Constructing condylar cartilage organoid to explore primary cilia functions

An organoid culture system better recapitulates the cellular structure, function, and interaction between cells and the extracellular matrix (ECM) than a two-dimensional (2D) culture system. We here constructed a condylar cartilage organoid to explore the regulatory role of primary cilia. Similar to the natural condylar cartilage, the condylar cartilage organoid exhibited abundant ECM and comprised superficial, proliferative, and hypertrophic zones. Primary cilia in the condylar cartilage organoid were shorter on average than those in the 2D culture chondrocytes, but their average length was equivalent to those in the natural condylar cartilage. Notably, primary cilia in each zone of the condylar cartilage organoid had an average length similar to that of primary cilia in the natural condylar cartilage. According to transcriptomic and biochemical analyses, the expression of cilia-related genes and cilia-related Hedgehog (HH) signaling differed between the condylar cartilage organoid and 2D culture systems. IFT88 knockdown promoted the protein levels of COL-Ⅹ, TRPV4, and HH signaling molecules in the condylar cartilage organoid, but decreased them in the 2D culture system. Notably, the protein levels of COL-Ⅹ, TRPV4, and HH signaling molecules increased in the superficial zone of the si IFT88 condylar cartilage organoid compared with the condylar cartilage organoid. However, the protein levels of aforementioned molecules were not significantly different in proliferative and hypertrophic zones. Collectively, we successfully constructed the condylar cartilage organoid with a better tissue structure and abundant ECM. Moreover, the condylar cartilage organoid is more suitable for exploring primary cilia functions.