Influence of osteoarthritis grade on molecular signature of human cartilage

Cartilage Integrity: A Review of Mechanical and Frictional Properties and Repair Approaches in Osteoarthritis

Osteoarthritis (OA) is one of the most common causes of disability around the globe, especially in aging populations. The main symptoms of OA are pain and loss of motion and function of the affected joint. Hyaline cartilage has limited ability for regeneration due to its avascularity, lack of nerve endings, and very slow metabolism. Total joint replacement (TJR) has to date been used as the treatment of end-stage disease. Various joint-sparing alternatives, including conservative and surgical treatment, have been proposed in the literature; however, no treatment to date has been fully successful in restoring hyaline cartilage. The mechanical and frictional properties of the cartilage are of paramount importance in terms of cartilage resistance to continuous loading. OA causes numerous changes in the macro- and microstructure of cartilage, affecting its mechanical properties. Increased friction and reduced load-bearing capability of the cartilage accelerate further degradation of tissue by exerting increased loads on the healthy surrounding tissues. Cartilage repair techniques aim to restore function and reduce pain in the affected joint. Numerous studies have investigated the biological aspects of OA progression and cartilage repair techniques. However, the mechanical properties of cartilage repair techniques are of vital importance and must be addressed too. This review, therefore, addresses the mechanical and frictional properties of articular cartilage and its changes during OA, and it summarizes the mechanical outcomes of cartilage repair techniques.

Long-Term Structural Changes in the Osteochondral Unit in Patients with Osteoarthritis Undergoing Corrective Osteotomy with Platelet-Rich Plasma or Stromal Vascular Fraction Post-Treatment

This pilot study examined the long-term structural changes in the osteochondral unit of 20 patients with knee osteoarthritis (KOA) who underwent high tibial osteotomy (HTO) and received post-treatment with either platelet-rich plasma (PRP) or stromal vascular fraction (SVF). Ten patients were injected with autologous PRP (PRP subgroup), while another ten patients received autologous SVF (SVF subgroup) six weeks after surgery and were monitored for 18 months. Histological samples of bone and cartilage (2 mm in diameter and 2 cm long) were taken from tibial and femoral sites during surgery and 18-month post-HTO, and morphometric analyses were conducted using Mega-Morf12 software. Both post-treatment resulted in an increase in articular cartilage height at both sites (p < 0.001 in the tibia and femur), indicating positive outcomes. Significant improvements in subchondral and trabecular bone architecture were also observed, with SVF injection showing higher reparative capacity in terms of bone volume (p < 0.001 for the tibia and p = 0.004 for the femur), subchondral bone height (p < 0.001 for the tibia and p = 0.014 for the femur), trabecular bone volume (p < 0.001 for the femur), and intertrabecular space (p = 0.009 for the tibia and p = 0.007 for the femur). This pilot study, for the first time, demonstrates that HTO surgery combined with PRP and SVF post-treatments can lead to significant enhancements in knee articular cartilage and bone architecture in KOA patients, with SVF showing higher regenerative potential. These findings may contribute to improving treatment strategies for better clinical outcomes in HTO therapy for patients with KOA.

The dysregulated autophagy in osteoarthritis: Revisiting molecular profile

The risk factors of osteoarthritis (OA) are different and obesity, lifestyle, inflammation, cell death mechanisms and diabetes mellitus are among them. The changes in the biological mechanisms are considered as main regulators of OA pathogenesis. The dysregulation of autophagy is observed in different human diseases. During the pathogenesis of OA, the autophagy levels (induction or inhibition) change. The supportive and pro-survival function of autophagy can retard the progression of OA. The protective autophagy prevents the cartilage degeneration. Moreover, autophagy demonstrates interactions with cell death mechanisms and through inhibition of apoptosis and necroptosis, it improves OA. The non-coding RNA molecules can regulate autophagy and through direct and indirect control of autophagy, they dually delay/increase OA pathogenesis. The mitochondrial integrity can be regulated by autophagy to alleviate OA. Furthermore, therapeutic compounds, especially phytochemicals, stimulate protective autophagy in chondrocytes to prevent cell death. The protective autophagy has ability of reducing inflammation and oxidative damage, as two key players in the pathogenesis of OA.

