Osteogenic protein 1 in synovial fluid from patients with rheumatoid arthritis or osteoarthritis: relationship with disease and levels of hyaluronan and antigenic keratan sulfate

HYBID in osteoarthritis: Potential target for disease progression

HYBID is a new hyaluronan-degrading enzyme and exists in various cells of the human body. Recently, HYBID was found to over-express in the osteoarthritic chondrocytes and fibroblast-like synoviocytes. According to these researches, high level of HYBID is significantly correlated with cartilage degeneration in joints and hyaluronic acid degradation in synovial fluid. In addition, HYBID can affect inflammatory cytokine secretion, cartilage and synovium fibrosis, synovial hyperplasia via multiple signaling pathways, thereby exacerbating osteoarthritis. Based on the existing research of HYBID in osteoarthritis, HYBID can break the metabolic balance of HA in joints through the degradation ability independent of HYALs/CD44 system and furthermore affect cartilage structure and mechanotransduction of chondrocytes. In particular, in addition to HYBID itself being able to trigger some signaling pathways, we believe that low-molecular-weight hyaluronan produced by excess degradation can also stimulate some disease-promoting signaling pathways by replacing high-molecular-weight hyaluronan in joints. The specific role of HYBID in osteoarthritis is gradually revealed, and the discovery of HYBID raises the new way to treat osteoarthritis. In this review, the expression and basic functions of HYBID in joints were summarized, and reveal potential role of HYBID as a key target in treatment for osteoarthritis.

ROS/TGF-β signal mediated accumulation of SOX4 in OA-FLS promotes cell senescence

Osteoarthritis (OA) is an age-related disease, which is mainly treated with oral, topical, and/or intra-articular options to relieve symptoms and lack of specific treatment measures. Fibroblasts (FLS) are crucial cells in joint inflammation and destruction. Cellular senescence plays an important role during OA pathogenesis and senescent cells exhibit cell-cycle arrest and senescence-associated secretory phenotype (SASP). SRY-related HMG-box 4 (SOX4) is a contributing factor during many developmental processes and is elevated in inflamed synovium than in noninflamed synovium from arthritis patients. This study was designed to investigate whether SOX4 participate in the pathogenesis of OA by affecting FLS senescence and explore the internal mechanism. Firstly, we found that FLS cells exhibited more cellular senescence in OA compared with control group. We also verified the role of reactive oxygen species (ROS)/TGF-β signal in the induction of OA-FLS senescence. During the exploration of SOX4 in cell senescence, the results indicated that SOX4 activation promotes cell senescence and SASP of OA-FLS. Apart from that, we also confirmed that SOX4, regulated by ROS/TGF-β signal, was critical transcription factor associated with OA-FLS senescence. Therefore, SOX4 is likely to be a novel therapeutic target and early diagnostic marker during OA pathogenesis.

Hypoxia/reoxygenation activates the JNK pathway and accelerates synovial senescence

Hypoxia/reoxygenation (H/R) may play an important role via senescence in the mechanism of osteoarthritis (OA) development. The synovial membrane is highly sensitive to H/R due to its oxygen consumption feature. Excessive mechanical loads and oxidative stress caused by H/R induce a senescence-associated secretory phenotype (SASP), which is related to the development of OA. The aim of the present study was to investigate the differences of SASP manifestation in synovial tissue masses between tissues from healthy controls and patients with OA. The present study used tumor necrosis factor-α (TNF-α) to pre-treat synovial tissue and fibroblast-like synoviocytes (FLS) to observe the effect of inflammatory cytokines on the synovial membrane before H/R. It was determined that H/R increased interleukin (IL)-1β and IL-6 expression levels in TNF-α-induced cell culture supernatants, increased the proportion of SA-β-gal staining, and increased the expression levels of high mobility group box 1, caspase-8, p16, p21, matrix metalloproteinase (MMP)-3 and MMP-13 in the synovium. Furthermore, H/R opened the mitochondrial permeability transition pore, caused the loss of mitochondrial membrane potential (ΔΨm) and increased the release of reactive oxygen species (ROS). Moreover, H/R caused the expansion of the mitochondrial matrix and rupture of the mitochondrial extracorporeal membrane, with a decrease in the number of cristae. In addition, H/R induced activation of the JNK signaling pathway in FLS to induce cell senescence. Thus, the present results indicated that H/R may cause inflammation and escalate synovial inflammation induced by TNF-α, which may lead to the pathogenesis of OA by increasing changes in synovial SASP and activating the JNK signaling pathway. Therefore, further studies expanding on the understanding of the pathogenesis of H/R etiology in OA are required.

