SOX9 and osteoarthritis: As key regulators of the major pathways involved, Sox9 and Runx2 are essential for chondrogenesis and osteogenesis, respectively, and are expressed by a unique progenitor cell population that can express moderate levels of both Sox9 and Runx2 that migrate from the bone marrow and support the repair of human articular cartilage during the late stages of osteoarthritis [51].