 and IL-17, which has not been investigated thus far.

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.

Influence of calcium hydroxide-loaded microcapsules on osteoprotegerin and receptor activator of nuclear factor kappa B ligand activity

INTRODUCTION

Calcium hydroxide (Ca[OH]2) microcapsules were synthesized to allow controlled release of Ca(OH)2. The aim of this study was to evaluate the influence of Ca(OH)2 microcapsules on osteoprotegerin (OPG) activity, receptor activator of nuclear factor kappa B ligand (RANKL) activity, and the OPG/RANKL ratio compared with pure Ca(OH)2 powder and Vitapex (Neo Dental Chemical Products Co Ltd, Tokyo, Japan).

METHODS

One formula of Ca(OH)2 microcapsules was evaluated, and pure Ca(OH)2 powder was used as a control. A commonly used Ca(OH)2 medication containing an oily vehicle (Vitapex) was also evaluated, and the in vitro release profile of Vitapex was studied. The human osteosarcoma cell line MG63 was used to evaluate the influence of Ca(OH)2 microcapsules, pure Ca(OH)2 powder, and Vitapex on OPG and RANKL activity. The relative messenger RNA (mRNA) expression of OPG and RANKL was determined by real-time polymerase chain reaction. The protein expression of OPG and RANKL in supernatants was measured using enzyme-linked immunosorbent assay.

RESULTS

Vitapex prolonged the release of Ca(OH)2 compared with pure Ca(OH)2 powder, and the release rate of Vitapex was faster than that of the microcapsules. The OPG/RANKL ratio in the microcapsules group was up-regulated at both the mRNA and protein levels compared with the negative control group and the pure Ca(OH)2 powder group. The ratio in the Vitapex group was lower than the microcapsule group both at the mRNA and protein levels.

CONCLUSIONS

Ca(OH)2 microcapsules increased the expression of OPG although they did not increase the expression of RANKL compared with pure Ca(OH)2 powder and Vitapex. This increase in expression led to an increase in the OPG/RANKL ratio and eventual inhibition of osteoclast activity.

The coupling of bone and cartilage turnover in osteoarthritis: opportunities for bone antiresorptives and anabolics as potential treatments?

Osteoarthritis (OA) is the most common form of arthritic disease, and a major cause of disability and impaired quality of life in the elderly. OA is a complex disease of the entire joint, affecting bone, cartilage and synovium that thereby presents multiple targets for treatment. This manuscript will summarise emerging observations from cell biology, preclinical and preliminary clinical trials that elucidate interactions between the bone and cartilage components in particular. Bone and cartilage health are tightly associated. Ample evidence has been found for bone changes during progression of OA including, but not limited to, increased turnover in the subchondral bone, undermineralisation of the trabecular structure, osteophyte formation, bone marrow lesions and sclerosis of the subchondral plate. Meanwhile, a range of investigations has shown positive effects on cartilage health when bone resorption is suppressed, or deterioration of the cartilage when resorption is increased. Known bone therapies, namely oestrogens, selective oestrogen receptor modifiers (SERMs), bisphosphonates, strontium ranelate, calcitonin and parathyroid hormone, might prove useful for treating two critical tissue components of the OA joint, the bone and the cartilage. An optimal treatment for OA likely targets at least these two tissue components. The patient subgroups for whom these therapies are most appropriate have yet to be fully defined but would likely include, at a minimum, those with high bone turnover.

Interplay between cartilage and subchondral bone contributing to pathogenesis of osteoarthritis

Osteoarthritis (OA) is a common debilitating joint disorder, affecting large sections of the population with significant disability and impaired quality of life. During OA, functional units of joints comprising cartilage and subchondral bone undergo uncontrolled catabolic and anabolic remodeling processes to adapt to local biochemical and biological signals. Changes in cartilage and subchondral bone are not merely secondary manifestations of OA but are active components of the disease, contributing to its severity. Increased vascularization and formation of microcracks in joints during OA have suggested the facilitation of molecules from cartilage to bone and vice versa. Observations from recent studies support the view that both cartilage and subchondral bone can communicate with each other through regulation of signaling pathways for joint homeostasis under pathological conditions. In this review we have tried to summarize the current knowledge on the major signaling pathways that could control the cartilage-bone biochemical unit in joints and participate in intercellular communication between cartilage and subchondral bone during the process of OA. An understanding of molecular communication that regulates the functional behavior of chondrocytes and osteoblasts in both physiological and pathological conditions may lead to development of more effective strategies for treating OA patients.

