Mitochondrial replacement in human oocytes carrying pathogenic mitochondrial DNA mutations

Area of Science:

• Genetics
• Reproductive Medicine
• Cell Biology

Background:

• Maternally inherited mitochondrial DNA (mtDNA) mutations cause severe childhood syndromes, with disease severity linked to heteroplasmy levels.
• Pathogenic mtDNA mutations affect approximately 778 children annually in the US, highlighting the need for preventative strategies.
• Mitochondrial replacement therapies (MRT) aim to prevent transmission of these mutations by replacing maternal mtDNA in oocytes.

Purpose of the Study:

• To evaluate the outcomes of mitochondrial replacement therapies (MRT) in families affected by common mitochondrial DNA (mtDNA) syndromes.
• To investigate the stability and maintenance of donor mtDNA in embryonic stem cells (ES cells) following MRT.
• To identify factors influencing donor-mtDNA compatibility and propose a matching paradigm for MRT.

Main Methods:

• Oocyte spindle transfer was used to replace maternal mtDNA with donor mtDNA in embryos from families with mtDNA syndromes.
• Embryonic stem cells (ES cells) were derived from resulting embryos to assess donor mtDNA stability.
• Analysis of mtDNA interactions, replication efficiency, and genetic polymorphisms to determine compatibility factors.

Main Results:

• Spindle transfer successfully replaced maternal mtDNA, achieving >99% donor mtDNA in resulting embryos.
• Donor mtDNA was stably maintained in most derived ES cell lines, but some showed gradual loss and reversal to the maternal haplotype.
• mtDNA compatibility appears to be linked to replication efficiency and specific polymorphisms (e.g., in the D-loop's conserved sequence box II), rather than simple mismatch or oxidative phosphorylation function.

Conclusions:

• Mitochondrial replacement therapy is effective in replacing mutant maternal mtDNA, but long-term stability of donor mtDNA is critical.
• Specific mtDNA polymorphisms influence replication efficiency and confer cellular growth advantages, impacting donor-mtDNA compatibility.
• A matching paradigm based on selecting compatible donor mtDNA, considering replication efficiency and polymorphisms, is proposed for successful MRT.