# The neuromodulatory fragility hypothesis of Alzheimer's disease pathogenesis

## TL;DR

This paper proposes a new theory for Alzheimer's disease, suggesting that fragile brain cells called neuromodulatory neurons are key to the disease's progression.

## Contribution

The paper introduces the 'neuromodulatory fragility hypothesis' as a novel framework linking neuromodulatory system dysfunction to Alzheimer's pathology.

## Key findings

- Neuromodulatory neurons are uniquely fragile due to their large size and high metabolic demands.
- Dysfunction in these neurons can explain both tau hyperphosphorylation and amyloid beta plaque formation.
- Strengthening neuromodulatory systems in midlife may be the best strategy to prevent Alzheimer's.

## Abstract

Sporadic Alzheimer's disease (AD) is associated with numerous risk factors, yet its precise cause remains unclear. Here, we describe a novel framework for AD pathogenesis, whereby diverse risk factors converge on neuromodulatory subcortical systems to confer AD risk or resilience. Neuromodulatory projection neurons are uniquely fragile due to their large size, sparse myelination, and high basal metabolic demands. We propose that the increased prevalence of AD in older adult populations likely reflects a universal weakness within these projection systems, which is increasingly exposed as cellular transport and maintenance mechanisms deteriorate with age. The key insight of this “neuromodulatory fragility hypothesis” is that neuromodulatory system dysfunction is sufficient to explain both tau hyperphosphorylation and amyloid beta plaque formation, the two pathological hallmarks of AD. We therefore predict that strengthening or preserving the endogenous functions of these systems in midlife represents the most effective strategy for preventing AD.

We describe a neuromodulatory fragility hypothesis for Alzheimer's disease (AD) pathogenesis.Neuromodulatory neurons are extremely fragile due to high metabolic demands.Their early dysfunction leads to downstream tau misfolding and amyloid beta (Aβ) pathology.Eventual Aβ–tau interactions cause rapid spreading of pathology and dementia onset.Improving neuromodulatory resilience presents the best dementia‐prevention strategy.

We describe a neuromodulatory fragility hypothesis for Alzheimer's disease (AD) pathogenesis.

Neuromodulatory neurons are extremely fragile due to high metabolic demands.

Their early dysfunction leads to downstream tau misfolding and amyloid beta (Aβ) pathology.

Eventual Aβ–tau interactions cause rapid spreading of pathology and dementia onset.

Improving neuromodulatory resilience presents the best dementia‐prevention strategy.