Knee Osteoarthritis Cartilage Research Articles

Genome-wide DNA methylation study of hip and knee cartilage reveals embryonic organ and ‎skeletal system morphogenesis as major pathways involved in osteoarthritis

Purpose: The objectives of this study were to describe the genome wide DNA methylation changes in hip ‎and knee osteoarthritis (OA) and to identify novel genes and pathways involved in OA by ‎comparing the DNA methylome of the hip and knee osteoarthritic cartilage with those of healthy ‎individuals. ‎ Methods: OA cartilage samples were collected from the tibial plateau and femoral head articular surfaces of ‎patients with severe OA undergoing total hip/knee replacement surgery. Healthy cartilage ‎samples were obtained from individuals with femoral neck fractures, but no OA. Chondrocyte ‎DNA methylation was assayed by Illumina Infinium HumanMethylation450 BeadChip array, ‎allowing for the analysis of >480,000 CpG sites. A sub-analysis was also done to compare hip ‎and knee OA. An independent sample T-test was conducted for each CpG site and those sites ‎with at least 10% methylation difference and a P-value of <0.0001 were selected as differentially ‎methylated regions (DMR). DAVID v6.7 was used for the functional annotation clustering of ‎the DMR genes. ‎ Results: The study population comprises 5 patients with hip OA, 6 patients with knee OA and 7 hip ‎samples from healthy individuals. The comparisons of hip, knee and combined hip/knee OA ‎patients with controls resulted in 26, 72, and 103 DMRs, respectively. The comparison between ‎hip and knee OA revealed 67 DMRs. The overall number of the sites after considering the ‎overlaps was 239, among which 151 sites were annotated to 145 genes. 28 of these genes were ‎reported in previous methylation studies of OA. The functional annotation clustering of the ‎identified genes revealed clusters significantly enriched in skeletal system morphogenesis ‎‎(bonferroni corrected p=8.4e-9) and development (bonferroni corrected p=9.0e-6), embryonic ‎organ (bonferroni corrected p=1.4e-5) and skeletal system morphogenesis (bonferroni corrected ‎p=9.9e-7), as well as Homeobox genes (bonferroni corrected p=3.1e-4). A sub-analysis after the ‎removal of the genes differentially methylated between hip and knee OA highlighted the same ‎pathways excluding Homeobox genes.‎ Conclusions: We demonstrated a number of CpG sites and genes across the genome differentially methylated ‎among OA patients and controls, a remarkable portion of which seem to be involved in potential ‎etiologic mechanisms of OA. Genes involved in skeletal developmental pathways and embryonic ‎organ morphogenesis may be a potential area of concentration for future osteoarthritis ‎genetic/epigenetic research. ‎

Are the inflammatory mechanism differentialy regulated across different osteoarthritic joints

Are the inflammatory mechanism differentialy regulated across different osteoarthritic joints

Gremlin1 induced by excessive mechanical stress loading enhances cartilage degradation

Gremlin1 induced by excessive mechanical stress loading enhances cartilage degradation

Correlation between Indian hedgehog and damage degree of knee osteoarthritis cartilage

To explore the correlation between the Indian hedgehog and severity of knee osteoarthritis cartilage damage. A total of 215 patients with osteoarthritis [97 males and 118 females with an average age of 65.2 ± 7.8 (49-78) years and 34 healthy persons [28 males and 6 females with an average age of 58.4 ± 8.7 (45-62) years were selected randomly and their cartilages in knee joints collected. The damage degree of osteoarthritis was evaluated by revised Markin scale. The Ihh mRNA was assessed by real-time polymerase chain reaction (PCR) and the Ihh protein expression examined by Western blot. According to the revised Mankin scale, the osteoarthritis samples were divided into 3 stages of severe, moderate and mild. Comparing with normal control group, the Ihh mRNA and protein expressions increased obviously in cartilage. With worsening cartilage damage, Ihh mRNA and protein expression increased accordingly. Statistical differences existed among the groups (normal: 1.00 ± 0.01; mild: 1.37 ± 0.02; moderate: 1.90 ± 0.02; severe: 2.13 ± 0.03; P < 0.01). And the damage degree of osteoarthritis was determined by injury extent of soft tissue in knee joint (Mankin scale). And the damage degree of cartilage was positively correlated with Ihh expression (r = 0.581, P < 0.01). Ihh expression is correlated with the damage degree of knee joint osteoarthritis.

