Cuproptosis-mediated mitochondrial dysfunction in cumulus cells inhibits bovine oocyte maturation

Copper is an important trace element required by mammals and is widely involved in regulating various life activities. Overload or imbalance of copper ions can activate specific signaling pathways, leading to impaired oocyte function, decreased ovulation efficiency, and impaired embryo implantation. However, whether these changes are related to cuproptosis, a copper-driven, mitochondrial form of regulated cell death triggered by proteotoxic stress, a newly discovered phenomenon in recent years, remains unclear. In this study, combination treatment with a specific concentration of CuSO₄ and elesclomol, a copper ionophore, delivered Cu⁺/Cu²⁺ to the mitochondrial matrix and potentiated cuproptosis, which triggered cuproptosis, leading to a decreased ability of cumulus cells to synthesize progesterone and estrogen. Moreover, during the maturation of oocytes, the expansion of cumulus cells and the levels of electron transport chain-related proteins decreased, whereas the calcium ion level, CaMKIIγ protein level, and phosphorylation level of CX43^Ser255 significantly increased. In addition, although cuproptosis in cumulus cells did not directly induce cuproptosis in oocytes, it decreased the quality and further maturation of oocytes. During this process, abnormalities in mitochondrial distribution and function, cortical granule distribution, spindle morphology, and intracellular cAMP levels were detected in oocytes. The protein level of CDK1 decreased, whereas that of Emi1 increased. These results suggest that in cumulus cells, cuproptosis impairs mitochondrial function and triggers abnormal intracellular calcium homeostasis, which subsequently leads to overactivation of CaMKIIγ, blockage of Cx43 channels between COCs, and abnormal accumulation of cAMP in oocytes. Consequently, aberrant expression of the cell cycle regulatory factors CDK1 and Emi1 ultimately inhibits the in vitro maturation of oocytes. These findings clarify the effect of cuproptosis on bovine oocyte maturation, which contributes to a deeper understanding of the regulatory mechanisms governing oocyte maturation and may provide new directions for optimizing in vitro oocyte culture systems.