Expression of CD44 in articular cartilage is associated with disease severity in knee osteoarthritis

Plasma Proteomic Analysis Based on 4D-DIA Evaluates the Clinical Response to Imrecoxib in the Early Treatment of Osteoarthritis

INTRODUCTION

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the primary treatment for osteoarthritis (OA), but prolonged use has adverse effects and varying efficacy. Among NSAIDs, imrecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, reduces side effects yet remains ineffective for half of the patient population. This study aims to identify biomarkers for early evaluation of imrecoxib efficacy in OA for personalized therapy optimization.

METHODS

From September 2021 to January 2022, imrecoxib was administered to patients with OA at Nanjing Drum Tower Hospital. Plasma samples from these patients underwent proteomic analysis through the four-dimensional data-independent acquisition (4D-DIA) method, followed by bioinformatics analysis. Potential differentially expressed proteins (DEPs) were validated using enzyme-linked immunosorbent assays (ELISA).

RESULTS

Sixty-six patients with knee OA were included and divided into responders (n = 35) and non-responders (n = 31). Proteomic analysis was conducted on 15 patients from each group, with ELISA validation for every patient. We found 140 DEPs between the two groups after imrecoxib treatment, characterized by 29 proteins showing upregulation and 111 displaying downregulation (P < 0.05, fold change >  ± 1.2). Galectin-1 (LGALS1), galectin-3 (LGALS3), and cluster of differentiation 44 (CD44) were identified as potential markers for evaluating clinical response to imrecoxib in OA following ELISA validation.

CONCLUSION

This study successfully identified biomarkers for evaluating imrecoxib's clinical response in patients with OA using 4D-DIA technology. These biomarkers may play a vital role in future personalized OA treatment strategies, pending further confirmation.

Mechanisms of vascular invasion after cartilage injury and potential engineering cartilage treatment strategies

Articular cartilage injury is one of the most common diseases in orthopedic clinics. Following an articular cartilage injury, an inability to resist vascular invasion can result in cartilage calcification by newly formed blood vessels. This process ultimately leads to the loss of joint function, significantly impacting the patient's quality of life. As a result, developing anti-angiogenic methods to repair damaged cartilage has become a popular research topic. Despite this, tissue engineering, as an anti-angiogenic strategy in cartilage injury repair, has not yet been adequately investigated. This exhaustive literature review mainly focused on the process and mechanism of vascular invasion in articular cartilage injury repair and summarized the major regulatory factors and signaling pathways affecting angiogenesis in the process of cartilage injury. We aimed to discuss several potential methods for engineering cartilage repair with anti-angiogenic strategies. Three anti-angiogenic tissue engineering methods were identified, including administering angiogenesis inhibitors, applying scaffolds to manage angiogenesis, and utilizing in vitro bioreactors to enhance the therapeutic properties of cultured chondrocytes. The advantages and disadvantages of each strategy were also analyzed. By exploring these anti-angiogenic tissue engineering methods, we hope to provide guidance for researchers in related fields for future research and development in cartilage repair.

Targeting CD44 Receptor Pathways in Degenerative Joint Diseases: Involvement of Proteoglycan-4 (PRG4)

Rheumatoid arthritis (RA), osteoarthritis (OA), and gout are the most prevalent degenerative joint diseases (DJDs). The pathogenesis underlying joint disease in DJDs remains unclear. Considering the severe toxicities reported with anti-inflammatory and disease-modifying agents, there is a clear need to develop new treatments that are specific in their effect while not being associated with significant toxicities. A key feature in the development of joint disease is the overexpression of adhesion molecules, e.g., CD44. Expression of CD44 and its variants in the synovial tissues of patients with DJDs is strongly associated with cartilage damage and appears to be a predicting factor of synovial inflammation in DJDs. Targeting CD44 and its downstream signaling proteins has emerged as a promising therapeutic strategy. PRG4 is a mucinous glycoprotein that binds to the CD44 receptor and is physiologically involved in joint lubrication. PRG4-CD44 is a pivotal regulator of synovial lining cell hemostasis in the joint, where lack of PRG4 expression triggers chronic inflammation and fibrosis, driven by persistent activation of synovial cells. In view of the significance of CD44 in DJD pathogenesis and the potential biological role for PRG4, this review aims to summarize the involvement of PRG4-CD44 signaling in controlling synovitis, synovial hypertrophy, and tissue fibrosis in DJDs.

