The homeostatic role of PRG4 in the joint is evidenced by the ability of purified native protein, recombinant full-length or truncated PRG4 to retard cartilage degeneration, enhance cartilage repair and reduce chondrocyte apoptosis in preclinical surgically induced osteoarthritis (OA) models [12–17]. This evidence concerns the gene PRG4 and osteoarthritis.