Knockdown of LINC01138 protects human chondrocytes against IL-1β-induced damage by regulating the hsa-miR-1207-5p/KIAA0101 axis

INTRODUCTION

Long intergenic non-protein coding RNA 1138 (LINC01138) plays a vital role in human cancers. In this study, we aimed to investigate the effect of LINC01138 on the progression of osteoarthritis (OA) and explore its potential mechanism of action.

METHODS

The expression of LINC01138, hsa-miR-1207-5p, and KIAA0101 in OA tissues and normal tissues was analyzed using GSEA datasets and confirmed in human specimens. Human chondrocytes were treated with interleukin (IL)-1β to establish an OA cell model. Quantitative real time PCR(qRT-PCR), enzyme-linked immunosorbent assay, and western blotting analyses were performed to evaluate the role of LINC01138, hsa-miR-1207-5p, and KIAA0101 during extracellular matrix (ECM) protein degeneration and cellular inflammatory response. The target relationship was predicted using DIANA-TarBase and TargetScan. The binding effects were verified by dual-luciferase reporter assay.

RESULTS

LINC01138 expression was higher in OA tissues than in normal controls. LINC01138 levels increased in chondrocytes treated with IL-1β. Silencing of LINC01138 attenuated the IL-1β-induced decrease in Col2α1, aggrecan, and sulphated glycosaminoglycan (sGAG), and inhibited the IL-1β-induced increase in matrix metalloproteinase (MMP)-13, IL-6, and tumor necrosis factor (TNF)-α. miR-1207-5p is weakly expressed in OA tissues and cell models. The inhibition of hsa-miR-1207-5p, a target of LINC01138, attenuated the effects of LINC01138 silencing on chondrocyte ECM degeneration and inflammatory responses. Silencing KIAA0101, a target of hsa-miR-1207-5p, alleviated the effect of hsa-miR-1207-5p on chondrocyte ECM degeneration and inflammatory responses. Furthermore, silencing of KIAA0101 inhibited the JAK/STAT and Wnt signaling pathways.

CONCLUSION

Silencing LINC01138 protected chondrocytes from IL-1β-induced damage, possibly by regulating the hsa-miR-1207-5p/KIAA0101 axis.

Interferon-gamma modulates articular chondrocyte and osteoblast metabolism through protein kinase R-independent and dependent mechanisms

Osteoarthritis (OA) affects multiple tissues of the synovial joint and is characterised by articular cartilage degeneration and bone remodelling. Interferon-γ (IFN-γ) is implicated in osteoarthritis pathology exerting its biological effects via various mechanisms including activation of protein kinase R (PKR), which has been implicated in inflammation and arthritis. This study investigated whether treatment of articular cartilage chondrocytes and osteoblasts with IFN-γ could induce a degradative phenotype that was mediated through the PKR signalling pathway. IFN-γ treatment of chondrocytes increased transcription of key inflammatory mediators (TNF-α, IL-6), matrix degrading enzymes (MMP-13), the transcription factor STAT1, and PKR. Activation of PKR was involved in the regulation of TNF-α, IL-6, and STAT1. In osteoblasts, IFN-γ increased human and mouse STAT1, and human IL-6 through a mechanism involving PKR. ALP, COL1A1 (human and mouse), RUNX2 (mouse), and PHOSPHO1 (mouse) were decreased by IFN-γ. The number of PKR positive cells were increased in post-traumatic OA (PTOA). This study has revealed that IFN-γ propagates inflammatory and degenerative events in articular chondrocytes and osteoblasts via PKR activation. Since IFN-γ and PKR signalling are both activated in early PTOA, these mechanisms are likely to contribute to joint degeneration after injury and might offer attractive targets for therapeutic intervention.