Periostin regulation and cartilage degradation early after anterior cruciate ligament reconstruction

OBJECTIVE AND DESIGN

The purpose of this study was to explore pathological processes during the first 4 weeks after anterior cruciate ligament reconstruction (ACLR).

SUBJECTS

Sixteen ACL-injured patients (8 females/8 males, mean age = 19.1, mean BMI = 28.6).

METHODS

Arthrocentesis was performed 1 and 4 weeks after ACLR. Proteins in the synovial fluid were identified using nanoLC-ESI-MS/MS. Differentially up- or down-regulated proteins were identified and quantified, and a pathway analysis was performed. All identified proteins were mapped into a protein-protein interaction (PPI) network, and networks of PPIs with a combined score > 0.9 were then visualized.

RESULTS

Seven pathways were upregulated after ACLR: PI3K-AKT signaling pathway, extracellular matrix (ECM)-receptor interaction, focal adhesion, protein digestion and absorption, ameobiasis, and platelet activation. Network analyses identified 8 proteins that were differentially upregulated with strong PPI interactions (periostin and 7 collagen-related proteins). Increases in periostin moderately correlated with increases in a synovial fluid biomarker of type II cartilage degradation (ρ = 0.51, p = 0.06).

CONCLUSION

Pro-inflammatory pathways and periostin were upregulated after ACLR. Periostin demonstrated strong network connections with markers of collagen breakdown, and future work is needed to determine whether periostin may offer a biomarker of early cartilage degradation after ACLR and/or play an active role in early post-traumatic osteoarthritis (PTOA) progression.

Chitosan-based biomaterials for the treatment of bone disorders

Bone is an alive and dynamic organ that is well-differentiated and originated from mesenchymal tissues. Bone undergoes continuous remodeling during the lifetime of an individual. Although knowledge regarding bones and their disorders has been constantly growing, much attention has been devoted to effective treatments that can be used, both from materials and medical performance points of view. Polymers derived from natural sources, for example polysaccharides, are generally biocompatible and are therefore considered excellent candidates for various biomedical applications. This review outlines the development of chitosan-based biomaterials for the treatment of bone disorders including bone fracture, osteoporosis, osteoarthritis, arthritis rheumatoid, and osteosarcoma. Different examples of chitosan-based formulations in the form of gels, micro/nanoparticles, and films are discussed herein. The work also reviews recent patents and important developments related to the use of chitosan in the treatment of bone disorders. Although most of the cited research was accomplished before reaching the clinical application level, this manuscript summarizes the latest achievements within chitosan-based biomaterials used for the treatment of bone disorders and provides perspectives for future scientific activities.

Discovery of surface biomarkers for cell mechanophenotype via an intracellular protein-based enrichment strategy

Cellular mechanophenotype is often a defining characteristic of conditions like cancer malignancy/metastasis, cardiovascular disease, lung and liver fibrosis, and stem cell differentiation. However, acquiring living cells based on mechanophenotype is challenging for conventional cell sorters due to a lack of biomarkers. In this study, we demonstrate a workflow for surface protein discovery associated with cellular mechanophenotype. We sorted heterogeneous adipose-derived stem/stromal cells (ASCs) into groups with low vs. high lamin A/C, an intracellular protein linked to whole-cell mechanophenotype. Proteomic data of enriched groups identified surface protein candidates as potential biochemical proxies for ASC mechanophenotype. Select surface biomarkers were used for live-cell enrichment, with subsequent single-cell mechanical testing and lineage-specific differentiation. Ultimately, we identified CD44 to have a strong inverse correlation with whole-cell elastic modulus, with CD44^lo cells exhibiting moduli three times greater than that of CD44^hi cells. Functionally, these stiff and soft ASCs showed enhanced osteogenic and adipogenic differentiation potential, respectively. The described workflow can be replicated for any phenotype with a known correlated intracellular protein, allowing for the acquisition of live cells for further characterization, diagnostics, or therapeutics.

