Advances in methods for reducing mitochondrial DNA disease by replacing or manipulating the mitochondrial genome.

Pavandeep K. Rai,Caterina Garone,Robert N. Lightowlers,Michal Minczuk,Oliver M. Russell,Lyndsey Craven,Kurt Hoogewijs

doi:10.1042/ebc20170113

Abstract

Mitochondrial DNA (mtDNA) is a multi-copy genome whose cell copy number varies depending on tissue type. Mutations in mtDNA can cause a wide spectrum of diseases. Mutated mtDNA is often found as a subset of the total mtDNA population in a cell or tissue, a situation known as heteroplasmy. As mitochondrial dysfunction only presents after a certain level of heteroplasmy has been acquired, ways to artificially reduce or replace the mutated species have been attempted. This review addresses recent approaches and advances in this field, focusing on the prevention of pathogenic mtDNA transfer via mitochondrial donation techniques such as maternal spindle transfer and pronuclear transfer in which mutated mtDNA in the oocyte or fertilized embryo is substituted with normal copies of the mitochondrial genome. This review also discusses the molecular targeting and cleavage of pathogenic mtDNA to shift heteroplasmy using antigenomic therapy and genome engineering techniques including Zinc-finger nucleases and transcription activator-like effector nucleases. Finally, it considers CRISPR technology and the unique difficulties that mitochondrial genome editing presents.

Highlights

Mitochondria serve a vital role in normal cellular homoeostasis
Mutations in mitochondrial DNA can lead to the development of mitochondrial disease
Methods for avoiding clinical manifestation of these diseases include preventing the transmission of mutated Mitochondrial DNA (mtDNA), either by selecting embryos with low levels of mutant mtDNA using prenatal genetic diagnosis (PGD) or via the use of mitochondrial donation, which aims to reduce or eliminate mutant mtDNA

Summary

Introduction

Mitochondria serve a vital role in normal cellular homoeostasis. A major function is the production of ATP via oxidative phosphorylation (OXPHOS) to drive cellular reactions. Pronuclear transfer (PNT) was originally developed in 1983 [29] and involves removal of the pronuclei in a membrane-bound karyoplast from a fertilized zygote and transfer to an enucleated donor zygote (Figure 1B) The potential for this technique to prevent transmission of mtDNA disease was first demonstrated in mouse embryos carrying an mtDNA mutation [30], followed by a report using abnormally fertilized human zygotes [31]. In this proof of concept study, reconstructed embryos that developed following PNT had the capacity to reach the blastocyst stage. If mitochondrial RNA import is a reality we would expect to see many future publications using such an approach

Conclusion

Summary