•IFN-γ treatment of chondrocytes increased transcription of TNF-α, IL-6, and STAT1 via PKR activation.

•In osteoblasts, IFN-γ increased STAT1 and IL-6 via PKR activation.

•The number of PKR positive cells were increased in post-traumatic OA (PTOA).

•IFN-γ propagates inflammatory and degenerative events in articular chondrocytes and osteoblasts via PKR activation.

•IFN-γ and PKR signalling are both activated in early PTOA and are likely to contribute to joint degeneration after injury.

Mitochondrial double-stranded RNAs govern the stress response in chondrocytes to promote osteoarthritis development

Protein kinase R (PKR) is an immune response protein that becomes activated by double-stranded RNAs (dsRNAs). PKR overactivation is associated with degenerative diseases with inflammation, including osteoarthritis (OA), but the dsRNA activator remains largely unknown. Here, we find that mitochondrial dsRNA (mt-dsRNA) expression and its cytosolic efflux are facilitated in chondrocytes under OA-eliciting conditions, leading to innate immune activation. Moreover, mt-dsRNAs are released to the extracellular space and activate Toll-like receptor 3 at the plasma membrane. Elevated levels of mt-dsRNAs in the synovial fluids and damaged cartilage of OA patients and in the cartilage of surgery-induced OA mice further support our data. Importantly, autophagy prevents PKR activation and protects chondrocytes from mitochondrial stress partly by removing cytosolic mtRNAs. Our study provides a comprehensive understanding of innate immune activation by mt-dsRNAs during stress responses that underlie the development of OA and suggests mt-dsRNAs as a potential target for chondroprotective intervention.

Long noncoding RNA H19 alleviates inflammation in osteoarthritis through interactions between TP53, IL-38, and IL-36 receptor

Aims

Osteoarthritis (OA) is a common degenerative joint disease characterized by chronic inflammatory articular cartilage degradation. Long noncoding RNAs (lncRNAs) have been previously indicated to play an important role in inflammation-related diseases. Herein, the current study set out to explore the involvement of lncRNA H19 in OA.

Methods

Firstly, OA mouse models and interleukin (IL)-1β-induced mouse chondrocytes were established. Expression patterns of IL-38 were determined in the synovial fluid and cartilage tissues from OA patients. Furthermore, the targeting relationship between lncRNA H19, tumour protein p53 (TP53), and IL-38 was determined by means of dual-luciferase reporter gene, chromatin immunoprecipitation, and RNA immunoprecipitation assays. Subsequent to gain- and loss-of-function assays, the levels of cartilage damage and proinflammatory factors were further detected using safranin O-fast green staining and enzyme-linked immunosorbent assay (ELISA) in vivo, respectively, while chondrocyte apoptosis was measured using Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) in vitro.

Results

IL-38 was highly expressed in lentivirus vector-mediated OA mice. Meanwhile, injection of exogenous IL-38 to OA mice alleviated the cartilage damage, and reduced the levels of proinflammatory factors and chondrocyte apoptosis. TP53 was responsible for lncRNA H19-mediated upregulation of IL-38. Furthermore, it was found that the anti-inflammatory effects of IL-38 were achieved by its binding with the IL-36 receptor (IL-36R). Overexpression of H19 reduced the expression of inflammatory factors and chondrocyte apoptosis, which was abrogated by knockdown of IL-38 or TP53.

Conclusion

Collectively, our findings evidenced that upregulation of lncRNA H19 attenuates inflammation and ameliorates cartilage damage and chondrocyte apoptosis in OA by upregulating TP53, IL-38, and by activating IL-36R.

Cite this article: Bone Joint Res 2022;11(8):594–607.

