Subtle genomic DNA damage induces intraneuronal production of amyloid-β (1-42) by increasing β-secretase activity

Aberrant accumulation of amyloid-beta (A beta) in brain is the major trigger for pathogenesis in Alzheimer's disease (AD). It is imperative to understand how A beta attains such toxic levels in the brain parenchyma. We detected that a subtle and tolerable amount of DNA damage, related to aging, increased intraneuronal A beta(1-42) production both in cultured neuron and in cortex of rodent brain. Strikingly, we also observed elevated levels of mitochondrial fusion and of its major driver protein, MFN2. Hyperfusion of mitochondria may be seen as an adaptive stress response resulting from the induction of ER stress since we detected the activation of both PERK and IRE1a arms of unfolded protein response of ER stress. We found increased phosphorylation of PERK substrate eukaryotic initiation factor 2 alpha (eIF2 alpha), and upregulation of the downstream effector proteins, ATF4 and CHOP. Concomitantly, increased XBP1 level, the direct effecter protein of IRE-1 alpha, was observed. Reports suggest that eIF2 alpha phosphorylation can increase BACE1 activity, the rate limiting enzyme in A beta production. Here, we show that inhibiting PERK, decreased A beta(1-42) level while direct BACE1 inhibition, reduced the mitochondrial fusion. We found increased MFN2 expression in young 5xFAD mice when A beta plaques and neurodegeneration were absent. Thus, our study indicates that mild DNA damage leads to increased A beta(1-42) production almost as a consequence of an initial ER stress-directed protective mitochondrial fusion in brain. We propose that an age-related subtle genomic DNA damage may trigger enhanced intraneuronal A beta(1-42) production in an apparently healthy neuron way before the appearance of clinical symptoms in AD.

Automated summary

Accumulation of amyloid-beta in the brain is a major trigger for Alzheimer's disease pathogenesis. Mild DNA damage leads to increased production of Aβ. Mitochondrial fusion and the protein MFN2 play a role in this process, potentially as an adaptive response to ER stress, which may contribute to increased Aβ production.