Integration Capacity of Human Induced Pluripotent Stem Cell-Derived Cartilage.

New cell and tissue sources are needed for the regenerative treatment of articular cartilage damage. Human induced pluripotent stem cells (hiPSCs) are an abundant cell source due to their self-renewal capacity. Hyaline cartilage tissue particles derived from hiPSCs (hiPS-Carts), 1-3 mm in diameter, are one candidate source that can be used for transplantation. When transplanted to fill the defects of articular cartilage, hiPS-Carts form a repair tissue by integrating with each other and with adjacent host tissue. In this study, we analyzed the integration capacity using an in vitro model and found that hiPS-Carts spontaneously integrate with each other in vitro. hiPS-Carts consist of cartilage at the center and perichondrium-like membrane that wraps around the cartilage. The integration started at the perichondrium-like membrane at around 1 week. Then, the integration progressed to the cartilage within 4-8 weeks. RNA sequencing analysis identified a higher expression of FGF18 in the perichondrium-like membrane in hiPS-Carts compared with the central cartilage. The addition of FGF18 to the model accelerated the integration of hiPS-Carts, whereas the addition of a FGFR inhibitor inhibited it. These results suggest that FGF18 secreted from the perichondrium-like membrane plays a role in the integration of hiPS-Carts. Understanding the integration mechanism of hiPS-Carts is expected to contribute to the realization of regenerative treatment for patients with articular cartilage damage.