PGE2 signal via EP2 receptors evoked by a selective agonist enhances regeneration of injured articular cartilage

Cause and chondroprotective effects of prostaglandin E2 secretion during mesenchymal stromal cell chondrogenesis

Mesenchymal stromal cells (MSCs) that are promising for cartilage tissue engineering secrete high amounts of prostaglandin E2 (PGE2), an immunoactive mediator involved in endochondral bone development. This study aimed to identify drivers of PGE2 and its role in the inadvertent MSC misdifferentiation into hypertrophic chondrocytes. PGE2 release, which rose in the first three weeks of MSC chondrogenesis, was jointly stimulated by endogenous BMP, WNT, and hedgehog activity that supported the exogenous stimulation by TGF-β1 and insulin to overcome the PGE2 inhibition by dexamethasone. Experiments with PGE2 treatment or the inhibitor celecoxib or specific receptor antagonists demonstrated that PGE2, although driven by prohypertrophic signals, exerted broad autocrine antihypertrophic effects. This chondroprotective effect makes PGE2 not only a promising option for future combinatorial approaches to direct MSC tissue engineering approaches into chondral instead of endochondral development but could potentially have implications for the use of COX-2-selective inhibitors in osteoarthritis pain management.

Revisiting prostaglandin E2: A promising therapeutic target for osteoarthritis

Osteoarthritis (OA) is a complex disease characterized by cartilage degeneration and persistent pain. Prostaglandin E2 (PGE2) plays a significant role in OA inflammation and pain. Recent studies have revealed the significant role of PGE2-mediated skeletal interoception in the progression of OA, providing new insights into the pathogenesis and treatment of OA. This aspect also deserves special attention in this review. Additionally, PGE2 is directly involved in pathologic processes including aberrant subchondral bone remodeling, cartilage degeneration, and synovial inflammation. Therefore, celecoxib, a commonly used drug to alleviate inflammatory pain through inhibiting PGE2, serves not only as an analgesic for OA but also as a potential disease-modifying drug. This review provides a comprehensive overview of the discovery history, synthesis and release pathways, and common physiological roles of PGE2. We discuss the roles of PGE2 and celecoxib in OA and pain from skeletal interoception and multiple perspectives. The purpose of this review is to highlight PGE2-mediated skeletal interoception and refresh our understanding of celecoxib in the pathogenesis and treatment of OA.

Relations between Structure/Composition and Mechanics in Osteoarthritic Regenerated Articular Tissue: A Machine Learning Approach

In the context of a large animal model of early osteoarthritis (OA) treated by orthobiologics, the purpose of this study was to reveal relations between articular tissues structure/composition and cartilage viscoelasticity. Twenty-four sheep, with induced knee OA, were treated by mesenchymal stem cells in various preparations-adipose-derived mesenchymal stem cells (ADSCs), stromal vascular fraction (SVF), and amniotic endothelial cells (AECs)-and euthanized at 3 or 6 months to evaluate the (i) biochemistry of synovial fluid; (ii) histology, immunohistochemistry, and histomorphometry of articular cartilage; and (iii) viscoelasticity of articular cartilage. After performing an initial analysis to evaluate the correlation and multicollinearity between the investigated variables, this study used machine learning (ML) models-Variable Selection Using Random Forests (VSURF) and Extreme Gradient Boosting (XGB)-to classify variables according to their importance and employ them for interpretation and prediction. The experimental setup revealed a potential relation between cartilage elastic modulus and cartilage thickness (CT), synovial fluid interleukin 6 (IL6), and prostaglandin E2 (PGE2), and between cartilage relaxation time and CT and PGE2. SVF treatment was the only limit on the deleterious OA effect on cartilage viscoelastic properties. This work provides indications to future studies aiming to highlight these and other relationships and focusing on advanced regeneration targets.

