Consistent self-organized emergence of hyaline cartilage in hiPSC-derived multi-tissue organoids

Existing protocols for in vitro hyaline cartilage production utilizing human induced pluripotent stem cells (hiPSCs) have several challenges including a complex culturing process that uses undefined culture media, phenotypic instability, and batch-to-batch variability of the cell product. Here, our primary objective is to describe a simple, xeno- and feeder-free protocol for the generation of hyaline cartilage utilizing multi-tissue organoids (MTOs). We investigated gene regulatory networks during hiPSC-MTO differentiation using RNA sequencing and bioinformatics analyses, as well as histological and immunohistochemical methods. Interplays between bone morphogenetic protein (BMP) and neural fibroblast growth factor (FGF) pathways associated with the phenotypic transition of MTOs are described. Comparisons across transcriptomes revealed that the expression of chondrocyte-specific genes in MTOs correlates strongly with fetal lower limb chondrocytes. Single-cell RNA sequencing findings confirmed that the majority of cells belonged to the chondrogenic lineage and that they were similar across MTO batches, suggesting uniformity of the culture process. Collectively, these findings demonstrate the consistent emergence of hyaline cartilage in MTOs and the molecular pathways that govern this process, thereby establishing an accessible source of functional chondrocytes for future therapeutic evaluations.