Endonuclease G promotes mitochondrial genome cleavage and replication

Area of Science:

• Mitochondrial biology
• Molecular cell biology
• Genetics

Background:

• Endonuclease G (EndoG) is a nuclear-encoded enzyme primarily localized in mitochondria.
• While EndoG's nuclear roles in DNA replication stress and apoptosis are known, its function in mitochondrial DNA (mtDNA) metabolism remains unclear.
• Understanding EndoG's impact on mtDNA is vital for comprehending mitochondrial health and disease.

Purpose of the Study:

• To investigate the role of EndoG in regulating mtDNA replication and the removal of damaged mtDNA copies.
• To elucidate the mechanisms by which EndoG influences mtDNA metabolism, particularly under stress conditions.

Main Methods:

• Utilized single-cell mitochondrial Transcription and Replication Imaging Protocol (mTRIP) and PCR-based assays.
• Employed knockdown/knockout and re-expression strategies for EndoG in human cells.
• Investigated the interplay between EndoG, oxidative stress, and base excision repair (BER).

Main Results:

• EndoG was found to stimulate both mtDNA replication initiation and mtDNA depletion, with these processes being interdependent and reliant on EndoG's nuclease activity.
• EndoG-mediated mtDNA replication stimulation occurred independently of 7S DNA processing at the replication origin.
• Oxidative stress enhanced both mtDNA-directed activities of EndoG, and its role in mtDNA removal was highlighted upon inhibition of base excision repair (BER).

Conclusions:

• EndoG plays a critical role in managing mtDNA integrity by promoting both the removal of damaged mtDNA and compensatory replication.
• These EndoG-dependent processes are significantly influenced by oxidative stress and are linked to base excision repair pathways.
• The study establishes EndoG's importance in maintaining mitochondrial homeostasis through its regulation of mtDNA metabolism.