G Protein-Coupled Receptors in Osteoarthritis

Osteoarthritis (OA) is the most common chronic joint disease characterized, for which there are no available therapies being able to modify the progression of OA and prevent long-term disability. Critical roles of G-protein coupled receptors (GPCRs) have been established in OA cartilage degeneration, subchondral bone sclerosis and chronic pain. In this review, we describe the pathophysiological processes targeted by GPCRs in OA, along with related preclinical model and/or clinical trial data. We review examples of GPCRs which may offer attractive therapeutic strategies for OA, including receptors for cannabinoids, hormones, prostaglandins, fatty acids, adenosines, chemokines, and discuss the main challenges for developing these therapies.

Prostaglandin signaling in ciliogenesis and development

Prostaglandin (PG) signaling regulates a wide variety of physiological and pathological processes, including body temperature, cardiovascular homeostasis, reproduction, and inflammation. Recent studies have revealed that PGs play pivotal roles in embryo development, ciliogenesis, and organ formation. Prostaglandin E2 (PGE2) and its receptor EP4 modulate ciliogenesis by increasing the anterograde intraflagellar transport. Many G-protein-coupled receptors (GPCRs) including EP4 are localized in cilia for modulating cAMP signaling under various conditions. During development, PGE2 signaling regulates embryogenesis, hepatocyte differentiation, hematopoiesis, and kidney formation. Prostaglandins are also essential for skeletal muscle repair. This review outlines recent advances in understanding the functions and mechanisms of prostaglandin signaling in ciliogenesis, embryo development, and organ formation.

Pharmaceutical therapeutics for articular regeneration and restoration: state-of-the-art technology for screening small molecular drugs

Articular cartilage damage caused by sports injury or osteoarthritis (OA) has gained increased attention as a worldwide health burden. Pharmaceutical treatments are considered cost-effective means of promoting cartilage regeneration, but are limited by their inability to generate sufficient functional chondrocytes and modify disease progression. Small molecular chemical compounds are an abundant source of new pharmaceutical therapeutics for cartilage regeneration, as they have advantages in design, fabrication, and application, and, when used in combination, act as powerful tools for manipulating cellular fate. In this review, we present current achievements in the development of small molecular drugs for cartilage regeneration, particularly in the fields of chondrocyte generation and reversion of chondrocyte degenerative phenotypes. Several clinically or preclinically available small molecules, which have been shown to facilitate chondrogenesis, chondrocyte dedifferentiation, and cellular reprogramming, and subsequently ameliorate cartilage degeneration by targeting inflammation, matrix degradation, metabolism, and epigenetics, are summarized. Notably, this review introduces essential parameters for high-throughput screening strategies, including models of different chondrogenic cell sources, phenotype readout methodologies, and transferable advanced systems from other fields. Overall, this review provides new insights into future pharmaceutical therapies for cartilage regeneration.

Prostanoid Receptor Subtypes and Its Endogenous Ligands with Processing Enzymes within Various Types of Inflammatory Joint Diseases

A complex inflammatory process mediated by proinflammatory cytokines and prostaglandins commonly occurs in the synovial tissue of patients with joint trauma (JT), osteoarthritis (OA), and rheumatoid arthritis (RA). This study systematically investigated the distinct expression profile of prostaglandin E2 (PGE2), its processing enzymes (COX-2), and microsomal PGES-1 (mPGES-1) as well as the corresponding prostanoid receptor subtypes (EP1-4) in representative samples of synovial tissue from these patients (JT, OA, and RA). Quantitative TaqMan®-PCR and double immunofluorescence confocal microscopy of synovial tissue determined the abundance and exact immune cell types expressing these target molecules. Our results demonstrated that PGE2 and its processing enzymes COX-2 and mPGES-1 were highest in the synovial tissue of RA, followed by the synovial tissue of OA and JT patients. Corresponding prostanoid receptor, subtypes EP3 were highly expressed in the synovium of RA, followed by the synovial tissue of OA and JT patients. These proinflammatory target molecules were distinctly identified in JT patients mostly in synovial granulocytes, in OA patients predominantly in synovial macrophages and fibroblasts, whereas in RA patients mainly in synovial fibroblasts and plasma cells. Our findings show a distinct expression profile of EP receptor subtypes and PGE2 as well as the corresponding processing enzymes in human synovium that modulate the inflammatory process in JT, OA, and RA patients.