Fracture healing in protease-activated receptor-2 deficient mice

Protease-activated receptor-2 (PAR-2) provides an important link between extracellular proteases and the cellular initiation of inflammatory responses. The effect of PAR-2 on fracture healing is unknown. This study investigates the in vivo effect of PAR-2 deletion on fracture healing by assessing differences between wild-type (PAR-2(+/+)) and knock-out (PAR-2(-/-)) mice. Unilateral mid-shaft femur fractures were created in 34 PAR-2(+/+) and 28 PAR-2(-/-) mice after intramedullary fixation. Histologic assessments were made at 1, 2, and 4 weeks post-fracture (wpf), and radiographic (plain radiographs, micro-computed tomography (µCT)) and biomechanical (torsion testing) assessments were made at 7 and 10 wpf. Both the fractured and un-fractured contralateral femur specimens were evaluated. Polar moment of inertia (pMOI), tissue mineral density (TMD), bone volume fraction (BV/TV) were determined from µCT images, and callus diameter was determined from plain radiographs. Statistically significant differences in callus morphology as assessed by µCT were found between PAR-2(-/-) and PAR-2(+/+) mice at both 7 and 10 wpf. However, no significant histologic, plain radiographic, or biomechanical differences were found between the genotypes. The loss of PAR-2 was found to alter callus morphology as assessed by µCT but was not found to otherwise effect fracture healing in young mice.

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.

Brachystemma calycinum D. Don Effectively Reduces the Locomotor Disability in Dogs with Naturally Occurring Osteoarthritis: A Randomized Placebo-Controlled Trial

Objective. The aim of this randomized placebo-controlled trial was to evaluate the beneficial effect of a whole plant extract of Brachystemma calycinum D. Don (BCD) in naturally occurring osteoarthritis (OA) in dogs. Methods. Dogs had stifle/hip OA and poor limb loading based on the peak of the vertically oriented ground reaction force (PVF) measured using a force platform. At baseline, PVF and case-specific outcome measure of disability (CSOM) were recorded. Dogs (16 per group) were then assigned to receive BCD (200 mg/kg/day) or a placebo. The PVF was measured at week (W) 3 and W6. Locomotor activity was recorded throughout the study duration using collar-mounted accelerometer, and CSOM was assessed biweekly by the owner. Results. BCD-treated dogs had higher PVF at W3 and W6 when compared to Baseline (P < 0.001) and at W6 when compared to placebo-treated dogs (P = 0.040). Higher daily duration (P = 0.024) and intensity (P = 0.012) of locomotor activity were observed in BCD-treated dogs compared to baseline. No significant change was observed in either group for CSOM. Conclusions. Treatment with BCD improved the limb impairment and enhanced the locomotor activity in dogs afflicted by naturally-occurring OA. Those preclinical findings provide interesting and new information about the potential of BCD as an OA therapeutic.

The osteoarthritic niche and modulation of skeletal stem cell function for regenerative medicine

Osteoarthritis (OA) is the most common cause of arthritis worldwide and represents a significant healthcare burden, particularly in the context of an ageing population. Traditionally, painkillers, injections and physiotherapy have been the mainstay of treatment, with patients being referred for joint replacement surgery (arthroplasty) when these options fail. Whilst effective in reducing pain and improving joint function, these approaches are not without potential complications. With the development of tissue-engineering techniques over recent years there has been considerable interest in applying these strategies to provide new, innovative, alternative effective means of treating OA. This review explores the unique microenvironment present within an osteoarthritic joint, highlighting the features that comprise the osteoarthritic niche and could be modulated in the development of novel treatments for OA. Existing tissue-engineering strategies for repairing bone and cartilage defects are discussed, with particular reference to how these might be modified, both to improve existing treatments, such as impaction bone grafting, as well as in the development of future treatments for OA.