Bone morphogenetic proteins in multiple sclerosis: Role in neuroinflammation

Bone morphogenetic proteins (BMPs) are growth factors that represent the largest subgroup of signalling ligands of the transforming growth factor beta (TGF-β) superfamily. Their participation in the proliferation, survival and cell fate of several cell types and their involvement in many pathological conditions are now well known. BMP expression is altered in multiple sclerosis (MS) patients, suggesting that BMPs have a role in the pathogenesis of this disease. MS is a demyelinating and neurodegenerative autoimmune disorder of the central nervous system (CNS). MS is a complex pathological condition in which genetic, epigenetic and environmental factors converge, although its aetiology remains elusive. Multifunctional molecules, such as BMPs, are extremely interesting in the field of MS because they are involved in the regulation of several adult tissues, including the CNS and the immune system. In this review, we discuss the extensive data available regarding the role of BMP signalling in neuronal progenitor/stem cell fate and focus on the participation and expression of BMPs in CNS demyelination. Additionally, we provide an overview of the involvement of BMPs as modulators of the immune system, as this subject has not been thoroughly explored even though it is of great interest in autoimmune disorders. Moreover, we describe the data on BMP signalling in autoimmunity and inflammatory diseases, including MS and its experimental models. Thus, we aim to provide an integrated view of the putative role of BMPs in MS pathogenesis and to open the field for the further development of alternative therapeutic strategies for MS patients.

Correlation of cartilage metabolic markers & antioxidants with the severity of knee osteoarthritis

Osteoarthritis is characterized by the degeneration of articular cartilage. Cartilage metabolic markers have been explored as possible markers for osteoarthritis, and osteogenic protein -1 (OP-1) has emerged out to play a major role in cartilage repair. Oxidative stress has been implicated as a mediator of cartilage damage in patients with osteoarthritis. The aim of this study was to correlate the cartilage metabolic markers and antioxidants with the severity of knee osteoarthritis.

The genetics behind osteoarthritis: Asian focus

Osteoarthritis (OA), a degenerative joint disease, is the most common form of arthritis in the elderly. Problems arising from the condition are not only health, physical, and psychological, but also economical and social. OA is a complex disease causes by environmental factors (obesity, female gender, advancing age) and genetics. A strong genetic contribution to primary OA has been observed in several studies. Asian population is undoubtedly genetically different from European, whom most studies have been performed. This review systematically compares results of molecules involved with OA from studies performed on Asian and Caucasian populations. The clear differences between Asian and Caucasian populations may be from the sex- and ethnic-specific nature of the disease, as well as from the inclusion criteria of the studies. Global collaboration is highly significant in understanding genetic underlying OA. Knowledge gained from genetic study is important to the development of prevention and therapeutic intervention, and to identify individuals at risk of developing severe or progressive OA.

Reduced response of human meniscal cells to Osteogenic Protein 1 during osteoarthritis and pro-inflammatory stimulation

OBJECTIVE

Many cell types lose responsiveness to anabolic factors during inflammation and disease. Osteogenic Protein 1 (OP1/BMP7) was evaluated for the ability to enhance extracellular matrix synthesis in healthy and OA meniscus cells. Mechanisms of cell response to OP1 were explored.

DESIGN

Meniscus and cartilage tissues from healthy tissue donors and osteoarthritis (OA) patients undergoing total knee arthroplasties were acquired. Primary cell cultures were stimulated with OP1 and/or inflammatory factors (IL1α, IL1β, or fibronectin fragments (FnF)) and cellular responses were analyzed by RT-qPCR and immunoblots. Frozen section immunohistochemistry (IHC) was conducted to assess OP1 and receptor proteins in normal and OA meniscus.

