Cytosolic delivery of small interfering RNA (siRNA) remains challenging, and a profound understanding of the cellular uptake and intracellular processing of siRNA delivery systems could greatly improve the development of siRNA-based therapeutics. Here, we show that caveolae-mediated endocytosis (CvME) accounts for the robust siRNA delivery of mannose-modified trimethyl chitosan-cysteine/tripolyphosphate nanoparticles (MTC/TPP NPs) to macrophages by circumventing lysosomes. We show that the Golgi complex and ER are key organelles required for the efficient delivery of siRNA to macrophages in which the siRNA accumulation positively correlates with its silencing efficiency (r = 0.94). We also identify syntaxin6 and Niemann-Pick type C1 (NPC1) as indispensable regulators for MTC/TPP NPs-delivered siRNA into macrophages both in vitro and in vivo. Syntaxin6 and NPC1 knockout substantially decrease the cellular uptake and gene silencing of the siRNA delivered in MTC/TPP NPs in macrophages, which result in poor therapeutic outcomes for mice bearing acute hepatic injury. Our results suggest that highly efficient siRNA delivery can be achieved via CvME, which would give ideas for designing optimal delivery vectors to facilitate the clinical translation of siRNA drugs.
Keywords: CvME; NPC1; Syntaxin6; anti-inflammatory efficacy; cytosolic delivery; key organelles; siRNA drugs.