Effect of a 16 weeks weight loss program on osteoarthritis biomarkers in obese patients with knee osteoarthritis: a prospective cohort study

Changes in biomarkers for bone and cartilage in knee osteoarthritis (KOA) may reflect changes in tissue turnover induced by interventions. The aim of this study was to assess the effect on osteoarthritis biomarkers of an intensive weight loss intervention in obese KOA patients. 192 obese KOA patients followed a 16 weeks weight loss intervention (ClinicalTrials.gov: NCT00655941). Serum Cartilage Oligomeric Matrix Protein (sCOMP), Urine C-terminal telopeptide of collagen type II (uCTX-II) and type I (uCTX-I) were determined by enzyme-linked immunoassay (ELISA) at baseline and after 16 weeks. Patient-reported symptoms were assessed by the Knee Injury and Osteoarthritis Outcome Score (KOOS) Questionnaire without the sports and recreation score (KOOS-4). Change from baseline was analyzed using Analysis of CoVariance (ANCOVA) adjusting for sex, age, and body mass index (BMI). Bivariate associations were analyzed using Spearman's test of rank correlation. 175 patients completed the treatment and lost mean 13.4 (95% CI: 12.5-14.4) kg. sCOMP concentration decreased on average 1.1 (95% CI:-1.5 to-0.8) U/L with a correlation to weight loss (r=-0.17, P=0.028), but not to change in KOOS-4 (r=-0.13, P=0.091). uCTX-II increased significantly, mean 69 (95% CI: 31-106) ng/mmol creatinine, with no relation to weight loss (P=0.14). Change in uCTX-II was reversely related to change in KOOS-4 (r=-0.28, P=0.0003). uCTX-I increased, mean 67 (95% CI: 47-87) μg/mmol creatinine, and correlated to weight loss (r=0.22, P=0.0007), while not to KOOS-4 (P=0.93). A rapid substantial weight loss in obese KOA patients was weakly, while significantly associated with a reduction in sCOMP, and increases in both uCTX-II and uCTX-I.

Human osteoarthritic knee cartilage: fingerprinting of adhesion/growth-regulatory galectins in vitro and in situ indicates differential upregulation in severe degeneration.

The apparent connection of galectin-3 to chondrocyte survival and osteoarthritis-like cartilage modifications in animal models provided incentive for the mapping of seven members of this family of adhesion/growth-regulatory proteins in human cartilage specimens. Starting with work in vitro, RT-qPCR analyses and immunocytochemistry revealed gene transcription and protein presence in cultured OA chondrocytes, especially for galectin-1, galectin-3 and galectin-8. Immunohistochemistry in clinical specimens with mild and severe cartilage degeneration detected galectins in chondrocytes-with upregulation, especially of galectin-1 in areas of severe degeneration-accompanied by α2,6-sialylation in the pericellular matrix. Given the possibility for additive/antagonistic activities between galectins, these results direct further research toward examining cellular effects of (1) these proteins (alone or in combination) on chondrocytes and (2) remodeling of the chondrocyte glycophenotype.

Human osteoarthritic cartilage shows reduced in vivo expression of IL-4, a chondroprotective cytokine that differentially modulates IL-1β-stimulated production of chemokines and matrix-degrading enzymes in vitro.