Fundamentals of bone vasculature: Specialization, interactions and functions

Angiogenesis, hematopoiesis and osteogenesis are fundamental processes mediating complex and essential biological functions. In the bone marrow, endothelial cells (ECs) are a principal mediator of regulatory signals that govern hematopoietic and mesenchymal stem cells. EC and osteoblast interactions and niche functions of ECs are fundamental in maintaining bone health and coordinating repair and regeneration following injury. These cellular interactions are subject to dysregulation and deterioration under stress, aging, chronic disease states and malignancy. Thus, the prospect of manipulating the bone vasculature has tremendous potential to advance therapeutic interventions for the management of bone diseases. This review discusses the current state of vascular-skeletal tissue interactions focusing on osteoblast and hematopoietic stem cells interaction with ECs.

Diversity of Vascular Niches in Bones and Joints During Homeostasis, Ageing, and Diseases

The bones and joints in the skeletal system are composed of diverse cell types, including vascular niches, bone cells, connective tissue cells and mineral deposits and regulate whole-body homeostasis. The capacity of maintaining strength and generation of blood lineages lies within the skeletal system. Bone harbours blood and immune cells and their progenitors, and vascular cells provide several immune cell type niches. Blood vessels in bone are phenotypically and functionally diverse, with distinct capillary subtypes exhibiting striking changes with age. The bone vasculature has a special impact on osteogenesis and haematopoiesis, and dysregulation of the vasculature is associated with diverse blood and bone diseases. Ageing is associated with perturbed haematopoiesis, loss of osteogenesis, increased adipogenesis and diminished immune response and immune cell production. Endothelial and perivascular cells impact immune cell production and play a crucial role during inflammation. Here, we discuss normal and maladapted vascular niches in bone during development, homeostasis, ageing and bone diseases such as rheumatoid arthritis and osteoarthritis. Further, we discuss the role of vascular niches during bone malignancy.

Overcoming the Dependence on Animal Models for Osteoarthritis Therapeutics - The Promises and Prospects of In Vitro Models

Osteoarthritis (OA) is a musculoskeletal disease characterized by progressive degeneration of osteochondral tissues. Current treatment is restricted to the reduction of pain and loss of function of the joint. To better comprehend the OA pathophysiological conditions, several models are employed, however; there is no consensus on a suitable model. In this review, different in vitro models being developed for possible therapeutic intervention of OA are outlined. Herein, various in vitro OA models starting from 2D model, co-culture model, 3D models, dynamic culture model to advanced technologies-based models such as 3D bioprinting, bioassembly, organoids, and organ-on-chip-based models are discussed with their advantages and disadvantages. Besides, different growth factors, cytokines, and chemicals being utilized for induction of OA condition are reviewed in detail. Furthermore, there is focus on scrutinizing different molecular and possible therapeutic targets for better understanding the mechanisms and OA therapeutics. Finally, the underlying challenges associated with in vitro models are discussed followed by future prospective. Taken together, a comprehensive overview of in vitro OA models, factors to induce OA-like conditions, and intricate molecular targets with the potential to develop personalized osteoarthritis therapeutics in the future with clinical translation is provided.

Engineered nasal cartilage for the repair of osteoarthritic knee cartilage defects

[Figure: see text].

Models of Osteoarthritis: Relevance and New Insights

Osteoarthritis (OA) is a progressive and disabling musculoskeletal disease affecting millions of people and resulting in major healthcare costs worldwide. It is the most common form of arthritis, characterised by degradation of the articular cartilage, formation of osteophytes, subchondral sclerosis, synovial inflammation and ultimate loss of joint function. Understanding the pathogenesis of OA and its multifactorial aetiology will lead to the development of effective treatments, which are currently lacking. Two-dimensional (2D) in vitro tissue models of OA allow affordable, high-throughput analysis and stringent control over specific variables. However, they are linear in fashion and are not representative of physiological conditions. Recent in vitro studies have adopted three-dimensional (3D) tissue models of OA, which retain the advantages of 2D models and are able to mimic physiological conditions, thereby allowing investigation of additional variables including interactions between the cells and their surrounding extracellular matrix. Numerous spontaneous and induced animal models are used to reproduce the onset and monitor the progression of OA based on the aetiology under investigation. This therefore allows elucidation of the pathogenesis of OA and will ultimately enable the development of novel and specific therapeutic interventions. This review summarises the current understanding of in vitro and in vivo OA models in the context of disease pathophysiology, classification and relevance, thus providing new insights and directions for OA research.

