Oocytes maintain ROS-free mitochondrial metabolism by suppressing complex I

Area of Science:

• Cell Biology
• Mitochondrial Biology
• Reproductive Biology

Background:

• Oocyte quality is crucial for female fertility, yet mechanisms for maintaining cellular fitness and age-related decline are poorly understood.
• Reactive oxygen species (ROS), by-products of mitochondrial activity, negatively impact fertilization and embryo survival.
• The balance between essential mitochondrial function and ROS production in oocytes remains unclear.

Purpose of the Study:

• To investigate how oocytes maintain cellular fitness and evade ROS.
• To elucidate the role of mitochondrial complex I in oocyte quality and longevity.
• To understand why complex I deficiencies do not cause subfertility in patients.

Main Methods:

• Live-cell imaging and proteomics were employed in human and Xenopus oocytes.
• Biochemical and functional assays were utilized to assess mitochondrial complex I activity.
• Analysis focused on the mitochondrial unfolded protein response and electron transport chain remodeling.

Main Results:

• Early oocytes exhibit significantly reduced levels of mitochondrial complex I.
• Complex I is neither assembled nor active in early oocytes, representing a unique physiological state.
• A highly active mitochondrial unfolded protein response indicates an imbalanced electron transport chain.

Conclusions:

• Oocytes evade ROS by remodeling the mitochondrial electron transport chain through the elimination of complex I.
• Complex I suppression is an evolutionarily conserved strategy for oocyte longevity and sustained biological activity.
• This finding clarifies the absence of subfertility in patients with complex I-related mitochondrial diseases.