Comprehensive proteomic profiling reveals mRNA splicing suppression during human oocyte aging

Reproductive aging impairs female fertility, and oocyte aging is considered a major driver of this phenotype, which manifests with increased aneuploidy and miscarriage risk, while no effective treatments have been widely implemented to date. Here, we report comprehensive protein expression profiling of oocytes during human aging, comparing fully grown germinal vesicle oocytes (FGO) and metaphase II (MII) oocytes; we describe the effect of aging on the maturation profiles across multiple age groups, including 25, 30, 35, and 40 years old. This analysis uncovered differential protein dynamics upon aging, with FGOs displaying protein expression alterations as early as 30 years, whereas these changes were delayed until the age of 35 or 40 in MII oocytes, particularly in proteins associated with mRNA splicing, translation, and chromosome segregation. Integration with transcriptomic data revealed suppression of splicing machineries as a potential initiating factor driving oocyte aging, characterized by deficiencies in mitochondrial function and chromosome segregation. This was validated by splicing inhibition, which suppressed mitochondrial function and ROS levels in mouse and human oocytes. Further, splicing factor DHX15 was identified as a candidate regulator of stage-specific oocyte aging. Together, our work systematically delineates the dynamic protein landscapes of human oocytes across multiple age groups, providing molecular targets and potential therapeutic strategies for clinical intervention.