An antagonist of human protease activated receptor-2 attenuates PAR2 signaling, macrophage activation, mast cell degranulation, and collagen-induced arthritis in rats

Multiple serine proteases exert proinflammatory actions by signaling through protease-activated receptor-2 (PAR2) on the cell surface. Although inhibitors of individual proteases are anti-inflammatory, we sought to discover whether the first potent antagonist of their common target PAR2 might be beneficial in treating chronic arthritis-like inflammatory disease. Using a fluorescence assay, a novel compound, GB88, was shown to antagonize PAR2-induced intracellular Ca(2+) release in human monocyte-derived macrophages, being 1000 times more potent than a control compound, ENMD-1068 (IC(50) 1.6 ± 0.5 μM vs. 1.2 ± 0.4 mM, respectively). In Wistar rats, GB88 was orally bioavailable (F=55%, T(max) 4 h, C(max) 1.7 μM, 10 mg/kg). GB88 inhibited the acute paw edema induced in Wistar rats by intraplantar λ-carrageenan or PAR2 agonists 2-furoyl-LIGRLO-NH(2) or mast cell β-tryptase, without inhibiting proteolytic activity of tryptase in vitro. In the chronic collagen-induced model of arthritis in rats, GB88 (10 mg/kg) was disease modifying and ameliorated pathological and histopathological changes (edema, pannus formation, synovial hyperplasia, collagen degradation, macrophage invasion, mast cell degranulation) compared to untreated arthritic controls. The results suggest that an orally active PAR2 antagonist is effective in treating chronic arthritis in rats through inhibiting macrophage infiltration, mast cell degranulation, and β-tryptase-PAR2 signaling in joint inflammation.

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.

Anti-Inflammatory mechanisms of the proteinase-activated receptor 2-inhibiting peptide in human synovial cells

Background

Osteoarthritis (OA) is a degenerative joint disease which affects the entire joint structure, including the synovial membrane. Disease progression was shown to involve inflammatory changes mediated by proteinase-activated receptor (PAR)-2. Previous studies demonstrated that PAR-2 messenger (m)RNA and protein levels increased in OA synovial cells, suggesting that PAR-2 is a potential therapeutic target of the disease.

Methods

We designed a PAR-2-inhibiting peptide (PAR2-IP) by changing an isoleucine residue in the PAR-2-activating peptide (PAR2-AP), SLIGKV, to alanine, generating the SLAGKV peptide. We used it to test PAR-2-mediated inflammatory responses, including the expressions of cyclooxygenase (COX)-2 and matrix metalloproteinase (MMP)-1 and activation of nuclear factor (NF)-κB in human synovial cells. As a control, expressions of COX-2 and MMP-1 were induced by trypsin at both the mRNA and protein levels.

Results

The PAR2-AP increased the expression of COX-2 more dramatically than that of MMP-1. When we treated cells with the designed PAR2-IP, the trypsin-induced COX-2 level was completely inhibited at a moderate concentration of the PAR2-IP. With further examination of trypsin-induced NF-κB activation, we observed sufficient inhibitory effects of the PAR2-IP in synoviosarcoma cells and primary synovial cells from OA patients.

Conclusions

Our study suggests that the PAR2-IP inhibits trypsin-induced NF-κB activation, resulting in a reduction in inflammatory COX-2 expression in synovial cells. Application of PAR2-IP is suggested as a potential therapeutic strategy for OA.

TGF-β1 induces proteinase-activated receptor 2 (PAR2) expression in endometriotic stromal cells and stimulates PAR2 activation-induced secretion of IL-6

BACKGROUND

Proteinase-activated receptor 2 (PAR2) is a G-protein-coupled receptor that is activated by several serine proteases. PAR2 activation in endometriotic stromal cells (ESCs) has been implicated in the development of endometriosis but the regulatory mechanism of PAR2 expression in ESC is unknown. Our objective was to study the mechanism by which PAR2 expression may be regulated in endometriotic lesions.