RESULTS

OP1 treatment of normal meniscus cells resulted in significant, dose-dependent increases in ACAN (aggrecan) and COL2A1, and decreased MMP13 gene transcription, while only ACAN was upregulated (P < 0.01) at the highest dose of OP1 in OA meniscus cells. OP1 induced significantly more ACAN gene transcription in normal meniscus than normal articular cartilage (P = 0.05), and no differences between normal and OA cartilage were detected. Receptor expression and kinetics of canonical signaling activation were similar between normal and OA specimens. Normal meniscus cells treated with inflammatory factors were refractory to OP1 stimulation. Smad1 phosphorylation at an inhibitory site was induced (P = 0.01 for both normal and OA meniscus) by inflammatory cytokine treatment.

CONCLUSIONS

The meniscus demonstrates resistance to OP1 stimulation in OA and in the presence of inflammatory mediators. MAPK-mediated Smad1 linker phosphorylation is a possible mediator of the loss of anabolic extracellular matrix production in the inflammatory cytokine affected meniscus.

Blockade of bone morphogenetic protein signaling potentiates the pro-inflammatory phenotype induced by interleukin-17 and tumor necrosis factor-α combination in rheumatoid synoviocytes

Introduction

Bone morphogenetic proteins (BMPs) are multifunctional secreted growth factors regulating a broad spectrum of functions in numerous systems. An increased expression and production of specific BMPs have been described in the rheumatoid arthritis (RA) synovium. The aim of this study was to analyze the involvement of the BMP signaling pathway in RA synoviocytes in response to interleukin-17 (IL-17) and tumor necrosis factor-alpha (TNF-α).

Methods

The expression of components of the BMP signaling pathway (BMP receptors, BMP ligands, BMP signal transducers, and BMP antagonists) was analyzed by quantitative polymerase chain reaction before and after treatment of RA synoviocytes with TNF-α or IL-17 or both. Regulation was studied in the presence of the specific BMP inhibitor DMH1 (dorsomorphin homologue 1) or an exogenous BMP ligand, BMP6. Expression and production of pro-inflammatory cytokines (IL-6 and granulocyte-macrophage colony-stimulating factor), chemokines (IL-8, CCL2, CCL5, and CXCL10), and matrix metalloproteinases (MMP-1, −2, −3, −9, and −13) were analyzed.

Results

RA synoviocytes express BMP receptors (mainly BMPRIA, ACTRIA, and BMPRII), signal transducers of the Smad family (Smad1 and 5 and co-Smad4), and different BMP antagonists. The modulation of the expression of the BMP target genes—Id (inhibitor of DNA-binding/differentiation) proteins and Runx (Runt-related transcription factor) transcription factors—after the addition of exogenous BMP shows that the BMP signaling pathway is active. RA synoviocytes also express BMP ligands (BMP2, BMP6, and BMP7) which are highly upregulated after activation with TNF-α and IL-17. Autocrine BMP signaling pathway can be blocked by treatment with the inhibitor DMH1, leading to an increase in the upregulated expression of pro-inflammatory cytokines, chemokines, and MMPs induced by the activation of RA synoviocytes with TNF-α and IL-17. Conversely, the additional stimulation of the BMP pathway with the exogenous addition of the BMP6 ligand decreases the expression of those pro-inflammatory and pro-destructive factors.

Conclusion

The results indicate that the canonical BMP pathway is functionally active in human RA synoviocytes and that the inhibition of autocrine BMP signaling exacerbates the pro-inflammatory phenotype induced in RA synoviocytes by the stimulation with IL-17 and TNF-α.

Production of a polyclonal antibody against osteogenic protein-1, and its role in the diagnosis of osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is a progressive degenerative disorder of the articular cartilage. Available diagnostic radiography has been poorly associated with the progress and severity of this clinical disease. As osteogenic protein-1 (OP-1) has been identified as a bone morphogenetic protein with a major role in cartilage repair, we aimed to evaluate its potential role in the diagnosis of OA.

METHODS

This was an experimental study conducted at the Department of Biochemistry, Sikkim Manipal Institute of Medical Sciences, India. Polyclonal antibodies (i.e. anti-OP-1[f]) were raised against OP-1 in mice, and subsequently used in a sandwich enzyme-linked immunosorbent assay (ELISA) to detect the presence of OP-1 in the synovial fluids of 75 osteoarthritic patients. For the purpose of correlation, the radiographic assessments of the knees of the 75 patients were graded using the Kellgren-Lawrence scoring system.

