Degeneration Of Articular Cartilage In Osteoarthritis Research Articles

Exploratory neutron tomography of articular cartilage

To investigate the feasibility of using neutron tomography to gain new knowledge of human articular cartilage degeneration in osteoarthritis (OA). Different sample preparation techniques were evaluated to identify maximum intra-tissue contrast. Human articular cartilage samples from 14 deceased donors (18-75 years, 9 males, 5 females) and 4 patients undergoing total knee replacement due to known OA (all female, 61-75 years) were prepared using different techniques: control in saline, treated with heavy water saline, fixed and treated in heavy water saline, and fixed and dehydrated with ethanol. Neutron tomographic imaging (isotropic voxel sizes from 7.5 to 13.5µm) was performed at two large scale facilities. The 3D images were evaluated for gradients in hydrogen attenuation as well as compared to images from absorption X-ray tomography, magnetic resonance imaging, and histology. Cartilage was distinguishable from background and other tissues in neutron tomographs. Intra-tissue contrast was highest in heavy water-treated samples, which showed a clear gradient from the cartilage surface to the bone interface. Increased neutron flux or exposure time improved image quality but did not affect the ability to detect gradients. Samples from older donors showed high variation in gradient profile, especially from donors with known OA. Neutron tomography is a viable technique for specialized studies of cartilage, particularly for quantifying properties relating to the hydrogen density of the tissue matrix or water movement in the tissue.

Cartilage-specific deficiency of clock gene Bmal1 accelerated articular cartilage degeneration in osteoarthritis by up-regulation of mTORC1 signaling.

Although a growing body of studies recently demonstrated that circadian clock gene Bmal1 plays an important role in cartilage development and homeostasis, evidence regarding the contribution of Bmal1 in articular cartilage of OA progression is still unclear. In the present study, we investigated the direct role of Bmal1 in articular cartilage homeostasis during OA progression using tamoxifen-induced cartilage-specific knockout mice. We found that the expression of BMAL1 was decreased in OA-damaged and aging cartilage tissues. Cartilage-specific deletion of Bmal1 promoted cartilage degradation and chondrocyte apoptosis, and inhibited chondrocyte anabolism in OA mice, leading to acceleration of articular cartilage degeneration and osteophyte formation during OA progression. Mechanistic study indicated that loss of Bmal1 resulted in hyperactivation of mammalian target of rapamycin complex 1(mTORC1) signaling in OA cartilage, and pharmacological inhibition of mTORC1 signaling pathway by rapamycin alleviated partially Bmal1 ablation-induced cartilage degradation and chondrocyte apoptosis in ex vivo OA model. Therefore, our results provide the evidence of a vital role for Bmal1 in cartilage degradation in post-traumatic OA by partially regulating the mTORC1 signaling.

New insights into the interplay between autophagy and cartilage degeneration in osteoarthritis.

Autophagy is an intracellular degradation system that maintains the stable state of cell energy metabolism. Some recent findings have indicated that autophagy dysfunction is an important driving factor for the occurrence and development of osteoarthritis (OA). The decrease of autophagy leads to the accumulation of damaged organelles and macromolecules in chondrocytes, which affects the survival of chondrocytes and ultimately leads to OA. An appropriate level of autophagic activation may be a new method to prevent articular cartilage degeneration in OA. This minireview discussed the mechanism of autophagy and OA, key autophagy targets regulating OA progression, and evaluated therapeutic applications of drugs targeting autophagy in preclinical and clinical research. Some critical issues worth paying attention to were also raised to guide future research efforts.

Cartilage-Specific Deficiency of Clock Gene Bmal1 Accelerated Articular Cartilage Degeneration in Osteoarthritis by Up-Regulation of mTORC1 Signaling

Cartilage-Specific Deficiency of Clock Gene Bmal1 Accelerated Articular Cartilage Degeneration in Osteoarthritis by Up-Regulation of mTORC1 Signaling

Secreted factors from synovial fibroblasts immediately regulate gene expression in articular chondrocytes

