Osteoarthritis (OA) is a debilitating degenerative joint disease that results in chronic pain and inflammation due to progressive mechanical and proteolytic cartilage degradation. Articular chondrocytes, the main cell type present in cartilage, are responsible for the deposition and maintenance of the cartilage extracellular matrix (ECM). However, following damage and inflammation, chondrocytes undergo hypertrophy, apoptosis, and contribute to inflammation and ECM degradation. NF-κB signaling is known to be dysregulated in OA. TRAPPC9, a vesicle trafficking protein, is known to directly activate NF-κB signaling in neuronal and bone cells, however, the biological significance of this protein in chondrocytes has yet to be elucidated. Here, we demonstrate that TRAPPC9 enhances pro-inflammatory gene and protein expression in murine primary articular chondrocytes. Furthermore, we show that TRAPPC9 elicits these responses via phosphorylation of P-100 that activates non-canonical NF-κB signaling. Taken together, these findings suggest TRAPPC9 may be a potential therapeutic target to decrease inflammation and matrix degradation during OA pathology.

Osteoarthritis (OA) is a joint disease involving cartilage degeneration. This study aimed to compare properties of chondrocytes from less-affected (LA-Cartilage) and severely-affected (SA-Cartilage) of human OA articular cartilage. Based on Dougados classification, OA cartilage was classified into two groups; less-affected (Grade 0–1) and severely-affected (Grade 2–3). Chondrocytes from each group were cultured until passage (P) 4. Growth, migration, stem cell properties and chondrogenic properties under normal and inflammatory conditions, and the formation of in vitro 3D cartilage tissues were compared between groups. The growth and migratory properties of LA-chondrocytes and SA-chondrocytes were similar, except that the migration rate of SA-chondrocytes was significantly higher at P0 compared to LA-chondrocytes. Both LA-chondrocytes and SA-chondrocytes expressed mesenchymal stem cell markers and tri-lineage differentiation, but the expression of stem cell markers decreased significantly with increasing passage number. Exposure to inflammatory conditions induced distinct morphological changes and significant increases in expression of SOX9 at P4 and MMP3 at P1 for LA-chondrocytes. LA-chondrocytes and SA-chondrocytes able to develop into in vitro 3D constructs, but SA-chondrocytes exhibited superior cartilage-like properties. Chondrocytes from both less- and severely-affected regions are suitable to be used in clinical applications, however, chondrocytes from severely-affected regions could be a more favorable cell source.

Background: Since cytokine receptor like factor 1 (CRLF1) has been implicated in tissue regeneration, we hypothesized that CRLF1 released by mesenchymal stem cells can promote the repair of osteochondral defects. Methods: The degree of a femoral osteochondral defect repair in rabbits after intra-articular injections of bone marrow derived mesenchymal stem cells (BMSCs) that were transduced with empty adeno associated virus (AAV) or AAV containing CRLF1 was determined by morpholog-ical, histological and microCT analyses. The effects of CRLF1 on chondrogenic differentiation of BMSCs or catabolic events of interleukin-1beta-treated chondrocyte cell line TC28a2 were deter-mined by alcian blue staining, gene expression levels of cartilage and catabolic marker genes us-ing real time PCR analysis, and immunoblot analysis of Smad2/3 and STAT3 signaling. Results: Intra-articular injections of BMSCs overexpressing CRLF1 markedly improved repair of a rabbit femoral osteochondral defect. Overexpression of CRLF1 in BMSCs resulted in the release of a homodimeric CRLF1 complex that stimulated chondrogenic differentiation of BMSCs via enhancing Smad2/3 signaling, whereas the suppression of CRLF1 expression inhibited chondro-genic differentiation. In addition, CRLF1 inhibited catabolic events in TC28a2 cells cultured in an inflammatory environment, while a heterodimeric complex of CRLF1 and Cardiotrophin like Cytokine (CLC) stimulated catabolic events via STAT3 activation. Conclusion: A homodimeric CRLF1 complex released by BMSCs enhanced the repair of osteochondral defects via the inhibition of catabolic events in chondrocytes and the stimulation of chondrogenic differentiation of precursor cells.

