Mitochondrial Methionine Sulfoxide Reductase B2 Links Oxidative Stress To Alzheimer’s Disease-like Pathology

Objective:Methionine sulfoxide reductase B2（MSRB2）is a mitochondrial protein that protects cell from oxidative stress.The antioxidant activity suggests that MSRB2 may play a role in the pathophysiology of Alzheimer’s disease（AD）.To investigate the expression of methionine sulfoxide reductase B2（MSRB2）in APP/PS1 AD model mice and to explore the relationship between MSRB2 and pathophysiology of Alzheimer’s disease（AD）.Methods:Western blot,immunohistochemistry were used to detect the expression of MSRB2 in the cortex and hippocampal brain tissue of AD and wild type（WT）mice at age of 6 and 18 months.In HEK293 cells that stably express human full-lengthβ-amyloid precursor protein（APP,HEK/APP）were transfected with MSRB2 plasmid or MSRB2 shRNA to over-express or knockdown it,then observed the expression of APP metabolic pathway-associated proteins and Tau phosphorylation at selective sites,with the concomitant alteration of the Tau kinases.The localization relationship between MSRB2 and mitochondria was detected by immunofluorescence.Overexpressing MSRB2 in cells,the expression level of ROS was observed and detected by immunofluorescence and fluorescence multilabel plate reader.Moreover,in cells treated with H₂O₂for 24 h,observed the alterations of APP processing and Tau phosphorylation whether could reversed by MSRB2 overexpression.Inhibitors of JNK and ERK were used to verify whether their signaling pathways are involved in MSRB2-mediated regulation of APP transcription levels.Western blot used to verify whether MSRB2 has an anti-apoptotic effect.Results:1.In APP/PS1 mice,an animal model of AD,MSRB2 protein levels were decreased in the hippocampus at both young（6 mon）and old（18 mon）age,and in the cortex only at an old age,respectively.2.In HEK/APP cells,MSRB2 reduced the protein and mRNA levels of APP andβ-amyloid converting enzyme 1（BACE1）,and the consequent amyloid beta peptide（Aβ）1-40 and Aβ1-42 levels.3.MSRB2 overexpression or knockdown also oppositely affected Tau phosphorylation at selective sites,with the concomitant alteration of the phosphorylated extracellular signal regulated kinase（p-ERK）and AMP-activated protein kinase（p-AMPK）levels.4.Immunofluorescence confirmed that MSRB2 is localized on mitochondria,and the intracellular ROS level was significantly lower than the control group.Moreover,in cells treated with long-term（24 h）hydrogen peroxide,the alterations of APP processing and Tau phosphorylation were reversed by MSRB2 overexpression.5.We further found that MSRB2-mediated regulation of APP transcription involved JNK and ERK signaling,as MSRB2 also reduced the levels of phosphorylated JNK（p-JNK）,and JNK or ERK inhibitor attenuated the effect of MSRB2 on APP proteins and transcripts.6.Finally,MSRB2 reduced apoptosis-related proteins Bax and caspase3 and enhanced the anti-apoptotic protein Bcl2.Conclusions:1.The expression of MSRB2 is decreased in the animal model of AD,suggesting that it is closely related to the pathophysiology of AD.2.MSRB2 is a mitochondrial-derived redox enzyme that can affect the production of Aβand the abnormal phosphorylation of Tau,suggesting that mitochondrial-derived oxidative stress plays an important role in the development of AD.3.MSRB2 affects the expression of BACE1 and APP,and the consequent of Aβis related to JNK pathway.The effect on Tau phosphorylation is mainly related to AMPK and ERK signaling pathways.4.These results indicated that the role for MSRB2 in AD-like pathology was closely associated with its antioxidant activity.By attenuating both amyloidogenesis and Tau phosphorylation,MSRB2 may serve as a potential therapeutic target for AD.