Although articular cartilage degeneration in osteoarthritis represents a major public health problem, there is still no molecular approach to prevent this pathology by blocking specific molecules. We have previously applied genome-wide expression analyses with porcine samples to identify specific markers of either growth plate or articular cartilage. Since the molecular differences were also found in cultured chondrocytes derived from both sites, we utilized primary porcine articular chondrocytes (PPACs) for the present study and analyzed, if and how they respond to synoviocyte-derived molecules. PPACs were treated by conditioned medium from porcine synovial fibroblasts (SF-CM) for 2, 6 and 24 h. Gene expression was subsequently monitored by qRT-PCR and microarray analysis. We found that short-term administration of SF-CM to PPACs significantly reduced expression of chondrocyte markers, while it induced expression of SDC4, encoding syndecan-4, a positive regulator of articular cartilage breakdown. Consistently, expression of MMP3, a putative downstream effector of syndecan-4 was strongly induced by SF-CM in PPACs. We identified an MMP3-inducing fraction in the range of 40 kDa after gel filtration, and we confirmed our findings in three-dimensional PPAC cultures, where SF-CM also reduced the glycosaminoglycan content. Taken together, our data suggest that synovial fibroblasts secrete one or more molecule(s) that activate specific signaling events in articular chondrocytes. Identifying a responsible ligand receptor pair(s) might pave the way to develop molecular therapies to reduce the severity of osteoarthritis.

Cationic poly-l-lysine-encapsulated melanin nanoparticles as efficient photoacoustic agents targeting to glycosaminoglycans for the early diagnosis of articular cartilage degeneration in osteoarthritis.

Cartilage degeneration is the hallmark of osteoarthritis (OA) and its early diagnosis is essential for effective cartilage repair. However, until now, there was still a lack of imaging modalities that can accurately detect and evaluate cartilage degeneration in its early stage. Herein, we introduce endogenous melanin nanoparticles (MNPs) encapsulated by poly-l-lysine (PLL) as positively charged contrast agents for the accurate photoacoustic (PA) imaging of cartilage degeneration through its strong electrostatic interaction with anionic glycosaminoglycans (GAGs) in the cartilage. PLL-MNPs presented high PA intensity, photostability and biocompatibility. In vitro PAI studies showed that PLL-MNPs with a zeta potential of +32.5 ± 9.3 mV had more cartilage uptake and longer retention time than anionic MNPs, and generated a positive relationship with the GAG content in the cartilage. After administration via intra-articular injection in living mouse models, PLL-MNPs exhibited about a two-fold stronger PA signal in a normal joint (with high GAG content) than an OA joint (with low GAG content). Furthermore, the obtained PAI results provided accurate information of the GAG content distribution in the OA knee joint. Consequently, by detecting and analyzing the changes of the GAG content in OA cartilage using PAI, we can clearly distinguish early OA from late OA and monitor the therapeutic efficacy in OA after drug treatment. All PAI results were examined histologically.

Danshen prevents articular cartilage degeneration via antioxidation in rabbits with osteoarthritis

To evaluate the efficacy of Danshen on histological parameters and antioxidative activity in the articular cartilage of rabbits with osteoarthritis (OA). Twenty-four rabbits were randomly divided into three groups (control, OA, and Danshen OA; eight rabbits per group). Anterior cruciate ligament transection (ACLT) of the left hind knees was performed in all rabbits in the OA and Danshen OA group for induction of OA. The rabbits in the control group underwent a sham operation. After surgery, 3 g/kg body weight of Danshen granules dissolved in 5 mL distilled water was administered by gastric intubation once per day and over a 6-week period to the Danshen OA group. The same volume of distilled water was administered to the OA and control groups. After 6 weeks, the medial femoral condyles and synoviums of the left hind knees in all three groups were harvested and used for histological and biochemical analyses. Severe articular cartilage degeneration as well as lower proteoglycan (PG) content were noted in the OA group compared to the Danshen OA group (P < 0.05). The glutathione (GSH) levels in the synovium and articular cartilage of the rabbits in the Danshen OA group were significantly higher compared to the OA group (P < 0.001). The malondialdehyde (MDA) levels of the synovium and articular cartilage in the Danshen OA group was markedly depleted compared to the OA group (P < 0.001). Danshen can prevent articular cartilage degeneration in OA through the defense against oxidative stress.

The dual role of autophagy in chondrocyte responses in the pathogenesis of articular cartilage degeneration in osteoarthritis

The present study aimed to analyze the responses to autophagy in osteoarthritis (OA) and aging chondrocytes in order to elucidate the role of autophagy in the pathogenesis of OA. We used multiple assays to confirm that autophagic activity was downregulated in chondrocytes of aged articular cartilage. Surprisingly, we found that the expression of autophagy-related proteins was not decreased in the tissues of patients with OA. We also observed that rapamycin-induced autophagy prevented the accumulation of subdiploid cells in young chondrocytes, while it induced cell death by autophagy in OA chondrocytes. Our results demonstrate that autophagic activity decreases with aging, and may be responsible for the cytoprotective effects in young cartilage. However, we found that autophagic activity in patients with OA was higher than in the aging group, and reported autophagic cell death in OA chondrocytes. These results suggest that autophagy plays both a cytoprotective and death-promoting role in the pathogenesis of OA.