Microencapsulated Recombinant Human Epidermal Growth Factor Ameliorates Osteoarthritis in a Murine Model

Osteoarthritis, a highly age-related and chronic inflammatory disorder with cartilage loss, causes patients difficultly in movement; there is no efficient and sustainable remedy for osteoarthritis currently. Although hyaluronic acid (HA) and platelet-rich plasma (PRP) have been used to alleviate osteoarthritis, the effects could be short and multiple injections might be required. To address this issue, we exploited the property of chitosan to encapsulate recombinant human epidermal growth factor and obtained microencapsulated rhEGF (Me-rhEGF). In the current study, we induced the osteoarthritis-like symptoms with monosodium iodoacetate (MIA) in rats and investigated the therapeutic effects of Me-rhEGF. Following administration of HA/Me-rhEGF in vivo, we observed that the total Mankin scores, cartilage oligomeric protein, C-telopeptide of type II collagen, IL-1β, IL-6, IL-17A, and TNF-α cytokines, nitric oxide, and prostaglandin E2 expressions were significantly inhibited. Our results also strongly indicate that individual use of HA or rhEGF slightly decreased the inflammation and restored the destructive joint structure, but was not as drastic as seen in the HA/Me-rhEGF. Moreover, HA/Me-rhEGF profoundly reduced cartilage destruction and proteoglycan loss and downregulated matrix metalloproteinase expressions. These findings reveal that the treatment of HA/Me-rhEGF could be more beneficial than the use of single HA or rhEGF in reliving osteoarthritis and demonstrate the therapeutic application of microencapsulation technology in difficult joint disorders. In essence, we believe that the Me-rhEGF could be promising for further research and development as a clinical treatment against osteoarthritis.

Cellular Uptake of Three Different Nanoparticles in an Inflammatory Arthritis Scenario versus Normal Conditions

Nanoparticles (NPs) have wide potential applications in the biomedical field. To promote targeted and controlled delivery of encapsulated drugs, it is fundamentally important to understand the factors regulating NP uptake by different cells. Thus, the goal of the present study is to assess the internalization rates of different NPs under normal and proinflammatory states in primary human articular chondrocytes (hACs), human umbilical vein endothelial cells (EA), and human monocytes (THP-1). Here, we compared chitosan-hyaluronic acid (Ch-HA) polymeric NPs, methoxypolyethylene glycol amine-glutathione-palmitic acid (mPEG-GSH_n-PA) micelles, and cholesterol/l-α-phosphatidylcholine/DSPE-PEG-Mal (Chol/EPC/DSPE-PEG-Mal) unilamellar liposomes (LUVs). Our results reveal the importance of surface charge and chemistry in determining the levels of NP internalization. Under normal conditions, the cellular uptake was ≈30% for Ch-HA NPs and ≈100% for mPEG-GSH_n-PA micelles and Chol/EPC/DSPE-PEG-Mal LUVs. A proinflammatory cell state promoted a higher uptake of the Ch-HA NPs by EA cells (93% after 24 h). Since the therapeutic efficacy of the NP-loaded cargo is dependent on trafficking routes after cellular internalization, we tested their internalization pathways. Accordingly, caveolae-mediated endocytosis or energy-independent non-endocytic pathways, which circumvent lysosomal degradation, were accomplished in hACs and EA by LUVs and in M1 polarized macrophages by micelles. The present outcomes highlight the importance of considering cellular uptake and internalization pathways by the target cell when designing functional NPs for therapeutic applications.

Synovial membrane mesenchymal stem cells: past life, current situation, and application in bone and joint diseases

Mesenchymal stem cells (MSCs) can be isolated from not only bone marrow, but also various adult mesenchymal tissues such as periosteum, skeletal muscle, and adipose tissue. MSCs from different tissue sources have different molecular phenotypes and differentiation potential. Synovial membrane (SM) is an important and highly specific component of synovial joints. Previous studies have suggested that the synovium is a structure with a few cell layers thick and consists mainly of fibroblast-like synoviocytes (FLS), which forms a layer that lining the synovial membrane on the joint cavity and synovial fluid through cell-cell contact. In recent years, studies have found that there are also mesenchymal stem cells in the synovium, and as an important part of the mesenchymal stem cell family, it has strong capabilities of cartilage forming and tissue repairing. This article reviews the sources, surface markers, subtypes, influencing factors, and applications in inflammatory joints of synovial membrane mesenchymal stem cells (SM-MSCs) in recent years, aiming to clarify the research status and existing problems of SM-MSCs.

