Department of Orthopaedic Surgery, Second Affiliated Hospital and Zhejiang University-University of Edinburgh Institute and School of Basic Medicine, Zhejiang University School of Medicine, Hangzhou 310058, China; Dr. Li Dak Sum & Yip Yio Chin Center for Stem Cells and Regenerative Medicine, Zhejiang University School of Medicine, Hangzhou 310058, China; Key Laboratory of Tissue Engineering and Regenerative Medicine of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou 310058, China; Department of Sports Medicine, Zhejiang University School of Medicine, Hangzhou 310058, China; China Orthopedic Regenerative Medicine Group (CORMed), Hangzhou 310058, China. Electronic address: [Email]
Articular cartilage injury and degeneration causing pain and loss of quality-of-life has become a serious problem for increasingly aged populations. Given the poor self-renewal of adult human chondrocytes, alternative functional cell sources are needed. Direct reprogramming by small molecules potentially offers an oncogene-free and cost-effective approach to generate chondrocytes, but has yet to be investigated. Here, we directly reprogrammed mouse embryonic fibroblasts into PRG4+ chondrocytes using a 3D system with a chemical cocktail, VCRTc (valproic acid, CHIR98014, Repsox, TTNPB, and celecoxib). Using single-cell transcriptomics, we revealed the inhibition of fibroblast features and activation of chondrogenesis pathways in early reprograming, and the intermediate cellular process resembling cartilage development. The in vivo implantation of chemical-induced chondrocytes at defective articular surfaces promoted defect healing and rescued 63.4% of mechanical function loss. Our approach directly converts fibroblasts into functional cartilaginous cells, and also provides insights into potential pharmacological strategies for future cartilage regeneration.