Macrophage phenotypic switch orchestrates the inflammation and repair/regeneration following acute pancreatitis injury

Background

Impaired or hyperactive pancreas regeneration after injury would cause exocrine insufficiency or recurrent / chronic pancreatitis and potentially carcinogenesis. Macrophages are the most abundant immune cells in the regenerative pancreas, however their phenotype and role remain poorly defined.

Method

Using caerulein-induced acute pancreatitis (AP) model, we examined the dynamic landscape of pancreatic macrophages throughout the acute inflammation to regeneration phases by flow cytometric and RNA-seq analyses. Liposome depletion of macrophages, Il4ra^−/− mice as well as inhibitors were used to elucidate the role and regulatory mechanism of macrophages during pancreatic regeneration.

Findings

We found that M1 macrophages dominated in the pro-inflammatory phase of AP, while M2-like macrophages dominated during pancreas repair/regeneration. Depletion of macrophages at early or late regenerative stage dramatically blocked the acinar-ductal metaplasia (ADM) or delayed inflammation resolution, respectively. Moreover, alternative activation of macrophages was partially dependent on IL-4RA signaling, and ECM/AKT activation in pancreatic macrophages facilitated inflammation resolution during tissue regeneration.

Interpretation

Our findings illustrate a dynamic phenotype and function of macrophages during AP repair/regeneration, helping us better understand the mechanism of pancreatic regeneration and providing clues for novel therapeutic strategy.

Cardiac injury modulates critical components of prostaglandin E2 signaling during zebrafish heart regeneration

The inability to effectively stimulate cardiomyocyte proliferation remains a principle barrier to regeneration in the adult human heart. A tightly regulated, acute inflammatory response mediated by a range of cell types is required to initiate regenerative processes. Prostaglandin E₂ (PGE₂), a potent lipid signaling molecule induced by inflammation, has been shown to promote regeneration and cell proliferation; however, the dynamics of PGE₂ signaling in the context of heart regeneration remain underexplored. Here, we employ the regeneration-competent zebrafish to characterize components of the PGE₂ signaling circuit following cardiac injury. In the regenerating adult heart, we documented an increase in PGE₂ levels, concurrent with upregulation of cox2a and ptges, two genes critical for PGE₂ synthesis. Furthermore, we identified the epicardium as the most prominent site for cox2a expression, thereby suggesting a role for this tissue as an inflammatory mediator. Injury also drove the opposing expression of PGE₂ receptors, upregulating pro-restorative ptger2a and downregulating the opposing receptor ptger3. Importantly, treatment with pharmacological inhibitors of Cox2 activity suppressed both production of PGE₂, and the proliferation of cardiomyocytes. These results suggest that injury-induced PGE₂ signaling is key to stimulating cardiomyocyte proliferation during regeneration.

Discovery of Novel Transient Receptor Potential Vanilloid 4 (TRPV4) Agonists as Regulators of Chondrogenic Differentiation: Identification of Quinazolin-4(3 H)-ones and in Vivo Studies on a Surgically Induced Rat Model of Osteoarthritis

Osteoarthritis (OA) is a degenerative disease characterized by joint destruction and loss of cartilage. There are many unmet needs in the treatment of OA and there are few promising candidates for disease-modifying OA drugs, particularly, anabolic agents. Here, we describe the identification of novel quinazolin-4(3 H)-one derivatives, which stimulate chondrocyte cartilage matrix production via TRPV4 and mitigate damaged articular cartilage. We successfully identified the water-soluble, highly potent quinazolin-4(3 H)-one derivative 36 and studied its intra-articular physicochemical profile to use in in vivo surgical OA model studies. Compound 36·HCl provided relief from OA damage in a rat medial meniscal tear (MT) model. Specifically, 36·HCl dose-dependently suppressed cartilage degradation and enhanced the messenger RNA expression of aggrecan and SOX9 in cartilage isolated from MT-operated rat knees compared with knees treated with vehicle. These results suggest that 36 induces anabolic changes in articular cartilage and consequently reduces OA progression.

