Biomimetic siRNA therapeutics attenuate mitochondrial DNA damage and cytokine storm in sepsis.

During the progression of severe sepsis, the oxidized mitochondrial DNA (mtDNA) in macrophages is cleaved by flap-structure-specific endonuclease 1 (FEN1) into small fragments, which are subsequently released into the cytosol and extracellular space to activate multiple pro-inflammatory signaling pathways such as NLRP3 inflammasome, cGAS-STING, and TLR9-NF-κB. Herein, biomimetic nanocomplexes (NCs) partially cloaked with macrophage membrane (MM) are developed to efficiently deliver FEN1 siRNA (siFEN1) into macrophages for sepsis management. To construct the NCs, membrane-penetrating, helical polypeptide (PG) first condenses siFEN1 and forms the cationic inner core, which is further coated with MM. By optimizing the membrane protein/siFEN1 weight ratios, partial membrane coating can be achieved, which enables the formation of NCs with both enhanced serum stability and efficient macrophage uptake efficiency. After systemic administration in cecal ligation and puncture-induced sepsis mice, the NCs exhibit prolonged blood circulation time and effective accumulation to the inflamed tissues, facilitated by MM-mediated charge neutralization of the cationic nanocore and inflammation homing. Subsequently, the NCs are efficiently internalized by macrophages through the interaction between the partially exposed polycationic core and the target cell membranes, provoking robust FEN1 silencing to suppress mtDNA fragmentation and leakage. Consequently, the NCs effectively restore immune homeostasis in sepsis mice, thereby mitigating cytokine storm and alleviating multiple organ failure.