Mitochondrial transport of catalytic RNAs and targeting of the organellar transcriptome in human cells.

Mutations in the small genome present in mitochondria often result in severe pathologies. Different genetic strategies have been explored, aiming to contribute to rescue such mutations. A number of these were based on the capacity of human mitochondria to import RNAs from the cytosol and were designed to repress the replication of the mutated genomes or to provide the organelles with wild-type versions of mutant transcripts. However, the mutant RNAs present in mitochondria turned out to be an obstacle to therapy and little attention has been devoted so far to their elimination. Here, we present the development of a strategy to knockdown mitochondrial RNAs in human cells using the transfer RNA-like structure of the Brome mosaic virus or the Tobacco mosaic virus as a shuttle to drive trans-cleaving ribozymes into the organelles in human cell lines. We obtained a specific knockdown of the targeted mitochondrial ATP6 mRNA, followed by a deep drop in ATP6 protein and a functional impairment of the oxidative phosphorylation chain. Our strategy opens a powerful approach to eliminate mutant organellar transcripts and to analyze the control and communication of the human organellar genetic system.