Engineered Exosomes with ATF5-Modified mRNA Loaded in Injectable Thermogels Alleviate Osteoarthritis by Targeting the Mitochondrial Unfolded Protein Response

Osteoarthritis (OA) progression is highly associated with chondrocyte mitochondrial dysfunction and disorders of catabolism and anabolism of the extracellular matrix (ECM) in the articular cartilage. The mitochondrial unfolded protein response (UPR^mt), which is an integral component of the mitochondrial quality control (MQC) system, is essential for maintaining chondrocyte homeostasis. We successfully validated the pivotal role of activating transcription factor 5 (ATF5) in upregulating the UPR^mt, mitigating IL-1β-induced inflammation and mitochondrial dysfunction, and promoting balanced metabolism in articular cartilage ECM, proving its potential as a promising therapeutic target for OA. Modified mRNAs (modRNAs) have emerged as novel and efficient gene delivery vectors for nucleic acid therapeutic approaches. In this study, we combined Atf5-modRNA (modAtf5) with engineered exosomes derived from bone mesenchymal stem cells (Ex^modAtf5) to exert cytoprotective effects on chondrocytes in articular cartilage via Atf5. However, the rapid localized metabolization of Ex^modAtf5 limits its application. PLGA-PEG-PLGA (Gel), an injectable thermosensitive hydrogel, was used as a carrier of Ex^modAtf5 (Gel@Ex^modAtf5) to achieve a sustained release of Ex^modAtf5. In vitro and in vivo, the use of Gel@Ex^modAtf5 was shown to be a highly effective strategy for OA treatment. The in vivo therapeutic effect of Gel@Ex^modAtf5 was evidenced by the preservation of the intact cartilage surface, low OARSI scores, fewer osteophytes, and mild subchondral bone sclerosis and cystic degeneration. Consequently, the combination of Ex^modAtf5 and PLGA-PEG-PLGA could significantly enhance the therapeutic efficacy and prolong the exosome release. In addition, the mitochondrial protease ClpP enhanced chondrocyte autophagy by modulating the mTOR/Ulk1 pathway. As a result of our research, Gel@Ex^modAtf5 can be considered to be effective at alleviating the progression of OA.