BackgroundIn osteoarthritis (OA), an inflammatory environment is responsible for the imbalance between the anabolic and catabolic activity of chondrocytes and, thus, for articular cartilage derangement. This study was aimed at providing further insight into the impairment of the anabolic cytokine IL-4 and its receptors in human OA cartilage, as well as the potential ability of IL-4 to antagonize the catabolic phenotype induced by IL-1β.Methodology/Principal FindingsThe in vivo expression of IL-4 and IL-4 receptor subunits (IL-4R, IL-2Rγ, IL-13Rα1) was investigated on full thickness OA or normal knee cartilage. IL-4 expression was found to be significantly lower in OA, both in terms of the percentage of positive cells and the amount of signal per cell. IL-4 receptor type I and II were mostly expressed in mid-deep cartilage layers. No significant difference for each IL-4 receptor subunit was noted. IL-4 anti-inflammatory and anti-catabolic activity was assessed in vitro in the presence of IL-1β and/or IL-4 for 24 hours using differentiated high density primary OA chondrocyte also exhibiting the three IL-4 R subunits found in vivo. Chemokines, extracellular matrix degrading enzymes and their inhibitors were evaluated at mRNA (real time PCR) and protein (ELISA or western blot) levels. IL-4 did not affect IL-1β-induced mRNA expression of GRO-α/CXCL1, IL-8/CXCL8, ADAMTS-5, TIMP-1 or TIMP-3. Conversely, IL-4 significantly inhibited RANTES/CCL5, MIP-1α/CCL3, MIP-1β/CCL4, MMP-13 and ADAMTS-4. These results were confirmed at protein level for RANTES/CCL5 and MMP-13.Conclusions/SignificanceOur results indicate for the first time that OA cartilage has a significantly lower expression of IL-4. Furthermore, we found differences in the spectrum of biological effects of IL-4. The findings that IL-4 has the ability to hamper the IL-1β-induced release of both MMP-13 and CCL5/RANTES, both markers of OA chondrocytes, strongly indicates IL-4 as a pivotal anabolic cytokine in cartilage whose impairment impacts on OA pathogenesis.

Inter-rater accuracy and precision of markerless quantification of 3d tibiofemoral displacement using dual fluoroscopy

Purpose: Early changes in osteoarthritic (OA) knee cartilage include tissue swelling and softening, which may predispose cartilage to mechanical damage during activities of daily living. Current clinical OA diagnosis relies on radiographic bone morphology change and pain, which can be insensitive to early change. Developing a marker that specifically targets early mechanical tissue changes may advance the current state of OA assessment. Potential candidates for such markers are in-vivo magnitude and rate of tibiofemoral (TF) soft tissue deformation during weight bearing (compression) and unloading (recovery). Respective joint “signatures” for healthy and OA groups may then allow for early OA identification. Dual Fluoroscopy (DF) is an emerging tool with the potential to provide the temporal and spatial resolutions necessary for such assessment. Tissue deformation mechanics may be derived using translation and rotation changes of the femur with respect to the tibia over time. Using a bead tracking technique, similar to radiostereometric analysis (RSA), translation changes of 0.05 mm (1/ 10th expected maximal cartilage deformation) have previously been accurately detected. It is however unknown if a non-invasive markerless DF approach is sufficiently accurate and precise for quantifying the small changes during weight bearing. The purpose of this study was to establish the Minimum Detectable Displacement (MDD) of 3D femoral translations with respect to the tibia in a custom built DF system using a markerless shape matching image registration approach. Methods: The DF system consisted of two X-ray tubes (Varian, USA) and generators (EMD, Canada), quad mode image intensifiers (Toshiba, Japan) and high speed digital video cameras (PCO, Germany). DF images were acquired with an entrance field diameter of 228 mm and 0.155 x 0.155 mm2 pixel resolution. Dry tibia and femur bones were fixed to a plexiglass frame, where the tibia remained stationary and the femur was translated using a digital micrometer (Mitutoyo, Japan). The frame was placed within the DF field-of-view and did not move during data capture. Ten displacement intervals (0.01-0.1 mm)were imagedwith 10 repetitions of each interval. DF calibration was performed using a calibration cube and modified direct linear transform. Images were distortion corrected using a perforated steel grid and XrayProject (Brown University, USA). 3D femur and tibia bone models were generated using segmentation (Amira, USA) of Computed Tomography image sequences (0.21 x 0.21 x 0.31 mm). 3D bone orientations were obtained by three raters using AutoScoper (Brown University, USA) and a markerless shape matching approach. Bone-specific models were positioned to align their visible features to those of the underlying 2D X-ray images. Relative femur and tibia displacements were obtained using the Euclidean distance between bone models. Independent samples t-tests were used to detect MDDs of the moving femur relative to the stationary tibia at each displacement interval. Accuracy and precision were computed as means and standard deviations of the absolute differences of the femur translations compared to the micrometer displacements. Inter-rater reliability values of the femur were computed using intra-class correlation coefficient (ICC). All statistical analyses were performed in SPSS (IBM, USA) and p 0.05. Results: Femur displacement measurements were significantly different from tibia (p<0.045) and had greater than 95% confidence in accuracy at micrometer displacements 0.:08mm (accuracy precision: 0.022 0.019) (Figure 1). Between raters femur displacement measurements were not significant for micrometer displacements 0.:05mm and inter-rater reliability across all displacements was 92%. Conclusions: These findings indicate that 3D bone translations within relevant in-vivo ranges can be observed accurately and precisely using a markerless DF shape matching approach. Femur displacements of 0.:08mm were accurately and reliably detected with respect to set micrometer displacements. The data further indicated good between rater agreement when quantifying femur displacements. Given the above system specifications, the markerless DF approach provides a means for non-invasive in-vivo quantification of TF tissue response to loading and unloading stimuli. Using this approach, further workwill be performed to establish the mechanical behaviour of TF soft tissues of healthy and ligament deficient and OA knees. While significant user input is required, compared to RSA type techniques, this non-invasive approach may be more readily applied in a future clinical setting.

