Thrombin-cleaved osteopontin levels in synovial fluid correlate with disease severity of knee osteoarthritis

Platelet-Rich Plasma Power-Mix Gel (ppm)-An Orthobiologic Optimization Protocol Rich in Growth Factors and Fibrin

Platelet- and fibrin-rich orthobiologic products, such as autologous platelet concentrates, have been extensively studied and appreciated for their beneficial effects on multiple conditions. Platelet-rich plasma (PRP) and its derivatives, including platelet-rich fibrin (PRF), have demonstrated encouraging outcomes in clinical and laboratory settings, particularly in the treatment of musculoskeletal disorders such as osteoarthritis (OA). Although PRP and PRF have distinct characteristics, they share similar properties. The relative abundance of platelets, peripheral blood cells, and molecular components in these orthobiologic products stimulates numerous biological pathways. These include inflammatory modulation, augmented neovascularization, and the delivery of pro-anabolic stimuli that regulate cell recruitment, proliferation, and differentiation. Furthermore, the fibrinolytic system, which is sometimes overlooked, plays a crucial role in musculoskeletal regenerative medicine by regulating proteolytic activity and promoting the recruitment of inflammatory cells and mesenchymal stem cells (MSCs) in areas of tissue regeneration, such as bone, cartilage, and muscle. PRP acts as a potent signaling agent; however, it diffuses easily, while the fibrin from PRF offers a durable scaffolding effect that promotes cell activity. The combination of fibrin with hyaluronic acid (HA), another well-studied orthobiologic product, has been shown to improve its scaffolding properties, leading to more robust fibrin polymerization. This supports cell survival, attachment, migration, and proliferation. Therefore, the administration of the "power mix" containing HA and autologous PRP + PRF may prove to be a safe and cost-effective approach in regenerative medicine.

Angiogenesis in the Outer Membrane of Chronic Subdural Hematomas through Thrombin-Cleaved Osteopontin and the Integrin α9 and Integrin β1 Signaling Pathways

BACKGROUND

A chronic subdural hematoma (CSDH) is considered to be an inflammatory and angiogenic disease. The CSDH outer membrane, which contains inflammatory cells, plays an important role in CSDH development. Osteopontin (OPN) is an extracellular matrix protein that is cleaved by thrombin, generating the N-terminal half of OPN, which is prominently involved in integrin signal transduction. We explored the expression of the N-terminal half of OPN in CSDH fluid and the expression of integrins α9 and β1 and the downstream components of the angiogenic signaling pathways in the outer membrane of CSDHs.

METHODS

Twenty samples of CSDH fluid and eight samples of CSDH outer membrane were collected from patients suffering from CSDHs. The concentrations of the N-terminal half of OPN in CSDH fluid samples were measured using ELISA kits. The expression levels of integrins α9 and β1, vinculin, talin-1, focal adhesion kinase (FAK), paxillin, α-actin, Src and β-actin were examined by Western blot analysis. The expression levels of integrins α9 and β1, FAK and paxillin were also examined by immunohistochemistry. We investigated whether CSDH fluid could activate FAK in cultured endothelial cells in vitro.

RESULTS

The concentration of the N-terminal half of OPN in CSDH fluid was significantly higher than that in the serum. Western blot analysis confirmed the presence of these molecules. In addition, integrins α9 and β1, FAK and paxillin were localized in the endothelial cells of vessels within the CSDH outer membrane. FAK was significantly phosphorylated immediately after treatment with CSDH fluid.

CONCLUSION

Our data suggest that the N-terminal half of OPN in CSDH fluid promotes neovascularization in endothelial cells through integrins α9 and β1. The N-terminal half of OPN, which is part of the extracellular matrix, plays a critical role in the promotion of CSDHs.

Intra-Articular Hyaluronic Acid in Osteoarthritis and Tendinopathies: Molecular and Clinical Approaches

Musculoskeletal diseases continue to rise on a global scale, causing significant socioeconomic impact and decreased quality of life. The most common disorders affecting musculoskeletal structures are osteoarthritis and tendinopathies, complicated orthopedic conditions responsible for major pain and debilitation. Intra-articular hyaluronic acid (HA) has been a safe, effective, and minimally invasive therapeutic tool for treating these diseases. Several studies from bedside to clinical practice reveal the multiple benefits of HA such as lubrication, anti-inflammation, and stimulation of cellular activity associated with proliferation, differentiation, migration, and secretion of additional molecules. Collectively, these effects have demonstrated positive outcomes that assist in the regeneration of chondral and tendinous tissues which are otherwise destroyed by the predominant catabolic and inflammatory conditions seen in tissue injury. The literature describes the physicochemical, mechanical, and biological properties of HA, their commercial product types, and clinical applications individually, while their interfaces are seldom reported. Our review addresses the frontiers of basic sciences, products, and clinical approaches. It provides physicians with a better understanding of the boundaries between the processes that lead to diseases, the molecular mechanisms that contribute to tissue repair, and the benefits of the HA types for a conscientious choice. In addition, it points out the current needs for the treatments.

