Facilitating siRNA delivery into mammalian cells via the LDL receptor

The interaction of low-density lipoproteins (LDLs) with specific receptors belonging to the LDL-receptor (LDLR) superfamily serves to internalize these lipoproteins into cells via receptor-mediated endocytosis (RME). Importantly, it is known that the receptor of one organism can interact with the LDL of other organisms and - of special relevance to this study - that vitellogenin (Vg), the yolk lipoprotein of invertebrates, can interact with the human LDLR. Our working hypothesis in the current study was thus that a Vg-derived peptide could be used as a tool for delivering RNA interference (RNAi)-activating molecules into human cells by leveraging the RME mechanism of LDLRs. We prepared two different chimera proteins comprising an amino acid stretch derived from Vg and a double-stranded RNA-binding domain (dsRBD) retrieved from a crustacean transcriptomic library. Each chimera protein was linked to small interfering RNA (siRNA) to form a complex that would interact with LDLRs to facilitate entry of the complex into human cells. We found siRNA delivered into different mammalian cell lines through the LDLR facilitated RNAi and hence approximately 50% gene silencing of various target genes. Importantly, administration of the chimera proteins to mice did not induce detectable toxicity or systemic immune responses, supporting their biocompatibility. The chimera protein tools provide a simple, reliable, and targeted approach to facilitate specific gene manipulation in mammalian cells for basic research on different diseases and, potentially, a safe method for in vivo gene silencing and drug delivery. In the long term, the proposed delivery system, being based on a native mechanism, may open the way for human gene silencing for treating certain diseases.