Effectiveness of Thermotherapy Using a Heat and Steam Generating Sheet for Cartilage in Knee Osteoarthritis

[Purpose] Superficial heat treatment is one of the most widely used physical therapies for osteoarthritis (OA). We clinically evaluated the effects of local heat treatment and exercise therapy for knee OA, and evaluated the articular cartilage using magnetic resonance imaging (MRI) T2 mapping. [Subjects and Methods] Eighteen females aged 50–69 (59.5 ± 8.5 years, mean ± SD) years diagnosed with early-stage knee OA were randomly assigned using computer-generated random numbers to either a local heat treatment group (LH group, 9 subjects) or an exercise therapy group (EX group, 9 subjects). These groups were subjected to a 12-week intervention experiment. MRI T2 mapping was performed for cartilage imaging and quantitative evaluation. For clinical evaluation, the Japanese Knee Osteoarthritis Measure (JKOM) and the Timed Up and Go (TUG) test were performed. Both clinical and MRI evaluations were performed at the beginning and end of the intervention (0 week (Time 0) and 12 weeks). [Results] The total JKOM score had a significantly decreased in the LH group at 12 weeks. However, in the EX group the total JKOM scores at Time 0 and 12 weeks were not significantly different. The TUG time in the EX group was significant shorter at 12 weeks, whereas it showed no significant change in the LH group at 12 weeks, though the TUG times of 7 of the 9 patients decreased, exhibiting some improvement. The T2 value of the LH group was significantly shorter at 12 weeks. However, the T2 value in the EX group showed no significant change at 12 weeks. [Conclusion] After local heat treatment using heat- and steam moisture-generating sheets for 12 weeks, we observed improvements in clinical symptoms and walking abilities. Moreover, positive effects on cartilage metabolism were suggested.

