Alzheimer's Disease as the Result of Aberrant Reactivation of Embryonic Brain Pathways Silenced Decades Earlier

Abstract Background A fundamental mystery in Alzheimer's disease (AD) is why established adult axonal networks undergo progressive "dying-back" axopathy. During embryogenesis, axon growth is governed by a volatile molecular oscillator balancing outward-pushing Arp2/3 branched actin waves and inward contractile non-muscle actomyosin forces. We hypothesize that chronic aging stress causes epigenetic derepression, aberrantly reactivating this silenced embryonic machinery in mature neurons and glia to trigger mechanical instability, microtubule buckling, and synaptic retraction. Methods We integrated systemic Phenome-wide Association Study (PheWeb) metrics with layer-stratified single-nucleus transcriptomic data from multi-ethnic prefrontal cortex cohort (The Mount Sinai Brain Bank MSBB Cohort MSBB-AD) mapping a strict 10-gene pathway matrix, alongside upstream driver SOX9 and engulfment receptor MEGF10. Results PheWeb screens linked core pathway genes to mechanical shear-stress phenotypes. Cortical layer stratification revealed coordinated astrocytic tension scaling tracking Tau tangle severity: mid-cortical Layer 4 Non-Muscle Myosin IIb (MYH10) scaled positively (beta = + 0.3413, p = 0.0284) while Layer 3 ARPC2 was suppressed (beta = -0.3459, p = 0.0570). Concurrently, MEGF10 exhibited spatial migration across disease stages, correlating heavily with cognitive decline in deep output Layer 5 (beta = -0.0355, p = 0.0023). Conclusions These findings shift AD modeling from passive proteotoxicity to an active, misregulated developmental structural engine, offering a mechanical framework that explains early olfactory vulnerability and non-linear anti-tau clinical trial responses.