Chondrocytes maintain the normal morphological structure and physiological function of articular cartilage. However, the increased expression of inflammatory mediators and matrix-degrading enzymes in chondrocytes can promote ECM degradation, consequently disrupting the physiological function of articular cartilage and ultimately leading to the onset of osteoarthritis (OA). Usnic acid (UA), an extract derived from plants, possesses multiple bioactive properties including anti-inflammatory and antioxidant effects. Hence, this study aims to explore the molecular mechanisms underlying its protective effects in an in vitro simulated model of OA in rat chondrocytes. In vivo experiments encompassed three groups: Control, Model, and Usnic acid (50 mg/kg), with sample extraction following 12 weeks of administration. Pathological alterations in articular cartilage were evaluated using Safranin O-fast green staining. Immunohistochemistry (ICH) analysis was employed to assess the expression of matrix degradation-related markers. The levels of serum cytokines were quantified via ELISA assays. In this study, primary rat chondrocytes were employed as the experimental subject. After a 24-hour treatment period, culture supernatants, total RNA, total protein, and nuclear protein were extracted from the different chondrocyte groups. ELISA and qPCR methods were used to measure levels of IL-6, TNF-α, and PGE2. WB and qPCR were employed to assess levels of p65, p-p65, IκBα, p-IκBα, Nrf2, HO-1, NQO1 ADAMTS-4, MMP-1, MMP-3, MMP-13, INOS, COX-2, and COL2A1. IF analysis was performed to examine Nrf2, p-p65 and COL2A1. Results: (1) In vivo, intraperitoneal injection of usnic acid (50mg/kg) can alleviate pathological changes in articular cartilage and the levels of inflammatory and oxidative-related matrix in the serum. (2) UA reduced the level of inflammatory cytokines in IL-1β-induced chondrocytes supernatant. (3) UA can produce anti-inflammatory and antioxidant effects and inhibit chondrocytes matrix degradation through the Nrf2 and NF-κB pathways. (3) The mechanism by which UA exerts a protective role in chondrocytes is mediated by Nrf2 Conclusion: UA inhibits the expression of chondrocyte matrix degradation-related components through Nrf2 mediated Nrf2 pathway and NF-κB pathway, promotes the production of protective substances, and ultimately exerts a protective effect on chondrocytes.

This study investigated the role of a pattern of microRNA (miRNA) as possible mediators of celecoxib and prescription-grade glucosamine sulfate (GS) effects in human osteoarthritis (OA) chondrocytes. Chondrocytes were treated with celecoxib (1.85 µM) and GS (9 µM), alone or in combination, for 24 hrs, with or without interleukin (IL)-1β (10 ng/mL). Viability was detected by MTT assay, apoptosis and reactive oxygen species (ROS) by cytometry, nitric oxide (NO) by Griess method. Gene levels of miRNA, antioxidant enzymes, nuclear factor erythroid (NRF)2, and B-cell lym-phoma (BCL)2 expressions were analyzed by quantitative real time PCR. Protein expression of NRF2 and BCL2 was also detected at immunofluorescence and western blot. Celecoxib and GS, alone or in combination, significantly increased viability, reduced apoptosis, ROS and NO production and the gene expression of miR-34a, -146a, -181a, -210, in comparison to baseline and to IL-1β. The transfection with miRNA specific inhibitors significantly counteracted the IL-1β activity and potentiated the properties of celecoxib and GS on viability, apoptosis and oxidant system, through NF-κB regulation. The observed effects were enhanced when the drugs were tested in combination. Our data confirmed the synergistic anti-inflammatory and chondroprotective properties of celecoxib and GS, suggesting miRNA as possible mediators.

Abstract: This article provides a brief review of the ontogeny of chondrocytes and the pathophysiology of osteoarthritis (OA), and details how physical exercise improves the health of osteoarthritic joints and enhances the potential of mesenchymal stem cells for successful transplantation therapy. In response to exercise chondrocytes increase their production of glycosaminoglycans, bone morphogenic proteins and antiinflammatory cytokines and decrease their production of proinflammatory cytokines and matrix degrading metalloproteinases. These changes are associated with improvements in cartilage organization and reductions in cartilage degeneration. Studies in humans indicate that exercise increases peripheral blood recruitment of bone marrow-derived mesenchymal stem cells (BM-MSC) and upregulates BM-MSC expression of osteogenic and chondrogenic genes, osteogenic micro-RNAs, and osteogenic growth factors. Rodent experiments are uniform in demonstrating that exercise enhances the osteogenic potential of BM-MSC while diminishing their adipogenic potential, and that exercise done after stem cell implantation may benefit stem cell transplant viability. Physical exercise also exerts a beneficial effect on the skeletal system by decreasing immune cell production of osteoclastogenic cytokines interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and interferon (INF)-γ while increasing their production anti-osteoclastogenic cytokines IL-10 and transforming growth factor (TGF)-β. In conclusion, physical exercise done both by stem cell donors and recipients may improve the outcome of mesenchymal stem cell transplantation.