English

Introduction We illustrated the anatomical aspect of the cartilage in a healthy and osteoarthritic knee joint. Osteoarthritis is a disease of high ethical and economical importance. In advanced stages, the patients suffer from severe pain, restriction of mobility and inability to work. In this mini review, we described the current knowledge about the macroscopic and microscopic anatomical features in healthy and osteoarthritic knee cartilage. Discussion Adult articular cartilage has a low capacity to repair itself, and thus even minor injuries may lead to progressive damage and osteoarthritic joint degeneration, resulting in significant pain and disability. Numerous studies on human osteoarthritic tissue and in animal models have addressed the microscopic and macroscopic anatomical aspects of OA progression to get a better understanding of the pathophysiology of this disease. Further, imaging studies show the macroscopic anatomical changes and are important for the diagnosis of this disease. Conclusion Further in vivo and in vitro studies must be carried out in order to improve the early diagnosis and the treatment of articular cartilage defects, leading to a better clinical outcome for the patients affected. Introduction The knee joint is a relatively complex anatomical structure. The stability of this synovial (or diarthrodial) joint is maintained by a variety of ligaments and the presence of large muscle groups1. Both the femur and tibia are enclosed in a joint capsule (Figure 1) lined with synovial tissue. Between the condyles of the femur and the condylar surface of the tibia, there are two C-shaped pieces of cartilage called menisci (Figure 2), which serve as shock absorbers for the knee joint, located medially and laterally inside the joint2–4. The joint capsule of the knee is strengthened by different ligaments: the patellar ligament or patellar tendon, the lateral and medial retinaculum of the patella, the medial and lateral alar ligaments, the medial and lateral collateral ligaments, the popliteal ligaments and the anterior and posterior cruciate ligaments (ACLs and PCLs) (Figure 3). Between each muscle group, there are fluid-filled sacs called bursa and fat bodies, which reduce friction and lend added protection to the joint capsule. The knee works during normal activity such as walking or running, and even for support while standing. It can tolerate moderate stress without significant injury. However, the knee lacks support to withstand many types of injury, especially rotational forces such as those seen in many athletic activities. The most important connective tissue for the correct functioning of the knee joint is the cartilage. Cartilage is classified into three types according to the amount of its components: elastic cartilage, hyaline cartilage and fibrocartilage5. Hyaline cartilage is a flexible connective tissue found in many areas of human and other animal bodies. It covers the opposing osseous ends of every synovial joint5–8, such as the knee joint, and it is found in the growth plate of the metaphysis9,10. Cartilage tissue has unique viscoelastic and compressive properties provided by the extracellular matrix, which is mainly composed of collagen type II and the large proteoglycan aggrecan5–8. Articular cartilage is not innervated and lacks blood vessels. For this reason, knee injuries, even though minor, if involving the cartilage, may have delayed healing time. Nutrients in the synovial fluid and cellular repair components are transported to the chondrocytes by diffusion from the synovial fluid5–8. Only small defects, associated with minimal loss of matrix components, can be regenerated by hyaline cartilage. * Corresponding author Email: g.musumeci@unict.it 1 Department of Bio-Medical Sciences, Human Anatomy and Histology Division, University of Catania, Italy 2 Department of Medical and Pediatric Sciences, Internal Medicine Division, University of Catania, Italy 3 Fondazione Mediterranea ‘‘G.B. Morgagni’’, Catania, Italy Figure 1: Surgery of the left knee with joint capsule on site.

Retropatellar fat pad–derived stem cells from older osteoarthritic patients have lesser differentiation capacity and expression of stemness genes

Background aimsThe use of retropatellar fat pad–derived mesenchymal stromal cells (RFMSCs) for cell-based therapy, particularly for cartilage repair, has been reported by several investigators in recent years. However, the effects of the donor's age and medical condition on the characteristics of RFMSCs have not been well established. The aim of this study was to determine whether age and medical condition can reduce the multipotential of stem cells isolated from the retropatellar fat pad. MethodsThe RFMSCs were isolated from patients with osteoarthritic knee cartilage (degenerative group; 40–60 years old) and compared with patients without degenerative knee disease (young group; <40 years old) in terms of their growth kinetics, immunophenotype, differentiation ability and stemness gene expression. ResultsData showed that RFMSCs from both groups have similar growth kinetics and immunophenotype profile at passage 3. However, RFMSCs from the degenerative group showed lower adipogenic, osteogenic and chondrogenic differentiation ability compared with RFMSCs derived from the young group. The stemness gene expression level of RFMSCs derived from the degenerative group was lower than that in the young group. RFMSCs from both groups met the minimum criteria of mesenchymal stromal cells and have the potential for cartilage regeneration. However, RFMSCs from the degenerative group showed lower regeneration capability. ConclusionsThese results indicate that older age and osteoarthritic condition did affect the multipotential of stem cells derived from the retropatellar fat pad under the current prescribed condition. More studies will be conducted to clarify whether the age or medical condition contributed more to the loss of differentiation capacity and stemness gene expression of RFMSCs.