Osteopontin, a bridge links osteoarthritis and osteoporosis

Osteoarthritis (OA) is the most prevalent joint disease characterized by degradation of articular cartilage, inflammation, and changes in periarticular and subchondral bone of joints. Osteoporosis (OP) is another systemic skeletal disease characterized by low bone mass and bone mineral density (BMD) accompanied by microarchitectural deterioration in bone tissue and increased bone fragility and fracture risk. Both OA and OP are mainly affected on the elderly people. Recent studies have shown that osteopontin (OPN) plays a vital role in bone metabolism and homeostasis. OPN involves these biological activities through participating in the proliferation, migration, differentiation, and adhesion of several bone-related cells, including chondrocytes, synoviocytes, osteoclasts, osteoblasts, and marrow mesenchymal stem cells (MSCs). OPN has been demonstrated to be closely related to the occurrence and development of many bone-related diseases, such as OA and OP. This review summarizes the role of OPN in regulating inflammation activity and bone metabolism in OA and OP. Furthermore, some drugs that targeted OPN to treat OA and OP are also summarized in the review. However, the complex mechanism of OPN in regulating OA and OP is not fully elucidated, which drives us to explore the depth effect of OPN on these two bone diseases.

Synovial Fluid Biomarkers in Knee Osteoarthritis: A Systematic Review and Quantitative Evaluation Using BIPEDs Criteria

OBJECTIVE

The aim of this systematic review was to analyze the evidence about the efficacy of the several synovial fluid (SF) biomarkers proposed for knee osteoarthritis (OA), categorizing them by both molecular characteristics and clinical use according to the BIPEDs criteria, to provide a comprehensive and structured overview of the current literature.

DESIGN

A systematic review was performed in May 2020 on PubMed, Cochrane Library, and Embase databases about SF biomarkers in patients with knee OA. The search was limited to articles in the last 20 years on human studies, involving patients with knee OA, reporting SF biomarkers. The evidence for each selected SF biomarker was quantified according to the 6 categories of BIPEDs classification.

RESULTS

A total of 159 articles were included in the qualitative data synthesis and 201 different SF biomarkers were identified. Among these, several were investigated multiple times in different articles, for a total of 373 analyses. The studies included 13,557 patients with knee OA. The most promising SF biomarkers were C4S, IL-6, IL-8, Leptin, MMP-1/3, TIMP-1, TNF-α, and VEGF. The "burden of disease" and "diagnostic" categories were the most represented with 132 and 106 different biomarkers, respectively.

CONCLUSIONS

The systematic review identified numerous SF biomarkers. However, despite the high number of studies on the plethora of identified molecules, the evidence about the efficacy of each biomarker is supported by limited and often conflicting findings. Further research efforts are needed to improve the understanding of SF biomarkers for a better management of patients with knee OA.

Both Full-Length and Protease-Cleaved Products of Osteopontin Are Elevated in Infectious Diseases

Circulating full-length osteopontin (FL-OPN) is elevated in plasma from patients with various infectious diseases, such as adult T-cell leukemia, Mycobacterium tuberculosis (TB), hepatitis virus infection, leptospirosis, acquired immune deficiency syndrome (AIDS), AIDS/TB, and coronavirus disease 2019 (COVID-19). Proteolysis of OPN by thrombin, matrix metalloproteases, caspase 8/3, cathepsin D, plasmin, and enterokinase generates various cleaved OPNs with a variety of bioactivities by binding to different target cells. Moreover, OPN is susceptible to gradual proteolysis. During inflammation, one of the cleaved fragments, N-terminal thrombin-cleaved OPN (trOPN or OPN-Arg¹⁶⁸ [OPN-R]), induces dendritic cell (DC) adhesion. Further cleavage by carboxypeptidase B2 or carboxypeptidase N removes Arg¹⁶⁸ from OPN-R to OPN-Leu¹⁶⁷ (OPN-L). Consequently, OPN-L decreases DC adhesion. In particular, the differences in plasma level over time are observed between FL-OPN and its cleaved OPNs during inflammation. We found that the undefined OPN levels (mixture of FL-OPN and cleaved OPN) were elevated in plasma and reflected the pathology of TB and COVID-19 rather than FL-OPN. These infections are associated with elevated levels of various proteases. Inhibition of the cleavage or the activities of cleaved products may improve the outcome of the therapy. Research on the metabolism of OPN is expected to create new therapies against infectious diseases.

