Scientists successfully correct harmful mutations in mitochondrial DNA with gene editing.

Researchers in the Netherlands have successfully edited harmful mutations in mitochondrial DNA using a genetic tool known as a base editor. The results, published June 24 in the open-access journal PLOS Biology, offer new hope for people with rare genetic diseases.

Mitochondria, often called the powerhouses of the cell, possess their own set of DNA. Mutations in this mitochondrial DNA can lead to a wide range of maternally inherited diseases , cancer, and aging-related conditions. While the development of CRISPR technology has given scientists new ways to correct mutations in nuclear DNA, this system cannot effectively traverse the mitochondrial membrane and reach mitochondrial DNA.

In the new study, the researchers used a tool called a base editor , specifically a DdCBE (double-stranded DNA deaminase toxin A-derived cytosine base editor). This tool allows scientists to modify a single letter of the DNA code without changing it, and it works on mitochondrial DNA.

The team demonstrated that they could efficiently generate and correct mitochondrial DNA mutations in multiple disease-associated cell types in the lab. First, they modified liver cells to carry a mitochondrial mutation that affects energy production. They then showed they could correct a different mutation in skin cells from a patient with Gitelman syndrome, a mitochondrial disorder, thereby restoring key signs of healthy mitochondrial function.

To facilitate the therapy's advancement to clinical use, the researchers also tested the efficacy of delivering the mitochondrial base editors as mRNA , rather than DNA, and within lipid nanoparticles. They showed that these approaches are more efficient and less toxic to cells than older methods, such as DNA plasmids. Notably, the edits were highly specific, with minimal off-target changes detected in nuclear DNA and multiple changes in mitochondrial DNA.

“The potential of mitochondrial base editing for disease modeling and potential therapeutic interventions makes it a promising avenue for future research and development in mitochondrial medicine,” the authors state, adding: “Patients with mitochondrial diseases have long been excluded from the CRISPR revolution, but recently, the technology has become available that finally allows us to repair mitochondrial mutations. In our study, we used this technology in human liver organoids to generate a model of mitochondrial disease. We employed a clinical-grade technique to repair a mutation in the mitochondrial DNA of patient-derived cells.”

“Building on previous developments of alternative technologies to CRISPR for precise mitochondrial DNA editing, the authors of this study demonstrated for the first time the utility of these tools in organoids (three-dimensional cell cultures), which can offer essential information in preclinical studies. Additionally, the authors corrected a mitochondrial DNA mutation in patient-derived cells, a strategy that has been explored in other studies, but which further demonstrates the therapeutic potential of mitochondrial DNA base editors . Finally, the authors explored the translational axis of their research by demonstrating for the first time the delivery of these editors in lipid nanoparticles, a promising strategy for the therapeutic transfer of these tools,” Santiago Restrepo Castillo, a postdoctoral researcher at the University of Texas at Austin (USA), explained to SMC Spain .

In his opinion, this study "represents a promising proof of concept, which will be complemented by new advances and applications of mitochondrial DNA editors in lipid nanoparticles, particularly for the development of personalized gene therapies using organoids derived from patients with different mitochondrial mutations."

Along the same lines, Lluís Montoliu, researcher at the CNB-CSIC and the CIBERER-ISCIII, believes, in statements to SMC Spain, that this work is "certainly relevant, as it opens the door to treating extremely serious congenital mitochondrial diseases , which until now were incurable, through the combined use of various cutting-edge technologies."