Oxidant conditioning protects cartilage from mechanically induced damage

Articular cartilage degeneration in osteoarthritis has been linked to abnormal mechanical stresses that are known to cause chondrocyte apoptosis and metabolic derangement in in vitro models. Evidence implicating oxidative damage as the immediate cause of these harmful effects suggests that the antioxidant defenses of chondrocytes might influence their tolerance for mechanical injury. Based on evidence that antioxidant defenses in many cell types are stimulated by moderate oxidant exposure, we hypothesized that oxidant preconditioning would reduce acute chondrocyte death and proteoglycan depletion in cartilage explants after exposure to abnormal mechanical stresses. Porcine cartilage explants were treated every 48 h with tert-butyl hydrogen peroxide (tBHP) at nonlethal concentrations (25, 100, 250, and 500 microM) for a varying number of times (one, two, or four) prior to a bout of unconfined axial compression (5 MPa, 1 Hz, 1800 cycles). When compared with untreated controls, tBHP had significant positive effects on post-compression viability, lactate production, and proteoglycan losses. Overall, the most effective regime was 100 microM tBHP applied four times. RNA analysis revealed significant effects of 100 microM tBHP on gene expression. Catalase, hypoxia-inducible factor-1alpha (HIF-1alpha), and glyceraldehyde 6-phosphate dehydrogenase (GAPDH) were significantly increased relative to untreated controls in explants treated four times with 100 microM tBHP, a regime that also resulted in a significant decrease in matrix metalloproteinase-3 (MMP-3) expression. These findings demonstrate that repeated exposure of cartilage to sublethal concentrations of peroxide can moderate the acute effects of mechanical stress, a conclusion supported by evidence of peroxide-induced changes in gene expression that could render chondrocytes more resistant to oxidative damage.

Transforming Growth Factor-β2 Suppresses Collagen Cleavage in Cultured Human Osteoarthritic Cartilage, Reduces Expression of Genes Associated with Chondrocyte Hypertrophy and Degradation, and Increases Prostaglandin E 2 Production

Articular cartilage degeneration in osteoarthritis (OA) involves type II collagen degradation and chondrocyte differentiation (hypertrophy). Because these changes resemble growth plate remodeling, we hypothesized that collagen degradation may be inhibitable by growth factors known to suppress growth plate hypertrophy, namely transforming growth factor (TGF)-beta2, fibroblast growth factor (FGF)-2, and insulin. Full-depth explants of human OA knee articular cartilage from arthroplasty were cultured with TGF-beta2, FGF-2, and insulin in combination (growth factors) or individually. In cultured explants from five OA patients, collagenase-mediated type II collagen cleavage was significantly down-regulated by combined growth factors as measured by enzyme-linked immunosorbent assay. Individually, FGF-2 and insulin failed to inhibit collagen cleavage in some OA explants whereas TGF-beta2 reduced collagen cleavage in these 5 explants and in 19 additional explants. Moreover, TGF-beta2 effectively suppressed cleavage at low concentrations. Together or individually these growth factors did not inhibit glycosaminoglycan (primarily aggrecan) degradation while TGF-beta2 occasionally did. Semiquantitative reverse transcriptase-polymerase chain reaction of articular cartilage from six OA patients revealed that TGF-beta2 suppressed expression of matrix metalloproteinase-13 and matrix metalloproteinase-9, early (PTHrP) and late (COL10A1) differentiation-related genes, and proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha). In contrast, TGF-beta2 up-regulated PGES-1 expression and prostaglandin E(2) release. These observations show that TGF-beta2 can suppress collagen resorption and chondrocyte differentiation in OA cartilage and that this may be mediated by prostaglandin E(2). Therefore TGF-beta2 could provide therapeutic control of type II collagen degeneration in OA.