Mechanistic Insight on the Interaction between OPN and Integrin ανβ3 in Osteoarthritis

Osteoarthritis (OA) is a joint disease characterized by cartilage degeneration. Osteopontin (OPN) is involved in the initiation, repair, and maintenance of metabolic homeostasis in normal articular cartilage. This study investigated the role of OPN and its interaction with the integrin ανβ3 receptor in the expression of hyaluronic acid (HA) in OA chondrocytes. Overexpression of OPN significantly increased the expression of integrin ανβ3 and hyaluronic acid synthases (HAS) and synthesis of HA. Depleting OPN in OA chondrocytes showed the opposite trend for integrin alpha;νβ3, HAS, and HA. Nonspecifically and specifically blocking integrin receptor using GRGDSP and integrin ανβ3 antibody downregulated HAS and HA; both were inhibited to similar extents. The expression of HAS and HA was predominantly regulated by the interaction between OPN and integrin ανβ3. Taken together, we have delineated the importance of the OPN/integrin ανβ3/HAS/HA axis in OA and identified OPN as a promising candidate for molecular therapy for use in patients with OA.

Degenerative osteoarthritis a reversible chronic disease

Osteoarthritis (OA) is the most common chronic musculoskeletal disorder. It can affect any joint and is the most frequent single cause of disability in older adults.

OA is a progressive degenerative disease involving the entire joint structure in a vicious circle that includes the capsule-bursa tissue inflammation, synovial fluid modifications, cartilage breakdown and erosions, osteochondral inflammatory damage leading to bone erosion and distortion.

Research has identified the initial inflammatory-immunologic process that starts this vicious cycle leading to so-called early OA. Research has also identified the role played in the disease advancement by synoviocytes type A and B, chondrocytes, extracellular matrix, local immune-inflammatory mediators and proteases.

This article investigates the joint-resident MSCs that play an essential local homeostatic role and regulate cell turn over and tissue repair. Resident MSCs establish and maintain a local regenerative microenvironment.

The understanding of OA physiopathology clarifies the core mechanisms by which minimally invasive interventions might be able to halt and reverse the course of early stage OA. Interventions employing PRP, MSCs and exosomes are considered in this article.

Leukocyte-rich PRP for knee osteoarthritis: Current concepts

Knee osteoarthritis is a major painful and debilitating orthopaedic disease affecting a large number of adult individuals on a global scale. Over the years, this severe condition has been widely studied and while many alternatives have been utilized, platelet-rich plasma (PRP) remains one of the most popular solutions among researchers and clinicians alike. While there are different formulations and techniques involved in the preparation of PRP, produced either manually or via the use of commercial kits, the presence of leukocytes in a PRP mixture is a factor that raises concern due to their well-known pro-inflammatory activity. Although it is reasonable to worry about this, it should be taken into consideration that in order for the healing process to occur, the inflammatory phase is necessary. Leukocytes present in the inflammatory phase release both pro and anti-inflammatory molecules and, when combined with activated platelets, their potential increases. Additionally, due to the macrophage's plasticity to switch from the subtype 1 to subtype 2, it is suggested that the inclusion of the components from the buffy coat layer in a PRP mixture, classifying it as leukocyte-rich platelet-rich plasma or L-PRP, may provide benefits instead of detriments, from a standpoint of the regenerative potential of PRP.

Plasma level of Osteopontin does not respond to total replacement Surgery in patients with severe Primary knee/Hip Osteoarthritis

OBJECTIVE

To test the response of Osteopontin levels in patients with knee/hip Osteoarthritis undergoing a replacement surgery.

METHOD

Plasma samples of 30 (16 with knee Osteoarthritis and 14 with hip Osteoarthritis) patients have been collected before and 3 month after a knee/hip replacement in order to investigate the above stated aim of this study.

RESULT

Osteopontin levels did not decrease after 3 months of the surgery.

CONCLUSION

Osteopontin levels showed no significant reduction and therefore do not respond to replacement treatment.

EGFR is a pivotal regulator of thrombin-mediated inflammation in primary human nucleus pulposus culture

We found that the coagulation and cytokine pathways were important mechanisms involve in the degeneration of intervertebral discs (IVD) using a microarray approach to analyze gene expression in different grades of specimens. Furthermore, using a cytokine/chemokine array, a significant increase in CXCL8 expression was observed in human nucleus pulposus (NP) cells after thrombin treatment. The enhancement of CXCL8 expression by thrombin was activated by the PAR1 receptor. Importantly, analysis of degenerated human NP tissue samples showed that EGFR expression positively correlated with the grade of tissue degeneration. In NP cells, thrombin caused an increase in phosphorylation of the EGFR at the Tyr1068, and treatment with the pharmacological EGFR inhibitor, AG1473 effectively blocked thrombin-enhanced CXCL8 production. Surprisingly, inhibition of STAT3 for 24 h decreased expression of EGFR. Treatment with thrombin also increased Akt and GSK3α/β activation; this activation was also blocked by EGFR inhibitor. Although c-Src, ERK, and FAK were activated by thrombin, only c-Src and ERK were involved in the STAT3/CXCL8 induction. Our findings indicate that stimulation of an inflammatory response in NP cells by thrombin is part of a specific pathophysiology that modulates the EGFR activation through activation of Src/ERK/STAT3 signaling.

Oxidative stress and chronic inflammation in osteoarthritis: can NRF2 counteract these partners in crime?