The roles of prostaglandin F2 in regulating the expression of matrix metalloproteinase-12 via an insulin growth factor-2-dependent mechanism in sheared chondrocytes

Osteoarthritis (OA) was recently identified as being regulated by the induction of cyclooxygenase-2 (COX-2) in response to high fluid shear stress. Although the metabolic products of COX-2, including prostaglandin (PG)E₂, 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂), and PGF_2α, have been reported to be effective in regulating the occurrence and development of OA by activating matrix metalloproteinases (MMPs), the roles of PGF_2α in OA are largely overlooked. Thus, we showed that high fluid shear stress induced the mRNA expression of MMP-12 via cyclic (c)AMP- and PGF_2α-dependent signaling pathways. Specifically, we found that high fluid shear stress (20 dyn/cm²) significantly increased the expression of MMP-12 at 6 h ( > fivefold), which then slightly decreased until 48 h ( > threefold). In addition, shear stress enhanced the rapid synthesis of PGE₂ and PGF_2α, which generated synergistic effects on the expression of MMP-12 via EP2/EP3-, PGF2α receptor (FPR)-, cAMP- and insulin growth factor-2 (IGF-2)-dependent phosphatidylinositide 3-kinase (PI3-K)/protein kinase B (AKT), c-Jun N-terminal kinase (JNK)/c-Jun, and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-activating pathways. Prolonged shear stress induced the synthesis of 15d-PGJ₂, which is responsible for suppressing the high levels of MMP-12 at 48 h. These in vitro observations were further validated by in vivo experiments to evaluate the mechanisms of MMP-12 upregulation during the onset of OA by high fluid shear stress. By delineating this signaling pathway, our data provide a targeted therapeutic basis for combating OA.

Shear stress induces cartilage cells to produce hormone-like molecules that activate the expression of an enzyme implicated in the development of osteoarthritis, a degenerative joint disease. Pu Wang and colleagues from Northeastern University in Shenyang, China, exposed human cartilage cells to high fluid shear stress for up to 2 days. This frictional strain rapidly stimulated the production of a proinflammatory enzyme, COX-2, which in turn promoted the synthesis of two hormone-like substances, called prostaglandins. These prostaglandins, PGE₂ and PGF_2α, then induced expression of an osteoarthritis-associated enzyme called MMP-12 that destroys the supporting structure that surrounds cartilage cells. The researchers, working both in human cells and in mouse models, further delineated several intermediate signaling molecules in the pathway linking shear stress with MMP-12 activation, thereby revealing several new potential drug targets for combating osteoarthritis in patients.

Intra-articular administration of EP2 enhances the articular cartilage repair in a rabbit model

We have reported the usefulness of chondrocyte sheets on articular cartilage repair in animal experiments. Here, we investigated the regenerative effects of EP2 signalling with or without chondrocyte sheets. Forty-five rabbits were used, with six rabbits in each of the six groups and nine rabbits for chondrocytes and synovial cells harvesting to fabricate triple-layered chondrocyte sheets: osteochondral defect only (control, Group A), EP2 agonist (Group B), EP2 antagonist (Group C), chondrocyte sheets (Group D), EP2 agonist and chondrocyte sheets (Group E), and EP2 antagonist and chondrocyte sheets (Group F). After surgery, the weight distribution ratio was measured as an indicator of pain alleviation. Injections of the EP2 agonist or EP2 antagonist were given from 4 weeks after surgery. The rabbits were sacrificed at 12 weeks, and the repaired tissues were evaluated for histology. The weight distribution ratio and International Cartilage Repair Society grading were as follows: Group A: 40.5% ± 0.2%, 14.8 ± 0.5; Group B: 43.4% ± 0.7%, 25.4 ± 0.8; Group C: 38.7% ± 0.7%, 13.7 ± 0.3; Group D: 48.6% ± 0.6%, 40.2 ± 0.5; Group E: 49.1% ± 0.3%, 40.5 ± 0.4; and Group F; 46.8% ± 0.4%, 38.7 ± 0.5. Significant differences in histology and pain alleviation were observed between groups except between Groups A and C, between Groups D and E, and between Groups D and F. These findings show that the intra-articular administration of an EP2 agonist achieved pain alleviation and tissue repair. However, no synergistic effect with chondrocyte sheets was observed.

