Background: Mitochondrial dynamics, particularly dynamin-related protein 1 (DRP1)-mediated mitochondrial fission, regulates cellular metabolism, proliferation, apoptosis, and cytoskeletal organisation. However, the role of oocyte mitochondrial dynamics in regulating ovarian function and folliculogenesis remains poorly understood.

Methods: We generated oocyte-specific Drp1 conditional knockout mice (Drp1^loxP/loxP; Gdf9-Cre) and examined ovarian follicle development using histology, immunofluorescence, confocal microscopy, ELISA, and proteomic profiling.

Results: Although follicle numbers were comparable between control and mutant ovaries at 4 weeks of age, by 5-7 weeks of age mutant ovaries exhibited a significant accumulation of primary follicles and reduction in antral follicles. This was accompanied by significantly reduced serum anti-Müllerian hormone (AMH) levels and increased ovarian fibrosis. Impaired folliculogenesis was associated with reduced granulosa cell proliferation (decreased Ki-67), increased oocyte apoptosis (cleaved caspase-3), increased lysosomal accumulation (LAMP1), and reduced LC3 expression, indicating impaired autophagic activity. Proteomic analysis further identified reduced expression of the autophagy-associated proteins SQSTM1 (p62) and SPNS1, supporting defective autophagic flux and lysosomal homeostasis.

Mutant ovaries also showed reduced expression of the oocyte-derived growth factor GDF9, decreased connexin 37 on the oocyte plasma membrane, and downregulation of radixin, a microvilli-associated protein involved in GDF9 transport to granulosa cells. Whole ovary, proteomic profile of mutant 6-week-old ovaries further revealed coordinated alterations in pathways associated with mitochondrial function, oxidative stress, intracellular trafficking, autophagy, cell-cycle regulation, and cellular adaptation. Reduced expression of mitochondrial proteins, including ADHFE1, TMEM70, GLRX2, and MRPL11, together with altered trafficking and cell-cycle regulators, supports widespread disruption of mitochondrial homeostasis and cellular function.

Conclusions: These findings demonstrate that disrupting loss of DRP1 in the oocyte, leads to profound defects in granulosa cell function, ultimately leading to arrest of folliculogenesis   and reduced fertility. This study identifies mitochondrial dynamics as a critical regulator of ovarian function and provides new mechanistic insights into female reproductive biology.