Osteoarthritis (OA) is an age-related joint degenerative disease associated with pain, joint deformity, and disability. The disease starts with cartilage damage but then progressively involves subchondral bone, causing an imbalance between osteoclast-driven bone resorption and osteoblast-driven remodeling. Here, we summarize the data for the role of oxidative stress and inflammation in OA pathology and discuss how these two processes are integrated during OA progression, as well as their contribution to abnormalities in cartilage/bone metabolism and integrity. At the cellular level, oxidative stress and inflammation are counteracted by transcription factor nuclear factor erythroid p45-related factor 2 (NRF2), and we describe the regulation of NRF2, highlighting its role in OA pathology. We also discuss the beneficial effect of some phytonutrients, including the therapeutic potential of NRF2 activation, in OA.

Phosphorylation of osteopontin has proapoptotic and proinflammatory effects on human knee osteoarthritis chondrocytes

The aim of the present study was to investigate the effects of phosphorylated osteopontin (p-OPN) on apoptosis and pro-inflammatory cytokine expression in human knee osteoarthritis (OA) chondrocytes. Human knee OA chondrocytes obtained from patients who underwent total knee arthroplasty were treated with p-OPN, OPN or buffer. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR) and western blot analysis were used to assess the expression levels of proinflammatory factors, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6 and nuclear factor (NF)-κB. Apoptosis of human knee OA chondrocytes was detected by Annexin V-fluorescein isothiocyanate/propidium iodide flow cytometry. Compared with the controls, chondrocytes treated with OPN exhibited higher mRNA and protein expression levels of proinflammatory factors (IL-1β, TNF-α, IL-6 and NF-κB), and a higher percentage of apoptotic chondrocytes. Furthermore, chondrocytes treated with p-OPN exhibited the highest mRNA and protein expression levels of proinflammatory factors (IL-1β, TNF-α, IL-6, NF-κB) and the highest percentage of apoptotic chondrocytes. p-OPN induces chondrocyte apoptosis and proinflammatory factor release, which suggests that p-OPN may contribute to OA pathogenesis, and inhibition of p-OPN may provide a novel effective strategy to slow or halt OA progression.

Synovial fluid adipokines are associated with clinical severity in knee osteoarthritis: a cross-sectional study in female patients with joint effusion

BACKGROUND

Adipokines are related to knee osteoarthritis, but their exact role is not well known. The aim of this study was to evaluate the association between adipokines in synovial fluid and clinical severity in patients with knee osteoarthritis with joint effusion.

METHODS

Cross-sectional study with systematic inclusion of female patients with symptomatic primary knee osteoarthritis with ultrasound-confirmed joint effusion. Age, physical exercise, knee osteoarthritis symptoms duration, classical cardiovascular risk factors and different anthropometric measurements were collected. Metabolic syndrome was defined in accordance to National Cholesterol Education Program-Adult Treatment Panel III. Radiographic severity was evaluated according to Kellgren-Lawrence scale and Lequesne index was used to assess clinical severity. Seven adipokines (leptin, adiponectin, resistin, visfatin, osteopontin, omentin and chemerin) and three inflammatory markers (tumor necrosis factor α, interleukin 6 and high sensitivity C-reactive protein) were measured by enzyme-linked immunosorbent assay in synovial fluid.

RESULTS

Kellgren-Lawrence grade, physical exercise, all anthropometric measurements (especially waist circumference), tumor necrosis factor α, and high levels of leptin, resistin, and ostepontin were related to knee osteoarthritis severity. After adjustment for clinical confounders (age, symptom duration, and radiology), anthropometric measurements, inflammatory markers, and all evaluated adipokines, there were independent associations with clinical severity for resistin (directly associated) and visfatin (inversely associated). No other adipokines or inflammatory markers were independently associated with Lequesne index. The association of radiological parameters, physical exercise, and waist circumference with Lequesne index remained after adjustment.

CONCLUSIONS

Resistin was directly associated, and visfatin was inversely associated, with clinical severity in female patients with knee osteoarthritis with joint effusion. These associations were more important after adjustment for confounders, especially when all adipokines were evaluated.

The Expression of Osteopontin and Wnt5a in Articular Cartilage of Patients with Knee Osteoarthritis and Its Correlation with Disease Severity

Objectives. This study is undertaken to investigate the relation between osteopontin (OPN) and Wnt5a expression in the progression and pathogenesis of osteoarthritis (OA). Methods. 50 cartilage tissues from knee OA patients and normal controls were divided into four groups of severe, moderate, minor, and normal lesions based on the modified grading system of Mankin. Immunohistochemistry and real-time PCR were utilized to analyze the OPN and Wnt5a expression in articular cartilage. Besides, the relations between OPN and Wnt5a expression and the severity of OA were explored. Results. OPN and Wnt5a could be identified in four groups' tissues. Amongst the groups, the intercomparisons of OPN expression levels showed statistical differences (P < 0.01). Besides, the intercomparisons of Wnt5a expression degrees showed statistical differences (P < 0.05), except that between the minor and normal groups (P > 0.05). The scores of Mankin were demonstrated to relate to OPN expression (r = -0.847, P < 0.01) and Wnt5a expression in every group (r = -0.843, P < 0.01). Also, a positive correlation can be observed between the OPN and Wnt5a expression (r = 0.769, P < 0.01). Conclusion. In articular cartilage, the expressions of OPN and Wnt5a are positively related to progressive damage of knee OA joint. The correlation between Wnt5a and OPN might be important to the progression and pathogenesis of knee OA.