Current Models for Development of Disease-Modifying Osteoarthritis Drugs

Osteoarthritis (OA) is a painful and disabling disease that affects millions of people worldwide. Symptom-alleviating treatments exist, although none with long-term efficacy. Furthermore, there are currently no disease-modifying OA drugs (DMOADs) with demonstrated efficacy in OA patients, which is, in part, attributed to a lack of full understanding of the pathogenesis of OA. The inability to translate findings from basic research to clinical applications also highlights the deficiencies in the available OA models at simulating the clinically relevant pathologies and responses to treatments in humans. In this review, the current status in the development of DMOADs will be first presented, with special attention to those in Phase II-IV clinical trials. Next, current in vitro, ex vivo, and in vivo OA models are summarized and the respective advantages and disadvantages of each are highlighted. Of note, the development and application of microphysiological or tissue-on-a-chip systems for modeling OA in humans are presented and the issues that need to be addressed in the future are discussed. Microphysiological systems should be given serious consideration for their inclusion in the DMOAD development pipeline, both for their ability to predict drug safety and efficacy in human clinical trials at present, as well as for their potential to serve as a test platform for personalized medicine. Impact statement At present, no disease-modifying osteoarthritis (OA) drugs (DMOADs) have been approved for widespread clinical use by regulatory bodies. The failure of developing effective DMOADs is likely owing to multiple factors, not the least of which are the intrinsic differences between the intact human knee joint and the preclinical models. This work summarizes the current OA models for the development of DMOADs, discusses the advantages/disadvantages of each, and then proposes future model development to aid in the discovery of effective and personalized DMOADs. The review also highlights the microphysiological systems, which are emerging as a new platform for drug development.

Construction of CII-Specific CAR-T to Explore the Cytokine Cascades Between Cartilage-Reactive T Cells and Chondrocytes

Cytokine cascades exist in many autoimmune disorders which amplify and sustain the autoimmune process and lead to chronic inflammatory injury to the host tissues. Increasing evidence indicates that chondrocytes can interact with T cells, which may be a crucial event in inflammatory arthritis. To address the reciprocal influences of cartilage-reactive T cells and chondrocytes, we constructed cartilage-reactive T cells by developing a type II collagen-specific chimeric antigen receptor (CII-CAR). An in vitro co-culture model of CII-CAR-T cells and fresh cartilage was developed, in which CII-CAR-T displayed specific proliferative capacity and cytokine release against fresh cartilage samples, and chondrocytes could respond to CII-CAR-T cells by secreting IL-6. The proposed model will help us to explore the possible cytokine cascades between cartilage-reactive T cells and cartilage.

Bone Angiogenesis and Vascular Niche Remodeling in Stress, Aging, and Diseases

The bone marrow (BM) vascular niche microenvironments harbor stem and progenitor cells of various lineages. Bone angiogenesis is distinct and involves tissue-specific signals. The nurturing vascular niches in the BM are complex and heterogenous consisting of distinct vascular and perivascular cell types that provide crucial signals for the maintenance of stem and progenitor cells. Growing evidence suggests that the BM niche is highly sensitive to stress. Aging, inflammation and other stress factors induce changes in BM niche cells and their crosstalk with tissue cells leading to perturbed hematopoiesis, bone angiogenesis and bone formation. Defining vascular niche remodeling under stress conditions will improve our understanding of the BM vascular niche and its role in homeostasis and disease. Therefore, this review provides an overview of the current understanding of the BM vascular niches for hematopoietic stem cells and their malfunction during aging, bone loss diseases, arthritis and metastasis.

