Figure 4. The apoptosis-related pathways in the aging oocytes and the effect of putrescine. (A) The phosphorylation levels of the AKT and ERK1/2 proteins and the expressions of BCL2 and BAX in the aging oocytes. The levels of p-AKT and p-ERK1/2 were significantly decreased in the oocytes during postovulatory aging, although the total level of AKT or ERK1/2 was not changed. The level of BCL2 was significantly decreased, and the level of BAX increased, as two subsequent factors of the AKT and ERK pathways. Putrescine rescued those effects in the aging oocytes.(B) The expression of caspase 9 as a key factor of the mitochondria-related apoptosis pathways. The level of cleaved caspase 9 was significantly increased in the aging oocytes. Putrescine significantly inhibited this incremental rise. Compared with the fresh MII oocytes, *p<0.05, ** p<0.01; compared with the aging oocytes, # p<0.05, ## p<0.01.