A systematic review on the role of eicosanoid pathways in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis is characterized by the production of eicosanoids, cytokines, adhesion molecules, infiltration of T and B lymphocytes in the synovium and oxygen reduction accompanied by the cartilage degradation. Eicosanoids are responsible for the progressive destruction of cartilage and bone, however neither steroids, nor the non steroidal anti-inflammatory drugs (NSAIDs), cannot slow down cartilage and bone destruction providing only symptomatic improvement. The current rheumatoid arthritis treatment options include mainly the use of disease-modifying anti-rheumatic drugs, the corticosteroids, the NSAIDs and biological agents.

METHODS

PubMed, Cochrane, and Embase electronic database were used as the main sources for extracting several articles, reviews, original papers in English for further review and analysis on the implication of arachidonic acid metabolites with rheumatoid arthritis and different strategies of targeting arachidonic acid metabolites, different enzymes or receptors for improving the treatment of rheumatoid arthritis patients.

RESULTS

We first focused on the role of individual prostaglandins and leukotrienes, in the inflammatory process of arthritis, concluding with an outline of the current clinical situation of rheumatoid arthritis and novel treatment strategies targeting the arachidonic acid pathway.

CONCLUSIONS

Extended research is necessary for the development of these novel compounds targeting the eicosanoid pathway, by increasing the levels of anti-inflammatory eicosanoids (PGD₂,15dPGJ₂), by inhibiting the production of pro-inflammatory eicosanoids (PGE₂, LTB₄, PGI₂) involved in rheumatoid arthritis or also by developing dual compounds displaying both the COX-2 inhibitor/TP antagonist activity within a single compound.

Synovial membrane receptors as therapeutic targets: A review of receptor localization, structure, and function

Joint pathology and degeneration is a significant cause of pain. The synovial membrane plays an important role in maintenance of the joint, contributes to the pathology of many arthropathies and may be adversely affected in joint disease. Improving knowledge of the receptors present within the synovium will aid in a better understanding of joint pathology and the development of new treatments for diseases such as osteoarthritis and rheumatoid arthritis. Knowledge of the location and function of synovial membrane receptors (both in healthy and diseased synovium) may provide important targets in the treatment of various arthropathies. Classic pain receptors such as opioid receptors in the synovium are a mainstay in local and systemic management of chronic pain in many species. In addition to these, many other receptors such as bradykinin, neurokinin, transient receptor potential vanilloid, and inflammatory receptors, such as prostanoid and interleukin receptors have been discovered within the synovial membrane. These receptors are important in pain, inflammation, and in maintenance of normal joint function and may serve as targets for pharmacologic intervention in pathologic states. The goal of this review is to outline synovial membrane receptor localization and local therapeutic modulation of these receptors, in order to stimulate further research into pharmacological management of arthropathies at the local level. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1589-1605, 2017.

Cartilage Repair in the Inflamed Joint: Considerations for Biological Augmentation Toward Tissue Regeneration

Cartilage repair/regeneration procedures (e.g., microfracture, autologous chondrocyte implantation [ACI]) typically result in a satisfactory outcome in selected patients. However, the vast majority of patients with chronic symptoms and, in general, a more diseased joint, do not benefit from these surgical techniques. The aims of this work were to (1) review factors negatively influencing the joint environment; (2) review current adjuvant therapies that can be used to improve results of cartilage repair/regeneration procedures in patients with more diseased joints, (3) outline future lines of research and promising experimental approaches. Chronicity of symptoms and advancing patient age appear to be the most relevant factors negatively affecting clinical outcome of cartilage repair/regeneration. Preliminary experience with hyaluronic acid, platelet-rich plasma, and mesenchymal stem cell has been positive but there is no strong evidence supporting the use of these products and this requires further assessment with high-quality, prospective clinical trials. The use of a Tissue Therapy strategy, based on more mature engineered tissues, holds promise to tackle limitations of standard ACI procedures. Current research has highlighted the need for more targeted therapies, and (1) induction of tolerance with granulocyte colony-stimulating factor (G-CSF) or by preventing IL-6 downregulation; (2) combined IL-4 and IL-10 local release; and (3) selective activation of the prostaglandin E2 (PGE2) signaling appear to be the most promising innovative strategies. For older patients and for those with chronic symptoms, adjuvant therapies are needed in combination with microfracture and ACI.