Longitudinal evaluation of T1ρ and T2 spatial distribution in osteoarthritic and healthy medial knee cartilage

To investigate longitudinal changes in laminar and spatial distribution of knee articular cartilage magnetic resonance imaging (MRI) T1ρ and T2 relaxation times, in individuals with and without medial compartment cartilage defects. All subjects (at baseline n=88, >18 years old) underwent 3-Tesla knee MRI at baseline and annually thereafter for 3 years. The MR studies were evaluated for presence of cartilage defects (modified Whole-Organ Magnetic Resonance Imaging Scoring - mWORMS), and quantitative T1ρ and T2 relaxation time maps. Subjects were segregated into those with (mWORMS ≥2) and without (mWORMS ≤1) cartilage lesions at the medial tibia (MT) or medial femur (MF) at each time point. Laminar (bone and articular layer) and spatial (gray level co-occurrence matrix - GLCM) distribution of the T1ρ and T2 relaxation time maps were calculated. Linear regression models (cross-sectional) and Generalized Estimating Equations (GEEs) (longitudinal) were used. Global T1ρ, global T2 and articular layer T2 relaxation times at the MF, and global and articular layer T2 relaxation times at the MT, were higher in subjects with cartilage lesions compared to those without lesions. At the MT global T1ρ relaxation times were higher at each time point in subjects with lesions. MT T1ρ and T2 became progressively more heterogeneous than control compartments over the course of the study. Spatial distribution of T1ρ and T2 relaxation time maps in medial knee OA using GLCM technique may be a sensitive indicator of cartilage deterioration, in addition to whole-compartment relaxation time data.

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

Objectives To investigate CD44 levels in articular cartilage of knee osteoarthritis (OA) and the relationship between CD44 and severity of the disease.Methods All 50 cartilage tissues included normal and OA cartilage, and were ascribed to the following four groups on the basis of modified Mankin score: normal, mild lesions, moderate lesions and severe lesions. CD44 levels in articular cartilage were assessed by immunohistochemical methods.Results CD44 levels were detected in all four groups. The difference in average gray value of CD44 expression showed statistical significance when compared between each group (P < 0.05). In addition, CD44 expression in each group correlated with disease severity, according to the modified Mankin score (ρ = −0.848, P < 0.01).Conclusions CD44 in articular cartilage is associated with progressive knee OA joint damage.

Correlation between senescence-associated beta-galactosidase expression in articular cartilage and disease severity of patients with knee osteoarthritis.

The purposes of this study were to investigate senescence-associated beta-galactosidase (SA-beta-Gal) levels in articular cartilage of knee osteoarthritis (OA) and the relationship with severity of the disease. All the 50 cartilage tissues, including normal (controls) and OA cartilage were ascribed to four groups of normal, mild lesions, moderate lesions and severe lesions on the basis of the modified Mankin score. Immunohistochemistry was used to assess the SA-beta-Gal expression in articular cartilage. No SA-beta-Gal staining was observed in the normal articular cartilage samples. SA-beta-Gal staining was found in a subset of the chondrocytes close to the lesion site of mild, moderate and severe damaged knee OA cartilage. The percentage of SA-beta-Gal-positive chondrocytes in articular cartilage was 0% in controls, 13.00±5.77% in mild lesions, 31.65±6.91% in moderate lesions and 51.95±6.21% in severe lesions. SA-beta-Gal expression in mild lesions, moderate lesions and severe lesions was higher compared with that of controls (P<0.0001). SA-beta-Gal expression in moderate lesions and severe lesions were higher with respect to mild lesion samples (P<0.0001). SA-beta-Gal expression in severe lesions was elevated compared with those of moderate lesions (P<0.0001). Subsequent analysis showed that articular cartilage SA-beta-Gal levels correlated with severity of disease (Spearman's ρ=0.94, P<0.0001). SA-beta-Gal expression in articular cartilage is associated with progressive knee OA joint damage and is a potential indictor of disease severity.