Osteopontin as a biochemical marker and severity indicator for idiopathic hip osteoarthritis

INTRODUCTION

A diagnostic evaluation of the severity and progression of hip osteoarthritis (OA) using biochemical markers is lacking in the current medical literature. Osteopontin (OPN) has been proved to correlate with the progression and severity of knee OA. Therefore, the examination of plasma OPN levels in patients with idiopathic hip OA and its correlation with disease severity and progression was necessary.

METHODS

Our study included 21 patients displaying symptomatic severe idiopathic hip OA; the diagnosis of the disease was based on the checklist of the American College of Rheumatology and the severity was evaluated according to the K-L grading (Kellgran and Lawrence score).

RESULTS

14 patients showed radiological changes according K-L grade 3 (66.66%), and 7 patients showed radiological changes according K-L grade 4 (33.33%). We observed a highly statistically significant increase of plasma OPN levels in comparison with normal referenced values, the cut off value for differentiating between normal people and patients with hip OA was 193.6 ng/ml. Furthermore, the mean of plasma OPN levels in idiopathic hip osteoarthritis patients with K-L grade 4 (362.51 ± 83.31 ng/mL) was greater than those with K-L grade 3 (283.41 ± 56.31 ng/mL), the difference being statistically significant.

CONCLUSIONS

plasma OPN levels are increased in idiopathic hip OA and are correlated with the severity of the disease.

Thrombin Cleavage of Osteopontin Modulates Its Activities in Human Cells In Vitro and Mouse Experimental Autoimmune Encephalomyelitis In Vivo

Osteopontin is a proinflammatory cytokine and plays a pathogenetic role in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), by recruiting autoreactive T cells into the central nervous system. Osteopontin functions are modulated by thrombin cleavage generating N- and C-terminal fragment, whose individual roles are only partly known. Published data are difficult to compare since they have been obtained with heterogeneous approaches. Interestingly, thrombin cleavage of osteopontin unmasks a cryptic domain of interaction with α₄β₁ integrin that is the main adhesion molecule involved in lymphocyte transmigration to the brain and is the target for natalizumab, the most potent drug preventing relapses. We produced recombinant osteopontin and its N- and C-terminal fragments in an eukaryotic system in order to allow their posttranslational modifications. We investigated, in vitro, their effect on human cells and in vivo in EAE. We found that the osteopontin cleavage plays a key role in the function of this cytokine and that the two fragments exert distinct effects both in vitro and in vivo. These findings suggest that drugs targeting each fragment may be used to fine-tune the pathological effects of osteopontin in several diseases.

The Effect of Polymorphisms in SPP1 on Risk of Fracture: A Case-Control Study

Background

The purpose of the study was to investigate the correlation between rs4754 and rs6840362 polymorphisms of secreted phosphoprotein 1 (SPP1) gene and fracture risk.

Material/Methods

rs4754 and rs6840362 were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 130 patients with fracture and 107 healthy controls matched with the former by age and sex. Hardy-Weinberg equilibrium (HWE) was assessed in the control group based on the genotype distributions of SSP1 poylmorphisms. The differences in genotype, allele, and haplotype frequencies between cases and controls were detected by the chi-square test, and the relative risk of fracture is expressed by odds ratio (OR) and 95% confidence interval (CI). The linkage disequilibrium (LD) and haplotype analyses were conducted with HaploView software.

Results

The TT genotype in rs4754 had significant difference in patients with fracture and controls (10.77% and 4.59%, P=0.04) and the results showed that people carrying TT genotype of rs4754 were more susceptible to fractures than CC genotype carriers (OR=3.00, 95%CI=1.02–8.89). The T allele also had 1.54 times higher risk of fractures (OR=1.54, 95%CI=1.04–2.30), but this was not true for the rs6840362 polymorphism. LD between the 2 polymorphisms and haplotype C-T (rs6840362-rs4754) increased the susceptibility to fracture (OR=2.01, 95%CI=1.23–3.28).

Conclusions

SPP1 rs4754 polymorphism may be related to risk of fracture, but not rs6840362.

