Real-time transcriptomic profiling of hPSC-derived cartilage during development identifies a key role for the extracellular matrix in homeostasis and protection

Articular and growth plate chondrocytes share a common progenitor but diverge during development to generate distinct cartilage tissues specific to their functions; permanent articular chondrocytes produce and maintain a frictionless surface for joint articulation, while transient growth plate chondrocytes lay a matrix foundation for new bone. Following injury, articular chondrocytes can aberrantly undergo changes akin to growth plate differentiation. The processes that control both the divergence of these lineages during development and the fate change in disease are poorly understood, but are essential in the design of novel therapeutics to attenuate joint degeneration. We established a model of human cartilage development using human pluripotent stem cells (hPSCs), where the cells themselves give rise to zonally organized articular cartilage tissues akin to native articular cartilage. We challenged these tissues at defined time-points during differentiation, pin-pointing the precise timing of lineage restriction. Long-term functional experiments coupled with single-cell RNA sequencing throughout differentiation and after challenge revealed a key role for the extracellular matrix in modulating chondrocyte activity, and identified therapeutic targets that may attenuate pathogenic differentiation and disease progression.