Characterizing healthy and osteoarthritic knee cartilage on phase contrast CT with geometric texture features.

The current approach to evaluating cartilage degeneration at the knee joint requires visualization of the joint space on radiographic images where indirect cues such as joint space narrowing serve as markers for osteoarthritis. A recent novel approach to visualizing the knee cartilage matrix using phase contrast imaging (PCI) with computed tomography (CT) was shown to allow direct examination of chondrocyte patterns and their subsequent correlation to osteoarthritis. This study aims to characterize chondrocyte cell patterns in the radial zone of the knee cartilage matrix in the presence and absence of osteoarthritic damage through texture analysis. Statistical features derived from gray-level co-occurrence matrices (GLCM) and geometric features derived from the Scaling Index Method (SIM) were extracted from 404 regions of interest (ROI) annotated on PCI images of healthy and osteoarthritic specimens of knee cartilage. These texture features were then used in a machine learning task to classify ROIs as healthy or osteoarthritic. A fuzzy k-nearest neighbor classifier was used and its performance was evaluated using the area under the Receiver Operating Characteristic (ROC) curve (AUC). The best classification performance was observed with high-dimensional geometrical feature vectors derived from SIM and GLCM correlation features. With the experimental conditions used in this study, both SIM and GLCM achieved a high classification performance (AUC value of 0.98) in the task of distinguishing between healthy and osteoarthritic ROIs. These results show that such quantitative analysis of chondrocyte patterns in the knee cartilage matrix can distinguish between healthy and osteoarthritic tissue with high accuracy.

The relation between quantitative delayed contrast-enhancement in meniscus and cartilage in knee osteoarthritis

The relation between quantitative delayed contrast-enhancement in meniscus and cartilage in knee osteoarthritis

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

To investigate CD44 levels in articular cartilage of knee osteoarthritis (OA) and the relationship between CD44 and severity of the disease. All 50 cartilage tissues included normal and OA cartilage, and were ascribed to the following four groups on the basis of modified Mankin score: normal, mild lesions, moderate lesions and severe lesions. CD44 levels in articular cartilage were assessed by immunohistochemical methods. CD44 levels were detected in all four groups. The difference in average gray value of CD44 expression showed statistical significance when compared between each group (P < 0.05). In addition, CD44 expression in each group correlated with disease severity, according to the modified Mankin score (ρ = -0.848, P < 0.01). CD44 in articular cartilage is associated with progressive knee OA joint damage.

C/EBP homologous protein drives pro-catabolic responses in chondrocytes

IntroductionExcess C/EBP homologous protein (CHOP) expression is one feature of the unfolded protein response (UPR) to endoplasmic reticulum (ER) stress. Here, we focused on CHOP expression and function in chondrocytes.MethodsWe studied human knee osteoarthritis (OA) cartilage, bovine chondrocytes cultured in alginate and subjected to sub-lethal biomechanical injury, and knee chondrocytes of human autopsy donors. We performed siRNA knockdown and transfection.ResultsUPR activation was increased in human knee OA cartilage in situ, and in biomechanically injured cultured chondrocytes in vitro. In normal human chondrocytes, CHOP “gain of function” sensitized chondrocytes to IL-1β induced nitric oxide (NO) and matrix metalloproteinase (MMP)-3 release without inducing these responses by itself. Excess CHOP expression, by itself, induced superoxide production and apoptosis. Conversely, siRNA knockdown of CHOP and the UPR-specific mediator X-box binding protein (XBP1) inhibited NO release by >80% (P <0.0005) in response to IL-1β, and blunted MMP-3 release, whereas there were only minimal effects of the UPR mediator GRP78 on these responses. The anti-inflammatory metabolic “super-regulator” AMP kinase (AMPK) is known to limit UPR activation in vascular muscle cells. Here, CHOP supported the capacity of IL-1β to suppress AMPK activity in chondrocytes. We also observed that inhibition of AMPK activity promoted an increase in chondrocyte CHOP expression. Conversely, pharmacologic activation of AMPK by 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) blunted chondrocyte CHOP expression in response to biomechanical injury.ConclusionsBiomechanical injury and IL-1 signaling stimulate UPR activation in chondrocytes. CHOP mediates chondrocyte catabolic and apoptotic responses to IL-1β, and does so partly by inhibiting AMPK activity. Conversely, development of excess CHOP activity is limited by AMPK activity in chondrocytes. Our findings suggest a mechanism for potential chondroprotection by AICAR and other AMPK activators. The work is of translational relevance for OA, since several drugs that activate AMPK are already in the clinic for arthritis (for example, allosteric AMPK activators sodium salicylate and high dose aspirin, and methotrexate, which activates AMPK by generating AICAR).

