ATF4-modified serum exosomes derived from osteoarthritic mice inhibit osteoarthritis by inducing autophagy.

Activating transcription factor 4 (ATF4) is critical for chondrocyte proliferation and bone formation. Exosomes are considered as promising gene-delivery vehicles for the treatment of osteoarthritis (OA). This study utilized the serum-derived exosomes from OA mice as the gene-delivery vehicles for ATF4 gene therapy and explored their therapeutic effects on OA. Meniscus injury-induced OA model was established by the excision of anterior part of medial meniscus in the right knee of C57BL/6J mice. Exosomes were isolated from serum samples of sham and OA mice, and were referred to as sham-Exo and OA-Exo, respectively. ATF4-overexpressing OA-Exo (ATF4-OA-Exo) was developed by introducing ATF4 mRNA into OA-Exo via electroporation. Four weeks after surgery, OA mice received intra-articular injections of sham-Exo, OA-Exo, and ATF4-OA-Exo, respectively. The results showed that intra-articular injection of ATF4-OA-Exo alleviated articular cartilage degeneration or damage and inflammatory response of OA mice. Autophagy was weakened in knee joint cartilage of OA mice, which was partially restored by intra-articular injection of ATF4-OA-Exo. Further in vitro assays revealed that ATF4-OA-Exo promoted chondrocyte autophagy and inhibited chondrocyte apoptosis in the TNF-α- or tunicamycin-treated chondrocytes. Together, ATF4-modified serum exosomes derived from OA mice protect cartilage and alleviate OA progression by inducing autophagy.