Inhibition of γ-secretase activity reduces Aβ production, reduces oxidative stress, increases mitochondrial activity and leads to reduced vulnerability to apoptosis: Implications for the treatment of Alzheimer's disease

It has been argued that γ-secretase should be considered as a pharmacological target, as there are few mechanism-based experimental and clinical studies on γ-secretase treatment. In this study, we found that N2a cells bearing APP695 or its Swedish mutant exhibited increased basal levels of ROS, nitric oxide (NO), protein carbonyls, MDA and intracellular calcium, as well as reduced level of the mitochondrial membrane potential and ATP. When the activity of γ-secretase was inhibited by expression of the D385A PS1 variant, cells (N2a/Swe.D385A) showed reduced basal levels of ROS, nitric oxide (NO), protein carbonyls, MDA and intracellular calcium, as well as increased mitochondrial membrane potential and ATP level. In addition, N2a/Swe.D385A cells showed reduced vulnerability to H2O2-induced apoptosis. The Bcl-2 and JNK/ERK pathways were proven to be involved in the change of vulnerability to H2O2-induced apoptosis. Moreover, we discovered that inhibition of γ-secretase by DAPT would lead to a reduction of ROS levels and stabilization of mitochondrial function in APP (N2a/APP695) and APP Swedish mutant (N2a/APPswe) transfected cells. At last, it was shown that Aβ antibody and antiserum prevented increase of ROS and reduction of mitochondrial membrane potential in N2a/Swe.ΔE9 cells but not in N2a/Swe.D385A cells, which indicated that reduced formation of Aβ was the reason for reduction of ROS formation and increase of mitochondrial membrane potential when PS-1 activity was impaired in N2a/Swe.D385A cells. We concluded that neurotoxicity was positively correlated with the activity of γ-secretase, which suggested inhibition of γ-secretase is a rational pharmacological target for Alzheimer's disease treatment.