Pre-transplantational control of the post-transplantational fate of human pluripotent stem cell-derived cartilage

Cartilage pellets generated from ectomesenchymal progeny of human pluripotent stem cells (hPSCs) in vitro eventually show signs of commitment of chondrocytes to hypertrophic differentiation. When transplanted subcutaneously, most of the surviving pellets were fully mineralized by 8 weeks. In contrast, treatment with the adenylyl cyclase activator, forskolin, in vitro resulted in slightly enlarged cartilage pellets containing an increased proportion of proliferating immature chondrocytes that expressed very low levels of hypertrophic/terminally matured chondrocyte-specific genes. Forskolin treatment also enhanced hyaline cartilage formation by reducing type I collagen gene expression and increasing sulfated glycosaminoglycan accumulation in the developed cartilage. Furthermore, forskolin treatment in vitro increased the frequency at which the cartilage pellets maintained unmineralized chondrocytes after subcutaneous transplantation. To elucidate the type of cartilage that forskolin preferentially promotes and potential molecular mechanisms involved in the forskolin-suppression of chondrocyte hypertrophic differentiation in vitro, we performed genome-wide, comparative transcriptomic analyses on the cartilage pellets formed from 3 to 4 independent pellet cultures of ectomesenchymal cells with or without forskolin treatment. RNAs were isolated on day 26-28 and mRNA-sequencing (RNA-seq) analyses were performed.