Long-term Silencing of Intersectin-1s in Mouse Lungs by Repeated Delivery of a Specific siRNA via Cationic Liposomes. Evaluation of Knockdown Effects by Electron Microscopy

Previous studies showed that knockdown of ITSN-1s (KD_ITSN), an endocytic protein involved in regulating lung vascular permeability and endothelial cells (ECs) survival, induced apoptotic cell death, a major obstacle in developing a cell culture system with prolonged ITSN-1s inhibition¹. Using cationic liposomes as carriers, we explored the silencing of ITSN-1s gene in mouse lungs by systemic administration of siRNA targeting ITSN-1 gene (siRNA_ITSN). Cationic liposomes offer several advantages for siRNA delivery: safe with repeated dosing, nonimmunogenic, nontoxic, and easy to produce². Liposomes performance and biological activity depend on their size, charge, lipid composition, stability, dose and route of administration³Here, efficient and specific KD_ITSN in mouse lungs has been obtained using a cholesterol and dimethyl dioctadecyl ammonium bromide combination. Intravenous delivery of siRNA_ITSN/cationic liposome complexes transiently knocked down ITSN-1s protein and mRNA in mouse lungs at day 3, which recovered after additional 3 days. Taking advantage of the cationic liposomes as a repeatable safe carrier, the study extended for 24 days. Thus, retro-orbital treatment with freshly generated complexes was administered every 3rd day, inducing sustained KD_ITSN throughout the study⁴. Mouse tissues collected at several time points post-siRNA_ITSN were subjected to electron microscopy (EM) analyses to evaluate the effects of chronic KD_ITSN, in lung endothelium. High-resolution EM imaging allowed us to evaluate the morphological changes caused by KDITSN in the lung vascular bed (i.e. disruption of the endothelial barrier, decreased number of caveolae and upregulation of alternative transport pathways), characteristics non-detectable by light microscopy. Overall these findings established an important role of ITSN-1s in the ECs function and lung homeostasis, while illustrating the effectiveness of siRNA-liposomes delivery in vivo.