Gene Expression in Meniscal Tears at the Time of Arthroscopic Partial Meniscectomy Predicts the Progression of Osteoarthritis Within 6 Years of Surgery

Background:

While knees with meniscal tears are associated with a heightened risk of developing osteoarthritis (OA), it is difficult to predict which patients are at the greatest risk for OA. Gene signatures in menisci that are resected during arthroscopic partial meniscectomy (APM) may provide insight into the risk of OA progression.

Hypothesis:

Meniscal gene signatures at the time of APM will predict radiographic OA progression.

Study Design:

Case series; Level of evidence, 4.

Methods:

Meniscal fragments were collected from 38 patients without OA during clinically indicated APM of the medial meniscus. The expression of 28 candidate genes with known roles in cartilage homeostasis, OA, extracellular matrix degradation, and obesity was assessed by quantitative real-time polymerase chain reaction. Weightbearing radiographs obtained before surgery and at final follow-up were graded by a musculoskeletal radiologist using the Kellgren-Lawrence classification of OA. The association of meniscal gene expression at baseline with the progression of radiographic OA was determined.

Results:

Gene expression and baseline and follow-up radiographic data were available from 31 patients (81.6%) at a mean follow-up of 6.2 ± 1.3 years. Patients without OA progression had significantly higher expression of 7 genes: MMP9 (5.1-fold; P = .002), IL8 (2.9-fold; P = .016), CCL3 (3.7-fold; P = .032), CCL3L1 (4.5-fold; P = .008), CXCL6 (6.2-fold; P = .010), LEP (5.2-fold; P = .004), and RETN (46-fold; P = .008).

Conclusion:

Gene expression in the meniscus at the time of APM may be associated with the risk for progression of OA after surgery. Elevated expression of the aforementioned genes may reflect a chondroprotective response. Stratifying the risk for OA progression after APM could facilitate targeted interventions to delay or prevent the development of OA. Further studies in a larger cohort with an extended follow-up, and inclusion of additional genes, are warranted to better characterize this association.

The relationship of platelet to lymphocyte ratio and neutrophil to monocyte ratio to radiographic grades of knee osteoarthritis

OBJECTIVE

Accumulating data show that platelet to lymphocyte ratio (PLR) and neutrophil to monocyte ratio (NMR) undergo changes during inflammation in various diseases; however, the clinical features remain unclear in knee osteoarthritis (OA) patients. The purpose of our study was to evaluate PLR and NMR in knee OA patients, and assess their relationship to knee OA's radiographic grades.

METHODS

A retrospective study on 132 adult knee OA patients and 162 healthy controls (HC) was performed. All clinical characteristics of the knee OA patients were obtained from their medical records. PLR and NMR were compared between knee OA patients and HC by non-parametric tests. Correlations of PLR and NMR with Kellgren-Lawrence (KL) classification (KL grade 2, KL grade 3, and KL grade 4) were also analyzed through a Spearman correlation test. Ordinal polytomous logistic regression was used to determine independent factors influencing radiographic grades of knee OA patients.

RESULTS

PLR was increased significantly in knee OA patients, while a statistical difference in NMR was not observed. However, PLR was not relevant to KL grades, while NMR was negatively correlated with these (r = -0.330, P < 0.01) and was independently associated with KL grades of knee OA.

CONCLUSION

PLR could reflect the inflammation response of knee OA. NMR emerged as an independent factor and could be used as a potential marker indicating the severity of knee OA.

