A study of the endocytosis mechanism and transendothelial activity of lung-targeted GALA-modified liposomes

The GALA peptide (WEAALAEALAEALAEHLAEALAEALEALAA) was originally designed to induce the destabilization of endosomal membranes based on its ability to undergo a pH-dependent conformational change from a random coil to an α-helix. We recently found that liposomes modified with GALA peptide (GALA-LPs) extensively accumulate in lung endothelial cells (ECs) after intravenous injection. However, the uptake mechanism of GALA-LPs and their ability to reach alveolar epithelium was unclear. We report herein that GALA-LPs are internalized into ECs via a clathrin-mediated pathway. Surprisingly, GALA-LPs had the ability to pass lung ECs and reach other cells through transcytosis. GALA-LPs were taken up by >70% of lung ECs, while they also accumulated in ~30% of type I alveolar epithelium (ATI). GALA-modified gold nanoparticles were detected in ECs, in the basement membrane and in other cells such as ATI, type II alveolar epithelium (ATII) and alveolar macrophages. Consistent with this result, a significant gene knockdown was achieved in lung epithelium cells using GALA-LPs encapsulating anti-podoplanin siRNA. This indicates that GALA-LPs can be used as a carrier for delivering macromolecules to parenchymal as well as to endothelial cells in the lung. Although caveolae are commonly linked to the transendothelial transport of proteins and antibodies, our data indicate that clathrin-mediated endocytosis might also participate in the transcytosis process.