SIRT1 reduces epigenetic and non-epigenetic changes to maintain the quality of postovulatory aged oocytes in mice

Postovulatory oocyte aging has a major influence on the development potential of embryos. Many antioxidants can delay oocyte aging by regulating the expression of SIRT1. However, there is a lack of knowledge on SIRT1 function in postovulatory oocyte aging. In vitro transcribed RNA of Sirt1 was injected into fresh oocytes to investigate the function of SIRT1 during postovulatory oocyte aging. In the present study, SIRT1 was found to be down-regulated in aged oocytes compared with fresh oocytes. Meanwhile the intensity of acetylation of H3K9 (H3K9ac) and H3K4 methylation increased in postovulatory aged oocytes. After the oocytes were injected with SIRT1 and aged for 12 h, the intensity of H3K9ac and H3K4 methylation markedly decreased compared with controls. Furthermore, SIRT1 overexpression also reduced the aging-induced oocyte morphological changes and reactive oxygen species accumulation, maintained the spindle normal morphology and attenuated the aging-associated abnormalities of mitochondrial function. The role of SIRT1 in protecting oocyte aging was diminished when oocytes with overexpressed SIRT1 were cultured with SIRT1 inhibitor EX-527. Briefly, these present results show that SIRT1 not only reduced the non-epigenetic changes such as abnormal oocyte morphology, ROS accumulation, spindle defects and mitochondrial dysfunctions but also regulated the epigenetic changes in order to maintain the quality of postovulatory aged oocytes.