Effects of receptor activator nuclear factor κB gene polymorphisms on the susceptibility to knee osteoarthritis: A case-control study

The present study aimed to explore genetic association of receptor activator nuclear factor κB (RANK) polymorphisms with individual susceptibility to knee osteoarthritis (OA) in different Kellgren-Lawrence (KL) grades.This case-control study included 138 knee OA patients and 145 healthy individuals. RANK rs1805034 and rs8086340 polymorphisms were genotyped through polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The effects of RANK polymorphisms on knee OA risk were analyzed via χ test or Fisher exact test, and the results were expressed using odds ratios (ORs) with corresponding 95% confidence intervals (CIs).The C allele of rs1805034 polymorphism had significantly higher frequency in knee OA patients than in controls (P = .044), indicating that this allele could increase the risk of knee OA (OR = 1.424, 95% CI = 1.010-2.008). Besides, the CC genotype and C allele of the rs1805034 polymorphism were significantly associated with elevated risk of knee OA in moderate grade (CC vs TT: P = .018, OR = 3.071, 95% CI = 1.187-7.941; C vs T: P = .012, OR = 1.787, 95% CI = 1.131-2.823). However, rs8086340 polymorphism had no significant association with knee OA riskThe C allele of RANK rs1805034 polymorphism is closely correlated with increased risk of knee OA, especially for moderate grade.

Hyaluronic Acid-Based Optical Probe for the Diagnosis of Human Osteoarthritic Cartilage

Osteoarthritis is typically caused by cartilage injury, followed by localized inflammatory responses and tissue deterioration. Early treatment of osteoarthritis is often impossible due to the lack of diagnostic options. Recent studies have supported that different imaging probes can be used for arthritis detection in mice. However, none of these diagnostic tools have been tested on human articular cartilage. To fill this gap, an optical imaging probe was developed to target activated macrophages and the accumulation of imaging probes on tissue was used to assess the severity of human osteoarthritis. Methods: The probe was fabricated using hyaluronic acid (HA) particles conjugated with near-infrared dye and folic acid (FA). The ability of the FA-HA probes to detect activated macrophages and quantify cartilage injury was evaluated using a cell culture model in vitro and human osteoarthritic cartilage explants ex vivo. Results: Our cell study results supported that the FA-HA probes are cell compatible (up to 0.5mg/mL) and can detect activated macrophages in 30 minutes. Using human articular cartilage, we verified the existence of activated macrophages on osteoarthritic cartilage with highly up-regulated expression of folate receptors (~13 folds by comparison with healthy control). In addition, we found that FA-HA probes had higher binding amounts (~3 folds) to osteoarthritic tissue than healthy ones. Histological analyses confirmed that there was a strong linear relationship (R=0.933) between the fluorescent intensity of tissue-associated probe and the extent of folate receptors on osteoarthritic cartilage. Finally, the co-localization of the imaging probe, folate receptors and cartilage degeneration on the tissue sections indicated the extraordinary accuracy and efficiency of this osteoarthritis diagnostic probe. Conclusions: Our results support the probe as an effective diagnostic tool to detect the area and severity of osteoarthritic human articular cartilage.

MicroRNA-181 inhibits proliferation and promotes apoptosis of chondrocytes in osteoarthritis by targeting PTEN

Objective: To investigate the effects of microRNA-181 (miR-181) on the proliferation and apoptosis of chondrocytes in osteoarthritis (OA) by targeting PTEN. Methods: The chondrocytes in logarithmic growth phase were selected and divided into 6 test groups: the normal, blank, negative control, miR-181 mimic, miR-181 inhibitor, and miR-181 inhibitor + PTEN-siRNA groups. Reverse transcription qPCR was used to detect the expressions of miR-181 and PTEN mRNA. MTT assay and flow cytometry were performed to detect cell proliferation and apoptosis. The protein expressions of PARP and caspase-3 and the activity of MMP-2 and MMP-9 were detected by Western blotting and gelatin zymography assay. Results: The miR-181 mimic group showed increased miR-181 expression and decreased PTEN expression compared with the other 5 groups. Also, by comparison with the other 5 groups, the cell proliferation rate declined and the rate of cell apoptosis was elevated in the miR-181 mimic group. The MiR-181 mimic group showed remarkably increased protein expression of caspase-3 and PARP compared with the other 5 groups. The activity of MMP-2 and MMP-9 was higher in the miR-181 mimic group than the other 5 groups. Conclusion: MiR-181 could up-regulate the expressions of caspase-3, PARP, MMP-2, and MMP-9, and thereby inhibit cell proliferation and promote apoptosis of chondrocytes in OA by targeting PTEN.

