Redox bioenergetics of neuronal senescence in Alzheimer's disease

Neuronal aging is a key but often overlooked part of Alzheimer's disease. It links age-related loss of cellular energy to long-lasting problems in neuronal function. Even though neurons don't usually divide, ongoing stressors like oxidative damage, mitochondrial dysfunction, and problems with protein handling can make them appear old. This is seen as lasting DNA damage, calcium imbalance, and the release of substances that cause inflammation. These changes are closely tied to loss of balance in cell energy and redox function. Mitochondria, which make most neurons' energy, are both a main source and a target for reactive oxygen species (ROS). Long-term redox imbalance damages energy production, lowers NAD⁺, and disrupts SIRT1 regulation. Eventually, this leads to energy failure and loss of synaptic function. In AD, excessive ROS production and redox imbalances interact with amyloid-β toxicity, tau hyperphosphorylation, and metal ion disturbances. This convergence increases mitochondrial damage and fragmentation. When mitophagy is impaired, dysfunctional mitochondria are not removed, leading to ROS accumulation that further damages cellular structures and reinforces oxidative stress. This forms a self-perpetuating cycle that accelerates neuronal aging and neurodegeneration. Notably, research shows that energy failure and redox imbalance often precede the formation of amyloid plaques and tangles, suggesting that these mechanisms may initiate disease onset. This chapter reviews core mechanisms underlying redox signaling and neuronal senescence. It details how altered mitochondrial function disrupts neuronal energy homeostasis and triggers a cascade of molecular events that underlie Alzheimer's disease. The proposed framework connects redox failure, cellular senescence, and neurodegeneration as interdependent drivers of disease progression.