Osteopontin inhibits osteoarthritis progression via the OPN/CD44/PI3K signal axis

Chondrocyte degeneration and extracellular matrix component loss are the primary causes of osteoarthritis (OA). OA can be treated by inhibiting chondrocyte degeneration and increasing extracellular matrix component secretion. Osteopontin (OPN), a multifunctional protein, has gained immense attention with regard to its involvement in OA. This study aimed to explore the therapeutic value and mechanism of action of OPN in OA treatment. Results of the histomorphological analysis revealed a worn-off OA cartilage tissue surface, cartilage matrix layer deterioration, and calcium salt deposition. Compared to that in normal chondrocytes, in OA chondrocytes, the OPN, CD44, and PI3K protein and mRNA expression was upregulated. Further, siOPN, rhOPN, and rhOPN plus LS-C179404 interfered with OA chondrocytes. As verified in mice, OPN directly inhibited the expression level of PI3K in OA chondrocytes by binding with CD44. Morphological analysis of the knee joints demonstrated that OPN effectively inhibited OA progression via the OPN/CD44/PI3K signal axis. In conclusion, OPN activates intracellular PI3K signaling molecules by binding to CD44 on the cell surface to cause downstream cascading effects, thereby delaying chondrocyte degeneration and reducing cartilage matrix component loss; therefore, OPN is a potential therapeutic agent for OA.

Maturity-dependent cartilage cell plasticity and sensitivity to external perturbation

OBJECTIVE

Articular cartilage undergoes biological and morphological changes throughout maturation. The prevalence of osteoarthritis in the aged population suggests that maturation predisposes cartilage to degradation and/or impaired regeneration, but this process is not fully understood. Therefore, the objective of this study was to characterize the cellular and genetic profile of cartilage, as well as biological plasticity in response to mechanical and culture time stimuli, as a function of animal maturity.

METHODS/DESIGN

Porcine articular cartilage explants were harvested from stifle joints of immature (2-4 weeks), adolescent (5-6 months), and mature (1-5 years) animals. Half of all samples were subjected to a single compressive mechanical load. Loaded samples were paired with unloaded controls for downstream analyses. Expression of cartilage progenitor cell markers CD105, CD44, and CD29 were determined via flow cytometry. Expression of matrix synthesis genes Col1, Col2, Col10, ACAN, and SOX9 were determined via qPCR. Tissue morphology and matrix content were examined histologically. Post-loading assays were performed immediately and following 7 days in culture.

RESULTS

CD105 and CD29 expression decreased with maturity, while CD44 expression was upregulated in cartilage from mature animals. Expression of matrix synthesis genes were generally upregulated in cartilage from mature animals, and adolescent animals showed the lowest expression of several matrix synthesizing genes. Culture time and mechanical loading analyses revealed greater plasticity to mechanical loading and culture time in cartilage from younger animals. Histology confirmed distinct structural and biochemical profiles across maturity.

CONCLUSION

This study demonstrates differential, nonlinear expression of chondroprogenitor markers and matrix synthesis genes as a function of cartilage maturity, as well as loss of biological plasticity in aged tissue. These findings have likely implications for age-related loss of regeneration and osteoarthritis progression.

