Oocytes Maintain Low ROS Levels to Support the Dormancy of Primordial Follicles

Primordial follicles (PFs) function as the long-term reserve for female reproduction, remaining dormant in the ovaries and becoming progressively depleted with age. Oxidative stress plays an important role in promoting female reproductive senescence during aging, but the underlying mechanisms remain unclear. Here, we find that low levels of reactive oxygen species (ROS) are essential for sustaining PF dormancy. Compared to growing follicles, oocytes within PFs were shown to be more susceptible to ROS, which accumulates and damages PFs to promote reproductive senescence. Mechanistically, oocytes within PFs were shown to express high levels of the intracellular antioxidant enzyme superoxide dismutase 1 (SOD1), counteracting ROS accumulation. Decreased SOD1 expression, as a result of aging or through the experimental deletion of the Sod1 gene in oocytes, resulted in increased oxidative stress and triggered ferroptosis within PFs. In conclusion, this study identified antioxidant defense mechanisms protecting PFs in mouse ovaries and characterized cell death mechanisms of oxidative stress-induced PF death.