COL2A1 and osteoarthritis: Our results showed that BMSC-Exos incubation significantly reversed the reduction of COL2A1, SOX9, Agg, and Prg4 expression levels induced by OA, which suggested that BMSC-Exos can protect chondrocyte homeostasis from osteoarthritis by promoting chondrogenesis and chondrocyte differentiation, cartilage matrix construction, cartilage degeneration, and synovial integrity.