Functional Recovery of Human Cells Harbouring the Mitochondrial DNA Mutation MERRF <b><i>A8344G</i></b> via Peptide-Mediated Mitochondrial Delivery

We explored the feasibility of mitochondrial therapy using the cell-penetrating peptide Pep-1 to transfer mitochondrial DNA (mtDNA) between cells and rescue a cybrid cell model of the mitochondrial disease myoclonic epilepsy with ragged-red fibres (MERRF) syndrome. Pep-1-conjugated wild-type mitochondria isolated from parent cybrid cells incorporating a mitochondria-specific tag were used as donors for mitochondrial delivery into MERRF cybrid cells (MitoB2) and mtDNA-depleted Rho-zero cells (Mitoρ°). Forty-eight hours later, translocation of Pep-1-labelled mitochondria into the mitochondrial regions of MitoB2 and Mitoρ° host cells was observed (delivery efficiencies of 77.48 and 82.96%, respectively). These internalized mitochondria were maintained for at least 15 days in both cell types and were accompanied by mitochondrial function recovery and cell survival by preventing mitochondria-dependent cell death. Mitochondrial homeostasis analyses showed that peptide-mediated mitochondrial delivery (PMD) also increased mitochondrial biogenesis in both cell types, but through distinct regulatory pathways involving mitochondrial dynamics. Dramatic decreases in mitofusin-2 (MFN2) and dynamin-related protein 1/fission 1 were observed in MitoB2 cells, while Mitoρ° cells showed a significant increase in optic atrophy 1 and MFN2. These findings suggest that PMD can be used as a potential therapeutic intervention for mitochondrial disorders.