Protease-shielded PRG4 self-amplifying RNA lipid nanoparticles restore cartilage homeostasis in osteoarthritis

Osteoarthritis (OA) is a debilitating joint disease characterized by progressive loss of boundary lubrication and disruption of cartilage homeostasis. Proteoglycan 4 (PRG4) is a critical boundary lubricant, but PRG4 function in OA may be compromised by reduced local expression, intra-articular clearance and protease-mediated processing within the inflamed joint microenvironment. Here we identified conserved downregulation of PRG4 in both human and mouse OA cartilage and developed a multifunctional lipid nanoparticle (LNP) platform, sa/A@E LNPs (PRG4 saRNA/AEBSF@EC12 LNPs), to achieve sustained lubrication and chondroprotection. In this system, PRG4 saRNA is delivered by LNPs formulated with a newly developed ionizable lipid, EC12, together with the broad serine protease inhibitor AEBSF. AEBSF is intended to shield endogenous and saRNA-expressed PRG4 from serine protease activity in the protease-rich OA microenvironment, whereas EC12 functions not only as a delivery component but also as an intrinsic activator of NRF2 signaling. Mechanistically, EC12 binds KEAP1, promotes NRF2 nuclear translocation, and increases NRF2 stability, thereby activating endogenous antioxidant responses. sa/A@E LNPs showed deep cartilage penetration. In a destabilization of the medial meniscus (DMM) mouse model, intra-articular administration of sa/A@E LNPs attenuated cartilage erosion and improved joint function. Together, these findings establish a multifunctional therapeutic strategy that integrates lubrication restoration, broad serine-protease shielding and antioxidant activation, supporting the further development of sa/A@E LNPs as a promising disease-modifying platform for OA treatment.