RESULT

The polyclonal antibody (i.e. anti-OP-1[f]) raised against OP-1 was able to detect the presence of OP-1 in the synovial fluids of all the osteoarthritic patients via sandwich ELISA. The level of the OP-1 was found to be much higher than the reference range and correlated positively with the severity of OA (r = 0.24; p = 0.04).

CONCLUSION

Our study shows that the polyclonal antibody, anti OP-1(f), could be used for the immunodiagnosis of osteoarthritis via sandwich ELISA.

BMP activation and Wnt-signalling affect biochemistry and functional biomechanical properties of cartilage tissue engineering constructs

OBJECTIVES

Bone morphogenetic protein (BMP-) and Wnt-signalling play crucial roles in cartilage homeostasis. Our objective was to investigate whether activation of the BMP-pathway or stimulation of Wnt-signalling cascades effectively enhances cartilage-specific extracellular matrix (ECM) accumulation and functional biomechanical parameters of chondrocyte-seeded tissue engineering (TE)-constructs.

DESIGN

Articular chondrocytes were cultured in collagen-type-I/III-matrices over 6 weeks to create a biomechanical standard curve. Effects of stimulation with 100 ng/mL BMP-4/-7 heterodimer or 10 mM lithium chloride (LiCl) on ECM-deposition was quantified and characterized histologically. Biomechanical parameters were determined by the Very Low Rubber Hardness (VLRH) method and under confined compression stress relaxation.

RESULTS

BMP-4/-7 treatment resulted in stronger collagen type-II staining and significantly enhanced glycosaminoglycan (GAG) deposition (3.2-fold; *P < 0.01) correlating with improved hardness (∼1.7-fold; *P = 0.001) reaching 83% of native cartilage values after 28 days, a value not reached before 9 weeks without stimulation. LiCl treatment enhanced VLRH slightly, but significantly (∼1.3-fold; *P = 0.016) with a trend to more ECM-deposition. BMP-4/-7 treatment significantly enhanced the E Modulus (105.7 ± 34.1 kPa; *P = 0.000001) compared to controls (8.0 ± 4.2 kPa). Poisson's ratio was significantly improved by BMP-4/-7 treatment (0.0703 ± 0.0409; *P = 0.013) vs controls (0.0432 ± 0.0284) and a significantly lower permeability (5.8 ± 2.1056 × 10(-14) m4/N.s; *P = 0.00001) was detected compared to untreated scaffolds (4.4 ± 3.1289 × 10(-13) m4/N.s).

CONCLUSIONS

While Wnt-activation is less effective, BMP-4/-7 heterodimer stimulation approximated native cartilage features in less than 50% of standard culture time representing a promising strategy for functional cartilage TE to improve biomechanical parameters of engineered cartilage.

Correlation of the Osteogenic Protein-1 (OP-1) with Age, Cartilage metabolic Markers and Antioxidants in the Osteoarthritic Patients of Sikkim

BACKGROUND

Age and oxidative stress have been implicated as the main causes of the cartilage damage in osteoarthritis (OA). The osteogenic protein-1(OP-1), a member of the bone morphogenetic family (BMP), plays a major role in cartilage repair.

AIM

To correlate the OP-1 in the synovial fluid with the age and antioxidants like superoxide dismutase (SOD), glutathione peroxidase (GPx) and uric acid (UA) in the blood and with the cartilage metabolic markers like hyaluronic acid (HA) and keratan sulphate (KS) in the synovial fluid of osteoarthritic patients.

METHOD

Seventy five osteoarthritic patients were taken up for the study. Heparinized blood samples were collected for the estimation of SOD, GPx and UA. Synovial fluid was aspirated for the estimation of HA, KS and OP-1. OP-1 was estimated by using a polyclonal antibody (anti-OP-1) which was produced against OP-1 in the mouse ascitic fluid by sandwich ELISA.

RESULT

Age and UA showed a significant correlation with OP-1. On the other hand, the correlations between OP-1 and the antioxidants (SOD and GPx) and the cartilage metabolic markers (HA and KS) were insignificant in osteoarthritic patients.

CONCLUSION

The study suggests about the important role of OP-1 in cartilage aging and degeneration, which may help us in understanding the potential for the therapeutic interventions in the treatment of cartilage degenerative processes.

