In Vivo Identification and Induction of Articular Cartilage Stem Cells by Inhibiting NF-κB Signaling in Osteoarthritis

Osteoarthritis (OA) is a highly prevalent and debilitating joint disorder characterized by the degeneration of articular cartilage. However, no effective medical therapy has been found yet for such condition. In this study, we directly confirmed the existence of articular cartilage stem cells (ACSCs) in vivo and in situ for the first time both in normal and OA articular cartilage, and explored their chondrogenesis in Interleukin-1 beta (IL-1 beta) induced inflammation environment and disclose whether the inhibition of NF-kappa B signaling can induce ACSCs activation thus improve the progression of experimental OA. We found an interesting phenomenon that ACSCs were activated and exhibited a transient proliferative response in early OA as an initial attempt for selfrepair. During the in vitro mechanism study, we discovered IL-1 beta can efficiently activate the NF-kappa B pathway and potently impair the responsiveness of ACSCs, whereas the NF-kappa B pathway inhibitor rescued the ACSCs chondrogenesis. The final in vivo experiments further confirmed ACSCs' activation were maintained by NF-kappa B pathway inhibitor, which induced cartilage regeneration, and protected articular cartilage from injury in an OA animal model. Our results provided in vivo evidence of the presence of ACSCs, and disclosed their action in the early OA stage and gradual quiet as OA process, presented a potential mechanism for both cartilage intrinsic repair and its final degradation, and demonstrated the feasibility of inducing endogenous adult tissuespecific mesenchymal stem cells for articular cartilage repair and OA therapy.