Figure 2. ROS accumulated in the aging oocytes and putrescine decreased ROS through the Sirt1-FOXO3a-SOD2 axis. (A) The accumulation of ROS in the oocytes during postovulatory aging. The level of ROS was significantly decreased in the putrescine-treated group. (B) The mRNA and protein expressions of SOD2. Both the mRNA and protein expressions of SOD2 were significantly decreased in the aging oocytes, while the expression of SOD2 was partially rescued by putrescine treatment. (C) The Sirt1-FOXO3a-SOD2 axis in the aging oocytes. The expressions of Sirt1, FOXO3a and SOD2 protein were significantly decreased in the postovulatory aging oocytes. Putrescine partially rescued the effects on the expressions of Sirt1, FOXO3a and SOD2 protein. Put, putrescine. Compared with the fresh MII oocytes, *p<0.05; compared with the aging oocytes, # p<0.05.