Recruitment of endogenous progenitor cells by erythropoietin loaded particles for in situ cartilage regeneration

Cartilage injury affects millions of people throughout the world, and at this time there is no cure. While transplantation of stem cells has shown some success in the treatment of injured cartilage, such treatment is limited by limited cell sources and safety concerns. To overcome these drawbacks, a microscaffolds system was developed capable of targeting, reducing the inflammatory response and recruiting endogenous progenitor cells to cartilage-defect. Erythropoietin (EPO)-loaded-hyaluronic acid (HA) microscaffolds (HA + EPO) were fabricated and characterized. HA-microscaffolds showed good cell-compatibility and could target chondrocytes via CD44 receptors. HA + EPO was designed to slowly release EPO while recruiting progenitor cells. Finally, the ability of HA + EPO to repair cartilage-defects was assessed using a rabbit model of full-thickness cartilage-defect. Our results showed that the intra-articular administration of EPO, HA, and EPO + HA reduced the number of inflammatory cells inside the synovial-fluid, while EPO + HA had the greatest anti-inflammatory effects. Furthermore, among all groups, EPO + HA achieved the greatest progenitor cell recruitment and subsequent chondrogenesis. The results of this work support that, by targeting and localizing the release of growth-factors, HA + EPO can reduce inflammatory responses and promote progenitor cells responses. This new platform represents an alternative treatment to stem-cell transplantation for the treatment of cartilage injury.

Design and Biological Evaluation of Colchicine-CD44-Targeted Peptide Conjugate in an In Vitro Model of Crystal Induced Inflammation

Gout is an inflammatory arthritis due to the joint deposition of monosodium urate (MSU) crystals. Phagocytosis of MSU crystals by tissue macrophages results in the generation of reactive oxygen species (ROS) and production of inflammatory cytokines and chemokines. Colchicine use in gout is limited by severe toxicity. CD44 is a transmembrane glycoprotein that is highly expressed in tissue macrophages and may be involved in gout pathogenesis. The P6 peptide is a 20-amino acid residue peptide that binds to CD44. We hypothesized that the conjugation of colchicine to the P6 peptide would reduce its off-target cytotoxicity while preserving its anti-inflammatory effect. A modified version of P6 peptide and colchicine-P6 peptide conjugate were synthesized using Fmoc/tBu solid-phase and solution-phase chemistry, respectively. A glutaryl amide was used as a linker. The P6 peptide was evaluated for its binding to CD44, association, and internalization by macrophages. Cytotoxic effects of P6 peptide, colchicine, and colchicine-P6 peptide on macrophages were compared and the inhibition of ROS generation and interleukin-8 (IL-8) secretion in MSU-stimulated macrophages treated with P6 peptide, colchicine, or colchicine-P6 peptide was studied. We confirmed that the P6 peptide binds to CD44 and its association and internalization by macrophages were CD44-dependent. Colchicine (1, 10, and 25 μM) demonstrated a significant cytotoxic effect on macrophages while the P6 peptide and colchicine-P6 peptide conjugate (1, 10 and 25 μM) did not alter the viability of the macrophages. The P6 peptide (10 and 25 μM) reduced ROS generation and IL-8 secretion mediated by a reduction in MSU phagocytosis by macrophages. The colchicine-P6 peptide significantly reduced ROS generation and IL-8 secretion compared to the P6 peptide alone at 1 and 10 μM concentrations. Conjugation of colchicine to the P6 peptide reduced the cytotoxic effect of colchicine while preserving its anti-inflammatory activity.

The autocrine role of proteoglycan-4 (PRG4) in modulating osteoarthritic synoviocyte proliferation and expression of matrix degrading enzymes

BACKGROUND

Lubricin/proteoglycan 4 (PRG4) is a mucinous glycoprotein secreted by synovial fibroblasts and superficial zone chondrocytes. Recently, we showed that recombinant human PRG4 (rhPRG4) is a putative ligand for CD44 receptor. rhPRG4-CD44 interaction inhibits cytokine-induced rheumatoid arthritis synoviocyte proliferation. The objective of this study is to decipher the autocrine function of PRG4 in regulating osteoarthritic synoviocyte proliferation and expression of catabolic and pro-inflammatory mediators under basal and interleukin-1 beta (IL-1β)-stimulated conditions.