Serum levels of BMP-2, 4, 7 and AHSG in patients with degenerative joint disease requiring total arthroplasty of the hip and temporomandibular joints

To date, there is no objective or reliable means of assessing the severity of degenerative joint disease (DJD) and need for joint replacement surgery. Hence, it is difficult to know when an individual with DJD has reached a point where total arthroplasty is indicated. The purpose of the present study is to determine whether serum levels of Alpha-2 HS-glycoprotein (AHSG) as well as bone morphogenetic proteins (BMP-2, 4, 7) can be used to predict the presence of severe DJD of the hip and/or temporomandibular joint (TMJ) (specifically: joints that require replacement). A total of 30 patients scheduled for arthroplasty (diseased) (15 HIP, 15 TMJ) and 120 age-matched controls (healthy/non-diseased) were included. Blood samples were collected from all patients ≥8 weeks after the last arthroplasty. Concentrations of serum analytes were measured using enzyme-linked immunosorbent assays, and these were compared between the Diseased and Healthy groups, utilizing the Mann-Whitney U-test. Patients with disease had significantly higher levels of BMP-2 and BMP-4 and lower levels of AHSG in serum compared to non-diseased humans (p < 0.01). Higher levels of BMP-2, 4 and reduced levels of AHSG appear to characterize patients who have DJD that is severe enough to require total joint replacement. Perhaps measurements of these proteins can be used to make objective decisions regarding the need for total arthroplasty as opposed to the current subjective approaches.

Pain perception in knees with circumscribed cartilage lesions is associated with intra-articular IGF-1 expression

BACKGROUND

Circumscribed cartilage defects are considered as prearthritic lesions and lead to differential intra-articular cytokine expression. Mechanisms of associated pain development and influence of smoking behavior are not yet fully understood in humans.

PURPOSE

This study aimed to reveal relations between synovial cytokine levels in knees with circumscribed cartilage defects and pain sensation.

STUDY DESIGN

Descriptive laboratory study.

METHODS

In a clinical trial, knee lavage fluids of 42 patients with circumscribed cartilage lesions treated by either microfracturing (n = 19) or by autologous chondrocyte implantation (n = 23) and fluids of 5 healthy control individuals were prospectively collected. Preoperative knee pain was evaluated according to frequency and strength; subjective knee function was assessed using a visual analog scale and the International Knee Documentation Committee (IKDC) score. Synovial concentrations of aggrecan, insulin-like growth factor (IGF)-I, basic fibroblast growth factor (bFGF), interleukin (IL)-1β, bone morphogenetic protein (BMP)-2, and BMP-7 were determined by enzyme-linked immunosorbent assay.

RESULTS

Pain strength showed a highly significant association with intra-articular IGF-1 levels (ρ = .48, P < .01), but no correlation with synovial concentrations of aggrecan, bFGF, IL-1β, BMP-2, and BMP-7. Although pain strength and frequency demonstrated a statistically significant relationship, no substantial association between pain frequency and any of the examined cytokine levels was found. Intra-articular IGF-1 concentrations significantly correlated with the area of cartilage damage (ρ = .35, P < .02); the other investigated cytokines failed to show this association. Neither of the determined intra-articular mediators demonstrated statistically significant correlations with subjective knee function or IKDC score. Only intra-articular concentrations of IGF-1 and BMP-2 statistically significantly correlated with age; total protein content was negatively associated with body mass index (P < .05). In smokers, synovial expression of total protein content, IGF-1, and bFGF was significantly diminished compared to nonsmokers (P < .05).

CONCLUSION

Insulin-like growth factor-I is present in knees with circumscribed cartilage lesions in a size-dependent manner. IGF-1 levels correlated with indicators of pain perception; smoking negatively influenced synovial cytokine expression related to cartilage metabolism, but pain perception was not altered.

The role of synovial fluid markers of catabolism and anabolism in osteoarthritis, rheumatoid arthritis and asymptomatic organ donors

Introduction

The purpose of this study was to correlate the level of anabolic and catabolic biomarkers in synovial fluid (SF) from patients with rheumatoid arthritis (RA), patients with osteoarthritis (OA) and asymptomatic organ donors.