Linked decreases in liver kinase B1 and AMP-activated protein kinase activity modulate matrix catabolic responses to biomechanical injury in chondrocytes

IntroductionAMP-activated protein kinase (AMPK) maintains cultured chondrocyte matrix homeostasis in response to inflammatory cytokines. AMPK activity is decreased in human knee osteoarthritis (OA) chondrocytes. Liver kinase B1 (LKB1) is one of the upstream activators of AMPK. Hence, we examined the relationship between LKB1 and AMPK activity in OA and aging cartilages, and in chondrocytes subjected to inflammatory cytokine treatment and biomechanical compression injury, and performed translational studies of AMPK pharmacologic activation.MethodsWe assessed activity (phosphorylation) of LKB1 and AMPKα in mouse knee OA cartilage, in aging mouse cartilage (6 to 24 months), and in chondrocytes after mechanical injury by dynamic compression, via immunohistochemistry or western blot. We knocked down LKB1 by siRNA transfection. Nitric oxide, matrix metalloproteinase (MMP)-3, and MMP-13 release were measured by Griess reaction and ELISA, respectively.ResultsKnockdown of LKB1 attenuated chondrocyte AMPK activity, and increased nitric oxide, MMP-3 and MMP-13 release (P <0.05) in response to IL-1β and TNFα. Both LKB1 and AMPK activity were decreased in mouse knee OA and aged knee cartilage, and in bovine chondrocytes after biomechanical injury. Pretreatment of bovine chondrocytes with AMPK activators AICAR and A-769662 inhibited both AMPKα dephosphorylation and catabolic responses after biomechanical injury.ConclusionLKB1 is required for chondrocyte AMPK activity, thereby inhibiting matrix catabolic responses to inflammatory cytokines. Concurrent loss of LKB1 and AMPK activity in articular chondrocytes is associated with OA, aging and biomechanical injury. Conversely, pharmacologic AMPK activation attenuates catabolic responses to biomechanical injury, suggesting a potentially novel approach to inhibit OA development and progression.

Increased apoptosis in human knee osteoarthritis cartilage related to the expression of protein kinase B and protein kinase Cα in chondrocytes

Protein kinase B (Akt) and protein kinase Cα (PKCα) play important roles in the regulation of cell apoptosis. The aim of this study was to investigate the expression of Akt and PKCa in chondrocytes of human knee osteoarthritic (OA) cartilage, further evaluating their role in chondrocyte apoptosis during OA progression. Human knee OA cartilages were obtained from 38 patients undergoing knee arthroplasty, which is the medium-late stage of OA. Healthy knee cartilages were obtained from 11 amputees. The samples taken from the condyle of femur were collected routinely for morphological, immunohistochemical and Western blot detection, respectively. Light microscopy and laser-scanning confocal microscopy were used for morphological observation. The optical density with computer image analysis evaluated the intensity of immunohistochemical reaction of Akt and PKCα in OA cartilage. Western blot detected the protein expression levels. The results indicated that Akt and PKCa were involved in OA progression, along with the increase of cell apoptosis. In OA cartilage, Akt decreased (p &lt; 0.05) and PKCα increased (p &lt; 0.05). There was a negative correlation and interaction between Akt and PKCα (r = -0.8). These results demonstrated that both Akt and PKCα are related to increased chondrocyte apoptosis in human OA cartilage. The correlation between human OA progression, the role of Akt and PKCα, and chondrocyte apoptosis allows for new therapeutic strategies to be considered.