Age-related changes of Nrf2 and phosphorylated GSK-3β in a mouse model of accelerated aging (SAMP8)

SAMP8 mice show spontaneously accelerated aging and a short life span with systemic accumulation of oxidative stress. Nrf2 translocates into the nucleus upon oxidative stress and induces the expression of detoxifying and antioxidant enzymes. Recently, several studies reported that Nrf2 is associated with aging and various diseases. In the present study, we investigated the levels of Nrf2 nuclear translocation and phosphorylation of Akt and GSK-3β in livers of SAMP8 and normal aging SAMR1 mice. The protein level of Nrf2 in the nucleus of the liver was significantly decreased in SAMP8 at 10 months old compared with that in age-matched SAMR1. The protein level of Keap1, which anchors Nrf2 in the cytoplasm, did not differ between SAMP8 and SAMR1. In addition, the mRNA expression of Nrf2 in the liver of SAMP8 was significantly lower than that of SAMR1. Moreover, mRNA levels of detoxification and antioxidant enzymes, GSTa1 and NQO1, were significantly decreased in SAMP8 compared with SAMR1. These results indicate that a higher level of oxidative stress in SAMP8 might be caused by a lower level of Nrf2. Furthermore, the phosphorylation of Akt and GSK-3β was significantly decreased in the liver of SAMP8 at 10 months old. Recent studies have suggested that the Akt/GSK-3β signaling pathway is involved in the nuclear translocation of Nrf2. Therefore, it is suggested that the reduction of the translocation of Nrf2 into the nucleus might be induced by a decrease of GSK-3β phosphorylation, resulting in an increase of oxidative stress in SAMP8 mice.