Quantitative criteria for evaluating the early development of osteoarthritis and the effect of diclofenac sodium

Proteomic Profile Analysis of Synovial Fluid in Patients With Anterior Cruciate Ligament Tears

BACKGROUND

Anterior cruciate ligament (ACL) tears are associated with posttraumatic osteoarthritis, but the early biological changes that initiate joint degeneration after this injury are not well characterized. ACL tears typically result in effusion in the knee, which may provide insight into the initial response of the joint to injuries.

HYPOTHESIS

Patient- and injury-specific factors are associated with the proteomics of synovial fluid in knees with ACL tears.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Synovial fluid was collected from 105 patients (38 male, 67 female) with an acute traumatic ACL tear. Patient- and injury-specific factors such as age, sex, body mass index, time from injury, presence/absence of concomitant meniscal tears, and location of concomitant bone bruises (if present) were recorded. The protein concentration of synovial fluid was measured, followed by benchmarking of samples for multi-affinity high-abundance protein depletion. An isotropically labeled high-resolution nano-liquid chromatography with tandem mass spectrometry-based proteomic approach was used to determine the synovial fluid protein profile. Data were processed, quality controlled, and analyzed computationally for each patient and injury factor.

RESULTS

The proteomics of synovial fluid from ACL tears was associated with patient sex, injury pattern, and location of bone bruises but not with patient age, body mass index, or time from injury. Knees with an isolated ACL tear had higher glutathione peroxidase 1 (GPX1) and plastin 3 levels than knees with an ACL tear and meniscal tear. A bone bruise on the lateral femoral condyle was associated with elevated leptin and glucose-6-phosphate dehydrogenase (G6PD) levels. A bone bruise on the lateral tibial plateau was associated with decreased GPX1 levels. Male patients had higher matrix metalloproteinase 9 and lower G6PD levels than female patients.

CONCLUSION

Patient sex, injury pattern, and bone bruise location were important determinants of the proteomic profile of effusion resulting from ACL tears.

CLINICAL RELEVANCE

Longitudinal follow-ups to see if and how proteomic differences relate to clinical outcomes and mechanistic studies to assess the role that specific proteins play in the joint are warranted. Ultimately, these investigations could lead to better approaches to predict clinical outcomes and identify possible interventions to optimize outcomes in these patients.

2-Deoxy-D-glucose regulates dedifferentiation through beta-catenin pathway in rabbit articular chondrocytes

2-deoxy-D-glucose (2DG) is known as a synthetic inhibitor of glucose. 2DG regulates various cellular responses including proliferation, apoptosis and differentiation by regulation of glucose metabolism in cancer cells. However, the effects of 2DG in normal cells, including chondrocytes, are not clear yet. We examined the effects of 2DG on dedifferentiation with a focus on the beta-catenin pathway in rabbit articular chondrocytes. The rabbit articular chondrocytes were treated with 5 mM 2DG for the indicated time periods or with various concentrations of 2DG for 24 h, and the expression of type II collagen, c-jun and beta-catenin was determined by Western blot, RT-PCR, immunofluorescence staining and immunohistochemical staining and reduction of sulfated proteoglycan synthesis detected by Alcain blue staining. Luciferase assay using a TCF (T cell factor)/LEF (lymphoid enhancer factor) reporter construct was used to demonstrate the transcriptional activity of beta-catenin. We found that 2DG treatment caused a decrease of type II collagen expression. 2DG induced dedifferentiation was dependent on activation of beta-catenin, as the 2DG stimulated accumulation of beta-catenin, which is characterized by translocation of beta-catenin into the nucleus determined by immunofluorescence staining and luciferase assay. Inhibition of beta-catenin degradation by inhibition of glycogen synthase kinase 3-beta with lithium chloride (LiCl) or inhibition of proteasome with z-Leu-Leu-Leu-CHO (MG132) accelerated the decrease of type II collagen expression in the chondrocytes. 2DG regulated the post-translational level of beta-catenin whereas the transcriptional level of beta-catenin was not altered. These results collectively showed that 2DG regulates dedifferentiation via beta-catenin pathway in rabbit articular chondrocytes.

Leptin plays a catabolic role on articular cartilage

Leptin has been shown to play a crucial role in the regulation of body weight. There is also evidence that this adipokine plays a key role in the process of osteoarthritis. However, the precise role of leptin on articular cartilage metabolism is not clear. We investigate the role of leptin on articular cartilage in vivo in this study. Recombinant rat leptin (100 μg) was injected into the knee joints of rats, 48 h later, messenger RNA (mRNA) expression and protein levels of basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), matrix metalloproteinases 2 and 9 (MMP-2, MMP-9), cathepsin D, and collagen II from articular cartilage were analyzed by real-time quantitative polymerase chain reaction (PCR) and western blot. Two important aggrecanases ADAMTS-4 and -5 (a disintegrin and metalloproteinase with thrombospondin motifs 4 and 5) were also analyzed by real-time quantitative PCR. Besides, articular cartilage was also assessed for proteoglycan/GAG content by Safranin O staining. Leptin significantly increased both gene and protein levels of MMP-2, MMP-9, cathepsin D, and collagen II, while decreased bFGF markedly in cartilage. Moreover, the gene expression of ADAMTS-4 and -5 were markedly increased, and histologically assessed depletion of proteoglycan in articular cartilage was observed after treatment with leptin. These results strongly suggest that leptin plays a catabolic role on cartilage metabolism and may be a disadvantage factor involve in the pathological process of OA.