Correlation between osteopontin and caveolin-1 in the pathogenesis and progression of osteoarthritis

Previous studies have produced contradictory results with regard to the role of osteopontin (OPN) and caveolin-1 in the pathology of osteoarthritis (OA). Thus, the aim of the present study was to investigate the correlation between OPN and caveolin-1 in the pathogenesis and progression of OA. Cartilage tissue samples were obtained from 50 individuals, of which 40 had been diagnosed with OA and 10 were normal healthy individuals. The samples were ascribed to four groups, namely the normal, minor, moderate and severe groups, on the basis of the improved Mankin grading system. Immunohistochemistry was applied to analyse the expression of OPN and caveolin-1. OPN and caveolin-1 were detected in the tissues of all four groups. The mutual comparisons of OPN expression levels among the groups revealed statistically significant differences (P<0.05). In addition, the mutual comparisons of caveolin-1 expression levels among the four groups demonstrated statistically significant differences (P<0.05), with the exception of that between the moderate and severe groups (P>0.05). Improved Mankin grading system scores were shown to correlate with the average grey level of OPN expression in each group (r=-0.824, P<0.01) and the average grey level of caveolin-1 expression (r=0.725, P<0.01). Furthermore, a statistically significant negative correlation was observed between the average grey levels of OPN and caveolin-1 expression (r=-0.676, P﹤0.05). Therefore, the results of the present study indicated that the correlation between OPN and caveolin-1 may play a significant role in the pathogenesis and progression of OA.

TRPV4 as a therapeutic target for joint diseases

Biomechanical factors play a critical role in regulating the physiology as well as the pathology of multiple joint tissues and have been implicated in the pathogenesis of osteoarthritis. Therefore, the mechanisms by which cells sense and respond to mechanical signals may provide novel targets for the development of disease-modifying osteoarthritis drugs (DMOADs). Transient receptor potential vanilloid 4 (TRPV4) is a Ca(2+)-permeable cation channel that serves as a sensor of mechanical or osmotic signals in several musculoskeletal tissues, including cartilage, bone, and synovium. The importance of TRPV4 in joint homeostasis is apparent in patients harboring TRPV4 mutations, which result in the development of a spectrum of skeletal dysplasias and arthropathies. In addition, the genetic knockout of Trpv4 results in the development of osteoarthritis and decreased osteoclast function. In engineered cartilage replacements, chemical activation of TRPV4 can reproduce many of the anabolic effects of mechanical loading to accelerate tissue growth and regeneration. Overall, TRPV4 plays a key role in transducing mechanical, pain, and inflammatory signals within joint tissues and thus is an attractive therapeutic target to modulate the effects of joint diseases. In pathological conditions in the joint, when the delicate balance of TRPV4 activity is altered, a variety of different tools could be utilized to directly or indirectly target TRPV4 activity.

Immunological blockade of adipocyte inflammation caused by increased matrix metalloproteinase-cleaved osteopontin in obesity

OBJECTIVE

Osteopontin (OPN) is upregulated in adipose tissue (AT) in obesity and contributes to subclinical inflammation, adipocyte dysfunction, and insulin resistance. OPN effects can be increased by cleavage by matrix metalloproteinases (MMP). This study aimed at investigating the presence of OPN cleavage products in human AT in obesity and their impact on adipocyte function and immunological blockade of these effects.

METHODS

AT of severely obese and control donors was investigated for OPN and MMP expression and the presence of OPN cleavage fragments. Primary adipocytes were isolated from human donors for in vitro investigation of cleaved OPN effects.

RESULTS

OPN and MMP-9 expression was highly correlated in AT from obese donors, and increased levels of cleaved OPN were detected in AT from obese individuals. The in vitro effect of OPN on adipocyte inflammation and insulin resistance was enhanced by protease cleavage, which could finally be blocked with a monoclonal antibody directed against the MMP cleavage site of OPN.

CONCLUSIONS

These findings show that MMP cleavage of OPN in AT occurs in obesity, thereby enhancing OPN's inflammatory and pro-diabetic activity on adipocytes. Specifically targeting MMP-cleaved OPN opens avenues for prevention and treatment of obesity-induced type 2 diabetes.

Elevated levels of full-length and thrombin-cleaved osteopontin during acute dengue virus infection are associated with coagulation abnormalities

INTRODUCTION

Dengue virus (DENV) is transmitted by the mosquito vector, and causes a wide range of symptoms that lead to dengue fever (DF) or life-threatening dengue hemorrhagic fever (DHF). The host and viral correlates that contribute to DF and DHF are complex and poorly understood, but appear to be linked to inflammation and impaired coagulation. Full-length osteopontin (FL-OPN), a glycoprotein, and its activated thrombin-cleaved product, trOPN, integrate multiple immunological signals through the induction of pro-inflammatory cytokines.

MATERIALS AND METHOD

To understand the role of OPN in DENV-infection, we assessed circulating levels of FL-OPN, trOPN, and several coagulation markers (D-dimer, thrombin-antithrombin complex [TAT], thrombomodulin [TM], and ferritin in blood obtained from 65 DENV infected patients in the critical and recovery phases of DF and DHF during a dengue virus epidemic in the Philippines in 2010.

