Protein kinase B is a serine/threonine kinase that plays a key role in cellular survival pathways in a variety of cell types.
23 The unphosphorylated form of AKT is virtually inactive, and its activation requires phosphorylation at Thr308 and Ser473. Protein kinase B phosphorylation/activation is involved in multiple cellular processes, such as glucose metabolism,
24 gene transcription,
25 protein synthesis,
26 cell proliferation,
27 and migration,
28 all working toward the goal of cell survival. Activation of the AKT pathway results in the inhibition of downstream proapoptotic molecules, including Bad, ASK1, Bax, and caspase 9, thus preventing cells from apoptosis.
29 At the early stage of oxidative stress, some endogenous protein kinases that have strong cytoprotective effects, including AKT and extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), are activated as stress adaption mechanisms.
30 In the retina, AKT pathway has been linked to the pathophysiology of AMD-inducing oxidative stress and has been proposed to enhance RPE cell survival.
16 In this study, our data clearly illustrated that H
2O
2 exposure led to transient and rapid activation of AKT in RPE cells. Upon oxidative stress, p-AKT in empty vector cells reached its maximum level within 30 minutes and gradually decreased to the basal level 2 hours after H
2O
2 treatment. These results are consistent with the findings reported previously by Jaffe et al.
16 Interestingly, we found that Grx1-overexpressing cells exhibited substantial increase in p-AKT, and the levels of AKT phosphorylation remained elevated throughout the 4-hour time course of H
2O
2 treatment. It has been shown that enhanced AKT phosphorylation protects a variety of cells from oxidant-induced cell death.
31 On the other hand, impaired AKT phosphorylation resulted in reduced AKT activity, subsequently sensitizing cells to oxidative stress–induced apoptosis.
16 Our findings highlight a critical role for the AKT pathway in regulating apoptotic pathway and promoting RPE cell survival following oxidation by H
2O
2.