METHODS

Cytosolic and nuclear levels of nuclear factor kappa B (NFκB) p50 and p65 subunits in Prg4 ^+/+ and Prg4 ^-/- synoviocytes were studied using western blot. Nuclear translocation of p50 and p65 proteins in osteoarthritis (OA) fibroblast-like synoviocytes (FLS) in response to IL-1β stimulation in the absence or presence of rhPRG4 was studied using DNA binding assays. OA synoviocyte (5000 cells per well) proliferation following IL-1β (20 ng/ml) treatment in the absence or presence of rhPRG4 (50-200 μg/ml) over 48 hours was determined using a colorimetric assay. Gene expression of matrix metalloproteinases (MMPs), tissue inhibitor of metallproteinases-1 (TIMP-1), TIMP-2, IL-1β, IL-6, IL-8, TNF-α, cycloxygenae-2 (COX2) and PRG4 in unstimulated and IL-1β (1 ng/ml)-stimulated OA synoviocytes, in the presence or absence of rhPRG4 (100 and 200 μg/ml), was studied following incubation for 24 hours.

RESULTS

Prg4 ^-/- synoviocytes contained higher nuclear p50 and p65 levels compared to Prg4 ^+/+ synoviocytes (p < 0.05). rhPRG4 (100 μg/ml) reduced p50 and p65 nuclear levels in Prg4 ^+/+ and Prg4 ^-/- synoviocytes (p < 0.001). Similarly, rhPRG4 (200 μg/ml) inhibited NFκB translocation and cell proliferation in OA synoviocytes in a CD44-dependent manner (p < 0.001) via inhibition of IκBα phosphorylation. IL-1β reduced PRG4 expression in OA synoviocytes and rhPRG4 (100 μg/ml) treatment reversed this effect (p < 0.001). rhPRG4 (200 μg/ml) reduced basal gene expression of MMP-1, MMP-3, MMP-13, IL-6, IL-8, and PRG4 in OA synoviocytes, while increasing TIMP-2 and cycloxygenase-2 (COX2) expression (p < 0.001). rhPRG4 (200 μg/ml) reduced IL-1β induction of MMP-1, MMP-3, MMP-9, MMP-13, IL-6, IL-8, and COX2 expression in a CD44-dependent manner (p < 0.001).

CONCLUSION

PRG4 plays an important anti-inflammatory role in regulating OA synoviocyte proliferation and reduces basal and IL-1β-stimulated expression of catabolic mediators. Exogenous rhPRG4 autoregulates native PRG4 expression in OA synoviocytes.

Intra-articular hyaluronic acid is superior to steroids in knee osteoarthritis: A comparative, randomized study

BACKGROUND

To compare the short and mid-term results of intraarticular triamcinolone hexacetonide and hyaluronic acid (HA) in knee osteoarthritis.

METHODS

A prospective randomized study including 40 patients in steroid and 42 patients in HA group. The outcome was evaluated with Knee Society Score (KSS) and Visual Analog Scale (VAS).

RESULT

On KSS function and VAS score, there was no difference till four weeks. On KSS pain there was no difference till 12 weeks (P > 0.05) after that score of steroid group deteriorated rapidly. At six months HA was significantly better than a steroid.

CONCLUSION

The HA seems to be better for pain relief and functionality in the short and mid-term periods.

Harnessing the Versatility of Bacterial Collagen to Improve the Chondrogenic Potential of Porous Collagen Scaffolds

Collagen I foams are used in the clinic as scaffolds to promote articular cartilage repair as they provide a bioactive environment for cells with chondrogenic potential. However, collagen I as a base material does not allow for precise control over bioactivity. Alternatively, recombinant bacterial collagens can be used as "blank slate" collagen molecules to offer a versatile platform for incorporation of selected bioactive sequences and fabrication into 3D scaffolds. Here, we show the potential of Streptococcal collagen-like 2 (Scl2) protein foams modified with peptides designed to specifically and noncovalently bind hyaluronic acid and chondroitin sulfate to improve chondrogenesis of human mesenchymal stem cells (hMSCs) compared to collagen I foams. Specific compositions of functionalized Scl2 foams lead to improved chondrogenesis compared to both nonfunctionalized Scl2 and collagen I foams, as indicated by gene expression, extracellular matrix accumulation, and compression moduli. hMSCs cultured in functionalized Scl2 foams exhibit decreased collagens I and X gene and protein expression, suggesting an advantage over collagen I foams in promoting a chondrocytic phenotype. These highly modular foams can be further modified to improve specific aspects chondrogenesis. As such, these scaffolds also have the potential to be tailored for other regenerative medicine applications.