RESULTS

Levels of FL-OPN, trOPN, D-dimer, TAT, and TM were significantly elevated in the critical phase in both the DF and DHF groups, as compared with healthy controls. During the recovery phase, FL-OPN levels declined while trOPN levels increased dramatically in both the DF and DHF groups. FL-OPN levels were directly correlated with D-dimer and ferritin levels, while the generation of trOPN was associated with TAT levels, platelet counts, and viral RNA load.

CONCLUSION

Our study demonstrated the marked elevation of plasma levels of FL-OPN and thrombin-cleaved OPN product, trOPN, in DENV-infection for the first time. Further studies on the biological functions of these matricellular proteins in DENV-infection would clarify its pathogenesis.

OPN gene polymorphisms influence the risk of knee OA and OPN levels in synovial fluid in a Chinese population

INTRODUCTION

A body of studies suggests the role of osteopontin (OPN) in onset and development of osteoarthritis (OA), however, the association between OPN polymorphisms and OA susceptibility as well as its clinical features has not been reported.

METHODS

A total of 750 patients with primary knee OA and 794 healthy volunteer were enrolled as controls. Both OA and control groups were interviewed to obtain demographic and clinical data. Three polymorphisms of OPN gene, namely, -156GG/G, -443C/T and -66T/G were determined. The levels of the full length and the thrombin-cleaved OPN in synovial fluid (SF) from OA subjects were measured.

RESULTS

We found the polymorphisms of the -443C/T and the -66/T/G were significantly associated with the OA risk and the radiographic severity. The -443TT and -66GG showed protective effect against developing OA and were associated with lower Kellgren-Lawrence grade. Besides, the polymorphisms of -443C/T and -66T/G significantly affected the thrombin-cleaved OPN levels in SF from OA subjects. Subjects with -443TT and -66GG genotypes had lower thrombin-cleaved OPN levels in SF. The thrombin-cleaved OPN levels in SF were positively correlated to the radiographic severity of OA.

CONCLUSIONS

Our findings suggest that certain OPN gene polymorphisms may be used as molecular markers for the susceptibility and severity of OA.

Usefulness of specific OA biomarkers, thrombin-cleaved osteopontin, in the posterior cruciate ligament OA rabbit model

OBJECTIVE

We undertook this study to determine whether thrombin-cleaved osteopontin (OPN) in synovial fluid (SF) represents a useful marker of osteoarthritis (OA) progression in the posterior cruciate ligament transection (PCLT) OA rabbit model.

METHOD

PCLT was performed on the right knee joints of 48 rabbits. The rabbits were then sacrificed separately at 4, 8, 16, and 24 weeks post-surgery, when the joint was harvested and macroscopic and histological assessments of articular cartilage were performed. Thrombin-cleaved OPN product in SF was determined using Western blotting and the levels were measured using an enzyme-linked immunoassay.

RESULTS

The macroscopic and histological scores for PCLT knees were already elevated 4 weeks after surgery and increased with time. Western blotting showed the presence of thrombin-cleaved OPN in SF from PCLT knees. Thrombin-cleaved OPN levels in SF were elevated at 4 weeks (P < 0.001) and were elevated peaking at 24 weeks (P < 0.00001) after PCLT compared to baseline. A positive significant correlation was found between thrombin-cleaved OPN levels and the macroscopic scores (8 weeks: ρ = 0.695, P = 0.012; 16 weeks: ρ = 0.751, P = 0.005; 24 weeks: ρ = 0.660, P = 0.020). Furthermore, the same correlation was noted between thrombin-cleaved OPN levels and the histological scores (4 weeks: ρ = 0.609, P = 0.036; 8 weeks: ρ = 0.662, P = 0.019; 16 weeks: ρ = 0.827, P = 0.001; 24 weeks: ρ = 0.813, P = 0.001).

CONCLUSION

In this rabbit model of PCLT, thrombin-cleaved OPN levels in SF appear to provide a useful marker of OA disease severity and progression.

Osteopontin level in synovial fluid is associated with the severity of joint pain and cartilage degradation after anterior cruciate ligament rupture

Objective

To explore the molecular function of Osteopontin (OPN) in the pathogenesis of human OA, we compared the expression levels of OPN in synovial fluid with clinical parameters such as arthroscopic observation of cartilage damage and joint pain after joint injury.

Methods

Synovial fluid was obtained from patients who underwent anterior cruciate ligament (ACL) reconstruction surgery from 2009 through 2011 in our university hospital. The amounts of intact OPN (OPN Full) and it’s N-terminal fragment (OPN N-half) in synovial fluid from each patient were quantified by ELISA and compared with clinical parameters such as severity of articular cartilage damage (TMDU cartilage score) and severity of joint pain (Visual Analogue Scale and Lysholm score).

Results

Within a month after ACL rupture, both OPN Full and N-half levels in patient synovial fluid were positively correlated with the severity of joint pain. In contrast, patients with ACL injuries greater than one month ago felt less pain if they had higher amounts of OPN N-half in synovial fluid. OPN Full levels were positively correlated with articular cartilage damage in lateral tibial plateau.

