Mitochondrial dysfunction in cumulus-oocyte complexes increases cell-free mitochondrial DNA.

Area of Science:

• Reproductive Biology
• Molecular Biology
• Biochemistry

Background:

• Cell-free mitochondrial DNA (cf-mtDNA) is increasingly recognized as a potential biomarker.
• Understanding cf-mtDNA dynamics in follicular fluid (FF) and its relation to mitochondrial function is crucial for reproductive research.

Purpose of the Study:

• To quantify cf-mtDNA in porcine FF and assess its correlation with follicle size.
• To investigate if cf-mtDNA levels in culture media reflect mitochondrial dysfunction in cumulus-oocyte complexes (COCs).

Main Methods:

• Polymerase chain reaction (PCR) and real-time PCR were used to detect and quantify cf-mtDNA in FF and spent culture media.
• Mitochondrial dysfunction was induced in COCs using carbonyl cyanide m-chlorophenyl hydrazone (CCCP).
• Analysis included cfDNA length, mtDNA copy number, nuclear DNA, cell viability, apoptosis, and lactate dehydrogenase levels.

Main Results:

• cf-mtDNA concentration was higher in smaller follicles compared to larger ones.
• cf-mtDNA in FF correlated with FF mtDNA copy number but not nuclear DNA.
• CCCP treatment significantly increased cf-mtDNA in the spent culture medium of COCs and granulosa cells, without affecting cell viability or other markers.
• Denuded oocytes showed minimal cf-mtDNA release after CCCP treatment, suggesting granulosa cells are a primary source.

Conclusions:

• cf-mtDNA is present in porcine FF across a broad size range.
• Mitochondrial dysfunction in COCs, particularly in associated granulosa cells, leads to increased active secretion of cf-mtDNA.
• cf-mtDNA in culture media can serve as a sensitive indicator of mitochondrial dysfunction in reproductive cells.