Time- and cell-specific activation of BMP signaling restrains chondrocyte hypertrophy

Differentiated chondrocytes from populations of human bone marrow stromal cells including skeletal stem cells (hBMSCs/SSCs) and induced pluripotent stem cells (hiPSCs) have the potential to restore damaged cartilage, yet chondrocyte hypertrophy is a barrier for translational therapy. However, hBMSCs/SSCs attached to a hyaluronic acid-coated fibrin microbead scaffold (HyA-FMBs) produce cartilage that resists hypertrophy. We show that HyA-FMBs initially suppress Bone Morphogenic Protein (BMP) signaling early in chondrogenic differentiation of hBMSCs/SSCs, then restore BMP signaling in a stable chondrogenic population enriched for Insulin-like Growth Factor Binding Protein 5 and Matrix Gla Protein. We subsequently developed a serumfree hiPSC differentiation strategy that inhibited, then activated BMP signaling in a purified subpopulation derived from ?chondrospheroids? that exhibited stable expression of Type II Collagen, Aggrecan (ACAN), and Lubricin (PRG4) and minimal e xpression of Type X Collagen. Overall, timed, and selective BMP signaling restrains chondrocyte hypertrophy, supporting the potential of chondrospheroid-derived cells for clinical utility in osteoarthritis.