Conclusion

Our data suggest that OPN Full and N-half have distinct functions in articular cartilage homeostasis and in human joint pain.

Phosphorylation of osteopontin in osteoarthritis degenerative cartilage and its effect on matrix metalloprotease 13

The purpose of this study is to observe the differences of osteopontin (OPN) phosphorylation in osteoarthritis (OA) cartilage and normal cartilage, and evaluate the possible correlations between the OPN phosphorylation and MMP-13 expression. Degenerative cartilage (n = 29) and normal cartilage (n = 10) were identified by hematoxylin-eosin, safranin-O staining and modified Mankin score. The phosphorylation level of OPN in OA cartilage and normal cartilage was detected by immunoprecipitation. Chondrocytes were treated with phospho-OPN, OPN or buffer. Quantitative reverse transcription polymerase chain reaction (qPCR) and ELISA were used to assess the expression of MMP-13 in different treatments. The OD values of phosphorylation of OPN in normal cartilage and OA cartilage were 137.89 ± 10.59 and 153.52 ± 8.80, respectively, (P = 0.000). Chondrocytes treated with OPN showed a higher MMP-13 expression at gene and protein level compared with control group. Chondrocytes treated with phospho-OPN showed the highest MMP-13 expression in gene and protein. In conclusion, our results revealed a higher phosphorylation level of OPN in OA cartilage than in normal cartilage. We found OPN leads to elevated expression of MMP-13 (both at gene level and protein level), and phospho-OPN had a more obvious upregulation effect on MMP-13 expression than nonphospho-OPN. Further studies are needed to reveal the mechanism of OPN phosphorylation on cartilage degeneration.

The importance of the SIBLING family of proteins on skeletal mineralisation and bone remodelling

The small integrin-binding ligand N-linked glycoprotein (SIBLING) family consists of osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein. These proteins share many structural characteristics and are primarily located in bone and dentin. Accumulating evidence has implicated the SIBLING proteins in matrix mineralisation. Therefore, in this review, we discuss the individual role that each of the SIBLING proteins has in this highly orchestrated process. In particular, we emphasise how the nature and extent of their proteolytic processing and post-translational modification affect their functional role. Finally, we describe the likely roles of the SIBLING proteins in clinical disorders of hypophosphataemia and their potential therapeutic use.

Inflammation and Joint Tissue Interactions in OA: Implications for Potential Therapeutic Approaches

It is increasingly recognized that the pathogenesis of cartilage degradation in osteoarthritis (OA) is multifactorial and involves the interactions between cartilage and its surrounding tissues. These interactions regulate proinflammatory cytokine-mediated cartilage destruction, contributing to OA progression as well as cartilage repair. This review explores the pathogenesis of OA in the context of the multiple tissue types in the joint and discusses the implications of such complex tissue interaction in the development of anti-inflammatory therapeutics for the treatment of OA.

Thrombin induces heme oxygenase-1 expression in human synovial fibroblasts through protease-activated receptor signaling pathways

Introduction

Thrombin is a key factor in the stimulation of fibrin deposition, angiogenesis, and proinflammatory processes. Abnormalities in these processes are primary features of osteoarthritis (OA). Heme oxygenase (HO)-1 is a stress-inducible rate-limiting enzyme in heme degradation that confers cytoprotection against oxidative injury. Here, we investigated the intracellular signaling pathways involved in thrombin-induced HO-1 expression in human synovial fibroblasts (SFs).

Methods

Thrombin-mediated HO-1 expression was assessed with quantitative real-time (q)PCR. The mechanisms of action of thrombin in different signaling pathways were studied by using Western blotting. Knockdown of protease-activated receptor (PAR) proteins was achieved by transfection with siRNA. Chromatin immunoprecipitation assays were used to study in vivo binding of Nrf2 to the HO-1 promoter. Transient transfection was used to examine HO-1 activity.

Results

Osteoarthritis synovial fibroblasts (OASFs) showed significant expression of thrombin, and expression was higher than in normal SFs. OASFs stimulation with thrombin induced concentration- and time-dependent increases in HO-1 expression. Pharmacologic inhibitors or activators and genetic inhibition by siRNA of protease-activated receptors (PARs) revealed that the PAR1 and PAR3 receptors, but not the PAR4 receptor, are involved in thrombin-mediated upregulation of HO-1. Thrombin-mediated HO-1 expression was attenuated by thrombin inhibitor (PPACK), PKCδ inhibitor (rottlerin), or c-Src inhibitor (PP2). Stimulation of cells with thrombin increased PKCδ, c-Src, and Nrf2 activation.

Conclusion

Our results suggest that the interaction between thrombin and PAR1/PAR3 increases HO-1 expression in human synovial fibroblasts through the PKCδ, c-Src, and Nrf2 signaling pathways.