Methods

SF was collected from the knees of 45 OA, 22 RA patients and 20 asymptomatic organ donors. Eight biomarkers were selected and analyzed by using an enzyme-linked immunosorbent assay: interleukin (IL)-1, IL-6, IL-8 and IL-11; leukemia-inhibitory factor (LIF); cartilage oligomeric protein (COMP); osteocalcin; and osteogenic protein 1 (OP-1). Data are expressed as medians (interquartile ranges). The effects of sex and disease activity were assessed on the basis of the Western Ontario and McMaster Universities index score for patients with OA and on the basis of white blood cell count, erythrocyte sedimentation rate and C-reactive protein level for patients with RA.

Results

The mean ages (± SD) of the patients were as follows: 53 ± 9 years for patients with OA, 54 ± 11 years for patients with RA and 52 ± 7 years for asymptomatic organ donors. No effect of participants' sex was identified. In the SF of patients with RA, four of five cytokines were higher than those in the SF of patients with OA and those of asymptomatic organ donors. The most significant differences were found for IL-6 and IL-8, where IL-6 concentration in SF of patients with RA was almost threefold higher than that in patients with OA and fourfold higher than that in asymptomatic donor controls: 354.7 pg/ml (1,851.6) vs. 119.4 pg/ml (193.2) vs. 86.97 pg/ml (82.0) (P < 0.05 and P < 0.05, respectively). IL-8 concentrations were higher in SF of patients with RA than that in patients with OA as well as that in asymptomatic donor controls: 583.6 pg/ml (1,086.4) vs. 429 pg/ml (87.3) vs. 451 pg/ml (170.1) (P < 0.05 and P < 0.05, respectively). No differences were found for IL-11 in the SF of patients with RA and that of patients with OA, while a 1.4-fold difference was detected in the SF of patients with OA and that of asymptomatic donor controls: 296.2 pg/ml (257.2) vs. 211.6 pg/ml (40.8) (P < 0.05). IL-1 concentrations were the highest in the SF of RA patients (9.26 pg/ml (11.1)); in the SF of asymptomatic donors, it was significantly higher than that in patients with OA (9.083 pg/ml (1.6) vs. 7.76 pg/ml (2.6); P < 0.05). Conversely, asymptomatic donor control samples had the highest LIF concentrations: 228.5 pg/ml (131.6) vs. 128.4 pg/ml (222.7) in the SF of patients with RA vs. 107.5 pg/ml (136.9) in the SF of patients with OA (P < 0.05). OP-1 concentrations were twofold higher in the SF of patients with RA than those in patients with OA and threefold higher than those in asymptomatic donor control samples (167.1 ng/ml (194.8) vs. 81.79 ng/ml (116.0) vs. 54.49 ng/ml (29.3), respectively; P < 0.05). The differences in COMP and osteocalcin were indistinguishable between the groups, as were the differences between active and inactive OA and RA.

Conclusions

Activation of selected biomarkers corresponds to the mechanisms that drive each disease. IL-11, LIF and OP-1 may be viewed as a cluster of biomarkers significant for OA; while profiling of IL-1, IL-6, IL-8, LIF and OP-1 may be more significant in RA. Larger, better-defined patient cohorts are necessary to develop a biomarker algorithm for prognostic use.

Association between expression of the bone morphogenetic proteins 2 and 7 in the repair of circumscribed cartilage lesions with clinical outcome

Background

Although there is much known about the role of BMPs in cartilage metabolism reliable data about the in vivo regulation in natural and surgically induced cartilage repair are still missing.

Methods

Lavage fluids of knee joints of 47 patients were collected during surgical therapy. 5 patients had no cartilage lesion and served as a control group, the other 42 patients with circumscribed cartilage defects were treated by microfracturing (19) or by an Autologous Chondrocyte Implantation (23). The concentrations of BMP-2 and BMP-7 were determined by ELISA. The clinical status was evaluated using the IKDC Score prior to and 1 year following the operation.