Osteoarthritic changes of the patellofemoral joint in STR/OrtCrlj mice are the earliest detectable changes and may be caused by internal tibial torsion

STR/ort mice develop a naturally occurring osteoarthritis (OA) of the knee joints. However, the evaluation of early OA changes has been difficult due to variability caused by gender, individual differences, and differences between the right and left lower limbs. The objective of this study was to analyze the variability of the early OA changes with age in STR/ort mice and to identify the cause of onset. A total of 115 STR/OrtCrlj mice aged 10-45 weeks were examined. In addition to conventional radiological and histological evaluation of the knee joints, histological sections were used to examine the patellofemoral, femorotibial, and growth plate cartilage under similar conditions. A morphological evaluation of tibiae, including micro-3-dimensional computed tomography, was performed. Radiological evaluation showed OA changes in the joints of mice over 35 weeks old and histological evaluation showed early OA changes in the femorotibial joints of mice over 26 weeks old. However, these changes were not common in all individuals. In contrast, most common and reproducible OA changes were observed in the bilateral patellofemoral joints of all individuals, and even in subjects ranging from 10 to 20 weeks of age. Morphological evaluations also demonstrated an abnormal tibial internal torsion that increased with age and was associated with medial patellar dislocation. In conclusion, the earliest histological OA change was observed in the patellofemoral joint prior to similar observations in the femorotibial joint. Internal tibial torsion may be a cause of OA in the patellofemoral joints, which leads to the development of medial femorotibial OA.

Distinct pathways regulate facilitated glucose transport in human articular chondrocytes during anabolic and catabolic responses

Articular cartilage is an avascular, non-insulin-sensitive tissue that utilizes glucose as the main energy source, a precursor for glycosaminoglycan synthesis, and a regulator of gene expression. Facilitated glucose transport represents the first rate-limiting step in glucose metabolism. Previously, we demonstrated that glucose transport in chondrocytes is regulated by proinflammatory cytokines via upregulation of GLUT mRNA and protein expression. The objective of the present study was to determine differences in molecular mechanisms regulating glucose transport in chondrocytes stimulated with the anabolic transforming growth factor-beta1 (TGF-beta1) vs. the catabolic and proinflammatory cytokine IL-1beta. Both TGF-beta1 and IL-1beta accelerate glucose transport in chondrocytes. Although both IL-1beta and TGF-beta1 enhance glucose transport in chondrocytes to a similar magnitude, IL-1beta induces significantly higher levels of lactate. TGF-beta1-stimulated glucose transport is not associated with increased expression or membrane incorporation of GLUT1, -3, -6, -8, and -10 and depends on PKC and ERK activation. In contrast, IL-1beta-stimulated glucose transport is accompanied by increased expression and membrane incorporation of GLUT1 and -6 and depends upon activation of PKC and p38 MAP kinase. In conclusion, anabolic and catabolic stimuli regulate facilitated glucose transport in human articular chondrocytes via different effector and signaling mechanisms, and they have distinct effects on glycolysis.

Inhibition of ADAM-TS4 and ADAM-TS5 prevents aggrecan degradation in osteoarthritic cartilage

Osteoarthritis is a degenerative joint disorder characterized by breakdown of articular cartilage. Degradation of aggrecan, which together with type II collagen provides cartilage with its unique characteristics of compressibility and elasticity, is an early and sustained feature of osteoarthritis. The present work was set up to identify the enzyme(s) responsible for aggrecan breakdown in osteoarthritis. We found that the two cartilage aggrecanases, ADAM-TS4 and ADAM-TS5, are present in osteoarthritic cartilage and that they are responsible for aggrecan degradation without the participation of matrix metalloproteinases. This is based on 1) neoepitopes found on aggrecan fragments in osteoarthritis (OA) cartilage explants in vitro, 2) aggrecan fragments detected in synovial fluid of OA patients, 3) the observation that an aggrecanase inhibitor, BB-16, blocked aggrecan degradation in OA cartilage in vitro, whereas the matrix metalloproteinase inhibitor XS309 did not, and 4) the presence of mRNA and protein for ADAM-TS4 and ADAM-TS5 in OA cartilage. These results suggest that ADAM-TS4 and ADAM-TS5 represent a potential target for the treatment of osteoarthritis.