Study of Fibroin-Cationic Lipid Complex for Direct Intracellular Protein Delivery

Abstract

Directly delivering therapeutic proteins into cells has promise as an intervention without side effects for protein deficiencies caused by genetic defects. However, as negatively charged macromolecules, proteins require carriers for achieving cellular uptake and maintaining their activity in the cytoplasm. The biodegradable natural polymer silk fibroin has demonstrated outstanding advantages as a protein drug scaffold in vitro and in vivo, but its usage has been limited in the extracellular space because of its negatively charged character. Here, we present an intracellular protein delivery system based on fibroin particles coated with cationic lipid layers, denoted as showed higher delivery efficiency than conventional delivery methods as well as long-term cargo release in the cytoplasm without toxicity. Furthermore, in vivo experiments showed that Fibroplex efficiently delivered tyrosinase and horseradish peroxidase, which led to hyper-pigmentation and tumor regression, respectively, suggesting its potential for therapeutic protein applications in hereditary diseases or cancer. Pin1 is a peptidyl prolyl cis-trans isomerase that specifically binds to the phosphoserine-proline or phosphothreonine-proline motifs of several proteins. We reported that Pin1 plays a critical role in the fate determination of Smad1/5, Runx2 and β-catenin that are indispensable nuclear proteins for osteoblast differentiation. Though several chemical inhibitors has been discovered for Pin1, no activator has been reported as of yet. In this study, we directly introduced recombinant Pin1 protein successfully into the cytoplasm via fibroin nanoparticle encapsulated in cationic lipid. This nanoparticle-lipid complex delivered its cargo with a high efficiency and a low cytotoxicity. Direct delivery of Pin1 leads to increased Runx2 and Smad signaling and resulted in recovery of the osteogenic marker genes expression and the deposition of mineral in Pin1 deficient cells. These result indicated that a direct Pin1 protein delivery method could be a potential therapeutics for the osteopenic diseases.