Differential acoustic properties of early cartilage lesions in living human knee and ankle joints

Although numerous studies have been performed to determine whether there are histologic, biochemical, biomechanical, and metabolic differences between knee and ankle cartilage, none have investigated the presence of such differences in living human cartilage. We previously developed an ultrasonic evaluation system for articular cartilage that analyzes the A-mode echogram using wavelet transformation. The current study was undertaken to determine whether the acoustic properties of living human cartilage differ between knee and ankle joints. Twenty-eight patients were subjected to ultrasonic evaluation under arthroscopy. After arthroscopic grading, the cartilage was measured using an ultrasonic probe. Two quantitative parameters were used, i.e., the maximum magnitude and the echo duration at the 95% interval of the maximum magnitude. In intact cartilage, the maximum magnitude and echo duration did not differ between the knee and the ankle. In lesional cartilage, in contrast, the maximum magnitude was higher, and the echo duration was shorter, in the ankle than in the knee. These differences were statistically significant. Ultrasound findings could be used to judge the degree of early cartilage degeneration in vivo on the basis of objective data such as the maximum magnitude and echo duration. Because we were unable to quantitatively analyze the biochemical and biomechanical properties of the cartilage in this study, our biochemical and biomechanical findings are based only on qualitative assessment. Nevertheless, the results indicate that this ultrasonic evaluation system may be useful for elucidating the processes of articular cartilage degeneration in osteoarthritis.

Up-regulation of CD44-positive cells in medial meniscus of medial compartmental osteoarthritis of the knee

The degeneration of medial meniscus in the medial compartmental osteoarthritic knee (OA knee) was investigated by the histological and immunohistochemical analysis. The series included 16 OA knees in 11 patients with mean age of 78.8±4.4 years (range, 73–86). The medial menisci were divided into the anterior, the middle and the posterior portion. They were subsequently stained with hematoxylin and eosin (H.E.) to evaluate the histological findings, and after that, immunohistochemical staining was performed and CD44-positive cells were counted. Tears of collagen fibers and degenerative changes of the medial meniscul structure were observed in all portions. The advancement of these degenerative changes was severer in the posterior portion than in the other and more remarkable as the osteoarthritis advanced. Immunohistochemical staining of the specimens revealed that CD44-positive cells concentrated around vessels and along tears adjacent to these vessels. In each grade (a radiographical grading system for OA knees — Koshino T, Machida J. Grading system of articular cartilage degeneration in osteoarthritis of the knee. Bull Hosp Jt Dis 1993;53:41–46), the mean number of CD44-positive cells in the middle and the posterior part was more than that in the anterior, especially in Grade 2 and 3 ( P<0.05). In the medial compartmental OA knee, the advancement of degeneration in the meniscus was positively correlated with the advancement of the radiological grade, and the mechanical stress on the middle and the posterior part may up-regulate CD44 expression.

Variation in proteoglycan metabolism by articular chondrocytes in different joint regions is determined by post-natal mechanical loading

In this study we investigated the hypothesis that cartilage from defined regions of ovine stifle joints, which were subjected to differing mechanical stresses, contained phenotypically distinct chondrocyte populations. Chondrocyte phenotypes were identified by the relative biosynthesis of the proteoglycans (PGs) aggrecan, biglycan and decorin. Articular cartilage (AC) from adult and neonatal ovine stifle joints were examined. Cells were cultured as both full-depth AC explants and in alginate beads after their isolation from the AC matrix. When chondrocytes from the various topographical regions of adult ovine knee joints were cultured as explants they demonstrated a consistent difference with regard to the metabolism of aggrecan and decorin. Significantly, this topographically-dependent phenotypic expression of PGs was preserved when the chondrocytes were cultured in alginate beads. In adult joints, chondrocytes from the central region of the tibial plateau not covered by the meniscus, which is subjected to high mechanical loads in-vivo, synthesized less aggrecan but more decorin than cells from regions covered by the meniscus. When chondrocytes from identical AC regions of neonatal ovine joints were cultured as explants, no topographical difference in aggrecan nor decorin metabolism could be detected. The results of this study, in association with the existing literature, lead us to propose that post-natal mechanical loading of AC could select for chondrocyte clones or induce a lasting modulation of chondrocyte phenotypic expression in different joint regions. Such cellular changes could result in the synthesis of PG populations that confer properties to AC most suited to resist the variable mechanical stresses in the different joint regions. This study serves to emphasize the importance of using cartilage from identical joint areas when examining PG metabolism by chondrocytes. Further investigation into the relationship between mechanical loading, regional chondrocyte phenotype selection and the response of these cells to anabolic and catabolic factors may provide important insights into the focal nature of AC degeneration in osteoarthritis.