Modulating synovial macrophage pyroptosis and mitophagy interactions to mitigate osteoarthritis progression using functionalized nanoparticles.

Synovial macrophages play an important role in the progression of osteoarthritis (OA). In this study, we noted that synovial macrophages can activate pyroptosis in a gasdermin d-dependent manner and produce reactive oxygen species (ROS), aberrantly activating the mammalian target of rapamycin complex 1 (mTORC1) pathway and matrix metalloproteinase-9 (MMP9) expression in synovial tissue samples collected from both patients with OA and collagen-induced osteoarthritis (CIOA) mouse model. To overcome this, we constructed rapamycin- (RAPA, a mTORC1 inhibitor) loaded mesoporous Prussian blue nanoparticles (MPB NPs, for catalyzing ROS) and modified the NPs with MMP9-targeted peptides (favor macrophage targeting) to develop RAPA@MPB-MMP9 NPs. The inherent enzyme-like activity and RAPA released from RAPA@MPB-MMP9 NPs synergistically impeded the pyroptosis of macrophages and the activation of the mTORC1 pathway. In particular, the NPs decreased pyroptosis-mediated ROS generation, thereby inhibiting cGAS-STING signaling pathway activation caused by the release of mitochondrial DNA. Moreover, the NPs promoted macrophage mitophagy to restore mitochondrial stability, alleviate pyroptosis-related inflammatory responses, and decrease senescent synoviocytes. After the as-prepared NPs were intra-articularly injected into the CIOA mouse model, they efficiently attenuated synovial macrophage pyroptosis and cartilage degradation. In conclusion, our study findings provide a novel therapeutic strategy for OA that modulates the pyroptosis and mitophagy of synovial macrophage by utilizing functionalized NPs. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) presents a significant global challenge owing to its complex pathogenesis and finite treatment options. Synovial macrophages have emerged as key players in the progression of OA, managing inflammation and tissue destruction. In this study, we discovered a novel therapeutic strategy in which the pyroptosis and mitophagy of synovial macrophages are targeted to mitigate OA pathology. For this, we designed and prepared rapamycin-loaded mesoporous Prussian blue nanoparticles (RAPA@MPB-MMP9 NPs) to specifically target synovial macrophages and modulate their inflammatory responses. These NPs could efficiently suppress macrophage pyroptosis, diminish reactive oxygen species production, and promote mitophagy, thereby alleviating inflammation and protecting cartilage integrity. Our study findings not only clarify the intricate mechanisms underlying OA pathogenesis but also present a promising therapeutic approach for effectively managing OA by targeting dysregulation in synovial macrophages.