Results

High level expression in the control group was found for BMP-2, concentrations of BMP-7 remained below detection levels. No statistical differences could be detected in concentrations of BMP-2 or BMP-7 in the lavage fluids of knees with cartilage lesions compared to the control group. Levels of BMP-7 did not change after surgical cartilage repair, whereas concentrations of BMP-2 statistically significant increased after the intervention (p < 0.001). The clinical outcome following cartilage regenerating surgery increased after 1 year by 29% (p < 0.001). The difference of the IKDC score after 1 year and prior to the operation was used to quantify the degree of improvement following surgery. This difference statistically significant correlated with initial BMP-2 (R = 0.554, p < 0.001) but not BMP-7 (R = 0.031, n.s.) levels in the knee joints.

Conclusions

BMP-2 seems to play an important role in surgically induced cartilage repair; synovial expression correlates with the clinical outcome.

Relationship of plasma and synovial fluid BMP-7 with disease severity in knee osteoarthritis patients: a pilot study

The objective of this study was to investigate bone morphogenetic protein-7 (BMP-7) levels in both plasma and synovial fluid of patients with primary knee osteoarthritis (OA) and to determine their relationship to disease severity. Thirty-two patients with knee OA and 15 healthy subjects were enrolled in the study. Anteroposterior knee radiographs were taken to determine the disease severity of the affected knee. The radiographic grading of OA in the knee was performed using the Kellgren-Lawrence criteria. BMP-7 levels in the plasma and synovial fluid were measured using enzyme-linked immunosorbent assay. The mean plasma BMP-7 concentration of the knee OA patients was significantly higher compared with that of healthy controls (12.1 +/- 1.6 vs 3.5 +/- 0.9 pg/ml, P = 0.001). Although BMP-7 levels in plasma were higher with respect to paired synovial fluid samples, the difference was not statistically significant (12.1 +/- 1.6 vs 10.5 +/- 2.2 pg/ml, P = 0.3). Subsequent analysis showed that plasma BMP-7 levels significantly correlated with disease severity (r = 0.77, P < 0.001). Furthermore, the synovial fluid levels of BMP-7 also correlated with disease severity (r = 0.60, P < 0.001). In addition, plasma BMP-7 levels showed a positive correlation with synovial fluid BMP-7 levels (r = 0.71, P < 0.001). Overexpression of BMP-7 in plasma and synovial fluid is related to progressive joint damage in knee OA. These findings suggest that BMP-7 might serve as a biochemical parameter for determining disease severity in primary knee OA and could play a potential role in cartilage protection and repair of OA.

A rapid and sensitive bioassay for the simultaneous measurement of multiple bone morphogenetic proteins. Identification and quantification of BMP4, BMP6 and BMP9 in bovine and human serum

Background

Bone morphogenetic proteins (BMPs) are pleiotropic members of the TGF-beta superfamily which regulate many biological processes during development and adult tissue homeostasis and are implicated in the pathogenesis of a number of human diseases. Their involvement in both normal and aberrant physiology creates a need for rapid, sensitive and methodologically simple assays to evaluate their activity from a variety of biological samples. Previously alkaline phosphatase based assays, ELISA and luciferase based bioassays have been developed to evaluate either individual or total BMP activity. In this paper, we describe a highly sensitive, rapid and specific cell based assay for the simultaneous quantification of total and isoform specific BMP activity from biological samples.

Results

A C2C12 cell line stably transfected with a reporter plasmid consisting of the BMP response element (BRE) from the Id1 promoter fused to a luciferase reporter gene was generated. Exposure of this cell line to human recombinant BMP2, BMP4, BMP6, BMP7, BMP9 and BMP10 induced the expression of luciferase which was quantified using a luminometer. This assay was specific for BMP activity as the other TGF-β superfamily members TGF-β 1, Nodal and Mullerian Inhibiting Substance (MIS) did not induce the reporter. Pretreatment of samples with isoform specific BMP blocking antibodies coupled with isoform specific titration analysis allowed the simultaneous identification and quantification of BMP4, BMP6 and BMP9 in serum samples.

Conclusion

The assay is rapid (<48 hours) and can be used to simultaneously measure isoform specific and total BMP activity in complex solutions.

