An Improved Diagnostic Tool to Predict Cartilage Formation in an Osteoarthritic Joint Environment

Osteoarthritis (OA) is characterized by progressive articular cartilage loss. Due to the chondrogenic potential of human mesenchymal stromal cells (MSCs), MSC-based therapies are promising treatment strategies for cartilage loss. However, the local joint microenvironment has a great impact on the success of cartilage formation by MSCs. There are great interpatient differences in this local joint environment, therefore, the result of MSC therapies is uncertain. We previously developed gene promoter-based reporter assays as a novel tool to predict the effect of a patient's OA joint microenvironment on the success of MSC-based cartilage formation. In this study, we describe an improved version of this molecular tool with increased prediction accuracy. For this, we generated 14 stable cell lines using transcription factor (TF)-binding elements (AP1, ARE, CRE, GRE, ISRE, NFAT5, NFκB, PPRE, SBE, SIE, SOX9, SRE, SRF, and TCF/LEF) to drive luciferase reporter gene expression, and evaluated the cell lines for their responsiveness to an osteoarthritic microenvironment by stimulation with OA synovium-conditioned medium (OAs-cm; n = 31). To determine the effect of this OA microenvironment on MSC-based cartilage formation, MSCs were stimulated with OAs-cm while cultured in a three-dimensional pellet culture model. Pellets were assessed histologically and sulfated glycosaminoglycan production was quantified as a measure of cartilage formation. Six TF reporters correlated significantly with the effect of OAs-cm on cartilage formation. We validated the predictive value of these TF reporters with an independent cohort of OAs-cm (n = 22) and compared the prediction accuracy between our previous and the current new tool. Furthermore, we investigated which combination of reporters could predict the effect of the OA microenvironment on cartilage repair with the highest accuracy. A combination between the TF (NFκB) and the promoter-based (IL6) reporter proved to reach a more accurate prediction compared with the tools separately. These developments are an important step toward a diagnostic tool that can be used for personalized cartilage repair strategies for OA patients. Impact Statement We demonstrate the improvement of a novel diagnostic tool to predict if an osteoarthritis joint microenvironment is permissive for cartilage repair or not. The enhanced prediction accuracy is of great importance for the development of a diagnostic tool that can determine the success of mesenchymal stromal cell-based cartilage repair strategies.