Changes in Membrane Receptors and Ion Channels as Potential Biomarkers for Osteoarthritis

Osteoarthritis (OA), a degenerative joint condition, is currently difficult to detect early enough for any of the current treatment options to be completely successful. Early diagnosis of this disease could increase the numbers of patients who are able to slow its progression. There are now several diseases where membrane protein biomarkers are used for early diagnosis. The numbers of proteins in the membrane is vast and so it is a rich source of potential biomarkers for OA but we need more knowledge of these before they can be considered practical biomarkers. How are they best measured and are they selective to OA or even certain types of OA? The first step in this process is to identify membrane proteins that change in OA. Here, we summarize several ion channels and receptors that change in OA models and/or OA patients, and may thus be considered candidates as novel membrane biomarkers of OA.

The growing role of eicosanoids in tissue regeneration, repair, and wound healing

Tissue repair and regeneration are essential processes in maintaining tissue homeostasis, especially in response to injury or stress. Eicosanoids are ubiquitous mediators of cell proliferation, differentiation, and angiogenesis, all of which are important for tissue growth. Eicosanoids regulate the induction and resolution of inflammation that accompany the tissue response to injury. In this review, we describe how this diverse group of molecules is a key regulator of tissue repair and regeneration in multiple organ systems and biologic contexts.

Prostaglandin E2 promotes cellular recovery from established nephrotoxic serum nephritis in mice, prosurvival, and regenerative effects on glomerular cells

We postulated that prostaglandin E2 (PGE2), which exhibits regulatory functions to control immune-mediated inflammation, fibrosis, oxidative stress, and tissue/cellular regeneration, has the potential to improve the course of nephritis. Therefore, the therapeutic potential of prostanoid on established nephritis in mice was evaluated focusing on its role on renal cellular recovery, with emphasis on its cytoprotecting and growth-promoting effects. Acute nephritis was induced in mice by single injection of nephrotoxic serum (NTS), followed by PGE2 administration with severity of nephritis evaluated over time. Mice injected with PGE2 recovered promptly with normalization of blood urea nitrogen and urine protein levels and histology. Recovery was observed with dosing of prostanoid at day 1, as well as day 4. With the use of selective EP1-4 receptor agonists, EP3 receptor has been identified as important in mediating beneficial effects of PGE2 in our system. PGE2 normalized glomerular cell losses during nephrotoxic serum-induced nephritis, restored synaptopodin distribution and F-actin filaments arrangement in glomeruli. In cell culture, PGE2 reduced nephrotoxim serum (NTS)-induced apoptosis of glomerular cells and promoted cell reproliferation after NTS-mediated injury. In conclusion, PGE2 treatment promotes resolution of glomerular inflammation. Consistent with this observation, the regenerative and cytoprotective effects of prostanoid on glomerular cells in culture were observed, suggesting that PGE2 may be beneficial in the treatment of glomerulonephritis.

Prostaglandins and rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, autoimmune, and complex inflammatory disease leading to bone and cartilage destruction, whose cause remains obscure. Accumulation of genetic susceptibility, environmental factors, and dysregulated immune responses are necessary for mounting this self-reacting disease. Inflamed joints are infiltrated by a heterogeneous population of cellular and soluble mediators of the immune system, such as T cells, B cells, macrophages, cytokines, and prostaglandins (PGs). Prostaglandins are lipid inflammatory mediators derived from the arachidonic acid by multienzymatic reactions. They both sustain homeostatic mechanisms and mediate pathogenic processes, including the inflammatory reaction. They play both beneficial and harmful roles during inflammation, according to their site of action and the etiology of the inflammatory response. With respect to the role of PGs in inflammation, they can be effective mediators in the pathophysiology of RA. Thus the use of agonists or antagonists of PG receptors may be considered as a new therapeutic protocol in RA. In this paper, we try to elucidate the role of PGs in the immunopathology of RA.