Effects induced by BMPS in cultures of human articular chondrocytes: comparative studies

We compared anabolic and anti-catabolic activities of selected bone morphogenetic proteins (BMP-2, -4, -6, and -7) and cartilage-derived morphogenetic proteins (CDMP-1 and -2) in human normal adult articular chondrocytes. Ankle chondrocytes were cultured in alginate beads in the presence of 10% serum and treated with either growth factors only (each at 100 ng/ml) or the combination of interleukin-1 (IL-1 beta) (0.1 ng/ml) and BMPs. Chondrocyte metabolism was assessed by proteoglycan (PG) synthesis, content, DNA content, and cell survival. The results showed that BMP-2, -4, and -7 were more potent in stimulating PGs than other growth factors tested. The highest levels of PG synthesis were detected at day 9 in the presence of BMP-7. With regard to anti-catabolic properties, the effect depended upon treatment scheme (simultaneous or sequential). Under simultaneous cultures, BMP-2, -4, and -6 failed to counteract IL-1 beta induced inhibition of PG synthesis, while the CDMPs restored this parameter to serum control levels. Only BMP-7 showed consistent and pronounced anti-catabolic activity in either culture treatment scheme. None of the factors induced cell death or chondrocyte proliferation. In conclusion, the growth factors tested showed different levels of effects on human chondrocytes in culture, but only BMP-7 displayed both strong anabolic and anti-catabolic properties.

Dynamic activation of bone morphogenetic protein signaling in collagen-induced arthritis supports their role in joint homeostasis and disease

Introduction

Rheumatoid arthritis is a chronic systemic autoimmune disease affecting peripheral joints and leading to loss of joint function. The severity and outcome of disease are dependent on the balance between inflammatory/destructive and homeostatic or repair pathways. Increasing evidence suggests a role for bone morphogenetic protein (BMP) signaling in joint homeostasis and disease.

Methods

Activation of BMP signaling in collagen-induced arthritis as a model of rheumatoid arthritis was studied by immunohistochemistry and Western blot for phosphorylated SMAD1/5 at different time points. Expression of different BMP ligands and noggin, a BMP antagonist, was determined on synovium and cartilage extracts of arthritic knees, at different time points, with quantitative polymerase chain reaction. At the protein level, BMP2 and BMP7 were studied with immunohistochemistry. Finally, the effect of anti-tumor necrosis factor-alpha (TNFα) treatment on the expression of BMP2, BMP7, and growth and differentiation factor-5 (GDF5) in synovium and cartilage of arthritic knees was investigated.

Results

A time-dependent activation of the BMP signaling pathway in collagen-induced arthritis was demonstrated with a dynamic and characteristic expression pattern of different BMP subfamily members in synovium and cartilage of arthritic knees. As severity increases, the activation of BMP signaling becomes more prominent in the invasive pannus tissue. BMP2 is present in cartilage and the hyperplastic lining layer. BMP7 is found in the sublining zone and inflammatory infiltrate. Treatment with etanercept slowed down progression of disease, but no change in expression of GDF5, BMP2, and BMP7 in synovium was found; in the cartilage, however, blocking of TNFα increased the expression of BMP7.

Conclusions

BMP signaling is dynamically activated in collagen-induced arthritis and is partly TNFα-independent. TNFα blocking increased the expression of BMP7 in the articular cartilage, possibly enhancing anabolic mechanisms. Different types of source and target cells are recognized. These data further support a role for BMP signaling in arthritis.

OP-1/BMP-7 in cartilage repair

Three years ago we published a book chapter on the role of bone morphogenetic proteins (BMPs) in cartilage repair. Since that time our understanding of the function of osteogenic protein-1 (OP-1) or BMP-7 in cartilage homeostasis and repair has substantially improved and therefore we decided to devote a current review solely to this BMP. Here we summarise the information accumulated on OP-1 from in vitro and ex vivo studies with cartilage cells and tissues as well as from in vivo studies of cartilage repair in various animal models. The primary focus is on articular chondrocytes and cartilage, but data will also be presented on nonarticular cartilage, particularly from the intervertebral disc. The data show that OP-1 is a unique growth factor which, unlike other members of the same BMP family, exhibits in addition to its strong pro-anabolic activity very prominent anti-catabolic properties. Animal studies have demonstrated that OP-1 has the ability to repair cartilage in vivo in various models of articular cartilage degradation, including focal osteochondral and chondral defects and osteoarthritis, as well as models of degeneration in intervertebral disc cartilage. Together our findings indicate a significant promise for OP-1 as therapeutic in cartilage repair.