Association between Wnt inhibitory factor-1 expression levels in articular cartilage and the disease severity of patients with osteoarthritis of the knee

Wnt inhibitory factor (WIF)-1 is a potent extracellular Wnt antagonist which may be used as a potential molecular therapy for the treatment of inflammatory and autoimmune diseases. Although previous studies have demonstrated that WIF-1 has a protective role in experimental studies of arthritis, its role in the various disease grades of osteoarthritis (OA) remains unclear. A total of 40 patients with various stages of primary OA of the knee and 10 control subjects were enrolled in the present study. Articular cartilage specimens were harvested from subjects following total knee arthroplasty or knee above amputation. Disease severity was determined according to Modified Mankin score and cartilage tissues were ascribed to four groups: Normal, mild, moderate and severe lesions. WIF-1 expression levels in articular cartilage were measured using immunohistochemical techniques. WIF-1 expression levels were detected in all cartilage tissues. As compared with the controls, patients with OA exhibited significantly decreased WIF-1 expression levels in the articular cartilage (0.19±0.05 vs. 0.26±0.04; P<0.01). Furthermore, articular cartilage WIF-1 expression levels in the moderate and severe lesion groups were significantly reduced, as compared with the controls (P<0.01) and mild lesion group (P<0.05). Subsequent analysis demonstrated that articular cartilage WIF-1 expression levels were negatively correlated with the severity of disease (r=-0.896, P<0.001). In conclusion, the results of the present study suggested that WIF-1 expression levels in articular cartilage may be negatively associated with progressive joint damage in patients with OA of the knee; therefore, WIF-1 expression may be a potential indictor for monitoring OA disease severity.

Age-independent effects of hyaluronan amide derivative and growth hormone on human osteoarthritic chondrocytes

AIM

Increased age is the most prominent risk factor for the initiation and progression of osteoarthritis (OA). The effects of human growth hormone (hGH) combined or not with hyaluronan amide derivative (HAD) were evaluated on human OA chondrocytes, to define their biological action and potentiality in OA treatment.

MATERIAL AND METHODS

Cell viability, metabolic activity, gene expression and factors released were tested at different time points on chondrocytes treated with different concentrations of hGH (0.01-10 μg/ml) alone or in combination with HAD (1 mg/ml).

RESULTS

We found that OA chondrocytes express GH receptor and that the different doses of hGH tested did not affect cell viability, metabolic activity or the expression of collagen type 2, 1, or 10 nor did it induce the release of IGF-1 or FGF-2. Conversely, hGH treatment increased the expression of hyaluronan receptor CD44. HAD combined with hGH reduced metabolic activity, IL6 release and gene expression, but not the suppressor of cytokine signaling 2 (SOCS2), which was significantly induced and translocated into the nucleus. The parameters analyzed, independently of the treatments used proportionally decreased with increasing age of the patients.

CONCLUSIONS

hGH only induced CD44 receptor on OA chondrocytes but did not affect other parameters, such as chondrocytic gene markers or IGF-1 or FGF-2 release. HAD reduced all the effects induced by hGH partially through a significant induction of SOCS2. These data show that GH or HAD treatment does not influence the response of the OA chondrocytes, thus the modulation of cellular response is age-independent.

Lubricin/Proteoglycan 4 Binding to CD44 Receptor: A Mechanism of the Suppression of Proinflammatory Cytokine-Induced Synoviocyte Proliferation by Lubricin

OBJECTIVE

To evaluate the binding of recombinant human proteoglycan 4 (rhPRG4) to CD44 receptor and its consequences on cytokine-induced synoviocyte proliferation.

