Subcellular proteomics and iPSC modeling uncover mechanisms of axonal pathology in Alzheimer’s disease

Amyloid deposits in Alzheimer’s disease (AD) are surrounded by large numbers of plaque-associated axonal spheroids (PAAS). PAAS disrupt axonal electrical conduction and neuronal network function and correlate with AD severity. However, the mechanisms of their formation remain largely unknown. To address this, we developed a proximity labeling approach to uncover the PAAS proteomes in human AD postmortem brains and mice. Proteomics analysis highlighted the activation of protein turnover, cytoskeleton dynamics and lipid transport. The PI3K/AKT/mTOR signaling, a master regulator of these biological processes, is also activated and expressed in PAAS, and strongly correlated with disease severity in AD humans. Using human iPSC modeling and Cre/lox mice, we found that mTOR inhibition markedly reduced PAAS formation in humans and mice. Together, we assembled a multidisciplinary toolkit and uncovered novel mechanisms of axonal spheroid pathology. This pipeline can be applied to examine new targets for axonal pathology in AD and neurodegeneration.