The Universal "Tear Repair" Function of Amyloid Precursor Protein and the Specialized Role of Tau: A First-Principle Hypothesis Reframing Alzheimer's Disease as a Convergent, Chronic, Non-Healing Synaptic Wound

Abstract

The amyloid cascade hypothesis, which positions the amyloid-beta (Aβ) peptide as the primary pathogenic trigger in Alzheimer's disease (AD), has been the dominant paradigm for three decades. The repeated failure of immunotherapies targeting Aβ plaques to halt cognitive decline, or to impact intracellular Tau pathology, signals a fundamental gap in our understanding. We propose a universal functional law for the Amyloid Precursor Protein (APP) and a specialized role for Tau, forming a single, unified repair catastrophe model. APP is acutely deployed at the site of any physical tear in connectivity between two cells, acting as a conserved extracellular mediator of junctional repair. Tau is the specialized intracellular "repair putty," uniquely deployed at the synaptic tear to stabilize the failing cytoskeleton. The intensity of this dual response is directly proportional to the system's criticality for immediate organismal survival. This convergent principle is demonstrated by APP's response at the torn synapse, ruptured cardiac intercalated disc, fractured osteocyte network, severed epithelial sheet, breached endothelial barrier, and at the brain's highest-priority survival interfaces (gut-brain axis, optic nerve, olfactory bulb). AD is radically reframed: it is not a proteinopathy driven by a rogue peptide, but the brain's chronic, non-healing wound state, concentrated at its most survival-critical nodes, where the universal extracellular repair (APP) and the brain-specific intracellular repair (Tau) fail simultaneously. Amyloid plaques are the extracellular scars; neurofibrillary tangles are the intracellular, inert "putty piles" of these failed, abandoned repair projects. This first-principle hypothesis offers a unified framework for APP and Tau biology, explains the unique dual pathology of AD, and charts a new course for diagnostics and therapeutics. We propose a "Liquid Tear Repair Biopsy"—a single, unified, cross-tissue panel of tissue-specific exosomal sAPPα measurements—to replace the current paradigm of fragmented, symptom-late, organ-siloed detection.

Keywords: Amyloid Precursor Protein, Tau, Universal Functional Law, Tear Repair, Synaptic Repair, Cellular Connectivity, Alzheimer's Disease, Synaptopathy, Non-Healing Wound, Survivability Hierarchy, Gut-Brain Axis, Optic Nerve, Olfactory Bulb, Liquid Biopsy, Exosomes, Biomarker, Unified Diagnostic Framework, Hypothesis