METHODS

The binding of rhPRG4 to CD44 and competition with high molecular weight (HMW) hyaluronic acid (HA) was evaluated using a direct enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance. Sialidase A and O-glycosidase digestion of rhPRG4 was performed, and CD44 binding was evaluated using ELISA. Rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) were stimulated with interleukin-1β (IL-1β) or tumor necrosis factor α (TNFα) for 48 hours in the presence or absence of rhPRG4 or HMW HA at 20, 40, and 80 μg/ml, and cell proliferation was measured. The contribution of CD44 was assessed by coincubation with a CD44 antibody (IM7). The antiproliferative effect of rhPRG4 was investigated following treatment of PRG4(-/-) mouse synoviocytes with IL-1β or TNFα in the presence or absence of IM7.

RESULTS

Recombinant human PRG4 bound CD44 and interfered with the binding of HMW HA to CD44. Removal of sialic acid and O-glycosylations significantly increased CD44 binding by rhPRG4 (P < 0.001). Both rhPRG4 and HMW HA at 40 and 80 μg/ml significantly suppressed IL-1β-induced proliferation of RA FLS (P < 0.05). Recombinant human PRG4 at 20, 40, and 80 μg/ml significantly suppressed TNFα-induced RA FLS proliferation (P < 0.05). CD44 neutralization reversed the effect of rhPRG4 on IL-1β- and TNFα-stimulated RA FLS and the effect of HMW HA on IL-1β-stimulated RA FLS. Recombinant human PRG4 inhibited cytokine-induced proliferation of PRG4(-/-) synoviocytes, which could be prevented by blocking CD44.

CONCLUSION

PRG4 (lubricin) is a novel putative ligand for CD44 and may control synoviocyte overgrowth in inflammatory arthropathies via a CD44-mediated mechanism.

Osteopontin inhibits HIF-2α mRNA expression in osteoarthritic chondrocytes

The aim of the present study was to investigate the in vitro effect of osteopontin (OPN) on the expression of hypoxia-inducible factor-2α (HIF-2α) in chondrocytes and the role of OPN in osteoarthritis (OA). Cartilage was purified from the tibial surfaces of patients with OA of the knee and cultured in vitro to obtain chondrocytes. Recombinant human OPN (rhOPN) and OPN small interfering RNA (siRNA) were used to treat the chondrocytes, and the changes in the expression levels of the HIF-2α gene were measured. An anti-CD44 blocking monoclonal antibody (mAb) was used to determine the probable ligand-receptor interactions. Reverse transcription-quantitative polymerase chain reaction assays were designed and validated with SYBR® Green dyes for the simultaneous quantification of the mRNA expression levels of OPN and HIF-2α. The mRNA expression level of HIF-2α was markedly decreased in the rhOPN-treated group compared with that in the control group; by contrast, OPN siRNA increased HIF-2α gene expression. CD44 blocking mAb suppressed the inhibitory effect of OPN on HIF-2α mRNA expression. The results of the present study suggest that OPN may play a protective role in OA by inhibiting HIF-2α gene expression in osteoarthritic chondrocytes through CD44 interaction.

Knee osteoarthritis: hyaluronic acid, platelet-rich plasma or both in association?

INTRODUCTION

Bidirectional interactions between cells and fluidic surroundings regulate cellular functions and maintain tissue or organ architecture. Accordingly, the synovial fluid is the primary source of environmental signals and determines to a great extent the molecular interactions within the joint capsule, both in homeostasis and pathology.

AREAS COVERED

We provided an update on hyaluronic acid (HA) and platelet-rich plasma (PRP) concepts necessary to build the rationale for creating a combined treatment. The information is based on a PubMed search using the terms 'platelet-rich plasma', 'hyaluronic acid', 'knee pathology', 'knee osteoarthritis' (OA).

EXPERT OPINION

In OA, a deleterious fluidic microenvironment is established, with presence of HA fragments, catabolic enzymes and inflammatory molecules. The central concept underlying intra-articular injection is to modify deleterious fluidic microenvironments. PRP administration has shown pain remission and function improvement, but less than half of the patients showed clinically significant improvement. PRP exceeds HA, the comparator used in PRP clinical trials, albeit both HA and PRP alleviate symptoms in mild-to-moderate OA patients. Combining PRP and HA may benefit from their dissimilar biological mechanisms and help in controlling delivery and presentation of signaling molecules. Three armed randomized studies, using both HA and PRP as comparators, will provide information about the impact of this approach.