High density micromass cultures of a human chondrocyte cell line: a reliable assay system to reveal the modulatory functions of pharmacological agents

Osteoarthritis is a highly prevalent and disabling disease for which we do not have a cure. The identification of suitable molecular targets is hindered by the lack of standardized, reproducible and convenient screening assays. Following extensive comparisons of a number of chondrocytic cell lines, culture conditions, and readouts, we have optimized an assay utilizing C-28/I2, a chondrocytic cell line cultured in high-density micromasses. Utilizing molecules with known effects on cartilage (e.g. IL-1β, TGFβ1, BMP-2), we have exploited this improved protocol to (i) evoke responses characteristic of primary chondrocytes; (ii) assess the pharmacodynamics of gene over-expression using non-viral expression vectors; (iii) establish the response profiles of known pharmacological treatments; and (iv) investigate their mechanisms of action. These data indicate that we have established a medium-throughput methodology for studying chondrocyte-specific cellular and molecular responses (from gene expression to rapid quantitative measurement of sulfated glycosaminoglycans by Alcian blue staining) that may enable the discovery of novel therapeutics for pharmacological modulation of chondrocyte activation in osteoarthritis.

Prostaglandin E2 receptor type 2-selective agonist prevents the degeneration of articular cartilage in rabbit knees with traumatic instability

Introduction

Osteoarthritis (OA) is a common cause of disability in older adults. We have previously reported that an agonist for subtypes EP2 of the prostaglandin E2 receptor (an EP2 agonist) promotes the regeneration of chondral and osteochondral defects. The purpose of the current study is to analyze the effect of this agonist on articular cartilage in a model of traumatic degeneration.

Methods

The model of traumatic degeneration was established through transection of the anterior cruciate ligament and partial resection of the medial meniscus of the rabbits. Rabbits were divided into 5 groups; G-S (sham operation), G-C (no further treatment), G-0, G-80, and G-400 (single intra-articular administration of gelatin hydrogel containing 0, 80, and 400 μg of the specific EP2 agonist, ONO-8815Ly, respectively). Degeneration of the articular cartilage was evaluated at 2 or 12 weeks after the operation.

Results

ONO-8815Ly prevented cartilage degeneration at 2 weeks, which was associated with the inhibition of matrix metalloproteinase-13 (MMP-13) expression. The effect of ONO-8815Ly failed to last, and no effects were observed at 12 weeks after the operation.

Conclusions

Stimulation of prostaglandin E2 (PGE2) via EP2 prevents degeneration of the articular cartilage during the early stages. With a system to deliver it long term, the EP2 agonist could be a new therapeutic tool for OA.

Prostaglandin E2 regulates the expression of connective tissue growth factor (CTGF/CCN2) in human osteoarthritic chondrocytes via the EP4 receptor

Background

The regulatory mechanisms of the expression of connective tissue growth factor/CCN family member 2 (CTGF/CCN2) in human articular chondrocytes have not been clarified. We investigated the effect of prostaglandin E₂ (PGE₂) on CTGF/CCN2 expression in chondrocytes.

Findings

Articular cartilage samples were obtained from patients with osteoarthritis (OA) and chondrocytes were isolated and cultured in vitro. Chondrocytes were stimulated with PGE₂, PGE receptor (EP)-specific agonists, or interleukin (IL)-1. CTGF expression was analyzed using quantitative polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay. The inhibitory effects of EP receptor antagonists (for EP2 and EP4) against PGE₂ stimulation were also investigated. Stimulation of chondrocytes with PGE₂ or IL-1 significantly suppressed CTGF expression. The suppressive effect of PGE₂ was reproduced by EP2/EP4 receptor agonists but not by EP1/EP3 receptor agonists, and was partially blocked by an EP4 receptor antagonist, suggesting that the EP4 receptor has a dominant role.

Conclusions

PGE₂ may be involved in the regulation of CTGF/CCN2 expression in human articular chondrocytes via the EP4 receptor. Elucidation of EP4-mediated signaling in chondrocytes may contribute to a better understanding of the effects of PGE₂ in arthritis.