Shrinking of Extracellular Space During Metabolic Stress Accelerates Amyloid-β Aggregation.

Pathological states associated with metabolic stress, such as traumatic brain injury (TBI), hypoxia, ischemic stroke, and migraine, are considered elevated risk factors for developing Alzheimer's disease (AD). However, the mechanism underlying the effect of these conditions on the progression of AD remains largely unknown. Here, we determine how metabolic stress associated with spreading depolarization (SD)-a hallmark of stroke, hypoxia, TBI, and migraine-modulates amyloid β (Aβ42) aggregation kinetics through dynamic changes in extracellular space (ECS). To achieve this, we used ThT fluorescence to determine how the formation of different Aβ42 aggregate species depends on Aβ42 concentrations. Based on this input, we build a multiscale computational framework that integrates volume regulation, including its dependence on neuronal ion homeostasis, and Aβ42 aggregation kinetics. Our model predicts that neuronal swelling during SD accelerates aggregation, where the impact of metabolic stress is highly dependent on the timing relative to aggregation progression and the initial monomer concentration. At low monomer concentrations, early SD events promote off-pathway oligomer formation, while at higher concentrations they rapidly drive fibril formation to saturation. In the absence of mature fibrils, recurrent metabolic stress events further amplify oligomer accumulation, whereas pre-existing fibril nuclei suppress oligomer formation at the expense of fibril nucleation and growth. Increasing the intensity of metabolic stress prolongs ECS shrinkage and enhances oligomer formation. These findings reveal a mechanistic link between SD-induced microenvironmental changes and Aβ aggregation dynamics, providing a quantitative framework for understanding how acute brain injury and metabolic stress may contribute to early AD pathogenesis.