Nampt affects mitochondrial function in aged oocytes by mediating the downstream effector FoxO3a

Maternal aging can impair the quality and decrease the developmental competence of ovulated oocytes. In this study, compromised germinal vesicle breakdown (GVBD) was found in aged mice oocytes. Furthermore, we observed increased reactive oxygen species (ROS) and mitochondrial Ca2+ levels, along with reduced mitochondrial temperature in aged oocytes. Maternal aging also changed the crotonylation level in oocytes. Forkhead box O3 (FoxO3a), a member of the forkhead protein family involved in the regulation of cell survival and life span reached a peak level in the metaphase II stage. Compared with a younger group, FoxO3a expression increased in aged oocytes. Intracellular localization of FoxO3a changed from the cytoplasm to chromatin in response to aging. The expression of the upstream regulator nicotinamide‐phosphoribosyltransferase (Nampt) peaked in the GVBD stage. Moreover, Nampt expression was increased in aged oocytes, and more intense staining of Nampt was found in aged mice ovary. To further study the role of Nampt in mitochondrial function, specific agonist P7C3 and inhibitor FK866 were applied to aged oocytes, and FK866 significantly decreased adenosine triphosphate and mitochondrial membrane potential. In conclusion, mitochondrial dysfunction in aged oocytes was associated with elevated FoxO3a, and suppression of Nampt could further impair mitochondrial function. Maternal aging impaired oocyte meiosis resumption and mitochondrial function, which was associated with increased expressions of both Nampt and FoxO3a. Specific inhibition of the Nampt enzyme activity can aggravate the adverse effect of FoxO3a on mitochondrial function. These data increase our understanding of the role of Nampt in mitochondrial function in aged oocytes by mediating the downstream effector FoxO3a.