Human iPSC can be differentiated in vitro to articular cartilage or to osteogenic organoids via the endochondral ossification transdifferentiation pathway

The ability to generate chondrocytes and osteoblasts from induced pluripotent stem cells (iPSCs) will provide insights into skeletal development and genetic skeletal disorders and generate cells for regenerative medicine applications. Here we describe a method that directs iPSC-derived sclerotome to chondroprogenitors in 3D pellet culture then to articular chondrocytes or, alternatively, along the growth plate cartilage pathway to become hypertrophic chondrocytes that can transdifferentiate to osteoblasts. Osteogenic organoids deposit and mineralize a collagen I extracellular matrix (ECM), mirroring in vivo endochondral bone formation. We have identified gene expression signatures at key developmental stages including chondrocyte maturation, hypertrophy and transdifferentiation to osteoblasts, and show that this system can be used to model genetic cartilage and bone disorders. Comparative RNAseq of iPSCs at different timepoints as they are differentiating to growth plate chondrocytes. Comparative RNAseq of articular vs growth plate chondrocytes. Comparative RNAseq of hypertrophic growth plate chondrocytes and osteoblasts/osteocytes. Data for two iPSC lines is presented.