A novel compressive stress-based osteoarthritis-like chondrocyte system

Mechanical stress damage and insufficient self-repair can contribute to osteoarthritis (OA) in the affected joint. As the effects of stress on chondrocyte metabolism can regulate cartilage homeostasis, the specific stress-response condition is therefore a key to the generation of an OA disease model. We aimed to produce a specific stress- and cell-based OA model after evaluating the metabolic responses of chondrocytes in response to a series of static and cyclic compression stressors. A static load exceeding 40 psi initiated extracellular matrix (ECM) degradation through a decrease in the sulphated-glycosaminoglycan (GAG) content, upregulation of catabolic matrix metalloproteinase (MMP)-13 encoding gene expression, and downregulation of the ECM-related aggrecan and type II collagen encoding genes within 24h. Indicators of pro-inflammatory events and oxidative stress were found to correlate with increased IL-6 expression and reactive oxygen species (ROS) production, respectively. However, chondrocytes stimulated by moderate cyclic loading (30-40 psi) exhibited increased ECM-related gene expression without significant changes in catabolic and pro-inflammatory gene expression. BMP-7 expression increased at cyclic loading levels above 30-60 psi. These results demonstrated that static compression exceeding 60 psi is sufficient to produce OA-like chondrocytes that exhibit signs of ECM degradation and inflammation. These OA-like chondrocytes could therefore be used as a novel cell-based drug screening system. Impact statement The lack of an effective treatment for osteoarthritis (OA) reflects the great need for alternative therapies and drug discovery. Disease models can be used for early-stage compound screening and disease studies. Chondrocytes are solely responsible for the maintenance of the articular cartilage extracellular matrix. Our strategy involved the generation of a cell-based model of OA, a more readily studied disease. Instead of using animal cartilage explants, we incorporated isolated porcine chondrocytes with hydrogel to form three-dimensional assemblies. We could identify the specific magnitude-dependent metabolic responses of chondrocytes by applying a series of static and cyclic compression, and therefore successfully generated a novel OA-like cell-based model for drug screening.