RNA Delivery to Mitochondria.

The approval of mRNA-containing lipid nanoparticles (LNPs) for use in a vaccine against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the clinical utility of RNA-loaded nanocapsules has stimulated a rapid acceleration in research in this area. The development of mRNA-containing LNP vaccines has been rapid, not only because of regulatory adjustments, but also to the advances made in nucleic acid delivery as the result of efforts by many basic researchers. RNA functions, not only in the nucleus and cytoplasm, but also in mitochondria, which have their own genomic apparatus. Mitochondrial diseases caused by mutations or defects in the mitochondrial genome, mitochondrial DNA (mtDNA) are intractable and are mainly treated symptomatically, but gene therapy as a fundamental treatment is expected to soon be a reality. To realize this therapy, a drug delivery system (DDS) that delivers nucleic acids including RNA to mitochondria is required, but efforts in this area have been limited compared to research targeting the nucleus and cytoplasm. This contribution provides an overview of mitochondria-targeted gene therapy strategies and discusses studies that have attempted to validate mitochondria-targeted RNA delivery therapies. We also present the results of 'RNA delivery to mitochondria' based on the use of our mitochondria-targeted DDS (MITO-Porter) that was developed in our laboratory.