Changes in the osteochondral unit during osteoarthritis: structure, function and cartilage-bone crosstalk

In diarthrodial joints, the articular cartilage, calcified cartilage, and subchondral cortical and trabecular bone form a biocomposite - referred to as the osteochondral unit - that is uniquely adapted to the transfer of load. During the evolution of the osteoarthritic process the compositions, functional properties, and structures of these tissues undergo marked alterations. Although pathological processes might selectively target a single joint tissue, ultimately all of the components of the osteochondral unit will be affected because of their intimate association, and thus the biological and physical crosstalk among them is of great importance. The development of targeted therapies against the osteoarthritic processes in cartilage or bone will, therefore, require an understanding of the state of these joint tissues at the time of the intervention. Importantly, these interventions will not be successful unless they are applied at the early stages of disease before considerable structural and functional alterations occur in the osteochondral unit. This Review describes the changes that occur in bone and cartilage during the osteoarthritic process, and highlights strategies for how this knowledge could be applied to develop new therapeutic interventions for osteoarthritis.

Bone-cartilage crosstalk: a conversation for understanding osteoarthritis

Although cartilage degradation is the characteristic feature of osteoarthritis (OA), it is now recognized that the whole joint is involved in the progression of OA. In particular, the interaction (crosstalk) between cartilage and subchondral bone is thought to be a central feature of this process. The interface between articular cartilage and bone of articulating long bones is a unique zone, which comprises articular cartilage, below which is the calcified cartilage sitting on and intercalated into the subchondral bone plate. Below the subchondral plate is the trabecular bone at the end of the respective long bones. In OA, there are well-described progressive destructive changes in the articular cartilage, which parallel characteristic changes in the underlying bone. This review examines the evidence that biochemical and biomechanical signaling between these tissue compartments is important in OA disease progression and asks whether such signaling might provide possibilities for therapeutic intervention to halt or slow disease development.

Early cathepsin K degradation of type II collagen in vitro and in vivo in articular cartilage

OBJECTIVE

To characterize the initial events in the cleavage of type II collagen mediated by cathepsin K and demonstrate the presence of the resulting products in human and equine articular osteoarthritic cartilage.

DESIGN

Equine type II collagen was digested with cathepsin K and the cleavage products characterized by mass spectrometry. Anti-neoepitope antibodies were raised against the most N-terminal cleavage products and used to investigate the progress of collagen cleavage, in vitro, and the presence of cathepsin K-derived products in equine and human osteoarthritic cartilage.

RESULTS

Six cathepsin K cleavage sites distributed throughout the triple helical region were identified in equine type II collagen. Most of the cleavages occurred following a hydroxyproline residue. The most N-terminal site was within three residues of the previously identified site in bovine type II collagen. Western blotting using anti-neoepitope antibodies showed that the initial cleavages occurred at the N-terminal sites and this was followed by more extensive degradation resulting in products too small to be resolved by SDS gel electrophoresis. Immunohistochemical staining of cartilage sections from equine or human osteoarthritic joints showed staining in lesional areas which was not observed in non-arthritic sites.

CONCLUSIONS

Cathepsin K cleaves triple helical collagen by erosion from the N-terminus and with subsequent progressive cleavages. The liberated fragments can be detected in osteoarthritic cartilage and may represent useful biomarkers for disease activity.