METHODS

Primary cultures of ESCs were treated with transforming growth factor-β (TGF-β) 1, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), and the expression of PAR2 was examined by real-time quantitative PCR. ESCs pretreated with or without TGF-β1 were treated with PAR2 agonist peptide (PAR2AP) and the secretion of the pro-endometriotic cytokine, IL-6, was measured using a specific enzyme-linked immunosorbent assay. Effects of TGF-β type 1 inhibitor, SB431542, and PAR2 small interfering RNA (siRNA) on the TGF-β1 stimulation of PAR2 gene expression and PAR2AP-induced IL-6 secretion were also evaluated. To study intracellular signaling, effects of inhibitors of mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K) and of Smad4 siRNA on the TGF-β1-induced PAR2 gene expression were studied.

RESULTS

Only TGF-β1, but neither TNF-α nor IL-1β, increased gene expression of PAR2. Activation of PAR2 with PAR2AP increased the secretion of IL-6 from ESCs. As expected, TGF-β1 pretreatment dose-dependently enhanced the PAR2AP-induced increase in IL-6 secretion from ESCs. Treatment of ESCs with the TGF-β type 1 inhibitor, SB431542, inhibited both TGF-β1-stimulation of PAR2 gene expression and PAR2AP-induced IL-6 secretion. Transfection of ESCs with PAR2 siRNA produced a similar inhibition of IL-6 secretion. The TGF-β1-induced increase in PAR2 gene expression was repressed by inhibition of p38 MAPK, p42/44 MAPK or PI3K, but not by knockdown of Smad4 expression.

CONCLUSIONS

In view of significant roles of PAR2 and IL-6 in endometriosis, the TGF-β1-induced increase in PAR2 expression may be an elaborate mechanism that augments the progression of the disease.

Proteinase-activated receptor-2 gene disruption limits the effect of osteoarthritis on cartilage in mice: a novel target in joint degradation

OBJECTIVE

Evidence indicates that proteinase-activated receptor (PAR)-2 participates in the degradative processes of human osteoarthritis (OA). We evaluated the in vivo effect of PAR-2 on articular lesions in a PAR-2-knockout (KO) mouse model of OA.

METHODS

OA was surgically induced by destabilization of the medial meniscus of the right knee in C57Bl/6 wild-type (WT) and PAR-2 KO mice. Knee swelling was measured throughout the duration of the study (8 weeks postsurgery) and histologic evaluation of cartilage was done to assess structure, cellularity, matrix staining, and remodeling in the deep zone. Morphometric analysis of subchondral bone was also performed.

RESULTS

Data showed significant knee swelling in the operated WT mice immediately following surgery, which increased with time (8 weeks post-surgery). Knee swelling was significantly lower (p ≤ 0.0001) in PAR-2 KO mice than in WT mice at both 4 and 8 weeks postsurgery. Cartilage damage was found in both operated WT and PAR-2 KO mice; however, lesions were significantly less severe (global score; p ≤ 0.05) in the PAR-2 KO mice at 4 weeks postsurgery. Operated WT mice showed reduced subchondral bone surface and trabecular thickness with significance reached at 4 weeks (p ≤ 0.03 and p ≤ 0.05, respectively), while PAR-2 KO mice demonstrated a gradual increase in subchondral bone surface with significance reached at 8 weeks (p ≤ 0.007).

CONCLUSION

We demonstrated the in vivo implication of PAR-2 in the development of experimental OA, thus confirming its involvement in OA joint structural changes and reinforcing the therapeutic potential of a PAR-2 antagonist for treatment of OA.

