High-Impact Fn1 Mutation Abrogates Response Of Chondrocytes To Hyper-Physiological Loading

Purpose: Previously, we identified a high-impact, missense mutation (C518F) in the gelatin-binding domain of FN1 that was causal to the early-onset osteoarthritis (OA) phenotype in an extended early-onset OA family. By introducing this high-impact mutation in human induced pluripotent stem cells (hiPSCs) using CRISPR/Cas9 gene editing and using them in an established in vitro organoid cartilage model, we showed that the chondrogenic potential and deposition of neo-cartilage of the FN1 mutant chondrocytes was decreased. Moreover, we demonstrated that the underlying pathogenic mechanism of the mutation is caused by a decreased binding of fibronectin to the surrounding extracellular matrix (ECM) protein collagen type II. Since fibronectin functions as a transducer of biomechanical signals from the ECM to chondrocytes via integrins, the decreased binding to collagen type II likely results in changed interactions between ECM and chondrocytes. Therefore, we aimed to investigate how the FN1 mutation affects the response of chondrocytes to hyper-physiological mechanical loading in our in vitro organoid cartilage model and further elucidate the function of fibronectin as mechanotransducer.