Reactive oxygen species stimulate mitochondrial allele segregation toward homoplasmy in human cells

Area of Science:

• Cell Biology
• Genetics
• Biochemistry

Background:

• Mitochondrial DNA (mtDNA) heteroplasmy occurs when cells contain a mix of mutant and wild-type mtDNA.
• Restoration of homoplasmy (a single type of mtDNA) is observed in human oogenesis and cell reprogramming, but the underlying mechanism is unclear.
• While budding yeast utilize reactive oxygen species (ROS)-induced concatemer formation for homoplasmy, this process is not well-understood in higher eukaryotes.

Purpose of the Study:

• To investigate the mechanism of mitochondrial DNA (mtDNA) allele segregation and homoplasmy restoration in human cells.
• To determine the role of reactive oxygen species (ROS) in mediating mtDNA segregation.
• To explore the involvement of mtDNA concatemers in the process of achieving mtDNA homoplasmy.

Main Methods:

• Utilized heteroplasmic m.3243A > G primary fibroblast cells from MELAS patients.
• Treated cells with hydrogen peroxide (H2O2) to modulate ROS levels.
• Analyzed mtDNA integrity, replication templates, and the formation of mtDNA concatemers.

Main Results:

• An optimal level of ROS was found to promote mtDNA allele segregation towards wild-type and mutant mtDNA homoplasmy.
• Elevated ROS levels decreased intact mtDNA replication templates but increased the production of linear tandem multimers (mtDNA concatemers).
• ROS-triggered segregation of mtDNA alleles correlated with increased mtDNA concatemer production.

Conclusions:

• Mitochondrial DNA (mtDNA) allele segregation towards homoplasmy is mediated by the formation of mtDNA concatemers.
• Reactive oxygen species (ROS) play a crucial role in this concatemer-mediated segregation process.
• This mechanism provides insight into how heteroplasmic cells can achieve homoplasmic states, relevant to mitochondrial diseases like MELAS.