Transient yet robust expression of proteins in the mouse liver via intravenous injection of lipid nanoparticle-encapsulated nucleoside-modified mRNA

With the recent availability of the SARS-CoV-2 mRNA-based vaccines, public attention has been drawn to this new technology and how it may be applied to other indications. Temporal activation of key hepatic regenerative pathways can induce liver regeneration, overcoming the lack of donor organs for liver transplantation and ineffectiveness of alternative treatments. Recombinant protein therapies and genetic therapies that target these pathways require frequent and repeated injections or, when integrated into the genome, may lead to deleterious effects. In contrast, nucleoside-modified mRNA encapsulated in lipid nanoparticles (mRNA-LNP) are non-integrative and induce transient yet robust expression of proteins that could serve as an ideal therapeutic tool to treat specific liver diseases. For instance, our recent publication in Nature Communications used mRNA-LNP to express hepatic mitogens, hepatocyte growth factor, and epidermal growth factor to induce liver regeneration following both acute and chronic liver injuries. Initial testing with firefly luciferase mRNA-LNP transfection and in vivo imaging confirmed specific hepatotropic delivery. In this protocol, we describe in detail the necessary steps to deliver mRNA-LNP to the murine liver and, following intravenous injection of eGFP mRNA-LNP, verify transfection efficiency using flow cytometry and liver cell specificity using immunofluorescence analyses. This procedure presents an unprecedented tool that can be customized with mRNA-LNP encoding any protein of interest to be expressed by virtually all hepatocytes, ~70% endothelial cells, and ~40% Kupffer cells for promoting liver function and/or regeneration.