The bone-cartilage unit in osteoarthritis

Osteoarthritis (OA) refers to a group of mechanically-induced joint disorders to which both genetic and acquired factors contribute. Current pathophysiological concepts focus on OA as a disease of the whole joint. Within these models, the functional unit formed by the articular cartilage and the subchondral bone seems to be of particular interest. Cartilage and bone receive and dissipate the stress associated with movement and loading, and are therefore continuously challenged biomechanically. Recent data support the view that cartilage and bone can communicate over the calcified tissue barrier; vessels reach out from bone into the cartilage zone, patches of uncalcified cartilage are in contact with bone, and microcracks and fissures further facilitate transfer of molecules. Several molecular signaling pathways such as bone morphogenetic proteins and Wnts are hypothesized to have a role in OA and can activate cellular and molecular processes in both cartilage and bone cells. In addition, intracellular activation of different kinase cascades seems to be involved in the molecular crosstalk between cartilage and bone cells. Further research is required to integrate these different elements into a comprehensive approach that will increase our understanding of the disease processes in OA, and that could lead to the development of specific therapeutics or treatment strategies.

New molecular targets for the treatment of osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disorder characterized by destruction of the articular cartilage, subchondral bone alterations and synovitis. Current treatments are focused on symptomatic relief but they lack efficacy to control the progression of this disease which is a leading cause of disability. Therefore, the development of effective disease-modifying drugs is urgently needed. Different initiatives are in progress to define the molecular mechanisms involved in the initiation and progression of OA. These studies support the therapeutic potential of pathways relevant in joint metabolism such as Wnt/beta-catenin, discoidin domain receptor 2 or proteinase-activated receptor 2. The dysregulation in cartilage catabolism and subchondral bone remodeling could be improved by selective inhibitors of matrix metalloproteinases, aggrecanases and other proteases. Another approach would favor the activity of anabolic processes by using growth factors or regulatory molecules. Recent studies have also revealed the role of oxidative stress and synovitis in the progression of this disease, supporting the development of a number of inhibitory strategies. Novel targets in OA are represented by genes involved in OA pathophysiology discovered using gene network, epigenetic and microRNA approaches. Further insights into the molecular mechanisms involved in OA initiation and progression may lead to the development of new therapies able to control joint destruction and repair.

Modulation of OPG, RANK and RANKL by human chondrocytes and their implication during osteoarthritis

OBJECTIVES

Earlier studies suggest the involvement of osteoprotegerin (OPG), RANK and RANK ligand (RANKL) in OA subchondral bone metabolism; however, few studies have looked at their functional consequences on chondrocytes. We compared the expression/production of OPG, RANK and RANKL on human normal and OA chondrocytes, and evaluated, on OA chondrocytes, their modulation by some catabolic factors. Furthermore, the role of OPG and RANKL on the production of catabolic/anabolic factors was assessed.

METHODS

Expression was determined using real-time PCR, production of RANK and RANKL by flow cytometry and that of OPG by ELISA. Modulation of these factors was determined upon treatment with IL-1beta, TNF-alpha and PGE(2). The functional consequences were examined following treatment with soluble RANKL or OPG-Fc (OPG without the heparin-binding domain).

RESULTS

OPG, RANK and RANKL were expressed and produced by human chondrocytes. Membranous RANK was produced only by an OA chondrocyte subpopulation (29%) localized throughout the cartilage. The OPG/RANKL ratio was significantly (P = 0.05) reduced on the OA chondrocytes, whereas the RANK/RANKL ratio was significantly (P < 0.03) increased. OPG and membranous RANKL levels were significantly enhanced by IL-1beta, TNF-alpha and PGE(2), whereas membranous RANK was significantly increased only with IL-1beta. Administration of soluble RANKL had no effect on the OA chondrocytes. However, addition of OPG-Fc significantly stimulated MMP-13 (P = 0.05) and protease-activated receptor-2 (PAR-2) (P < 0.04) production.

CONCLUSIONS

Our findings showed that human chondrocytes express and produce OPG, RANK and RANKL. OA chondrocyte treatment with catabolic factors pointed towards an increased biological effect of OPG. Interestingly, OPG appears to be involved in OA progression by increasing two catabolic factors involved in cartilage pathophysiology.